The CeO2 and Ce x Zr1 - x O2 reduction by hydrogen was studied using IR spectroscopy to follow the evolution of the ν(OH) vibrational modes and a magnetic balance to estimate the global reduction percentage from the magnetic susceptibility. H2 was introduced between 298 and 873 K on activated samples. On ceria, different OH groups exist depending on cerium unsaturation. In particular, the band due to OH type II shifts toward higher frequencies when ceria is reduced. It is therefore possible to monitor the surface oxidation state of ceria or mixed oxides through the ν(OH) band wavenumber. For ceria, the surface reduction begins at around 573 K. That leads to the formation of OH(I) species and adsorbed H2O which are observed at the beginning of the reduction. Their elimination leads to the creation of surface O-vacancies. At higher temperatures, there is a surface/subsurface reorganization through the reverse migration of O-vacancies and O-ions from the bulk. However, the adsorption sites are conserved during the evacuation step, the bonded OH, OH(II−B), and OH(II-A) species disappearing by evacuation in the range 773−873 K through H2 (and not H2O) evolution. For mixed Ce x Zr1 - x O2 compounds, the most interesting OH species are those adsorbed on cerium ions. The results lead to the conclusion that the mechanism of reduction is the same as in the case of pure ceria but that an increased mobility of bulk oxygen (in relation with the Zr content) for mixed compounds allows surface oxygen vacancies to be faster filled from O migration in subsurface underlayers. The hydrogen reduction was also followed in a magnetic balance in the case of Ce0.5Zr0.5O2 mixed oxide. The Ce3+ content obtained at different temperatures confirms that the surface reduction is easier for the mixed oxide, the hydrogen chemisorption occurring for T > 373 K and the reduction of Ce4+ into Ce3+ ions beginning at 473 K. Moreover, the better reducibility of the bulk that is observed (76% of Ce3+ at 873 K for the mixed oxide instead of 17% for ceria) evidences the higher oxygen mobility in the bulk, in good agreement with the FTIR conclusions.

The objective of this study was to examine the mechanism of the reduction by hydrogen of ceria-zirconia (CZ) mixed oxides having a high BET surface area (100 m 2 g -1 ). Three methods were used in parallel to assess the Ce 3+ content, the surface and bulk oxygen vacancy concentrations, and the resulting oxygen storage capacity (OSC): temperature programmed reduction, Fourier transform infrared (FT-IR) measurements of methanol adsorbed on the reduced surfaces, and a Faraday microbalance to determine the magnetic susceptibility of the reduced oxides. The three methods conclude that the introduction of zirconium into the ceria lattice has a positive influence on the OSC. Compared to pure ceria, the CZ mixed oxides exhibit better redox properties, with a lower temperature of initial reduction and a higher reduction percentage for all compositions. The reducibility increases with the zirconium content, however the OSC per gram of solid is practically the same for Zr contents between 20% and 50%. The reduction process very rapidly involves the bulk, but a treatment at room temperature under oxygen of the reduced samples oxidizes them almost completely. However, the FT-IR results underline the differing behavior of ceria for the distinct surface and bulk reduction processes.

The surface properties of iron, chromium, and aluminum fluorides in their hexagonal tungsten bronze (HTB) form have been investigated by infrared spectroscopy. The presence of hydroxyls is clearly observed. H/D exchange experiments with different deuterated probe molecules having various molecular sizes show that they are localized inside of the channels of the structure. The ν(OH) bands in the infrared spectra of these materials are downward shifted compared to those of corresponding metal oxides, whereas the δ(OH) in-plane bending mode presents an unusual high wavenumber. These spectral features are compared to those observed on zeolites, for which hydroxyl environment and bridged conformation are similar. HTB compounds exhibit both strong Lewis and Brønsted acid sites. The use of two basic probes with a different size (pyridine and ammonia) allows one to localize and to quantify these two kinds of acidity. Brønsted acidity is related to the presence of hydroxy groups into the microporous channels and to chemisorbed HF, whereas Lewis acidity is due to defect sites both on the outer surface of crystallites and in the channels. The strength of acid sites is unambiguously found stronger than that reported for Al, Cr, and Fe oxides. This result is discussed taking into account the electronegativity of fluorine but also the bridged conformation of OH groups, as in the case of zeolites.

Why Hybrid Porous Solids Capture Greenhouse Gases? -[78 refs.]. -(FEREY*, G.; SERRE, C.; DEVIC, T.; MAURIN, G.; JOBIC, H.; LLEWELLYN, P. L.; DE WEIRELD, G.; VIMONT, A.; DATURI, M.; CHANG, J.-S.; Chem. Soc. Rev. 40 (2011) 2, 550-562, http://dx.doi.org/10.1039/c0cs00040j ; Inst. Lavoisier, CNRS, Univ. Versailles St. Quentin, F-78035 Versailles, Fr.; Eng.) -Lindner 22-272

Cu-SAPO-34 (Cu-CZC) and Fe-Mordenite (Fe-MOR) and their mechanical mixture (50:50) have been exhaustively investigated by means of operando X-ray absorption spectroscopy under NH3-SCR conditions. Fe K-edge XANES and EXAFS analysis...

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The controlled reducibility of coordinatively unsaturated iron sites in MIL‐100(Fe), [Fe3O(H2O)2F0.81(OH)0.19{C6H3(CO2)3}2]⋅14.5 H2O, is described by J.‐S. Chang and co‐workers in their Communication on Thermal activation of MIL‐100(Fe) generates coordinatively unsaturated sites with mixed‐valence FeII/FeIII, leading to preferential sorption selectivity towards unsaturated gas molecules such as propylene.

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