Mixed oxide

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

Investigation of reactive cerium-based oxides for H2 production by thermochemical two-step water-splitting

Abstract: This study focuses on the use of cerium-based mixed oxides for hydrogen production by solar-driven thermochemical two-step water-splitting. Mixed cerium oxides are proposed in order to decrease the reduction temperature of ceria and to avoid material sublimation occurring above 2,000 °C during the high-temperature solar step. Ceria-based nanopowders were synthesized by soft chemistry methods including the modified Pechini method. The influence of the synthesis method, the type of cationic element mixed with cerium, and the content of this added element was investigated by comparing the reduction temperatures of the derived materials. The synthesized powders were characterized by X-ray diffraction, thermogravimetric analysis, SEM, and Raman spectroscopy. Results showed that the synthesized pure cerium oxide is more reactive toward reduction than a commercial powder. Among the different elements added to ceria that were screened, the addition of zirconium significantly improved the reduction of ceria at temperatures below 1,500 °C. Increasing zirconium content further favored cerium reduction yield up to 70%. Water-splitting tests were performed to demonstrate the reactivity of the developed materials for H2 production. The amount of H2 evolved was enhanced with a temperature increase, the maximum H2 production from Ce0.75Zr0.25O2−δ was 0.24 mmol/g at 1,045 °C, and the powder reactivity upon cycling was demonstrated via thermogravimetry through two successive reduction–hydrolysis reactions.

Low-Temperature Selective Catalytic Reduction of NOx with NH3 over Fe–Mn Mixed-Oxide Catalysts Containing Fe3Mn3O8 Phase

Abstract: Novel Fe–Mn mixed-oxide catalysts were prepared for the low-temperature selective catalytic reduction (SCR) of NOx with ammonia in the presence of excess oxygen. It was found that Fe(0.4)–MnOx catalyst showed the highest activity, yielding 98.8% NOx conversion and 100% selectivity of N2 at 120 °C at a space velocity of 30 000 h–1. XRD results suggested that a new crystal phase of Fe3Mn3O8 was formed in the Fe–MnOx catalysts. TPR and Raman data showed that there was a strong interaction between the iron oxide and manganese oxide, which is responsible for the formation of the active center―Fe3Mn3O8. Intensive analysis of fresh, used, and regenerated catalysts by XPS revealed that electron transfer between Fen+ and Mnn+ ions in Fe3Mn3O8 may account for the long lifetime of the Fe(0.4)–MnOx catalyst. In addition, the SCR activity was suppressed a little in the presence of SO2 and H2O, but it was reversible after their removal.

An XPS study of the dispersion of MoO3 on TiO2–ZrO2, TiO2–SiO2, TiO2–Al2O3, SiO2–ZrO2, and SiO2–TiO2–ZrO2 mixed oxides

Abstract: X-ray photoelectron spectroscopy technique was employed to characterize TiO 2 –ZrO 2 , TiO 2 –SiO 2 , TiO 2 –Al 2 O 3 , SiO 2 –ZrO 2 , and SiO 2 –TiO 2 –ZrO 2 mixed oxide supported MoO 3 catalysts. The investigated mixed oxide supports are obtained by a homogeneous coprecipitation method using urea as hydrolyzing agent. Molybdena (12 wt.%) was impregnated over these calcined (773 K) mixed oxide supports by a wet impregnation method from aqueous ammonium heptamolybdate solution. The XPS binding energy (BE) values of all the metals in the mixed oxide supports as well as Mo-containing catalysts are found to shift from the values of the individual metal component oxides. The shift in BE suggests that the Zr in TiO 2 –ZrO 2 and Ti in TiO 2 –Al 2 O 3 acquire more negative charge after doping with MoO 3 on these supports. The observed BE shifts, due to variation in the lattice potential, are explained in terms of Kung’s model. The XPS atomic intensity ratio measurements show that the interaction between Mo and Al is strong and the dispersion of molybdena is more on Al 2 O 3 portion of the TiO 2 –Al 2 O 3 mixed oxide. In the case of MoO 3 /TiO 2 –ZrO 2 and MoO 3 /SiO 2 –TiO 2 –ZrO 2 samples, the Mo:Ti and Mo:Zr ratios show that the Ti 4+ and Zr 4+ both contribute equally in the dispersion of molybdenum on these corresponding mixed oxides. The FWHM values indicate the presence of different Mo(VI) species on TiO 2 –Al 2 O 3 , and a homogeneous distribution on TiO 2 –ZrO 2 and TiO 2 –SiO 2 mixed oxide surfaces.

Adsorption of Fluoride from Aqueous Solution by a Synthetic Iron(III)−Aluminum(III) Mixed Oxide

Abstract: This paper presents the synthesis of iron(III)−aluminum(III) mixed oxide with some of its physicochemical characteristics and fluoride adsorption behavior thereon. Results showed that the optimum i...