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Catalysts, Volume 7, Issue 5 (May 2017)

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Cover Story (view full-size image) The search for an efficient electrocatalyst for the oxygen-evolution reaction (OER) made of [...] Read more.
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Open AccessArticle Catalytic Decomposition of N2O over Cu–Zn/ZnAl2O4 Catalysts
Catalysts 2017, 7(5), 166; https://doi.org/10.3390/catal7050166
Received: 18 April 2017 / Revised: 12 May 2017 / Accepted: 17 May 2017 / Published: 22 May 2017
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Abstract
The catalytic decomposition of N2O was investigated over Cu-Zn/ZnAl2O4 catalysts in the temperature range of 400–650 °C Catalytic samples have been prepared by wet impregnation method. Prepared catalysts were characterized using several techniques like BET surface area, X-ray
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The catalytic decomposition of N2O was investigated over Cu-Zn/ZnAl2O4 catalysts in the temperature range of 400–650 °C Catalytic samples have been prepared by wet impregnation method. Prepared catalysts were characterized using several techniques like BET surface area, X-ray diffraction (XRD), and Scanning electron microscopy (SEM). The Cu-Zn/ZnAl2O4 showed higher catalytic performance along with long term stability during N2O decomposition. The Cu-Zn/ZnAl2O4 catalysts yielded 100% N2O conversion at 650 °C. The Cu-Zn/ZnAl2O4 catalysts are promising for decrease this strong greenhouse gas in the chemical industry. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessFeature PaperPerspective Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters
Catalysts 2017, 7(5), 165; https://doi.org/10.3390/catal7050165
Received: 5 May 2017 / Revised: 15 May 2017 / Accepted: 18 May 2017 / Published: 22 May 2017
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Abstract
Schiff base macrocycles are emerging as useful scaffolds for binding two or more catalytic metals in close proximity. Such coordination chemistry allows for the evaluation of potentially beneficial catalytic cooperative effects. In the field of ring opening polymerization (ROP) of cyclic esters, only
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Schiff base macrocycles are emerging as useful scaffolds for binding two or more catalytic metals in close proximity. Such coordination chemistry allows for the evaluation of potentially beneficial catalytic cooperative effects. In the field of ring opening polymerization (ROP) of cyclic esters, only a handful of metal systems bound by Schiff base [2 + 2] type macrocycles have been studied. Nevertheless, results to date have, for certain metals, identified some interesting structure activity relationships, whilst for other systems results have revealed particular combinations of metals and macrocycles to be virtually inactive. This perspective review takes a look at two types of recently-reported Schiff base macrocycles that have been employed as pro-ligands in the metal-catalyzed ROP of cyclic esters, specifically ε-caprolactone and rac-lactide. Full article
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Open AccessArticle Solar and Visible Light Illumination on Immobilized Nano Zinc Oxide for the Degradation and Mineralization of Orange G in Wastewater
Catalysts 2017, 7(5), 164; https://doi.org/10.3390/catal7050164
Received: 4 March 2017 / Revised: 2 May 2017 / Accepted: 10 May 2017 / Published: 20 May 2017
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Abstract
An advanced oxidation process (AOP) utilizing immobilized zinc oxide (ZnO) photocatalyst was employed to decolorize and mineralize orange G (OG) azo dye in wastewater under solar and visible light irradiation. This AOP employed visible light and ZnO in a so-called Vis/ZnO process. Operating
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An advanced oxidation process (AOP) utilizing immobilized zinc oxide (ZnO) photocatalyst was employed to decolorize and mineralize orange G (OG) azo dye in wastewater under solar and visible light irradiation. This AOP employed visible light and ZnO in a so-called Vis/ZnO process. Operating parameters, including ZnO dosage, initial OG concentration, pH, visible-light intensity, catalyst loaded area, and treatment volume were investigated to illustrate their influences on OG degradation and mineralization. From the results, neither visible light alone, nor the ZnO adsorption process could degrade or remove OG from wastewater. However, for the Vis/ZnO process, the higher ZnO dosage and visible light intensity are two major parameters to improve the OG degradation and total organic carbons (TOC) mineralization. The initial pH of 11 was the most effective pH condition on the OG degradation. The first-order rate constant is exponentially decreased from 0.025 to 0.0042 min−1 with the increase of the initial OG concentration and an empirical equation can be derived to estimate the first-order rate constant with a known initial OG concentration. In contrast, the first-order rate constant is linearly increased from 0.0027 to 0.0083 min−1 by increasing the visible light intensity. The results present that the Vis/ZnO process is an effective AOP for the degradation of OG in wastewater. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessReview Catalytic Processes for Utilizing Carbohydrates Derived from Algal Biomass
Catalysts 2017, 7(5), 163; https://doi.org/10.3390/catal7050163
Received: 18 April 2017 / Revised: 10 May 2017 / Accepted: 15 May 2017 / Published: 19 May 2017
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Abstract
The high productivity of oil biosynthesized by microalgae has attracted increasing attention in recent years. Due to the application of such oils in jet fuels, the algal biosynthetic pathway toward oil components has been extensively researched. However, the utilization of the residue from
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The high productivity of oil biosynthesized by microalgae has attracted increasing attention in recent years. Due to the application of such oils in jet fuels, the algal biosynthetic pathway toward oil components has been extensively researched. However, the utilization of the residue from algal cells after oil extraction has been overlooked. This residue is mainly composed of carbohydrates (starch), and so we herein describe the novel processes available for the production of useful chemicals from algal biomass-derived sugars. In particular, this review highlights our latest research in generating lactic acid and levulinic acid derivatives from polysaccharides and monosaccharides using homogeneous catalysts. Furthermore, based on previous reports, we discuss the potential of heterogeneous catalysts for application in such processes. Full article
(This article belongs to the Special Issue Catalytic Sustainable Processes in Biorefineries)
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Open AccessArticle Cellulose with a High Fractal Dimension Is Easily Hydrolysable under Acid Catalysis
Catalysts 2017, 7(5), 162; https://doi.org/10.3390/catal7050162
Received: 2 March 2017 / Revised: 16 April 2017 / Accepted: 12 May 2017 / Published: 19 May 2017
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Abstract
The adsorption of three diverse amino acids couples onto the surface of microcrystalline cellulose was studied. Characterisation of modified celluloses included changes in the polarity and in roughness. The amino acids partially break down the hydrogen bonding network of the cellulose structure, leading
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The adsorption of three diverse amino acids couples onto the surface of microcrystalline cellulose was studied. Characterisation of modified celluloses included changes in the polarity and in roughness. The amino acids partially break down the hydrogen bonding network of the cellulose structure, leading to more reactive cellulose residues that were easily hydrolysed to glucose in the presence of hydrochloric acid or tungstophosphoric acid catalysts. The conversion of cellulose and selectivity for glucose was highly dependent on the self-assembled amino acids adsorbed onto the cellulose and the catalyst. Full article
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Open AccessArticle Reactivity of Copper Electrodes towards Functional Groups and Small Molecules in the Context of CO2 Electro-Reductions
Catalysts 2017, 7(5), 161; https://doi.org/10.3390/catal7050161
Received: 28 March 2017 / Revised: 2 May 2017 / Accepted: 4 May 2017 / Published: 18 May 2017
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Abstract
The direct electro-reduction of CO2 to functional molecules like ethene is a highly desirable variant of CO2 utilization. The formation of, for example, ethene from CO2 is a multistep electrochemical process going through various intermediates. As these intermediates are organic
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The direct electro-reduction of CO2 to functional molecules like ethene is a highly desirable variant of CO2 utilization. The formation of, for example, ethene from CO2 is a multistep electrochemical process going through various intermediates. As these intermediates are organic species, the CO2 reducing electro-catalyst has to be competent for a variety of organic functional group transformations to yield the final product. In this work, the activity of an in situ-grown nano-structured copper catalyst towards a variety of organic functional group conversions was studied. The model reagents were selected from the product spectrum of actual CO2 reduction reaction (CO2RR) experiments and from proposals in the literature. The CO2 bulk electrolysis benchmark was conducted at 170 mAcm−2 current density with up to 43% Faradaic Efficiency (FE) for ethene and 23% FE for ethanol simultaneously. To assure relevance for application-oriented conditions, the reactivity screening was conducted at elevated current densities and, thus, overpotentials. The found reactivity pattern was then also transferred to the CO reduction reaction (CORR) under benchmark conditions yielding additional insights. The results suggest that at high current density/high overpotential conditions, also other ethene formation pathways apart from acetaldehyde reduction such as CH2 dimerization are present. A new suggestion for a high current density mechanism will be presented, which is in agreement with the experimental observations and the found activity pattern of copper cathodes toward organic functional group conversion. Full article
(This article belongs to the Special Issue Small Molecule Activation and Catalysis)
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Open AccessArticle Catalytic Behaviour of CuO-CeO2 Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO2-H2O Feed Stream
Catalysts 2017, 7(5), 160; https://doi.org/10.3390/catal7050160
Received: 10 April 2017 / Revised: 10 May 2017 / Accepted: 15 May 2017 / Published: 18 May 2017
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Abstract
CuO-CeO2 catalysts, with 6 wt % of Cu, have been synthesised by different preparation methods (calcination of nitrate precursors, thermal urea-nitrate combustion, freeze-drying method, using polymethyl metacrylate PMMA microspheres as template and precipitation using NaOH or the decomposition of urea as precipitating
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CuO-CeO2 catalysts, with 6 wt % of Cu, have been synthesised by different preparation methods (calcination of nitrate precursors, thermal urea-nitrate combustion, freeze-drying method, using polymethyl metacrylate PMMA microspheres as template and precipitation using NaOH or the decomposition of urea as precipitating agents). The obtained materials have been characterised by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, N2 adsorption-desorption at −196 °C, H2 thermoprogrammed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts displayed high dispersion of copper oxide, obtaining CO conversion values of 90–100% at 115 °C in the CO preferential oxidation in excess of hydrogen (CO-PROX) and maintaining this activity even after 48 h of time on stream. The incorporation of CO2 and H2O in the feed stream (simulating a PROX unit) caused a decrease in the CO conversion, except for the catalyst synthesised using PMMA microspheres as a template which maintained a CO conversion of 95% at 115 °C. This catalyst exhibits an excellent catalytic performance, also under real operating conditions, thanks to many and concomitant factors, such as the very small CeO2 particle size (5.6 nm), the surface being rich in copper (atomic ratio Cu/Ce = 0.35) that is easily reducible, and the peculiar morphology and porosity of the material. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessFeature PaperReview Process Simulation for the Design and Scale Up of Heterogeneous Catalytic Process: Kinetic Modelling Issues
Catalysts 2017, 7(5), 159; https://doi.org/10.3390/catal7050159
Received: 18 March 2017 / Revised: 21 April 2017 / Accepted: 10 May 2017 / Published: 18 May 2017
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Abstract
Process simulation represents an important tool for plant design and optimization, either applied to well established or to newly developed processes. Suitable thermodynamic packages should be selected in order to properly describe the behavior of reactors and unit operations and to precisely define
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Process simulation represents an important tool for plant design and optimization, either applied to well established or to newly developed processes. Suitable thermodynamic packages should be selected in order to properly describe the behavior of reactors and unit operations and to precisely define phase equilibria. Moreover, a detailed and representative kinetic scheme should be available to predict correctly the dependence of the process on its main variables. This review points out some models and methods for kinetic analysis specifically applied to the simulation of catalytic processes, as a basis for process design and optimization. Attention is paid also to microkinetic modelling and to the methods based on first principles, to elucidate mechanisms and independently calculate thermodynamic and kinetic parameters. Different case studies support the discussion. At first, we have selected two basic examples from the industrial chemistry practice, e.g., ammonia and methanol synthesis, which may be described through a relatively simple reaction pathway and the relative available kinetic scheme. Then, a more complex reaction network is deeply discussed to define the conversion of bioethanol into syngas/hydrogen or into building blocks, such as ethylene. In this case, lumped kinetic schemes completely fail the description of process behavior. Thus, in this case, more detailed—e.g., microkinetic—schemes should be available to implement into the simulator. However, the correct definition of all the kinetic data when complex microkinetic mechanisms are used, often leads to unreliable, highly correlated parameters. In such cases, greater effort to independently estimate some relevant kinetic/thermodynamic data through Density Functional Theory (DFT)/ab initio methods may be helpful to improve process description. Full article
(This article belongs to the Special Issue Computational Methods and Their Application in Catalysis)
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Open AccessArticle Influence of Dissolved Ions on the Water Purification Performance of TiO2-Impregnated Porous Silica Tubes
Catalysts 2017, 7(5), 158; https://doi.org/10.3390/catal7050158
Received: 27 April 2017 / Revised: 10 May 2017 / Accepted: 10 May 2017 / Published: 16 May 2017
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Abstract
TiO2-coated porous silica glass tubes containing macropores were fabricated and evaluated for their water-purification capacity using aqueous solutions of methylene blue. From the results of photocatalytic degradation tests at different initial methylene blue concentrations, the equilibrium adsorption constant (K)
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TiO2-coated porous silica glass tubes containing macropores were fabricated and evaluated for their water-purification capacity using aqueous solutions of methylene blue. From the results of photocatalytic degradation tests at different initial methylene blue concentrations, the equilibrium adsorption constant (K) was determined to be 4.6 × 10−2 L µmol−1, and the Langmuir-Hinshelwood rate constant (kLH) was calculated as 2.6 µM min−1. To determine the influence of ions on the efficiency of methylene blue degradation, we examined both Milli-Q water (soft water) and Contrex water (hard water) as solvents, and confirmed the reduced purification for the Contrex solution. It was, therefore, considered that the presence of inorganic salts decreased the photocatalytic efficiency. Furthermore, variations in the methylene blue decomposition ability were observed between anion-free and cation-free Contrex. Finally, we concluded that the efficiency of photocatalytic decomposition of TiO2 was influenced by multiple parameters, including the presence of anions and cations, as well as the solution pH. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessFeature PaperArticle Development of Active and Stable Low Nickel Content Catalysts for Dry Reforming of Methane
Catalysts 2017, 7(5), 157; https://doi.org/10.3390/catal7050157
Received: 30 March 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 16 May 2017
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Abstract
Methane dry reforming (DRM) was investigated over highly active Ni catalysts with low metal content (2.5 wt %) supported on Mg-Al mixed oxide. The aim was to minimize carbon deposition and metal sites agglomeration on the working catalyst which are known to cause
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Methane dry reforming (DRM) was investigated over highly active Ni catalysts with low metal content (2.5 wt %) supported on Mg-Al mixed oxide. The aim was to minimize carbon deposition and metal sites agglomeration on the working catalyst which are known to cause catalyst deactivation. The solids were characterized using N2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The results showed that MgO-Al2O3 solid solution phases are obtained when calcining Mg-Al hydrotalcite precursor in the temperature range of 550–800 °C. Such phases contribute to the high activity of catalysts with low Ni content even at low temperature (500 °C). Modifying the catalyst preparation with citric acid significantly slows the coking rate and reduces the size of large octahedrally coordinated NiO-like domains, which may easily agglomerate on the surface during DRM. The most effective Ni catalyst shows a stable DRM course over 60 h at high weight hourly space velocity with very low coke deposition. This is a promising result for considering such catalyst systems for further development of an industrial DRM technology. Full article
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Open AccessArticle Effective Electron Transfer Pathway of the Ternary TiO2/RGO/Ag Nanocomposite with Enhanced Photocatalytic Activity under Visible Light
Catalysts 2017, 7(5), 156; https://doi.org/10.3390/catal7050156
Received: 24 March 2017 / Revised: 4 May 2017 / Accepted: 10 May 2017 / Published: 15 May 2017
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Abstract
Mesoporous TiO2/reduced graphene oxide/Ag (TiO2/RGO/Ag) ternary nanocomposite with an effective electron transfer pathway is obtained by an electrostatic self-assembly method and photo-assisted treatment. Compared with bare mesoporous TiO2 (MT) and mesoporous TiO2/RGO (MTG), the ternary mesoporous
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Mesoporous TiO2/reduced graphene oxide/Ag (TiO2/RGO/Ag) ternary nanocomposite with an effective electron transfer pathway is obtained by an electrostatic self-assembly method and photo-assisted treatment. Compared with bare mesoporous TiO2 (MT) and mesoporous TiO2/RGO (MTG), the ternary mesoporous TiO2/RGO/Ag (MTGA) nanocomposite exhibited superior photocatalytic performance for the degradation of methylene blue (MB) under visible light, and the degradation rate reached 0.017 min−1, which was 3.4-times higher than that of MTG. What is more, the degradation rate of MTGA nanocomposite after three cycle times is 91.2%, and the composition is unchanged. In addition, we found that the OH•, h+ and especially O2•− contribute to the high photocatalytic activity of MTGA for MB degradation. It is proposed that Ag nanoparticles can form the local surface plasmon resonance (LSPR) to absorb the visible light and distract the electrons into MT, and RGO can accept the electrons from MT to accelerate the separation efficiency of photogenerated carriers. The establishment of MTGA ternary nanocomposite makes the three components act synergistically to enhance the photocatalytic performance. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessArticle Methanation of CO2 on Ni/Al2O3 in a Structured Fixed-Bed Reactor—A Scale-Up Study
Catalysts 2017, 7(5), 152; https://doi.org/10.3390/catal7050152
Received: 31 March 2017 / Revised: 24 April 2017 / Accepted: 4 May 2017 / Published: 15 May 2017
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Abstract
Due to the ongoing change of energy supply, the availability of a reliable high-capacity storage technology becomes increasingly important. While conventional large-scale facilities are either limited in capacity respective supply time or their extension potential is little (e.g., pumped storage power stations), decentralized
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Due to the ongoing change of energy supply, the availability of a reliable high-capacity storage technology becomes increasingly important. While conventional large-scale facilities are either limited in capacity respective supply time or their extension potential is little (e.g., pumped storage power stations), decentralized units could contribute to energy transition. The concepts of PtX (power-to-X) storage technologies and in particular PtG (power-to-gas) aim at fixation of electric power in chemical compounds. CO2 hydrogenation (methanation) is the foundation of the PtG idea as H2 (via electrolysis) and CO2 are easily accessible. Methane produced in this way, often called substitute natural gas (SNG), is a promising solution since it can be stored in the existing gas grid, tanks or underground cavern storages. Methanation is characterized by a strong exothermic heat of reaction which has to be handled safely. This work aims at getting rid of extreme temperature hot-spots in a tube reactor by configuring the catalyst bed structure. Proof of concept studies began with a small tube reactor (V = 12.5 cm3) with a commercial 18 wt % Ni/Al2O3 catalyst. Later, a double-jacket tube reactor was built (V = 452 cm3), reaching a production rate of 50 L/h SNG. The proposed approach not only improves the heat management and process safety, but also increases the specific productivity and stability of the catalyst remarkably. Full article
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Open AccessArticle Catalytic Performance of MgO-Supported Co Catalyst for the Liquid Phase Oxidation of Cyclohexane with Molecular Oxygen
Catalysts 2017, 7(5), 155; https://doi.org/10.3390/catal7050155
Received: 21 March 2017 / Revised: 27 April 2017 / Accepted: 9 May 2017 / Published: 13 May 2017
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Abstract
A highly-efficient and stable MgO-supported Co (Co/MgO) catalyst was developed for the oxidation of cyclohexane with oxygen. The effects of the Co loading and support on the catalytic activity of the supported Co3O4 catalyst were investigated. The results show that
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A highly-efficient and stable MgO-supported Co (Co/MgO) catalyst was developed for the oxidation of cyclohexane with oxygen. The effects of the Co loading and support on the catalytic activity of the supported Co3O4 catalyst were investigated. The results show that the Co supported on MgO presented excellent activity and stability. When the Co/MgO catalyst with the Co content of 0.2 wt% (0.2%Co/MgO) was used, 12.5% cyclohexane conversion and 74.7% selectivity to cyclohexanone and cyclohexanol (KA oil) were achieved under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h. After being repeatedly used 10 times, its catalytic activity was hardly changed. Further research showed that the high catalytic performance of the 0.2%Co/MgO catalyst is attributed to its high oxygen-absorbing ability and the high ratio between the amount of weak and medium base sites with the help of the synergistic interaction between Co and MgO. Full article
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Open AccessFeature PaperReview Perovskite Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media
Catalysts 2017, 7(5), 154; https://doi.org/10.3390/catal7050154
Received: 21 March 2017 / Revised: 28 April 2017 / Accepted: 10 May 2017 / Published: 13 May 2017
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Abstract
Oxygen reduction is considered a key reaction for electrochemical energy conversion but slow kinetics hamper application in fuel cells and metal-air batteries. In this review, the prospect of perovskite oxides for the oxygen reduction reaction (ORR) in alkaline media is reviewed with respect
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Oxygen reduction is considered a key reaction for electrochemical energy conversion but slow kinetics hamper application in fuel cells and metal-air batteries. In this review, the prospect of perovskite oxides for the oxygen reduction reaction (ORR) in alkaline media is reviewed with respect to fundamental insight into activity and possible mechanisms. For gaining these insights, special emphasis is placed on highly crystalline perovskite films that have only recently become available for electrochemical interrogation. The prospects for applications are evaluated based on recent progress in the synthesis of perovskite nanoparticles. The review concludes with the current understanding of oxygen reduction on perovskite oxides and a perspective on opportunities for future fundamental and applied research. Full article
(This article belongs to the Special Issue (Photo)Electrochemistry of Perovskites)
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Open AccessArticle Structure-Dependent Photocatalytic Performance of BiOBrxI1−x Nanoplate Solid Solutions
Catalysts 2017, 7(5), 153; https://doi.org/10.3390/catal7050153
Received: 19 April 2017 / Revised: 8 May 2017 / Accepted: 9 May 2017 / Published: 13 May 2017
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Abstract
BiOXxY1−x (X, Y = Cl, Br, and I) solid solutions have been regarded as promising photocatalysts attributed to their unique layered structure, tunable band structure, and chemical and optical stability. In this study, BiOBrxI1−x nanoplate
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BiOXxY1−x (X, Y = Cl, Br, and I) solid solutions have been regarded as promising photocatalysts attributed to their unique layered structure, tunable band structure, and chemical and optical stability. In this study, BiOBrxI1−x nanoplate solid solutions with a high exposure of {001} crystal facets were prepared by a facile alcoholysis method at room temperature and atmospheric pressure. X-ray diffraction (XRD) peaks exhibited a slight shift to lower diffraction angle with the increase of I content in BiOBrxI1−x samples, which resulted in a gradual increase in their cell parameters. Field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) images revealed that BiOBrxI1−x samples exhibited 2D plate-like structure with the in-plane wrinkles. The regular changes in optical absorption threshold and Eg value seen in UV-vis diffuse reflectance spectra (UV-vis DRS) indicated that the optical absorption property and band structure could be modulated by the formation of BiOBrxI1−x solid solutions. The photocatalytic degradation of active dye Rhodamine B (RhB) over BiOBrxI1−x solid solutions showed that BiOBr0.75I0.25 had the best photocatalytic activity. The RhB photodegradation processes followed a pseudo-first-order kinetic model. The synergistic effect of structural factors (including amount of exposed {001} facets, interlayer spacing of (001) plane, and energy-level position of the valence band) determined the photocatalytic performance of BiOBrxI1−x solid solutions. Full article
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