FTIR and kinetic studies of the mechanism of Fe3+-exchanged TiO2-pillared clay catalyst for selective catalytic reduction of NO with ammonia

A series of FTIR spectroscopic and kinetic studies of the selective catalyt ic reduction (SCR) of nitric oxide by ammonia were conducted on Fe3+-exchan ged TiO2-pillared clay (Fe-TiO2-PILC) catalyst. It was found that NO molecu les were adsorbed on the fresh Fe-TiO2-PILC catalyst and then oxidized by O -2 to adsorbed NO2 and nitrate species. These NOx adspecies could be reduce d by NH3 at high temperatures. NH3 molecules could also be adsorbed on the Bronsted acid and Lewis acid sites on the Fe-TiO2-PILC catalyst to generate , respectively, NH4+ ions and coordinated NH3 species. These NH3 adspecies were active in reacting with NO, NO + O-2 and NO2, but the reaction rates o f NH3 + NO + O-2 and NH3 + NO2 were much higher than that of NO + NH3. Howe ver, under reaction conditions, the surface of Fe-TiO2-PILC was mainly cove red by NH4+ ions and coordinated NH3, and no NOx adspecies were detected. T his is in agreement with the zero-order for the SCR reaction with respect t o NH3. A possible reaction scheme for the SCR reaction on Fe-TiO2-PILC was proposed. NO reduction initially involved the reaction between NO2 and pair s of NH3 adspecies to form an active intermediate, which finally reacted wi th gaseous or weakly adsorbed NO to produce N-2 and H2O. a 2000 Academic Pr ess.