Enhanced catalytic performance of highly mesoporous hydrotalcite/SBA-15 composites involved in chromene multicomponent synthesis

Abstract

Abstract A series of highly porous hydrotalcite/SBA-15 composites were synthesized and used as catalysts, for the first time, in the multicomponent synthesis of chromenes, from 2-hydroxybenzaldehydes and cyano compounds, with enolizable hydrogens, under solvent-free and mild conditions. The composites were prepared by ultrasound irradiation in the crystallization step, as non-conventional energy source, using different hydrotalcite/SBA-15 proportions. HT30-SBA composite, with lower hydrotalcite loading and high developed porosity, presented superior catalytic performance affording the corresponding chromenes in excellent conversions with total selectivity, after considerably decreased reaction times. The observed reactivity was mainly attributed to the high dispersion of small particles of hydrotalcite on the SBA-15 component, contributing to a great enhancement of the mesoporosity. The high dispersion promoted the increase of the surface area given rise to a high concentration of superficial hydroxyls as more accessible catalytic sites, responsible to the catalytic activity. Therefore, our results demonstrate that percentage of hydrotalcite component, dispersion of hydrotalcite nanoparticles and texture of the composites strongly influence the catalytic performance.