Enhancement of the Mo–V–Sb–Nb–O Catalyst for Propane Selective Ammoxidation by a Steam Treatment Method

The decay of catalytic abilities in the ammoxidation reaction of propane over the Mo–V–Sb–Nb–O catalyst, the regeneration process, its mechanism, stability of catalytic activity, and repeatability of the regeneration process were investigated by activity tests, kinetic studies, atomistic simulation, and various characterizations such as X-ray diffraction, X-ray absorption fine structure, scanning electron microscopy with energy-dispersive X-ray spectroscopy, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, H 2 temperature-programmed reduction, and Raman spectroscopy. Long-term use of the catalyst caused a decline of crystallinities and formation of Sb 2 O 5, which decreased the acrylonitrile (AN) yield and increased the CO x yields. Heat treatment under a N 2 flow containing steam caused recrystallization of used catalysts and transformation of Sb 2 O 5 to Sb 2 O 4 as well as recovering the catalytic abilities of used catalysts as much as that of a fresh catalyst. Though the similar decay of the regenerated catalyst occurred after the reaction under excessive oxidation conditions as accelerated aging tests, the Sb 2 O 4 amount did not change. Catalytic abilities and the Sb 2 O 4 amount further increased by repeating the same steam treatment. The improvement of crystallinity and the high olefin adsorption ability of Sb 2 O 4 led to an improvement of AN yield.