Ag Catalysts Supported on CeO₂, MnO₂ and CeMnO_x Mixed Oxides for Selective Catalytic Reduction of NO by C₃H₆

Abstract

In the present study CeO2, MnO2 and CeMnOx 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(NH3)2]NO3 aqueous solution. The selective catalytic reduction of NO by C3H6 was investigated in a fixed-bed quartz reactor using a reaction mixture composed of 1000 ppm NO, 3600 ppm C3H6, 10 vol.% O2, 2.9 vol.% H2 and He as a balance gas, at WHSV of 25,000 mL g−1 h−1.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/CeMnOx catalyst (NO conversion at 300 °C is 44% and N2 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+/Agnδ+ species improve the low-temperature catalyst of NO reduction by C3H6 performance compared to Ag/CeO2 and Ag/MnOx systems.

Keywords

• Ag⁺
• CeMnO_x
• C₃H₆-SCR of NO
• oxide microstructure
• HRTEM
• Raman