Impact of surface mobility in selective oxidation. Isotopic exchange of ~(18)O_2 with ~(16)O_2 on various oxides: MoO_3, SnO_2 and Sb_2O_4. Effect of a reducer gas

摘要

Isotopic oxygen exchange experiments were carried out on simple oxides (Sb_2O_4, MoO_3 and SnO_2) and mechanical mixtures of MoO_3 or SnO_2 (acceptor phase) with Rh/Al_2O_3 or Sb_2O_4 (donor phase). With Rh/Al_2O_3 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 Sb_2O_4 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 Sb_2O_4 decreases the rate of total oxidation by blocking, by oxygen spillover, the most active sites for oxidation.