Two series of nanostructured oxidized copper-cerium catalysts with varying copper loadings, and prepared, respectively, by impregnation of ceria and by coprecipitation of the two components within reverse microemulsions, have been characterized in detail at structural and electronic levels by X-ray diffraction (XRD), Raman spectroscopy, high-resolution electron microscopy (HREM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) (including Ar + -sputtering), and X-ray absorption fine structure (XAFS). These results have been correlated with analysis of their catalytic properties for preferential oxidation of CO in a H 2 -rich stream (CO-PROX), complemented by Operando-DRIFTS. A relevant difference between the two series of catalysts concerns the nature of the support for the surface-dispersed copper oxide entities, which is essentially ceria for the samples prepared by impregnation and a Ce-Cu mixed oxide for those prepared by microemulsion-coprecipitation. The existence of copper segregation in the form of copper oxide or copper-enriched Cu-Ce mixed oxides for the latter type of samples is uniquely revealed by nanoprobe XEDS and XPS Ar + -sputtering experiments. The CO oxidation activity under CO-PROX conditions is correlated to the degree of support-promoted reduction achieved by the dispersed copper oxide particles under reaction conditions. Nevertheless, catalysts which display higher CO oxidation activity are generally more efficient also for the undesired H 2 oxidation reaction. The balance between both reactions results in differences in the CO-PROX activity between the two series of catalysts which are examined on the basis of the structural differences found.

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Nanostructured TiO2 samples with primary particle size in the 4−20 nm range were prepared by either hydrothermal (H) or thermal (T) treatment of an amorphous precursor, and their behavior under UV illumination at 77 K was studied by means of EPR spectroscopy. The samples of the H series present the smallest crystallite size and after irradiation in a vacuum show some Ti3+ centers. In contrast, under these conditions only weak signals associated with oxygenated radicals are observed for the T samples. However, when oxygen is preadsorbed, several oxygenated complexes (O-, O2 -, O2H•, and O3 -) are photogenerated in proportions that depend on the characteristics of the material. Subsurface O- species are exclusively detected in the case of the samples of the H series, whereas ozonide radicals and surface O- are stabilized on materials with larger crystalline domains. These oxygenated complexes are thermally unstable, and they disappeared after warming to room temperature in the case of the T samples, but they are transformed to O2 - on the surface of the hydrothermally treated TiO2. Since adsorbed water and different types of free hydroxyls are present on these materials, as revealed by FTIR, a number of surface reactions have to be considered in order to account for the formation and stability of such photogenerated species.

The electronic structure and properties of the orthorhombic phase of the CH 3 NH 3 PbI 3 perovskite are computed with density functional theory. The structure, optimized using a van der Waals functional, reproduces closely the unit cell volume. The experimental band gap is reproduced accurately by combining spin-orbit effects and a hybrid functional in which the fraction of exact exchange is tuned self-consistently to the optical dielectric constant. Including spin-orbit coupling strongly reduces the anisotropy of the effective mass tensor, predicting a low electron effective mass in all crystal directions. The computed binding energy of the unrelaxed exciton agrees with experimental data, and the values found imply a fast exciton dissociation at ambient temperature. Also polaron masses for the separated carriers are estimated. The values of all these parameters agree with recent indications that fast dynamics and large carrier diffusion lengths are key in the high photovoltaic efficiencies shown by these materials.

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NO adsorption on CeO, pre-outgassed at different temperatures (T,) has been studied by EPR and FTIR. The results are compared with those obtained by measuring the products of the reaction, performed at 323 K, between NO and CeO, samples activated by previous heating under N, flow. EPR results indicate that, for T, 2 573 K, NO molecules are adsorbed in radical form at 77 K and react at 298 K with surface oxygen vacancies generating diamagnetic products. FTIR spectra show correspondingly the formation of hyponitrites, nitrites and nitrates upon NO adsorption at 298 K on CeO, outgassed at different temperatures. The hyponitrites can decompose at ambient temperatures to produce N,O; the process leads to modification (probably reoxidation) of the surface centres initially present. This can be followed by 0, adsorption and EPR spectroscopy, which shows that 0,adsorbed on the modified vacancies is less stable than on CeO, without NO adsorbed, its reaction leading in some cases to the formation of peroxynitrate-type radicals. The reaction at 323 K of NO on the pretreated CeO, surface produced N, O for pretreatment temperatures T, 2 573 K, in amounts increasing with J , . The results indicate that surface centres containing associated oxygen vacancies are active sites for this process.The use of CeO, as an additive in many 'three way' catalyst formulations used in car exhausts has caused a great interest in the properties of this oxide.'-3 Initially, CeO, was included to act as oxygen storage, supplying oxygen to the reaction under hydrocarbon-rich conditions and withdrawing oxygen under poor conditions, thus widening the catalyst operation window near the stoichiometric conditions. However, some additional effects of CeO, have been found, such as improving the active metal dispersion4*' or catalysing by itself some of the reactions that take place on the car exhaust c a t a l y ~t . ~? ~ To determine how CeO, participates in these processes, a first aspect to clarify is the effect that the reaction conditions have on the state of the ceria surface. Considering that oxygen vacancies, together with Ce3 .t ions, are expected to be formed easily on CeO, under reducing conditions, these ions can be postulated as possible active sites for redox reactions.In a previous work, we studied the formation of reduced centres involving oxygen vacancies at the CeO, surface as a result of outgassing treatments. 0, adsorption, followed by EPR, was used there as a method to classify the different types of vacancies.8 Thus, on the basis of their EPR signal parameters the 0,species could be grouped into two types, which were assigned to 0, -radicals adsorbed, respectively, at isolated and associated oxygen vacancies. The different EPR parameters of the superoxide radicals formed at the two types of adsorption sites suggested that these had different electron densities, possibly implying different reactivities toward adsorbed species.To clarify this point, in the present work we studied by EPR and FTIR the adsorbed species formed by exposing ...

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