Further on the mechanism of the synergy between MoO 3 and α-Sb 2O 4 in the selective oxidation of isobutene to methacrolein: Reconstuction of MoO 3 via spillover oxygen

Abstract

This paper concerns the synergetic effects between a (010) oriented MoO 3 and α-Sb 2O 4 in the oxidation of isobutene to methacrolein at 420°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 MoO 3 into steps exposing (100) faces, when the reaction is carried out in the presence of α-Sb 2O 4. It is known from literature that the (100) face of MoO 3 performs selectively partial oxidation, while the (010) face is not selective. On the other hand, α-Sb 2O 4 has shown to produce spillover oxygen, which flows onto the MoO 3 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.