Selective Catalytic Reduction of NO x over Au/Al2O3: Influence of the Gold Loading on the Promoting Effect of H2 in H2-Assisted C3H6-SCR of NO x

Abstract

This article reports on the promotional effect of adding H2 to the reaction feed for the selective catalytic reduction of NO x with propene (H2–C3H6-SCR) over Au/Al2O3 catalysts. For this purpose, the influence of the Au loading in H2–C3H6-SCR was investigated. The H2 promoting effect in C3H6-SCR, well-established for Ag/Al2O3, was also demonstrated for Au/Al2O3. Although less pronounced than for Ag-based systems, the H2 effect allowed for a substantial increase in NO x conversion at temperatures higher than 250 °C on Au/Al2O3 samples. The highest NO x to N2 conversion in H2–C3H6-SCR was obtained for lowly-loaded gold samples (~ 1 wt% Au) with the smallest gold particle sizes. An increase in H2 concentration in the reaction feed also led to an increase in NO x conversion. The experiments performed in the present study as a function of the reaction temperature underlined the fact that concomitant activation of H2 and C3H6 is critical to achieve a high H2 promoting effect in H2–C3H6-SCR. Whereas this requirement is fulfilled for Ag/Al2O3, a temperature gap between the oxidation profiles of H2 and C3H6 remains for Au/Al2O3 due to the early oxidation of H2 on gold nanoparticles, which therefore limits the NO x conversion at low temperature.