Catalysts

22 pages, 4034 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Deciphering the Mechanism of Silver Catalysis of “Click” Chemistry in Water by Combining Experimental and MEDT Studies

by Hicham Ben El Ayouchia, Lahoucine Bahsis, Ismail Fichtali, Luis R. Domingo, Mar Ríos-Gutiérrez, Miguel Julve and Salah-Eddine Stiriba

Catalysts 2020, 10(9), 956; https://doi.org/10.3390/catal10090956 - 20 Aug 2020

Cited by 19 | Viewed by 3525

Abstract

A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation [...] Read more.

A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation of 1,4-disubstituted-1,2,3-triazoles in the presence of AgCl as catalyst and water as reaction solvent at room temperature and pressure. The MEDT was performed by applying Density Functional Theory (DFT) calculations at both B3LYP/6-31G(d,p) (LANL2DZ for Ag) and ωB97XD/6-311G(d,p) (LANL2DZ for Ag) levels with a view to decipher the observed regioselectivity in AgAAC reactions, and so to set out the number of silver(I) species and their roles in the formation of 1,4-disubstituted-1,2,3-triazoles. The comparison of the values of the energy barriers for the mono- and dinuclear Ag(I)-acetylide in the AgAAC reaction paths shows that the calculated energy barriers of dinuclear processes are smaller than those of the mononuclear one. The type of intramolecular interactions in the investigated AgAAC click chemistry reaction accounts for the regioselective formation of the 1,4-regiosisomeric triazole isomer. The ionic character of the starting compounds, namely Ag-acetylide, is revealed for the first time. This finding rules out any type of covalent interaction, involving the silver(I) complexes, along the reaction pathway. Electron localization function (ELF) topological analysis of the electronic structure of the stationary points reaffirmed the zw-type (zwitterionic-type) mechanism of the AgAAC reactions. Full article

(This article belongs to the Special Issue Computational Chemistry and Catalysis: Prediction and Design)

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38 pages, 25382 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

by Guillaume Noirbent and Frédéric Dumur

Catalysts 2020, 10(9), 953; https://doi.org/10.3390/catal10090953 - 20 Aug 2020

Cited by 35 | Viewed by 4635

Abstract

Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their [...] Read more.

Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes. Full article

(This article belongs to the Special Issue Recent Advances in Photoredox Catalysts)

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22 pages, 5403 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

by Kateřina Karásková, Kateřina Pacultová, Anna Klegova, Dagmar Fridrichová, Marta Valášková, Květuše Jirátová, Paweł Stelmachowski, Andrzej Kotarba and Lucie Obalová

Catalysts 2020, 10(8), 931; https://doi.org/10.3390/catal10080931 - 13 Aug 2020

Cited by 9 | Viewed by 2969

Abstract

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium [...] Read more.

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H₂), temperature-programmed desorption of CO₂ (TPD-CO₂), X-ray powder diffraction (XRD), N₂ physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity. Full article

(This article belongs to the Special Issue Catalytic Decomposition of N2O and NO)

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18 pages, 671 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects

by Lu Lin, Wenbin Jiang, Lin Chen, Pei Xu and Huiyao Wang

Catalysts 2020, 10(8), 924; https://doi.org/10.3390/catal10080924 - 12 Aug 2020

Cited by 89 | Viewed by 6116

Abstract

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated [...] Read more.

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water. Full article

(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification)

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22 pages, 6164 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review on Catalysts Development for Steam Reforming of Biodiesel Derived Glycerol; Promoters and Supports

by Nasim Ghaffari Saeidabad, Young Su Noh, Ali Alizadeh Eslami, Hyun Tae Song, Hyun Dong Kim, Ali Fazeli and Dong Ju Moon

Catalysts 2020, 10(8), 910; https://doi.org/10.3390/catal10080910 - 10 Aug 2020

Cited by 31 | Viewed by 4656

Abstract

In the last decades, environmental crises and increasing energy demand have motivated researchers to investigate the practical techniques for the production of clean fuels through renewable energy resources. It is essential to develop technologies to utilize glycerol as a byproduct derived from biodiesel. [...] Read more.

In the last decades, environmental crises and increasing energy demand have motivated researchers to investigate the practical techniques for the production of clean fuels through renewable energy resources. It is essential to develop technologies to utilize glycerol as a byproduct derived from biodiesel. Glycerol is known as a sustainable and clean source of energy, which can be an alternative resource for the production of value-added chemicals and hydrogen. The hydrogen production via steam reforming (SR) of glycerol using Ni-based catalysts is one of the promising approaches for the entry of the hydrogen economy. The purpose of this review paper is to highlight the recent trends in hydrogen production over Ni-based catalysts using the SR of glycerol. The intrinsic ability of Ni to disperse easily over variable supports makes it a more viable active phase for the SR catalysts. The optimal reaction conditions have been indicated as 650–900 °C, 1 bar, and 15 wt% Ni in catalysts for high glycerol conversion. In this review paper, the effects of various supports, different promoters (K, Ca, Sr, Ce, La, Cr, Fe), and process conditions on the catalytic performance have been summarized and discussed to provide a better comparison for the future works. It was found that Ce, Mg, and La have a significant effect on catalytic performance as promoters. Moreover, SR of glycerol over hydrotalcite and perovskite-based catalysts have been reviewed as they suggest high catalytic performance in SR of glycerol with improved thermal stability and coke resistance. More specifically, the Ni/LaNi_0.9Cu_0.1O₃ synthesized using perovskite-type supports has shown high glycerol conversion and sufficient hydrogen selectivity at low temperatures. On the other hand, hydrotalcite-like catalysts have shown higher catalytic stability due to high thermal stability and low coke formation. It is vital to notice that the primary concern is developing a high-performance catalyst to utilize crude glycerol efficiently. Full article

(This article belongs to the Special Issue Catalytic Steam Reforming)

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25 pages, 2166 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Value-Added Bio-Chemicals Commodities from Catalytic Conversion of Biomass Derived Furan-Compounds

by Aitziber Iriondo, Ion Agirre, Nerea Viar and Jesús Requies

Catalysts 2020, 10(8), 895; https://doi.org/10.3390/catal10080895 - 7 Aug 2020

Cited by 17 | Viewed by 4263

Abstract

The depletion of fossil resources in the near future and the need to decrease greenhouse gas emissions lead to the investigation of using alternative renewable resources as raw materials. One of the most promising options is the conversion of lignocellulosic biomass (like forestry [...] Read more.

The depletion of fossil resources in the near future and the need to decrease greenhouse gas emissions lead to the investigation of using alternative renewable resources as raw materials. One of the most promising options is the conversion of lignocellulosic biomass (like forestry residues) into bioenergy, biofuels and biochemicals. Among these products, the production of intermediate biochemicals has become an important goal since the petrochemical industry needs to find sustainable alternatives. In this way, the chemical industry competitiveness could be improved as bioproducts have a great potential market. Thus, the main objective of this review is to describe the production processes under study (reaction conditions, type of catalysts, solvents, etc.) of some promising intermediate biochemicals, such as; alcohols (1,2,6-hexanetriol, 1,6-hexanetriol and pentanediols (1,2 and 1,5-pentanediol)), maleic anhydride and 5-alkoxymethylfuran. These compounds can be produced using 5-hydroxymethylfurfural and/or furfural, which they both are considered one of the main biomass derived building blocks. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis in Green Chemistry)

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18 pages, 4444 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Low Temperature Synthesis of Photocatalytic Mesoporous TiO₂ Nanomaterials

by Massimo Dell’Edera, Francesca Petronella, Alessandra Truppi, Leonarda Francesca Liotta, Nunzio Gallì, Teresa Sibillano, Cinzia Giannini, Rosaria Brescia, Francesco Milano, Marinella Striccoli, Angela Agostiano, Maria Lucia Curri and Roberto Comparelli

Catalysts 2020, 10(8), 893; https://doi.org/10.3390/catal10080893 - 7 Aug 2020

Cited by 15 | Viewed by 3989

Abstract

We report the synthesis of mesoporous TiO₂ nanostructures based on the decomposition of TiOSO₄ in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110 °C) in an oven and suitable to yield up to 40 g of product [...] Read more.

We report the synthesis of mesoporous TiO₂ nanostructures based on the decomposition of TiOSO₄ in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110 °C) in an oven and suitable to yield up to 40 g of product per batch. The duration of the thermal treatment was found to be crucial to control crystalline phase composition, specific surface area, surface chemistry and, accordingly, the photocatalytic properties of the obtained TiO₂ nanocrystals. The thorough investigation of the prepared samples allowed us to explain the relationship between the structure of the obtained nanoparticles and their photocatalytic behavior, that was tested in a model reaction. In addition, the advantage of the mild treatment against a harsher calcination at 450 °C was illustrated. The proposed approach represents a facile and sustainable route to promptly access an effective photocatalyst, thus holding a significant promise for the development of solutions suitable to real technological application in environmental depollution. Full article

(This article belongs to the Special Issue Nanomaterials in Photo(Electro)catalysis)

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27 pages, 5286 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Enzyme-Coated Micro-Crystals: An Almost Forgotten but Very Simple and Elegant Immobilization Strategy

by Rodolpho R. C. Monteiro, José C. S. dos Santos, Andrés R. Alcántara and Roberto Fernandez-Lafuente

Catalysts 2020, 10(8), 891; https://doi.org/10.3390/catal10080891 - 6 Aug 2020

Cited by 36 | Viewed by 4473

Abstract

The immobilization of enzymes using protein coated micro-crystals (PCMCs) was reported for the first time in 2001 by Kreiner and coworkers. The strategy is very simple. First, an enzyme solution must be prepared in a concentrated solution of one compound (salt, sugar, amino [...] Read more.

The immobilization of enzymes using protein coated micro-crystals (PCMCs) was reported for the first time in 2001 by Kreiner and coworkers. The strategy is very simple. First, an enzyme solution must be prepared in a concentrated solution of one compound (salt, sugar, amino acid) very soluble in water and poorly soluble in a water-soluble solvent. Then, the enzyme solution is added dropwise to the water soluble solvent under rapid stirring. The components accompanying the enzyme are called the crystal growing agents, the solvent being the dehydrating agent. This strategy permits the rapid dehydration of the enzyme solution drops, resulting in a crystallization of the crystal formation agent, and the enzyme is deposited on this crystal surface. The reaction medium where these biocatalysts can be used is marked by the solubility of the PCMC components, and usually these biocatalysts may be employed in water soluble organic solvents with a maximum of 20% water. The evolution of these PCMC was to chemically crosslink them and further improve their stabilities. Moreover, the PCMC strategy has been used to coimmobilize enzymes or enzymes and cofactors. The immobilization may permit the use of buffers as crystal growth agents, enabling control of the reaction pH in the enzyme environments. Usually, the PCMC biocatalysts are very stable and more active than other biocatalysts of the same enzyme. However, this simple (at least at laboratory scale) immobilization strategy is underutilized even when the publications using it systematically presented a better performance of them in organic solvents than that of many other immobilized biocatalysts. In fact, many possibilities and studies using this technique are lacking. This review tried to outline the possibilities of this useful immobilization strategy. Full article

(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)

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56 pages, 12251 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Decomposition of Ruthenium Olefin Metathesis Catalyst

by Magdalena Jawiczuk, Anna Marczyk and Bartosz Trzaskowski

Catalysts 2020, 10(8), 887; https://doi.org/10.3390/catal10080887 - 5 Aug 2020

Cited by 43 | Viewed by 8205

Abstract

Ruthenium olefin metathesis catalysts are one of the most commonly used class of catalysts. There are multiple reviews on their uses in various branches of chemistry and other sciences but a detailed review of their decomposition is missing, despite a large number of [...] Read more.

Ruthenium olefin metathesis catalysts are one of the most commonly used class of catalysts. There are multiple reviews on their uses in various branches of chemistry and other sciences but a detailed review of their decomposition is missing, despite a large number of recent and important advances in this field. In particular, in the last five years several new mechanism of decomposition, both olefin-driven as well as induced by external agents, have been suggested and used to explain differences in the decomposition rates and the metathesis activities of both standard, N-heterocyclic carbene-based systems and the recently developed cyclic alkyl amino carbene-containing complexes. Here we present a review which explores the last 30 years of the decomposition studied on ruthenium olefin metathesis catalyst driven by both intrinsic features of such catalysts as well as external chemicals. Full article

(This article belongs to the Special Issue New Trends in Metathesis Catalysts)

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18 pages, 2596 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Degradation of Acid Orange 7 Azo Dye in Aqueous Solution by a Catalytic-Assisted, Non-Thermal Plasma Process

by Giuseppina Iervolino, Vincenzo Vaiano, Giacomo Pepe, Pietro Campiglia and Vincenzo Palma

Catalysts 2020, 10(8), 888; https://doi.org/10.3390/catal10080888 - 5 Aug 2020

Cited by 23 | Viewed by 4012

Abstract

The aim of this work was the optimization of the performance of the cold plasma technology coupled with a structured catalyst for the discoloration and mineralization of “acid orange 7” (AO7) azo dye. The structured catalyst consists of Fe₂O₃ immobilized [...] Read more.

The aim of this work was the optimization of the performance of the cold plasma technology coupled with a structured catalyst for the discoloration and mineralization of “acid orange 7” (AO7) azo dye. The structured catalyst consists of Fe₂O₃ immobilized on glass spheres, and it was prepared by the “dip coating” method and characterized by different chemico-physical techniques. The experiments were carried out in a dielectric barrier discharge (DBD) reactor. Thanks to the presence of the catalytic packed material, the complete discoloration and mineralization of the dye was achieved with voltage equal to 12 kV, lower than those generally used with this technology (approximately 20–40 kV). The best result in terms of discoloration and mineralization (80% after only 5 min both for discoloration and mineralization) was obtained with 0.25 wt% of Fe₂O₃ immobilized on the glass spheres, without formation of reaction by-products, as shown by the HPLC analysis. The optimized catalyst was reused for several reuse cycles without any substantial decrease of performances. Moreover, tests with radical scavengers evidenced that the most responsible oxidizing species for the degradation of AO7 dye was O2^•−. Full article

(This article belongs to the Special Issue Nonthermal Plasma-Assisted Catalytic Reactions for Environmental Protection)

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26 pages, 8791 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Transition Metal-Catalyzed α-Position Carbon–Carbon Bond Formations of Carbonyl Derivatives

by Ha-Eun Lee, Dopil Kim, Ahrom You, Myung Hwan Park, Min Kim and Cheoljae Kim

Catalysts 2020, 10(8), 861; https://doi.org/10.3390/catal10080861 - 2 Aug 2020

Cited by 26 | Viewed by 5924

Abstract

α-Functionalization of carbonyl compounds in organic synthesis has traditionally been accomplished via classical enolate chemistry. As α-functionalized carbonyl moieties are ubiquitous in biologically and pharmaceutically valuable molecules, catalytic α-alkylations have been extensively studied, yielding a plethora of practical and efficient methodologies. Moreover, stereoselective [...] Read more.

α-Functionalization of carbonyl compounds in organic synthesis has traditionally been accomplished via classical enolate chemistry. As α-functionalized carbonyl moieties are ubiquitous in biologically and pharmaceutically valuable molecules, catalytic α-alkylations have been extensively studied, yielding a plethora of practical and efficient methodologies. Moreover, stereoselective carbon–carbon bond formation at the α-position of achiral carbonyl compounds has been achieved by using various transition metal–chiral ligand complexes. This review describes recent advances—in the last 20 years and especially focusing on the last 10 years—in transition metal-catalyzed α-alkylations of carbonyl compounds, such as aldehydes, ketones, imines, esters, and amides and in efficient carbon–carbon bond formations. Active catalytic species and ligand design are discussed, and mechanistic insights are presented. In addition, recently developed photo-redox catalytic systems for α-alkylations are described as a versatile synthetic tool for the synthesis of chiral carbonyl-bearing molecules. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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18 pages, 5168 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Catalytic Hydrogen Production from Methane: A Review on Recent Progress and Prospect

by Luning Chen, Zhiyuan Qi, Shuchen Zhang, Ji Su and Gabor A. Somorjai

Catalysts 2020, 10(8), 858; https://doi.org/10.3390/catal10080858 - 2 Aug 2020

Cited by 192 | Viewed by 18062

Abstract

Natural gas (Methane) is currently the primary source of catalytic hydrogen production, accounting for three quarters of the annual global dedicated hydrogen production (about 70 M tons). Steam–methane reforming (SMR) is the currently used industrial process for hydrogen production. However, the SMR process [...] Read more.

Natural gas (Methane) is currently the primary source of catalytic hydrogen production, accounting for three quarters of the annual global dedicated hydrogen production (about 70 M tons). Steam–methane reforming (SMR) is the currently used industrial process for hydrogen production. However, the SMR process suffers with insufficient catalytic activity, low long-term stability, and excessive energy input, mostly due to the handling of large amount of CO₂ coproduced. With the demand for anticipated hydrogen production to reach 122.5 M tons in 2024, novel and upgraded catalytic processes are desired for more effective utilization of precious natural resources. In this review, we summarized the major descriptors of catalyst and reaction engineering of the SMR process and compared the SMR process with its derivative technologies, such as dry reforming with CO₂ (DRM), partial oxidation with O₂, autothermal reforming with H₂O and O₂. Finally, we discussed the new progresses of methane conversion: direct decomposition to hydrogen and solid carbon and selective oxidation in mild conditions to hydrogen containing liquid organics (i.e., methanol, formic acid, and acetic acid), which serve as alternative hydrogen carriers. We hope this review will help to achieve a whole picture of catalytic hydrogen production from methane. Full article

(This article belongs to the Special Issue Nanocatalysts for Hydrogen Production)

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22 pages, 6935 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Plasmonic Photocatalysts for Microbiological Applications

by Maya Endo-Kimura and Ewa Kowalska

Catalysts 2020, 10(8), 824; https://doi.org/10.3390/catal10080824 - 23 Jul 2020

Cited by 25 | Viewed by 3430

Abstract

Wide-bandgap semiconductors modified with nanostructures of noble metals for photocatalytic activity under vis irradiation due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively investigated over the last decade. Most literature reports discuss the properties and activities of plasmonic [...] Read more.

Wide-bandgap semiconductors modified with nanostructures of noble metals for photocatalytic activity under vis irradiation due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively investigated over the last decade. Most literature reports discuss the properties and activities of plasmonic photocatalysts for the decomposition of organic compounds and solar energy conversion. Although noble metals, especially silver and copper, have been known since ancient times as excellent antimicrobial agents, there are only limited studies on plasmonic photocatalysts for the inactivation of microorganisms (considering vis-excitation). Accordingly, this review has discussed the available literature reports on microbiological applications of plasmonic photocatalysis, including antibacterial, antiviral and antifungal properties, and also a novel study on other microbiological purposes, such as cancer treatment and drug delivery. Although some reports indicate high antimicrobial properties of these photocatalysts and their potential for medical/pharmaceutical applications, there is still a lack of comprehensive studies on the mechanism of their interactions with microbiological samples. Moreover, contradictory data have also been published, and thus more study is necessary for the final conclusions on the key-factor properties and the mechanisms of inactivation of microorganisms and the treatment of cancer cells. Full article

(This article belongs to the Special Issue Plasmonic Photocatalysts)

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20 pages, 5573 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO₂ with Epoxides

by Veronica Paradiso, Vito Capaccio, David Hermann Lamparelli and Carmine Capacchione

Catalysts 2020, 10(8), 825; https://doi.org/10.3390/catal10080825 - 23 Jul 2020

Cited by 23 | Viewed by 5461

Abstract

Coupling of CO₂ with epoxides is a green emerging alternative for the synthesis of cyclic organic carbonates (COC) and aliphatic polycarbonates (APC). The scope of this work is to provide a comprehensive overview of metal complexes having sulfur-containing ligands as homogeneous catalytic [...] Read more.

Coupling of CO₂ with epoxides is a green emerging alternative for the synthesis of cyclic organic carbonates (COC) and aliphatic polycarbonates (APC). The scope of this work is to provide a comprehensive overview of metal complexes having sulfur-containing ligands as homogeneous catalytic systems able to efficiently promote this transformation with a concise discussion of the most significant results. The crucial role of sulfur as the hemilabile ligand and its influence on the catalytic activity are highlighted as well. Full article

(This article belongs to the Special Issue Catalysts for CO₂ Utilization)

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20 pages, 4897 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photonic Crystals for Plasmonic Photocatalysis

by Tharishinny Raja-Mogan, Bunsho Ohtani and Ewa Kowalska

Catalysts 2020, 10(8), 827; https://doi.org/10.3390/catal10080827 - 23 Jul 2020

Cited by 29 | Viewed by 4234

Abstract

Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports [...] Read more.

Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports have already been published, discussing the optimal properties, synthesis methods and mechanism clarification. It has been proposed that both efficient light harvesting and charge carriers’ migration are detrimental for high and stable activity under Vis irradiation. Accordingly, photonic crystals (PCs) with photonic bandgap (PBG) and slow photon effects seem to be highly attractive for efficient use of incident photons. Therefore, the study on PCs-based plasmonic photocatalysts has been conducted, mainly on titania inverse opal (IO) modified with nanoparticles (NPs) of NM. Although, the research is quite new and only several reports have been published, it might be concluded that the matching between LSPR and PBG (especially at red edge) by tuning of NMNPs size and IO-void diameter, respectively, is the most crucial for the photocatalytic activity. Full article

(This article belongs to the Special Issue Plasmonic Photocatalysts)

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35 pages, 8152 KiB

Open AccessFeature PaperEditor’s ChoiceReview

The Role of Alkali and Alkaline Earth Metals in the CO₂ Methanation Reaction and the Combined Capture and Methanation of CO₂

by Anastasios I. Tsiotsias, Nikolaos D. Charisiou, Ioannis V. Yentekakis and Maria A. Goula

Catalysts 2020, 10(7), 812; https://doi.org/10.3390/catal10070812 - 21 Jul 2020

Cited by 98 | Viewed by 10974

Abstract

CO₂ methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO₂) to synthetic natural gas (CH₄). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts [...] Read more.

CO₂ methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO₂) to synthetic natural gas (CH₄). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts and as adsorbent phases upon the combined capture and methanation of CO₂. Their promotion effect during methanation of carbon dioxide mainly relies on their ability to generate new basic sites on the surface of metal oxide supports that favour CO₂ chemisorption and activation. However, suppression of methanation activity can also occur under certain conditions. Regarding the combined CO₂ capture and methanation process, the development of novel dual-function materials (DFMs) that incorporate both adsorption and methanation functions has opened a new pathway towards the utilization of carbon dioxide emitted from point sources. The sorption and catalytically active phases on these types of materials are crucial parameters influencing their performance and stability and thus, great efforts have been undertaken for their optimization. In this review, we present some of the most recent works on the development of alkali and alkaline earth metal promoted CO₂ methanation catalysts, as well as DFMs for the combined capture and methanation of CO₂. Full article

(This article belongs to the Special Issue Catalysis for Energy Production)

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49 pages, 10500 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Synthesis of Biodegradable Polymers: A Review on the Use of Schiff-Base Metal Complexes as Catalysts for the Ring Opening Polymerization (ROP) of Cyclic Esters

by Orlando Santoro, Xin Zhang and Carl Redshaw

Catalysts 2020, 10(7), 800; https://doi.org/10.3390/catal10070800 - 18 Jul 2020

Cited by 78 | Viewed by 7527

Abstract

This review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization [...] Read more.

This review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization process and the characteristics of the polymers formed, will be discussed. Full article

(This article belongs to the Special Issue Catalysis in Plastics for the 21st Century)

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25 pages, 9275 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Effect of Noble Metal (M: Ir, Pt, Pd) on M/Ce₂O₃-γ-Al₂O₃ Catalysts for Hydrogen Production via the Steam Reforming of Glycerol

by Nikolaos D. Charisiou, Georgios I. Siakavelas, Kyriakos N. Papageridis, Davide Motta, Nikolaos Dimitratos, Victor Sebastian, Kyriaki Polychronopoulou and Maria A. Goula

Catalysts 2020, 10(7), 790; https://doi.org/10.3390/catal10070790 - 15 Jul 2020

Cited by 18 | Viewed by 3575

Abstract

A promising route for the energetic valorisation of the main by-product of the biodiesel industry is the steam reforming of glycerol, as it can theoretically produce seven moles of H₂ for every mole of C₃H₈O₃. In [...] Read more.

A promising route for the energetic valorisation of the main by-product of the biodiesel industry is the steam reforming of glycerol, as it can theoretically produce seven moles of H₂ for every mole of C₃H₈O₃. In the work presented herein, CeO₂–Al₂O₃ was used as supporting material for Ir, Pd and Pt catalysts, which were prepared using the incipient wetness impregnation technique and characterized by employing N₂ adsorption–desorption, X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The catalytic experiments aimed at identifying the effect of temperature on the total conversion of glycerol, on the conversion of glycerol to gaseous products, the selectivity towards the gaseous products (H₂, CO₂, CO, CH₄) and the determination of the H₂/CO and CO/CO₂ molar ratios. The main liquid effluents produced during the reaction were quantified. The results revealed that the Pt/CeAl catalyst was more selective towards H₂, which can be related to its increased number of Brønsted acid sites, which improved the hydrogenolysis and dehydrogenation–dehydration of condensable intermediates. The time-on-stream experiments, undertaken at low Water Glycerol Feed Ratios (WGFR), showed gradual deactivation for all catalysts. This is likely due to the dehydration reaction, which leads to the formation of unsaturated hydrocarbon species and eventually to carbon deposition. The weak metal–support interaction shown for the Ir/CeAl catalyst also led to pronounced sintering of the metallic particles. Full article

(This article belongs to the Special Issue The Design and Development of Precious Metal Catalysts)

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24 pages, 6385 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synthesis and Characterization of Metal Modified Catalysts for Decomposition of Ibuprofen from Aqueous Solutions

by Soudabeh Saeid, Matilda Kråkström, Pasi Tolvanen, Narendra Kumar, Kari Eränen, Markus Peurla, Jyri-Pekka Mikkola, Laurent Maël, Leif Kronberg, Patrik Eklund and Tapio Salmi

Catalysts 2020, 10(7), 786; https://doi.org/10.3390/catal10070786 - 14 Jul 2020

Cited by 12 | Viewed by 3484

Abstract

The presence of pharmaceuticals in surface water, drinking water, and wastewater has attracted significant concern because of the non-biodegradability, resistance, and toxicity of pharmaceutical compounds. The catalytic ozonation of an anti-inflammatory pharmaceutical, ibuprofen was investigated in this work. The reaction mixture was analyzed [...] Read more.

The presence of pharmaceuticals in surface water, drinking water, and wastewater has attracted significant concern because of the non-biodegradability, resistance, and toxicity of pharmaceutical compounds. The catalytic ozonation of an anti-inflammatory pharmaceutical, ibuprofen was investigated in this work. The reaction mixture was analyzed and measured by high-performance liquid chromatography (HPLC). Liquid chromatography-mass spectrometry (LC-MS) was used for the quantification of by-products during the catalytic ozonation process. Ibuprofen was degraded by ozonation under optimized conditions within 1 h. However, some intermediate oxidation products were detected during the ibuprofen ozonation process that were more resistant than the parent compound. To optimize the process, nine heterogeneous catalysts were synthesized using different preparation methods and used with ozone to degrade the ibuprofen dissolved in aqueous solution. The aim of using several catalysts was to reveal the effect of various catalyst preparation methods on the degradation of ibuprofen as well as the formation and elimination of by-products. Furthermore, the goal was to reveal the influence of various support structures and different metals such as Pd-, Fe-, Ni-, metal particle size, and metal dispersion in ozone degradation. Most of the catalysts improved the elimination kinetics of the by-products. Among these catalysts, Cu-H-Beta-150-DP synthesized by the deposition–precipitation process showed the highest decomposition rate. The regenerated Cu-H-Beta-150-DP catalyst preserved the catalytic activity to that of the fresh catalyst. The catalyst characterization methods applied in this work included nitrogen adsorption–desorption, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The large pore volume and small metal particle size contributed to the improved catalytic activity. Full article

(This article belongs to the Special Issue Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Applications in Catalysis)

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115 pages, 22188 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

by Luca Piccirilli, Danielle Lobo Justo Pinheiro and Martin Nielsen

Catalysts 2020, 10(7), 773; https://doi.org/10.3390/catal10070773 - 11 Jul 2020

Cited by 70 | Viewed by 14613

Abstract

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy [...] Read more.

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO₂ capture and conversion, N₂ fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production. Full article

(This article belongs to the Special Issue Green Synthesis and Catalysis)

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21 pages, 5519 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Exploring the Photothermo-Catalytic Performance of Brookite TiO₂-CeO₂ Composites

by Marianna Bellardita, Roberto Fiorenza, Luisa D'Urso, Luca Spitaleri, Antonino Gulino, Giuseppe Compagnini, Salvatore Scirè and Leonardo Palmisano

Catalysts 2020, 10(7), 765; https://doi.org/10.3390/catal10070765 - 9 Jul 2020

Cited by 36 | Viewed by 3965

Abstract

The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO₂-CeO₂ composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease [...] Read more.

The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO₂-CeO₂ composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease in the conversion temperatures of the organic compounds. In particular, in the photothermo-catalytic runs, for the most active samples (TiO₂-3 wt% CeO₂ and TiO₂-5 wt% CeO₂), the temperature at which 90% of VOC conversion occurred was about 60 °C, 40 °C and 20 °C lower than in the thermocatalytic tests for 2-propanol, ethanol and toluene, respectively. Furthermore, the addition of cerium oxide to brookite TiO₂ favored the total oxidation to CO₂ already in the photocatalytic tests at room temperature. The presence of small amounts of cerium oxide allowed to obtain efficient brookite-based composites facilitating the space charge separation and increasing the lifetime of the photogenerated holes and electrons as confirmed by the characterization measurements. The possibility to concurrently utilize the photocatalytic properties of brookite and the redox properties of CeO₂, both activated in the photothermal tests, is an attractive approach easily applicable to purify air from VOCs. Full article

(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)

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27 pages, 4091 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Most Recent Advances in Diesel Engine Catalytic Soot Abatement: Structured Catalysts and Alternative Approaches

by Eugenio Meloni and Vincenzo Palma

Catalysts 2020, 10(7), 745; https://doi.org/10.3390/catal10070745 - 5 Jul 2020

Cited by 38 | Viewed by 5045

Abstract

Diesel engine emissions are typically composed of several hundred chemical compounds, partly present in the gas phase and partly in solid phase as particles, the so-called particulate matter or soot. The morphology of the catalyst is an important characteristic of soot particles’ abatement, [...] Read more.

Diesel engine emissions are typically composed of several hundred chemical compounds, partly present in the gas phase and partly in solid phase as particles, the so-called particulate matter or soot. The morphology of the catalyst is an important characteristic of soot particles’ abatement, since a good contact between catalyst and soot is mandatory. For practical purposes, the active species should be supported as a film on the structured carrier, in order to allow simultaneous soot filtration and combustion. This review focuses on the most recent advances in the development of structured catalysts for diesel engine catalytic soot combustion, characterized by different active species and supports, as well as by different geometric configurations (monoliths, foams, ceramic papers, or wire mesh); the most important peculiar properties are highlighted and summarized. Moreover, a critical review of the most recent advances in modeling studies is also presented in this paper. In addition, some highlights on some of the most recent alternative approaches proposed for limiting the soot emissions from diesel engines have been given, delineating feasible alternatives to the classical strategies nowadays used. Full article

(This article belongs to the Special Issue New Catalysts and Catalytic Technologies for Diesel Soot Emission Reduction)

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25 pages, 2944 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Novel Routes in Transformation of Lignocellulosic Biomass to Furan Platform Chemicals: From Pretreatment to Enzyme Catalysis

by Grigorios Dedes, Anthi Karnaouri and Evangelos Topakas

Catalysts 2020, 10(7), 743; https://doi.org/10.3390/catal10070743 - 4 Jul 2020

Cited by 31 | Viewed by 6711

Abstract

The constant depletion of fossil fuels along with the increasing need for novel materials, necessitate the development of alternative routes for polymer synthesis. Lignocellulosic biomass, the most abundant carbon source on the planet, can serve as a renewable starting material for the design [...] Read more.

The constant depletion of fossil fuels along with the increasing need for novel materials, necessitate the development of alternative routes for polymer synthesis. Lignocellulosic biomass, the most abundant carbon source on the planet, can serve as a renewable starting material for the design of environmentally-friendly processes for the synthesis of polyesters, polyamides and other polymers with significant value. The present review provides an overview of the main processes that have been reported throughout the literature for the production of bio-based monomers from lignocellulose, focusing on physicochemical procedures and biocatalysis. An extensive description of all different stages for the production of furans is presented, starting from physicochemical pretreatment of biomass and biocatalytic decomposition to monomeric sugars, coupled with isomerization by enzymes prior to chemical dehydration by acid Lewis catalysts. A summary of all biotransformations of furans carried out by enzymes is also described, focusing on galactose, glyoxal and aryl-alcohol oxidases, monooxygenases and transaminases for the production of oxidized derivatives and amines. The increased interest in these products in polymer chemistry can lead to a redirection of biomass valorization from second generation biofuels to chemical synthesis, by creating novel pathways to produce bio-based polymers. Full article

(This article belongs to the Section Biocatalysis)

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19 pages, 3422 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Immobilized Biocatalysts of Eversa^® Transform 2.0 and Lipase from Thermomyces Lanuginosus: Comparison of Some Properties and Performance in Biodiesel Production

by Javier A. Martínez-Sanchez, Sara Arana-Peña, Diego Carballares, Malcom Yates, Cristina Otero and Roberto Fernandez-Lafuente

Catalysts 2020, 10(7), 738; https://doi.org/10.3390/catal10070738 - 3 Jul 2020

Cited by 23 | Viewed by 3786

Abstract

Eversa^® Transform (ET), and the lipase from Thermomyces lanuginosus (TLL), liquid commercial lipases formulations, have been immobilized on octyl agarose beads and their stabilities were compared. Immobilized and free ET forms were more thermostable than TLL formulations at pH 5.0, 7.0, and [...] Read more.

Eversa^® Transform (ET), and the lipase from Thermomyces lanuginosus (TLL), liquid commercial lipases formulations, have been immobilized on octyl agarose beads and their stabilities were compared. Immobilized and free ET forms were more thermostable than TLL formulations at pH 5.0, 7.0, and 9.0, and the ET immobilized form was more stable in the presence of 90% methanol or dioxane at 25 °C and pH 7. Specific activity versus p-nitrophenyl butyrate was higher for ET than for TLL. However, after immobilization the differences almost disappeared because TLL was very hyperactivated (2.5-fold) and ET increased the activity only by 1.6 times. The enzymes were also immobilized in octadecyl methacrylate beads. In both cases, the loading was around 20 mg/g. In this instance, activity was similar for immobilized TLL and ET using triacetin, while the activity of immobilized ET was lower using (S)-methyl mandelate. When the immobilized enzymes were used to produce biodiesel from sunflower oil and methanol in tert-butanol medium, their performance was fairly similar. Full article

(This article belongs to the Section Biocatalysis)

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44 pages, 11660 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Metal–Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) Applied to Photocatalytic Organic Transformations

by Alberto López-Magano, Alicia Jiménez-Almarza, Jose Alemán and Rubén Mas-Ballesté

Catalysts 2020, 10(7), 720; https://doi.org/10.3390/catal10070720 - 27 Jun 2020

Cited by 53 | Viewed by 10846

Abstract

Among the different alternatives for catalysis using metal–organic frameworks (MOFs) or covalent organic frameworks (COFs), photocatalysis has remarkably evolved during the last decade. Photocatalytic reticular materials allowed recyclability and easy separation of catalyst from the product, also reaching the activity and selectivity commonly [...] Read more.

Among the different alternatives for catalysis using metal–organic frameworks (MOFs) or covalent organic frameworks (COFs), photocatalysis has remarkably evolved during the last decade. Photocatalytic reticular materials allowed recyclability and easy separation of catalyst from the product, also reaching the activity and selectivity commonly observed for molecular systems. Recently, photocatalytic MOFs and COFs have been applied to synthetic applications in order to obtain organic molecules of different complexity. However, although a good number of works have been devoted to this issue, an updated comprehensive revision on this field is still needed. The aim of this review was to fill this gap covering the following three general aspects: (1) common strategies on the design of reticular photocatalytic materials, (2) a comprehensive discussion of the photocatalytic organic reactions achieved by the use of COFs and MOFs, and (3) some critical considerations highlighting directions that should be considered in order to make advances in the study of photocatalytic COFs and MOFs. Full article

(This article belongs to the Section Catalytic Materials)

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20 pages, 4430 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

CFD Simulations of Radiative Heat Transport in Open-Cell Foam Catalytic Reactors

by Christoph Sinn, Felix Kranz, Jonas Wentrup, Jorg Thöming, Gregor D. Wehinger and Georg R. Pesch

Catalysts 2020, 10(6), 716; https://doi.org/10.3390/catal10060716 - 26 Jun 2020

Cited by 15 | Viewed by 5160

Abstract

The heat transport management in catalytic reactors is crucial for the overall reactor performance. For small-scale dynamically-operated reactors, open-cell foams have shown advantageous heat transport characteristics over conventional pellet catalyst carriers. To design efficient and safe foam reactors as well as to deploy [...] Read more.

The heat transport management in catalytic reactors is crucial for the overall reactor performance. For small-scale dynamically-operated reactors, open-cell foams have shown advantageous heat transport characteristics over conventional pellet catalyst carriers. To design efficient and safe foam reactors as well as to deploy reliable engineering models, a thorough understanding of the three heat transport mechanisms, i.e., conduction, convection, and thermal radiation, is needed. Whereas conduction and convection have been studied extensively, the contribution of thermal radiation to the overall heat transport in open-cell foam reactors requires further investigation. In this study, we simulated a conjugate heat transfer case of a µCT based foam reactor using OpenFOAM and verified the model against a commercial computational fluid dynamics (CFD) code (STAR-CCM+). We further explicitly quantified the deviation made when radiation is not considered. We studied the effect of the solid thermal conductivity, the superficial velocity and surface emissivities in ranges that are relevant for heterogeneous catalysis applications (solid thermal conductivities 1–200 W m⁻¹ K⁻¹; superficial velocities 0.1–0.5 m s⁻¹; surface emissivities 0.1–1). Moreover, the temperature levels correspond to a range of exo- and endothermal reactions, such as CO₂ methanation, dry reforming of methane, and methane steam reforming. We found a significant influence of radiation on heat flows (deviations up to 24%) and temperature increases (deviations up to 400 K) for elevated temperature levels, low superficial velocities, low solid thermal conductivities and high surface emissivities. Full article

(This article belongs to the Special Issue Design of Heterogeneous Catalysts and Adsorbents)

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35 pages, 4352 KiB

Open AccessEditor’s ChoiceReview

Fundamentals of Gas Diffusion Electrodes and Electrolysers for Carbon Dioxide Utilisation: Challenges and Opportunities

by Sandra Hernandez-Aldave and Enrico Andreoli

Catalysts 2020, 10(6), 713; https://doi.org/10.3390/catal10060713 - 26 Jun 2020

Cited by 71 | Viewed by 22512

Abstract

Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO₂ conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has [...] Read more.

Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO₂ conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has emerged as the Achilles heel of CO₂ electrolysis. Too often, catalysts are assessed in electrochemical settings that are far removed from industrially relevant operational conditions, where CO₂ mass transport limitations should be minimised. To overcome this issue, gas diffusion electrodes and gas-fed electrolysers need to be developed and applied, presenting new challenges and opportunities to the CO₂ electrolysis community. In this review, we introduce the reader to the fundamentals of gas diffusion electrodes and gas-fed electrolysers, highlighting their advantages and disadvantages. We discuss in detail the design of gas diffusion electrodes and their operation within gas-fed electrolysers in both flow-through and flow-by configurations. Then, we correlate the structure and composition of gas diffusion electrodes to the operational performance of electrolysers, indicating options and prospects for improvement. Overall, this study will equip the reader with the fundamental understanding required to enhance and optimise CO₂ catalysis beyond the laboratory scale. Full article

(This article belongs to the Section Electrocatalysis)

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34 pages, 1724 KiB

Open AccessEditor’s ChoiceReview

Recent Progresses on Metal Halide Perovskite-Based Material as Potential Photocatalyst

by Bianca-Maria Bresolin, Yuri Park and Detlef W. Bahnemann

Catalysts 2020, 10(6), 709; https://doi.org/10.3390/catal10060709 - 24 Jun 2020

Cited by 65 | Viewed by 8122

Abstract

Recent years have witnessed an incredibly high interest in perovskite-based materials. Among this class, metal halide perovskites (MHPs) have attracted a lot of attention due to their easy preparation and excellent opto-electronic properties, showing a remarkably fast development in a few decades, particularly [...] Read more.

Recent years have witnessed an incredibly high interest in perovskite-based materials. Among this class, metal halide perovskites (MHPs) have attracted a lot of attention due to their easy preparation and excellent opto-electronic properties, showing a remarkably fast development in a few decades, particularly in solar light-driven applications. The high extinction coefficients, the optimal band gaps, the high photoluminescence quantum yields and the long electron–hole diffusion lengths make MHPs promising candidates in several technologies. Currently, the researchers have been focusing their attention on MHPs-based solar cells, light-emitting diodes, photodetectors, lasers, X-ray detectors and luminescent solar concentrators. In our review, we firstly present a brief introduction on the recent discoveries and on the remarkable properties of metal halide perovskites, followed by a summary of some of their more traditional and representative applications. In particular, the core of this work was to examine the recent progresses of MHPs-based materials in photocatalytic applications. We summarize some recent developments of hybrid organic–inorganic and all-inorganic MHPs, recently used as photocatalysts for hydrogen evolution, carbon dioxide reduction, organic contaminant degradation and organic synthesis. Finally, the main limitations and the future potential of this new generation of materials have been discussed. Full article

(This article belongs to the Special Issue Progression in Photocatalytic Materials for Efficient Performance)

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31 pages, 3058 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials

by Valeria Califano and Aniello Costantini

Catalysts 2020, 10(6), 706; https://doi.org/10.3390/catal10060706 - 23 Jun 2020

Cited by 37 | Viewed by 4744

Abstract

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme [...] Read more.

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme loading and finely dispersing the biocatalyst molecules. The easily tunable pore morphology allows for creating a proper environment to host an enzyme. The confining effect of mesopores can improve the enzyme stability and its resistance to extreme pH and temperatures. Benefits also arise from other peculiarities of nanoparticles such as Brownian motion and easy dispersion. Fossil fuel depletion and environmental pollution have led to the need for alternative sustainable and renewable energy sources such as biofuels. In this context, lignocellulosic biomass has been considered as a strategic fuel source. Cellulases are a class of hydrolytic enzymes that convert cellulose into fermentable sugars. This review is intended to survey the immobilization of cellulolytic enzymes (cellulases and β-glucosidase) onto mesoporous silica nanoparticles and their catalytic performance, with the aim to give a contribution to the urgent action required against climate change and its impacts, by biorefineries’ development. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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18 pages, 7441 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Utilization of Waste Grooved Razor Shell (GRS) as a Catalyst in Biodiesel Production from Refined and Waste Cooking Oils

by Abdellah Aitlaalim, Fatiha Ouanji, Abdellah Benzaouak, Mohammed El Mahi, El Mostapha Lotfi, Mohamed Kacimi and Leonarda Francesca Liotta

Catalysts 2020, 10(6), 703; https://doi.org/10.3390/catal10060703 - 22 Jun 2020

Cited by 16 | Viewed by 2964

Abstract

Biodiesel is a potential alternative for fossil fuel. However, its large-scale application is held up by the disadvantage of a homogenous process, the scarce availability of raw materials and the production cost, which is higher than for fossil diesel. In this work, biodiesel [...] Read more.

Biodiesel is a potential alternative for fossil fuel. However, its large-scale application is held up by the disadvantage of a homogenous process, the scarce availability of raw materials and the production cost, which is higher than for fossil diesel. In this work, biodiesel production was carried out using both refined and used cooking oils. The process was investigated in a batch reactor, in the presence of CaO as a heterogeneous catalyst prepared by the calcination of the natural Waste Grooved Razor Shell (GRS). Characterizations by X-Ray Diffraction (XRD) and Thermal Gravimetric (TG)/Differential Thermal Analysis (DTA) showed that the as-received GRS consists of aragonite, (i.e., CaCO₃) as the main component and of water and organic matter in a lower amount. After calcination at 900 °C, CaO was formed as the only crystalline phase. The effects of several experimental parameters in the transesterification reactions were studied, and their impact on the produced biodiesel properties was investigated. The studied variables were the methanol/oil molar ratio, the catalyst weight percentage (with respect to the oil mass), the calcination temperature of the parent GRS and the recycling and regeneration of the catalyst. The physico-chemical and fuel properties, i.e., viscosity, density and acid value of used oils and of the produced biodiesel, were determined by conventional methods (American Society for Testing and Materials (ASTM) methods) and compared with the European standards of biodiesel. The optimal identified conditions were the following: the use of a 15:1 methanol/oil molar ratio and 5 wt% of CaO with respect to the oil mass. After 3 h of reaction at 65 °C, the biodiesel yield was equal to 94% and 99% starting from waste and refined oils, respectively. Full article

(This article belongs to the Special Issue Selected Papers from Elitecat 2019, 1-5 July 2019, Villeurbanne, France)

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29 pages, 6870 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Trends in Biomaterials for Immobilization of Lipases for Application in Non-Conventional Media

by Robson Carlos Alnoch, Leandro Alves dos Santos, Janaina Marques de Almeida, Nadia Krieger and Cesar Mateo

Catalysts 2020, 10(6), 697; https://doi.org/10.3390/catal10060697 - 20 Jun 2020

Cited by 37 | Viewed by 4364

Abstract

The utilization of biomaterials as novel carrier materials for lipase immobilization has been investigated by many research groups over recent years. Biomaterials such as agarose, starch, chitin, chitosan, cellulose, and their derivatives have been extensively studied since they are non-toxic materials, can be [...] Read more.

The utilization of biomaterials as novel carrier materials for lipase immobilization has been investigated by many research groups over recent years. Biomaterials such as agarose, starch, chitin, chitosan, cellulose, and their derivatives have been extensively studied since they are non-toxic materials, can be obtained from a wide range of sources and are easy to modify, due to the high variety of functional groups on their surfaces. However, although many lipases have been immobilized on biomaterials and have shown potential for application in biocatalysis, special features are required when the biocatalyst is used in non-conventional media, for example, in organic solvents, which are required for most reactions in organic synthesis. In this article, we discuss the use of biomaterials for lipase immobilization, highlighting recent developments in the synthesis and functionalization of biomaterials using different methods. Examples of effective strategies designed to result in improved activity and stability and drawbacks of the different immobilization protocols are discussed. Furthermore, the versatility of different biocatalysts for the production of compounds of interest in organic synthesis is also described. Full article

(This article belongs to the Special Issue Enzymes in Sustainable Chemistry)

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32 pages, 3997 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Exploring the Mechanism of Catalysis with the Unified Reaction Valley Approach (URVA)—A Review

by Elfi Kraka, Wenli Zou, Yunwen Tao and Marek Freindorf

Catalysts 2020, 10(6), 691; https://doi.org/10.3390/catal10060691 - 19 Jun 2020

Cited by 17 | Viewed by 4222

Abstract

The unified reaction valley approach (URVA) differs from mainstream mechanistic studies, as it describes a chemical reaction via the reaction path and the surrounding reaction valley on the potential energy surface from the van der Waals region to the transition state and far [...] Read more.

The unified reaction valley approach (URVA) differs from mainstream mechanistic studies, as it describes a chemical reaction via the reaction path and the surrounding reaction valley on the potential energy surface from the van der Waals region to the transition state and far out into the exit channel, where the products are located. The key feature of URVA is the focus on the curving of the reaction path. Moving along the reaction path, any electronic structure change of the reacting molecules is registered by a change in their normal vibrational modes and their coupling with the path, which recovers the curvature of the reaction path. This leads to a unique curvature profile for each chemical reaction with curvature minima reflecting minimal change and curvature maxima, the location of important chemical events such as bond breaking/forming, charge polarization and transfer, rehybridization, etc. A unique decomposition of the path curvature into internal coordinate components provides comprehensive insights into the origins of the chemical changes taking place. After presenting the theoretical background of URVA, we discuss its application to four diverse catalytic processes: (i) the Rh catalyzed methanol carbonylation—the Monsanto process; (ii) the Sharpless epoxidation of allylic alcohols—transition to heterogenous catalysis; (iii) Au(I) assisted [3,3]-sigmatropic rearrangement of allyl acetate; and (iv) the Bacillus subtilis chorismate mutase catalyzed Claisen rearrangement—and show how URVA leads to a new protocol for fine-tuning of existing catalysts and the design of new efficient and eco-friendly catalysts. At the end of this article the pURVA software is introduced. The overall goal of this article is to introduce to the chemical community a new protocol for fine-tuning existing catalytic reactions while aiding in the design of modern and environmentally friendly catalysts. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate "Computational Catalysis"—Trends and Outlook)

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15 pages, 1599 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stable Continuous Production of γ-Valerolactone from Biomass-Derived Levulinic Acid over Zr–Al-Beta Zeolite Catalyst

by Clara López-Aguado, Marta Paniagua, Juan A. Melero, Jose Iglesias, Pablo Juárez, Manuel López Granados and Gabriel Morales

Catalysts 2020, 10(6), 678; https://doi.org/10.3390/catal10060678 - 17 Jun 2020

Cited by 25 | Viewed by 3932

Abstract

The one-pot conversion of biomass-derived platform molecules such as levulinic acid (LA) and furfural (FAL) into γ-valerolactone (GVL) is challenging because of the need for adequate multi-functional catalysts and high-pressure gaseous hydrogen. As a more sustainable alternative, here we describe the transfer hydrogenation [...] Read more.

The one-pot conversion of biomass-derived platform molecules such as levulinic acid (LA) and furfural (FAL) into γ-valerolactone (GVL) is challenging because of the need for adequate multi-functional catalysts and high-pressure gaseous hydrogen. As a more sustainable alternative, here we describe the transfer hydrogenation of LA to GVL using isopropanol as a hydrogen donor over a Zr-modified beta zeolite catalyst in a continuous fixed-bed reactor. A stable sustained production of GVL was achieved from the levulinic acid, with both high LA conversion (ca. 95%) and GVL yield (ca. 90%), for over at least 20 days in continuous operation at 170 °C. Importantly, the small decay in activity can be advantageously overcome by the means of a simple in situ thermal regeneration in the air atmosphere, leading to a complete recovery of the catalyst activity. Key to this outstanding result is the use of a Zr-modified dealuminated beta zeolite with a tailored Lewis/Brønsted acid sites ratio, which can synergistically catalyze the tandem steps of hydrogen transfer and acid-catalyzed transformations, leading to such a successful and stable production of GVL from LA. Full article

(This article belongs to the Special Issue Multifunctional Heterogeneous Catalysis)

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20 pages, 4973 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Defective TiO₂ Core-Shell Magnetic Photocatalyst Modified with Plasmonic Nanoparticles for Visible Light-Induced Photocatalytic Activity

by Zuzanna Bielan, Agnieszka Sulowska, Szymon Dudziak, Katarzyna Siuzdak, Jacek Ryl and Anna Zielińska-Jurek

Catalysts 2020, 10(6), 672; https://doi.org/10.3390/catal10060672 - 15 Jun 2020

Cited by 18 | Viewed by 2642

Abstract

In the presented work, for the first time, the metal-modified defective titanium(IV) oxide nanoparticles with well-defined titanium vacancies, was successfully obtained. Introducing platinum and copper nanoparticles (NPs) as surface modifiers of defective d-TiO₂ significantly increased the photocatalytic activity in both UV-Vis and [...] Read more.

In the presented work, for the first time, the metal-modified defective titanium(IV) oxide nanoparticles with well-defined titanium vacancies, was successfully obtained. Introducing platinum and copper nanoparticles (NPs) as surface modifiers of defective d-TiO₂ significantly increased the photocatalytic activity in both UV-Vis and Vis light ranges. Moreover, metal NPs deposition on the magnetic core allowed for the effective separation and reuse of the nanometer-sized photocatalyst from the suspension after the treatment process. The obtained Fe₃O₄@SiO₂/d-TiO₂-Pt/Cu photocatalysts were characterized by X-ray diffractometry (XRD) and specific surface area (BET) measurements, UV-Vis diffuse reflectance spectroscopy (DR-UV/Vis), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Further, the mechanism of phenol degradation and the role of four oxidative species (h⁺, e⁻, ^•OH, and ^•O₂⁻) in the studied photocatalytic process were investigated. Full article

(This article belongs to the Special Issue Plasmonic Photocatalysts)

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74 pages, 6329 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Bioalcohol Reforming: An Overview of the Recent Advances for the Enhancement of Catalyst Stability

by Vincenzo Palma, Concetta Ruocco, Marta Cortese and Marco Martino

Catalysts 2020, 10(6), 665; https://doi.org/10.3390/catal10060665 - 12 Jun 2020

Cited by 40 | Viewed by 4827

Abstract

The growing demand for energy production highlights the shortage of traditional resources and the related environmental issues. The adoption of bioalcohols (i.e., alcohols produced from biomass or biological routes) is progressively becoming an interesting approach that is used to restrict the consumption of [...] Read more.

The growing demand for energy production highlights the shortage of traditional resources and the related environmental issues. The adoption of bioalcohols (i.e., alcohols produced from biomass or biological routes) is progressively becoming an interesting approach that is used to restrict the consumption of fossil fuels. Bioethanol, biomethanol, bioglycerol, and other bioalcohols (propanol and butanol) represent attractive feedstocks for catalytic reforming and production of hydrogen, which is considered the fuel of the future. Different processes are already available, including steam reforming, oxidative reforming, dry reforming, and aqueous-phase reforming. Achieving the desired hydrogen selectivity is one of the main challenges, due to the occurrence of side reactions that cause coke formation and catalyst deactivation. The aims of this review are related to the critical identification of the formation of carbon roots and the deactivation of catalysts in bioalcohol reforming reactions. Furthermore, attention is focused on the strategies used to improve the durability and stability of the catalysts, with particular attention paid to the innovative formulations developed over the last 5 years. Full article

(This article belongs to the Special Issue Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration)

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14 pages, 1899 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Three-Step Process for the Bioconversion of Whey Permeate into a Glucose-Free D-Tagatose Syrup

by Fadia V. Cervantes, Sawssan Neifar, Zoran Merdzo, Javier Viña-Gonzalez, Lucia Fernandez-Arrojo, Antonio O. Ballesteros, Maria Fernandez-Lobato, Samir Bejar and Francisco J. Plou

Catalysts 2020, 10(6), 647; https://doi.org/10.3390/catal10060647 - 9 Jun 2020

Cited by 18 | Viewed by 3983

Abstract

We have developed a sustainable three-stage process for the revaluation of cheese whey permeate into D-tagatose, a rare sugar with functional properties used as sweetener. The experimental conditions (pH, temperature, cofactors, etc.) for each step were independently optimized. In the first step, concentrated [...] Read more.

We have developed a sustainable three-stage process for the revaluation of cheese whey permeate into D-tagatose, a rare sugar with functional properties used as sweetener. The experimental conditions (pH, temperature, cofactors, etc.) for each step were independently optimized. In the first step, concentrated whey containing 180–200 g/L of lactose was fully hydrolyzed by β-galactosidase from Bifidobacterium bifidum (Saphera^®) in 3 h at 45 °C. Secondly, glucose was selectively removed by treatment with Pichia pastoris cells for 3 h at 30 °C. The best results were obtained with 350 mg of cells (previously grown for 16 h) per mL of solution. Finally, L-arabinose isomerase US100 from Bacillus stearothermophilus was employed to isomerize D-galactose into D-tagatose at pH 7.5 and 65 °C, in presence of 0.5 mM MnSO₄. After 7 h, the concentration of D-tagatose was approximately 30 g/L (33.3% yield, referred to the initial D-galactose present in whey). The proposed integrated process takes place under mild conditions (neutral pH, moderate temperatures) in a short time (13 h), yielding a glucose-free syrup containing D-tagatose and galactose in a ratio 1:2 (w/w). Full article

(This article belongs to the Special Issue Applied Biocatalysis in Europe: A Sustainable Tool for Improving Life Quality)

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18 pages, 3508 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

FeCeO_x Supported Ni, Sn Catalysts for the High-Temperature Water–Gas Shift Reaction

by Devaiah Damma and Panagiotis G. Smirniotis

Catalysts 2020, 10(6), 639; https://doi.org/10.3390/catal10060639 - 8 Jun 2020

Cited by 8 | Viewed by 3136

Abstract

In this work, the effect of monometallic Ni or Sn and bimetallic NiSn deposition on the activity of FeCeO_x catalysts in high-temperature water–gas (HT-WGS) reactions was investigated. It was found that the HT-WGS performance of FeCeO_x has significantly improved after the [...] Read more.

In this work, the effect of monometallic Ni or Sn and bimetallic NiSn deposition on the activity of FeCeO_x catalysts in high-temperature water–gas (HT-WGS) reactions was investigated. It was found that the HT-WGS performance of FeCeO_x has significantly improved after the deposition of Sn together with Ni on it. Furthermore, the bimetallic NiSn/FeCeO_x catalyst showed higher activity compared to the monometallic Ni/FeCeO_x and Sn/FeCeO_x catalysts within the tested temperature range (450–600 °C). Although the Ni/FeCeO_x catalyst showed methanation activity at a temperature below 550 °C, the NiSn/FeCeO_x catalyst suppressed the methane formation to zero in the WGS. Besides, the NiSn/FeCeO_x catalyst exhibited an excellent time-on-stream stability without methanation reaction, even at a steam-to-CO ratio as low as 0.8. The combination of Ni and Sn supported on FeCeO_x led to a large lattice strain, the formation of NiSn alloy, and a strong synergistic effect between the bimetallic NiSn and FeCeO_x mixed oxide support interface. All these features are very important in achieving the best activity and stability of NiSn/FeCeO_x in the HT-WGS reaction. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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72 pages, 17150 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Homogeneous Catalysis via Metal–Ligand Cooperation Involving Aromatization and Dearomatization

by Takuya Shimbayashi and Ken-ichi Fujita

Catalysts 2020, 10(6), 635; https://doi.org/10.3390/catal10060635 - 7 Jun 2020

Cited by 43 | Viewed by 6296

Abstract

Recently, an increasing number of metal complex catalysts have been developed to achieve the activation or transformation of substrates based on cooperation between the metal atom and its ligands. In such “cooperative catalysis,” the ligand not only is bound to the metal, where [...] Read more.

Recently, an increasing number of metal complex catalysts have been developed to achieve the activation or transformation of substrates based on cooperation between the metal atom and its ligands. In such “cooperative catalysis,” the ligand not only is bound to the metal, where it exerts steric and electronic effects, but also functionally varies its structure during the elementary processes of the catalytic reaction. In this review article, we focus on metal–ligand cooperation involving aromatization and dearomatization of the ligand, thus introducing the newest developments and examples of homogeneous catalytic reactions. Full article

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14 pages, 2853 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Selective Hydrogenation of Acetylene over Pd-Mn/Al₂O₃ Catalysts

by Dmitry Melnikov, Valentine Stytsenko, Elena Saveleva, Mikhail Kotelev, Valentina Lyubimenko, Evgenii Ivanov, Aleksandr Glotov and Vladimir Vinokurov

Catalysts 2020, 10(6), 624; https://doi.org/10.3390/catal10060624 - 4 Jun 2020

Cited by 15 | Viewed by 3941

Abstract

Novel bimetallic Pd-Mn/Al₂O₃ catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al₂O₃ in an H₂ atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are [...] Read more.

Novel bimetallic Pd-Mn/Al₂O₃ catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al₂O₃ in an H₂ atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N₂ adsorption, H₂ pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H₂), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al₂O₃ catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al₂O₃ to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts. Full article

(This article belongs to the Special Issue Heterogeneous Catalysts for Petrochemical Synthesis and Oil Refining)

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20 pages, 2032 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Valorization of Biodiesel Byproduct Crude Glycerol for the Production of Bioenergy and Biochemicals

by Niravkumar Mahendrasinh Kosamia, Mahdieh Samavi, Bijaya Kumar Uprety and Sudip Kumar Rakshit

Catalysts 2020, 10(6), 609; https://doi.org/10.3390/catal10060609 - 1 Jun 2020

Cited by 52 | Viewed by 7189

Abstract

The rapid growth of global biodiesel production requires simultaneous effective utilization of glycerol obtained as a by-product of the transesterification process. Accumulation of the byproduct glycerol from biodiesel industries can lead to considerable environment issues. Hence, there is extensive research focus on the [...] Read more.

The rapid growth of global biodiesel production requires simultaneous effective utilization of glycerol obtained as a by-product of the transesterification process. Accumulation of the byproduct glycerol from biodiesel industries can lead to considerable environment issues. Hence, there is extensive research focus on the transformation of crude glycerol into value-added products. This paper makes an overview of the nature of crude glycerol and ongoing research on its conversion to value-added products. Both chemical and biological routes of glycerol valorization will be presented. Details of crude glycerol conversion into microbial lipid and subsequent products will also be highlighted. Full article

(This article belongs to the Special Issue New Glycerol Upgrading Processes)

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20 pages, 3426 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO₂ Photocatalysis

by Xiuyan Yang, Jacek A. Koziel, Yael Laor, Wenda Zhu, J. (Hans) van Leeuwen, William S. Jenks, Steven J. Hoff, Jeffrey Zimmerman, Shicheng Zhang, Uzi Ravid and Robert Armon

Catalysts 2020, 10(6), 607; https://doi.org/10.3390/catal10060607 - 1 Jun 2020

Cited by 31 | Viewed by 4512

Abstract

Control of gaseous emissions from livestock operations is needed to ensure compliance with environmental regulations and sustainability of the industry. The focus of this research was to mitigate livestock odor emissions with UV light. Effects of the UV dose, wavelength, TiO₂ catalyst, [...] Read more.

Control of gaseous emissions from livestock operations is needed to ensure compliance with environmental regulations and sustainability of the industry. The focus of this research was to mitigate livestock odor emissions with UV light. Effects of the UV dose, wavelength, TiO₂ catalyst, air temperature, and relative humidity were tested at lab scale on a synthetic mixture of nine odorous volatile organic compounds (VOCs) and real poultry manure offgas. Results show that it was feasible to control odorous VOCs with both photolysis and photocatalysis (synthetic VOCs mixture) and with photocatalysis (manure offgas). The treatment effectiveness R (defined as % conversion), was proportional to the light intensity for synthetic VOCs mixtures and followed an order of UV_185+254 + TiO₂ > UV₂₅₄ + TiO₂ > UV_185+254; no catalyst > UV₂₅₄; no catalyst. VOC conversion R > 80% was achieved when light energy was >~60 J L⁻¹. The use of deep UV (UV_185+254) improved the R, particularly when photolysis was the primary treatment. Odor removal up to ~80% was also observed for a synthetic VOCs mixture, and actual poultry manure offgas. Scale-up studies are warranted. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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13 pages, 4856 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Catalytic Micro-Combustor Inspired by the Nasal Geometry of Reindeer: CFD Modeling and Simulation

by Valeria Di Sarli, Marco Trofa and Almerinda Di Benedetto

Catalysts 2020, 10(6), 606; https://doi.org/10.3390/catal10060606 - 31 May 2020

Cited by 6 | Viewed by 2585

Abstract

A three-dimensional CFD model of a novel configuration of catalytic micro-combustor inspired by the nasal geometry of reindeer was developed using the commercial code ANSYS Fluent 19.0. The thermal behavior of this nature-inspired (NI) configuration was investigated through simulations of lean propane/air combustion [...] Read more.

A three-dimensional CFD model of a novel configuration of catalytic micro-combustor inspired by the nasal geometry of reindeer was developed using the commercial code ANSYS Fluent 19.0. The thermal behavior of this nature-inspired (NI) configuration was investigated through simulations of lean propane/air combustion performed at different values of residence time (i.e., inlet gas velocity) and (external convective) heat transfer coefficient. Simulations at the same conditions were also run for a standard parallel-channel (PC) configuration of equivalent dimensions. Numerical results show that the operating window of stable combustion is wider in the case of the NI configuration. In particular, the blow-out behavior is substantially the same for the two configurations. Conversely, the extinction behavior, which is dominated by competition between the heat losses towards the external environment and the heat produced by combustion, differs. The NI configuration exhibits a greater ability than the PC configuration to keep the heat generated by combustion trapped inside the micro-reactor. As a consequence, extinction occurs at higher values of residence time and heat transfer coefficient for this novel configuration. Full article

(This article belongs to the Special Issue Novel Structured Catalytic Reactors)

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58 pages, 11423 KiB

Open AccessFeature PaperEditor’s ChoiceReview

One Pot Use of Combilipases for Full Modification of Oils and Fats: Multifunctional and Heterogeneous Substrates

by Sara Arana-Peña, Diego Carballares, Ángel Berenguer-Murcia, Andrés R. Alcántara, Rafael C. Rodrigues and Roberto Fernandez-Lafuente

Catalysts 2020, 10(6), 605; https://doi.org/10.3390/catal10060605 - 29 May 2020

Cited by 57 | Viewed by 5378

Abstract

Lipases are among the most utilized enzymes in biocatalysis. In many instances, the main reason for their use is their high specificity or selectivity. However, when full modification of a multifunctional and heterogeneous substrate is pursued, enzyme selectivity and specificity become a problem. [...] Read more.

Lipases are among the most utilized enzymes in biocatalysis. In many instances, the main reason for their use is their high specificity or selectivity. However, when full modification of a multifunctional and heterogeneous substrate is pursued, enzyme selectivity and specificity become a problem. This is the case of hydrolysis of oils and fats to produce free fatty acids or their alcoholysis to produce biodiesel, which can be considered cascade reactions. In these cases, to the original heterogeneity of the substrate, the presence of intermediate products, such as diglycerides or monoglycerides, can be an additional drawback. Using these heterogeneous substrates, enzyme specificity can promote that some substrates (initial substrates or intermediate products) may not be recognized as such (in the worst case scenario they may be acting as inhibitors) by the enzyme, causing yields and reaction rates to drop. To solve this situation, a mixture of lipases with different specificity, selectivity and differently affected by the reaction conditions can offer much better results than the use of a single lipase exhibiting a very high initial activity or even the best global reaction course. This mixture of lipases from different sources has been called “combilipases” and is becoming increasingly popular. They include the use of liquid lipase formulations or immobilized lipases. In some instances, the lipases have been coimmobilized. Some discussion is offered regarding the problems that this coimmobilization may give rise to, and some strategies to solve some of these problems are proposed. The use of combilipases in the future may be extended to other processes and enzymes. Full article

(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)

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16 pages, 6504 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermal Post-Treatments to Enhance the Water Stability of NH₂-MIL-125(Ti)

by Almudena Gómez-Avilés, Virginia Muelas-Ramos, Jorge Bedia, Juan Jose Rodriguez and Carolina Belver

Catalysts 2020, 10(6), 603; https://doi.org/10.3390/catal10060603 - 29 May 2020

Cited by 31 | Viewed by 5535

Abstract

NH₂-MIL-125(Ti) is a metal organic framework (MOF) based on Ti-oxo-clusters widely investigated in water-related applications. Such applications require MOFs with an excellent stability in the aqueous phase, but, despite this, the extent of MOFs’ degradation in water is still not yet [...] Read more.

NH₂-MIL-125(Ti) is a metal organic framework (MOF) based on Ti-oxo-clusters widely investigated in water-related applications. Such applications require MOFs with an excellent stability in the aqueous phase, but, despite this, the extent of MOFs’ degradation in water is still not yet fully understood. In this study, we report a quantitative study of the water stability of NH₂-MIL-125(Ti), analyzing the ligand release along the contact time in water. This study demonstrates that NH₂-MIL-125(Ti) easily leached out over time while maintaining its structure. The effect of different thermal treatments applied to NH₂-MIL-125(Ti) was investigated to enhance its water stability. The structural and textural properties of those modified MOFs were studied in detail and those maintaining the NH₂-MIL-125(Ti) properties were exposed to aqueous medium. The analysis of the released ligand concentration in the filtrate can provide information on the water stability of this material. Full article

(This article belongs to the Special Issue MOFs for Advanced Applications)

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16 pages, 3638 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Transition Metal Sulfides- and Noble Metal-Based Catalysts for N-Hexadecane Hydroisomerization: A Study of Poisons Tolerance

by Aleksey Pimerzin, Aleksander Savinov, Anna Vutolkina, Anna Makova, Aleksandr Glotov, Vladimir Vinokurov and Andrey Pimerzin

Catalysts 2020, 10(6), 594; https://doi.org/10.3390/catal10060594 - 26 May 2020

Cited by 22 | Viewed by 3456

Abstract

Bifunctional catalysts on the base of transition metal sulfides (CoMoS and NiWS) and platinum as noble metal were synthesized via wetness impregnation of freshly synthesized Al₂O₃-SAPO-11 composites, supported with favorable acidic properties. The physical-chemical properties of the prepared materials [...] Read more.

Bifunctional catalysts on the base of transition metal sulfides (CoMoS and NiWS) and platinum as noble metal were synthesized via wetness impregnation of freshly synthesized Al₂O₃-SAPO-11 composites, supported with favorable acidic properties. The physical-chemical properties of the prepared materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), low-temperature N₂ adsorption and high resolution transmission electron microscopy (HR TEM) methods. Catalytic properties were studied in n-hexadecane isomerization using a fixed-bed flow reactor. The catalytic poisons tolerance of transition metal sulfides (TMS)- and Pt-catalysts has been studied for sulfur and nitrogen, with the amount of 10–100 ppm addition to feedstock. TMS-catalysts show good stability during sulfur-containing feedstock processing, whereas Pt-catalyst loses much of its isomerization activity. Nitrogen-containing compounds in the feedstock has a significant impact on the catalytic activity of both TMS and Pt-based catalysts. Full article

(This article belongs to the Special Issue Heterogeneous Catalysts for Petrochemical Synthesis and Oil Refining)

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17 pages, 2739 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High Temperature Water Gas Shift Reactivity of Novel Perovskite Catalysts

by Janko Popovic, Lorenz Lindenthal, Raffael Rameshan, Thomas Ruh, Andreas Nenning, Stefan Löffler, Alexander Karl Opitz and Christoph Rameshan

Catalysts 2020, 10(5), 582; https://doi.org/10.3390/catal10050582 - 22 May 2020

Cited by 15 | Viewed by 4770

Abstract

High temperature water-gas shift (HT-WGS) is an industrially highly relevant reaction. Moreover, climate change and the resulting necessary search for sustainable energy sources are making WGS and reverse-WGS catalytic key reactions for synthetic fuel production. Hence, extensive research has been done to develop [...] Read more.

High temperature water-gas shift (HT-WGS) is an industrially highly relevant reaction. Moreover, climate change and the resulting necessary search for sustainable energy sources are making WGS and reverse-WGS catalytic key reactions for synthetic fuel production. Hence, extensive research has been done to develop improved or novel catalysts. An extremely promising material class for novel highly active HT-WGS catalysts with superior thermal stability are perovskite-type oxides. With their large compositional flexibility, they enable new options for rational catalyst design. Particularly, both cation sites (A and B in ABO₃) can be doped with promoters or catalytically active elements. Additionally, B-site dopants are able to migrate to the surface under reducing conditions (a process called exsolution), forming catalytically active nanoparticles and creating an interface that can strongly boost catalytic performance. In this study, we varied A-site composition and B-site doping (Ni, Co), thus comparing six novel perovskites and testing them for their HT-WGS activity: La_0.9Ca_0.1FeO_3-δ, La_0.6Ca_0.4FeO_3-δ, Nd_0.9Ca_0.1FeO_3-δ, Nd_0.6Ca_0.4FeO_3-δ, Nd_0.6Ca_0.4Fe_0.9Ni_0.1O_3-δ and Nd_0.6Ca_0.4Fe_0.9Co_0.1O_3-δ. Cobalt and Nickel doping resulted in the highest activity observed in our study, highlighting that doped perovskites are promising novel HT-WGS catalysts. The effect of the compositional variations is discussed considering the kinetics of the two partial reactions of WGS-CO oxidation and water splitting. Full article

(This article belongs to the Special Issue Surface Chemistry in Catalysis)

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31 pages, 6010 KiB

Open AccessFeature PaperEditor’s ChoiceReview

POM@MOF Hybrids: Synthesis and Applications

by Jiamin Sun, Sara Abednatanzi, Pascal Van Der Voort, Ying-Ya Liu and Karen Leus

Catalysts 2020, 10(5), 578; https://doi.org/10.3390/catal10050578 - 21 May 2020

Cited by 58 | Viewed by 10425

Abstract

The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a [...] Read more.

The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a low surface area, and a high solubility. MOFs are ideal hosts because of their high surface area, long-range ordered structure, and high tunability in terms of the pore size and channels. In some cases, MOFs add an extra dimension to the functionality of hybrids. This review summarizes the recent developments in the field of POM@MOF hybrids. The most common applied synthesis strategies are discussed, together with major applications, such as their use in catalysis (organocatalysis, electrocatalysis, and photocatalysis). The more than 100 papers on this topic have been systematically summarized in a handy table, which covers almost all of the work conducted in this field up to now. Full article

(This article belongs to the Special Issue MOFs for Advanced Applications)

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22 pages, 5867 KiB

Open AccessFeature PaperEditor’s ChoiceReview

α-Functionalization of Imines via Visible Light Photoredox Catalysis

by Alberto F. Garrido-Castro, M. Carmen Maestro and José Alemán

Catalysts 2020, 10(5), 562; https://doi.org/10.3390/catal10050562 - 19 May 2020

Cited by 49 | Viewed by 12768

Abstract

The innate electrophilicity of imine building blocks has been exploited in organic synthetic chemistry for decades. Inspired by the resurgence in photocatalysis, imine reactivity has now been redesigned through the generation of unconventional and versatile radical intermediates under mild reaction conditions. While novel [...] Read more.

The innate electrophilicity of imine building blocks has been exploited in organic synthetic chemistry for decades. Inspired by the resurgence in photocatalysis, imine reactivity has now been redesigned through the generation of unconventional and versatile radical intermediates under mild reaction conditions. While novel photocatalytic approaches have broadened the range and applicability of conventional radical additions to imine acceptors, the possibility to use these imines as latent nucleophiles via single-electron reduction has also been uncovered. Thus, multiple research programs have converged on this issue, delivering creative and practical strategies to achieve racemic and asymmetric α-functionalizations of imines under visible light photoredox catalysis. Full article

(This article belongs to the Special Issue New Trends in Asymmetric Catalysis)

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16 pages, 4873 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Pt/Re/CeO₂ Based Catalysts for CO-Water–Gas Shift Reaction: from Powders to Structured Catalyst

by Vincenzo Palma, Fausto Gallucci, Pluton Pullumbi, Concetta Ruocco, Eugenio Meloni and Marco Martino

Catalysts 2020, 10(5), 564; https://doi.org/10.3390/catal10050564 - 19 May 2020

Cited by 13 | Viewed by 3107

Abstract

This work focuses on the development of a Pt/Re/CeO₂-based structured catalyst for a single stage water–gas shift process. In the first part of the work, the activity in water–gas shift reactions was evaluated for three Pt/Re/CeO₂-based powder catalysts, with [...] Read more.

This work focuses on the development of a Pt/Re/CeO₂-based structured catalyst for a single stage water–gas shift process. In the first part of the work, the activity in water–gas shift reactions was evaluated for three Pt/Re/CeO₂-based powder catalysts, with Pt/Re ratio equal to 1/1, 1/2 ad 2/1 and total loading ≈ 1 wt%. The catalysts were prepared by sequential dry impregnation of commercial ceria, with the salts precursors of rhenium and platinum; the activity tests were carried out by feeding a reacting mixture with a variable CO/H₂O ratio, equal to 7/14, 7/20 and 7/24, and the kinetic parameters were determined. The model which better described the experimental results involves the water–gas shift (WGS) reaction and CO as well as CO₂ methanation. The preliminary tests showed that the catalyst with the Pt/Re ratio equal to 2/1 had the best performance, and this was selected for further investigations. In the second part of the work, a structured catalyst, obtained by coating a commercial aluminum alloy foam with the chosen catalytic formulation, was prepared and tested in different reaction conditions. The results demonstrated that a single stage water–gas shift process is achievable, obtaining a hydrogen production rate of 18.7 mmol/min at 685 K, at τ = 53 ms, by feeding a simulated reformate gas mixture (37.61 vol% H₂, 9.31 vol% CO₂, 9.31 vol% CO, 42.19 vol% H₂O, 1.37 vol% CH₄). Full article

(This article belongs to the Special Issue Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration)

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14 pages, 1426 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synthesis of DHA/EPA Ethyl Esters via Lipase-Catalyzed Acidolysis Using Novozym^® 435: A Kinetic Study

by Chia-Hung Kuo, Chun-Yung Huang, Chien-Liang Lee, Wen-Cheng Kuo, Shu-Ling Hsieh and Chwen-Jen Shieh

Catalysts 2020, 10(5), 565; https://doi.org/10.3390/catal10050565 - 19 May 2020

Cited by 12 | Viewed by 4845

Abstract

DHA/EPA ethyl ester is mainly used in the treatment of arteriosclerosis and hyperlipidemia. In this study, DHA+EPA ethyl ester was synthesized via lipase-catalyzed acidolysis of ethyl acetate (EA) with DHA+EPA concentrate in n-hexane using Novozym^® 435. The DHA+EPA concentrate (in free [...] Read more.

DHA/EPA ethyl ester is mainly used in the treatment of arteriosclerosis and hyperlipidemia. In this study, DHA+EPA ethyl ester was synthesized via lipase-catalyzed acidolysis of ethyl acetate (EA) with DHA+EPA concentrate in n-hexane using Novozym^® 435. The DHA+EPA concentrate (in free fatty acid form), contained 54.4% DHA and 16.8% EPA, was used as raw material. A central composite design combined with response surface methodology (RSM) was used to evaluate the relationship between substrate concentrations and initial rate of DHA+EPA ethyl ester production. The results indicated that the reaction followed the ordered mechanism and as such, the ordered mechanism model was used to estimate the maximum reaction rate (Vmax) and kinetic constants. The ordered mechanism model was also combined with the batch reaction equation to simulate and predict the conversion of DHA+EPA ethyl ester in lipase-catalyzed acidolysis. The integral equation showed a good predictive relationship between the simulated and experimental results. 88–94% conversion yields were obtained from 100–400 mM DHA+EPA concentrate at a constant enzyme activity of 200 U, substrate ratio of 1:1 (DHA+EPA: EA), and reaction time of 300 min. Full article

(This article belongs to the Special Issue Biocatalytic Process Optimization)

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