Catalysts

15 pages, 1650 KiB

Open AccessArticle

Comparison of the Photocatalytic Activity of ZnO/CeO₂ and ZnO/Yb₂O₃ Mixed Systems in the Phenol Removal from Water: A Mechanicistic Approach

by Erik Cerrato, Nuno Paulo Ferreira Gonçalves, Paola Calza and Maria Cristina Paganini

Catalysts 2020, 10(10), 1222; https://doi.org/10.3390/catal10101222 - 21 Oct 2020

Cited by 7 | Viewed by 2817

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

Open AccessFeature PaperEditor’s ChoiceReview

Direct Alcoholysis of Carbohydrate Precursors and Real Cellulosic Biomasses to Alkyl Levulinates: A Critical Review

by Anna Maria Raspolli Galletti, Claudia Antonetti, Sara Fulignati and Domenico Licursi

Catalysts 2020, 10(10), 1221; https://doi.org/10.3390/catal10101221 - 21 Oct 2020

Cited by 41 | Viewed by 4892

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

Open AccessArticle

Fabrication of Ni-Based Bimodal Porous Catalyst for Dry Reforming of Methane

by Linghui Lyu, Yunxing Han, Qingxiang Ma, Shengene Makpal, Jian Sun, Xinhua Gao, Jianli Zhang, Hui Fan and Tian-Sheng Zhao

Catalysts 2020, 10(10), 1220; https://doi.org/10.3390/catal10101220 - 20 Oct 2020

Cited by 8 | Viewed by 3287

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

Open AccessArticle

Catalytic Formation of Lactic and Levulinic Acids from Biomass Derived Monosaccarides through Sn-Beta Formed by Impregnation

by Andrew Kohler, Wayne Seames, Ian Foerster and Clancy Kadrmas

Catalysts 2020, 10(10), 1219; https://doi.org/10.3390/catal10101219 - 20 Oct 2020

Cited by 12 | Viewed by 3545

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

Open AccessReview

Progress and Challenges of Mercury-Free Catalysis for Acetylene Hydrochlorination

by Yanxia Liu, Lin Zhao, Yagang Zhang, Letao Zhang and Xingjie Zan

Catalysts 2020, 10(10), 1218; https://doi.org/10.3390/catal10101218 - 20 Oct 2020

Cited by 16 | Viewed by 5215

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

Open AccessArticle

CO₂ and H₂O Coadsorption and Reaction on the Low-Index Surfaces of Tantalum Nitride: A First-Principles DFT-D3 Investigation

by Nelson Y. Dzade

Catalysts 2020, 10(10), 1217; https://doi.org/10.3390/catal10101217 - 20 Oct 2020

Cited by 6 | Viewed by 3638

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

Open AccessFeature PaperArticle

A Multi-Enzyme Cascade for the Production of High-Value Aromatic Compounds

by Claudia Engelmann, Jens Johannsen, Thomas Waluga, Georg Fieg, Andreas Liese and Paul Bubenheim

Catalysts 2020, 10(10), 1216; https://doi.org/10.3390/catal10101216 - 20 Oct 2020

Cited by 14 | Viewed by 4322

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

Open AccessArticle

Selective Hydrogenation of Naphthalene over γ-Al₂O₃-Supported NiCu and NiZn Bimetal Catalysts

by Jingqiu Li, Liu Shi, Gang Feng, Zhangping Shi, Chenglin Sun and Dejin Kong

Catalysts 2020, 10(10), 1215; https://doi.org/10.3390/catal10101215 - 20 Oct 2020

Cited by 13 | Viewed by 3910

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 NiO_x and Al₂O₃ in NiZn/Al₂O₃ catalysts, which efficiently increased the reduction ability of NiO_x species and, thus, improved the naphthalene hydrogenation activity. The electron transfer from ZnO to NiO_x 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

(This article belongs to the Special Issue Advancements in Environmental Catalysis - The 19th National Congress on Catalysis of China)

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12 pages, 1509 KiB

Open AccessArticle

Spirogyra Oil-Based Biodiesel: Response Surface Optimization of Chemical and Enzymatic Transesterification and Exhaust Emission Behavior

by Saqib Sohail, Muhammad Waseem Mumtaz, Hamid Mukhtar, Tooba Touqeer, Muhammad Kafeel Anjum, Umer Rashid, Wan Azlina Wan Ab Karim Ghani and Thomas Shean Yaw Choong

Catalysts 2020, 10(10), 1214; https://doi.org/10.3390/catal10101214 - 20 Oct 2020

Cited by 8 | Viewed by 3925

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

Open AccessCommunication

Effect of Cu and Cs in the β-Mo₂C System for CO₂ Hydrogenation to Methanol

by Ana Belén Dongil, Qi Zhang, Laura Pastor-Pérez, Tomás Ramírez-Reina, Antonio Guerrero-Ruiz and Inmaculada Rodríguez-Ramos

Catalysts 2020, 10(10), 1213; https://doi.org/10.3390/catal10101213 - 20 Oct 2020

Cited by 21 | Viewed by 3478

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

Open AccessArticle

Improved NOx Reduction Using C₃H₈ and H₂ with Ag/Al₂O₃ Catalysts Promoted with Pt and WOx

by Naomi N. González Hernández, José Luis Contreras, Marcos Pinto, Beatriz Zeifert, Jorge L. Flores Moreno, Gustavo A. Fuentes, María E. Hernández-Terán, Tamara Vázquez, José Salmones and José M. Jurado

Catalysts 2020, 10(10), 1212; https://doi.org/10.3390/catal10101212 - 19 Oct 2020

Cited by 12 | Viewed by 3131

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⁺, Ag_n^δ+ 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

Open AccessArticle

Double Spirocyclization of Arylidene-Δ²-Pyrrolin-4-Ones with 3-Isothiocyanato Oxindoles

by Sebastijan Ričko, Žan Testen, Luka Ciber, Franc Požgan, Bogdan Štefane, Helena Brodnik, Jurij Svete and Uroš Grošelj

Catalysts 2020, 10(10), 1211; https://doi.org/10.3390/catal10101211 - 19 Oct 2020

Cited by 7 | Viewed by 2900

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

Open AccessFeature PaperEditor’s ChoiceReview

Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights

by Chin Hin Leung, Marco Baron and Andrea Biffis

Catalysts 2020, 10(10), 1210; https://doi.org/10.3390/catal10101210 - 19 Oct 2020

Cited by 42 | Viewed by 5842

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

Open AccessFeature PaperArticle

Development of Facile and Simple Processes for the Heterogeneous Pd-Catalyzed Ligand-Free Continuous-Flow Suzuki–Miyaura Coupling

by Tsuyoshi Yamada, Jing Jiang, Naoya Ito, Kwihwan Park, Hayato Masuda, Chikara Furugen, Moeka Ishida, Seiya Ōtori and Hironao Sajiki

Catalysts 2020, 10(10), 1209; https://doi.org/10.3390/catal10101209 - 19 Oct 2020

Cited by 10 | Viewed by 3605

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

Open AccessArticle

Tuning Photocatalytic Performance of Multilayer ZnO for Water Splitting by Biaxial Strain Composites

by Xiaofan Cai, Yuewu Huang, Jinzhi Hu, Shiwei Zhu, Xiaohua Tian, Kun Zhang, Guangju Ji, Yunxiao Zhang, Zhendong Fu and Changlong Tan

Catalysts 2020, 10(10), 1208; https://doi.org/10.3390/catal10101208 - 19 Oct 2020

Cited by 7 | Viewed by 2721

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

(This article belongs to the Special Issue Non-Precious Metal Electrocatalysts: Synthesis, Characterization, and Application)

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23 pages, 2237 KiB

Open AccessFeature PaperArticle

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

by Sara Arana-Peña, Diego Carballares, Vicente Cortés Corberan and Roberto Fernandez-Lafuente

Catalysts 2020, 10(10), 1207; https://doi.org/10.3390/catal10101207 - 19 Oct 2020

Cited by 31 | Viewed by 3813

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

Open AccessFeature PaperEditor’s ChoiceReview

Gold-Catalyzed Addition of Carboxylic Acids to Alkynes and Allenes: Valuable Tools for Organic Synthesis

by Victorio Cadierno

Catalysts 2020, 10(10), 1206; https://doi.org/10.3390/catal10101206 - 18 Oct 2020

Cited by 25 | Viewed by 5369

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

Open AccessArticle

Removal of Nonylphenol Polyethylene Glycol (NPEG) with Au-TiO₂ Catalysts: Kinetic and Initial Transformation Path

by Claudia Aguilar, Mayra Garcia, Carlos Montalvo, Francisco Anguebes, Edgar Moctezuma, Mohamed Abatal and Sandra Figueroa

Catalysts 2020, 10(10), 1205; https://doi.org/10.3390/catal10101205 - 17 Oct 2020

Cited by 1 | Viewed by 2584

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

Open AccessArticle

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

by Toshiki Nishitoba, Takuya Nozaki, Sungsik Park, Yong Wang, Junko N. Kondo, Hermann Gies and Toshiyuki Yokoi

Catalysts 2020, 10(10), 1204; https://doi.org/10.3390/catal10101204 - 17 Oct 2020

Cited by 21 | Viewed by 4499

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

(This article belongs to the Special Issue Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Applications in Catalysis)

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9 pages, 2387 KiB

Open AccessArticle

Large-Area Patterning of Oil-Based Inks on Superhydrophobic TiO₂ Nanotubular Layers by Photocatalytic Wettability Conversion

by Jiao Jin, Huihui Ren and Zhaoyue Liu

Catalysts 2020, 10(10), 1203; https://doi.org/10.3390/catal10101203 - 17 Oct 2020

Cited by 3 | Viewed by 2162

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

Open AccessFeature PaperEditor’s ChoiceArticle

Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing

by Mahmoud Rahal, Haifaa Mokbel, Bernadette Graff, Joumana Toufaily, Tayssir Hamieh, Frédéric Dumur and Jacques Lalevée

Catalysts 2020, 10(10), 1202; https://doi.org/10.3390/catal10101202 - 17 Oct 2020

Cited by 35 | Viewed by 3645

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

Open AccessArticle

CO₂ Methanation of Biogas over 20 wt% Ni-Mg-Al Catalyst: on the Effect of N₂, CH₄, and O₂ on CO₂ Conversion Rate

by Danbee Han, Yunji Kim, Hyunseung Byun, Wonjun Cho and Youngsoon Baek

Catalysts 2020, 10(10), 1201; https://doi.org/10.3390/catal10101201 - 16 Oct 2020

Cited by 24 | Viewed by 3752

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

Open AccessArticle

Kinetics and Nanoparticle Catalytic Enhancement of Biogas Production from Wastewater Using a Magnetized Biochemical Methane Potential (MBMP) System

by Emmanuel Kweinor Tetteh and Sudesh Rathilal

Catalysts 2020, 10(10), 1200; https://doi.org/10.3390/catal10101200 - 16 Oct 2020

Cited by 23 | Viewed by 3772

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

(This article belongs to the Special Issue Innovative Catalytic and Photocatalytic Systems for Environmental Remediation)

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25 pages, 6979 KiB

Open AccessReview

Evolution of Pauson-Khand Reaction: Strategic Applications in Total Syntheses of Architecturally Complex Natural Products (2016–2020)

by Sijia Chen, Chongguo Jiang, Nan Zheng, Zhen Yang and Lili Shi

Catalysts 2020, 10(10), 1199; https://doi.org/10.3390/catal10101199 - 16 Oct 2020

Cited by 35 | Viewed by 8140

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

(This article belongs to the Special Issue Metal Promoted Cyclocarbonylation Reactions in the Synthesis of Heterocycles)

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14 pages, 2185 KiB

Open AccessArticle

High-Loaded Nickel Based Sol–Gel Catalysts for Methylcyclohexane Dehydrogenation

by Yuliya K. Gulyaeva, Maria V. Alekseeva (Bykova), Dmitry Yu. Ermakov, Olga A. Bulavchenko, Olesya O. Zaikina and Vadim A. Yakovlev

Catalysts 2020, 10(10), 1198; https://doi.org/10.3390/catal10101198 - 16 Oct 2020

Cited by 23 | Viewed by 3953

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

Open AccessArticle

Catalytic Technologies for Solving Environmental Problems in the Production of Fuels and Motor Transport in Kazakhstan

by Alma Massenova, Maxat Kalykberdiyev, Alexandr Sass, Nail Kenzin, Abzal Ussenov, Amankeldi Baiken and Kenzhegul Rakhmetova

Catalysts 2020, 10(10), 1197; https://doi.org/10.3390/catal10101197 - 16 Oct 2020

Cited by 5 | Viewed by 2820

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

Open AccessFeature PaperArticle

Vis-Responsive Copper-Modified Titania for Decomposition of Organic Compounds and Microorganisms

by Maya Endo-Kimura, Bariş Karabiyik, Kunlei Wang, Zhishun Wei, Bunsho Ohtani, Agata Markowska-Szczupak and Ewa Kowalska

Catalysts 2020, 10(10), 1194; https://doi.org/10.3390/catal10101194 - 16 Oct 2020

Cited by 17 | Viewed by 2956

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 Cu_xO (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

Open AccessCommunication

Combination of CTec2 and GH5 or GH26 Endo-Mannanases for Effective Lignocellulosic Biomass Degradation

by Samkelo Malgas and Brett I. Pletschke

Catalysts 2020, 10(10), 1193; https://doi.org/10.3390/catal10101193 - 16 Oct 2020

Cited by 8 | Viewed by 2515

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

Open AccessFeature PaperEditor’s ChoiceArticle

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

by Ke Sun, Shaohui Liu, Corentin Pigot, Damien Brunel, Bernadette Graff, Malek Nechab, Didier Gigmes, Fabrice Morlet-Savary, Yijun Zhang, Pu Xiao, Frédéric Dumur and Jacques Lalevée

Catalysts 2020, 10(10), 1196; https://doi.org/10.3390/catal10101196 - 15 Oct 2020

Cited by 39 | Viewed by 3262

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

Open AccessArticle

Rhodium Nanoparticles Stabilized by PEG-Tagged Imidazolium Salts as Recyclable Catalysts for the Hydrosilylation of Internal Alkynes and the Reduction of Nitroarenes

by Guillem Fernández and Roser Pleixats

Catalysts 2020, 10(10), 1195; https://doi.org/10.3390/catal10101195 - 15 Oct 2020

Cited by 7 | Viewed by 3095

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

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