This article reports on the promotional effect of adding H-2 to the reaction feed for the selective catalytic reduction of NO (x) with propene (H-2-C3H6-SCR) over Au/Al2O3 catalysts. For this purpose, the influence of the Au loading in H-2-C3H6-SCR was investigated. The H-2 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 H-2 effect allowed for a substantial increase in NO (x) conversion at temperatures higher than 250 A degrees C on Au/Al2O3 samples. The highest NO (x) to N-2 conversion in H-2-C3H6-SCR was obtained for lowly-loaded gold samples (similar to 1 wt% Au) with the smallest gold particle sizes. An increase in H-2 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 H-2 and C3H6 is critical to achieve a high H-2 promoting effect in H-2-C3H6-SCR. Whereas this requirement is fulfilled for Ag/Al2O3, a temperature gap between the oxidation profiles of H-2 and C3H6 remains for Au/Al2O3 due to the early oxidation of H-2 on gold nanoparticles, which therefore limits the NO (x) conversion at low temperature. Graphical Abstract [GRAPHICS] .