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Catalysts, Volume 11, Issue 6 (June 2021) – 106 articles

Cover Story (view full-size image): The prevalence of ether and amine motifs in various areas of chemistry has driven the development of original and innovative methods for their efficient synthesis. The most attractive and atom-economical approach towards these prevalent motifs is undoubtedly the addition of N–H or O-H -bond onto unactivated alkenes—referred to as alkene hydroamination or hydroalkoxylation. The current booming trend for the use of earth-abundant, first-row late transition metals in catalysis has reshaped the field of alkene hydrofunctionalization and given birth to efficient strategies that not only rely on classical activation modes but also on novel radical-type reactivities. This review will survey the most relevant achievements in the field of the intra- and intermolecular hydroalkoxylation and hydroamination of unactivated alkenes promoted by earth-abundant 3D transition metal catalysts from manganese to zinc. [...] Read more.
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17 pages, 2108 KiB  
Review
Light-Driven Hydrogen Evolution Assisted by Covalent Organic Frameworks
by Nuria Romero, Roger Bofill, Laia Francàs, Jordi García-Antón and Xavier Sala
Catalysts 2021, 11(6), 754; https://doi.org/10.3390/catal11060754 - 21 Jun 2021
Cited by 15 | Viewed by 3902
Abstract
Covalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semiconducting units, such as triazine rings or diacetylene bridges. The bandgap, charge separation capacity, porosity, wettability, and chemical stability of COFs [...] Read more.
Covalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semiconducting units, such as triazine rings or diacetylene bridges. The bandgap, charge separation capacity, porosity, wettability, and chemical stability of COFs can be tuned by properly choosing their constitutive building blocks, by extension of conjugation, by adjustment of the size and crystallinity of the pores, and by synthetic post-functionalization. This review focuses on the recent uses of COFs as photoactive platforms for the hydrogen evolution reaction (HER), in which usually metal nanoparticles (NPs) or metallic compounds (generally Pt-based) act as co-catalysts. The most promising COF-based photocatalytic HER systems will be discussed, and special emphasis will be placed on rationalizing their structure and light-harvesting properties in relation to their catalytic activity and stability under turnover conditions. Finally, the aspects that need to be improved in the coming years will be discussed, such as the degree of dispersibility in water, the global photocatalytic efficiency, and the robustness and stability of the hybrid systems, putting emphasis on both the COF and the metal co-catalyst. Full article
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17 pages, 3384 KiB  
Article
Shape Effects of Ceria Nanoparticles on the Water‒Gas Shift Performance of CuOx/CeO2 Catalysts
by Maria Lykaki, Sofia Stefa, Sónia A. C. Carabineiro, Miguel A. Soria, Luís M. Madeira and Michalis Konsolakis
Catalysts 2021, 11(6), 753; https://doi.org/10.3390/catal11060753 - 21 Jun 2021
Cited by 12 | Viewed by 2444
Abstract
The copper–ceria (CuOx/CeO2) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, [...] Read more.
The copper–ceria (CuOx/CeO2) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx/CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R > P > C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+) through the Cu2+/Cu+ and Ce4+/Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx/CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350 °C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance. Full article
(This article belongs to the Special Issue Gold, Silver and Copper Catalysis)
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4 pages, 178 KiB  
Editorial
Catalysts for Production and Conversion of Syngas
by Rufino M. Navarro Yerga
Catalysts 2021, 11(6), 752; https://doi.org/10.3390/catal11060752 - 21 Jun 2021
Cited by 10 | Viewed by 2962
Abstract
Synthesis gas, or syngas for short, is a mixture of CO, CO2, and H2 [...] Full article
(This article belongs to the Special Issue Catalysts for Production and Conversion of Syngas)
13 pages, 2727 KiB  
Article
Critical Role of Al Pair Sites in Methane Oxidation to Methanol on Cu-Exchanged Mordenite Zeolites
by Peijie Han, Zhaoxia Zhang, Zheng Chen, Jingdong Lin, Shaolong Wan, Yong Wang and Shuai Wang
Catalysts 2021, 11(6), 751; https://doi.org/10.3390/catal11060751 - 19 Jun 2021
Cited by 5 | Viewed by 2948
Abstract
Cu-exchanged aluminosilicate zeolites have been intensively studied for the selective oxidation of methane to methanol via a chemical looping manner, while the nature of active Cu-oxo species for these catalysts is still under debate. This study inquired into the effects of Al distribution [...] Read more.
Cu-exchanged aluminosilicate zeolites have been intensively studied for the selective oxidation of methane to methanol via a chemical looping manner, while the nature of active Cu-oxo species for these catalysts is still under debate. This study inquired into the effects of Al distribution on methane oxidation over Cu-exchanged aluminosilicate zeolites, which provided an effective way to discern the activity difference between mononuclear and polynuclear Cu-oxo species. Specifically, conventional Na+/Co2+ ion-exchange methods were applied to quantify isolated Al and Al pair (i.e., Al−OH−(Si−O)1–3−Al−OH) sites for three mordenite (MOR) zeolites, and a correlation was established between the reactivity of the resultant Cu-MOR catalysts and the portions of the accessible framework Al sites. These results indicated that the Cu-oxo clusters derived from the Al pair sites were more reactive than the CuOH species grafted at the isolated Al sites, which is consistent with in situ ultraviolet-visible spectroscopic characterization and density functional theory calculations. Further theoretical analysis of the first C–H bond cleavage in methane on these Cu-oxo species unveiled that stabilization of the formed methyl group was the predominant factor in determining the reactivity of methane oxidation. Full article
(This article belongs to the Special Issue Catalysis on Zeolites and Zeolite-Like Materials)
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17 pages, 1673 KiB  
Article
The Impact of Biomass and Acid Loading on Methanolysis during Two-Step Lignin-First Processing of Birchwood
by Panos D. Kouris, Xiaoming Huang, Xianhong Ouyang, Dannie J. G. P. van Osch, Geert J. W. Cremers, Michael D. Boot and Emiel J. M. Hensen
Catalysts 2021, 11(6), 750; https://doi.org/10.3390/catal11060750 - 19 Jun 2021
Cited by 12 | Viewed by 3199
Abstract
We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol [...] Read more.
We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol solvent. The impact of reaction temperature (140–200 °C), acid loading (0.24–0.81 wt%, dry biomass), methanol/biomass ratio (2.3/1–15.8/1 w/w) and reaction time (2 h and 0.5 h) was investigated. At high biomass loadings (ratio < 6.3/1 w/w), operation at elevated pressure facilitates delignification by keeping methanol in the liquid phase. A high degree of delignification goes together to a large extent with C5 sugar release, mostly in the form of methyl xylosides. Gel permeation chromatography and heteronuclear single quantum coherence NMR of lignin fractions obtained at high acid (0.81 wt%) and low biomass (15.8/1 w/w) loading revealed extensive cleavage of β-O-4′ bonds during acidolysis at 180 °C for 2 h. At an optimized methanol/biomass ratio of 2.3/1 w/w and acid loading (0.24 wt%), more β-O-4′ bonds could be preserved, i.e., about 33% after 2 h and 47% after 0.5 h. The high reactivity of the extracted lignin fragments was confirmed by a second hydrogenolysis step. Reductive treatment with Pd/C under mild conditions led to disappearance of ether linkages and molecular weight reduction in the hydrotreated lignin oil. Full article
(This article belongs to the Special Issue Catalytic Biomass Upgrading)
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19 pages, 3205 KiB  
Article
Development of a Novel Bi-Enzymatic Nanobiocatalyst for the Efficient Bioconversion of Oleuropein to Hydroxytyrosol
by Archontoula Giannakopoulou, Alexandra V. Chatzikonstantinou, Nikolaos Chalmpes, Georgia Tsapara, Dimitrios Gournis, Angeliki C. Polydera and Haralambos Stamatis
Catalysts 2021, 11(6), 749; https://doi.org/10.3390/catal11060749 - 19 Jun 2021
Cited by 8 | Viewed by 2772
Abstract
Lipase A from Candida antarctica (CalA) and β-glucosidase from Thermotoga maritima (bgl) were covalently co-immobilized onto the surface of chitosan-coated magnetic nanoparticles (CS-MNPs). Several parameters regarding the co-immobilization procedure (glutaraldehyde concentration, incubation time, CS-MNPs to enzyme mass ratio and bgl to CalA [...] Read more.
Lipase A from Candida antarctica (CalA) and β-glucosidase from Thermotoga maritima (bgl) were covalently co-immobilized onto the surface of chitosan-coated magnetic nanoparticles (CS-MNPs). Several parameters regarding the co-immobilization procedure (glutaraldehyde concentration, incubation time, CS-MNPs to enzyme mass ratio and bgl to CalA mass ratio) were evaluated and optimized. The developed nanobiocatalyst was characterized by various spectroscopic techniques. Biochemical parameters such as kinetic constants and thermal stability were also evaluated. The nanobiocatalytic system revealed an increase in the Km constant followed by a decrease in Vmax value compared with the native enzymes, while a significant increase (>5-fold higher) of the thermal stability of the immobilized CalA, both in individual and in co-immobilized form, was observed after 24 h incubation at 60 °C. Finally, the nanobiocatalyst was efficiently applied for the bioconversion of oleuropein to hydroxytyrosol, one of the most powerful naturally derived antioxidants, and it could be recycled for up to 10 reaction cycles (240 h of constant operation) at 60 °C, retaining more than 50% of its initial activity. Full article
(This article belongs to the Special Issue State of the Art and Future Trends in Nanostructured Biocatalysis)
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15 pages, 2090 KiB  
Article
Aqueous Extraction of Seed Oil from Mamey Sapote (Pouteria sapota) after Viscozyme L Treatment
by Veymar G. Tacias-Pascacio, Arnulfo Rosales-Quintero, Rafael C. Rodrigues, Daniel Castañeda-Valbuena, Pablo F. Díaz-Suarez, Beatriz Torrestiana-Sánchez, Erik F. Jiménez-Gómez and Roberto Fernandez-Lafuente
Catalysts 2021, 11(6), 748; https://doi.org/10.3390/catal11060748 - 19 Jun 2021
Cited by 10 | Viewed by 3588
Abstract
In this study, aqueous enzymatic extraction (AEE) was evaluated during the process of obtaining oil from mamey sapote seed (OMSS). Viscozyme L enzyme complex was used at pH 4 and 50 °C during the optimization of the extraction process by central composite design [...] Read more.
In this study, aqueous enzymatic extraction (AEE) was evaluated during the process of obtaining oil from mamey sapote seed (OMSS). Viscozyme L enzyme complex was used at pH 4 and 50 °C during the optimization of the extraction process by central composite design and response surface methodology. Optimal conditions were: 3.5% (w/w) of enzyme (regarding the seed weight), 5.5 h of incubation time, 235 rpm of agitation rate, and 1:3.5 of solid-to-liquid ratio. These conditions enabled us to obtain an OMSS yield of 66%. No statistically significant differences were found in the fatty acid profile and physicochemical properties, such as the acid and iodine values and the percentage of free fatty acids, between the oil obtained by AEE or by the conventional solvent extraction (SE). However, the oxidative stability of the oil obtained by AEE (11 h) was higher than that obtained by SE (9.33 h), therefore, AEE, in addition to being an environmentally friendly method, produces a superior quality oil in terms of oxidative stability. Finally, the high oil content in mamey sapote seed, and the high percentage of oleic acid (around 50% of the total fatty acid) found in this oil, make it a useful edible vegetable oil. Full article
(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)
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12 pages, 1978 KiB  
Article
Theoretical Investigation of the Deactivation of Ni Supported Catalysts for the Catalytic Deoxygenation of Palm Oil for Green Diesel Production
by Sanaa Hafeez, Sultan M Al-Salem, Kyriakos N Papageridis, Nikolaos D Charisiou, Maria A Goula, George Manos and Achilleas Constantinou
Catalysts 2021, 11(6), 747; https://doi.org/10.3390/catal11060747 - 18 Jun 2021
Cited by 8 | Viewed by 2803
Abstract
For the first time, a fully comprehensive heterogeneous computational fluid dynamic (CFD) model has been developed to predict the selective catalytic deoxygenation of palm oil to produce green diesel over an Ni/ZrO2 catalyst. The modelling results were compared to experimental data, and [...] Read more.
For the first time, a fully comprehensive heterogeneous computational fluid dynamic (CFD) model has been developed to predict the selective catalytic deoxygenation of palm oil to produce green diesel over an Ni/ZrO2 catalyst. The modelling results were compared to experimental data, and a very good validation was obtained. It was found that for the Ni/ZrO2 catalyst, the paraffin conversion increased with temperature, reaching a maximum value (>95%) at 300 °C. However, temperatures greater than 300 °C resulted in a loss of conversion due to the fact of catalyst deactivation. In addition, at longer times, the model predicted that the catalyst activity would decline faster at temperatures higher than 250 °C. The CFD model was able to predict this deactivation by relating the catalytic activity with the reaction temperature. Full article
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13 pages, 3507 KiB  
Article
Selective Catalytic Oxidation of Lean-H2S Gas Stream to Elemental Sulfur at Lower Temperature
by Daniela Barba, Vincenzo Vaiano and Vincenzo Palma
Catalysts 2021, 11(6), 746; https://doi.org/10.3390/catal11060746 - 18 Jun 2021
Cited by 6 | Viewed by 2219
Abstract
Ceria-supported vanadium catalysts were studied for H2S removal via partial and selective oxidation reactions at low temperature. The catalysts were characterized by N2 adsorption at 77 K, Raman spectroscopy, X-ray diffraction techniques, and X-ray fluorescence analysis. X-ray diffraction and Raman [...] Read more.
Ceria-supported vanadium catalysts were studied for H2S removal via partial and selective oxidation reactions at low temperature. The catalysts were characterized by N2 adsorption at 77 K, Raman spectroscopy, X-ray diffraction techniques, and X-ray fluorescence analysis. X-ray diffraction and Raman analysis showed a good dispersion of the V-species on the support. A preliminary screening of these samples was performed at fixed temperature (T = 327 °C) and H2S inlet concentration (10 vol%) in order to study the catalytic performance in terms of H2S conversion and SO2 selectivity. For the catalyst that exhibited the higher removal efficiency of H2S (92%) together with a lower SO2 selectivity (4%), the influence of temperature (307–370 °C), contact time (0.6–1 s), and H2S inlet concentration (6–15 vol%) was investigated. Full article
(This article belongs to the Special Issue Catalysts and Processes for H2S Conversion to Sulfur)
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16 pages, 3567 KiB  
Article
Transformation of Resinous Components of the Ashalcha Field Oil during Catalytic Aquathermolysis in the Presence of a Cobalt-Containing Catalyst Precursor
by Irek I. Mukhamatdinov, Indad Sh.S. Salih, Ilfat Z. Rakhmatullin, Nikita N. Sviridenko, Galina S. Pevneva, Rakesh K. Sharma and Alexey V. Vakhin
Catalysts 2021, 11(6), 745; https://doi.org/10.3390/catal11060745 - 18 Jun 2021
Cited by 14 | Viewed by 2319
Abstract
The aim of this work was to study the fractional composition of super-viscous oil resins from the Ashalcha field, as well as the catalytic aquathermolysis product in the presence of a cobalt-containing catalyst precursor and a hydrogen donor. The study was conducted at [...] Read more.
The aim of this work was to study the fractional composition of super-viscous oil resins from the Ashalcha field, as well as the catalytic aquathermolysis product in the presence of a cobalt-containing catalyst precursor and a hydrogen donor. The study was conducted at various durations of thermal steam exposure. In this regard, the work enabled the identification of the distribution of resin fractions. These fractions, obtained by liquid adsorption chromatography, were extracted with individual solvents and their binary mixtures in various ratios. The results of MALDI spectroscopy revealed a decrease in the molecular mass of all resin fractions after catalytic treatment, mainly with a hydrogen donor. However, the elemental analysis data indicated a decrease in the H/C ratio for resin fractions as a result of removing alkyl substituents in resins and asphaltenes. Moreover, the data of 1H NMR spectroscopy of resin fractions indicated an increase in the aliphatic hydrogen index during catalytic aquathermolysis at the high molecular parts of the resins R3 and R4. Finally, a structural group analysis was carried out in this study, and hypothetical structures of the initial oil resin molecules and aquathermolysis products were constructed as well. Full article
(This article belongs to the Special Issue Heavy Oil In Situ Upgrading and Catalysis)
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8 pages, 895 KiB  
Article
Polymeric Nanoparticles Decorated with Monoclonal Antibodies: A New Immobilization Strategy for Increasing Lipase Activity
by Laura Chronopoulou, Viviana Couto Sayalero, Hassan Rahimi, Aurelia Rughetti and Cleofe Palocci
Catalysts 2021, 11(6), 744; https://doi.org/10.3390/catal11060744 - 17 Jun 2021
Cited by 2 | Viewed by 2006
Abstract
Recent advances in nanotechnology techniques enable the production of polymeric nanoparticles with specific morphologies and dimensions and, by tailoring their surfaces, one can manipulate their characteristics to suit specific applications. In this work we report an innovative approach for the immobilization of a [...] Read more.
Recent advances in nanotechnology techniques enable the production of polymeric nanoparticles with specific morphologies and dimensions and, by tailoring their surfaces, one can manipulate their characteristics to suit specific applications. In this work we report an innovative approach for the immobilization of a commercial lipase from Candida rugosa (CRL) which employs nanostructured polymeric carriers conjugated with anti-lipase monoclonal antibodies (MoAbs). MoAbs were chemically conjugated on the surface of polymeric nanoparticles and used to selectively adsorb CRL molecules. Hydrolytic enzymatic assays evidenced that such immobilization technique afforded a significant enhancement of enzymatic activity in comparison to the free enzyme. Full article
(This article belongs to the Special Issue Enzyme Immobilization and Biocatalysis)
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17 pages, 3503 KiB  
Article
n-Butene Synthesis in the Dimethyl Ether-to-Olefin Reaction over Zeolites
by Toshiaki Hanaoka, Masaru Aoyagi and Yusuke Edashige
Catalysts 2021, 11(6), 743; https://doi.org/10.3390/catal11060743 - 17 Jun 2021
Cited by 3 | Viewed by 2178
Abstract
Zeolite catalysts that could allow the efficient synthesis of n-butene, such as 1-butene, trans-2-butene, and cis-2-butene, in the dimethyl ether (DME)-to-olefin (DTO) reaction were investigated using a fixed-bed flow reactor. The zeolites were characterized by N2 adsorption and desorption, [...] Read more.
Zeolite catalysts that could allow the efficient synthesis of n-butene, such as 1-butene, trans-2-butene, and cis-2-butene, in the dimethyl ether (DME)-to-olefin (DTO) reaction were investigated using a fixed-bed flow reactor. The zeolites were characterized by N2 adsorption and desorption, X-ray diffraction (XRD), thermogravimetry (TG), and NH3 temperature-programmed desorption (NH3-TPD). A screening of ten available zeolites indicated that the ferrierite zeolite with NH4+ as the cation showed the highest n-butene yield. The effect of the temperature of calcination as a pretreatment method on the catalytic performance was studied using three zeolites with suitable topologies. The calcination temperature significantly affected DME conversion and n-butene yield. The ferrierite zeolite showed the highest n-butene yield at a calcination temperature of 773 K. Multiple regression analysis was performed to determine the correlation between the six values obtained using N2 adsorption/desorption and NH3-TPD analyses, and the n-butene yield. The contribution rate of the strong acid site alone as an explanatory variable was 69.9%; however, the addition of micropore volume was statistically appropriate, leading to an increase in the contribution rate to 76.1%. Insights into the mechanism of n-butene synthesis in the DTO reaction were obtained using these parameters. Full article
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18 pages, 4622 KiB  
Article
Synthesis of Gd2O3 Nanoparticles and Their Photocatalytic Activity for Degradation of Azo Dyes
by Sugyeong Jeon, Jeong-Won Ko and Weon-Bae Ko
Catalysts 2021, 11(6), 742; https://doi.org/10.3390/catal11060742 - 17 Jun 2021
Cited by 26 | Viewed by 3114
Abstract
Gadolinium oxide (Gd2O3) nanoparticles were prepared via the reaction of gadolinium nitrate hexahydrate (Gd (NO3)3·6H2O) and ethylamine (C2H5NH2), and their surface morphology, particle size, and properties were [...] Read more.
Gadolinium oxide (Gd2O3) nanoparticles were prepared via the reaction of gadolinium nitrate hexahydrate (Gd (NO3)3·6H2O) and ethylamine (C2H5NH2), and their surface morphology, particle size, and properties were examined by using scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet visible (UV-vis) spectroscopy. The Gd2O3 nanoparticles were used as the photocatalyst for the degradation of various azo dyes, such as methyl orange (MO), acid orange 7 (AO7), and acid yellow 23 (AY23) under irradiation with UV light. The effect of the experimental parameters (initial concentration of azo dyes, dosage of catalyst, and wavelength of UV light) on the photocatalytic properties of the Gd2O3 nanoparticles were investigated. At a constant H2O2 concentration, the photocatalytic degradation efficiency of the Gd2O3 nanoparticles for various azo dyes was in the order: methyl orange > acid orange 7 > acid yellow 23. The kinetics study showed that the photocatalytic degradation of azo dyes was followed by a pseudo first-order reaction rate law. Full article
(This article belongs to the Section Environmental Catalysis)
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14 pages, 5279 KiB  
Article
Exploring the Stability of Fe–Ni Alloy Nanoparticles Exsolved from Double-Layered Perovskites for Dry Reforming of Methane
by Alfonso J. Carrillo and José Manuel Serra
Catalysts 2021, 11(6), 741; https://doi.org/10.3390/catal11060741 - 16 Jun 2021
Cited by 18 | Viewed by 3813
Abstract
Exsolution is emerging as a promising route for the creation of nanoparticles that remain anchored to the oxide support, imparting remarkable stability in high temperature chemical processes such as dry reforming of methane. This process takes place at temperatures around 850 °C, which [...] Read more.
Exsolution is emerging as a promising route for the creation of nanoparticles that remain anchored to the oxide support, imparting remarkable stability in high temperature chemical processes such as dry reforming of methane. This process takes place at temperatures around 850 °C, which causes sintering-related issues in catalysts prepared using conventional impregnation methods, which could be overcome by using exsolution functionalized oxides. In this work, FeNi3 alloy nanoparticles exsolved from Sr2FexNi1-xMoO6-δ double-layered perovskites were evaluated as a dry reforming catalyst, paying special attention to structure–activity relationships. Our results indicate that increasing the Ni content favors the nanoparticle dispersion, eventually leading to increased CO2 and CH4 conversions. The exsolved nanoparticles presented remarkable nanoparticle size (ca. 30 nm) stability after the 10 h treatment, although the formation of some phase segregations over the course of the reaction caused a minor decrease in the nanoparticle population. Overall, the results presented here serve as materials processing guidelines that could find further potential use in the design of more efficient (electro)catalysts in other fuel production or energy conversion technologies. Full article
(This article belongs to the Special Issue Oxidative Catalysis Processes)
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9 pages, 2024 KiB  
Article
High Catalytic Performance and Sustainability of Zr Modified Aluminophosphate for Vapor-Phase Selective O-Methylation of Catechol with Methanol
by Xinfeng Ren, Dongfei Xu, Yuchen Yin, Xiujing Zou, Yankai Wang, Xingfu Shang and Xueguang Wang
Catalysts 2021, 11(6), 740; https://doi.org/10.3390/catal11060740 - 16 Jun 2021
Cited by 3 | Viewed by 1581
Abstract
Guaiacol produced by O-methylation of catechol with methanol over solid catalysts is a green environmental synthesis route. In order to achieve high catalytic efficiency, it is quite necessary to employ low-cost catalysts with high activity and stability. Herein, series of aluminophosphate catalysts [...] Read more.
Guaiacol produced by O-methylation of catechol with methanol over solid catalysts is a green environmental synthesis route. In order to achieve high catalytic efficiency, it is quite necessary to employ low-cost catalysts with high activity and stability. Herein, series of aluminophosphate catalysts were synthesized by a simple precipitation route modified by Zr. The characterization results indicated that the prepared Al-P-Zr catalysts possessed appropriate weak acid and weak base sites, which were beneficial for the O-methylation of catechol with methanol. Different Zr amount and calcined temperature exerted a significant influence on physicochemical properties of the catalysts and catalytic performance. The Al-P-Zr catalysts containing Zr/Al molar ratio of 0.012 calcined under 400 °C showed the optimal catalytic activity and long-term stability for vapor-phase selective O-methylation of catechol with methanol. Full article
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11 pages, 2847 KiB  
Review
Research Progress in Enzymatic Synthesis of Vitamin E Ester Derivatives
by Zhiqiang Zou, Lingmei Dai, Dehua Liu and Wei Du
Catalysts 2021, 11(6), 739; https://doi.org/10.3390/catal11060739 - 16 Jun 2021
Cited by 13 | Viewed by 3864
Abstract
Vitamin E is easily oxidized by light, air, oxidizing agents and heat, limiting its application in many ways. Compared to vitamin E, vitamin E ester derivatives exhibit improved stability and a stronger antioxidant capacity, and even gain new biological functions. In recent years, [...] Read more.
Vitamin E is easily oxidized by light, air, oxidizing agents and heat, limiting its application in many ways. Compared to vitamin E, vitamin E ester derivatives exhibit improved stability and a stronger antioxidant capacity, and even gain new biological functions. In recent years, enzymatic synthesis of vitamin E ester derivatives has received increasing attention due to its environmental friendliness, high catalytic efficiency, and inherent selectivity. This paper reviews the related progress of lipase-mediated preparation of vitamin E ester derivatives. The function of different vitamin E ester derivatives, and the main factors influencing the enzymatic acylation process, including enzyme species, acyl donor and acceptor, reaction media and water activity, are summarized in this paper. Finally, the perspective of lipase-catalyzed synthesis of vitamin E ester derivatives is also discussed. Full article
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13 pages, 4392 KiB  
Article
Single Atomic Pt on SrTiO3 Catalyst in Reverse Water Gas Shift Reactions
by Yimeng Xing, Mengyao Ouyang, Lingling Zhang, Ming Yang, Xiaodong Wu, Rui Ran, Duan Weng, Feiyu Kang and Zhichun Si
Catalysts 2021, 11(6), 738; https://doi.org/10.3390/catal11060738 - 16 Jun 2021
Cited by 8 | Viewed by 2769
Abstract
Copper catalysts were widely developed for CO2 conversion, but suffered severe sintering at temperatures higher than 300 °C. Platinum was the most active and stable metal for RWGS reactions. However, the high price and scarcity of platinum restrained its application. Downsizing the [...] Read more.
Copper catalysts were widely developed for CO2 conversion, but suffered severe sintering at temperatures higher than 300 °C. Platinum was the most active and stable metal for RWGS reactions. However, the high price and scarcity of platinum restrained its application. Downsizing the metal particles can significantly improve the atom efficiency of the precious metal but the size effect of Pt on RWGS reactions was still unclear. In the present work, the single atomic Pt on SrTiO3 was prepared using an impregnation leaching method, and the catalyst showed significant activity for an RWGS reaction, achieving a CO2 conversion rate of 45%, a CO selectivity of 100% and a TOF of 0.643 s−1 at 500 °C. The structures of the catalysts were characterized using XRD, STEM and EXAFS. Especially, the size effect of Pt in RWGS was researched using in situ FTIR and DFT calculations. The results reveal that single Pt atoms are the most active species in RWGS via a “–COOH route” while larger Pt cluster and nanoparticles facilitate the further hydrogenation of CO. The reaction between formate and H* is the rate determination step of an RWGS reaction on a catalyst, in which the reaction barrier can be lowered from 1.54 eV on Pt clusters to 1.29 eV on a single atomic Pt. Full article
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8 pages, 1847 KiB  
Article
Energy-Dependent Time-Resolved Photoluminescence of Self-Catalyzed InN Nanocolumns
by Fang-I Lai, Jui-Fu Yang, Wei-Chun Chen, Dan-Hua Hsieh, Woei-Tyng Lin, Yu-Chao Hsu and Shou-Yi Kuo
Catalysts 2021, 11(6), 737; https://doi.org/10.3390/catal11060737 - 16 Jun 2021
Cited by 2 | Viewed by 1671
Abstract
In this study, we report the optical properties and carrier dynamics of different surface dimensionality n-type wurtzite InN with various carrier concentrations using photoluminescence (PL) and an energy-dependent, time-resolved photoluminescence (ED-TRPL) analysis. Experimental results indicated that the InN morphology can be controlled by [...] Read more.
In this study, we report the optical properties and carrier dynamics of different surface dimensionality n-type wurtzite InN with various carrier concentrations using photoluminescence (PL) and an energy-dependent, time-resolved photoluminescence (ED-TRPL) analysis. Experimental results indicated that the InN morphology can be controlled by the growth temperature, from one-dimensional (1D) nanorods to two-dimensional (2D) films. Moreover, donor-like nitrogen vacancy (VN) is responsible for the increase in carrier concentration due to the lowest formation energies in the n-type InN samples. The PL results also reveal that the energies of emission peaks are higher in the InN samples with 2D features than that with 1D features. These anomalous transitions are explained as the recombination of Mahan excitons and localized holes, and further proved by a theoretical model, activation energy and photon energy-dependent lifetime analysis. Full article
(This article belongs to the Special Issue Growth of Catalyst-Free InN Nanocolumns)
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17 pages, 4177 KiB  
Article
Structural Requirements for Chemoselective Ammonolysis of Ethylene Glycol to Ethanolamine over Supported Cobalt Catalysts
by Xianchi Lei, Guoding Gu, Yafei Hu, Haoshang Wang, Zhaoxia Zhang and Shuai Wang
Catalysts 2021, 11(6), 736; https://doi.org/10.3390/catal11060736 - 15 Jun 2021
Cited by 4 | Viewed by 5670
Abstract
Ethylene glycol is regarded as a promising C2 platform molecule due to the fast development of its production from sustainable biomass. This study inquired the structural requirements of Co-based catalysts for the liquid-phase ammonolysis of ethylene glycol to value-added ethanolamine. We showed [...] Read more.
Ethylene glycol is regarded as a promising C2 platform molecule due to the fast development of its production from sustainable biomass. This study inquired the structural requirements of Co-based catalysts for the liquid-phase ammonolysis of ethylene glycol to value-added ethanolamine. We showed that the rate and selectivity of ethylene glycol ammonolysis on γ-Al2O3-supported Co catalysts were strongly affected by the metal particle size within the range of 2–10 nm, among which Co nanoparticles of ~4 nm exhibited both the highest ethanolamine selectivity and the highest ammonolysis rate based on the total Co content. Doping of a moderate amount of Ag further promoted the catalytic activity without affecting the selectivity. Combined kinetic and infrared spectroscopic assessments unveiled that the addition of Ag significantly destabilized the adsorbed NH3 on the Co surface, which would otherwise be strongly bound to the active sites and inhibit the rate-determining dehydrogenation step of ethylene glycol. Full article
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11 pages, 1256 KiB  
Article
Synergistic Effect of Alkali Na and K Promoter on Fe-Co-Cu-Al Catalysts for CO2 Hydrogenation to Light Hydrocarbons
by Yuhao Zheng, Chenghua Xu, Xia Zhang, Qiong Wu and Jie Liu
Catalysts 2021, 11(6), 735; https://doi.org/10.3390/catal11060735 - 15 Jun 2021
Cited by 9 | Viewed by 2679
Abstract
Alkali metal K- and/or Na-promoted FeCoCuAl catalysts were synthesized by precipitation and impregnation, and their physicochemical and catalytic performance for CO2 hydrogenation to light hydrocarbons was also investigated in the present work. The results indicate that Na and/or K introduction leads to [...] Read more.
Alkali metal K- and/or Na-promoted FeCoCuAl catalysts were synthesized by precipitation and impregnation, and their physicochemical and catalytic performance for CO2 hydrogenation to light hydrocarbons was also investigated in the present work. The results indicate that Na and/or K introduction leads to the formation of active phase metallic Fe and Fe-Co crystals in the order Na < K < K-Na. The simultaneous introduction of Na and K causes a synergistic effect on increasing the basicity and electron-rich property, promoting the formation of active sites Fe@Cu and Fe-Co@Cu with Cu0 as a crystal core. These effects are advantageous to H2 dissociative adsorption and CO2 activation, giving a high CO2 conversion with hydrogenation. Moreover, electron-rich Fe@Cu (110) and Fe-Co@Cu (200) provide active centers for further H2 dissociative adsorption and O-C-Fe intermediate formation after adsorption of CO produced by RWGS. It is beneficial for carbon chain growth in C2+ hydrocarbons, including olefins and alkanes. FeCoCuAl simultaneously modified by K-Na exhibits the highest CO2 conversion and C2+ selectivity of 52.87 mol% and 89.70 mol%, respectively. Full article
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13 pages, 1347 KiB  
Article
Integrated Cleaner Biocatalytic Process for Biodiesel Production from Crude Palm Oil Comparing to Refined Palm Oil
by Papasanee Muanruksa, Phavit Wongsirichot, James Winterburn and Pakawadee Kaewkannetra
Catalysts 2021, 11(6), 734; https://doi.org/10.3390/catal11060734 - 15 Jun 2021
Cited by 2 | Viewed by 2558
Abstract
An integrated cleaner biocatalyst process was performed for biodiesel production from crude palm oil (CPO) and refined palm oil (RPO). It was evaluated on process efficiency in terms of high purity of biodiesel as well as by-products without purification, less wastewater, less time [...] Read more.
An integrated cleaner biocatalyst process was performed for biodiesel production from crude palm oil (CPO) and refined palm oil (RPO). It was evaluated on process efficiency in terms of high purity of biodiesel as well as by-products without purification, less wastewater, less time consuming, and a simple downstream process. A first saponification step was carried out in both f CPO and RPO, a high purity of glycerol (86.25% and 87.5%) was achieved, respectively, while free fatty acids (FFASs) in soap were obtained after hexane extraction. High yields of FFASs were obtained from both CPO and RPO (98.83% and 90.94%). Subsequently, the FFAs were esterified to biodiesel by a biocatalyst of immobilized lipase. The highest biodiesel yields achieved were of 92.14% and 92.58% (CPO and RPO). Remarkably, biodiesel yields obtained from CPO and RPO achieved satisfactory values and the biocatalyst used could be reused for more than 16–17 cycles. Full article
(This article belongs to the Special Issue Biocatalysis in Lipids Modification)
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21 pages, 5669 KiB  
Article
Economic and Ultrafast Photocatalytic Degradation of Orange II Using Ceramic Powders
by Dikra Bouras, Abla Mecif, Abdelhamid Harabi, Régis Barillé, Abdel hakim Mahdjoub and Mourad Zaabat
Catalysts 2021, 11(6), 733; https://doi.org/10.3390/catal11060733 - 14 Jun 2021
Cited by 10 | Viewed by 2130
Abstract
Different percentages of CuO and ZnO were added into a local kaolin ceramic-based powder (DD3) with and without ZrO2. The modified powders were first characterized, then, a test for the photocatalytic degradation of dyes with orange II (OII) was carried out. [...] Read more.
Different percentages of CuO and ZnO were added into a local kaolin ceramic-based powder (DD3) with and without ZrO2. The modified powders were first characterized, then, a test for the photocatalytic degradation of dyes with orange II (OII) was carried out. The DD3 powders that were obtained with the addition of ZrO2, ZnO, and CuO, were prepared by two different methods and have shown a large and very fast photocatalytic activity. Discoloration ratios of about 93.6% and 100% were reached after 15 min and 45 min, for CuO and ZnO respectively. Finally, an alternative photocatalysis mechanism, based purely on chemical reaction processes, is proposed. The photocatalysis results with modified powders are compared with the results obtained with thin films, made with the same materials. Full article
(This article belongs to the Special Issue Recent Advances in Photocatalysis Technology in Europe and Asia)
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16 pages, 2662 KiB  
Article
Passivation of Co/Al2O3 Catalyst by Atomic Layer Deposition to Reduce Deactivation in the Fischer–Tropsch Synthesis
by José Antonio Díaz-López, Jordi Guilera, Martí Biset-Peiró, Dan Enache, Gordon Kelly and Teresa Andreu
Catalysts 2021, 11(6), 732; https://doi.org/10.3390/catal11060732 - 14 Jun 2021
Cited by 4 | Viewed by 2886
Abstract
The present work explores the technical feasibility of passivating a Co/γ-Al2O3 catalyst by atomic layer deposition (ALD) to reduce deactivation rate during Fischer–Tropsch synthesis (FTS). Three samples of the reference catalyst were passivated using different numbers of ALD cycles (3, [...] Read more.
The present work explores the technical feasibility of passivating a Co/γ-Al2O3 catalyst by atomic layer deposition (ALD) to reduce deactivation rate during Fischer–Tropsch synthesis (FTS). Three samples of the reference catalyst were passivated using different numbers of ALD cycles (3, 6 and 10). Characterization results revealed that a shell of the passivating agent (Al2O3) grew around catalyst particles. This shell did not affect the properties of passivated samples below 10 cycles, in which catalyst reduction was hindered. Catalytic tests at 50% CO conversion evidenced that 3 and 6 ALD cycles increased catalyst stability without significantly affecting the catalytic performance, whereas 10 cycles caused blockage of the active phase that led to a strong decrease of catalytic activity. Catalyst deactivation modelling and tests at 60% CO conversion served to conclude that 3 to 6 ALD cycles reduced Co/γ-Al2O3 deactivation, so that the technical feasibility of this technique was proven in FTS. Full article
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12 pages, 3138 KiB  
Article
Studies of Nickel/Samarium-Doped Ceria for Catalytic Partial Oxidation of Methane and Effect of Oxygen Vacancy
by Andrew C. Chien, Nicole J. Ye, Chao-Wei Huang and I-Hsiang Tseng
Catalysts 2021, 11(6), 731; https://doi.org/10.3390/catal11060731 - 14 Jun 2021
Cited by 5 | Viewed by 2675
Abstract
We investigated the performance of nickel/samarium-doped ceria (Ni/SDC) nanocatalysts on the catalytic partial oxidation of methane (CPOM). Studies of temperature-programmed surface reaction and reduction reveal that catalytic activity is determined by a synergistic effect produced by Ni metals and metal-support interaction. Catalytic activity [...] Read more.
We investigated the performance of nickel/samarium-doped ceria (Ni/SDC) nanocatalysts on the catalytic partial oxidation of methane (CPOM). Studies of temperature-programmed surface reaction and reduction reveal that catalytic activity is determined by a synergistic effect produced by Ni metals and metal-support interaction. Catalytic activity was more dependent on the Ni content below 600 °C, while there is not much difference for all catalysts at high temperatures. The catalyst exhibiting high activities toward syngas production (i.e., a CH4 conversion >90% at 700 °C) requires a medium Ni-SDC interaction with an Sm/Ce ratio of about 1/9 to 2/8. This is accounted for by optimum oxygen vacancies and adequate ion diffusivity in the SDCs which, as reported, also display the highest ion conductivity for fuel cell applications. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Hydrocarbons)
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8 pages, 1465 KiB  
Article
Synthesis and Advanced Characterization of Polymer–Protein Core–Shell Nanoparticles
by Erik Sarnello and Tao Li
Catalysts 2021, 11(6), 730; https://doi.org/10.3390/catal11060730 - 13 Jun 2021
Cited by 2 | Viewed by 1895
Abstract
Enzyme immobilization techniques are widely researched due to their wide range of applications. Polymer–protein core–shell nanoparticles (CSNPs) have emerged as a promising technique for enzyme/protein immobilization via a self-assembly process. Based on the desired application, different sizes and distribution of the polymer–protein CSNPs [...] Read more.
Enzyme immobilization techniques are widely researched due to their wide range of applications. Polymer–protein core–shell nanoparticles (CSNPs) have emerged as a promising technique for enzyme/protein immobilization via a self-assembly process. Based on the desired application, different sizes and distribution of the polymer–protein CSNPs may be required. This work systematically studies the assembly process of poly(4-vinyl pyridine) and bovine serum albumin CSNPs. Average particle size was controlled by varying the concentrations of each reagent. Particle size and size distributions were monitored by dynamic light scattering, ultra-small-angle X-ray scattering, small-angle X-ray scattering and transmission electron microscopy. Results showed a wide range of CSNPs could be assembled ranging from an average radius as small as 52.3 nm, to particles above 1 µm by adjusting reagent concentrations. In situ X-ray scattering techniques monitored particle assembly as a function of time showing the initial particle growth followed by a decrease in particle size as they reach equilibrium. The results outline a general strategy that can be applied to other CSNP systems to better control particle size and distribution for various applications. Full article
(This article belongs to the Special Issue Towards Polymeric Biocatalysts)
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9 pages, 1902 KiB  
Article
Inversion of the Photogalvanic Effect of Conductive Polymers by Porphyrin Dopants
by Alexey A. Petrov, Daniil A. Lukyanov, Oleg A. Kopytko, Julia V. Novoselova, Elena V. Alekseeva and Oleg V. Levin
Catalysts 2021, 11(6), 729; https://doi.org/10.3390/catal11060729 - 12 Jun 2021
Cited by 6 | Viewed by 2194
Abstract
Conductive polymers are widely used as active and auxiliary materials for organic photovoltaic cells due to their easily tunable properties, high electronic conductivity, and light absorption. Several conductive polymers show the cathodic photogalvanic effect in pristine state. Recently, photoelectrochemical oxygen reduction has been [...] Read more.
Conductive polymers are widely used as active and auxiliary materials for organic photovoltaic cells due to their easily tunable properties, high electronic conductivity, and light absorption. Several conductive polymers show the cathodic photogalvanic effect in pristine state. Recently, photoelectrochemical oxygen reduction has been demonstrated for nickel complexes of Salen-type ligands. Herein, we report an unexpected inversion of the photogalvanic effect caused by doping of the NiSalen polymers with anionic porphyrins. The observed effect was studied by means of UV-Vis spectroscopy, cyclic voltammetry and chopped light chronoamperometry. While pristine NiSalens exhibit cathodic photopolarization, doping with porphyrins inverts the polarization. As a result, photoelectrochemical oxidation of the ascorbate proceeds smoothly on the NiSalen electrode doped with zinc porphyrins. The highest photocurrents were observed on NiSalen polymer with o-phenylene imine bridge, doped with anionic zinc porphyrin. Assuming this, porphyrin serves both as a catalytic center for the oxidation of ascorbate and an internal electron donor, facilitating the photoinduced charge transport and anodic depolarization. Full article
(This article belongs to the Special Issue Catalysts in Energy Applications)
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44 pages, 4493 KiB  
Review
Application of TiO2-Based Photocatalysts to Antibiotics Degradation: Cases of Sulfamethoxazole, Trimethoprim and Ciprofloxacin
by Anastasiya Kutuzova, Tetiana Dontsova and Witold Kwapinski
Catalysts 2021, 11(6), 728; https://doi.org/10.3390/catal11060728 - 12 Jun 2021
Cited by 68 | Viewed by 6395
Abstract
The extensive application of antibiotics in human and veterinary medicine has led to their widespread occurrence in a natural aquatic environment. Global health crisis is associated with the fast development of antimicrobial resistance, as more and more infectious diseases cannot be treated more [...] Read more.
The extensive application of antibiotics in human and veterinary medicine has led to their widespread occurrence in a natural aquatic environment. Global health crisis is associated with the fast development of antimicrobial resistance, as more and more infectious diseases cannot be treated more than once. Sulfamethoxazole, trimethoprim and ciprofloxacin are the most commonly detected antibiotics in water systems worldwide. The persistent and toxic nature of these antibiotics makes their elimination by conventional treatment methods at wastewater treatment plants almost impossible. The application of advanced oxidation processes and heterogeneous photocatalysis over TiO2-based materials is a promising solution. This highly efficient technology has the potential to be sustainable, cost-efficient and energy-efficient. A comprehensive review on the application of various TiO2-based photocatalysts for the degradation of sulfamethoxazole, trimethoprim and ciprofloxacin is focused on highlighting their photocatalytic performance under various reaction conditions (different amounts of pollutant and photocatalyst, pH, light source, reaction media, presence of inorganic ions, natural organic matter, oxidants). Mineralization efficiency and ecotoxicity of final products have been also considered. Further research needs have been presented based on the literature findings. Among them, design and development of highly efficient under sunlight, stable, recyclable and cost-effective TiO2-based materials; usage of real wastewaters for photocatalytic tests; and compulsory assessment of products ecotoxicity are the most important research tasks in order to meet requirements for industrial application. Full article
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15 pages, 2452 KiB  
Article
Synthesis and Laccase-Mediated Oxidation of New Condensed 1,4-Dihydropyridine Derivatives
by Jelena Milovanovic, Miyase Gözde Gündüz, Anastasia Zerva, Milos Petkovic, Vladimir Beskoski, Nikolaos S. Thomaidis, Evangelos Topakas and Jasmina Nikodinovic-Runic
Catalysts 2021, 11(6), 727; https://doi.org/10.3390/catal11060727 - 12 Jun 2021
Cited by 5 | Viewed by 2590
Abstract
We describe herein the synthesis and laccase mediated oxidation of six novel 1,4-dihydropyridine (DHP)-based hexahydroquinolines (DHP1-DHP3) and decahydroacridines (DHP4-DHP6). We employed different laccase enzymes with varying redox potential to convert DHP1-DHP3 and DHP4-DHP6 to the corresponding pyridine-containing tetrahydroquinoline and octahydroacridine derivatives, respectively. Intensively [...] Read more.
We describe herein the synthesis and laccase mediated oxidation of six novel 1,4-dihydropyridine (DHP)-based hexahydroquinolines (DHP1-DHP3) and decahydroacridines (DHP4-DHP6). We employed different laccase enzymes with varying redox potential to convert DHP1-DHP3 and DHP4-DHP6 to the corresponding pyridine-containing tetrahydroquinoline and octahydroacridine derivatives, respectively. Intensively coloured products were detected in all biocatalytic reactions using laccase from Trametes versicolor (TvLacc), possibly due to the presence of conjugated chromophores formed in products after oxidation. The NMR assessment confirmed that the oxidation product of DHP1 was its corresponding pyridine-bearing tetrahydroquinoline derivative. Laccase from Bacillus subtillis (BacillusLacc) was the most efficient enzyme for this group of substrates using HPLC assessment. Overall, it could be concluded that DHP2 and DHP5, bearing catecholic structures, were easily oxidized by all tested laccases, while DHP3 and DHP6 containing electron-withdrawing nitro-groups are not readily oxidized by laccases. DHP4 with decahydroacridine moiety consisting of three condensed six-membered rings that contribute not only to the volume but also to the higher redox potential of the substrate rendered this compound not to be biotransformed with any of the mentioned enzymes. Overall, we showed that multiple analytical approaches are needed in order to assess biocatalytical reactions. Full article
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20 pages, 3971 KiB  
Article
Characterization of an Immobilized Amino Acid Racemase for Potential Application in Enantioselective Chromatographic Resolution Processes
by Isabel Harriehausen, Jonas Bollmann, Thiane Carneiro, Katja Bettenbrock and Andreas Seidel-Morgenstern
Catalysts 2021, 11(6), 726; https://doi.org/10.3390/catal11060726 - 11 Jun 2021
Cited by 4 | Viewed by 1956
Abstract
Enantioselective resolution processes can be improved by integration of racemization. Applying environmentally friendly enzymatic racemization under mild conditions is in particular attractive. Owing to the variety of enzymes and the progress in enzyme engineering, suitable racemases can be found for many chiral systems. [...] Read more.
Enantioselective resolution processes can be improved by integration of racemization. Applying environmentally friendly enzymatic racemization under mild conditions is in particular attractive. Owing to the variety of enzymes and the progress in enzyme engineering, suitable racemases can be found for many chiral systems. An amino acid racemase (AAR) from P. putida KT2440 is capable of processing a broad spectrum of amino acids at fast conversion rates. The focus of this study is the evaluation of the potential of integrating AAR immobilized on Purolite ECR 8309 to racemize L- or D-methionine (Met) within an enantioselective chromatographic resolution process. Racemization rates were studied for different temperatures, pH values, and fractions of organic co-solvents. The long-term stability of the immobilized enzyme at operating and storage conditions was found to be excellent and recyclability using water with up to 5 vol% ethanol at 20 °C could be demonstrated. Packed as an enzymatic fixed bed reactor, the immobilized AAR can be coupled with different resolution processes; for instance, with chromatography or with preferential crystallization. The performance of coupling it with enantioselective chromatography is estimated quantitatively, exploiting parametrized sub-models. To indicate the large potential of the AAR, racemization rates are finally given for lysine, arginine, serine, glutamine, and asparagine. Full article
(This article belongs to the Special Issue Enzyme Immobilization and Biocatalysis)
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15 pages, 1838 KiB  
Article
Preparation of Pd/SiO2 Catalysts by a Simple Dry Ball-Milling Method for Lean Methane Oxidation and Probe of the State of Active Pd Species
by Li Yang, Chao Fan, Li Luo, Yanyan Chen, Zhiwei Wu, Zhangfeng Qin, Mei Dong, Weibin Fan and Jianguo Wang
Catalysts 2021, 11(6), 725; https://doi.org/10.3390/catal11060725 - 11 Jun 2021
Cited by 8 | Viewed by 2889
Abstract
A series of Pd/SiO2 catalysts were prepared with different Pd precursors by a dry ball-milling method and used in the catalytic oxidation of lean methane at low temperature. The effect of Pd precursors on the catalytic performance was investigated and the state [...] Read more.
A series of Pd/SiO2 catalysts were prepared with different Pd precursors by a dry ball-milling method and used in the catalytic oxidation of lean methane at low temperature. The effect of Pd precursors on the catalytic performance was investigated and the state of the most active Pd species was probed. The results indicate that dry ball-milling is a simple but rather effective method to prepare the Pd/SiO2 catalysts for lean methane oxidation, and palladium acetylacetonate is an ideal precursor to obtain a highly active Pd/SiO2-Acac catalyst with well- and stably dispersed Pd species, owing to the tight contact between acetylacetonate and Si–OH on the SiO2 support. Besides the size and dispersion of Pd particles, the oxidation state of Pd species also plays a crucial role in determining the catalytic activity of Pd/SiO2 in lean methane oxidation at low temperature. A non-monotonic dependence of the catalytic activity on the Pd oxidation state is observed. The activity of various Pd species follows the order of PdOx >> Pd > PdO; the PdOx/SiO2-Acac catalysts (in particular for PdO0.82/SiO2-Acac when x = 0.82) exhibit much higher activity in lean methane oxidation at low temperature than Pd/SiO2-Acac and PdO/SiO2-Acac. The catalytic activity of PdOx/SiO2 may degrade during the methane oxidation due to the gradual transformation of PdOx to PdO in the oxygen-rich ambiance; however, such degradation is reversible and the activity of a degraded Pd/SiO2 catalyst can be recovered through a redox treatment to regain the PdOx species. This work helps to foster a better understanding of the relationship between the structure and performance of supported Pd catalysts by clarifying the state of active Pd species, which should be beneficial to the design of an active catalyst in lean methane oxidation at low temperature. Full article
(This article belongs to the Special Issue Advances in Catalytic Oxidation of Methane and Carbon Monoxide)
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