Ag Catalysts Supported on CeO, MnO and CeMnO Mixed Oxides for Selective Catalytic Reduction of NO by CH.

In the present study CeO, MnO and CeMnO mixed oxide (with molar ratio Ce/Mn = 1) were prepared by sol-gel method using citric acid as a chelating agent and calcined at 500 °C. The silver catalysts (1 wt.% Ag) over the obtained supports were synthesized by the incipient wetness impregnation method with [Ag(NH)]NO aqueous solution. The selective catalytic reduction of NO by CH was investigated in a fixed-bed quartz reactor using a reaction mixture composed of 1000 ppm NO, 3600 ppm CH, 10 vol.% O, 2.9 vol.% H and He as a balance gas, at WHSV of 25,000 mL g h.The physical-chemical properties of the as-prepared catalysts were studied by several characterization techniques, such as X-ray fluorescence analysis, nitrogen adsorption/desorption, X-ray analysis, Raman spectroscopy, transmission electron microscopy with analysis of the surface composition by X-ray energy dispersive spectroscopy and X-ray photo-electron spectroscopy. Silver oxidation state and its distribution on the catalysts surface as well as the support microstructure are the main factors determining the low temperature activity in NO selective catalytic reduction. The most active Ag/CeMnO catalyst (NO conversion at 300 °C is 44% and N selectivity is ~90%) is characterized by the presence of the fluorite-type phase with high dispersion and distortion. The characteristic "patchwork" domain microstructure of the mixed oxide along with the presence of dispersed Ag/Ag species improve the low-temperature catalyst of NO reduction by CH performance compared to Ag/CeO and Ag/MnO systems.