Vapor-phase synthesis of 3-methylindole from glycerol and aniline: the effect of Al₂O₃ promoter and the preparation method on the performance of the Cu–Al₂O₃/SiO₂ catalyst

Abstract

An Al₂O₃-modified Cu/SiO₂ catalyst was used in the vapor-phase synthesis of 3-methylindole from glycerol and aniline. The effect of Al₂O₃ and the preparation method of the Cu–Al₂O₃/SiO₂ catalyst on the activity and selectivity of the catalyst were investigated. The catalysts were characterized by XRD, TEM, H₂-TPR, NH₃-TPD and TG techniques. The results indicated that the addition of Al₂O₃ to Cu/SiO₂ increased the activity and selectivity remarkably. Cu–Al₂O₃/SiO₂ prepared by co-precipitation (COP) exhibited better catalytic performance compared with the catalyst prepared by incipient wetness impregnation (IWI) or ultrasonic impregnation (UI), because the catalyst possessed a good dispersion of Cu particles, a better resistance to the sintering of Cu particles as well as a larger amount of weak acid sites. Over Cu–Al₂O₃/SiO₂ (COP) with the Al₂O₃ content of 1.1 mmol/g, the yield of 3-methylindole reached 44 % at the third hour of reaction, and the yield could be kept to 41 % even after the reaction time of 51 h.