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Catalysts, Volume 10, Issue 9 (September 2020) – 153 articles

Cover Story (view full-size image): Optimal photocatalytic air purification designs are the result of key factors such as photocatalysis, irradiation, fluid dynamics, reaction kinetics, as well as quantum and thermodynamic efficiencies. This work presents a critical review of advanced green technologies and their applications, for the removal of both organic pollutants and viruses. View this paper
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35 pages, 5772 KiB  
Review
Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts
by Matthew E. Potter, Joshua J.M. Le Brocq, Alice E. Oakley, Evangeline B. McShane, Bart D. Vandegehuchte and Robert Raja
Catalysts 2020, 10(9), 1099; https://doi.org/10.3390/catal10091099 - 22 Sep 2020
Cited by 11 | Viewed by 8145
Abstract
The growing demand for isobutane as a vital petrochemical feedstock and chemical intermediate has for many decades surpassed industrial outputs that can be supplied through liquified petroleum gases. Alternative methods to resource the isobutane market have been explored, primarily the isomerization of linear [...] Read more.
The growing demand for isobutane as a vital petrochemical feedstock and chemical intermediate has for many decades surpassed industrial outputs that can be supplied through liquified petroleum gases. Alternative methods to resource the isobutane market have been explored, primarily the isomerization of linear n-butane to the substituted isobutane. To date the isobutane market is valued at over 20 billion US dollars, enticing researchers to seek unique and novel catalytic materials to improve on current commercial practices. Two main classes of catalysts have dominated the butane isomerization literature in the last few decades; namely microporous zeolites and sulfated zirconia. Both have been widely researched for butane isomerization, to the point where key catalytic descriptors such as acidity, framework topology and metal doping are becoming well understood. While this provides new researchers with a roadmap for developing new materials, it is has also begun developing into an invaluable tool for diagnosing and understanding the effect of these individual descriptors on catalytic properties. In this review we explore the different factors that influence the active site behavior of particularly zeolites and sulfated zirconia catalysts towards understanding the use of butane isomerization as a diagnostic tool for solid-acid catalysts. Full article
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11 pages, 3151 KiB  
Article
Enhanced Phenol Tert-Butylation Reaction Activity over Hierarchical Porous Silica-Alumina Materials
by Ling Xu, Fan Wang, Zhi Xiu, Limei Duan, Zongrui Liu and Jingqi Guan
Catalysts 2020, 10(9), 1098; https://doi.org/10.3390/catal10091098 - 22 Sep 2020
Cited by 1 | Viewed by 2192
Abstract
Hierarchical aluminum-silicon materials have been successfully prepared by mixing pre-crystallization of silica-alumina sol and citric acid under hydrothermal conditions. The influence of pre-crystallization time on the micro-mesoporous structure is studied using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N2 physical [...] Read more.
Hierarchical aluminum-silicon materials have been successfully prepared by mixing pre-crystallization of silica-alumina sol and citric acid under hydrothermal conditions. The influence of pre-crystallization time on the micro-mesoporous structure is studied using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N2 physical adsorption, and high-resolution transmission electron microscopy (HRTEM). The catalytic performance of hierarchical silica-alumina material is evaluated by alkylation of phenol with tert-butanol. The results show that the silica-alumina materials with a pre-crystallization time of 16 h show micro-mesoporous structure and excellent catalytic activity. Full article
(This article belongs to the Special Issue Porous Materials and Catalysts)
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26 pages, 7512 KiB  
Article
Comparison of Ag and AgI-Modified ZnO as Heterogeneous Photocatalysts for Simulated Sunlight Driven Photodegradation of Metronidazole
by Chao Ding, Kun Fu, Yishuai Pan, Jia Liu, Huiping Deng and Jun Shi
Catalysts 2020, 10(9), 1097; https://doi.org/10.3390/catal10091097 - 22 Sep 2020
Cited by 20 | Viewed by 3004
Abstract
Ag and AgI-modified ZnO composites (Ag/ZnO and AgI/ZnO) were synthesized in facile ways. The photocatalysts were used for the photodegradation of metronidazole (MNZ) under the irradiation of simulated sunlight. The results of experiments showed that both Ag/ZnO and AgI/ZnO had a specific molar [...] Read more.
Ag and AgI-modified ZnO composites (Ag/ZnO and AgI/ZnO) were synthesized in facile ways. The photocatalysts were used for the photodegradation of metronidazole (MNZ) under the irradiation of simulated sunlight. The results of experiments showed that both Ag/ZnO and AgI/ZnO had a specific molar ratio to reach the best performance. Ag/ZnO performed better in the photodegradation of MNZ than AgI/ZnO under the same conditions. The reaction rate constant of AgI/ZnO was less affected by the variation of initial concentration of MNZ or pH values. The main reactive oxygen species of the photocatalytic process are OH, O2 and h+, but the free radicals which play the most critical part differ in Ag/ZnO and AgI/ZnO. Several intermediates were revealed by LC–MS/MS analysis. The stability of the photocatalysts was evaluated by a series of repeated MNZ photodegradation experiments. The results showed that AgI/ZnO had better stability than Ag/ZnO. Full article
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14 pages, 3237 KiB  
Article
Hydrogenative Cyclization of Levulinic Acid to γ-Valerolactone with Methanol and Ni-Fe Bimetallic Catalysts
by Ligang Luo, Xiao Han and Qin Zeng
Catalysts 2020, 10(9), 1096; https://doi.org/10.3390/catal10091096 - 21 Sep 2020
Cited by 15 | Viewed by 3114
Abstract
A series of Ni-Fe/SBA-15 catalysts was prepared and tested for the catalytic hydrogenation of levulinic acid to γ-valerolactone, adopting methanol as the only hydrogen donor, and investigating the synergism between Fe and Ni, both supported on SBA-15, towards this reaction. The characterization of [...] Read more.
A series of Ni-Fe/SBA-15 catalysts was prepared and tested for the catalytic hydrogenation of levulinic acid to γ-valerolactone, adopting methanol as the only hydrogen donor, and investigating the synergism between Fe and Ni, both supported on SBA-15, towards this reaction. The characterization of the synthesized catalysts was carried out by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), H2-TPD (hydrogen temperature-programmed desorption), XPS (X-ray photoelectron spectroscopy), and in situ FT-IR (Fourier transform–infrared spectroscopy) techniques. H2-TPD and XPS results have shown that electron transfer occurs from Fe to Ni, which is helpful both for the activation of the C=O bond and for the dissociative activation of H2 molecules, also in agreement with the results of the in situ FT-IR spectroscopy. The effect of temperature and reaction time on γ-valerolactone production was also investigated, identifying the best reaction conditions at 200 °C and 180 min, allowing for the complete conversion of levulinic acid and the complete selectivity to γ-valerolactone. Moreover, methanol was identified as an efficient hydrogen donor, if used in combination with the Ni-Fe/SBA-15 catalyst. The obtained results are promising, especially if compared with those obtained with the traditional and more expensive molecular hydrogen and noble-based catalysts. Full article
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7 pages, 1890 KiB  
Communication
Coupling Pre-Reforming and Partial Oxidation for LPG Conversion to Syngas
by Dmitriy I. Potemkin, Vladimir N. Rogozhnikov, Sergey I. Uskov, Vladislav A. Shilov, Pavel V. Snytnikov and Vladimir A. Sobyanin
Catalysts 2020, 10(9), 1095; https://doi.org/10.3390/catal10091095 - 21 Sep 2020
Cited by 7 | Viewed by 2120
Abstract
Coupling of the pre-reforming and partial oxidation was considered for the conversion of liquefied petroleum gas to syngas for the feeding applications of solid oxide fuel cells. Compared with conventional two step steam reforming, it allows the amount of water required for the [...] Read more.
Coupling of the pre-reforming and partial oxidation was considered for the conversion of liquefied petroleum gas to syngas for the feeding applications of solid oxide fuel cells. Compared with conventional two step steam reforming, it allows the amount of water required for the process, and therefore the energy needed for water evaporation, to be lowered; substitution of high-potential heat by lower ones; and substitution of expensive tubular steam reforming reactors by adiabatic ones. The supposed process is more productive due to the high reaction rate of partial oxidation. The obtained syngas contains only ca. 10 vol.% H2O and ca. 50 vol.% of H2 + CO, which is attractive for the feeding application of solid oxide fuel cells. Compared with direct partial oxidation of liquefied petroleum gas, the suggested scheme is more energy efficient and overcomes problems with coke formation and catalyst overheating. The proof-of-concept experiments were carried out. The granular Ni-Cr2O3-Al2O3 catalyst was shown to be effective for propane pre-reforming at 350–400 °C, H2O:C molar ratio of 1.0, and flow rate of 12,000 h−1. The composite Rh/Ce0.75Zr0.25O2-δ–ƞ-Al2O3/FeCrAl catalyst was shown to be active and stable under conditions of partial oxidation of methane-rich syngas after pre-reforming and provided a syngas (H2 + CO) productivity of 28 m3·Lcat−1·h−1 (standard temperature and pressure). Full article
(This article belongs to the Special Issue Heterogeneous Catalysts for Petrochemical Synthesis and Oil Refining)
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14 pages, 7483 KiB  
Article
Zn-Al Mixed Oxides Decorated with Potassium as Catalysts for HT-WGS: Preparation and Properties
by Katarzyna Antoniak-Jurak, Paweł Kowalik, Kamila Michalska, Wiesław Próchniak and Robert Bicki
Catalysts 2020, 10(9), 1094; https://doi.org/10.3390/catal10091094 - 21 Sep 2020
Cited by 7 | Viewed by 2722
Abstract
A set of ex-ZnAl-LDHs catalysts with a molar ratio of Zn/Al in the range of 0.3–1.0 was prepared using co-precipitation and thermal treatment. The samples were characterized using various methods, including X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), [...] Read more.
A set of ex-ZnAl-LDHs catalysts with a molar ratio of Zn/Al in the range of 0.3–1.0 was prepared using co-precipitation and thermal treatment. The samples were characterized using various methods, including X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy FT-IR, N2 adsorption, Temperature-programmed desorption of CO2 (TPD-CO2) as well as Scanning electron microscopy (SEM-EDS). Catalyst activity and long-term stability measurements were carried out in a high-temperature water–gas shift (HT-WGS) reaction. Mixed oxide catalysts with various Zn/Al molar ratios decorated with potassium showed high activity in the HT-WGS reaction within the temperature range of 330–400 °C. The highest activity was found for the Zn/Al molar ratio of 0.5 corresponding to spinel stoichiometry. However, the catalyst with a stoichiometric spinel molar ratio of Zn/Al (ZnAl_0.5_K) revealed a higher tendency for surface migration and/or vaporization of potassium during overheating at 450 °C. The correlation of the activity results and TPD-CO2 data show that medium basic sites enhance the progress of the HT-WGS reaction. Full article
(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)
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19 pages, 6794 KiB  
Review
Antiviral Effect of Visible Light-Sensitive CuxO/TiO2 Photocatalyst
by Masahiro Miyauchi, Kayano Sunada and Kazuhito Hashimoto
Catalysts 2020, 10(9), 1093; https://doi.org/10.3390/catal10091093 - 21 Sep 2020
Cited by 56 | Viewed by 10547
Abstract
Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2 [...] Read more.
Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2). The antiviral CuxO/TiO2 photocatalyst is functionalised by a different mechanism in addition to the photocatalytic oxidation process. The CuxO nanocluster consists of the valence states of Cu(I) and Cu(II); herein, the Cu(I) species denaturalizes the protein of the virus, thereby resulting in significant antiviral properties even under dark conditions. Moreover, the Cu(II) species in the CuxO nanocluster serves as an electron acceptor through photo-induced interfacial charge transfer, which leads to the formation of an anti-virus Cu(I) species and holes with strong oxidation power in the valence band of TiO2 under visible-light irradiation. The antiviral function of the CuxO/TiO2 photocatalyst is maintained under indoor conditions, where light illumination is enabled during the day but not during the night; this is because the remaining active Cu(I) species works under dark conditions. The CuxO/TiO2 photocatalyst can thus be used to reduce the risk of virus infection by acting as an antiviral coating material. Full article
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13 pages, 3327 KiB  
Review
Iron-Catalyzed Carbonyl–Alkyne and Carbonyl–Olefin Metathesis Reactions
by Benedikt W. Grau and Svetlana B. Tsogoeva
Catalysts 2020, 10(9), 1092; https://doi.org/10.3390/catal10091092 - 21 Sep 2020
Cited by 5 | Viewed by 4158
Abstract
Construction of carbon–carbon bonds is one of the most important tools for the synthesis of complex organic molecules. Among multiple possibilities are the carbonyl–alkyne and carbonyl–olefin metathesis reactions, which are used to form new carbon–carbon bonds between carbonyl derivatives and unsaturated organic compounds. [...] Read more.
Construction of carbon–carbon bonds is one of the most important tools for the synthesis of complex organic molecules. Among multiple possibilities are the carbonyl–alkyne and carbonyl–olefin metathesis reactions, which are used to form new carbon–carbon bonds between carbonyl derivatives and unsaturated organic compounds. As many different approaches have already been established and offer reliable access to C=C bond formation via carbonyl–alkyne and carbonyl–olefin metathesis, focus is now shifting towards cost efficiency, sustainability and environmentally friendly metal catalysts. Iron, which is earth-abundant and considered as an eco-friendly and inexpensive option in comparison to traditional metal catalysts, fulfils these requirements. Hence, the focus of this review is on recent advances in the iron-catalyzed carbonyl–alkyne, carbonyl–olefin and related C–O/C–O metathesis reactions. The still large research potential for ecologically and economically attractive and sustainable iron-based catalysts is demonstrated. Full article
(This article belongs to the Special Issue New Trends in Metathesis Catalysts)
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10 pages, 3026 KiB  
Article
Titanium-Modified MIL-101(Cr) Derived Titanium-Chromium-Oxide as Highly Efficient Oxidative Desulfurization Catalyst
by Xiaolin Li, Liang Zhang and Yinyong Sun
Catalysts 2020, 10(9), 1091; https://doi.org/10.3390/catal10091091 - 20 Sep 2020
Cited by 8 | Viewed by 2219
Abstract
A titanium-chromium-oxide catalyst was prepared by a facile calcination of titanium-modified MIL-101(Cr). The resulting material, possessing a surface area of 60 m2 g−1 and a titania content of 50.0 wt%, can be directly used as the catalyst for oxidative desulfurization (ODS) [...] Read more.
A titanium-chromium-oxide catalyst was prepared by a facile calcination of titanium-modified MIL-101(Cr). The resulting material, possessing a surface area of 60 m2 g−1 and a titania content of 50.0 wt%, can be directly used as the catalyst for oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT). This novel ODS catalyst can remove 900 ppm sulfur-containing compounds in a reaction time of 30 min at 60 °C. The experimental results showed that the specific activity increased with the titanium content. The specific activity of the catalyst with 50%Ti reached 129 μmol/m2, which was much higher than that of reported Ti-based catalysts. Full article
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15 pages, 2709 KiB  
Article
Recovering Secondary REE Value from Spent Oil Refinery Catalysts Using Biogenic Organic Acids
by Melisa Pramesti Dewi, Himawan Tri Bayu Murti Petrus and Naoko Okibe
Catalysts 2020, 10(9), 1090; https://doi.org/10.3390/catal10091090 - 20 Sep 2020
Cited by 9 | Viewed by 2419
Abstract
Spent catalysts produced by oil refinery industries are regarded as an important secondary source for valuable metals. In particular, spent fluid catalytic cracking (FCC) catalysts represent a potential source for rare earth elements (REEs). This study aimed to exploit the leachability of spent [...] Read more.
Spent catalysts produced by oil refinery industries are regarded as an important secondary source for valuable metals. In particular, spent fluid catalytic cracking (FCC) catalysts represent a potential source for rare earth elements (REEs). This study aimed to exploit the leachability of spent FCC catalysts as a secondary source for La, by using an alternative organic acid lixiviant produced under optimized fungal fermentation conditions. The first chemical leaching tests revealed that citric acid (>100 mM) is a comparable alternative lixiviant to conventional inorganic acids (1 M) and that the La dissolution behavior changed significantly with different types of organic acids. The initial fungal fermentation conditions (e.g., inoculum level, substrate concentration, pH) largely affected the resultant biogenic acid composition, and its manipulation was possible in order to almost solely ferment citric acid (~130 mM) while controlling the production of unwanted oxalic acid. The performance of actual biogenic acids (direct use of cell-free spent media) and artificially reconstituted biogenic acids (a mixture of chemical reagents) was nearly identical, achieving a final La dissolution of ~74% at a pulp density of 5%. Overall, the microbiological fermentation of organic acids could become a promising approach to supply an efficient and environmentally benign alternative lixiviant for REE scavenging from spent FCC catalyst wastes. Full article
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14 pages, 2275 KiB  
Article
Structural Disorder of Mechanically Activated δ-MgCl2 Studied by Synchrotron X-ray Total Scattering and Vibrational Spectroscopy
by Toru Wada, Ashutosh Thakur, Patchanee Chammingkwan, Minoru Terano, Toshiaki Taniike, Alessandro Piovano and Elena Groppo
Catalysts 2020, 10(9), 1089; https://doi.org/10.3390/catal10091089 - 20 Sep 2020
Cited by 13 | Viewed by 2537
Abstract
A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. [...] Read more.
A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. Four types of mechanically activated MgCl2 samples are prepared using ball-milling in the absence and presence of different donors. The development of structural disorder along the grinding time is compared. It was found that the presence of donors accelerates the formation of δ-MgCl2 in an early stage of grinding, while elongated grinding eventually results in δ-MgCl2 with similar extents of structural disorder in the absence and presence of different donors. The FT-IR investigation consistently verified the morphological similarity between the firmly ground samples. Thus, the structure of δ-MgCl2 is likely governed by mechanical energy when sufficiently ground. Full article
(This article belongs to the Section Catalytic Materials)
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4 pages, 178 KiB  
Editorial
Editorial Catalysts: Special Issue on Novel Enzyme and Whole-Cell Biocatalysts
by Anwar Sunna and Richard Daniellou
Catalysts 2020, 10(9), 1088; https://doi.org/10.3390/catal10091088 - 20 Sep 2020
Cited by 1 | Viewed by 1756
(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysts)
11 pages, 3681 KiB  
Article
Precise Catalyst Production for Carbon Nanotube Synthesis with Targeted Structure Enrichment
by Xiao Zhang, Ying Deng, Brian Graves, Michael De Volder and Adam Boies
Catalysts 2020, 10(9), 1087; https://doi.org/10.3390/catal10091087 - 19 Sep 2020
Cited by 5 | Viewed by 3158
Abstract
The direct growth of single-walled carbon nanotubes (SWCNTs) with a narrow distribution of diameter or chirality remains elusive despite significant benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT synthesis, but how to precisely manipulate their chemistry, size, concentration, and deposition [...] Read more.
The direct growth of single-walled carbon nanotubes (SWCNTs) with a narrow distribution of diameter or chirality remains elusive despite significant benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT synthesis, but how to precisely manipulate their chemistry, size, concentration, and deposition remains difficult, especially within a continuous production process from the gas phase. Here, we demonstrate the preparation of W6Co7 alloyed nanoparticle catalysts with precisely tunable stoichiometry using electrospray, which remain solid state during SWCNT growth. We also demonstrate continuous production of liquid iron nanoparticles with in-line size selection. With the precise size manipulation of catalysts in the range of 1–5 nm, and a nearly monodisperse distribution (σg < 1.2), an excellent size selection of SWCNTs can be achieved. All of the presented techniques show great potential to facilitate the realization of single-chirality SWCNTs production. Full article
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11 pages, 2866 KiB  
Article
Microwave-Assisted Solvothermal Synthesis of UiO-66-NH2 and Its Catalytic Performance toward the Hydrolysis of a Nerve Agent Simulant
by Zenghui Zhang, Cheng-An Tao, Jie Zhao, Fang Wang, Jian Huang and Jianfang Wang
Catalysts 2020, 10(9), 1086; https://doi.org/10.3390/catal10091086 - 19 Sep 2020
Cited by 23 | Viewed by 5721
Abstract
Zr-containing metal-organic frameworks (MOFs) exhibit a good performance of catalyzing the hydrolysis of chemical warfare agents, which is closely related to the size of MOF particles and its defects, but these two factors are often intertwined. In this article, we synthesized UiO-66-NH2 [...] Read more.
Zr-containing metal-organic frameworks (MOFs) exhibit a good performance of catalyzing the hydrolysis of chemical warfare agents, which is closely related to the size of MOF particles and its defects, but these two factors are often intertwined. In this article, we synthesized UiO-66-NH2 nanoparticles using a microwave-assisted hydrothermal method. By using a new modulator 4-Fluoro-3-Formyl-Benzoic Acid (FFBA) in different proportions, MOF particles with the same defect degree but different scales and those with similar sizes but different defect degrees can be obtained. The performance of the obtained MOF particles to catalyze the hydrolysis of the nerve agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP), was investigated, and the effects of single factors of size or defect were compared for the first time. As the size of the obtained MOF particles increased from 81 nm to 159 nm, the catalytic degradation efficiency toward DMNP gradually decreased, and the half-life increased from 3.9 min to 11.1 min. For MOFs that have similar crystal sizes, the catalytic degradation half-life of MOF3 is only 5 min, which is much smaller than that of MOF5 due to the defects increase from 1.2 to 1.8 per Zr6 cluster. Full article
(This article belongs to the Special Issue Catalysts by Metal Organic Frameworks)
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11 pages, 1995 KiB  
Article
Nanoencapsulated Laccases Obtained by Double-Emulsion Technique. Effects on Enzyme Activity pH-Dependence and Stability
by Rocío Chong-Cerda, Laura Levin, Rocío Castro-Ríos, Carlos Eduardo Hernández-Luna, Azucena González-Horta, Guadalupe Gutiérrez-Soto and Abelardo Chávez-Montes
Catalysts 2020, 10(9), 1085; https://doi.org/10.3390/catal10091085 - 18 Sep 2020
Cited by 15 | Viewed by 3241
Abstract
One primary drawback of enzyme catalysis at industrial scale is the short-term service life of the enzymes, they lose their activity due to oxidation or other processes which results in less stability and a shorter lifetime thereby rendering them less efficient. An effective [...] Read more.
One primary drawback of enzyme catalysis at industrial scale is the short-term service life of the enzymes, they lose their activity due to oxidation or other processes which results in less stability and a shorter lifetime thereby rendering them less efficient. An effective way to increase the stability of the enzymes is to attach them to nanoparticles. In this work, the polymer Eudragit® L 100-55 sensitive to pH was used to prepare laccase polymeric nanoparticles by the double-emulsion solvent evaporation approach. The size and morphology of the nanoparticles obtained were evaluated—as well as the encapsulation efficiency and zeta potential. pH effect on activity and stability was compared between free and immobilized laccase. Their stability was also determined in a sequential assay involving acidic pHs up to alkaline ones. The nanoparticles had a spherical shape with a mean size of 147 nm, zeta potential of −22.7 mV at pH 7.0 and load efficiency of 87%. The optimum pH of both free and immobilized laccases was 3.0, being the nanoparticles more stable at acidic pHs. Thus, this would be the first report of obtaining laccase nanoparticles with potential application in animal feed due to the stability conferred to enzymatic activity at pHs similar to those present in the gastrointestinal tract of rabbits, which would allow their potential use in animal feed. Full article
(This article belongs to the Special Issue Biocatalysts and Biocatalysis in Food Industry)
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23 pages, 7882 KiB  
Article
Syntheses of 3,3-Disubstituted Dihydrobenzofurans, Indolines, Indolinones and Isochromanes by Palladium-Catalyzed Tandem Reaction Using Pd(PPh3)2Cl2/(±)-BINAP as a Catalytic System
by Guizhou Yue, Sicheng Li, Dan Jiang, Gang Ding, Juhua Feng, Huabao Chen, Chunping Yang, Zhongqiong Yin, Xu Song, Xiaoxia Liang, Li Zhang, Xianxiang Wang and Cuifen Lu
Catalysts 2020, 10(9), 1084; https://doi.org/10.3390/catal10091084 - 18 Sep 2020
Cited by 3 | Viewed by 2572
Abstract
A general procedure for the tandem arylation reaction of arylbromide with heteroaryl compounds was developed by using Pd(PPh3)2Cl2/(±)-BINAP (1,1′-Binaphthalene-2,2′-diylbis (diphenylphosphane)) as catalytic system. Both sulphur- and oxygen-containing heterocycles were also employed as an efficient reagent for arylation, [...] Read more.
A general procedure for the tandem arylation reaction of arylbromide with heteroaryl compounds was developed by using Pd(PPh3)2Cl2/(±)-BINAP (1,1′-Binaphthalene-2,2′-diylbis (diphenylphosphane)) as catalytic system. Both sulphur- and oxygen-containing heterocycles were also employed as an efficient reagent for arylation, which gave moderate to excellent yields with moderate to good regioselectivities (5:1 to > 20:1 ir (isomer ratio)). Except for dihydrobenzofurans, indolines and indolinones, this type of tandem reaction was also expanded to synthesize isochromanes. The synthesized new compounds were well characterized through different spectroscopic techniques, such as 1H and 13C NMR (nuclear magnetic resonance), and mass spectral analysis. Full article
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17 pages, 2631 KiB  
Article
A Novel Thermostable Cytochrome P450 from Sequence-Based Metagenomics of Binh Chau Hot Spring as a Promising Catalyst for Testosterone Conversion
by Kim-Thoa Nguyen, Ngọc-Lan Nguyen, Nguyen Van Tung, Huy Hoang Nguyen, Mohammed Milhim, Thi-Thanh-Xuan Le, Thi-Hong-Nhung Lai, Thi-Tuyet-Minh Phan and Rita Bernhardt
Catalysts 2020, 10(9), 1083; https://doi.org/10.3390/catal10091083 - 18 Sep 2020
Cited by 4 | Viewed by 3292
Abstract
Biotechnological applications of cytochromes P450 show difficulties, such as low activity, thermal and/or solvent instability, narrow substrate specificity and redox partner dependence. In an attempt to overcome these limitations, an exploitation of novel thermophilic P450 enzymes from nature via uncultured approaches is desirable [...] Read more.
Biotechnological applications of cytochromes P450 show difficulties, such as low activity, thermal and/or solvent instability, narrow substrate specificity and redox partner dependence. In an attempt to overcome these limitations, an exploitation of novel thermophilic P450 enzymes from nature via uncultured approaches is desirable due to their great advantages that can resolve nearly all mentioned impediments. From the metagenomics library of the Binh Chau hot spring, an open reading frame (ORF) encoding a thermostable cytochrome P450—designated as P450-T3—which shared 66.6% amino acid sequence identity with CYP109C2 of Sorangium cellulosum So ce56 was selected for further identification and characterization. The ORF was synthesized artificially and heterologously expressed in Escherichia coli C43(DE3) using the pET17b system. The purified enzyme had a molecular weight of approximately 43 kDa. The melting temperature of the purified enzyme was 76.2 °C and its apparent half-life at 60 °C was 38.7 min. Redox partner screening revealed that P450-T3 was reduced well by the mammalian AdR-Adx4-108 and the yeast Arh1-Etp1 redox partners. Lauric acid, palmitic acid, embelin, retinoic acid (all-trans) and retinoic acid (13-cis) demonstrated binding to P450-T3. Interestingly, P450-T3 also bound and converted testosterone. Overall, P450-T3 might become a good candidate for biocatalytic applications on a larger scale. Full article
(This article belongs to the Section Biocatalysis)
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18 pages, 6242 KiB  
Article
Reverse Water Gas Shift by Chemical Looping with Iron-Substituted Hexaaluminate Catalysts
by Natalie Utsis, Miron V. Landau, Alexander Erenburg and Moti Herskowitz
Catalysts 2020, 10(9), 1082; https://doi.org/10.3390/catal10091082 - 18 Sep 2020
Cited by 12 | Viewed by 3101
Abstract
The Fe-substituted Ba-hexaaluminates (BaFeHAl) are active catalysts for reverse water-gas shift (RWGS) reaction conducted in chemical looping mode. Increasing of the degree of substitution of Al3+ for Fe3+ ions in co-precipitated BaHAl from 60% (BaFeHAl) to 100% (BaFe-hexaferrite, BaFeHF), growing its [...] Read more.
The Fe-substituted Ba-hexaaluminates (BaFeHAl) are active catalysts for reverse water-gas shift (RWGS) reaction conducted in chemical looping mode. Increasing of the degree of substitution of Al3+ for Fe3+ ions in co-precipitated BaHAl from 60% (BaFeHAl) to 100% (BaFe-hexaferrite, BaFeHF), growing its surface area from 5 to 30 m2/g, and promotion with potassium increased the CO capacity in isothermal RWGS-CL runs at 350–450 °C, where the hexaaluminate/hexaferrite structure is stable. Increasing H2-reduction temperature converts BaFeHAl to a thermally stable BaFeHF modification that contains additional Ba-O-Fe bridges in its structure, reinforcing the connection between alternatively stacked spinel blocks. This material displayed the highest CO capacity of 400 µmol/g at isothermal RWGS-CL run conducted at 550 °C due to increased concentration of oxygen vacancies reflected by greater surface Fe2+/Fe3+ ratio detected by XPS. The results demonstrate direct connection between CO capacity measured in RWGS-CL experiments and calculated CO2 conversion. Full article
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13 pages, 10418 KiB  
Article
Palladium PEPPSI-IPr Complex Supported on a Calix[8]arene: A New Catalyst for Efficient Suzuki–Miyaura Coupling of Aryl Chlorides
by Axel Labattut, Ibrahim Abdellah, Julien Buendia, Sandra Abi Fayssal, Erika Adhel, Diana Dragoe, Cyril Martini, Emmanuelle Schulz and Vincent Huc
Catalysts 2020, 10(9), 1081; https://doi.org/10.3390/catal10091081 - 18 Sep 2020
Cited by 10 | Viewed by 3285
Abstract
We report here the synthesis and characterization of a new calix[8]arene-supported PEPPSI-IPr Pd polymetallic complex. This complex, showing greater steric hindrance around the Pd centers compared with previous calix[8]arene-based catalysts, demonstrated high reactivity and selectivity for the Suzuki–Miyaura coupling of aryl chlorides under [...] Read more.
We report here the synthesis and characterization of a new calix[8]arene-supported PEPPSI-IPr Pd polymetallic complex. This complex, showing greater steric hindrance around the Pd centers compared with previous calix[8]arene-based catalysts, demonstrated high reactivity and selectivity for the Suzuki–Miyaura coupling of aryl chlorides under mild conditions. Along with this good performance, the new catalyst showed low Pd leaching into the final Suzuki–Miyaura coupling products, indicative of a heterogeneous-type reactivity. This rare combination of good reactivity towards challenging substrates and low metal leaching offers great promise at both academic and industrial levels. Full article
(This article belongs to the Special Issue Supramolecules for Catalysis)
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20 pages, 5073 KiB  
Article
Comparison of Catalytic Properties of Vanadium Centers Introduced into BEA Zeolite and Present on (010) V2O5 Surface–DFT Studies
by Agnieszka Drzewiecka-Matuszek, Renata Tokarz-Sobieraj, Małgorzata Witko and Dorota Rutkowska-Zbik
Catalysts 2020, 10(9), 1080; https://doi.org/10.3390/catal10091080 - 18 Sep 2020
Cited by 5 | Viewed by 2779
Abstract
Vanadium-based catalysts, in which vanadium is present either as bulk V2O5 or as isolated species, are active in numerous oxidation reactions. In the present study, vanadium speciation and the possibility of its introduction in various forms (V=O, V–OH, V(=O)(–OH)) into [...] Read more.
Vanadium-based catalysts, in which vanadium is present either as bulk V2O5 or as isolated species, are active in numerous oxidation reactions. In the present study, vanadium speciation and the possibility of its introduction in various forms (V=O, V–OH, V(=O)(–OH)) into the structurally different crystallographic positions in BEA zeolite was considered by means of Density Functional Theory (DFT). Out of nine nonequivalent positions, T2 and T3 positions are the most preferred. The former may accommodate V=O or V–OH, the latter V–OH or V(=O)(–OH). The structural and electronic properties of all possible centers present in the BEA zeolite are then compared with the characteristics of the same species on the most abundant (010) V2O5 surface. It is demonstrated that they exhibit higher nucleophilic character when introduced into the zeolite, and thus, may be more relevant for catalysis. Full article
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14 pages, 5110 KiB  
Article
Asymmetric Cyanation of Activated Olefins with Ethyl Cyanoformate Catalyzed by Ti(IV)-Catalyst: A Theoretical Study
by Zhishan Su, Changwei Hu, Nasir Shahzad and Chan Kyung Kim
Catalysts 2020, 10(9), 1079; https://doi.org/10.3390/catal10091079 - 18 Sep 2020
Cited by 3 | Viewed by 2492
Abstract
The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed [...] Read more.
The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed by cinchona alkaloid catalyst. The cyanation reaction of olefin proceeded through a two-step mechanism, in which the C-C bond construction was followed by H-transfer to generate a cyanide adduct. For non-catalytic reaction, the activation barrier for the rate-determining C-H bond construction step was 34.2 kcal mol−1, via a four-membered transition state. The self-assembly Ti(IV)-catalyst from tetraisopropyl titanate, (R)-3,3′-disubstituted biphenol, and cinchonidine accelerated the addition of cyanide to the C=C double bond by a dual activation process, in which titanium cation acted as a Lewis acid to activate the olefin and HNC was orientated by hydrogen bonding. The steric repulsion between the 9-phenanthryl at the 3,3′-position in the biphenol ligand and the Ph group in olefin raised the Pauli energy (ΔEPauli) of reacting fragments at the re-face attack transition state, leading to the predominant R-product. Full article
(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)
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12 pages, 6718 KiB  
Article
Catalytic Degradation of Chitosan by Supported Heteropoly Acids in Heterogeneous Systems
by Hang Zhang, Zhipeng Ma, Yunpeng Min, Huiru Wang, Ru Zhang, Xuecheng Zhang and Yimin Song
Catalysts 2020, 10(9), 1078; https://doi.org/10.3390/catal10091078 - 18 Sep 2020
Viewed by 1891
Abstract
Several kinds of composite materials with phosphotungstic acid (PTA) as the catalyst were prepared with activated carbon as support, and their structures were characterized. According to the Box–Behnken central combination principle, the mathematical model of the heterogeneous system is established. Based on the [...] Read more.
Several kinds of composite materials with phosphotungstic acid (PTA) as the catalyst were prepared with activated carbon as support, and their structures were characterized. According to the Box–Behnken central combination principle, the mathematical model of the heterogeneous system is established. Based on the single-factor experiments, the reaction temperature, the reaction time, the amount of hydrogen peroxide and the loading capacity of PTA were selected as the influencing factors to study the catalyzed oxidation of hydrogen peroxide and degradation of high molecular weight chitosan. The results of IR showed that the catalyst had a Keggin structure. The results of the mercury intrusion test showed that the pore structure of the supported PTA catalyst did not change significantly, and with the increase of PTA loading, the porosity and pore volume decreased regularly, which indicated that PTA molecules had been absorbed and filled into the pore of activated carbon. The results of Response Surface Design (RSD) showed that the optimum reaction conditions of supported PTA catalysts for oxidative degradation of high molecular weight chitosan by hydrogen peroxide were as follows: reaction temperature was 70 ℃, reaction time was 3.0 h, the ratio of hydrogen peroxide to chitosan was 2.4 and the catalyst loading was 30%. Under these conditions, the yield and molecular weight of water-soluble chitosan were 62.8% and 1290 Da, respectively. The supported PTA catalyst maintained high catalytic activity after three reuses, which indicated that the supported PTA catalyst had excellent catalytic activity and stable performance compared with the PTA catalyst. Full article
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14 pages, 2023 KiB  
Article
Biocatalyzed Reactions towards Functional Food Components 4-Alkylcatechols and Their Analogues
by Ludmila Martínková, Romana Příhodová, Natalia Kulik, Helena Pelantová, Barbora Křístková, Lucie Petrásková and David Biedermann
Catalysts 2020, 10(9), 1077; https://doi.org/10.3390/catal10091077 - 18 Sep 2020
Cited by 2 | Viewed by 2181
Abstract
Catechols are antioxidants and radical scavengers with a broad medical potential. 4-Methylcatechol (1b) and 4-ethylcatechol (2b) (occurring in some traditional fermented and smoked foods) activate the cell defense against oxidative stress. We examined the biocatalyzed reactions towards 4-n [...] Read more.
Catechols are antioxidants and radical scavengers with a broad medical potential. 4-Methylcatechol (1b) and 4-ethylcatechol (2b) (occurring in some traditional fermented and smoked foods) activate the cell defense against oxidative stress. We examined the biocatalyzed reactions towards 4-n-alkylcatechols with different side chains length, which is a factor important for the biological activities of catechols. 4-n-Alkylcatechols with methyl through heptyl side chains (1b7b) were obtained in one pot by (i) oxidation of phenols 1a7a with tyrosinase from Agaricus bisporus followed by (ii) reduction of ortho-quinones (intermediates) with L-ascorbic acid sodium salt. The conversions decreased with increasing side chain length. The preparative reactions were carried out with substrates 1a5a. The isolated yields of the purified products decreased from 59% in 2b to 10% in 5b in correlation with logP of the substrates. Homology modeling indicated that the affinities of two tyrosinase isoforms (PPO3 and PPO4) to the substrates with side chains longer than C2 decreased with increasing side chain length. This was probably due to steric limitations and to missing interactions of the extended side chains in the active sites. We envisage using the model to predict further substrates of tyrosinase and testing the products, catechols, for radical-scavenging and biological activities. Full article
(This article belongs to the Special Issue Biocatalysis in Food Technology and Processing)
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11 pages, 9812 KiB  
Article
Molybdenum and Nickel Nanoparticles Synthesis by Laser Ablation towards the Preparation of a Hydrodesulfurization Catalyst
by Viviana Londoño-Calderón, Rogelio Ospina, Jhonatan Rodriguez-Pereira, Sergio A. Rincón-Ortiz and Elisabeth Restrepo-Parra
Catalysts 2020, 10(9), 1076; https://doi.org/10.3390/catal10091076 - 18 Sep 2020
Cited by 8 | Viewed by 2662
Abstract
A clean straightforward laser ablation method in deionized (DI) water is reported for the synthesis of Molybdenum (Mo) and Nickel (Ni) nanoparticles (NPs). The structural, morphological, and optical properties of the as-synthesized nanoparticles were investigated. Particle size was estimated to be less than [...] Read more.
A clean straightforward laser ablation method in deionized (DI) water is reported for the synthesis of Molybdenum (Mo) and Nickel (Ni) nanoparticles (NPs). The structural, morphological, and optical properties of the as-synthesized nanoparticles were investigated. Particle size was estimated to be less than 10 nm, the UV–vis spectra of the samples show the formation of H2MoO4 and NiO. The XRD results for the Ni sample show the presence of two phases, cubic nickel oxide, and an fcc metallic nickel phase, indicating the possible formation of Ni/NiO compound. The nanoparticles synthesized were used as precursors in the production of a NiMo/γ-Al2O3 catalyst. The textural and structural properties, chemical composition, and catalytic performance in a hydrodesulfurization (HDS) reaction are reported. The textural and structural properties results show the lack of pore-blocking due to the small sizes and the distribution of the metallic nanoparticles on the support. Chemical composition measured by XPS shows a ratio Ni/Mo of 1.34. Therefore, possibly Ni was deposited on Mo covering part of its active area, occupying active sites of Mo, removing its effective surface and resulting in a relatively low conversion of DBT (17%). A lower Ni/Mo ratio is required to improve the model system, which could be achieved by changing parameters at the production of the nanoparticles. The model system can also be further tuned by changing the size of the nanoparticles. Full article
(This article belongs to the Special Issue Advanced Nanomaterials - Synthesis and Applications in Catalysis)
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25 pages, 7145 KiB  
Review
The Role of CO2 as a Mild Oxidant in Oxidation and Dehydrogenation over Catalysts: A Review
by Sheikh Tareq Rahman, Jang-Rak Choi, Jong-Hoon Lee and Soo-Jin Park
Catalysts 2020, 10(9), 1075; https://doi.org/10.3390/catal10091075 - 17 Sep 2020
Cited by 14 | Viewed by 6206
Abstract
Carbon dioxide (CO2) is widely used as an enhancer for industrial applications, enabling the economical and energy-efficient synthesis of a wide variety of chemicals and reducing the CO2 levels in the environment. CO2 has been used as an enhancer [...] Read more.
Carbon dioxide (CO2) is widely used as an enhancer for industrial applications, enabling the economical and energy-efficient synthesis of a wide variety of chemicals and reducing the CO2 levels in the environment. CO2 has been used as an enhancer in a catalytic system which has revived the exploitation of energy-extensive reactions and carry chemical products. CO2 oxidative dehydrogenation is a greener alternative to the classical dehydrogenation method. The availability, cost, safety, and soft oxidizing properties of CO2, with the assistance of appropriate catalysts at an industrial scale, can lead to breakthroughs in the pharmaceutical, polymer, and fuel industries. Thus, in this review, we focus on several applications of CO2 in oxidation and oxidative dehydrogenation systems. These processes and catalytic technologies can reduce the cost of utilizing CO2 in chemical and fuel production, which may lead to commercial applications in the imminent future. Full article
(This article belongs to the Special Issue New Trends in Catalysis for Sustainable CO2 Conversion)
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18 pages, 5029 KiB  
Article
Effect of Synthesis Conditions of Nitrogen and Platinum Co-Doped Titania Films on the Photocatalytic Performance under Simulated Solar Light
by Daryna Ihnatiuk, Camilla Tossi, Ilkka Tittonen and Oksana Linnik
Catalysts 2020, 10(9), 1074; https://doi.org/10.3390/catal10091074 - 17 Sep 2020
Cited by 8 | Viewed by 2096
Abstract
Platinum and nitrogen co-doped titania films of different surface morphologies obtained via a sol-gel process have been tested for tetracycline hydrochloride photocatalytic decomposition under simulated solar light. Titania crystallization to anatase is shown by XRD for all films. A shift of the bandgap [...] Read more.
Platinum and nitrogen co-doped titania films of different surface morphologies obtained via a sol-gel process have been tested for tetracycline hydrochloride photocatalytic decomposition under simulated solar light. Titania crystallization to anatase is shown by XRD for all films. A shift of the bandgap edge toward the visible region in absorption spectra and, consequently, a narrowing of the bandgap is observed for some films doped with nitrogen and/or exposed to UV pretreatment. The surface peculiarities of the samples are presented by an SEM and TEM investigation. The surface saturation by Pt and N with a homogeneous distribution of Pt ions on the surface as well as bulk as established by XPS and EDS data can be achieved with a certain synthesis procedure. The influence of the platinum content and of the pretreatment procedure on the state and atomic surface concentration of incorporated nitrogen and platinum is studied by XPS analysis: substitutional and interstitial nitrogen, non-metal containing fragments, Pt0, Pt2+ and Pt4+ ions. The photocatalytic activity of the films is ruled by the presence of Pt2+ ions and N rather than Pt0. The formation of the polycrystalline titania structure and Pt0 nanoparticles (NPs) is confirmed by TEM and electron diffraction images. The mechanism of primary photocatalytic processes is proposed. Full article
(This article belongs to the Special Issue Photocatalysis in Europe: Recent Advances and Future Prospects)
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19 pages, 3154 KiB  
Article
Immobilization of Aldoxime Dehydratases and Their Use as Biocatalysts in Aqueous Reaction Media
by Alessa Hinzmann, Michael Stricker and Harald Gröger
Catalysts 2020, 10(9), 1073; https://doi.org/10.3390/catal10091073 - 17 Sep 2020
Cited by 10 | Viewed by 3165
Abstract
Immobilization of biocatalysts is a current topic in research enabling the easy recovery of catalysts from the reaction medium after the reaction, and it is often accompanied by a stabilization of the catalysts, which enables recycling. Within our ongoing research on the utilization [...] Read more.
Immobilization of biocatalysts is a current topic in research enabling the easy recovery of catalysts from the reaction medium after the reaction, and it is often accompanied by a stabilization of the catalysts, which enables recycling. Within our ongoing research on the utilization of aldoxime dehydratases in the cyanide-free synthesis of nitriles through dehydration of readily available aldoximes, a screening of different immobilization methods for free enzymes was performed. The applied immobilization methods are based on covalent binding and hydrophobic interactions of the enzyme with the carrier material and whole-cell immobilization in calcium alginate beads with and without subsequent coating. In our study, we found that the immobilization with purified free aldoxime dehydratases from OxdRE (Rhodococcus erythropolis) and OxdB (Bacillus sp. strain OxB-1) leads to high immobilization efficiencies, but also to a strong loss of activity with a residual activity of <20%, regardless of the carrier material used. However, when using whole cells for immobilization instead of purified enzymes, we could increase the residual activity significantly. Escherichia coli BL21(DE3)-CodonPlus-RIL OxdRE and OxdB whole cells were entrapped in calcium alginate beads and coated with silica using tetraethylorthosilicate (TEOS), leading to immobilized catalysts with up to 75% residual activity and a higher stability compared to the free whole cells. Even after three rounds of recycling, which corresponds to a 3 d reaction time, the immobilized OxdB whole cells showed a residual activity of 85%. Full article
(This article belongs to the Special Issue Multi-Step Syntheses in Biology & Chemistry)
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21 pages, 5501 KiB  
Article
Phylogeny and Structure of Fatty Acid Photodecarboxylases and Glucose-Methanol-Choline Oxidoreductases
by Vladimir A. Aleksenko, Deepak Anand, Alina Remeeva, Vera V. Nazarenko, Valentin Gordeliy, Karl-Erich Jaeger, Ulrich Krauss and Ivan Gushchin
Catalysts 2020, 10(9), 1072; https://doi.org/10.3390/catal10091072 - 17 Sep 2020
Cited by 16 | Viewed by 4990
Abstract
Glucose-methanol-choline (GMC) oxidoreductases are a large and diverse family of flavin-binding enzymes found in all kingdoms of life. Recently, a new related family of proteins has been discovered in algae named fatty acid photodecarboxylases (FAPs). These enzymes use the energy of light to [...] Read more.
Glucose-methanol-choline (GMC) oxidoreductases are a large and diverse family of flavin-binding enzymes found in all kingdoms of life. Recently, a new related family of proteins has been discovered in algae named fatty acid photodecarboxylases (FAPs). These enzymes use the energy of light to convert fatty acids to the corresponding Cn-1 alkanes or alkenes, and hold great potential for biotechnological application. In this work, we aimed at uncovering the natural diversity of FAPs and their relations with other GMC oxidoreductases. We reviewed the available GMC structures, assembled a large dataset of GMC sequences, and found that one active site amino acid, a histidine, is extremely well conserved among the GMC proteins but not among FAPs, where it is replaced with alanine. Using this criterion, we found several new potential FAP genes, both in genomic and metagenomic databases, and showed that related bacterial, archaeal and fungal genes are unlikely to be FAPs. We also identified several uncharacterized clusters of GMC-like proteins as well as subfamilies of proteins that lack the conserved histidine but are not FAPs. Finally, the analysis of the collected dataset of potential photodecarboxylase sequences revealed the key active site residues that are strictly conserved, whereas other residues in the vicinity of the flavin adenine dinucleotide (FAD) cofactor and in the fatty acid-binding pocket are more variable. The identified variants may have different FAP activity and selectivity and consequently may prove useful for new biotechnological applications, thereby fostering the transition from a fossil carbon-based economy to a bio-economy by enabling the sustainable production of hydrocarbon fuels. Full article
(This article belongs to the Special Issue Biocatalysis for Green Chemistry)
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22 pages, 6553 KiB  
Article
Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity
by Elena Millán, Noelia Mota, Rut Guil-López, Bárbara Pawelec, José L. García Fierro and Rufino M. Navarro
Catalysts 2020, 10(9), 1071; https://doi.org/10.3390/catal10091071 - 17 Sep 2020
Cited by 12 | Viewed by 4630
Abstract
The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. We studied the effect [...] Read more.
The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. We studied the effect of the HPW loading on TiO2 (from 1.4 to 2.7 monolayers) on the dispersion and acid characteristics of the HPW clusters. When the concentration of the heteropoliacid is slightly higher than the monolayer (1.4 monolayers) the acidity of the clusters is perturbed by the surface of titania, while for concentration higher than 1.7 monolayers results in the formation of three-dimensional HPW nanocrystals with acidity similar to the bulk heteropolyacid. Physical hybridization of supported heteropolyacids with the Cu-ZnO(Al) catalyst modifies both the acid characteristics of the supported heteropolyacids and the copper surface area of the Cu-ZnO(Al) catalyst. Hybridization gives rise to a decrease in the copper surface area and the disappearance of the strong acidic sites typical of HPW nanocrystals, showing all hybrids similar acid sites of weak or medium strength. The activity of the hybrids was tested for direct DME synthesis from syngas at 30 bar and 250 °C; only the hybrids with HPW loading higher than 1.4 monolayers showed activity for the direct synthesis of DME, showing that the sample loaded with 2.7 monolayers of heteropolyacid had higher activity than the reference hybrid representative of the most widely applied catalysts based on the combination of Cu-ZnO(Al) with HZSM-5. In spite of the high activity of the hybrids, they show a moderate loss in the DME production with TOS that denotes some kind of deactivation of the acidity function under reaction conditions. Full article
(This article belongs to the Special Issue Catalysts for Production and Conversion of Syngas)
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25 pages, 11781 KiB  
Review
Morphology-Governed Performance of Plasmonic Photocatalysts
by Zhishun Wei, Marcin Janczarek, Kunlei Wang, Shuaizhi Zheng and Ewa Kowalska
Catalysts 2020, 10(9), 1070; https://doi.org/10.3390/catal10091070 - 17 Sep 2020
Cited by 18 | Viewed by 2887
Abstract
Plasmonic photocatalysts have been extensively studied for the past decade as a possible solution to energy crisis and environmental problems. Although various reports on plasmonic photocatalysts have been published, including synthesis methods, applications, and mechanism clarifications, the quantum yields of photochemical reactions are [...] Read more.
Plasmonic photocatalysts have been extensively studied for the past decade as a possible solution to energy crisis and environmental problems. Although various reports on plasmonic photocatalysts have been published, including synthesis methods, applications, and mechanism clarifications, the quantum yields of photochemical reactions are usually too low for commercialization. Accordingly, it has been proposed that preparation of plasmonic photocatalysts with efficient light harvesting and inhibition of charge carriers’ recombination might result in improvement of photocatalytic activity. Among various strategies, nano-architecture of plasmonic photocatalysts seems to be one of the best strategies, including the design of properties for both semiconductor and noble-metal-deposits, as well as the interactions between them. For example, faceted nanoparticles, nanotubes, aerogels, and super-nano structures of semiconductors have shown the improvement of photocatalytic activity and stability. Moreover, the selective deposition of noble metals on some parts of semiconductor nanostructures (e.g., specific facets, basal or lateral surfaces) results in an activity increase. Additionally, mono-, bi-, and ternary-metal-modifications have been proposed as the other ways of performance improvement. However, in some cases, the interactions between different noble metals might cause unwanted charge carriers’ recombination. Accordingly, this review discusses the recent strategies on the improvements of the photocatalytic performance of plasmonic photocatalysts. Full article
(This article belongs to the Special Issue Plasmonic Photocatalysts)
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