Protection Against Deactivation of Selective Oxidation Catalysts Due To Spillover Oxygen

We review recent results obtained in our laboratory, which show that certain oxides, called Donors (e.g. alpha-Sb2O4, BiPO4, etc.) effectively protect phases active in selective oxidation against various deactivation processes. The results were obtained with simple mechanical mixtures of oxides, using the oxidation of isobutene to methacrolein and the oxidative dehydrogenation of n-butene to butadiene as a test reaction and several characterization techniques (surface area measurement, x-ray diffraction [XRD], x-ray photoelectron spectroscopy [XPS] and Fourier transform infrared [FTIR]). The presence of a Donor phase exerts several effects, often in conjunction: prevention of the reduction of the surface of the active phase, inhibition of coke formation, stabilization against segregation in certain cases, or promotion of favorable solid-state reactions. This results in improved activity and selectivity and slower deactivation. These effects are attributed to spillover oxygen, emitted by the Donor phases. This constitutes one facet of the role of the remote control mechanism in multiphase, multicomponent oxidation catalysts.