Physical mixture of Ag/Al2O3 and Zn/ZSM-5 as an active catalyst component for selective catalytic reduction of NOx with n-C10H22

• Combination of Ag/Al2O3 + Zn/ZSM-5 showed significant enhancement in NOx conversion.
• Intermediates formed by Zn/ZSM-5 react over Ag/Al2O3 increasing NOx reduction.
• Acidity and Zn properties are important for the production of active intermediates.
• 1:2 mixture of 4%Ag/Al2O3 and 5%Zn/ZSM-5 yielded effective NOx conversion.

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 °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 NOx 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 °C.

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