Study of cesium or cesium-transition metal-substituted Keggin-type phosphomolybdic acid as isobutane oxidation catalysts

Cesium and copper- or iron-substituted Keggin-type phosphomolybdic heteropo lycompounds with the general formula Cs2Mxy+H1-xyPMo12O40 (M = Fe3+ and Cu2 + and 0 less than or equal to x less than or equal to 0.43) have been teste d as catalysts in the oxidation of isobutane to methacrylic acid in order t o study the effect of the transition metal ion on the catalytic properties. Copper appears to have a positive effect on the activity and a negative ef fect on the selectivity in methacrylic acid. Iron has almost no effect on t he activity but a positive one on the selectivity, although this trend is r eversed at higher iron content levels. These results have been correlated t o the reducibility and the acidity of the catalysts. (C) 1999 Academic Pres s.