OXIDATIVE DEHYDROGENATION OF ISOBUTYRALDEHYDE TO METHACROLEIN OVER IRON PHOSPHATE CATALYST

The oxidative dehydrogenation of isobutyraldehyde was studied at 400-d egrees-C in the presence of a large amount of steam using an iron phos phate with a P/Fe atomic ratio of 1.2 as the catalyst. The main produc ts were methacrolein, CO, and CO2; methacrylic acid was not formed fro m isobutyraldehyde unlike the case of the reaction over heteropoly com pound catalysts. Even in the absence of catalyst, large amounts of iso butyraldehyde were consumed, although the conversion of isobutyraldehy de increased as the contact time increased. With an oxygen/isobutyrald ehyde molar ratio of 0.9, the yield of methacrolein reached 68 mol% wi th a conversion of 88% (nominal selectivity to methacrolein of 77 mol% ). The true selectivity to methacrolein on the catalyst was estimated to be 90 mol%. It was found that the fresh catalyst consisting of only Fe3+ ions was reduced to iron(II) pyrophosphate via an unidentified i ntermediate phase during the reaction. The effects of oxygen and water on the catalytic behavior and the structures of catalyst were studied .