Investigating the promotional effect of methanol on the low temperature SCR reaction on Ag/Al2O3

Abstract

Methanol has been shown to promote the hydrocarbon selective catalytic reduction of NOx with octane and toluene over 2wt% Ag/Al2O3 catalyst for the first time. In order to understand its role in the reaction fast transient kinetic methods and in situ DRIFTS analysis have been used. The catalytic activity tests showed that the addition of methanol to the HC-SCR reaction results in a significant improvement in the low temperature activity of a Ag/Al2O3 catalyst, despite the fact that methanol on its own is not reactive for the HC-SCR reaction. This promotional effect of methanol is dependent on the concentration of added methanol and is not necessarily associated with a higher concentration of reductant in the SCR feed. The fast transient kinetic analysis has shown that at each temperature the addition of methanol enhances the conversions of both NOx and octane and the production of N2 with high selectivity in comparison with those observed with n-octane or toluene alone. This phenomenon is similar to the effect of H2 which may be associated with the release of hydrogen and ammonia during the transient switches at 250 and 300°C. Together with the fast transient experiments, the DRIFTS results showed that NCO species are formed when introducing methanol to the n-octane-SCR feed while CN species are removed/consumed from the surfaces of the Ag catalyst. These NCO species formed by adding methanol may play a vital role in promoting the catalytic activity of NOx reduction and methanol itself can be an in situ source for hydrogen formation, which subsequently enhances the SCR reaction.