Ottinger, N., Veele, R., Xi, Y., and Liu, Z., "Conversion of Short-Chain Alkanes by Vanadium-Based and Cu/Zeolite SCR Catalysts," SAE Int. J. Engines 9(2):1241-1246, 2016, doi:10.4271/2016-01-0913.
The oxidation of short-chain alkanes, such as methane, ethane, and propane, from the exhaust of lean-burn natural gas and lean-burn dual-fuel (natural gas and diesel) engines poses a unique challenge to the exhaust aftertreatment community. Emissions of these species are currently regulated by the US Environmental Protection Agency (EPA) as either methane (Greenhouse Gas Emissions Standards) or non-methane hydrocarbon (NMHC). However, the complete catalytic oxidation of short-chain alkanes is challenging due to their thermodynamic stability. The present study focuses on the oxidation of short-chain alkanes by vanadium-based and Cu/zeolite selective catalytic reduction (SCR) catalysts, generally utilized to control NOx emissions from lean-burn engines. Results reveal that these catalysts are active for short-chain alkane oxidation, albeit, at conversions lower than those generally reported in the literature for Pd-based catalysts, typically used for short-chain alkane conversion. While the Cu/zeolite SCR catalyst had the highest conversion of CO, CH4, and C2H6, the V-SCR catalyst had higher C3H8 conversion likely due to pore diffusion limitations of the small-pore Cu/zeolite SCR. None of the SCR catalysts stored short-chain alkanes or were impacted by water vapor, and only the Cu/zeolite catalyst was affected by sulfation. NOx conversion was not impacted as a result of the presence of CO and short-chain alkanes. These results indicate that, in addition to NOx conversion, SCR catalysts may be part of the short-chain alkane oxidation solution.