Reaction kinetics and mechanism of CH4-SCR on Ru–In/H-SSZ-13

Abstract

The reaction kinetics and mechanism of CH₄-SCR on Ru–In/H-SSZ-13 as a model multifunctional catalyst, together with Ru/H-SSZ-13 and In/H-SSZ-13 for reference, were investigated. In the low-temperature region (<260 °C), quite different apparent activation energy values were obtained for the three catalysts investigated, while similar apparent activation energy values were obtained in the high-temperature region (>260 °C). With increasing reaction temperatures from 250 to 500 °C, the reaction orders of NO in CH₄-SCR on Ru–In/H-SSZ-13 gradually decreased from 1.80 to 0.43 while the reaction orders of CH₄ gradually increased from 0.33 to 0.86 instead. The surface species formed on the catalyst samples and their evolutions at 250 and 400 °C were monitored by in situ DRIFT spectroscopy. The organonitrogen compounds, i.e. methyl nitrite and its isomer nitromethane, were identified as the key intermediates in CH₄-SCR, and their existence was further confirmed by temperature-programmed surface reaction and pulse-response experiments. According to the above-mentioned results, the temperature-dependent CH₄-SCR mechanism on Ru–In/H-SSZ-13 was finally established.