Photocatalytic Production of Vanillin over CeOx and ZrO2 Modified Biomass-Templated Titania

Walnut shell residues have been used as a sacrificial template in the synthesis of TiO2-based materials via mechanochemical synthesis. To improve the photocatalytic efficiency of the synthesized titania nanomaterials, functionalization with ceria and zircona was also investigated. Samples were characterized using a multitechnique approach, including X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectroscopy, and scanning electron microscopy. Synthesized materials were employed as catalysts in the photooxidation reaction of vanillyl alcohol toward vanillin, a compound of great interest due to its organoleptic properties. Such photocatalytic experiments were carried out in a batch-type photoreactor using a LED 12 V efficient emission lamp with a wavelength of 395 nm. The use of walnut shell could facilitate the preparation of nanostructured materials. The incorporation of Ce and Zr oxides on the titania surface gave rise to an increased absorption of visible light, together with the improvement of electronic properties, therefore enhancing photocatalytic efficiency as compared to pure TiO2. An optimum catalytic behavior was observed for 1Ce/TiO2-BS and 5Zr/TiO2-BS, with a maximum conversion of 39.7% and 52.4% for ceria and zirconia modified samples, respectively. Selectivity values of 99% toward vanillin and a carbon balance higher than 98% were achieved in all cases.