Hierarchical Na-doped cubic ZrO₂ synthesis by a simple hydrothermal route and its application in biodiesel production

Hierarchical growth of cubic ZrO₂ phase was successfully synthesized via a simple hydrothermal process in the presence of different surfactants (cationic, non-ionic and anionic) and sodium hydroxide. The structural and microstructural characterizations of different ZrO₂ powders were performed using various techniques, such as X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption, scanning electron microscopy and infrared. Results indicated that sodium addition stabilized the cubic ZrO₂ phase by a Na-doping process, independently of the surfactant used. In contrast, microstructural characteristics varied as a function of the surfactant and sodium presence. In addition, water vapor (H₂O) and carbon dioxide (CO₂) sorption properties were evaluated on ZrO₂ samples. Results evidenced that sample surface reactivity changed as a function of the sodium content. Finally, this surface reactivity was evaluated on the biodiesel transesterification reaction using the different synthesized samples, obtaining yields of 93%.