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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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TL;DR: In this article, the authors investigated the effect of ceria in composite oxides for cyclohexanol de-hydrogenation and hydrogen transfer reactions, and showed that the presence of the ceria enhances the surface area and acid-base properties.
Abstract: CeO2–ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV–vis–NIR diffuse reflectance, SEM and acid–base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid–base properties facilitating the dehydrogenation process. At low ceria content, the CeO2–ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)–ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2–ZnO catalysts for reactions involving acid–base sites.
127 citations
TL;DR: In this article, the authors used Ni−Co−Zn−Al mixed oxide catalysts for the steam reforming of ethanol in flow-robot experiments and obtained a yield to hydrogen exceeding 90% with a water to ethanol feed ratio of 6.6%.
127 citations
TL;DR: In this article, a detailed description of the bulk and surface structure of each system was achieved by means of measurements of specific surface area, XRD, XPS, FT-IR, and Mossbauer spectroscopies.
Abstract: Manganese iron or nickel mixed oxide catalysts (MnFe or MnNi, respectively) were obtained by coprecipitation varying the aging time. A detailed description of the bulk and surface structure of each system was achieved by means of measurements of specific surface area, XRD, XPS, FT-IR, and Mossbauer spectroscopies. The characterisation results show that MnNi catalysts are formed by NiMnO3 and Ni6MnO8 mixed oxides besides a little amount of Mn2O3. In contrast, MnFe catalysts consist of an oxide mixture (Fe2O3, Mn2O3 and Mn5O8) forming incipiently a solid solution. The catalytic activity was evaluated in the combustion of propane and ethanol, selected as model volatile organic compounds. In propane combustion, the best results were obtained with MnNi catalysts whereas MnFe catalysts showed the best performance in ethanol combustion. The catalytic behaviour was correlated with catalyst affinity by oxygen, which was determined by studies of O2-TPD and TPR. The variation of the precipitated aging time modifies neither the catalyst structure nor the catalytic performance.
126 citations
TL;DR: In this paper, the authors used coprecipitation methods to obtain coprocessions of mixed oxides and characterized them by x-ray powder diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy.
Abstract: One composition of Pr–Ce mixed oxide and a range of compositions of Pr–Zr mixed oxide were prepared by coprecipitation methods and characterized by x-ray powder diffraction, thermogravimetric analysis, and x-ray photoelectron spectroscopy. Based on phases formed, the PrOy—ZrO2 system in an oxygen-containing atmosphere at moderate temperatures (up to 800–1000 °C) is analogous to that of CeO2–ZrO2. Addition of either Ce or Zr to pure Pr oxide affects both the total amount of oxygen that can be reversibly exchanged between oxide and gas phase and the kinetics of the redox processes. Ce dramatically increases the amount (per Pr atom) and lowers the temperature of exchange, Zr slightly decreases the amount and also lowers the temperature of exchange, and both modifiers speed up the rate. These observations are rationalized in terms of bulk and surface structural features of the mixed oxides.
126 citations
TL;DR: A ternary mixed oxide containing SnO2, RuO2 and IrO2 was shown to exhibit a more stable electrocatalytic behavior than simpler catalysts consisting of noble metal oxides only as discussed by the authors.
Abstract: A ternary mixed oxide containing SnO2, RuO2 and IrO2 was shown to exhibit a more stable electrocatalytic behaviour than simpler catalysts consisting of noble metal oxides only. X-ray diffraction and transmission electron microscopy were used to characterize the structure of these oxide catalysts. It was found that precipitation of the fine catalyst powders resulted in the formation of a mixed (Sn, Ru, Ir)O2 rutile phase. This phase was shown to be thermodynamically unstable, decomposing to SnO2 and (Ru, Ir)O2 on annealing at 800° C. X-ray photoelectron spectroscopy revealed that the surface composition of these mixed oxide catalysts varies considerably from the bulk composition. The formation of such metastable, mixed oxides is discussed.
125 citations