Abstract
The effect of the ZrO(2) loading was studied on spherical SiO(2)@ZrO(2)-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 N(2) adsorption, where the increment in SiO(2) spheres' surface areas was reached with the incorporation of ZrO(2). 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 SiO(2)@ZrO(2) 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 SiO(2) 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-ZrO(2) phase changed in to m-ZrO(2) by incorporating calcium, which was confirmed by Raman spectroscopy. The purity of the SiO(2) spheres, as well as the presence of Zr and Ca in the core-shell, was assessed by the Fourier transform infrared (FTIR) method. CO(2) temperature programmed desorption (TPD-CO(2)) 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.