Effect of metal oxide contents on the structure and performance of spray-dried CrVO4/SiO2 catalysts for the ammoxidation of chlorotoluenes

Abstract

This work aims at developing a customized ammoxidation catalyst through optimizing the metal oxide content in CrVO₄/SiO₂ catalysts. Various amounts of Cr–V–O with 1:1 molar ratio of Cr/V were successfully loaded on SiO₂ via spray-drying method with colloidal silica as the binder. Polarized light microscope illustrated that the CrVO₄/SiO₂ particles presented as well dispersed microspheres in the microsize (20–80 μm). X-ray diffraction spectra confirmed the formation of monoclinic CrVO₄ phase wherein the metal oxide content was ranged from 30 to 70 weight percent. FT-IR spectra indicated that the introduction of metal oxide had no obvious effects on the skeletal structure of SiO₂. X-ray photoelectron spectroscopy analysis revealed that the valence state of V and Cr was hardly affected with increasing the metal oxide content. Performances of the obtained CrVO₄/SiO₂ catalysts with different metal oxide contents were investigated via the ammoxidation of a model compound, namely para-chlorotoluene (PCT) to para-chlorobenzonitrile (PCBN). A maximum conversion of 99.6% of PCT and 86.5% yield and 86.8% selectivity to PCBN have been obtained over the CrVO₄/SiO₂ catalyst with 60% weight of metal oxides at a temperature of 410 °C, n(PCT):n(NH₃):n(air) = 1:3:15 and reaction load = 0.13 g/gCat·h. In addition, this catalyst was efficient and selective toward ammoxidation reactions of toluene, ortho- and meta-chlorotoluenes.

Graphical abstract