Selective catalytic reduction of NO by CO over MOF-based CuOx@ZIF-67 catalysts and reaction mechanism

Abstract

The selective catalytic reduction of NOx using CO as a reduction gas (CO-SCR) is a promising method to eliminate NO and CO simultaneously and attracted much of the attention recently. Currently, the majority of CO-SCR catalysts tested showed high activity in the absence of oxygen, but their performance was poor when oxygen was present. As a result, it is important to explore an effective catalyst under aerobic conditions. This work proposed a new catalysts for CO-SCR based on metal organic framework (MOF) material, specially, ZIF-67. A series ofx%CuOx@ZIF-67 catalysts were successfully prepared and the CO-SCR reactivity was evaluated in a fixed-bed micro reactor with simulated flue gas in the presence of O2, containing 500 ppm NO, 1000 ppm CO, 0–10% O2 balanced by N2 at a temperature range of 200–375 °C. The catalysts were characterized by SEM, XRD, TGA, NH3-TPD, XPS, BET, H2-TPR, and in situ DRIFTS to investigate the influence of microstructure, texture, and chemical properties of the catalyst on the SCR performance. The result demonstrates that the CuOx@ZIF-67 catalysts were effective for CO-SCR performance and NO conversion was 100% at 300 °C for 8.0 %CuOx@ZIF-67 catalyst. Cu improved the surface oxygen vacancies and the reduction ability of the catalyst. The synergy effect of Cu on Co can increase the acid sites and the amount of Lewis acid on the catalyst surface. The primary intermediate species, according to in situ DRIFTS analysis, were Cu+–CO, bidentate nitrate, and bridging nitrate. The reaction path of CO-SCR on CuOx@ZIF-67 was proposed based on the in situ DRIFTS analysis.