Elucidating the role of Mo doping in enhancing the meta-Xylene ammoxidation performance over the CeVO4 catalyst

Abstract

Vanadium-based oxides-catalyzed conversion of meta-xylene (m-X) directly to isophthalonitrile (IPN) through vapor phase ammoxidation is a short-flow, sustainable and economic process. Herein, effects of molybdenum promoter loadings are systematically studied on the ammoxidation performance over the SiO2 supported V-Ce composite oxide catalyst prepared by spray drying method. The roles of Mo addition were elucidated by series of structure characterizations. It had been revealed that the addition of Mo can promote the formation of specific crystal face of CeVO4 species which works as the active phase of the catalyst. Meanwhile, the Mo addition can suppress the surface V2O5 species formation, and thus lower the oxidation state and the acid strength of the catalyst. The Ce3+/Ce4+ ratio is also increased with the rising of Mo amount, and the chemisorbed oxygen amount is lowered, leading to a moderate activation of the reactants. The modified physicochemical properties originated from the Mo promoter doped on the CeVO4 surface. At last, the performances of the Mo-modified and Mo-free catalysts are evaluated in the fluidized bed under 415 °C. The oxidation degree of the feeding m-X of the Mo containing catalyst is obviously lower than the Mo-free catalyst, and as a result the yield of IPN is improved. However, the Mo/V cannot be excessively increased, because at high Mo/V, the weaker adsorption of reactant would cause the incomplete m-X conversion, and the selectivity for monocyano product, i.e., metatolunitrile, rises, lowering the selectivity of the main product (IPN).