SELECTIVE CATALYTIC REDUCTION OF NO WITH NH3 ON SO4(-2)/TIO2 SUPERACID CATALYST

SO-24/TiO2 superacid is studied for selective catalytic reduction (SCR) of NO with NH3. Since SO-2 4/TiO2 is formed on TiO2 under SCR reaction conditions when SO2 is present, the results also elucidate the role of TiO2 support (and SO2) in the SCR reaction. SO-2 4/TiO2 exhibits a considerable activity, exceeding that of V2O5/TiO2 at temperatures above 400°C, and reaches a peak activity at 500-525°C. TGA, XPS, and IR analyses of the catalyst indicate that SO-2 4 ions are formed on TiO2 and the structure of the TiO2 surface sulfate under the SCR reaction conditions is bridged bidentate, Ti2SO3(OH). XPS and chemisorption measurements along with SCR kinetic results indicate that the reaction takes place by an Eley-Rideal mechanism, on Brønsted-acid sites on SO-2 4/TiO2 surface. At 400°C. about 70% of the SO-2 4 ions are occupied by ammonia, and about a half of the chemisorbed ammonia is active for reaction with NO. © 1993 Academic Press, Inc.