Spillover-induced synergetic effects and reconstructions of oxides surfaces during oxidation reactions

Abstract

Synergetic effects between MoO3 and alpha-Sb2O4 were recently investigated in the selective oxidation of isobutene to methacrolein. Owing to the absence of mutual contamination between the two phases, the observed enhancements of the conversion of isobutene and of the selectivity for methacrolein were explained by a remote control mechanism. Namely, this was the creation of new selective sites by spillover oxygen during catalysis. We showed that by tuning the coordination of surface Mo atoms, this phenomenon triggered the reconstruction of the non selective (010) faces of MoO3 crystallites to selective (100) ones. The picture fitted perfectly with the occurence of the synergetic effects. The present investigation aims at further supporting this picture. If the role attributed before to Oso for the creation of new sites is correct, it could be speculated that whatever the source of Oso, namely whatever the Oso donor phase with which MoO3 was mixed, the effects on its surface should be the same. Parallel experiments to the ones described previously were performed using BiPO4, another Oso donor, instead of alpha-Sb2O4. The results, synergism - creation of sites - with simultaneous reconstruction, obtained with BiPO4 are identical to those obtained with alpha-Sb2O4. The only difference is that the effects are less intense with BiPO4 than with alpha-Sb2O4. This is consistent with the fact that BiPO4 is a weaker Oso donor than alpha-Sb2O4. The experiments with BiPO4 reinforce the validity of the model proposed for the creation of sites under the action of Oso. Some other results open new lines of discussion for the understanding of the different roles and the mechanisms of action of Oso at the surface of oxides.