Reduction Site in Ce n V m O k + Revealed by Gas Phase Thermal Desorption Spectrometry

Abstract

Vanadia supported on ceria shows particularly high catalytic reactivity. To elucidate its reduction site, cationic cerium-vanadium oxide clusters, Ce _n V _m O _x ⁺ (n = 1–6, m = 0–5), were generated in the gas phase and their thermal response, such as reduction by oxygen release, was investigated by gas phase thermal desorption spectrometry. Stoichiometric and near-stoichiometric Ce _n V _m O _x ⁺ clusters were dominantly formed, suggesting that Ce and V atoms in thermally stable clusters at 310 K have the oxidation states of + 4 and + 5, respectively. An oxygen molecule O₂ was found to desorb from the clusters, resulting in formation of Ce _n V _m O _x−2 ⁺, upon heating. Presence of more than two Ce atoms in the clusters for odd values of m, or more than three Ce atoms for even values of m lowered the desorption temperature, indicating that not V atoms (+ 5 to + 4) but Ce atoms (+ 4 to + 3) in Ce _n V _m O _x ⁺ tend to be reduced.