SYNERGETIC EFFECTS IN MULTIPHASE CATALYSTS - THE ROLE OF FESBO4 AS DONOR-ACCEPTOR OF SPILLOVER OXYGEN

The present work reports experimental data to further investigate the role of FeSbO4 in multiphase catalysts used in the selective oxidation of isobutene to methacrolein. Its oxygen acceptor and donor propertie s have been evaluated by showing the effect of admired alpha-Sb2O4, wh ich is a good oxygen donor able to increase the selectivity of an acce ptor phase, and of MoO3 which generally acts as a good oxygen acceptor , namely carries all the functions necessary for oxidation, but has on ly a weak ability to dissociate oxygen. Catalysts containing FeSbO4 an d alpha-Sb2O4 or MoO3 were prepared: (1) by mechanical mixture; and (2 ) by artificial deposition of Sb and Mo ions on FeSbO4. The catalysts were characterized, before and after the test, by S-BET, XRD and XPS. The mechanical mixtures and impregnated catalysts gave a synergy in th e yield and in the selectivity to methacrolein. Characterization shows that the catalysts are formed by two separate non-contaminated phases in contact. Synergy is explained by the remote control mechanism. It is proposed that FeSbO4 act as a donor of oxygen spillover when it is mixed with MoO3, and as an acceptor in presence of alpha-Sb2O4.