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Mixed oxide

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


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Journal ArticleDOI
21 May 2005-Langmuir
TL;DR: Electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy clearly demonstrated that the observed pseudocapacitive behavior results from reversible extraction/insertion of hydrated protons to balance the charge upon oxidation/reduction of Mn3+/Mn4+ in the film.
Abstract: Manganese and molybdenum mixed oxides in a thin film form were deposited anodically on a platinum substrate by cycling the electrode potential between 0 and +1.0 V vs Ag/AgCl in aqueous manganese(II) solutions containing molybdate anion (MoO42-). A possible mechanism for the film formation is as follows. First, electrooxidation of Mn2+ ions with H2O yields Mn oxide and protons. Then, the protons being accumulated near the electrode surface react with MoO42- to form polyoxomolybdate through a dehydrated condensation reaction (by protonation and dehydration). The condensed product coprecipitates with the Mn oxide. Cyclic voltammetry of the Mn/Mo oxide film-coated electrode in aqueous 0.5 M Na2SO4 solution exhibited a pseudocapacitive behavior with higher capacitance and better rate capability than that of the pure Mn oxide prepared similarly, most likely as a result of an increase in electrical conductivity of the film. Electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy clearly...

164 citations

Journal ArticleDOI
TL;DR: In this article, the optimum performance in electrocatalytic activity for oxygen evolution reaction in alkaline media was obtained on the Co+Ni mixed oxide deposited from the solution containing Co{sup 2+}/Ni{sup2+} ratio of 1:1.

164 citations

Journal ArticleDOI
TL;DR: In this article, the results of a TPR and XPS investigation of CoxOy-CuO mixed oxides in the range of composition Co : Cu=100:0-8:92 are reported and compared.
Abstract: In this work the results of a TPR and XPS investigation of CoxOy–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N2 at 723 K for 24 h of single‐phase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co2+[Co3]2O4 (Co3O4) spinel phase. The copper‐containing catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co 1-x 2+ Cu x 2+ [Co3+]2O4 and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N2 formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu+Co3+O2 compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO2 phase was the main component. A further addition of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N2‐calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.

163 citations

Journal ArticleDOI
TL;DR: In this article, the properties of calcined and sulfided CoO/SiO{sub 2} catalysts were analyzed using XPS, TPR, TEM, DRS-VIS, and XRD techniques.
Abstract: Physicochemical characterization of calcined and sulfided CoO/SiO{sub 2} catalysts were carried out to reveal the interaction modes between cobalt and SiO{sub 2} using XPS, TPR, TEM, DRS-VIS, and XRD techniques. The CoO/SiO{sub 2} catalysts were prepared by an impregnation method using cobalt acetate as well as cobalt nitrate and by an ion-exchange technique. It was found that several kinds of cobalt species are formed on CoO/SiO{sub 2}. These species are assigned to Co{sub 3}O{sub 4}, Co-Si-O mixed oxide, surface Co{sup 3+} species, surface silicate, surface Co{sup 2+} species in the order of the TPR reduction temperature. Their proportions strongly depended on the starting salt, cobalt content, and preparation method. Cobalt acetate was found to provide highly dispersed CoO/SiO{sub 2} catalysts with a uniform distribution of cobalt species throughout the catalyst particles as compared to conventionally employed cobalt nitrate. The proportion of Co{sup 3+} greatly decreases when cobalt acetate was used instead of cobalt nitrate. All the cobalt species interacting with SiO{sub 2} were found to be sulfided at 673 K.

163 citations

Journal ArticleDOI
TL;DR: In this article, the performance of the Co-Mn-Al mixed oxide (Co:Mn:Al molar ratio of 4:1:1) was examined in total oxidation of toluene and ethanol.
Abstract: Catalytic activity of the Co–Mn–Al mixed oxide catalyst (Co:Mn:Al molar ratio of 4:1:1) modified with various amounts of potassium (0–3 wt%) was examined in total oxidation of toluene and ethanol. The prepared catalysts were characterized by chemical analysis (AAS), powder X-ray diffraction (XRD), surface area measurements, temperature programmed techniques (TPR, TPD), voltammetry of microparticles, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The non-modified catalyst was composed of spinel-like Co–Mn–Al mixed oxide as the only XRD crystalline phase. The surface concentrations of metal components obtained by XPS were different from the bulk ones determined by chemical analysis and the segregation of the metal components depended on the actual potassium content. The low K additions changed mainly the surface acid–base properties of the catalyst. According to XRD and voltammetry measurements, Mn oxides segregated from the original spinel-like phase at high concentration of potassium (2.7 and 3.0 wt%); XPS showed an enrichment of the catalysts surface with Mn. The K addition caused significant changes in the catalyst efficiency. The highest conversion in toluene oxidation was achieved with the catalyst containing about 1 wt% K; no reaction by-products were observed beside H2O and CO2. In ethanol oxidation, the catalysts activity gradually increased with increasing potassium content up to about 3 wt% K, but the presence of excess potassium in the Co–Mn–Al catalyst negatively affected formation of reaction by-products: acetaldehyde production steeply increased with potassium concentration higher than 1 wt%.

163 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202318
202265
2021184
2020198
2019175
2018178