Enhanced activity of sol-gel prepared SnOx-TiO2 in photocatalytic methanol reforming

Objective: In this contribution a simple method is elaborated for the preparation of Pt/SnOx-TiO2 catalysts which are active in the photocatalytic reforming of methanol. The region of low tin content (Sn/Ti atomic ratio: 0-0.015) is explored. Tin content related activity changes of the catalysts are discussed in terms of the results of structural characterization. Methods: Tin-modified anatase TiO2 samples were obtained from sol-gel method by use of Ti-isopropoxide, SnCl4 or Sn(OBu)4 and citric acid in absolute ethanol solution followed by calcinations at 400°C in air. After loading Pt by impregnation the catalytic activity has been tested irradiating the slurry of the catalysts suspended in mixture of water and methanol by means of two different light sources, one working exclusively in the visible region and one in a broader spectral range including a UV-component, respectively. Hydrogen production activity has been correlated with structural data obtained from different characterization techniques such as ESR spectroscopy, XRD, XPS, SEM and Raman spectroscopy as well as diffuse reflectance UV-Vis spectrophotometry. Results: According to ESR spectroscopic measurements the presence of oxygen vacancies was responsible for the slight visible light absorption. XRD, XPS, SEM and Raman spectroscopic results indicated that highly dispersed SnOx accumulated in the surface region of TiO2, no tin incorporation into the lattice was observed. The fundamental band gap was not influenced by the presence of tin. Loading of the tin-modified samples by 0.5 wt% Pt increased the hydrogen production in comparison to 0.5 wt% Pt/TiO2 samples. Conclusions: The improvement in the catalytic activity was explained by formation of new tin related charge carrier traps leading to (i) prevention of electron-hole recombination and (ii) additional modification of the adsorption of reactants. Details of the two different working mechanisms are described. Practice implication The increased hydrogen production over the tin modified samples provides a promising step toward practical usage of light for hydrogen production. © 2013 Elsevier B.V. All rights reserved