Further on the mechanism of the synergy between MoO3 and alpha-Sb2O4 in the selective oxidation of isobutene to methacrolein: Reconstruction of MoO3 via spillover oxygen

This paper concerns the synergetic effects between a (010) oriented MoO3 and alpha-Sb2O4 in the oxidation of isobutene to methacrolein at 420 degrees C. The catalysts were prepared by mechanical mixture of the pure oxides prepared separately. Important increases were observed both for the conversion of isobutene and for the selectivity to methacrolein, suggesting that new selective sites have been created. The characterization of the samples before and after the reaction by SEM and XRD shows an important reconstruction of the (010) face of MoO3 into steps exposing (100) faces, when the reaction is carried out in the presence of alpha-Sb2O4. It is known from literature that the (100) face of MoO3 performs selectively partial oxidation, while the (010) face is not selective. On the other hand, alpha-Sb2O4 has shown to produce spillover oxygen, which flows onto the MoO3 surface. It is, therefore, concluded that the increase of selectivity is intimately connected to the reconstruction under the action of spillover oxygen. Spillover oxygen would favour the ''selective coordination'' of Mo atoms or groups of atoms, typical of (100), at the expense of the ''non-selective one'', typical of (010). This result corresponds to the theoretical prediction of the Remote Control theory.