Catalysts

6730 KiB

Open AccessArticle

Catalytic Decomposition of N₂O over Cu–Zn/ZnAl₂O₄ Catalysts

by Xiaoying Zheng, Runhu Zhang, Fang Bai and Chao Hua

Catalysts 2017, 7(5), 166; https://doi.org/10.3390/catal7050166 - 22 May 2017

Cited by 7 | Viewed by 4908

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 [...] Read more.

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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2008 KiB

Open AccessFeature PaperPerspective

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

by Carl Redshaw

Catalysts 2017, 7(5), 165; https://doi.org/10.3390/catal7050165 - 22 May 2017

Cited by 58 | Viewed by 5863

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 [...] Read more.

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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3530 KiB

Open AccessArticle

Solar and Visible Light Illumination on Immobilized Nano Zinc Oxide for the Degradation and Mineralization of Orange G in Wastewater

by Hung-Yee Shu, Ming-Chin Chang and Tien-Hsin Tseng

Catalysts 2017, 7(5), 164; https://doi.org/10.3390/catal7050164 - 20 May 2017

Cited by 9 | Viewed by 5424

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 [...] Read more.

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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4214 KiB

Open AccessReview

Catalytic Processes for Utilizing Carbohydrates Derived from Algal Biomass

by Sho Yamaguchi, Ken Motokura, Kan Tanaka and Sousuke Imamura

Catalysts 2017, 7(5), 163; https://doi.org/10.3390/catal7050163 - 19 May 2017

Cited by 8 | Viewed by 5651

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 [...] Read more.

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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2396 KiB

Open AccessArticle

Cellulose with a High Fractal Dimension Is Easily Hydrolysable under Acid Catalysis

by Mariana Díaz, Magali Hernández, Ilich A. Ibarra, Ariel Guzmán, Victor Lara and Enrique Lima

Catalysts 2017, 7(5), 162; https://doi.org/10.3390/catal7050162 - 19 May 2017

Cited by 7 | Viewed by 5074

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 [...] Read more.

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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1580 KiB

Open AccessArticle

Reactivity of Copper Electrodes towards Functional Groups and Small Molecules in the Context of CO₂ Electro-Reductions

by Bernhard Schmid, Christian Reller, Sebastian S. Neubauer, Maximilian Fleischer, Romano Dorta and Guenter Schmid

Catalysts 2017, 7(5), 161; https://doi.org/10.3390/catal7050161 - 18 May 2017

Cited by 28 | Viewed by 8333

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 [...] Read more.

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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3329 KiB

Open AccessArticle

Catalytic Behaviour of CuO-CeO₂ Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO₂-H₂O Feed Stream

by Juan Antonio Cecilia, Ana Arango-Díaz, Jaasiel Marrero-Jerez, Pedro Núñez, Elisa Moretti, Loretta Storaro and Enrique Rodríguez-Castellón

Catalysts 2017, 7(5), 160; https://doi.org/10.3390/catal7050160 - 18 May 2017

Cited by 30 | Viewed by 6387

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 [...] Read more.

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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5936 KiB

Open AccessFeature PaperReview

Process Simulation for the Design and Scale Up of Heterogeneous Catalytic Process: Kinetic Modelling Issues

by Antonio Tripodi, Matteo Compagnoni, Rocco Martinazzo, Gianguido Ramis and Ilenia Rossetti

Catalysts 2017, 7(5), 159; https://doi.org/10.3390/catal7050159 - 18 May 2017

Cited by 26 | Viewed by 14219

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 [...] Read more.

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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3905 KiB

Open AccessArticle

Influence of Dissolved Ions on the Water Purification Performance of TiO₂-Impregnated Porous Silica Tubes

by Mio Hayashi, Tsuyoshi Ochiai, Shoko Tago, Hiromasa Tawarayama, Toshifumi Hosoya, Tsukaho Yahagi and Akira Fujishima

Catalysts 2017, 7(5), 158; https://doi.org/10.3390/catal7050158 - 16 May 2017

Cited by 8 | Viewed by 4218

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) [...] Read more.

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 (k_LH) 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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6003 KiB

Open AccessFeature PaperArticle

Development of Active and Stable Low Nickel Content Catalysts for Dry Reforming of Methane

by Quan Luu Manh Ha, Udo Armbruster, Hanan Atia, Matthias Schneider, Henrik Lund, Giovanni Agostini, Jörg Radnik, Huyen Thanh Vuong and Andreas Martin

Catalysts 2017, 7(5), 157; https://doi.org/10.3390/catal7050157 - 16 May 2017

Cited by 51 | Viewed by 7554

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 [...] Read more.

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

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Emeritus Calvin H. Bartholomew in Anticipation of His 75th Birthday)

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6182 KiB

Open AccessArticle

Effective Electron Transfer Pathway of the Ternary TiO₂/RGO/Ag Nanocomposite with Enhanced Photocatalytic Activity under Visible Light

by Hongwei Tian, Chenxing Wan, Xin Xue, Xiaoying Hu and Xiaoyi Wang

Catalysts 2017, 7(5), 156; https://doi.org/10.3390/catal7050156 - 15 May 2017

Cited by 75 | Viewed by 7755

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 [...] Read more.

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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9418 KiB

Open AccessArticle

Methanation of CO₂ on Ni/Al₂O₃ in a Structured Fixed-Bed Reactor—A Scale-Up Study

by Daniel Türks, Hesham Mena, Udo Armbruster and Andreas Martin

Catalysts 2017, 7(5), 152; https://doi.org/10.3390/catal7050152 - 15 May 2017

Cited by 44 | Viewed by 11382

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 [...] Read more.

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

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Emeritus Calvin H. Bartholomew in Anticipation of His 75th Birthday)

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4166 KiB

Open AccessArticle

Catalytic Performance of MgO-Supported Co Catalyst for the Liquid Phase Oxidation of Cyclohexane with Molecular Oxygen

by Mingzhou Wu, Yu Fu, Wangcheng Zhan, Yanglong Guo, Yun Guo, Yunsong Wang and Guanzhong Lu

Catalysts 2017, 7(5), 155; https://doi.org/10.3390/catal7050155 - 13 May 2017

Cited by 32 | Viewed by 8735

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 [...] Read more.

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

(This article belongs to the Special Issue Activation of Dioxygen and Liquid Phase Oxidation Catalysis for Fine Chemistry)

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3564 KiB

Open AccessFeature PaperReview

Perovskite Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

by Marcel Risch

Catalysts 2017, 7(5), 154; https://doi.org/10.3390/catal7050154 - 13 May 2017

Cited by 91 | Viewed by 14772

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 [...] Read more.

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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6796 KiB

Open AccessArticle

Structure-Dependent Photocatalytic Performance of BiOBr_xI_1−x Nanoplate Solid Solutions

by Huan-Yan Xu, Xu Han, Qu Tan, Xiu-Lan He and Shu-Yan Qi

Catalysts 2017, 7(5), 153; https://doi.org/10.3390/catal7050153 - 13 May 2017

Cited by 20 | Viewed by 7277

Abstract

BiOX_xY_1−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, BiOBr_xI_1−x nanoplate [...] Read more.

BiOX_xY_1−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, BiOBr_xI_1−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 BiOBr_xI_1−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 BiOBr_xI_1−x samples exhibited 2D plate-like structure with the in-plane wrinkles. The regular changes in optical absorption threshold and E_g 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 BiOBr_xI_1−x solid solutions. The photocatalytic degradation of active dye Rhodamine B (RhB) over BiOBr_xI_1−x solid solutions showed that BiOBr_0.75I_0.25 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 BiOBr_xI_1−x solid solutions. Full article

(This article belongs to the Special Issue Photocatalytic materials alternative to TiO₂ for environmental remediation, sustainable chemistry and energy conversion)

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6567 KiB

Open AccessArticle

Effect of Citric Acid on MoO₃/Al₂O₃ Catalysts for Sulfur-Resistant Methanation

by Dajun Meng, Baowei Wang, Wenxia Yu, Weihan Wang, Zhenhua Li and Xinbin Ma

Catalysts 2017, 7(5), 151; https://doi.org/10.3390/catal7050151 - 12 May 2017

Cited by 21 | Viewed by 6550

Abstract

A series of MoO₃/Al₂O₃ catalysts with different amounts (molar ratio of CA/Mo = 0, 1, 1.5, and 2) of citric acid (CA) prepared by simultaneous impregnation were evaluated for sulfur-resistant methanation. Based on the evaluation results, catalytic activity [...] Read more.

A series of MoO₃/Al₂O₃ catalysts with different amounts (molar ratio of CA/Mo = 0, 1, 1.5, and 2) of citric acid (CA) prepared by simultaneous impregnation were evaluated for sulfur-resistant methanation. Based on the evaluation results, catalytic activity increased accompanied with the rise of citric acid amount. Combine with the analysis of N₂-physisorption, XRD, H₂-TPR, XPS, and TEM, the catalyst saturated loading capacity improved, resulting in increasing dispersion of Mo species on Al₂O₃ surface clearly. According to H₂-TPR result, the Mo oxide precursors can be more easily sulfureted when citric acid is added. Moreover, based on the Raman analysis, increasingly tetrahedrally coordinated Mo⁶⁺ species with high methanation performance are generated after citric acid treatment. These factors probably together accelerate MoO₃/Al₂O₃ catalytic activity growth for methanation. Full article

(This article belongs to the Special Issue C1 Chemistry—C1-Platform Chemicals as Cornerstone for a Sustainable Energy)

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6604 KiB

Open AccessArticle

Synthesis of SAPO-34 Molecular Sieves via Novel Intermittent Hydrothermal Treatment and Its Effect on the Crystallization and Product Properties

by Zhihui Guo, Ping Miao, Weiping Zhu, Lei Guo, Fei Li, Yunpeng Xue, Qi Yin, Ruixue Yuan and Lianbin Xu

Catalysts 2017, 7(5), 150; https://doi.org/10.3390/catal7050150 - 11 May 2017

Cited by 4 | Viewed by 5541

Abstract

Intermittent hydrothermal treatment was introduced into the synthesis of SAPO-34 molecular sieves to control the nucleation and the growth in the crystallization. The effect of the crystallization time, the order of long-time and short-time crystallization in two-stage crystallization, and frequency in multi-stage crystallization [...] Read more.

Intermittent hydrothermal treatment was introduced into the synthesis of SAPO-34 molecular sieves to control the nucleation and the growth in the crystallization. The effect of the crystallization time, the order of long-time and short-time crystallization in two-stage crystallization, and frequency in multi-stage crystallization on synthesis, physicochemical properties and catalytic performance for conversion of methanol to light olefins (MTO) has been studied. The results show that pure SAPO-34 can be obtained with increasing crystallization time. The interruption of the initial crystallization is more beneficial for improving the Si distribution and the MTO catalytic performance of SAPO-34 molecular sieves. The sample obtained by repeatedly alternating heating and cooling during crystallization shows smaller particle size, higher acidity, longer lifetimes and higher yields of ethylene than that obtained by the conventional continuous crystallization at high temperature. Full article

(This article belongs to the Special Issue C1 Chemistry—C1-Platform Chemicals as Cornerstone for a Sustainable Energy)

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3898 KiB

Open AccessFeature PaperReview

Factors Controlling the Redox Activity of Oxygen in Perovskites: From Theory to Application for Catalytic Reactions

by Chunzhen Yang and Alexis Grimaud

Catalysts 2017, 7(5), 149; https://doi.org/10.3390/catal7050149 - 11 May 2017

Cited by 89 | Viewed by 14727

Abstract

Triggering the redox reaction of oxygens has become essential for the development of (electro) catalytic properties of transition metal oxides, especially for perovskite materials that have been envisaged for a variety of applications such as the oxygen evolution or reduction reactions (OER and [...] Read more.

Triggering the redox reaction of oxygens has become essential for the development of (electro) catalytic properties of transition metal oxides, especially for perovskite materials that have been envisaged for a variety of applications such as the oxygen evolution or reduction reactions (OER and ORR, respectively), CO or hydrocarbons oxidation, NO reduction and others. While the formation of ligand hole for perovskites is well-known for solid state physicists and/or chemists and has been widely studied for the understanding of important electronic properties such as superconductivity, insulator-metal transitions, magnetoresistance, ferroelectrics, redox properties etc., oxygen electrocatalysis in aqueous media at low temperature barely scratches the surface of the concept of oxygen ions oxidation. In this review, we briefly explain the electronic structure of perovskite materials and go through a few important parameters such as the ionization potential, Madelung potential, and charge transfer energy that govern the oxidation of oxygen ions. We then describe the surface reactivity that can be induced by the redox activity of the oxygen network and the formation of highly reactive surface oxygen species before describing their participation in catalytic reactions and providing mechanistic insights and strategies for designing new (electro) catalysts. Finally, we give a brief overview of the different techniques that can be employed to detect the formation of such transient oxygen species. Full article

(This article belongs to the Special Issue (Photo)Electrochemistry of Perovskites)

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4667 KiB

Open AccessFeature PaperArticle

Methanol Steam Reforming: Na Doping of Pt/YSZ Provides Fine Tuning of Selectivity

by Michela Martinelli, Gary Jacobs, Uschi M. Graham and Burtron H. Davis

Catalysts 2017, 7(5), 148; https://doi.org/10.3390/catal7050148 - 10 May 2017

Cited by 15 | Viewed by 5952

Abstract

In this work, we found that sodium doping can be used to improve CO₂ selectivity for supported Pt catalyst during methanol steam reforming. These materials are usually very active in the low temperature range; however, they are characterized by high selectivity of [...] Read more.

In this work, we found that sodium doping can be used to improve CO₂ selectivity for supported Pt catalyst during methanol steam reforming. These materials are usually very active in the low temperature range; however, they are characterized by high selectivity of CO, which is a poison in downstream polymer electrolyte membrane fuel cells (PEM-FC) application. With Na doping, we found that CO₂ selectivity was higher than 90% when 2.5 wt.% of sodium was added to Pt/YSZ. We have speculated that the different product distribution is due to a different reaction pathway being opened for CH₃OH decomposition. Methanol decarbonylation was favored when Na was absent or low, while a formate decarboxylation pathway was favored when Na content reached 2.5 wt.%. The proposal is rooted in the observed weakening of the C-H bond of formate, as demonstrated in in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and kinetic isotope effect (KIE) experiments for the water-gas shift reaction conducted at low temperature. When adsorbed methoxy, produced when methanol is dissociatively adsorbed, was converted in the presence of H₂O in DRIFTS spectroscopy, formate species were prevalent for a 2% Pt–2.5% Na/YSZ catalyst, while only a minor contribution was observed for 2% Pt/YSZ. Moreover, the formate produced on Na-doped Pt/YSZ exhibited ν(CH) stretching bands at low wavenumber, consistent with C–H bond weakening, thus favoring dehydrogenation (and decarboxylation). It is proposed that when Na is present, formate is likely an intermediate, and because its dehydrogenation is favored, selectivity can be fine-tuned between decarbonylation and decarboxylation based on Na dopant level. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Emeritus Calvin H. Bartholomew in Anticipation of His 75th Birthday)

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5485 KiB

Open AccessArticle

Spongin-Based Scaffolds from Hippospongia communis Demosponge as an Effective Support for Lipase Immobilization

by Jakub Zdarta, Małgorzata Norman, Wojciech Smułek, Dariusz Moszyński, Ewa Kaczorek, Allison L. Stelling, Hermann Ehrlich and Teofil Jesionowski

Catalysts 2017, 7(5), 147; https://doi.org/10.3390/catal7050147 - 10 May 2017

Cited by 43 | Viewed by 5860

Abstract

The main purpose of the study was to achieve effective immobilization of lipase B from Candida antarctica (CALB) onto 3D spongin-based scaffolds from Hippospongia communis marine demosponge for rapeseed oil transesterification. Successful immobilization onto the marine sponge skeleton was confirmed for the first [...] Read more.

The main purpose of the study was to achieve effective immobilization of lipase B from Candida antarctica (CALB) onto 3D spongin-based scaffolds from Hippospongia communis marine demosponge for rapeseed oil transesterification. Successful immobilization onto the marine sponge skeleton was confirmed for the first time. Lipase B-containing biocatalytic system exhibited the highest catalytic activity retention (89%) after 60 min of immobilization at pH 7 and temperature of 4 °C. Immobilization was found to improve the thermal and chemical stability compared to free lipase, and retain over 80% of its initial catalytic activity over a wide range of temperature (30–60 °C) and pH (6–9). Additionally, immobilized lipase has good storage stability and retains over 70% of its initial activity even after catalyzing of 25 reaction cycles. The obtained product was used in a transesterification reaction of rapeseed oil with methanol and proved to be an efficient biocatalyst for biofuel production. The highest conversion value and fatty acids methyl esters (FAME) concentration were observed after a process conducted at 40 °C and pH 10. The possible mechanism of interaction between the enzyme and the spongin-based support is proposed and discussed. Full article

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5537 KiB

Open AccessFeature PaperReview

Palladium-Catalyzed Suzuki–Miyaura Cross-Coupling in Continuous Flow

by Christophe Len, Sophie Bruniaux, Frederic Delbecq and Virinder S. Parmar

Catalysts 2017, 7(5), 146; https://doi.org/10.3390/catal7050146 - 9 May 2017

Cited by 69 | Viewed by 19820

Abstract

Carbon–carbon cross-coupling reactions are among the most important processes in organic chemistry and Suzuki–Miyaura reactions are the most widely used protocols. For a decade, green chemistry and particularly catalysis and continuous flow, have shown immense potential in achieving the goals of “greener synthesis”. [...] Read more.

Carbon–carbon cross-coupling reactions are among the most important processes in organic chemistry and Suzuki–Miyaura reactions are the most widely used protocols. For a decade, green chemistry and particularly catalysis and continuous flow, have shown immense potential in achieving the goals of “greener synthesis”. To date, it seems difficult to conceive the chemistry of the 21st century without the industrialization of continuous flow process in the area of pharmaceuticals, drugs, agrochemicals, polymers, etc. A large variety of palladium Suzuki–Miyaura cross-coupling reactions have been developed using a continuous flow sequence for preparing the desired biaryl derivatives. Our objective is to focus this review on the continuous flow Suzuki–Miyaura cross-coupling using homogeneous and heterogeneous catalysts. Full article

(This article belongs to the Special Issue Suzuki–Miyaura Cross-Coupling Reaction and Potential Applications)

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1826 KiB

Open AccessArticle

Hydrogenation of Phenol over Pt/CNTs: The Effects of Pt Loading and Reaction Solvents

by Feng Li, Bo Cao, Wenxi Zhu, Hua Song, Keliang Wang and Cuiqin Li

Catalysts 2017, 7(5), 145; https://doi.org/10.3390/catal7050145 - 8 May 2017

Cited by 32 | Viewed by 5821

Abstract

Carbon nanotubes (CNTs)-supported Pt nanoparticles were prepared with selective deposition of Pt nanoparticles inside and outside CNTs (Pt–in/CNTs and Pt–out/CNTs). The effects of Pt loading and reaction solvents on phenol hydrogenation were investigated. The Pt nanoparticles in Pt–in/CNTs versus Pt–out/CNTs are smaller and [...] Read more.

Carbon nanotubes (CNTs)-supported Pt nanoparticles were prepared with selective deposition of Pt nanoparticles inside and outside CNTs (Pt–in/CNTs and Pt–out/CNTs). The effects of Pt loading and reaction solvents on phenol hydrogenation were investigated. The Pt nanoparticles in Pt–in/CNTs versus Pt–out/CNTs are smaller and better dispersed. The catalytic activity and reuse stability toward phenol hydrogenation both improved markedly. The dichloromethane–water mixture as the reaction solvent, compared with either pure medium, decreased the catalytic activity toward phenol hydrogenation and selectivity of cyclohexanone over Pt–in/CNTs, but significantly improved the catalytic activity toward phenol hydrogenation and selectivity of cyclohexanone over Pt–out/CNTs. Full article

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2873 KiB

Open AccessArticle

Catalysts Promoted with Niobium Oxide for Air Pollution Abatement

by Wendi Xiang, Xiaochen Han, Jennifer Astorsdotter and Robert Farrauto

Catalysts 2017, 7(5), 144; https://doi.org/10.3390/catal7050144 - 8 May 2017

Cited by 5 | Viewed by 5270

Abstract

Pt-containing catalysts are currently used commercially to catalyze the conversion of carbon monoxide (CO) and hydrocarbon (HC) pollutants from stationary chemical and petroleum plants. It is well known that Pt-containing catalysts are expensive and have limited availability. The goal of this research is [...] Read more.

Pt-containing catalysts are currently used commercially to catalyze the conversion of carbon monoxide (CO) and hydrocarbon (HC) pollutants from stationary chemical and petroleum plants. It is well known that Pt-containing catalysts are expensive and have limited availability. The goal of this research is to find alternative and less expensive catalysts to replace Pt for these applications. This study found that niobium oxide (Nb₂O₅), as a carrier or support for certain transition metal oxides, promotes oxidation activity while maintaining stability, making them candidates as alternatives to Pt. The present work reports that the orthorhombic structure of niobium oxide (formed at 800 °C in air) promotes Co₃O₄ toward the oxidation of both CO and propane, which are common pollutants in volatile organic compound (VOC) applications. This was a surprising result since this structure of Nb₂O₅ has a very low surface area (about 2 m²/g) relative to the more traditional Al₂O₃ support, with a surface area of 150 m²/g. The results reported demonstrate that 1% Co₃O₄/Nb₂O₅ has comparable fresh and aged catalytic activity to 1% Pt/γ-Al₂O₃ and 1% Pt/Nb₂O₅. Furthermore, 6% Co₃O₄/Nb₂O₅ outperforms 1% Pt/Al₂O₃ in both catalytic activity and thermal stability. These results suggest a strong interaction between niobium oxide and the active component—cobalt oxide—likely by inducing an oxygen defect structure with oxygen vacancies leading to enhanced activity toward the oxidation of CO and propane. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Emeritus Calvin H. Bartholomew in Anticipation of His 75th Birthday)

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Open AccessArticle

Preparation of Salen–Metal Complexes (Metal = Co or Ni) Intercalated ZnCr-LDHs and Their Photocatalytic Degradation of Rhodamine B

by Yue Meng, Wei Luo, Shengjie Xia and Zheming Ni

Catalysts 2017, 7(5), 143; https://doi.org/10.3390/catal7050143 - 7 May 2017

Cited by 22 | Viewed by 6419

Abstract

Salen–metal complexes (SalenM) were successfully intercalated into ZnCr layered double hydroxides (LDHs) through coprecipitation method, then a series of novel organic–inorganic hybrid materials were obtained. The structure and properties of the materials were thoroughly characterized by inductively-coupled plasma atomic emission spectrometry (ICP-AES), powder [...] Read more.

Salen–metal complexes (SalenM) were successfully intercalated into ZnCr layered double hydroxides (LDHs) through coprecipitation method, then a series of novel organic–inorganic hybrid materials were obtained. The structure and properties of the materials were thoroughly characterized by inductively-coupled plasma atomic emission spectrometry (ICP-AES), powder X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), and ultraviolet visible diffuse reflectance spectroscopy (UV-Vis DRS). Meanwhile, with Rhodamine B (RhB) as a target contaminant, the photocatalytic activities of SalenM-intercalated ZnCr-LDHs were investigated and compared with the traditional LDHs (ZnCr-LDHs, ZnCoCr-LDHs, and ZnNiCr-LDHs). Furthermore, the effect of the intercalation amount of SalenM (M = Co or Ni) on the photocatalytic activity was studied. The results showed that when the molar ratio of SalenM to Cr was 0.75, SalenM-intercalated ZnCr-LDHs exhibited significantly higher photocatalytic activities than the traditional LDHs. The degradation rates of RhB reached about 90%, and all of them had good recycling rates. In addition, the kinetics of photocatalytic process and the mechanism of photocatalysis are discussed. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)

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4137 KiB

Open AccessArticle

Are Directed Evolution Approaches Efficient in Exploring Nature’s Potential to Stabilize a Lipase in Organic Cosolvents?

by Ulrich Markel, Leilei Zhu, Victorine Josiane Frauenkron-Machedjou, Jing Zhao, Marco Bocola, Mehdi D. Davari, Karl-Erich Jaeger and Ulrich Schwaneberg

Catalysts 2017, 7(5), 142; https://doi.org/10.3390/catal7050142 - 7 May 2017

Cited by 35 | Viewed by 7230

Abstract

Despite the significant advances in the field of protein engineering, general design principles to improve organic cosolvent resistance of enzymes still remain undiscovered. Previous studies drew conclusions to engineer enzymes for their use in water-miscible organic solvents based on few amino acid substitutions. [...] Read more.

Despite the significant advances in the field of protein engineering, general design principles to improve organic cosolvent resistance of enzymes still remain undiscovered. Previous studies drew conclusions to engineer enzymes for their use in water-miscible organic solvents based on few amino acid substitutions. In this study, we conduct a comparison of a Bacillus subtilis lipase A (BSLA) library—covering the full natural diversity of single amino acid substitutions at all 181 positions of BSLA—with three state of the art random mutagenesis methods: error-prone PCR (epPCR) with low and high mutagenesis frequency (epPCR-low and high) as well as a transversion-enriched Sequence Saturation Mutagenesis (SeSaM-Tv P/P) method. Libraries were searched for amino acid substitutions that increase the enzyme’s resistance to the water-miscible organic cosolvents 1,4-dioxane (DOX), 2,2,2-trifluoroethanol (TFE), and dimethyl sulfoxide (DMSO). Our analysis revealed that 5%–11% of all possible single substitutions (BSLA site-saturation mutagenesis (SSM) library) contribute to improved cosolvent resistance. However, only a fraction of these substitutions (7%–12%) could be detected in the three random mutagenesis libraries. To our knowledge, this is the first study that quantifies the capability of these diversity generation methods generally employed in directed evolution campaigns and compares them to the entire natural diversity with a single substitution. Additionally, the investigation of the BSLA SSM library revealed only few common beneficial substitutions for all three cosolvents as well as the importance of introducing surface charges for organic cosolvent resistance—most likely due to a stronger attraction of water molecules. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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5814 KiB

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Post Synthesis of Aluminum Modified Mesoporous TUD-1 Materials and Their Application for FCC Diesel Hydrodesulfurization Catalysts

by Zesheng Xia, Jianye Fu, Aijun Duan, Longnian Han, Huadong Wu, Zhen Zhao, Chunming Xu, Dong Wang, Bo Wang and Qian Meng

Catalysts 2017, 7(5), 141; https://doi.org/10.3390/catal7050141 - 7 May 2017

Cited by 13 | Viewed by 5975

Abstract

Post-synthesis methods are a promising technology and have received much attention. In this paper, a series of post-synthesis aluminum modified TUD-1 (PAT) materials with different Al contents were successfully prepared by using aluminum isopropoxide to be Al sources, then the as-synthesized materials were [...] Read more.

Post-synthesis methods are a promising technology and have received much attention. In this paper, a series of post-synthesis aluminum modified TUD-1 (PAT) materials with different Al contents were successfully prepared by using aluminum isopropoxide to be Al sources, then the as-synthesized materials were adopted as support additives mixed with commercial γ-Al₂O₃ to prepare hydrodesulfurization (HDS) catalysts for FCC diesel. The supports and catalysts were analyzed using N₂ adsorption-desorption, XRD, SEM, Py-IR, ICP, ²⁷Al MAS NMR, UV-vis, H₂-TPR and HRTEM techniques. The results of Py-IR and ²⁷Al MAS NMR indicated that the addition of Al species could bring Lewis (L) and Brönsted (B) sites into Si-TUD-1, and that the material of PAT-3 had the highest total acidity sites and Brönsted acid sites among the series PAT composites. The HRTEM technique showed that, compared to the traditional catalyst NiMo/γ-Al₂O₃, the sulfided catalyst NiMo/APAT-3 had a relatively short length (3.2 nm) and suitable stacking number (2.5) of MoS₂ slabs. The HDS efficiencies of all the catalysts were tested in a fixed bed micro-reactor with FCC diesel as feedstock. The catalytic results confirmed that the catalyst NiMo/APAT-3 possessed the highest HDS efficiency (97.0%), due to synergistic effects of advantageous properties such as higher acidity, moderate MSI, and relatively short length of the MoS₂ slabs. Full article

(This article belongs to the Special Issue Mesostructured Materials and Their Catalytic Applications)

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4159 KiB

Open AccessArticle

Exploring Promising Catalysts for Chemical Hydrogen Storage in Ammonia Borane: A Density Functional Theory Study

by Sateesh Bandaru, Niall J. English, Andrew D. Phillips and J. M. Don MacElroy

Catalysts 2017, 7(5), 140; https://doi.org/10.3390/catal7050140 - 5 May 2017

Cited by 13 | Viewed by 6630

Abstract

Density functional theory (DFT) has been applied to study potential ammonia borane (AB) dehydrogenation pathways via new bifunctional ruthenium-based catalysts, alongside their computationally-designed iron-based counterparts (i.e., four catalysts), using the wB97XD (dispersion-included) functional. The efficiency of each catalyst was under scrutiny based on [...] Read more.

Density functional theory (DFT) has been applied to study potential ammonia borane (AB) dehydrogenation pathways via new bifunctional ruthenium-based catalysts, alongside their computationally-designed iron-based counterparts (i.e., four catalysts), using the wB97XD (dispersion-included) functional. The efficiency of each catalyst was under scrutiny based on the addition of ammonia borane, with a focus on the associated activation-energy barriers, whilst hydrogen release from the catalyst was also studied in detail. Here, natural-population analysis charges were key quantities of interest. It was found that the iron-based catalysts display more promising dehydrogenation energy barriers vis- Full article

(This article belongs to the Special Issue Ruthenium Catalysts)

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3397 KiB

Open AccessFeature PaperArticle

Tailoring the Oxygen Evolution Activity and Stability Using Defect Chemistry

by Julius Scholz, Marcel Risch, Garlef Wartner, Christoph Luderer, Vladimir Roddatis and Christian Jooss

Catalysts 2017, 7(5), 139; https://doi.org/10.3390/catal7050139 - 5 May 2017

Cited by 29 | Viewed by 7377

Abstract

Improving the activity of catalysts for the oxygen evolution reaction (OER) requires a detailed understanding of the surface chemistry and structure to deduce structure-function relationships (descriptors) for fundamental insight. We chose epitaxial (100)-oriented La_0.6Sr_0.4Mn_1−δO₃ (LSMO) thin [...] Read more.

Improving the activity of catalysts for the oxygen evolution reaction (OER) requires a detailed understanding of the surface chemistry and structure to deduce structure-function relationships (descriptors) for fundamental insight. We chose epitaxial (100)-oriented La_0.6Sr_0.4Mn_1−δO₃ (LSMO) thin films as a model system with high electrochemical activity comparable to (110)-oriented IrO₂ to investigate the effect of Mn off-stoichiometry on both catalytic activity and stability. Extensive structural characterization was performed by microscopic and spectroscopic methods before and after electrochemical characterization using rotating ring-disk studies. Stoichiometric LSMO had the highest activity, while both Mn deficiency and excess reduced the catalytic activity. Furthermore, all samples preserved the crystal structure up to the very surface. Mn excess improved the long-term activity, and we hypothesize that excess Mn stabilizes the surface chemistry during catalysis. Our data show that the defect chemistry should be considered when designing catalysts with enhanced activity and rugged stability. Full article

(This article belongs to the Special Issue (Photo)Electrochemistry of Perovskites)

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6632 KiB

Open AccessArticle

Cobalt-iron Oxide, Alloy and Nitride: Synthesis, Characterization and Application in Catalytic Peroxymonosulfate Activation for Orange II Degradation

by Kaixin Zhu, Changzi Jin, Zoltán Klencsár, Ayyakannu Sundaram Ganeshraja and Junhu Wang

Catalysts 2017, 7(5), 138; https://doi.org/10.3390/catal7050138 - 4 May 2017

Cited by 59 | Viewed by 12503

Abstract

In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray [...] Read more.

In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ⁵⁷Fe Mössbauer spectroscopy were employed to characterize the composition, morphology, crystal structure and chemical state of the prepared catalysts. It was shown that calcination in air, nitrogen and ammonia atmospheres generated Co-Fe catalysts with cobalt ferrite (CoFe₂O₄), Co-Fe alloy and Co-Fe nitride as dominant phases, respectively. The prepared Co/Fe-based catalysts were demonstrated to be highly efficient in activating peroxymonosulfate (PMS) for organic Orange II degradation. The activation efficiency of the different catalysts was found to increase in the order CoFe₂O₄ < Co-Fe nitride < Co-Fe alloy. Sulfate radical was found to be the primary active intermediate species contributing to the dye degradation for all the participating catalysts. Furthermore, a possible reaction mechanism was proposed for each of the studied catalysts. This study achieves progress in efficient cobalt-iron catalysts using in the field of SR-AOPs, with potential applications in environment remediation. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)

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5189 KiB

Open AccessArticle

Catalytic Abatement of Nitrous Oxide Coupled with Ethane Oxydehydrogenation over Mesoporous Cr/Al₂O₃ Catalyst

by Yan Zhang, Suresh Kumar Megarajan, Xia Xu, Jingting Lu and Heqing Jiang

Catalysts 2017, 7(5), 137; https://doi.org/10.3390/catal7050137 - 4 May 2017

Cited by 6 | Viewed by 5366

Abstract

Waste nitrous oxide (N₂O) was utilized as an oxidant for ethane oxydehydrogenation reaction at the temperature range from 450 °C to 700 °C over the mesoporous Cr/Al₂O₃ catalyst synthesized via the one-pot evaporation-induced self-assembly (EISA) method. The catalyst [...] Read more.

Waste nitrous oxide (N₂O) was utilized as an oxidant for ethane oxydehydrogenation reaction at the temperature range from 450 °C to 700 °C over the mesoporous Cr/Al₂O₃ catalyst synthesized via the one-pot evaporation-induced self-assembly (EISA) method. The catalyst was characterized by X-ray diffraction, transmission electron microscopy, and nitrogen adsorption-desorption analysis. The obtained mesoporous material with favorable textural property and advantageous thermal stability was investigated as the catalyst for ethane oxydehydrogenation. It was found that the utilization of N₂O as an oxidant for the oxydehydrogenation reaction of ethane resulted in simultaneous and complete N₂O abatement. Moreover, the catalytic conversion of C₂H₆ to C₂H₄ was increased from 18% to 43% as the temperature increased from 450 °C to 700 °C. The increased N₂O concentration from 5 vol % to 20 vol % resulted in an increased ethane conversion but decreased ethylene selectivity because the nonselective reactions occurred. Ethane was converted into ethylene with approximately 51% selectivity and 22% yield at 700 °C and N₂O concentration of 10%. After a catalytic steady state was reached, no obvious decline was observed during a 15 h evaluation period. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)

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