Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

3-D flower like Ce–Zr–Cu mixed oxide systems in the CO preferential oxidation (CO-PROX): Effect of catalyst composition

Abstract: Ce–Zr–Cu mixed oxide systems, with different contents of ZrO2 and CuO, were prepared by slow co-precipitation method, leading to the formation of materials with a flower-like morphology. It was evaluated both the role of CuO loading (3–7 wt%), by maintaining constant the amount of ZrO2 (7 wt%), and the role of ZrO2 (2–10 wt%) with a fixed amount of CuO (7 wt%). The prepared catalysts were characterized by means of ICP-OES, SEM, N2 physisorption, quantitative XRD, H2-TPR, and XPS. Their catalytic performances in the preferential oxidation of CO in excess of H2 (CO-PROX) were evaluated, in the 40–190 °C temperature range. Characterization and catalytic results showed that an optimum Zr/Ce molar ratio and CuO loading are required to attain the best catalytic performance over the studied nanostructured Ce/Zr/Cu oxide system. Characterization results revealed that, regardless of the sample composition, all of them presented similar flower-like morphology and textural properties. Instead, the catalyst composition determined the crystalline phases formed, their reducibility and surface distribution. The catalyst containing an intermediate ZrO2 loading (7 wt%) and the highest studied CuO amount (7 wt%), FCZCu77, showed the higher fraction of undetectable CuO from XRD, that is the highest proportion of highly dispersed Cu species also observed from H2-TPR. These characteristics justify how FCZCu77 catalyst exhibited a quite higher catalytic activity than the others samples.

Highly dispersed phosphate supported in a binary silica-titania matrix : Preparation and characterization

Abstract: Titanium phosphate supported in a mixed oxide matrix was prepared by reacting SiO2/TiO2, obtained from the sol−gel process, with phosphoric acid. HPO42- is the species present in the matrix, and it is immobilized by the Ti−O−P bond on the surface. The titanium phosphate is highly and homogeneously dispersed in the SiO2/TiO2 matrix, with the domain of titanium oxide particles about 1 nm, estimated from the UV absorption band threshold. The specific surface areas, determined by the BET multipoint method, changed between 397 and 755 m2 g-1 and the average pore volumes between 0.38 and 0.63 mL g-1 for samples prepared with different contents of titanium phosphate. The titanium hydrogenphosphate is thermally very stable and showed a high proton exchange capacity between 0.50 and 1.10 mmol g-1.

Novel Semiconducting Electrodes for the Photosensitized Electrolysis of Water

Abstract: The preparation of novel semiconducting electrodes, based on polycrystalline titanium dioxide having exceptionally good current-voltage characteristics, is reported. These electrodes are formed by mixed oxide TiO/sub 2/-M/sub x/O/sub y/ deposits on metallic titanium substrates, M being a divalent or trivalent element. The mixed oxide coatings were prepared by spraying a solution containing, for example, chlorides of both metals (elements) entering the film composition on Ti metal and heating at approximately 450/sup 0/C in air to decompose the chlorides. Several layers, generally between 6 and 12, were deposited on each substrate. The electrodes were finally activated in argon at 600 to 800/sup 0/C during 30 to 60 min. The current-potential characteristics of the mixed oxide electrodes (area 0.9 cm/sup 2/) were measured in a two compartment cell using 1N sodium hydroxide solution. Results are presented and discussed.

Revisiting the catalytic activity of a doped SrFeO3 for water pollutants removal: Effect of light and temperature

Abstract: A Sr0.85Ce0.15FeO3-δ perovskite-type mixed oxide was prepared by solution combustion synthesis from citric acid and carefully characterized for the structure by X-ray diffraction coupled with Rietveld analysis, for the microstructure/morphology by HRTEM and SEM, for texture by N2 uptake at low temperature, for surface charge by ζ potential measurements and for reactive species by Electron Paramagnetic Resonance (EPR). Photocatalytic activity was tested in the presence of simulated solar light towards Orange II and Rhodamine B as model pollutants. Despite this compound is known as photocatalyst, a good reactivity was evidenced in the 55–80 °C temperature range without light irradiation, indicating that it can work as well in the dark after thermal-activation. Therefore, experimental data obtained in this work suggest to carefully reconsidering the role of this mixed oxide as photocatalyst. EPR spin-trapping tests allowed to deepen the aspects related to reactive species generated by Sr0.85Ce0.15FeO3-δ, revealing that the temperature increase promotes hydroxyl radicals and singlet oxygen production. Furthermore, an interesting selectivity towards the degradation of different dyes was found.

Characterization and catalytic activity of cobalt-chromium mixed oxides

Abstract: Three cobalt-chromium mixed oxide samples having Co:Cr atomic ratios 33:67, 50:50, and 75:25 (indicated as Co33, Co50, and Co75, respectively) were prepared by a coprecipitation method and characterized structurally before and after catalytic CO hydrogenation. Before reaction, all the catalysts are monophasic, with normal spinel structures, and are covered by chromate species, with Co{sup 3+} and Cr ions in a relatively high oxidation state (+3 or higher) exposed on the surface. Co33 corresponds to the compound CoCr{sub 2}O{sub 4}, and its bulk structure is substantially unaltered after the catalytic tests, independently from the reduction temperature adopted. The other two catalysts are solid solutions of CoCr{sub 2}O{sub 4} and Co{sub 3}O{sub 4}, which, upon reduction up to 623 K, evolve toward rock salt type structures and segregate crystallized cubic metallic cobalt when activated at higher temperature. All three powders act as catalysts for CO hydrogenation to hydrocarbons, with low catalytic activities when reduced up to 623 K; in these conditions, methanol was also produced in small amount with Co33. After reduction up to 773 K, a strong increase of catalytic activity was observed mainly for Co50 and Co75 catalysts, over which an increase of methane formation is also observed. A correlationmore » between IR and catalytic data is discussed, evidencing the role of the calcination and reduction steps on bulk and surface properties and on catalytic activity.« less