Catalysts

10 pages, 3439 KiB

Open AccessCommunication

Composites of Laminar Nanostructured ZnO and VOx-Nanotubes Hybrid as Visible Light Active Photocatalysts

by Eglantina Benavente, Daniel Navas, Sindy Devis, Marjorie Segovia, Clivia Sotomayor-Torres and Guillermo González

Catalysts 2018, 8(2), 93; https://doi.org/10.3390/catal8020093 - 24 Feb 2018

Cited by 12 | Viewed by 4376

Abstract

A series of hybrid heterostructured nanocomposites of ZnO with V₂O₅ nanotubes (VOx-NTs) in different mixing ratios were synthesized, with the aim of reducing the recombination of photoinduced charge carriers and to optimize the absorption of visible light. The study was [...] Read more.

A series of hybrid heterostructured nanocomposites of ZnO with V₂O₅ nanotubes (VOx-NTs) in different mixing ratios were synthesized, with the aim of reducing the recombination of photoinduced charge carriers and to optimize the absorption of visible light. The study was focused on the use of heterostructured semiconductors that can extend light absorption to the visible range and enhance the photocatalytic performance of ZnO in the degradation of methylene blue as a model pollutant. The addition of VOx-NTs in the synthesis mixture led to a remarkable performance in the degradation of the model dye, with hybrid ZnO (stearic acid)/VOx-NTs at a ratio of 1:0.06 possessing the highest photocatalytic activity, about seven times faster than pristine zinc oxide. Diffuse reflectance spectroscopic measurements and experiments in the presence of different trapping elements allowed us to draw conclusions regarding the band positions and photocatalytic degradation mechanism. The photocatalytic activity measured in three subsequent cycles showed good reusability as no significant loss in efficiency of dye degradation was observed. Full article

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27 pages, 1154 KiB

Open AccessReview

A General Overview of Support Materials for Enzyme Immobilization: Characteristics, Properties, Practical Utility

by Jakub Zdarta, Anne S. Meyer, Teofil Jesionowski and Manuel Pinelo

Catalysts 2018, 8(2), 92; https://doi.org/10.3390/catal8020092 - 24 Feb 2018

Cited by 709 | Viewed by 35272

Abstract

In recent years, enzyme immobilization has been presented as a powerful tool for the improvement of enzyme properties such as stability and reusability. However, the type of support material used plays a crucial role in the immobilization process due to the strong effect [...] Read more.

In recent years, enzyme immobilization has been presented as a powerful tool for the improvement of enzyme properties such as stability and reusability. However, the type of support material used plays a crucial role in the immobilization process due to the strong effect of these materials on the properties of the produced catalytic system. A large variety of inorganic and organic as well as hybrid and composite materials may be used as stable and efficient supports for biocatalysts. This review provides a general overview of the characteristics and properties of the materials applied for enzyme immobilization. For the purposes of this literature study, support materials are divided into two main groups, called Classic and New materials. The review will be useful in selection of appropriate support materials with tailored properties for the production of highly effective biocatalytic systems for use in various processes. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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32 pages, 4795 KiB

Open AccessEditor’s ChoiceReview

The Design of MnO_x Based Catalyst in Post-Plasma Catalysis Configuration for Toluene Abatement

by Zhiping Ye, Jean-Marc Giraudon, Nathalie De Geyter, Rino Morent and Jean-François Lamonier

Catalysts 2018, 8(2), 91; https://doi.org/10.3390/catal8020091 - 23 Feb 2018

Cited by 43 | Viewed by 9789

Abstract

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles [...] Read more.

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles of PPC are exposed based on the coupling of two mature technologies such as NTP (Non thermal plasma) and catalysis. In that respect, the presentation of the abundant manganese oxides will be firstly given. Then in a second step the main features of MnO_x allowing better performances in the reactions expected to occur in the abatement of toluene in PPC process are reviewed including ozone decomposition, toluene ozonation, CO oxidation and toluene total oxidation. Finally, in a last part the current status of the applications of PPC using MnO_x on toluene abatement are discussed. In a first step, the selected variables of the hybrid process related to the experimental conditions of toluene abatement in air are identified. The selected variables are those expected to play a role in the performances of PPC system towards toluene abatement. Then the descriptors linked to the performances of the hybrid process in terms of efficiency are given and the effects of the variables on the experimental outcomes (descriptors) are discussed. The review would serve as a reference guide for the optimization of the PPC process using MnO_x-based oxides for toluene abatement. Full article

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33 pages, 18969 KiB

Open AccessReview

Advances in Enantioselective C–H Activation/Mizoroki-Heck Reaction and Suzuki Reaction

by Shuai Shi, Khan Shah Nawaz, Muhammad Kashif Zaman and Zhankui Sun

Catalysts 2018, 8(2), 90; https://doi.org/10.3390/catal8020090 - 23 Feb 2018

Cited by 18 | Viewed by 8256

Abstract

Traditional cross-coupling reactions, like Mizoroki-Heck Reaction and Suzuki Reaction, have revolutionized organic chemistry and are widely applied in modern organic synthesis. With the rapid development of C–H activation and asymmetric catalysis in recent years, enantioselective C–H activation/cross-coupling reactions have drawn much attention from [...] Read more.

Traditional cross-coupling reactions, like Mizoroki-Heck Reaction and Suzuki Reaction, have revolutionized organic chemistry and are widely applied in modern organic synthesis. With the rapid development of C–H activation and asymmetric catalysis in recent years, enantioselective C–H activation/cross-coupling reactions have drawn much attention from researchers. This review summarizes recent advances in enantioselective C–H activation/Mizoroki-Heck Reaction and Suzuki Reaction, with emphasis on the structures and functions of chiral ligands utilized in different reactions. Full article

(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)

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22 pages, 5845 KiB

Open AccessReview

Catalysis and Downsizing in Mg-Based Hydrogen Storage Materials

by Jianding Li, Bo Li, Huaiyu Shao, Wei Li and Huaijun Lin

Catalysts 2018, 8(2), 89; https://doi.org/10.3390/catal8020089 - 23 Feb 2018

Cited by 62 | Viewed by 7875

Abstract

Magnesium (Mg)-based materials are promising candidates for hydrogen storage due to the low cost, high hydrogen storage capacity and abundant resources of magnesium for the realization of a hydrogen society. However, the sluggish kinetics and strong stability of the metal-hydrogen bonding of Mg-based [...] Read more.

Magnesium (Mg)-based materials are promising candidates for hydrogen storage due to the low cost, high hydrogen storage capacity and abundant resources of magnesium for the realization of a hydrogen society. However, the sluggish kinetics and strong stability of the metal-hydrogen bonding of Mg-based materials hinder their application, especially for onboard storage. Many researchers are devoted to overcoming these challenges by numerous methods. Here, this review summarizes some advances in the development of Mg-based hydrogen storage materials related to downsizing and catalysis. In particular, the focus is on how downsizing and catalysts affect the hydrogen storage capacity, kinetics and thermodynamics of Mg-based hydrogen storage materials. Finally, the future development and applications of Mg-based hydrogen storage materials is discussed. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis & Hydrogen Storage)

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10 pages, 5790 KiB

Open AccessArticle

Ruthenium(II)-Arene Complexes of the Water-Soluble Ligand CAP as Catalysts for Homogeneous Transfer Hydrogenations in Aqueous Phase

by Antonella Guerriero, Maurizio Peruzzini and Luca Gonsalvi

Catalysts 2018, 8(2), 88; https://doi.org/10.3390/catal8020088 - 22 Feb 2018

Cited by 18 | Viewed by 5204

Abstract

The neutral Ru(II) complex κP-[RuCl₂(η⁶-p-cymene)(CAP)] (1), and the two ionic complexes κP-[RuCl(η⁶-p-cymene)(MeCN)(CAP)]PF₆ (2) and κP-[RuCl(η⁶-p-cymene)(CAP)₂]PF₆ [...] Read more.

The neutral Ru(II) complex κP-[RuCl₂(η⁶-p-cymene)(CAP)] (1), and the two ionic complexes κP-[RuCl(η⁶-p-cymene)(MeCN)(CAP)]PF₆ (2) and κP-[RuCl(η⁶-p-cymene)(CAP)₂]PF₆ (3), containing the water-soluble phosphine 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP), were tested as catalysts for homogeneous hydrogenation of benzylidene acetone, selectively producing the saturated ketone as product. The catalytic tests were carried out in aqueous phase under transfer hydrogenation conditions, at mild temperatures using sodium formate as hydrogen source. Complex 3, which showed the highest stability under the reaction conditions applied, was also tested for C=N bond reduction from selected cyclic imines. Preliminary NMR studies run under pseudo-catalytic conditions starting from 3 showed the formation of κP-[RuH(η⁶-p-cymene)(CAP)₂]PF₆ (4) as the pivotal species in catalysis. Full article

(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)

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12 pages, 2406 KiB

Open AccessArticle

The H₂-Treated TiO₂ Supported Pt Catalysts Prepared by Strong Electrostatic Adsorption for Liquid-Phase Selective Hydrogenation

by Sasithorn Kuhaudomlap, Okorn Mekasuwandumrong, Piyasan Praserthdam, Shin-Ichiro Fujita, Masahiko Arai and Joongjai Panpranot

Catalysts 2018, 8(2), 87; https://doi.org/10.3390/catal8020087 - 22 Feb 2018

Cited by 13 | Viewed by 5498

Abstract

The H₂-treated TiO₂ supported Pt catalysts were prepared by strong electrostatic adsorption method and tested in the liquid-phase selective hydrogenation of various organic compounds such as 3-nitrostyrene to vinylaniline (VA) and furfural to furfuryl alcohol (FA). A combination of high [...] Read more.

The H₂-treated TiO₂ supported Pt catalysts were prepared by strong electrostatic adsorption method and tested in the liquid-phase selective hydrogenation of various organic compounds such as 3-nitrostyrene to vinylaniline (VA) and furfural to furfuryl alcohol (FA). A combination of high Pt dispersion, strong interaction of Pt-TiO_x, and the presence of low coordination Pt sites was necessary for high hydrogenation activity. However, while the selectivity of VA in 3-nitrostyrene hydrogenation did not depend much on the catalyst preparation method used, the selectivity of FA in furfural hydrogenation was much higher when the catalysts were prepared by SEA, comparing to those obtained by impregnation in which the solvent product was formed, due probably to the non-acidic conditions used during Pt loading by SEA method. Full article

(This article belongs to the Special Issue Active Sites in Catalytic Reaction)

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14 pages, 11223 KiB

Open AccessFeature PaperArticle

Improved Kinetic Data Acquisition Using An Optically Accessible Catalytic Plate Reactor with Spatially-Resolved Measurement Techniques. Case of Study: CO₂ Methanation

by Jose A. Hernandez Lalinde, Kevin Kofler, Xuejie Huang and Jan Kopyscinski

Catalysts 2018, 8(2), 86; https://doi.org/10.3390/catal8020086 - 21 Feb 2018

Cited by 12 | Viewed by 5613

Abstract

Modelling and optimization of chemical reactors require a good understanding of the reactions mechanism with the corresponding kinetic description. Therefore, high quality kinetic data are needed, which can be challenging to obtain, especially for fast and highly exothermic reactions such as the CO [...] Read more.

Modelling and optimization of chemical reactors require a good understanding of the reactions mechanism with the corresponding kinetic description. Therefore, high quality kinetic data are needed, which can be challenging to obtain, especially for fast and highly exothermic reactions such as the CO₂ methanation. Traditionally, kinetic studies rely on measuring the exit gas composition (1 data point per species and experiment) using differential reactors with diluted catalyst beds and reactants to avoid temperature change. Therefore, an optically accessible catalytic channel reactor was designed, which allowed for the chance to gather spatially-resolved information on axial gas composition and catalyst surface temperature, specifically by means of a movable sampling capillary and shortwave infrared-thermography (SWIR), respectively. A catalyst coated plate was placed at the bottom of the channel, while a set of two quartz glass plates covers the top. In the current study 35 data points per gas species were collect for 1 experiment conducted under laminar flow conditions at 425 °C. Catalyst surface temperature determined via a SWIR camera was not influenced by polyatomic molecules partaking in the reaction and thus did not falsify the kinetic data. The catalyst mass distribution along the reactor axis was determined, enabling the development of a correct reactor model for kinetic parameter estimation and model discrimination. Full article

(This article belongs to the Special Issue Design Challenges for Catalytic and Photocatalytic Reactors)

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18 pages, 4975 KiB

Open AccessArticle

Influence of an Electronic Structure of N-TiO₂ on Its Photocatalytic Activity towards Decomposition of Acetaldehyde under UV and Fluorescent Lamps Irradiation

by Beata Tryba, Magdalena Wozniak, Grzegorz Zolnierkiewicz, Nikos Guskos, Antoni Morawski, Christophe Colbeau-Justin, Rafał Wrobel, Akio Nitta and Bunsho Ohtani

Catalysts 2018, 8(2), 85; https://doi.org/10.3390/catal8020085 - 20 Feb 2018

Cited by 38 | Viewed by 4950

Abstract

The electronic structure of N-TiO₂ samples prepared by a sol-gel method was investigated by EPR (Electronic Paramagnetic Resonance) measurements and the energy-resolved distribution of electron traps. In EPR spectra, some of the resonance lines assigned to paramagnetic species of nitrogen and Ti [...] Read more.

The electronic structure of N-TiO₂ samples prepared by a sol-gel method was investigated by EPR (Electronic Paramagnetic Resonance) measurements and the energy-resolved distribution of electron traps. In EPR spectra, some of the resonance lines assigned to paramagnetic species of nitrogen and Ti³⁺ were detected. Sample prepared at 300 °C revealed the highest intensity line of the nitrogen paramagnetic centers, whereas that prepared at 400 °C showed a paramagnetic line for Ti³⁺. Measurements of the electron trap distribution showed higher density of electron traps for sample prepared at 400 °C than that at 300 °C. Sample prepared at 300 °C, which revealed the highest amount of nitrogen built in the titania in the interstitial position was the most active under visible light. It was evidenced that photocatalytic decomposition of acetaldehyde was dependent strongly on the BET surface area and electrokinetic potential of the photocatalyst surface. The UV content in the fluorescent lamp affected the yield of acetaldehyde decomposition. Full article

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17 pages, 3305 KiB

Open AccessArticle

Immobilization Effects on the Catalytic Properties of Two Fusarium Verticillioides Lipases: Stability, Hydrolysis, Transesterification and Enantioselectivity Improvement

by Fernanda Dell Antonio Facchini, Marita Gimenez Pereira, Ana Claudia Vici, Marco Filice, Benevides Costa Pessela, Jose Manuel Guisan, Glória Fernandez-Lorente and Maria De Lourdes Teixeira de Moraes Polizeli

Catalysts 2018, 8(2), 84; https://doi.org/10.3390/catal8020084 - 16 Feb 2018

Cited by 19 | Viewed by 4464

Abstract

Fusarium verticillioides lipases were purified in a “cascade” method using octadecyl Sepabeads and octyl Sepharose resins, which led to the isolation of two proteins with lipolytic activities. Lip 1 was purified after octyl Sepharose adsorption presenting 30.3 kDa and, Lip 2 presented 68.0 [...] Read more.

Fusarium verticillioides lipases were purified in a “cascade” method using octadecyl Sepabeads and octyl Sepharose resins, which led to the isolation of two proteins with lipolytic activities. Lip 1 was purified after octyl Sepharose adsorption presenting 30.3 kDa and, Lip 2 presented 68.0 kDa after octadecyl adsorption. These immobilization processes resulted in an increase of 3-fold in activity of each immobilized enzyme. These enzymes presented optima of pH of 5.0 and 6.0, respectively and temperature at 40 °C. They were thermostable at 40 °C and both remained more than 50% of its activity at the pH range of 5.0 to 7.0, with 180 min of incubation. The sardine oil hydrolysis showed higher EPA/DHA ratio. Concerning the ethanolysis reaction, Lip 2 showed higher conversion (5.5%) and both lipases showed activity in the release of the S enantiomers from 2-O-butyryl-2-phenylacetic acid (mandelic butyrate acid) and HPBE hydrolysis. Lip 2 also demonstrated capacity of transesterification. These applications made these enzymes attractive for industrial application. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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10 pages, 3223 KiB

Open AccessArticle

Aerobic Oxidation of Benzyl Alcohol on a Strontium-Based Gold Material: Remarkable Intrinsic Basicity and Reusable Catalyst

by Karla Patrícia R. Castro, Marco Aurélio S. Garcia, Wiury C. de Abreu, Samuel Anderson A. de Sousa, Carla Verônica R. de Moura, Jean Cláudio S. Costa and Edmilson M. de Moura

Catalysts 2018, 8(2), 83; https://doi.org/10.3390/catal8020083 - 15 Feb 2018

Cited by 18 | Viewed by 4448

Abstract

The development of stable and active gold catalysts has arisen as a significant strategy for oxidation of alcohols. Nano-size PVA-stabilized gold nanoparticles immobilized on Sr(OH)₂ by colloidal deposition presented high catalytic activity for benzyl alcohol oxidation. In 2.5 h, 2 bar of [...] Read more.

The development of stable and active gold catalysts has arisen as a significant strategy for oxidation of alcohols. Nano-size PVA-stabilized gold nanoparticles immobilized on Sr(OH)₂ by colloidal deposition presented high catalytic activity for benzyl alcohol oxidation. In 2.5 h, 2 bar of O₂ and without extra-base addition, the calcined support reached 54.6% (100 °C) and 67.4% (140 °C) of conversion, presenting the remarkable and unexplored intrinsic basicity that strontium-based materials retain. With sub-stoichiometric K₂CO₃ adding, under the same catalytic conditions, the catalyst conducted the reaction with similar activity, but with excellent reusability in the process, without any gold leaching. We investigated the influence that the support synthesis method and the solvent used for the NPs stabilization have on the oxidation activity. The produced materials were fully characterized by XPS, Rietveld refinement, and TEM. Full article

(This article belongs to the Special Issue New Developments in Heterogeneous Partial and Total Oxidation Catalysis)

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13 pages, 5112 KiB

Open AccessArticle

Catalytic Fast Pyrolysis of Kraft Lignin over Hierarchical HZSM-5 and Hβ Zeolites

by Yadong Bi, Xiaojuan Lei, Guihua Xu, Hui Chen and Jianli Hu

Catalysts 2018, 8(2), 82; https://doi.org/10.3390/catal8020082 - 14 Feb 2018

Cited by 46 | Viewed by 4930

Abstract

The hierarchical HZSM-5 and Hβ zeolites were prepared by alkaline post-treatment methods adopting Na₂CO₃, TMAOH/NaOH mixture, and NaOH as desilication sources, respectively. More mesopores are produced over two kinds of zeolites, while the micropores portion is well preserved. The [...] Read more.

The hierarchical HZSM-5 and Hβ zeolites were prepared by alkaline post-treatment methods adopting Na₂CO₃, TMAOH/NaOH mixture, and NaOH as desilication sources, respectively. More mesopores are produced over two kinds of zeolites, while the micropores portion is well preserved. The mesopores formed in hierarchical Hβ zeolites were directly related to the basicity of the alkaline solution, indicating that Hβ zeolite is more sensitive to the alkaline post-treatment. The hierarchical HZSM-5 and Hβ zeolites are more active than the parent one for catalytic fast pyrolysis (CFP) of Kraft lignin. Hierarchical zeolites retained the function of acid catalysis, while additionally creating larger mesopores to ensure the entry of bulkier reactant molecules. The increase of the condensable volatiles yield can be attributed to the improvement of the mass transfer performance, which correlates well with the change of mesoporous surface area. In particular, the condensable volatiles yield for the optimized hierarchical Hβ reached approximately two times that of the parent Hβ zeolites. In contrast to the parent HZSM-5, the optimized hierarchical HZSM-5 zeolite significantly reduced the selectivity of oxygenates from 27.2% to 3.3%. Full article

(This article belongs to the Special Issue Catalytic Pyrolysis)

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16 pages, 3830 KiB

Open AccessArticle

Optimization of Biodiesel Production from Waste Cooking Oil Using Waste Eggshell as a Base Catalyst under a Microwave Heating System

by Yen-Ping Peng, Kassian T. T. Amesho, Chin-En Chen, Syu-Ruei Jhang, Feng-Chih Chou and Yuan-Chung Lin

Catalysts 2018, 8(2), 81; https://doi.org/10.3390/catal8020081 - 14 Feb 2018

Cited by 50 | Viewed by 7651

Abstract

This paper intends to explore the most affordable and environmentally friendly method for the synthesis of biodiesel. Substitute fuel is presently a significant topic all over the world, attributable to the efforts of reducing global warming, which is the result arising from the [...] Read more.

This paper intends to explore the most affordable and environmentally friendly method for the synthesis of biodiesel. Substitute fuel is presently a significant topic all over the world, attributable to the efforts of reducing global warming, which is the result arising from the combustion of petroleum or petrol diesel fuel. Due to its advantages of being renewable and environmentally friendly, biodiesel production has the potential to become the major substitute of petrol diesel fuel. Biodiesel is non-toxic, biodegradable, is produced from renewable sources, and contributes a small amount of greenhouse gas (e.g., CO₂ and SO₂) emissions to the atmosphere. Research has established that one of the key obstacles to the commercialization of biodiesel is the high price of biodiesel production due to the shortage of suitable raw materials. However, waste-cooking-oil (WCO) is one of the most cost-effective sources of biodiesel synthesis, and can practically minimize the raw material cost. The research was carried out to produce biodiesel from waste cooking oil in order to reduce the cost, waste, and pollution associated with biodiesel production. The application of a microwave heating system towards enhancing the production of biodiesel from waste cooking oil has been given little consideration in the preceding research, particularly with the application of eggshell as a heterogeneous catalyst. However, the tentative results in this study show significant performance in terms of biodiesel production, as follows: (1) the increasing of the reaction time from 120 to 165 min considerably increased the biodiesel production, which declined with a further rise to 210 min; (2) the results of this study reveal that a methanol-to-oil molar ratio of nine is appropriate and can be used for the best production of biodiesel; (3) the production of biodiesel in this study demonstrated a significant increase in response to the further increasing of power; (4) a 120 min response time, a ratio of 9:1 methanol-to-oil molar fraction, 65 °C temperature; (5) and 5 wt % catalyst were found to be the most ideal reaction conditions during this study. In summary, recycled eggshell was re-used as a suitable catalyst to produce new biodiesel from waste cooking oil, applicable to diesel engines. Full article

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30 pages, 7088 KiB

Open AccessReview

Oriented Decoration in Metal-Functionalized Ordered Mesoporous Silicas and Their Catalytic Applications in the Oxidation of Aromatic Compounds

by Shijian Zhou, Fu Yang, Bangbang Wang, Hang Su, Kangchao Lu, Yun Ding, Kai Lei, Man Xu, Bo Shao, Yun Wang and Yan Kong

Catalysts 2018, 8(2), 80; https://doi.org/10.3390/catal8020080 - 13 Feb 2018

Cited by 11 | Viewed by 5250

Abstract

Ordered mesoporous silicas (OMSs) attract considerable attention due to their advanced structural properties. However, for the pristine silica materials, the inert property greatly inhibits their catalytic applications. Thus, to contribute to the versatile surface of OMSs, different metal active sites, including acidic/basic sites [...] Read more.

Ordered mesoporous silicas (OMSs) attract considerable attention due to their advanced structural properties. However, for the pristine silica materials, the inert property greatly inhibits their catalytic applications. Thus, to contribute to the versatile surface of OMSs, different metal active sites, including acidic/basic sites and redox sites, have been introduced into specific locations (mesoporous channels and framework) of OMSs and the metal-functionalized ordered mesoporous silicas (MOMSs) show great potential in the catalytic applications. In this review, we first present the categories of metal active sites. Then, the synthesized processes of MOMSs are thoroughly discussed, in which the metal active sites would be introduced with the assistance of organic groups into the specific locations of OMSs. In addition, the structural morphologies of OMSs are elaborated and the catalytic applications of MOMSs in the oxidation of aromatic compounds are illustrated in detail. Finally, the prospects for the future development in this field are proposed. Full article

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14 pages, 900 KiB

Open AccessArticle

Heterogeneous Catalysis by Tetraethylammonium Tetrachloroferrate of the Photooxidation of Toluene by Visible and Near-UV Light

by Kelsie R. Barnard, Valerie R. Bright, Robert J. Enright, Kira M. Fahy, Adam C. Liu and Patrick E. Hoggard

Catalysts 2018, 8(2), 79; https://doi.org/10.3390/catal8020079 - 13 Feb 2018

Cited by 13 | Viewed by 4617

Abstract

Titanium dioxide is the most extensively used heterogeneous catalyst for the photooxidation of toluene and other hydrocarbons, but it has low utility for the synthesis of benzyl alcohol, of which little is produced, or benzaldehyde, due to further oxidation to benzoic acid and [...] Read more.

Titanium dioxide is the most extensively used heterogeneous catalyst for the photooxidation of toluene and other hydrocarbons, but it has low utility for the synthesis of benzyl alcohol, of which little is produced, or benzaldehyde, due to further oxidation to benzoic acid and cresol, among other oxidation products, and eventually complete mineralization to CO₂. Et₄N[FeCl₄] functions as a photocatalyst through the dissociation of chlorine atoms, which abstract hydrogen from toluene, and the photooxidation of toluene proceeds only as far as benzyl alcohol and benzaldehyde. Unlike TiO₂, which requires ultraviolet (UV) irradiation, Et₄N[FeCl₄] catalyzes the photooxidation of toluene with visible light alone. Even under predominantly UV irradiation, the yield of benzyl alcohol plus benzaldehyde is greater with Et₄N[FeCl₄] than with TiO₂. Et₄N[FeCl₄] photocatalysis yields benzyl chloride as a side product, but it can be minimized by restricting irradiation to wavelengths above 360 nm and by the use of long irradiation times. The photonic efficiency of oxidation in one experiment was found to be 0.042 mol/einstein at 365 nm. The use of sunlight as the irradiation source was explored. 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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11 pages, 3418 KiB

Open AccessArticle

Photocatalytic Reduction of CO₂ from Simulated Flue Gas with Colored Anatase

by Yebin Guan, Ming Xia, Alessandro Marchetti, Xiaohong Wang, Weicheng Cao, Hanxi Guan and Xueqian Kong

Catalysts 2018, 8(2), 78; https://doi.org/10.3390/catal8020078 - 13 Feb 2018

Cited by 8 | Viewed by 4688

Abstract

Photocatalytic reduction with sunlight is an economical and promising advanced approach for reducing the excessive emissions of CO₂ from the combustion of fossil fuels. Aimed at practical applications, a type of inexpensive colored anatase material was used to evaluate CO₂ photoreduction [...] Read more.

Photocatalytic reduction with sunlight is an economical and promising advanced approach for reducing the excessive emissions of CO₂ from the combustion of fossil fuels. Aimed at practical applications, a type of inexpensive colored anatase material was used to evaluate CO₂ photoreduction performance on a platform with a continuous flow of gas mixtures (10 vol % CO₂, 90% N₂), which resembles realistic flue gas conditions. The results showed an enhanced photocatalytic activity compared with standard P25 and significant improvement over pristine anatase. Based on a series of characterization techniques, we propose that the oxygen vacancies and surface hydroxyl groups on colored anatase can reduce the bandgap and assist the binding of CO₂ molecules. Our results showed that photoreduction of CO₂ is feasible under practical conditions, and the efficiency could be improved through modification of catalysts. Full article

(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)

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17 pages, 3581 KiB

Open AccessArticle

Effect of Support Pretreatment Temperature on the Performance of an Iron Fischer–Tropsch Catalyst Supported on Silica-Stabilized Alumina

by Kamyar Keyvanloo, Baiyu Huang, Trent Okeson, Hussein H. Hamdeh and William C. Hecker

Catalysts 2018, 8(2), 77; https://doi.org/10.3390/catal8020077 - 12 Feb 2018

Cited by 18 | Viewed by 4956

Abstract

The effect of support material pretreatment temperature, prior to adding the active phase and promoters, on Fischer–Tropsch activity and selectivity was explored. Four iron catalysts were prepared on silica-stabilized alumina (AlSi) supports pretreated at 700 °C, 900 °C, 1100 °C or 1200 °C. [...] Read more.

The effect of support material pretreatment temperature, prior to adding the active phase and promoters, on Fischer–Tropsch activity and selectivity was explored. Four iron catalysts were prepared on silica-stabilized alumina (AlSi) supports pretreated at 700 °C, 900 °C, 1100 °C or 1200 °C. Addition of 5% silica to alumina made the AlSi material hydrothermally stable, which enabled the unusually high support pretreatment temperatures (>900 °C) to be studied. High-temperature dehydroxylation of the AlSi before impregnation greatly reduces FeO·Al₂O₃ surface spinel formation by removing most of the support-surface hydroxyl groups leading to more effectively carbided catalyst. The activity increases more than four-fold for the support calcined at elevated temperatures (1100–1200 °C) compared with traditional support calcination temperatures of <900 °C. This unique pretreatment also facilitates the formation of ε′-Fe_2.2C rather than χ-Fe_2.5C on the AlSi support, which shows an excellent correlation with catalyst productivity. 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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14 pages, 3032 KiB

Open AccessArticle

Mn-Ce-V-WO_x/TiO₂ SCR Catalysts: Catalytic Activity, Stability and Interaction among Catalytic Oxides

by Xuteng Zhao, Lei Mao and Guojun Dong

Catalysts 2018, 8(2), 76; https://doi.org/10.3390/catal8020076 - 12 Feb 2018

Cited by 26 | Viewed by 5704

Abstract

A series of Mn-Ce-V-WO_x/TiO₂ composite oxide catalysts with different molar ratios (active components/TiO₂ = 0.1, 0.2, 0.3, 0.6) have been prepared by wet impregnation method and tested in selective catalytic reduction (SCR) of NO by NH₃ in a [...] Read more.

A series of Mn-Ce-V-WO_x/TiO₂ composite oxide catalysts with different molar ratios (active components/TiO₂ = 0.1, 0.2, 0.3, 0.6) have been prepared by wet impregnation method and tested in selective catalytic reduction (SCR) of NO by NH₃ in a wide temperature range. These catalysts were also characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), in situ Fourier Transform infrared spectroscopy (in situ FTIR), H₂-Temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The results show the catalyst with a molar ratio of active components/TiO₂ = 0.2 exhibits highest NO conversion value between 150 °C to 400 °C and good resistance to H₂O and SO₂ at 250 °C with a gas hourly space velocity (GHSV) value of 40,000 h⁻¹. Different oxides are well dispersed and interact with each other. NH₃ and NO are strongly adsorbed on the catalyst surface and the adsorption of the reactant gas leads to a redox cycle with the valence state change among the surface oxides. The adsorption of SO₂ on Mn⁴⁺ and Ce⁴⁺ results in good H₂O and SO₂ resistance of the catalyst, but the effect of Mn and Ce are more than superior water and sulfur resistance. The diversity of valence states of the four active components and their high oxidation-reduction performance are the main reasons for the high NO conversion in this system. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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28 pages, 6004 KiB

Open AccessFeature PaperEditor’s ChoiceReview

One-Pot Combination of Metal- and Bio-Catalysis in Water for the Synthesis of Chiral Molecules

by Nicolás Ríos-Lombardía, Joaquín García-Álvarez and Javier González-Sabín

Catalysts 2018, 8(2), 75; https://doi.org/10.3390/catal8020075 - 10 Feb 2018

Cited by 49 | Viewed by 8145

Abstract

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually [...] Read more.

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually room temperature) and in the presence of air. Herein, a comprehensive account of the state-of-the-art in the development of catalytic networks by combining metallic and biological catalysts in aqueous media (the natural environment of enzymes) is presented. Among others, the combination of metal-catalyzed isomerizations, cycloadditions, hydrations, olefin metathesis, oxidations, C-C cross-coupling and hydrogenation reactions, with several biocatalyzed transformations of organic groups (enzymatic reduction, epoxidation, halogenation or ester hydrolysis), are discussed. Full article

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47 pages, 13106 KiB

Open AccessReview

g-C₃N₄-Based Nanomaterials for Visible Light-Driven Photocatalysis

by Santosh Kumar, Sekar Karthikeyan and Adam F. Lee

Catalysts 2018, 8(2), 74; https://doi.org/10.3390/catal8020074 - 9 Feb 2018

Cited by 209 | Viewed by 29234

Abstract

Graphitic carbon nitride (g-C₃N₄) is a promising material for photocatalytic applications such as solar fuels production through CO₂ reduction and water splitting, and environmental remediation through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties [...] Read more.

Graphitic carbon nitride (g-C₃N₄) is a promising material for photocatalytic applications such as solar fuels production through CO₂ reduction and water splitting, and environmental remediation through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties of g-C₃N₄ nanostructures, notably high surface area, quantum efficiency, interfacial charge separation and transport, and ease of modification through either composite formation or the incorporation of desirable surface functionalities. Here, we review recent progress in the synthesis and photocatalytic applications of diverse g-C₃N₄ nanostructured materials, and highlight the physical basis underpinning their performance for each application. Potential new architectures, such as hierarchical or composite g-C₃N₄ nanostructures, that may offer further performance enhancements in solar energy harvesting and conversion are also outlined. 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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13 pages, 3912 KiB

Open AccessArticle

Wood-Biochar-Supported Magnetite Nanoparticles for Remediation of PAH-Contaminated Estuary Sediment

by Cheng-Di Dong, Chiu-Wen Chen, Chih-Ming Kao, Chuan-Chi Chien and Chang-Mao Hung

Catalysts 2018, 8(2), 73; https://doi.org/10.3390/catal8020073 - 9 Feb 2018

Cited by 89 | Viewed by 6340

Abstract

In this study, we investigated the ability of a magnetic wood biochar (WB)-based composite catalyst (Fe₃O₄–WB) to catalyze sodium persulfate (PS) for the remediation of estuary sediment contaminated with polycyclic aromatic hydrocarbons (PAHs). The effects of various critical parameters, [...] Read more.

In this study, we investigated the ability of a magnetic wood biochar (WB)-based composite catalyst (Fe₃O₄–WB) to catalyze sodium persulfate (PS) for the remediation of estuary sediment contaminated with polycyclic aromatic hydrocarbons (PAHs). The effects of various critical parameters, including the catalyst dose and initial pH, were investigated. The degradation of the PAHs was found to be related to the number of rings in their structure. The results showed that Fe₃O₄–WB is an efficient catalyst for the removal of high-ring PAHs (HPAHs), with the highest degradation rates for the 6-, 5-, and 4-ringed PAHs being 90%, 84%, and 87%, respectively, for a PS concentration of 2 × 10⁻⁵ M, catalyst concentration of 3.33 g/L, and pH of 3.0. That the reduction rate of the HPAHs was greater than that of the low-ring PAHs can be attributed to the strong affinity of the HPAHs for biochar derived from wood biomass. Overall, this study revealed that the WB-mediated electron transfer catalysis of the surface functional groups in a wide range of pH in the Fe₃O₄–WB/PS system and potentially application in the remediation of sediments contaminated with PAHs. Full article

(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)

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13 pages, 1432 KiB

Open AccessArticle

Modeling of a Pilot-Scale Fixed-Bed Reactor for Dehydration of 2,3-Butanediol to 1,3-Butadiene and Methyl Ethyl Ketone

by Daesung Song

Catalysts 2018, 8(2), 72; https://doi.org/10.3390/catal8020072 - 9 Feb 2018

Cited by 10 | Viewed by 5574

Abstract

A 1D heterogeneous reactor model accounting for interfacial and intra-particle gradients was developed to simulate the dehydration of 2,3-Butanediol (2,3-BDO) to 1,3-Butadiene (1,3-BD) and Methyl Ethyl Ketone (MEK) over an amorphous calcium phosphate (a-CP) catalyst in a pilot-scale fixed-bed reactor. The developed model [...] Read more.

A 1D heterogeneous reactor model accounting for interfacial and intra-particle gradients was developed to simulate the dehydration of 2,3-Butanediol (2,3-BDO) to 1,3-Butadiene (1,3-BD) and Methyl Ethyl Ketone (MEK) over an amorphous calcium phosphate (a-CP) catalyst in a pilot-scale fixed-bed reactor. The developed model was validated with experimental data in terms of a fluid temperature profile along with the length of the catalyst bed, 2,3-BDO conversion, and selectivity for the major products, 1,3-BD and MEK, at the outlet of the reactor. The fluid temperature profile obtained from the model along the length of the catalyst bed coincides satisfactorily with the experimental observations. The difference between the experimental data and the 1D heterogeneous reactor model prediction for 2,3-BDO conversion and selectivity of 1,3-BD and MEK were 0.1%, 9 wt %, and 2 wt %, respectively. In addition, valuable insights related to the feeding system of a commercial-scale plant were made through troubleshooting of the pilot tests. Notably, if the feed including only 2,3-BDO and furnaces that increase the temperature of the feed to the reaction temperature were used in a commercial plant, the feeding system could not be operational because of the presence of heavy chemicals considered oligomers of 2,3-BDO. Full article

(This article belongs to the Special Issue Multiscale and Innovative Kinetic Approaches in Heterogeneous Catalysis)

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11 pages, 2865 KiB

Open AccessArticle

Effect of Dopant Loading on the Structural and Catalytic Properties of Mn-Doped SrTiO₃ Catalysts for Catalytic Soot Combustion

by Santiago Iván Suárez-Vázquez, Arquímedes Cruz-López, Carlos Eduardo Molina-Guerrero, Astrid Iriana Sánchez-Vázquez and Carlos Macías-Sotelo

Catalysts 2018, 8(2), 71; https://doi.org/10.3390/catal8020071 - 9 Feb 2018

Cited by 27 | Viewed by 4684

Abstract

Soot particles have been associated with respiratory diseases and cancer. To decrease these emissions, perovskite-mixed oxides have been proposed due to their thermal stability and redox surface properties. In this work, SrTiO₃ doped with different amounts of Mn were synthesized by the [...] Read more.

Soot particles have been associated with respiratory diseases and cancer. To decrease these emissions, perovskite-mixed oxides have been proposed due to their thermal stability and redox surface properties. In this work, SrTiO₃ doped with different amounts of Mn were synthesized by the hydrothermal method and tested for soot combustion. Results show that at low Mn content, structural distortion, and higher O_ads/O_lat ratio were observed which was attributed to the high content of Mn³⁺ in Ti sites. On the other hand, increasing the Mn content led to surface segregation of manganese oxide. All synthesized catalysts showed mesopores in the range of 32–47 nm. In the catalytic combustion of soot, the samples synthesized in this work lowered the combustion temperature by more than 100 °C compared with the uncatalyzed reaction. The sample doped with 1 wt % of Mn showed the best catalytic activity. The activation energy of these samples was also calculated, and the order of decreasing activation energy is as follows: uncatalyzed > Mn0 > Mn8 > Mn4 > Mn1. The best catalytic activity for Mn1 was attributed to its physicochemical properties and the mobility of the oxygen from the bulk to the surface at temperatures higher than 500 °C. Full article

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10 pages, 3890 KiB

Open AccessArticle

Low Temperature Synthesis of Nest-Like Microsphere with Exposed (001) Facets and Its Enhanced Photocatalytic Performance by NaOH Alkalization

by Chentao Hou, Jiaming Zhu and Qiaoqiao Song

Catalysts 2018, 8(2), 70; https://doi.org/10.3390/catal8020070 - 8 Feb 2018

Cited by 8 | Viewed by 3649

Abstract

In this study, we completed a simple low-temperature synthesis of nest-like titanium oxide (TiO₂) microspheres with exposed (001) facets. For the first time, the photocatalytic performance was enhanced by sodium hydroxide (NaOH) alkalization. The characterization of as-synthesized F-TiO₂ and OH-TiO [...] Read more.

In this study, we completed a simple low-temperature synthesis of nest-like titanium oxide (TiO₂) microspheres with exposed (001) facets. For the first time, the photocatalytic performance was enhanced by sodium hydroxide (NaOH) alkalization. The characterization of as-synthesized F-TiO₂ and OH-TiO₂ were analyzed by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, fourier transform infrared spectroscopic analysis, ultraviolet-vis diffuse reflection spectra and Raman spectroscopy. The photocatalytic activity of the as-prepared catalyst was evaluated through the photocatalytic degradation of methylene blue (MB) and Rhodamine B (RhB) under simulated solar light. The results showed that modification using NaOH can lead to an increase in the percentage of (001) facets from 27.8% for F-TiO₂ to 39.2% for OH-TiO₂. OH-TiO₂ showed superior catalytic photoactivity toward MB. The mechanism of NaOH on TiO₂ is also discussed. Full article

(This article belongs to the Special Issue Organic Photoredox Catalysis)

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11 pages, 1863 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

New Trendy Magnetic C-Scorpionate Iron Catalyst and Its Performance towards Cyclohexane Oxidation

by Ana P. C. Ribeiro, Inês A. S. Matias, Elisabete C. B. A. Alegria, Ana M. Ferraria, Ana M. Botelho do Rego, Armando J. L. Pombeiro and Luísa M. D. R. S. Martins

Catalysts 2018, 8(2), 69; https://doi.org/10.3390/catal8020069 - 8 Feb 2018

Cited by 15 | Viewed by 4985

Abstract

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide [...] Read more.

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes. Full article

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13 pages, 1128 KiB

Open AccessReview

Nano-Immobilized Biocatalysts for Biodiesel Production from Renewable and Sustainable Resources

by Keon Hee Kim, Ok Kyung Lee and Eun Yeol Lee

Catalysts 2018, 8(2), 68; https://doi.org/10.3390/catal8020068 - 8 Feb 2018

Cited by 83 | Viewed by 9821

Abstract

The cost of biodiesel production relies on feedstock cost. Edible oil is unfavorable as a biodiesel feedstock because of its expensive price. Thus, non-edible crop oil, waste oil, and microalgae oil have been considered as alternative resources. Non-edible crop oil and waste cooking [...] Read more.

The cost of biodiesel production relies on feedstock cost. Edible oil is unfavorable as a biodiesel feedstock because of its expensive price. Thus, non-edible crop oil, waste oil, and microalgae oil have been considered as alternative resources. Non-edible crop oil and waste cooking oil are more suitable for enzymatic transesterification because they include a large amount of free fatty acids. Recently, enzymes have been integrated with nanomaterials as immobilization carriers. Nanomaterials can increase biocatalytic efficiency. The development of a nano-immobilized enzyme is one of the key factors for cost-effective biodiesel production. This paper presents the technology development of nanomaterials, including nanoparticles (magnetic and non-magnetic), carbon nanotubes, and nanofibers, and their application to the nano-immobilization of biocatalysts. The current status of biodiesel production using a variety of nano-immobilized lipase is also discussed. Full article

(This article belongs to the Special Issue Nanobiotechnology for Biofuel Production: Renewable and Sustainable Sources)

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8 pages, 1094 KiB

Open AccessArticle

Catalytic Wet Oxidation of Pharmaceutical Sludge by Molecular Sieve Loaded with Cu/Ce

by Xu Zeng, Jun Liu and Jianfu Zhao

Catalysts 2018, 8(2), 67; https://doi.org/10.3390/catal8020067 - 8 Feb 2018

Cited by 12 | Viewed by 4405

Abstract

In the present study, the catalytic wet oxidation of pharmaceutical sludge by molecular sieve loaded with Cu/Ce as catalyst was investigated. Experiments were performed in an experimental batch reactor. Reaction parameters including catalyst dose, temperature, time, and oxygen pressure were discussed. The results [...] Read more.

In the present study, the catalytic wet oxidation of pharmaceutical sludge by molecular sieve loaded with Cu/Ce as catalyst was investigated. Experiments were performed in an experimental batch reactor. Reaction parameters including catalyst dose, temperature, time, and oxygen pressure were discussed. The results showed that the catalysts prepared by co-precipitating method have good catalytic performance. Under optimum conditions, the highest volatile suspended solids (VSS) removal rate approximately 92% and chemical oxygen demand (COD) removal rate of 75% were obtained at 260 °C for 60 min with initial oxygen pressure 1.0 MPa and the catalyst 10 g/L. These results implied that the catalytic wet oxidation of pharmaceutical sludge by molecular sieve loaded with Cu/Ce is a promising method for the highly efficient degradation of the sludge. Full article

(This article belongs to the Special Issue Catalytic Wet-Air Oxidation Processes)

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19 pages, 10341 KiB

Open AccessArticle

Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

by Mahmoud M. Khader, Mohammed J. Al-Marri, Sardar Ali and Ahmed G. Abdelmoneim

Catalysts 2018, 8(2), 66; https://doi.org/10.3390/catal8020066 - 7 Feb 2018

Cited by 16 | Viewed by 5605

Abstract

We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), [...] Read more.

We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), SCS preparative methodology resulted in segregating both Pd and Ce on the surface of the Al₂O₃ support. Furthermore, HTEM showed that bigger Pd particles (5 nm and more) were surrounded by CeO₂, resembling a core shell structure, while smaller Pd particles (1 nm and less) were not associated with CeO₂. The intimate Pd-CeO₂ attachment resulted in insertion of Pd ions into the ceria lattice, and associated with the reduction of Ce⁴⁺ into Ce³⁺ ions; consequently, the formation of oxygen vacancies. XPS showed also that Pd had three oxidation states corresponding to Pd⁰, Pd²⁺ due to PdO, and highly ionized Pd ions (Pd^(2+x)+) which might originate from the insertion of Pd ions into the ceria lattice. The formation of intrinsic Ce³⁺ ions, highly ionized (Pd²⁺ species inserted into the lattice of CeO₂) Pd ions (Pd^(2+x)+) and oxygen vacancies is suggested to play a major role in the unique catalytic activity. The results indicated that the Pd-SCS nano-catalysts were exceptionally more active and stable than conventional catalysts. Under similar reaction conditions, the methane combustion rate over the SCS catalyst was ~18 times greater than that of conventional catalysts. Full methane conversions over the SCS catalysts occurred at around 400 °C but were not shown at all with conventional catalysts. In addition, contrary to the conventional catalysts, the SCS catalysts exhibited superior activity with no sign of deactivation in the temperature range between ~400 and 800 °C. Full article

(This article belongs to the Special Issue Catalytic Oxidation of Methane)

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18 pages, 2723 KiB

Open AccessReview

Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

by Zhenghua Tang, Wen Wu and Kai Wang

Catalysts 2018, 8(2), 65; https://doi.org/10.3390/catal8020065 - 7 Feb 2018

Cited by 64 | Viewed by 11181

Abstract

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. [...] Read more.

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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20 pages, 2744 KiB

Open AccessFeature PaperArticle

The CoAlCeO Mixed Oxide: An Alternative to Palladium-Based Catalysts for Total Oxidation of Industrial VOCs

by Julien Brunet, Eric Genty, Cédric Barroo, Fabrice Cazier, Christophe Poupin, Stéphane Siffert, Diane Thomas, Guy De Weireld, Thierry Visart de Bocarmé and Renaud Cousin

Catalysts 2018, 8(2), 64; https://doi.org/10.3390/catal8020064 - 6 Feb 2018

Cited by 25 | Viewed by 5351

Abstract

Catalytic total oxidation is an effective technique for the treatment of industrial VOCs principally resulting from industrial processes using solvents, and usually containing mono-aromatics (BTEX) and oxygenated compounds (acetone, ethanol, butanone). The catalytic total oxidation of VOCs on noble metal materials is effective. [...] Read more.

Catalytic total oxidation is an effective technique for the treatment of industrial VOCs principally resulting from industrial processes using solvents, and usually containing mono-aromatics (BTEX) and oxygenated compounds (acetone, ethanol, butanone). The catalytic total oxidation of VOCs on noble metal materials is effective. However, the cost of catalysts is a main obstacle for the industrial application of these VOC removal processes. Therefore, the aim of this work is to propose an alternative material to palladium-based catalysts (which are suitable for VOCs’ total oxidation): a mixed oxide synthesized in the hydrotalcite way, namely CoAlCeO. This material was compared to four catalytic materials containing palladium, selected according to the literature: Pd/α-Al₂O₃, Pd/HY, Pd/CeO₂ and Pd/γAl₂O₃. These materials have been studied for the total oxidation of toluene, butanone, and VOCs mixtures. Catalysts’ performances were compared, taking into account the oxidation byproducts emitted from the process. This work highlight that the CoAlCeO catalyst presents better efficiency than Pd-based materials for the total oxidation of a VOCs mixture. Full article

(This article belongs to the Special Issue New Concepts in Oxidation Processes)

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