Si/Zr mesoporous catalysts for the vapour phase synthesis of alkylindoles

Abstract

Si/Zr mesoporous MCM-41 catalysts were investigated in the vapour phase synthesis of 7-ethylindole (7-ETI) starting from 2-ethylaniline (2-ETAN) and ethylene glycol (EG). The catalysts were prepared from the corresponding alkoxides in the presence of a cationic surfactant, which acts as a structure-directing agent. After removal of the surfactant, the resulting mesoporous solids were characterised by X-ray diffraction, N 2 adsorption–desorption, temperature programmed desorption (TPD) of NH 3 and pyridine adsorption coupled with FTIR spectroscopy. As the amount of ZrO 2 increased in the catalysts, the BET surface area decreased, while an enhancement of the acidity took place. The activation of EG to 2-hydroxyacetaldehyde and its attack on 2-ETAN, leading to the formation of 7-ETI, was favoured by increasing the amount of ZrO 2 The maximum yield for the catalyst was obtained with ca. 50 wt.% of ZrO 2, which promoted the presence of Lewis and Brönsted acid sites of suitable strength and concentration, although mesoporous catalysts exhibited very good regenerability.