OXIDATIVE DEHYDROGENATION OF ISOBUTYRALDEHYDE TO METHACROLEIN OVER IRON PHOSPHATE CATALYST

The oxidative dehydrogenation of isobutyraldehyde was studied at 400-degrees-C in the presence of a large amount of steam using an iron phosphate with a P/Fe atomic ratio of 1.2 as the catalyst. The main products were methacrolein, CO, and CO2; methacrylic acid was not formed from isobutyraldehyde unlike the case of the reaction over heteropoly compound catalysts. Even in the absence of catalyst, large amounts of isobutyraldehyde were consumed, although the conversion of isobutyraldehyde increased as the contact time increased. With an oxygen/isobutyraldehyde molar ratio of 0.9, the yield of methacrolein reached 68 mol% with 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 intermediate phase during the reaction. The effects of oxygen and water on the catalytic behavior and the structures of catalyst were studied.