An in situ UV-vis and FTIR spectroscopy study of the effect of H2 and CO during the selective catalytic reduction of nitrogen oxides over a silver alumina catalyst

The effect of hydrogen and carbon monoxide on the selective catalytic reduction of NOx with decane over a 2 wt% Ag/Al2O3 catalyst was investigated. Hydrogen promoted NOx conversion during the SCR reaction, in contrast to carbon monoxide, which had a slightly detrimental effect on catalyst activity. However, in situ UV-vis spectroscopy showed that both carbon monoxide and hydrogen promoted the formation of Ag clusters during the reaction. This, coupled with previous EXAFS experiments and UV-vis data on the rate of change of cluster formation, demonstrate that the enhanced activity from the addition of hydrogen to the NOx-SCR mix cannot be attributed exclusively to the formation of Ag clusters. It is proposed that hydrogen itself participates directly in the reaction mechanism.