2023

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16 pages, 6264 KiB

Open AccessArticle

Effect of Potassium Doping on the Structural and Catalytic Properties of Co/MnO_x Catalyst in the Steam Reforming of Ethanol

by Magdalena Greluk, Marek Rotko, Grzegorz Słowik, Sylwia Turczyniak-Surdacka, Gabriela Grzybek and Katarzyna Tyszczuk-Rotko

Materials 2023, 16(15), 5377; https://doi.org/10.3390/ma16155377 - 31 Jul 2023

Viewed by 702

Abstract

The promotional effect of potassium (~1.25 wt%) on a Co/MnO_x catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H₂O/EtOH molar ratio of 12/1. The catalysts [...] Read more.

The promotional effect of potassium (~1.25 wt%) on a Co/MnO_x catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H₂O/EtOH molar ratio of 12/1. The catalysts were characterized using physicochemical methods to study their textural, structural, and redox properties. The XRD studies revealed that, during the treatment of both cobalt-based catalysts under a hydrogen atmosphere at 500 °C, Co⁰ and MnO phases were formed by the reduction in Co₃O₄ and Mn₂O₃/Mn₃O₄ phases, respectively. Potassium doping significantly improved stability and ability for the C–C bond cleavage of the Co/MnO_x catalyst. The enhancement of activity (at ~25%) and selectivity to hydrogen (at ca. 10%) and the C1 product, mainly carbon dioxide (at ~20%), of the Co/MnO_x catalyst upon potassium doping was clarified by the alkali promoter’s impact on the reducibility of the cobalt and manganese oxides. The microscopic observations revealed that fibrous carbon deposits are present on the surface of Co/MnOx and KCo/MnOx catalysts after the SRE reaction and their formation is the main reason these catalysts deactivate under SRE conditions. However, carbon accumulation on the surface of the potassium-promoted catalyst was ca. 12% lower after 18 h of SRE reaction compared to the unpromoted sample. Full article

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15 pages, 6184 KiB

Open AccessArticle

Synergistic Effect of P Doping and Mo-Ni-Based Heterostructure Electrocatalyst for Overall Water Splitting

by Feihong Jia, Xiangyu Zou, Xueling Wei, Weiwei Bao, Taotao Ai, Wenhu Li and Yuchen Guo

Materials 2023, 16(9), 3411; https://doi.org/10.3390/ma16093411 - 27 Apr 2023

Cited by 2 | Viewed by 1359

Abstract

Heterostructure construction and heteroatom doping are powerful strategies for enhancing the electrolytic efficiency of electrocatalysts for overall water splitting. Herein, we present a P-doped MoS₂/Ni₃S₂ electrocatalyst on nickel foam (NF) prepared using a one-step hydrothermal method. The optimized [...] Read more.

Heterostructure construction and heteroatom doping are powerful strategies for enhancing the electrolytic efficiency of electrocatalysts for overall water splitting. Herein, we present a P-doped MoS₂/Ni₃S₂ electrocatalyst on nickel foam (NF) prepared using a one-step hydrothermal method. The optimized P_[0.9mM]-MoS₂/Ni₃S₂@NF exhibits a cluster nanoflower-like morphology, which promotes the synergistic electrocatalytic effect of the heterostructures with abundant active centers, resulting in high catalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte. The electrode exhibits low overpotentials and Tafel slopes for the HER and OER. In addition, the catalyst electrode used in a two-electrode system for overall water splitting requires an ultralow voltage of 1.42 V at 10 mA·cm⁻² and shows no obvious increase in current within 35 h, indicating excellent stability. Therefore, the combination of P doping and the heterostructure suggests a novel path to formulate high-performance electrocatalysts for overall water splitting. Full article

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18 pages, 6456 KiB

Open AccessReview

Supported Ionic Liquid Phase Catalysts Dedicated for Continuous Flow Synthesis

by Piotr Latos, Anna Wolny and Anna Chrobok

Materials 2023, 16(5), 2106; https://doi.org/10.3390/ma16052106 - 05 Mar 2023

Cited by 3 | Viewed by 2011

Abstract

Heterogeneous catalysis, although known for over a century, is constantly improved and plays a key role in solving the present problems in chemical technology. Thanks to the development of modern materials engineering, solid supports for catalytic phases having a highly developed surface are [...] Read more.

Heterogeneous catalysis, although known for over a century, is constantly improved and plays a key role in solving the present problems in chemical technology. Thanks to the development of modern materials engineering, solid supports for catalytic phases having a highly developed surface are available. Recently, continuous-flow synthesis started to be a key technology in the synthesis of high added value chemicals. These processes are more efficient, sustainable, safer and cheaper to operate. The most promising is the use of heterogeneous catalyst with column-type fixed-bed reactors. The advantages of the use of heterogeneous catalyst in continuous flow reactors are the physical separation of product and catalyst, as well as the reduction in inactivation and loss of the catalyst. However, the state-of-the-art use of heterogeneous catalysts in flow systems compared to homogenous ones remains still open. The lifetime of heterogeneous catalysts remains a significant hurdle to realise sustainable flow synthesis. The goal of this review article was to present a state of knowledge concerning the application of Supported Ionic Liquid Phase (SILP) catalysts dedicated for continuous flow synthesis. Full article

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13 pages, 5276 KiB

Open AccessArticle

The Visible-Light-Driven Activity of Biochar-Doped TiO₂ Photocatalysts in β-Blockers Removal from Water

by Agata Kowalczyk, Bożena Zgardzińska, Karol Osipiuk, Katarzyna Jędruchniewicz, Katarzyna Tyszczuk-Rotko, Magdalena Goździuk, Haitao Wang and Bożena Czech

Materials 2023, 16(3), 1094; https://doi.org/10.3390/ma16031094 - 27 Jan 2023

Cited by 1 | Viewed by 1449

Abstract

Water is the most important life-giving resource on earth. Nowadays, intensive growth of the world population has resulted in increased water consumption and the production of wastewater. Additionally, the presence of pharmaceuticals in treated conventional wastewater or even in the environment is strictly [...] Read more.

Water is the most important life-giving resource on earth. Nowadays, intensive growth of the world population has resulted in increased water consumption and the production of wastewater. Additionally, the presence of pharmaceuticals in treated conventional wastewater or even in the environment is strictly indicating that present techniques of wastewater treatment are not efficient enough and are not designed to remove such pollutants. Scarce water resources in the world are the main driving force for the innovation of novel techniques of water and wastewater treatment. Photocatalysis, as one of the advanced oxidation processes, enables the transformation of recalcitrant and toxic pollutants into CO₂, water, and inorganic salts. In the present paper, the photocatalytic oxidation of β-blockers—metoprolol and propranolol—are described. For photocatalytic oxidation, novel TiO₂ photocatalysts modified with biochar were used. Photocatalysts were prepared by sol-gel method and the effect of photocatalysts type, presence of inorganic ions, dissolved organic matter, and different water matrix was established. The results indicate that using only the decrease in the tested pollutant concentration is not effective enough in establishing the treatment method’s safety. There is a need to use additional testing such as ecotoxicity tests; however, the key parameter is the properly chosen tested organism. Full article

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2022

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13 pages, 4963 KiB

Open AccessArticle

Modification of CeNi_0.9Zr_0.1O₃ Perovskite Catalyst by Partially Substituting Yttrium with Zirconia in Dry Reforming of Methane

by Mahmud S. Lanre, Ahmed E. Abasaeed, Anis H. Fakeeha, Ahmed A. Ibrahim, Abdullah A. Alquraini, Salwa B. AlReshaidan and Ahmed S. Al-Fatesh

Materials 2022, 15(10), 3564; https://doi.org/10.3390/ma15103564 - 16 May 2022

Cited by 10 | Viewed by 1722

Abstract

Methane Dry Reforming is one of the means of producing syngas. CeNi_0.9Zr_0.1O₃ catalyst and its modification with yttrium were investigated for CO₂ reforming of methane. The experiment was performed at 800 °C to examine the effect of [...] Read more.

Methane Dry Reforming is one of the means of producing syngas. CeNi_0.9Zr_0.1O₃ catalyst and its modification with yttrium were investigated for CO₂ reforming of methane. The experiment was performed at 800 °C to examine the effect of yttrium loading on catalyst activity, stability, and H₂/CO ratio. The catalyst activity increased with an increase in yttrium loading with CeNi_0.9Zr_0.01Y_0.09O₃ catalyst demonstrating the best activity with CH₄ conversion >85% and CO₂ conversion >90% while the stability increased with increases in zirconium loading. The specific surface area of samples ranged from 1–9 m²/g with a pore size of 12–29 nm. The samples all showed type IV isotherms. The XRD peaks confirmed the formation of a monoclinic phase of zirconium and the well-crystallized structure of the perovskite catalyst. The Temperature Program Reduction analysis (TPR) showed a peak at low-temperature region for the yttrium doped catalyst while the un-modified perovskite catalyst (CeNi_0.9Zr_0.1O₃) showed a slight shift to a moderate temperature region in the TPR profile. The Thermogravimetric analysis (TGA) curve showed a weight loss step in the range of 500–700 °C, with CeNi_0.9Zr_0.1O₃ having the least carbon with a weight loss of 20%. Full article

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2021

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16 pages, 3483 KiB

Open AccessArticle

Outperformance in Acrylation: Supported D-Glucose-Based Ionic Liquid Phase on MWCNTs for Immobilized Lipase B from Candida antarctica as Catalytic System

by Anna Szelwicka, Karol Erfurt, Sebastian Jurczyk, Slawomir Boncel and Anna Chrobok

Materials 2021, 14(11), 3090; https://doi.org/10.3390/ma14113090 - 04 Jun 2021

Cited by 12 | Viewed by 2107

Abstract

This study presents a highly efficient method of a synthesis of n-butyl acrylate via esterification of acrylic acid and n-butanol in the presence of supported ionic liquid phase (SILP) biocatalyst consisting of the lipase B from Candida antarctica (CALB) and multi-walled [...] Read more.

This study presents a highly efficient method of a synthesis of n-butyl acrylate via esterification of acrylic acid and n-butanol in the presence of supported ionic liquid phase (SILP) biocatalyst consisting of the lipase B from Candida antarctica (CALB) and multi-walled carbon nanotubes (MWCNTs) modified by D-glucose-based ionic liquids. Favorable reaction conditions (acrylic acid: n-butanol molar ratio 1:2, cyclohexane as a solvent, biocatalyst 0.150 g per 1 mmol of acrylic acid, temperature 25 °C) allowed the achievement of a 99% yield of n-butyl acrylate in 24 h. Screening of various ionic liquids showed that the most promising result was obtained if N-(6-deoxy-1-O-methoxy-α-D-glucopyranosyl)-N,N,N-trimethylammonium bis-(trifluoromethylsulfonyl)imide ([N(CH₃)₃GlcOCH₃][N(Tf)₂]) was selected in order to modify the outer surface of MWCNTs. The final SILP biocatalyst–CNTs-[N(CH₃)₃GlcOCH₃][N(Tf)₂]-CALB contained 1.8 wt.% of IL and 4.2 wt.% of CALB. Application of the SILP biocatalyst led to the enhanced activity of CALB in comparison with the biocatalyst prepared via physical adsorption of CALB onto MWCNTs (CNTs-CALB), as well as with commercially available Novozyme 435. Thus, the crucial role of IL in the stabilization of biocatalysts was clearly demonstrated. In addition, a significant stability of the developed biocatalytic system was confirmed (three runs with a yield of ester over 90%). Full article

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2020

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15 pages, 3105 KiB

Open AccessArticle

Fast and Efficient Piezo/Photocatalytic Removal of Methyl Orange Using SbSI Nanowires

by Krystian Mistewicz, Mirosława Kępińska, Marian Nowak, Agnieszka Sasiela, Maciej Zubko and Danuta Stróż

Materials 2020, 13(21), 4803; https://doi.org/10.3390/ma13214803 - 28 Oct 2020

Cited by 21 | Viewed by 3494

Abstract

Piezocatalysis is a novel method that can be applied for degradation of organic pollutants in wastewater. In this paper, ferroelectric nanowires of antimony sulfoiodide (SbSI) have been fabricated using a sonochemical method. Methyl orange (MO) was chosen as a typical pollutant, as it [...] Read more.

Piezocatalysis is a novel method that can be applied for degradation of organic pollutants in wastewater. In this paper, ferroelectric nanowires of antimony sulfoiodide (SbSI) have been fabricated using a sonochemical method. Methyl orange (MO) was chosen as a typical pollutant, as it is widely used as a dye in industry. An aqueous solution of MO at a concentration of 30 mg/L containing SbSI nanowires (6 g/L) was subjected to ultrasonic vibration. High degradation efficiency of 99.5% was achieved after an extremely short period of ultrasonic irradiation (40 s). The large reaction rate constant of 0.126(8) s⁻¹ was determined for piezocatalytic MO decomposition. This rate constant is two orders of magnitude larger than values of reaction rate constants reported in the literature for the most efficient piezocatalysts. These promising experimental results have proved a great potential of SbSI nanowires for their application in environmental purification and renewable energy conversion. Full article

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12 pages, 3072 KiB

Open AccessArticle

Study on Rh(I)/Ru(III) Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid

by Shasha Zhang, Wenxin Ji, Ning Feng, Liping Lan, Yuanyuan Li and Yulong Ma

Materials 2020, 13(18), 4026; https://doi.org/10.3390/ma13184026 - 11 Sep 2020

Cited by 5 | Viewed by 2954

Abstract

In this study, a Rh(I)/Ru(III) catalyst with a bimetallic space structure was designed and synthesized. The interaction between the metals of the bimetallic catalyst and the structure of the bridged dimer can effectively reduce the steric hindrance effect and help speed up the [...] Read more.

In this study, a Rh(I)/Ru(III) catalyst with a bimetallic space structure was designed and synthesized. The interaction between the metals of the bimetallic catalyst and the structure of the bridged dimer can effectively reduce the steric hindrance effect and help speed up the reaction rate while ensuring the stability of the catalyst. X-ray photoelectron spectroscopy (XPS) results show that rhodium accepts electrons from chlorine, thereby increasing the electron-rich nature of rhodium and improving the catalytic activity. This promotes the nucleophilic reaction of the catalyst with methyl iodide and reduces the reaction energy barrier. The methanol carbonylation performance of the Rh/Ru catalyst was evaluated, and the results show that the conversion rate of methyl acetate and the yield of acetic acid are 96.0% under certain conditions. Furthermore, during the catalysis, no precipitate is formed and the amount of water is greatly reduced. It can be seen that the catalyst has good stability and activity. Full article

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13 pages, 3427 KiB

Open AccessArticle

Synthesis and Performance of TiO₂/Fly Ash Cenospheres as a Catalytic Film in a Novel Type of Periodic Air-Sparged Photocatalytic Reactor

by Witold Żukowski, Przemysław Migas, Dariusz Bradło and Piotr Dulian

Materials 2020, 13(7), 1691; https://doi.org/10.3390/ma13071691 - 04 Apr 2020

Cited by 6 | Viewed by 2856

Abstract

The results of a photocatalytic process performed in a new type of inclined, three-phase fluidised bed reactor with a periodic photocatalyst film are presented. These phases were fly ash cenospheres coated with TiO₂, an aqueous solution of methylene blue and an [...] Read more.

The results of a photocatalytic process performed in a new type of inclined, three-phase fluidised bed reactor with a periodic photocatalyst film are presented. These phases were fly ash cenospheres coated with TiO₂, an aqueous solution of methylene blue and an air stream passing from the bottom of the photoreactor. The cenospheres have a density lower than water and could thus form a catalytic film on a top irradiated window. The formed surface film is stable but is easy to break and be reproduced in a cyclic air-sparged process. Mixing was performed in either a cyclic or a continuous manner. From an operational point of view, the best variant of mixing was a 10 s air-sparge/10 s break with a 50% duty cycle, because it provided the same discolouration efficiency and reduced energy demand by 50% in comparison with the continuous mixing. Due to film formation, the proposed catalytic reactor enables a substantial reduction in the energy required for mixing while maintaining the desired degree of discolouration. Full article

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17 pages, 4834 KiB

Open AccessArticle

Liquid Phase Hydrogenation of Pharmaceutical Interest Nitroarenes over Gold-Supported Alumina Nanowires Catalysts

by Krishnamoorthy Shanmugaraj, Tatiana M. Bustamante, Cristian H. Campos and Cecilia C. Torres

Materials 2020, 13(4), 925; https://doi.org/10.3390/ma13040925 - 19 Feb 2020

Cited by 11 | Viewed by 2603

Abstract

In this work, Au nanoparticles, supported in Al₂O₃ nanowires (ANW) modified with (3-aminopropyl)trimethoxysilane were synthetized, for their use as catalysts in the hydrogenation reaction of 4-(2-fluoro-4-nitrophenyl)-morpholine and 4-(4-nitrophenyl)morpholin-3-one. ANW was obtained by hydrothermal techniques and the metal was incorporated by [...] Read more.

In this work, Au nanoparticles, supported in Al₂O₃ nanowires (ANW) modified with (3-aminopropyl)trimethoxysilane were synthetized, for their use as catalysts in the hydrogenation reaction of 4-(2-fluoro-4-nitrophenyl)-morpholine and 4-(4-nitrophenyl)morpholin-3-one. ANW was obtained by hydrothermal techniques and the metal was incorporated by the reduction of the precursor with NaBH₄ posterior to superficial modification. The catalysts were prepared at different metal loadings and were characterized by different techniques. The characterization revealed structured materials in the form of nanowires and a successful superficial modification. All catalysts show that Au is in a reduced state and the shape of the nanoparticles is spherical, with high metal dispersion and size distributions from 3.7 to 4.6 nm. The different systems supported in modified-ANW were active and selective in the hydrogenation reaction of both substrates, finding for all catalytic systems a selectivity of almost 100% to the aromatic amine. Catalytic data showed pseudo first-order kinetics with respect to the substrate for all experimental conditions used in this work. The solvent plays an important role in the activity and selectivity of the catalyst, where the highest efficiency and operational stability was achieved when ethanol was used as the solvent. Full article

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19 pages, 7058 KiB

Open AccessFeature PaperArticle

Effect of Metal Content on Ethanol Decomposition over Ni-Co Catalysts Supported on La-Ce Oxides

by Harold R. Vergara, Maria H. Brijaldo, José J. Martinez, Hugo A. Rojas, José Pedraza, Fabio B. Passos, Luiz Pereira da Costa, Daniela Gonzalez-Vera and Paula Osorio-Vargas

Materials 2020, 13(3), 759; https://doi.org/10.3390/ma13030759 - 07 Feb 2020

Cited by 2 | Viewed by 2453

Abstract

The search for catalysts with features that can improve coke resistance and decrease byproduct formation is a current goal in H₂ production from renewable sources. In this work, the effect of the presence of Ni nanoparticles over Co/La-Ce oxides on the ethanol [...] Read more.

The search for catalysts with features that can improve coke resistance and decrease byproduct formation is a current goal in H₂ production from renewable sources. In this work, the effect of the presence of Ni nanoparticles over Co/La-Ce oxides on the ethanol decomposition reaction was studied. Catalysts were synthetized using as precursor a La_0.8Ce_0.2Ni_xCo_1-xO₃ perovskite-type material to ensure a low segregation of phases and a high dispersion of metals. After reduction at 873 K, the perovskite structure was destroyed, and metal Co-Ni particles were supported over a lanthanum-cerium oxide. The materials were characterized by different techniques before and after reaction. Solids exhibited metal particle sizes between 5 and 15 nm demonstrating the advantages of the preparation method to obtain Ni-Co alloys. Although the results of adsorption of ethanol followed by diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) showed acetate species strongly adsorbed on the catalyst’s surface, the material (Ni_0.7Co_0.3/La_0.8Ce_0.2) with the lowest particle size was the most stable system leading to the lowest amount of carbon deposits during ethanol decomposition. This catalyst showed the better performance, with a higher ethanol conversion (98.4%) and hydrogen selectivity (75%). All catalysts exhibited carbonaceous deposits, which were an ordered and disordered carbon phase mixture. Full article

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17 pages, 1957 KiB

Open AccessArticle

Thermal Modification Effect on Supported Cu-Based Activated Carbon Catalyst in Hydrogenolysis of Glycerol

by Juan Seguel, Rafael García, Ricardo José Chimentão, José Luis García-Fierro, I. Tyrone Ghampson, Néstor Escalona and Catherine Sepúlveda

Materials 2020, 13(3), 603; https://doi.org/10.3390/ma13030603 - 29 Jan 2020

Cited by 7 | Viewed by 3662

Abstract

Glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) was performed over activated carbon supported copper-based catalysts. The catalysts were prepared by impregnation using a pristine carbon support and thermally-treated carbon supports (450, 600, 750, and 1000 °C). The final hydrogen adsorption capacity, porous structure, and total [...] Read more.

Glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) was performed over activated carbon supported copper-based catalysts. The catalysts were prepared by impregnation using a pristine carbon support and thermally-treated carbon supports (450, 600, 750, and 1000 °C). The final hydrogen adsorption capacity, porous structure, and total acidity of the catalysts were found to be important descriptors to understand catalytic performance. Oxygen surface groups on the support controlled copper dispersion by modifying acidic and adsorption properties. The amount of oxygen species of thermally modified carbon supports was also found to be a function of its specific surface area. Carbon supports with high specific surface areas contained large amount of oxygen surface species, inducing homogeneous distribution of Cu species on the carbon support during impregnation. The oxygen surface groups likely acted as anchorage centers, whereby the more stable oxygen surface groups after the reduction treatment produced an increase in the interaction of the copper species with the carbon support, and determined catalytic performances. Full article

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13 pages, 5413 KiB

Open AccessArticle

A Fenton-Like Nanocatalyst Based on Easily Separated Magnetic Nanorings for Oxidation and Degradation of Dye Pollutant

by Xiaonan Li, Jinghua Li, Weilu Shi, Jianfeng Bao and Xianyuan Yang

Materials 2020, 13(2), 332; https://doi.org/10.3390/ma13020332 - 11 Jan 2020

Cited by 15 | Viewed by 2971

Abstract

In this study, uniform Fe₃O₄ magnetic nanorings (Fe₃O₄-MNRs) were prepared through a simple hydrothermal method. The morphology, magnetic properties, and structure of the product were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), high [...] Read more.

In this study, uniform Fe₃O₄ magnetic nanorings (Fe₃O₄-MNRs) were prepared through a simple hydrothermal method. The morphology, magnetic properties, and structure of the product were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The Fe₃O₄-MNRs were used as Fenton-like catalysts in the presence of hydrogen peroxide (H₂O₂) and showed excellent Fenton-catalytic activity for degradation of organic dyes such as Methylene blue (MB), Rhodamine B (RhB), and Bromophenol blue (BPB). Furthermore, the obtained Fe₃O₄-MNRs could be recycled after used for several times and still remained in a relative high activity and could rapidly be separated from the reaction medium using a magnet without considerable loss. All results reveal that Fe₃O₄-MNRs have potential for the treatment of dyes pollutants. Full article

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16 pages, 3201 KiB

Open AccessArticle

The Effect of the ZrO₂ Loading in SiO₂@ZrO₂-CaO Catalysts for Transesterification Reaction

by Daniela Salinas, Sichem Guerrero, Cristian H. Campos, Tatiana M. Bustamante and Gina Pecchi

Materials 2020, 13(1), 221; https://doi.org/10.3390/ma13010221 - 04 Jan 2020

Cited by 6 | Viewed by 3539

Abstract

The effect of the ZrO₂ loading was studied on spherical SiO₂@ZrO₂-CaO structures synthetized by a simple route that combines the Stöber and sol-gel methods. The texture of these materials was determined using S_BET by N₂ adsorption, [...] Read more.

The effect of the ZrO₂ loading was studied on spherical SiO₂@ZrO₂-CaO structures synthetized by a simple route that combines the Stöber and sol-gel methods. The texture of these materials was determined using S_BET by N₂ adsorption, where the increment in SiO₂ spheres’ surface areas was reached with the incorporation of ZrO₂. Combined the characterization techniques of using different alcoholic dissolutions of zirconium (VI) butoxide 0.04 M, 0.06 M, and 0.08 M, we obtained SiO₂@ZrO₂ materials with 5.7, 20.2, and 25.2 wt % of Zr. Transmission electron microscopy (TEM) analysis also uncovered the shape and reproducibility of the SiO₂ spheres. The presence of Zr and Ca in the core–shell was also determined by TEM. X-ray diffraction (XRD) profiles showed that the c-ZrO₂ phase changed in to m-ZrO₂ by incorporating calcium, which was confirmed by Raman spectroscopy. The purity of the SiO₂ spheres, as well as the presence of Zr and Ca in the core–shell, was assessed by the Fourier transform infrared (FTIR) method. CO₂ temperature programmed desorption (TPD-CO₂) measurements confirmed the increment in the amount of the basic sites and strength of these basic sites due to calcium incorporation. The catalyst reuse in FAME production from canola oil transesterification allowed confirmation that these calcium core@shell catalysts turn out to be actives and stables for this reaction. Full article

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2019

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12 pages, 2536 KiB

Open AccessArticle

Magnetic Fe₃O₄@SiO₂–Pt and Fe₃O₄@SiO₂–Pt@SiO₂ Structures for HDN of Indole

by Robinson Dinamarca, Verónica Valles, Brenda Ledesma, Cristian H. Campos, Gina Pecchi and Andrea Beltramone

Materials 2019, 12(23), 3878; https://doi.org/10.3390/ma12233878 - 24 Nov 2019

Cited by 3 | Viewed by 3707

Abstract

The effect of a second porous SiO₂ shell in the activity and selectivity of the Fe₃O₄@SiO₂–Pt catalyst in the hydrodenitrogenation of indole is reported. The double Fe₃O₄@SiO₂–Pt@SiO₂ structure was [...] Read more.

The effect of a second porous SiO₂ shell in the activity and selectivity of the Fe₃O₄@SiO₂–Pt catalyst in the hydrodenitrogenation of indole is reported. The double Fe₃O₄@SiO₂–Pt@SiO₂ structure was prepared by coating Fe₃O₄ nanoparticles with tetraethyl orthosilicate (TEOS) with a further impregnation of 1.0 wt.% of Pt on the (3-aminopropyl)triethoxysilane functionalized Fe₃O₄@SiO₂ structures. The second porous SiO₂ shell, obtained by using a hexadecyltrimethylammonium bromide (CTAB) template, covered the Fe₃O₄@SiO₂–Pt catalyst with a well-defined and narrow pore-sized distribution. The full characterization by TEM, inductively coupled plasma-optical emission spectroscopy (ICP-OES), XRD, and N₂ adsorption isotherm at 77 K and vibrating sample magnetometry (VSM) of the catalysts indicates homogeneous core@shell structures with a controlled nano-size of metallic Pt. A significant effect of the double SiO₂ shell in the catalytic performance was demonstrated by both a higher activity to eliminate the nitrogen atom of the indole molecule present in model liquid fuel and the improvement of the catalytic stability reaching four consecutive reaction cycles with only a slight conversion level decrease. Full article

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15 pages, 3109 KiB

Open AccessFeature PaperArticle

Impact of Support (MCF, ZrO₂, ZSM-5) on the Efficiency of Ni Catalyst in High-Temperature Conversion of Lignocellulosic Biomass to Hydrogen-Rich Gas

by Jacek Grams, Robert Ryczkowski, Karolina Chałupka, Izabela Sobczak, Izabela Rzeźnicka and Kamila Przybysz

Materials 2019, 12(22), 3792; https://doi.org/10.3390/ma12223792 - 19 Nov 2019

Cited by 10 | Viewed by 2816

Abstract

The main objective of this work was to evaluate an impact of a support on the efficiency of nickel catalysts in the high-temperature conversion of lignocellulosic biomass to hydrogen-rich gas. The most important parameters influencing catalytic performance of the catalysts were identified. The [...] Read more.

The main objective of this work was to evaluate an impact of a support on the efficiency of nickel catalysts in the high-temperature conversion of lignocellulosic biomass to hydrogen-rich gas. The most important parameters influencing catalytic performance of the catalysts were identified. The properties of three materials (ZSM-5, ZrO₂, and MCF (mesostructured cellular foam)) used as a support differing in surface acidity, surface area, pore structure, ability to interact with an active phase, and resistance to coking, have been studied. The results revealed that Ni/MCF, characterized by large pore size and pore volume, low acidity, small NiO crystallites size, and moderate interaction with the active phase, is the most efficient among studied catalysts, while an application of Ni on ZSM-5 support with high-acidity was not beneficial. The results suggest that structure of the support, in particular larger pore size and a better contact between an active phase and reaction intermediates, play an important role in the formation of gaseous products during thermal decomposition of lignocellulosic feedstock. On the other hand, high acidity of the support did not increase the formation of large amounts of hydrogen-rich gaseous products. Full article

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16 pages, 5946 KiB

Open AccessArticle

Low Temperature NH₃-SCR over Mn-Ce Oxides Supported on MCM-41 from Diatomite

by Mingxuan Ma, Xiaoyu Ma, Suping Cui, Tingting Liu, Yingliang Tian and Yali Wang

Materials 2019, 12(22), 3654; https://doi.org/10.3390/ma12223654 - 06 Nov 2019

Cited by 9 | Viewed by 2555

Abstract

A series of MCM-41 molecular sieves with different molar ratio of template to silicon were synthesized through hydrothermal synthesis method by using cetyltrimethylammonium bromide (CTAB) as the template, diatomite as the silicon source. By using impregnation method, the Mn-Ce/MCM-41 SCR molecular sieve-based catalysts [...] Read more.

A series of MCM-41 molecular sieves with different molar ratio of template to silicon were synthesized through hydrothermal synthesis method by using cetyltrimethylammonium bromide (CTAB) as the template, diatomite as the silicon source. By using impregnation method, the Mn-Ce/MCM-41 SCR molecular sieve-based catalysts were prepared. The results observed that when the molar ratio of template to silicon was 0.2:1, the MCM-41 as catalyst carrier has the highest surface area and largest pore volume, it also presented typically ordered hexagonal arrays of uniform channels. The denitration catalytic material based on this carrier has a high number of Lewis acidic sites, and the denitration efficiency can reach more than 93%. Full article

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17 pages, 6959 KiB

Open AccessArticle

Novel Route to Obtain Carbon Self-Doped TiO₂ Mesoporous Nanoparticles as Efficient Photocatalysts for Environmental Remediation Processes under Visible Light

by Pablo A. Ochoa Rodríguez, Tamara B. Benzaquén, Gina A. Pecchi, Sandra G. Casuscelli, Verónica R. Elías and Griselda A. Eimer

Materials 2019, 12(20), 3349; https://doi.org/10.3390/ma12203349 - 14 Oct 2019

Cited by 8 | Viewed by 2727

Abstract

Titanium dioxide materials were synthesized using two different methods. The samples were characterized by X-ray diffraction (XRD), UV–Visible diffusion reflectance spectroscopy (UV-Vis DR), Raman spectroscopy, N₂ adsorption/desorption, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron spectroscopy (TEM) and X-ray photoelectron [...] Read more.

Titanium dioxide materials were synthesized using two different methods. The samples were characterized by X-ray diffraction (XRD), UV–Visible diffusion reflectance spectroscopy (UV-Vis DR), Raman spectroscopy, N₂ adsorption/desorption, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Although both kind of materials were found to have mesoporous structure and anatase crystalline phase, one of them was obtained from a synthesis method that does not involve the use of surfactants, and therefore, does not require calcination at high temperatures. This implies that the synthesized solid was self-doped with carbon species, coming only from the same source used for titanium. Then, the relationship between the presence of these species, the final calcination temperature, and the photocatalytic activity of the solids was studied in terms of the degradation and mineralization of an Acid Orange 7 aqueous solution, under visible radiation. A photosensitizing effect caused by the non-metal presence, that allows the solid to extend its absorption range, was found. Hence, a novel route to prepare C-modified photoactive mesoporous TiO₂, simpler and cheaper, where neither a template nor an external carbon source is used, could be performed. Full article

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20 pages, 8226 KiB

Open AccessFeature PaperArticle

Mesoporous Palladium N,N’-Bis(3-Allylsalicylidene)o-Phenylenediamine-Methyl Acrylate Resins as Heterogeneous Catalysts for the Heck Coupling Reaction

by Claudio Mella, Cecilia C. Torres, Gina Pecchi and Cristian H. Campos

Materials 2019, 12(16), 2612; https://doi.org/10.3390/ma12162612 - 16 Aug 2019

Cited by 1 | Viewed by 2969

Abstract

Palladium N,N’-bis(3-allylsalicylidene)o-phenylenediamine complex (PdAS) immobilized onto mesoporous polymeric methyl acrylate (MA) based resins (PdAS(x)-MA, x = 1, 2, 5, or 10 wt.%) were successfully prepared as heterogeneous catalysts for the Heck reaction. The catalysts were synthesized via radical suspension polymerization using PdAS as [...] Read more.

Palladium N,N’-bis(3-allylsalicylidene)o-phenylenediamine complex (PdAS) immobilized onto mesoporous polymeric methyl acrylate (MA) based resins (PdAS(x)-MA, x = 1, 2, 5, or 10 wt.%) were successfully prepared as heterogeneous catalysts for the Heck reaction. The catalysts were synthesized via radical suspension polymerization using PdAS as a metal chelate monomer, divinylbenzene and MA as co-monomers. The effect of the PdAS(x) content on the physicochemical properties of the resins is also reported. The catalysts were characterized by using a range of analytical techniques. The large surface area (>580 m²·g⁻¹) and thermal stability (up to 250 °C) of the PdAS(x)-MA materials allows their application as catalysts in the C–C coupling reaction between iodobenzene and MA in the presence of trimethylamine at 120 °C using DMF as the solvent. The PdAS(10)-MA catalyst exhibited the highest catalytic performance with no significant catalytic loss being observed after five reuses, thereby indicating excellent catalyst stability in the reaction medium. Full article

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16 pages, 4283 KiB

Open AccessArticle

Effect of SO₂ on the Selective Catalytic Reduction of NO_x over V₂O₅-CeO₂/TiO₂-ZrO₂ Catalysts

by Yaping Zhang, Peng Wu, Ke Zhuang, Kai Shen, Sheng Wang and Wanqiu Guo

Materials 2019, 12(16), 2534; https://doi.org/10.3390/ma12162534 - 09 Aug 2019

Cited by 13 | Viewed by 2717

Abstract

The effect of SO₂ on the selective catalytic reduction of NO_x by NH₃ over V₂O₅-0.2CeO₂/TiO₂-ZrO₂ catalysts was studied through catalytic activity tests and various characterization methods, like Brunner−Emmet−Teller (BET) surface measurement, [...] Read more.

The effect of SO₂ on the selective catalytic reduction of NO_x by NH₃ over V₂O₅-0.2CeO₂/TiO₂-ZrO₂ catalysts was studied through catalytic activity tests and various characterization methods, like Brunner−Emmet−Teller (BET) surface measurement, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray fluorescence (XRF), hydrogen temperature-programmed desorption (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The results showed that the catalyst exhibited superior SO₂ resistance when the volume fraction of SO₂ was below 0.02%. As the SO₂ concentration further increased, the NO_x conversion exhibited some degree of decline but could restore to the original level when stopping feeding SO₂. The deactivation of the catalyst caused by water in the flue gas was reversible. However, when 10% H₂O was introduced together with 0.06% SO₂, the NO_x conversion was rapidly reduced and became unrecoverable. Characterizations indicated that the specific surface area of the deactivated catalyst was significantly reduced and the redox ability was weakened, which was highly responsible for the decrease of the catalytic activity. XPS results showed that more Ce³⁺ was generated in the case of reacting with SO₂. In situ DRIFTS results confirmed that the adsorption capacity of SO₂ was enhanced obviously in the presence of O₂, while the SO₂ considerably refrained the adsorption of NH₃. The adsorption of NO_x was strengthened by SO₂ to some extent. In addition, NH₃ adsorption was improved after pre-adsorbed by SO₂ + O₂, indicating that the Ce³⁺ and more oxygen vacancy were produced. Full article

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16 pages, 9198 KiB

Open AccessArticle

Synthesis of Petal-Like MnO₂ Nanosheets on Hollow Fe₃O₄ Nanospheres for Heterogeneous Photocatalysis of Biotreated Papermaking Effluent

by Yangliu Du, Fuqiang Li, Yecan Peng, Shaowu Jia, Lei Lan, Jinghong Zhou and Shuangfei Wang

Materials 2019, 12(15), 2346; https://doi.org/10.3390/ma12152346 - 24 Jul 2019

Cited by 3 | Viewed by 3057

Abstract

Owing to the implementation of increasingly stringent water conservation policies and regulations, the pulp and paper mill industry must make increased efforts to meet the limits for pollutant emissions. The primary pretreatment and secondary biochemical treatment methods used currently generally fail to meet [...] Read more.

Owing to the implementation of increasingly stringent water conservation policies and regulations, the pulp and paper mill industry must make increased efforts to meet the limits for pollutant emissions. The primary pretreatment and secondary biochemical treatment methods used currently generally fail to meet the country-specific environmental regulations, and the wastewater must be processed further even after being subjected to secondary biochemical treatments. In this work, we synthesized Fe₃O₄/MnO₂ nanocomposites (FMNs) with a flower-like structure for use in the heterogeneous photocatalytic treatment of biotreated papermaking wastewater. FMNs1.25, which were formed using a KMnO₄/Fe₃O₄ molar ratio of 1.25, could be separated readily using an external magnetic field and exhibited higher photocatalytic activity than those of the other samples as well as MnO₂ and Fe₃O₄. The effects of various experimental parameters on the photocatalytic activity of FMNs1.25, including the initial pH of the wastewater and the catalyst dosage, were determined. The common chemical oxygen demand (COD_Cr) reduction rate in the case of this sample reached 56.58% within 120 min at a pH of 3, the COD_Cr of effluent after treatment was 52.10 mg/L. Further, even under neutral conditions, the COD_Cr of the treated effluent was below the current limit for discharge in China. Moreover, the nanocomposites exhibited good recyclability, and their catalytic activity did not decrease significantly even after five usage cycles. This study should serve as a platform for the fabrication of effective photocatalysts for the advanced treatment of biotreated papermaking effluent and refractory organic wastewater. Full article

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11 pages, 3900 KiB

Open AccessArticle

Cyclodehydration of 1,4-butanediol over Zr-Al Catalysts: Effect of Reaction Medium

by Kuo-Tseng Li and Kuan-Wen Chen

Materials 2019, 12(13), 2092; https://doi.org/10.3390/ma12132092 - 28 Jun 2019

Cited by 5 | Viewed by 3870

Abstract

The conversion of 1,4-butanediol (BDO) to tetrahydrofuran (THF) in aqueous phase is desirable because BDO production technology is shifting to bio-based aqueous fermentation routes. In this study, liquid-phase cyclodehydration of BDO to THF was studied in two reaction media (pure BDO and aqueous [...] Read more.

The conversion of 1,4-butanediol (BDO) to tetrahydrofuran (THF) in aqueous phase is desirable because BDO production technology is shifting to bio-based aqueous fermentation routes. In this study, liquid-phase cyclodehydration of BDO to THF was studied in two reaction media (pure BDO and aqueous BDO feeds) at 200–240 °C using ZrO₂-Al₂O₃ (ZA) mixed oxides, which were made with a co-precipitation method and were characterized with XRD, BET, SEM/EDX, pyridine and n-butylamine adsorptions. The maximum acidity and the largest surface area occurred at Zr/Al atomic ratios of 1/1 (ZA11) and 1/3 (ZA13), respectively. The reaction exhibited pseudo-first-order; aqueous BDO feed had much greater rate constant than pure BDO feed, ascribed to the acidic properties of adsorbed water molecules (coordinated to surface metal cations) for the former case. For pure BDO feed, linear relation was observed between rate constant and catalyst acidity, and ZA11 reached a THF yield of 90.1% at 240 °C. With aqueous BDO feed, rate constant increased linearly with increasing surface area and ZA13 reached a THF yield of 97.1% at 220 °C. The change of optimum catalyst composition with reaction medium suggests that active sites for catalyzing BDO cyclodehydration changed with the reaction environment. Full article

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26 pages, 5883 KiB

Open AccessReview

Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review

by Jianlong Ge, Yifan Zhang and Soo-Jin Park

Materials 2019, 12(12), 1916; https://doi.org/10.3390/ma12121916 - 13 Jun 2019

Cited by 94 | Viewed by 5796

Abstract

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously [...] Read more.

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously limit the practical applications of photocatalysts. As a solution, the introduction of carbonaceous materials with different structures and properties into a photocatalyst system to further increase the activity has attracted much research attention. This mini review surveys the related literatures and highlights recent progress in the development of carbonaceous photocatalysts, which include various metal semiconductors with activated carbon, carbon dots, carbon nanotubes/nanofibers, graphene, fullerene, and carbon sponges/aerogels. Moreover, graphitic carbon nitride is also discussed as a carbon-rich and metal-free photocatalyst. The recently developed synthesis strategies and proposed mechanisms underlying the photocatalytic activity enhancement for different applications are summarized and discussed. Finally, ongoing challenges and the developmental direction for carbonaceous photocatalysts are proposed. Full article

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12 pages, 5839 KiB

Open AccessArticle

Influence of Nature Support on Methane and CO₂ Conversion in a Dry Reforming Reaction over Nickel-Supported Catalysts

by Anis Hamza Fakeeha, Samsudeen Olajide Kasim, Ahmed Aidid Ibrahim, Ahmed Elhag Abasaeed and Ahmed Sadeq Al-Fatesh

Materials 2019, 12(11), 1777; https://doi.org/10.3390/ma12111777 - 31 May 2019

Cited by 23 | Viewed by 3893

Abstract

A promising method to reduce global warming has been methane reforming with CO₂, as it combines two greenhouse gases to obtain useful products. In this study, Ni-supported catalysts were synthesized using the wet impregnation method to obtain 5%Ni/Al₂O₃ [...] Read more.

A promising method to reduce global warming has been methane reforming with CO₂, as it combines two greenhouse gases to obtain useful products. In this study, Ni-supported catalysts were synthesized using the wet impregnation method to obtain 5%Ni/Al₂O₃(SA-5239), 5%Ni/Al₂O₃(SA-6175), 5%Ni/SiO₂, 5%Ni/MCM41, and 5%Ni/SBA15. The catalysts were tested in dry reforming of methane at 700 °C, 1 atm, and a space velocity of 39,000 mL/gcat h, to study the interaction of Ni with the supports, and evaluation was based on CH₄ and CO₂ conversions. 5%Ni/Al₂O₃(SA-6175) and 5%Ni/SiO₂ gave the highest conversion of CH₄ (78 and 75%, respectively) and CO₂ (84 and 82%, respectively). The catalysts were characterized by some techniques. Ni phases were identified by X-ray diffraction patterns. Brunauer–Emmett–Teller analysis showed different surface areas of the catalysts with the least being 4 m²/g and the highest 668 m²/g belonging to 5%Ni/Al₂O₃(SA-5239) and 5%Ni/SBA15, respectively. The reduction profiles revealed weak NiO-supports interaction for 5%Ni/Al₂O₃(SA-5239), 5%Ni/MCM41, and 5%Ni/SBA15; while strong interaction was observed in 5%Ni/Al₂O₃(SA-6175) and 5%Ni/SiO₂. The 5%Ni/Al₂O₃(SA-6175) and 5%Ni/SiO₂ were close with respect to performance; however, the former had a higher amount of carbon deposit, which is mostly graphitic, according to the conducted thermal analysis. Carbon deposits on 5%Ni/SiO₂ were mainly atomic in nature. Full article

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13 pages, 4776 KiB

Open AccessArticle

Highly Active AuCu-Based Catalysts for Acetylene Hydrochlorination Prepared Using Organic Aqua Regia

by Haihua He, Jia Zhao, Bolin Wang, Yuxue Yue, Gangfeng Sheng, Qingtao Wang, Lu Yu, Zhong-Ting Hu and Xiaonian Li

Materials 2019, 12(8), 1310; https://doi.org/10.3390/ma12081310 - 22 Apr 2019

Cited by 8 | Viewed by 3651

Abstract

Development of a sustainable process for designing and synthesising an active and stable catalyst for hydrochlorination of acetylene is challenging, yet crucial, for industrial vinyl chloride monomer (VCM) production. Herein, direct synthesis of bimetallic AuCu catalysts using organic aqua regia (OAR) preparation methods [...] Read more.

Development of a sustainable process for designing and synthesising an active and stable catalyst for hydrochlorination of acetylene is challenging, yet crucial, for industrial vinyl chloride monomer (VCM) production. Herein, direct synthesis of bimetallic AuCu catalysts using organic aqua regia (OAR) preparation methods was investigated. In comparison with conventional aqua regia (AR), bimetallic AuCu catalysts synthesised from OAR exhibit enhanced activity and stability. After careful characterisation of the catalyst samples using X-ray diffraction patterns (XRD), Scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and Temperature-programmed desorption (TPD), this observation was justified for the following reasons: 1) the existence of sulphur and nitrogen atoms stabilised the cationic Au active sites, and 2) OAR helped to sustain the function of the Cu promotor by stabilising it. Advanced understanding on the importance of promoter stability has unveiled new perspectives for this research area. Full article

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14 pages, 4415 KiB

Open AccessArticle

The Influence of Si/Al Ratios on Adsorption and Desorption Characterizations of Pd/Beta Served as Cold-Start Catalysts

by Ming Jiang, Jun Wang, Jianqiang Wang and Meiqing Shen

Materials 2019, 12(7), 1045; https://doi.org/10.3390/ma12071045 - 29 Mar 2019

Cited by 17 | Viewed by 3107

Abstract

The majority of NO_x is exhausted during the cold-start period for the low temperature of vehicle emissions, which can be solved by using Pd/zeolite catalysts to trap NO_x at low temperature and release NO_x at a high temperature that must [...] Read more.

The majority of NO_x is exhausted during the cold-start period for the low temperature of vehicle emissions, which can be solved by using Pd/zeolite catalysts to trap NO_x at low temperature and release NO_x at a high temperature that must be higher than the operating temperature of selective catalytic reduction catalysts (SCR). In this work, several Pd/Beta catalysts were prepared to identify the influence of Si/Al ratios on NO and C₃H₆ adsorption and desorption characterizations. The physicochemical properties were identified using N₂ physical adsorption, Fourier Transform Infrared Spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photo electron spectroscopy (XPS), and Na⁺ titration, while the adsorption and desorption characterizations were investigated by catalyst evaluation. The results indicated that the amount of dispersed Pd ions, the main active sites for NO and C₃H₆ adsorption, decreased with the increase of Si/Al ratios. Besides this, the intensity of Brønsted and Lewis acid decreased with the increase of Si/Al ratios, which also led to the decrease of NO and C₃H₆ adsorption amounts. Therefore, Pd dispersion and the acidic properties of Pd/Beta together determined the adsorption ability of NO and C₃H₆. Moreover, lower Si/Al ratios resulted in the formation of an additional dispersed Pd cationic species, Pd(OH)⁺, from which adsorbed NO released at a much lower temperature. Finally, an optimum Si/Al ratio of Pd/Beta was found at around 55 due to the balanced performance between the adsorption amounts and desorption temperature. Full article

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16 pages, 2723 KiB

Open AccessArticle

Combustion Synthesis of Non-Precious CuO-CeO₂ Nanocrystalline Catalysts with Enhanced Catalytic Activity for Methane Oxidation

by Abdallah F. Zedan and Amina S. AlJaber

Materials 2019, 12(6), 878; https://doi.org/10.3390/ma12060878 - 15 Mar 2019

Cited by 23 | Viewed by 3738

Abstract

In this study, xCuO-CeO₂ mixed oxide catalysts (Cu weight ratio x = 1.5, 3, 4.5, 6 and 15 wt.%) were prepared using solution combustion synthesis (SCS) and their catalytic activities towards the methane (CH₄) oxidation reaction were studied. The combustion [...] Read more.

In this study, xCuO-CeO₂ mixed oxide catalysts (Cu weight ratio x = 1.5, 3, 4.5, 6 and 15 wt.%) were prepared using solution combustion synthesis (SCS) and their catalytic activities towards the methane (CH₄) oxidation reaction were studied. The combustion synthesis of the pure CeO₂ and the CuO-CeO₂ solid solution catalysts was performed using copper and/or cerium nitrate salt as an oxidizer and citric acid as a fuel. A variety of standard techniques, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to reveal the microstructural, crystal, thermal and electronic properties that may affect the performance of CH₄ oxidation. The CuO subphase was detected in the prepared solid solution and confirmed with XRD and Raman spectroscopy, as indicated by the XRD peaks at diffraction angles of 35.3° and 38.5° and the A_g Raman mode at 289 cm⁻¹, which are characteristics of tenorite CuO. A profound influence of Cu content was evident, not only affecting the structural and electronic properties of the catalysts, but also the performance of catalysts in the CH₄ oxidation. The presence of Cu in the CeO₂ lattice obviously promoted its catalytic activity for CH₄ catalytic oxidation. Among the prepared catalysts, the 6% CuO-CeO₂ catalyst demonstrated the highest performance, with T₅₀ = 502 °C and T₈₀ = 556 °C, an activity that is associated with the availability of a fine porous structure and the enhanced surface area of this catalyst. The results demonstrate that nanocrystalline copper-ceria mixed oxide catalysts could serve as an inexpensive and active material for CH₄ combustion. Full article

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