Sulfated Alumina Aerogels: Effect of the Sulfur Introduction Method on the Catalytic Performance in Acid-Catalyzed Reactions

Abstract

The goal of this study was to prepare sulfated alumina aerogels and investigate their textural properties, morphology, acidity, and catalytic activity in ethanol dehydration and esterification of decanoic acid with methanol. Alumina aerogels were synthesized by hydrolysis of an aluminum isopropoxide solution in isopropanol followed by supercritical drying in an autoclave at 265 °C. For the synthesis of sulfated alumina aerogels, sulfuric acid was either introduced into the solution prior to hydrolysis and formation of the gels or added by incipient wetness impregnation of the alumina aerogel calcined at 550 °C using an H2SO4 solution in ethanol. Sulfated alumina aerogels prepared by solution modification with H2SO4 had significantly higher concentrations of weak electron-acceptor sites compared to pure alumina. The catalytic activity of the prepared aerogels was tested in two catalytic reactions taking place on surface acid sites: ethanol dehydration and esterification of decanoic acid with methanol. Only the sample prepared by impregnation showed high catalytic activity in both studied reactions. This sample also had a substantially higher concentration of Br nsted acid sites measured by Fourier-transform infrared (FTIR) after adsorption of pyridine. So, it appears to be a promising acid catalyst with high surface area and high acidity.