Ag/Al$_2$O$_3$/FeAl(110): Electronic structure and NO$_2$ adsorption

Ag/Al$_2$O$_3$ systems are widely studied as catalysts in the selective catalytic reduction of NO$_x$ with hydrocarbons. The exact nature of the active sites and the role of the Ag clusters in such reactions is still not fully understood. In this study, we characterize thermally evaporated Ag clusters on the ultrathin alumina film produced by oxidizing FeAl(110). ARPES demonstrates the evolution of Ag cluster electronic structure and morphology with increasing Ag coverage. Changes in electronic binding energy distinguish charged from metallic clusters. Vibrational EELS of NO$_2$ adsorbed on the Ag/Al$_2$O$_3$/FeAl(110) system elucidates the nature of the NO$_x$ binding site and the changes in the surface chemistry both as a function of Ag cluster size and NO$_x$ adsorption temperature.