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Catalysts, Volume 13, Issue 11 (November 2023) – 66 articles

Cover Story (view full-size image): GH11 xylanases play an essential role in sugar metabolism and are one of the most widely used enzymes in various industries, such as pulp and paper, food and feed, biorefinery, textile, and pharmaceutical industries. pH is a crucial factor influencing the biochemical properties of GH11 xylanase and its application in bioprocessing. This review provides an overview of recent advancements in the characterization and engineering of GH11 xylanases, providing a guide for future research in this field. View this paper
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27 pages, 10357 KiB  
Review
Co3O4 Catalysts for Complete Toluene Oxidation: Review including Meta-Analysis of Catalyst Activity Data
Catalysts 2023, 13(11), 1454; https://doi.org/10.3390/catal13111454 - 20 Nov 2023
Viewed by 838
Abstract
Designing highly active catalysts for the oxidation of volatile organic compounds (VOCs) involves fine-tuning the catalytic surface and improving its interaction with VOCs. The present review assesses various studies conducted in the last decade on Co3O4 catalysts for the complete [...] Read more.
Designing highly active catalysts for the oxidation of volatile organic compounds (VOCs) involves fine-tuning the catalytic surface and improving its interaction with VOCs. The present review assesses various studies conducted in the last decade on Co3O4 catalysts for the complete oxidation of toluene (C7H8) and provides information on the synthesis and physicochemical characterization of these catalysts. Taking this one step further, data from the literature were carefully chosen for an extensive meta-analysis aiming at elucidating the structure sensitivity of toluene oxidation over Co3O4 catalysts. Specifically, the specific reaction rate was calculated and correlated with the physicochemical properties of the catalysts, namely, the specific surface area, faceting, and Co3+/Co2+ ratio. Based on this analysis, the specific surface area does not exert a significant impact on the specific activity of Co3O4 catalysts for the total oxidation of toluene. Instead, the specific reaction rates are influenced by the morphology, surface concentration, exposed crystallographic planes, and oxidation state of cobalt cations. These factors determine the catalyst’s specific activity by creating defects, oxygen vacancies, or oxygen species with different reactivities. It was also found that a high surface Co3+/Co2+ ratio is necessary for achieving high catalytic performance in the oxidation of VOCs. Full article
(This article belongs to the Section Catalytic Materials)
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19 pages, 2873 KiB  
Article
Ni-BaMnO3 Perovskite Catalysts for NOx-Assisted Soot Oxidation: Analyzing the Effect of the Nickel Addition Method
Catalysts 2023, 13(11), 1453; https://doi.org/10.3390/catal13111453 - 20 Nov 2023
Viewed by 749
Abstract
In this study, we analyzed the role of a series of BaMn1−xNixO3 (x = 0, 0.2, and 0.4) mixed oxide catalysts, synthesized using the sol–gel method, in NOx-assisted diesel soot oxidation. ICP-OES, XRD, XPS, and H [...] Read more.
In this study, we analyzed the role of a series of BaMn1−xNixO3 (x = 0, 0.2, and 0.4) mixed oxide catalysts, synthesized using the sol–gel method, in NOx-assisted diesel soot oxidation. ICP-OES, XRD, XPS, and H2-TPR techniques were used for characterization and Temperature-Programmed Reaction experiments (NOx-TPR and Soot-NOx-TPR), and isothermal reactions at 450 °C (for the most active sample) were carried out to determine the catalytic activity. All samples catalyzed NO and soot oxidation at temperatures below 400 °C, presenting nickel-containing catalysts with the highest soot conversion and selectivity to CO2. However, the nickel content did not significantly modify the catalytic performance, and in order to improve it, two catalysts (5 wt % in Ni) were synthesized via the hydrothermal method (BMN2H) and the impregnation of nickel on a BaMnO3 perovskite as support (M5). The two samples presented higher activity for NO and soot oxidation than BMN2E (obtained via the sol–gel method) as they presented more nickel on the surface (as determined via XPS). BMN2H was more active than M5 as it presented (i) more surface oxygen vacancies, which are active sites for oxidation reactions; (ii) improved redox properties; and (iii) a lower average crystal size for nickel (as NiO). As a consequence of these properties, BMN2H featured a high soot oxidation rate at 450 °C, which hindered the accumulation of soot during the reaction and, thus, the deactivation of the catalyst. Full article
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26 pages, 5995 KiB  
Review
Catalysis for CO2 Hydrogenation—What We Have Learned/Should Learn from the Hydrogenation of Syngas to Methanol
Catalysts 2023, 13(11), 1452; https://doi.org/10.3390/catal13111452 - 20 Nov 2023
Cited by 1 | Viewed by 1251
Abstract
This short review provides an in-depth analysis of the achievements and further developments of the catalytic hydrogenation of carbon dioxide (CO2) to methanol from those that are worth learning about based on the transformation of syngas into methanol. We begin by [...] Read more.
This short review provides an in-depth analysis of the achievements and further developments of the catalytic hydrogenation of carbon dioxide (CO2) to methanol from those that are worth learning about based on the transformation of syngas into methanol. We begin by exploring the environmental and energy-related implications of utilizing CO2 as a feedstock for methanol production by emphasizing its potential to mitigate greenhouse gas emissions and facilitate renewable energy integration. Then, different catalytic formulations focusing on precious metals, copper-based catalysts, and metal oxides are summarized, and insights into their advantages and limitations in the aspects of catalytic activity, selectivity, and stability are discussed. Precious metal catalysts, such as platinum and iridium, exhibit high activity but are cost-prohibitive, while copper-based catalysts present a promising and cost-effective alternative. Metal oxides are considered for their unique properties in CO2 activation. Mechanistic insights into reaction pathways are explored, with a particular emphasis on copper-based catalysts. Moreover, the complex steps involved in CO2 hydrogenation to methanol are discussed to shed light on the key intermediates and active sites responsible for catalysis, which is crucial for catalyst design and optimization. Finally, we stress the importance of ongoing research and development efforts to enhance catalyst efficiency, mechanistic comprehension, and process optimization. This review serves as a valuable resource for researchers, engineers, and policymakers working toward a more sustainable and carbon-neutral energy future. By harnessing CO2 as a carbon feedstock for methanol synthesis, we have the potential to address environmental concerns and advance the utilization of renewable energy sources, further contributing to the transition to a cleaner and more sustainable energy landscape. Full article
(This article belongs to the Special Issue Catalysis for Selective Hydrogenation of CO and CO2)
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4 pages, 212 KiB  
Editorial
Metal-Based Aerogels and Porous Composites as Efficient Catalysts: Synthesis and Catalytic Performance
Catalysts 2023, 13(11), 1451; https://doi.org/10.3390/catal13111451 - 20 Nov 2023
Viewed by 752
Abstract
Faced with the threat of energy shortage and environment pollution in modern society, the development of efficient and cost-effective catalytic systems is becoming increasingly important [...] Full article
15 pages, 4299 KiB  
Article
S-Scheme WO3/SnIn4S8 Heterojunction for Water Purification: Enhanced Photocatalytic Performance and Mechanism
Catalysts 2023, 13(11), 1450; https://doi.org/10.3390/catal13111450 - 20 Nov 2023
Viewed by 892
Abstract
Photocatalysis is a promising technology for removing micropollutants in water. However, developing efficient and stable catalysts remains a challenge. In this work, a novel step-scheme (S-scheme) heterojunction of WO3/SnIn4S8 (WSI) was constructed through the combined process of in [...] Read more.
Photocatalysis is a promising technology for removing micropollutants in water. However, developing efficient and stable catalysts remains a challenge. In this work, a novel step-scheme (S-scheme) heterojunction of WO3/SnIn4S8 (WSI) was constructed through the combined process of in situ precipitation with hydrothermal synthesis to simultaneously realize photocatalytic degradation of bisphenol A(BPA) and reduction of Cr(VI) in contaminated water. Results showed that the WSI S-scheme heterojuction has a synergistic effect for the removal of BPA and Cr(VI). An optimum case of the WSI-12% heterojunction exhibited the highest photocatalytic efficiency in the degradation of BPA under visible light, which is ca. 2.5 and 3.8 times more than the pure WO3 and SIS, respectively. The enhanced photocatalytic activity is attributed to the formation of the WSI S-scheme heterojunctions which facilitate the spatial separation of charge carriers and preserve strong photoredox ability. Further, the S-scheme mechanism of enhanced photocatalysis was examined by the radical-trapping experiment and ESR, and superoxide and hydroxyl radicals were determined to be the major reactive oxygen species responsible for BPA degradation and Cr(VI) reduction by WSI. This work provides a novel strategy for tailoring high-performance S-scheme heterojunctions and shows the promising application in purifying wastewater with complex pollutants. Full article
(This article belongs to the Topic Advanced Oxidation Processes for Wastewater Purification)
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12 pages, 2456 KiB  
Article
Organically Functionalized Porous Aluminum Phosphonate for Efficient Synthesis of 5-Hydroxymethylfurfural from Carbohydrates
Catalysts 2023, 13(11), 1449; https://doi.org/10.3390/catal13111449 - 19 Nov 2023
Viewed by 843
Abstract
Naturally occurring fossil fuels are the major resource of energy in our everyday life, but with the huge technological development over the years and subsequent energy demand, the reserve of this energy resource is depleting at an alarming rate, which will challenge our [...] Read more.
Naturally occurring fossil fuels are the major resource of energy in our everyday life, but with the huge technological development over the years and subsequent energy demand, the reserve of this energy resource is depleting at an alarming rate, which will challenge our net energy resources in the near future. Thus, an alternative sustainable energy resource involving biomass and bio-refinery has become the most emerging and demanding approach, where biofuels can be derived effectively from abundant biomass via valuable chemical intermediates like 5-hydroxymethylfurfural (5-HMF). 5-HMF is a valuable platform chemical for the synthesis of fuel and fine chemicals. Herein, we report the synthesis of the organically functionalized porous aluminum phosphonate materials: Ph-ALPO-1 in the absence of any template and Ph-ALPO-2 by using 1,3-diaminopropane-N,N,N′,N′-tetraacetic acid as a small organic molecule template and phenylphosphonic acid as a phosphate source. These hybrid phosphonates are used as acid catalysts for the synthesis of 5-HMF from carbohydrates derived from biomass resources. These Ph-ALPO-1 and Ph-ALPO-2 materials catalyzed the dehydration of fructose to 5-HMF with total yields of 74.6% and 90.7%, respectively, in the presence of microwave-assisted optimized reaction conditions. Full article
(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts, 2nd Edition)
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24 pages, 1866 KiB  
Review
Green Synthesis of Biocatalysts Based on Nanocarriers Promises an Effective Role in Pharmaceutical and Biomedical Fields
Catalysts 2023, 13(11), 1448; https://doi.org/10.3390/catal13111448 - 17 Nov 2023
Cited by 2 | Viewed by 906
Abstract
Nanobiocatalysts (NBCs) are a promising new class of biocatalysts that combine the advantages of enzymes and nanomaterials. Enzymes are biological catalysts that are highly selective and efficient, but they can be unstable in harsh environments. Nanomaterials, on the other hand, are small particles [...] Read more.
Nanobiocatalysts (NBCs) are a promising new class of biocatalysts that combine the advantages of enzymes and nanomaterials. Enzymes are biological catalysts that are highly selective and efficient, but they can be unstable in harsh environments. Nanomaterials, on the other hand, are small particles with unique properties that can improve the stability, activity, and selectivity of enzymes. The development of NBCs has been driven by the need for more sustainable and environmentally friendly bioprocessing methods. Enzymes are inherently green catalysts, but they can be expensive and difficult to recover and reuse. NBCs can address these challenges by providing a stable and reusable platform for enzymes. One of the key challenges in the development of NBCs is the immobilization of enzymes on nanomaterials. Enzyme immobilization is a process that attaches enzymes to a solid support, which can protect the enzymes from harsh environments and make them easier to recover and reuse. There are many different methods for immobilizing enzymes, and the choice of method depends on the specific enzyme and nanomaterial being used. This review explores the effective role of NBCs in pharmaceutical and biomedical fields. Full article
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13 pages, 1414 KiB  
Article
Efficient Synthesis of 2-Aminoquinazoline Derivatives via Acid-Mediated [4+2] Annulation of N-Benzyl Cyanamides
Catalysts 2023, 13(11), 1447; https://doi.org/10.3390/catal13111447 - 17 Nov 2023
Viewed by 608
Abstract
The synthesis of 2-aminoquinazoline derivatives is achieved by using hydrochloric acid as a mediator in the [4+2] annulation reaction between N-benzyl cyanamides and 2-amino aryl ketones. In addition, 2-amino-4-iminoquinazolines are synthesized by the reaction of 2-aminobenzonitriles, instead of 2-amino aryl ketones, with [...] Read more.
The synthesis of 2-aminoquinazoline derivatives is achieved by using hydrochloric acid as a mediator in the [4+2] annulation reaction between N-benzyl cyanamides and 2-amino aryl ketones. In addition, 2-amino-4-iminoquinazolines are synthesized by the reaction of 2-aminobenzonitriles, instead of 2-amino aryl ketones, with N-benzyl cyanamides. A wide range of substrates can be used and high yields are obtained, demonstrating the practicality of this method for the synthesis of 2-aminoquinazoline derivatives. Full article
(This article belongs to the Special Issue Catalytic Annulation Reactions)
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20 pages, 5044 KiB  
Review
Comprehensive Review on Multifaceted Carbon Dot Nanocatalysts: Sources and Energy Applications
Catalysts 2023, 13(11), 1446; https://doi.org/10.3390/catal13111446 - 16 Nov 2023
Viewed by 1061
Abstract
In recent decades, several studies have been conducted on sustainability progress with high efficiency of renewable energies by utilizing advanced nano-module catalysts. Some collaborative studies advocate the unique characteristics of unconventional materials, including carbon nanotubes, nanosheets, nanoparticles, conducting polymers, integrated nano polymers, nano [...] Read more.
In recent decades, several studies have been conducted on sustainability progress with high efficiency of renewable energies by utilizing advanced nano-module catalysts. Some collaborative studies advocate the unique characteristics of unconventional materials, including carbon nanotubes, nanosheets, nanoparticles, conducting polymers, integrated nano polymers, nano enzymes, and zero-dimensional nanomaterials/carbon dots (CDs) at the atomic and molecular level to generate efficient energy from various biomass substrates. Nanotechnology-based catalysts are considered a crucial tool for revolutionizing various energy-related applications. This review article addresses the sustainable and scarce biomass resources to synthesize CDs, properties, mechanisms, and insights with the advancement of research on CDs as nanocatalysts in the field of energy applications. These materials possess exceptional and rapidly expanding features such as being non-toxic, biocompatible, having excellent electrocatalytic activity and photoluminescence, and being highly dispersible in water. Because of these advantages, they are appealing for use in energy conversion and as storage material. Moreover, the emphasis is placed on the function of CDs as nanocatalysts for energy storage devices, and relevant instances are provided to clarify the concepts. These advanced strategies of nanotechnology for energy storage and conversion are expected to play a vital role in promoting sustainability. Full article
(This article belongs to the Special Issue Nanotechnology in Catalysis, 2nd Edition)
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13 pages, 4536 KiB  
Communication
Phenomenal Insight into Electrochemically Induced Photocatalytic Degradation of Nitrobenzene on Variant Au-Modified TiO2 Nanotubes
Catalysts 2023, 13(11), 1445; https://doi.org/10.3390/catal13111445 - 16 Nov 2023
Viewed by 663
Abstract
TiO2 nanotubes are a prominent type of TiO2-based nanostructure compared to nanorod arrays. A promising way to improve photocatalytic performance is modifying TiO2 nanotubes with metals, either on the surface or inside the tubes. There is a substantial demand [...] Read more.
TiO2 nanotubes are a prominent type of TiO2-based nanostructure compared to nanorod arrays. A promising way to improve photocatalytic performance is modifying TiO2 nanotubes with metals, either on the surface or inside the tubes. There is a substantial demand for enhancing the conductivity and charge separation of TiO2 nanotubes, with a major focus on gold (Au) modification. Gold (Au) coatings have significantly improved the photocatalytic activity of TiO2 nanotubes, particularly in pollutant oxidation. However, the mechanism underlying the action of Au-modified TiO2 nanotubes in photocatalytic nitrobenzene oxidation under electrochemical induction remains unclear. Therefore, we conducted related experiments to explore the optimal Au concentration under various conditions. Under electric field induction, the maximum removal rate achieved was 54.9%. Lastly, we analyzed the relevant photocatalytic mechanism to elucidate the responses of electrons and holes to a simulated contaminant under a photo-electrochemical field. Full article
(This article belongs to the Section Photocatalysis)
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16 pages, 2855 KiB  
Article
Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO2
Catalysts 2023, 13(11), 1444; https://doi.org/10.3390/catal13111444 - 15 Nov 2023
Viewed by 825
Abstract
The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during [...] Read more.
The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during the reaction were investigated. The photocatalytic WGSR rate under light excitation with wavelengths extending from 320 to 1100 nm was found to be higher than the thermal reaction alone at the same temperature (85 °C). A H2/CO2 ratio of near unity was found at high concentrations of CO. The addition of molecular oxygen during the reaction resulted in a slight decrease in molecular hydrogen production, while the rates of CO2 formation and CO consumption changed by one order of magnitude. More importantly, it was found that the WGSR rates were still high under only visible light excitation (600–700 nm). The results prove that Au LSP alone triggers this chemical reaction without requiring the excitation of the semiconductor on which they are deposited. Full article
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23 pages, 3768 KiB  
Article
Catalytic Ability of K- and Co-Promoted Oxo-Re and Oxo-ReMo Nanosized Compositions for Water–Gas Shift Reaction
Catalysts 2023, 13(11), 1443; https://doi.org/10.3390/catal13111443 - 15 Nov 2023
Viewed by 796
Abstract
The water–gas shift (WGS) reaction (CO + H2O ↔ CO2 + H2) plays an important role in the hydrogen economy because it is an effective way to reduce the carbon release to net-zero CO2 emissions. The general [...] Read more.
The water–gas shift (WGS) reaction (CO + H2O ↔ CO2 + H2) plays an important role in the hydrogen economy because it is an effective way to reduce the carbon release to net-zero CO2 emissions. The general goal of this research is to develop nanosized oxo-rhenium catalyst formulations promoted by K and Co components for the WGS process. Rhenium, as a low-cost catalyst component, is a good choice compared to platinum group metals. A surface density of 2 Re atoms/nm2 on a γ-Al2O3 support as well as cobalt (3 wt.% CoO) and potassium (5 wt.% K2O) amounts were chosen to match the composition of our own active sour WGS KCoRe catalyst developed some years ago. An initial evaluation of the impact of replacing half of the rhenium with molybdenum, which is more affordable, was also studied. The purpose of this study is to explore the catalytic ability of CoRe, K-CoRe, CoReMo, and K-CoReMo formulations in the WGS reaction and elucidate the effect of a CO/Ar reaction mixture used in an activation–reduction pretreatment to form active catalyst structures. Oxo-K-Co-Re(Mo) entities formed in synthesized samples and their reducibility were analyzed via several physicochemical methods, such as N2 physisorption, PXRD, UV-vis DRS, and H2-TPR. In summary, the selected potassium- and cobalt-promoted Re-containing formulations have potential as catalysts for the classical WGS reaction. The selection of an appropriate procedure for activation–reduction, involving the reducing gas (CO or H2), temperature, and duration, was needed for tuning the K-CoRe catalyst’s high activity for the WGS reaction with structural stability and longevity. Full article
(This article belongs to the Special Issue Advances in Catalysts for Water-Gas Shift Reaction)
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4 pages, 178 KiB  
Editorial
Novel Photo(electro)catalysts for Energy and Environmental Applications
Catalysts 2023, 13(11), 1442; https://doi.org/10.3390/catal13111442 - 15 Nov 2023
Viewed by 750
Abstract
Photo(electro)catalysis is regarded as one of the most promising approaches to addressing energy and environmental issues and thus achieving the sustainable development of human society; as such, various catalytic materials have been developed in recent decades [...] Full article
21 pages, 4893 KiB  
Review
Chiral Catalysts for the Enantioselective Carbon Dioxide-Based Cyclic Carbonates and Polycarbonates
Catalysts 2023, 13(11), 1441; https://doi.org/10.3390/catal13111441 - 14 Nov 2023
Viewed by 892
Abstract
Using carbon dioxide as a feedstock for synthesizing organic molecules with added value can contribute to a more sustainable chemical industry since CO2 is an abundant, inexpensive, and nontoxic renewable carbon resource. In this regard, the synthesis of cyclic carbonates and related [...] Read more.
Using carbon dioxide as a feedstock for synthesizing organic molecules with added value can contribute to a more sustainable chemical industry since CO2 is an abundant, inexpensive, and nontoxic renewable carbon resource. In this regard, the synthesis of cyclic carbonates and related organic compounds from CO2 as building blocks has been widely studied, and less attention has been paid to their stereocontrolled process. Therefore, this review focuses on the recent development of enantioselective catalysts for the CO2-mediated formation of chiral organic carbonates. Full article
(This article belongs to the Special Issue Catalysis for Reducing Carbon Footprint and Environmental Impacts)
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47 pages, 6925 KiB  
Review
Review on Recent Advances in the Removal of Organic Drugs by Advanced Oxidation Processes
Catalysts 2023, 13(11), 1440; https://doi.org/10.3390/catal13111440 - 14 Nov 2023
Viewed by 977
Abstract
In recent years, due to the high consumption of drugs both for human needs and for their growing use, especially as regards antibiotics, in the diet of livestock, water pollution has reached very high levels and attracted widespread attention. Drugs have a stable [...] Read more.
In recent years, due to the high consumption of drugs both for human needs and for their growing use, especially as regards antibiotics, in the diet of livestock, water pollution has reached very high levels and attracted widespread attention. Drugs have a stable chemical structure and are recalcitrant to many treatments, especially biological ones. Among the methods that have shown high efficiency are advanced oxidation processes (AOPs) which are, among other things, inexpensive and eco-friendly. AOPs are based on the production of reactive oxygen species (ROS) able to degrade organic pollutants in wastewater. The main problem related to the degradation of drugs is their partial oxidation to compounds that are often more harmful than their precursors. In this review, which is not intended to be exhaustive, we provide an overview of recent advances in the removal of organic drugs via advanced oxidation processes (AOPs). The salient points of each process, highlighting advantages and disadvantages, have been summarized. In particular, the use of AOPs such as UV, ozone, Fenton-based AOPs and heterogeneous photocatalysis in the removal of some of the most common drugs (tetracycline, ibuprofen, oxytetracycline, lincomycin) has been reported. Full article
(This article belongs to the Special Issue Environmental Catalysis in Advanced Oxidation Processes, 2nd Edition)
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32 pages, 3029 KiB  
Review
Recent Developments in Lignocellulosic Biofuel Production with Nanotechnological Intervention: An Emphasis on Ethanol
Catalysts 2023, 13(11), 1439; https://doi.org/10.3390/catal13111439 - 14 Nov 2023
Viewed by 1227
Abstract
Biofuel, an inexhaustible fuel source, plays a pivotal role in the contemporary era by diminishing the dependence on non-renewable energy sources and facilitating the mitigation of CO2 emissions. Due to the many constraints in existing technology and the resulting increased costs, the [...] Read more.
Biofuel, an inexhaustible fuel source, plays a pivotal role in the contemporary era by diminishing the dependence on non-renewable energy sources and facilitating the mitigation of CO2 emissions. Due to the many constraints in existing technology and the resulting increased costs, the production of biofuels on a large scale is a laborious process. Furthermore, the methods used to convert varied feedstock into the intended biofuel may vary based on the specific techniques and materials involved. The demand for bioethanol is increasing worldwide due to the implementation of regulations by world nations that mandates the blending of bioethanol with petrol. In this regard, second-generation bioethanol made from lignocellulosic biomass is emerging at a rapid rate. Pre-treatment, hydrolysis, and fermentation are some of the technical, practical, and economic hurdles that the biochemical conversion method must overcome. Nanoparticles (NPs) provide a very effective approach to address the present obstacles in using biomass, due to their selectivity, energy efficiency, and time management capabilities, while also reducing costs. NPs smaller dimensions allow them to be more effective at interacting with lignocellulosic components at low concentrations to release carbohydrates that can be utilized to produce bioethanol. This article provides a concise overview of various biofuels and the nanotechnological advancements in producing it, with a particular emphasis on ethanol. It provides a detailed discussion on the application of nanotechnology at each stage of ethanol production, with a particular emphasis on understanding the mechanism of how nanoparticles interact with lignocellulose. Full article
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15 pages, 3976 KiB  
Article
A Novel Strategy for the Preparation of Supported Pd as an Efficient Catalyst for the Hydrogenation of Nitrobenzene in Mild Conditions
Catalysts 2023, 13(11), 1438; https://doi.org/10.3390/catal13111438 - 14 Nov 2023
Viewed by 817
Abstract
An advanced strategy was developed for the synthesis of molecular sieve-supported Pd catalysts. In this method, reductant containing C=C was in-situ prepared and pre-dispersed in the pore of the zeolites. The C=C group in the reductant can reduce the Pd2+ to Pd [...] Read more.
An advanced strategy was developed for the synthesis of molecular sieve-supported Pd catalysts. In this method, reductant containing C=C was in-situ prepared and pre-dispersed in the pore of the zeolites. The C=C group in the reductant can reduce the Pd2+ to Pd0 efficiently, leading to the formation of small and uniform Pd nanoparticles (~2 nm). The physical and chemical properties of the catalyst were characterized by XRD, TEM, XPS (ICP-OES), N2 isothermal adsorption-desorption, and H2-TPR. These catalysts showed high catalytic performance for the hydrogenation of nitrobenzene to aniline. All the TOFs for 1.5 Pd/Y, 1.5 Pd/ZSM-5, and 1.5 Pd/MOR with 1.5 wt% Pd loading are higher than 1000 h−1 at 30 °C and 0.1 MPa H2. Meanwhile, kinetic analysis for 2.0 Pd/Y was carried out, and an apparent activation energy of 28.88 kJ mol−1 was obtained, which is lower than most of the reported values in the literature. Furthermore, these catalysts were stable and recyclable. Full article
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Green Catalysts)
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17 pages, 3641 KiB  
Review
Advances and Prospects of d-Tagatose Production Based on a Biocatalytic Isomerization Pathway
Catalysts 2023, 13(11), 1437; https://doi.org/10.3390/catal13111437 - 14 Nov 2023
Cited by 1 | Viewed by 1033
Abstract
d-tagatose is a low-calorie alternative to sucrose natural monosaccharide that is nearly as sweet. As a ketohexose, d-tagatose has disease-relieving and health-promoting properties. Due to its scarcity in nature, d-tagatose is mainly produced through chemical and biological methods. Compared to [...] Read more.
d-tagatose is a low-calorie alternative to sucrose natural monosaccharide that is nearly as sweet. As a ketohexose, d-tagatose has disease-relieving and health-promoting properties. Due to its scarcity in nature, d-tagatose is mainly produced through chemical and biological methods. Compared to traditional chemical methods, biological methods use whole cells and isolated enzymes as catalysts under mild reaction conditions with few by-products and no pollution. Nowadays, biological methods have become a very important topic in related fields due to their high efficiency and environmental friendliness. This paper introduces the functions and applications of d-tagatose and systematically reviews its production, especially by l-arabinose isomerase (L-AI), using biological methods. The molecular structures and catalytic mechanisms of L-AIs are also analyzed. In addition, the properties of L-AIs from different microbial sources are summarized. Finally, we overview strategies to improve the efficiency of d-tagatose production by engineering L-AIs and provide prospects for the future bioproduction of d-tagatose. Full article
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Green Catalysts)
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19 pages, 6203 KiB  
Article
Structure and Catalytic Performance of Carbon-Based Solid Acids from Biomass Activated by ZnCl2
Catalysts 2023, 13(11), 1436; https://doi.org/10.3390/catal13111436 - 14 Nov 2023
Viewed by 766
Abstract
In the current investigation, carbon-based solid acid catalysts were synthesized from peanut shells (PSs) and rice straw (RS) using ZnCl2 activation and concentrated sulfuric acid sulfonation. These catalysts were then employed for the hydration of pinene to produce terpineol. The research findings [...] Read more.
In the current investigation, carbon-based solid acid catalysts were synthesized from peanut shells (PSs) and rice straw (RS) using ZnCl2 activation and concentrated sulfuric acid sulfonation. These catalysts were then employed for the hydration of pinene to produce terpineol. The research findings suggest that the natural porous structure of RS is more amenable to ZnCl2 activation compared to PSs. Furthermore, the catalysts prepared from fully activated RS by ZnCl2 (RSA-C-S) had a higher SBET and higher density of oxygen-containing groups (–COOH) in comparison with unactivated RS-based solid acids (RSC-S). The characterization outcomes revealed that RSA-C-S possesses a specific surface area of 527.0 m2/g, significantly outperforming RSC-S, which has a surface area of 420.9 m2/g. Additionally, RSA-C-S registered a higher –COOH density of 1.37 mmol/g, as opposed to RSC-S’s, with 1.07 mmol/g, attributable to the partial oxidation of internal –OH groups during activation. Experimental data from hydration tests confirmed that the catalyst’s superior performance is largely attributed to its elevated specific surface area and a high density of –COOH functional groups. Under optimal reaction parameters, RSA-C-S demonstrated unparalleled catalytic efficiency in the synthesis of α-terpineol via hydration of α-pinene, achieving conversion and selectivity rates of 87.15% and 54.19%, respectively. Full article
(This article belongs to the Special Issue Catalytic Conversion of Biomass to Chemicals)
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9 pages, 1974 KiB  
Article
The Origin of the Size Effect in the Oxidation of CO on Supported Palladium Nanoparticles
Catalysts 2023, 13(11), 1435; https://doi.org/10.3390/catal13111435 - 13 Nov 2023
Viewed by 722
Abstract
Two Pd/TiO2 catalysts with mean particle sizes of 1 and 3 nm were prepared and tested in the low-temperature oxidation of CO. It was found that the first catalyst with higher dispersion is more active. Turnover frequencies varied for these catalysts by [...] Read more.
Two Pd/TiO2 catalysts with mean particle sizes of 1 and 3 nm were prepared and tested in the low-temperature oxidation of CO. It was found that the first catalyst with higher dispersion is more active. Turnover frequencies varied for these catalysts by almost six times. In contrast, the apparent activation energy of the oxidation of CO on the catalyst with smaller Pd nanoparticles was estimated at 76 kJ/mol, and for the catalyst with larger Pd nanoparticles at 58 kJ/mol. According to in situ XANES studies, the particle size effect originates from the oxidation of small palladium nanoparticles under reaction conditions, whereas larger nanoparticles are stable and consist of palladium atoms mainly in the metallic state. Palladium oxide is more active in the low-temperature oxidation of CO than metallic palladium. This means that the origin of size-dependent activity of Pd nanoparticles in the low-temperature oxidation of CO is associated with the change in the chemical composition of nanoparticles that leads to a change in the reaction mechanism and, as a result, in their activity. Full article
(This article belongs to the Section Nanostructured Catalysts)
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27 pages, 8891 KiB  
Review
Sulfur and Water Resistance of Carbon-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NOx: A Review
Catalysts 2023, 13(11), 1434; https://doi.org/10.3390/catal13111434 - 13 Nov 2023
Viewed by 749
Abstract
Low-temperature NH3-SCR is an efficient technology for NOx removal from flue gas. The carbon-based catalyst designed by using porous carbon material with great specific surface area and interconnected pores as the support to load the active components shows excellent NH [...] Read more.
Low-temperature NH3-SCR is an efficient technology for NOx removal from flue gas. The carbon-based catalyst designed by using porous carbon material with great specific surface area and interconnected pores as the support to load the active components shows excellent NH3-SCR performance and has a broad application prospect. However, overcoming the poor resistance of H2O and SO2 poisoning for carbon-based catalysts remains a great challenge. Notably, reviews on the sulfur and water resistance of carbon-based low-temperature NH3-SCR catalysts have not been previously reported to the best of our knowledge. This review introduces the reaction mechanism of the NH3-SCR process and the poisoning mechanism of SO2 and H2O to carbon-based catalysts. Strategies to improve the SO2 and H2O resistance of carbon-based catalysts in recent years are summarized through the effect of support, modification, structure control, preparation methods and reaction conditions. Perspective for the further development of carbon-based catalysts in NOx low-temperature SCR is proposed. This study provides a new insight and guidance into the design of low-temperature SCR catalysts resistant to SO2 and H2O in the future. Full article
(This article belongs to the Special Issue Nanotechnology in Catalysis, 2nd Edition)
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18 pages, 5555 KiB  
Article
Cyano/Hydroxyl Groups Co-Functionalized g-C3N4 for Photocatalytic NO Removal: A Synergistic Strategy towards Inhibition of Toxic Intermediate NO2
Catalysts 2023, 13(11), 1433; https://doi.org/10.3390/catal13111433 - 13 Nov 2023
Cited by 1 | Viewed by 794
Abstract
Photocatalytic NO removal is usually accompanied by the generation of NO2, an intermediate with a higher toxicity than NO. Therefore, it is critically important to develop new photocatalysts capable of NO selective conversion. Herein, we report on the synergistic roles of [...] Read more.
Photocatalytic NO removal is usually accompanied by the generation of NO2, an intermediate with a higher toxicity than NO. Therefore, it is critically important to develop new photocatalysts capable of NO selective conversion. Herein, we report on the synergistic roles of cyano and hydroxyl functional groups in photocatalytic NO removal. According to the results, the NO2 production efficiencies on cyano/hydroxyl-group-modified g-C3N4 (DCN-O-R) was limited to 4.8%, which was lower than that of cyano-group-modified g-C3N4 (DCN, 38.6%) and pure g-C3N4 (CN, 50.0%). Meanwhile, the photocatalytic NO conversion efficiency over DCN-O-R was higher than that of DCN and g-C3N4. It was found that the insertion of cyano groups favorably changes the energy band of g-C3N4 towards the generation of •O2. NO can only be oxidized to NO2 by the photogenerated holes. When NO2 is adsorbed on the surface of hydroxyl groups, it can be further oxidized to the product NO3 by •O2. The synergistic effect of bifunctional groups regulates the conversion pathway from NO→NO2 to NO→NO2→NO3. This work provides a strategy to abate toxic intermediates during the NO removal process, underlining the importance of surface/interface molecular engineering in regulating catalytic reaction pathways. Full article
(This article belongs to the Special Issue Nanotechnology in Catalysis, 2nd Edition)
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16 pages, 3063 KiB  
Article
Nanosized Silica-Supported 12-Tungstophosphoric Acid: A Highly Active and Stable Catalyst for the Alkylation of p-Cresol with tert-Butanol
Catalysts 2023, 13(11), 1432; https://doi.org/10.3390/catal13111432 - 13 Nov 2023
Viewed by 708
Abstract
12-Tungstophosphoric acid supported on nanosilica (TPA/SiO2) was employed as a catalyst for the tertiary butylation of p-cresol using tertiary butanol as an alkylating agent. The TPA/SiO2 catalyst was synthesized using the wet impregnation method followed by steaming at 150 [...] Read more.
12-Tungstophosphoric acid supported on nanosilica (TPA/SiO2) was employed as a catalyst for the tertiary butylation of p-cresol using tertiary butanol as an alkylating agent. The TPA/SiO2 catalyst was synthesized using the wet impregnation method followed by steaming at 150 °C for 6 h. The catalysts were characterized by means of X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis. The surface acidity of the untreated and steamed catalysts was characterized via FTIR and DSC thermal analysis using pyridine as a probe molecule. The fresh and spent catalysts were characterized via TGA analysis. The catalytic activity studies showed that the steamed catalyst displayed higher activity, with a higher desired yield of 2-tert-butyl cresol (2-TBC) compared to the untreated catalyst, and that this activity was related to the presence of stronger Brønsted acid sites in the steamed catalyst. A detailed analysis of the TPA/SiO2 steamed catalyst was performed to study the effects of reactant time-on-stream, reactant feed rate, reaction temperature, and the molar ratio of tert-butanol to p-cresol. The optimum reaction temperature, tert-butanol/p-cresol molar ratio, feed rate, and time-on-stream were 413 K, a molar ratio of 2:1, 6 mL/min, and 2 h, respectively. The present study demonstrates that the TPA/SiO2 catalyst exhibits high activity in terms of % conversion and high % selectivity of 2-TBC under the optimized conditions. The characterization of fresh and spent catalysts confirmed the occurrence of coke deposition after the catalytic reaction. The catalyst was regenerated via heat treatment at 400 °C for 5 h. The regenerated catalyst was reused for subsequent runs for three cycles without showing a loss in its activity. Full article
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16 pages, 23832 KiB  
Article
Bacterial Cellulose and Biodegradable Superbase for Heterogeneous Transesterification to Alkyl Esters
Catalysts 2023, 13(11), 1431; https://doi.org/10.3390/catal13111431 - 13 Nov 2023
Viewed by 707
Abstract
Heterogeneous catalysts, basic, acidic or bifunctional, can catalyze transesterification reactions where the raw material has a significant content of FFA fatty acids, such as used cooking oils or other lipid-based residues, which do not have the purity required for homogeneous catalysis, in which [...] Read more.
Heterogeneous catalysts, basic, acidic or bifunctional, can catalyze transesterification reactions where the raw material has a significant content of FFA fatty acids, such as used cooking oils or other lipid-based residues, which do not have the purity required for homogeneous catalysis, in which case the purity of the triglycerides above 99.5% is the first condition for the initiation of the reaction, to avoid saponification. In this work, a green supported catalyst was developed, using bacterial cellulose as catalytic support and biodegradable superbase as a chemical compound, for transesterification reaction to obtain alkyl esters, yielding over 99% of its content at 70 °C temperature and 7.5% catalyst loading (1.5/20 w/w catalyst:oil). A Plackett-–Burman design was used for screening experiments to explore the main effect in terms of catalytic activity and performance of the triglyceride conversion reaction. Full article
(This article belongs to the Special Issue Applications of Heterogeneous Catalysts in Green Chemistry)
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13 pages, 4387 KiB  
Article
Effect of Support on Oxidative Esterification of 2,5-Furandiformaldehyde to Dimethyl Furan-2,5-dicarboxylate
Catalysts 2023, 13(11), 1430; https://doi.org/10.3390/catal13111430 - 13 Nov 2023
Viewed by 943
Abstract
One-step oxidative esterification of 2,5-furandiformaldehyde (DFF) derived from biomass to prepare Dimethyl Furan-2,5-dicarboxylate (FDMC) not only simplifies the catalytic process and increases the purity of the product, but also avoids the polymerization of 5-hydroxymethylfurfural (HMF) at high-temperature conditions. Gold supported on a series [...] Read more.
One-step oxidative esterification of 2,5-furandiformaldehyde (DFF) derived from biomass to prepare Dimethyl Furan-2,5-dicarboxylate (FDMC) not only simplifies the catalytic process and increases the purity of the product, but also avoids the polymerization of 5-hydroxymethylfurfural (HMF) at high-temperature conditions. Gold supported on a series of acidic oxide, alkaline oxide, and hydrotalcite was prepared using colloidal deposition to explore the effect of support on the catalytic activities. The Au/Mg3Al-HT exhibited the best catalytic activity, with 97.8% selectivity of FDMC at 99.9% conversion of DFF. This catalyst is also suitable for oxidative esterification of benzaldehyde and furfural. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and CO2 temperature programmed desorption (CO2-TPD) were performed to characterize the catalysts. The results indicated that the medium and strong basic sites in the catalysts benefited for the absorption of intermediate agents and facilitated the oxidative esterification of aldehyde groups, while neutral or acidic supports tended to produce an acetal reaction. It is worth noting that basicity on the support surface reduced the electronic state of the Au nanoparticle (Auδ−) and, thus, enhanced the catalytic selectivity of oxidative esterification. This finding demonstrated that the support plays a crucial role in oxidative esterification. Full article
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17 pages, 3237 KiB  
Article
GC/MS Profiling, In Vitro Antidiabetic Efficacy of Origanum compactum Benth. Essential Oil and In Silico Molecular Docking of Its Major Bioactive Compounds
Catalysts 2023, 13(11), 1429; https://doi.org/10.3390/catal13111429 - 13 Nov 2023
Viewed by 1253
Abstract
Diabetes is a global health concern with significant implications for individuals and healthcare systems. Finding effective and safe antidiabetic agents is crucial for the management of this chronic disease. Natural products have emerged as potential alternatives to allopathic drugs, offering a vast source [...] Read more.
Diabetes is a global health concern with significant implications for individuals and healthcare systems. Finding effective and safe antidiabetic agents is crucial for the management of this chronic disease. Natural products have emerged as potential alternatives to allopathic drugs, offering a vast source of bioactive compounds. In this study, we conducted an assessment of the antidiabetic potential of Origanum compactum essential oil, employing a two-pronged approach, i.e., experimental investigation and computational docking analysis. The results of gas chromatography–mass spectrometry (GC-MS) showed that thymol (54.6%), carvacrol (23.18%), and p-cymene (7.12%) were the major compounds. Experimental assessments revealed higher IC50 values (150 µg/mL for α-amylase; 120 µg/mL for α-glucosidase) of O. compactum oil, compared to the control drug acarbose. In silico analysis revealed the best binding affinity of the oil components (carvacrol and thymol) with human NADPH oxidase, while the lysosomal acid-α-glucosidase and salivary amylase also demonstrated good binding affinity towards carvacrol and thymol. Our findings highlight the translational potential of O. compactum oil-based treatment for diabetes mellitus and provide a basis for further studies on the modulation of NADPH oxidase, amylase inhibition, and α-glucosidase by antidiabetic natural products. However, further in vivo investigations are strongly required to confirm the results of in vitro antidiabetic effect of O. compactum EO. Full article
(This article belongs to the Section Biocatalysis)
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15 pages, 5264 KiB  
Article
Efficient Hydrogen Production from the Aqueous-Phase Reforming of Biomass-Derived Oxygenated Hydrocarbons over an Ultrafine Pt Nanocatalyst
Catalysts 2023, 13(11), 1428; https://doi.org/10.3390/catal13111428 - 12 Nov 2023
Viewed by 916
Abstract
Hydrogen from biomass, as a promising alternative fuel, is becoming considerably attractive due to its high energy density and clean emissions. The aqueous phase reforming (APR) of biomass-derived oxygenated hydrocarbons and water is a renewable and efficient pathway for hydrogen production and shows [...] Read more.
Hydrogen from biomass, as a promising alternative fuel, is becoming considerably attractive due to its high energy density and clean emissions. The aqueous phase reforming (APR) of biomass-derived oxygenated hydrocarbons and water is a renewable and efficient pathway for hydrogen production and shows great potential. However, the key to the application of this technique is to develop catalysts with high hydrogen productivity. In this work, we first synthesized polyaniline–platinum (PANI-Pt) organo-metallic hybrid precursors and then obtained a high-loaded (~32 wt.% Pt) and highly dispersed (~3 nm Pt particles) Pt@NC−400 catalyst after pyrolysis at 400 °C, and the nanoparticles were embedded in a nitrogen-doped carbon (NC) support. The Pt@NC−400 catalyst showed an almost three times higher hydrogen production rate (1013.4 μmolH2/gcat./s) than the commercial 20% Pt/C catalyst (357.3 μmolH2/gcat./s) for catalyzing methanol–water reforming at 210 °C. The hydrogen production rate of 1,2-propanediol APR even reached 1766.5 μmolH2/gcat./s over the Pt@NC−400 catalyst at 210 °C. In addition, Pt@NC−400 also exhibited better hydrothermal stability than 20% Pt/C. A series of characterizations, including ICP, XRD, TEM, SEM, XPS, N2 physisorption, and CO chemisorption, were conducted to explore the physiochemical properties of these catalysts and found that Pt@NC−400, although with higher loading than 20% Pt/C (~23 wt.% Pt, ~4.5 nm Pt particle), possessed a smaller particle size, a more uniform particle distribution, a better pore structure, and more Pt metal active sites. This study provides a strategy for preparing high-loaded and highly dispersed nanoparticle catalysts with high hydrogen productivity and sheds light on the design of stable and efficient APR catalysts. Full article
(This article belongs to the Special Issue Recent Advances in Heterogeneous Catalysis for Low-Carbon Fuels)
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21 pages, 2931 KiB  
Article
Solketal Production Using Eco-Friendly Reduced Graphene Oxide as the Catalyst
Catalysts 2023, 13(11), 1427; https://doi.org/10.3390/catal13111427 - 10 Nov 2023
Viewed by 791
Abstract
In this study, two materials based on reduced graphene oxide (rGOH or rGOE) were synthesized through the Hummers methodology and a more sustainable electrochemical method. These materials were extensively characterized and tested as catalysts in solketal production. Both rGOH [...] Read more.
In this study, two materials based on reduced graphene oxide (rGOH or rGOE) were synthesized through the Hummers methodology and a more sustainable electrochemical method. These materials were extensively characterized and tested as catalysts in solketal production. Both rGOH and rGOE demonstrated significant catalytic activity, achieving 66.18% and 63.97% conversion rates, respectively. The catalytic activity of the synthesized materials was 30 times more efficient than the homogeneous catalyst p-Toluenesulfonic acid. Pseudo-homogeneous and heterogeneous kinetic models were employed to gain further insights into the glycerol ketalization reaction with acetone. The pseudo-homogeneous model suggested that the direct rate constant was lower than the reverse rate constant. In this sense, a reversible bimolecular reaction was proposed. The heterogeneous kinetic models revealed that in the Langmuir-Hinshelwood-Hougen-Watson mechanism, the controlling step of the reaction was the glycerol-acetone surface reaction on the catalyst. In contrast, in the Eley-Rideal mechanism, the reaction was controlled by the adsorbed glycerol on the reaction surface reacting with the available acetone in the bulk fluid. In the reusability tests, the rGOE catalyst demonstrated superior performance over five consecutive cycles, maintaining the highest activity without needing post-reaction washing or treatment. Full article
(This article belongs to the Topic Biomass Transformation: Sustainable Development)
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13 pages, 2927 KiB  
Article
Constructing Stable MoOx-NiSx Film via Electrodeposition and Hydrothermal Method for Water Splitting
Catalysts 2023, 13(11), 1426; https://doi.org/10.3390/catal13111426 - 09 Nov 2023
Viewed by 713
Abstract
The hydrothermal method is a frequently used approach for synthesizing HER electrocatalysts. However, a weak tolerance to high temperature is an intrinsic property of carbon cloth (CC) in most situations, and CC-based catalysts, which require complex technological processes in low-temperature environments, exhibit weak [...] Read more.
The hydrothermal method is a frequently used approach for synthesizing HER electrocatalysts. However, a weak tolerance to high temperature is an intrinsic property of carbon cloth (CC) in most situations, and CC-based catalysts, which require complex technological processes in low-temperature environments, exhibit weak stability and electrochemical performance. Hence, we provide a new solution for these issues. In this work, MoO3-NiSx films of 9H5E-CC catalysts are synthesized, first through electrodeposition to form Ni particles on CC and then through a hydrothermal reaction to reform the reaction. The advantages of this synthetic process include mild reaction conditions and convenient operation. The obtained MoO3-NiSx film presents excellent catalytic activity and stability for HER. MoO3-NiSx film requires only a low overpotential of 142 mV to drive 10 mA cm−2 for HER in 1.0 m KOH, and the obtained 9H5E-CF film only needs 294 mV to achieve 50 mA cm−2 for OER. Remarkably, they also show excellent OER, HER, and full water splitting long-term electrochemical stability, maintaining their performance for at least 72 h. This work can be expanded to provide a new strategy for the fabrication of stable, high-performing electrodes using simple, mild reaction conditions. Full article
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14 pages, 1057 KiB  
Review
An Approach towards the Conversion of Biomass Feedstocks into Biofuel Using a Zeolite Socony Mobil-5-Based Catalysts via the Hydrothermal Liquefaction Process: A Review
Catalysts 2023, 13(11), 1425; https://doi.org/10.3390/catal13111425 - 09 Nov 2023
Viewed by 1032
Abstract
The conversion of biomass to biofuels as a renewable energy source is continuously gaining momentum due to the environmental concerns associated with using fossil fuels. Biomass is a cost-effective, long-term natural resource that may be converted to biofuels such as biodiesel, biogas, bio-oil, [...] Read more.
The conversion of biomass to biofuels as a renewable energy source is continuously gaining momentum due to the environmental concerns associated with using fossil fuels. Biomass is a cost-effective, long-term natural resource that may be converted to biofuels such as biodiesel, biogas, bio-oil, and biohydrogen using a variety of chemical, thermal, and biological methods. Thermochemical processes are one of the most advanced biomass conversion methods, with much potential and room for improvement. Among various thermochemical processes, hydrothermal liquefaction (HTL) is a promising technology that can convert higher water-content feedstocks into biofuel with significantly lower oxygen content and higher calorific value without requiring the biomass to be dried first. In HTL, temperature, pressure, residence time, catalyst, and solvent all play a vital role in bio-oil quality. This study provides a comprehensive review of the research and development on the effects of catalysts and the need to optimise existing catalysts for optimum biomass conversion into high-value bio-oil and other products. The catalyst of interest is ZSM-5, a heterogenous catalyst that has been seen to increase the hydrocarbon content and decrease oxygenated compounds and other unwanted by-products. The use and modification of this catalyst will play a vital role in generating renewable and carbon-neutral fuels. Full article
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