Mixed oxide

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

CeO2–MO x (M: Zr, Ti, Cu) mixed metal oxides with enhanced oxygen storage capacity

Abstract: The effect of composition on the thermal stability and oxygen storage capacity (OSC) of a series of CeO2–MOx (M: Zr, Ti, Cu) mixed oxides was investigated. X-ray diffraction, N2 adsorption–desorption analysis (BET), transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to examine structural and microstructural properties. The total OSC of the fresh and aged mixed oxides were measured using thermogravimetric–differential thermal analysis at 600 °C, under alternating reductive and oxidative environment. Ceria doping was found to be effective toward an enhancement of its redox properties. The addition of Zr4+ into the CeO2 lattice was found to have the least effect in enhancing the catalytic properties. In contrast with other studies in the literature [1, 2], increasing ZrO2 content led to an increase of the OSC of the samples of up to 522 μmol O2 g−1 for 75 % Zr4+ content. On the other hand, the CeO2–CuO with (1:3) molar ratio showed an almost three times higher OSC value than CeO2–ZrO2, which is deemed in the literature as one of the most promising OSC materials. In this work, the highest OSC values (1565 μmol-O2 g−1) were obtained for the fresh sample with CeO2–CuO (25:75) composition. The CeO2–CuO (25:75) mixed oxide still showed the highest OSC values with an only 6 % drop of OSC after aging at 900 °C for 6 h among all aged catalysts. On the other hand, ZrO2 containing samples showed the best thermal resistance against aging.

Oxidative methane coupling over Mg, Al, Ca, Ba, Pb-promoted SrTiO3 and Sr2TiO4: Influence of surface composition and microstructure

Abstract: Mg, Al, Ca, Ba, Pb-substituted titanates SrTi1−xAxO3 (A = Mg, Al, Ca, Ba, Pb, x = 0.1) and Sr2Ti1−xAxO4 (A = Mg, Al, x = 0.1) were synthesized using mechanochemical method (sintering at 1100 °C in air for 4 h) and tested in oxidative coupling of methane (OCM) at 850 and 900 °C. The obtained samples were double-phase samples consisting of Mg, Ca, Ba substituted perovskite (SrTiO3) and “layered” perovskite – (Sr2TiO4 or Sr3Ti2O7). In case of Al and Pb, it was shown that these cations most probably did not replace Ti in the perovskite structure and formed the Sr3Al2O6 and SrPbO3 individual phases. The most active samples were Mg- and Al-doped SrTiO3 and Sr2TiO4, which in their mixture with inert quartz particles showed C2 yield up to 25% and C2 selectivity around 66%. Microstructure analysis of Mg-substituted titanates revealed that under reaction conditions the “layered” perovskite decomposed releasing (Sr, Mg)O mixed oxide segregated to the surface. The samples characterized by the highest surface content of the (Sr, Mg)O oxide, which was estimated by IR CO2 adsorption, demonstrated both the highest activity in methane activation and the highest rate of methyl radical generation to the gas phase. The influence of the (Sr, Mg)O segregation on the formation of active oxygen species is discussed.

The oxidation of trichloroethylene over different mixed oxides derived from hydrotalcites

Abstract: The activity of different Mg(Fe/Al), Ni(Fe/Al) and Co(Fe/Al) mixed oxides based on hydrotalcite-like compounds have been studied for the catalytic oxidation of trichloroethylene. It has been shown that the Co catalysts are more active than the Ni catalyst, being the Mg catalysts the less active ones. The activity of all the catalysts improves when iron is substituted by aluminum in the catalyst composition. The best results have been obtained with the CoAl mixed oxide derived from hydrotalcite that is a stable, highly active and selective catalyst. These results have been related with the presence of aluminum in the Co 3 O 4 structure that favors, in the presence of oxygen, the formation of O 2 − sites and enhances the acid properties of the catalyst. The combination of both characteristics maximizes the adsorption and oxidation of the TCE.