CaO catalysts supported on Zr-doped Puralox alumina for biodiesel production via transesterification

Abstract The development of stable, recyclable solid-based catalysts remains a major challenge in heterogeneous biodiesel production, due to CaO leaching and limited durability. This study evaluates, for the first time, the use of a commercial Zr-doped alumina support (Sasol Puralox SCFa-190 Zr20) combined with eggshell-derived CaO as a potential strategy to enhance catalyst stabilization. CaO was calcined at 800 °C and impregnated onto the support at 40, 50, and 60 wt% loadings, yielding catalysts CaP40, CaP50, and CaP60. Structural characterization by XRD and SEM revealed the formation of portlandite and calcium aluminate phases with high crystallinity, along with progressive surface coverage of alumina particles by calcic agglomerates and flake-like structures. The supported catalysts exhibited strong basicity and a significant increase in basic site density compared to the bare support. Under reaction conditions (60 °C, methanol-to-oil molar ratio 10:1, 6 wt% catalyst, 1 h), CaP50 and CaP60 achieved biodiesel yields of 98% using soybean oil and waste palm olein. However, catalytic activity decreased upon reuse due to Ca leaching and surface blockage; thermal reactivation at 800 °C partially restored performance. These results indicate that the alumina-zirconia support promotes the dispersion of active Ca species and favors the formation of mixed oxide phases, thereby improving structural stability during reuse.