Catalysts

13 pages, 1211 KiB

Open AccessArticle

Efficient Biocatalytic Preparation of Optically Pure (R)-1-[4-(Trifluoromethyl)phenyl]ethanol by Recombinant Whole-Cell-Mediated Reduction

by Ying Chen, Nana Xia, Yuewang Liu and Pu Wang

Catalysts 2019, 9(4), 391; https://doi.org/10.3390/catal9040391 - 25 Apr 2019

Cited by 6 | Viewed by 3539

Abstract

(R)-1-[4-(Trifluoromethyl)phenyl]ethanol is an important pharmaceutical intermediate of a chemokine CCR5 antagonist. In the present study, a bioprocess for the asymmetric reduction of 4-(trifluoromethyl)acetophenone to (R)-1-[4-(trifluoromethyl)phenyl]ethanol was developed by recombinant Escherichia coli cells with excellent enantioselectivity. In order to overcome [...] Read more.

(R)-1-[4-(Trifluoromethyl)phenyl]ethanol is an important pharmaceutical intermediate of a chemokine CCR5 antagonist. In the present study, a bioprocess for the asymmetric reduction of 4-(trifluoromethyl)acetophenone to (R)-1-[4-(trifluoromethyl)phenyl]ethanol was developed by recombinant Escherichia coli cells with excellent enantioselectivity. In order to overcome the conversion limitation performed in the conventional buffer medium resulting from poor solubility of non-natural substrate, we subsequently established a polar organic solvent-aqueous medium to improve the efficacy. Isopropanol was selected as the most suitable cosolvent candidate, based on the investigation on a substrate solubility test and cell membrane permeability assay in different organic solvent-buffer media. Under the optimum conditions, the preparative-scale asymmetric reduction generated a 99.1% yield with >99.9% product enantiomeric excess (ee) in a 15% (v/v) isopropanol proportion, at 100 mM of 4-(trifluoromethyl)acetophenone within 3 h. Compared to bioconversion in the buffer medium, the developed isopropanol-aqueous system enhanced the substrate concentration by 2-fold with a remarkably improved yield (from 62.5% to 99.1%), and shortened the reaction time by 21 h. Our study gave the first example for a highly enantioselective production of (R)-1-[4-(trifluoromethyl)phenyl]ethanol by a biological method, and the bioreduction of 4-(trifluoromethyl)acetophenone in a polar organic solvent-aqueous system was more efficient than that in the buffer solution only. This process is also scalable and has potential in application. Full article

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

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13 pages, 2377 KiB

Open AccessArticle

Hierarchically-Structured TiO₂/MnO₂ Hollow Spheres Exhibiting the Complete Mineralization of Phenol

by Caiguo Jiang, Yi Ge, Wenjing Chen, Li Hua, Huiquan Li, Ying Zhang and Shunsheng Cao

Catalysts 2019, 9(4), 390; https://doi.org/10.3390/catal9040390 - 25 Apr 2019

Cited by 5 | Viewed by 4243

Abstract

Although TiO₂ or MnO₂-based materials have been widely used for the degradation of phenolic compounds, complete mineralization is still a challenge, especially for TiO₂-based materials. Here, we devise a hierarchically-structured TiO₂/MnO₂ (HTM) hollow sphere, in [...] Read more.

Although TiO₂ or MnO₂-based materials have been widely used for the degradation of phenolic compounds, complete mineralization is still a challenge, especially for TiO₂-based materials. Here, we devise a hierarchically-structured TiO₂/MnO₂ (HTM) hollow sphere, in which hollow TiO₂ acts as a skeleton for the deposition of MnO₂ in order to prevent the aggregation of MnO₂ nanoparticles and to maintain its hollow structure. During the oxidation reaction, the as-synthesized HTM can fully exert their respective advantages of the TiO₂ and MnO₂ species to realize the first stage of the rapid oxidation degradation of phenol and the second stage of the complete photo-mineralization of residual phenol and its intermediates, which efficiently overcomes the incomplete mineralization of phenolic compounds. The degradation mechanism and pathway of phenol are also proposed according to the analysis of Mass Spectrometry (MS). Therefore, this work provides a new insight for exploring hierarchically-structured materials with two or more species. Full article

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

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11 pages, 1970 KiB

Open AccessArticle

Solar-Driven Removal of 1,4-Dioxane Using WO₃/nγ-Al₂O₃ Nano-catalyst in Water

by Xiyan Xu, Shuming Liu, Yong Cui, Xiaoting Wang, Kate Smith and Yujue Wang

Catalysts 2019, 9(4), 389; https://doi.org/10.3390/catal9040389 - 25 Apr 2019

Cited by 16 | Viewed by 4566

Abstract

Increasing demand for fresh water in extreme drought regions necessitates potable water reuse. However, current membrane-based water reclamation approaches cannot effectively remove carcinogenic 1,4-dioxane. The current study reports on the solar-driven removal of 1,4-dioxane (50 mg L⁻¹) using a homemade WO [...] Read more.

Increasing demand for fresh water in extreme drought regions necessitates potable water reuse. However, current membrane-based water reclamation approaches cannot effectively remove carcinogenic 1,4-dioxane. The current study reports on the solar-driven removal of 1,4-dioxane (50 mg L⁻¹) using a homemade WO₃/nγ-Al₂O₃ nano-catalyst. Characterization methods including scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) analyses are used to investigate the surface features of the catalyst. The 1,4-dioxane mineralization performance of this catalyst under various reaction conditions is studied. The effect of the catalyst dosage is tested. The mean oxidation state carbon (MOSC) values of the 1,4-dioxane solution are followed during the reaction. The short chain organic acids after treatment are measured. The results showed that over 75% total organic carbon (TOC) removal was achieved in the presence of 300 mg L⁻¹ of the catalyst with a simulated solar irradiation intensity of 40 mW cm⁻². Increasing the dose of the catalyst from 100 to 700 mg L⁻¹ can improve the treatment efficiency to some extent. The TOC reduction curve fits well with an apparent zero-order kinetic model and the corresponding constant rates are within 0.0927 and 0.1059 mg L⁻¹ s⁻¹, respectively. The MOSC values of the 1,4-dioxane solution increase from 1.3 to 3 along the reaction, which is associated with the formation of some short chain acids. The catalyst can be effectively reused 7 times. This work provides an oxidant-free and energy saving approach to achieve efficient removal of 1,4-dioxane and thus shows promising potential for potable reuse applications. Full article

(This article belongs to the Special Issue Trends in Catalytic Wet Peroxide Oxidation Processes)

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16 pages, 3032 KiB

Open AccessArticle

Synthesis of the First Resorcin[4]arene-Functionalized Triazolium Salts and Their Use in Suzuki–Miyaura Cross-Coupling Reactions

by David Sémeril, Dominique Matt and Rengan Ramesh

Catalysts 2019, 9(4), 388; https://doi.org/10.3390/catal9040388 - 25 Apr 2019

Cited by 3 | Viewed by 3895

Abstract

Two bulky triazolium salts, namely 1-{4(24),6(10),12(16),18(22)-tetramethylenedioxy- 2,8,14,20-tetrapentylresorcin[4]arene-5-yl}-4-phenyl-3-methyl-1H-1,2,3-triazolium tetrafluoro borate (1) and 1,4-bis{4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentyl resorcin[4]arene-5-yl}-3-methyl-1H-1,2,3-triazolium iodide (2), have been synthesized and assessed in the palladium-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides, with aryl boronic acids. As a general [...] Read more.

Two bulky triazolium salts, namely 1-{4(24),6(10),12(16),18(22)-tetramethylenedioxy- 2,8,14,20-tetrapentylresorcin[4]arene-5-yl}-4-phenyl-3-methyl-1H-1,2,3-triazolium tetrafluoro borate (1) and 1,4-bis{4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentyl resorcin[4]arene-5-yl}-3-methyl-1H-1,2,3-triazolium iodide (2), have been synthesized and assessed in the palladium-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides, with aryl boronic acids. As a general trend, the reaction rates obtained with 1 were significantly higher (up to 5 times) than those observed for 2, this mainly reflected a sterically more accessible metal center in the catalytic intermediates formed with 1. The presence of flexible pentyl chains in these intermediates, which might sterically interact with the metal center, when the latter adopts an exo-orientation with respect to the cavity, were likely responsible for the observed good performance. Full article

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

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18 pages, 9636 KiB

Open AccessArticle

Electrocatalytic Oxidation of Small Molecule Alcohols over Pt, Pd, and Au Catalysts: The Effect of Alcohol’s Hydrogen Bond Donation Ability and Molecular Structure Properties

by Bei Wang, Liu Tao, Yu Cheng, Fang Yang, Yuguang Jin, Chunmei Zhou, Hao Yu and Yanhui Yang

Catalysts 2019, 9(4), 387; https://doi.org/10.3390/catal9040387 - 25 Apr 2019

Cited by 43 | Viewed by 5640

Abstract

The direct alcohol fuel cell is a kind of power generation device that directly converts the chemical energy of small molecule alcohols into electric energy. In this paper, the electro-oxidation behaviors of some typical alcohols (methanol, ethanol, ethylene glycol, n-propanol, 2-propanol, and glycerol) [...] Read more.

The direct alcohol fuel cell is a kind of power generation device that directly converts the chemical energy of small molecule alcohols into electric energy. In this paper, the electro-oxidation behaviors of some typical alcohols (methanol, ethanol, ethylene glycol, n-propanol, 2-propanol, and glycerol) over Pt, Pd, and Au electrodes were investigated in acidic, neutral, and alkaline media, respectively. By analyzing the activity information from a cyclic voltammetry (CV) method and some dynamic tests, several regularities were revealed in those electro-oxidation behaviors. Firstly, alkaline media is the best for the electro-oxidation of all these alcohols over Pt, Pd, and Au catalysts. Secondly, the hydrogen bond donation abilities (HBD) of different alcohols were found have a great relationship with the catalytic performance. In alkaline media, on Pt electrodes, the solute HBD is positively correlated with the ease of electrooxidation within the scope of this experiment. Contrarily, it is negatively correlated on Pd and Au electrodes. Additionally, for Pt catalysts in acidic and neutral media, the relationship becomes negative again as the HBD increases. Finally, the alcohol’s molecular structure properties were found to have a remarkably influence on the activity of different catalysts. Over the Pt electrode in alkaline media, the activation energy of methanol oxidation is 44.1 KJ/mol, and is obviously lower than the oxidation of other alcohols. Under similar conditions, the lowest activation energy was measured in the oxidation of n-propanol (14.4 KJ/mol) over the Pd electrode, and in the oxidation of glycerol (42.2 KJ/mol) over the Au electrode. Totally, among all these electrodes, Pt electrodes showed the best activities on the oxidation of C1 alcohol, Pd electrodes were more active on the oxidation of C2-3 monobasic alcohols, and Au electrodes were more active on the oxidation of polybasic alcohols. Full article

(This article belongs to the Special Issue Catalysis for Electro-oxidation of Ethanol & Methanol)

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10 pages, 2653 KiB

Open AccessArticle

Point-Defect-Rich Carbon Sheets as the High-Activity Catalyst Toward Oxygen Reduction and Hydrogen Evolution

by Wenjing Yuan, Fuhua Zhang, Yaoyao Wu, Xiaotao Chen, Chihhsiang Fang and Chuanhao Li

Catalysts 2019, 9(4), 386; https://doi.org/10.3390/catal9040386 - 25 Apr 2019

Cited by 9 | Viewed by 3538

Abstract

Exploring a novel approach for the synthesis of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysts with inexpensive and high-activity is desirable. Herein, we report a bubble templating method to synthesize the graphene-like mesoporous carbon sheets with point defects as ORR/HER [...] Read more.

Exploring a novel approach for the synthesis of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysts with inexpensive and high-activity is desirable. Herein, we report a bubble templating method to synthesize the graphene-like mesoporous carbon sheets with point defects as ORR/HER bifunctional electrocatalysts. The typical product shows excellent ORR performance including the positive onset potential (740 mV) and high diffusion-limiting current density (4.07 mA cm⁻²). Along with small Tafel slopes, the overpotential is determined to be about −453 and −378 mV at 10 mA cm⁻² in both alkaline and acidic media, which suggests a good candidate for HER reaction as well. The superior catalytic activities are derived from the abundant point defects on the mesoporous carbon sheets surface, especially the existence of pyridinic and pyrrolic nitrogen species. This study may be an alternative route to prepare the novel functional materials for the applications of ORR and HER. Full article

(This article belongs to the Special Issue Electro-Catalysts for Energy Conversion and Storage Devices)

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14 pages, 3796 KiB

Open AccessCommunication

Ultra-Small Pd Nanoparticles on Ceria as an Advanced Catalyst for CO Oxidation

by Andrei Tereshchenko, Vladimir Polyakov, Alexander Guda, Tatiana Lastovina, Yulia Pimonova, Alexey Bulgakov, Andrey Tarasov, Leonid Kustov, Vera Butova, Alexander Trigub and Alexander Soldatov

Catalysts 2019, 9(4), 385; https://doi.org/10.3390/catal9040385 - 24 Apr 2019

Cited by 20 | Viewed by 5783

Abstract

In this study, we demonstrate the preparation and characterization of small palladium nanoparticles (Pd NPs) on modified ceria support (Pd/CeO₂) using wet impregnation and further reduction in an H₂/Ar flow. The obtained particles had a good dispersion, but their [...] Read more.

In this study, we demonstrate the preparation and characterization of small palladium nanoparticles (Pd NPs) on modified ceria support (Pd/CeO₂) using wet impregnation and further reduction in an H₂/Ar flow. The obtained particles had a good dispersion, but their small size made it difficult to analyze them by conventional techniques such as transmission electron microscopy (TEM) and X-ray powder diffraction (XRPD). The material demonstrated a high catalytic activity in the CO oxidation reaction: the 100% of CO conversion was achieved at ~50 °C, whereas for most of the cited literature, such a high conversion usually was observed near 100 °C or higher for Pd NPs. Diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy in combination with CO probe molecules was used to investigate the size and morphology of NPs and the ceria support. On the basis of the area ratio under the peaks attributed to bridged (B) and linear (L) carbonyls, high-dispersion Pd NPs was corroborated. Obtained results were in good agreement with data of X-ray absorption near edge structure analysis (XANES) and CO chemisorption measurements. Full article

(This article belongs to the Special Issue Heterogeneous Catalytic Materials: Synthesis, Characterization and Applications for Energetic Purposes)

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12 pages, 1927 KiB

Open AccessArticle

Hydroconversion of Aromatic Hydrocarbons over Bimetallic Catalysts

by Aleksandr Glotov, Valentine Stytsenko, Maria Artemova, Michail Kotelev, Evgenii Ivanov, Pavel Gushchin and Vladimir Vinokurov

Catalysts 2019, 9(4), 384; https://doi.org/10.3390/catal9040384 - 24 Apr 2019

Cited by 14 | Viewed by 4831

Abstract

Bimetallic catalysts (BMC) for hydroconversion of aromatic hydrocarbons (ArH) have been designed by modification of Ni/Al₂O₃ with chromium(0) compounds and phosphoromolybdic heteropolyacid (HPA). Catalysts were tested in hydrogenation of benzene and toluene, in hydrodemethylation of pure toluene and they were [...] Read more.

Bimetallic catalysts (BMC) for hydroconversion of aromatic hydrocarbons (ArH) have been designed by modification of Ni/Al₂O₃ with chromium(0) compounds and phosphoromolybdic heteropolyacid (HPA). Catalysts were tested in hydrogenation of benzene and toluene, in hydrodemethylation of pure toluene and they were shown to possess a high activity, selectivity and sulfur tolerance under conditions of the processes above. The activity of BMC in these processes was much higher as compared with that of two-component (Ni-Cr, Ni-HPA) or conventional Ni/Al₂O₃ catalysts. Using BMC, hydrogenation of benzene and toluene proceeds with activity increased (up to 34–38 mol/kg·h) and toluene hydrodemethylation may be performed with improved selectivity (90.3%) and benzene yield (81%). The high sulfur tolerance of BMC was demonstrated by performing hydrodemethylation of toluene containing up to 500 ppm S. Full article

(This article belongs to the Special Issue Catalytic Applications of Bimetallic Nanoparticles)

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12 pages, 3928 KiB

Open AccessArticle

Formation of CuO on TiO₂ Surface Using its Photocatalytic Activity

by Hiromasa Nishikiori, Naoya Harata, Saho Yamaguchi, Takashi Ishikawa, Hayato Kondo, Ayaka Kikuchi, Tomohiko Yamakami and Katsuya Teshima

Catalysts 2019, 9(4), 383; https://doi.org/10.3390/catal9040383 - 24 Apr 2019

Cited by 12 | Viewed by 3929

Abstract

Some co-catalyst nanoparticles can enhance the activity of photocatalysts due to prolonging the charge separation lifetime by promoting the electron or hole transfer. CuO particles were prepared from an aqueous solution of copper (II) nitrate at 351 K on a TiO₂ surface [...] Read more.

Some co-catalyst nanoparticles can enhance the activity of photocatalysts due to prolonging the charge separation lifetime by promoting the electron or hole transfer. CuO particles were prepared from an aqueous solution of copper (II) nitrate at 351 K on a TiO₂ surface by a photocatalytic reaction and heating at 573 or 673 K. The amount and size of the particles deposited during the photocatalytic reaction can be controlled by changing the amount of the irradiated photons. The CuO crystals with about 50−250 nm-sized particles were formed. Nitrate ions were reduced to nitrite ions in the solution by the photocatalytic activity of the TiO₂, and water was simultaneously transformed into hydroxide ions. An increase in the basicity on the TiO₂ surface induced formation of a copper hydroxide. The copper hydroxide was subsequently dehydrated and transformed into CuO by heating. The TiO₂ loading of a small amount of CuO demonstrated a higher photocatalytic activity for methylene blue degradation compared to the original TiO₂ due to the electron transfer from the TiO₂ conduction bands to the CuO conduction band. Full article

(This article belongs to the Section Photocatalysis)

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16 pages, 10268 KiB

Open AccessArticle

Mechanically-Induced Catalyzation of MgH₂ Powders with Zr₂Ni-Ball Milling Media

by M. Sherif El-Eskandarany, Fahad Al-Ajmi and Mohammad Banyan

Catalysts 2019, 9(4), 382; https://doi.org/10.3390/catal9040382 - 24 Apr 2019

Cited by 13 | Viewed by 3303

Abstract

Magnesium hydride (MgH₂) holds immense promises as a cost-effective hydrogen storage material that shows excellent storage capacity suitable for fuel cell applications. Due to its slow hydrogen charging/discharging kinetics and high apparent activation energy of decomposition, MgH₂ is usually doped [...] Read more.

Magnesium hydride (MgH₂) holds immense promises as a cost-effective hydrogen storage material that shows excellent storage capacity suitable for fuel cell applications. Due to its slow hydrogen charging/discharging kinetics and high apparent activation energy of decomposition, MgH₂ is usually doped with one or more catalytic agents to improve its storage capacity. So often, milling the metal hydride with proper amounts of catalyst leads to heterogeneous distribution of the catalytic agent(s) in MgH₂ matrix. The present work proposes a cost-effective process for doping Mg powders with Zr₂Ni particles upon ball milling the powders with Zr₂Ni-balls milling media under pressurized hydrogen. Fine Zr₂Ni particles were gradually eroded from the balls and homogeneously embedded into the milled powders upon increasing the ball milling time. As a result, these fine hard intermetallic particles acted as micro-milling media and leading to the reduction the Mg/MgH₂ powders. Meanwhile, Zr₂Ni eroded particles possessed excellent heterogeneous catalytic effect for improving the hydrogenation/dehydrogenation kinetics of MgH₂. This is implied by the short time required to absorb (425 s)/desorb (700 s) 6.2 wt% H₂ at 200 °C and 225 °C, respectively. The as-milled MgH₂ with Zr₂Ni balls possessed excellent cyclability, indexed by achieving continuous 646 cycles in 985.5 h (~1.5 cycle per hour) without serious degradation. Full article

(This article belongs to the Section Catalytic Materials)

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14 pages, 4555 KiB

Open AccessFeature PaperArticle

Catalytic Properties of Double Substituted Lanthanum Cobaltite Nanostructured Coatings Prepared by Reactive Magnetron Sputtering

by Mohammad Arab Pour Yazdi, Leonardo Lizarraga, Philippe Vernoux, Alain Billard and Pascal Briois

Catalysts 2019, 9(4), 381; https://doi.org/10.3390/catal9040381 - 23 Apr 2019

Cited by 6 | Viewed by 3222

Abstract

Lanthanum perovskites are promising candidates to replace platinum group metal (PGM), especially regarding catalytic oxidation reactions. We have prepared thin catalytic coatings of Sr and Ag doped lanthanum perovskite by using the cathodic co-sputtering magnetron method in reactive condition. Such development of catalytic [...] Read more.

Lanthanum perovskites are promising candidates to replace platinum group metal (PGM), especially regarding catalytic oxidation reactions. We have prepared thin catalytic coatings of Sr and Ag doped lanthanum perovskite by using the cathodic co-sputtering magnetron method in reactive condition. Such development of catalytic films may optimize the surface/bulk ratio to save raw materials, since a porous coating can combine a large exchange surface with the gas phase with an extremely low loading. The sputtering deposition process was optimized to generate crystallized and thin perovskites films on alumina substrates. We found that high Ag contents has a strong impact on the morphology of the coatings. High Ag loadings favor the growth of covering films with a porous wire-like morphology showing a good catalytic activity for CO oxidation. The most active composition displays similar catalytic performances than those of a Pt film. In addition, this porous coating is also efficient for CO and NO oxidation in a simulated Diesel exhaust gas mixture, demonstrating the promising catalytic properties of such nanostructured thin sputtered perovskite films. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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22 pages, 6763 KiB

Open AccessArticle

Numerical Evaluation of Potential Catalyst Savings for Ventilation Air Methane Catalytic Combustion in Helical Coil Reactors with Selective Wall Coating

by Jundika C. Kurnia, Benitta A. Chaedir, Desmond C. Lim, Lianjun Chen, Lishuai Jiang and Agus P. Sasmito

Catalysts 2019, 9(4), 380; https://doi.org/10.3390/catal9040380 - 23 Apr 2019

Cited by 4 | Viewed by 4517

Abstract

During active mining operation of a gassy underground mine, large amounts of methane will be released from the mine ventilation shaft. To eliminate the harmful effects of this ventilation air methane and minimize the wastage of this potential energy resource, considerable effort has [...] Read more.

During active mining operation of a gassy underground mine, large amounts of methane will be released from the mine ventilation shaft. To eliminate the harmful effects of this ventilation air methane and minimize the wastage of this potential energy resource, considerable effort has been devoted to converting this alternative fuel using catalytic combustion. This study numerically investigated the reaction performance of ventilation air methane (VAM) in helical coil tubes of various configurations utilizing a computational fluid dynamics (CFDs) approach. Several key factors affecting the catalytic combustion performance such as curvature, inlet Reynolds number, and cross-section aspect ratio were evaluated. Recalling the high cost of the catalyst used in this reaction—platinum—optimization of catalyst usage by implementing selective catalyst coating was conducted and investigated. For evaluation purposes, the reaction performance of the helical coil tube was compared to its straight counterpart. The results gave a firm confirmation of the superior performance of the helical coil tube compared to the straight one. In addition, it was found that the selective inner wall coating in the circular cross-section at a higher Reynolds number gave rise to the highest figure of merit (FoM), defined as the net energy produced per mg of catalyst platinum. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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12 pages, 6624 KiB

Open AccessArticle

MoS₂/CdS Heterostructure for Enhanced Photoelectrochemical Performance under Visible Light

by Guannan He, Yimin Zhang and Qinyu He

Catalysts 2019, 9(4), 379; https://doi.org/10.3390/catal9040379 - 23 Apr 2019

Cited by 37 | Viewed by 5989

Abstract

High-rate recombination of photogenerated electron and hole pairs will lead to low photocatalytic activity. Constructing heterostructure is a way to address this problem and thus increase the photoelectrochemical performance of the photocatalysts. In this article, molybdenum sulfide (MoS₂)/cadmium sulfide (CdS) nanocomposites [...] Read more.

High-rate recombination of photogenerated electron and hole pairs will lead to low photocatalytic activity. Constructing heterostructure is a way to address this problem and thus increase the photoelectrochemical performance of the photocatalysts. In this article, molybdenum sulfide (MoS₂)/cadmium sulfide (CdS) nanocomposites were fabricated by a facile solvothermal method after sonication. The CdS nanoparticles immobilized on the MoS₂ sheet retained the original crystal structure and morphology. The composites exhibit higher photoelectrochemical properties compared with pure MoS₂ nanosheets or CdS powder. When the precursor concentration of CdS is 0.015 M, the MoS₂/CdS composites yield the highest photocurrent, which is enhanced nearly five times compared with pure CdS or MoS₂. The improved photoelectrochemical performance can be ascribed to the increase of light harvest, as well as to the heterostructure that decreases the recombination rate of the photogenerated electron and hole pairs. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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14 pages, 1858 KiB

Open AccessArticle

Improved Etherification of Glycerol with Tert-Butyl Alcohol by the Addition of Dibutyl Ether as Solvent

by Carmen M. Dominguez, Arturo Romero and Aurora Santos

Catalysts 2019, 9(4), 378; https://doi.org/10.3390/catal9040378 - 23 Apr 2019

Cited by 19 | Viewed by 4854

Abstract

The etherification of glycerol with tert-butyl alcohol in the presence of acid catalysts gives rise to the production of ethers (monoethers, diethers and triethers) of high added-value, which can be used as oxygenated additives in fuels. This reaction is limited by the [...] Read more.

The etherification of glycerol with tert-butyl alcohol in the presence of acid catalysts gives rise to the production of ethers (monoethers, diethers and triethers) of high added-value, which can be used as oxygenated additives in fuels. This reaction is limited by the thermodynamic equilibrium, which can be modified by the addition of solvents that selectively solubilize the products of interest along with tert-butyl alcohol, leading to the progress of the reaction. In this work, it has been demonstrated that the addition of dibutyl ether allows shifting the reaction equilibrium, increasing the production of diethers. From the study of the main operating conditions, it was determined that an increase in the concentration of the solvent has a positive effect on the selectivity towards the production of diethers, the concentration of the catalyst (a commercial ion exchange resin, Amberlyst 15, named A-15) and the reaction temperature were also determining variables. Working with concentrations of tert-butyl alcohol above the stoichiometric one did not report great advantages. The optimal operating conditions to maximize the conversion of glycerol and the selectivity towards diethers were: 70 °C, 20% catalyst (referred to the total starting mass of the system), the stoichiometric ratio of glycerol:tert-butyl alcohol (G:TB = 1:3) and 1:2 molar ratio of dibutyl ether:tert-butyl alcohol. A study of three consecutive reaction cycles showed the high stability of the catalyst, obtaining identical results. Full article

(This article belongs to the Special Issue Catalysis for Global Development. Contributions around the Iberoamerican Federation of Catalysis)

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29 pages, 10708 KiB

Open AccessArticle

Effect of Cerium Precursor in the Synthesis of Ce-MCM-41 and in the Efficiency for Liquid-Phase Oxidation of Benzyl Alcohol

by Carlos M. Aiube, Karolyne V. de Oliveira and Julio L. de Macedo

Catalysts 2019, 9(4), 377; https://doi.org/10.3390/catal9040377 - 23 Apr 2019

Cited by 9 | Viewed by 4504

Abstract

Understanding the effects of synthetic parameters in the catalytic activity of heterogeneous catalysts is of utmost importance when aiming for optimal reaction conditions. Hence, we disclose in this work the synthesis and characterization of cerium-modified MCM-41 materials. In addition, it was observed for [...] Read more.

Understanding the effects of synthetic parameters in the catalytic activity of heterogeneous catalysts is of utmost importance when aiming for optimal reaction conditions. Hence, we disclose in this work the synthesis and characterization of cerium-modified MCM-41 materials. In addition, it was observed for the first time, differences in catalytic activity when using different cerium synthetic precursors: CeCl₃·7H₂O and Ce(NO₃)₃·6H₂O (Ce-MCM-Cl and Ce-MCM-NO₃, respectively). A mechanism for cerium incorporation in MCM-41 was proposed, where [Ce(OH)₃] species were hydrogen bonded to silicate anions, forming framework Ce-O-Si bonds during condensation and, consequently, causing distortion of the typical hexagonal mesophase. It was also observed that Ce(OH)₃ formed aggregated layers with template assemblies during synthesis, resulting in non-framework CeO₂ species on the MCM-41 surface after calcination. These CeO₂ species were preferentially formed for Ce-MCM-NO₃ and were attributed to the nitrate ions’ strong binding to template molecules. In the solvent free liquid-phase oxidation of benzyl alcohol (BzOH), Ce-MCM-Cl achieved better BzOH conversions and benzaldehyde (BzD) yields, while Ce-MCM-NO₃ offered increased BzD selectivity. The catalysts’ reusability was also studied over three catalytic runs, where Ce-MCM-NO₃ was more resistant than Ce-MCM-Cl towards deactivation. The observed catalytic behavior shows the importance of metal precursors in the obtainment of materials with desirable final properties. Full article

(This article belongs to the Special Issue Catalysis for Global Development. Contributions around the Iberoamerican Federation of Catalysis)

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13 pages, 3567 KiB

Open AccessFeature PaperArticle

Hydrogen Production from Formic Acid over Au Catalysts Supported on Carbon: Comparison with Au Catalysts Supported on SiO₂ and Al₂O₃

by Dmitri A. Bulushev, Vladimir I. Sobolev, Larisa V. Pirutko, Anna V. Starostina, Igor P. Asanov, Evgenii Modin, Andrey L. Chuvilin, Neeraj Gupta, Alexander V. Okotrub and Lyubov G. Bulusheva

Catalysts 2019, 9(4), 376; https://doi.org/10.3390/catal9040376 - 22 Apr 2019

Cited by 25 | Viewed by 4517

Abstract

Characteristics and catalytic activity in hydrogen production from formic acid of Au catalysts supported on porous N-free (Au/C) and N-doped carbon (Au/N-C) have been compared with those of Au/SiO₂ and Au/Al₂O₃ catalysts. Among the catalysts examined, the Au/N-C catalyst [...] Read more.

Characteristics and catalytic activity in hydrogen production from formic acid of Au catalysts supported on porous N-free (Au/C) and N-doped carbon (Au/N-C) have been compared with those of Au/SiO₂ and Au/Al₂O₃ catalysts. Among the catalysts examined, the Au/N-C catalyst showed the highest Au mass-based catalytic activity. The following trend was found at 448 K: Au/N-C > Au/SiO₂ > Au/Al₂O₃, Au/C. The trend for the selectivity in hydrogen production was different: Au/C (99.5%) > Au/Al₂O₃ (98.0%) > Au/N-C (96.3%) > Au/SiO₂ (83.0%). According to XPS data the Au was present in metallic state in all catalysts after the reaction. TEM analysis revealed that the use of the N-C support allowed obtaining highly dispersed Au nanoparticles with a mean size of about 2 nm, which was close to those for the Au catalysts on the oxide supports. However, it was by a factor of 5 smaller than that for the Au/C catalyst. The difference in dispersion could explain the difference in the catalytic activity for the carbon-based catalysts. Additionally, the high activity of the Au/N-C catalyst could be related to the presence of pyridinic type nitrogen on the N-doped carbon surface, which activates the formic acid molecule forming pyridinium formate species further interacting with Au. This was confirmed by density functional theory (DFT) calculations. The results of this study may assist the development of novel Au catalysts for different catalytic reactions. Full article

(This article belongs to the Special Issue Metal Catalysts for Renewable Energies)

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13 pages, 2443 KiB

Open AccessFeature PaperArticle

Structure-Sensitivity of CO₂ Methanation over Nanostructured Ni Supported on CeO₂ Nanorods

by Eleonora Marconi, Simonetta Tuti and Igor Luisetto

Catalysts 2019, 9(4), 375; https://doi.org/10.3390/catal9040375 - 22 Apr 2019

Cited by 49 | Viewed by 5720

Abstract

Ni-based oxides are widely investigated as catalysts for CO₂ methanation due to their high activity, high selectivity and low cost. The catalytic performances of Ni-based catalysts depend on support properties that strongly influence the dispersion of the catalytic active phase and the [...] Read more.

Ni-based oxides are widely investigated as catalysts for CO₂ methanation due to their high activity, high selectivity and low cost. The catalytic performances of Ni-based catalysts depend on support properties that strongly influence the dispersion of the catalytic active phase and the Ni–support interaction. Although the CO₂ methanation is widely studied, the structure sensitivity of methanation on nickel is not completely assessed. Ni/CeO₂ nanorods with different nickel/ceria molar ratios (0.05, 0.10, 0.20, 0.30) were prepared by one-pot hydrothermal synthesis. The effect of nickel content and metal particle size on catalytic activity and selectivity for CO₂ methanation were studied using CO₂:H₂ = 1:4 stoichiometric ratio at high space velocity (300 L g⁻¹ h⁻¹). Sample structure and morphology were studied by X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis, field-emission scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), H₂-temperature programmed reduction (TPR), H₂-temperature-programmed desorption (TPD). Both the CO production and the turnover frequency appear depending on nickel particle size, suggesting a structure sensitivity of the CO₂ methanation on nickel supported on ceria. Full article

(This article belongs to the Special Issue Supported Catalysts for Carbon Oxides Methanation)

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13 pages, 4201 KiB

Open AccessArticle

Liquid-Phase Catalytic Oxidation of Limonene to Carvone over ZIF-67(Co)

by Yizhou Li, Yepeng Yang, Daomei Chen, Zhifang Luo, Wei Wang, Yali Ao, Lin Zhang, Zhiying Yan and Jiaqiang Wang

Catalysts 2019, 9(4), 374; https://doi.org/10.3390/catal9040374 - 21 Apr 2019

Cited by 15 | Viewed by 5076

Abstract

Liquid-phase catalytic oxidation of limonene was carried out under mild conditions, and carvone was produced in the presence of ZIF-67(Co), cobalt based zeolitic imidazolate framework, as catalyst, using t-butyl hydroperoxide (t-BHP) as oxidant and benzene as solvent. As a heterogeneous catalyst, the zeolitic [...] Read more.

Liquid-phase catalytic oxidation of limonene was carried out under mild conditions, and carvone was produced in the presence of ZIF-67(Co), cobalt based zeolitic imidazolate framework, as catalyst, using t-butyl hydroperoxide (t-BHP) as oxidant and benzene as solvent. As a heterogeneous catalyst, the zeolitic imidazolate framework ZIF-67(Co) exhibited reasonable substrate–product selectivity (55.4%) and conversion (29.8%). Finally, the X-ray diffraction patterns of the catalyst before and after proved that ZIF-67(Co) acted as a heterogeneous catalyst, and can be reused without losing its activity to a great extent. Full article

(This article belongs to the Special Issue Iron and Cobalt Catalysts)

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14 pages, 747 KiB

Open AccessArticle

Acid–Base Catalytic Effects on Reduction of Methanol in Hot Water

by Satoshi Inaba

Catalysts 2019, 9(4), 373; https://doi.org/10.3390/catal9040373 - 21 Apr 2019

Cited by 3 | Viewed by 3440

Abstract

We have performed a number of quantum chemical simulations to examine the reduction process of methanol in hot water. Methanol is converted into a methane by capturing a hydrogen molecule and leaving a water molecule behind. The required energy for the reduction is [...] Read more.

We have performed a number of quantum chemical simulations to examine the reduction process of methanol in hot water. Methanol is converted into a methane by capturing a hydrogen molecule and leaving a water molecule behind. The required energy for the reduction is too high to proceed in the gas phase. The energy barrier for the reduction of methanol is reduced by the catalytic effect of water molecules when we consider the reduction in aqueous solution. However, the calculated reduction rate is still much slower than that found experimentally. The ion product of water tends to increase in hot water, even though it eventually decreases at the high temperature of supercritical water. It is valuable to consider the acid–base catalytic effects on the reduction of methanol in hot water. The significant reduction of the energy barrier is accomplished by the acid–base catalytic effects due to hydronium or hydroxyde. Mean collision time between a hydronium and a methanol in hot water is shorter than the reduction time, during which a methanol is converted into a methane. The calculated reduction rate with the acid–base catalytic effects agrees well with that determined by laboratory experiments. The present study reveals a crucial role of the acid–base catalytic effects on reactions in hot water. Full article

(This article belongs to the Section Computational Catalysis)

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14 pages, 6786 KiB

Open AccessArticle

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

by Mohammad I. M. Al-Zeer and Kenneth J. D. MacKenzie

Catalysts 2019, 9(4), 372; https://doi.org/10.3390/catal9040372 - 19 Apr 2019

Cited by 28 | Viewed by 4499

Abstract

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple [...] Read more.

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Brønsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF). Full article

(This article belongs to the Special Issue Frontiers in Heterogeneous Catalysis for Sustainable Chemical Transformations)

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21 pages, 3396 KiB

Open AccessEditor’s ChoiceArticle

Facet-Dependent Reactivity of Fe₂O₃/CeO₂ Nanocomposites: Effect of Ceria Morphology on CO Oxidation

by Maria Lykaki, Sofia Stefa, Sόnia A. C. Carabineiro, Pavlos K. Pandis, Vassilis N. Stathopoulos and Michalis Konsolakis

Catalysts 2019, 9(4), 371; https://doi.org/10.3390/catal9040371 - 19 Apr 2019

Cited by 67 | Viewed by 6939

Abstract

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of [...] Read more.

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe₂O₃/CeO₂). A full characterization study involving N₂ adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe²⁺ species. Full article

(This article belongs to the Special Issue Rational Design of Non-precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes)

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25 pages, 11745 KiB

Open AccessReview

Hierarchical Nanostructured Photocatalysts for CO₂ Photoreduction

by Chaitanya Hiragond, Shahzad Ali, Saurav Sorcar and Su-Il In

Catalysts 2019, 9(4), 370; https://doi.org/10.3390/catal9040370 - 19 Apr 2019

Cited by 56 | Viewed by 7872

Abstract

Practical implementation of CO₂ photoreduction technologies requires low-cost, highly efficient, and robust photocatalysts. High surface area photocatalysts are notable in that they offer abundant active sites and enhanced light harvesting. Here we summarize the progress in CO₂ photoreduction with respect to [...] Read more.

Practical implementation of CO₂ photoreduction technologies requires low-cost, highly efficient, and robust photocatalysts. High surface area photocatalysts are notable in that they offer abundant active sites and enhanced light harvesting. Here we summarize the progress in CO₂ photoreduction with respect to synthesis and application of hierarchical nanostructured photocatalysts. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Energy Conversion)

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19 pages, 7068 KiB

Open AccessArticle

Modeling and Order Reduction for the Thermodynamics of a Diesel Oxidation Catalyst with Hydrocarbon Dosing

by Feng Wu, Benxi Zhang, Dongwei Yao and Yanxiang Yang

Catalysts 2019, 9(4), 369; https://doi.org/10.3390/catal9040369 - 18 Apr 2019

Cited by 4 | Viewed by 4171

Abstract

This paper presents an order reduction for the thermal dynamics of a diesel oxidation catalyst (DOC) with hydrocarbon (HC) dosing. The original model includes the pyrolysis of diesel droplets and a wall storage process in the upstream of the DOC. The order reduction [...] Read more.

This paper presents an order reduction for the thermal dynamics of a diesel oxidation catalyst (DOC) with hydrocarbon (HC) dosing. The original model includes the pyrolysis of diesel droplets and a wall storage process in the upstream of the DOC. The order reduction process is derived from the thermodynamics model of the DOC for further control design. The results are compared with experimental data. It is found that the DOC can be simplified as a second-order model using the HC dosing model, which has more than 94% fitness, reflecting the thermodynamics of the system. According to this research, the DOC thermal dynamics can be considered to be equivalent to a time-varying second-order system for the investigation. The second-order parameters of K, T_w, and ζ are also investigated in this paper. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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29 pages, 4110 KiB

Open AccessArticle

Laccase-Catalyzed Oxidation of Mixed Aqueous Phenolic Substrates at Low Concentrations

by Stoyan Rangelov and Jim A. Nicell

Catalysts 2019, 9(4), 368; https://doi.org/10.3390/catal9040368 - 18 Apr 2019

Cited by 6 | Viewed by 2900

Abstract

It has been proposed that Trametes versicolor laccase can be used to detoxify wastewaters that are contaminated with phenolic pollutants. However, the oxidation of phenols at low concentrations may be impacted if other substrates tend to interfere with or enhance the oxidation of [...] Read more.

It has been proposed that Trametes versicolor laccase can be used to detoxify wastewaters that are contaminated with phenolic pollutants. However, the oxidation of phenols at low concentrations may be impacted if other substrates tend to interfere with or enhance the oxidation of the target substrate. To test this, experiments were conducted to evaluate effects arising from the simultaneous presence of mixed substrates including phenol (P), estradiol (E2), cumylphenol (CP), and triclosan (TCL), each of which are characterized by different rates of oxidation and tendencies to inactivate laccase. Slower and faster substrates were found to have only minor negative impacts upon the rate of conversion of targeted substrates, except where they tended to cause inactivation. No enhancements in substrate oxidation were observed. A multi-substrate kinetic model was shown to be able to accurately predict the time course of reactions of mixed substrates over extended periods at micromolar and sub-micromolar concentrations, except when estradiol and triclosan were simultaneously present. In this case, more enzyme inactivation was observed than would be expected from the oxidation of individual substrates alone. The utility of the model for providing insights into the reaction phenomenon and for evaluating the feasibility of oxidizing targeted substrates in the presence of other substrates is demonstrated. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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13 pages, 3182 KiB

Open AccessArticle

Preparation of Metal Amalgam Electrodes and Their Selective Electrocatalytic CO₂ Reduction for Formate Production

by Syed Asad Abbas, Seong-Hoon Kim, Hamza Saleem, Sung-Hee Ahn and Kwang-Deog Jung

Catalysts 2019, 9(4), 367; https://doi.org/10.3390/catal9040367 - 18 Apr 2019

Cited by 11 | Viewed by 5382

Abstract

Electrochemical CO₂ reduction to produce formate ions has studied for the sustainable carbon cycle. Mercury in the liquid state is known to be an active metallic component to selectively convert CO₂ to formate ions, but it is not scalable to use [...] Read more.

Electrochemical CO₂ reduction to produce formate ions has studied for the sustainable carbon cycle. Mercury in the liquid state is known to be an active metallic component to selectively convert CO₂ to formate ions, but it is not scalable to use as an electrode in electrochemical CO₂ reduction. Therefore, scalable amalgam electrodes with different base metals are tested to produce formate by an electrochemical CO₂ reduction. The amalgam electrodes are prepared by the electrodeposition of Hg on the pre-electrodeposited Pd, Au, Pt and Cu nanoparticles on the glassy carbon. The formate faradaic efficiency with the Pd, Au, Pt and Cu is lower than 25%, while the one with the respective metal amalgams is higher than 50%. Pd amalgam among the tested samples shows the highest formate faradic efficiency and current density. The formate faradaic efficiency is recorded 85% at −2.1 V vs SCE and the formate current density is −6.9 mA cm⁻². It is concluded that Pd₂Hg₅ alloy on the Pd amalgam electrode is an active phase for formate production in the electrochemical CO₂ reduction. Full article

(This article belongs to the Special Issue Catalysis and Catalytic Processes for CO₂ Conversion)

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18 pages, 3665 KiB

Open AccessArticle

Tuning Selectivity of Maleic Anhydride Hydrogenation Reaction over Ni/Sc-Doped ZrO₂ Catalysts

by Lili Zhao, Yin Zhang, Tianjie Wu, Min Zhao, Yongzhao Wang, Jianghong Zhao, Tiancun Xiao and Yongxiang Zhao

Catalysts 2019, 9(4), 366; https://doi.org/10.3390/catal9040366 - 18 Apr 2019

Cited by 10 | Viewed by 4022

Abstract

A series of Sc-doped ZrO₂ supports, with Sc₂O₃ content in the range of 0 to 7.5% (mol/mol), were prepared using the hydrothermal method. Ni/Sc-doped ZrO₂ catalysts with nickel loading of 10% (w/w) were prepared [...] Read more.

A series of Sc-doped ZrO₂ supports, with Sc₂O₃ content in the range of 0 to 7.5% (mol/mol), were prepared using the hydrothermal method. Ni/Sc-doped ZrO₂ catalysts with nickel loading of 10% (w/w) were prepared using impregnation method, and characterized with the use of XRD, Raman, H₂ temperature-programmed reduction (H₂-TPR), H₂ temperature-programmed desorption (H₂-TPD), XPS, and in situ FT-IR techniques. The catalytic performances of Ni/Sc-doped ZrO₂ catalysts in maleic anhydride hydrogenation were tested. The results showed that the introduction of Sc³⁺ into ZrO₂ support could effectively manipulate the distribution of maleic anhydride hydrogenation products. γ-butyrolactone was the major hydrogenation product over Sc-free Ni/ZrO₂ catalyst with selectivity as high as 65.8% at 210 °C and 5 MPa of H₂ pressure. The Ni/Sc-doped ZrO₂ catalyst, with 7.5 mol% of Sc₂O₃ content, selectively catalyzed maleic anhydride hydrogenation to succinic anhydride, the selectivity towards succinic anhydride was up to 97.6% under the same reaction condition. The results of the catalysts’ structure–activity relationships revealed that there was an interdependence between the surface structure of ZrO₂-based support and the C=O hydrogenation performance of the ZrO₂-based supported nickel catalysts. By controlling the Sc₂O₃ content, the surface structure of ZrO₂-based support could be regulated effectively. The different surface structure of ZrO₂-based supports, resulted in the different degree of interaction between the nickel species and ZrO₂-based supports; furthermore, the different interaction led to the different surface oxygen vacancies electron properties of ZrO₂-based supported nickel catalysts and the C=O hydrogenation activity of the catalyst. This result provides new insight into the effect of ZrO₂ support on the selective hydrogenation activity of ZrO₂-supported metal catalysts and contributes to the design of selective hydrogenation catalysts for other unsaturated carbonyl compounds. Full article

(This article belongs to the Special Issue Catalysis and Fine Chemicals)

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11 pages, 2482 KiB

Open AccessArticle

BaTi_0.8B_0.2O₃ (B = Mn, Fe, Co, Cu) LNT Catalysts: Effect of Partial Ti Substitution on NOx Storage Capacity

by Craig Aldridge, Verónica Torregrosa-Rivero, Vicente Albaladejo-Fuentes, María-Salvadora Sánchez-Adsuar and María-José Illán-Gómez

Catalysts 2019, 9(4), 365; https://doi.org/10.3390/catal9040365 - 18 Apr 2019

Cited by 2 | Viewed by 3010

Abstract

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi_0.8B_0.2O₃ lean NOx trap (LNT) catalyst has been analyzed. The BaTi_0.8B_0.2O₃ catalysts were [...] Read more.

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi_0.8B_0.2O₃ lean NOx trap (LNT) catalyst has been analyzed. The BaTi_0.8B_0.2O₃ catalysts were prepared using the Pechini’s sol–gel method for aqueous media. The characterization of the catalysts (BET, ICP-OES, XRD and XPS) reveals that: i) the partial substitution of Ti by Mn, Co, or Fe changes the perovskite structure from tetragonal to cubic, whilst Cu distorts the raw tetragonal structure and promotes the segregation of Ba₂TiO₄ (which is an active phase for NOx storage) as a minority phase and ii) the amount of oxygen vacancies increases after partial Ti substitution, with the BaTi_0.8Cu_0.2O₃ catalyst featuring the largest amount. The BaTi_0.8Cu_0.2O₃ catalyst shows the highest NSC at 400 °C, based on NOx storage cyclic tests, which is within the range of highly active noble metal-based catalysts. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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18 pages, 3346 KiB

Open AccessArticle

H-ZSM-5 Materials Embedded in an Amorphous Silica Matrix: Highly Selective Catalysts for Propylene in Methanol-to-Olefin Process

by Huda Sharbini Kamaluddin, Sulaiman Nassir Basahel, Katabathini Narasimharao and Mohamed Mokhtar

Catalysts 2019, 9(4), 364; https://doi.org/10.3390/catal9040364 - 17 Apr 2019

Cited by 20 | Viewed by 8080

Abstract

H-ZSM-5 materials embedded in an amorphous silica were successfully synthesized with three different Si/Al ratios (i.e., 40, 45, and 50). The presence of the MFI structure in the synthesized samples was confirmed by X-ray diffraction (XRD), Fourier transform infra-red (FT-IR), and solid state-nuclear [...] Read more.

H-ZSM-5 materials embedded in an amorphous silica were successfully synthesized with three different Si/Al ratios (i.e., 40, 45, and 50). The presence of the MFI structure in the synthesized samples was confirmed by X-ray diffraction (XRD), Fourier transform infra-red (FT-IR), and solid state-nuclear magnetic resonance (SSNMR) techniques. The morphology and textural properties of the samples were investigated by scanning electron microscopy (SEM), TEM, and N₂-physisorption measurements. Furthermore, acidic properties of the synthesized catalysts have been studied by NH₃-TPD and FT-IR spectroscopy of CO adsorption studies. Variation of the Si/Al ratio affected the crystal morphology, porosity, and particle size, as well as the strength and distribution of acid sites. The synthesized zeolite materials possessed low acid-site density and exhibited high catalytic activity in the methanol-to-olefin (MTO) reaction. To study the intermediate species responsible for catalyst deactivation, the MTO reaction was carried out at high temperature (500 °C) to accelerate catalyst deactivation. Interestingly, the synthesized catalysts offered high selectivity towards the formation of propylene (C₃₌), in comparison to a commercial microporous crystalline H-ZSM-5 with Si/Al = 40, under the same reaction conditions. The synthesized H-ZSM-5 materials offered a selectivity ratio of C₃₌/C₂₌ 12, while it is around 2 for the commercial H-ZSM-5 sample. The formation of hydrocarbon species during MTO reaction over zeolite samples has been systematically studied with operando UV-vis spectroscopy and online gas chromatography. It is proposed that the strength and type of acid sites of catalyst play a role in propylene selectivity as well as the fast growing of active intermediate species. The effective conversion of methanol into propylene in the case of synthesized H-ZSM-5 materials was observed due to possession of weak acid sites. This effect is more pronounced in H-ZSM-5 sample with a Si/Al ratio of 45. Full article

(This article belongs to the Special Issue Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Applications in Catalysis)

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11 pages, 4631 KiB

Open AccessFeature PaperArticle

Oxidative Coupling of Methane over Mn₂O₃-Na₂WO₄/SiC Catalysts

by Jieun Kim, La-Hee Park, Jeong-Myeong Ha and Eun Duck Park

Catalysts 2019, 9(4), 363; https://doi.org/10.3390/catal9040363 - 15 Apr 2019

Cited by 18 | Viewed by 5344

Abstract

The oxidative coupling of methane (OCM) is operated at high temperatures and is a highly exothermic reaction; thus, hotspots form on the catalyst surface during reaction unless the produced heat is removed. It is crucial to control the heat formed because surface hotspots [...] Read more.

The oxidative coupling of methane (OCM) is operated at high temperatures and is a highly exothermic reaction; thus, hotspots form on the catalyst surface during reaction unless the produced heat is removed. It is crucial to control the heat formed because surface hotspots can degrade catalytic performance. Herein, we report the preparation of Mn₂O₃-Na₂WO₄/SiC catalysts using SiC, which has high thermal conductivity and good stability at high temperatures, and the catalyst was applied to the OCM. Two Mn₂O₃-Na₂WO₄/SiC catalysts were prepared by wet-impregnation on SiC supports having different particle sizes. For comparison, the Mn₂O₃-Na₂WO₄/SiO₂ catalyst was also prepared by the same method. The catalysts were analyzed by nitrogen adsorption–desorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The transformation of SiC into α-cristobalite was observed for the Mn₂O₃-Na₂WO₄/SiC catalysts. Because SiC was completely converted into α-cristobalite for the nano-sized SiC-supported Mn₂O₃-Na₂WO₄ catalyst, the catalytic performance for the OCM reaction of Mn₂O₃-Na₂WO₄/n-SiC was similar to that of Mn₂O₃-Na₂WO₄/SiO₂. However, only the surface layer of SiC was transformed into α-cristobalite for the micro-sized SiC (m-SiC) in Mn₂O₃-Na₂WO₄/m-SiC, resulting in a SiC@α-cristobalite core–shell structure. The Mn₂O₃-Na₂WO₄/m-SiC showed higher methane conversion and C₂₊ yield at 800 and 850 °C than Mn₂O₃-Na₂WO₄/SiO₂. Full article

(This article belongs to the Special Issue Catalysts for Stable Molecules (CO₂, CO, CH₄, NH₃) Conversion)

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15 pages, 2402 KiB

Open AccessArticle

Oxychlorination Redispersion of Pt Catalysts: Surface Species and Pt-Support Interactions Characterized by X-ray Absorption and FT-IR Spectroscopy

by Chia-Ching Hung, Cheng-Yang Yeh, Cheng-Chieh Shih and Jen-Ray Chang

Catalysts 2019, 9(4), 362; https://doi.org/10.3390/catal9040362 - 15 Apr 2019

Cited by 9 | Viewed by 5386

Abstract

To help elucidate the oxychlorination redispersion reaction mechanism, the surface species formed on the surface of γ-Al₂O₃ was characterized by X-ray absorption spectroscopy (XAS). The efficacy of redispersion was assessed by the Pt–Pt coordination number (CN_Pt–Pt) of redispersed, [...] Read more.

To help elucidate the oxychlorination redispersion reaction mechanism, the surface species formed on the surface of γ-Al₂O₃ was characterized by X-ray absorption spectroscopy (XAS). The efficacy of redispersion was assessed by the Pt–Pt coordination number (CN_Pt–Pt) of redispersed, and then reduced samples. A nearly fully redispersed complex (Pt_rd52) was prepared by treating a sintered model Pt/γ-Al₂O₃ catalyst at 520 °C, Air/EDC (ethylene dichloride) of 30, and WHSV (Weight Hourly Space Velocity) of 0.07 h⁻¹ for 16 h. For investigating temperature effects, samples treated at 460 (Pt_rd46) and 560 °C (Pt_rd56) were also prepared for comparison. It was found that, while an octahedral resembling Pt(O_s)_3–4(O–Cl)_2–3 (O_s represents support oxygen or hydroxyl oxygen) complex was formed on γ-Al₂O₃ of Pt_rd52, less O–Cl ligands were formed on the redispersed complexes, Pt_rd46 and Pt_rd56. A negative correlation of CN_Pt–Pt with CN_Pt–Cl* (Cl* represents the Cl atom in O–Cl ligand) for these three samples further suggested that the formation of Pt–O–Cl played a key role in the redispersion process. Pt–O–Cl could be formed in the reaction of reactive Cl⋅ and PtO₂. At an operation temperature of lower-than-optimal temperatures of 520 °C, less Cl₂ dissociation and less O–Cl ligands were formed. On the other hand, higher temperatures may facilitate Cl₂ dissociation, but reduce the equilibrium conversion of HCl to Cl₂, leading to increased HCl reaction with Pt (PtO₂) clusters to form Pt–Cl (Cl is the atom bonded directly to Pt), and decreased formation of Pt–O–Cl. Full article

(This article belongs to the Special Issue Recent Advances in Pt-Based Catalysts: Theoretical and Experimental Results)

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