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

Combustion synthesis was used to prepare zirconia, which was sulfated to increase the sulfur content to 15% w/w with retention of the tetragonal phase, which rendered it a very strong superacidity. This high value is reported for the first time. The catalyst synthesis parameters were optimized using Friedel–Crafts alkylation as a probe reaction. The catalyst was fully characterized and used in Pechmann condensation. [Display omitted] ► A novel zirconia-based catalyst through combustion synthesis. ► First report of highest superacidity relative to the conventional sulfated zirconia. ► Characterization by XRD, FTIR, TPD, EDAX, SEM, and BET surface area and pore size analysis. ► Pechmann condensation reaction of resorcinol and ethyl acetoacetate. ► Mechanism and kinetics of reaction. 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.