Effect of alkali and alkaline earth metal ions on benzyl alcohol oxidation activity of titanate nanotube-supported Au catalystsElectronic supplementary information (ESI) available: XRD, CO2-TPD profiles, DRUV-vis spectra and XPS profiles of Au/ATNT, N2 physisorption of supports, correlation profiles of basicity versus uptake and particle size of Au and B.E. values versus TOF and catalytic activity data. See DOI: 10.1039/c5ra06496a

• Main Authors: Nepak, Devadutta, Srinivas, Darbha
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c5ra06496a

Sodium titanate nanotubes (NaTNTs) were prepared by alkali treatment of anatase titania. They were then ion-exchanged with alkali and alkaline earth metal ions to get ATNTs (A = Li + , K + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ ). Gold (1-5 wt%) was supported on these nanotubes by a deposition-precipitation method and investigated as a catalyst for the selective oxidation of benzyl alcohol with air/molecular oxygen (1 atm) under solvent- and alkali-free conditions. Detailed characterization by X-ray powder diffraction, high resolution transmission electron microscopy, N 2 -physisorption, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy and CO 2 -temperature-programmed desorption techniques revealed that the basicity of the catalyst influences the uptake, mean particle size, electronic properties and oxidation activity of the supported gold. Benzaldehyde formed with a selectivity of about 99%. The catalytic activity (turnover frequency) was found to have a direct relationship with the basicity and an inverse relationship with the Au particle size. Among the catalysts investigated, Au/BaTNTs, having higher basicity, smaller Au particles and higher metal dispersion, showed enhanced catalytic activity than the other Au/ATNT catalysts. Pd addition to Au leading to Au-Pd/BaTNTs increased the activity (TOF) but lowered the selectivity for benzaldehyde (80 wt%). Titanate nanotubes donate electron density to Au particles, yielding electron rich Au ions, which are responsible for activating molecular oxygen and oxidizing benzyl alcohol. Au/BaTNTs, having higher basicity and lower size Au nanoparticles than the other Au/ATNT, activates molecular oxygen more easily and thereby enhances the catalytic activity. Au supported on barium titanate nanotubes showed higher catalytic activity for selective oxidation of benzyl alcohol with molecular oxygen.