Search results for "Mixed oxide"

Tuning of solid state properties of Al-Ta mixed oxides

2014

Matrix isolation studies on the co-condensation reactions of molecular SiO and GeO: the characterisation of the novel cyclic species SiGeO(2), Si(2)G…

2010

Matrix isolation IR studies, together with DFT calculations, have established that the co-condensation of molecular SiO and GeO in low temperature (12 K) nitrogen matrices leads to the formation of the novel silicon germanium oxide species SiGeO(2), Si(2)GeO(3) and SiGe(2)O(3) analogous to the known dimer and trimer species M(2)O(2) and M(3)O(3) (M = Si, Ge). Controlled diffusion studies in the temperature range 20-34 K result in a significant increase in trimer formation, which implies a very low activation energy for this oligomerisation step. Characteristic IR modes are assigned for all three novel mixed oxide molecules, and the DFT calculations establish that these species have cyclic C…

Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation

2019

[EN] Tungsten oxide bronze-based materials show extremely adaptive structural and compositional features that make them suitable for functional properties modulation. Herein we report the preparation of a series of Ti-containing tungsten oxide catalysts presenting a hexagonal tungsten bronze-type structure. The insertion of Ti4+ within the structure (likely in the octahedral framework of the hexagonal tungsten bronze) leads to an increase in the number of strong acid sites, and the disappearance of W5+ surface species found in the undoped tungsten oxide. With the aim of studying the acid-redox properties of the titled catalysts, the catalytic transformation of methanol has been carried out …

Selective Surface Modification of SiO2−TiO2 Supports with Phosphonic Acids

2004

The selective surface modification by phosphonic acids of SiO2−TiO2 supports at the micrometer and molecular scale was investigated. Under aqueous conditions, phosphonic acids bind to TiO2 and not to SiO2 surfaces. A micropatterned support was prepared by electron beam microlithography and selectivity, of the surface modification was evidenced using scanning Auger electron spectroscopy (SAES). The second support was a mesoporous SiO2−TiO2 mixed oxide (10 mol % Ti) epoxidation catalyst prepared by sol−gel processing. Selectivity was deduced from the decrease of the catalytic activity upon modification and from chemical analysis; bonding modes to the surface were investigated using solid-stat…

Structural evolution of Pt/ceria-zirconia TWC catalysts during the oxidation of carbon monoxide

2004

The structural evolution of two Pt/ceria–zirconia catalysts, characterized by different amounts of supported Pt, was monitored by in situ X-ray diffraction during the anaerobic oxidation of CO at different temperatures. In a first phase, oxygen coming from the surface layers of the ceria–zirconia mixed oxide is consumed and no structural variation of the support is observed. After this induction time, bulk reduction of Pt/ceria–zirconia takes place as a step-like process, while the CO2 production continues at a nearly constant rate. This behavior is totally different from that of the metal-free support in similar reaction conditions, that show a gradual bulk reduction. In repeated oxidation…

Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

2007

Abstract Te-free and Te-containing Mo–V–Nb mixed oxide catalysts were diluted with several metal oxides (SiO 2 , γ -Al 2 O 3 , α -Al 2 O 3 , Nb 2 O 5 , or ZrO 2 ), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo–V–Nb–Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions 10 % , whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the forma…

NOx selective catalytic reduction at high temperatures with mixed oxides derived from layered double hydroxides

2012

[EN] Mixed oxides derived from layered double hydroxides (LDHs) have been investigated as potential catalysts for the NOx removal at high temperatures. The best results were obtained with Co–Al mixed oxides derived from LDHs that are active at 750 ◦C in the presence of oxygen and water. These catalysts could reduce or/and decompose the NOx formed in the dense phase of the FCC regenerator, being deactivated at oxygen concentrations higher than 1.5%. Nevertheless this deactivation is not permanent and they would be regenerated after reduction with hydrogen at 530 ◦C. The influence of the layered double hydroxides (LDHs) preparation method on the catalyst activity was studied, observing that t…

Highly Active Co3O4-Based Catalysts for Total Oxidation of Light C1–C3 Alkanes Prepared by a Simple Soft Chemistry Method: Effect of the Heat-T…

2021

9 figures, 2 tables.

Tailoring of the solid state properties of Al-Nb mixed oxides: A photoelectrochemical study

2013

Al-Nb containing mixed oxides were grown by anodizing sputter-deposited Al-Nb alloys of different compositions. A photoelectrochemical investigation was carried out in order to estimate the band gap, flat band potential, and conductivity type of these oxides as a function of their composition. The dependence of the band gap on the composition of mixed sp-d metal oxides has been rationalized by using a semiempirical correlation between the difference of electronegativity and band gap of oxides proposed in the literature some years ago and recently tested for regular d-d metal mixed oxides. The band gap increase observed as a function of Al content into the oxides seems mainly depending on th…

Unlocking mixed oxides with unprecedented stoichiometries from heterometallic metalorganic frameworks for the catalytic hydrogenation of CO 2

2021

[EN] Their complex surface chemistry and high oxygen lattice mobilities place mixed-metal oxides among the most important families of materials. Modulation of stoichiometry in mixed-metal oxides has been shown to be a very powerful tool for tuning optical and catalytic properties. However, accessing different stoichiometries is not always synthetically possible. Here, we show that the thermal decomposition of the recently reported metal-organic framework MUV-101(Fe, Ti) results in the formation of carbon-supported titanomaghemite nanoparticles with an unprecedented Fe/Ti ratio close to 2, not achievable by soft-chemistry routes. The resulting titanomaghemite phase displays outstanding catal…