Mixed oxide

About: Mixed oxide is a(n) research topic. Over the lifetime, 5224 publication(s) have been published within this topic receiving 115567 citation(s).

Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CexTiyOz)

Abstract: This article presents an XPS study of Ce 3d emission spectra dominated by atomic multiplet effects in core level spectroscopy of rare earth compounds (Ce oxides). Core level spectroscopy has been used to study the electronic states of Ce 3d5/2 and Ce 3d3/2 levels in Ce4+ and Ce3+ states. The well-resolved components of Ce 3d5/2 and Ce 3d3/2 spin-orbit components, due to various final states (4f0, 4f1, 4f2 configurations), were determined on 3d XPS spectra from commercial powders (CeO2, CePO4). These results were used to study the 3d spin-orbit component of mixed cerium-titanium oxide. This compound was prepared by co-melting commercial powders of CeO2 and TiO2 at 1800 K under air using a solar furnace with a flux density of 16 MW.m−2 at the focal point of the parabolic concentrator. The mixed oxide Ce2Ti2O7 was produced and contained Ce(III) species which may be reactive with water to give back the initial metal oxides and generate hydrogen, a valuable product considered as a promising energy carrier in the future in replacement of oil. The 3d photoemission spectra revealed the presence of mixed components attributed to mainly Ce(III) and Ce(IV) species. Copyright © 2008 John Wiley & Sons, Ltd.

MnOx-CeO2 mixed oxide catalysts for complete oxidation of formaldehyde: Effect of preparation method and calcination temperature

Abstract: MnO x –CeO 2 mixed oxides prepared by sol–gel method, coprecipitation method and modified coprecipitation method were investigated for the complete oxidation of formaldehyde. Structure analysis by H 2 -TPR and XPS revealed that there were more Mn 4+ species and richer lattice oxygen on the surface of the catalyst prepared by the modified coprecipitation method than those of the catalysts prepared by sol–gel and coprecipitation methods, resulting in much higher catalytic activity toward complete oxidation of formaldehyde. The effect of calcination temperature on the structural features and catalytic behavior of the MnO x –CeO 2 mixed oxides prepared by the modified coprecipitation was further examined, and the catalyst calcined at 773 K showed 100% formaldehyde conversion at a temperature as low as 373 K. For the samples calcined below 773 K, no any diffraction peak corresponding to manganese oxides could be detected by XRD measurement due to the formation of MnO x –CeO 2 solid solution. While the diffraction peaks corresponding to MnO 2 phase in the samples calcined above 773 K were clearly observed, indicating the occurrence of phase segregation between MnO 2 and CeO 2 . Accordingly, it was supposed that the strong interaction between MnO x and CeO 2 , which depends on the preparation route and the calcination temperature, played a crucial role in determining the catalytic activity toward the complete oxidation of formaldehyde.

Production of cuprous oxide, a solar cell material, by thermal oxidation and a study of its physical and electrical properties

Abstract: Cuprous oxide (Cu 2 O) is a non stoichiometric defect semiconductor. It is envisaged that this semiconductor could be utilised for the fabrication of low-cost solar cells. Copper foil samples, were oxidised in air between 200°C and 1050°C. The oxide films grown were then investigated by means of both XRD and SEM. The electrical characteristics of Cu 2 O films were analysed by means of the hot-probe thermoelectric method, resistivity and mobility measurements. Oxide films formed between 1040°C and 1050°C were observed to consist entirely of Cu 2 O and showed p-type semiconductivity while those grown between 200°C and 970°C consists of a mixture of cupric oxide (CuO) and Cu 2 O. The CuO layer formed was found to be also p-type semiconducting. Thermodynamic calculations indicate that CuO in the mixed oxide layer could be explained in terms of the oxidation of Cu 2 O. Cu 2 O layers grown in air without the annealing process gave resistivities in the range 2×10 3 –3×10 3 Ω cm. A substantial reduction in the resistivity of the samples was achieved by doping with chlorine during growth and annealing. An average mobility of 75 cm 2 V −1 s −1 , at room temperature, was obtained for eight unannealed Cu 2 O samples. This average value increased to 130 cm 2 V −1 s −1 , after doping the samples with chlorine and annealing.

A superior Ce-W-Ti mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

Abstract: A superior Ce-W-Ti mixed oxide catalyst prepared by a facile homogeneous precipitation method showed excellent NH3-SCR activity and 100% N2 selectivity with broad operation temperature window and extremely high resistance to space velocity, which is a very promising catalyst for NOx abatement from diesel engine exhaust. The excellent catalytic performance is associated with the highly dispersed active Ce and promotive W species on TiO2. The introduction of W species could increase the amount of active sites, oxygen vacancies, and Bronsted and Lewis acid sites over the catalyst, which is also beneficial to improve the low temperature activity by facilitating “fast SCR” reaction and enhance both of the high temperature activity and N2 selectivity simultaneously by inhibiting the unselective oxidation of NH3 at high temperatures.

Formation of Prussian-Blue-Analog Nanocages via a Direct Etching Method and their Conversion into Ni–Co-Mixed Oxide for Enhanced Oxygen Evolution

Abstract: Novel Ni-Co-Prussian-blue-analog nano-cages consisting of pyramid-like walls were prepared via a facile chemical etching process with ammonia at room temperature. After annealing in air, the derived Ni-Co mixed oxide nanocages exhibit enhanced electrocatalytic activity and excellent stability toward the oxygen-evolution reaction.