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12 pages, 6889 KiB

Open AccessArticle

Unraveling FeO_x Nanoparticles Confined on Fibrous Mesoporous Silica Catalyst Construction and CO Catalytic Oxidation Performance

by Guobo Li, Weiwei Feng, Yiwei Luo, Jie Yan, Yining Cai, Yiling Wang, Shule Zhang, Wenming Liu and Honggen Peng

Catalysts 2024, 14(1), 63; https://doi.org/10.3390/catal14010063 - 14 Jan 2024

Viewed by 1042

Abstract

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this study, a mesoporous silica material, KCC-1, was synthesized and used as a carrier with a high specific surface area to confine active component FeO_x nanoparticles (NPs), and [...] Read more.

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this study, a mesoporous silica material, KCC-1, was synthesized and used as a carrier with a high specific surface area to confine active component FeO_x nanoparticles (NPs), and the CO catalytic oxidation performance of x%Fe@KCC-1 catalysts (x represents the mass loading of Fe) was studied. The experimental results showed that due to its large specific surface area and abundant mesopores, the FeO_x NPs were highly dispersed on the surface of the KCC-1 carrier. The particle size of FeO_x was very small, resulting in strong interactions between FeO_x NPs and KCC-1, which enhanced the catalytic oxidation reaction on the catalyst. The FeO_x loading improved the CO adsorption capability of the catalyst, which facilitated the catalytic oxidation of CO, with the 7%Fe@KCC-1 catalyst achieving 100% CO conversion at 160 °C. The CO catalytic removal mechanism was investigated by a combination of in-situ DRIFTS and DFT calculations. This study advances scientific understanding of the application potential of nano-catalysts in important oxidation reactions and provides valuable insights into the development of efficient CO oxidation catalysts. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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13 pages, 3290 KiB

Open AccessFeature PaperArticle

Cerium Doping Effect in 3DOM Perovskite-Type La_2−xCe_xCoNiO₆ Catalysts for Boosting Soot Oxidation

by Kaixuan Chen, Linsheng Xu, Yuanfeng Li, Jing Xiong, Dawei Han, Yaxiao Ma, Peng Zhang, Haoqi Guo and Yuechang Wei

Catalysts 2024, 14(1), 18; https://doi.org/10.3390/catal14010018 - 26 Dec 2023

Viewed by 1132

Abstract

Herein, we present an in-depth investigation into the enhancement of catalytic soot oxidation through cerium-doped three-dimensional ordered macroporous (3DOM) La-Co-Ni-based perovskites synthesized with the colloidal crystal template (CCT) method. The 3DOM structure significantly contributes to the accessibility and interaction efficiency between soot and [...] Read more.

Herein, we present an in-depth investigation into the enhancement of catalytic soot oxidation through cerium-doped three-dimensional ordered macroporous (3DOM) La-Co-Ni-based perovskites synthesized with the colloidal crystal template (CCT) method. The 3DOM structure significantly contributes to the accessibility and interaction efficiency between soot and catalyst. Based on the results of powder X-ray diffraction (XRD), N₂ adsorption-desorption measurements, scanning electron microscopy (SEM), temperature-programmed oxidation of NO (NO-TPO), temperature-programmed reduction of H₂ (H₂-TPR), in situ infrared Fourier transform spectroscopy (In-situ DRIFTS), and temperature-programmed oxidation (TPO) reactions, the role of cerium doping in modifying the structural and catalytic properties of 3DOM perovskite-type La_2−xCe_xCoNiO₆ catalysts was investigated systematically. The optimized cerium doping ratio in La_2−xCe_xCoNiO₆ catalysts can improve the microenvironment for efficient soot-catalyst contact, enhancing the catalytic activity of soot oxidation. Among the catalysts, the 3DOM La_0.8Ce_1.2CoNiO₆ catalyst shows the highest catalytic activity for soot oxidation, whose T₁₀, T₅₀, and T₉₀ values are 306 °C, 356 °C, and 402 °C, respectively. The mechanism of the cerium doping effect for boosting soot oxidation is proposed: The doping of Ce ions can increase the surface oxygen species, which is the main active species for promoting the key step of NO oxidation to NO₂ in catalyzing soot oxidation. This research provides a new strategy to develop high-efficient non-noble metal catalysts for soot oxidation in pollution control and sustainable environmental practices. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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14 pages, 8293 KiB

Open AccessFeature PaperArticle

Steam Treatment Promotion on the Performance of Pt/CeO₂ Three-Way Catalysts for Emission Control of Natural Gas-Fueled Vehicles

by Xi Liu, Yuankai Shao, Xiaoning Ren, Anqi Dong, Kaixiang Li, Bingjie Zhou, Chunqing Yang, Yatao Liu and Zhenguo Li

Catalysts 2024, 14(1), 17; https://doi.org/10.3390/catal14010017 - 25 Dec 2023

Viewed by 1104

Abstract

Three-way catalyst (TWC) is the mainstream technology for stoichiometric natural gas vehicle gas emission purification to meet the China VI emission standard for heavy-duty vehicles. Due to the high price of Pd-Rh TWC widely used at present, it is of great significance to [...] Read more.

Three-way catalyst (TWC) is the mainstream technology for stoichiometric natural gas vehicle gas emission purification to meet the China VI emission standard for heavy-duty vehicles. Due to the high price of Pd-Rh TWC widely used at present, it is of great significance to develop cheaper Pt-only catalysts as substitutes. However, there are few studies on Pt-only TWC, especially for natural gas vehicles. It remains a formidable challenge to develop Pt-only TWC with excellent activity and stability. In this study, we significantly improved the catalytic performance of Pt/CeO₂ TWC through thermal treatment, especially steam treatment at 800 °C, and used XRD, TEM, H₂-TPR, and XPS techniques to investigate how Pt/CeO₂ can be activated via these treatments. Our results suggested that after these treatments, CeO₂ crystallites sintered slightly, while platinum particles remained highly dispersed. Moreover, these treatments also weakened the Pt-CeO₂ interaction, promoted the formation of oxygen vacancies in CeO₂ support, and generated a new type of active surface oxygen in the vicinity of Pt^δ+, thus improving the activity of the catalyst. After 800 °C steam treatment, the T₅₀ of CH₄ and NO decreased by 31 and 36 °C, respectively. The results obtained in this study provide implications for the synthesis of efficient Pt-based catalysts. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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17 pages, 10980 KiB

Open AccessArticle

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH₃-SCR of NO_x

by Ahui Tang, Fuzhen Yang, Ying Xin, Xiaoli Zhu, Long Yu, Shuai Liu, Dongxu Han, Junxiu Jia, Yaning Lu, Zhenguo Li and Zhaoliang Zhang

Catalysts 2024, 14(1), 10; https://doi.org/10.3390/catal14010010 - 21 Dec 2023

Cited by 2 | Viewed by 1061

Abstract

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NO_x removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NO_x emissions during the [...] Read more.

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NO_x removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NO_x emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnO_x/Cu-SSZ-39) and references (CeO₂/Cu-SSZ-39 and MnO_x/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH₃-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnO_x/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NO_x conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnO_x improves the redox properties and acidity of the catalyst due to the presence of Ce³⁺, Mn⁴⁺, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnO_x with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnO_x provides access to fast SCR reaction pathways by oxidizing NO to NO₂, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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15 pages, 3847 KiB

Open AccessArticle

New Insights into the Effect of Ce Doping on the Catalytic Performance and Hydrothermal Stability of Cu-USY Zeolite Catalysts for the Selective Catalytic Reduction of NO with NH₃

by Qi Sun, Haipeng Yang, Jie Wan, Wanru Hua, Yanjun Liu, Xiaoli Wang, Chunxiao Shi, Qingai Shi, Gongde Wu and Renxian Zhou

Catalysts 2023, 13(12), 1485; https://doi.org/10.3390/catal13121485 - 30 Nov 2023

Viewed by 957

Abstract

5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) was evaluated on [...] Read more.

5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) was evaluated on both fresh and aged catalysts. Physical/chemical characterizations such as X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS) were performed, along with detailed in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) experiments including CO adsorption, NH₃ adsorption, and NO + O₂ reactions. Results showed that, for the 5Cu-USY catalyst, hydrothermal ageing treatment could somehow improve the low-temperature SCR activity, but it also led to significant formation of unfavorable byproducts NO₂ and N₂O. Such an activity change can be attributed to hydrothermal ageing inducing the migration of isolated Cu⁺ species in the sodalite cavities towards the super cages of the USY zeolites. The increased content of Cu⁺ species in the super cages was beneficial for the low-temperature activity improvement, but, at the same time, it also facilitated ammonia oxidation at high temperatures. Ce doping after hydrothermal ageing has a “double-edged sword” effect on the catalytic performance. First of all, Ce doping can inhibit Cu species migration by self-occupying the internal cage sites; thus, the catalytic performance of 5Cu8Ce-USY-700H remains stable after ageing. Secondly, Ce doping introduces a CuO_x–CeO₂ strong interaction, which facilitates lattice oxygen mobility by forming more oxygen vacancies so as to increase the concentration of surface active oxygen. These changes, on the one hand, could help to promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance. But, on the other hand, it also causes the byproduct generation to become more severe. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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11 pages, 6021 KiB

Open AccessArticle

Enhanced Soot Oxidation Activity of a CuO-Doped CeO₂ Catalyst via Acid Etching

by Changlong Zheng, Xiaodong Wu, Zhenguo Li, Rui Ran and Duan Weng

Catalysts 2023, 13(12), 1463; https://doi.org/10.3390/catal13121463 - 23 Nov 2023

Cited by 1 | Viewed by 834

Abstract

Copper oxides tend to agglomerate on the surface of CeO₂, with a high amount of Cu. In this study, a CeO₂ catalyst with a high CuO doping amount was treated with nitric acid to improve its catalytic performance for soot [...] Read more.

Copper oxides tend to agglomerate on the surface of CeO₂, with a high amount of Cu. In this study, a CeO₂ catalyst with a high CuO doping amount was treated with nitric acid to improve its catalytic performance for soot oxidation. The effect of acid etching on the structural properties of the CuO-doped CeO₂ catalyst were elucidated. The characterization results indicated that aggregated CuO particles formed over CuCe. The acid etching resulted in a remarkable increase in the surface area of CuCe. Additionally, acid etching promoted the formation of surface-adsorbed oxygen species and oxygen vacancy, and reduced the content of CuO_x species with weak interaction with CeO₂. The soot temperature-programmed oxidation results show the acid etching of CuCe catalyst could reduce the T₅₀ from 443 to 383 °C. The isothermal reaction results also suggest that acid etching of CuCe leads to an increase in reaction rate from 16.2 to 46.0 μmol min⁻¹ g⁻¹. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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Review

Jump to: Research

19 pages, 3920 KiB

Open AccessReview

Preparation of Mesoporous Zeolites and Their Applications in Catalytic Elimination of Atmospheric Pollutants

by Chuchen Miao, Lanyi Wang, Shengran Zhou, Di Yu, Chunlei Zhang, Siyu Gao, Xuehua Yu and Zhen Zhao

Catalysts 2024, 14(1), 75; https://doi.org/10.3390/catal14010075 - 17 Jan 2024

Cited by 1 | Viewed by 1181

Abstract

With increasing environmental awareness, the issue of atmospheric pollution has gained significant attention. Specifically, three types of atmospheric pollutants, namely, nitrogen oxides, volatile organic compounds, and carbon monoxide, have become the focus of widespread concern. In addressing these pollutants, mesoporous zeolites have emerged [...] Read more.

With increasing environmental awareness, the issue of atmospheric pollution has gained significant attention. Specifically, three types of atmospheric pollutants, namely, nitrogen oxides, volatile organic compounds, and carbon monoxide, have become the focus of widespread concern. In addressing these pollutants, mesoporous zeolites have emerged as promising materials due to their large specific surface area, which enables effective dispersion of active sites, and their large pore volume, which facilitates efficient diffusion. This article provides a comprehensive overview of the preparation methods of mesoporous zeolites and their applications in removing nitrogen oxides, volatile organic compounds, and carbon monoxide. It also highlights the challenges and limitations faced by the application of mesoporous zeolites in pollutant removal and emphasizes their potential as efficient catalysts. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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30 pages, 9516 KiB

Open AccessReview

Application of Unconventional External-Field Treatments in Air Pollutants Removal over Zeolite-Based Adsorbents/Catalysts

by Haodan Cheng, Xiaoning Ren, Yuan Yao, Xiaolong Tang, Honghong Yi, Fengyu Gao, Yuansong Zhou and Qingjun Yu

Catalysts 2023, 13(12), 1461; https://doi.org/10.3390/catal13121461 - 23 Nov 2023

Cited by 1 | Viewed by 1370

Abstract

Zeolite-based materials are widely used as adsorbents and catalysts for purifying air pollutants like NO_x and VOCs due to abundant pore structure, regular pore distribution, and numerous ion exchange sites. Thermal treatment is a necessary procedure for both removing impurities in pores [...] Read more.

Zeolite-based materials are widely used as adsorbents and catalysts for purifying air pollutants like NO_x and VOCs due to abundant pore structure, regular pore distribution, and numerous ion exchange sites. Thermal treatment is a necessary procedure for both removing impurities in pores and promoting the metal active dispersed evenly before the zeolite-based adsorbents/catalysts were applied for purifying the NO_x/VOCs. Nevertheless, the conventional thermal field treatment (i.e., high-temperature calcination, high-temperature purging, etc.) takes large energy consumption. In contrast, unconventional external-field treatments such as non-thermal plasma and microwave show significant advantages of high efficiency, low energy consumption as well and low pollution, which were used to substitute the traditional thermal treatment in many fields. In this paper, the roles of non-thermal plasma or microwave in the adsorption/catalysis of the NO_x/VOCs are reviewed from three aspects assisting activation of materials, cooperative catalysis process, and assisting zeolites synthesis. The reasons for unconventional treatments in improving textural properties, active sites, performance, etc. of zeolite-based materials were illuminated in detail. Moreover, the influences of various parameters (i.e., power, time, temperature, etc.) on the above aspects are elaborated. It is hoped that this review could provide some advanced guidance for the researchers to develop highly efficient materials. Full article

(This article belongs to the Special Issue Catalysts for Mobile Source: Low-Carbon and Pollution Emission Control)

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