Enhancement of catalytic activity of the ammonium/potassium salt of 12-molybdophosphoric acid by iron ion addition for the oxidation of isobutane to methacrylic acid

The oxidation of isobutane to methacrolein and methacrylic acid was carried out over potassium/ammonium salts of 12-molybdophosphoric acid (Keggin-type heteropoly compounds), with overall selectivity to the desired products higher than 50%. The addition of iron to the catalyst composition led to a substantial enhancement of the catalytic activity, with an increase in the yield to the desired products, even though the selectivity decreased. The catalysts all have a secondary cubic structure, and are stable in the reaction environment. No trace of structural decomposition was found in spent catalysts. It was found that the addition of iron led to a substantial increase in the catalyst acidity and it is proposed that the Lewis acidity might play a role in the activation of the paraffin.