Pretreatment and activation of a vanadium phosphate catalyst for butane oxidation to maleic anhydride

A vanadium phosphate catalyst precursor (P/V = 1.2) was prepared using an organic medium. The precursor was calcined at 400°C and portions were subjected to further treatments before being placed under reaction conditions (430°C, 1.2% butane/air feed) for 72-95 h. The changes in activity and selectivity with time on stream were monitored, and catalysts were characterized before and after reaction by XRD, IR, B.E.T. surface area, and redox titrometry. No general correlation between solid state properties and reactivity was found. None of the pretreatments caused catalyst performance to stabilize before 48 h on stream. Severely reducing (butane, 480°C) or oxidizing (air, 480°C) treatments were particularly deleterious to selectivity. The treatments leading to the best catalytic performance were to simply run under reaction conditions or to wash the catalyst in boiling methanol. The washing appeared to remove an inert surface phase.