CATALYSIS BY HETEROPOLY COMPOUNDS .28. ACIDIC CESIUM SALTS OF MOLYBDOVANADOPHOSPHORIC ACIDS AS EFFICIENT CATALYSTS FOR OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID

Oxidative dehydrogenation of isobutyric acid to methacrylic acid has b een studied using Cs salts of 12-molybdovanadophosphoric acids as cata lysts (CsnH3+x-nPMo12-xVxO40, n = 0-(3 + x), x = 0-2, which will be ab breviated as CsnMo12-xVx). Among them, Cs2.75Mo11V showed remarkably h igh performance; the hi hest conversion (97%) and selectivity for meth acrylic acid (MAA, 78%) at 623 K. At the same reaction conditions, Mo1 1V (i.e. n = 0, x = 1) gave only 40% conversion and 52% selectivity, A s for the series of Cs2.75Mo12-xVx, the activity was in the order of x = 1 > x = 2 > x = 0 and the MAA selectivity, x = 1 greater than or eq ual to x = 2 > is = 0. The nature of Mo11V was confirmed by IR to be p artially destroyed during pretreatment in O-2 at 623 K, while Cs2.75Mo 11V decomposed only slightly, This fact indicates that the thermal sta bility afforded this catalyst to make efficient use of the redox abili ty controlled by incorporation of V, and the enhanced redox ability, h igh surface area, and high surface acidity of Cs salts would be the ma in reasons for their effectiveness.