Showing papers by "Marcos Fernández-García published in 2011"

Morphological and Structural Changes during the Reduction and Reoxidation of CuO/CeO2 and Ce1-xCuxO2 Nanocatalysts: In Situ Studies with Environmental TEM XRD and XAS

Abstract: We have studied the structural, morphological, and electronic properties of CuO/CeO2 and Ce1–xCuxO2 nanocatalysts during reduction/oxidation cycles using H2 and O2 as chemical probes. Time-resolved in situ characterization was performed by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) as well as aberration-corrected environmental transmission electron microscopy (ETEM). We have found that both types of nanocatalysts reduce to a Cu/CeO2 biphase system with significant oxygen vacancies in CeO2. Important variations are seen in the Cu particle size and metal dispersion depending on the initial state of the copper oxide–ceria systems. During subsequent in situ oxygen annealing, the Cu precipitated from the CuO/CeO2 system reoxidized to form CuO through a Cu2O intermediate phase as expected. However, the Cu precipitated from the Ce0.8Cu0.2O2 solid solution behaved rather differently under oxidizing conditions, and neither oxidized to form CuO nor fully returned to a bulk Ce0.8Cu0.2O2 phase in...

Nanoparticulate Pd supported catalysts: size-dependent formation of Pd(I)/Pd(0) and their role in CO elimination

Abstract: A combination of time-resolved X-ray absorption spectroscopy (XAS), hard X-ray diffraction (HXRD), diffuse reflectance infrared spectroscopy (DRIFTS), and mass spectrometry (MS) reveals a series of size-dependent phenomena at Pd nanoparticles upon CO/(NO+O2) cycling conditions. The multitechnique approach and analysis show that such size-dependent phenomena are critical for understanding Pd CO elimination behavior and, particularly, that different Pd(I) and Pd(0) centers act as active species for a size estimated by XAS to be, respectively, below and above ca. 3 nm. The relative catalytic performance of these two noble metal species indicates the intrinsic higher activity of the Pd(I) species.

Tailoring polymer–TiO2 film properties by presence of metal (Ag, Cu, Zn) species: Optimization of antimicrobial properties

Abstract: Presence of metallic Ag or oxidic Cu and Zn species on an anatase surface is shown to allow drastic improvement of the disinfection capability of polymer-based TiO2-containing nanocomposite films against both gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria and upon both ultraviolet and visible light excitations. The inorganic incorporation to the polymer matrix is reached without alteration of the main physico-chemical (structural and thermal) characteristics of the organic component. Irrespective of the excitation wavelength, the disinfection capability improvement is observed for Ag and Zn promoted film materials but not for the Cu-containing composite. A study of the optical properties attempts to interpret the biocidal enhancement observed in presence of such Ag, Cu, and Zn-containing species at inorganic–organic interfaces.