The activity of single and two-component catalyst systems consisting of a partial oxidation catalyst and a reduction catalyst (Ag/Al2O3), were investigated for selective catalytic reduction (SCR) of nitrogen oxides (NOx) with n-decane (HC) as a reductant. The single component Ag/Al2O3 catalyst showed a maximum NOx conversion of 28% at 400 degrees C and formation of minor amounts of hydrocarbon cracking products. Co-presence of partial oxidation catalyst, especially metal/ZSM-5, along with Ag/Al2O3 enhanced the NO conversion of the composite catalysts. Among the composite catalysts, Zn/ZSM-5-Ag/Al2O3 combination led to the most increase in NOx conversion. It was identified that the n-decane can be more effectively converted, on Zn/ZSM-5, to smaller hydrocarbons (such as ethene, propane and propene) intermediates. These in situ generated intermediates were found to enhance the NOx conversion of Zn/ZSM-5-Ag/Al2O3 composite catalysts. Catalyst optimization showed that the NOx conversion increased with increase in zinc loading of up to 5 wt% in ZSM-5 and by increasing Zn/ZSM-5 content in the composite mixture catalyst. A combination of 17 mg of Ag/Al2O3 and 33 mg of 5%Zn/ZSM-5 led to the most active catalyst showing a maximum NOx conversion of about 67% at 400 degrees C. (C) 2013 Elsevier B.V. All rights reserved.