THE OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID TO METHACRYLIC-ACID ON ION-EXCHANGE MODIFIED 12-HETEROPOLY OXOMETALATES

The oxidative dehydrogenation of isobutyric acid (IBA) to methacrylic acid (MAA) has been studied over a series of 12-heteropoly oxometalate catalysts. H3PMo12O40, Cs3PMo12O40. (NH4)3PMo12O40, and a series of catalysts prepared using an ion exchange modification that resulted in the formation of mixed cation composition salts (NH4+/Cs+) were studied to investigate the contribution of the cation in the IBA to MAA process. Whereas the product selectivities obtained with the parent acid and ammonium salt were similar, those obtained with the cesium salt were markedly different. Studies of the self exchanged salts provided insight into the role of protons in the process, while investigations of the Cs+/NH4+ ion exchanged materials indicated that the cation can participate directly in the IBA to MAA reaction. The formation of MAA and acetone appears to involve a common intermediate, whereas propene forms through a different route. © 1991.