Impact of surface mobility in selective oxidation. Isotopic exchange of O2 with O2 on various oxides: MoO3, SnO2 and Sb2O4. Effect of a reducer gas

Isotopic oxygen exchange experiments were carried out on simple oxides (Sb₂O₄, MoO₃ and SnO₂) and mechanical mixtures of MoO₃ or SnO₂(acceptor phase) with Rh//Al₂O₃ or Sb₂O₄ (donor phase). With Rh//Al₂O₃ a synergy effect is found: the amount of oxygen exchanged on the mixture is higher than the sum of oxygen exchanged on the two separate phases. This is a prove of oxygen mobility between donor and acceptor phases. With Sb₂O₄ this effect is less marked suggesting that the presence of a reducer gas is required. In presence of hydrocarbon, no isotopic exchange is observed: only total oxidation occurs. The presence of Sb₂O₄ decreases the rate of total oxidation by blocking, by oxygen spillover, the most active sites for oxidation.