Solvent-free technique was employed in this work in order to assess the influence of the calcination temperature on the activity of Al-promoted sulfated zirconia. The catalyst was analyzed by XRD and IR-spectrum method, and catalytic activity was examined by esterification reaction of oleic acid. XRD analysis revealed that a decline in the percentage of tetragonal phases of zirconia was observed by increasing the calcination temperature from 500 to 900 °C. In addition, a reduction of sulfate groups as SO4 (2–) on zirconia surface was observed. As a consequence, a decline in Brønsted sites with calcination temperature enhancement also prevailed. Therefore, the size of Al-promoted sulfated zirconia particles was increased accordingly. On the other hand, with the aluminum sulfate loading, the amount of sulfate ions on Al-promoted sulfated zirconia surface was enhanced and a reduction in particle size of Al2O3/S-ZrO2 was also observed, as compared to non-promoted. The result of this study revealed that an increase of sulfate and alumina groups causes a raise in the acidity of catalyst. Furthermore, the calcined Al-promoted and non-promoted sulfated zirconia would convert 96.10 % and 89.36 % of oleic acid to biodiesel, respectively. Therefore, Al2O3/S-ZrO2 as a catalyst exhibits a higher activity than S-ZrO2.

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