Catalysts

13 pages, 2788 KiB

Open AccessArticle

TiO₂-SiO₂-PMMA Terpolymer Floating Device for the Photocatalytic Remediation of Water and Gas Phase Pollutants

by Valentina Sabatini, Luca Rimoldi, Laura Tripaldi, Daniela Meroni, Hermes Farina, Marco Aldo Ortenzi and Silvia Ardizzone

Catalysts 2018, 8(11), 568; https://doi.org/10.3390/catal8110568 - 21 Nov 2018

Cited by 8 | Viewed by 4388

Abstract

Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species [...] Read more.

Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species close to the water surface. The device was prepared on a novel tailored ter-polymer substrate based on methylmethacrylate, α-methylstyrene and perfluoroctyl methacrylate. The ad hoc synthesized support presents optimal characteristics in terms of buoyancy, transparency, gas permeability, mechanical, UV and thermal stability. The adhesion of the TiO₂ top layer was favoured by the adopted casting procedure, followed by a corona pre-treatment and by the deposition of an intermediate SiO₂ layer, the latter aimed also at protecting the polymer support from photocatalytic oxidation. The device was characterized by contact angle measurement, UV-vis transmittance and scanning electron microscopy. The final device was tested for the photocatalytic degradation of an emerging water pollutant as well as of vapors of a model volatile organic compound. Relevant activity was observed also under simulated solar irradiation and the device showed good stability and recyclability, prospecting its use for the photocatalytic degradation of pollutants in large water basins. Full article

(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)

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16 pages, 3927 KiB

Open AccessArticle

In Situ Regeneration of Alumina-Supported Cobalt–Iron Catalysts for Hydrogen Production by Catalytic Methane Decomposition

by Anis H. Fakeeha, Siham Barama, Ahmed A. Ibrahim, Raja-Lafi Al-Otaibi, Akila Barama, Ahmed E. Abasaeed and Ahmed S. Al-Fatesh

Catalysts 2018, 8(11), 567; https://doi.org/10.3390/catal8110567 - 21 Nov 2018

Cited by 15 | Viewed by 5700

Abstract

A novel approach to the in situ regeneration of a spent alumina-supported cobalt–iron catalyst for catalytic methane decomposition is reported in this work. The spent catalyst was obtained after testing fresh catalyst in catalytic methane decomposition reaction during 90 min. The regeneration evaluated [...] Read more.

A novel approach to the in situ regeneration of a spent alumina-supported cobalt–iron catalyst for catalytic methane decomposition is reported in this work. The spent catalyst was obtained after testing fresh catalyst in catalytic methane decomposition reaction during 90 min. The regeneration evaluated the effect of forced periodic cycling; the cycles of regeneration were performed in situ at 700 °C under diluted O₂ gasifying agent (10% O₂/N₂), followed by inert treatment under N₂. The obtained regenerated catalysts at different cycles were tested again in catalytic methane decomposition reaction. Fresh, spent, and spent/regenerated materials were characterized using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), N₂-physisorption, H₂-temperature programmed reduction (H₂-TPR), thermogravimetric analysis (TGA), and atomic absorption spectroscopy (AAS). The comparison of transmission electron microscope and X-ray powder diffraction characterizations of spent and spent/regenerated catalysts showed the formation of a significant amount of carbon on the surface with a densification of catalyst particles after each catalytic methane decomposition reaction preceded by regeneration. The activity results confirm that the methane decomposition after regeneration cycles leads to a permanent deactivation of catalysts certainly provoked by the coke deposition. Indeed, it is likely that some active iron sites cannot be regenerated totally despite the forced periodic cycling. Full article

(This article belongs to the Special Issue Catalysts for Syngas Production)

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12 pages, 4324 KiB

Open AccessArticle

Nickel Nanowires: Synthesis, Characterization and Application as Effective Catalysts for the Reduction of Nitroarenes

by Tomasz Wasiak, Lukasz Przypis, Krzysztof Z. Walczak and Dawid Janas

Catalysts 2018, 8(11), 566; https://doi.org/10.3390/catal8110566 - 20 Nov 2018

Cited by 14 | Viewed by 6399

Abstract

We have demonstrated a convenient method of synthesizing nickel nanowires (NiNWs), which could be easily tuned to produce materials with a carefully defined nanostructure. By varying the concentration of the Ni precursor, pH of the medium or reaction temperature, we directly affected the [...] Read more.

We have demonstrated a convenient method of synthesizing nickel nanowires (NiNWs), which could be easily tuned to produce materials with a carefully defined nanostructure. By varying the concentration of the Ni precursor, pH of the medium or reaction temperature, we directly affected the diameter of the formed product as well as the yield of the process. The obtained material consisted of straight bundles of NiNWs, which revealed powerful catalytic action for the reduction of nitroarenes to appropriate amine derivatives. A selection of substrates were employed and all of them were successfully converted into the corresponding aromatic amine despite the presence of different substituents on the aromatic ring with high yields, even in large scale reactions. The results showed that NiNW-based catalysts could constitute efficient catalytic systems for the synthesis of aryl amines at industrial levels. Full article

(This article belongs to the Section Nanostructured Catalysts)

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11 pages, 2276 KiB

Open AccessArticle

Three Component Controls in Pillared Metal-Organic Frameworks for Catalytic Carbon Dioxide Fixation

by Jinmi Noh, Dasom Kim, Jihyun Lee, Minyoung Yoon, Myung Hwan Park, Kang Mun Lee, Youngjo Kim and Min Kim

Catalysts 2018, 8(11), 565; https://doi.org/10.3390/catal8110565 - 20 Nov 2018

Cited by 5 | Viewed by 5768

Abstract

Three components of pillared metal-organic frameworks (MOFs, three components = metal ion, carboxylic acid ligand, and N-chelating ligand) were controlled for CO₂ cycloaddition catalysts to synthesize organic cyclic carbonates. Among the divalent metals, Zn²⁺ showed the best catalytic activity, and [...] Read more.

Three components of pillared metal-organic frameworks (MOFs, three components = metal ion, carboxylic acid ligand, and N-chelating ligand) were controlled for CO₂ cycloaddition catalysts to synthesize organic cyclic carbonates. Among the divalent metals, Zn²⁺ showed the best catalytic activity, and in DABCO (1,4-diazabicyclo[2.2.2]octane)-based MOFs, hydroxy-functionalized DMOF-OH was the most efficient MOF for CO₂ cycloaddition. For the BPY (4,4’-bipyridyl)-type MOFs, all five prepared BMOFs (BPY MOFs) showed similar and good conversions for CO₂ cycloaddition. Finally, this pillared MOF could be recycled up to three times without activity and crystallinity loss. Full article

(This article belongs to the Special Issue Catalysis by Metal-Organic Frameworks)

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14 pages, 1167 KiB

Open AccessReview

V-Containing Mixed Oxide Catalysts for Reduction–Oxidation-Based Reactions with Environmental Applications: A Short Review

by M. Olga Guerrero-Pérez

Catalysts 2018, 8(11), 564; https://doi.org/10.3390/catal8110564 - 20 Nov 2018

Cited by 22 | Viewed by 5643

Abstract

V-containing mixed oxide catalytic materials are well known as active for partial oxidation reactions. Oxidation reactions are used in industrial chemistry and for the abatement of pollutants. An analysis of the literature in this field during the past few years shows a clear [...] Read more.

V-containing mixed oxide catalytic materials are well known as active for partial oxidation reactions. Oxidation reactions are used in industrial chemistry and for the abatement of pollutants. An analysis of the literature in this field during the past few years shows a clear increase in the use of vanadium-based materials as catalysts for environmental applications. The present contribution makes a brief revision of the main applications of vanadium containing mixed oxides in environmental catalysis, analyzing the properties that present the catalysts with a better behavior that, in most cases, is related with the stabilization of reduced vanadium species (as V⁴⁺/V³⁺) during reaction. Full article

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

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18 pages, 5351 KiB

Open AccessArticle

Promotional Effect of Gold on the WGS Activity of Alumina-Supported Copper-Manganese Mixed Oxides

by Tatyana Tabakova, Ivan Ivanov, Yordanka Karakirova, Daniela Karashanova, Anna Maria Venezia, Petya Petrova, Georgi Avdeev, Elitsa Kolentsova and Krasimir Ivanov

Catalysts 2018, 8(11), 563; https://doi.org/10.3390/catal8110563 - 20 Nov 2018

Cited by 10 | Viewed by 3679

Abstract

The water-gas shift (WGS) reaction is a well-known industrial process used for the production of hydrogen. During the last few decades, it has attracted renewed attention due to the need for high-purity hydrogen for fuel-cell processing systems. The aim of the present study [...] Read more.

The water-gas shift (WGS) reaction is a well-known industrial process used for the production of hydrogen. During the last few decades, it has attracted renewed attention due to the need for high-purity hydrogen for fuel-cell processing systems. The aim of the present study was to develop a cost-effective and catalytically efficient formulation that combined the advantageous properties of transition metal oxides and gold nanoparticles. Alumina-supported copper- manganese mixed oxides were prepared by wet impregnation. The deposition-precipitation method was used for the synthesis of gold catalysts. The effect of the Cu:Mn molar ratio and the role of Au addition on the WGS reaction’s performance was evaluated. Considerable emphasis was put on the characterization of the as-prepared and WGS-tested samples by means of a number of physicochemical methods (X-ray powder diffraction, high-resolution transmission electron microscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and temperature-programmed reduction) in order to explain the relationship between the structure and the reductive and WGS behavior. Catalytic tests revealed the promotional effect of gold addition. The best performance of the gold-promoted sample with a higher Cu content, i.e., a Cu:Mn molar ratio of 2:1 might be related to the beneficial role of Au on the spinel decomposition and the highly dispersed copper particle formation during the reaction, thus, ensuring the presence of two highly dispersed active metallic phases. High-surface-area alumina that was modified with a surface fraction of Cu–Mn mixed oxides favored the stabilization of finely dispersed gold particles. These new catalytic systems are very promising for practical applications due to their economic viability because the composition mainly includes alumina (80%). Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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14 pages, 1527 KiB

Open AccessReview

Biochars and Their Use as Transesterification Catalysts for Biodiesel Production: A Short Review

by John Vakros

Catalysts 2018, 8(11), 562; https://doi.org/10.3390/catal8110562 - 20 Nov 2018

Cited by 65 | Viewed by 7602

Abstract

Biodiesel can be a significant alternative for diesel. Usually, it is produced through transesterification with a base catalyst. Using heterogeneous catalysts for transesterification, the process can be more efficient. Among the possible catalysts that can be used, biochars combine high performance for transesterification [...] Read more.

Biodiesel can be a significant alternative for diesel. Usually, it is produced through transesterification with a base catalyst. Using heterogeneous catalysts for transesterification, the process can be more efficient. Among the possible catalysts that can be used, biochars combine high performance for transesterification and valorization of waste biomass. Biochars are cheap materials, and are easy to activate through chemical treatment with acid or base solutions. In this short review, the application of biochar as solid heterogeneous catalysts for transesterification of lipids to produce biodiesel is discussed. Full article

(This article belongs to the Section Biomass Catalysis)

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12 pages, 2236 KiB

Open AccessArticle

Construction of a Vitreoscilla Hemoglobin Promoter-Based Tunable Expression System for Corynebacterium glutamicum

by Kei-Anne Baritugo, Hee Taek Kim, Mi Na Rhie, Seo Young Jo, Tae Uk Khang, Kyoung Hee Kang, Bong Keun Song, Binna Lee, Jae Jun Song, Jong Hyun Choi, Dae-Hee Lee, Jeong Chan Joo and Si Jae Park

Catalysts 2018, 8(11), 561; https://doi.org/10.3390/catal8110561 - 19 Nov 2018

Cited by 9 | Viewed by 4506

Abstract

Corynebacterium glutamicum is an industrial strain used for the production of valuable chemicals such as L-lysine and L-glutamate. Although C. glutamicum has various industrial applications, a limited number of tunable systems are available to engineer it for efficient production of platform chemicals. Therefore, [...] Read more.

Corynebacterium glutamicum is an industrial strain used for the production of valuable chemicals such as L-lysine and L-glutamate. Although C. glutamicum has various industrial applications, a limited number of tunable systems are available to engineer it for efficient production of platform chemicals. Therefore, in this study, we developed a novel tunable promoter system based on repeats of the Vitreoscilla hemoglobin promoter (P_vgb). Tunable expression of green fluorescent protein (GFP) was investigated under one, four, and eight repeats of P_vgb (P_vgb, P_vgb4, and P_vgb8). The intensity of fluorescence in recombinant C. glutamicum strains increased as the number of P_vgb increased from single to eight (P_vgb8) repeats. Furthermore, we demonstrated the application of the new P_vgb promoter-based vector system as a platform for metabolic engineering of C. glutamicum by investigating 5-aminovaleric acid (5-AVA) and gamma-aminobutyric acid (GABA) production in several C. glutamicum strains. The profile of 5-AVA and GABA production by the recombinant strains were evaluated to investigate the tunable expression of key enzymes such as DavBA and GadB_mut. We observed that 5-AVA and GABA production by the recombinant strains increased as the number of P_vgb used for the expression of key proteins increased. The recombinant C. glutamicum strain expressing DavBA could produce higher amounts of 5-AVA under the control of P_vgb8 (3.69 ± 0.07 g/L) than the one under the control of P_vgb (3.43 ± 0.10 g/L). The average gamma-aminobutyric acid production also increased in all the tested strains as the number of P_vgb used for GadB_mut expression increased from single (4.81–5.31 g/L) to eight repeats (4.94–5.58 g/L). Full article

(This article belongs to the Special Issue Recent Advances in Biocatalysis and Metabolic Engineering for Biomanufacturing)

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24 pages, 2891 KiB

Open AccessArticle

Effect of Ni–Mo Carbide Catalyst Formation on Furfural Hydrogenation

by Ivan N. Shilov, Andrey A. Smirnov, Olga A. Bulavchenko and Vadim A. Yakovlev

Catalysts 2018, 8(11), 560; https://doi.org/10.3390/catal8110560 - 19 Nov 2018

Cited by 18 | Viewed by 5494

Abstract

High-loading Ni–Mo carbide catalysts were prepared by the modified gel-combustion method under various thermal treatment conditions. All samples were studied by X-ray diffraction (XRD) analysis, which showed that the catalysts could contain cubic and hexagonal molybdenum carbides, nickel, nickel oxide and Ni–Mo solid [...] Read more.

High-loading Ni–Mo carbide catalysts were prepared by the modified gel-combustion method under various thermal treatment conditions. All samples were studied by X-ray diffraction (XRD) analysis, which showed that the catalysts could contain cubic and hexagonal molybdenum carbides, nickel, nickel oxide and Ni–Mo solid solutions, depending on the thermal treatment conditions. Study of catalyst activity and selectivity in the hydrogenation of furfural was carried out in a batch reactor at 150 °C and hydrogen pressure 6.0 MPa. Analysis of the reaction products showed that the highest yields of 2-methylfuran (2-MF) and furfuryl alcohol (FA) were achieved using catalysts synthesized by calcination of the nickel-molybdenum-carbon precursor at 400 °С with the following reduction in a stream of hydrogen at 600 °C. The best results for production of FA with a yield of 80 mol % and 2-MF with a yield of 29 mol % were observed using Ni₆MoC–SiO₂ (400/600) and Ni₁MoC–SiO₂ (400/600) catalysts, respectively. It has been shown that the addition of nickel to the carbide molybdenum catalyst significantly increases the activity of the catalytic systems. In addition, nickel also contributes to the formation of products formed by hydrogenation of the aromatic ring tetrahydrofurfuryl alcohol (THFA) and 2-methyltetrahydrofuran (2-MTHF). Full article

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43 pages, 11426 KiB

Open AccessReview

Recent Advances of Cobalt-Based Electrocatalysts for Oxygen Electrode Reactions and Hydrogen Evolution Reaction

by Haihong Zhong, Carlos A. Campos-Roldán, Yuan Zhao, Shuwei Zhang, Yongjun Feng and Nicolas Alonso-Vante

Catalysts 2018, 8(11), 559; https://doi.org/10.3390/catal8110559 - 19 Nov 2018

Cited by 117 | Viewed by 17769

Abstract

This review summarizes recent progress in the development of cobalt-based catalytic centers as the most potentially useful alternatives to noble metal-based electrocatalysts (Pt-, Ir-, and Ru-based) towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in acid [...] Read more.

This review summarizes recent progress in the development of cobalt-based catalytic centers as the most potentially useful alternatives to noble metal-based electrocatalysts (Pt-, Ir-, and Ru-based) towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in acid and alkaline media. A series of cobalt-based high-performance electrocatalysts have been designed and synthesized including cobalt oxides/chalcogenides, Co–N_x/C, Co-layered double hydroxides (LDH), and Co–metal-organic frameworks (MOFs). The strategies of controllable synthesis, the structural properties, ligand effect, defects, oxygen vacancies, and support materials are thoroughly discussed as a function of the electrocatalytic performance of cobalt-based electrocatalysts. Finally, prospects for the design of novel, efficient cobalt-based materials, for large-scale application and opportunities, are encouraged. Full article

(This article belongs to the Special Issue Novel Non-Precious Metal Electrocatalysts for Oxygen Electrode Reactions)

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19 pages, 2302 KiB

Open AccessArticle

Synthesis, APPI Mass-Spectrometric Characterization, and Polymerization Studies of Group 4 Dinuclear Bis(ansa-metallocene) Complexes

by Gilles Schnee, Mathilde Farenc, Leslie Bitard, Aurelien Vantomme, Alexandre Welle, Jean-Michel Brusson, Carlos Afonso, Pierre Giusti, Jean-François Carpentier and Evgueni Kirillov

Catalysts 2018, 8(11), 558; https://doi.org/10.3390/catal8110558 - 19 Nov 2018

Cited by 7 | Viewed by 3441

Abstract

New ligand platforms of the type p- or m-Ph{-CR(3,6-tBu₂Flu)(Cp)}₂ (para-, R = Me (2a), H (2b); meta-, R = Me (2c)) were synthesized via nucleophilic addition of [...] Read more.

New ligand platforms of the type p- or m-Ph{-CR(3,6-tBu₂Flu)(Cp)}₂ (para-, R = Me (2a), H (2b); meta-, R = Me (2c)) were synthesized via nucleophilic addition of the 3,6-tBu₂-fluorenyl-anion onto the parent phenylene-bridged difulvenes (1a–c). The corresponding discrete homodinuclear zirconium and hafnium bis(dichloro ansa-metallocene) complexes, Ph[{-CR(3,6-tBu₂Flu)(Cp)}MCl₂]₂ (p-, R = Me (3a-Zr₂, 3a-Hf₂), R = H (3b-Zr₂); m-, R = Me (3c-Zr₂), were prepared by salt metathesis reactions. An attempt to generate in situ a heterodinuclear complex 3a-Zr-Hf was also undertaken. For the first time, Atmospheric Pressure PhotoIonization (APPI) mass-spectrometric data were obtained for all dinuclear compounds and found to be in excellent agreement with the simulated ones. Preliminary studies on the catalytic performances of these dinuclear complexes, upon activation with MAO, in ethylene homopolymerization and ethylene/1-hexene copolymerization revealed a few differences as compared to those of the monometallic analogues. In particular, slightly lower molecular weights and a greater formation of short methyl and ethyl branches were obtained with the dinuclear systems. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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12 pages, 11630 KiB

Open AccessArticle

Full-Spectrum Photocatalytic Activity of ZnO/CuO/ZnFe₂O₄ Nanocomposite as a PhotoFenton-Like Catalyst

by Zhenzhen Li, Huabin Chen and Wenxia Liu

Catalysts 2018, 8(11), 557; https://doi.org/10.3390/catal8110557 - 18 Nov 2018

Cited by 49 | Viewed by 7653

Abstract

Deriving photocatalysts by the calcination of hydrotalcite-like compounds has attracted growing interest for extending their photocatalytic activity to the visible and even near-infrared (NIR) light regions. Herein, we describe the acquisition of a ZnO/CuO/ZnFe₂O₄ nanocomposite with good photoFenton-like catalytic activity [...] Read more.

Deriving photocatalysts by the calcination of hydrotalcite-like compounds has attracted growing interest for extending their photocatalytic activity to the visible and even near-infrared (NIR) light regions. Herein, we describe the acquisition of a ZnO/CuO/ZnFe₂O₄ nanocomposite with good photoFenton-like catalytic activity under UV, visible and near-infrared (NIR) light irradiation by optimizing the calcination temperature of the coprecipitation product of Zn²⁺, Cu²⁺ and Fe³⁺. The ZnO/CuO/ZnFe₂O₄ nanocomposite is composed of symbiotic crystals of ZnO, CuO and ZnFe₂O₄, which enable the nanocomposite to show absorption in the UV, visible and NIR light regions and to produce a transient photocurrent in the presence of H₂O₂ under NIR irradiation. The full-spectrum photoFenton-like catalyst shows improved performance for the degradation of methyl orange with an increasing amount of H₂O₂ and is very stable in the recycling process. We believe that the ZnO/CuO/ZnFe₂O₄ nanocomposite is a promising full-spectrum photoFenton-like catalyst for the degradation of organic pollutants. Full article

(This article belongs to the Special Issue Nanostructured Materials for Photocatalysis)

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19 pages, 4517 KiB

Open AccessArticle

Experimental Evaluation of a Membrane Micro Channel Reactor for Liquid Phase Direct Synthesis of Hydrogen Peroxide in Continuous Flow Using Nafion^® Membranes for Safe Utilization of Undiluted Reactants

by Manuel Selinsek, Manfred Kraut and Roland Dittmeyer

Catalysts 2018, 8(11), 556; https://doi.org/10.3390/catal8110556 - 17 Nov 2018

Cited by 11 | Viewed by 5205

Abstract

In recent years, various modular micro channel reactors have been developed to overcome limitations in challenging chemical reactions. Direct synthesis of hydrogen peroxide from hydrogen and oxygen is a very interesting process in this regard. However, the complex triphasic process (gaseous reactants, reaction [...] Read more.

In recent years, various modular micro channel reactors have been developed to overcome limitations in challenging chemical reactions. Direct synthesis of hydrogen peroxide from hydrogen and oxygen is a very interesting process in this regard. However, the complex triphasic process (gaseous reactants, reaction in liquid solvent, solid catalyst) still holds challenges regarding safety, selectivity and productivity. The membrane micro reactor system for continuous liquid phase H₂O₂ direct synthesis was designed to reduce safety issues by separate dosing of the gaseous reactants via a membrane into a liquid-flow channel filled with a catalyst. Productivity is increased by enhanced mass transport, attainable in micro channels and by multiple re-saturation of the liquid with the reactants over the length of the reaction channel. Lastly, selectivity is optimized by controlling the reactant distribution. The influence of crucial technical features of the design, such as micro channel geometry, were studied experimentally in relationship with varying reaction conditions such as residence time, pressure, reactant ratio and solvent flow rate. Successful continuous operation of the reactor at pressures up to 50 bars showed the feasibility of this system. During the experiments, control over the reactant ratio was found to be crucial in order to maximize product yield. Thereby, yields above 80% were achieved. The results obtained are the key elements for future development and optimization of this reactor system, which will hopefully lead to a breakthrough in decentralized H₂O₂ production. Full article

(This article belongs to the Special Issue Direct Synthesis of Hydrogen Peroxide)

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25 pages, 4205 KiB

Open AccessReview

Catalyst-Doped Anodic TiO₂ Nanotubes: Binder-Free Electrodes for (Photo)Electrochemical Reactions

by Hyeonseok Yoo, Moonsu Kim, Yong-Tae Kim, Kiyoung Lee and Jinsub Choi

Catalysts 2018, 8(11), 555; https://doi.org/10.3390/catal8110555 - 17 Nov 2018

Cited by 36 | Viewed by 6974

Abstract

Nanotubes of the transition metal oxide, TiO₂, prepared by electrochemical anodization have been investigated and utilized in many fields because of their specific physical and chemical properties. However, the usage of bare anodic TiO₂ nanotubes in (photo)electrochemical reactions is limited [...] Read more.

Nanotubes of the transition metal oxide, TiO₂, prepared by electrochemical anodization have been investigated and utilized in many fields because of their specific physical and chemical properties. However, the usage of bare anodic TiO₂ nanotubes in (photo)electrochemical reactions is limited by their higher charge transfer resistance and higher bandgaps than those of semiconductor or metal catalysts. In this review, we describe several techniques for doping TiO₂ nanotubes with suitable catalysts or active materials to overcome the insulating properties of TiO₂ and enhance its charge transfer reaction, and we suggest anodization parameters for the formation of TiO₂ nanotubes. We then focus on the (photo)electrochemistry and photocatalysis-related applications of catalyst-doped anodic TiO₂ nanotubes grown on Ti foil, including water electrolysis, photocatalysis, and solar cells. We also discuss key examples of the effects of doping and the resulting improvements in the efficiency of doped TiO₂ electrodes for the desired (photo)electrochemical reactions. Full article

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16 pages, 4022 KiB

Open AccessArticle

Synthesis, Characterization of g-C₃N₄/SrTiO₃ Heterojunctions and Photocatalytic Activity for Organic Pollutants Degradation

by Panagiotis-Spyridon Konstas, Ioannis Konstantinou, Dimitrios Petrakis and Triantafyllos Albanis

Catalysts 2018, 8(11), 554; https://doi.org/10.3390/catal8110554 - 17 Nov 2018

Cited by 80 | Viewed by 8318

Abstract

Perovskite-structure SrTiO₃ (STO) and graphitic carbon nitride (g-C₃N₄, CN) have attracted considerable attention in photocatalytic technology due to their unique properties, but also suffer from some drawbacks. The development of composite photocatalysts that combine properties of the individual [...] Read more.

Perovskite-structure SrTiO₃ (STO) and graphitic carbon nitride (g-C₃N₄, CN) have attracted considerable attention in photocatalytic technology due to their unique properties, but also suffer from some drawbacks. The development of composite photocatalysts that combine properties of the individual semiconductors with enhanced charge separation is the current major trend in the photocatalysis field. In this study, SrTiO₃/g-C₃N₄ (CNSTO) composites with different ratios (10, 20, 30, 40 and 50% g-C₃N₄) were prepared with a sonication mixing method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ porosimetry, Fourrier transform infra-red spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS) and dynamic light scattering (DLS). STO spherical particles were successfully loaded on the g-C₃N₄ planes forming heterojunction composite materials. The photocatalytic activity was tested against the degradation of methylene blue (MB) dye under simulated solar light (SSL) irradiation following first-order kinetics. The photocatalytic activity followed the trend: 20CNSTO > 30CNSTO > 40CNSTO > 50CNSTO ≈ 10CNSTO, in accordance with the amount of ^•OH radicals determined by fluorescence spectroscopy. A Z-scheme mechanism was proposed for the enhanced photocatalytic degradation of MB as evidenced by trapping experiments with scavengers. Finally, significant stability and reusability was exhibited, indicating that such composites are of potential interest for photocatalytic treatments under sunlight irradiation. Full article

(This article belongs to the Special Issue Photocatalysis Science and Engineering in Europe)

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99 pages, 25940 KiB

Open AccessFeature PaperReview

Heterogeneous Photocatalysis and Prospects of TiO₂-Based Photocatalytic DeNOxing the Atmospheric Environment

by Nick Serpone

Catalysts 2018, 8(11), 553; https://doi.org/10.3390/catal8110553 - 16 Nov 2018

Cited by 56 | Viewed by 9020

Abstract

This article reviews the efforts of the last two decades to deNOxify the atmospheric environment with TiO₂-based photocatalytic materials supported on various cementitious-like substrates. Prior to undertaking this important aspect of applied photocatalysis with metal-oxide emiconductor photocatalysts, however, it is pertinent [...] Read more.

This article reviews the efforts of the last two decades to deNOxify the atmospheric environment with TiO₂-based photocatalytic materials supported on various cementitious-like substrates. Prior to undertaking this important aspect of applied photocatalysis with metal-oxide emiconductor photocatalysts, however, it is pertinent to describe and understand the fundamentals of Heterogeneous Photocatalysis. The many attempts done in a laboratory setting to degrade (deNOxify) the major components that make up the NO_x, namely nitric oxide (NO) and nitrogen dioxide (NO₂), but most importantly the efforts expended in deNOxifying the real environment upon depositing titania-based coatings on various model and authentic infrastructures, such as urban roads, highway noise barriers, tunnels, and building external walls among others, are examined. Both laboratory and outdoor experimentations have been performed toward NO_x being oxidized to form nitrates (NO₃⁻) that remain adsorbed on the TiO₂-based photocatalytic surfaces (except in tunnels—indoor walls) but get subsequently dislodged by rain or by periodic washings of the infrastructures. However, no serious considerations have been given to the possible conversion of NO_x via photocatalytic reduction back to N₂ and O₂ gases that would restore the atmospheric environment, as the adsorbed nitrates block the surface-active sites of the photocatalyst and when washed-off ultimately cause unduly damages to the environment. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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16 pages, 4510 KiB

Open AccessArticle

Pd/DNA as Highly Active and Recyclable Catalyst of Suzuki–Miyaura Coupling

by M. Mart, W. Tylus and A. M. Trzeciak

Catalysts 2018, 8(11), 552; https://doi.org/10.3390/catal8110552 - 16 Nov 2018

Cited by 17 | Viewed by 4463

Abstract

Pd/DNA catalysts were prepared in a mixed H₂O/EtOH solvent using palladium precursors, Pd(OAc)₂ and PdCl₂, in different dosages and salmon fish sperm DNA. As prepared, the Pd/DNA contained Pd(II) and Pd(0) nanoparticles of various sizes and morphologies, depending [...] Read more.

Pd/DNA catalysts were prepared in a mixed H₂O/EtOH solvent using palladium precursors, Pd(OAc)₂ and PdCl₂, in different dosages and salmon fish sperm DNA. As prepared, the Pd/DNA contained Pd(II) and Pd(0) nanoparticles of various sizes and morphologies, depending on the preparation method. Pd/DNA efficiently catalyzed the Suzuki–Miyaura cross-coupling of various aryl bromides with phenylboronic acids. The catalyst was recovered by simple phase separation and then reused in seven consecutive cycles with a high activity. Full article

(This article belongs to the Special Issue Catalysts for Suzuki–Miyaura Coupling Reaction)

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29 pages, 6308 KiB

Open AccessFeature PaperReview

Layered Ternary and Quaternary Transition Metal Chalcogenide Based Catalysts for Water Splitting

by Anand P. Tiwari, Travis G. Novak, Xiuming Bu, Johnny C. Ho and Seokwoo Jeon

Catalysts 2018, 8(11), 551; https://doi.org/10.3390/catal8110551 - 16 Nov 2018

Cited by 51 | Viewed by 9149

Abstract

Water splitting plays an important role in the electrochemical and photoelectrochemical conversion of energy devices. Electrochemical water splitting by the hydrogen evolution reaction (HER) is a straightforward route to producing hydrogen (H₂), which requires an efficient electrocatalyst to minimize energy consumption. [...] Read more.

Water splitting plays an important role in the electrochemical and photoelectrochemical conversion of energy devices. Electrochemical water splitting by the hydrogen evolution reaction (HER) is a straightforward route to producing hydrogen (H₂), which requires an efficient electrocatalyst to minimize energy consumption. Recent advances have created a rapid rise in new electrocatalysts, particularly those based on non-precious metals. In this review, we present a comprehensive overview of the recent developments of ternary and quaternary 6d-group transition metal chalcogenides (TMCs) based electrocatalysts for water splitting, especially for HER. Detailed discussion is organized from binary to quaternary TMCs including, surface engineering, heterostructures, chalcogen substitutions and hierarchically structural design in TMCs. Moreover, emphasis is placed on future research scope and important challenges facing these electrocatalysts for further development in their performance towards water splitting. Full article

(This article belongs to the Section Electrocatalysis)

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20 pages, 3393 KiB

Open AccessReview

RNA-Cleaving DNAzymes: Old Catalysts with New Tricks for Intracellular and In Vivo Applications

by JingJing Zhang

Catalysts 2018, 8(11), 550; https://doi.org/10.3390/catal8110550 - 16 Nov 2018

Cited by 41 | Viewed by 9999

Abstract

DNAzymes are catalytically active DNA molecules that are normally isolated through in vitro selection methods, among which RNA-cleaving DNAzymes that catalyze the cleavage of a single RNA linkage embedded within a DNA strand are the most studied group of this DNA enzyme family. [...] Read more.

DNAzymes are catalytically active DNA molecules that are normally isolated through in vitro selection methods, among which RNA-cleaving DNAzymes that catalyze the cleavage of a single RNA linkage embedded within a DNA strand are the most studied group of this DNA enzyme family. Recent advances in DNA nanotechnology and engineering have generated many RNA-cleaving DNAzymes with unique recognition and catalytic properties. Over the past decade, numerous RNA-cleaving, DNAzymes-based functional probes have been introduced into many research areas, such as in vitro diagnostics, intracellular imaging, and in vivo therapeutics. This review focus on the fundamental insight into RNA-Cleaving DNAzymes and technical tricks for their intracellular and in vivo applications, highlighting the recent progress in the clinical trial of RNA-Cleaving DNAzymes with selected examples. The challenges and opportunities for the future translation of RNA-cleaving DNAzymes for biomedicine are also discussed. Full article

(This article belongs to the Section Biocatalysis)

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16 pages, 8790 KiB

Open AccessReview

N-Heterocyclic Carbene Catalysis under Oxidizing Conditions

by Krzysztof Dzieszkowski and Zbigniew Rafiński

Catalysts 2018, 8(11), 549; https://doi.org/10.3390/catal8110549 - 16 Nov 2018

Cited by 27 | Viewed by 6911

Abstract

N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis [...] Read more.

N-heterocyclic carbene organocatalysis under oxidizing conditions provides a vast range of various synthetic procedures via diverse mechanisms. The available catalysts, bases, oxidants, and oxidizing methods afford numerous opportunities for developing this branch of organocatalysis. Furthermore, implementation of tandem reactions and cooperative catalysis in the described methodology significantly expands the possibilities of modern organic chemistry. This approach allows the synthesis of different structurally complex and often enantiomerically enriched substances, which can be interesting in terms of biological activity and natural product synthesis. Many esters, amides, thioesters, lactams, lactones, and other cyclic compounds obtained in oxidative or oxygenative reactions promoted by N-heterocyclic carbenes can be interesting precursors in advanced organic synthesis. Sophistication and broad applicability prove that the described synthetic approaches are exceptionally worthy of further development. Full article

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12 pages, 3712 KiB

Open AccessArticle

Highly Efficient Synthesis of 2,5-Dihydroxypyridine using Pseudomonas sp. ZZ-5 Nicotine Hydroxylase Immobilized on Immobead 150

by Caiwen Dong, Yadong Zheng, Hongzhi Tang, Zhangde Long, Jigang Li, Zhiping Zhang, Sumeng Liu, Duobin Mao and Tao Wei

Catalysts 2018, 8(11), 548; https://doi.org/10.3390/catal8110548 - 16 Nov 2018

Cited by 2 | Viewed by 3156

Abstract

In this report, the use of immobilized nicotine hydroxylase from Pseudomonas sp. ZZ-5 (HSPH_ZZ) for the production of 2,5-dihydroxypyridine (2,5-DHP) from 6-hydroxy-3-succinoylpyridine (HSP) in the presence of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) is described. HSPH_ZZ was [...] Read more.

In this report, the use of immobilized nicotine hydroxylase from Pseudomonas sp. ZZ-5 (HSPH_ZZ) for the production of 2,5-dihydroxypyridine (2,5-DHP) from 6-hydroxy-3-succinoylpyridine (HSP) in the presence of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) is described. HSPH_ZZ was covalently immobilized on Immobead 150 (ImmHSPH_ZZ). ImmHSPH_ZZ (obtained with 5–30 mg of protein per gram of support) catalyzed the hydrolysis of HSP to 2,5-DHP. At a protein loading of 15 mg g⁻¹, ImmHSPH_ZZ converted 93.6% of HSP to 2,5-DHP in 6 h. The activity of ImmHSPH_ZZ was compared with that of free HSPH_ZZ under various conditions, including pH, temperature, enzyme concentration, substrate concentration and stability over time, and kinetic parameters were measured. The results showed that ImmHSPH_ZZ performed better over wider ranges of pH and temperature when compared with that of HSPH_ZZ. The optimal concentrations of ImmHSPH_ZZ and substrate were 30 mg L⁻¹ and 0.75 mM, respectively. Under optimal conditions, 94.5 mg L⁻¹ of 2,5-DHP was produced after 30 min with 85.4% conversion. After 8 reaction cycles and 6 days of storage, 51.3% and 75.0% of the initial enzyme activity remained, respectively. The results provide a framework for development of commercially suitable immobilized enzymes that produce 2,5-DHP. Full article

(This article belongs to the Special Issue Biocatalysts: Design and Application)

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13 pages, 4181 KiB

Open AccessArticle

The Heterogeneous Aminohydroxylation Reaction Using Hydrotalcite-Like Catalysts Containing Osmium

by Mohamed I. Fadlalla, Glenn E. M. Maguire and Holger B. Friedrich

Catalysts 2018, 8(11), 547; https://doi.org/10.3390/catal8110547 - 16 Nov 2018

Cited by 1 | Viewed by 3121

Abstract

The aminohydroxylation reaction of olefins is a key organic transformation reaction, typically carried out homogeneously with toxic and expensive osmium (Os) catalysts. Therefore, heterogenisation of this reaction can unlock its industrial potential by allowing reusability of the catalyst. Os–Zn–Al hydrotalcite-like compounds (HTlcs), as [...] Read more.

The aminohydroxylation reaction of olefins is a key organic transformation reaction, typically carried out homogeneously with toxic and expensive osmium (Os) catalysts. Therefore, heterogenisation of this reaction can unlock its industrial potential by allowing reusability of the catalyst. Os–Zn–Al hydrotalcite-like compounds (HTlcs), as potential heterogeneous aminohydroxylation catalysts, were synthesised by the co-precipitation method and characterised by several techniques. Reaction parameters (i.e., solvent system, reaction temperature, and catalyst structure) were optimized with cyclohexene, styrene, and hexene as substrates. The different classes of olefins (aliphatic, aromatic, and functionalised) that were tested gave >99% conversion and high selectivity (>97%) to the corresponding β-amino alcohol. The catalyst HTlc structure had a significant effect on the reaction time and yield of the β-amino alcohols. Under the same testing conditions, a heat treated catalyst (non-HTlc) showed a shorter reaction time, but drop in the yield of β-amino alcohols and rise in diol formation was observed. Leaching tests showed that 2.9% and 3.4% of Os (inactive) leached from the catalyst to the reaction solution when MeCN/water (1:1 v/v) and t-BuOH/water (1:1 v/v), respectively, were used as the solvent system. Recycling studies showed that the catalyst can be reused at least thrice, with no significant difference in the yield of the β-amino-alcohol. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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10 pages, 3110 KiB

Open AccessArticle

HKUST-1 Supported on Zirconium Phosphate as an Efficient Catalyst for Solvent Free Oxidation of Cyclohexene: DFT Study

by Razia Aman, Abraham Clearfield, Mohammad Sadiq and Zahid Ali

Catalysts 2018, 8(11), 546; https://doi.org/10.3390/catal8110546 - 15 Nov 2018

Cited by 4 | Viewed by 4551

Abstract

Layer by layer metal-organic framework (MOF) supported on zirconium phosphate (ZrP) was synthesized at very mild conditions and used for the liquid phase oxidation of cyclohexene in solvent free condition in the presence of molecular oxygen. The MOF-ZrP was characterized by X-ray diffractometer [...] Read more.

Layer by layer metal-organic framework (MOF) supported on zirconium phosphate (ZrP) was synthesized at very mild conditions and used for the liquid phase oxidation of cyclohexene in solvent free condition in the presence of molecular oxygen. The MOF-ZrP was characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), thermal gravimetric analyzer (TGA), Fourier-transform infrared spectrometer (FT-IR) and Brunauer-Emmett-Teller (BET) surface area analyzer. The characterization shows a smooth morphology of MOF-ZrP with good stability under 200 °C having surface area 285 m²/g. The catalytic activity of the MOF-ZrP revealed that increase of layers of MOF on ZrP enhances conversion, as well as selectivity of oxidation of cyclohexene. DFT studies were used to explore the structure and electron properties of HKUST-1 (Hong Kong University of Science and Technology), which is a clue for the catalytic behavior of the catalyst. Full article

(This article belongs to the Special Issue Catalysis by Metal-Organic Frameworks)

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10 pages, 722 KiB

Open AccessArticle

Copper-Modified Zeolites and Silica for Conversion of Methane to Methanol

by Xueting Wang, Natalia M. Martin, Johan Nilsson, Stefan Carlson, Johan Gustafson, Magnus Skoglundh and Per-Anders Carlsson

Catalysts 2018, 8(11), 545; https://doi.org/10.3390/catal8110545 - 15 Nov 2018

Cited by 26 | Viewed by 6445

Abstract

Powder materials containing copper ions supported on ZSM-5 (Cu-Zeolite Socony Mobil-5) and SSZ-13 (Cu-Standard Oil synthesised zeolite-13), and predominantly CuO nanoparticles on amorphous SiO

_{2}

were synthesised, characterised, wash-coated onto ceramic monoliths and, for the first time, compared as catalysts for direct conversion [...] Read more.

Powder materials containing copper ions supported on ZSM-5 (Cu-Zeolite Socony Mobil-5) and SSZ-13 (Cu-Standard Oil synthesised zeolite-13), and predominantly CuO nanoparticles on amorphous SiO

_{2}

were synthesised, characterised, wash-coated onto ceramic monoliths and, for the first time, compared as catalysts for direct conversion of methane to methanol (DCMM) at ambient pressure (1 atm) using O

_{2}

, N

_{2}

O and NO as oxidants. Methanol production was monitored and quantified using Fourier transform infrared spectroscopy. Methanol is formed over all monolith samples, though the formation is considerably higher for the copper-exchanged zeolites. Hence, copper ions are the main active sites for DCMM. The minor amount of methanol produced over the Cu/SiO

_{2}

sample, however, suggests that zeolites are not the sole substrate that can host those active copper sites but also silica. Further, we present the first ambient pressure in situ infrared spectroscopic measurements revealing the formation and consumption of surface methoxy species, which are considered to be key intermediates in the DCMM reaction. Full article

(This article belongs to the Section Environmental Catalysis)

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20 pages, 5547 KiB

Open AccessArticle

Steam Reforming of Methanol over Nanostructured Pt/TiO₂ and Pt/CeO₂ Catalysts for Fuel Cell Applications

by Joan Papavasiliou, Alexandra Paxinou, Grzegorz Słowik, Stylianos Neophytides and George Avgouropoulos

Catalysts 2018, 8(11), 544; https://doi.org/10.3390/catal8110544 - 15 Nov 2018

Cited by 30 | Viewed by 5343

Abstract

A research and technological challenge for fuel processors integrated with High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFCs), also known as Internal Reforming Methanol Fuel Cells (IRMFCs), operating at 200–220 °C, is the development of highly efficient catalysts, which will be able to [...] Read more.

A research and technological challenge for fuel processors integrated with High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFCs), also known as Internal Reforming Methanol Fuel Cells (IRMFCs), operating at 200–220 °C, is the development of highly efficient catalysts, which will be able to selectively (low CO and other by-products formation) produce the required quantity of hydrogen at these temperatures. In this work, various amounts of platinum were dispersed via deposition-precipitation (DP) and impregnation (I) methods onto the surface of hydrothermally prepared ceria nanorods (CNRs) and titania nanotubes (TNTs). These nanostructured catalysts were evaluated in steam reforming of methanol process targeting the operation level of IRMFCs. The (DP) method resulted in highly (atomically) dispersed platinum-based catalysts, as confirmed with Scanning Transmission Electron Microscopy (STEM) analysis, with a mean particle size of less than 1 nm in the case of 0.35 wt.% Pt/CNRs catalyst. Ultra-fine dispersion of platinum species correlated with the presence of oxygen vacancies, together with the enrichment of CNRs surface with active metallic phase resulted in a highly active catalyst achieving at 220 °C a hydrogen production rate of 5500 cm³ min⁻¹ per g of loaded platinum. Full article

(This article belongs to the Special Issue Catalysis in Steam Reforming)

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3 pages, 169 KiB

Open AccessEditorial

Homogeneous Catalysis and Mechanisms in Water and Biphasic Media

by Luca Gonsalvi

Catalysts 2018, 8(11), 543; https://doi.org/10.3390/catal8110543 - 14 Nov 2018

Cited by 5 | Viewed by 2689

Abstract

After its discovery in the early 1980s and successful application on an industrial scale (Ruhrchemie/Rhone-Poulenc process) [...] Full article

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

15 pages, 3061 KiB

Open AccessFeature PaperArticle

Mechanistic Study on Facet-Dependent Deposition of Metal Nanoparticles on Decahedral-Shaped Anatase Titania Photocatalyst Particles

by Kenta Kobayashi, Mai Takashima, Mai Takase and Bunsho Ohtani

Catalysts 2018, 8(11), 542; https://doi.org/10.3390/catal8110542 - 13 Nov 2018

Cited by 11 | Viewed by 4458

Abstract

Facet-selective gold or platinum-nanoparticle deposition on decahedral-shaped anatase titania particles (DAPs) exposing {001} and {101} facets via photodeposition (PD) from metal-complex sources was reexamined using DAPs prepared with gas-phase reaction of titanium (IV) chloride and oxygen by quantitatively evaluating the area deposition density [...] Read more.

Facet-selective gold or platinum-nanoparticle deposition on decahedral-shaped anatase titania particles (DAPs) exposing {001} and {101} facets via photodeposition (PD) from metal-complex sources was reexamined using DAPs prepared with gas-phase reaction of titanium (IV) chloride and oxygen by quantitatively evaluating the area deposition density on {001} and {101} and comparing with the results of deposition from colloidal metal particles in the dark (CDD) or under photoirradiation (CDL). The observed facet selectivity, more or less {101} preferable, depended mainly on pH of the reaction suspensions and was almost non-selective at low pH regardless of the deposition method, PD or CDL, and the metal-source materials. Based on the results, the present authors propose that facet selectivity is attributable to surface charges (zeta potential) depending on the kind of facets, {001} and {101}, and pH of the reaction mixture and that this concept can explain the observed facet selectivity and possibly the reported facet selectivity without taking into account facet-selective reaction of photoexcited electrons and positive holes on {101} and {001} facets, respectively. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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16 pages, 3001 KiB

Open AccessArticle

Influence of Sulfur-Containing Sodium Salt Poisoned V₂O₅–WO₃/TiO₂ Catalysts on SO₂–SO₃ Conversion and NO Removal

by Haiping Xiao, Chaozong Dou, Hao Shi, Jinlin Ge and Li Cai

Catalysts 2018, 8(11), 541; https://doi.org/10.3390/catal8110541 - 13 Nov 2018

Cited by 12 | Viewed by 4736

Abstract

A series of poisoned catalysts with various forms and contents of sodium salts (Na₂SO₄ and Na₂S₂O₇) were prepared using the wet impregnation method. The influence of sodium salts poisoned catalysts on SO₂ oxidation [...] Read more.

A series of poisoned catalysts with various forms and contents of sodium salts (Na₂SO₄ and Na₂S₂O₇) were prepared using the wet impregnation method. The influence of sodium salts poisoned catalysts on SO₂ oxidation and NO reduction was investigated. The chemical and physical features of the catalysts were characterized via NH₃-temperature programmed desorption (NH₃-TPD), H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR). The results showed that sodium salts poisoned catalysts led to a decrease in the denitration efficiency. The 3.6% Na₂SO₄ poisoned catalyst was the most severely deactivated with denitration efficiency of only 50.97% at 350 °C. The introduction of SO₄²⁻ and S₂O₇²⁻ created new Brønsted acid sites, which facilitated the adsorption of NH₃ and NO reduction. The sodium salts poisoned catalysts significantly increased the conversion of SO₂–SO₃. 3.6%Na₂S₂O₇ poisoned catalyst had the strongest effect on SO₂ oxidation and the catalyst achieved a maximum SO₂–SO₃-conversion of 1.44% at 410 °C. Characterization results showed sodium salts poisoned catalysts consumed the active ingredient and lowered the V⁴⁺/V⁵⁺ ratio, which suppressed catalytic performance. However, they increased the content of chemically adsorbed oxygen and the strength of V⁵⁺=O bonds, which promoted SO₂ oxidation. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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13 pages, 2722 KiB

Open AccessArticle

Elucidation and Characterization of New Chlorinated By-Products after Electrochemical Degradation of Hydrochlorothiazide Using Graphite–Poly Vinyl Chloride Electrode

by Zainab Haider Mussa, Fouad Fadhil Al-Qaim, Ali Yuzir, Hirofumi Hara, Shamila Azman and Shreeshivadasan Chelliapan

Catalysts 2018, 8(11), 540; https://doi.org/10.3390/catal8110540 - 13 Nov 2018

Cited by 8 | Viewed by 2601

Abstract

This paper describes an electrochemical treatment process of hydrochlorothiazide (HDZ) under different conditions such as initial concentration, sodium chloride and applied voltage. In this present study, HDZ was treated by electrochemical oxidation process using graphite-PVC composite electrode as anode and Platinum (Pt) as [...] Read more.

This paper describes an electrochemical treatment process of hydrochlorothiazide (HDZ) under different conditions such as initial concentration, sodium chloride and applied voltage. In this present study, HDZ was treated by electrochemical oxidation process using graphite-PVC composite electrode as anode and Platinum (Pt) as cathode. All results were analyzed using liquid chromatography-time of flight/mass spectrometry (LC-TOF/MS). It was found that at high applied voltages, and high amounts of NaCl, the electrochemical treatment process was more efficient. The removal% of HDZ was 92% at 5 V after 60 min. From the obtained results, the electrochemical oxidation process of HDZ followed pseudo first order with rate constant values ranged between 0.0009 and 0.0502 min⁻¹, depending on the experimental conditions. Energy consumption was also considered in this study, it was ranged between 0.9058 and 5.56 Wh/mg using 0.5, 0.3 and 0.1 g NaCl within interval times of (10, 20, 30, 40, 50, 60, 70, and 80 min). Five chlorinated and one non-chlorinated by-products were formed and analyzed in negative ionization (NI) mode during the electrochemical process. Due to the strong oxidizing potential of the chlorine (Cl₂) and hypochlorite ion (ClO⁻), HDZ and its by-products were removed after 140 min. Furthermore, a novel synthesis of chlorothiaizde as one of the new by-products was reported in this present study. Toxicity was impacted by the formation of the by-products, especially at 20 min. The inhibition percentage (I%) of E. coli bacteria was decreased to be the lowest value after 140 min. Full article

(This article belongs to the Section Electrocatalysis)

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12 pages, 3589 KiB

Open AccessArticle

MPV Reduction of Furfural to Furfuryl Alcohol on Mg, Zr, Ti, Zr–Ti, and Mg–Ti Solids: Influence of Acid–Base Properties

by Jesús Hidalgo-Carrillo, Almudena Parejas, Manuel Jorge Cuesta-Rioboo, Alberto Marinas and Francisco José Urbano

Catalysts 2018, 8(11), 539; https://doi.org/10.3390/catal8110539 - 13 Nov 2018

Cited by 18 | Viewed by 4788

Abstract

The Meerwein–Ponndorf–Verley (MPV) reaction is an environmentally-friendly process consisting of the reduction of a carbonyl compound through hydrogen transfer from a secondary alcohol. This work deals with MPV reduction of furfural to furfuryl alcohol on different ZrO_x, MgO_x, TiO [...] Read more.

The Meerwein–Ponndorf–Verley (MPV) reaction is an environmentally-friendly process consisting of the reduction of a carbonyl compound through hydrogen transfer from a secondary alcohol. This work deals with MPV reduction of furfural to furfuryl alcohol on different ZrO_x, MgO_x, TiO_x, and Mg–Ti, as well as Zr–Ti mixed systems. The solids were synthesized through the sol–gel process and subsequently calcined at 200 °C. Characterization was performed using a wide range of techniques: ICP-MS, N₂ adsorption-desorption isotherms, EDX, TGA-DTA, XRD, XPS, TEM, TPD of pre-adsorbed pyridine (acidity) and CO₂ (basicity), DRIFT of adsorbed pyridine, and methylbutynol (MBOH) test reaction. ZrO_x showed the highest conversion and selectivity values, which was attributed to the existence of acid–base pair sites (as evidenced by the MBOH test reaction), whereas the introduction of titanium resulted in the drop of both conversion and selectivity probably due to the increase in Brönsted-type acidity. As for MgO_x, it had a predominantly basic character that led to the production of the condensation product of one molecule of furfural and one molecule of acetone, and thus resulted in a lower selectivity to furfuryl alcohol. The TiO_x solid was found to be mainly acidic and exhibited both Lewis and Brönsted acid sites. The presence of the latter could account for the lower selectivity to furfuryl alcohol. All in all, these results seemed to suggest that the MPV reaction is favored on Lewis acid sites and especially on acid–base pair sites. The process was accelerated under microwave irradiation. Full article

(This article belongs to the Special Issue Catalytic Transformation of Renewables (Olefin, Bio-sourced, et. al))

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