Looking inside the pores of a MCM-41 based Mo heterogeneous styrene oxidation catalyst: an inelastic neutron scattering study.

Styrene oxidation mediated by a Mo-based mesoporous catalyst can yield selectively styrene oxide or benzaldehyde. Kinetic data evidenced that styrene oxide is the initial single-product formed by the catalytic Mo-mediated process. However, after some hours of reaction benzaldehyde yield rises while that of the epoxide decreases concomitantly. The mechanistic proposal pointed to a surface assisted acid-base mechanism by which styrene oxide is interconverted into benzaldehyde through over-oxidation and cleavage of the C-C bond and releases formaldehyde as well. In an attempt to gain some insight into whether this mechanistic proposal is realistic we have conducted a combined DRIFT and inelastic neutron scattering (INS) study to assess the adsorbed species at the catalyst's surface and confirm the mechanistic proposal. INS and DRIFT provided complementary insight into surface-adsorbed species by probing donor (INS) and acceptor (DRIFT) species. INS also allowed for an estimation of product selectivity by means of a Job method stressing the power of the technique.