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M(iii)–O and M(iii)–N interaction in [M(Et-Pic)3]3+ (M = Ln and Am; Et-Pic: N,N,N′,N′-tetraethyl-2,6-carboxamidopyridine) complexes were studied. NMR and TRLFS data suggest an increased partial covalent interaction in the An(iii)–N bond.

Model catalysts containing disordered CuO and ZnO species in the pores of SBA-15 were reduced under different conditions (standard: H2, 513 K; severe: CO/H2, 673 K), studied by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) including operando work and used as catalysts for methanol synthesis at pressures up to 8 bar, where they were comparable with a commercial reference in terms of reaction rates related to Cu surface area. Severe reduction caused significant activation of the Cu sites beyond the sizeable level achieved already after standard reduction. In XRD, which failed to detect most of the active components, owing to small particle sizes, weak indications of alloy formation were found after severe reduction. XAFS, which averages over all species present, showed the interaction of Cu with zinc ions to increase by severe reduction, while formation of Zn0 was below detection limit. On this basis, the promoting interaction of Zn to Cu was ascribed to an interaction of zinc cations with Cu0. (Less)

Methanol synthesis was studied with catalysts containing Cu and ZnO in the interior space or on the exterior surface of multi-walled carbon nanotubes (CNTs) and were activated by different procedures – reduction in dilute H 2 at 513 K with or without subsequent exposure to 10% CO/H 2 at 673 K for 30 min. Characterization of the transition-metal species after these treatments by XRD and XAFS revealed striking differences. After mild reduction, XRD reflections related to Cu were missing or were of weak intensity, which could be assigned to very low primary particle sizes as detected by EXAFS. After treatment in CO/H 2 , reflections arising from alloy phases were obtained for all samples while non-alloyed Cu, although observed by EXAFS, escaped detection by XRD due to small primary particle sizes. Reduction of Zn 2+ to Zn(0) was revealed by Zn K XANES only for some samples, which qualifies Zn(0) as a minority oxidation state for the remaining ones. Based on the XANES evidence, a new feature in Zn K EXAFS developing after CO/H 2 treatment was interpreted as arising from either alloying or from an SMSI-type interaction of ZnO 1− x entities with Cu nanoparticle surfaces. The catalysts exhibited very different productivities and responses to the CO/H 2 treatment. In terms of specific activity (related to m 2 Cu), the better samples achieved a multiple of the performance shown by a commercial reference, but suffered from insufficient stability. By contrast, such stability was demonstrated for a catalyst containing Cu/ZnO hosted in SBA-15. A catalyst series based on narrow CNTs previously functionalized by thermal shocks in flowing air stood out due to poor performance for unknown reasons. Due to these uncertainties, the data does not permit clear conclusions on the oxidation state of Zn in the promoting interaction with Cu although the general trends favor Zn 2+ over Zn(0).

Copper and zinc oxide nanoparticles have been reproducibly deposited into carbon nanotubes (CNT) of 6–7 nm internal diameter via simple impregnation techniques with different metal salts followed by thermal decomposition of the precursors and reduction in H2 in case of Cu. Oxygen functionalization via a gas-phase method involving thermal shocks was a critical step while traditional functionalization with nitric acid resulted in failures. Intra-CNT location of CuO particles could be proven by STEM images, and was examined by TEM for materials prepared by various routes. It was found that Cu and Zn oxide nanoparticles could be deposited throughout the whole interior CNT space. The filling capacity depended on the preparation conditions, on conditions of subsequent precursor decomposition, and on the inner diameter of the CNTs. After the reduction of the CuO nanoparticles, XRD, XAFS, and N2O reactive frontal chromatography indicated a bimodal particle size distribution due to the presence of agglomerates outside the CNTs. To enhance selectivity for endohedral location, a washing step with HNO3 with the inner CNT space blocked by xylene was applied to selectively remove aggregates in the outer space. Based on the best procedures for introduction of CuO and ZnO, a bimetallic CuZnO@CNT sample was prepared via a consecutive preparation route.

$Au/TiO_{2}$-Katalysatoren, die durch das “Deposition-Precipitation”-Verfahren hergestellt und ohne Kalzinierung eingesetzt wurden, erreichten in der CO-Oxidation hohe, weitgehend temperaturunabhängige Umsätze. Dagegen erschien nach thermischen Vorbehandlungen, z. B. in He bei 623 K, die Umsatz-Temperatur-Charakteristik in der bekannten S-Form, mit Aktivierungsenergien nahe $30 kJ mol^{−1}$. Charakterisierung der Proben durch XAFS und HAADF-STEM sowie eine Tieftemperatur-IR-Studie von Adsorption und Oxidation des CO zeigten, dass letzteres am frisch präparierten (gefriergetrockneten) Katalysator, der Gold ausschließlich als $Au^{3+}$ enthielt, bereits bei 90 K durch Gasphasensauerstoff oxidiert wurde. Nach Aktivierung im Reaktantenstrom geht der CO-Umsatz bei niedrigen Reaktionstemperaturen auf Zentren zurück, die $Au^{III}$ enthalten, bei höheren Temperaturen wird er von $Au^{0}$ getragen. Nach thermischen Behandlungen wird CO im ganzen Temperaturbereich an Zentren umgesetzt, die ausschließlich metallisches Gold enthalten.

The present investigation was undertaken to know the influence of different dopants on the physicochemical properties and catalytic behavior of nano-Au/CeO2 catalyst for CO oxidation. Accordingly, various metal ions namely, Fe3+, La3+ and Zr4+ were incorporated into the ceria lattice by a facile coprecipitation approach using ultra-high dilute aqueous solutions. An anion adsorption method was used to prepare the Au/doped-CeO2 catalysts in the absence of any base, reducing and protective agents. The physicochemical characterization was performed by XRD, BET surface area, ICP-AES, TG-DTA, FT-IR, TEM, UV–vis DRS, Raman, XPS and TPD techniques. Doped CeO2 exhibited smaller crystallite size, higher BET surface area and larger amount of oxygen vacancies than the pure CeO2. These remarkable properties showed a beneficial effect toward gold particle size as confirmed by XRD and TEM studies. XPS results revealed that Au is present in the metallic state and Ce in both +3 and +4 oxidation states. Incorporation of Zr into the Au/CeO2 resulted in high CO oxidation activity attributed to the presence of more Ce3+ ions and oxygen vacancies. In contrast, the La-incorporation caused an opposite effect due to the presence of carbonate species on the surface of Au/CeO2–La2O3 catalyst, which blocked the active sites essential for CO oxidation. It was shown that accumulation of carbonate species strongly depends on the acid–base properties of the supports. The catalytic performance of Au catalysts is highly dependent on the nature of the support.

An overview of work with model systems designed to study metal–support interactions in heterogeneous catalysts is given. In these models, metal and support are both miniaturized by introduction as guests into a mesoporous host. The use of such models is demonstrated with AuTiO2 clusters encaged in MCM-48, and CuZnO clusters encapsulated in siliceous mesopore systems and in carbon nanotubes. The models promise a better opportunity to track changes in the support component during catalyst activation and catalysis, including the action of poisons that may at first be trapped on the support surface. Challenges to be met are the stabilization of the mesoporous matrix during synthesis and catalysis, possible reactivity of the matrix surface towards any of the catalyst components, as well as clustering and segregation of the latter from the matrix. The challenges were encountered as pore damage during preparation of AuTiO2/MCM-48 catalysts, as deactivating interactions of siliceous walls with zinc ions during deposition of zinc species from aqueous media, and as clustering of the Cu component during calcination and reduction. Among the conclusions drawn from the studies are the irrelevance of order at the AuTiO2 interface (and, hence, of epitaxy and of crystal strain in gold) for high activity of Au/TiO2 catalysts in CO oxidation. In the models for CuZnO methanol synthesis catalysts, two different types of CuZn interaction could be observed: a direct contact between Zn2+ and Cu(0) under strong reducing conditions, and the formation of alloy nanoparticles (nano-brass). A discussion of the relevance of these interactions for the methanol synthesis reaction is given.

$TiO_{2}$-supported gold species were prepared via the deposition-precipitation route, with conservation of the initial speciation by freeze-drying. The structural and electronic properties of the Au species were investigated by X-ray absorption spectroscopy, electron microscopy, and IR spectroscopy of adsorbed CO in four states. Exclusively $Au^{III}$ was deposited on the $TiO_{2}$ surface in patches ranging from isolated Au ions to three-dimensional clusters. This paper illustrates in detail the unique contributions of all characterization techniques to this structural model.

Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15 wt% and calcination temperatures of 673, 973, and 1073 K indicates that Co2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active. Fil: Bordoloi, Ankur. Indian Institute of Petroleum; India Fil: Sanchez, Miguel Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Noei, Heshmat. Research Group X-Ray Physics and Nanoscience Deutsches Elektronen-Synchrotron; Alemania Fil: Kaluza, Stefan. Fraunhofer Institute of Environmental, Safety, and Energy Technology; Alemania Fil: Großmann, Dennis. Ruhr Universität Bochum; Alemania Fil: Wang, Yuemin. Ruhr Universität Bochum; Alemania Fil: Grünert, Wolfgang. Ruhr Universität Bochum; Alemania Fil: Muhler, Martin. Ruhr Universität Bochum; Alemania

Au/TiO2 catalysts prepared by a deposition-precipitation process and used for CO oxidation without previous calcination exhibited high, largely temperature-independent conversions at low temperatures, with apparent activation energies of about zero. Thermal treatments, such as He at 623 K, changed the conversion-temperature characteristics to the well-known S-shape, with activation energies slightly below 30 kJ mol(-1). Sample characterization by XAFS and electron microscopy and a low-temperature IR study of CO adsorption and oxidation showed that CO can be oxidized by gas-phase O2 at 90 K already over the freeze-dried catalyst in the initial state that contained Au exclusively in the +3 oxidation state. CO conversion after activation in the feed at 303 K is due to Au(III)-containing sites at low temperatures, while Au(0) dominates conversion at higher temperatures. After thermal treatments, CO conversion in the whole investigated temperature range results from sites containing exclusively Au(0).