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Catalysts, Volume 10, Issue 10 (October 2020) – 123 articles

Cover Story (view full-size image): Solar hydrogen generation from water splitting by photocatalysis is a promising approach to solving the energy crisis and environmental pollution issues. Ultrathin 2D semiconductor-based photocatalysts have been extensively studied due to their superior thickness-dependent physical, chemical, mechanical, and optical properties. View this paper
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0 pages, 1650 KiB  
Article
Comparison of the Photocatalytic Activity of ZnO/CeO2 and ZnO/Yb2O3 Mixed Systems in the Phenol Removal from Water: A Mechanicistic Approach
Catalysts 2020, 10(10), 1222; https://doi.org/10.3390/catal10101222 - 21 Oct 2020
Cited by 5 | Viewed by 2069
Abstract
In this paper we compare the photocatalytic activity of two semiconductors based on ZnO: ZnO/CeO2 and ZnO/Yb2O3. The two samples were prepared via hydrothermal synthesis and fully characterized by X-ray diffraction technique, diffuse reflectance Ultra Violet- Visible spectroscopy [...] Read more.
In this paper we compare the photocatalytic activity of two semiconductors based on ZnO: ZnO/CeO2 and ZnO/Yb2O3. The two samples were prepared via hydrothermal synthesis and fully characterized by X-ray diffraction technique, diffuse reflectance Ultra Violet- Visible spectroscopy (UV-Vis), high resolution transmission electron microscopy and finally with electron paramagnetic resonance spectroscopy. The prepared materials were also tested in their photocatalytic performances both through Electron Paramagnetic Resonance (EPR) analyzing the formation of charge carriers and with the abatement of a probe molecule like phenol, in presence and in absence of scavengers. Full article
(This article belongs to the Special Issue Photocatalysis and Environment)
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61 pages, 1805 KiB  
Review
Direct Alcoholysis of Carbohydrate Precursors and Real Cellulosic Biomasses to Alkyl Levulinates: A Critical Review
Catalysts 2020, 10(10), 1221; https://doi.org/10.3390/catal10101221 - 21 Oct 2020
Cited by 28 | Viewed by 3582
Abstract
Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, [...] Read more.
Alkyl levulinates (ALs) represent outstanding bio-fuels and strategic bio-products within the context of the marketing of levulinic acid derivatives. However, their synthesis by acid-catalyzed esterification of pure levulinic acid, or by acid-catalyzed alcoholysis of furfuryl alcohol, although relatively simple, is still economically disadvantageous, due to the high costs of the pure precursors. The direct one-pot alcoholysis of model C6 carbohydrates and raw biomass represents an alternative approach for the one-step synthesis of ALs. In order to promote the market for these bio-products and, concurrently, the immediate development of new applications, it is necessary to speed up the intensification of their production processes, and this important achievement is onlypossible by using low-cost or, even better, waste biomasses, as starting feedstocks. This review provides an overview of the most recent and promising advances on the one-pot production of ALs from model C6 carbohydrates and real biomasses, in the presence of homogeneous or heterogeneous acid catalysts. The use of model C6 carbohydrates allows for the identification of the best obtainable ALs yields, resulting in being strategic for the development of new smart catalysts, whose chemical properties must be properly tuned, taking into account the involved reaction mechanism. On the other hand, the transition to the real biomass now represents a necessary choice for allowing the next ALs production on a larger scale. The improvement of the available synthetic strategies, the use of raw materials and the development of new applications for ALs will contribute to develop more intensified, greener, and sustainable processes. Full article
(This article belongs to the Section Biomass Catalysis)
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15 pages, 7869 KiB  
Article
Fabrication of Ni-Based Bimodal Porous Catalyst for Dry Reforming of Methane
Catalysts 2020, 10(10), 1220; https://doi.org/10.3390/catal10101220 - 20 Oct 2020
Cited by 7 | Viewed by 2433
Abstract
Dry reforming of methane (DRM) can effectively convert two greenhouse gases into high-valued chemicals, in which the syngas produced by the reaction can be directly used as raw gases for Fischer–Tropsch synthesis and methanol synthesis. Ni-based catalysts for the DRM reaction with comparable [...] Read more.
Dry reforming of methane (DRM) can effectively convert two greenhouse gases into high-valued chemicals, in which the syngas produced by the reaction can be directly used as raw gases for Fischer–Tropsch synthesis and methanol synthesis. Ni-based catalysts for the DRM reaction with comparable initial activity to noble metals are the focus of most researchers, but their poor carbon deposition resistance easily causes their low stability. More importantly, the nickel loading will affect the catalytic activity and carbon deposition resistance of the catalyst. Herein, a series of Ni/Al2O3 catalysts with bimodal pores was prepared and characterized by X-ray diffraction (XRD), N2 physical adsorption–desorption, H2-temperature programmed reduction (H2-TPR), temperature programmed hydrogenation (TPH), Raman, and thermogravimetric analysis (TG). The results show that the interesting bimodal structure catalysts could provide a high surface area and contribute to the mass transfer. Besides, the catalytic performance of the DRM reaction is sensitive to nickel loadings. In this study, the Ni/Al2O3 catalyst with nickel loadings of 6% and 8% exhibited excellent catalytic activity and carbon deposition resistance. These findings will provide a new strategy to design a highly efficient and stable heterogeneous catalyst for industry. Full article
(This article belongs to the Special Issue Bimodal Porous Catalysts)
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16 pages, 1937 KiB  
Article
Catalytic Formation of Lactic and Levulinic Acids from Biomass Derived Monosaccarides through Sn-Beta Formed by Impregnation
Catalysts 2020, 10(10), 1219; https://doi.org/10.3390/catal10101219 - 20 Oct 2020
Cited by 6 | Viewed by 2601
Abstract
In the present study, the use of Sn-Beta zeolite to facilitate the conversion of lignocellulosic biomass-derived glucose and xylose into lactic and levulinic acid was explored. The reactions were carried out in a batch reactor using water as the solvent. Water is the [...] Read more.
In the present study, the use of Sn-Beta zeolite to facilitate the conversion of lignocellulosic biomass-derived glucose and xylose into lactic and levulinic acid was explored. The reactions were carried out in a batch reactor using water as the solvent. Water is the preferred solvent over methanol as it reduces downstream product acid recovery and purification complexity. Optimization experiments were performed for reaction temperature and residence time. Under optimized reaction conditions, the Sn-Beta facilitated reaction of a pure sugar solution resulted in lactic acid yields of 13 and 19 wt% of inlet carbon of glucose and xylose, respectively, plus levulinic acid yields of 18 and 0.8 wt%, respectively. When actual biomass-derived sugar solutions were tested, the yields of lactic acid were significantly higher than those from the optimized model solution experiments with lactic acid yields of 34 wt%. These biomass-derived sugar solutions contained residual levels of CaSO4 from the neutralization step of the hydrolysis process. Further experiments were performed to examine the potential effects from CaSO4 contributing to this increase. It was found that the sulfate ions increased the Brønsted basicity and the calcium increased the Lewis acidity of the reaction solution, and that the combination of both effects increased the conversion of the original sugars into lactic acid. These effects were verified by testing other organic bases to isolate the Brønsted acid neutralization effect and the Lewis acid enhancement effect. The addition of CaSO4 resulted in attractive lactic acid yields, 68 wt% and 50 wt% of inlet carbon from pure glucose and xylose solutions, respectively. Increasing the actual corn stover and forage sorghum derived sugars concentration (in water) allowed lactic acids yields of greater than 60 wt% to be achieved. When the optimized Sn-Beta reaction system was applied to corn stover and forage sorghum mixtures, it was found that the ratio of lactic-to-levulinic acid generated was inversely dependent upon the glucose-to-xylose ratio in the recovered sugar mixture. Full article
(This article belongs to the Special Issue Catalysis on Zeolites and Zeolite-Like Materials)
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29 pages, 12891 KiB  
Review
Progress and Challenges of Mercury-Free Catalysis for Acetylene Hydrochlorination
Catalysts 2020, 10(10), 1218; https://doi.org/10.3390/catal10101218 - 20 Oct 2020
Cited by 13 | Viewed by 3968
Abstract
Activated carbon-supported HgCl2 catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl2 is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis [...] Read more.
Activated carbon-supported HgCl2 catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl2 is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis of mercury-free and environmentally benign catalysts with high activity has become an urgent need for vinyl chloride monomer (VCM) production. This review summarizes research progress on the design and development of mercury-free catalysts for acetylene hydrochlorination. Three types of catalysts for acetylene hydrochlorination in the chlor-alkali chemical industry are discussed. These catalysts are a noble metal catalyst, non-noble metal catalyst, and non-metallic catalyst. This review serves as a guide in terms of the catalyst design, properties, and catalytic mechanism of mercury-free catalyst for the acetylene hydrochlorination of VCM. The key problems and issues are discussed, and future trends are envisioned. Full article
(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)
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15 pages, 6151 KiB  
Article
CO2 and H2O Coadsorption and Reaction on the Low-Index Surfaces of Tantalum Nitride: A First-Principles DFT-D3 Investigation
Catalysts 2020, 10(10), 1217; https://doi.org/10.3390/catal10101217 - 20 Oct 2020
Cited by 6 | Viewed by 2707
Abstract
A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 [...] Read more.
A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 in the absence and presence of H2O on the (001), (010), and (110) surfaces of tantalum nitride (Ta3N5), a photocatalysts of significant technological interest. The stability of the different Ta3N surfaces is shown to dictate the strength of adsorption and the extent of activation of CO2 and H2O species, which bind strongest to the least stable Ta3N5(001) surface and weakest to the most stable Ta3N5(110) surface. The adsorption of the CO2 on the Ta3N5(001), (010), and (110) surfaces is demonstrated to be characterized by charge transfer from surface species to the CO2 molecule, resulting in its activation (i.e., forming negatively charged bent CO2−δ species, with elongated C–O bonds confirmed via vibrational frequency analyses). Compared to direct CO2 dissociation, H2O dissociates spontaneously on the Ta3N5 surfaces, providing the necessary hydrogen source for CO2 reduction reactions. The coadsorption reactions of CO2 and H2O are demonstrated to exhibit the strongest attractive interactions on the (010) surface, giving rise to proton transfer to the CO2 molecule, which causes its spontaneous dissociation to form CO and 2OH species. These results demonstrate that Ta3N5, a narrow bandgap photocatalyst able to absorb visible light, can efficiently activate the CO2 molecule and photocatalytically reduce it with water to produce value-added fuels. Full article
(This article belongs to the Section Computational Catalysis)
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13 pages, 1661 KiB  
Article
A Multi-Enzyme Cascade for the Production of High-Value Aromatic Compounds
Catalysts 2020, 10(10), 1216; https://doi.org/10.3390/catal10101216 - 20 Oct 2020
Cited by 13 | Viewed by 3402
Abstract
Cascade reactions are the basis of life in nature and are adapted to research and industry in an increasing manner. The focus of this study is the production of the high-value aromatic ester cinnamyl cinnamate, which can be applied in flavors and fragrances. [...] Read more.
Cascade reactions are the basis of life in nature and are adapted to research and industry in an increasing manner. The focus of this study is the production of the high-value aromatic ester cinnamyl cinnamate, which can be applied in flavors and fragrances. A three-enzyme cascade was established to realize the synthesis, starting from the corresponding aldehyde with in situ cofactor regeneration in a two-phase system. After characterization of the enzymes, a screening with different organic solvents was carried out, whereby xylene was found to be the most suitable solvent for the second phase. The reaction stability of the formate dehydrogenase (FDH) from Candida boidinii is the limiting step during cofactor regeneration. However, the applied enzyme cascade showed an overall yield of 54%. After successful application on lab scale, the limitation by the FDH was overcome by immobilization of the enzymes and an optimized downstream process, transferring the cascade into a miniplant. The upscaling resulted in an increased yield for the esterification, as well as overall yields of 37%. Full article
(This article belongs to the Special Issue Multi-Step Syntheses in Biology & Chemistry)
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14 pages, 46546 KiB  
Article
Selective Hydrogenation of Naphthalene over γ-Al2O3-Supported NiCu and NiZn Bimetal Catalysts
Catalysts 2020, 10(10), 1215; https://doi.org/10.3390/catal10101215 - 20 Oct 2020
Cited by 9 | Viewed by 2745
Abstract
A series of Cu and Zn modified Ni/Al2O3 catalysts were prepared using an incipient impregnation method for the selective hydrogenation of naphthalene into tetralin. X-ray diffraction (XRD), H2-Temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and [...] Read more.
A series of Cu and Zn modified Ni/Al2O3 catalysts were prepared using an incipient impregnation method for the selective hydrogenation of naphthalene into tetralin. X-ray diffraction (XRD), H2-Temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were applied to reveal the structure regulation, and density functional theory (DFT) calculations were performed to investigate the electronic effect and reactant adsorptions on the active sites. The results showed that the addition of CuO promoted the hydrogenation of naphthalene with an inhibited tetraline selectivity. However, a simultaneously increasing naphthalene conversion and tetraline selectivity were achieved over the Zn modified Ni/Al2O3 catalysts. The characterization and calculation results revealed that the doping of CuO improved the hydrogenation activity with a low tetralin selectivity due to the H spillover from the Cu. The addition of ZnO decreased the interaction between NiOx and Al2O3 in NiZn/Al2O3 catalysts, which efficiently increased the reduction ability of NiOx species and, thus, improved the naphthalene hydrogenation activity. The electron transfer from ZnO to NiOx weakened the adsorption of tetraline and resulted in increased tetraline selectivity. This work provides insight into developing efficient catalysts for heavy aromatics conversions via rational surface engineering. Full article
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12 pages, 1509 KiB  
Article
Spirogyra Oil-Based Biodiesel: Response Surface Optimization of Chemical and Enzymatic Transesterification and Exhaust Emission Behavior
Catalysts 2020, 10(10), 1214; https://doi.org/10.3390/catal10101214 - 20 Oct 2020
Cited by 5 | Viewed by 2986
Abstract
Algae are emerging as a major and reliable source of renewable biodiesel that could meet the energy requirements of the world. Like plants, algae produce and store oils in their cells. Algal samples were collected from Gujrat District, Pakistan, their oil content was [...] Read more.
Algae are emerging as a major and reliable source of renewable biodiesel that could meet the energy requirements of the world. Like plants, algae produce and store oils in their cells. Algal samples were collected from Gujrat District, Pakistan, their oil content was analyzed, and the best oil producing alga was identified as Spirogyra crassa. After collecting sample, oil was extracted using the Soxhlet extraction method. Spirogyra oil was characterized physico-chemically for the evaluation of its quality. Acid value, density, saponification value, peroxide value, as well as viscosity and iodine values were determined and their values were 16.67 ± 3.53 mg KOH/g, 0.859 ± 0.050 g/cm3, 165.33 ± 13.20 mg KOH/g, 4.633 ± 0.252 meq/kg, 5.63 ± 0.833 mm2/mL, and 117.67 ± 13.01 mg I2/g, respectively. Chemical as well as enzymatic transesterification protocols were employed for biodiesel production using NaOCH3 and NOVOZYME-435, respectively. Different reactions parameters involved in transesterification were optimized by the response surface methodology. The optimized yield of biodiesel (77.3 ± 1.27%) by the chemical transesterification of algal oil (spirogyra) was observed by carrying out the reaction for 90 minutes at a reaction temperature of 45 °C using 1.13% catalyst (NaOCH3) concentration and 6:1 methanol:oil. Meanwhile, for enzymatic transesterification, the optimized yield (93.2 ± 1.27%) was obtained by conducting the reaction for 42.5 h at the temperature of 35 °C using 1% enzyme concentration and 4.5:1 methanol:oil. Fuel properties, including flash point, pour point, cloud point, fire point, kinematic viscosity, and density, were determined and their values are 125.67 ± 2.11 °C, −19.67 ± 0.8 °C, −13 ± 1 °C, 138.667 ± 2.52 °C, 5.87 ± 2.20 mm2/mL, and 0.85 6 ± 0.03 g/cm3, respectively. Fourier transfer infrared spectroscopic (FTIR) and Gas chromatography with flame ionization detector (GC-FID) analysis were performed for the monitoring of the transesterification process and fatty acid methyl acid (FAME) profiling, respectively. Full article
(This article belongs to the Special Issue Biocatalysis and Whole-Cell Biotransformation in Biomanufacturing)
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9 pages, 2751 KiB  
Communication
Effect of Cu and Cs in the β-Mo2C System for CO2 Hydrogenation to Methanol
Catalysts 2020, 10(10), 1213; https://doi.org/10.3390/catal10101213 - 20 Oct 2020
Cited by 18 | Viewed by 2593
Abstract
Mitigation of anthropogenic CO2 emissions possess a major global challenge for modern societies. Herein, catalytic solutions are meant to play a key role. Among the different catalysts for CO2 conversion, Cu supported molybdenum carbide is receiving increasing attention. Hence, in the [...] Read more.
Mitigation of anthropogenic CO2 emissions possess a major global challenge for modern societies. Herein, catalytic solutions are meant to play a key role. Among the different catalysts for CO2 conversion, Cu supported molybdenum carbide is receiving increasing attention. Hence, in the present communication, we show the activity, selectivity and stability of fresh-prepared β-Mo2C catalysts and compare the results with those of Cu/Mo2C, Cs/Mo2C and Cu/Cs/Mo2C in CO2 hydrogenation reactions. The results show that all the catalysts were active, and the main reaction product was methanol. Copper, cesium and molybdenum interaction is observed, and cesium promoted the formation of metallic Mo on the fresh catalyst. The incorporation of copper is positive and improves the activity and selectivity to methanol. Additionally, the addition of cesium favored the formation of Mo0 phase, which for the catalysts Cs/Mo2C seemed to be detrimental for the conversion and selectivity. Moreover, the catalysts promoted by copper and/or cesium underwent redox surface transformations during the reaction, these were more obvious for cesium doped catalysts, which diminished their catalytic performance. Full article
(This article belongs to the Special Issue Catalysts for CO2 Conversion, Upgrading and Recycling)
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23 pages, 4008 KiB  
Article
Improved NOx Reduction Using C3H8 and H2 with Ag/Al2O3 Catalysts Promoted with Pt and WOx
Catalysts 2020, 10(10), 1212; https://doi.org/10.3390/catal10101212 - 19 Oct 2020
Cited by 6 | Viewed by 2264
Abstract
The addition of Pt (0.1 wt%Pt) to the 2 wt%Ag/Al2O3-WOx catalyst improved the C3H8– Selective Catalytic Reduction (SCR) of NO assisted by H2 and widened the range of the operation window. During H2 [...] Read more.
The addition of Pt (0.1 wt%Pt) to the 2 wt%Ag/Al2O3-WOx catalyst improved the C3H8– Selective Catalytic Reduction (SCR) of NO assisted by H2 and widened the range of the operation window. During H2–C3H8–SCR of NO, the bimetallic Pt–Ag catalyst showed two maxima in conversion: 80% (at 130 °C) and 91% (between 260 and 350 °C). This PtAg bimetallic catalyst showed that it could combine the catalytic properties of Pt at low temperature, with the properties of Ag/Al2O3 at high temperature. These PtAg catalysts were composed of Ag+, Agnδ+ clusters, and PtAg nanoparticles. The catalysts were characterized by Temperature Programmed Reduction (TPR), Ultraviolet Visible Spectroscopy (UV-Vis), Scanning Electron Microscopy (SEM)/ Energy Dispersed X-ray Spectroscopy (EDS), x-ray Diffraction (XRD) and N2 physisorption. The PtAg bimetallic catalysts were able to chemisorb H2. The dispersion of Pt in the bimetallic catalysts was the largest for the catalyst with the lowest Pt/Ag atomic ratio. Through SEM, mainly spherical clusters smaller than 10 nm were observed in the PtAg catalyst. There were about 32% of particles with size equal or below 10 nm. The PtAg bimetallic catalysts produced NO2 in the intermediate temperature range as well as some N2O. The yield to N2O was proportional to the Pt/Ag atomic ratio and reached 8.5% N2O. WOx stabilizes Al2O3 at temperatures ≥650 °C, and also stabilizes Pt when it is reduced in H2 at high temperature (800 °C). Full article
(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)
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13 pages, 4200 KiB  
Article
Double Spirocyclization of Arylidene-Δ2-Pyrrolin-4-Ones with 3-Isothiocyanato Oxindoles
Catalysts 2020, 10(10), 1211; https://doi.org/10.3390/catal10101211 - 19 Oct 2020
Cited by 7 | Viewed by 2175
Abstract
Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single [...] Read more.
Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed double spirocyclization with 3-isothiocianato oxindoles in a domino 1,4/1,2-addition sequence. The products contain three contiguous stereocenters (ee up to 98%, dr up to 99:1, 12 examples). The absolute configuration of the major diastereomer was determined by single crystal X-ray analysis. Along with heterocyclic Michael acceptors based on oxazolone, isoxazolone, thiazolidinone, pyrazolone, and pyrimidinedione, the reported results display the applicability of unsaturated Δ2-pyrrolin-4-ones (pyrrolones) for the organocatalyzed construction of 3D-rich pyrrolone-containing heterocycles. Full article
(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)
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35 pages, 4679 KiB  
Review
Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights
Catalysts 2020, 10(10), 1210; https://doi.org/10.3390/catal10101210 - 19 Oct 2020
Cited by 31 | Viewed by 4015
Abstract
An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using [...] Read more.
An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using different nucleophiles HNu that add to the alkyne triple bond are presented and discussed. The effects of the nature of the employed alkyne substrate and of the gold catalyst (employed ligands, counteranions, gold oxidation state), of additional additives and of the reaction conditions are also considered. Aim of this work is to provide the reader with a detailed mechanistic knowledge of this important reaction class, which will be invaluable for rapidly developing and optimizing synthetic protocols involving a gold-catalyzed alkyne hydrofunctionalization as a reaction step. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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13 pages, 1992 KiB  
Article
Development of Facile and Simple Processes for the Heterogeneous Pd-Catalyzed Ligand-Free Continuous-Flow Suzuki–Miyaura Coupling
Catalysts 2020, 10(10), 1209; https://doi.org/10.3390/catal10101209 - 19 Oct 2020
Cited by 6 | Viewed by 2712
Abstract
The Suzuki–Miyaura coupling reaction is one of the most widely utilized C–C bond forming methods to create (hetero)biaryl scaffolds. The continuous-flow reaction using heterogeneous catalyst-packed cartridges is a practical and efficient synthetic method to replace batch-type reactions. A continuous-flow ligand-free Suzuki–Miyaura coupling reaction [...] Read more.
The Suzuki–Miyaura coupling reaction is one of the most widely utilized C–C bond forming methods to create (hetero)biaryl scaffolds. The continuous-flow reaction using heterogeneous catalyst-packed cartridges is a practical and efficient synthetic method to replace batch-type reactions. A continuous-flow ligand-free Suzuki–Miyaura coupling reaction of (hetero)aryl iodides, bromides, and chlorides with (hetero)aryl boronic acids was developed using cartridges packed with spherical resin (tertiary amine-based chelate resin: WA30)-supported palladium catalysts (7% Pd/WA30). The void space in the cartridge caused by the spherical catalyst structures enables the smooth flow of a homogeneously dissolved reaction solution that consists of a mixture of organic and aqueous solvents and is delivered by the use of a single syringe pump. Clogging or serious backpressure was not observed. Full article
(This article belongs to the Special Issue Advances in Catalytic Coupling Reactions)
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9 pages, 2650 KiB  
Article
Tuning Photocatalytic Performance of Multilayer ZnO for Water Splitting by Biaxial Strain Composites
Catalysts 2020, 10(10), 1208; https://doi.org/10.3390/catal10101208 - 19 Oct 2020
Cited by 6 | Viewed by 2106
Abstract
Novel two-dimensional (2D) materials have received extensive attention in the field of photocatalysis due to their unique properties. Traditional ZnO material with wurtzite structure transforms into a stable graphite-like structure that has the characteristics of 2D material when its thickness is less than [...] Read more.
Novel two-dimensional (2D) materials have received extensive attention in the field of photocatalysis due to their unique properties. Traditional ZnO material with wurtzite structure transforms into a stable graphite-like structure that has the characteristics of 2D material when its thickness is less than a few atomic layers. In this work, using first-principles calculations, we investigated the potential of multilayer graphite-like ZnO as a photocatalyst for water splitting. The results showed that multilayer ZnO is a series of direct bandgap semiconductors, and their band edge positions all straddle the redox potential of water. Increasing with the number of layers, the bandgap of multilayer ZnO decreased from 3.20 eV for one layer to 2.21 eV for six layers, and visible light absorption capacity was significantly enhanced. Hence, multilayer ZnO was indeed promising for photocatalytic water splitting. Furthermore, suitable biaxial tensile strain could decrease the bandgap and maintain the stable graphite-like structure at a broader thickness range. In contrast, excessive biaxial tensile strain could change the redox capacity of multilayer ZnO and prevent it from catalyzing water splitting. Our theoretical results show that six-layer ZnO under 1% biaxial strain had direct bandgap of 2.07 eV and represents the most excellent photocatalytic performance among these multilayer ZnO materials. Full article
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23 pages, 2237 KiB  
Article
Multi-Combilipases: Co-Immobilizing Lipases with Very Different Stabilities Combining Immobilization via Interfacial Activation and Ion Exchange. The Reuse of the Most Stable Co-Immobilized Enzymes after Inactivation of the Least Stable Ones
Catalysts 2020, 10(10), 1207; https://doi.org/10.3390/catal10101207 - 19 Oct 2020
Cited by 28 | Viewed by 2663
Abstract
The lipases A and B from Candida antarctica (CALA and CALB), Thermomyces lanuginosus (TLL) or Rhizomucor miehei (RML), and the commercial and artificial phospholipase Lecitase ultra (LEU) may be co-immobilized on octyl agarose beads. However, LEU and RML became almost fully inactivated under [...] Read more.
The lipases A and B from Candida antarctica (CALA and CALB), Thermomyces lanuginosus (TLL) or Rhizomucor miehei (RML), and the commercial and artificial phospholipase Lecitase ultra (LEU) may be co-immobilized on octyl agarose beads. However, LEU and RML became almost fully inactivated under conditions where CALA, CALB and TLL retained full activity. This means that, to have a five components co-immobilized combi-lipase, we should discard 3 fully active and immobilized enzymes when the other two enzymes are inactivated. To solve this situation, CALA, CALB and TLL have been co-immobilized on octyl-vinyl sulfone agarose beads, coated with polyethylenimine (PEI) and the least stable enzymes, RML and LEU have been co-immobilized over these immobilized enzymes. The coating with PEI is even favorable for the activity of the immobilized enzymes. It was checked that RML and LEU could be released from the enzyme-PEI coated biocatalyst, although this also produced some release of the PEI. That way, a protocol was developed to co-immobilize the five enzymes, in a way that the most stable could be reused after the inactivation of the least stable ones. After RML and LEU inactivation, the combi-biocatalysts were incubated in 0.5 M of ammonium sulfate to release the inactivated enzymes, incubated again with PEI and a new RML and LEU batch could be immobilized, maintaining the activity of the three most stable enzymes for at least five cycles of incubation at pH 7.0 and 60 °C for 3 h, incubation on ammonium sulfate, incubation in PEI and co-immobilization of new enzymes. The effect of the order of co-immobilization of the different enzymes on the co-immobilized biocatalyst activity was also investigated using different substrates, finding that when the most active enzyme versus one substrate was immobilized first (nearer to the surface of the particle), the activity was higher than when this enzyme was co-immobilized last (nearer to the particle core). Full article
(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)
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36 pages, 12381 KiB  
Review
Gold-Catalyzed Addition of Carboxylic Acids to Alkynes and Allenes: Valuable Tools for Organic Synthesis
Catalysts 2020, 10(10), 1206; https://doi.org/10.3390/catal10101206 - 18 Oct 2020
Cited by 21 | Viewed by 4138
Abstract
In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the [...] Read more.
In this contribution, the application of gold-based catalysts in the hydrofunctionalization reactions of alkynes and allenes with carboxylic acids is comprehensively reviewed. Both intra- and intermolecular processes, leading respectively to lactones and linear unsaturated esters, are covered. In addition, cascade transformations involving the initial cycloisomerization of an alkynoic acid are also discussed. Full article
(This article belongs to the Special Issue Recent Advances in Organometallic Chemistry and Catalysis)
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12 pages, 3907 KiB  
Article
Removal of Nonylphenol Polyethylene Glycol (NPEG) with Au-TiO2 Catalysts: Kinetic and Initial Transformation Path
Catalysts 2020, 10(10), 1205; https://doi.org/10.3390/catal10101205 - 17 Oct 2020
Viewed by 2017
Abstract
The purpose of this study was to evaluate the efficiency of the Au-TiO2 catalyst in the degradation of nonylphenol polyethylene glycol (NPEG). In the first part of the study, the catalyst was synthesized and characterized. Initially, the catalyst (TiO2 Degussa P-25) [...] Read more.
The purpose of this study was to evaluate the efficiency of the Au-TiO2 catalyst in the degradation of nonylphenol polyethylene glycol (NPEG). In the first part of the study, the catalyst was synthesized and characterized. Initially, the catalyst (TiO2 Degussa P-25) was doped with gold precursor salts (HAuCl4) at different concentrations (5, 10, and 15%) and the photodeposition method with UV light. It was determined by diffuse reflectance (DF) and scanning electron microscopy (SEM) that the photodeposition method was effective for the inclusion of gold particles on the surface. The catalyst band gap showed a reduction to 2.9 e.v (compared to TiO2 Degussa P-25), and it was observed that the gold-doped catalyst showed absorption in the visible light range 500 to 600 nm. The percentage of deposited gold was determined by energy dispersive spectroscopy (EDS). In the second part of the study, various NPEG degradation experiments were performed; with the catalyst that showed the best conversion percentages of NPEG, the experimental data were analyzed using UV-Vis spectrophotometry and TOC (total organic carbon). With these results, a carbon-based mass balance and reaction kinetics were generated using the Langmuir–Hinshelwood (L–H) heterogeneous catalysis model. For the estimation of the kinetic constants, the non-linear regression of the Levenger–Marquardt algorithm was used. With these results, kinetic models of the degradation of the molecule and the generation and consumption of organic intermediate products (OIPs) were generated. Full article
(This article belongs to the Special Issue Environmental Catalysis in Advanced Oxidation Processes)
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16 pages, 6115 KiB  
Article
CHA-Type Zeolite Prepared by Interzeolite Conversion Method Using FAU and LTL-Type Zeolite: Effect of the Raw Materials on the Crystallization Mechanism, and Physicochemical and Catalytic Properties
Catalysts 2020, 10(10), 1204; https://doi.org/10.3390/catal10101204 - 17 Oct 2020
Cited by 16 | Viewed by 3449
Abstract
The effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agents (OSDAs) on the crystallization mechanism, and physicochemical and catalytic properties of the CHA-type aluminosilicate zeolite was investigated. For this purpose, the FAU-type and the LTL-type zeolites were [...] Read more.
The effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agents (OSDAs) on the crystallization mechanism, and physicochemical and catalytic properties of the CHA-type aluminosilicate zeolite was investigated. For this purpose, the FAU-type and the LTL-type zeolites were used as raw material, and trymethyladamantyl ammonium hydroxide and tetraethyl ammonium hydroxide were used as OSDAs. We firstly found that the CHA-type aluminosilicate zeolite was crystallized from the combination of the LTL-type zeolite and tetraethyl ammonium hydroxide as raw materials. The crystallization behaviors were also monitored in detail. The crystallization was delayed by using the LTL-type zeolite as the starting material regardless of the type of OSDA because of the low solubility of the LTL-type zeolite compared to the FAU-type zeolite. We have found that the Al distribution in the CHA framework was dependent on the raw materials. Thus, the prepared CHA-type aluminosilicate zeolite from the LTL-type zeolite exhibited a high thermal stability and catalytic performance in the methanol to olefins reaction. Full article
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9 pages, 2387 KiB  
Article
Large-Area Patterning of Oil-Based Inks on Superhydrophobic TiO2 Nanotubular Layers by Photocatalytic Wettability Conversion
Catalysts 2020, 10(10), 1203; https://doi.org/10.3390/catal10101203 - 17 Oct 2020
Cited by 3 | Viewed by 1704
Abstract
Patterning an oil-based ink on a solid surface based on a wettability difference is of significant importance for the application of offset printing. Herein, we describe a large-area patterning of oil-based ink on a self-organized TiO2 nanotubular layer based on a photocatalytic [...] Read more.
Patterning an oil-based ink on a solid surface based on a wettability difference is of significant importance for the application of offset printing. Herein, we describe a large-area patterning of oil-based ink on a self-organized TiO2 nanotubular layer based on a photocatalytic wettability conversion. The TiO2 nanotubular layer was fabricated by electrochemical anodization, which demonstrated a superhydrophobic wettability after modification with a self-assembled molecular layer. Subsequently, area-selective ultraviolet (UV) irradiation through a pre-designed pattern of water-based UV-resistant ink formed by an ink-jet technique was used to form a wettability difference. After removing the water-based ink, an oil-based ink was capable of depositing selectively on the superhydrophobic area to form the same pattern as the pre-designed pattern of water-based ink. This large-area patterning of an oil-based ink based on the photocatalytic wettability conversion is potentially applicable in offset printing. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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18 pages, 49862 KiB  
Article
Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing
Catalysts 2020, 10(10), 1202; https://doi.org/10.3390/catal10101202 - 17 Oct 2020
Cited by 34 | Viewed by 2917
Abstract
This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. [...] Read more.
This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. The different coumarin derivatives can also be employed in three component photoinitiating systems with a Iod/amine (ethyl 4-dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)) couple for FRP upon irradiation with an LED @ 405 nm. These compounds showed excellent photoinitiating abilities, and high polymerization rates and final conversions (FC) were obtained. The originality of this work relies on the comparison of the photoinitiating abilities of monofunctional (Coum1 and Coum2) vs. difunctional (Coum3) compounds. Coum3 is a combined structure of Coum1 and Coum2, leading to a sterically hindered chemical structure with a relatively high molecular weight. As a general rule, a high molecular weight should reduce the migration of initiating molecules and favor photochemical properties such as photobleaching of the final polymer. As attempted, from the efficiency point of view, Coum3 can initiate the FRP, but a low reactivity was observed compared to the monofunctional compound (Coum1 and Coum2). Indeed, to study the photochemical and photophysical properties of these compounds, different parameters were taken into account, e.g., the light absorption and emission properties, steady state photolysis, and fluorescence quenching. To examine these different points, several techniques were used including UV-visible spectroscopy, real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), fluorescence spectroscopy, and cyclic voltammetry. The photochemical mechanism involved in the polymerization process is also detailed. The best coumarins investigated in this work were used for laser writing (3D printing) experiments and also for photocomposite synthesis containing glass fibers. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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16 pages, 6346 KiB  
Article
CO2 Methanation of Biogas over 20 wt% Ni-Mg-Al Catalyst: on the Effect of N2, CH4, and O2 on CO2 Conversion Rate
Catalysts 2020, 10(10), 1201; https://doi.org/10.3390/catal10101201 - 16 Oct 2020
Cited by 22 | Viewed by 2723
Abstract
Biogas contains more than 40% CO2 that can be removed to produce high quality CH4. Recently, CH4 production from CO2 methanation has been reported in several studies. In this study, CO2 methanation of biogas was performed over [...] Read more.
Biogas contains more than 40% CO2 that can be removed to produce high quality CH4. Recently, CH4 production from CO2 methanation has been reported in several studies. In this study, CO2 methanation of biogas was performed over a 20 wt% Ni-Mg-Al catalyst, and the effects of CO2 conversion rate and CH4 selectivity were investigated as a function of CH4, O2, H2O, and N2 compositions of the biogas. At a gas hourly space velocity (GHSV) of 30,000 h−1, the CO2 conversion rate was ~79.3% with a CH4 selectivity of 95%. In addition, the effects of the reaction temperature (200–450 °C), GHSV (21,000–50,000 h−1), and H2/CO2 molar ratio (3–5) on the CO2 conversion rate and CH4 selectivity over the 20 wt% Ni-Mg-Al catalyst were evaluated. The characteristics of the catalyst were analyzed using Brunauer–Emmett–Teller surface area analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The catalyst was stable for approximately 200 h at a GHSV of 30,000 h−1 and a reaction temperature of 350 °C. CO2 conversion and CH4 selectivity were maintained at 75% and 93%, respectively, and the catalyst was therefore concluded to exhibit stable activity. Full article
(This article belongs to the Special Issue Characterization Analysis of Heterogeneous Catalysts)
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19 pages, 5214 KiB  
Article
Kinetics and Nanoparticle Catalytic Enhancement of Biogas Production from Wastewater Using a Magnetized Biochemical Methane Potential (MBMP) System
Catalysts 2020, 10(10), 1200; https://doi.org/10.3390/catal10101200 - 16 Oct 2020
Cited by 21 | Viewed by 2930
Abstract
This study presents magnetized nanoparticles (NPs) as a catalyst to accelerate anaerobic digestion (AD) potential for clean and ecofriendly energy (biogas) from wastewater settings. The effects of iron oxides (Ms) and aluminum sulphate (Alum) were investigated using two chronological experiments: (i) the Jar [...] Read more.
This study presents magnetized nanoparticles (NPs) as a catalyst to accelerate anaerobic digestion (AD) potential for clean and ecofriendly energy (biogas) from wastewater settings. The effects of iron oxides (Ms) and aluminum sulphate (Alum) were investigated using two chronological experiments: (i) the Jar test technique to generate residue slurry as organic fertilizer potential and (ii) a magnetized biochemical methane potential (MBMP) system for biogas production at mesophilic conditions for 21 days. X-ray diffraction and Fourier Transform Infrared spectroscopy were carried out to establish the Ms Crystallite and active functional groups respectively. Scanning electronic microscopy coupled with energy dispersive X-ray spectrometer and elemental analysis were used to track and confirm NPs inclusion after the post-AD process. Coagulation at 50 mg/L and magnetic exposure time of 30 min showed above 85% treatability performance by Ms as compared to 70% for Alum. Owing to the slow kinetics of the AD process, additional NPs content in the digesters coupled with an external magnetic field improved their performance. Cumulative biogas yields of 1460 mL/d > 610 mL/d > 505 mL/d for Ms > Control > Alum respectively representing 80% > 61% > 52% of CH4 were attained. The modified Gompertz model shows that the presence of NPs shortens the lag phase of the control system with kinetics rate constants of 0.285 1/d (control) to 0.127 1/d (Ms) < 0.195 1/d (Alum). Full article
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25 pages, 6979 KiB  
Review
Evolution of Pauson-Khand Reaction: Strategic Applications in Total Syntheses of Architecturally Complex Natural Products (2016–2020)
Catalysts 2020, 10(10), 1199; https://doi.org/10.3390/catal10101199 - 16 Oct 2020
Cited by 27 | Viewed by 6161
Abstract
Metal-mediated cyclizations are important transformations in a natural product total synthesis. The Pauson-Khand reaction, particularly powerful for establishing cyclopentenone-containing structures, is distinguished as one of the most attractive annulation processes routinely employed in synthesis campaigns. This review covers Co, Rh, and Pd catalyzed [...] Read more.
Metal-mediated cyclizations are important transformations in a natural product total synthesis. The Pauson-Khand reaction, particularly powerful for establishing cyclopentenone-containing structures, is distinguished as one of the most attractive annulation processes routinely employed in synthesis campaigns. This review covers Co, Rh, and Pd catalyzed Pauson-Khand reaction and summarizes its strategic applications in total syntheses of structurally complex natural products in the last five years. Additionally, the hetero-Pauson-Khand reaction in the synthesis of heterocycles will also be discussed. Focusing on the panorama of organic synthesis, this review highlights the strategically developed Pauson-Khand reaction in fulfilling total synthetic tasks and its synthetic attractiveness is aimed to be illustrated. Full article
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14 pages, 2185 KiB  
Article
High-Loaded Nickel Based Sol–Gel Catalysts for Methylcyclohexane Dehydrogenation
Catalysts 2020, 10(10), 1198; https://doi.org/10.3390/catal10101198 - 16 Oct 2020
Cited by 17 | Viewed by 3050
Abstract
Application of liquid organic hydrogen carriers, such as “methylcyclohexane (MCH)–toluene” chemical couple, is one of the promising approaches for hydrogen storage and transportation. In the present study, copper-modified nickel catalysts with high metal loading of 75 wt% were synthesized via heterophase sol–gel technique, [...] Read more.
Application of liquid organic hydrogen carriers, such as “methylcyclohexane (MCH)–toluene” chemical couple, is one of the promising approaches for hydrogen storage and transportation. In the present study, copper-modified nickel catalysts with high metal loading of 75 wt% were synthesized via heterophase sol–gel technique, and investigated in the dehydrogenation of MCH. Two approaches towards the copper introduction were applied. The catalyst samples prepared via wetness impregnation of the nickel sol–gel catalyst are characterized by more effective Ni-Cu interaction compared to those where two metals were introduced simultaneously by the mixing of their solid precursors. As a result, the “impregnated” catalysts revealed higher selectivity towards toluene. The addition of copper up to 30 wt% of total metal content was shown to increase significantly toluene selectivity and yield without a noticeable decrease in MCH conversion. The catalyst with the active component including 80 wt% of Ni and 20 wt% of Cu demonstrated 96% and 89% toluene selectivity at 40% and 80% MCH conversion, respectively. Based on the obtained data, this non-noble catalytic system appears quite promising for the MCH dehydrogenation. Full article
(This article belongs to the Special Issue The New Catalytic Processes in Alternative Fuel Production)
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21 pages, 11131 KiB  
Article
Catalytic Technologies for Solving Environmental Problems in the Production of Fuels and Motor Transport in Kazakhstan
Catalysts 2020, 10(10), 1197; https://doi.org/10.3390/catal10101197 - 16 Oct 2020
Cited by 3 | Viewed by 2104
Abstract
This research is devoted to solving an environmental problem, cleaning of the Kazakhstan air basin, through treatment of auto-transport toxic exhaust by improving the hydrocarbon composition of motor fuels and neutralizing exhaust gas toxic components. The catalytic hydrodearomatization of gasoline fractions (from the [...] Read more.
This research is devoted to solving an environmental problem, cleaning of the Kazakhstan air basin, through treatment of auto-transport toxic exhaust by improving the hydrocarbon composition of motor fuels and neutralizing exhaust gas toxic components. The catalytic hydrodearomatization of gasoline fractions (from the reforming stage) of the Atyrau and Pavlodar Refineries and the neutralization of exhaust gas toxic components from an internal combustion engine (ICE) were studied. Two hydrotreated gasoline fractions were tested during ICE operation. The research shows that 100% benzene conversion is observed over Rh-Pt(9:1)/γ-Al2O3 catalysts; that is, benzene is completely removed from both fractions, and the aromatics content decreases from 56.24–58.12% to 21.29–21.89%, within the values of the Euro-5,6 standard. Catalytic treatment of fuels reduces fuel consumption of the ICE engine by 2–3% compared to the initial gasoline fractions, the CO content in the exhaust gases decreases by 6.6–16.2%, and the hydrocarbon content decreases by 7.8–24.7%. In order to neutralize the ICE exhaust gas toxic components, the catalyst 10% Co + 0.5% Pt/Al2O3 was used, with which the CO conversion reaches 100% and the hydrocarbon conversion 94.2% and 91.5% for both gasoline fractions. The catalysts were characterized by electron microscopy (EM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), thermoprogrammed desorption (TPD) and thermoprogrammed reduction (TPR) methods. It was shown by the TPD and EM methods that at the addition of Pt to the Rh-catalyst, the formation of mixed bimetallic Rh-Pt-agglomerates occurs, and hydrogen appears in the TPD spectrum, adsorbed in the form of a new single peak uncharacteristic for the Rh-catalyst. This leads to high activity and selectivity in the hydrogenation of benzene and aromatic compounds in the gasoline fractions. The XRD and TPR results show the formation of CoAl2O4 spinels, on which inactive oxygen is formed for the oxidation of CO and hydrocarbons. Modification of the catalyst by Pt and Mg prevents spinel formation, thereby increasing the activity of the catalysts. Full article
(This article belongs to the Section Environmental Catalysis)
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26 pages, 7260 KiB  
Article
Vis-Responsive Copper-Modified Titania for Decomposition of Organic Compounds and Microorganisms
Catalysts 2020, 10(10), 1194; https://doi.org/10.3390/catal10101194 - 16 Oct 2020
Cited by 14 | Viewed by 2279
Abstract
Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), [...] Read more.
Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Although zero-valent copper was deposited on the surface of titania, oxidized forms of copper, post-formed in ambient conditions, were also detected in dried samples. All samples could absorb visible light (vis), due to localized surface plasmon resonance (LSPR) of zero-valent copper and by other copper species, including Cu2O, CuO and CuxO (x:1-2). The photocatalytic activities of samples were investigated under both ultraviolet (UV) and visible light irradiation (>450 nm) for oxidative decomposition of acetic acid. It was found that titania modification with copper significantly enhanced the photocatalytic activity, especially for anatase samples. The prolonged irradiation (from 1 to 5 h) during samples’ preparation resulted in aggregation of copper deposits, thus being detrimental for vis activity. It is proposed that oxidized forms of copper are more active under vis irradiation than plasmonic one. Antimicrobial properties against bacteria (Escherichia coli) and fungi (Aspergillus niger) under vis irradiation and in the dark confirmed that Cu/TiO2 exhibits a high antibacterial effect, mainly due to the intrinsic activity of copper species. Full article
(This article belongs to the Special Issue Plasmonic Photocatalysts)
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8 pages, 586 KiB  
Communication
Combination of CTec2 and GH5 or GH26 Endo-Mannanases for Effective Lignocellulosic Biomass Degradation
Catalysts 2020, 10(10), 1193; https://doi.org/10.3390/catal10101193 - 16 Oct 2020
Cited by 7 | Viewed by 1912
Abstract
Among endo-mannanases, glycoside hydrolase (GH) family 26 enzymes have been shown to be more catalytically active than GH5 enzymes on mannans. However, only GH5 endo-mannanases have been used for the formulation of enzyme cocktails. In this study, Bacillus sp.-derived GH5 and GH26 endo-mannanases [...] Read more.
Among endo-mannanases, glycoside hydrolase (GH) family 26 enzymes have been shown to be more catalytically active than GH5 enzymes on mannans. However, only GH5 endo-mannanases have been used for the formulation of enzyme cocktails. In this study, Bacillus sp.-derived GH5 and GH26 endo-mannanases were comparatively analysed biochemically for their synergistic action with a commercial cellulase blend, CTec2, during pre-treated lignocellulose degradation. Substrate specificity and thermo-stability studies on mannan substrates showed that GH26 endo-mannanase was more catalytically active and stable than GH5. GH26 also exhibited higher binding affinity for mannan than GH5, while GH5 showed more affinity for lignocellulosic substrates than GH26. Applying the endo-mannanases in combination with CTec2 for lignocellulose degradation led to synergism with a 1.3-fold increase in reducing sugar release compared to when CTec2 was used alone. This study showed that using the activity of endo-mannanases displayed with model substrates is a poor predictor of their activity and synergism on complex lignocelluloses. Full article
(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)
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20 pages, 5718 KiB  
Article
Novel Push–Pull Dyes Derived from 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as Versatile Photoinitiators for Photopolymerization and Their Related Applications: 3D Printing and Fabrication of Photocomposites
Catalysts 2020, 10(10), 1196; https://doi.org/10.3390/catal10101196 - 15 Oct 2020
Cited by 37 | Viewed by 2542
Abstract
A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 [...] Read more.
A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 nm. Notably, polymerization reactions could be initiated with light-emitting diodes (LEDs) which constitute a unique opportunity to promote the free radical polymerization under mild conditions, i.e., low light intensity (e.g., sunlight) and under air. Photopolymerization is an active research field, and push–pull dyes have already been investigated for this purpose. Besides, it remains of crucial interest to investigate new reactive structures capable of efficiently initiating photopolymerization reactions. The plausible potential of these structures to act as efficient photoinitiators in vat photopolymerization (or 3D printing) and fabrication of photocomposites prompts us to select eleven new push–pull dyes to design multi-component photoinitiating systems activable with LEDs emitting at 405 nm. Precisely, a tertiary amine, i.e., ethyl dimethylaminobenzoate (EDB) used as an electron/hydrogen donor and an iodonium salt used as an electron acceptor were selected to behave as powerful co-initiators to construct three-component photoinitiating systems (PISs) with the different push–pull dyes. Among these new PISs, dye 8 and 9-based PISs could efficiently promote the free radical photopolymerization of acrylates upon exposure to a LED emitting at 405 nm also upon sunlight irradiation, highlighting their huge performance. Photoinitiating abilities could be explained on the basis of steady state photolysis experiments. Fluorescence measurements and electron spin resonance (ESR) spin-trapping experiments were also performed to obtain a deeper insight into the chemical mechanisms supporting the polymerization reaction and determine the way the initiating species, i.e., the radicals, are observed. Finally, two investigated dye-based PISs were applied to the fabrications of photocomposites. Three-dimensional patterns with excellent spatial resolutions were generated by the laser writing technique to identify the effects of photopolymerization of acrylates both in the absence and presence of fillers (silica). Interestingly, comparison between the 3D objects fabricated by the PISs/monomer systems and the PISs/monomer/filler photocomposites indicates that the newly designed photocomposites are suitable for practical applications. Full article
(This article belongs to the Special Issue Progression in Photocatalytic Materials for Efficient Performance)
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18 pages, 8514 KiB  
Article
Rhodium Nanoparticles Stabilized by PEG-Tagged Imidazolium Salts as Recyclable Catalysts for the Hydrosilylation of Internal Alkynes and the Reduction of Nitroarenes
Catalysts 2020, 10(10), 1195; https://doi.org/10.3390/catal10101195 - 15 Oct 2020
Cited by 6 | Viewed by 2363
Abstract
PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts containing triazole linkers have been used as stabilizers for the preparation of water-soluble rhodium(0) nanoparticles by reduction of rhodium trichloride with sodium borohydride in water at room temperature. The nanomaterials have been characterized (Transmission [...] Read more.
PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts containing triazole linkers have been used as stabilizers for the preparation of water-soluble rhodium(0) nanoparticles by reduction of rhodium trichloride with sodium borohydride in water at room temperature. The nanomaterials have been characterized (Transmission Electron Microscopy, Electron Diffraction, X-ray Photoelectron Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy). They proved to be efficient and recyclable catalysts for the stereoselective hydrosilylation of internal alkynes, in the presence or absence of solvent, and in the reduction of nitroarenes to anilines with ammonia-borane as hydrogen donor in aqueous medium (1:4 tetrahydrofuran/water). Full article
(This article belongs to the Special Issue Metal Nanoparticle Catalysis)
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