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6 pages, 212 KiB

Open AccessEditorial

Editorial Catalysts: Catalysis for the Removal of Gas-Phase Pollutants

by Antonio Eduardo Palomares

Catalysts 2022, 12(3), 280; https://doi.org/10.3390/catal12030280 - 2 Mar 2022

Viewed by 1670

Abstract

Air pollution is one of the greatest concerns affecting the world today [...] Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

Research

Jump to: Editorial, Review

20 pages, 3426 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO₂ Photocatalysis

by Xiuyan Yang, Jacek A. Koziel, Yael Laor, Wenda Zhu, J. (Hans) van Leeuwen, William S. Jenks, Steven J. Hoff, Jeffrey Zimmerman, Shicheng Zhang, Uzi Ravid and Robert Armon

Catalysts 2020, 10(6), 607; https://doi.org/10.3390/catal10060607 - 1 Jun 2020

Cited by 32 | Viewed by 5011

Abstract

Control of gaseous emissions from livestock operations is needed to ensure compliance with environmental regulations and sustainability of the industry. The focus of this research was to mitigate livestock odor emissions with UV light. Effects of the UV dose, wavelength, TiO₂ catalyst, [...] Read more.

Control of gaseous emissions from livestock operations is needed to ensure compliance with environmental regulations and sustainability of the industry. The focus of this research was to mitigate livestock odor emissions with UV light. Effects of the UV dose, wavelength, TiO₂ catalyst, air temperature, and relative humidity were tested at lab scale on a synthetic mixture of nine odorous volatile organic compounds (VOCs) and real poultry manure offgas. Results show that it was feasible to control odorous VOCs with both photolysis and photocatalysis (synthetic VOCs mixture) and with photocatalysis (manure offgas). The treatment effectiveness R (defined as % conversion), was proportional to the light intensity for synthetic VOCs mixtures and followed an order of UV_185+254 + TiO₂ > UV₂₅₄ + TiO₂ > UV_185+254; no catalyst > UV₂₅₄; no catalyst. VOC conversion R > 80% was achieved when light energy was >~60 J L⁻¹. The use of deep UV (UV_185+254) improved the R, particularly when photolysis was the primary treatment. Odor removal up to ~80% was also observed for a synthetic VOCs mixture, and actual poultry manure offgas. Scale-up studies are warranted. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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13 pages, 3995 KiB

Open AccessArticle

Promoting Effect of Ti Species in MnO_x-FeO_x/Silicalite-1 for the Low-Temperature NH₃-SCR Reaction

by Jialiang Gu, Rudi Duan, Weibin Chen, Yan Chen, Lili Liu and Xidong Wang

Catalysts 2020, 10(5), 566; https://doi.org/10.3390/catal10050566 - 19 May 2020

Cited by 9 | Viewed by 2775

Abstract

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NO_x with NH₃ (NH₃-SCR), respectively. The optimized catalyst demonstrates an increased NO_x [...] Read more.

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NO_x with NH₃ (NH₃-SCR), respectively. The optimized catalyst demonstrates an increased NO_x conversion efficiency of 20% below 150 °C, with a space velocity of 18,000 h⁻¹, which can be attributed to the incorporation of Ti species. The presence of Ti species enhances surface acidity and redox ability of the catalyst without changing the structure of supporter. Moreover, further researches based on in situ NH₃ adsorption reveal that Lewis acid sites linked to Mn⁴⁺ on the surface have a huge influence on the improvement of denitration efficiency of the catalyst at low temperatures. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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16 pages, 6977 KiB

Open AccessArticle

Zeolite Beta Doped with La, Fe, and Pd as a Hydrocarbon Trap

by Rasmus Jonsson, Jungwon Woo, Magnus Skoglundh and Louise Olsson

Catalysts 2020, 10(2), 173; https://doi.org/10.3390/catal10020173 - 2 Feb 2020

Cited by 11 | Viewed by 3666

Abstract

Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta [...] Read more.

Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta (BEA) with Fe, Pd, and La on the storage and release of propene and toluene is studied. Five monolith samples were prepared; Fe/BEA, La/BEA, Pd/BEA, Pd/Fe/BEA, and Pd/La/BEA using incipient wetness impregnation, and the corresponding powder samples were used for catalyst characterization by Inductively coupled plasma sector field mass spectrometry (ICP-SFMS), Temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and Scanning transmission electron microscopy with Energy dispersive X-ray analysis (STEM-EDX). The hydrocarbon trapping ability of the samples was quantified using Temperature-programmed desorption (TPD) of propene and toluene, and in situ Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from the TPD experiments show that the addition of Pd and La to the zeolite affected the release patterns of the stored hydrocarbons on the trapping material in a positive way. The in situ DRIFTS results indicate that these elements provide H-BEA with additional sites for the storage of hydrocarbons. Furthermore, EDX-mapping showed that the La and Pd are located in close connection. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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13 pages, 3237 KiB

Open AccessArticle

Effect of Water Molecule on Photo-Assisted Nitrous Oxide Decomposition over Oxotitanium Porphyrin: A Theoretical Study

by Phornphimon Maitarad, Vinich Promarak, Liyi Shi and Supawadee Namuangruk

Catalysts 2020, 10(2), 157; https://doi.org/10.3390/catal10020157 - 1 Feb 2020

Cited by 2 | Viewed by 2827

Abstract

Water vapor has generally been recognized as an inhibitor of catalysts in nitrous oxide (N₂O) decomposition because it limits the lifetime of catalytic reactors. Oxygen produced in reactions also deactivates the catalytic performance of bulk surface catalysts. Herein, we propose a [...] Read more.

Water vapor has generally been recognized as an inhibitor of catalysts in nitrous oxide (N₂O) decomposition because it limits the lifetime of catalytic reactors. Oxygen produced in reactions also deactivates the catalytic performance of bulk surface catalysts. Herein, we propose a potential catalyst that is tolerant of water and oxygen in the process of N₂O decomposition. By applying density functional theory calculations, we investigated the reaction mechanism of N₂O decomposition into N₂ and O₂ catalyzed by oxotitanium(IV) porphyrin (TiO-por) with interfacially bonded water. The activation energies of reaction Path A and B are compared under thermal and photo-assisted conditions. The obtained calculation results show that the photo-assisted reaction in Path B is highly exothermic and proceeds smoothly with the low activation barrier of 27.57 kcal/mol at the rate determining step. The produced O₂ is easily desorbed from the surface of the catalyst, requiring only 4.96 kcal/mol, indicating the suppression of catalyst deactivation. Therefore, TiO-por is theoretically proved to have the potential to be a desirable catalyst for N₂O decomposition with photo-irradiation because of its low activation barrier, water resistance, and ease of regeneration. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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22 pages, 5598 KiB

Open AccessFeature PaperArticle

Cu-Mg-Fe-O-(Ce) Complex Oxides as Catalysts of Selective Catalytic Oxidation of Ammonia to Dinitrogen (NH₃-SCO)

by Sylwia Górecka, Kateřina Pacultová, Kamil Górecki, Aneta Smýkalová, Katarzyna Pamin and Lucie Obalová

Catalysts 2020, 10(2), 153; https://doi.org/10.3390/catal10020153 - 28 Jan 2020

Cited by 17 | Viewed by 3649

Abstract

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH₃-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 °C. Some catalysts were doped with cerium by the wet [...] Read more.

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH₃-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 °C. Some catalysts were doped with cerium by the wet impregnation method. Not only simple oxides, but also complex spinel-like phases were formed during calcination. The influence of chemical composition, especially the occurrence of spinel phases, copper loading and impregnation by cerium, were investigated. Materials were characterized by several techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption (BET), cyclic voltammetry (CV), temperature programmed reduction (H₂-TPR), UV-vis diffuse reflectance spectroscopy and scanning electron microscopy (SEM). Examined oxides were found to be active as catalysts of selective catalytic oxidation of ammonia with high selectivity to N₂ at temperatures above 300 °C. Catalysts with low copper amounts (up to 12 wt %) impregnated by Ce were slightly more active at lower temperatures (up to 350 °C) than non-impregnated samples. However, when an optimal amount of copper (12 wt %) was used, the presence of cerium did not affect catalytic properties. Copper overloading caused a rearrangement of present phases accompanied by the steep changes in reducibility, specific surface area, direct band gap, crystallinity, dispersion of CuO active phase and Cu²⁺ accessibility leading to the decrease in catalytic activity. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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12 pages, 2025 KiB

Open AccessArticle

The Influence of the Support on the Activity of Mn–Fe Catalysts Used for the Selective Catalytic Reduction of NO_x with Ammonia

by Irene López-Hernández, Jesús Mengual and Antonio Eduardo Palomares

Catalysts 2020, 10(1), 63; https://doi.org/10.3390/catal10010063 - 1 Jan 2020

Cited by 12 | Viewed by 3256

Abstract

Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH₃–SCR of NO_x was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. [...] Read more.

Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH₃–SCR of NO_x was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. Nevertheless, the activity of the bimetallic catalysts depends very much on the support selected. The influence of the support on the catalyst activity has been studied using materials with different textural and acid–base properties. Microporous (BEA-zeolite), mesoporous (SBA15 and MCM41) and bulk (metallic oxides) materials with different acidity have been used as supports for the Mn–Fe catalysts. It has been shown that the activity depends on the acidity of the support and on the surface area. Acid sites are necessary for ammonia adsorption and high surface area produces a better dispersion of the active sites resulting in improved redox properties. The best results have been obtained with the catalysts supported on alumina and on beta zeolite. The first one is the most active at low temperatures but it presents some reversible deactivation in the presence of water. The Mn–Fe catalyst supported on beta zeolite is the most active at temperatures higher than 350 °C, without any deactivation in the presence of water and with a 100% selectivity towards nitrogen. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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11 pages, 3809 KiB

Open AccessArticle

The Structure Effect on the Activity and Strength of an Industrial Honeycomb Catalyst Derived from Different Ti Sources

by Yunjia Li, Abdullahi Abubakar, Lin Huangfu, Changming Li, Jianling Li, Jian Yu and Shiqiu Gao

Catalysts 2020, 10(1), 42; https://doi.org/10.3390/catal10010042 - 31 Dec 2019

Cited by 2 | Viewed by 2052

Abstract

A new honeycomb production process was proposed with both filter cake (from hydrothermal treatment of metatitanic acid) and industrial titanium dioxide as Ti sources. The strength of the obtained pilot product was comparable with the current industrial honeycomb product from only filter cake, [...] Read more.

A new honeycomb production process was proposed with both filter cake (from hydrothermal treatment of metatitanic acid) and industrial titanium dioxide as Ti sources. The strength of the obtained pilot product was comparable with the current industrial honeycomb product from only filter cake, but its denitration (DeNO_x) efficiency was elevated up to 15 percentage points. Multiple characterizations revealed the filter cake and industrial titanium dioxide to be composed of primary particles and secondary particles, respectively, and the introduced secondary particles from industrial titanium dioxide resulted in increased specific surface area and pore size/volume, facilitating the exposure of more active sites with improved activity. Moreover, a positive correlation property was found between the honeycomb strength and crystallinity for the samples from different titanium sources. The filter cake with rich hydroxyl groups and weak crystallinity could be fused more easily among these primary particles to have a higher strength than industrial titanium dioxide, and the primary particle of the filter cake could fill the pile pore of industrial titanium dioxide and act as a solid phase binder to acquire good strength for the honeycomb using both the filter cake and titanium dioxide as Ti sources. The improved honeycomb product with good activity and strength may have more widespread application for the purification of low temperature flue gas in industry. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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11 pages, 2269 KiB

Open AccessArticle

Electric Field Promoted Complete Oxidation of Benzene over PdCe_xCo_y Catalysts at Low Temperature

by Feixiang Shen, Ke Li, Dejun Xu, Xiaobo Li, Xuteng Zhao, Ting Chen, Reggie Zhan and He Lin

Catalysts 2019, 9(12), 1071; https://doi.org/10.3390/catal9121071 - 16 Dec 2019

Cited by 5 | Viewed by 2905

Abstract

The application of electric field promotes benzene oxidation significantly over Pd/Co_xCe_y catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 [...] Read more.

The application of electric field promotes benzene oxidation significantly over Pd/Co_xCe_y catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 °C lower than the temperature demanded for complete benzene conversion without electric field. The introduction of electric field can save Pd loading in the catalysts while maintaining high benzene conversion. The characterization experiments showed that CeO₂ reduction was accelerated with electric field and created more active oxygen, promoting the formation of active sites on the catalyst surface. The OH removal ability of PdO was enhanced by forming CoO(OH) species, which can easily dehydroxylate since the reduction of Co³⁺ was promoted by the electric field. The optimized Ce/Co ratio is a balance between oxygen availability and OH removal ability. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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15 pages, 4811 KiB

Open AccessArticle

{CeO₂/Bi₂Mo_1−xRu_xO₆} and {Au/Bi₂Mo_1−xRu_xO₆} Catalysts for Low-Temperature CO Oxidation

by Edson Edain González, Ricardo Rangel, Javier Lara, Pascual Bartolo-Pérez, Juan José Alvarado-Gil, Donald Homero Galván and Rafael García

Catalysts 2019, 9(11), 947; https://doi.org/10.3390/catal9110947 - 12 Nov 2019

Cited by 4 | Viewed by 2662

Abstract

Nowadays, one of the most important challenges that humanity faces is to find alternative ways of reducing pollutant emissions. CeO₂/Bi₂Mo_1−xRu_xO₆ and Au/Bi₂Mo_1−xRu_xO₆ catalysts were prepared to efficiently [...] Read more.

Nowadays, one of the most important challenges that humanity faces is to find alternative ways of reducing pollutant emissions. CeO₂/Bi₂Mo_1−xRu_xO₆ and Au/Bi₂Mo_1−xRu_xO₆ catalysts were prepared to efficiently transform carbon monoxide (CO) to carbon dioxide (CO₂) at low temperatures. The systems were prepared in a two-step process. First, Bi₂Mo_1−xRu_xO₆ supports were synthesized through the hydrothermal procedure under microwave heating. Then, CeO₂ was deposited on Bi₂Mo_1−xRu_xO₆ using the wet impregnation method, while the incipient impregnation method was selected to deposit gold nanoparticles. The CeO₂/Bi₂Mo_1−xRu_xO₆ and Au/Bi₂Mo_1−xRu_xO₆ catalysts were characterized using SEM microscopy and XRD. Furthermore, energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used. Tests were carried out for the supported catalysts in CO oxidation, and high conversion values, nearing 100%, was observed in a temperature range of 100 to 250 °C. The results showed that the best system was the Au/Bi₂Mo_0.95Ru_0.05O₆ catalyst, with CO oxidation starting at 50 °C and reaching 100% conversion at 186 °C. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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20 pages, 5368 KiB

Open AccessArticle

Structure and Catalytic Behavior of Alumina Supported Bimetallic Au-Rh Nanoparticles in the Reduction of NO by CO

by Xianwei Wang, Hongji Wang, Nobutaka Maeda and Alfons Baiker

Catalysts 2019, 9(11), 937; https://doi.org/10.3390/catal9110937 - 8 Nov 2019

Cited by 13 | Viewed by 3341

Abstract

Alumina-supported bimetallic AuRh catalysts, as well as monometallic reference catalysts, were examined with regard to their structural and catalytic properties in the reduction of NO by CO. Depending on the molar ratio of Au:Rh, the nanoparticles prepared by borohydride co-reduction of corresponding metal [...] Read more.

Alumina-supported bimetallic AuRh catalysts, as well as monometallic reference catalysts, were examined with regard to their structural and catalytic properties in the reduction of NO by CO. Depending on the molar ratio of Au:Rh, the nanoparticles prepared by borohydride co-reduction of corresponding metal salt solutions had a size of 3.5–6.7 nm. The particles consisted of well-dispersed noble metal atoms with some enrichment of Rh in their surface region. NO conversion of AuRh/Al₂O₃ shifted to lower temperatures with increasing Rh content, reaching highest activity and highest N₂ selectivity for the monometallic Rh/Al₂O₃ catalyst. This behavior is attributed to the enhanced adsorption of CO on the bimetallic catalyst resulting in unfavorable cationic Rh clusters Rh⁺-(CO)₂. Doping with ceria of AuRh/Al₂O₃ and Rh/Al₂O₃ catalysts increased the surface population of metallic Rh sites, which are considered most active for the reduction of NO by CO and enhancement of the formation of intermediate isocyanate (-NCO) surface species and their reaction with NO to form N₂ and CO₂. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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14 pages, 2773 KiB

Open AccessArticle

Deactivation of Cu/SSZ-13 NH₃-SCR Catalyst by Exposure to CO, H₂, and C₃H₆

by Xavier Auvray, Oana Mihai, Björn Lundberg and Louise Olsson

Catalysts 2019, 9(11), 929; https://doi.org/10.3390/catal9110929 - 6 Nov 2019

Cited by 9 | Viewed by 4902

Abstract

Lean nitric oxide (NO_x)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NO_x. The combination of LNT and SCR catalysts improves overall NO_x removal, but there is a risk that the SCR catalyst [...] Read more.

Lean nitric oxide (NO_x)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NO_x. The combination of LNT and SCR catalysts improves overall NO_x removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H₂, C₃H₆, and the combination of CO + H₂ were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH₃-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH₃ and NO). The combination of CO and H₂ was especially detrimental to SCR activity and to NH₃ oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH₃ oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu²⁺/CuOH⁺ ratio in favor of the monovalent CuOH⁺ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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16 pages, 1719 KiB

Open AccessArticle

Cobalt Oxide Catalysts in the Form of Thin Films Prepared by Magnetron Sputtering on Stainless-Steel Meshes: Performance in Ethanol Oxidation

by Květa Jirátová, Roman Perekrestov, Michaela Dvořáková, Jana Balabánová, Pavel Topka, Martin Koštejn, Jiří Olejníček, Martin Čada, Zdeněk Hubička and František Kovanda

Catalysts 2019, 9(10), 806; https://doi.org/10.3390/catal9100806 - 26 Sep 2019

Cited by 31 | Viewed by 4253

Abstract

Catalytic total oxidation is an effective procedure to minimize emissions of volatile organic compounds (VOC) emissions in industrial gases. Catalysts in the form of meshes are remarkable as they minimize the internal diffusion of reactants during the reaction as well as the need [...] Read more.

Catalytic total oxidation is an effective procedure to minimize emissions of volatile organic compounds (VOC) emissions in industrial gases. Catalysts in the form of meshes are remarkable as they minimize the internal diffusion of reactants during the reaction as well as the need of expensive active components. In this paper, various conditions of radio frequency magnetron sputtering of cobalt on stainless-steel meshes was applied during catalyst preparation. Properties of the supported Co₃O₄ catalysts were characterized by SEM, XRD, temperature programmed reduction (H₂-TPR), FTIR, XPS, and Raman spectroscopy. Catalytic activity was examined in deep oxidation of ethanol chosen as a model VOC. Performance of the catalysts depended on the amount of Co₃O₄ deposited on the supporting meshes. According to specific activities (the amounts of ethanol converted per unit weight of Co₃O₄), smaller Co₃O₄ particle size led to increased catalytic activity. The catalyst prepared by sputtering in an Ar+O₂ atmosphere without calcination showed the highest catalytic activity, which decreased after calcination due to enlargement of Co₃O₄ particles. However, specific activity of this catalyst was more than 20 times higher than that of pelletized commercial Co₃O₄ catalyst used for comparison. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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15 pages, 2552 KiB

Open AccessArticle

Effect of Copper Precursors on the Activity and Hydrothermal Stability of Cu^II−SSZ−13 NH₃−SCR Catalysts

by Meixin Wang, Zhaoliang Peng, Changming Zhang, Mengmeng Liu, Lina Han, Yaqin Hou, Zhanggen Huang, Jiancheng Wang, Weiren Bao and Liping Chang

Catalysts 2019, 9(9), 781; https://doi.org/10.3390/catal9090781 - 19 Sep 2019

Cited by 10 | Viewed by 2930

Abstract

A series of Cu^II−SSZ−13 catalysts are prepared by in-situ hydrothermal method using different copper precursors (Cu^II(NO₃)₂, Cu^IISO₄, Cu^IICl₂) for selective catalytic reduction of NO by NH₃ [...] Read more.

A series of Cu^II−SSZ−13 catalysts are prepared by in-situ hydrothermal method using different copper precursors (Cu^II(NO₃)₂, Cu^IISO₄, Cu^IICl₂) for selective catalytic reduction of NO by NH₃ in a simulated diesel vehicle exhaust. The catalysts were characterized by X−ray diffraction (XRD), scanning electron microscope (SEM), X−ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption, hydrogen-temperature-programmed reduction (H₂−TPR), ammonia temperature-programmed desorption (NH₃−TPD), and ²⁷Al and ²⁹Si solid state Nuclear Magnetic Resonance (NMR). The Cu^II−SSZ−13 catalyst prepared by Cu^II(NO₃)₂ shows excellent catalytic activity and hydrothermal stability. The NO conversion of Cu^II−SSZ−13 catalyst prepared by Cu^II(NO₃)₂ reaches 90% at 180 °C and can remain above 90% at a wide temperature range of 180–700 °C. After aging treatment at 800 °C for 20 h, the Cu^II−SSZ−13 catalyst prepared by Cu^II(NO₃)₂ still exhibits above 90% NO conversion under a temperature range of 240–600 °C. The distribution of Cu species and the Si/Al ratios in the framework of the synthesized Cu^II−SSZ−13 catalysts, which determine the catalytic activity and the hydrothermal stability of the catalysts, are dependent on the adsorption capacity of anions to the cation during the crystallization process due to the so called Hofmeister anion effects, the NO₃⁻ ion has the strongest adsorption capacity among the three kinds of anions (NO₃⁻, Cl⁻, and SO₄²⁻), followed by Cl^– and SO₄^2– ions. Therefore, the Cu^II−SSZ−13 catalyst prepared by Cu^II(NO₃)₂ possess the best catalytic ability and hydrothermal stability. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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13 pages, 2826 KiB

Open AccessArticle

Recycling of Gas Phase Residual Dichloromethane by Hydrodechlorination: Regeneration of Deactivated Pd/C Catalysts

by Sichen Liu, María Martin-Martinez, María Ariadna Álvarez-Montero, Alejandra Arevalo-Bastante, Juan José Rodriguez and Luisa María Gómez-Sainero

Catalysts 2019, 9(9), 733; https://doi.org/10.3390/catal9090733 - 29 Aug 2019

Cited by 9 | Viewed by 4062

Abstract

Dichloromethane (DCM) is an important pollutant with very harmful effects on human health and the environment. Catalytic hydrodechlorination (HDC) is an environmentally friendly technology for its removal from gas streams; it avoids the formation of hazardous pollutants like dioxins and phosgene (produced by [...] Read more.

Dichloromethane (DCM) is an important pollutant with very harmful effects on human health and the environment. Catalytic hydrodechlorination (HDC) is an environmentally friendly technology for its removal from gas streams; it avoids the formation of hazardous pollutants like dioxins and phosgene (produced by other techniques), and the products obtained can be reused in other industries. When compared to other precious metals, Pd/C catalyst exhibited a better catalytic activity. However, the catalyst showed a significant deactivation during the reaction. In this study, the oxidation state and particle size of Pd was monitored with time on stream in order to elucidate the transformations that the catalyst undergoes during HDC. The deactivation can be ascribed to the formation of a new PdC_x phase during the first hour of reaction. Carbon atoms incorporated to Pd lattice come from (chloro)-hydrocarbons adsorbed in the metallic species, whose transformation is promoted by the HCl originating in the reaction. Nevertheless, the catalyst was regenerated by air flow treatment at 250 °C, recovering the catalyst more than 80% of initial DCM conversion. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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19 pages, 6237 KiB

Open AccessArticle

High Performance of Mn-Doped MgAlO_x Mixed Oxides for Low Temperature NO_x Storage and Release

by Chenchen Cui, Junwei Ma, Zhongpeng Wang, Wei Liu, Wenxu Liu and Liguo Wang

Catalysts 2019, 9(8), 677; https://doi.org/10.3390/catal9080677 - 9 Aug 2019

Cited by 10 | Viewed by 3226

Abstract

NO_x storage-reduction (NSR) is a potential approach for the effective removal of NO_x under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlO_x) with high performance for low temperature NO_x storage and release were derived from [...] Read more.

NO_x storage-reduction (NSR) is a potential approach for the effective removal of NO_x under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlO_x) with high performance for low temperature NO_x storage and release were derived from hydrotalcites precursors prepared by a facile coprecipitation method. The catalysts were characterized by X-ray diffraction (XRD), SEM, N₂ adsorption-desorption, H₂-TPR, FT-IR, and X-ray photoelectron spectroscopy (XPS) techniques. The Mn-doped MgAlO_x catalysts exhibited high NO_x storage capacity (NSC) at low temperature range (150–300 °C), which was related to their increased surface area, improved reducibility and higher surface Mn³⁺ content. The largest NSC measured, 426 μmol/g, was observed for NO_x adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NO_x adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NO_x storage and release due to their ability to store NO_x mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NO_x removal rate of Mn15 sample can reach above 70% within the wide temperature range of 150–250 °C. Besides, the influence of CO₂, soot, H₂O and SO₂ on NO_x storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NO_x storage capacity, NSR cycling performance, and resistance to CO₂, soot, SO₂ and H₂O, the Mn-doped MgAlO_x NSR catalysts have broad application prospects in NO_x control at low temperatures. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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14 pages, 7062 KiB

Open AccessArticle

A Novel Porous Ceramic Membrane Supported Monolithic Cu-Doped Mn–Ce Catalysts for Benzene Combustion

by Zhaxi Cuo, Dongdong Wang, Yan Gong, Feng Zhao, Haidi Liu and Yunfa Chen

Catalysts 2019, 9(8), 652; https://doi.org/10.3390/catal9080652 - 30 Jul 2019

Cited by 11 | Viewed by 2958

Abstract

Porous ceramic membranes (PCMs) are considered as an efficient hot gas filtration material in industrial systems. Functionalization of the PCMs with high-efficiency catalysts for the abatement of volatile organic compounds (VOCs) during dust elimination is a promising way to purify the industrial exhaust [...] Read more.

Porous ceramic membranes (PCMs) are considered as an efficient hot gas filtration material in industrial systems. Functionalization of the PCMs with high-efficiency catalysts for the abatement of volatile organic compounds (VOCs) during dust elimination is a promising way to purify the industrial exhaust gases. In this work, we prepared PCMs (porosity: 70%) in a facile sintering process and integrated Cu-doped Mn–Ce oxides into the PCMs as monolithic catalysts by the sol–gel method for benzene oxidation. Through this method, the catalysts are dispersed evenly throughout the PCMs with excellent adhesion, and the catalytic PCMs provided more active sites for the reactant gases during the catalytic reaction process compared to the powder catalysts. The physicochemical properties of PCMs and catalytic PCMs were characterized systematically, and the catalytic activities were measured in total oxidation of benzene. As a result, all the prepared catalytic PCMs exhibited high catalytic activity for benzene oxidation. Significantly, the monolithic catalyst of Cu_0.2Mn_0.6Ce_0.2/PCMs obtained the lowest temperature for benzene conversion efficiency of 90% (T₉₀) at 212 °C with a high gaseous hourly space velocity of 5000 h⁻¹ and showed strong resistance to high humidity (90 vol.%, 20 °C) with long-term stability in continuous benzene stream, which is caused by abundant active adsorbed oxygen, more surficial oxygen vacancy, and lower-temperature reducibility. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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17 pages, 5520 KiB

Open AccessArticle

Effect of Small Molecular Organic Acids on the Structure and Catalytic Performance of Sol–Gel Prepared Cobalt Cerium Oxides towards Toluene Combustion

by Jianmeng Chen, Junhong Lin, Jinghuan Chen and Jiade Wang

Catalysts 2019, 9(5), 483; https://doi.org/10.3390/catal9050483 - 24 May 2019

Cited by 7 | Viewed by 3584

Abstract

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and [...] Read more.

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and tartaric acid (TA), were selected. The effect of organic acids on the composition, structure, morphology and catalytic performance of metal oxides is discussed in details. The cobalt cerium oxides catalysts were characterized by various techniques, including TG–DSC, XRD, SEM–EDS, N₂–adsorption and desorption, XPS, and H₂–TPR analyses. The results show that the nature of organic acids influenced the hydrolysis, condensation and calcination processes, as well as strongly affected the textural and physicochemical properties of the metal oxides synthesized. The best catalytic activity was obtained with the CoCe–MA catalyst, and the toluene conversion reached 90% at 242 °C. This outstanding catalytic activity could be related to its textural, redox properties and unique surface compositions and oxidation states. In addition, the CoCe–MA catalyst also showed excellent stability in long–time activity test. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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15 pages, 9362 KiB

Open AccessArticle

Self-Templating Synthesis of 3D Hierarchical NiCo₂O₄@NiO Nanocage from Hydrotalcites for Toluene Oxidation

by Dongdong Wang, Shuangde Li, Yingchao Du, Xiaofeng Wu and Yunfa Chen

Catalysts 2019, 9(4), 352; https://doi.org/10.3390/catal9040352 - 11 Apr 2019

Cited by 37 | Viewed by 5433

Abstract

Rational design LDHs (layered double hydroxides) with 3D hierarchical hollow structures have generated widespread interest for catalytic oxidation due to the high complexity in shell architecture and composition. Herein, we reported a handy two-step method to construct a 3D hierarchical NiCo₂O [...] Read more.

Rational design LDHs (layered double hydroxides) with 3D hierarchical hollow structures have generated widespread interest for catalytic oxidation due to the high complexity in shell architecture and composition. Herein, we reported a handy two-step method to construct a 3D hierarchical NiCo₂O₄/NiO nanocage. This synthetic strategy contains a partial in situ transformation of ZIF-67 (zeolitic imidazolate framework-67) into Co-NiLDH yolk-shelled structures following ethanol etching, and a structure-preserved transformation from Co-NiLDH@ZIF-67 to a biphase nanocage following calcination. CoNi-yh-T (varied reaction time and calcination temperature) nanocages were investigated systematically by Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), H₂- temperature-programmed reduction (TPR), NH₃-temperature-programmed desorption (TPD) and studied for toluene oxidation. The CoNi-6h-350 sample showed much higher activity with 90% toluene conversion (T₉₀) at 229 °C at a high space velocity (SV = 60,000 mL g⁻¹ h⁻¹) than other catalysts (T₉₀ >240 °C). Abundant surface high valence Co ions caused by the novel hierarchical nanostructures, together with adsorbed oxygen species and abundant medium-strength surface acid sites, played a key role for catalytic activities. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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17 pages, 6822 KiB

Open AccessArticle

Selective Catalytic Reduction of Nitric Oxide with Propylene over Fe/Beta Catalysts Under Lean-Burn Conditions

by Hao Zhou, Mengyao Ge, Huishuang Zhao, Shiguo Wu, Mengyu Li and Yaxin Su

Catalysts 2019, 9(2), 205; https://doi.org/10.3390/catal9020205 - 23 Feb 2019

Cited by 14 | Viewed by 5261

Abstract

Fe/Beta catalysts were used for the selective catalytic reduction of nitric oxide with propylene (C₃H₆-SCR) under lean-burn conditions, which were prepared by liquid ion-exchange (LIE), solid-state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods. The iron species on Fe/Beta were [...] Read more.

Fe/Beta catalysts were used for the selective catalytic reduction of nitric oxide with propylene (C₃H₆-SCR) under lean-burn conditions, which were prepared by liquid ion-exchange (LIE), solid-state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods. The iron species on Fe/Beta were characterized and identified by a combination of several characterization techniques. The results showed preparation methods had a significant influence on the composition and distribution of iron species, LIE method inclined to produce more isolated Fe³⁺ ions at ion-exchanged sites than IWI and SIE method. C₃H₆-SCR activity tests demonstrated Fe/Beta(LIE) possessed remarkable catalytic activity and N₂ selectivity at temperature 300–450 °C. Kinetic studies of C₃H₆-SCR reaction suggested that isolated Fe³⁺ species were more active for NO reduction, whereas Fe₂O₃ nanoparticles enhanced the hydrocarbon combustion in excess of oxygen. According to the results of in situ DRIFTS, more isolated Fe³⁺ sites on Fe/Beta(LIE) would promote the formation of the key intermediates, i.e., NO₂ adspecies and formate species, then led to the superior C₃H₆-SCR activity. The slight decrease of SCR activity after hydrothermal aging of Fe/Beta(LIE) catalyst might be due to the migration of isolated Fe³⁺ ions into oligomeric clusters and/or Fe₂O₃ nanoparticles. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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17 pages, 3126 KiB

Open AccessArticle

Bimetallic AgFe Systems on Mordenite: Effect of Cation Deposition Order in the NO Reduction with C₃H₆/CO

by Perla Sánchez-López, Yulia Kotolevich, Serguei Miridonov, Fernando Chávez-Rivas, Sergio Fuentes and Vitalii Petranovskii

Catalysts 2019, 9(1), 58; https://doi.org/10.3390/catal9010058 - 8 Jan 2019

Cited by 20 | Viewed by 4047

Abstract

Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying [...] Read more.

Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV–Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag⁺ is reduced with the participation of the Fe²⁺/Fe³⁺ ions transition and is present in the form of a Ag reduced state in different proportions of Ag_m clusters and Ag⁰ NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C₃H₆/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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13 pages, 3843 KiB

Open AccessArticle

High Selectivity and Stability of Nickel Catalysts for CO₂ Methanation: Support Effects

by Jeremías Martínez, Edgar Hernández, Salvador Alfaro, Ricardo López Medina, Guadalupe Valverde Aguilar, Elim Albiter and Miguel A. Valenzuela

Catalysts 2019, 9(1), 24; https://doi.org/10.3390/catal9010024 - 30 Dec 2018

Cited by 39 | Viewed by 6890

Abstract

In this work, we present an investigation concerning the evaluation of the catalytic properties of Ni nanoparticles supported on ZrO₂, SiO₂, and MgAl₂O₄ for CO₂ hydrogenation to methane. The supports were prepared by coprecipitation and [...] Read more.

In this work, we present an investigation concerning the evaluation of the catalytic properties of Ni nanoparticles supported on ZrO₂, SiO₂, and MgAl₂O₄ for CO₂ hydrogenation to methane. The supports were prepared by coprecipitation and sol-gel, while Ni was incorporated by impregnation (10–20 wt %). X-ray diffraction, nitrogen physisorption, temperature-programmed reduction, H₂ pulse chemisorption, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were the main characterization techniques employed. A laboratory fixed-bed reactor operated at atmospheric pressure, a temperature range of 350–500 °C, and a stoichiometric H₂/CO₂ molar ratio was used for catalyst evaluation. The most outstanding results were obtained with nickel catalysts supported on ZrO₂ with CO₂ conversions of close to 60%, and selectivity to methane formation was 100% on a dry basis, with high stability after 250 h of reaction time. The majority presence of tetragonal zirconia, as well as the strong Ni–ZrO₂ interaction, were responsible for the high catalytic performance of the Ni/ZrO₂ catalysts. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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20 pages, 5273 KiB

Open AccessArticle

AuPd/3DOM TiO₂ Catalysts: Good Activity and Stability for the Oxidation of Trichloroethylene

by Xing Zhang, Yuxi Liu, Jiguang Deng, Kunfeng Zhang, Jun Yang, Zhuo Han and Hongxing Dai

Catalysts 2018, 8(12), 666; https://doi.org/10.3390/catal8120666 - 18 Dec 2018

Cited by 17 | Viewed by 4371

Abstract

Three-dimensionally ordered macroporous (3DOM) TiO₂-supported AuPd alloy (xAu_yPd/3DOM TiO₂ (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials [...] Read more.

Three-dimensionally ordered macroporous (3DOM) TiO₂-supported AuPd alloy (xAu_yPd/3DOM TiO₂ (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49–53 m²/g. The noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the surface of 3DOM TiO₂. The 0.91Au_0.51Pd/3DOM TiO₂ sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au_0.51Pd/3DOM TiO₂ sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H₂O introduction of 0.91Au_0.51Pd/3DOM TiO₂ was reversible, while that induced by CO₂ addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au_0.51Pd/3DOM TiO₂. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au_0.51Pd/3DOM TiO₂ sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO₂ as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au_0.51Pd/3DOM TiO₂. We believe that 0.91Au_0.51Pd/3DOM TiO₂ may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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12 pages, 2028 KiB

Open AccessArticle

Photocatalytic Oxidation of Toluene on Fluorine Doped TiO₂/SiO₂ Catalyst Under Simulant Sunlight in a Flat Reactor

by Lu Qiu, Yanan Wang, Hanlinag Li, Gang Cao, Feng Ouyang and Rongshu Zhu

Catalysts 2018, 8(12), 596; https://doi.org/10.3390/catal8120596 - 1 Dec 2018

Cited by 23 | Viewed by 4741

Abstract

Improving the capacity of TiO₂ semiconductors for visible light response is a key problem for utilization of solar energy in photo-catalytic degradation of organic pollutants. Both catalyst character and reactor conditions are important for the reaction efficiency. The fluorine ion doped TiO [...] Read more.

Improving the capacity of TiO₂ semiconductors for visible light response is a key problem for utilization of solar energy in photo-catalytic degradation of organic pollutants. Both catalyst character and reactor conditions are important for the reaction efficiency. The fluorine ion doped TiO₂/SiO₂ catalyst was prepared by sol-gel method using HF solution as fluorine source. The activity test and UV–vis results indicated that this catalyst was superior to TiO₂ P25 in photocatalytic oxidation of gaseous toluene under simulant sunlight irradiation due to the enhancement of visible and ultraviolet light absorbance. GC-MS results indicated that the main intermediates accumulated on active sites included benzoic acid, benzaldehyde, and phenol. A flat interlaid reactor was designed for continuous treatment of the stream with F-TiO₂/SiO₂ film. The results showed that coating the catalyst on the surface of both top and bottom glass substrates, through the knife coating method with an optimal reactor height, attained the highest efficiency. In addition, the presence of water and oxygen enhanced the oxidation of toluene due to the generation of hydroxyl radicals and peroxy radicals, respectively. The toluene oxidation rate increased with the increase in water vapor concentration in the range of 0~60 vol.%. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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Review

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18 pages, 3518 KiB

Open AccessReview

Analysis of Research Status of CO₂ Conversion Technology Based on Bibliometrics

by Yi Xing, Zhiliang Ma, Wei Su, Qunhui Wang, Xiaona Wang and Hui Zhang

Catalysts 2020, 10(4), 370; https://doi.org/10.3390/catal10040370 - 30 Mar 2020

Cited by 32 | Viewed by 4728

Abstract

The concentration of carbon dioxide in the air has risen sharply due to the use of fossil fuels, causing environmental problems such as the greenhouse effect, which seriously threatens humans’ living environment. Reducing carbon dioxide emissions while addressing energy shortages requires the conversion [...] Read more.

The concentration of carbon dioxide in the air has risen sharply due to the use of fossil fuels, causing environmental problems such as the greenhouse effect, which seriously threatens humans’ living environment. Reducing carbon dioxide emissions while addressing energy shortages requires the conversion of CO₂ into high added-value products. In this paper, the status of CO₂ conversion research in the past ten years is analyzed using the bibliometric method; the influence of countries and institutions, journal article statistics and other aspects are statistically analyzed, and the research status of carbon dioxide catalytic conversion is briefly introduced. Finally, according to the analysis results and the existing problems of CO₂ catalytic conversion research, the future development direction of CO₂ catalytic conversion research is prospected. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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