A novel selective oxidation catalyst: ultrafine complex molybdenum based oxide particles

Abstract

Mo-based and V-based oxides have been widely used as selective oxidation catalysts and the studies on the structure and catalytic properties of these oxides have demonstrated that the nature of oxygen species in the oxides is one of the most important parameters, influencing catalytic selectivity. To increase the reactivity of lattice oxygen species and to improve the catalytic selectivity, great efforts have been made to modify the state of lattice oxygen species by adding some promoters to these oxides. It has been found that Bi, Fe, Sn, W, and rare earth oxides are the effective promoters of the molybdenum-based and vanadium-based oxide catalysts for selective oxidation of toluene to benzaldehyde. The ultrafine complex oxide particles are potentially new catalytic materials for selective oxidation reactions. It has been found that the reactivity of lattice oxygen ions can be improved by decreasing the oxide particle size to nano-scale and that the ultrafine oxide particles exhibit unique catalytic properties for selective oxidation. The interaction of Ce with Mo and its effect on the nature of active oxygen species in the complex oxides were studied by using temperature-programmed reduction (TPR) and laser Raman spectroscopy (LRS). The morphology of Mo–Ce oxide samples (Ce/Mo atomic ratio = 2/3) prepared by different methods are presented in this chapter. It can been seen that the particle size of Mo–Ce(sg) was in the range of 20-80 nm, while that of Mo–Ce(cp) was higher than 500nm. These results have shown that the Mo-Ce oxides prepared by the sol-gel method are actually the ultrafine oxide particles (<100nm).