In-situ XANES studies of the reduction process of Ce0.9Zr0.1O2 nanocatalysts

M.G. ZIMICZ; LARRONDO S.A.; R.J. PRADO; D.G. LAMAS

Campinas

Congreso; 21ª RAU (Reunión Anual de Usuarios del Laboratorio Nacional de Luz Sincrotron); 2011

The reduction of particle size to the nanometric level has put in evidence its influence in the structural, electronic and chemical properties of solids. Due to the fact that heterogeneous catalysis is related with surface structure and gas-solid or liquid-solid surface interactions, there is a strong influence of particle size in catalysts performances. In this work the objective was to study the interaction of Hydrogen (H2) with the Ce-Zr mixed oxide with nominal composition Ce0.9Zr0.1O2, synthesized via the nitrate- a-aminoacid combustion process using different a-aminoacids. All the solids have nanometric particle size. Temperature Programmed Reduction (TPR) and in-situ XANES experiments near the Ce LIII edge were performed. In both experiments, the sample was heated with a temperature ramp of 10°C/min in a flow consisted of Hydrogen (H2) (5% mol) in Helium (He). The TPR experiments were carried out with a Micromeritics Autochem II 2920. The in-situ XANES experiments were carried out at the D06A-DXAS dispersive beamline of the Brazilian synchrotron Light Laboratory (LNLS), Campinas, Brazil. The D06A-DXAS dispersive beamline is equipped with a Si(111) monochromator and an image-plate detector to collect the absorption spectra. Besides, a mass spectrometer Quadrupole Mass Spectrometer QMS 422 Pfeiffer was connected to exhaust gases in order to register H2 and water concentration during in-situ XANES experiments. The analysis of the experimental results allow to establish the influence of synthesis conditions on the temperatures of the beginning and end of the reduction process and the evolution of the ratio Ce3+/Ce4+ during the reduction process. With this analysis, a better understanding of the reduction mechanism of the solids was achieved.