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

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.