Catalysts

12 pages, 882 KiB

Open AccessArticle

Atoms vs. Ions: Intermediates in Reversible Electrochemical Hydrogen Evolution Reaction

by Jurga Juodkazytė, Kȩstutis Juodkazis and Saulius Juodkazis

Catalysts 2021, 11(9), 1135; https://doi.org/10.3390/catal11091135 - 21 Sep 2021

Cited by 8 | Viewed by 3569

We present a critical analysis of the mechanism of

r e v e r s i b l e

hydrogen evolution reaction based on thermodynamics of hydrogen processes considering atomic and ionic species as intermediates. Clear distinction between molecular hydrogen evolution/oxidation (H

_{2}

[...] Read more.

We present a critical analysis of the mechanism of

r e v e r s i b l e

hydrogen evolution reaction based on thermodynamics of hydrogen processes considering atomic and ionic species as intermediates. Clear distinction between molecular hydrogen evolution/oxidation (H

_{2}

ER and H

_{2}

OR) and atomic hydrogen evolution/oxidation (HER and HOR) reactions is made. It is suggested that the main reaction describing

r e v e r s i b l e

H

_{2}

ER and H

_{2}

OR in acidic and basic solutions is:

H_{3} O^{+} + 2 e^{-} \overset{{(H_{2}^{+})}_{a d}}{⇌} H_{2} + {OH}^{-}

and its standard potential is

E^{0}

= −0.413 V (vs. standard hydrogen electrode, SHE). We analyse experimentally reported data with models which provide a quantitative match (R.J.Kriek et al., Electrochem. Sci. Adv. e2100041 (2021)). Presented analysis implies that

r e v e r s i b l e

H₂ evolution is a two-electron transfer process which proceeds via the stage of adsorbed hydrogen molecular ion H

_{2}^{+}

as intermediate, rather than H

_{ad}

as postulated in the Volmer-Heyrovsky-Tafel mechanism. We demonstrate that in theory, two slopes of

p o t e n t i a l

vs.

\lg (c u r r e n t)

plots are feasible in the discussed reversible region of H₂ evolution:

2.3 R T / F \approx 60

mV and

2.3 R T / 2 F \approx 30

mV, which is corroborated by the results of electrocatalytic hydrogen evolution studies reported in the literature. Upon transition to

i r r e v e r s i b l e

H

_{2}

ER, slowdown of H

_{2}^{+}

formation in the first electron transfer stage manifests, and the slope increases to

2.3 R T / 0.5 F \approx 120

mV;

R, F, T

are the universal gas, Faraday constants and absolute temperature, respectively. Full article

(This article belongs to the Special Issue Efficient PGM Electrocatalysts for Hydrogen Evolution Reaction)

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14 pages, 3375 KiB

Open AccessArticle

Organocatalytic Asymmetric Michael Addition in Aqueous Media by a Hydrogen-Bonding Catalyst and Application for Inhibitors of GABA_B Receptor

by Jae Ho Shim, Yeonsun Hong, Ji Hae Kim, Hyeon Soo Kim and Deok-Chan Ha

Catalysts 2021, 11(9), 1134; https://doi.org/10.3390/catal11091134 - 21 Sep 2021

Cited by 6 | Viewed by 3125

Abstract

Catalysts based on (R, R)-1,2-diphenylethylenediamine are, as chiral organic catalysts, applied to the asymmetric Michael addition to α, β-unsaturated nitroalkenes under neutral conditions. The role of an aqueous medium for organic catalytic activity can be reversed concerning hydrophilic-hydrophobic [...] Read more.

Catalysts based on (R, R)-1,2-diphenylethylenediamine are, as chiral organic catalysts, applied to the asymmetric Michael addition to α, β-unsaturated nitroalkenes under neutral conditions. The role of an aqueous medium for organic catalytic activity can be reversed concerning hydrophilic-hydrophobic function depending on the reaction conditions. In this study, to provide an environmentally friendly system, the thiourea-based catalyst substituted with 3,5-(CF₃)₂-Ph was used in water solvents. The hydrophobic effect of the substituent provided fast reaction, high chemical yield, and mirror-image selectivity. This reaction allowed the preparation of GABA_B agonists in an optically pure manner. Additionally, GABA (γ-aminobutyric acid) analogs such as baclofen and phenibut were synthesized as R-type S-type with high optical purity. Full article

(This article belongs to the Special Issue Organocatalysis: Mechanistic Investigations, Design, and Applications)

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16 pages, 3560 KiB

Open AccessArticle

Covalent Organic Frameworks for Simultaneous CO₂ Capture and Selective Catalytic Transformation

by Yaling Li, Jianqiang Zhang, Kaiming Zuo, Zhongping Li, Yu Wang, Hui Hu, Chaoyuan Zeng, Huanjun Xu, Baoshan Wang and Yanan Gao

Catalysts 2021, 11(9), 1133; https://doi.org/10.3390/catal11091133 - 21 Sep 2021

Cited by 16 | Viewed by 4560

Abstract

Combination of capture and simultaneous conversion of CO₂ into valuable chemicals is a fascinating strategy for reducing CO₂ emissions. Therefore, searching for heterogeneous catalysts for efficient catalytic conversion of CO₂ is of great importance for carbon capture and utilization. Herein, [...] Read more.

Combination of capture and simultaneous conversion of CO₂ into valuable chemicals is a fascinating strategy for reducing CO₂ emissions. Therefore, searching for heterogeneous catalysts for efficient catalytic conversion of CO₂ is of great importance for carbon capture and utilization. Herein, we report a metalloporphyrin-based covalent organic framework (Co(II)@TA-TF COF) that can capture CO₂ and simultaneously convert it into cyclic carbonates under mild conditions. The COF was designed to possess micropores for the adsorption of CO₂ and integrated with cobalt(II) porphyrin (Co(II)@TAPP) units as catalytic sites into the vertices of the layered tetragonal networks. The structure of the Co(II)@TA-TF COF is unique where Co(II)@TAPP units are alternately stacked along the z direction with a slipped distance of 1.7 Å, which gives an accessible space to accommodate small molecules, making it possible to expose catalytic sites to substrates within the adjacent stacked layers. As a result, this COF is found to be highly effective for the addition of CO₂ and epoxides. Importantly, the Co(II)@TA-TF COF exhibited a dramatic size selectivity for substrates. In conjunction with its reusability, our results highlight the development of a new function of COFs for targeting simultaneous CO₂ absorption and utilization upon complementary exploration of the structural features of skeletons and pores. Such promising catalytic performance of the COF makes it possible for its potential practical application. Full article

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17 pages, 6662 KiB

Open AccessFeature PaperArticle

Mesoporous Carbon Production by Nanocasting Technique Using Boehmite as a Template

by María Ortega-Franqueza, Svetlana Ivanova, María Isabel Domínguez and Miguel Ángel Centeno

Catalysts 2021, 11(9), 1132; https://doi.org/10.3390/catal11091132 - 21 Sep 2021

Cited by 3 | Viewed by 1888

Abstract

A series of mesoporous carbonaceous materials were synthesized by the nanocasting technique using boehmite as a template and glucose as a carbon precursor. After pyrolysis and template removal, the resulting material is a mesoporous carbon that can be additionally doped with N, B [...] Read more.

A series of mesoporous carbonaceous materials were synthesized by the nanocasting technique using boehmite as a template and glucose as a carbon precursor. After pyrolysis and template removal, the resulting material is a mesoporous carbon that can be additionally doped with N, B and K during prepyrolysis impregnation. In addition, the influence of doping on the morphology, crystallinity and stability of the synthesized carbons was studied using X-ray diffraction, nitrogen physisorption, thermogravimetry, Raman and IR spectroscopy and transmission electron microscopy. While the nanocasting process is effective for the formation of mesopores, KOH and urea do not modify the textural properties of carbon. The use of H₃PO₄ as a dopant, however, led to the formation of an AlPO₄ compound and resulted in a solid with a lower specific surface area and higher microporosity. All doped solids present higher thermal stability as a positive effect of the introduction of heteroatoms to the carbon skeleton. The phosphorus-doped sample has better oxidation resistance, with a combustion temperature 120–150 °C higher than those observed for the other materials. Full article

(This article belongs to the Special Issue New Trends in Carbon-Based Catalysts)

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30 pages, 743 KiB

Open AccessReview

Nanocatalysts for Oxidative Desulfurization of Liquid Fuel: Modern Solutions and the Perspectives of Application in Hybrid Chemical-Biocatalytic Processes

by Olga Maslova, Olga Senko, Argam Akopyan, Sergey Lysenko, Alexander Anisimov and Elena Efremenko

Catalysts 2021, 11(9), 1131; https://doi.org/10.3390/catal11091131 - 21 Sep 2021

Cited by 10 | Viewed by 2777

Abstract

In this paper, the current advantages and disadvantages of using metal-containing nanocatalysts (NCs) for deep chemical oxidative desulfurization (ODS) of liquid fuels are reviewed. A similar analysis is performed for the oxidative biodesulfurization of oil along the 4S-pathway, catalyzed by various aerobic bacterial [...] Read more.

In this paper, the current advantages and disadvantages of using metal-containing nanocatalysts (NCs) for deep chemical oxidative desulfurization (ODS) of liquid fuels are reviewed. A similar analysis is performed for the oxidative biodesulfurization of oil along the 4S-pathway, catalyzed by various aerobic bacterial cells of microorganisms. The preferences of using NCs for the oxidation of organic sulfur-containing compounds in various oil fractions seem obvious. The text discusses the development of new chemical and biocatalytic approaches to ODS, including the use of both heterogeneous NCs and anaerobic microbial biocatalysts that catalyze the reduction of chemically oxidized sulfur-containing compounds in the framework of methanogenesis. The addition of anaerobic biocatalytic stages to the ODS of liquid fuel based on NCs leads to the emergence of hybrid technologies that improve both the environmental characteristics and the economic efficiency of the overall process. The bioconversion of sulfur-containing extracts from fuels with accompanying hydrocarbon residues into biogas containing valuable components for the implementation of C-1 green chemistry processes, such as CH₄, CO₂, or H₂, looks attractive for the implementation of such a hybrid process. Full article

(This article belongs to the Special Issue Nanostructured Catalysts for Petrochemistry and Oil Processing: Recent Advances and Prospectives)

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16 pages, 8992 KiB

Open AccessFeature PaperArticle

Assembly of CaIn₂S₄ on Defect-Rich BiOCl for Acceleration of Interfacial Charge Separation and Photocatalytic Phenol Degradation via S-Scheme Electron Transfer Mechanism

by Zhuangzhuang Zhang, Yuanyuan Zhang, Xuanxuan Han, Li Guo, Danjun Wang and Kangle Lv

Catalysts 2021, 11(9), 1130; https://doi.org/10.3390/catal11091130 - 20 Sep 2021

Cited by 20 | Viewed by 2596

Abstract

The novel 2D/2D S-scheme heterostructure of BiOCl nanosheets coupled with CaIn₂S₄ nanosheets (CaIn₂S₄/BiOCl-SOVs), which contains surface oxygen vacancies (SOVs), has been successfully prepared by high-temperature calcination combined with a solvothermal synthetic strategy. Under visible-light irradiation, the [...] Read more.

The novel 2D/2D S-scheme heterostructure of BiOCl nanosheets coupled with CaIn₂S₄ nanosheets (CaIn₂S₄/BiOCl-SOVs), which contains surface oxygen vacancies (SOVs), has been successfully prepared by high-temperature calcination combined with a solvothermal synthetic strategy. Under visible-light irradiation, the apparent rate constant (K_app/mim⁻¹) for phenol degradation on the 1 wt% CaIn₂S₄/BiOCl-SOVs photocatalyst is about 32.8 times higher than that of pure BiOCl. The superior performance was attributed to the synergistic effect between the SOVs, CaIn₂S₄, and BiOCl, which can effectively narrow the bandgap and accelerate the interfacial charge separation of CaIn₂S₄/BiOCl-SOVs heterojunctions. Subsequently, it significantly promotes the generation of superoxide radicals (O₂⁻), hydroxyl radicals, and h⁺, which participate in the photodegradation process of phenol. The catalyst still maintained a relatively high activity after repeated tests as a demonstration of its photostability. This work successfully proposed an efficient method to design a new 2D/2D S-scheme heterostructure with SOVs as possible photocatalysts in the field of environmental remediation. Full article

(This article belongs to the Special Issue Photocatalytic Degradation of Organic Wastes in Water)

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20 pages, 3548 KiB

Open AccessFeature PaperReview

Molecular Dynamics and Machine Learning in Catalysts

by Wenxiang Liu, Yang Zhu, Yongqiang Wu, Cen Chen, Yang Hong, Yanan Yue, Jingchao Zhang and Bo Hou

Catalysts 2021, 11(9), 1129; https://doi.org/10.3390/catal11091129 - 19 Sep 2021

Cited by 15 | Viewed by 7612

Abstract

Given the importance of catalysts in the chemical industry, they have been extensively investigated by experimental and numerical methods. With the development of computational algorithms and computer hardware, large-scale simulations have enabled influential studies with more atomic details reflecting microscopic mechanisms. This review [...] Read more.

Given the importance of catalysts in the chemical industry, they have been extensively investigated by experimental and numerical methods. With the development of computational algorithms and computer hardware, large-scale simulations have enabled influential studies with more atomic details reflecting microscopic mechanisms. This review provides a comprehensive summary of recent developments in molecular dynamics, including ab initio molecular dynamics and reaction force-field molecular dynamics. Recent research on both approaches to catalyst calculations is reviewed, including growth, dehydrogenation, hydrogenation, oxidation reactions, bias, and recombination of carbon materials that can guide catalyst calculations. Machine learning has attracted increasing interest in recent years, and its combination with the field of catalysts has inspired promising development approaches. Its applications in machine learning potential, catalyst design, performance prediction, structure optimization, and classification have been summarized in detail. This review hopes to shed light and perspective on ML approaches in catalysts. Full article

(This article belongs to the Special Issue Emerging Nanocatalysts for Efficient Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution)

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17 pages, 3774 KiB

Open AccessFeature PaperArticle

Enhanced Catalytic Soot Oxidation by Ce-Based MOF-Derived Ceria Nano-Bar with Promoted Oxygen Vacancy

by Yu-Chih Tsai, Jechan Lee, Eilhann Kwon, Chao-Wei Huang, Nguyen Nhat Huy, Siming You, Pei-Syuan Hsu, Wen Da Oh and Kun-Yi Andrew Lin

Catalysts 2021, 11(9), 1128; https://doi.org/10.3390/catal11091128 - 18 Sep 2021

Cited by 4 | Viewed by 2898

Abstract

As CeO₂ is a useful catalyst for soot elimination, it is important to develop CeO₂ with higher contact areas, and reactivities for efficient soot oxidation and catalytic soot oxidation are basically controlled by structures and surface properties of catalysts. Herein, a [...] Read more.

As CeO₂ is a useful catalyst for soot elimination, it is important to develop CeO₂ with higher contact areas, and reactivities for efficient soot oxidation and catalytic soot oxidation are basically controlled by structures and surface properties of catalysts. Herein, a Ce-Metal organic framework (MOFs) consisting of Ce and benzene-1,3,5-tricarboxylic acid (H₃BTC) is employed as the precursor as CeBTC exhibits a unique bar-like high-aspect-ratio morphology, which is then transformed into CeO₂ with a nanoscale bar-like configuration. More importantly, this CeO₂ nanobar (CeONB) possesses porou, and even hollow structures, as well as more oxygen vacancies, enabling CeONB to become a promising catalyst for soot oxidation. Thus, CeONB shows a much higher catalytic activity than commercial CeO₂ nanoparticle (comCeO) for soot oxidation with a significantly lower ignition temperature (T_ig). Moreover, while soot oxidation by comCeO leads to production of CO together with CO₂, CeONB can completely convert soot to CO₂. The tight contact mode also enables CeONB to exhibit a very low T_ig of 310 °C, whereas the existence of NO also enhances the soot oxidation by CeONB to reduce the T_ig. The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the formation and transformation of nitrogen-containing intermediates. CeONB is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that CeONB is a promising and easily prepared high-aspect-ratio Ce-based catalyst for soot oxidation. Full article

(This article belongs to the Special Issue Air Pollution Control: Catalytic Oxidation and Reduction of Gaseous Pollutants)

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38 pages, 5802 KiB

Open AccessFeature PaperReview

Carbon Monoxide Tolerant Pt-Based Electrocatalysts for H₂-PEMFC Applications: Current Progress and Challenges

by Costas Molochas and Panagiotis Tsiakaras

Catalysts 2021, 11(9), 1127; https://doi.org/10.3390/catal11091127 - 18 Sep 2021

Cited by 37 | Viewed by 6915

Abstract

The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H₂-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H₂ fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been [...] Read more.

The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H₂-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H₂ fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges. Full article

(This article belongs to the Section Electrocatalysis)

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17 pages, 12618 KiB

Open AccessArticle

Engineering of a Novel, Magnetic, Bi-Functional, Enzymatic Nanobiocatalyst for the Highly Efficient Synthesis of Enantiopure (R)-3-quinuclidinol

by Qingman Li, Qihua Jiang, Pengcheng Gu, Lianju Ma and Yiwu Wang

Catalysts 2021, 11(9), 1126; https://doi.org/10.3390/catal11091126 - 18 Sep 2021

Cited by 1 | Viewed by 1561

Abstract

Ni²⁺-NTA-boosted magnetic porous silica nanoparticles (Ni@MSN) to serve as ideal support for bi-functional enzyme were fabricated for the first time. The versatility of this support was validated by one-step purification and immobilization of bi-functional enzyme MLG consisting of 3-Quinuclidinone reductase and [...] Read more.

Ni²⁺-NTA-boosted magnetic porous silica nanoparticles (Ni@MSN) to serve as ideal support for bi-functional enzyme were fabricated for the first time. The versatility of this support was validated by one-step purification and immobilization of bi-functional enzyme MLG consisting of 3-Quinuclidinone reductase and glucose dehydrogenase, which can simultaneously catalyze both carbonyl reduction and cofactor regeneration, to fabricate an artificial bi-functional nanobiocatalyst (namely, MLG-Ni@MSN). The enzyme loading of 71.7 mg/g support and 92.7% immobilization efficiency were obtained. Moreover, the immobilized MLG showed wider pH and temperature tolerance and greater storage stability than free MLG under the same conditions. The nanosystem was employed as biocatalyst to accomplish the 3-quinuclidinone (70 g/L) to (R)-3-quinuclidinol biotransformation in 100% conversion yield with >99% selectivity within 6 h and simultaneous cofactor regeneration. Furthermore, the immobilized MLG retained up to 80.3% (carbonyl reduction) and 78.0% (cofactor regeneration) of the initial activity after being recycled eight times. In addition, the MLG-Ni@MSN system exhibited almost no enzyme leaching during biotransformation and recycling. Therefore, we have reason to believe that the Ni@MSN support gave great promise for constructing a new biocatalytic nanosystem with multifunctional enzymes to achieve some other complex bioconversions. Full article

(This article belongs to the Special Issue Enzyme Immobilization and Biocatalysis)

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12 pages, 2186 KiB

Open AccessArticle

Photocatalytic Removal of Pharmaceuticals from Greywater

by Bukola Ojobe, Radek Zouzelka, Barbora Satkova, Magdalena Vagnerova, Alzbeta Nemeskalova, Martin Kuchar, Jan Bartacek and Jiri Rathousky

Catalysts 2021, 11(9), 1125; https://doi.org/10.3390/catal11091125 - 18 Sep 2021

Cited by 5 | Viewed by 2425

Abstract

High concentrations of pharmaceuticals have been detected in greywater effluents treated using up-to-date technologies. Finding a suitable additional treatment before this effluent is reused is urgently needed to ensure the reused water meets quality standards. This paper reports the use of heterogeneous photocatalysis [...] Read more.

High concentrations of pharmaceuticals have been detected in greywater effluents treated using up-to-date technologies. Finding a suitable additional treatment before this effluent is reused is urgently needed to ensure the reused water meets quality standards. This paper reports the use of heterogeneous photocatalysis on anatase and rutile nanopowders to remove naproxen, metformin and sulfamethoxazole, at practically relevant concentrations found in membrane bioreactor (MBR)-treated greywater. A low anatase concentration of 400 mg L⁻¹ was sufficient to efficiently degrade the pharmaceuticals listed above, with complete degradation observed in 5 h. The effect of background species presented in greywater was, to some extent, comparable to that of the OH-radical scavenger. These results prove that photocatalysis using anatase TiO₂ is a feasible additional treatment for greywater recycling. Full article

(This article belongs to the Special Issue Advances in Photoassisted and Photocatalytic Processes for Water Remediation)

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23 pages, 4340 KiB

Open AccessArticle

Synthesis of Catalytic Ni/Cu Nanoparticles from Simulated Wastewater on Li–Al Mixed Metal Oxides for a Two-Stage Catalytic Process in Ethanol Steam Reforming: Catalytic Performance and Coke Properties

by Yu-Jia Chen, Song-Hui Huang, Jun-Yen Uan and Hao-Tung Lin

Catalysts 2021, 11(9), 1124; https://doi.org/10.3390/catal11091124 - 18 Sep 2021

Cited by 4 | Viewed by 3351

Abstract

This work recovered Ni or Cu cations from simulated electroplating wastewater to synthesize Ni/Cu nano-catalysts for H₂ generation by ethanol steam reforming (ESR). Aluminum lathe waste was used as a framework to prepare the structured catalyst. Li–Al–CO₃ layered double hydroxide (LDH) [...] Read more.

This work recovered Ni or Cu cations from simulated electroplating wastewater to synthesize Ni/Cu nano-catalysts for H₂ generation by ethanol steam reforming (ESR). Aluminum lathe waste was used as a framework to prepare the structured catalyst. Li–Al–CO₃ layered double hydroxide (LDH) was electrodeposited on the surface of the framework. The LDH was in a platelet-like structure, working as a support for the formation of the precursor of the metal catalysts. The catalytic performance and the coke properties of a 6Cu_6Ni two-stage catalyst configuration herein used for ESR catalytic reaction were studied. The Cu–Ni two-stage catalyst configuration (6Cu_6Ni) yielded more H₂ (~10%) than that by using the Ni-based catalyst (6Ni) only. The 6Cu_6Ni catalyst configuration also resulted in a relatively stable H₂ generation rate vs. time, with nearly no decline during the 5-h reaction. Through the pre-reaction of ethanol-steam mixture with Cu/LiAlO₂ catalyst, the Ni/LiAlO₂ catalyst in the 6Cu_6Ni catalyst configuration could steadily decompose acetaldehyde, and rare acetate groups, which would evolve condensed coke, were formed. The Ni nanoparticles were observed to be lifted and separated by the carbon filaments from the support and had no indication of sintering, contributing to the bare deactivation of the Ni/LiAlO₂ catalyst in 6Cu_6Ni. Full article

(This article belongs to the Special Issue Application of Metal-Based Nanocatalysts for Addressing Environmental Issues and Energy Demand)

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15 pages, 2696 KiB

Open AccessFeature PaperReview

Nanoscale Cerium Oxide: Synthesis, Biocatalytic Mechanism, and Applications

by Guangchun Song, Nan Cheng, Junjie Zhang, Huixian Huang, Yanfang Yuan, Xiaoyun He, Yunbo Luo and Kunlun Huang

Catalysts 2021, 11(9), 1123; https://doi.org/10.3390/catal11091123 - 18 Sep 2021

Cited by 30 | Viewed by 4620

Abstract

Nanoscale cerium oxide has excellent catalytic performance due to its unique surface properties and has very important applications in various fields. In this paper, the synthesis methods, catalytic mechanism and activity regulation of nanoscale cerium oxide in recent years are reviewed. Secondly, the [...] Read more.

Nanoscale cerium oxide has excellent catalytic performance due to its unique surface properties and has very important applications in various fields. In this paper, the synthesis methods, catalytic mechanism and activity regulation of nanoscale cerium oxide in recent years are reviewed. Secondly, the application of cerium oxide in the detection of organic and inorganic molecules is summarized, and its latest progress and applications in antibacterial, antioxidant and anticancer are discussed. Finally, the future development prospect of nanoscale cerium oxide is summarized and prospected. Full article

(This article belongs to the Special Issue State of the Art and Future Trends in Nanostructured Biocatalysis)

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15 pages, 1574 KiB

Open AccessFeature PaperArticle

Preparation of Extremely Active Ethylene Tetramerization Catalyst [iPrN(PAr₂)₂−CrCl₂]⁺[B(C₆F₅)₄]^– (Ar = −C₆H₄-p-SiR₃)

by Jung Hyun Lee, Jun Won Baek, Dong Geun Lee, Ji Hyeong Ko, Dong Geun Lee, Kye Sung Cho, Jin Woo Lee and Bun Yeoul Lee

Catalysts 2021, 11(9), 1122; https://doi.org/10.3390/catal11091122 - 18 Sep 2021

Cited by 7 | Viewed by 2453

Abstract

Numerous efforts have been made to achieve “on-purpose” 1-octene production since Sasol discovered a Cr-based selective ethylene tetramerization catalyst in the early 2000s. By preparing a series of bis(phosphine) ligands iPrN(PAr₂)₂ where the Ar contains a bulky –SiR₃ substituent [...] Read more.

Numerous efforts have been made to achieve “on-purpose” 1-octene production since Sasol discovered a Cr-based selective ethylene tetramerization catalyst in the early 2000s. By preparing a series of bis(phosphine) ligands iPrN(PAr₂)₂ where the Ar contains a bulky –SiR₃ substituent (Ar = −C₆H₄-p-Si(nBu)₃ (1), −C₆H₄-p-Si(1-hexyl)₃ (2), −C₆H₄-p-Si(1-octyl)₃ (3), −C₆H₄-p-Si(2-ethylhexyl)₃ (4), −C₆H₄-p-Si(3,7-dimethyloctyl)₃ (5)), we obtained an extremely active catalyst that meets the criteria for commercial utilization. The Cr complexes [iPrN(PAr₂)₂−CrCl₂]⁺[B(C₆F₅)₄]^–, obtained by reacting ligands 1–5 with [(CH₃CN)₄CrCl₂]⁺[B(C₆F₅)₄]^–, showed high activity exceeding 6000 kg/g-Cr/h, when combined with the inexpensive iBu₃Al, thus avoiding the use of expensive modified methylaluminoxane (MMAO). The bulky –SiR₃ substituents played a key role in the success of catalysis by blocking the formation of inactive species (Cr complexes coordinated by two iPrN(PAr₂)₂ ligands, that is, [(iPrN(PAr₂)₂)₂−CrCl₂]⁺[B(C₆F₅)₄]^–). Among the complexes prepared, [3−CrCl₂]⁺[B(C₆F₅)₄]^– exhibited the highest activity (11,100 kg/g-Cr/h, 100 kg/g-catalyst) with high 1-octene selectivity (75 wt%) and, moreover, mitigated the generation of undesired > C10 fractions (10.7 wt%). A 10-g-scale synthesis of 3 was developed, as well as a facile and low-cost synthetic method for [(CH₃CN)₄CrCl₂]⁺[B(C₆F₅)₄]^–. Full article

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

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37 pages, 548 KiB

Open AccessReview

Current State and Perspectives on Transesterification of Triglycerides for Biodiesel Production

by Mohammed Salaheldeen, Abdalbasit Adam Mariod, Mohamed Kheireddine Aroua, S. M. Ashrafur Rahman, Manzoore Elahi M. Soudagar and I. M. Rizwanul Fattah

Catalysts 2021, 11(9), 1121; https://doi.org/10.3390/catal11091121 - 18 Sep 2021

Cited by 53 | Viewed by 9048

Abstract

Triglycerides are the main constituents of lipids, which are the fatty acids of glycerol. Natural organic triglycerides (viz. virgin vegetable oils, recycled cooking oils, and animal fats) are the main sources for biodiesel production. Biodiesel (mono alkyl esters) is the most attractive alternative [...] Read more.

Triglycerides are the main constituents of lipids, which are the fatty acids of glycerol. Natural organic triglycerides (viz. virgin vegetable oils, recycled cooking oils, and animal fats) are the main sources for biodiesel production. Biodiesel (mono alkyl esters) is the most attractive alternative fuel to diesel, with numerous environmental advantages over petroleum-based fuel. The most practicable method for converting triglycerides to biodiesel with viscosities comparable to diesel fuel is transesterification. Previous research has proven that biodiesel–diesel blends can operate the compression ignition engine without the need for significant modifications. However, the commercialization of biodiesel is still limited due to the high cost of production. In this sense, the transesterification route is a crucial factor in determining the total cost of biodiesel production. Homogenous base-catalyzed transesterification, industrially, is the conventional method to produce biodiesel. However, this method suffers from limitations both environmentally and economically. Although there are review articles on transesterification, most of them focus on a specific type of transesterification process and hence do not provide a comprehensive picture. This paper reviews the latest progress in research on all facets of transesterification technology from reports published by highly-rated scientific journals in the last two decades. The review focuses on the suggested modifications to the conventional method and the most promising innovative technologies. The potentiality of each technology to produce biodiesel from low-quality feedstock is also discussed. Full article

(This article belongs to the Special Issue Catalytic Processes in Biofuel Production and Biomass Valorization)

48 pages, 122805 KiB

Open AccessReview

Recent Progress in Catalytic Synthesis of 1,2,3-Triazoles

by Antonio De Nino, Loredana Maiuolo, Paola Costanzo, Vincenzo Algieri, Antonio Jiritano, Fabrizio Olivito and Matteo Antonio Tallarida

Catalysts 2021, 11(9), 1120; https://doi.org/10.3390/catal11091120 - 17 Sep 2021

Cited by 30 | Viewed by 5660

Abstract

1,2,3-triazoles represent a functional heterocyclic core that has been at the center of modern organic chemistry since the beginning of click chemistry. Being a versatile framework, such an aromatic ring can be observed in uncountable molecules useful in medicine and photochemistry, just to [...] Read more.

1,2,3-triazoles represent a functional heterocyclic core that has been at the center of modern organic chemistry since the beginning of click chemistry. Being a versatile framework, such an aromatic ring can be observed in uncountable molecules useful in medicine and photochemistry, just to name a few. This review summarizes the progress achieved in their synthesis from 2015 to today, with particular emphasis on the development of new catalytic and eco-compatible approaches. In doing so, we subdivided the report based on their degree of functionalization and, for each subparagraph, we outlined the role of the catalyst employed. Full article

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14 pages, 2756 KiB

Open AccessArticle

Synthesis of Linoleic Acid 13-Hydroperoxides from Safflower Oil Utilizing Lipoxygenase in a Coupled Enzyme System with In-Situ Oxygen Generation

by Valentin Gala Marti, Anna Coenen and Ulrich Schörken

Catalysts 2021, 11(9), 1119; https://doi.org/10.3390/catal11091119 - 17 Sep 2021

Cited by 7 | Viewed by 3095

Abstract

Linoleic acid hydroperoxides are versatile intermediates for the production of green note aroma compounds and bifunctional ω-oxo-acids. An enzyme cascade consisting of lipoxygenase, lipase and catalase was developed for one-pot synthesis of 13-hydroperoxyoctadecadienoic acid starting from safflower oil. Reaction conditions were optimized for [...] Read more.

Linoleic acid hydroperoxides are versatile intermediates for the production of green note aroma compounds and bifunctional ω-oxo-acids. An enzyme cascade consisting of lipoxygenase, lipase and catalase was developed for one-pot synthesis of 13-hydroperoxyoctadecadienoic acid starting from safflower oil. Reaction conditions were optimized for hydroperoxidation using lipoxygenase 1 from Glycine max (LOX-1) in a solvent-free system. The addition of green surfactant Triton CG-110 improved the reaction more than two-fold and yields of >50% were obtained at linoleic acid concentrations up to 100 mM. To combine hydroperoxidation and oil hydrolysis, 12 lipases were screened for safflower oil hydrolysis under the reaction conditions optimized for LOX-1. Lipases from Candida rugosa and Pseudomonas fluorescens were able to hydrolyze safflower oil to >75% within 5 h at a pH of 8.0. In contrast to C. rugosa lipase, the enzyme from P. fluorescens did not exhibit a lag phase. Combination of P. fluorescens lipase and LOX-1 worked well upon LOX-1 dosage and a synergistic effect was observed leading to >80% of hydroperoxides. Catalase from Micrococcus lysodeikticus was used for in-situ oxygen production with continuous H₂O₂ dosage in the LOX-1/lipase reaction system. Foam generation was significantly reduced in the 3-enzyme cascade in comparison to the aerated reaction system. Safflower oil concentration was increased up to 300 mM linoleic acid equivalent and 13-hydroperoxides could be produced in a yield of 70 g/L and a regioselectivity of 90% within 7 h. Full article

(This article belongs to the Special Issue Enzyme Catalysis: Advances, Techniques and Outlooks)

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30 pages, 1947 KiB

Open AccessFeature PaperReview

The Catalysed Transformation of Vegetable Oils or Animal Fats to Biofuels and Bio-Lubricants: A Review

by Martin Hájek, Aleš Vávra, Héctor de Paz Carmona and Jaroslav Kocík

Catalysts 2021, 11(9), 1118; https://doi.org/10.3390/catal11091118 - 17 Sep 2021

Cited by 41 | Viewed by 6313

Abstract

This review paper summarizes the current state-of-the-art of the chemical transformation of oils/fats (i.e., triacylglycerols) to the use of biofuels or bio-lubricants in the means of transport, which is a novelty. The chemical transformation is necessary to obtain products that are more usable [...] Read more.

This review paper summarizes the current state-of-the-art of the chemical transformation of oils/fats (i.e., triacylglycerols) to the use of biofuels or bio-lubricants in the means of transport, which is a novelty. The chemical transformation is necessary to obtain products that are more usable with properties corresponding to fuels synthesized from crude oil. Two types of fuels are described—biodiesel (the mixture of methyl esters produced by transesterification) and green diesel (paraffins produced by hydrogenation of oils). Moreover, three bio-lubricant synthesis methods are described. The transformation, which is usually catalysed, depends on: (i) the type and composition of the raw material, including alcohols for biodiesel production and hydrogen for green diesel; (ii) the type of the catalyst in the case of catalysed reactions; (iii) the reaction conditions; and (iv) types of final products. The most important catalysts, especially heterogeneous and including reaction conditions, for each product are described. The properties of biodiesel and green diesel and a comparison with diesel from crude oil are also discussed. Full article

(This article belongs to the Special Issue Advances in Catalysis for Fuel and Chemical Production from Biomass Feedstocks)

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12 pages, 3329 KiB

Open AccessArticle

Well-Dispersed MgAl₂O₄ Supported Ni Catalyst with Enhanced Catalytic Performance and the Reason of Its Deactivation for Long-Term Dry Methanation Reaction

by Fen Wang, Xiumiao Yang and Jingcai Zhang

Catalysts 2021, 11(9), 1117; https://doi.org/10.3390/catal11091117 - 16 Sep 2021

Cited by 1 | Viewed by 1779

Abstract

Dry methanation of syngas is a promising route for synthetic natural gas production because of its water and cost saving characteristics, as we reported previously. Here, we report a simple soaking process for the preparation of well-dispersed Ni/MgAl₂O₄-E catalyst [...] Read more.

Dry methanation of syngas is a promising route for synthetic natural gas production because of its water and cost saving characteristics, as we reported previously. Here, we report a simple soaking process for the preparation of well-dispersed Ni/MgAl₂O₄-E catalyst with an average Ni size of 6.4 nm. The catalytic test results showed that the Ni/MgAl₂O₄-E catalyst exhibited considerably higher activity and better stability than Ni/MgAl₂O₄-W catalyst prepared by conventional incipient wetness impregnation method in dry methanation reaction. The long-term stability test result of 335 h has demonstrated that the deactivation of the Ni/MgAl₂O₄-E catalyst is inevitable. With multiple characterization techniques including ICP, EDS, XRD, STEM, TEM, SEM and TG, we reveal that the graphitic carbon encapsulating Ni nanoparticles are the major reasons responsible for catalyst deactivation, and the rate of carbon deposition decreases with reaction time. Full article

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15 pages, 2507 KiB

Open AccessFeature PaperArticle

Conversion of Scenedesmus rubescens Lipid into Biodiesel by Biochar of Different Origin

by Vasiliki D. Tsavatopoulou, Andriana F. Aravantinou, John Vakros and Ioannis D. Manariotis

Catalysts 2021, 11(9), 1116; https://doi.org/10.3390/catal11091116 - 16 Sep 2021

Cited by 5 | Viewed by 1822

Abstract

One of the most recent applications studied in recent years is the use of biochar as a catalyst for the conversion of oils into biodiesel. The scope of this work was to evaluate the efficiency of biochars as heterogeneous catalysts for the conversion [...] Read more.

One of the most recent applications studied in recent years is the use of biochar as a catalyst for the conversion of oils into biodiesel. The scope of this work was to evaluate the efficiency of biochars as heterogeneous catalysts for the conversion of Scenedesmus rubescens lipids into biodiesel. Biochar from different materials were employed, namely, malt spent rootlets (MSR), coffee spent grounds (CSG), and olive kernels (OK). Materials were charred at two temperatures (400 and 850 °C) in order to examine the effect of pyrolysis temperature. Homogeneous catalysts such as sulfuric acid and sodium hydroxide were also employed for comparison purposes. In order to explain the different performance of biochar as catalyst, we conducted detailed characterization of these materials. The results of this study showed that homogeneous catalysts (H₂SO₄ and NaOH) had similar results to the CSG biochar at 400 °C, which was the most productive tested biochar. The pyrolysis temperatures affected the FAMEs recovery of OK and CSG biochar. Full article

(This article belongs to the Special Issue Advances in the Application of Biochar in Catalytic Processes)

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14 pages, 4721 KiB

Open AccessCommunication

Valence Regulation of Ultrathin Cerium Vanadate Nanosheets for Enhanced Photocatalytic CO₂ Reduction to CO

by Lujia Ding, Qiutong Han, Hong Lu, Yong Yang, Gang Lu, Hui Zhang, Xueqin Ran, Yingdong Xia, Ping Li, Yonghua Chen and Yong Zhou

Catalysts 2021, 11(9), 1115; https://doi.org/10.3390/catal11091115 - 16 Sep 2021

Cited by 11 | Viewed by 2100

Abstract

Atomic valence state regulation is an advantageous approach for improving photocatalytic efficiency and product selectivity. However, it is difficult to precisely control the ratio of the different valence states on the surface and the relationship between the surface valence change and catalytic efficiency [...] Read more.

Atomic valence state regulation is an advantageous approach for improving photocatalytic efficiency and product selectivity. However, it is difficult to precisely control the ratio of the different valence states on the surface and the relationship between the surface valence change and catalytic efficiency in the photocatalytic reaction process is unclear. Herein, CeVO₄ ultrathin nanosheets were fabricated by one-step solvothermal method with ethanolamine (MEA) as the structure-directing agent. The ratio of the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions is precisely modulated from 19.82:100 to 13.33:100 changed by the volume of MEA added without morphology modification. The photocatalytic efficiency increases as the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions decrease and CV3 (prepared with 3 mL of MEA) shows the highest CO generation rate approximately 6 and 14 times larger than CV (prepared without MEA) and CV1 (prepared with 1 mL of MEA), respectively, in the photocatalytic CO₂ reduction. Interestingly, about 6.8% photo-induced Ce⁴⁺ ions were generated on the surface of the catalysts during the photocatalytic CO₂ reduction without any phase and morphology changes for CV3. The photocatalytic reaction mechanism is proposed considering the intrinsic and photo-induced Ce⁴⁺ ions to obtain efficient photocatalysts. Full article

(This article belongs to the Special Issue New Trends in Photocatalysis: Photocatalytic Materials and Applications)

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13 pages, 1018 KiB

Open AccessFeature PaperReview

Understanding the Catalytic Activity of Microporous and Mesoporous Zeolites in Cracking by Experiments and Simulations

by Shih-Cheng Li, Yen-Chun Lin and Yi-Pei Li

Catalysts 2021, 11(9), 1114; https://doi.org/10.3390/catal11091114 - 16 Sep 2021

Cited by 8 | Viewed by 4006

Abstract

Porous zeolite catalysts have been widely used in the industry for the conversion of fuel-range molecules for decades. They have the advantages of higher surface area, better hydrothermal stability, and superior shape selectivity, which make them ideal catalysts for hydrocarbon cracking in the [...] Read more.

Porous zeolite catalysts have been widely used in the industry for the conversion of fuel-range molecules for decades. They have the advantages of higher surface area, better hydrothermal stability, and superior shape selectivity, which make them ideal catalysts for hydrocarbon cracking in the petrochemical industry. However, the catalytic activity and selectivity of zeolites for hydrocarbon cracking are significantly affected by the zeolite topology and composition. The aim of this review is to survey recent investigations on hydrocarbon cracking and secondary reactions in micro- and mesoporous zeolites, with the emphasis on the studies of the effects of different porous environments and active site structures on alkane adsorption and activation at the molecular level. The pros and cons of different computational methods used for zeolite simulations are also discussed in this review. Full article

(This article belongs to the Special Issue Experimental and Theoretical Studies of Active Sites in Catalysts)

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16 pages, 1549 KiB

Open AccessReview

Recent Advances in Catalytic Conversion of Biomass to 2,5-Furandicarboxylic Acid

by Hanyu Cong, Haibo Yuan, Zekun Tao, Hanlin Bao, Zheming Zhang, Yi Jiang, Di Huang, Hongling Liu and Tengfei Wang

Catalysts 2021, 11(9), 1113; https://doi.org/10.3390/catal11091113 - 16 Sep 2021

Cited by 23 | Viewed by 5023

Abstract

Converting biomass into high value-added compounds has attracted great attention for solving fossil fuel consumption and global warming. 5-Hydroxymethylfurfural (HMF) has been considered as a versatile biomass-derived building block that can be used to synthesize a variety of sustainable fuels and chemicals. Among [...] Read more.

Converting biomass into high value-added compounds has attracted great attention for solving fossil fuel consumption and global warming. 5-Hydroxymethylfurfural (HMF) has been considered as a versatile biomass-derived building block that can be used to synthesize a variety of sustainable fuels and chemicals. Among these derivatives, 2,5-furandicarboxylic acid (FDCA) is a desirable alternative to petroleum-derived terephthalic acid for the synthesis of biodegradable polyesters. Herein, to fully understand the current development of the catalytic conversion of biomass to FDCA, a comprehensive review of the catalytic conversion of cellulose biomass to HMF and the oxidation of HMF to FDCA is presented. Moreover, future research directions and general trends of using biomass for FDCA production are also proposed. Full article

(This article belongs to the Special Issue Advances in Catalysis for Fuel and Chemical Production from Biomass Feedstocks)

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21 pages, 9016 KiB

Open AccessArticle

Iron-Zinc Co-Doped Titania Nanocomposite: Photocatalytic and Photobiocidal Potential in Combination with Molecular Docking Studies

by Nadia Riaz, Debra Adelina Chia Siew Fen, Muhammad Saqib Khan, Sadia Naz, Rizwana Sarwar, Umar Farooq, Mohamad Azmi Bustam, Gaber El-Saber Batiha, Islam H. El Azab, Jalal Uddin and Ajmal Khan

Catalysts 2021, 11(9), 1112; https://doi.org/10.3390/catal11091112 - 16 Sep 2021

Cited by 10 | Viewed by 2225

Abstract

In the current research study, iron-zinc co-doped TiO₂ was reported as an energy efficient material for the degradation of DIPA and inactivation of E. coli and S. aureus under visible light irradiation. In addition, molecular docking simulation was performed to provide further [...] Read more.

In the current research study, iron-zinc co-doped TiO₂ was reported as an energy efficient material for the degradation of DIPA and inactivation of E. coli and S. aureus under visible light irradiation. In addition, molecular docking simulation was performed to provide further insight into possible targets for inhibiting bacterial development. The synthesized nanocomposites were screened and optimized for different synthesis and reaction parameters. The physicochemical properties of the synthesized nanocomposites were evaluated through different characterization techniques. The wet impregnation (WI) approach was among the most successful methods for the synthesis of Fe-Zn-TiO₂ nanocomposite (NC) utilizing anatase titanium. Moreover, 66.5% (60 min reaction time) and 100% (190 min reaction time) chemical oxygen demand (COD) removal was obtained through optimized NC, i.e., 0.1Fe-0.4Zn metal composition and 300 °C calcination temperature. The energy consumption for the best NC was 457.40 KW h m⁻³. Moreover, 0.1Fe-0.4Zn-TiO₂-300 was more efficient against S. aureus compared to E. coli with 100% reduction in 90 min of visible light irradiations. Furthermore, 0.1Fe-0.4Zn-TiO₂-300 NC showed that the binding score for best docked conformation was −5.72 kcal mol⁻¹ against β-lactamase from E. coli and −3.46 kcal mol⁻¹ from S. aureus. The studies suggested the Fe-Zn in combination with TiO₂ to be a possible inhibitor of β-lactamase that can be further tested in enzyme inhibition studies. Full article

(This article belongs to the Special Issue Energy-Efficient Catalytic Oxidation)

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13 pages, 4623 KiB

Open AccessArticle

Removal of Tar Contents Derived from Lignocellulosic Biomass Gasification Facilities Using MgAl-LDH@clinoptilolite

by I-Tae Kim, Kwang-Ho Ahn, Jinhong Jung, Yoonah Jeong, Dong-Chul Shin and Ye-Eun Lee

Catalysts 2021, 11(9), 1111; https://doi.org/10.3390/catal11091111 - 16 Sep 2021

Cited by 4 | Viewed by 2612

Abstract

Gasification of lignocellulosic biomass requires the effective removal method of tar. This study focused on the application of specially designed Mg/Al-layered double hydroxides clinoptilolite (Mg/Al-LDH@clinoptilolite) to improve the removal efficiency of tar, which would eventually lead to enhancing the power efficiency of gasification, [...] Read more.

Gasification of lignocellulosic biomass requires the effective removal method of tar. This study focused on the application of specially designed Mg/Al-layered double hydroxides clinoptilolite (Mg/Al-LDH@clinoptilolite) to improve the removal efficiency of tar, which would eventually lead to enhancing the power efficiency of gasification, preventing damage to facilities, and deducing durability improvement plans. Zeolite-layered double hydroxides impregnated with clinoptilolite, a natural zeolite, and Mg/Al-layered double hydroxide incorporated into conventional water scrubbers were prepared to enhance the removal efficiency of the tar and improve the quality of the syngas produced during the gasification process. The simultaneous removal of moisture and CO₂ in the syngas was also investigated during the removal of the tar. The drastic decrease in tar and CO₂ concentration was confirmed, which triggered a relative increase in the effective content of inflammable gas. The findings of the present study provide a practical approach to increasing power efficiency and durability during the gasification of lignocellulosic biomass. Full article

(This article belongs to the Special Issue Advanced Nanomaterials - Synthesis and Applications in Catalysis)

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12 pages, 1789 KiB

Open AccessArticle

Catalytic Activity Enhancement of Cu-Zn-Based Catalyst for Methanol Steam Reforming with Magnetic Inducement

by Sasimas Katanyutanon, Dilpium Samarasinghe, Luckhana Lawtrakul and Pisanu Toochinda

Catalysts 2021, 11(9), 1110; https://doi.org/10.3390/catal11091110 - 16 Sep 2021

Cited by 3 | Viewed by 2285

Abstract

Magnetic inducement was applied during metal loading to enhance Cu-Zn catalysts for methanol steam reforming in the temperature range of 200–300 °C. The supports used in this study were the γ-Al₂O₃ support and CeO₂-Al₂O₃ supports [...] Read more.

Magnetic inducement was applied during metal loading to enhance Cu-Zn catalysts for methanol steam reforming in the temperature range of 200–300 °C. The supports used in this study were the γ-Al₂O₃ support and CeO₂-Al₂O₃ supports prepared under different magnetic environments. Cu-Zn loading between the north and south poles (N-S) on the CeO₂-Al₂O₃ support, prepared between two north poles (N-N), led to the highest H₂ production at 300 °C (2796 ± 76 µmol/min), which is triple that of Cu-Zn/CeO₂-Al₂O₃ prepared without magnetic inducement and ~11-fold the activity of the Cu-Zn/Al₂O₃ reference catalyst. The N-S magnetic environment during metal loading leads to lower reduction temperatures and larger Cu(1+):Cu(2+) ratio. These results showed that the pole arrangement of magnets during metal loading could affect the catalytic activity of the Cu-Zn catalyst owing to its influence on the reducibility and the oxidation state of Cu active metal. Full article

(This article belongs to the Section Catalysis for Sustainable Energy)

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45 pages, 13529 KiB

Open AccessFeature PaperReview

Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests

by Sergei Khairulin, Mikhail Kerzhentsev, Anton Salnikov and Zinfer R. Ismagilov

Catalysts 2021, 11(9), 1109; https://doi.org/10.3390/catal11091109 - 15 Sep 2021

Cited by 11 | Viewed by 6158

Abstract

This article is devoted to scientific and technical aspects of the direct catalytic oxidation of hydrogen sulfide for the production of elemental sulfur. It includes a detailed description of the Claus process as the main reference technology for hydrogen sulfide processing methods. An [...] Read more.

This article is devoted to scientific and technical aspects of the direct catalytic oxidation of hydrogen sulfide for the production of elemental sulfur. It includes a detailed description of the Claus process as the main reference technology for hydrogen sulfide processing methods. An overview of modern catalytic systems for direct catalytic oxidation technology and known processes is presented. Descriptions of the scientific results of the Institute of Catalysis of the SB RAS in a study of the physical and chemical foundations of the process and the creation of a catalyst for it are included. The Boreskov Institute of Catalysis SB RAS technologies based on fundamental studies and their pilot and industrial testing results are described. Full article

(This article belongs to the Special Issue Catalysts and Processes for H₂S Conversion to Sulfur)

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21 pages, 3920 KiB

Open AccessFeature PaperReview

Advances in Green Catalysis for the Synthesis of Medicinally Relevant N-Heterocycles

by A. Sofia Santos, Daniel Raydan, José C. Cunha, Nuno Viduedo, Artur M. S. Silva and M. Manuel B. Marques

Catalysts 2021, 11(9), 1108; https://doi.org/10.3390/catal11091108 - 15 Sep 2021

Cited by 7 | Viewed by 2846

Abstract

N-heterocycles, both saturated and unsaturated, are ubiquitous biologically active molecules that are extremely appealing scaffolds in drug discovery programs. Although classical synthetic methods have been developed to access many relevant N-heterocyclic scaffolds, representing well-established and reliable routes, some do not meet [...] Read more.

N-heterocycles, both saturated and unsaturated, are ubiquitous biologically active molecules that are extremely appealing scaffolds in drug discovery programs. Although classical synthetic methods have been developed to access many relevant N-heterocyclic scaffolds, representing well-established and reliable routes, some do not meet the needs of sustainability. In this context, several advances have been made towards the sustainable synthesis of N-heterocycles. This review focuses on the most recent examples from the last five years of catalytic synthesis of several heterocyclic compounds of medicinal relevance. Thus, the synthesis of isoindoloquinazolines, quinazolines and azaindoles, among others, are covered. The synthetic methods selected include the use of homogeneous and heterogeneous catalysts and the use of alternative and sustainable methods such as, for example, metal-catalyzed acceptorless coupling and one-pot reactions. The green aspects of the individual synthetic approaches are highlighted, and the scope of each methodology is described. Full article

(This article belongs to the Special Issue Advances in Green Catalysis for Sustainable Organic Synthesis)

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15 pages, 3773 KiB

Open AccessArticle

A Novel Machine Learning Model to Predict the Photo-Degradation Performance of Different Photocatalysts on a Variety of Water Contaminants

by Zhuoying Jiang, Jiajie Hu, Matthew Tong, Anna C. Samia, Huichun (Judy) Zhang and Xiong (Bill) Yu

Catalysts 2021, 11(9), 1107; https://doi.org/10.3390/catal11091107 - 15 Sep 2021

Cited by 16 | Viewed by 4269

Abstract

This paper describes an innovative machine learning (ML) model to predict the performance of different metal oxide photocatalysts on a wide range of contaminants. The molecular structures of metal oxide photocatalysts are encoded with a crystal graph convolution neural network (CGCNN). The structure [...] Read more.

This paper describes an innovative machine learning (ML) model to predict the performance of different metal oxide photocatalysts on a wide range of contaminants. The molecular structures of metal oxide photocatalysts are encoded with a crystal graph convolution neural network (CGCNN). The structure of organic compounds is encoded via digital molecular fingerprints (MF). The encoded features of the photocatalysts and contaminants are input to an artificial neural network (ANN), named as CGCNN-MF-ANN model. The CGCNN-MF-ANN model has achieved a very good prediction of the photocatalytic degradation rate constants by different photocatalysts over a wide range of organic contaminants. The effects of the data training strategy on the ML model performance are compared. The effects of different factors on photocatalytic degradation performance are further evaluated by feature importance analyses. Examples are illustrated on the use of this novel ML model for optimal photocatalyst selection and for assessing other types of photocatalysts for different environmental applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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13 pages, 3219 KiB

Open AccessArticle

Continuous Diastereomeric Kinetic Resolution—Silybins A and B

by David Biedermann, Martina Hurtová, Oldřich Benada, Kateřina Valentová, Lada Biedermannová and Vladimír Křen

Catalysts 2021, 11(9), 1106; https://doi.org/10.3390/catal11091106 - 14 Sep 2021

Cited by 4 | Viewed by 2248

Abstract

The natural diastereomeric mixture of silybins A and B is often used (and considered) as a single flavonolignan isolated from the fruit extract of milk thistle (Silybum marianum), silymarin. However, optically pure silybin diastereomers are required for the evaluation of their [...] Read more.

The natural diastereomeric mixture of silybins A and B is often used (and considered) as a single flavonolignan isolated from the fruit extract of milk thistle (Silybum marianum), silymarin. However, optically pure silybin diastereomers are required for the evaluation of their biological activity. The separation of silybin diastereomers by standard chromatographic methods is not trivial. Preparative chemoenzymatic resolution of silybin diastereomers has been published, but its optimization and scale-up are needed. Here we present a continuous flow reactor for the chemoenzymatic kinetic resolution of silybin diastereomers catalyzed by Candida antarctica lipase B (CALB) immobilized on acrylic resin beads (Novozym^® 435). Temperature, flow rate, and starting material concentration were varied to determine optimal reaction conditions. The variables observed were conversion and diastereomeric ratio. Optimal conditions were chosen to allow kilogram-scale reactions and were determined to be −5 °C, 8 g/L silybin, and a flow rate of 16 mL/min. No significant carrier degradation was observed after approximately 30 cycles (30 days). Under optimal conditions and using a 1000 × 15 mm column, 20 g of silybin per day can be easily processed, yielding 6.7 and 5.6 g of silybin A and silybin B, respectively. Further scale-up depends only on the size of the reactor. Full article

(This article belongs to the Special Issue Biotransformation Catalyzed by Immobilized Enzyme)

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