The Effect Of Alkaline-earth Metal Promoters On The Cu/SiO₂-Al₂O₃Catalyst For The Vapor-phase Synthesis Of3-methylindole

As an important indole derivative and nitrogen-containing heterocyclic chemical,3-methylindole is widely applied in the fields of industry, agriculture and medicine. Thevapor-phase synthesis of3-methylindole from aniline and biomass-derived glycerin is aperfect route because it is not only low price but also green environmental-protection.In this paper, we reported the effect of alkaline-earth metal oxides on the Cu/SiO₂-Al₂O₃catalysts for the vapor-phase synthesis of3-methylindole. The Cu-based catalysts wereprepared by sequential incipient wetness impregnation. The catalysts were characterized byX-ray diffraction, transmission electron microscopy, H2temperature-programmed reduction,NH₃temperature-programmed desorption, thermogravimetric and differential thermalanalysis to investigate and explain the relationship between the structure of Cu-based catalystsand their catalytic performances.The results indicated that MgO could reinforce the interaction between the activecomponent and the support, which promoted the dispersion of Cu particles on the support. Inaddition, MgO could decrease the amount of the middle-strong acid sites of the catalyst andinhibit the formation of the coke during the reaction. As a result, the addition of MgO toCu/SiO₂-Al₂O₃increased the performance of the catalyst. For Cu-MgO/SiO₂-Al₂O₃catalyst,when the amount of MgO was0.1mmol/g and the catalyst was reduced at250℃, the yield of3-methylindole could be up to46%. Adding CaO, SrO or BaO to Cu/SiO₂-Al₂O₃tookdisadvantage of the synthesis of3-methylindole because the dispersion of Cu particles on thesupport became worse and the amount of the weak acid sites on Cu-SrO/SiO₂-Al₂O₃orCu-BaO/SiO₂-Al₂O₃was fewer. Alkaline-earth metal oxides did not change the texture of thecoke.