The mechanism of n‐butane oxidation. Characterization of titania‐supported V‐P‐O catalysts by pulse‐flow experiments and in‐situ XANES spectroscopy

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Abstract
Well‐dispersed supported V‐P‐O (Vanadium Phosphorus Oxyde) catalysts were prepared and tested in the selective oxidation of n‐butane to maleic anhydride. Because of their high activity, it was possible to test titania‐supported catalysts in a two‐step oxidation reduction process at low temperatures. After n‐butane adsorption and activation in the absence of molecular oxygen, desorption took place after subsequent introduction of molecular oxygen into the gas stream, leading to the selective formation of maleic anhydride.In‐situ XANES spectroscopy was performed under reaction conditions in the two‐step oxidation reduction process with a special titania‐supported V‐P‐O catalyst with a high loading. The results of these experiments showed that, after equilibration, no more changes in the valence state of vanadium were observed after reduction or subsequent re‐oxidation. This indicates that the generally assumed Mars‐Van‐Krevelen mechanism is not operative for the titania‐supported V‐P‐O catalyst.