Adsorption of probe molecules to investigate by EPR the redox properties of silver loaded on ceria

Abstract 10% wt Ag/CeO 2 solids were prepared by impregnation (Imp) and deposition-precipitation (DP) and their catalytic activity towards many oxidation reactions were studied in previous works. Three Ag 2+ signals were identified by electron paramagnetic resonance technique (EPR) only in the (Imp) solid. Further studies of the active sites of 10% Ag/CeO 2 (Imp) and (DP) were conducted in this work. Adsorptions of probe molecules (O 2 , CO, CO 2 , N 2 O, NO, and NO 2 ) were carried out on the (Imp) and (DP) solids. Adsorption of O 2 , CO, CO 2 , N 2 O, NO results in the formation of O 2 − species adsorbed on the surface of both (Imp) and (DP) solids according to: O 2 - 2 XO + Ag 0 / CeO 2 → Ag + / CeO 2 + 2 X (case of (DP) and (Imp)) Or O 2 - 2 XO + Ag + / CeO 2 → Ag 2 + / CeO 2 + 2 X (case of (Imp) solid) These O 2 − species were adsorbed on Ce 4+ species with a weak energy of adsorption since the signal of O 2 − disappeared on the spectra recorded at ambient temperatures. However, some O 2 − species were more stable than other ones and resisted to heating treatments. The Ag 2+ species that were reduced due to the vacuum atmosphere used previously to the adsorption were re-oxidized after treatment by nitrogen oxides (N 2 O, NO, and NO 2 ).