Reactivity of Surface Nitrates in H2-Assisted SCR of NO_x Over Ag/Al2O3 Catalyst

摘要

The role of nitrate ad-species in H2-assisted SCR over Ag/Al2O3 was compared in NH3-SCR and n-C6H_(14)-SCR processes. It was found that nitrates could be reduced by NH3 or n-C6H_(14) at similar rates with H2 co-feeding which indicates a common rate-limiting step. However, contributions of surface nitrate reduction to the overall NH3-SCR or n-C6H_(14) are different as revealed by comparing the rates of nitrate reduction with the rates of steady-state processes. The rate of the steady-state n-C6H_(14)-SCR is virtually identical to the rate of surface nitrate reduction suggesting a significant contribution of the surface nitrates reduction to the overall n-C6H_(14)-SCR process. On the other hand, the steady-state rate of NH3-SCR is by -15 times higher, which indicates that the reduction of surface nitrates plays a marginal role in the overall NH3-SCR.