Amorphous Sn/Si Mixed Oxides, Mild Solid Lewis Acid Catalysts for Esterification and Etherification Reactions

Novel amorphous porous mixed oxides of Sn, Si, and Al were prepared by the sol–gel process for use as solid acid catalysts. The materials were characterized by XRD, HRTEM, SEM, EDX, argon-physisorption, DRIFTS, and pyridine adsorption followed by FTIR. The catalysts show very few Brønsted sites and some Lewis acid sites. The pore architecture of the materials was studied by the hydrocracking test of decane which indicated weak activity but clear shape selectivity for most of the mixed oxides. Further catalytic testing included the direct esterification reaction of pentaerythritol with stearic acid to pentaerythritoltetrastearate and the etherification of 1-hexanol and 1-naphthol with isobutene. The esterification reaction was studied under reaction conditions close to industrial ones. The catalysts were found to be as active as commercial homogeneous and heterogeneous catalysts. While the activity found in the esterification reaction can be correlated with the increase in surface area and the decrease in Sn content, no correlation with microstructural parameters was found in the etherification reactions.