The effect of the ZrO₂ loading in SiO₂@ZrO₂-CaO catalysts for transesterification reaction

The effect of the ZrO₂ loading was studied on spherical SiO₂@ZrO₂-CaO structures synthetized by a simple route that combines the Stöber and sol-gel methods. The texture of these materials was determined using S_BET by N₂ adsorption, where the increment in SiO₂ spheres' surface areas was reached with the incorporation of ZrO₂. Combined the characterization techniques of using different alcoholic dissolutions of zirconium (VI) butoxide 0.04 M, 0.06 M, and 0.08 M, we obtained SiO₂@ZrO₂ materials with 5.7, 20.2, and 25.2 wt % of Zr. Transmission electron microscopy (TEM) analysis also uncovered the shape and reproducibility of the SiO₂ spheres. The presence of Zr and Ca in the core-shell was also determined by TEM. X-ray diffraction (XRD) profiles showed that the c-ZrO₂ phase changed in to m-ZrO₂ by incorporating calcium, which was confirmed by Raman spectroscopy. The purity of the SiO₂ spheres, as well as the presence of Zr and Ca in the core-shell, was assessed by the Fourier transform infrared (FTIR) method. CO₂ temperature programmed desorption (TPD-CO₂) measurements confirmed the increment in the amount of the basic sites and strength of these basic sites due to calcium incorporation. The catalyst reuse in FAME production from canola oil transesterification allowed confirmation that these calcium core@shell catalysts turn out to be actives and stables for this reaction.