Selective catalytic reduction of NO x over Ag/Al2O3 using various bio-diesels as reducing agents

The effect of bio-diesel compounds (vegetable methyl and ethyl laurate and hexadecane) as reducing agents on the selective catalytic reduction of NO _x over a 2 wt.% Ag/Al₂O₃ was investigated. These components were found to have a two-fold effect on the SCR over Ag/Al₂O₃. First, the reduction activity below 400 °C was higher with bio-diesel than with n-octane, which is a representative compound for fossil fuels. This effect is attributed to the presence of the ester group in these molecules. However, the conversion above 400 °C decreased sharply and was considerable lower than with n-octane. The most interesting observation was found when the reduction efficiency of bio-diesel components was tested in the presence of hydrogen. The well known low temperature boosting effect of hydrogen was visible not only at lower temperatures, but also above 400 °C. Mechanistically the observation is extremely interesting and indicates that hydrogen effect cannot directly be connected to reduction of surface nitrates, which can be operative only at low temperature domain.