Promotional mechanism of propane on selective catalytic reduction of NO _x by methane over In/H-BEA at low temperature

Effects of propane/methane ratios on NO _x reduction by mixtures of methane and propane over In/H-BEA catalyst were investigated at temperatures ranging from 250 to 550 °C. The higher catalytic activity of In/H-BEA was exhibited for CH ₄ -SCR at high temperatures above 450 °C, while the higher NO _x conversion was achieved in C ₃ H ₈ -SCR at below 425 °C. A broadened temperature window and enhanced CO ₂ selectivity were achieved by combining of methane and propane as the co-reductant. The mixtures with propane/methane of 1/2 showed the most superior T ₅₀ (325 °C) and T ₉₀ (500 °C) temperatures for NO _x reduction over In/H-BEA catalyst. For the promotion mechanism of propane on NO reduction by methane at low temperature, the formation of carbonaceous species (e.g. R-COOH) were enhanced by the activation of C ₃ H ₈ on Brønsted acid sites at low temperature, and further promoted the generation of [sbnd]NCO species, which was a crucial determining step for NO reduction.