Application of microwave irradiation for fabrication of sulfated ZrO2– Al2O3 nanocomposite via combustion method for esterification reaction: process condition evaluation

The zirconia–alumina nanocatalyst was prepared using microwave combustion method, and the effects of alumina/zirconia ratio, fuel-to-oxidizer ratio, and calcination temperature on its structural and chemical performance were examined. Furthermore, the most suitable synthesized nanocatalyst was impregnated using different dosages of sulfate group to improve the activity of the sample for the esterification reaction. The results revealed that there was a significant improvement in the crystalline structure of alumina and zirconia for the samples having the alumina/zirconia ratio of 2. It was also noted that some amorphous structures were observed for low fuel dosages, while the activity of the sample was reduced with higher fuel consumption than the stoichiometric ratio, which can be attributed to the increase in the crystallite size and formation of different alumina phases. Based on calcination results, non-considerable changes were observed in the morphology and activity of the catalyst. It can be concluded that the solution combustion method is suitable for nanocatalyst preparation without any requirement of further thermal treatment. In addition, the activity of the sample was enhanced by impregnation with H2SO4 where the conversion of 91.6% was achieved. The catalyst showed high reusability at least for seven times as well as high stability of zirconia–alumina as a support.