EFFECTS OF WATER-VAPOR IN THE OXIDATIVE DEHYDROGENATION OF ISOBUTYRICACID TO METHACRYLIC-ACID OVER IRON PHOSPHATE CATALYST

The effects of water vapor on the oxidative dehydrogenation of isobuty ric acid to methacrylic acid over an iron phosphate catalyst were stud ied. The presence of water vapor suppresses both the carbon deposit an d the formation of phosphorus-rich species on the surface of the catal yst and, as a result, it prevents the degradation in both the catalyti c activity and the selectivity which occurs during the reaction, thoug h it has no clear influence on both the redox properties and the struc ture of the catalyst. The pretreatment of the catalyst with a gas cont aining water vapor or the reaction in the presence of water vapor rest ores the activity and selectivity of the degraded catalyst. It is prop osed that water plays a role in removing the carbon and oxygenated pro ducts from the surface, in suppressing the side reaction, that is, the decomposition of isobutyric acid to propylene and CO, and also in mod ifying the surface species.