Kinetic considerations of H2 assisted hydrocarbon selective catalytic reduction of NO over Ag/Al2O3: I. Kinetic behaviour

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 °C at steady state conditions was examined in the concentration range: PH2=0.25PH2=0.25, 0.5 and 1 vol.%, PNO = 375, 500 and 1000 ppm, Poctane = 187.5, 375 and 500 ppm and PO2=1.5PO2=1.5, 3 and 6 vol.%. The results showed that all the rates increased along the increasing H2 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 N2 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.