The role of WOx and dopants (ZrO2 and SiO2) on CeO2-based nanostructure catalysts in the selective oxidation of benzyl alcohol to benzaldehyde under ambient conditions

Abstract

Herein, the efficacy of WO_x-promoted CeO₂–SiO₂ and CeO₂–ZrO₂ mixed oxide catalysts in the solvent-free selective oxidation of benzyl alcohol to benzaldehyde using molecular oxygen as an oxidant is reported. We evaluated the effects of the oxidant and catalyst concentration, reaction duration, and temperature on the reaction with an aim to optimize the reaction conditions. The as-prepared CeO₂, CeO₂–ZrO₂, CeO₂–SiO₂, WO_x/CeO₂, WO_x/CeO₂–ZrO₂, and WO_x/CeO₂–SiO₂ catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, Raman spectroscopy, temperature-programmed desorption of ammonia (TPD-NH₃), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). These characterisation results indicated that the WO_x/CeO₂–SiO₂ catalyst possessed improved physicochemical (i.e., structural, textural, and acidic) properties owing to the strong interactivity between WO_x and CeO₂–SiO₂. A higher number of Ce³⁺ ions (I_u′′′/I_Total) were created with the WO_x/CeO₂–SiO₂ catalyst than those with the other catalysts in this work, indicating the generation of a high number of oxygen vacancies. The WO_x/CeO₂–SiO₂ catalyst exhibited a high conversion of benzyl alcohol (>99%) and a high selectivity (100%) toward benzaldehyde compared to the other promoted catalysts (i.e., WO_x/CeO₂ and WO_x/CeO₂–ZrO₂), which is attributed to the smaller particle size of the WO_x and CeO₂ and their high specific surface area, more significant number of acidic sites, and superior number of oxygen vacancies. The WO_x/CeO₂–SiO₂ catalyst could be quickly recovered and utilized at least five times without suffering any appreciable activity loss.