Isotopic exchange of molecular oxygen with the oxygen of ferric molybdate

Abstract

The kinetics and mechanism of exchange of gas-phase oxygen with the surface oxygen of both stoichiometric and partially reduced ferric molybdates have been studied by a static-circulation method. The surface oxygen in the stoichiometric compound behaves in a manner energetically uniform with respect to the exchange. The prevailing mechanism of exchange includes the participation of two oxygen atoms from the surface. The activation energy determined in the range 800–900 K is 210 ± 15 kJ mol^–1. Partial reduction (2 monolayers) of Fe₂(MoO₄)₃ leads to very fast low-temperature exchange. This type of exchange has been found to proceed by two parallel mechanisms with the participation of (a) two and (b) one surface oxygen atom. A reaction path via the formation of O^–₂ and O^–₃ species on the surface is suggested.