Analysis of transesterification activity at high temperature of zirconia-based solid solution catalysts

Solid solution catalysts composed of ZrO₂ and a group 2 metal oxide MgO, CaO or SrO were prepared by milling with a planetary mill and subsequent calcination, and the relationship between the properties of MgO‒ZrO₂, CaO‒ ZrO₂ and SrO‒ZrO₂ and their catalytic transesterification activities was examined. XRD and Raman spectroscopy helped to confirm that zirconia-based solid solution catalysts of MgO‒ZrO₂, CaO‒ZrO₂ and SrO‒ZrO₂ were composed of multiple crystal phases of which the tetragonal or cubic phase was predominant. Analysis of CO₂-TPD and NH₃-TPD data suggested that the electronegativity of group 2 metals should affect the acidity of solid solution catalysts. Batch transesterification of rapeseed oil with ethanol at 473 K with solid solution catalysts having a 1: 4 mol ratio of group 2 metal to Zr revealed that MgO‒ZrO₂ with the weakest acidic strength of the catalysts tested had the highest catalytic activity. The results of characterization and batch transesterification with MgO‒ZrO₂ catalysts having different Mg contents showed that the mole ratio of Mg to Zr determines the acidity of the catalyst. Thus, the acidity of the solid solution catalysts significantly affects the catalytic transesterification activity.