Ammoxidation of 3-Picoline over V_2O_5/TiO_2 Catalysts: Effects of TiO_2 Supports on the Catalytic Performance

摘要

A series of V_2O_5/TiO_2 catalysts were prepared by wet impregnation, and these prepared catalysts were characterized by XRD, N_2 adsorption-desorption, H_2-TPR, and TEM techniques and used in the selective ammoxidation of 3-picoline to 3-cyanopyridine. The effects of TiO_2 supports on the catalytic properties of the resulting catalysts for the ammoxidation of 3-picoline to 3-cyanopyridine were investigated in detail. It is found that the V~(5+)/V~(4+) transformation during ammoxidation is more favorable than the V~(5+)/V~(3+) transformation for the selective ammoxidation of 3-picoline to 3-cyanopyridine. The V_2O_5/TiO_2 catalysts prepared from the nanosized TiO_2 particles as supports show a high activity for the direct oxidation of 3-picoline by air, resulting in a low selectivity for 3-cyanopyridine. This could be due to the fact that the active species vanadium oxides could be only supported on the external surface of the nano-sized TiO_2 particles with very minor contact area, leading to the weak interactions between active species and support.