Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B2O3/TiO2-ZrO2: the effect of catalyst calcination temperature and solvent

The effect of calcination temperature (500-700 °C) on the performance of B2O3/TiO2-ZrO2 catalyst for vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam was investigated. Catalysts were characterized by adsorption of nitrogen, X-ray diffraction and ammonia temperature-programmed desorption. The results indicated that the percent of acid sites of medium strength within the total acid sites and the pore size both increased with calcination temperature. Such increases led to increases of the oxime conversion and caprolactam selectivity. However, a large amount of crystalline B2O3 appeared after calcination at 700 °C and caused the decrease of the total amount of acid sites, which resulted in remarkable decrease in the activity of the catalyst. Another part of this work focused on the effect of solvent on the catalytic performance of B2O3/TiO2-ZrO2. Solvents with various polarities were investigated for the reaction. It was found that acetonitrile, which has the highest polarity for solvents examined here, was the most effective for the formation of caprolactam. The solvent with high polarity increases the desorption rate of produced caprolactam from catalyst surface, resulting in a high selectivity to caprolactam and low catalyst deactivation rate. FT-IR measurements confirmed the efficient desorption of caprolactam induced by the attack of the acetonitrile molecule.