Silver Valence State Determines the Water Tolerance of Ag/Al2O3 for the H2–C3H6–SCR of NOx

Abstract

The influence of the silver valence state on Ag/Al2O3 on the water tolerance of H2-C3H6-SCR of NOx was investigated. The valence state of silver species on Ag/Al2O3, which was carefully characterized by XPS, UV-vis, and XANES measurements, was adjusted by varying the calcination temperature from 500 oC to 900 oC. Oxidized silver species were predominant on Ag/Al2O3 calcined at temperatures below 600 oC (LT-catalysts), while further increasing the calcination (temperatures above 600 oC, HT-catalysts) promoted the transformation of oxidized silver species into metallic silver clusters. The samples with higher amounts of oxidized silver species exhibited better water tolerance in the H2-C3H6-SCR. Activation energy measurements confirmed that the mechanism of NOx reduction on these catalysts was the same. In situ DRIFTS studies demonstrated that metallic silver species promoted the formation of active enolic species and the complete oxidation of formate, thus improving the low-temperature activity of HT-catal...