Support modification for improving the performance of MnOx–CeOy/γ-Al2O3 in selective catalytic reduction of NO by NH3

Abstract

The catalytic performances of catalysts with binary-oxides supports in selective catalytic reduction (SCR) of NO by NH3 were studied. Binary metal oxides supports γ-Al2O3–SiO2, γ-Al2O3–TiO2, and γ-Al2O3–ZrO2 were prepared by hydrolyzation and coprecipitation methods, after that MnOx–CeOy was loaded using isovolumetric impregnation method. Characterizations for the samples involved N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR) and Fourier Transform infrared spectroscopy (FTIR). In the SCR tests, MnOx–CeOy/γ-Al2O3–ZrO2 (MCAZ) showed outstanding NO removal efficiency and could abate the deactivation brought by SO2 and H2O. Moreover, the fluctuation of gas hourly space velocity (GHSV) appeared only a bit of influence on the activity at middle temperature. The characterization results exhibited that MnOx–CeOy/γ-Al2O3–ZrO2 owned bigger specific surface area and appropriate pore diameter, highly dispersed amorphous Mn2O3 as well as rational ratio of Ce4+/Ce3+. The H2-TPR results presented the promotion of the activity was partially due to the stronger oxidation ability at low temperature. Through the FTIR analysis, and combining with the mechanism proposed by earlier research, it was supposed that the highly reactive nitrates on the surface favored the high NO conversion. Besides, FTIR revealed that the bidentate sulfates formed by adsorbed SO2 produced new Lewis acid sites which promoted NH3 adsorption and reduced the poisoning effect of SO2 and H2O.