Preparation of highly superacidic sulfated zirconia via combustion synthesis and its application in Pechmann condensation of resorcinol with ethyl acetoacetate

Abstract

A novel zirconia-based catalyst, with high sulfur content (15% w/w) and preservation of the tetragonal phase of zirconia, was synthesized for the first time via a solution combustion synthesis approach. Such high sulfur content with preservation of the tetragonal phase has not been reported so far. The catalyst synthesis parameters were optimized using a probe reaction of Friedel–Crafts alkylation. The optimized catalysts, fuel-lean sulfated zirconia (FLSZ) and fuel-rich sulfated zirconia (FRSZ), were characterized by XRD, FTIR, TPD, EDAX, SEM, and BET surface area and pore size analysis. Further, the activity and stability of FLSZ was tested using a Pechmann condensation reaction between resorcinol and ethyl acetoacetate to produce 7-hydroxy 4-methyl coumarin selectively. A complete theoretical and experimental analysis is presented, and a kinetic model is developed for this reaction. The model explains the experimental data well. The characterization and reaction studies show that combustion-synthesized sulfated zirconia exhibits higher superacidity than the conventional sulfated zirconia catalyst.