The effect of hydrogen on the selective catalytic reduction of NO, with n-octane, methylcyclohexane and toluene over a 2 wt.% Ag/Al2O3 was investigated. Diesel fuels contain, in addition to straight hydrocarbons, varying amounts of cyclic and aromatic compounds, which have a detrimental effect on the Ag/Al2O3 catalyst activity. The results showed that the NO to N-2 conversion was significantly promoted, independent of the nature (straight, cyclic or aromatic) of the hydrocarbon, in the presence of 1 vol.% H-2. The role of hydrogen is connected to a faster oxidation of the hydrocarbons and to enhanced formation of amines, which react with activated NO to form N-2. (c) 2006 Elsevier B.V. All rights reserved.