Bubble-template synthesis of WO3·0.5H2O hollow spheres as a high-activity catalyst for catalytic oxidation of benzyl alcohol to benzaldehyde

Abstract

Although significant progress has been made in WO₃ hollow spheres, it is still a challenge to synthesize WO₃·0.5H₂O hollow spheres. Herein, a strategy for the preparation of well-shaped WO₃·0.5H₂O hollow spheres was developed by a facile bubble-template method using urea as a foaming agent in the solvothermal process with EtOH–H₂O mixture solvent. In this process, the growth of WO₃·0.5H₂O nanoparticles is limited by N-containing organic compounds, thus these nanoparticles tend to agglomerate along the surface of bubbles (CO₂ and NH₃) to fabricate hollow spheres with pores formed in the wall, and after low temperature calcination, pure WO₃·0.5H₂O hollow spheres are obtained. The obtained WO₃·0.5H₂O hollow spheres exhibit enhanced activity in catalytic oxidation of benzyl alcohol to benzaldehyde: the conversions of benzyl alcohol, 4-methyl, 3-methyl, 2-methyl, 4-bromo and 4-nitro benzyl alcohol are 99.2%, 95.0%, 97.1%, 86.7%, 98.0%, 90.6%, respectively, and the selectivities to corresponding benzaldehydes are all greater than 98%. The high activity of WO₃·0.5H₂O hollow spheres could be attributed to surface –OH groups and the hollow and porous structure.