Hydrogen assisted n-octane-SCR under lean conditions over a 1.91 wt.% Ag/alumina catalyst was studied. The kinetic behaviour of the catalytic reaction at 200 degrees C at steady state conditions was examined in the concentration range: P-H2 = 0.25, 0.5 and 1 vol.%, P-NO = 375, 500 and 1000 ppm, P-octane = 187.5, 375 and 500 ppm and P-O2 = 1.5, 3 and 6 vol.%. The results showed that all the rates increased along the increasing H-2 concentration with the reaction order equal to 0.4 in NO and 1.4 in octane at 0.5 vol.% hydrogen concentration. Moreover it was observed that the effect of hydrogen was more predominant on the NO to N-2 reduction than varying reactant (NO, C8H18) concentration. The main mechanistic effect of hydrogen in significantly improving the low temperature performance of silver/alumina catalysts in HC-SCR cannot only be attributed to the reduction of surface nitrates with hydrogen suggesting its involvement in the catalytic cycle of NO reduction. (c) 2006 Elsevier B.V. All rights reserved.