SYNTHESIS AND CHARACTERIZATION OF CERIA-TITANIA BASED PHOTOCATALYSTS WITH FLOWER-LIKE MORPHOLOGY FOR THE PREFERENTIAL OXIDATION OF CO IN H2-RICH STREAM

Abstract

Despite of the huge number of applications of titania (TiO2), a non-toxic, low cost and very promising photocatalyst, there are some critical factors that limit its photoactivity, first of all the fact that titania is a semiconductor only active in the UV region of the light spectrum. Several methods have been proposed to extend its working region of light spectrum by reducing its energy-gap value, for example noble metal deposition, surface modifications and doping with transition metal ions or rare earth elements. Ceria (CeO2) has attracted great attentions due to its unique properties, such as biocompatibility, chemical inertness and strong oxidizing capability related to the formation of oxygen defects. CeO2-TiO2 systems seem to exhibit improved photocatalytic activity due to the enhanced mobility of excitons and/or a reduced band gap. Also noble metal nanoparticles such as Au, Ag, Pd or Pt have arisen as excellent means to enhance photocatalytic activity thanks to their outstanding properties. Their high optical absorption in a wide range of solar light, together with their reactivity at low temperatures and low cytotoxicity makes them suitable candidates for a new generation of proficient sunlight photocatalysts for environmental applications. The present work sets out to analyse the photocatalytic activity of Au nanoparticles supported on CeO2-TiO2 matrices with a flower-like morphology in the CO preferential oxidation in hydrogen rich streams, at atmospheric pressure and ambient temperature, assessing not only the role of each component in the system and on the catalytic response, but also how the role of a peculiar morphology can affect the photocatalysis. CeO2 samples containing different TiO2 loadings (10-90 wt%) were synthesized with a flower-like morphology by a slow co-precipitation method. Au nanoparticles (1.0 wt% nominal loading) were deposited on the surface of the mixed oxide by a deposition-precipitation method and characterized by many techniques. Surface and bulk chemistry was evaluated by using X-ray powder diffraction (XRPD), X-ray photoelectron Spectroscopy (XPS); morphological characterization was carried out by high resolution transmission electron microscopy (HRTEM) and by Scanning Electron Microscope (SEM); porosity and textural properties were measured by N2 physisorption and the optical properties were studied by UV-vis spectroscopy (DRIFT UV-vis). Finally, the samples were tested in the preferential photo-oxidation of CO to CO2 in excess of hydrogen under simulated solar light.