Enhanced catalytic activity for emission control of CO and NH3 by solid-state impregnation of Ag on γ-Al2O3 support

Abstract

While metallic Ag species are known for superior active sites for oxidation reactions of NH3 and CO compared to Ag oxides, achieving precise control over the surface Ag phase through the conventional wet method has been a significant challenge, primarily due to the strong metal-support interaction on the γ-Al2O3 surface. This study unveiled that the chemical state of the Ag precursor before calcination is a crucial factor in determining these interactions, affecting the surface Ag phase. We found that the ionic state of Ag in aqueous solution, via a conventional preparation method, actively forms a strong bonding with surface hydroxyl groups on γ-Al2O3, leading to the formation of well-dispersed Ag oxide species unfavorable for catalytic reactivity. By employing the solid-state impregnation method, we successfully suppressed this metal-support interaction, favoring the formation of metallic Ag nanoparticles. The resultant catalyst exhibited remarkable oxidation activities of CO or NH3, outperforming conventional impregnated catalysts. TEM and UV–vis spectroscopy confirmed that the Ag/γ-Al2O3 with solid-state impregnation exhibited pronounced metallic characteristics of Ag species, even at low Ag loadings.