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Catalysts, Volume 10, Issue 1 (January 2020) – 142 articles

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Cover Story (view full-size image) The “one-pot” synthesis of vidarabine 5′-monophosphate (araA-MP), an antiviral drug, was carried [...] Read more.
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Open AccessReview
A Review on Quantum Dots Modified g-C3N4-Based Photocatalysts with Improved Photocatalytic Activity
Catalysts 2020, 10(1), 142; https://doi.org/10.3390/catal10010142 - 20 Jan 2020
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Abstract
In the 21st century, the development of sustainable energy and advanced technologies to cope with energy shortages and environmental pollution has become vital. Semiconductor photocatalysis is a promising technology that can directly convert solar energy to chemical energy and is extensively used for [...] Read more.
In the 21st century, the development of sustainable energy and advanced technologies to cope with energy shortages and environmental pollution has become vital. Semiconductor photocatalysis is a promising technology that can directly convert solar energy to chemical energy and is extensively used for its environmentally-friendly properties. In the field of photocatalysis, graphitic carbon nitride (g-C3N4) has obtained increasing interest due to its unique physicochemical properties. Therefore, numerous researchers have attempted to integrate quantum dots (QDs) with g-C3N4 to optimize the photocatalytic activity. In this review, recent progress in combining g-C3N4 with QDs for synthesizing new photocatalysts was introduced. The methods of QDs/g-C3N4-based photocatalysts synthesis are summarized. Recent studies assessing the application of photocatalytic performance and mechanism of modification of g-C3N4 with carbon quantum dots (CQDs), graphene quantum dots (GQDs), and g-C3N4 QDs are herein discussed. Lastly, challenges and future perspectives of QDs modified g-C3N4-based photocatalysts in photocatalytic applications are discussed. We hope that this review will provide a valuable overview and insight for the promotion of applications of QDs modified g-C3N4 based-photocatalysts. Full article
(This article belongs to the Special Issue Advances in Solar- and Visible-Light Photocatalysis)
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Open AccessReview
Recent Advances in Non-Precious Transition Metal/Nitrogen-doped Carbon for Oxygen Reduction Electrocatalysts in PEMFCs
Catalysts 2020, 10(1), 141; https://doi.org/10.3390/catal10010141 - 20 Jan 2020
Viewed by 122
Abstract
The proton exchange membrane fuel cells (PEMFCs) have been considered as promising future energy conversion devices, and have attracted immense scientific attention due to their high efficiency and environmental friendliness. Nevertheless, the practical application of PEMFCs has been seriously restricted by high cost, [...] Read more.
The proton exchange membrane fuel cells (PEMFCs) have been considered as promising future energy conversion devices, and have attracted immense scientific attention due to their high efficiency and environmental friendliness. Nevertheless, the practical application of PEMFCs has been seriously restricted by high cost, low earth abundance and the poor poisoning tolerance of the precious Pt-based oxygen reduction reaction (ORR) catalysts. Noble-metal-free transition metal/nitrogen-doped carbon (M–NxC) catalysts have been proven as one of the most promising substitutes for precious metal catalysts, due to their low costs and high catalytic performance. In this review, we summarize the development of M–NxC catalysts, including the previous non-pyrolyzed and pyrolyzed transition metal macrocyclic compounds, and recent developed M–NxC catalysts, among which the Fe–NxC and Co–NxC catalysts have gained our special attention. The possible catalytic active sites of M–NxC catalysts towards the ORR are also analyzed here. This review aims to provide some guidelines towards the design and structural regulation of non-precious M–NxC catalysts via identifying real active sites, and thus, enhancing their ORR electrocatalytic performance. Full article
(This article belongs to the Special Issue Transition Metal Catalysis)
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Open AccessArticle
Preparation of Quasi-MIL-101(Cr) Loaded Ceria Catalysts for the Selective Catalytic Reduction of NOx at Low Temperature
Catalysts 2020, 10(1), 140; https://doi.org/10.3390/catal10010140 - 20 Jan 2020
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Abstract
At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO2/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, [...] Read more.
At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO2/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, which are characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and so on. The results show that the increase of Ce content has a great influence on the catalytic property of the catalyst. The introduction of Ce can promote the conversion between Cr3+ and Cr5+ and increase the proportion of lattice oxygen, which improves the activity of the catalyst. However, the catalyst will be peroxidized when the content of Ce is too high, resulting in the decline of the catalytic activity. This experiment indicates that CeO2/quasi-MIL-101 plays a significant role in the NH3-SCR process at the low temperature when the loading of Ce is 0.5%. This work has proved the potential of this kind of material in NH3-SCR process at the low temperature, providing help for subsequent studies. Full article
(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)
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Open AccessArticle
The Use of Tunable Optical Absorption Plasmonic Au and Ag Decorated TiO2 Structures as Efficient Visible Light Photocatalysts
Catalysts 2020, 10(1), 139; https://doi.org/10.3390/catal10010139 - 20 Jan 2020
Viewed by 156
Abstract
Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded [...] Read more.
Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded as one of the most effective solutions. The perfect match of the SPR absorption band with the spectrum of incident light is an essential factor for plasmonic enhancement. However, modifying with sole noble metal is often limited as it tunes wavelength of only several nanometers. To overcome this drawback, an alternative approach can be offered by decoration with more than one noble metal. For instance, Au-Ag co-decoration displays greatly adjustable, composition-dependent SPR agent over a broad range of the visible light spectrum (ca. from 415 to 525 nm). Hence Au-Ag complex is a remarkable candidate for tuning the photo adsorption of TiO2 from UV to visible light. This study presents a novel and tailored method for the fabrication of Au-Ag co-modified TiO2 particles, and how Au-Ag dependent SPR was applied as the visible light-responsive TiO2 based photocatalysts in a simple but reliable way. The fabricated Au-Ag co-decorated TiO2 (AuxAg(1−x)/TiO2) was characterized and proved to own excellent stability and large specific surface area. The optimization of these particles against the wavelength of maximal solar light intensity was confirmed by photo degradation of methylene blue under visible light radiation. This work may provide further insight into the design of TiO2-based composites with improved photocatalytic properties for environmental remediation and renewable energy utilization. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Rapid Removal of Azophloxine via Catalytic Degradation by a Novel Heterogeneous Catalyst under Visible Light
Catalysts 2020, 10(1), 138; https://doi.org/10.3390/catal10010138 - 19 Jan 2020
Viewed by 117
Abstract
Azo dyes are the most widely used synthetic dyes in the printing and dyeing process. However, the discharge of untreated azo dyes poses a potential threat to aqueous ecosystems and human health. Herein, we fabricated a novel heterogeneous catalyst: activated-carbon-fiber-supported ferric alginate (FeAlg-ACF). [...] Read more.
Azo dyes are the most widely used synthetic dyes in the printing and dyeing process. However, the discharge of untreated azo dyes poses a potential threat to aqueous ecosystems and human health. Herein, we fabricated a novel heterogeneous catalyst: activated-carbon-fiber-supported ferric alginate (FeAlg-ACF). Together with peroxymonosulfate (PMS) and visible light, this photocatalytic oxidation system was used to remove an azo dye—azophloxine. The results indicated that the proposed catalytic oxidation system can remove 100% of azophloxine within 24 min, while under the same system, the removal rates were only 92% and 84% when ferric alginate was replaced with ferric citrate and ferric oxalate, respectively, which showed the superiority of FeAlg-ACF. The degradation of azophloxine is achieved by the active radicals (SO4•− and •OH) released from PMS and persistent free radicals from activated carbon fiber. Moreover, due to ferric alginate’s highly intrinsic photosensitivity, visible radiation can further enhance the ligand-to-metal charge transfer (LMCT) processes. After 24 min of treatment, the total organic carbon of the azophloxine solution (50 μmol/L) decreased from 1.82 mg/L to 79.3 μg/L and the concentration of nitrate ions increased from 0.3 mg/L to 8.6 mg/L. That is, up to 93.5% of azophloxine molecules were completely degraded into inorganic compounds. Consequently, potential secondary contamination by intermediate organic products during catalytic degradation was prohibited. The azophloxine removal ratio was kept almost constant after seven cycles, indicating the recyclability and longevity of this system. Furthermore, the azophloxine removal was still promising at high concentrations of Cl, HCO3, and CO32−. Therefore, our proposed system is potentially effective at removing dye pollutants from seawater. It provides a feasible method for the development of efficient and environmentally friendly PMS activation technology combined with FeAlg-ACF, which has significant academic and application value. Full article
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Open AccessArticle
DERA in Flow: Synthesis of a Statin Side Chain Precursor in Continuous Flow Employing Deoxyribose-5-Phosphate Aldolase Immobilized in Alginate-Luffa Matrix
Catalysts 2020, 10(1), 137; https://doi.org/10.3390/catal10010137 - 18 Jan 2020
Viewed by 155
Abstract
Statins, cholesterol-lowering drugs used for the treatment of coronary artery disease (CAD), are among the top 10 prescribed drugs worldwide. However, the synthesis of their characteristic side chain containing two chiral hydroxyl groups can be challenging. The application of deoxyribose-5-phosphate aldolase (DERA) is [...] Read more.
Statins, cholesterol-lowering drugs used for the treatment of coronary artery disease (CAD), are among the top 10 prescribed drugs worldwide. However, the synthesis of their characteristic side chain containing two chiral hydroxyl groups can be challenging. The application of deoxyribose-5-phosphate aldolase (DERA) is currently one of the most promising routes for the synthesis of this side chain. Herein, we describe the development of a continuous flow process for the biosynthesis of a side chain precursor. Design of experiments (DoE) was used to optimize the reaction conditions (pH value and temperature) in batch. A pH of 7.5 and a temperature of 32.5 °C were identified to be the optimal process settings within the reaction space considered. Additionally, an immobilization method was developed using the alginate-luffa matrix (ALM), which is a fast, simple, and inexpensive method for enzyme immobilization. Furthermore, it is non-toxic, biodegradable, and from renewable resources. The final continuous process was operated stable for 4 h and can produce up to 4.5 g of product per day. Full article
(This article belongs to the Special Issue Biocatalytic Process Optimization)
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Open AccessReview
Recent Developments in the Immobilization of Palladium Complexes on Renewable Polysaccharides for Suzuki–Miyaura Cross-Coupling of Halobenzenes and Phenylboronic Acids
Catalysts 2020, 10(1), 136; https://doi.org/10.3390/catal10010136 - 18 Jan 2020
Viewed by 111
Abstract
Polysaccharides derived from natural sources exhibit unique structures and functional groups, which have recently garnered them increased attention for their potential applicability as supports for metal catalysts. Renewable polysaccharide matrices were employed as supports for palladium complexes, with or without previous modification of [...] Read more.
Polysaccharides derived from natural sources exhibit unique structures and functional groups, which have recently garnered them increased attention for their potential applicability as supports for metal catalysts. Renewable polysaccharide matrices were employed as supports for palladium complexes, with or without previous modification of the support, and were used in Suzuki cross-coupling of halobenzenes and phenylboronic acid derivatives. In this review, recent developments in the immobilization of palladium-based complexes are reported, including descriptions of the preparation procedures and catalytic activity of each system. In addition, the effects of the nature of the polymeric support and of the reaction conditions on catalytic performance are discussed. Full article
(This article belongs to the Special Issue Palladium-Catalyzed Reactions)
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Open AccessArticle
DeNOx of Nano-Catalyst of Selective Catalytic Reduction Using Active Carbon Loading MnOx-Cu at Low Temperature
Catalysts 2020, 10(1), 135; https://doi.org/10.3390/catal10010135 - 18 Jan 2020
Viewed by 118
Abstract
With the improvement of environmental protection standards, selective catalytic reduction (SCR) has become the mainstream technology of flue gas deNOx. Especially, the low-temperature SCR nano-catalyst has attracted more and more attention at home and abroad because of its potential performance and [...] Read more.
With the improvement of environmental protection standards, selective catalytic reduction (SCR) has become the mainstream technology of flue gas deNOx. Especially, the low-temperature SCR nano-catalyst has attracted more and more attention at home and abroad because of its potential performance and economy in industrial applications. In this paper, low-temperature SCR catalysts were prepared using the activated carbon loading MnOx-Cu. Then, the catalysts were packed into the fiedbed stainless steel micro-reactor to evaluate the selective catalytic reduction of NO performance. The influence of reaction conditions was investigated on the catalytic reaction, including the MnOx-Cu loading amount, calcination and reaction temperature, etc. The experimental results indicate that SCR catalysts show the highest catalytic activity for NO conversion when the calcination temperature is 350 °C, MnOx loading amount is 5%, Cu loading amount is 3%, and reaction temperature is 200 °C. Under such conditions, the NO conversion arrives at 96.82% and the selectivity to N2 is almost 99%. It is of great significance to investigate the influence of reaction conditions in order to provide references for industrial application. Full article
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Open AccessArticle
Sucrose-Assisted Solution Combustion Synthesis of Doped Strontium Ferrate Perovskite-Type Electrocatalysts: Primary Role of the Secondary Fuel
Catalysts 2020, 10(1), 134; https://doi.org/10.3390/catal10010134 - 18 Jan 2020
Viewed by 143
Abstract
The methodologies and experimental conditions used for the synthesis of cathode materials for electrochemical devices strongly influence their electrocatalytic performance. In particular, solution combustion synthesis is a convenient and versatile methodology allowing a fine-tuning of the properties of the material. In this work, [...] Read more.
The methodologies and experimental conditions used for the synthesis of cathode materials for electrochemical devices strongly influence their electrocatalytic performance. In particular, solution combustion synthesis is a convenient and versatile methodology allowing a fine-tuning of the properties of the material. In this work, we used for the first time a sucrose assisted-solution combustion synthesis for the preparation of Cerium and Cobalt-doped SrFeO3–δ electrocatalysts and we investigated the effect of polyethylene glycol (PEG) addition as a secondary fuel on their structural, microstructural, redox and electrochemical properties. The perovskite-type powders were characterized by X-ray diffraction coupled with Rietveld refinement, scanning, and high-resolution transmission electron microscopies, thermogravimetric analysis, nitrogen adsorption measurements, and temperature-programmed reduction. Electrical conductivity and overpotential measurements were performed after the deposition of the powders onto a Gd-doped ceria electrolyte pellet. Stable high-valence B-site cations were detected in the powders prepared from sucrose-PEG fuel mixtures, although a substantial improvement of the conductivity and a decrease of the overpotential values were obtained only with high molecular weight PEG. The superior electrochemical performance obtained using PEG with high molecular weight has been ascribed to a faster interaction of the powder with the oxygen gas phase favored by the nanometer-sized crystalline domains. Full article
(This article belongs to the Section Catalytic Materials)
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Open AccessArticle
Improvement of Ethylene Removal Performance by Adsorption/Oxidation in a Pin-Type Corona Discharge Coupled with Pd/ZSM-5 Catalyst
Catalysts 2020, 10(1), 133; https://doi.org/10.3390/catal10010133 - 17 Jan 2020
Viewed by 167
Abstract
The adsorption and plasma-catalytic oxidation of dilute ethylene were performed in a pin-type corona discharge-coupled Pd/ZSM-5 catalyst. The catalyst has an adsorption capacity of 320.6 μ mol   g cat 1 . The catalyst was found to have two different active sites [...] Read more.
The adsorption and plasma-catalytic oxidation of dilute ethylene were performed in a pin-type corona discharge-coupled Pd/ZSM-5 catalyst. The catalyst has an adsorption capacity of 320.6 μ mol   g cat 1 . The catalyst was found to have two different active sites activated at around 340 and 470 °C for ethylene oxidation. The removal of ethylene in the plasma catalyst was carried out by cyclic operation consisting of repetitive steps: (1) adsorption (60 min) followed by (2) plasma-catalytic oxidation (30 min). For the purpose of comparison, the removal of ethylene in the continuous plasma-catalytic oxidation mode was also examined. The ethylene adsorption performance of the catalyst was improved by the cyclic plasma-catalytic oxidation. With at least 80% of C2H4 in the feed being adsorbed, the cyclic plasma-catalytic oxidation was carried out for the total adsorption time of 8 h, whereas it occurred within 2 h of early adsorption in the case of catalyst alone. There was a slight decrease in catalyst adsorption capability with an increased number of adsorption cycles due to the incomplete release of CO2 during the plasma-catalytic oxidation step. However, the decreased rate of adsorption capacity was negligible, which is less than one percent per cycle. Since the activation temperature of all active sites of Pd/ZSM-5 for ethylene oxidation is 470 °C, the specific input energy requirement by heating the feed gas in order to activate the catalyst is estimated to be 544 J/L. This value is higher than that of the continuous plasma-catalytic oxidation (450 J/L) for at least 86% ethylene conversion. Interestingly, the cyclic adsorption and plasma-catalytic oxidation of ethylene is not only a low-temperature oxidation process but also reduces energy consumption. Specifically, the input energy requirement was 225 J/L, which is half that of the continuous plasma-catalytic oxidation; however, the adsorption efficiency and conversion rate were maintained. To summarize, cyclic plasma treatment is an effective ethylene removal technique in terms of low-temperature oxidation and energy consumption. Full article
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Open AccessReview
Design and Synthesis of Photoactive Iron N-Heterocyclic Carbene Complexes
Catalysts 2020, 10(1), 132; https://doi.org/10.3390/catal10010132 - 17 Jan 2020
Viewed by 181
Abstract
The use of iron in photoactive metal complexes has been investigated for decades. In this respect, the charge transfer (CT) states are of particular interest, since they are usually responsible for the photofunctionality of such compounds. However, only recently breakthroughs have been made [...] Read more.
The use of iron in photoactive metal complexes has been investigated for decades. In this respect, the charge transfer (CT) states are of particular interest, since they are usually responsible for the photofunctionality of such compounds. However, only recently breakthroughs have been made in extending CT excited state lifetimes that are notoriously short-lived in classical polypyridine iron coordination compounds. This success is in large parts owed to the use of strongly σ-donating N-heterocyclic carbene (NHC) ligands that help manipulating the photophysical and photochemical properties of iron complexes. In this review we aim to map out the basic design principles for the generation of photofunctional iron NHC complexes, summarize the progress made so far and recapitulate on the synthetic methods used. Further, we want to highlight the challenges still existing and give inspiration for future generations of photoactive iron complexes. Full article
(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)
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Open AccessArticle
In-Situ FT-IR Spectroscopy Investigation of CH4 and CO2 Reaction
Catalysts 2020, 10(1), 131; https://doi.org/10.3390/catal10010131 - 16 Jan 2020
Viewed by 146
Abstract
An exclusive trace of CH4 direct carboxylation with CO2 by a stepwise technology was investigated using in-situ FT-IR spectroscopy. The results showed that CH4 was dissociated to atomic hydrogen and M-CHx species on catalyst surface when it was first [...] Read more.
An exclusive trace of CH4 direct carboxylation with CO2 by a stepwise technology was investigated using in-situ FT-IR spectroscopy. The results showed that CH4 was dissociated to atomic hydrogen and M-CHx species on catalyst surface when it was first introduced in the system, then CO2 was inserted into the intermediate to direct carboxylate. Finally, the subsequent adsorption of CH4 provided active hydrogen for the species of previous surface reaction, thus leading to the formation of the product. It was also found that the first introduction of CO2 on the surface of the “clean” catalyst might likely react with surface H species, which had an irreversible effect on the catalytic activity of CH4. Full article
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Open AccessFeature PaperArticle
The Positive Effect of Iron Doping in the Electrocatalytic Activity of Cobalt Hexacyanoferrate
Catalysts 2020, 10(1), 130; https://doi.org/10.3390/catal10010130 - 16 Jan 2020
Viewed by 272
Abstract
The lack of an earth-abundant, robust, and fast electrocatalyst for the oxygen evolution reaction (water oxidation) is a major bottleneck for the development of an scalable scheme towards the production of electrolytic hydrogen and other synthetic fuels from renewable energy and natural feedstocks. [...] Read more.
The lack of an earth-abundant, robust, and fast electrocatalyst for the oxygen evolution reaction (water oxidation) is a major bottleneck for the development of an scalable scheme towards the production of electrolytic hydrogen and other synthetic fuels from renewable energy and natural feedstocks. While many transition metal oxides work reasonably well in basic media, very few alternatives are available in neutral or acidic media. One promising candidate comes from the Prussian blue family, cobalt hexacyanoferrate. This electrocatalyst offers robust activity in a large pH range ( 0 < pH < 13 ), although current densities are limited due to slow charge transfer kinetics. Herein, we report how the partial substitution of catalytically active Co centres by additional Fe boosts current densities, reaching over 100 mA/cm 2 , more than double the performance of the parent Co 2 [Fe(CN) 6 ]. Those new results clearly increase the opportunity for this catalyst to become relevant in industrial-ready electrolyser architectures. Full article
(This article belongs to the Special Issue Electrocatalytic Water Oxidation)
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Open AccessEditorial
Acknowledgement to Reviewers of Catalysts in 2019
Catalysts 2020, 10(1), 129; https://doi.org/10.3390/catal10010129 - 16 Jan 2020
Viewed by 171
Abstract
The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not [...] Full article
Open AccessArticle
Unique Features of a New Baeyer–Villiger Monooxygenase from a Halophilic Archaeon
Catalysts 2020, 10(1), 128; https://doi.org/10.3390/catal10010128 - 16 Jan 2020
Viewed by 194
Abstract
Type I Baeyer–Villiger monooxygenases (BVMOs) are flavin-dependent monooxygenases that catalyze the oxidation of ketones to esters or lactones, a reaction otherwise performed in chemical processes by employing hazardous and toxic peracids. Even though various BVMOs are extensively studied for their promising role in [...] Read more.
Type I Baeyer–Villiger monooxygenases (BVMOs) are flavin-dependent monooxygenases that catalyze the oxidation of ketones to esters or lactones, a reaction otherwise performed in chemical processes by employing hazardous and toxic peracids. Even though various BVMOs are extensively studied for their promising role in industrial biotechnology, there is still a demand for enzymes that are able to retain activity at high saline concentrations. To this aim, and based on comparative in silico analyses, we cloned HtBVMO from the extremely halophilic archaeon Haloterrigena turkmenica DSM 5511. When expressed in standard mesophilic cell factories, proteins adapted to hypersaline environments often behave similarly to intrinsically disordered polypeptides. Nevertheless, we managed to express HtBVMO in Escherichia coli and could purify it as active enzyme. The enzyme was characterized in terms of its salt-dependent activity and resistance to some water–organic-solvent mixtures. Although HtBVMO does not seem suitable for industrial applications, it provides a peculiar example of an alkalophilic and halophilic BVMO characterized by an extremely negative charge. Insights into the behavior and structural properties of such salt-requiring may contribute to more efficient strategies for engineering the tuned stability and solubility of existing BVMOs. Full article
(This article belongs to the Special Issue Flavin Monooxygenases)
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Open AccessCommunication
Additive-Free Baeyer–Villiger Oxidation of Cyclic Ketone Catalyzed by Carboxylic-Functionalized Poly(Ionic Liquids) and Polyoxometalate Ionic Self-Assemblies
Catalysts 2020, 10(1), 127; https://doi.org/10.3390/catal10010127 - 16 Jan 2020
Viewed by 129
Abstract
Two carboxylic functionalized poly(ionic liquids) and polyoxometalate ionic self-assemblies with tunable amphiphilic and oxidative activity and porous structure were designed and synthesized. They were used as efficient heterogeneous catalysts exhibiting excellent catalytic activity and quite stable reusability in additive–free Baeyer-Villiger oxidation of cyclic [...] Read more.
Two carboxylic functionalized poly(ionic liquids) and polyoxometalate ionic self-assemblies with tunable amphiphilic and oxidative activity and porous structure were designed and synthesized. They were used as efficient heterogeneous catalysts exhibiting excellent catalytic activity and quite stable reusability in additive–free Baeyer-Villiger oxidation of cyclic ketones, directly using 30% H2O2 solution in liquids–phase. Under optimum conditions, the corresponding lactones were obtained with yields ranging from 59.6 to 90.5%. The unique combination of carboxylic group with polyoxometalate anion, amphiphilic property, and porous structure is revealed to be responsible for their excellent catalytic performances in oxidation. Full article
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Open AccessFeature PaperReview
Recent Advances in Niobium-Based Materials for Photocatalytic Solar Fuel Production
Catalysts 2020, 10(1), 126; https://doi.org/10.3390/catal10010126 - 16 Jan 2020
Viewed by 166
Abstract
The search for renewable and clean energy sources is a key aspect for sustainable development as energy consumption has continuously increased over the years concomitantly with environmental concerns caused by the use of fossil fuels. Semiconductor materials have great potential for acting as [...] Read more.
The search for renewable and clean energy sources is a key aspect for sustainable development as energy consumption has continuously increased over the years concomitantly with environmental concerns caused by the use of fossil fuels. Semiconductor materials have great potential for acting as photocatalysts for solar fuel production, a potential energy source able to solve both energy and environmental concerns. Among the studied semiconductor materials, those based on niobium pentacation are still shallowly explored, although the number of publications and patents on Nb(V)-based photocatalysts has increased in the last years. A large variety of Nb(V)-based materials exhibit suitable electronic/morphological properties for light-driving reactions. Not only the extensive group of Nb2O5 polymorphs is explored, but also many types of layered niobates, mixed oxides, and Nb(V)-doped semiconductors. Therefore, the aim of this manuscript is to provide a review of the latest developments of niobium based photocatalysts for energy conversion into fuels, more specifically, CO2 reduction to hydrocarbons or H2 evolution from water. Additionally, the main strategies for improving the photocatalytic performance of niobium-based materials are discussed. Full article
(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)
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Open AccessArticle
Selective Hydration of Nitriles to Corresponding Amides in Air with Rh(I)-N-Heterocyclic Complex Catalysts
Catalysts 2020, 10(1), 125; https://doi.org/10.3390/catal10010125 - 16 Jan 2020
Viewed by 177
Abstract
A new synthetic method for obtaining [RhCl(cod)(NHC)] complexes (14) (cod = η4-1,5-cyclooctadiene, NHC = N-heterocyclic carbene: IMes, SIMes, IPr, and SIPr, respectively) is reported together with the catalytic properties of 14 in nitrile hydration. [...] Read more.
A new synthetic method for obtaining [RhCl(cod)(NHC)] complexes (14) (cod = η4-1,5-cyclooctadiene, NHC = N-heterocyclic carbene: IMes, SIMes, IPr, and SIPr, respectively) is reported together with the catalytic properties of 14 in nitrile hydration. In addition to the characterization of 14 in solution by 13C NMR spectroscopy, the structures of complexes 3, and 4 have been established also in the solid state with single-crystal X-ray diffraction analysis. The Rh(I)-NHC complexes displayed excellent catalytic activity in hydration of aromatic nitriles (up to TOF = 276 h−1) in water/2-propanol (1/1 v/v) mixtures in air. Full article
(This article belongs to the Special Issue Catalysis in Heterocyclic and Organometallic Synthesis)
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Open AccessArticle
Kinetic Model of the Action of 17α-Ethynylestradiol on the Capacitation of Mouse Sperm, Monitored by HPLC-MS/MS
Catalysts 2020, 10(1), 124; https://doi.org/10.3390/catal10010124 - 15 Jan 2020
Viewed by 235
Abstract
17α-Ethynylestradiol (EE2), a synthetic estrogen used in contraceptive pills, is resistant to hepatic degradation and is excreted in the urine. It is chemically stable and has a negative impact on the endocrine system. The aim of this work was to mathematically describe the [...] Read more.
17α-Ethynylestradiol (EE2), a synthetic estrogen used in contraceptive pills, is resistant to hepatic degradation and is excreted in the urine. It is chemically stable and has a negative impact on the endocrine system. The aim of this work was to mathematically describe the possible interaction of EE2 (200, 20, and 2 μg/L) with sperm estrogen receptors during sperm maturation, which is called capacitation. The concentrations of the unbound EE2 remaining in capacitating medium during 180 min of sperm capacitation were determined at 30 min intervals by high performance liquid chromatography with tandem mass spectrometric detection (HPLC-MS/MS) and the data obtained (relative concentrations Bt) were subjected to kinetic analysis. The suggested kinetic schema was described by the system of differential equations with the optimization of rate constants used to calculate the theoretical Bt values. Optimal parameters (overall rate constants K1K5 and molar ratio n) were determined by searching the minimum of absolute values of the difference between theoretical and experimental Bt values. These values were used for the design of the theoretical B(t) curves which fit to experimental points. The proposed kinetic model assumes the formation of an unstable adduct between EE2 and the receptor in cytoplasm, which acts as an autocatalytic agent and gradually decomposes. Full article
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Open AccessArticle
Determining the Location of Co2+ in Zeolites by UV-Vis Diffuse Reflection Spectroscopy: A Critical View
Catalysts 2020, 10(1), 123; https://doi.org/10.3390/catal10010123 - 15 Jan 2020
Viewed by 135
Abstract
UV–Vis spectroscopy as well as in situ FTIR spectroscopy of pyridine and CO adsorption were applied to determine the nature of Co species in microporous, mesoporous, and mixed oxide materials like Co–ZSM-5, Co/Na–ZSM-5, Co/Al–SBA-15, and Co/Al2O3–SiO2. Because [...] Read more.
UV–Vis spectroscopy as well as in situ FTIR spectroscopy of pyridine and CO adsorption were applied to determine the nature of Co species in microporous, mesoporous, and mixed oxide materials like Co–ZSM-5, Co/Na–ZSM-5, Co/Al–SBA-15, and Co/Al2O3–SiO2. Because all sample types show comparable UV–Vis spectra with a characteristic band triplet, the former described UV–Vis band deconvolution method for determination and quantification of individual cationic sites in the zeolite appears doubtful. This is also confirmed by results of pyridine and CO adsorption revealing that all Co–zeolite samples contain two types of Co2+ species located at exchange positions as well as in oxide-like clusters independent of the Co content, while in Co/Al–SBA-15 and Co/Al2O3–SiO2 only Co2+ species in oxide-like clusters occur. Consequently, the measured UV–Vis spectra represent not exclusively isolated Co2+ species, and the characteristic triplet band is not only related to γ-, β-, and α-type Co2+ sites in the zeolite but also to those dispersed on the surface of different oxide supports. The study demonstrates that for proper characterization of the formed Co species, the use of complementary methods is required. Full article
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Open AccessArticle
Chemically Bonded N-PDI-P/WO3 Organic-Inorganic Heterojunction with Improved Photoelectrochemical Performance
Catalysts 2020, 10(1), 122; https://doi.org/10.3390/catal10010122 - 15 Jan 2020
Viewed by 135
Abstract
The chemical bonding of bandgap adjustable organic semiconductors with inorganic semiconducting materials is effective in constructing a high-performance heterogeneous photoanode. In this study, a new asymmetric perylene diimide derivative molecule (N-PDI-P) was synthesized by connecting tert-butoxycarbonyl on an N-site at one end of [...] Read more.
The chemical bonding of bandgap adjustable organic semiconductors with inorganic semiconducting materials is effective in constructing a high-performance heterogeneous photoanode. In this study, a new asymmetric perylene diimide derivative molecule (N-PDI-P) was synthesized by connecting tert-butoxycarbonyl on an N-site at one end of a PDI molecule through methylene and connecting naphthalene directly onto the other end. This molecule was bonded onto the WO3 film surface, thereby forming the photoanode of organic-inorganic heterojunction. Under light illumination, the photocurrent density of chemically bonded N-PDI-P/WO3 heterojunction was twofold higher than that of physically adhered heterojunction for photoelectrochemical water oxidation at 0.6 V (vs. Ag/AgCl). Energy band structure and charge transfer dynamic analyses revealed that photogenerated electron carriers on the highest occupied molecular orbital (HOMO) of an N-PDI-P molecule can be transferred to the conduction band of WO3. The charge transfer and separation rates were accelerated considerably after the chemical bond formed at the N-PDI-P/WO3 interface. The proposed method provides a new way for the design and construction of organic-inorganic composite heterojunction. Full article
(This article belongs to the Section Catalytic Materials)
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Open AccessArticle
Characteristic and Catalytic Performance of Co and Co-Mo Metal Impregnated in Sarulla Natural Zeolite Catalyst for Hydrocracking of MEFA Rubber Seed Oil into Biogasoline Fraction
Catalysts 2020, 10(1), 121; https://doi.org/10.3390/catal10010121 - 15 Jan 2020
Viewed by 191
Abstract
This research was aimed to investigate the effect of Co and Co-Mo metal loaded on Sarulla Natural Zeolite which has been activated and calcined (SNZ-Cal) as supports for better understanding of characterization and catalytic activity on hydrocracking of MEFA rubber seed oil. The [...] Read more.
This research was aimed to investigate the effect of Co and Co-Mo metal loaded on Sarulla Natural Zeolite which has been activated and calcined (SNZ-Cal) as supports for better understanding of characterization and catalytic activity on hydrocracking of MEFA rubber seed oil. The Co and Co-Mo metal was added through a wet impregnation method using Co(NO3)2·6H2O and (NH4)·6Mo7O24·4H2O precursor salts. The catalyst was oxidized at 500 °C for 2 h within oxygen gas flow, followed by a reduction process with H2 gas flow with similar condition to obtain the catalysts. Based on the result, it was found that the resulted catalysts displayed an increase in crystal grain size compared to the metal-free catalyst. Particularly, catalyst that was impregnated with Co metal has a larger surface area and pore diameter and smaller pore volume than Co-Mo metal impregnated to the catalyst. In fact, it was revealed that this catalyst possessed the highest catalytic activity and selectivity. Furthermore, the resulting gas products reached 64 wt.% and the distribution of biogasoline fraction of hydrocarbons (C6-C12) amounted to 83.19 wt.%. Full article
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Open AccessReview
Recent Developments in Metal-Based Catalysts for the Catalytic Aerobic Oxidation of 5-Hydroxymethyl-Furfural to 2,5-Furandicarboxylic Acid
Catalysts 2020, 10(1), 120; https://doi.org/10.3390/catal10010120 - 15 Jan 2020
Viewed by 150
Abstract
Biomass can be used as an alternative feedstock for the production of fuels and valuable chemicals, which can alleviate the current global dependence on fossil resources. One of the biomass-derived molecules, 2,5-furandicarboxylic acid (FDCA), has attracted great interest due to its broad applications [...] Read more.
Biomass can be used as an alternative feedstock for the production of fuels and valuable chemicals, which can alleviate the current global dependence on fossil resources. One of the biomass-derived molecules, 2,5-furandicarboxylic acid (FDCA), has attracted great interest due to its broad applications in various fields. In particular, it is considered a potential substitute of petrochemical-derived terephthalic acid (PTA), and can be used for the preparation of valuable bio-based polyesters such as polyethylene furanoate (PEF). Therefore, significant attempts have been made for efficient production of FDCA and the catalytic chemical approach for FDCA production, typically from a biomass-derived platform molecule, 5-hydroxymethylfurfural (HMF), over metal catalysts is the focus of great research attention. In this review, we provide a systematic critical overview of recent progress in the use of different metal-based catalysts for the catalytic aerobic oxidation of HMF to FDCA. Catalytic performance and reaction mechanisms are described and discussed to understand the details of this reaction. Special emphasis is also placed on the base-free system, which is a more green process considering the environmental aspect. Finally, conclusions are given and perspectives related to further development of the catalysts are also provided, for the potential production of FDCA on a large scale in an economical and environmentally friendly manner. Full article
(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts)
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Open AccessCommunication
Potential Cycling Effects on Activities of Nickel-Mediated Benzyl Alcohol and Glycine Electrooxidation in Alkaline Solutions
Catalysts 2020, 10(1), 119; https://doi.org/10.3390/catal10010119 - 15 Jan 2020
Viewed by 175
Abstract
Nickel electrodes under continuous potential cycling were applied for the electrooxidation of benzyl alcohol and glycine in KOH solutions, and their activities were measured and compared by cyclic voltammetry. It is shown that intrinsic activities of both reactions decrease with the increasing catalyst [...] Read more.
Nickel electrodes under continuous potential cycling were applied for the electrooxidation of benzyl alcohol and glycine in KOH solutions, and their activities were measured and compared by cyclic voltammetry. It is shown that intrinsic activities of both reactions decrease with the increasing catalyst loadings, and a more significant decreasing trend was observed in glycine electrooxidation when compared to benzyl alcohol electrooxidation. These phenomena may be explained by an increasing of mass loading induced a decrease of the catalyst surface conductivity, structure changes of Ni(OH)2 from α-phase to β-phase, and the intercalation of glycine molecules into nickel hydroxide interlayers. Full article
(This article belongs to the Special Issue Electrocatalysis in Energy and Green Chemistry)
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Open AccessArticle
Characterization and Comparative Performance of TiO2 Photocatalysts on 6-Mercaptopurine Degradation by Solar Heterogeneous Photocatalysis
Catalysts 2020, 10(1), 118; https://doi.org/10.3390/catal10010118 - 14 Jan 2020
Viewed by 211
Abstract
The crystallographic properties of two titanium dioxide (TiO2) photocatalysts, P25, and commercial C1-TiO2 reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation [...] Read more.
The crystallographic properties of two titanium dioxide (TiO2) photocatalysts, P25, and commercial C1-TiO2 reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation of 6-mercaptopurine (6-MP) by heterogeneous photocatalysis with solar radiation under different pH conditions and the addition of hydrogen peroxide (H2O2); the degradation efficiency was monitored by UV–Vis spectrophotometry. The XRD analysis showed that both photocatalysts studied have anatase phase, while only P25 contains rutile; the band gap values were lower, in both catalysts, than those reported for catalysts obtained by the sol-gel method. With both photocatalysts, degradation experiments showed efficiency greater than 98% in experiments in the presence of H2O2 regardless of pH. The properties of the photocatalysts, along with the data obtained from the experimentation, helped determine the best semiconductor for the degradation of 6-MP with these operating conditions in this work. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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Open AccessArticle
Photodegradation of Gas Phase Benzene by SnO2 Nanoparticles by Direct Hole Oxidation Mechanism
Catalysts 2020, 10(1), 117; https://doi.org/10.3390/catal10010117 - 14 Jan 2020
Viewed by 175
Abstract
Photodegradation of gas phase benzene by SnO2 nanoparticles has been studied in humid air, dry air and N2 by using a tubular photoreactor. The SnO2 nanoparticles are synthesized by the oxidation of anhydrous stannic chloride (SnCl4) in a [...] Read more.
Photodegradation of gas phase benzene by SnO2 nanoparticles has been studied in humid air, dry air and N2 by using a tubular photoreactor. The SnO2 nanoparticles are synthesized by the oxidation of anhydrous stannic chloride (SnCl4) in a propane/air turbulent flame. Direct hole oxidation and the ·OH radical mechanisms have been discussed based on experimental results. The goal of this research is to explore a viable and efficient alternative photocatalyst and photocatalytic process, in particular, for humidity-tolerant photocatalyst or photocatalytic process in environmental applications. Full article
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Open AccessArticle
Valorization of Glycerol through the Enzymatic Synthesis of Acylglycerides with High Nutritional Value
Catalysts 2020, 10(1), 116; https://doi.org/10.3390/catal10010116 - 14 Jan 2020
Viewed by 163
Abstract
The production of specific acylglycerides from the selective esterification of glycerol is an attractive alternative for the valorization of this by-product of the biodiesel industry. In this way, products with high added value are generated, increasing the profitability of the overall process and [...] Read more.
The production of specific acylglycerides from the selective esterification of glycerol is an attractive alternative for the valorization of this by-product of the biodiesel industry. In this way, products with high added value are generated, increasing the profitability of the overall process and reducing an associated environmental threat. In this work, nutritional and medically interesting glycerides were obtained by enzymatic esterification through a two-stage process. In the first stage, 1,3-dicaprin was obtained by the regioselective esterification of glycerol and capric acid mediated by the commercial biocatalyst Lipozyme RM IM. Under optimal reaction conditions, 73% conversion of fatty acids and 76% selectivity to 1,3-dicaprin was achieved. A new model to explain the participation of lipase in the acyl migration reaction is presented. It evaluates the conditions in the microenvironment of the active site of the enzyme during the formation of the tetrahedral intermediate. In the second stage, the esterification of the sn-2 position of 1,3-dicaprin with palmitic acid was performed using the lipase from Burkholderia cepacia immobilized on chitosan as the biocatalyst. A biocatalyst containing 3 wt % of lipase showed good activity to esterify the sn-2 position of 1,3-dicaprin. A mixture of acylglycerides consisting mainly of capric acid esterified at sn-1 and sn-3, and of palmitic acid at the sn-2 position was obtained as the reaction product. The influence of the biocatalyst mass, the reaction temperature, and the molar ratio of substrates were evaluated for this reaction using a factorial design. Simple models were used to adjust the consumption of reagents and the generation of different products. The reaction product contained between 76% and 90% of acylglycerides with high nutritional value, depending on the reaction conditions. Full article
(This article belongs to the Special Issue New Glycerol Upgrading Processes)
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Open AccessArticle
Selective Hydrogenation of Acetylene Catalysed by a B12N12 Cluster Doped with a Single Nickel Atom: A DFT Study
Catalysts 2020, 10(1), 115; https://doi.org/10.3390/catal10010115 - 13 Jan 2020
Viewed by 210
Abstract
To obtain a catalyst based on a non-precious metal that can replace traditional palladium-based selective catalysts of acetylene hydrogenation, the catalytic performances of two different configurations of a B12N12 cluster doped with a single nickel atom were studied by a [...] Read more.
To obtain a catalyst based on a non-precious metal that can replace traditional palladium-based selective catalysts of acetylene hydrogenation, the catalytic performances of two different configurations of a B12N12 cluster doped with a single nickel atom were studied by a density functional theory computational approach. After analysing the effect that the adsorption of reactants onto the clusters has on the reaction path, we determined the lowest energy path for the acetylene double hydrogenation. Comparing the acetylene hydrogenation activities and ethylene product selectivities of the B11N12Ni and B12N11Ni clusters, which have different doping sites, we determined the activities of these two catalysts to be similar to each other; however, the B11N12Ni cluster was calculated to have higher selectivity for ethylene as a product. This difference may be related to the moderate adsorption of hydrogen and acetylene on the B11N12Ni cluster. As a new type of nickel-based single-atom catalyst, B11N12Ni clusters may have research value in the selective hydrogenation of acetylene. Full article
(This article belongs to the Special Issue Recent Advances in Nickel-Based Catalysts)
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Open AccessFeature PaperArticle
The Composition and Structure of Ultra-Dispersed Mixed Oxide (II, III) Particles and Their Influence on In-Situ Conversion of Heavy Oil
Catalysts 2020, 10(1), 114; https://doi.org/10.3390/catal10010114 - 13 Jan 2020
Viewed by 183
Abstract
This paper discusses the role of magnetite in the conversion of heavy oil from the Ashal’cha reservoir. The effect of catalysts on the in-situ upgrading of heavy oil is directed on the reduction of high-molecular components of oil such as resins and asphaltenes [...] Read more.
This paper discusses the role of magnetite in the conversion of heavy oil from the Ashal’cha reservoir. The effect of catalysts on the in-situ upgrading of heavy oil is directed on the reduction of high-molecular components of oil such as resins and asphaltenes and their molecular masses. Moreover, it is directed on the significant increase in saturates and aromatic fractions. Measuring the temperature-dependent viscosity characteristics revealed the tremendous viscosity decrease of the obtained catalytic aquathermolysis products. X-ray analysis exposed the composition of the initial catalyst that consisted of mixed iron oxides (II, III), as well as catalysts that were extracted from the treated crude oil. The particle size of the catalysts was investigated by scanning electron microscopy. According to the SEM data, aggregates of 200 nm were formed that were in the range of ultra-dispersed particles (200 to 500 nm). Full article
(This article belongs to the Special Issue The Development of Catalytic Systems for Heavy Oil)
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Open AccessArticle
Effect of Reduction of Pt–Sn/α-Al2O3 on Catalytic Dehydrogenation of Mixed-Paraffin Feed
Catalysts 2020, 10(1), 113; https://doi.org/10.3390/catal10010113 - 13 Jan 2020
Viewed by 160
Abstract
The effect of the Pt–Sn/α-Al2O3 catalyst reduction method on dehydrogenation of mixed-light paraffins to olefins has been studied in this work. Pt–Sn/α-Al2O3 catalysts were prepared by two different methods: (a) liquid phase reduction with NaBH4 and [...] Read more.
The effect of the Pt–Sn/α-Al2O3 catalyst reduction method on dehydrogenation of mixed-light paraffins to olefins has been studied in this work. Pt–Sn/α-Al2O3 catalysts were prepared by two different methods: (a) liquid phase reduction with NaBH4 and (b) gas phase reduction with hydrogen. The catalytic performance of these two catalysts for dehydrogenation of paraffins was compared. Also, the synergy between the catalyst reduction method and mixed-paraffin feed (against individual paraffin feed) was studied. The catalysts were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. The individual and mixed-paraffin feed dehydrogenation experiments were carried out in a packed bed reactor fabricated from Inconel 600, operating at 600 °C and 10 psi pressure. The dehydrogenation products were analyzed using an online gas chromatograph (GC) with flame ionization detector (FID). The total paraffin conversion and olefin selectivity for individual paraffin feed (propane only and butane only) and mixed-paraffin feed were compared. The conversion of propane only feed was found to be 10.7% and 9.9%, with olefin selectivity of 499% and 490% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of butane only feed was found to be 24.4% and 23.3%, with olefin selectivity of 405% and 418% for NaBH4 and hydrogen reduced catalysts, respectively. The conversion of propane and butane during mixed-feed dehydrogenation was measured to be 21.4% and 30.6% for the NaBH4 reduced catalyst, and 17.2%, 22.4% for the hydrogen reduced catalyst, respectively. The olefin selectivity was 422% and 415% for NaBH4 and hydrogen reduced catalysts, respectively. The conversions of propane and butane for mixed-paraffin feed were found to be higher when compared with individual paraffin dehydrogenation. The thermogravimetric studies of used catalysts under oxygen atmosphere showed that the amount of coke deposited during mixed-paraffin feed is less compared with individual paraffin feed for both catalysts. The study showed NaBH4 as a simple and promising alternative reduction method for the synthesis of Pt–Sn/Al2O3 catalyst for paraffin dehydrogenation. Further, the studies revealed that mixed-paraffin feed dehydrogenation gave higher conversions without significantly affecting olefin selectivity. Full article
(This article belongs to the Section Catalytic Materials)
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