(618a) Selective Oxidation of Propene On Bismuth Molybdenum Based Oxide Catalysts

The selective catalytic oxidation of lower olefins to produce α,β-unsaturated aldehydes is one of the essential processes for preparing monomers and intermediates in industry. Among the most successful of these reactions is the selective oxidation of propene to acrolein [1], a commodity chemical produced at the level of 10⁸kg/year [2]. The most effective catalysts for the oxidation of propene are multi-component oxide systems based on bismuth molybdate. However, it is still difficult to explain what the role of the additional elements is in the multicomponent bismuth molybdate catalysts.

In this work, we aim to understand the effects of catalyst composition on catalyst activity and selectivity. To do this, we first prepared and investigated a series of scheelite-type multi-component bismuth molybdate catalysts doped with a third element (iron, gallium or vanadium, etc). Several characterizations and oxidation of propene to acrolein reaction were then performed on these catalysts. We conducted. XRD data showed that all the catalysts have similar scheelite-type structures. X-ray absorption near edge spectroscopy (XANES) was used to characterize metal oxidation state before and after exposure of the catalyst to propene. The diffuse reflectance UV-VIS-NIR spectra were measured to calculate band gap based on the absorption edge. Measurements of reaction rates and product distributions were performed on these catalysts. All these measurements illustrate that the production of the main product of these catalysts, acrolein, follows first order dependence of C₃H₆ and zero dependence of O₂ under operation conditions for most catalysts except gallium doped bismuth molybdate. For gallium doped catalysts, our measurements show they have the highest activation energy, while vanadium doped catalysts provide the lowest one. These activation energies have positive correlations with the band gaps for different catalysts with different additives. Generally, the structures of the catalyst, as well as the electronic properties, are influenced by the properties of additional elements, i.e. iron, gallium or vanadium.  How these properties further influence acrolein production is discussed.

_{[1] G.W. Keulks, L.D. Krenzke, T. M. Notermann, Adv. Catal. 27 (1978) 183-225.}

_{[2] G. Ertl, H. Knozinger, F. Schuth, J. Weitkamp (Eds.) Handbook of Heterogeneous Catalysis, Wiley}