Catalytic performance of vanadyl pyrophosphate in the partial oxidation of toluene to benzaldehyde

Vanadyl pyrophosphate catalysts were generated by dehydrating VOHPO4.(1/2)H2O at different temperatures and duration of the dehydration procedure. The as-synthesised materials were characterised by X-ray diffractometry, FTIR spectroscopy and temperature-programmed reduction. The prolongation of the formation period at higher temperatures led to improved crystallinity and lower BET surface areas of the vanadyl pyrophosphate specimens and, additionally, a significantly impeded reducibility of the vanadyl sites was observed. The catalytic performance of the samples was tested in the partial oxidation of toluene to benzaldehyde. The obtained results revealed an increasing benzaldehyde selectivity with improved catalyst crystallinity. In situ FTIR and ESR spectroscopy were used to throw more light on the interaction of the toluene-air feed with the surface of the catalyst.