STABILITY OF BISMUTH MOLYBDATE CATALYSTS AT ELEVATED-TEMPERATURES IN AIR AND UNDER REACTION CONDITIONS

The stability of bismuth molybdate catalysts during use for the partial oxidation of propylene has been investigated in situ using Raman spectroscopy and a novel reactor cell. These studies were supplemented by X-ray diffraction analyses. A phase change of 5% was detectable via Raman spectroscopy at 400°C, and a phase change of 2% could be seen at room temperature. Evidence has previously been reported for the occurrence of alterations in the structure of bismuth molybdate catalysts which were seen only under reaction conditions. In this study it was found that the alpha, beta, and gamma phases of bismuth molybdate were all completely stable under the conditions normally employed for the catalytic partial oxidation reaction. The reasons underlying conflicting opinions concerning the thermodynamic stability of beta bismuth molybdate have been discovered and the conflict resolved. This in situ investigation of the stability of bismuth molybdates is the first to have been conducted under conditions normally employed for the catalytic partial oxidation of propylene. © 1991.