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Enhanced activity of CuO/K₂CO₃/MgAl₂O₄ catalyst for lean NOₓ storage and reduction at high temperatures

Author:
Liu, Yaoyao, Guo, Lihong, Zhao, Dongyue, Li, Xingang, Gao, Zhongnan, Ding, Tong, Tian, Ye, Jiang, Zheng
Source:
RSC advances 2017 v.7 no.44 pp. 27405-27414
ISSN:
2046-2069
Subject:
adsorption, aluminum oxide, catalysts, copper, cupric oxide, nitrates, nitrogen, nitrogen oxides, oxidation, potassium carbonate, temperature, thermal stability
Abstract:
Herein, we designed a new NOₓ storage and reduction CuO/K₂CO₃/MgAl₂O₄ catalyst operating within the high temperature region of 350–550 °C. Compared with the Al₂O₃ supported catalyst with the same Cu and K loading, it exhibits superior NOₓ storage and reduction performance. The NOₓ reduction percentage (NRP) of the CuO/K₂CO₃/MgAl₂O₄ catalyst remains above 90% over a wide temperature range (400–550 °C), and reaches the highest NRP of 99.9% at 450 °C with the N₂ selectivity of 99.7%. Uncovered CuO particles with better reducibility exist on the CuO/K₂CO₃/MgAl₂O₄ catalyst, with the high NOₓ oxidation and reduction ability above 400 °C. Potassium carbonates on the CuO/K₂CO₃/MgAl₂O₄ catalyst mainly exist in three forms, including free ionic carbonate, bridging bidentate carbonate and chelating bidentate carbonate. Under lean-burn conditions, most of carbonates on the CuO/K₂CO₃/MgAl₂O₄ catalyst can store NOₓ to form nitrates, but only parts of them participate in NOₓ storage on the CuO/K₂CO₃/Al₂O₃ catalyst. The MgAl₂O₄ support offers additional sites for NOₓ adsorption, while the formed nitrate on it shows low thermal stability. So, NOₓ is mainly stored on K₂CO₃ at high temperatures, because MgAl₂O₄ can enhance the thermal stability of the supported K₂CO₃ on it. Our results show that the thermal stability of K₂CO₃ directly determines the thermal stability of the formed nitrates. Accordingly, the CuO/K₂CO₃/MgAl₂O₄ catalyst shows the high NSR activity because of the efficient redox ability of CuO and high thermal stability of K₂CO₃ at high operating temperatures.
Agid:
6416355