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Catalysts, Volume 10, Issue 8 (August 2020) – 134 articles

Cover Story (view full-size image): Continuous co-precipitation results in improved Cu/ZnO/ZrO2 (CZZ) catalysts that are used in direct DME production from CO2/CO/H2. As this approach offers excellent fine-tuning of relevant catalytic properties, it is believed to have a generally applicable potential for multicomponent catalyst materials. View this paper
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17 pages, 6884 KiB  
Article
Synthesis of SiC/BiOCl Composites and Its Efficient Photocatalytic Activity
by Wanli Liu, Qi Li, Xianglong Yang, Xiufang Chen and Xiangang Xu
Catalysts 2020, 10(8), 946; https://doi.org/10.3390/catal10080946 - 18 Aug 2020
Cited by 8 | Viewed by 2584
Abstract
BiOCl nanosheets nucleated and grew on cottage cheese-like SiC substrate via hydrothermal procedure, through which a tight heterojunction was formed. SiC/BiOCl composites with varied morphologies were acquired that the formation of BiOCl was involved with different form of carbon existed on surface of [...] Read more.
BiOCl nanosheets nucleated and grew on cottage cheese-like SiC substrate via hydrothermal procedure, through which a tight heterojunction was formed. SiC/BiOCl composites with varied morphologies were acquired that the formation of BiOCl was involved with different form of carbon existed on surface of SiC. The photocatalytic mechanism analysis revealed that the combination of SiC and BOC significantly enhanced photocatalytic activities owing to the improved visible light utilization, efficient separation of photo-generated carriers, and promoted reactive area. The main active species during the photocatalytic reaction was determined as ·O2− radical by additionally adding trapping agent into the reactant. The SiC-BOC composites showed much higher photoactivities in photocurrent responses and photocatalytic degradation of TC-HCl, which mainly attributed to the well-built heterointerface promoted by Bi-C bonds and the interlaced structure obtained by increasing exposure of (010) facets in BiOCl. The nucleation, growth and combination architecture of BiOCl was all influenced by the involvement of SiC. Full article
(This article belongs to the Section Catalytic Materials)
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16 pages, 4264 KiB  
Article
Visible Light Driven Spherical CuBi2O4 with Surface Oxygen Vacancy Enhanced Photocatalytic Activity: Catalyst Fabrication, Performance, and Reaction Mechanism
by Xin Zhong, Yihong Cai, Heping Bai, Wei Huang and Binxue Zhou
Catalysts 2020, 10(8), 945; https://doi.org/10.3390/catal10080945 - 17 Aug 2020
Cited by 16 | Viewed by 2952
Abstract
Here, a spherical CuBi2O4 catalyst with surface oxygen vacancy was fabricated through a facile hydrothermal method, which exhibited remarkable enhanced photocatalytic activity of refractory chemicals in the heterogeneous sulfate radical-based Fenton-like reaction under visible light emitting diode (LED) light irradiation. [...] Read more.
Here, a spherical CuBi2O4 catalyst with surface oxygen vacancy was fabricated through a facile hydrothermal method, which exhibited remarkable enhanced photocatalytic activity of refractory chemicals in the heterogeneous sulfate radical-based Fenton-like reaction under visible light emitting diode (LED) light irradiation. The property of the catalysts was systematically characterized by scanning electron microscopy (SEM)/high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV/vis methods. The effects of parameters of solution pH, potassium peroxymonosulfate (PMS) concentration, catalyst dosage, and catalyst reusability on Rhodamine B (RhB) degradation were investigated. In the interface reaction, the improved photodegradation efficiency could be attributed to the decomposition of PMS, which produced sulfate radicals and hydroxyl radicals owing to the transmission of photo-generated electron/hole pairs. Herein, the introduction of surface oxygen vacancy as well as the cycling of copper valence states (Cu(II)/Cu(I) pairs) can facilitate the production of free reactive radicals, leading to the high degradation efficiency. The catalyst showed high removal efficiency and presented good cycle stability in the reaction. Additionally, the free radical quencher experiment and electron spin resonance (EPR) experiments were conducted, and a proposed photocatalytic mechanism was also illustrated. Full article
(This article belongs to the Special Issue Photocatalysis in the Wastewater Treatment)
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26 pages, 5427 KiB  
Article
CO2 Methanation on Supported Rh Nanoparticles: The combined Effect of Support Oxygen Storage Capacity and Rh Particle Size
by Georgia Botzolaki, Grammatiki Goula, Anatoli Rontogianni, Ersi Nikolaraki, Nikolaos Chalmpes, Panagiota Zygouri, Michalis Karakassides, Dimitrios Gournis, Nikolaos Charisiou, Maria Goula, Stylianos Papadopoulos and Ioannis Yentekakis
Catalysts 2020, 10(8), 944; https://doi.org/10.3390/catal10080944 - 17 Aug 2020
Cited by 36 | Viewed by 4464
Abstract
CO2 hydrogenation toward methane, a reaction of high environmental and sustainable energy importance, was investigated at 200–600 °C and H2/CO2 = 4/1, over Rh nanoparticles dispersed on supports with different oxygen storage capacity characteristics (γ-Al2O3, [...] Read more.
CO2 hydrogenation toward methane, a reaction of high environmental and sustainable energy importance, was investigated at 200–600 °C and H2/CO2 = 4/1, over Rh nanoparticles dispersed on supports with different oxygen storage capacity characteristics (γ-Al2O3, alumina-ceria-zirconia, and ceria-zirconia). The effects of the support OSC and Rh particle size on reaction behavior under both integral and differential conditions were investigated, to elucidate the combined role of these crucial catalyst design parameters on methanation efficiency. A volcano-type variation of methanation turnover frequency was found in respect to support OSC; Rh/ACZ, with intermediate OSC, was the optimal catalyst. The structure sensitivity of the reaction was found to be a combined function of support OSC and Rh particle size: For Rh/γ-Al2O3 (lack of OSC) methanation was strongly favored on small particles—the opposite for Rh/CZ (high OSC). The findings are promising for rational design and optimization of CO2 methanation catalysts by tailoring the aforementioned characteristics. Full article
(This article belongs to the Special Issue Nanomaterials in Catalysis Applications)
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13 pages, 2195 KiB  
Article
Efficient Oxidation of Methyl Glycolate to Methyl Glyoxylate Using a Fusion Enzyme of Glycolate Oxidase, Catalase and Hemoglobin
by Xiangxian Ying, Can Wang, Shuai Shao, Qizhou Wang, Xueting Zhou, Yanbing Bai, Liang Chen, Chenze Lu, Man Zhao and Zhao Wang
Catalysts 2020, 10(8), 943; https://doi.org/10.3390/catal10080943 - 17 Aug 2020
Cited by 9 | Viewed by 3297
Abstract
Possessing aldehyde and carboxyl groups, glyoxylic acid and its ester derivatives serve as platform chemicals for the synthesis of vanillin, (R)-pantolactone, antibiotics or agrochemicals. Methyl glycolate is one of the by-products in the coal-to-glycol industry, and we attempted its value-added use [...] Read more.
Possessing aldehyde and carboxyl groups, glyoxylic acid and its ester derivatives serve as platform chemicals for the synthesis of vanillin, (R)-pantolactone, antibiotics or agrochemicals. Methyl glycolate is one of the by-products in the coal-to-glycol industry, and we attempted its value-added use through enzymatic oxidation of methyl glycolate to methyl glyoxylate. The cascade catalysis of glycolate oxidase from Spinacia oleracea (SoGOX), catalase from Helicobacter pylori (HpCAT) and hemoglobin from Vitreoscilla stercoraria (VsHGB) was firstly constructed, despite poor catalytic performance. To enable efficient oxidation of methyl glycolate, eight fusion enzymes of SoGOX, HpCAT and VsHGB were constructed by varying the orientation and the linker length. The fusion enzyme VsHGB-GSG-SoGOX-GGGGS-HpCAT was proved to be best, which reaction yield was 2.9 times higher than that of separated enzymes. The enzyme SoGOX was further subjected to directed evolution and site-saturation mutagenesis. The reaction yield of the resulting variant M267T/S362G was 1.9 times higher than that of the wild type. Then, the double substitution M267T/S362G was integrated with fusion expression to give the fusion enzyme VsHGB-GSG-SoGOXmut-GGGGS-HpCAT, which crude enzyme was used as biocatalyst. The use of crude enzyme virtually eliminated side reactions and simplified the preparation of biocatalysts. Under the optimized conditions, the crude enzyme VsHGB-GSG-SoGOXmut-GGGGS-HpCAT catalyzed the oxidation of 200 mM methyl glycolate for 6 h, giving a yield of 95.3%. The development of efficient fusion enzyme and the use of its crude enzyme paved the way for preparative scale application on enzymatic oxidation of methyl glycolate to methyl glyoxylate. Full article
(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)
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14 pages, 4828 KiB  
Article
Curcumin Doped SiO2/TiO2 Nanocomposites for Enhanced Photocatalytic Reduction of Cr (VI) under Visible Light
by Zhiying Yan, Zijuan He, Mi Li, Lin Zhang, Yao Luo, Jiao He, Yongjuan Chen and Jiaqiang Wang
Catalysts 2020, 10(8), 942; https://doi.org/10.3390/catal10080942 - 17 Aug 2020
Cited by 14 | Viewed by 2928
Abstract
In order to further improve the photocatalytic performance of the SiO2/TiO2 composite under visible light irradiation, curcumin-doped SiO2/TiO2 nanocomposites were synthesized via directly incorporating it into the structure of SiO2/TiO2 during the synthesis using [...] Read more.
In order to further improve the photocatalytic performance of the SiO2/TiO2 composite under visible light irradiation, curcumin-doped SiO2/TiO2 nanocomposites were synthesized via directly incorporating it into the structure of SiO2/TiO2 during the synthesis using an inexpensive and readily available natural pigment (curcumin) as doping agent. The physicochemical properties of SiO2/TiO2 nanocomposites were characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform-infrared spectroscopy, N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The results indicate that all SiO2/TiO2 nanocomposites exhibited an anatase phase with a typical mesoporous structure. It was found that the dope of curcumin in the SiO2/TiO2 composite could decrease the crystal size, slightly improve the specific surface areas, significantly enhance the visible light absorption, and effectively narrow the band gap energy from 3.04 to 10(eV). Compared with bare SiO2/TiO2, the curcumin-doped SiO2/TiO2 resulted in enhanced photocatalytic reduction activity for Cr(VI) under visible light irradiation, and the CTS (12) sample with the appropriate content of curcumin of 12 wt % shows the photocatalytic yield reaching 100% within 2.5 hours, which is larger than CT (12) without silica. This could be attributed to the curcumin doping and the synergetic effects of SiO2 and TiO2 in SiO2/TiO2 nanocomposites. Full article
(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)
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17 pages, 5458 KiB  
Article
(S)-Pramipexole and Its Enantiomer, Dexpramipexole: A New Chemoenzymatic Synthesis and Crystallographic Investigation of Key Enantiomeric Intermediates
by Samuele Ciceri, Patrizia Ferraboschi, Paride Grisenti, Shahrzad Reza Elahi, Carlo Castellano, Matteo Mori and Fiorella Meneghetti
Catalysts 2020, 10(8), 941; https://doi.org/10.3390/catal10080941 - 16 Aug 2020
Cited by 2 | Viewed by 3556
Abstract
A new chemoenzymatic method has been developed for the synthesis of (S)- and (R)-N-(6-hydroxy-4,5,6,7-tetrahydrobenzo[d]thiazol-2-yl) acetamide, two key synthons for the preparation of (S)-pramipexole, an anti-Parkinson drug, and its enantiomer dexpramipexole, which is currently under investigation [...] Read more.
A new chemoenzymatic method has been developed for the synthesis of (S)- and (R)-N-(6-hydroxy-4,5,6,7-tetrahydrobenzo[d]thiazol-2-yl) acetamide, two key synthons for the preparation of (S)-pramipexole, an anti-Parkinson drug, and its enantiomer dexpramipexole, which is currently under investigation for the treatment of eosinophil-associated disorders. These two building blocks have been obtained in good yields and high enantiomeric excess (30% and >98% ee for the R-enantiomer, and 31% and >99% ee for the S- one) through a careful optimization of the reaction conditions, starting from the corresponding racemic mixture and using two consecutive irreversible transesterifications, catalyzed by Candida antarctica lipase type A. Single crystal X-ray analysis has been carried out to unambiguously define the stereochemistry of the two enantiomers, and to explore in depth their three-dimensional features. Full article
(This article belongs to the Special Issue Use of Hydrolases in Organic Synthesis)
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21 pages, 12568 KiB  
Communication
The Impact of Surficial Biochar Treatment on Acute H2S Emissions during Swine Manure Agitation before Pump-Out: Proof-of-the-Concept
by Baitong Chen, Jacek A. Koziel, Andrzej Białowiec, Myeongseong Lee, Hantian Ma, Peiyang Li, Zhanibek Meiirkhanuly and Robert C. Brown
Catalysts 2020, 10(8), 940; https://doi.org/10.3390/catal10080940 - 16 Aug 2020
Cited by 13 | Viewed by 3789
Abstract
Acute releases of hydrogen sulfide (H2S) are of serious concern in agriculture, especially when farmers agitate manure to empty storage pits before land application. Agitation can cause the release of dangerously high H2S concentrations, resulting in human and animal [...] Read more.
Acute releases of hydrogen sulfide (H2S) are of serious concern in agriculture, especially when farmers agitate manure to empty storage pits before land application. Agitation can cause the release of dangerously high H2S concentrations, resulting in human and animal fatalities. To date, there is no proven technology to mitigate these short-term releases of toxic gas from manure. In our previous research, we have shown that biochar, a highly porous carbonaceous material, can float on manure and mitigate gaseous emissions over extended periods (days–weeks). In this research, we aim to test the hypothesis that biochar can mitigate H2S emissions over short periods (minutes–hours) during and shortly after manure agitation. The objective was to conduct proof-of-the-concept experiments simulating the treatment of agitated manure. Two biochars, highly alkaline and porous (HAP, pH 9.2) made from corn stover and red oak (RO, pH 7.5), were tested. Three scenarios (setups): Control (no biochar), 6 mm, and 12 mm thick layers of biochar were surficially-applied to the manure. Each setup experienced 3 min of manure agitation. Real-time concentrations of H2S were measured immediately before, during, and after agitation until the concentration returned to the initial state. The results were compared with those of the Control using the following three metrics: (1) the maximum (peak) flux, (2) total emission from the start of agitation until the concentration stabilized, and (3) the total emission during the 3 min of agitation. The Gompertz’s model for determination of the cumulative H2S emission kinetics was developed. Here, 12 mm HAP biochar treatment reduced the peak (1) by 42.5% (p = 0.125), reduced overall total emission (2) by 17.9% (p = 0.290), and significantly reduced the total emission during 3 min agitation (3) by 70.4%. Further, 6 mm HAP treatment reduced the peak (1) by 60.6%, and significantly reduced overall (2) and 3 min agitation’s (3) total emission by 64.4% and 66.6%, respectively. Moreover, 12 mm RO biochar treatment reduced the peak (1) by 23.6%, and significantly reduced overall (2) and 3 min total (3) emission by 39.3% and 62.4%, respectively. Finally, 6 mm RO treatment significantly reduced the peak (1) by 63%, overall total emission (2) by 84.7%, and total emission during 3 min agitation (3) by 67.4%. Biochar treatments have the potential to reduce the risk of inhalation exposure to H2S. Both 6 and 12 mm biochar treatments reduced the peak H2S concentrations below the General Industrial Peak Limit (OSHA PEL, 50 ppm). The 6 mm biochar treatments reduced the H2S concentrations below the General Industry Ceiling Limit (OSHA PEL, 20 ppm). Research scaling up to larger manure volumes and longer agitation is warranted. Full article
(This article belongs to the Special Issue Catalysts and Processes for H2S Conversion to Sulfur)
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8 pages, 754 KiB  
Article
Efficient Chemo-Enzymatic Flow Synthesis of High Value Amides and Esters
by Francesca Annunziata, Martina Letizia Contente, Daniele Betti, Cecilia Pinna, Francesco Molinari, Lucia Tamborini and Andrea Pinto
Catalysts 2020, 10(8), 939; https://doi.org/10.3390/catal10080939 - 16 Aug 2020
Cited by 21 | Viewed by 3353
Abstract
A flow-based chemo-enzymatic synthesis of selected APIs (i.e., butacaine, procaine and procainamide) has been developed. A bioreactor made of MsAcT, a versatile acyltransferase from Mycobacterium smegmatis, immobilised on glyoxyl–garose, was exploited to efficiently prepare amide and ester intermediates in gram scale. Immobilised [...] Read more.
A flow-based chemo-enzymatic synthesis of selected APIs (i.e., butacaine, procaine and procainamide) has been developed. A bioreactor made of MsAcT, a versatile acyltransferase from Mycobacterium smegmatis, immobilised on glyoxyl–garose, was exploited to efficiently prepare amide and ester intermediates in gram scale. Immobilised MsAcT was employed in pure organic solvent, demonstrating high stability and reusability. In-line purification of the key intermediates using polymer-bound sulphonyl chloride was added after the bioreactor, enhancing the automation of the process. A final hydrogenation step using the H-Cube reactor was further carried out to obtain the selected APIs in excellent yields (>99%), making the process fast, safe and easily handled. Full article
(This article belongs to the Special Issue Continuous-Flow Catalysis)
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23 pages, 5341 KiB  
Review
Developing Low-Cost, High Performance, Robust and Sustainable Perovskite Electrocatalytic Materials in the Electrochemical Sensors and Energy Sectors: “An Overview”
by Tse-Wei Chen, Rasu Ramachandran, Shen-Ming Chen, Narayanasamy Kavitha, Kannaiyan Dinakaran, Ramanjam Kannan, Ganesan Anushya, Nagulan Bhuvana, Tharini Jeyapragasam, Vinitha Mariyappan, Selvarajan Divya Rani and Selvam Chitra
Catalysts 2020, 10(8), 938; https://doi.org/10.3390/catal10080938 - 16 Aug 2020
Cited by 28 | Viewed by 5770
Abstract
Since its discovery in 1839, research on the synthesis and application of perovskite materials has multiplied largely due to their suitability to be used in the fields of nanotechnology, chemistry and material science. Appropriate changes in composition or addition of other elements or [...] Read more.
Since its discovery in 1839, research on the synthesis and application of perovskite materials has multiplied largely due to their suitability to be used in the fields of nanotechnology, chemistry and material science. Appropriate changes in composition or addition of other elements or blending with polymers may result in new hybrid and/or composite perovskite materials that will be applied in advanced fields. In this review, we have recapitulated the recent progress on perovskite nanomaterial in solar cell, battery, fuel cell and supercapacitor applications, and the prominence properties of perovskite materials, such as excellent electronic, physical, chemical and optical properties. We discussed in detail the synthesis and results of various perovskite hybrid nanomaterials published elsewhere. We have also discussed the results of various studies on these low dimensional composite nanomaterials in broad sectors such as electronics/optoelectronics, batteries, supercapacitors, solar cells and electrochemical sensors. Full article
(This article belongs to the Special Issue Electrocatalysts for Energy Conversion and Storage-Related Reactions)
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17 pages, 1738 KiB  
Article
Performance of 1-(3-Sulfopropyl)-3-Methylimidazolium Hydrogen Sulfate as a Catalyst for Hardwood Upgrading into Bio-Based Platform Chemicals
by Mar López, Sandra Rivas, Carlos Vila, Valentín Santos and Juan Carlos Parajó
Catalysts 2020, 10(8), 937; https://doi.org/10.3390/catal10080937 - 15 Aug 2020
Cited by 4 | Viewed by 2802
Abstract
The acidic ionic liquid 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) was employed as a catalyst for manufacturing polysaccharide-derived products (soluble hemicellulose-derived saccharides, furans, and/or organic acids) from Eucalyptus globulus wood. Operation was performed in aqueous media supplemented with [C3SO3Hmim]HSO [...] Read more.
The acidic ionic liquid 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) was employed as a catalyst for manufacturing polysaccharide-derived products (soluble hemicellulose-derived saccharides, furans, and/or organic acids) from Eucalyptus globulus wood. Operation was performed in aqueous media supplemented with [C3SO3Hmim]HSO4 and methyl isobutyl ketone, following two different processing schemes: one-pot reaction or the solubilization of hemicelluloses by hydrothermal processing followed by the separate manufacture of the target compounds from both hemicellulose-derived saccharides and cellulose. Depending on the operational conditions, the one-pot reaction could be directed to the formation of furfural (at molar conversions up to 92.6%), levulinic acid (at molar conversions up to 45.8%), or mixtures of furfural and levulinic acid (at molar conversions up to 81.3% and 44.8%, respectively). In comparison, after hydrothermal processing, the liquid phase (containing hemicellulose-derived saccharides) yielded furfural at molar conversions near 78%, whereas levulinic acid was produced from the cellulose-enriched, solid phase at molar conversions up to 49.5%. Full article
(This article belongs to the Special Issue Ionic Liquids in Catalysis)
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16 pages, 3293 KiB  
Article
Understanding the Effect of Multiple Domain Deletion in DNA Polymerase I from Geobacillus Sp. Strain SK72
by Waqiyuddin Hilmi Hadrawi, Anas Norazman, Fairolniza Mohd Shariff, Mohd Shukuri Mohamad Ali and Raja Noor Zaliha Raja Abd Rahman
Catalysts 2020, 10(8), 936; https://doi.org/10.3390/catal10080936 - 15 Aug 2020
Cited by 2 | Viewed by 2845
Abstract
The molecular structure of DNA polymerase I or family A polymerases is made up of three major domains that consist of a single polymerase domain with two extra exonuclease domains. When the N-terminal was deleted, the enzyme was still able to perform basic [...] Read more.
The molecular structure of DNA polymerase I or family A polymerases is made up of three major domains that consist of a single polymerase domain with two extra exonuclease domains. When the N-terminal was deleted, the enzyme was still able to perform basic polymerase activity with additional traits that used isothermal amplification. However, the 3′-5′ exonuclease domain that carries a proofreading activity was disabled. Yet, the structure remained attached to the 5′-3′ polymerization domain without affecting its ability. The purpose of this non-functional domain still remains scarce. It either gives negative effects or provides structural support to the DNA polymerase. Here, we compared the effect of deleting each domain against the polymerase activity. The recombinant wild type and its variants were successfully purified and characterized. Interestingly, SK72-Exo (a large fragment excluding the 5′-3′ exonuclease domain) exhibited better catalytic activity than the native SK72 (with all three domains) at similar optimum temperature and pH profile, and it showed longer stability at 70 °C. Meanwhile, SK72-Exo2 (polymerization domain without both the 5′-3′ and 3′-5′ exonuclease domain) displayed the lowest activity with an optimum at 40 °C and favored a more neutral environment. It was also the least stable among the variants, with almost no activity at 50 °C for the first 10 min. In conclusion, cutting both exonuclease domains in DNA polymerase I has a detrimental effect on the polymerization activity and structural stability. Full article
(This article belongs to the Special Issue Catalysts for Structure-Functional Analysis and Enzyme Optimization)
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15 pages, 2221 KiB  
Article
In Vivo, High-Throughput Selection of Thermostable Cyclohexanone Monooxygenase (CHMO)
by Sarah Maxel, Linyue Zhang, Edward King, Ana Paula Acosta, Ray Luo and Han Li
Catalysts 2020, 10(8), 935; https://doi.org/10.3390/catal10080935 - 13 Aug 2020
Cited by 4 | Viewed by 3322
Abstract
Cyclohexanone monooxygenase (CHMO) from Acinetobacter sp. NCIMB 9871 is characterized as having wide substrate versatility for the biooxidation of (cyclic) ketones into esters and lactones with high stereospecificity. Despite industrial potential, CHMO usage is restricted by poor thermostability. Limited high-throughput screening tools and [...] Read more.
Cyclohexanone monooxygenase (CHMO) from Acinetobacter sp. NCIMB 9871 is characterized as having wide substrate versatility for the biooxidation of (cyclic) ketones into esters and lactones with high stereospecificity. Despite industrial potential, CHMO usage is restricted by poor thermostability. Limited high-throughput screening tools and challenges in rationally engineering thermostability have impeded CHMO engineering efforts. We demonstrate the application of an aerobic, high-throughput growth selection platform in Escherichia coli (strain MX203) for the discovery of thermostability enhancing mutations for CHMO. The selection employs growth for the easy readout of CHMO activity in vivo, by requiring nicotinamide adenine dinucleotide phosphate (NADPH)-consuming enzymes to restore cellular redox balance. In the presence of the native substrate cyclohexanone, variant CHMO GV (A245G-A288V) was discovered from a random mutagenesis library screened at 42 °C. This variant retained native activity, exhibited ~4.4-fold improvement in residual activity after 30 °C incubation, and demonstrated ~5-fold higher cyclohexanone conversion at 37 °C compared to the wild type. Molecular modeling indicates that CHMO GV experiences more favorable residue packing and supports additional backbone hydrogen bonding. Further rational design resulted in CHMO A245G-A288V-T415C with improved thermostability at 45 °C. Our platform for oxygenase evolution enabled the rapid engineering of protein stability critical for industrial scalability. Full article
(This article belongs to the Special Issue Bioprocess Engineering and Enzyme Application)
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19 pages, 7771 KiB  
Article
Hydrogenation of Furfural to Furfuryl Alcohol over Ru Particles Supported on Mildly Oxidized Biochar
by Raoof Bardestani, Rouholamin Biriaei and Serge Kaliaguine
Catalysts 2020, 10(8), 934; https://doi.org/10.3390/catal10080934 - 13 Aug 2020
Cited by 13 | Viewed by 3763
Abstract
Catalytic hydrogenation of aldehydes is required as the stabilizing step in bio-oils conversion. Ruthenium supported on carbon was used in the present work for hydrogenation of furfural (FF) to furfuryl alcohol (FA). Converting a biochar with no surface area and low carboxyl groups [...] Read more.
Catalytic hydrogenation of aldehydes is required as the stabilizing step in bio-oils conversion. Ruthenium supported on carbon was used in the present work for hydrogenation of furfural (FF) to furfuryl alcohol (FA). Converting a biochar with no surface area and low carboxyl groups surface density to an outstanding catalyst support using a very simple mild air/steam oxidation is the original contribution of this work. The mildly oxidized biochar is impregnated with a targeted loading of 2.5 wt.% Ru via ion-exchange, using Ru(NH3)6Cl2 precursor. ICP analysis shows that the mild oxidation increases Ru adsorption capacity of untreated biochar from 1.2 to 2.2 wt.%. H2 chemisorption and TEM analysis indicate that the preliminary mild oxidation leads to higher Ru dispersion. XPS analysis also shows that the treatment prevents Ru from surface segregation. The highest value of 93% FA selectivity at 53% FF conversion was obtained in a batch autoclave reactor under optimized conditions. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)
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15 pages, 8145 KiB  
Article
Strong Activity Enhancement of the Photocatalytic Degradation of an Azo Dye on Au/TiO2 Doped with FeOx
by Ammara Waheed, Quanquan Shi, Nobutaka Maeda, Daniel M. Meier, Zhaoxian Qin, Gao Li and Alfons Baiker
Catalysts 2020, 10(8), 933; https://doi.org/10.3390/catal10080933 - 13 Aug 2020
Cited by 15 | Viewed by 3198
Abstract
The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites [...] Read more.
The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites containing different molar ratios of Au:Fe were synthesized, and X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM) analyses indicated that the TiO2-supported Au nanoparticles were partially covered with an amorphous layer of FeOx species, in which the iron was present as Fe2+ and Fe3+. The metal-semiconductor system, i.e., Au/TiO2, showed only a moderate degradation rate, whereas doping with FeOx strongly enhanced the degradation activity. The bandgap energy decreased gradually from Au/TiO2 (3.13 eV) to the catalyst with the highest FeOx loading Au-FeOx (1:2)/TiO2 (2.23 eV), and this decrease was accompanied by a steady increase in the degradation activity of the catalysts. XPS analyses revealed that compared to Au/TiO2, on Au-FeOx/TiO2 a much higher population density of chemisorbed and/or dissociated oxygen species was generated, which together with the decreased bandgap resulted in the highest photocatalytic activity observed with Au-FeOx (1:2)/TiO2. The processes occurring during reaction on the catalyst surface and in the bulk liquid phase were investigated using operando attenuated total reflection IR spectroscopy (ATR-IR) combined with modulation excitation spectroscopy (MES), which showed that the doping of Au/TiO2 with FeOx weakens the interaction of the dye with the catalyst surface and strongly enhances the cleavage of the azo bond. Full article
(This article belongs to the Special Issue TiO2-Based Nanostructures and Photocatalysts)
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12 pages, 1748 KiB  
Article
Effect of Metal Composition and Carbon Support on the Durability of the Reversal-Tolerant Anode with IrRu Alloy Catalyst
by Eunyoung You, Seung Woo Lee, Daejong You, Bongho Lee and Chanho Pak
Catalysts 2020, 10(8), 932; https://doi.org/10.3390/catal10080932 - 13 Aug 2020
Cited by 11 | Viewed by 3005
Abstract
In polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles, cell reversal (CR) at the anode side can occasionally occur—usually when hydrogen supply is interrupted—which results in degradation of the anode. To mitigate this problem, reversal-tolerant anodes (RTAs) using oxygen evolution [...] Read more.
In polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles, cell reversal (CR) at the anode side can occasionally occur—usually when hydrogen supply is interrupted—which results in degradation of the anode. To mitigate this problem, reversal-tolerant anodes (RTAs) using oxygen evolution reaction catalysts have been generally applied. Adding such materials promotes water oxidation and, thus, provides the protons and electrons during CR situation, while minimizing the carbon-oxidation reaction. In this study, we performed a detailed investigation of the sole use of IrxRuy/C catalysts for RTAs in the membrane electrode assembly (MEA)—including the effects of the IrRu alloy composition and the degree of graphitization of the carbon support on the durability under fuel starvation. Supported IrRu alloy catalysts with different Ir/Ru ratios were prepared via a facile impregnation method on carbon supports with differing degrees of graphitization by heat-treatment at a range of high temperatures. X-ray diffraction patterns indicated that the crystal structure of the alloy nanoparticles depended on the alloy composition, showing the development of a hexagonal closely packed structure with increasing Ru content. Raman spectroscopy indicated an increase in the degree of graphitization of carbon with progressively higher processing temperatures. IrxRuy alloys were found to be a suitable replacement for Pt anode from single-cell MEA performance testing. Furthermore, we examined the synergic enhancement of the CR durability of IrRu alloys with different compositions comparing to the Ir and Ru metals by measuring the initial and total voltage change of MEAs under hydrogen starvation. For the same alloy composition, higher CR durability was observed for MEAs with catalysts prepared using a higher degree of graphitization of the carbon support. Based on the results, we concluded that to develop efficient catalysts for RTAs of automotive PEMFCs, it is important to consider both the durability of the carbon support under high voltages and the catalyst composition. Full article
(This article belongs to the Special Issue State-of-the-Art Catalytical Technology in South Korea)
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22 pages, 5403 KiB  
Article
Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition
by Kateřina Karásková, Kateřina Pacultová, Anna Klegova, Dagmar Fridrichová, Marta Valášková, Květuše Jirátová, Paweł Stelmachowski, Andrzej Kotarba and Lucie Obalová
Catalysts 2020, 10(8), 931; https://doi.org/10.3390/catal10080931 - 13 Aug 2020
Cited by 9 | Viewed by 3046
Abstract
Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium [...] Read more.
Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity. Full article
(This article belongs to the Special Issue Catalytic Decomposition of N2O and NO)
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21 pages, 6050 KiB  
Review
Pt-Ni Nanoalloys for H2 Generation from Hydrous Hydrazine
by Liu Zhou, Xianjin Luo, Lixin Xu, Chao Wan and Mingfu Ye
Catalysts 2020, 10(8), 930; https://doi.org/10.3390/catal10080930 - 13 Aug 2020
Cited by 15 | Viewed by 3565
Abstract
Hydrous hydrazine (N2H4∙H2O) is a candidate for a hydrogen carrier for storage and transportation due to low material cost, high hydrogen content of 8.0%, and liquid stability at room temperature. Pt and Pt nanoalloy catalysts have been [...] Read more.
Hydrous hydrazine (N2H4∙H2O) is a candidate for a hydrogen carrier for storage and transportation due to low material cost, high hydrogen content of 8.0%, and liquid stability at room temperature. Pt and Pt nanoalloy catalysts have been welcomed by researchers for the dehydrogenation of hydrous hydrazine recently. Therefore, in this review, we give a summary of Pt nanoalloy catalysts for the dehydrogenation of hydrous hydrazine and briefly introduce the decomposition mechanism of hydrous hydrazine to prove the design principle of the catalyst. The chemical characteristics of hydrous hydrazine and the mechanism of dehydrogenation reaction are briefly introduced. The catalytic activity of hydrous hydrazine on different supports and the factors affecting the selectivity of hydrogen catalyzed by Ni-Pt are analyzed. It is expected to provide a new way for the development of high-activity catalysts for the dehydrogenation of hydrous hydrazine to produce hydrogen. Full article
(This article belongs to the Special Issue Noble Metal Catalysts)
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27 pages, 8089 KiB  
Review
Atomic-Level Functionalized Graphdiyne for Electrocatalysis Applications
by Xiaodong Qian, Yongshen Zheng, Songhua Chen and Jialiang Xu
Catalysts 2020, 10(8), 929; https://doi.org/10.3390/catal10080929 - 13 Aug 2020
Cited by 10 | Viewed by 3953
Abstract
Graphdiyne (GDY) is a two-dimensional (2D) electron-rich full-carbon planar material composed of sp2- and sp-hybridized carbon atoms, which features highly conjugated structures, uniformly distributed pores, tunable electronic characteristics and high specific surface areas. The synthesis strategy of GDY by facile coupling [...] Read more.
Graphdiyne (GDY) is a two-dimensional (2D) electron-rich full-carbon planar material composed of sp2- and sp-hybridized carbon atoms, which features highly conjugated structures, uniformly distributed pores, tunable electronic characteristics and high specific surface areas. The synthesis strategy of GDY by facile coupling reactions under mild conditions provides more convenience for the functional modification of GDY and offers opportunities for realizing the special preparation of GDY according to the desired structure and unique properties. These structural characteristics and excellent physical and chemical properties of GDY have attracted increasing attention in the field of electrocatalysis. Herein, the research progress in the synthesis of atomic-level functionalized GDYs and their electrocatalytic applications are summarized. Special attention was paid to the research progress of metal-atom-anchored and nonmetallic-atom-doped GDYs for applications in the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) catalytic processes. In addition, several potential development prospects and challenges of these 2D highly conjugated electron-rich full-carbon materials in the field of electrocatalysis are presented. Full article
(This article belongs to the Section Electrocatalysis)
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16 pages, 2054 KiB  
Article
Arsenic Removal by Advanced Electrocoagulation Processes: The Role of Oxidants Generated and Kinetic Modeling
by Micah Flor V. Montefalcon, Meliton R. Chiong III, Augustus C. Resurreccion, Sergi Garcia-Segura and Joey D. Ocon
Catalysts 2020, 10(8), 928; https://doi.org/10.3390/catal10080928 - 12 Aug 2020
Cited by 10 | Viewed by 4171
Abstract
Arsenic (As) is a naturally occurring element in the environment that poses significant risks to human health. Several treatment technologies have been successfully used in the treatment of As-contaminated waters. However, limited literature has explored advanced electrocoagulation (EC) processes for As removal. The [...] Read more.
Arsenic (As) is a naturally occurring element in the environment that poses significant risks to human health. Several treatment technologies have been successfully used in the treatment of As-contaminated waters. However, limited literature has explored advanced electrocoagulation (EC) processes for As removal. The present study evaluates the As removal performance of electrocoagulation, electrochemical peroxidation (ECP), and photo-assisted electrochemical peroxidation (PECP) technologies at circumneutral pH using electroactive iron electrodes. The influence of As speciation and the role of oxidants in As removal were investigated. We have identified the ECP process to be a promising alternative for the conventional EC with around 4-fold increase in arsenic removal capacity at a competitive cost of 0.0060 $/m3. Results also indicated that the rate of As(III) oxidation at the outset of electrochemical treatment dictates the extent of As removal. Both ECP and PECP processes reached greater than 96% As(III) conversion at 1 C/L and achieved 86% and 96% As removal at 5 C/L, respectively. Finally, the mechanism of As(III) oxidation was evaluated, and results showed that Fe(IV) is the intermediate oxidant generated in advanced EC processes, and the contribution of •OH brought by UV irradiation is insignificant. Full article
(This article belongs to the Section Electrocatalysis)
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19 pages, 5418 KiB  
Article
Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions
by Xinhui Sun, Antonios Arvanitis, Devaiah Damma, Noe T. Alvarez, Vesselin Shanov, Panagiotis G. Smirniotis and Junhang Dong
Catalysts 2020, 10(8), 927; https://doi.org/10.3390/catal10080927 - 12 Aug 2020
Cited by 3 | Viewed by 3482
Abstract
A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further [...] Read more.
A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas. Full article
(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)
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64 pages, 9135 KiB  
Review
Development of Stable Oxygen Carrier Materials for Chemical Looping Processes—A Review
by Yoran De Vos, Marijke Jacobs, Pascal Van Der Voort, Isabel Van Driessche, Frans Snijkers and An Verberckmoes
Catalysts 2020, 10(8), 926; https://doi.org/10.3390/catal10080926 - 12 Aug 2020
Cited by 62 | Viewed by 8434
Abstract
This review aims to give more understanding of the selection and development of oxygen carrier materials for chemical looping. Chemical looping, a rising star in chemical technologies, is capable of low CO2 emissions with applications in the production of energy and chemicals. [...] Read more.
This review aims to give more understanding of the selection and development of oxygen carrier materials for chemical looping. Chemical looping, a rising star in chemical technologies, is capable of low CO2 emissions with applications in the production of energy and chemicals. A key issue in the further development of chemical looping processes and its introduction to the industry is the selection and further development of an appropriate oxygen carrier (OC) material. This solid oxygen carrier material supplies the stoichiometric oxygen needed for the various chemical processes. Its reactivity, cost, toxicity, thermal stability, attrition resistance, and chemical stability are critical selection criteria for developing suitable oxygen carrier materials. To develop oxygen carriers with optimal properties and long-term stability, one must consider the employed reactor configuration and the aim of the chemical looping process, as well as the thermodynamic properties of the active phases, their interaction with the used support material, long-term stability, internal ionic migration, and the advantages and limits of the employed synthesis methods. This review, therefore, aims to give more understanding into all aforementioned aspects to facilitate further research and development of chemical looping technology. Full article
(This article belongs to the Special Issue Chemical Looping for Catalysis)
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15 pages, 5121 KiB  
Article
Rhodium Nanoparticles Incorporated Mesoporous Silica as an Active Catalyst for Cyclohexene Hydrogenation under Ambient Conditions
by Mohamed S. Hamdy, Abdullah M. Alhanash, Mhamed Benaissa, Ali Alsalme, Fahad A. Alharthi and Nabil Al-Zaqri
Catalysts 2020, 10(8), 925; https://doi.org/10.3390/catal10080925 - 12 Aug 2020
Cited by 4 | Viewed by 2589
Abstract
Rhodium (Rh) nanoparticles were embedded in the mesopores of TUD-1 siliceous material and denoted as Rh-TUD-1. Five samples of Rh-TUD-1 were prepared with different loadings of Rh that ranged from 0.1 to 2 wt% using the sol-gel technique. The prepared samples were characterized [...] Read more.
Rhodium (Rh) nanoparticles were embedded in the mesopores of TUD-1 siliceous material and denoted as Rh-TUD-1. Five samples of Rh-TUD-1 were prepared with different loadings of Rh that ranged from 0.1 to 2 wt% using the sol-gel technique. The prepared samples were characterized by means of several chemical and physical techniques. The obtained characterization results show the formation of highly distributed Rh0 nanoparticles with an average size ranging from 3 to 5 nm throughout the three-dimensional silica matrix of TUD-1. The catalytic activity of the prepared catalysts was evaluated in the solvent-free hydrogenation of cyclohexene to cyclohexane at room temperature using 1atm of hydrogen gas. The obtained catalytic results confirm the high activity of Rh-TUD-1, in which a turn over frequency (TOF) ranging from 4.94 to 0.54 s−1 was obtained. Moreover, the change in reaction temperature during the reaction was monitored, and it showed an obvious increase in the reaction temperature as an indication of the spontaneous and exothermic nature of the reactions. Other optimization parameters, such as the substrate/catalyst ratio, and performing the reaction under non-ambient conditions (temperature = 60 °C and hydrogen pressure = 5 atm) were also investigated. Rh-TUD-1 exhibited a high stability in a consecutive reaction of five runs under either ambient or non-ambient conditions. Full article
(This article belongs to the Section Catalytic Materials)
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18 pages, 671 KiB  
Review
Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects
by Lu Lin, Wenbin Jiang, Lin Chen, Pei Xu and Huiyao Wang
Catalysts 2020, 10(8), 924; https://doi.org/10.3390/catal10080924 - 12 Aug 2020
Cited by 89 | Viewed by 6313
Abstract
Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated [...] Read more.
Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water. Full article
(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification)
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14 pages, 885 KiB  
Article
Reducing Immunoreactivity of Gliadins and Coeliac-Toxic Peptides Using Peptidases from L. acidophilus 5e2 and A. niger
by Bartosz Brzozowski, Katarzyna Stasiewicz, Mateusz Ostolski and Marek Adamczak
Catalysts 2020, 10(8), 923; https://doi.org/10.3390/catal10080923 - 11 Aug 2020
Cited by 6 | Viewed by 3931
Abstract
Wheat storage proteins and products of their hydrolysis may cause coeliac sprue in genetically predisposed individuals with high expression of main histocompatibility complex HLA-DQ2 or DQ8, since by consuming wheat, they become exposed to proline- (P) and glutamine (Q)-rich gluten. In bread-making, the [...] Read more.
Wheat storage proteins and products of their hydrolysis may cause coeliac sprue in genetically predisposed individuals with high expression of main histocompatibility complex HLA-DQ2 or DQ8, since by consuming wheat, they become exposed to proline- (P) and glutamine (Q)-rich gluten. In bread-making, the hydrolysis of gliadins and coeliac-toxic peptides occurs with varied efficiency depending on the fermentation pH and temperature. Degradation of gliadins catalysed by Lactobacillus acidophilus 5e2 peptidases and a commercial prolyl endopeptidase synthesised by A. niger, carried out at pH 4.0 and 37 °C, reduces the gliadin concentration over 110-fold and decreases the relative immunoreactivity of the hydrolysate to 0.9% of its initial value. Hydrolysis of coeliac-toxic peptides: LGQQQPFPPQQPY (P1) and PQPQLPYPQPQLP (P2) under the same conditions occurs with the highest efficiency, reaching 99.8 ± 0.0% and 97.5 ± 0.1%, respectively. The relative immunoreactivity of peptides P1 and P2 was 0.8 ± 0.0% and 3.2 ± 0.0%, respectively. A mixture of peptidases from L. acidophilus 5e2 and A. niger may be used in wheat sourdough fermentation to reduce the time needed for degradation of proteins and products of their hydrolysis. Full article
(This article belongs to the Special Issue Biocatalysts and Biocatalysis in Food Industry)
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21 pages, 3464 KiB  
Article
Microkinetic Modeling of the Oxidation of Methane Over PdO Catalysts—Towards a Better Understanding of the Water Inhibition Effect
by Kevin Keller, Patrick Lott, Henning Stotz, Lubow Maier and Olaf Deutschmann
Catalysts 2020, 10(8), 922; https://doi.org/10.3390/catal10080922 - 11 Aug 2020
Cited by 22 | Viewed by 3974
Abstract
Water, which is an intrinsic part of the exhaust gas of combustion engines, strongly inhibits the methane oxidation reaction over palladium oxide-based catalysts under lean conditions and leads to severe catalyst deactivation. In this combined experimental and modeling work, we approach this challenge [...] Read more.
Water, which is an intrinsic part of the exhaust gas of combustion engines, strongly inhibits the methane oxidation reaction over palladium oxide-based catalysts under lean conditions and leads to severe catalyst deactivation. In this combined experimental and modeling work, we approach this challenge with kinetic measurements in flow reactors and a microkinetic model, respectively. We propose a mechanism that takes the instantaneous impact of water on the noble metal particles into account. The dual site microkinetic model is based on the mean-field approximation and consists of 39 reversible surface reactions among 23 surface species, 15 related to Pd-sites, and eight associated with the oxide. A variable number of available catalytically active sites is used to describe light-off activity tests as well as spatially resolved concentration profiles. The total oxidation of methane is studied at atmospheric pressure, with space velocities of 160,000 h−1 in the temperature range of 500–800 K for mixtures of methane in the presence of excess oxygen and up to 15% water, which are typical conditions occurring in the exhaust of lean-operated natural gas engines. The new approach presented is also of interest for modeling catalytic reactors showing a dynamic behavior of the catalytically active particles in general. Full article
(This article belongs to the Special Issue Palladium-Catalyzed Reactions)
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32 pages, 3950 KiB  
Review
Progress in Graphene/Metal Oxide Composite Photocatalysts for Degradation of Organic Pollutants
by Xiaodong Hong, Xu Wang, Yang Li, Jiawei Fu and Bing Liang
Catalysts 2020, 10(8), 921; https://doi.org/10.3390/catal10080921 - 11 Aug 2020
Cited by 29 | Viewed by 4806
Abstract
The sewage discharge of industrial wastewater seriously pollutes the water source and rivers, which is very harmful to the health of humans and wildlife. Among those methods for treating wastewater, photocatalysis is a sustainable and environmental-friendly technique for removing the organic pollutants with [...] Read more.
The sewage discharge of industrial wastewater seriously pollutes the water source and rivers, which is very harmful to the health of humans and wildlife. Among those methods for treating wastewater, photocatalysis is a sustainable and environmental-friendly technique for removing the organic pollutants with no secondary pollution. As a popular photocatalyst, graphene/metal oxide nanocomposites have been widely reported in the photocatalysis field. In this review, the recent progress of graphene/metal oxide composites including binary and ternary composites is summarized in detail. The synthesis, microstructure design, and application performance of graphene/TiO2, graphene/ZnO, graphene/SnO2, graphene/WO3, graphene/Fe2O3, and graphene/Cu2O composites are introduced firstly. Then, the synthesis, the selection of components, and the performance of various ternary composites are summarized specifically, including graphene/TiO2-, graphene/ZnO-, graphene/SnO2-, graphene/Cu2O-, graphene/FexOy-, and graphene/Bi-containing ternary composites. At last, the possible research directions of graphene/metal oxide nanocomposites are put forward. The main purpose is to provide a theoretical guidance for designing high-performance graphene/metal oxide photocatalysts for wastewater treatment. Full article
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9 pages, 1668 KiB  
Communication
Rhodium (II)-Catalyzed Synthesis of Tetracyclic 3,4-Fused Indoles and Dihydroindoles
by Hongwei Qiao, Jiakun Bai, Mengyao Zhu, Juanhong Gao, Anna, Sichun Zhang and Chao Li
Catalysts 2020, 10(8), 920; https://doi.org/10.3390/catal10080920 - 11 Aug 2020
Cited by 4 | Viewed by 3004
Abstract
An efficient synthetic method of tetracyclic 3,4-fused indoles and dihydroindoles via rhodium-catalyzed (3+2) cycloaddition of N-tosyl-4-(2-phenoxyphenyl)-1,2,3-triazole was described. The aromatized xanthene derivatives can be achieved in a one-pot synthesis starting from 1-ethynyl-2-phenoxybenzene. The xanthene-based fused heterocycles were considered as the valuable fluorophore. Full article
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14 pages, 1612 KiB  
Article
Piperidinium and Pyrrolidinium Ionic Liquids as Precursors in the Synthesis of New Platinum Catalysts for Hydrosilylation
by Magdalena Jankowska-Wajda, Olga Bartlewicz, Przemysław Pietras and Hieronim Maciejewski
Catalysts 2020, 10(8), 919; https://doi.org/10.3390/catal10080919 - 10 Aug 2020
Cited by 7 | Viewed by 2818
Abstract
Six new air-stable anionic platinum complexes were synthesized in simple reactions of piperidinium [BMPip]Cl or pyrrolidinium [BMPyrr]Cl ionic liquids with platinum compounds ([Pt(cod)Cl2] or K2[PtCl6]). All these compounds were subjected to isolation and spectrometric characterization using NMR [...] Read more.
Six new air-stable anionic platinum complexes were synthesized in simple reactions of piperidinium [BMPip]Cl or pyrrolidinium [BMPyrr]Cl ionic liquids with platinum compounds ([Pt(cod)Cl2] or K2[PtCl6]). All these compounds were subjected to isolation and spectrometric characterization using NMR and ESI-MS techniques. Furthermore, the determination of melting points and thermal stability of the above derivatives was performed with the use of thermogravimetric analysis. The catalytic performance of the synthesized complexes was tested in hydrosilylation of 1-octene and allyl glycidyl ether with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The study has shown that they have high catalytic activity and are insoluble in the reaction medium which enabled them to isolate and reuse them in consecutive catalytic cycles. The most active complex [BMPip]2[PtCl6] makes it possible to conduct at least 10 catalytic runs without losing activity which makes it an attractive alternative not only to commonly used homogeneous catalysts, but also to heterogeneous catalysts for hydrosilylation processes. The activity of the studied catalysts is also affected by the kind of anion and, to some extent, the kind of cation. Full article
(This article belongs to the Special Issue Ionic Liquids in Catalysis)
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17 pages, 5373 KiB  
Article
Efficient One-Step Immobilization of CaLB Lipase over MOF Support NH2-MIL-53(Al)
by Victoria Gascón-Pérez, Mayra Belen Jiménez, Asunción Molina, Rosa María Blanco and Manuel Sánchez-Sánchez
Catalysts 2020, 10(8), 918; https://doi.org/10.3390/catal10080918 - 10 Aug 2020
Cited by 14 | Viewed by 4453
Abstract
Metal-organic framework (MOF) materials possess the widest versatility in structure, composition, and synthesis procedures amongst the known families of materials. On the other hand, the extraordinary affinity between MOFs and enzymes has led to widely investigating these materials as platforms to support these [...] Read more.
Metal-organic framework (MOF) materials possess the widest versatility in structure, composition, and synthesis procedures amongst the known families of materials. On the other hand, the extraordinary affinity between MOFs and enzymes has led to widely investigating these materials as platforms to support these catalytic proteins in recent years. In this work, the MOF material NH2-MIL-53(Al) has been tested as a support to immobilize by one-step methodology (in situ) the enzyme lipase CaLB from Candida antarctica by employing conditions that are compatible with its enzymatic activity (room temperature, aqueous solution, and moderate pH values). Once the nature of the linker deprotonating agent or the synthesis time were optimized, the MOF material resulted in quite efficient entrapping of the lipase CaLB through this in situ approach (>85% of the present enzyme in the synthesis media) while the supported enzyme retained acceptable activity (29% compared to the free enzyme) and had scarce enzyme leaching. The equivalent post-synthetic method led to biocatalysts with lower enzyme loading values. These results make clear that the formation of MOF support in the presence of the enzyme to be immobilized substantially improves the efficiency of the biocatalysts support for retaining the enzyme and limits their leaching. Full article
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16 pages, 3324 KiB  
Article
Photocatalytic Activity of Aeroxide TiO2 Sensitized by Natural Dye Extracted from Mangosteen Peel
by Malini Ghosh, Pankaj Chowdhury and Ajay K. Ray
Catalysts 2020, 10(8), 917; https://doi.org/10.3390/catal10080917 - 10 Aug 2020
Cited by 11 | Viewed by 3779
Abstract
Natural dye sensitizers are environment-friendly and inexpensive substances that could be used for photocatalytic decontamination of organic pollutants. In this study, a natural dye extracted from mangosteen peel, containing a significant amount of anthocyanin dye, has been successfully employed to sensitize aeroxide TiO [...] Read more.
Natural dye sensitizers are environment-friendly and inexpensive substances that could be used for photocatalytic decontamination of organic pollutants. In this study, a natural dye extracted from mangosteen peel, containing a significant amount of anthocyanin dye, has been successfully employed to sensitize aeroxide TiO2 to lower its bandgap, thereby making the process visible sunlight-driven. We have demonstrated the photocatalytic activity of mangosteen dye-sensitized-TiO2 (MS-TiO2) under visible solar light by studying the degradation of methylene blue (MB), a well-studied model compound. A multivariate parametric study was performed using factorial design methodology with three factors—pH, MS-TiO2 dosage, and visible light intensity. The study indicated that pH and MS-TiO2 dosage are the two most dominant factors for MB degradation under visible solar light. The kinetic rate constant and adsorption equilibrium constant were determined, and a Langmuir-Hinshelwood-type equation was proposed to describe MB degradation on MS-TiO2 under visible solar light. Apparent quantum yield was also reported for the MS-TiO2 photocatalyst at optimum experimental conditions. Full article
(This article belongs to the Special Issue State-of-the-Art Photocatalytical Technology in North America)
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