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Catalysts, Volume 8, Issue 4 (April 2018)

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Cover Story (view full-size image) Under Sonogashira cross-coupling conditions the base (triethylamine molecule) as a circular saw [...] Read more.
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Open AccessArticle Conversion of South African Coal Fly Ash into High-Purity ZSM-5 Zeolite without Additional Source of Silica or Alumina and Its Application as a Methanol-to-Olefins Catalyst
Catalysts 2018, 8(4), 124; https://doi.org/10.3390/catal8040124
Received: 19 October 2017 / Revised: 10 November 2017 / Accepted: 14 November 2017 / Published: 21 March 2018
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Abstract
Characteristics of ZSM-5 synthesized from H2SO4-treated coal fly ash and fused coal fly ash extracts are compared in this study. In the synthesis process, fused coal fly ash extract (without an additional silica source) was used in the synthesis
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Characteristics of ZSM-5 synthesized from H2SO4-treated coal fly ash and fused coal fly ash extracts are compared in this study. In the synthesis process, fused coal fly ash extract (without an additional silica source) was used in the synthesis of ZSM-5. The effect of the structure-directing agent (tetrapropylammonium bromide, 1,6-hexanediamine or 1-propylamine) on the properties and methanol-to-olefins (MTO) effectiveness of the fly ash-based ZSM-5 was also investigated. A pure ZSM-5 synthesized from the fused coal fly ash extract led to a methanol conversion higher than 90% after 5 h on stream. The template 1,6-hexanediamine led to the synthesis of the most stable fly ash-based catalyst keeping a 44% methanol conversion after 24 h on stream. Full article
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Open AccessArticle Active Component Migration and Catalytic Properties of Nitrogen Modified Composite Catalytic Materials
Catalysts 2018, 8(4), 125; https://doi.org/10.3390/catal8040125
Received: 2 February 2018 / Revised: 7 March 2018 / Accepted: 16 March 2018 / Published: 21 March 2018
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Abstract
During the catalytic combustion reaction of methane, the migration of the active species on surface facilitates the catalytic reaction, and the element doping can improve the redox performance of the catalyst. Nitrogen-modified perovskite type composite catalysts were prepared by hydrothermal method and then
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During the catalytic combustion reaction of methane, the migration of the active species on surface facilitates the catalytic reaction, and the element doping can improve the redox performance of the catalyst. Nitrogen-modified perovskite type composite catalysts were prepared by hydrothermal method and then characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), temperature-programmed reductions (TPR), and X-ray photoelectron spectra (XPS). The results revealed that nitrogen sources (urea, biuret, melamine, carbohydrazide, and semicarbazide hydrochloride) and nitrogen source addition changed the catalytic performance in physical and chemical properties, the migration of reactive species and the catalytic performance. When the addition amount of semicarbazide hydrochloride was three times that of LaCoO3, the composite catalysts had high Co3+/Co2+ (1.39) and Oads/Olat (15.18) and showed the best catalytic performance: the temperatures that are required for achieving methane conversion of 50% and 90% were 277 and 360 °C, which are more effective than noble metal oxides. Moreover, the in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) were applied to elucidate the efficient for CH4 removal and also can further explain the surface reaction mechanism of the composite catalyst during the methane catalytic combustion. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessArticle Vanadium Supported on Alumina and/or Zirconia Catalysts for the Selective Transformation of Ethane and Methanol
Catalysts 2018, 8(4), 126; https://doi.org/10.3390/catal8040126
Received: 2 February 2018 / Revised: 13 March 2018 / Accepted: 19 March 2018 / Published: 22 March 2018
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Abstract
Vanadium supported on pure (Al2O3, ZrO2) or mixed zirconia-alumina (with Al/(Al + Zr) ratio of 0.75 or 0.25) catalysts have been prepared by wet impregnation, using homemade prepared supports. The catalysts have been characterized and tested in
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Vanadium supported on pure (Al2O3, ZrO2) or mixed zirconia-alumina (with Al/(Al + Zr) ratio of 0.75 or 0.25) catalysts have been prepared by wet impregnation, using homemade prepared supports. The catalysts have been characterized and tested in the oxidative dehydrogenation (ODH) of ethane and in the methanol aerobic transformation. The catalytic performance strongly depends on the nature of the metal oxide support. Thus, activity decreases in the order: VOx/ZrO2 > VOx/(Al,Zr-oxides) > VOx/Al2O3. On the other hand, at low and medium ethane conversions, the selectivity to ethylene presents an opposite trend: VOx/Al2O3 > VOx/(Al,Zr-oxides) > VOx/ZrO2. The different selectivity to ethylene at high conversion is due to the lower/higher initial ethylene formation and to the extent of the ethylene decomposition. Interestingly, VOx/(Al,Zr-oxides) with low Zr-loading present the lowest ethylene decomposition. The catalytic results obtained mainly depend on the nature of the supports whereas the role of the dispersion of vanadium species is unclear. In methanol oxidation, the catalysts tested present similar catalytic activity regardless of the support (Al2O3, ZrO2 or mixed Al2O3-ZrO2) but strong differences in the selectivity to the reaction products. Thus, dimethyl ether was mainly observed on alumina-supported vanadium oxide catalysts (which is associated to the presence of acidic sites on the surface of the catalyst, as determined by TPD-NH3). Formaldehyde was the main reaction product on catalysts supported on Zr-containing oxides (which can be related to a low presence of acid sites). In this article, the importance of the presence of acid sites in ethane ODH, which can be estimated using the methanol transformation reaction, is also discussed. Full article
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Open AccessArticle Liquid-Phase Hydrodeoxygenation of Guaiacol over Mo2C Supported on Commercial CNF. Effects of Operating Conditions on Conversion and Product Selectivity
Catalysts 2018, 8(4), 127; https://doi.org/10.3390/catal8040127
Received: 26 February 2018 / Revised: 20 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
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Abstract
In this work, a Mo2C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the
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In this work, a Mo2C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the conversion of guaiacol and products selectivity were studied. The major reaction products were cresol and phenol, followed by xylenols and toluene. The use of more severe operating conditions during the HDO of guaiacol caused a diversification in the reaction pathways, and consequently in the selectivity to products. The formation of phenol may have occurred by demethylation of guaiacol, followed by dehydroxylation of catechol, together with other reaction pathways, including direct guaiacol demethoxylation, and demethylation of cresols. X-ray diffraction (XRD) analysis of spent catalysts did not reveal any significant changes as compared to the fresh catalyst. Full article
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Open AccessArticle Investigation of Catalytic Ozonation of Recalcitrant Organic Chemicals in Aqueous Solution over Various ZSM-5 Zeolites
Catalysts 2018, 8(4), 128; https://doi.org/10.3390/catal8040128
Received: 31 January 2018 / Revised: 9 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
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Abstract
Catalytic ozonation processes (COPs) are an emerging technology for wastewater treatments. NaZSM-5 zeolites in three different SiO2/Al2O3 ratios (31, 45, and 120) and their metallic oxides loaded samples were compared for COP of nitrobenzene solution. NaZSM-5(120) showed high
[...] Read more.
Catalytic ozonation processes (COPs) are an emerging technology for wastewater treatments. NaZSM-5 zeolites in three different SiO2/Al2O3 ratios (31, 45, and 120) and their metallic oxides loaded samples were compared for COP of nitrobenzene solution. NaZSM-5(120) showed high total organic carbon (TOC) removals (70.2–74.0%) by adsorption relative to NaZSM-5(45) (0.4–0.6%) at various initial pH conditions. NaZSM-5(31) was obtained by NaOH treatment of NaZSM-5(45) and displayed 20.9–23.8% of TOC removals by adsorption. In COPs, the different ZSM-5 zeolites exhibited various TOC removals and different reaction pathways. COP-NaZSM-5(120) showed high TOC removals compared to COP-NaZSM-5(45) and COP-NaZSM-5(31). The repeated uses of zeolites in COPs were performed to understand the reaction pathways and contribution of adsorption versus ozonation (i.e., catalytic oxidation and/or direct ozonation). Both adsorption and direct ozonation in COP-NaZSM-5(120) contributed TOC removal for the first use, whereas direct ozonation and •OH mediated oxidation dominated the process for eight repeated uses. Direct ozonation and •OH-mediated oxidation controlled the COP-NaZSM-5(45) process for the first and eight repeated uses. Adsorption and direct ozonation governed the COP-NaZSM-5(31) process for the first use, whereas the direct ozonation dominated it for eight repeated uses. In COPs, NaZSM-5(120) and NaZSM-5(45) showed the catalytic activity, whereas NaZSM-5(31) displayed negligible catalytic activity. The high catalytic activity of NaZSM-5(120) may be due to more Si-O bonds on zeolite surfaces. The results revealed that loading of Mg oxide on ZSM-5 zeolites can increase catalytic activity in COPs. These results show the application potential of ZSM-5 zeolites in ozonation of recalcitrant chemical wastewaters. Full article
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Open AccessCommunication A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water
Catalysts 2018, 8(4), 129; https://doi.org/10.3390/catal8040129
Received: 28 February 2018 / Revised: 21 March 2018 / Accepted: 22 March 2018 / Published: 25 March 2018
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Abstract
A new chiral Mn–salen catalyst, functionalized with a long aliphatic chain and a choline group, able to act as surfactant catalyst for green epoxidation in water, is here described. This catalyst was employed with a commercial surfactant (CTABr) leading to a nanoreactor for
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A new chiral Mn–salen catalyst, functionalized with a long aliphatic chain and a choline group, able to act as surfactant catalyst for green epoxidation in water, is here described. This catalyst was employed with a commercial surfactant (CTABr) leading to a nanoreactor for the enantioselective epoxidation of some selected alkenes in water, using NaClO as oxidant. This is the first example of a nanoreactor for enantioselective epoxidation of non-functionalized alkenes in water. Full article
(This article belongs to the Special Issue Reactions in Water and in Micelles)
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Open AccessArticle Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH3-SCR
Catalysts 2018, 8(4), 130; https://doi.org/10.3390/catal8040130
Received: 7 March 2018 / Revised: 22 March 2018 / Accepted: 22 March 2018 / Published: 26 March 2018
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Abstract
FeVO4 and Fe0.5Er0.5VO4 were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO2-WO3-SiO2 (TWS) and redox active supports like CeO2 and CeZrO2 with the aim of
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FeVO4 and Fe0.5Er0.5VO4 were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO2-WO3-SiO2 (TWS) and redox active supports like CeO2 and CeZrO2 with the aim of finding a suitable formulation for simultaneous soot abatement and NH3-SCR and to understand the level of interaction between the two reactions. A suitable bi-functional material was identified in the composition FeVO4/CeZrO2 where an SCR active component is added over a redox active support, to increase carbon oxidation properties. The influence of the presence of ammonia in soot oxidation and the effect of the presence of soot on SCR reaction have been addressed. It is found that the addition of NO and NO/NH3 mixtures decreases at different levels the oxidation temperature of carbon soot, while the presence of carbon adversely affects the NH3-SCR reaction by increasing the oxidation of NH3 to NO, thus lowering the NO removal efficiency. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Heavy Oil Upgrading and Enhanced Recovery in a Steam Injection Process Assisted by NiO- and PdO-Functionalized SiO2 Nanoparticulated Catalysts
Catalysts 2018, 8(4), 132; https://doi.org/10.3390/catal8040132
Received: 27 February 2018 / Revised: 22 March 2018 / Accepted: 22 March 2018 / Published: 29 March 2018
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Abstract
This work aims to investigate the effect of active catalytic nanoparticles on the improvement of the efficiency in recovery of a continuous steam injection process. Catalytic nanoparticles were selected through batch-adsorption experiments and the subsequent evaluation of the temperature for catalytic steam gasification
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This work aims to investigate the effect of active catalytic nanoparticles on the improvement of the efficiency in recovery of a continuous steam injection process. Catalytic nanoparticles were selected through batch-adsorption experiments and the subsequent evaluation of the temperature for catalytic steam gasification in a thermogravimetric analyzer. A nanoparticulated SiO2 support was functionalized with 1.0 wt % of NiO and PdO nanocrystals, respectively, to improve the catalytic activity of the nanoparticles. Oil recovery was evaluated using a sand pack in steam injection scenarios in the absence and presence of a 500 mg/L SiNi1Pd1 nanoparticles-based nanofluid. The displacement test was carried out by constructing the base curves with water injection followed by steam injection in the absence and presence of the prepared treatment. The oil recovery increased 56% after steam injection with nanoparticles in comparison with the steam injection in the absence of the catalysts. The API gravity increases from 7.2° to 12.1°. Changes in the asphaltenes fraction corroborated the catalytic effect of the nanoparticles by reducing the asphaltenes content and the 620 °C+ residue 40% and 47%, respectively. Also, rheological measurements showed that the viscosity decreased by up to 85% (one order of magnitude) after the nanofluid treatment during the steam injection process. Full article
(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)
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Open AccessArticle MgAl-Layered Double Hydroxide Solid Base Catalysts for Henry Reaction: A Green Protocol
Catalysts 2018, 8(4), 133; https://doi.org/10.3390/catal8040133
Received: 28 February 2018 / Revised: 24 March 2018 / Accepted: 27 March 2018 / Published: 29 March 2018
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Abstract
A series of MgAl-layered double hydroxide (MgAl-HT), the calcined form at 500 °C (MgAlOx), and the rehydrated one at 25 °C (MgAl-HT-RH) were synthesized. Physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Surface
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A series of MgAl-layered double hydroxide (MgAl-HT), the calcined form at 500 °C (MgAlOx), and the rehydrated one at 25 °C (MgAl-HT-RH) were synthesized. Physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Surface area of the as-synthesized, calcined, and rehydrated catalysts was determined by N2 physisorption at −196 °C. CO2 temperature-programmed desorption (CO2-TPD) was applied to determine the basic sites of catalysts. The catalytic test reaction was carried out using benzaldehyde and their derivatives with nitromethane and their derivatives. The Henry products (1–15) were obtained in a very good yield using MgAl-HT-RH catalyst either by conventional method at 90 °C in liquid phase or under microwave irradiation method. The mesoporous structure and basic nature of the rehydrated solid catalyst were responsible for its superior catalytic efficiency. The robust nature was determined by using the same catalyst five times, where the product % yield was almost unchanged significantly. Full article
(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)
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Open AccessArticle The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts
Catalysts 2018, 8(4), 134; https://doi.org/10.3390/catal8040134
Received: 28 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 30 March 2018
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Abstract
Promotion of 2.73% Fe2O3 in an in-house-made V2O5-WO3/TiO2 (VWT) and a commercial V2O5-WO3/TiO2 (c-VWT) has been investigated as a cost effective approach to the suppression of
[...] Read more.
Promotion of 2.73% Fe2O3 in an in-house-made V2O5-WO3/TiO2 (VWT) and a commercial V2O5-WO3/TiO2 (c-VWT) has been investigated as a cost effective approach to the suppression of N2O formation in the selective catalytic reduction of NO by NH3 (NH3-SCR). The promoted VWT and c-VWT catalysts all gave a significantly decreased N2O production at temperatures >400 °C compared to the unpromoted samples. However, such a promotion led to the loss in high temperature NO conversion, mainly due to the oxidation of NH3 to N-containing gases, particularly NO. Characterization of the unpromoted and promoted catalysts using X-ray diffraction (XRD), NH3 adsorption-desorption, and Raman spectroscopy techniques could explain the reason why the promotion showed much lower N2O formation levels at high temperatures. The addition of Fe2O3 to c-VWT resulted in redispersion of the V2O5 species, although this was not visible for 2.73% Fe2O3/VWT. The iron oxides exist as a highly-dispersed noncrystalline α-Fe2O3 in the promoted catalysts. These Raman spectra had a new Raman signal that could be tentatively assigned to Fe2O3-induced tetrahedrally coordinated polymeric vanadates and/or surface V-O-Fe species with significant electronic interactions between the both metal oxides. Calculations of the monolayer coverage of each metal oxide and the surface total coverage are reasonably consistent with Raman measurements. The proposed vanadia-based surface polymeric entities may play a key role for the substantial reduction of N2O formed at high temperatures by NH3 species adsorbed strongly on the promoted catalysts. This reaction is a main pathway to greatly suppress the extent of N2O formation in NH3-SCR reaction over the promoted catalysts. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessCommunication [(PhCH2O)2P(CH3)2CHNCH(CH3)2]2PdCl2/CuI as Cocatalyst for Coupling-Cyclization of 2-Iodophenol with Terminal Alkynes in Water
Catalysts 2018, 8(4), 136; https://doi.org/10.3390/catal8040136
Received: 3 March 2018 / Revised: 25 March 2018 / Accepted: 26 March 2018 / Published: 30 March 2018
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Abstract
A new and efficient [(PhCH2O)2P(CH3)2CHNCH(CH3)2]2PdCl2/CuI-co-catalyzed coupling-cyclization reactions of 2-iodophenol with terminal alkynes is described. Different 2-substitued benzo[b]furan derivatives are obtained in good to excellent yields. This protocol employs a relatively low palladium(II) catalyst loading in water under air conditions. Full article
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Open AccessFeature PaperArticle The First Catalytic Direct C–H Arylation on C2 and C3 of Thiophene Ring Applied to Thieno-Pyridines, -Pyrimidines and -Pyrazines
Catalysts 2018, 8(4), 137; https://doi.org/10.3390/catal8040137
Received: 13 March 2018 / Revised: 27 March 2018 / Accepted: 28 March 2018 / Published: 30 March 2018
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Abstract
A practical one-pot procedure for the preparation of diverse thieno[3,2-d]pyrimidines is reported here for the first time. This two-step process via C–H activation in position C-2 of thiophene led to the development of an improved methodology for the synthesis of numerous
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A practical one-pot procedure for the preparation of diverse thieno[3,2-d]pyrimidines is reported here for the first time. This two-step process via C–H activation in position C-2 of thiophene led to the development of an improved methodology for the synthesis of numerous compounds. This new methodology is an efficient alternative to the conventional methods currently applied. The C–H activation of the thiophene C-3 position was also achieved and can be selective. The optimized conditions can also be applied to thienopyridines and thienopyrazines. Full article
(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)
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Open AccessArticle Efficiently Enhancing Electrocatalytic Activity of α-MnO2 Nanorods/N-Doped Ketjenblack Carbon for Oxygen Reduction Reaction and Oxygen Evolution Reaction Using Facile Regulated Hydrothermal Treatment
Catalysts 2018, 8(4), 138; https://doi.org/10.3390/catal8040138
Received: 6 March 2018 / Revised: 25 March 2018 / Accepted: 28 March 2018 / Published: 30 March 2018
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Abstract
Scalable, low-cost and highly efficient catalysis of oxygen electrocatalytic reactions (ORR/OER) are required for the rapid development of clean and renewable energy conversion/storage technologies. Herein, two types of α-MnO2 nanorods were prepared under hydrothermal treatment at 150 °C for 0.5 h (MnO
[...] Read more.
Scalable, low-cost and highly efficient catalysis of oxygen electrocatalytic reactions (ORR/OER) are required for the rapid development of clean and renewable energy conversion/storage technologies. Herein, two types of α-MnO2 nanorods were prepared under hydrothermal treatment at 150 °C for 0.5 h (MnO2-150-0.5) or 120 °C for 12 h (MnO2-120-12), then supported on N-doped ketjenblack carbon (N-KB) as bi-functional ORR/OER catalysts. Their electrocatalytic activities toward ORR and OER were investigated systematically. As a result, MnO2-150-0.5/N-KB displays superior ORR catalytic activity, with much more positive half-wave potential and much larger limiting current density (0.76 V and 6.0 mA cm−2), comparable to those of 20 wt. % Pt/C (0.82 V and 5.10 mA cm−2). MnO2-150-0.5/N-KB also shows high electron transfer number (3.86~3.97) and low yield of peroxides (1–7%) during ORR process in the whole potential range of 0–1.0 V (vs. RHE). Meanwhile, the MnO2-150-0.5/N-KB also exhibits better OER activity with low overpotential, comparable to IrO2/N-KB. The excellent electrocatalytic activity of MnO2-150-0.5/N-KB can be attributed to the synergistic effect, relatively smaller size, higher amount of Mn3+, and low charge transfer resistance. This work offers a new strategy for scalable preparation of more efficient and cost-effective α-MnO2 bi-functional oxygen catalysts. Full article
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Open AccessFeature PaperCommunication Palladium-Catalyzed Regioselective Alkoxylation via C-H Bond Activation in the Dihydrobenzo[c]acridine Series
Catalysts 2018, 8(4), 139; https://doi.org/10.3390/catal8040139
Received: 12 March 2018 / Revised: 26 March 2018 / Accepted: 29 March 2018 / Published: 31 March 2018
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Abstract
5,6-Dihydrobenzo[c]acridine belongs to the large aza-polycyclic compound family. Such molecules are not fully planar due to the presence of a partially hydrogenated ring. This paper describes the first Pd-catalyzed alkoxylation via C-H bond activation of variously substituted 5,6-dihydrobenzo[c]acridines. We
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5,6-Dihydrobenzo[c]acridine belongs to the large aza-polycyclic compound family. Such molecules are not fully planar due to the presence of a partially hydrogenated ring. This paper describes the first Pd-catalyzed alkoxylation via C-H bond activation of variously substituted 5,6-dihydrobenzo[c]acridines. We determined suitable conditions to promote the selective formation of C-O bonds using 10% Pd(OAc)2, PhI(OAc)2 (2 eq.) and MeOH as the best combination of oxidant and solvent, respectively. Under these conditions, 5,6-dihydrobenzo[c]acridines bearing substituents at both rings A and D were successfully functionalized, giving access to polysubstitutited acridine motifs. Full article
(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)
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Open AccessFeature PaperArticle Polystyrene-Supported Acyclic Diaminocarbene Palladium Complexes in Sonogashira Cross-Coupling: Stability vs. Catalytic Activity
Catalysts 2018, 8(4), 141; https://doi.org/10.3390/catal8040141
Received: 9 March 2018 / Revised: 22 March 2018 / Accepted: 28 March 2018 / Published: 2 April 2018
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Abstract
Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-PdII) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-PdII, systems are found to have different catalytic activity and stability regarding
[...] Read more.
Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-PdII) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-PdII, systems are found to have different catalytic activity and stability regarding Pd-leaching. PdII-diaminocarbenes possessing protons at both nitrogen atoms smoothly decompose into Pd0-containing species providing a catalytic “cocktail system” with high activity and ability to reuse within nine runs. Polymer-supported palladium (II) complex bearing NBn–Ccarbene–NH-moiety exhibits greater stability while noticeably lower activity under Sonogashira cross-coupling. Four molecular ADC-PdII complexes are also synthesized and investigated with the aim of confirming proposed base-promoted pathway of ADC-PdII conversion through carbodiimide into an active Pd0 forms. Full article
(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)
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Open AccessArticle Continuous Dimethyl Carbonate Synthesis from CO2 and Methanol Using Cu-Ni@VSiO as Catalyst Synthesized by a Novel Sulfuration Method
Catalysts 2018, 8(4), 142; https://doi.org/10.3390/catal8040142
Received: 23 January 2018 / Revised: 26 March 2018 / Accepted: 29 March 2018 / Published: 3 April 2018
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Abstract
Conversion of carbon dioxide into useful chemicals is a valuable task. One way to perform it is to transform CO2 into dimethyl carbonate (DMC) by a reaction with methanol. Catalyst exerts significant impact on this process. During this work, Cu-Ni@VSiO bimetallic catalysts
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Conversion of carbon dioxide into useful chemicals is a valuable task. One way to perform it is to transform CO2 into dimethyl carbonate (DMC) by a reaction with methanol. Catalyst exerts significant impact on this process. During this work, Cu-Ni@VSiO bimetallic catalysts were successfully synthesized by traditional solution and novel sulfuration methods. The catalytic materials were characterized by several analytical techniques and were tested in a continuous fixed-bed reactor under different reaction conditions to promote DMC synthesis from CO2 and methanol in the absence of dehydrating agents. The effects of reaction temperature, pressure, space velocity, metal loading, and bulk density on the catalytic performance were investigated in detail. It was found that the activity of Cu-Ni@VSiO catalyst with the support obtained by the novel sulfuration method is about three times higher when compared to that of the catalyst with the support that is synthesized by the traditional solution method. This result may stem from the difference in microstructure of the studied catalytic materials. Full article
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Open AccessArticle DRIFT Study on Promotion Effect of the Keggin Structure over V2O5-MoO3/TiO2 Catalysts for Low Temperature NH3-SCR Reaction
Catalysts 2018, 8(4), 143; https://doi.org/10.3390/catal8040143
Received: 10 March 2018 / Revised: 30 March 2018 / Accepted: 30 March 2018 / Published: 3 April 2018
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Abstract
Heteropoly acids (HPAs) with the Keggin structure have been widely used in NOx removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH3-SCR reaction. A
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Heteropoly acids (HPAs) with the Keggin structure have been widely used in NOx removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH3-SCR reaction. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analyses are conducted to investigate the surface-adsorbed species on the catalysts during the SCR reaction. The mechanism for enhancing low-temperature activity of the catalysts is proposed. Furthermore, the effect of NH4+ in the Keggin structure is also investigated. Results indicate that both the Langmuir–Hinshelwood (L-H) and Eley–Rideal (E-R) mechanisms occurred in the NH3-SCR reaction over the catalyst with the Keggin structure (Cat-A); in addition, when more acid sites are provided, NOx species activity is improved and more NH4+ ions participate in reaction over Cat-A, thus promoting SCR activity. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Controlled Synthesis of Heterostructured SnO2-CuO Composite Hollow Microspheres as Efficient Cu-Based Catalysts for the Rochow Reaction
Catalysts 2018, 8(4), 144; https://doi.org/10.3390/catal8040144
Received: 7 March 2018 / Revised: 28 March 2018 / Accepted: 28 March 2018 / Published: 3 April 2018
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Abstract
In this work, we report the design and synthesis of a series of heterostructured SnO2-CuO hollow microspherical catalysts (H-SnO2(x)-CuO, x is the weight ratio of Sn/Cu) for the Rochow reaction. The microspherical catalysts with nanosheets and nanoparticles
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In this work, we report the design and synthesis of a series of heterostructured SnO2-CuO hollow microspherical catalysts (H-SnO2(x)-CuO, x is the weight ratio of Sn/Cu) for the Rochow reaction. The microspherical catalysts with nanosheets and nanoparticles as building blocks were prepared by a facile one-pot hydrothermal method coupled with calcination. When tested for the Rochow reaction, the prepared H-SnO2(0.2)-CuO composite exhibited higher dimethyldichlorosilane selectivity (88.2%) and Si conversion (36.7%) than the solid CuO, hollow CuO and other H-SnO2(x)-CuO microspherical samples, because in the former there is a stronger synergistic interaction between CuO and SnO2. Full article
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Open AccessFeature PaperArticle Gaseous Nitric Acid Activated Graphite Felts as Hierarchical Metal-Free Catalyst for Selective Oxidation of H2S
Catalysts 2018, 8(4), 145; https://doi.org/10.3390/catal8040145
Received: 5 March 2018 / Revised: 29 March 2018 / Accepted: 30 March 2018 / Published: 4 April 2018
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Abstract
In this study, we reported on the influence of gaseous HNO3 treatment on the formation of defects decorated with oxygenated functional groups on commercial graphite felts (GFs). The gaseous acid treatment also leads to a remarkable increase of the specific as well
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In this study, we reported on the influence of gaseous HNO3 treatment on the formation of defects decorated with oxygenated functional groups on commercial graphite felts (GFs). The gaseous acid treatment also leads to a remarkable increase of the specific as well as effective surface area through the formation of a highly porous graphite structure from dense graphite filamentous. The as-synthesized catalyst was further used as a metal-free catalyst in the selective oxidation of H2S in industrial waste effluents. According to the results, the defects decorated with oxygenated groups were highly active for performing selective oxidation of H2S into elemental sulfur. The desulfurization activity was relatively high and extremely stable as a function of time on stream which indicated the high efficiency of these oxidized un-doped GFs as metal-free catalysts for the selective oxidation process. The high catalytic performance was attributed to both the presence of structural defects on the filamentous carbon wall, which acting as a dissociative adsorption center for the oxygen, and the oxygenated functional groups, which could play the role of active sites for the selective oxidation process. Full article
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Open AccessArticle Porous Organic Polymers-Supported Metallocene Catalysts for Ethylene/1-Hexene Copolymerization
Catalysts 2018, 8(4), 146; https://doi.org/10.3390/catal8040146
Received: 27 February 2018 / Revised: 20 March 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
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Abstract
Porous organic polymers (POPs) have received much attention in adsorption, separation, and catalysis. In this paper, porous organic polymers with different pore structure were used as metallocene catalyst supports, and ethylene/1-hexene copolymerizations were conducted using the POPs-supported metallocene catalyst. The pore structure of
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Porous organic polymers (POPs) have received much attention in adsorption, separation, and catalysis. In this paper, porous organic polymers with different pore structure were used as metallocene catalyst supports, and ethylene/1-hexene copolymerizations were conducted using the POPs-supported metallocene catalyst. The pore structure of the prepared POPs and the supported metallocene catalyst were characterized by nitrogen sorption porosimetry and non-local density functional theory simulation, and the molecular chain structure of the produced ethylene/1-hexene copolymers were investigated through gel permeation chromatography (GPC), IR analysis, differential scanning calorimetry (DSC), and temperature rising elution fractionation (TREF). The results show that the loading amount of active sites varied with different pore structures of the POP supports, and the active species scattered in different pore sizes had a moderate impact on the molecular chain growth and the molecular weight distribution. The IR, DSC, and TREF analysis revealedthat different branching degree, double bond content, and chemical composition distributions were detected from the molecular chain structure of the ethylene/α-olefin copolymers from different POPs and silica-supported metallocene catalysts, despite their similar IR, DSC, and TREF curves due to the same active species. Scanning electron microscopy (SEM) showed that porous ethylene/α-olefin copolymers with varied surface morphology were obtained from the POPs-supported metallocene catalysts with different pore structure. Full article
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Open AccessArticle Enhancing Light-Driven Production of Hydrogen Peroxide by Anchoring Au onto C3N4 Catalysts
Catalysts 2018, 8(4), 147; https://doi.org/10.3390/catal8040147
Received: 27 February 2018 / Revised: 30 March 2018 / Accepted: 31 March 2018 / Published: 4 April 2018
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Abstract
Light-driven production of hydrogen peroxide (H2O2) is a green and sustainable way to achieve solar-to-chemical energy conversion. During such a conversion, both the high activity and the stability of catalysts were critical. We prepared an Au-supported C3N
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Light-driven production of hydrogen peroxide (H2O2) is a green and sustainable way to achieve solar-to-chemical energy conversion. During such a conversion, both the high activity and the stability of catalysts were critical. We prepared an Au-supported C3N4 catalyst—i.e., Au/C3N4-500(N2)—by strongly anchoring Au nanoparticles (~5 nm) onto a C3N4 matrix—which simultaneously enhanced the activity towards the photosynthesis of H2O2 and the stability when it was reused. The yield of H2O2 reached 1320 μmol L−1 on Au/C3N4-500(N2) after 4 h of light irradiation in an acidic solution (pH 3), which was higher than that (1067 μmol L−1) of the control sample Au/C3N4-500(Air) and 2.3 times higher than that of the pristine C3N4. Particularly, the catalyst Au/C3N4-500(N2) retained a much higher stability. The yield of H2O2 had a marginal decrease on the spent catalyst—i.e., 98% yield was kept. In comparison, only 70% yield was obtained from the spent control catalyst. The robust anchoring of Au onto C3N4 improved their interaction, which remarkably decreased the Au leaching when it was used and avoided the aggregation and aging of Au particles. Minimal Au leaching was detected on the spent catalyst. The kinetic analyses indicated that the highest formation rate of H2O2 was achieved on the Au/C3N4-500(N2) catalyst. The decomposition tests and kinetic behaviors of H2O2 were also carried out. These findings suggested that the formation rate of H2O2 could be a determining factor for efficient production of H2O2. Full article
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Open AccessArticle Insights in the Rhodium-Catalyzed Tandem Isomerization-Hydroformylation of 10-Undecenitrile: Evidence for a Fast Isomerization Regime
Catalysts 2018, 8(4), 148; https://doi.org/10.3390/catal8040148
Received: 20 March 2018 / Revised: 27 March 2018 / Accepted: 2 April 2018 / Published: 5 April 2018
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Abstract
The tandem isomerization-hydroformylation of 10-undecenitrile (1) into the corresponding linear aldehyde (2) with a Rh-biphephos system was studied and the formation of internal olefin isomers (1-int-x) was monitored over time. The existence of an “isomerization
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The tandem isomerization-hydroformylation of 10-undecenitrile (1) into the corresponding linear aldehyde (2) with a Rh-biphephos system was studied and the formation of internal olefin isomers (1-int-x) was monitored over time. The existence of an “isomerization phenomenon” was evidenced, where fast isomerization of 1 into up to 70% of 1-int-x followed by fast back-isomerization of 1-int-x into 1 and, in turn, into 2 occurs. This fast dynamic isomerization regime is favored at high syngas pressure (40 bar) and low biphephos-to-Rh ratio (5–10), and it is best observed at relatively high catalyst loadings ([1]0/[Rh] ≤ 3000). The latter regime is indeed evanescent, and gives place to a second stage in which isomerization of internal olefins (and eventual conversion into 2) proceeds much more slowly. The results are tentatively rationalized by the formation of an unstable species that promotes dynamic isomerization and which slowly vanishes or collapses into a Rh-biphephos species which is the one responsible for hydroformylation. Full article
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Open AccessArticle Immobilization/Stabilization of Ficin Extract on Glutaraldehyde-Activated Agarose Beads. Variables That Control the Final Stability and Activity in Protein Hydrolyses
Catalysts 2018, 8(4), 149; https://doi.org/10.3390/catal8040149
Received: 12 March 2018 / Revised: 26 March 2018 / Accepted: 2 April 2018 / Published: 6 April 2018
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Abstract
Ficin extract has been immobilized on different 4% aminated-agarose beads. Using just ion exchange, immobilization yield was poor and expressed activity did not surpass 10% of the offered enzyme, with no significant effects on enzyme stability. The treatment with glutaraldehyde of this ionically
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Ficin extract has been immobilized on different 4% aminated-agarose beads. Using just ion exchange, immobilization yield was poor and expressed activity did not surpass 10% of the offered enzyme, with no significant effects on enzyme stability. The treatment with glutaraldehyde of this ionically exchanged enzyme produced an almost full enzyme inactivation. Using aminated supports activated with glutaraldehyde, immobilization was optimal at pH 7 (at pH 5 immobilization yield was 80%, while at pH 9, the immobilized enzyme became inactivated). At pH 7, full immobilization was accomplished maintaining 40% activity versus a small synthetic substrate and 30% versus casein. Ficin stabilization upon immobilization could be observed but it depended on the inactivation pH and the substrate employed, suggesting the complexity of the mechanism of inactivation of the immobilized enzyme. The maximum enzyme loading on the support was determined to be around 70 mg/g. The loading has no significant effect on the enzyme stability or enzyme activity using the synthetic substrate but it had a significant effect on the activity using casein; the biocatalysts activity greatly decreased using more than 30 mg/g, suggesting that the near presence of other immobilized enzyme molecules may generate some steric hindrances for the casein hydrolysis. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Stereoselective Enzymatic Reduction of 1,4-Diaryl-1,4-Diones to the Corresponding Diols Employing Alcohol Dehydrogenases
Catalysts 2018, 8(4), 150; https://doi.org/10.3390/catal8040150
Received: 18 January 2018 / Revised: 27 March 2018 / Accepted: 3 April 2018 / Published: 6 April 2018
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Abstract
Due to the steric hindrance of the starting prochiral ketones, the preparation of chiral 1,4-diaryl-1,4-diols through the asymmetric hydrogen transfer reaction has been mainly restricted to the use of metal-based catalysts, oxazaborolidines, or organocatalysts. Herein, we demonstrated the versatility of oxidoreductases, finding overexpressed
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Due to the steric hindrance of the starting prochiral ketones, the preparation of chiral 1,4-diaryl-1,4-diols through the asymmetric hydrogen transfer reaction has been mainly restricted to the use of metal-based catalysts, oxazaborolidines, or organocatalysts. Herein, we demonstrated the versatility of oxidoreductases, finding overexpressed alcohol dehydrogenase from Ralstonia sp. (E. coli/RasADH) as the most active and stereoselective biocatalyst. Thus, the preparation of a set of 1,4-diaryl-1,4-diols bearing different pattern substitutions in the aromatic ring was achieved with complete diastereo- and enantioselectivity under mild reaction conditions. Full article
(This article belongs to the Special Issue Enzyme-Mediated Stereoselective Synthesis)
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Open AccessArticle Synthesis and Characterization of CNT/TiO2/ZnO Composites with High Photocatalytic Performance
Catalysts 2018, 8(4), 151; https://doi.org/10.3390/catal8040151
Received: 26 March 2018 / Revised: 26 March 2018 / Accepted: 6 April 2018 / Published: 9 April 2018
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Abstract
Novel carbon nanotubes (CNTs)/titanium dioxide (TiO2)/zinc oxide (ZnO) composites have been successfully synthesized via a two-step solution method using titanyl sulfate as the titanium precursor. Its structural performances were researched by various characterization methods, such as X-ray powder diffraction (XRD), scanning
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Novel carbon nanotubes (CNTs)/titanium dioxide (TiO2)/zinc oxide (ZnO) composites have been successfully synthesized via a two-step solution method using titanyl sulfate as the titanium precursor. Its structural performances were researched by various characterization methods, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The performance of the composites was tested by degrading rhodamine B (RhB) under UV-vis illumination and found to strongly rely on the content of ZnO. The experimental results showed that the CNT/TiO2/ZnO-90 wt % expressed more outstanding photocatalytic performance compared to the corresponding binary composites and the CNT/TiO2/ZnO-85 wt %, CNT/TiO2/ZnO-95 wt % materials. The improved photocatalytic activity was attributed to synergistic effect of CNT, TiO2 and ZnO, in which ZnO can absorb photons to produce electrons and holes, whereas TiO2 and CNT can reduce the electron-hole recombination. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Energy Conversion)
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Open AccessCommunication Catalytic Efficiency of Basidiomycete Laccases: Redox Potential versus Substrate-Binding Pocket Structure
Catalysts 2018, 8(4), 152; https://doi.org/10.3390/catal8040152
Received: 15 March 2018 / Revised: 30 March 2018 / Accepted: 2 April 2018 / Published: 9 April 2018
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Abstract
Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly
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Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly provides these differences. The purpose of this work was to study the features of the substrate specificity of four laccases from basidiomycete fungi Trametes hirsuta, Coriolopsis caperata, Antrodiella faginea, and Steccherinum murashkinskyi, which have different redox potentials of the T1 copper center and a different structure of substrate-binding pockets. Enzyme activity toward 20 monophenolic substances and 4 phenolic dyes was measured spectrophotometrically. The kinetic parameters of oxidation of four lignans and lignan-like substrates were determined by monitoring of the oxygen consumption. For the oxidation of the high redox potential (>700 mV) monophenolic substrates and almost all large substrates, such as phenolic dyes and lignans, the redox potential difference between the enzyme and the substrate (ΔE) played the defining role. For the low redox potential monophenolic substrates, ΔE did not directly influence the laccase activity. Also, in the special cases, the structure of the large substrates, such as dyes and lignans, as well as some structural features of the laccases (flexibility of the substrate-binding pocket loops and some amino acid residues in the key positions) affected the resulting catalytic efficiency. Full article
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Open AccessArticle The Deoxygenation Pathways of Palmitic Acid into Hydrocarbons on Silica-Supported Ni12P5 and Ni2P Catalysts
Catalysts 2018, 8(4), 153; https://doi.org/10.3390/catal8040153
Received: 3 March 2018 / Revised: 31 March 2018 / Accepted: 7 April 2018 / Published: 11 April 2018
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Abstract
Pure Ni12P5/SiO2 and pure Ni2P/SiO2 catalysts were obtained by adjusting the Ni and P molar ratios, while Ni/SiO2 catalyst was prepared as a reference against which the deoxygenation pathways of palmitic acid were investigated.
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Pure Ni12P5/SiO2 and pure Ni2P/SiO2 catalysts were obtained by adjusting the Ni and P molar ratios, while Ni/SiO2 catalyst was prepared as a reference against which the deoxygenation pathways of palmitic acid were investigated. The catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission election microscopy (TEM), infrared spectroscopy of pyridine adsorption (Py-IR), H2-adsorption and temperature-programmed desorption of hydrogen (H2-TPD). The crystallographic planes of Ni(111), Ni12P5(400), Ni2P(111) were found mainly exposed on the above three catalysts, respectively. It was found that the deoxygenation pathway of palmitic acid mainly proceeded via direct decarboxylation (DCO2) to form C15 on Ni/SiO2. In contrast, on the Ni12P5/SiO2 catalyst, there were two main competitive pathways producing C15 and C16, one of which mainly proceeded via the decarbonylation (DCO) to form C15 accompanying water formation, and the other pathway produced C16 via the dehydration of hexadecanol intermediate, and the yield of C15 was approximately twofold that of C16. Over the Ni2P/SiO2 catalyst, two main deoxygenation pathways formed C15, one of which was mainly the DCO pathway and the other was dehydration accompanying the hexadecanal intermediate and then direct decarbonylation without water formation. The turn over frequency (TOF) followed the order: Ni12P5/SiO2 > Ni/SiO2 > Ni2P/SiO2. Full article
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Open AccessArticle Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater
Catalysts 2018, 8(4), 154; https://doi.org/10.3390/catal8040154
Received: 26 March 2018 / Revised: 8 April 2018 / Accepted: 8 April 2018 / Published: 11 April 2018
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Abstract
In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and
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In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessFeature PaperArticle Gas-Phase Phosphorous Poisoning of a Pt/Ba/Al2O3 NOx Storage Catalyst
Catalysts 2018, 8(4), 155; https://doi.org/10.3390/catal8040155
Received: 9 March 2018 / Revised: 5 April 2018 / Accepted: 7 April 2018 / Published: 11 April 2018
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Abstract
The effect of phosphorous exposure on the NOx storage capacity of a Pt/Ba/Al2O3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H2O
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The effect of phosphorous exposure on the NOx storage capacity of a Pt/Ba/Al2O3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H2O and O2. The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NOx storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N2-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P4O10. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO3). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Open AccessArticle The Effects of Coordinated Molecules of Two Gly-Schiff Base Copper Complexes on Their Oxygen Reduction Reaction Performance
Catalysts 2018, 8(4), 156; https://doi.org/10.3390/catal8040156
Received: 23 March 2018 / Revised: 8 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
In this study, two simple Schiff base copper complexes [Cu(H2O)2(HL)]·2H2O (Complex 1) (H3L = 2-OH-4-(OH)-C6H2CH=NCH2CO2H) and [Cu(py)2(HL)] (Complex 2) (Py = pyridine) were
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In this study, two simple Schiff base copper complexes [Cu(H2O)2(HL)]·2H2O (Complex 1) (H3L = 2-OH-4-(OH)-C6H2CH=NCH2CO2H) and [Cu(py)2(HL)] (Complex 2) (Py = pyridine) were initially achieved and authenticated by single-crystal X-ray structure analyses (SXRD), powder X-ray diffraction analyses (PXRD), FT-IR spectroscopy, and elemental analyses. The SXRD reveals that the Cu2+ center in Complex 1 exhibited a distorted square pyramidal geometry, which is constructed based on phenolate oxygen, water molecules, carboxylate oxygen, and imine nitrogen from a deprotonated H3L ligand in an NO4 fashion. The Cu2+ atom in Complex 2 had distorted square pyramidal geometry, and was coordinated with two pyridine molecules and one Gly-Schiff base ligand, exhibiting an N3O2 binding set. Additionally, the free water molecules in Complex 1 linked independent copper complexes by intermolecular hydrogen bond to form a 2D framework. However, the one-dimensional chain supramolecular structure of Complex 2 was formed by the intermolecular O–H…O hydrogen bonds. The oxygen reduction performance of the two complexes was analyzed by cyclic voltammetry (CV) and the rotating disk electrode (RDE) method. Both complexes could catalyze the conversion of oxygen to water through a predominant four-electron pathway, and the Cu–NxOy moieties might be the functional moieties for the catalytic activity. The catalytic pathways and underlying mechanisms are also discussed in detail, from which the structure–activity relationship of the complexes was obtained. Full article
(This article belongs to the Special Issue Platinum-Free Electrocatalysts)
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Open AccessArticle Catalytic Role of H2O Molecules in Oxidation of CH3OH in Water
Catalysts 2018, 8(4), 157; https://doi.org/10.3390/catal8040157
Received: 22 March 2018 / Revised: 7 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
We have examined the catalytic role of H2O molecules in the oxidation of CH3OH in water by quantum chemical simulations. A CH3OH is decomposed into molecules, a formaldehyde and an H2, in water, while it
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We have examined the catalytic role of H2O molecules in the oxidation of CH3OH in water by quantum chemical simulations. A CH3OH is decomposed into molecules, a formaldehyde and an H2, in water, while it is converted into radicals in a gas phase reaction at a high temperature. H2O molecules located near a CH3OH form a first hydration shell and act as catalyst for the oxidation of CH3OH in water. The oxidation process of a CH3OH in water begins when a proton is delivered to a neighbor H2O molecule from a hydroxyl of a CH3OH. The H2O molecule transfers an extra proton to a second H2O molecule, a proton of which is combined with a proton detached from the methyl of the CH3OH, forming an H2. The energy barrier to decompose a CH3OH is significantly reduced by the catalyst of H2O molecules in water. A cluster of H2O molecules arise in water as an enclosed chain of hydrogen bonds between H2O molecules. A proton is transferred with less energy between H2O molecules within a cluster of H2O molecules. A cluster of five H2O molecules further reduces the energy barrier. The calculated oxidation rate of CH3OH with the transition state theory agrees well with that determined by experiments. Full article
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Open AccessFeature PaperArticle Binary Nitrogen Precursor-Derived Porous Fe-N-S/C Catalyst for Efficient Oxygen Reduction Reaction in a Zn-Air Battery
Catalysts 2018, 8(4), 158; https://doi.org/10.3390/catal8040158
Received: 2 March 2018 / Revised: 16 March 2018 / Accepted: 19 March 2018 / Published: 13 April 2018
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Abstract
It is still a challenge to synthesize non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) to replace the state-of-the art Pt/C catalyst. Herein, a Fe, N, S co-doped porous carbon (Fe-NS/PC) is developed by using g-C3N
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It is still a challenge to synthesize non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) to replace the state-of-the art Pt/C catalyst. Herein, a Fe, N, S co-doped porous carbon (Fe-NS/PC) is developed by using g-C3N4 and 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) as binary nitrogen precursors. The interaction of binary nitrogen precursors not only leads to the formation of more micropores, but also increases the doping amount of both iron and nitrogen dispersed in the carbon matrix. After a second heat-treatment, the best Fe/NS/C-g-C3N4/TPTZ-1000 catalyst exhibits excellent ORR performance with an onset potential of 1.0 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.868 V (RHE) in alkaline medium. The long-term durability is even superior to the commercial Pt/C catalyst. In the meantime, an assembled Zn-air battery with Fe/NS/C-g-C3N4/TPTZ-1000 as the cathode shows a maximal power density of 225 mW·cm−2 and excellent durability, demonstrating the great potential of practical applications in energy conversion devices. Full article
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Open AccessFeature PaperArticle Immobilization of Enterobacter aerogenes by a Trimeric Autotransporter Adhesin, AtaA, and Its Application to Biohydrogen Production
Catalysts 2018, 8(4), 159; https://doi.org/10.3390/catal8040159
Received: 30 March 2018 / Revised: 13 April 2018 / Accepted: 13 April 2018 / Published: 16 April 2018
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Abstract
Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5.
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Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5. AtaA protein on the E. aerogenes cells carrying the ataA gene was demonstrated by immunoblotting and flow cytometry. The AtaA-producing cells exhibited stronger adherence and auto-agglutination characteristics than wild-type cells, and were successfully immobilized (at approximately 2.5 mg/cm3) on polyurethane foam. Hydrogen production from the cell-immobilized polyurethane foams was monitored in repetitive batch reactions and flow reactor studies. The total hydrogen production in triple-repetitive batch reactions reached 0.6 mol/mol glucose, and the hydrogen production rate in the flow reactor was 42 mL·h−1·L−1. The AtaA production achieved simple and immediate immobilization of E. aerogenes on the foam, enabling repetitive and continuous hydrogen production. This report newly demonstrates the production of AtaA on the cell surfaces of bacterial genera other than Acinetobacter, and can simplify and accelerate the immobilization of whole-cell catalysts. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Catalytic Activities of Noble Metal Phosphides for Hydrogenation and Hydrodesulfurization Reactions
Catalysts 2018, 8(4), 160; https://doi.org/10.3390/catal8040160
Received: 27 February 2018 / Revised: 12 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
In this work, the development of a highly active noble metal phosphide (NMXPY)-based hydrodesulfurization (HDS) catalyst with a high hydrogenating ability for heavy oils was studied. NMXPY catalysts were obtained by reduction of P-added noble metals
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In this work, the development of a highly active noble metal phosphide (NMXPY)-based hydrodesulfurization (HDS) catalyst with a high hydrogenating ability for heavy oils was studied. NMXPY catalysts were obtained by reduction of P-added noble metals (NM-P, NM: Rh, Pd, Ru) supported on SiO2. The order of activities for the hydrogenation of biphenyl was Rh-P > NiMoS > Pd-P > Ru-P. This order was almost the same as that of the catalytic activities for the HDS of dibenzothiophene. In the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT), the HDS activity of the Rh-P catalyst increased with increasing reaction temperature, but the maximum HDS activity for the NiMoS catalyst was observed at 270 °C. The Rh-P catalyst yielded fully hydrogenated products with high selectivity compared with the NiMoS catalyst. Furthermore, XRD analysis of the spent Rh-P catalysts revealed that the Rh2P phase possessed high sulfur tolerance and resistance to sintering. Full article
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Open AccessArticle A Comparative Study of Gold Impregnation Methods for Obtaining Metal/Semiconductor Nanophotocatalysts: Direct Turkevich, Inverse Turkevich, and Progressive Heating Methods
Catalysts 2018, 8(4), 161; https://doi.org/10.3390/catal8040161
Received: 21 March 2018 / Revised: 16 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
ZnO nanostructures decorated with gold nanoparticles (Au-NPs) were synthesized by thermal decomposition of ZnO2 powders and their subsequent impregnation of metal nanoparticles using either the Direct Turkevich Method, the Inverse Turkevich Method, or the Progressive Heating Method. It was found that the
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ZnO nanostructures decorated with gold nanoparticles (Au-NPs) were synthesized by thermal decomposition of ZnO2 powders and their subsequent impregnation of metal nanoparticles using either the Direct Turkevich Method, the Inverse Turkevich Method, or the Progressive Heating Method. It was found that the impregnation approach influences the resulting microstructure and photocatalytic activity of the obtained materials. While the Direct Turkevich approach gave the highest yield of metal loading, the smallest Au-NPs were obtained by Inverse Turkevich and the Progressive Heating Method. The photocatalytic activity of the pristine support and gold-loaded samples was studied in the decolorization of Rhodamine B solutions using UV- and pure visible-light illumination. All Au-NPs/ZnO samples showed higher photocatalytic activity than the bare support when UV-light was used. This effect is attributed to a charge carrier separation due to electron transfer from ZnO to the metal nanoparticles and the built-in electric field at the interfaces. Contrarily to most reports, visible-light sensitization using plasmonic nanoparticles was not observed. The experimental evidence points against hot-electron injection from Au-NPs to the semiconductor component. This behavior is associated with the height of the Schottky barrier at the metal-semiconductor junctions. The differences in the photocatalytic performance among the samples under UV- and visible-light are explained in terms of the characteristics of the Au-NPs driven by the growth mechanism involved in each impregnation method and the physicochemical properties of the generated interfaces. Full article
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Open AccessArticle Mobility of NH3-Solvated CuII Ions in Cu-SSZ-13 and Cu-ZSM-5 NH3-SCR Catalysts: A Comparative Impedance Spectroscopy Study
Catalysts 2018, 8(4), 162; https://doi.org/10.3390/catal8040162
Received: 14 March 2018 / Revised: 8 April 2018 / Accepted: 9 April 2018 / Published: 18 April 2018
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Abstract
The mobility of NH3-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NOx with NH3 (NH3-SCR) over Cu-zeolite catalysts at low temperatures.
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The mobility of NH3-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NOx with NH3 (NH3-SCR) over Cu-zeolite catalysts at low temperatures. Here, we utilize in situ impedance spectroscopy to explore the mobility of NH3-solvated CuII ions, i.e., CuII(NH3)n, in Cu-SSZ-13 and Cu-ZSM-5 zeolites with varied Cu ion exchange levels, and observed that both the zeolite framework (CHA or MFI) and the Cu exchange level influence the high-frequency dielectric relaxation processes that are associated with the short-range (local) motion of CuII(NH3)n. Our results suggest that the local motion of CuII(NH3)n species is favored within the CHA framework due to the unique cage structure, and thereby contribute to the overall ion conductivity at high frequencies, which, on the contrary, is not observed for ZSM-5, where NH3-solvated Cu2+ ions do not experience a comparable constrained space for local motion. This study sheds new light on the mobility of Cu active sites under NH3-SCR related reaction conditions and may contribute to an advanced understanding of the underlying mechanism. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Surface Reduced CeO2 Nanowires for Direct Conversion of CO2 and Methanol to Dimethyl Carbonate: Catalytic Performance and Role of Oxygen Vacancy
Catalysts 2018, 8(4), 164; https://doi.org/10.3390/catal8040164
Received: 14 March 2018 / Revised: 4 April 2018 / Accepted: 4 April 2018 / Published: 19 April 2018
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Abstract
Ultralong 1D CeO2 nanowires were synthesized via an advanced solvothermal method, surface reduced under H2 atmosphere, and first applied in direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH. The micro morphologies, physical parameters of nanowires were
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Ultralong 1D CeO2 nanowires were synthesized via an advanced solvothermal method, surface reduced under H2 atmosphere, and first applied in direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3OH. The micro morphologies, physical parameters of nanowires were fully investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectrum (XPS), and temperature-programmed desorption of ammonia/carbon dioxide (NH3-TPD/CO2-TPD). The effects of surface oxygen vacancy and acidic/alkaline sites on the catalytic activity was explored. After reduction, the acidic/alkaline sites of CeO2 nanowires can be dramatically improved and evidently raised the catalytic performance. CeO2 nanowires reduced at 500 °C (CeO2_NW_500) exhibited notably superior activity with DMC yield of 16.85 mmol gcat−1. Furthermore, kinetic insights of initial rate were carried out and the apparent activation energy barrier of CeO2_NW_500 catalyst was found to be 41.9 kJ/mol, much tiny than that of CeO2_NW catalyst (74.7 KJ/mol). Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Asymmetric Ketone Reduction by Immobilized Rhodotorula mucilaginosa
Catalysts 2018, 8(4), 165; https://doi.org/10.3390/catal8040165
Received: 29 March 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
In our previous study, Rhodotorula mucilaginosa (R. mucilaginosa) was selected via high throughput screening as a very active and selective whole-cell biocatalyst for the asymmetric reduction of ketones. In this study, the reduction of ketones to the desired chiral alcohols by
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In our previous study, Rhodotorula mucilaginosa (R. mucilaginosa) was selected via high throughput screening as a very active and selective whole-cell biocatalyst for the asymmetric reduction of ketones. In this study, the reduction of ketones to the desired chiral alcohols by immobilized cells of this strain was investigated. Characterization with Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed that whole R. mucilaginosa cells were successfully immobilized on support matrices composed of agar, calcium alginate, PVA-alginate and chitosan. The immobilized cells were applied to the enantioselective reduction of fourteen different aromatic ketones. Good to excellent results were achieved with R. mucilaginosa cells immobilized on agar and calcium alginate. The immobilized cells on the selected support matrix composed of agar exhibited a significant increase in pH tolerance at pH 3.5–9 and demonstrated highly improved thermal stability compared to free cells. The cells immobilized on agar retained 90% activity after 60 days storage at 4 °C and retained almost 100% activity after 6 reuse cycles. In addition, the immobilization procedures are very simple and cause minimal pollution. These results suggest that the application of immobilized R. mucilaginosa can be practical on an industrial scale to produce chiral alcohols. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Unprecedented Proline-Based Heterogeneous Organocatalyst for Selective Production of Vanillin
Catalysts 2018, 8(4), 167; https://doi.org/10.3390/catal8040167
Received: 3 April 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
An organocatalytic system based on an unprecedented proline analogue and iron oxide magnetic nanoparticles (Prn/Fe2O3@SiO2) was designed and employed in vanillin production from isoeugenol and vanillyl alcohol. Full characterization of the obtained catalyst revealed the successful functionalization
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An organocatalytic system based on an unprecedented proline analogue and iron oxide magnetic nanoparticles (Prn/Fe2O3@SiO2) was designed and employed in vanillin production from isoeugenol and vanillyl alcohol. Full characterization of the obtained catalyst revealed the successful functionalization of the nanoparticle surface with the organic moieties. The activity of the magnetic bifunctional material was compared with its proton-unexchanged counterpart. Interestingly, the oxidation of isoeugenol resulted in being highly dependent on the acidic functionalities of the organocatalyst. Nonetheless, the catalytic performance of the proton-unexchanged catalyst suggested that the acidic and basic sites of the Prn/Fe2O3@SiO2 exhibited a synergic effect, giving rise to higher conversion and selectivity. The presence of bifunctional groups in the proline analogue, together with the magnetic properties of the iron oxide nanoparticles, could lead to high efficiency, versatility, recoverability, and reusability. Full article
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Open AccessArticle Co-Immobilization of Ketoreductase and Glucose Dehydrogenase
Catalysts 2018, 8(4), 168; https://doi.org/10.3390/catal8040168
Received: 29 March 2018 / Revised: 12 April 2018 / Accepted: 18 April 2018 / Published: 20 April 2018
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Abstract
A two-enzyme system composed of immobilized ketoreductase (Hansenula polymorpha) and glucose dehydrogenase (Bacillus megaterium) was developed for the asymmetric reduction of keto esters to optically active hydroxy esters via immobilization in polyvinyl alcohol (PVA) gel particles. The concentration of
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A two-enzyme system composed of immobilized ketoreductase (Hansenula polymorpha) and glucose dehydrogenase (Bacillus megaterium) was developed for the asymmetric reduction of keto esters to optically active hydroxy esters via immobilization in polyvinyl alcohol (PVA) gel particles. The concentration of enzymes was optimized, and the final particles were used 18 times in a row in a batch mode to achieve minimal loss of activity and complete conversion of the model substrate, β-ketoester ethyl-2-methylacetoacetate. Excellent stability was also achieved using new storage conditions of PVA particles, with 80% of activity being retained after almost 10 months. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessFeature PaperArticle A Biorefinery Cascade Conversion of Hemicellulose-Free Eucalyptus Globulus Wood: Production of Concentrated Levulinic Acid Solutions for γ-Valerolactone Sustainable Preparation
Catalysts 2018, 8(4), 169; https://doi.org/10.3390/catal8040169
Received: 14 March 2018 / Revised: 18 April 2018 / Accepted: 19 April 2018 / Published: 21 April 2018
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Abstract
Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic
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Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic acid through a sulfuric acid-catalyzed reaction. These runs were carried out in a microwave-heated reactor at different temperatures and reaction times, operating in single-batch or cross-flow modes, in order to identify the most favorable operational conditions. Selected liquid phases deriving from these experiments, which resulted in concentrated levulinic acid up to 408 mmol/L, were then employed for γ-valerolactone production by levulinc acid hydrogenation in the presence of the commercial 5% Ru/C catalyst. In order to assess the effects of the main reaction parameters, hydrogenation experiments were performed at different temperatures, reaction times, amounts of ruthenium catalyst and hydrogen pressure. Yields of γ-valerolactone in the range of 85–90 mol % were obtained from the hydrogenation of the wood-derived solutions containing levulinic acid, obtained by single-batch operation or by the cross-flow process. The negative effect of co-produced formic acid present in crude levulinic acid solutions was evidenced and counteracted efficiently by allowing the preliminary thermal decomposition of formic acid itself. Full article
(This article belongs to the Special Issue Catalytic Transformation of Lignocellulosic Platform Chemicals)
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Open AccessArticle Maltose Production Using Starch from Cassava Bagasse Catalyzed by Cross-Linked β-Amylase Aggregates
Catalysts 2018, 8(4), 170; https://doi.org/10.3390/catal8040170
Received: 20 March 2018 / Revised: 17 April 2018 / Accepted: 19 April 2018 / Published: 21 April 2018
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Abstract
Barley β-amylase was immobilized using different techniques. The highest global yield was obtained using the cross-linked enzyme aggregates (CLEA) technique, employing bovine serum albumin (BSA) or soy protein isolate (SPI) as feeder proteins to reduce diffusion problems. The CLEAs produced using BSA or
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Barley β-amylase was immobilized using different techniques. The highest global yield was obtained using the cross-linked enzyme aggregates (CLEA) technique, employing bovine serum albumin (BSA) or soy protein isolate (SPI) as feeder proteins to reduce diffusion problems. The CLEAs produced using BSA or SPI showed 82.7 ± 5.8 and 53.3 ± 2.4% global yield, respectively, and a stabilization effect was observed upon immobilization at neutral pH value, e.g., after 12 h at 55 °C, the free β-amylase is fully inactivated, while CLEAs retained 25 and 15% of activity (using BSA and SPI, respectively). CLEA using SPI was selected because of its easier recovery, being chosen to convert the residual starch contained in cassava bagasse into maltose. This biocatalyst permitted to reach almost 70% of maltose conversion in 4 h using 30.0 g/L bagasse starch solution (Dextrose Equivalent of 15.88) and 1.2 U of biocatalyst per gram of starch at pH 7.0 and 40 °C. After 4 reuses (batches of 12 h) the CLEA using SPI maintained 25.50 ± 0.01% of conversion due to the difficulty of recovering. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle CuO Nanoparticles Supported on TiO2 with High Efficiency for CO2 Electrochemical Reduction to Ethanol
Catalysts 2018, 8(4), 171; https://doi.org/10.3390/catal8040171
Received: 7 March 2018 / Revised: 7 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
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Abstract
Non-noble metal oxides consisting of CuO and TiO2 (CuO/TiO2 catalyst) for CO2 reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO2 catalyst, which could efficiently
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Non-noble metal oxides consisting of CuO and TiO2 (CuO/TiO2 catalyst) for CO2 reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO2 catalyst, which could efficiently catalyze CO2 reduction to multi-carbon oxygenates (ethanol, acetone, and n-propanol) with a maximum overall faradaic efficiency of 47.4% at a potential of −0.85 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO3 solution. The catalytic activity for CO2 electroreduction strongly depends on the CuO contents of the catalysts as-prepared, resulting in different electrochemistry surface areas. The significantly improved CO2 catalytic activity of CuO/TiO2 might be due to the strong CO2 adsorption ability. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Jump to: Research

Open AccessReview Catalytic Hydroisomerization Upgrading of Vegetable Oil-Based Insulating Oil
Catalysts 2018, 8(4), 131; https://doi.org/10.3390/catal8040131
Received: 9 February 2018 / Revised: 18 March 2018 / Accepted: 28 March 2018 / Published: 28 March 2018
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Abstract
Due to its high biodegradability, high dielectric strength, and good thermal stability, vegetable oil is under consideration as an alternative transformer fluid for power system equipment, replacing traditional petroleum-based insulating oils. Its main drawbacks are its poor low-temperature properties arising from the crystallization
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Due to its high biodegradability, high dielectric strength, and good thermal stability, vegetable oil is under consideration as an alternative transformer fluid for power system equipment, replacing traditional petroleum-based insulating oils. Its main drawbacks are its poor low-temperature properties arising from the crystallization of its long-chain normal paraffins, and its lower oxidative stability arising from its higher concentration of unsaturated fatty acids. Hydroisomerization/isomerization over bifunctional catalysts is considered to be an efficient pathway to upgrade vegetable oil-based insulating oil; this converts saturated/unsaturated long-chain fatty acids to branched isomers. The efficiency of this process depends crucially on the behavior of the catalyst system. This paper extensively reviews recent results on the influence that the metal phase and acidity, the effects of pore channels, and the balance between metal and acid sites have upon the activity and selectivity of catalytic hydroisomerization. Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
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Open AccessFeature PaperReview Strategies of Coping with Deactivation of NH3-SCR Catalysts Due to Biomass Firing
Catalysts 2018, 8(4), 135; https://doi.org/10.3390/catal8040135
Received: 28 February 2018 / Revised: 22 March 2018 / Accepted: 22 March 2018 / Published: 30 March 2018
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Abstract
Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly
[...] Read more.
Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessFeature PaperReview Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts
Catalysts 2018, 8(4), 140; https://doi.org/10.3390/catal8040140
Received: 2 March 2018 / Revised: 27 March 2018 / Accepted: 28 March 2018 / Published: 31 March 2018
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Abstract
Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a
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Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessReview An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations
Catalysts 2018, 8(4), 163; https://doi.org/10.3390/catal8040163
Received: 19 March 2018 / Revised: 7 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Synthetic zeolites are widely used as catalysts/carriers for many petrochemical reactions and in refining processes. These materials are usually synthesized in a powder form and must be shaped prior to use in industrial reactors. This review presents the state-of-the-art of the zeolite shaping
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Synthetic zeolites are widely used as catalysts/carriers for many petrochemical reactions and in refining processes. These materials are usually synthesized in a powder form and must be shaped prior to use in industrial reactors. This review presents the state-of-the-art of the zeolite shaping technology describing the main modifications induced by the interactions between the zeolite and the binder. Additionally, a strategy is presented to overcome the diffusion limitations associated to the microporous structure of zeolites, consisting in the introduction of hierarchical porosity in the binder. Several developments in the field of hierarchical aluminas are summarized in this article, highlighting the possibility to design different ordered/disordered mesoporous and macroporous structures. Full article
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Open AccessReview Applications of Immobilized Bio-Catalyst in Metal-Organic Frameworks
Catalysts 2018, 8(4), 166; https://doi.org/10.3390/catal8040166
Received: 9 April 2018 / Revised: 18 April 2018 / Accepted: 18 April 2018 / Published: 20 April 2018
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Abstract
Immobilization of bio-catalysts in solid porous materials has attracted much attention in the last few decades due to its vast application potential in ex vivo catalysis. Despite the high efficiency and selectivity of enzymatic catalytic processes, enzymes may suffer from denaturation under industrial
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Immobilization of bio-catalysts in solid porous materials has attracted much attention in the last few decades due to its vast application potential in ex vivo catalysis. Despite the high efficiency and selectivity of enzymatic catalytic processes, enzymes may suffer from denaturation under industrial production conditions, which, in turn, diminish their catalytic performances and long-term recyclability. Metal-organic frameworks (MOFs), as a growing type of hybrid materials, have been identified as promising platforms for enzyme immobilization owing to their enormous structural and functional tunability, and extraordinary porosity. This review mainly focuses on the applications of enzyme@MOFs hybrid materials in catalysis, sensing, and detection. The improvements of catalytic activity and robustness of encapsulated enzymes over the free counterpart are discussed in detail. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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