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Selective catalytic reduction of NO _x with NH₃: opportunities and challenges of Cu-based small-pore zeolites.

ABSTRACT: Zeolites, as efficient and stable catalysts, are widely used in the environmental catalysis field. Typically, Cu-SSZ-13 with small-pore structure shows excellent catalytic activity for selective catalytic reduction of NO _x with ammonia (NH₃-SCR) as well as high hydrothermal stability. This review summarizes major advances in Cu-SSZ-13 applied to the NH₃-SCR reaction, including the state of copper species, standard and fast SCR reaction mechanism, hydrothermal deactivation mechanism, poisoning resistance and synthetic methodology. The review gives a valuable summary of new insights into the matching between SCR catalyst design principles and the characteristics of Cu²⁺-exchanged zeolitic catalysts, highlighting the significant opportunity presented by zeolite-based catalysts. Principles for designing zeolites with excellent NH₃-SCR performance and hydrothermal stability are proposed. On the basis of these principles, more hydrothermally stable Cu-AEI and Cu-LTA zeolites are elaborated as well as other alternative zeolites applied to NH₃-SCR. Finally, we call attention to the challenges facing Cu-based small-pore zeolites that still need to be addressed.

SUBMITTER: Shan Y

PROVIDER: S-EPMC8566184 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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Selective catalytic reduction of NO x with NH3: opportunities and challenges of Cu-based small-pore zeolites.

Shan Yulong Y Du Jinpeng J Zhang Yan Y Shan Wenpo W Shi Xiaoyan X Yu Yunbo Y Zhang Runduo R Meng Xiangju X Xiao Feng-Shou FS He Hong H

National science review 20210116 10

Zeolites, as efficient and stable catalysts, are widely used in the environmental catalysis field. Typically, Cu-SSZ-13 with small-pore structure shows excellent catalytic activity for selective catalytic reduction of NO x with ammonia (NH3-SCR) as well as high hydrothermal stability. This review summarizes major advances in Cu-SSZ-13 applied to the NH3-SCR reaction, including the state of copper species, standard and fast SCR reaction mechanism, hydrother ...[more]

PMID: 34858603

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Project description:In this paper, a series of tungsten-zirconium mixed binary oxides (denoted as W m ZrO x ) were synthesized via co-precipitation as supports to prepare Ce0.4/W m ZrO x catalysts through an impregnation method. The promoting effect of W doping in ZrO2 on selective catalytic reduction (SCR) performance of Ce0.4/ZrO2 catalysts was investigated. The results demonstrated that addition of W in ZrO2 could remarkably enhance the catalytic performance of Ce0.4/ZrO2 catalysts in a broad temperature range. Especially when the W/Zr molar ratio was 0.1, the Ce0.4/W0.1ZrO x catalyst exhibited the widest active temperature window of 226-446 °C (NO x conversion rate > 80%) and its N2 selectivity was almost 100% in the temperature of 150-450 °C. Moreover, the Ce0.4/W0.1ZrO x catalyst also exhibited good SO2 tolerance, which could maintain more than 94% of NO x conversion efficiency after being exposed to a 100 ppm SO2 atmosphere for 18 h. Various characterization results manifested that a proper amount of W doping in ZrO2 was not only beneficial to enlarge the specific surface area of the catalyst, but also inhibited the growth of fluorite structure CeO2, which were in favor of CeO2 dispersion on the support. The presence of W was conducive to the growth of a stable tetragonal phase crystal of ZrO2 support, and a part of W and Zr combined to form W-Zr-O x solid super acid. Both of them resulted in abundant Lewis acid sites and Brønsted acid sites, enhancing the total surface acidity, thus significantly improving NH3 species adsorption on the surface of the Ce0.4/W0.1ZrO x catalyst. Furthermore, the promoting effect of adding W on SCR performance was also related to the improved redox capability, higher Ce3+/(Ce3+ + Ce4+) ratio and abundant surface chemisorbed oxygen species. The in situ DRIFTS results indicated that nitrate species adsorbed on the surface of the Ce0.4/W0.1ZrO x catalyst could react with NH3 due to the activation of W. Therefore, the reaction pathway over the Ce0.4/W0.1ZrO x catalyst followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms at 250 °C.

Dataset Information

Selective catalytic reduction of NO _x with NH₃: opportunities and challenges of Cu-based small-pore zeolites.

Publications

Selective catalytic reduction of NO <i><sub>x</sub></i> with NH<sub>3</sub>: opportunities and challenges of Cu-based small-pore zeolites.

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