Abstract
This paper reports promotion effect of HC-SCR activity of Ag/Al2O3 catalyst by the control of reaction atmospheres, i.e., (1) the use of higher hydrocarbons as reductants, (2) co-feeding of water vapour, and (3) co-feeding of small amount of hydrogen. Although Ag/Al2O3 was not active for propane-SCR below 623 K, the conversions of NO to N2 were above 65 % when n-octane was used. Co-feeding of water vapour resulted in nearly 100 % NO conversion in the SCR by n-octane, which may be because of the suppression of the poisoning by carbonaceous deposits. In the case of SCR by lower alkanes at lower temperatures, it was clarified that the co-feeding of small amount of hydrogen is effective. The promotion effect of hydrogen is caused by the modification of Ag species on alumina, i.e., Ag+ species was reduced and agglomerated by hydrogen into Ag cluster, which is active for the SCR reaction. These effects of reaction atmospheres are discussed from a point of view of surface reaction pathway and dynamics of active species measured by in-situ FT/IR and in-situ UV-Vis spectra.
