Abstract: The effect of the addition of an alkaline-earth metal oxide (MgO, CaO, SrO or BaO) to a Cu/SiO₂-Al₂O₃ catalyst for the vapor-phase synthesis of 3-methylindole from glycerol and aniline was investigated. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption, and thermogravimetric and differential thermal analysis. MgO reinforced the interaction between copper and the support, which promoted the dispersion of Cu particles. In addition, MgO increased the amount of weak acid sites and inhibited the formation of coke. As a result, the addition of MgO to Cu/SiO₂-Al₂O₃ gave a much improved catalyst. Adding CaO, SrO or BaO to Cu/SiO₂-Al₂O₃ deteriorated the catalysts because the dispersion of Cu particles became worse and the amounts of weak acid sites on Cu-SrO/SiO₂-Al₂O₃ and Cu-BaO/SiO₂-Al₂O₃ were fewer. The addition of the alkaline-earth metal oxides did not change the texture of the coke formed.

Key words: copper, silica, aluminum oxide, alkaline-earth metal oxides, 3-methylindole, glycerol, aniline