Catalysts

12 pages, 1713 KiB

Open AccessArticle

Quaternary Ammonium Salts Interact with Enolates and Sulfonates via Formation of Multiple ⁺N-C-H Hydrogen Bonding Interactions

by Grazia Bencivenni, Nathalie Saraiva Rosa, Paolo Grieco, Malachi W. Gillick-Healy, Brian G. Kelly, Brendan Twamley and Mauro F. A. Adamo

Catalysts 2022, 12(7), 803; https://doi.org/10.3390/catal12070803 - 21 Jul 2022

Cited by 1 | Viewed by 1975

Abstract

We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and ¹H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative ⁺N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. [...] Read more.

We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and ¹H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative ⁺N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. This finding, which has been often invoked by calculations, is herein substantiated by the preparation of two model compounds and an analysis of their X-ray crystal structures in the solid state and ¹H-NMR spectra in solution. These observations are particularly pertinent for the rational design of novel catalyses and catalysts and providing guidance to an understanding of these species in solution and during asymmetric enantioselective catalysis. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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16 pages, 3218 KiB

Open AccessArticle

Microwave-Assisted CO Oxidation over Perovskites as a Model Reaction for Exhaust Aftertreatment—A Critical Assessment of Opportunities and Challenges

by Daniel Röhrens, Ahed Abouserie, Bangfen Wang, Greta Haselmann and Ulrich Simon

Catalysts 2022, 12(7), 802; https://doi.org/10.3390/catal12070802 - 21 Jul 2022

Cited by 2 | Viewed by 1617

Abstract

We introduce a microwave (MW)-assisted heterogeneous catalytical setup, which we carefully examined for its thermal and performance characteristics. Although MW-assisted heterogeneous catalysis has been widely explored in the past, there is still need for attention towards the specific experimental details, which may complicate [...] Read more.

We introduce a microwave (MW)-assisted heterogeneous catalytical setup, which we carefully examined for its thermal and performance characteristics. Although MW-assisted heterogeneous catalysis has been widely explored in the past, there is still need for attention towards the specific experimental details, which may complicate the interpretation of results and comparability in general. In this study we discuss technical and material related factors influencing the obtained data from MW-assisted heterogeneous catalysis, specifically in regards to the oxidation of carbon monoxide over a selected perovskite catalyst, which shall serve as a model reaction for exhaust gas aftertreatment. A high degree of comparability between different experiments, both in terms of setup and the catalysts, is necessary to draw conclusions regarding this promising technology. Despite significant interest from both fundamental and applied research, many questions and controversies still remain and are discussed in this study. A series of deciding parameters is presented and the influence on the data is discussed. To control these parameters is both a challenge but also an opportunity to gain advanced insight into MW-assisted catalysis and to develop new materials and processes. The results and discussion are based upon experiments conducted in a monomode MW-assisted catalysis system employing powdered solid-state perovskite oxides in a fixed bed reactor. The discussion covers critical aspects concerning the determination of the actual catalyst temperature, the homogeneity of the thermal distribution, time, and local temperature relaxation (i.e., thermal runaway effects and hotspot formation), particle size effects, gas flow considerations, and system design. Full article

(This article belongs to the Special Issue Catalysis by Unconventional Heating)

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15 pages, 3999 KiB

Open AccessArticle

Decorating of Ag and CuO on ZnO Nanowires by Plasma Electrolyte Oxidation Method for Enhanced Photocatalytic Efficiency

by Phung Thi Thu, Vu Duy Thinh, Vu Dinh Lam, Ta Ngoc Bach, Le Thi Hong Phong, Do Hoang Tung, Do Hung Manh, Nguyen Van Khien, Trinh Xuan Anh and Ngo Thi Hong Le

Catalysts 2022, 12(7), 801; https://doi.org/10.3390/catal12070801 - 21 Jul 2022

Cited by 10 | Viewed by 2004

Abstract

In this work, photocatalytic performance is divulged in the ternary CuO-Ag-ZnO nanowire synthesized via a two-step approach. The decoration of Ag and CuO nanostructures onto the surface of ZnO nanowires was simply carried out by using the plasma electrolytic oxidation method in a [...] Read more.

In this work, photocatalytic performance is divulged in the ternary CuO-Ag-ZnO nanowire synthesized via a two-step approach. The decoration of Ag and CuO nanostructures onto the surface of ZnO nanowires was simply carried out by using the plasma electrolytic oxidation method in a short time. The structure, size, morphology, and optical properties of as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, and spectrophotometry measurements. The diameters of Ag nanoparticles and ZnO nanoflowers are in the range of 5–20 nm and 20–60 nm, respectively. Within the first 15 min, methyl orange was decolorized 96.3 and 82.8% in the CuO-Ag-ZnO and Ag-ZnO, respectively, and there is only about 46.7% of that decomposed in pure ZnO. The CuO-Ag-ZnO shows a higher rate constant k = 0.2007 min⁻¹ and a lower half-life time t = 6.1 min compared to Ag-ZnO and bare ZnO nanowires. The photo-reusability of the ternary nanostructures was estimated to be much outweighed compared to ZnO nanowires. Interestingly, the synergic incorporation between noble metal–semiconductor or semiconductor–semiconductor in the interfaces of Ag-CuO, Ag-ZnO, and CuO-ZnO expands the visible light absorption range and eliminates the photogenerated electron–hole recombination, resulting in a superior visible-light-driven photocatalyst. Full article

(This article belongs to the Topic Catalysis for Sustainable Chemistry and Energy)

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10 pages, 1731 KiB

Open AccessArticle

Enhancement on PrBa_0.5Sr_0.5Co_1.5Fe_0.5O₅ Electrocatalyst Performance in the Application of Zn-Air Battery

by Chengcheng Wang, Ziheng Zheng, Zian Chen, Xinlei Luo, Bingxue Hou, Mortaza Gholizadeh, Xiang Gao, Xincan Fan and Zanxiong Tan

Catalysts 2022, 12(7), 800; https://doi.org/10.3390/catal12070800 - 20 Jul 2022

Cited by 4 | Viewed by 1441

Abstract

Due to the insufficient stability and expensive price of commercial precious metal catalysts like Pt/C and IrO₂, it is critical to study efficiently, stable oxygen reduction reaction as well as oxygen evolution reaction (ORR/OER) electrocatalysts of rechargeable Zn-air batteries. PrBa_0.5 [...] Read more.

Due to the insufficient stability and expensive price of commercial precious metal catalysts like Pt/C and IrO₂, it is critical to study efficiently, stable oxygen reduction reaction as well as oxygen evolution reaction (ORR/OER) electrocatalysts of rechargeable Zn-air batteries. PrBa_0.5Sr_0.5Co_1.5Fe_0.5O₅ (PBSCF) double perovskite was adopted due to its flexible electronic structure as well as higher electro catalytic activity. In this study, PBSCF was prepared by the citrate-EDTA method and the optimized amount of PBSCF-Pt/C composite was used as a potential ORR/OER bifunctional electrocatalyst in 0.1 M KOH. The optimized composite exhibited excellent OER intrinsic activity with an onset potential of 1.6 V and Tafel slope of 76 mV/dec under O₂-saturated 0.1 M KOH. It also exhibited relatively competitive ORR activity with an onset potential of 0.9 V and half-wave potential of 0.78 V. Additionally, Zn–air battery with PBSCF composite catalyst showed relatively good stability. All these results illustrate that PBSCF-Pt/C composite is a promising bifunctional electrocatalyst for rechargeable Zn-air batteries. Full article

(This article belongs to the Special Issue Pt-M (M = Ni,Co,Cu, etc.)/C Electrocatalysts)

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15 pages, 5709 KiB

Open AccessArticle

Sn(IV) Porphyrin-Based Ionic Self-Assembled Nanostructures and Their Application in Visible Light Photo-Degradation of Malachite Green

by Nirmal Kumar Shee and Hee-Joon Kim

Catalysts 2022, 12(7), 799; https://doi.org/10.3390/catal12070799 - 20 Jul 2022

Cited by 13 | Viewed by 1636

Abstract

A series of porphyrin-based ionic complexes were prepared through the reaction of two porphyrin precursors, 5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrin H₂TPhPyP (1) and trans-dihydroxo [5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrinato]tin(IV) Sn(OH)₂TPhPyP (2), with various acids (HCl, HNO₃, CF₃COOH, H [...] Read more.

A series of porphyrin-based ionic complexes were prepared through the reaction of two porphyrin precursors, 5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrin H₂TPhPyP (1) and trans-dihydroxo [5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrinato]tin(IV) Sn(OH)₂TPhPyP (2), with various acids (HCl, HNO₃, CF₃COOH, H₂SO₄, H₂CO₃, and H₃PO₄). The complexes were characterized via elemental analysis, ¹H nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV)-visible spectroscopy, fluorescence spectroscopy, and field-emission scanning electron microscopy (FE-SEM). Each compound exhibited different results for UV-visible, fluorescence, FT-IR, and FE-SEM studies depending on the counter anions. The complexes possessed different self-assembled nanostructures based on electronic interactions between the cations of compounds 1 and 2 with different counter anions. These aggregated species are stabilized by electrostatic forces and the π-π stacking interactions between the two porphyrin rings, in which the counter anions play an important bridging role. The counter anions also play an important role in controlling the morphology and photocatalytic properties of the as-developed materials. The complexes were then used for the photocatalytic degradation of the malachite green (MG) dye in aqueous media under visible light irradiation for up to 70 min. A morphology-dependent photocatalytic degradation of the MG dye was observed for all the ionic complexes, with efficiencies ranging from 50% to 95%. Full article

(This article belongs to the Special Issue Nanostructured Materials for Solar and Visible Light Driven Photocatalysis)

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35 pages, 6956 KiB

Open AccessFeature PaperReview

A Review on Production and Surface Modifications of Biochar Materials via Biomass Pyrolysis Process for Supercapacitor Applications

by Rifat Mehdi, Asif Hussain Khoja, Salman Raza Naqvi, Ningbo Gao and Nor Aishah Saidina Amin

Catalysts 2022, 12(7), 798; https://doi.org/10.3390/catal12070798 - 20 Jul 2022

Cited by 30 | Viewed by 4150

Abstract

Biochar (BC) based materials are solid carbon enriched materials produced via different thermochemical techniques such as pyrolysis. However, the non-modified/non-activated BC-based materials obtained from the low-temperature pyrolysis of biomass cannot perform well in energy storage applications due to the mismatched physicochemical and electrical [...] Read more.

Biochar (BC) based materials are solid carbon enriched materials produced via different thermochemical techniques such as pyrolysis. However, the non-modified/non-activated BC-based materials obtained from the low-temperature pyrolysis of biomass cannot perform well in energy storage applications due to the mismatched physicochemical and electrical properties such as low surface area, poor pore features, and low density and conductivity. Therefore, to improve the surface features and structure of the BC and surface functionalities, surface modifications and activations are introduced to improve its properties to achieve enhanced electrochemical performance. The surface modifications use various activation methods to modify the surface properties of BC to achieve enhanced performance for supercapacitors in energy storage applications. This article provides a detailed review of surface modification methods and the application of modified BC to be used for the synthesis of electrodes for supercapacitors. The effect of those activation methods on physicochemical and electrical properties is critically presented. Finally, the research gap and future prospects are also elucidated. Full article

(This article belongs to the Special Issue Recent Advancements in Biomass/Waste-Derived Materials in Catalysis, Energy Storage, and Computational Modeling)

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22 pages, 5210 KiB

Open AccessArticle

Ordered Mesoporous nZVI/Zr-Ce-SBA-15 Catalysts Used for Nitrate Reduction: Synthesis, Optimization and Mechanism

by Ruimin Zhang, Haixia Liu, Weili Jiang and Weijing Liu

Catalysts 2022, 12(7), 797; https://doi.org/10.3390/catal12070797 - 19 Jul 2022

Cited by 2 | Viewed by 1401

Abstract

Excessive concentrations of nitrate (NO₃-N) in water lead to the deterioration of water quality, reducing biodiversity and destroying ecosystems. Therefore, the present study investigated NO₃-N removal from simulated wastewater by nanoscale zero-valent iron-supported ordered mesoporous Zr-Ce-SBA-15 composites (nZVI/Zr-Ce-SBA-15) assisted [...] Read more.

Excessive concentrations of nitrate (NO₃-N) in water lead to the deterioration of water quality, reducing biodiversity and destroying ecosystems. Therefore, the present study investigated NO₃-N removal from simulated wastewater by nanoscale zero-valent iron-supported ordered mesoporous Zr-Ce-SBA-15 composites (nZVI/Zr-Ce-SBA-15) assisted by response surface methodology (RSM), an artificial neural network combined with a genetic algorithm (ANN-GA) and a radial basis neural network (RBF). The successful support of nZVI on Zr-Ce-SBA-15 was confirmed using XRD, FTIR, TEM, SEM–EDS, N₂ adsorption and XPS, which indicated ordered mesoporous materials. The results showed that ANN-GA was better than the RSM for optimizing the conditions of NO₃-N removal and the RBF neural network further confirmed the reliability of the ANN-GA model. The removal rate of NO₃-N by the composites reached 95.71% under the optimized experimental conditions (initial pH of 4.89, contact time = of 62.27 min, initial NO₃-N concentration of 74.84 mg/L and temperature of 24.77 °C). The process of NO₃-N adsorption onto Zr-Ce-SBA-15 composites was followed by the Langmuir model (maximum adsorption capacity of 45.24 mg/g), pseudo-second-order kinetics, and was spontaneous, endothermic and entropy driven. The yield of N₂ can be improved after nZVI was supported on Zr-Ce-SBA-15, and the composites exhibited a strong renewability in the short term within three cycles. The resolution of Fe²⁺ experiments confirmed that nZVI/Zr-Ce-SBA-15 was simultaneously undergoing adsorption and catalysis in the process of NO₃-N removal. Our study suggests that the ordered mesoporous nZVI/Zr-Ce-SBA-15 composites are a promising material for simultaneously performing NO₃-N removal and improving the selectivity of N₂, which provides a theoretical reference for NO₃-N remediation from wastewater. Full article

(This article belongs to the Special Issue Microporous and Mesoporous Materials for Catalytic Applications)

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11 pages, 1402 KiB

Open AccessArticle

Silica Bifunctional Supports for the Direct Synthesis of H₂O₂: Optimization of Br/Acid Sites and Pd/Br Ratio

by Gema Blanco-Brieva, Frederique Desmedt, Pierre Miquel, Jose M. Campos-Martin and Jose L. G. Fierro

Catalysts 2022, 12(7), 796; https://doi.org/10.3390/catal12070796 - 19 Jul 2022

Cited by 2 | Viewed by 1499

Abstract

We have studied the direct synthesis of hydrogen peroxide using a catalytic system consisting of palladium supported on silica bifunctionalized with sulfonic acid groups and bromide in the absence of acid and halide promoters in solution. Catalysts with several bromide substituents were employed [...] Read more.

We have studied the direct synthesis of hydrogen peroxide using a catalytic system consisting of palladium supported on silica bifunctionalized with sulfonic acid groups and bromide in the absence of acid and halide promoters in solution. Catalysts with several bromide substituents were employed in the catalyst synthesis. The prepared samples were characterized by TXRF, XPS, and hydrogen peroxide decomposition. Catalysts characterization indicated the presence of only palladium (II) species in all of the samples, with similar values for surface and bulk of Pd/Br atomic ratio. The catalysts were tested via direct synthesis, and all samples were able to produce hydrogen peroxide at 313 K and 5.0 MPa. The hydrogen peroxide yield and selectivity changed with the Pd/Br ratio. A decrease in the Pd/Br ratio increases the final hydrogen peroxide concentration, and the selectivity for H₂O₂ reaches a maximum at a Pd/Br ratio around 0.16 and then decreases. However, the maximum hydrogen peroxide concentration and selectivity occur at slightly different Pd/Br ratios, i.e., resp. 0.4 vs. 0.16. Full article

(This article belongs to the Section Catalytic Materials)

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20 pages, 2711 KiB

Open AccessFeature PaperReview

Progress & Prospect of Enzyme-Mediated Structured Phospholipids Preparation

by Yuhan Li, Lingmei Dai, Dehua Liu and Wei Du

Catalysts 2022, 12(7), 795; https://doi.org/10.3390/catal12070795 - 19 Jul 2022

Cited by 3 | Viewed by 1740

Abstract

In recent years, structured phospholipids (SPLs), which are modified phospholipids (PLs), have attracted more attention due to their great potential for application in the field of pharmacy, food, cosmetics, and health. SPLs not only possess enhanced chemical, physical and nutritional properties, but also [...] Read more.

In recent years, structured phospholipids (SPLs), which are modified phospholipids (PLs), have attracted more attention due to their great potential for application in the field of pharmacy, food, cosmetics, and health. SPLs not only possess enhanced chemical, physical and nutritional properties, but also present superior bioavailability in comparison with other lipid forms, such as triacylglycerols, which make SPLs become more competitive carriers to increase the absorption of the specific fatty acids in the body. Compared with chemical-mediated SPLs, the process of enzyme-mediated SPLs has the advantages of high product variety, high substrate selectivity, and mild operation conditions. Both lipases and phospholipases can be used in the enzymatic production of SPLs, and the main reaction type contains esterification, acidolysis, and transesterification. During the preparation, reaction medium, acyl migration, water content/activity, substrates and enzymes, and some other parameters have significant effects on the production and purity of the desired PLs products. In this paper, the progress in enzymatic modification of PLs over the last 20 years is reviewed. Reaction types and characteristic parameters are summarized in detail and the parameters affecting acyl migration are first discussed to give the inspiration to optimize the enzyme-mediated SPLs preparation. To expand the application of enzyme-mediated SPLs in the future, the prospect of further study on SPLs is also proposed at the end of the paper. Full article

(This article belongs to the Special Issue Enzymatic Catalysis in Bio-Based Chemicals Production)

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8 pages, 2954 KiB

Open AccessArticle

An Efficient Electrocatalyst (PtCo/C) for the Oxygen Reduction Reaction

by Bingxue Hou, Xinlei Luo, Ziheng Zheng, Rui Tang, Qi Zhang, Mortaza Gholizadeh, Chengcheng Wang and Zanxiong Tan

Catalysts 2022, 12(7), 794; https://doi.org/10.3390/catal12070794 - 19 Jul 2022

Cited by 3 | Viewed by 2114

Abstract

The oxygen reduction reaction (ORR) is paid much more attention because of the high overpotential required for driving the four-electron process in the field of storage and sustainable energy conversion, including fuel cell applications. In this paper, PtCo nanoparticles encapsulated on carbon supports [...] Read more.

The oxygen reduction reaction (ORR) is paid much more attention because of the high overpotential required for driving the four-electron process in the field of storage and sustainable energy conversion, including fuel cell applications. In this paper, PtCo nanoparticles encapsulated on carbon supports were prepared by a simple modified polyol method with ethylene glycol. Structural as well as electrochemical characterizations illustrated that the PtCo/C electrocatalysts had a minimum particle size of 4.8 nm, which is close to the commercial 40 wt% Pt/JM. Moreover, the electrochemical measurements indicated that ORR activity was competitive with the commercial 40 wt% Pt/JM catalyst. The synthesis method is a critical way to produce PtCo/C catalysts for use in polymer electrolyte membranes in fuel cells (PEMFCs). Full article

(This article belongs to the Special Issue Pt-M (M = Ni,Co,Cu, etc.)/C Electrocatalysts)

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10 pages, 2126 KiB

Open AccessArticle

Differentiating the Reactivity of ZrO₂-Bound Formates Formed on Cu/ZrO₂ during CO₂ Hydrogenation

by Frederic C. Meunier, Isaac Dansette, Kimleang Eng and Yves Schuurman

Catalysts 2022, 12(7), 793; https://doi.org/10.3390/catal12070793 - 19 Jul 2022

Cited by 9 | Viewed by 1739

Abstract

The surface species formed during the hydrogenation of CO₂ with H₂ over a ZrO₂-supported Cu catalyst were investigated by operando diffuse reflectance FT-IR spectroscopy at 220 °C and 3 bar. The reactivity of two different formates located on zirconia [...] Read more.

The surface species formed during the hydrogenation of CO₂ with H₂ over a ZrO₂-supported Cu catalyst were investigated by operando diffuse reflectance FT-IR spectroscopy at 220 °C and 3 bar. The reactivity of two different formates located on zirconia could be unraveled. The data pointed to ZrO₂ hydroxyl groups at 3755 cm⁻¹ as the sites on which carbonates and then formates were hydrogenated to methoxy species. Formate hydrogenation appeared as the slowest step. The most reactive ZrO₂-bound formates exhibited a rate constant of reaction about 65 times higher than that of the slower formate. Full article

(This article belongs to the Special Issue Heterogeneous Catalytic Materials: Synthesis, Characterization and Applications for Energetic Purposes, 2nd Edition)

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28 pages, 9838 KiB

Open AccessReview

Recent Breakthrough in Layered Double Hydroxides and Their Applications in Petroleum, Green Energy, and Environmental Remediation

by Mohsen S. Mostafa, Lan Chen, Mohamed S. Selim, Ruiyi Zhang and Guanglu Ge

Catalysts 2022, 12(7), 792; https://doi.org/10.3390/catal12070792 - 19 Jul 2022

Viewed by 2365

Abstract

The fast development of the world civilization is continuously based on huge energy consumption. The extra-consumption of fossil fuel (petroleum, coal, and gas) in past decades has caused several political and environmental crises. Accordingly, the world, and especially the scientific community, should discover [...] Read more.

The fast development of the world civilization is continuously based on huge energy consumption. The extra-consumption of fossil fuel (petroleum, coal, and gas) in past decades has caused several political and environmental crises. Accordingly, the world, and especially the scientific community, should discover alternative energy sources to safe-guard our future from severe climate changes. Hydrogen is the ideal energy carrier, where nanomaterials, like layered double hydroxides (LDHs), play a great role in hydrogen production from clean/renewable sources. Here, we review the applications of LDHs in petroleum for the first time, as well as the recent breakthrough in the synthesis of 1D-LDHs and their applications in water splitting to H₂. By 1D-LDHs, it is possible to overcome the drawbacks of commercial TiO₂, such as its wide bandgap energy (3.2 eV) and working only in the UV-region. Now, we can use TiO₂-modified structures for infrared (IR)-induced water splitting to hydrogen. Extending the performance of TiO₂ into the IR-region, which includes 53% of sunlight by 1D-LDHs, guarantees high hydrogen evolution rates during the day and night and in cloudy conditions. This is a breakthrough for global hydrogen production and environmental remediation. Full article

(This article belongs to the Special Issue Catalysis for Energy – Efficient Production and Conversion of Solar and Synthetic Fuels)

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21 pages, 3414 KiB

Open AccessEditor’s ChoiceArticle

An In-Depth Exploration of the Electrochemical Oxygen Reduction Reaction (ORR) Phenomenon on Carbon-Based Catalysts in Alkaline and Acidic Mediums

by Niladri Talukder, Yudong Wang, Bharath Babu Nunna and Eon Soo Lee

Catalysts 2022, 12(7), 791; https://doi.org/10.3390/catal12070791 - 19 Jul 2022

Cited by 13 | Viewed by 4693

Abstract

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce [...] Read more.

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce the loading of expensive platinum group metal (PGM)-based catalysts for ORR in the electrochemical systems, many carbon-based catalysts have already shown promising results and numerous investigations on those catalysts are in progress. Most of these studies show the catalyst materials’ ORR performance as current density data obtained through the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) experiments taking cyclic voltammograms (CV) or linear sweep voltammograms (LSV) approaches. However, the provided descriptions or interpretations of those data curves are often ambiguous and recondite which can lead to an erroneous understanding of the ORR phenomenon in those specific systems and inaccurate characterization of the catalyst materials. In this paper, we presented a study of ORR on a newly developed carbon-based catalyst, the nitrogen-doped graphene/metal-organic framework (N-G/MOF), through RDE and RRDE experiments in both alkaline and acidic mediums, taking the LSV approach. The functions and crucial considerations for the different parts of the RDE/RRDE experiment such as the working electrode, reference electrode, counter electrode, electrolyte, and overall RDE/RRDE process are delineated which can serve as guidelines for the new researchers in this field. Experimentally obtained LSV curves’ shapes and their correlations with the possible ORR reaction pathways within the applied potential range are discussed in depth. We also demonstrated how the presence of hydrogen peroxide (H₂O₂), a possible intermediate of ORR, in the alkaline electrolyte and the concentration of acid in the acidic electrolyte can maneuver the ORR current density output in compliance with the possible ORR pathways. Full article

(This article belongs to the Special Issue Graphene in Photocatalysis/Electrocatalysis)

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13 pages, 2794 KiB

Open AccessArticle

Insights into the Capture of CO₂ by Nickel Hydride Complexes

by Min Zhang, Xiaoqing Liang, Yaozheng Wang, Hongyu Yang and Guangchao Liang

Catalysts 2022, 12(7), 790; https://doi.org/10.3390/catal12070790 - 19 Jul 2022

Cited by 3 | Viewed by 1778

Abstract

As a desired feedstock for sustainable energy source and for chemical synthesis, the capture and utilization of CO₂ have attracted chemists’ continuous efforts. The homogeneous CO₂ insertion into a nickel hydride complex to generate formate provides insight into the role of [...] Read more.

As a desired feedstock for sustainable energy source and for chemical synthesis, the capture and utilization of CO₂ have attracted chemists’ continuous efforts. The homogeneous CO₂ insertion into a nickel hydride complex to generate formate provides insight into the role of hydrogen as an active hydride form in the hydrogenation of CO₂, which serves as a practicable approach for CO₂ utilization. To parameterize the activities and to model the structure–activity relationship in the CO₂ insertion into nickel hydride, the comprehensive mechanism of CO₂ insertion into a series of square planar transition metal hydride (TM–H, TM = Ni, Pd, and Co) complexes was investigated using density functional theory (DFT) computations. The stepwise pathway with the TM-(H)-formate intermediate for the CO₂ insertion into all seven square planar transition metal hydride (TM–H) complexes was observed. The overall rate-determining step (RDS) was the nucleophilic attraction of the terminal O atom on the Ni center in Ni-(H)-formate to form Ni-(O)-(exo)formate. The charge of the Ni atom in the axially vacant [Ni]⁺ complex was demonstrated as the dominant factor in CO₂ insertion, which had an excellent linear correction (R² = 0.967) with the Gibbs barrier (ΔG^‡) of the RDS. The parameterized activities and modeled structure–activity relationship provided here light the way to the design of a more efficient Ni–H complex in the capture and utilization of CO₂. Full article

(This article belongs to the Special Issue Computational Insights into Small Molecule Activation)

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31 pages, 29703 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study

by Marek Freindorf and Elfi Kraka

Catalysts 2022, 12(7), 789; https://doi.org/10.3390/catal12070789 - 18 Jul 2022

Cited by 4 | Viewed by 3946

Abstract

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as [...] Read more.

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions. Full article

(This article belongs to the Special Issue Catalytic Epoxidation Reaction)

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15 pages, 2097 KiB

Open AccessFeature PaperArticle

Optimization of Autohydrolysis of Olive Pomaces to Obtain Bioactive Oligosaccharides: The Effect of Cultivar and Fruit Ripening

by Laura Freitas, Rita Simões, Isabel Miranda, Fátima Peres and Suzana Ferreira-Dias

Catalysts 2022, 12(7), 788; https://doi.org/10.3390/catal12070788 - 18 Jul 2022

Cited by 3 | Viewed by 1501

Abstract

The valorisation of agro-industrial residues presents a challenge in obtaining economically sustainable and environmentally friendly industrial processes. Olive pomace is a by-product generated in large quantities, from olive oil extraction. This residue mostly consists of lignocellulosic materials. The aim of this study was [...] Read more.

The valorisation of agro-industrial residues presents a challenge in obtaining economically sustainable and environmentally friendly industrial processes. Olive pomace is a by-product generated in large quantities, from olive oil extraction. This residue mostly consists of lignocellulosic materials. The aim of this study was to evaluate the potential use of extracted olive pomaces (EOP) obtained from olives with different ripening indexes (RI) and from different cultivars (Cobrançosa; RI = 2.5; 3.3 and 4.7; and Galega Vulgar; RI = 1.8; 2.9 and 4.8), to produce bioactive oligosaccharides from hemicelluloses by autohydrolysis. The hydrothermal treatment conditions were optimized by Response Surface Methodology, following a central composite rotatable design (CCRD), as a function of temperature (T: 142–198 °C) and time (t: 48–132 min), corresponding to severity factor (SF) values from 3.2 to 4.9. For all pomace samples, soluble sugar production was described by concave surfaces as a function of temperature and time. Autohydrolysis with SF equal or higher than 4.0 produced higher sugar yields, with maximum values around 180 g glucose equivalent/kg EOP for SF of 4.7 (190 °C/120 min) or 4.9 (198 °C/90 min). These values were similar for both cultivars and were not dependent on the ripening stage of the olives. Maximum oligosaccharide (OS) yields of 98% were obtained by autohydrolysis with SF of 4.0. The increase in SF to 4.9 resulted in a decrease in OS yield to 86–92%, due to the release of monomeric sugars. The monosaccharides were mostly xylose (55.8–67.7% in Galega; 50.4–69.0% in Cobrançosa liquid phases), and glucose, galactose, arabinose and rhamnose, in smaller quantities. Therefore, the production of bioactive xylo-oligosaccharides (XOS) from olive pomaces mainly depends on the hydrothermal conditions used. Full article

(This article belongs to the Special Issue Catalysis in Biorefinery)

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14 pages, 3012 KiB

Open AccessArticle

Engineering Noble Metal-like Bi onto Hierarchical SrWO₄ for the Enhancement of Photocatalytic Activity

by Liang Tang, Jian Zhao, Xiao Wang, Jiajun Wang and Peng Zhang

Catalysts 2022, 12(7), 787; https://doi.org/10.3390/catal12070787 - 18 Jul 2022

Cited by 2 | Viewed by 1117

Abstract

Solar-driven hydrogen production from water has attracted increasing attention due to sustainable H₂ fuel generation with zero-emissions. However, the design of a photocatalyst without noble metals to enable efficient water splitting is still critical for practical applications. In this study, the hierarchical [...] Read more.

Solar-driven hydrogen production from water has attracted increasing attention due to sustainable H₂ fuel generation with zero-emissions. However, the design of a photocatalyst without noble metals to enable efficient water splitting is still critical for practical applications. In this study, the hierarchical microspheres of SrWO₄ assembled with well-defined metallic Bi nanoparticles were synthesized through mild hydrothermal aging. The resultant photocatalyst with optimum proportion exhibited the competitive performance of a high hydrogen-generation rate at 4.5 mmol·h⁻¹·g⁻¹, outperforming SrWO₄ and Bi by factors of 2.0 and 2.4, respectively. Both the experimental characterization and active analysis revealed that the synergistic effect of noble metal-like behavior of Bi and their electron-sink capacity mainly contribute to boosting the overall photocatalytic efficiency. This work may provide advanced insights into the application of economical bismuth elements as co-catalysts, instead of noble metals, to improve photocatalytic efficiency in solar-fuel conversion and environmental remediation. Full article

(This article belongs to the Section Photocatalysis)

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9 pages, 3255 KiB

Open AccessArticle

Quantum-Chemical Modeling of the Catalytic Activity of Graphene Doped with Metal Phthalocyanines in ORR

by Kirill Y. Vinogradov, Anzhela V. Bulanova, Roman V. Shafigulin, Elena O. Tokranova and Hong Zhu

Catalysts 2022, 12(7), 786; https://doi.org/10.3390/catal12070786 - 18 Jul 2022

Cited by 5 | Viewed by 1581

Abstract

The active centers of carbon catalysts doped with cobalt, nickel, copper, manganese, zinc, and chromium were modeled by density functional theory methods. Likewise, the thermodynamics of the oxygen reduction reaction (ORR) on model catalysts were determined. The features of the chemical properties of [...] Read more.

The active centers of carbon catalysts doped with cobalt, nickel, copper, manganese, zinc, and chromium were modeled by density functional theory methods. Likewise, the thermodynamics of the oxygen reduction reaction (ORR) on model catalysts were determined. The features of the chemical properties of chromium-containing material, namely its spontaneous oxidation into the hydroxo form, were revealed. In addition, it was established that among the studied catalysts, graphene doped with cobalt showed the best properties. Full article

(This article belongs to the Special Issue Advances in Graphene/Nanocomposites for Catalytic Applications)

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13 pages, 4195 KiB

Open AccessFeature PaperArticle

Facile Preparation of Highly Active CO₂ Reduction (001)TiO₂/Ti₃C₂T_x Photocatalyst from Ti₃AlC₂ with Less Fluorine

by Jibai Li, Kaining Li, Qiuyan Tan, Qin Li, Jiajie Fan, Chao Wu and Kangle Lv

Catalysts 2022, 12(7), 785; https://doi.org/10.3390/catal12070785 - 18 Jul 2022

Cited by 13 | Viewed by 3013

Abstract

To date, (001)TiO₂/Ti₃C₂T_x hybridized photocatalyst is usually prepared through the complicated treatment of Ti₃AlC₂ in the presence of corrosive fluorine with a molar ratio of nF:nTi of more than 20. To reduce the [...] Read more.

To date, (001)TiO₂/Ti₃C₂T_x hybridized photocatalyst is usually prepared through the complicated treatment of Ti₃AlC₂ in the presence of corrosive fluorine with a molar ratio of nF:nTi of more than 20. To reduce the use of corrosive fluorine, herein, exploiting beyond the conventional method, we report a facile synthetic method for (001)TiO₂/Ti₃C₂T_x, elaborately using HF as both an etchant for Al elimination and a morphology control agent for the growth of (001)TiO₂ nanosheets, with a sharply diminished use of fluorine (nF:nTi = 4:1) and simplified operation procedures. After optimization, the resulting (001)TiO₂/Ti₃C₂T_x heterojunction exhibited markedly high photocatalytic activity with the CO₂ reduction rate of 13.45 μmol g⁻¹ h⁻¹, which even surpasses that of P25 (10.95 μmol g⁻¹ h⁻¹), while the photoelectron selectivity to CH₄ is approaching 92.84%. The superior photoactivity is interpreted as the fact that Ti₃C₂T_x with a lower work function induces photoinduced hole transfer and suppresses the charge recombination, thus facilitating the CO₂ multi-electron reduction. This study provides a novel and simple synthesis for (001)TiO₂/Ti₃C₂T_x towards sustainable energy transformations. Full article

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

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18 pages, 4726 KiB

Open AccessArticle

Cloning of Cold-Adapted Dextranase and Preparation of High Degree Polymerization Isomaltooligosaccharide

by Huanyu Wang, Qianru Lin, Dongxue Dong, Yingying Xu, Mingwang Liu, Jing Lu, Mingsheng Lyu and Shujun Wang

Catalysts 2022, 12(7), 784; https://doi.org/10.3390/catal12070784 - 17 Jul 2022

Cited by 3 | Viewed by 1438

Abstract

Intestinal diseases are mainly caused by a decrease in the relative abundance of probiotics and an increase in the number of pathogenic bacteria due to dysbiosis of the intestinal flora. High degree polymerization isomaltooligosaccharide (IMO) can promote probiotic metabolism and proliferation. In this [...] Read more.

Intestinal diseases are mainly caused by a decrease in the relative abundance of probiotics and an increase in the number of pathogenic bacteria due to dysbiosis of the intestinal flora. High degree polymerization isomaltooligosaccharide (IMO) can promote probiotic metabolism and proliferation. In this study, the dextranase (PsDex1711) gene of marine bacterial Pseudarthrobacter sp. RN22 was cloned and expressed in Escherichia coli BL21 (DE3). The optimal pH and temperature of the dextranase were 6.0 and 30 °C, respectively, showing the highest stability at 20 °C. The dextran T70 could be hydrolyzed to produce IMO3, IMO4, IMO5, and IMO6 with a high degree of polymerization. The hydrolysate of 1 mg/mL could significantly promote the growth of Lactobacillus and Bifidobacterium after 12 h culture and the formation of biofilms by 58.2%. The hydrolysates could promote the proliferation of probiotics. Furthermore, the IC₅₀ of scavenging rate of DPPH, hydroxyl radical, and superoxide anion was less than 20 mg/mL. This study provides a crucial theoretical basis for the application of dextranase such as pharmaceutical and food industries. Full article

(This article belongs to the Section Biocatalysis)

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18 pages, 22951 KiB

Open AccessFeature PaperArticle

Selective Synthesis of Levulinic Ester from Furfural Catalyzed by Hierarchical Zeolites

by Sancler C. Vasconcelos, Luiz F. C. Pinhel, Vinicius G. C. Madriaga, Vinicius Rossa, Leyliane G. S. Batinga, Domingos S. A. Silva, Rodrigo D. dos Santos, André V. H. Soares, Ernesto A. Urquieta-González, Fabio Barboza Passos, Rajender S. Varma and Thiago M. Lima

Catalysts 2022, 12(7), 783; https://doi.org/10.3390/catal12070783 - 15 Jul 2022

Cited by 3 | Viewed by 2139

Abstract

Furfural is a platform molecule that can be catalytically converted using a cascade series of reactions into levulinic esters, essential compounds used as fuel additives. Bifunctional catalysts containing Lewis and Brønsted acid sites such as zeolites are commonly used for these conversions. However, [...] Read more.

Furfural is a platform molecule that can be catalytically converted using a cascade series of reactions into levulinic esters, essential compounds used as fuel additives. Bifunctional catalysts containing Lewis and Brønsted acid sites such as zeolites are commonly used for these conversions. However, microporous zeolites often present diffusional restriction due to the size similarity of furfural and other molecules to the zeolites’ micropores. Thus, incorporating mesopores in these materials through post-synthetic protocols is a promising pathway to circumventing these limitations. This study presents the creation of hierarchical beta and mordenite using Si or Al removal and their employment in the furfural conversion to isopropyl levulinate (PL). Mordenite zeolite did not produce satisfactory mesopores, while the beta was more efficient in generating them by both acid and alkaline treatments. Beta zeolite treated in an alkaline solution presented larger mesopores (14.9 and 34.0 nm), maintaining a total acidity value close to its parent zeolite and a higher Lewis/Brønsted ratio. The combination of these features led to an improved diffusion of bulkier products and the highest furfural conversion (94%) and PL selectivity (90%), suggesting that a post-modification of beta zeolites produced efficient catalysts for upgrading abundantly available furfural. Full article

(This article belongs to the Special Issue Recent Trends in Catalytic Functionalization of Platform Molecules Derived from Raw Materials)

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18 pages, 2638 KiB

Open AccessFeature PaperReview

Mitigation of Air Pollutants by UV-A Photocatalysis in Livestock and Poultry Farming: A Mini-Review

by Myeongseong Lee, Jacek A. Koziel, Peiyang Li and William S. Jenks

Catalysts 2022, 12(7), 782; https://doi.org/10.3390/catal12070782 - 15 Jul 2022

Cited by 3 | Viewed by 2190

Abstract

Ultraviolet (UV)-based photocatalysis has been the subject of numerous investigations focused on mitigating undesirable pollutants in the gas phase. Few works report on applications beyond the proof of the concept. Even less is known about the current state of the art of UV [...] Read more.

Ultraviolet (UV)-based photocatalysis has been the subject of numerous investigations focused on mitigating undesirable pollutants in the gas phase. Few works report on applications beyond the proof of the concept. Even less is known about the current state of the art of UV photocatalysis in the context of animal agriculture. A growing body of research published over the last 15 years has advanced the knowledge and feasibility of UV-A photocatalysis for swine and poultry farm applications. This review paper summarizes UV-A photocatalysis technology’s effectiveness in mitigating targeted air pollutants in livestock and poultry farms. Specifically, air pollutants include odor, odorous VOCs, NH₃, H₂S and greenhouse gases (CO₂, CH₄, N₂O). We trace the progression of UV-A photocatalysis applications in animal farming since the mid-2000 and developments from laboratory to farm-scale trials. In addition, this review paper discusses the practical limitations and outlines the research needs for increasing the technology readiness and practical UV application in animal farming. Full article

(This article belongs to the Special Issue Environmental Catalysis for Air Pollution Applications)

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16 pages, 30374 KiB

Open AccessArticle

A Novel NADP(H)-Dependent 7alpha-HSDH: Discovery and Construction of Substrate Selectivity Mutant by C-Terminal Truncation

by Yinping Pan, Shijin Tang, Minghai Zhou, Fanglin Ao, Zhuozhou Tang, Liancai Zhu, Deshuai Lou, Jun Tan and Bochu Wang

Catalysts 2022, 12(7), 781; https://doi.org/10.3390/catal12070781 - 14 Jul 2022

Cited by 2 | Viewed by 1487

Abstract

7α-Hydroxysteroid dehydrogenase (7α-HSDH) plays an important role in the biosynthesis of tauroursodeoxycholic acid (TUDCA) using complex substrate chicken bile powder as raw material. However, chicken bile powder contains 4.74% taurocholic acid (TCA), and a new by-product tauroursocholic acid (TUCA) will be produced, having [...] Read more.

7α-Hydroxysteroid dehydrogenase (7α-HSDH) plays an important role in the biosynthesis of tauroursodeoxycholic acid (TUDCA) using complex substrate chicken bile powder as raw material. However, chicken bile powder contains 4.74% taurocholic acid (TCA), and a new by-product tauroursocholic acid (TUCA) will be produced, having the risk of causing colorectal cancer. Here, we obtained a novel NADP(H)-dependent 7α-HSDH with good thermostability from Ursus thibetanus gut microbiota (named St-2-2). St-2-2 could catalyze taurochenodeoxycholic acid (TCDCA) and TCA with the catalytic activity of 128.13 and 269.39 U/mg, respectively. Interestingly, by a structure-based C-terminal truncation strategy, St-2-2△C10 only remained catalytic activity on TCDCA (14.19 U/mg) and had no activity on TCA. As a result, it can selectively catalyze TCDCA in waste chicken bile powder. MD simulation and structural analysis indicated that enhanced surface hydrophilicity and improved C-terminal rigidity affected the entry and exit of substrates. Hydrogen bond interactions between different subunits and interaction changes in Phe249 of the C-terminal loop inverted the substrate catalytic activity. This is the first report on substrate selectivity of 7α-HSDH by C-terminal truncation strategy and it can be extended to other 7α-HSDHs (J-1-1, S1-a-1). Full article

(This article belongs to the Topic Advances in Enzymes and Protein Engineering)

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18 pages, 5029 KiB

Open AccessArticle

Ag-Mn_xO_y on Graphene Oxide Derivatives as Oxygen Reduction Reaction Catalyst in Alkaline Direct Ethanol Fuel Cells

by Sigrid Wolf, Michaela Roschger, Boštjan Genorio, Mitja Kolar, Daniel Garstenauer, Brigitte Bitschnau and Viktor Hacker

Catalysts 2022, 12(7), 780; https://doi.org/10.3390/catal12070780 - 14 Jul 2022

Cited by 14 | Viewed by 2201

Abstract

In this study, Ag-Mn_xO_y/C composite catalysts deposited on reduced graphene oxide (rGO) and, for the first time on N-doped graphene oxide (NGO), were prepared via a facile synthesis method. The influence of the carbon support material on the activity [...] Read more.

In this study, Ag-Mn_xO_y/C composite catalysts deposited on reduced graphene oxide (rGO) and, for the first time on N-doped graphene oxide (NGO), were prepared via a facile synthesis method. The influence of the carbon support material on the activity and stability of the oxygen reduction reaction (ORR) and on the tolerance to ethanol in alkaline medium was focused and investigated. The physicochemical properties of the Ag-Mn_xO_y/C catalysts were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) method, atomic absorption spectroscopy (AAS), inductively coupled plasma-mass spectrometry (ICP-MS), and thermogravimetric gas analysis (TGA). Electrochemical characterization was performed by rotating disk electrode (RDE) experiments. The results show that the active manganese species MnO₂ was assembled as nanorods and nanospheres on rGO and NGO, respectively. Ag was assumed to be present as very small or amorphous particles. Similar redox processes for Ag-Mn_xO_y/rGO and Ag-Mn_xO_y/NGO were examined via cyclic voltammetry. The Ag-Mn_xO_y/rGO resulted in a more negative diffusion limiting current density of −3.01 mA cm⁻² compared to Ag-Mn_xO_y/NGO. The onset potential of approximately 0.9 V vs. RHE and the favored 4-electron transfer pathway were independent of the support material. Ag-Mn_xO_y/NGO exhibited a higher ORR stability, whereas Ag-Mn_xO_y/rGO showed a better ethanol tolerance. Full article

(This article belongs to the Section Electrocatalysis)

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17 pages, 5792 KiB

Open AccessArticle

Employing an Artificial Neural Network in Correlating a Hydrogen-Selective Catalytic Reduction Performance with Crystallite Sizes of a Biomass-Derived Bimetallic Catalyst

by Ibrahim Yakub, Ahmad Beng Hong Kueh, Edwin Andres Pineda De La O, Md. Rezaur Rahman, Mohamad Hardyman Barawi, Mohammad Omar Abdullah, Mugahed Amran, Roman Fediuk and Nikolai Ivanovich Vatin

Catalysts 2022, 12(7), 779; https://doi.org/10.3390/catal12070779 - 14 Jul 2022

Cited by 11 | Viewed by 1573

Abstract

A predictive model correlating the properties of a catalyst with its performance would be beneficial for the development, from biomass waste, of new, carbon-supported and Earth-abundant metal oxide catalysts. In this work, the effects of copper and iron oxide crystallite size on the [...] Read more.

A predictive model correlating the properties of a catalyst with its performance would be beneficial for the development, from biomass waste, of new, carbon-supported and Earth-abundant metal oxide catalysts. In this work, the effects of copper and iron oxide crystallite size on the performance of the catalysts in reducing nitrogen oxides, in terms of nitrogen oxide conversion and nitrogen selectivity, are investigated. The catalysts are prepared via the incipient wetness method over activated carbon, derived from palm kernel shells. The surface morphology and particle size distribution are examined via field emission scanning electron microscopy, while crystallite size is determined using the wide-angle X-ray scattering and small-angle X-ray scattering methods. It is revealed that the copper-to-iron ratio affects the crystal phases and size distribution over the carbon support. Catalytic performance is then tested using a packed-bed reactor to investigate the nitrogen oxide conversion and nitrogen selectivity. Departing from chemical characterization, two predictive equations are developed via an artificial neural network technique—one for the prediction of NO_x conversion and another for N₂ selectivity. The model is highly applicable for 250–300 °C operating temperatures, while more data are required for a lower temperature range. Full article

(This article belongs to the Section Biomass Catalysis)

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13 pages, 4360 KiB

Open AccessArticle

Lignin-Derived Ternary Polymeric Carbon as a Green Catalyst for Ethyl Levulinate Upgrading from Fructose

by Dayong Yu, Xiaofang Liu, Hangyu Luo, Jinshu Huang and Hu Li

Catalysts 2022, 12(7), 778; https://doi.org/10.3390/catal12070778 - 14 Jul 2022

Viewed by 1330

Abstract

Currently, the utilization of lignocellulose mainly focuses on the conversion of polysaccharide components to value-added chemicals, such as ethyl levulinate (EL). Lignin is an important component of lignocellulosic biomass that is often neglected. Herein, ternary polymeric carbon (TPC–S) was synthesized by polymerization of [...] Read more.

Currently, the utilization of lignocellulose mainly focuses on the conversion of polysaccharide components to value-added chemicals, such as ethyl levulinate (EL). Lignin is an important component of lignocellulosic biomass that is often neglected. Herein, ternary polymeric carbon (TPC–S) was synthesized by polymerization of mixed monomers (4-methylphenol, 4-ethylphenol, and 4-propylphenol) derived from lignin and subsequent sulfonation, which was used as a heterogeneous catalyst for the transformation of fructose to EL. Through a series of characterization methods, it was illustrated that the prepared catalyst had a layered porous structure. The calculated carbon layer spacing is 0.413 nm, and the average pore size is 5.1 nm. This structure greatly increases the specific surface area (165.2 m²/g) of the catalyst, which makes it possible to introduce more –SO₃H species in the process of sulfonation, thus furnishing EL with increased yield. The effects of reaction temperature, time, catalyst dosage, and fructose initial concentration on the production of EL were investigated. It was found that 70.3% EL yield was detected at 130 °C for 10 h. In addition, the catalyst had good stability and could obtain 65.6% yield of EL in the fourth cycle. The obtained catalyst has the advantages of low cost, easy preparation, and high catalytic efficiency, which is expected to achieve efficient utilization of lignin and provide a potential solution for the future production of EL. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Valorization of Lignocellulosic Biomass II)

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11 pages, 2799 KiB

Open AccessArticle

Stable Nickel-Based Metal–Organic Framework Containing Thiophene/Diimidazole Units for Effective Near-Infrared Photothermal Conversion

by Xiangran Pei, Lilong Dang, Tingting Zhang, Tian Chen, Fuxuan Ren and Shuiren Liu

Catalysts 2022, 12(7), 777; https://doi.org/10.3390/catal12070777 - 13 Jul 2022

Cited by 2 | Viewed by 1603

Abstract

Herein, a new Ni-based metal–organic framework (MOF, 1) bearing highly structural stability is synthesized by the reaction of utilizing a rigid and functionalized linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo[1,2-d:4,5-d′]diimidazole (BBI4PY), in combination with Ni(NO₃)₂·6H₂O and dibenzo[b,d]thiophene-3,7-dicarboxylic acid 5,5-dioxide [...] Read more.

Herein, a new Ni-based metal–organic framework (MOF, 1) bearing highly structural stability is synthesized by the reaction of utilizing a rigid and functionalized linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo[1,2-d:4,5-d′]diimidazole (BBI4PY), in combination with Ni(NO₃)₂·6H₂O and dibenzo[b,d]thiophene-3,7-dicarboxylic acid 5,5-dioxide (L1) under solvothermal conditions. The crystal structure of complex 1 is determined by single-crystal X-ray diffraction and is demonstrated to be a two-dimensional layered structure. In addition, PXRD, IR, TGA and UV/Vis-NIR spectra are also tested carefully to explore the solid structure of this complex. Remarkably, although no significant accumulation effect could be observed between the two-dimensional layers, a stacking interaction between DMF solvent molecules and ligand L1 could be found, which might promote non-radiative transitions and trigger obvious near-infrared photothermal conversion. Under 660 nm laser (0.6 W cm⁻²) illumination, the temperature of complex 1 increased rapidly from room temperature to 45.2 °C, with good thermal stability and cycle durability. Its photothermal conversion efficiency could reach 10.75%. This work provides an efficient way for assessing the promise of materials in the field of photothermal therapy. Full article

(This article belongs to the Special Issue MOFs Catalyst for Energy-Related Reactions)

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28 pages, 5634 KiB

Open AccessArticle

Mixture of Sludge and Chicken Manure in Membrane-Less Microbial Fuel Cell for Simultaneous Waste Treatment and Energy Recovery

by Nurul Najwa Adam Malik, Muhammad Najib Ikmal Mohd Sabri, Husnul Azan Tajarudin, Noor Fazliani Shoparwe, Hafiza Shukor, Muaz Mohd Zaini Makhtar, Syed Zaghum Abbas, Yang-Chun Yong and Mohd Rafatullah

Catalysts 2022, 12(7), 776; https://doi.org/10.3390/catal12070776 - 13 Jul 2022

Cited by 2 | Viewed by 1557

Abstract

In addition to disposal issues, the abundance of sludge and chicken manure has been a rising issue in Malaysia. Membrane-less microbial fuel cell (ML-MFC) technology can be considered as one of the potential solutions to the issues of disposal and electricity generation. However, [...] Read more.

In addition to disposal issues, the abundance of sludge and chicken manure has been a rising issue in Malaysia. Membrane-less microbial fuel cell (ML-MFC) technology can be considered as one of the potential solutions to the issues of disposal and electricity generation. However, there is still a lack of information on the performance of an ML-MFC powered by sludge and chicken manure. Hence, with this project, we studied the performance of an ML-MFC supplemented with sludge and chicken manure, and its operating parameters were optimized using response surface methodology (RSM) through central composite design (CCD). The optimum operating parameters were determined to be 35 °C, 75% moisture content, and an electrode distance of 3 cm. Correspondingly, the highest power density, COD removal efficiency, and biomass acquired through this study were 47.2064 mW/m², 98.0636%, and 19.6730 mg/L, respectively. The obtained COD values for dewatered sludge and chicken manure were 708 mg/L and 571 mg/L, respectively. COD values were utilized as a standard value for the substrate degradation by Bacillus subtilis in the ML-MFC. Through proximate analyses conducted by elemental analysis and atomic absorption spectrometry (AAS), the composition of carbon and magnesium for sludge and chicken manure was23.75% and 34.20% and 78.1575 mg/L and 71.6098 mg/L, respectively. The proposed optimal RSM parameters were assessed and validated to determine the ML-MFC operating parameters to be optimized by RSM (CCD). Full article

(This article belongs to the Special Issue Biocatalysts Advancement for Optimum Performance in Microbial Fuel Cells and Their Sub-types)

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14 pages, 8719 KiB

Open AccessArticle

Excellent Catalytic Performance of Ce–MOF with Abundant Oxygen Vacancies Supported Noble Metal Pt in the Oxidation of Toluene

by Yang Liu, Gongda Chen, Jianjun Chen and Hejingying Niu

Catalysts 2022, 12(7), 775; https://doi.org/10.3390/catal12070775 - 13 Jul 2022

Cited by 13 | Viewed by 2906

Abstract

Metal organic framework (MOF) is a type of porous organic material. In this work, three catalysts loaded with noble metal Pt were prepared by NaBH₄ reduction method with three different morphologies of Ce–MOF as carriers. Their physicochemical properties were characterized by XRD, [...] Read more.

Metal organic framework (MOF) is a type of porous organic material. In this work, three catalysts loaded with noble metal Pt were prepared by NaBH₄ reduction method with three different morphologies of Ce–MOF as carriers. Their physicochemical properties were characterized by XRD, Raman, FTIR, N₂ adsorption, SEM, XPS, and TGA. The catalytic performances of different catalysts were evaluated via toluene oxidation and CO₂ selectivity. Rod–shaped Pt/MOF–BTC exhibited best catalytic performance compared to Pt/MOF–808 and Pt/UiO–66, its T₅₀ and T₉₀ were 140 °C and 149 °C, respectively. After deducting the effect of specific surface, Pt/MOF–BTC still had the lowest apparent activation energy (62.8 kJ·mol⁻¹), which is due to the abundant atomic Pt and oxygen vacancy content on its surface. After the reaction, the structure of Pt/MOF–BTC may become amorphous according to XRD results. Furthermore, the presence of amorphous structure had no effect on the catalytic activity of the catalyst. In the stability test of Pt/MOF–BTC to toluene oxidation, both toluene conversion and CO₂ selectivity remained at 100%, and remained stable for 11 h. Moreover, Pt/MOF–BTC also had better resistance to high weight hourly space velocity (WHSV) or water resistance. The catalyst maintained high catalytic activity for 3 times reusability. This study provides valuable experience for the future work of MOF in the field of VOC catalytic oxidation. Full article

(This article belongs to the Section Catalytic Materials)

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15 pages, 4102 KiB

Open AccessArticle

Degradation of Tetracycline Hydrochloride by a Novel CDs/g-C₃N₄/BiPO₄ under Visible-Light Irradiation: Reactivity and Mechanism

by Wei Qian, Wangtong Hu, Zhifei Jiang, Yongyi Wu, Zihuan Li, Zenghui Diao and Mingyu Li

Catalysts 2022, 12(7), 774; https://doi.org/10.3390/catal12070774 - 13 Jul 2022

Cited by 6 | Viewed by 1678

Abstract

In recent years, with the large-scale use of antibiotics, the pollution of antibiotics in the environment has become increasingly serious and has attracted widespread attention. In this study, a novel CDs/g-C₃N₄/BiPO₄ (CDBPC) composite was successfully synthesized by a [...] Read more.

In recent years, with the large-scale use of antibiotics, the pollution of antibiotics in the environment has become increasingly serious and has attracted widespread attention. In this study, a novel CDs/g-C₃N₄/BiPO₄ (CDBPC) composite was successfully synthesized by a hydrothermal method for the removal of the antibiotic tetracycline hydrochloride (TC) in water. The experimental results showed that the synthesized photocatalyst was crystalline rods and cotton balls, accompanied by overlapping layered nanosheet structures, and the specific surface area was as high as 518.50 m²/g. This photocatalyst contains g-C₃N₄ and bismuth phosphate (BiPO₄) phases, as well as abundant surface functional groups such as C=N, C-O, and P-O. When the optimal conditions were pH 4, CDBPC dosage of 1 g/L, and TC concentration of 10 mg/L, the degradation rate of TC reached 75.50%. Active species capture experiments showed that the main active species in this photocatalytic system were holes (h⁺), hydroxyl radicals, and superoxide anion radicals. The reaction mechanism for the removal of TC by CDBPC was also proposed. The removal of TC was mainly achieved by the synergy between the adsorption of CDBPC and the oxidation of both holes and hydroxyl radicals. In this system, TC was adsorbed on the surface of CDBPC, and then the adsorbed TC was degraded into small molecular products by an attack with holes and hydroxyl radicals and finally mineralized into carbon dioxide and water. This study indicated that this novel photocatalyst CDBPC has a huge potential for antibiotic removal, which provides a new strategy for antibiotic treatment of wastewater. Full article

(This article belongs to the Special Issue New Insights into Novel Catalysts for Treatment of Pollutants in Wastewater)

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