Abstract
A series of vanadium–chromium oxide (VCrO) catalysts supported on silica was prepared by wetness impregnation method with different Cr/V molar ratios from 0.2 to 1.0. These catalysts were characterized by XRD, TG, temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectra (XPS), and Raman spectroscopy, and their catalytic activity was evaluated in the ammoxidation of 3-picoline (3-PIC) to nicotinonitrile (NN). The results of XRD, TG, Raman, and XPS confirmed that the active components on the silica surface were mainly amorphous V2O5 and CrVO4. The results of NH3-TPD showed that acidity of the catalysts decreased with the increase of Cr/V ratio. Catalytic results revealed that acidity of the catalysts was closely related to the catalytic performance. Low acidity gave low conversion of 3-PIC and high NN selectivity. Furthermore, the conversion of 3-PIC increased with rise in reaction temperature, and the selectivity of NN was slightly influenced by the 3-PIC conversion. Therefore, among the catalysts (Cr/V ratio was 0.2, 0.4, 0.6) tested, Cr/V-0.6 catalyst retained the lowest acidity and exhibited the highest selectivity and yield of NN in the ammoxidation of 3-PIC.
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