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Catalysts, Volume 9, Issue 10 (October 2019)

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Open AccessArticle
Screening and Comparative Characterization of Microorganisms from Iranian Soil Samples Showing ω-Transaminase Activity toward a Plethora of Substrates
Catalysts 2019, 9(10), 874; https://doi.org/10.3390/catal9100874 (registering DOI) - 22 Oct 2019
Abstract
In this study, soil microorganisms from Iran were screened for ω-transaminase (ω-TA) activity based on growth on minimal media containing (rac)-α-methylbenzylamine (rac-α-MBA) as a sole nitrogen source. Then, for the selection of strains with high enzyme activity, a colorimetric o-xylylendiamine assay [...] Read more.
In this study, soil microorganisms from Iran were screened for ω-transaminase (ω-TA) activity based on growth on minimal media containing (rac)-α-methylbenzylamine (rac-α-MBA) as a sole nitrogen source. Then, for the selection of strains with high enzyme activity, a colorimetric o-xylylendiamine assay was conducted. The most promising strains were identified by 16S rDNA sequencing. Five microorganisms showing high ω-TA activity were subjected to determine optimal conditions for ω-TA activity, including pH, temperature, co-solvent, and the specificity of the ω-TA toward different amine donors and acceptors. Among the five screened microorganisms, Bacillus halotolerans turned out to be the most promising strain: Its cell-free extract showed a highly versatile amino donor spectrum toward aliphatic, aromatic chiral amines and a broad range of pH activity. Transaminase activity also exhibited excellent solvent tolerance, with maximum turnover in the presence of 30% (v/v) DMSO. Full article
(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysts)
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Open AccessReview
Biocatalytic Synthesis of Natural Green Leaf Volatiles Using the Lipoxygenase Metabolic Pathway
Catalysts 2019, 9(10), 873; https://doi.org/10.3390/catal9100873 (registering DOI) - 22 Oct 2019
Abstract
In higher plants, the lipoxygenase enzymatic pathway combined actions of several enzymes to convert lipid substrates into signaling and defense molecules called phytooxylipins including short chain volatile aldehydes, alcohols, and esters, known as green leaf volatiles (GLVs). GLVs are synthesized from C18:2 and [...] Read more.
In higher plants, the lipoxygenase enzymatic pathway combined actions of several enzymes to convert lipid substrates into signaling and defense molecules called phytooxylipins including short chain volatile aldehydes, alcohols, and esters, known as green leaf volatiles (GLVs). GLVs are synthesized from C18:2 and C18:3 fatty acids that are oxygenated by lipoxygenase (LOX) to form corresponding hydroperoxides, then the action of hydroperoxide lyase (HPL) produces C6 or C9 aldehydes that can undergo isomerization, dehydrogenation, and esterification. GLVs are commonly used as flavors to confer a fresh green odor of vegetable to perfumes, cosmetics, and food products. Given the increasing demand in these natural flavors, biocatalytic processes using the LOX pathway reactions constitute an interesting application. Vegetable oils, chosen for their lipid profile are converted in natural GLVs with high added value. This review describes the enzymatic reactions of GLVs biosynthesis in the plant, as well as the structural and functional properties of the enzymes involved. The various stages of the biocatalytic production processes are approached from the lipid substrate to the corresponding aldehyde or alcoholic aromas, as well as the biotechnological improvements to enhance the production potential of the enzymatic catalysts. Full article
(This article belongs to the Special Issue Green Synthesis and Catalysis)
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Open AccessArticle
Kinetics of Fischer–Tropsch Synthesis in a 3-D Printed Stainless Steel Microreactor Using Different Mesoporous Silica Supported Co-Ru Catalysts
Catalysts 2019, 9(10), 872; https://doi.org/10.3390/catal9100872 - 21 Oct 2019
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Abstract
Fischer–Tropsch (FT) synthesis was carried out in a 3D printed stainless steel (SS) microchannel microreactor using bimetallic Co-Ru catalysts on three different mesoporous silica supports. CoRu-MCM-41, CoRu-SBA-15, and CoRu-KIT-6 were synthesized using a one-pot hydrothermal method and characterized by Brunner–Emmett–Teller (BET), temperature programmed [...] Read more.
Fischer–Tropsch (FT) synthesis was carried out in a 3D printed stainless steel (SS) microchannel microreactor using bimetallic Co-Ru catalysts on three different mesoporous silica supports. CoRu-MCM-41, CoRu-SBA-15, and CoRu-KIT-6 were synthesized using a one-pot hydrothermal method and characterized by Brunner–Emmett–Teller (BET), temperature programmed reduction (TPR), SEM-EDX, TEM, and X-ray photoelectron spectroscopy (XPS) techniques. The mesoporous catalysts show the long-range ordered structure as supported by BET and low-angle XRD studies. The TPR profiles of metal oxides with H2 varied significantly depending on the support. These catalysts were coated inside the microchannels using polyvinyl alcohol and kinetic performance was evaluated at three different temperatures, in the low-temperature FT regime (210–270 °C), at different Weight Hourly Space Velocity (WHSV) in the range of 3.15–25.2 kgcat.h/kmol using a syngas ratio of H2/CO = 2. The mesoporous supports have a significant effect on the FT kinetics and stability of the catalyst. The kinetic models (FT-3, FT-6), based on the Langmuir–Hinshelwood mechanism, were found to be statistically and physically relevant for FT synthesis using CoRu-MCM-41 and CoRu-KIT-6. The kinetic model equation (FT-2), derived using Eley–Rideal mechanism, is found to be relevant for CoRu-SBA-15 in the SS microchannel microreactor. CoRu-KIT-6 was found to be 2.5 times more active than Co-Ru-MCM-41 and slightly more active than CoRu-SBA-15, based on activation energy calculations. CoRu-KIT-6 was ~3 and ~1.5 times more stable than CoRu-SBA-15 and CoRu-MCM-41, respectively, based on CO conversion in the deactivation studies. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
Open AccessArticle
Eco-Toxicological and Kinetic Evaluation of TiO2 and ZnO Nanophotocatalysts in Degradation of Organic Dye
Catalysts 2019, 9(10), 871; https://doi.org/10.3390/catal9100871 - 21 Oct 2019
Viewed by 117
Abstract
In this study, the photocatalytic degradation of azo dye “Food Black 1” (FB1) was investigated using TiO2 and ZnO nanoparticles under ultraviolet (UV) light. The performances of the two photocatalysts were evaluated in terms of key parameters (e.g., decolorization, dearomatization, mineralization, and [...] Read more.
In this study, the photocatalytic degradation of azo dye “Food Black 1” (FB1) was investigated using TiO2 and ZnO nanoparticles under ultraviolet (UV) light. The performances of the two photocatalysts were evaluated in terms of key parameters (e.g., decolorization, dearomatization, mineralization, and detoxification of dye) in relation to variables including pre-adsorption period, pH, and temperature. Under acidic conditions (pH 5), the ZnO catalyst underwent photocorrosion to increase the concentration of zinc ions in the system, thereby increasing the toxic properties of the treated effluent. In contrast, TiO2 efficiently catalyzed the degradation of the dye at pH 5 following the Langmuir–Hinshelwood (L–H) kinetic model. The overall results of this study indicate that the decolorization rate of TiO2 on the target dye was far superior to ZnO (i.e., by 1.5 times) at optimum catalyst loading under UV light. Full article
(This article belongs to the Special Issue Nanomaterials in Photo(Electro)catalysis)
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Open AccessEditorial
Photocatalysts for Organics Degradation
Catalysts 2019, 9(10), 870; https://doi.org/10.3390/catal9100870 - 21 Oct 2019
Viewed by 87
Abstract
Organics degradation is one of the challenges of Advanced Oxidation Processes (AOPs), which are mainly employed for the removal of water and air pollutants [...] Full article
(This article belongs to the Special Issue Photocatalysts for Organics Degradation)
Open AccessArticle
The Steric Effect in Green Benzylation of Arenes with Benzyl Alcohol Catalyzed by Hierarchical H-beta Zeolite
Catalysts 2019, 9(10), 869; https://doi.org/10.3390/catal9100869 - 20 Oct 2019
Viewed by 175
Abstract
For decades the steric effect was still ambiguously understood in catalytic benzylation reactions of arenes with benzyl alcohol, which limited the green synthesis of phenylmethane derivates in industrial scale. This research applies a series of silica–alumina beta zeolites to systematically evaluate factors like [...] Read more.
For decades the steric effect was still ambiguously understood in catalytic benzylation reactions of arenes with benzyl alcohol, which limited the green synthesis of phenylmethane derivates in industrial scale. This research applies a series of silica–alumina beta zeolites to systematically evaluate factors like catalyst porosity, reactants molecule size, and reaction temperature on catalytic benzylation. First, a suitable hierarchical beta zeolite catalyst was screened out by X-ray powder diffraction, N2 adsorption−desorption, and probe benzylation with p-xylene. In the following substrates expanding study, for a typical benzylation of benzene, it showed extraordinary performance among literature reported ones that the conversion was 98% while selectivity was 90% at 353 K only after 10 min. The steric effect of aromatics with different molecular sizes on benzylation was observed. The reaction activities of four different aromatics followed the order: benzene > toluene > p-xylene > mesitylene. Combined with macroscopic kinetic analysis, this comprehensive study points out for the first time that the nature of this steric effect was dominated by the relative adsorption efficiency of different guest aromatic molecules on the host zeolite surface. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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Open AccessReview
Cofactor F420-Dependent Enzymes: An Under-Explored Resource for Asymmetric Redox Biocatalysis
Catalysts 2019, 9(10), 868; https://doi.org/10.3390/catal9100868 - 20 Oct 2019
Viewed by 253
Abstract
The asymmetric reduction of enoates, imines and ketones are among the most important reactions in biocatalysis. These reactions are routinely conducted using enzymes that use nicotinamide cofactors as reductants. The deazaflavin cofactor F420 also has electrochemical properties that make it suitable as [...] Read more.
The asymmetric reduction of enoates, imines and ketones are among the most important reactions in biocatalysis. These reactions are routinely conducted using enzymes that use nicotinamide cofactors as reductants. The deazaflavin cofactor F420 also has electrochemical properties that make it suitable as an alternative to nicotinamide cofactors for use in asymmetric reduction reactions. However, cofactor F420-dependent enzymes remain under-explored as a resource for biocatalysis. This review considers the cofactor F420-dependent enzyme families with the greatest potential for the discovery of new biocatalysts: the flavin/deazaflavin-dependent oxidoreductases (FDORs) and the luciferase-like hydride transferases (LLHTs). The characterized F420-dependent reductions that have the potential for adaptation for biocatalysis are discussed, and the enzymes best suited for use in the reduction of oxidized cofactor F420 to allow cofactor recycling in situ are considered. Further discussed are the recent advances in the production of cofactor F420 and its functional analog FO-5′-phosphate, which remains an impediment to the adoption of this family of enzymes for industrial biocatalytic processes. Finally, the prospects for the use of this cofactor and dependent enzymes as a resource for industrial biocatalysis are discussed. Full article
(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysts)
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Open AccessArticle
Overcoming Stability Problems in Microwave-Assisted Heterogeneous Catalytic Processes Affected by Catalyst Coking
Catalysts 2019, 9(10), 867; https://doi.org/10.3390/catal9100867 - 19 Oct 2019
Viewed by 174
Abstract
Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed [...] Read more.
Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed as the main factor of the process selectivity enhancement towards the products of interest in a number of hydrocarbon conversion processes. However, MHC is traditionally restricted to catalytic reactions in the absence of catalyst coking. As excellent MW-susceptors, carbon deposits represent an enormous drawback of the MHC technology, being main responsible of long-term process malfunctions. This work addresses the potentials and limitations of MHC for such processes affected by coking (MHCC). It also intends to evaluate the use of different catalyst and reactor configurations to overcome heating stability problems derived from the undesired coke deposits. The concept of long-term MHCC operation has been experimentally tested/applied to for the methane non-oxidative coupling reaction at 700 °C on Mo/[email protected] structured catalysts. Preliminary process scalability tests suggest that a 6-fold power input increases the processing of methane flow by 150 times under the same controlled temperature and spatial velocity conditions. This finding paves the way for the implementation of high-capacity MHCC processes at up-scaled facilities. Full article
(This article belongs to the Special Issue Microwave-Assisted Catalysis)
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Open AccessArticle
Fe Speciation in Iron Modified Natural Zeolites as Sustainable Environmental Catalysts
Catalysts 2019, 9(10), 866; https://doi.org/10.3390/catal9100866 - 19 Oct 2019
Viewed by 156
Abstract
Natural purified mordenite from Palmarito de Cauto (ZP) deposit, Cuba, was subjected to a hydrothermal ion exchange process in acid medium with Fe2+ or Fe3+ salts (Fe2+ZP and Fe3+ZP). The set of samples was characterized regarding their [...] Read more.
Natural purified mordenite from Palmarito de Cauto (ZP) deposit, Cuba, was subjected to a hydrothermal ion exchange process in acid medium with Fe2+ or Fe3+ salts (Fe2+ZP and Fe3+ZP). The set of samples was characterized regarding their textural properties, morphology, and crystallinity, and tested in the NO reduction with CO/C3H6. Infrared spectroscopy coupled with NO as a probe molecule was used to give a qualitative description of the Fe species’ nature and distribution. The exchange process caused an increase in the iron loading of the samples and a redistribution, resulting in more dispersed Fe2+ and Fe3+ species. When contacted with the NO probe, Fe2+ZP showed the highest intensity of nitrosyl bands, assigned to NO adducts on isolated/highly dispersed Fe2+/Fe3+ extra-framework sites and FexOy clusters. This sample is also characterized by the highest NO sorption capacity and activity in NO reduction. Fe3+ZP showed a higher intensity of nitrosonium (NO+) species, without a correlation to NO storage and conversion, pointing to the reactivity of small FexOy aggregates in providing oxygen atoms for the NO to NO+ reaction. The same sites are proposed to be responsible for the higher production of CO2 observed on this sample, and thus to be detrimental to the activity in NO SCR. Full article
(This article belongs to the Special Issue Sustainable and Environmental Catalysis)
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Open AccessArticle
Optimized Pore Structures of Hierarchical HY Zeolites for Highly Selective Production of Methyl Methoxyacetate
Catalysts 2019, 9(10), 865; https://doi.org/10.3390/catal9100865 - 18 Oct 2019
Viewed by 112
Abstract
Several organic templates were introduced during acid or alkaline treatment to optimize pore structures of hierarchical HY zeolites. The influences of category and concentration of templates on the pore structures and acidity of hierarchical HY zeolites were systemically studied. The N2 adsorption-desorption [...] Read more.
Several organic templates were introduced during acid or alkaline treatment to optimize pore structures of hierarchical HY zeolites. The influences of category and concentration of templates on the pore structures and acidity of hierarchical HY zeolites were systemically studied. The N2 adsorption-desorption showed that the micropore amount of the optimized HY zeolites obviously increased, while both the large mesopore size and amount remained almost unchanged. The XRD and NH3-TPD revealed that the optimized HY zeolites exhibited higher relative crystallinity and medium-strong acid sites amount than those of hierarchical HY zeolites produced without the addition of templates. The optimized HY zeolites were used for the synthesis of methyl methoxyacetate (MMAc) from dimethoxymethane (DMM) carbonylation. In comparison with parent HY, the conversion and the selectivity clearly increased from 36.43% to 96.32% and from 11.06% to 92.35%, respectively. The stability of the optimized zeolite was also conducted under the same conditions. The conversion and the selectivity remained nearly unchanged even through 24 h reaction, showing that the performance was extremely stable. The TG-DTA and GC-MS also indicated that the generation of coke was effectively inhibited. This catalyst treatment method, which is facile and highly efficient, provided a route for producing mesoporous zeolites. Full article
(This article belongs to the Special Issue Advances in Catalytic Fundamentals and Catalyst Design)
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Open AccessFeature PaperArticle
Biodiesel Production from Castor Oil by Two-Step Catalytic Transesterification: Optimization of the Process and Economic Assessment
Catalysts 2019, 9(10), 864; https://doi.org/10.3390/catal9100864 - 17 Oct 2019
Viewed by 128
Abstract
The use of biodiesel and the requirement of improving its production in a more efficient and sustainable way are becoming more and more important. In this research work, castor oil was demonstrated to be an alternative feedstock for obtaining biodiesel. The production of [...] Read more.
The use of biodiesel and the requirement of improving its production in a more efficient and sustainable way are becoming more and more important. In this research work, castor oil was demonstrated to be an alternative feedstock for obtaining biodiesel. The production of biodiesel was optimized by the use of a two-step process. In this process, methanol and KOH (as a catalyst) were added in each step, and the glycerol produced during the first stage was removed before the second reaction. The reaction conditions were optimized, considering catalyst concentration and methanol/oil molar ratio for both steps. A mathematical model was obtained to predict the final ester content of the biodiesel. Optimal conditions (0.08 mol·L−1 and 0.01 mol·L−1 as catalyst concentration, 5.25:1 and 3:1 as methanol/oil molar ratio for first and second step, respectively) were established, taking into account the biodiesel quality and an economic analysis. This type of process allowed cost saving, since the amounts of methanol and catalyst were significantly reduced. An estimation of the final manufacturing cost of biodiesel production was carried out. Full article
(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts)
Open AccessReview
The Combination of Lewis Acid with N-Heterocyclic Carbene (NHC) Catalysis
Catalysts 2019, 9(10), 863; https://doi.org/10.3390/catal9100863 - 16 Oct 2019
Viewed by 169
Abstract
In the last ten years, the combination of Lewis acid with N-heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in a variety of important asymmetric synthesis, due to the ready availability of starting materials, operational simplicity and mild reaction conditions. [...] Read more.
In the last ten years, the combination of Lewis acid with N-heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in a variety of important asymmetric synthesis, due to the ready availability of starting materials, operational simplicity and mild reaction conditions. Recent findings illustrate that Lewis acid could largely enhance the efficiency and enantioselectivity, reverse the diastereoselectivity, and even influence the pathway of the same reaction partners. Herein, this review aims to reveal the recent advances in NHC-Lewis acid synergistically promoted enantioselective reactions for the expeditious assembly of versatile biologically important chiral pharmaceuticals and natural products. Full article
(This article belongs to the Special Issue New Trends in Asymmetric Catalysis)
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Open AccessArticle
Fischer-Tropsch Synthesis: Cd, In and Sn Effects on a 15%Co/Al2O3 Catalyst
Catalysts 2019, 9(10), 862; https://doi.org/10.3390/catal9100862 - 16 Oct 2019
Viewed by 122
Abstract
The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al2O3 catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H [...] Read more.
The effects of 1% of Cd, In and Sn additives on the physicochemical properties and Fischer-Tropsch synthesis (FTS) performance of a 15% Co/Al2O3 catalyst were investigated. The fresh and spent catalysts were characterized by BET, temperature programmed reduction (TPR), H2-chemisorption, NH3 temperature programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X ray diffraction (XRD). The catalysts were tested in a 1 L continuously stirred tank reactor (CSTR) at 220 °C, 2.2 MPa, H2/CO = 2.1 and 20–55% CO conversion. Addition of 1% of Cd or In enhanced the reduction degree of 15%Co/Al2O3 by ~20%, while addition of 1% Sn slightly hindered it. All three additives adversely impacted Co dispersion by 22–32% by increasing apparent Co cluster size based on the H2-chemisorption measurements. However, the decreased Co active site density resulting from the additives did not result in a corresponding activity loss; instead, the additives decreased the activity of the Co catalysts to a much greater extent than expected, i.e., 82–93%. The additional detrimental effect on catalyst activity likely indicates that the Cd, In and Sn additives migrated to and covered active sites during reaction and/or provided an electronic effect. XANES results showed that oxides of the additives were present during the reaction, but that a fraction of metal was also likely present based on the TPR and reaction testing results. This is in contrast to typical promoters that become metallic at or below ~350 °C, such as noble metal promoters (e.g., Pt, Ru) and Group 11 promoters (e.g., Ag, Au) on Co catalysts in earlier studies. In the current work, all three additives remarkably increased CH4 and CO2 selectivities and decreased C5+ selectivity, with the Sn and In additives having a greater effect. Interestingly, the Cd, In, or Sn additives were found to influence hydrogenation and isomerization activities. At a similar conversion level (i.e., in the range of 40–50%), the additives significantly increased 2-C4 olefin content from 3.8 to 10.6% and n-C4 paraffin from 50 to 61% accompanied by decreases in 1-C4 olefin content from 48 to 30%. The Sn contributed the greatest impact on the secondary reactions of 1-olefins, followed by the In and Cd. NH3-TPD results suggest enhanced acid sites on cobalt catalysts resulting from the additives, which likely explains the change in selectivities for the different catalysts. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
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Open AccessArticle
Simultaneous Optimal Production of Flavonol Aglycones and Degalloylated Catechins from Green Tea Using a Multi-Function Food-Grade Enzyme
Catalysts 2019, 9(10), 861; https://doi.org/10.3390/catal9100861 - 16 Oct 2019
Viewed by 178
Abstract
(1) Background: Green tea (GT) contains well-known phytochemical compounds; namely, it is rich in flavan-3-ols (catechins) and flavonols comprising all glycoside forms. These compounds in GT might show better biological activities after a feasible enzymatic process, and the process on an industrial scale [...] Read more.
(1) Background: Green tea (GT) contains well-known phytochemical compounds; namely, it is rich in flavan-3-ols (catechins) and flavonols comprising all glycoside forms. These compounds in GT might show better biological activities after a feasible enzymatic process, and the process on an industrial scale should consider enzyme specificity and cost-effectiveness. (2) Methods: In this study, we evaluated the most effective method for the enzymatic conversion of flavonoids from GT extract. One enzyme derived from Aspergillus niger (molecular weight 80–90 kDa) was ultimately selected, showing two distinct but simultaneous activities: intense glycoside hydrolase activity via deglycosylation and weak tannin acyl hydrolase activity via degalloylation. (3) Results: The optimum conditions for producing flavonol aglycones were pH 4.0 and 50 °C. Myricetin glycosides were cleaved 3.7–7.0 times faster than kaempferol glycosides. Flavonol aglycones were produced effectively by both enzymatic and hydrochloride treatment in a time-course reaction. Enzymatic treatment retained 80% (w/w) catechins, whereas 70% (w/w) of catechins disappeared by hydrochloride treatment. (4) Conclusions: This enzymatic process offers an effective method of conditionally producing flavonol aglycones and de-galloylated catechins from conversion of food-grade enzyme. Full article
(This article belongs to the Special Issue Biocatalytic Process Optimization)
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Open AccessArticle
Galvanic Exchange as a Novel Method for Carbon Nitride Supported CoAg Catalyst Synthesis for Oxygen Reduction and Carbon Dioxide Conversion
Catalysts 2019, 9(10), 860; https://doi.org/10.3390/catal9100860 - 16 Oct 2019
Viewed by 121
Abstract
A bimetallic alloy of CoAg nanoparticles (NPs) on a carbon nitride (CN) surface was synthesized using a galvanic exchange process for the oxygen reduction reaction (ORR) and carbon dioxide electrocatalytic conversion. The reduction potential of cobalt is ([Co2+(aq) + 2e [...] Read more.
A bimetallic alloy of CoAg nanoparticles (NPs) on a carbon nitride (CN) surface was synthesized using a galvanic exchange process for the oxygen reduction reaction (ORR) and carbon dioxide electrocatalytic conversion. The reduction potential of cobalt is ([Co2+(aq) + 2e → Co(s)], −0.28 eV) is smaller than that of Ag ([Ag+(aq) + e → Ag(s)], 0.80 eV), which makes Co(0) to be easily replaceable by Ag+ ions. Initially, Co NPs (nanoparticles) were synthesized on a CN surface via adsorbing the Co2+ precursor on the surface of CN and subsequently reducing them with NaBH4 to obtain Co/CN NP. The Co NPs on the surface of CN were then subjected to galvanic exchange, where the sacrificial Co atoms were replaced by Ag atoms. As the process takes place on a solid surface, only the partial replacement of Co by Ag was possible generating CoAg/CN NPs. Synthesized CoAg/CN bimetallic alloy were characterized using different techniques such as powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDS) to confirm the product. Both the catalysts, Co/CN and CoAg/CN, were evaluated for oxygen reduction reaction in 1M KOH solution and carbon dioxide conversion in 0.5 M KHCO3. In the case of ORR, the CoAg/CN was found to be an efficient electrocatalyst with the onset potential of 0.93 V, which is comparable to commercially available Pt/C having Eonset at 0.91 V. In the electrocatalytic conversion of CO2, the CoAg/CN showed better performance than Co/CN. The cathodic current decreased dramatically below −0.9V versus Ag/AgCl indicating the high conversion of CO2. Full article
(This article belongs to the Special Issue Synthesis and Applications of Nano-Catalytic Materials)
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Open AccessArticle
Heterogeneous Catalytic Performance and Stability of Iron-Loaded ZSM-5, Zeolite-A, and Silica for Phenol Degradation: A Microscopic and Spectroscopic Approach
Catalysts 2019, 9(10), 859; https://doi.org/10.3390/catal9100859 - 15 Oct 2019
Viewed by 181
Abstract
In this study, we compared the performances of three iron-containing crystalline and amorphous catalysts, that is, Fe-Zeo-A, Fe-ZSM-5, and Fe-silica, respectively, for the degradation of phenol in an aqueous solution. Catalytic activity for the degradation of phenol was assessed by heterogeneous photolysis, Fenton, [...] Read more.
In this study, we compared the performances of three iron-containing crystalline and amorphous catalysts, that is, Fe-Zeo-A, Fe-ZSM-5, and Fe-silica, respectively, for the degradation of phenol in an aqueous solution. Catalytic activity for the degradation of phenol was assessed by heterogeneous photolysis, Fenton, and photo-Fenton oxidation. All catalysts exhibited higher activity in the photo-Fenton process. In addition, the catalyst stability was evaluated by the estimation of the iron loss and structural variations after the oxidation processes. Results revealed that Fe-silica and Fe-ZSM-5 exhibit higher catalytic activity (~100% phenol removal), while only 64% of phenol removal over Fe-Zeo-A was observed. Moreover, among all catalysts, Fe-ZSM-5 exhibited higher stability with low iron leaching, attributed to the uniform distribution of bonded Fe in the crystalline framework and narrow channels. On the contrary, amorphous Fe-silica exhibited higher iron leaching due to the presence of isolated iron species in the structure, leading to the partial involvement of a homogeneous reaction during the degradation of phenol. The structural stability of Fe-based catalysts was examined using microscopic and spectroscopic techniques. Full article
(This article belongs to the Section Environmental Catalysis)
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Open AccessArticle
Fermentative Conversion of Two-Step Pre-Treated Lignocellulosic Biomass to Hydrogen
Catalysts 2019, 9(10), 858; https://doi.org/10.3390/catal9100858 - 15 Oct 2019
Viewed by 137
Abstract
Fermentative hydrogen production via dark fermentation with the application of lignocellulosic biomass requires a multistep pre-treatment procedure, due to the complexed structure of the raw material. Hence, the comparison of the hydrogen productivity potential of different lignocellulosic materials (LCMs) in relation to the [...] Read more.
Fermentative hydrogen production via dark fermentation with the application of lignocellulosic biomass requires a multistep pre-treatment procedure, due to the complexed structure of the raw material. Hence, the comparison of the hydrogen productivity potential of different lignocellulosic materials (LCMs) in relation to the lignocellulosic biomass composition is often considered as an interesting field of research. In this study, several types of biomass, representing woods, cereals and grass were processed by means of mechanical pre-treatment and alkaline and enzymatic hydrolysis. Hydrolysates were used in fermentative hydrogen production via dark fermentation process with Enterobacter aerogenes (model organism). The differences in the hydrogen productivity regarding different materials hydrolysates were analyzed using chemometric methods with respect to a wide dataset collected throughout this study. Hydrogen formation, as expected, was positively correlated with glucose concentration and total reducing sugars amount (YTRS) in enzymatic hydrolysates of LCMs, and negatively correlated with concentrations of enzymatic inhibitors i.e., HMF, furfural and total phenolic compounds in alkaline-hydrolysates LCMs, respectively. Interestingly, high hydrogen productivity was positively correlated with lignin content in raw LCMs and smaller mass loss of LCM after pre-treatment step. Besides results of chemometric analysis, the presented data analysis seems to confirm that the structure and chemical composition of lignin and hemicellulose present in the lignocellulosic material is more important to design the process of its bioconversion than the proportion between the cellulose, hemicellulose and lignin content in this material. For analyzed LCMs we found remarkable higher potential of hydrogen production via bioconversion process of woods i.e., beech (24.01 mL H2/g biomass), energetic poplar (23.41 mL H2/g biomass) or energetic willow (25.44 mL H2/g biomass) than for cereals i.e., triticale (17.82 mL H2/g biomass) and corn (14.37 mL H2/g biomass) or for meadow grass (7.22 mL H2/g biomass). Full article
(This article belongs to the Special Issue Catalysis in Lignocellulosic Biomass Conversion)
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Open AccessFeature PaperArticle
Fischer–Tropsch Synthesis: Computational Sensitivity Modeling for Series of Cobalt Catalysts
Catalysts 2019, 9(10), 857; https://doi.org/10.3390/catal9100857 - 15 Oct 2019
Viewed by 143
Abstract
Nearly a century ago, Fischer and Tropsch discovered a means of synthesizing organic compounds ranging from C1 to C70 by reacting carbon monoxide and hydrogen on a catalyst. Fischer–Tropsch synthesis (FTS) is now known as a pseudo-polymerization process taking a mixture [...] Read more.
Nearly a century ago, Fischer and Tropsch discovered a means of synthesizing organic compounds ranging from C1 to C70 by reacting carbon monoxide and hydrogen on a catalyst. Fischer–Tropsch synthesis (FTS) is now known as a pseudo-polymerization process taking a mixture of CO as H2 (also known as syngas) to produce a vast array of hydrocarbons, along with various small amounts of oxygenated materials. Despite the decades spent studying this process, it is still considered a black-box reaction with a mechanism that is still under debate. This investigation sought to improve our understanding by taking data from a series of experimental Fischer–Tropsch synthesis runs to build a computational model. The experimental runs were completed in an isothermal continuous stirred-tank reactor, allowing for comparison across a series of completed catalyst tests. Similar catalytic recipes were chosen so that conditional comparisons of pressure, temperature, SV, and CO/H2 could be made. Further, results from the output of the reactor that included the deviations in product selectivity, especially that of methane and CO2, were considered. Cobalt was chosen for these exams for its industrial relevance and respectfully clean process as it does not intrinsically undergo the water–gas shift (WGS). The primary focus of this manuscript was to compare runs using cobalt-based catalysts that varied in two oxide catalyst supports. The results were obtained by creating two differential equations, one for H2 and one for CO, in terms of products or groups of products. These were analyzed using sensitivity analysis (SA) to determine the products or groups that impact the model the most. The results revealed a significant difference in sensitivity between the two catalyst–support combinations. When the model equations for H2 and CO were split, the results indicated that the CO equation was significantly more sensitive to CO2 production than the H2 equation. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
Open AccessArticle
Development of Nickel-BTC-MOF-Derived Nanocomposites with rGO Towards Electrocatalytic Oxidation of Methanol and Its Product Analysis
Catalysts 2019, 9(10), 856; https://doi.org/10.3390/catal9100856 - 14 Oct 2019
Viewed by 186
Abstract
In this study, electrochemical oxidation of methanol to formic acid using the economical and highly active catalytic Nickel Benzene tricarboxylic acid metal organic framework (Ni-BTC-MOF) and reduced graphene oxide (rGO) nanocomposites modified glassy carbon electrode GCE in alkaline media, which was examined via [...] Read more.
In this study, electrochemical oxidation of methanol to formic acid using the economical and highly active catalytic Nickel Benzene tricarboxylic acid metal organic framework (Ni-BTC-MOF) and reduced graphene oxide (rGO) nanocomposites modified glassy carbon electrode GCE in alkaline media, which was examined via cyclic voltammetry technique. Nickel based MOF and rGO nanocomposites were prepared by solvothermal approach, followed by morphological and structural characterization of prepared samples through X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and energy dispersive X-ray (EDX) analysis. The electrochemical testing of synthesized materials represents the effect of the sequential increase in rGO concentration on electrocatalytic activity. The Ni-BTC/4 wt % rGO composite with a pronounced current density of 200.22 mA/cm2 at 0.69 V versus Hg/HgO electrode at 50 mV/s was found to be a potential candidate for methanol oxidation in Direct Methanol Fuel Cell (DMFC) applications. Product analysis was carried out through Gas Chromatography (GC) and Nuclear Magnetic Resonance (NMR) spectroscopy, which confirmed the formation of formic acid during the oxidation process, with approximately 62% yield. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessEditorial
Nanomaterials for Environmental Purification and Energy Conversion
Catalysts 2019, 9(10), 855; https://doi.org/10.3390/catal9100855 - 14 Oct 2019
Viewed by 140
Abstract
Nanomaterials, engineered structures of which a single unit is sized (in at least one dimension) between 1 to 100 nm, are probably the fastest growing market in the world [...] Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle
Optimizing the Aromatic Product Distribution from Catalytic Fast Pyrolysis of Biomass Using Hydrothermally Synthesized Ga-MFI Zeolites
Catalysts 2019, 9(10), 854; https://doi.org/10.3390/catal9100854 - 13 Oct 2019
Viewed by 255
Abstract
A series of gallium-containing MFI (Ga-MFI) zeolites with varying Ga2O3/Al2O3 ratios were synthesized using hydrothermal synthesis and tested as catalyst in catalytic fast pyrolysis (CFP) of beech wood for aromatic production. The results show that the [...] Read more.
A series of gallium-containing MFI (Ga-MFI) zeolites with varying Ga2O3/Al2O3 ratios were synthesized using hydrothermal synthesis and tested as catalyst in catalytic fast pyrolysis (CFP) of beech wood for aromatic production. The results show that the incorporation of Ga slightly reduced the effective pore size of Ga-MFI zeolites compared to conventional HZSM-5 zeolites. Therefore, the Ga-MFI zeolites increased the aromatic selectivity for smaller aromatics such as benzene, toluene, and p-xylene and decreased the aromatic selectivity for bulkier ones such as m-xylene, o-xylene, and polyaromatics in CFP of beech wood relative to HSZM-5. In particular, the yield and selectivity of p-xylene, the most desired product from CFP of biomass, increased considerably from 1.64 C% and 33.3% for conventional HZSM-5 to 2.98–3.34 C% and 72.1–79.6% for the synthesized Ga-MFI zeolites. These results suggest that slightly reducing the pore size of MFI zeolite by Ga incorporation has a beneficial effect on optimizing the aromatic selectivity toward more valuable monoaromatic products, especially p-xylene, during CFP of biomass. Full article
(This article belongs to the Special Issue Catalytic Fast Pyrolysis)
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Open AccessArticle
Plasma-Assisted Selective Catalytic Reduction for Low-Temperature Removal of NOx and Soot Simulant
Catalysts 2019, 9(10), 853; https://doi.org/10.3390/catal9100853 - 13 Oct 2019
Viewed by 204
Abstract
The challenge that needs to be overcome regarding the removal of nitrogen oxides (NOx) and soot from exhaust gases is the low activity of the selective catalytic reduction of NOx at temperatures fluctuating from 150 to 350 °C. The primary [...] Read more.
The challenge that needs to be overcome regarding the removal of nitrogen oxides (NOx) and soot from exhaust gases is the low activity of the selective catalytic reduction of NOx at temperatures fluctuating from 150 to 350 °C. The primary goal of this work was to enhance the conversion of NOx and soot simulant by employing a Ag/α-Al2O3 catalyst coupled with dielectric barrier discharge plasma. The results demonstrated that the use of a plasma-catalyst process at low operating temperatures increased the removal of both NOx and naphthalene (soot simulant). Moreover, the soot simulant functioned as a reducing agent for NOx removal, but with low NOx conversion. The high efficiency of NOx removal required the addition of hydrocarbon fuel. In summary, the combined use of the catalyst and plasma (specific input energy, SIE ≥ 60 J/L) solved the poor removal of NOx and soot at low operating temperatures or during temperature fluctuations in the range of 150–350 °C. Specifically, highly efficient naphthalene removal was achieved with low-temperature adsorption on the catalyst followed by the complete decomposition by the plasma-catalyst at 350 °C and SIE of 90 J/L. Full article
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Open AccessArticle
Single and Dual Metal Oxides as Promising Supports for Carbon Monoxide Removal from an Actual Syngas: The Crucial Role of Support on the Selectivity of the Au–Cu System
Catalysts 2019, 9(10), 852; https://doi.org/10.3390/catal9100852 - 13 Oct 2019
Viewed by 257
Abstract
A catalytic screening was performed to determine the effect of the support on the performance of an Au–Cu based system for the removal of CO from an actual syngas. First, a syngas was obtained from reforming of ethanol. Then, the reformer outlet was [...] Read more.
A catalytic screening was performed to determine the effect of the support on the performance of an Au–Cu based system for the removal of CO from an actual syngas. First, a syngas was obtained from reforming of ethanol. Then, the reformer outlet was connected to a second reactor, where Au–Cu catalysts supported on several single and dual metal oxides (i.e., CeO2, SiO2, ZrO2, Al2O3, La2O3, Fe2O3, CeO2-SiO2, CeO2-ZrO2, and CeO2-Al2O3) were evaluated. AuCu/CeO2 was the most active catalyst due to an elevated oxygen mobility over the surface, promoting CO2 formation from adsorption of C–O* and OH intermediates on Au0 and CuO species. However, its lower capacity to release the surface oxygen contributes to the generation of stable carbon deposits, which lead to its rapid deactivation. On the other hand, AuCu/CeO2-SiO2 was more stable due to its high surface area and lower formation of formate and carbonate intermediates, mitigating carbon deposits. Therefore, use of dual supports could be a promising strategy to overcome the low stability of AuCu/CeO2. The results of this research are a contribution to integrated production and purification of H2 in a compact system. Full article
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Open AccessArticle
Application of Phase Transfer Catalysis in the Esterification of Organic Acids: The Primary Products from Ring Hydrocarbon Oxidation Processes
Catalysts 2019, 9(10), 851; https://doi.org/10.3390/catal9100851 - 13 Oct 2019
Viewed by 234
Abstract
For enhancing the cetane number (CN) of diesel fraction, the selective oxidative ring opening method was applied to upgrade ring hydrocarbons. Organic acids, one of the main products from this oxidative reaction, being esterified by the phase transfer catalysis (PTC) approach were studied. [...] Read more.
For enhancing the cetane number (CN) of diesel fraction, the selective oxidative ring opening method was applied to upgrade ring hydrocarbons. Organic acids, one of the main products from this oxidative reaction, being esterified by the phase transfer catalysis (PTC) approach were studied. Adipic acid, benzoic acid, and phthalic acid were used as model compounds. Reaction time, reaction temperature, the amount of water, and the amount of catalyst in the esterification process were investigated and optimized using orthogonal experimental design method. The kinetics of esterification process was then conducted under the optimal condition. The types of catalysts and organic acids, the amount of catalyst and water were also investigated. The PTC esterification was one rate controlling reaction on the interface between the aqueous phase and the oil phase. Hydrophobicity is a key factor for converting benzoic acid, adipic acid, and phthalic acid to the corresponding esters. It was found that around 5–8% water is the optimal quantity for the given reaction system. Two cases of esterification processes of PTC were proposed. Full article
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Open AccessArticle
Enzymatic Production of Biodiesel Using Immobilized Lipase on Core-Shell Structured Fe3O4@MIL-100(Fe) Composites
Catalysts 2019, 9(10), 850; https://doi.org/10.3390/catal9100850 - 12 Oct 2019
Viewed by 241
Abstract
In this research, core–shell structured Fe3O4@MIL-100(Fe) composites were prepared by coating Fe3O4 magnetite with porous MIL-100(Fe) metal-organic framework (MOF) material, which were then utilized as magnetic supports for the covalent immobilization of the lipase from Candida rugosa [...] Read more.
In this research, core–shell structured Fe3O4@MIL-100(Fe) composites were prepared by coating Fe3O4 magnetite with porous MIL-100(Fe) metal-organic framework (MOF) material, which were then utilized as magnetic supports for the covalent immobilization of the lipase from Candida rugosa through amide linkages. By using the carbodiimide/hydroxysulfosuccinimide (EDC/NHS) activation strategy, the lipase immobilization efficiency could reach 83.1%, with an activity recovery of 63.5%. The magnetic Fe3O4@MIL-100(Fe) composite and immobilized lipase were characterized by several techniques. The characterization results showed that the Fe3O4 core was coated with MIL-100(Fe) shell with the formation of perfect core–shell structured composites, and moreover, the lipase was covalently tethered on the magnetic carrier. The immobilized lipase displayed a strong magnetic response and could be facilely separated by an external magnetic field. With this magnetic biocatalyst, the maximum biodiesel conversion attained 92.3% at a methanol/oil molar ratio of 4:1, with a three-step methanol addition manner, and a reaction temperature of 40 °C. Moreover, the biocatalyst prepared in the present study was recycled easily by magnetic separation without significant mass loss, and displayed 83.6% of its initial activity as it was reused for five runs, thus allowing its potential application for the cleaner production of biodiesel. Full article
(This article belongs to the Section Biocatalysis)
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Open AccessArticle
Performance of Catalytic Fast Pyrolysis using a γ-Al2O3 Catalyst with Compound Modification of ZrO2 and CeO2
Catalysts 2019, 9(10), 849; https://doi.org/10.3390/catal9100849 - 12 Oct 2019
Viewed by 149
Abstract
To investigate the catalytic pyrolysis performance of complex metal oxide catalysts for biomass, γ-Al2O3 was prepared through the precipitation method, and then ZrO2 and γ-Al2O3 were blended in the proportion of 2:8 using the co-precipitation method. [...] Read more.
To investigate the catalytic pyrolysis performance of complex metal oxide catalysts for biomass, γ-Al2O3 was prepared through the precipitation method, and then ZrO2 and γ-Al2O3 were blended in the proportion of 2:8 using the co-precipitation method. Next, CeO2 was loaded on the surface of the catalyst for further modification. The three catalysts, A, ZA and CZA, were obtained. The specific surface and acidity of the catalysts were characterized by nitrogen adsorption–desorption and NH3-Temperature Programmed Desorption (NH3-TPD) respectively. The catalytic pyrolysis performance of catalysts for bamboo residues was investigated by Pyrolysis gas chromatography mass spectrometry (Py-GC/MS). Chromatograms were analyzed for identification of the pyrolysis products and the relative amounts of each component were calculated. Experimental results indicated that catalyst A had a good catalytic activity for the fast pyrolysis of bamboo residues. The addition of ZrO2 and CeO2 could continuously enhance the acidity of the catalyst and further promote the pyrolysis of macromolecular compounds and deoxidation of oxygen-containing compounds. Finally, catalyst CZA, obtained by compound modification, could not only dramatically reduce the relative content of phenol, acid and aldehyde and other oxygen-containing compounds, but also achieved the maximum hydrocarbon yield of 23.38%. The catalytic performance of catalyst CZA improved significantly compared with catalyst A. Full article
Open AccessArticle
Indium Tin-Oxide Wrapped 3D rGO and TiO2 Composites: Development, Characterization, and Enhancing Photocatalytic Activity for Methylene Blue
Catalysts 2019, 9(10), 848; https://doi.org/10.3390/catal9100848 - 12 Oct 2019
Viewed by 138
Abstract
A hybrid material of indium tin-oxide (ITO) wrapped titanium dioxide and reduced graphene oxide (ITO-rGO and TiO2) was prepared using a facile hydrothermal technique. TiO2 nanorods were in situ grown on the surface of rGO (rGO and TiO2), [...] Read more.
A hybrid material of indium tin-oxide (ITO) wrapped titanium dioxide and reduced graphene oxide (ITO-rGO and TiO2) was prepared using a facile hydrothermal technique. TiO2 nanorods were in situ grown on the surface of rGO (rGO and TiO2), and which was then assembled onto ITO substrate layer by layer with formation of a 3D structure. ITO-rGO and TiO2 exhibit low charge transfer resistance at the electrode-electrolyte interface and have good photoresponsive ability. Methylene blue (MB) can be effectively adsorbed and enriched onto ITO-rGO and TiO2 surface. The adsorption kinetics and thermodynamics of ITO-rGO and TiO2 were evaluated, showing that the exothermic and entropy-driven reaction were the main thermodynamic processes, and the Langmuir isotherm was the ideal model for adsorption fitting. Meanwhile, ITO greatly improved degradation of rGO and TiO2 because electrons can be collected by ITO before recombination and MB can easily enter into the 3D structure of rGO and TiO2. The highest photodegradation rate of MB reached 93.40% for ITO-rGO and TiO2 at pH 9. Additionally, ITO-rGO and TiO2 successfully solved the problems of being difficult to recycle and causing secondary pollution of traditional TiO2 catalysts. Therefore, ITO-rGO and TiO2 may be a potential photocatalyst for degrading organic pollutants in water. Full article
(This article belongs to the Special Issue Hybrid Metal/Metal Oxide-Carbon Nanomaterials Catalysts)
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Open AccessArticle
Oxidized Palladium Supported on Ceria Nanorods for Catalytic Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde in Protic Solvents
Catalysts 2019, 9(10), 847; https://doi.org/10.3390/catal9100847 - 12 Oct 2019
Viewed by 157
Abstract
In the present study, the catalytic activity of palladium oxide (PdOx) supported on ceria nanorods (CeO2-NR) for aerobic selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) was evaluated. The CeO2-NR was synthesized hydrothermally and the Pd(NO [...] Read more.
In the present study, the catalytic activity of palladium oxide (PdOx) supported on ceria nanorods (CeO2-NR) for aerobic selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) was evaluated. The CeO2-NR was synthesized hydrothermally and the Pd(NO3)2 was deposited by a wet impregnation method, followed by calcination to acquire PdOx/CeO2-NR. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). In addition, the TPR-reduced PdOx/CeO2-NR (PdOx/CeO2-NR-Red) was studied by XRD, BET, and XPS. Characterizations showed the formation of CeO2-NR with (111) exposed plane and relatively high BET surface area. PdOx (x > 1) was detected to be the major oxide species on the PdOx/CeO2-NR. The activities of the catalysts in BnOH oxidation were evaluated using air, as an environmentally friendly oxidant, and various solvents. Effects of temperature, solvent nature and palladium oxidation state were investigated. The PdOx/CeO2-NR showed remarkable activity when protic solvents were utilized. The best result was achieved using PdOx/CeO2-NR and boiling ethanol as solvent, leading to 93% BnOH conversion and 96% selectivity toward PhCHO. A mechanistic hypothesis for BnOH oxidation with PdOx/CeO2-NR in ethanol is presented. Full article
(This article belongs to the Section Nanostructured Catalysts)
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Open AccessArticle
Effect of a Substituent in Cyclopentadienyl Ligand on Iridium-Catalyzed Acceptorless Dehydrogenation of Alcohols and 2-Methyl-1,2,3,4-tetrahydroquinoline
Catalysts 2019, 9(10), 846; https://doi.org/10.3390/catal9100846 - 12 Oct 2019
Viewed by 175
Abstract
New iridium(III)-bipyridonate complexes having cyclopentadienyl ligands with a series of alkyl substituents were synthesized for the purpose of tuning the catalytic activity for acceptorless dehydrogenation reactions. A comparison of the catalytic activity was performed for the reaction of alcoholic substrates such as 1-phenylethanol, [...] Read more.
New iridium(III)-bipyridonate complexes having cyclopentadienyl ligands with a series of alkyl substituents were synthesized for the purpose of tuning the catalytic activity for acceptorless dehydrogenation reactions. A comparison of the catalytic activity was performed for the reaction of alcoholic substrates such as 1-phenylethanol, 2-octanol, and benzyl alcohol. The 1-t-butyl-2,3,4,5-tetramethylcyclopentadienyl iridium complex exhibited the best performance, which surpassed that of the 1,2,3,4,5-pentamethylcyclopentadienyl (Cp*) iridium catalyst in the dehydrogenation reaction of alcohols. The catalytic activity in the dehydrogenation of 2-methyl-1,2,3,4-tetrahydroquinoline was also examined. The highest efficiency was obtained in the reaction catalyzed by the same t-butyl-substituted cyclopentadienyl iridium complex. Full article
(This article belongs to the Special Issue Transition-Metal-Catalyzed Reactions in Organic Synthesis)
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Open AccessArticle
Conversion of 5-Methyl-3-Heptanone to C8 Alkenes and Alkane over Bifunctional Catalysts
Catalysts 2019, 9(10), 845; https://doi.org/10.3390/catal9100845 - 12 Oct 2019
Viewed by 179
Abstract
A one-step catalytic process was used to catalyze the hydrodeoxygenation of 5-methyl-3-heptanone (C8 ketone) to a mixture of 5-methyl-3-heptene, 5-methyl-2-heptene (C8 alkenes), and 3-methyl heptane (C8 alkane). High conversion of C8 ketone to the desired products was achieved over [...] Read more.
A one-step catalytic process was used to catalyze the hydrodeoxygenation of 5-methyl-3-heptanone (C8 ketone) to a mixture of 5-methyl-3-heptene, 5-methyl-2-heptene (C8 alkenes), and 3-methyl heptane (C8 alkane). High conversion of C8 ketone to the desired products was achieved over a single bed of a supported catalyst (bifunctional heterogeneous catalyst) consisting of one transition metal (copper (Cu) or platinum (Pt)) loaded on alumina (Al2O3) under mild operating conditions (reaction temperatures were varied between 180 °C to 260 °C, and the pressure was 1 atm). The C8 ketone was hydrogenated to 5-methyl-3-heptanol (C8 alcohol) over metal sites, followed by dehydration of the latter on acid sites on the support to obtain a mixture of C8 alkenes. These C8 alkenes can be further hydrogenated on metal sites to make a C8 alkane. The results showed that the main products over copper loaded on alumina (20 wt% Cu–Al2O3) were a mixture of C8 alkenes and C8 alkane in different amounts depending on the operating conditions (the highest selectivity for C8 alkenes (~82%) was obtained at 220 °C and a H2/C8 ketone molar ratio of 2). However, over platinum supported on alumina (1 wt% Pt–Al2O3), the major product was a C8 alkane with a selectivity up to 97% and a conversion of 99.9% at different temperatures and all H2/C8 ketone ratios. Full article
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