Nano-crystalline, mesoporous aerogel sulfated zirconia as an efficient catalyst for esterification of stearic acid with methanol

Abstract Aerogel sulfated zirconia (A-SZr) solid acid catalyst was prepared by sol–gel method followed by supercritical drying (SCD) using n-propanol as alcoholic solvent. For comparison, xerogel sulfated zirconia (X-SZr) was also prepared by sol–gel followed by conventional thermal drying method. A-SZr catalyst has lower nano-crystallite size, higher BET surface area, pore volume and ordered mesoporous structure with complete absence of micropores along with more number of scattered and accessible Bronsted and Lewis acid sites as compared to X-SZr. The evaluation of its catalytic performance for esterification of stearic acid with methanol exhibited 88% yield of methyl stearate at 60 °C after 7 h. A-SZr catalyst showed significant higher reaction rate (18.94 mmol h−1 g−1) and TOF (8.55 h−1) than X-SZr (12.94 mmol h−1 g−1 and 3.92 h−1, respectively). A-SZr catalyst also exhibited higher activity than other heterogeneous acid catalysts such as ion-exchange resins, Nafion and acid clay under the similar reaction conditions; as well as it showed comparable activity with conventional Bronsted (H2SO4) and Lewis (ZrOCl2) acids indicating its potential to replace the homogeneous acid catalysts.