Propane oxydehydrogenation reaction on a VPO/TiO 2 catalyst. Role of the nature of acid sites determined by dynamic in-situ IR studies

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A VPO/TiO 2 catalyst tested in the oxydehydrogenation reaction (ODH) of propane between 300 and 400°C shows satisfactory performances (up to 80% of propene selectivity at 2% of propane conversion at 300°C or 56% of propene selectivity at 9% of propane conversion at 400°C). Addition of water or pyridine in the feed gas tends to decrease the propane conversion and enhances the propene selectivity. It is shown that water increases the number of Brönsted surface acid sites by dissociative adsorption which, in turn, enhances propene selectivity at the expense of the CO x selectivity. These results are in good agreement with spectroscopic IR observations performed under catalytic conditions showing that the Lewis acid sites are linked to CO xformation, whereas it seems that Brönsted sites would rather be linked to propene formation.