Mixed oxide

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

Effect of Co-content on the structure and activity of Co–Al hydrotalcite-like materials as catalyst precursors for CO oxidation

Abstract: The present investigation was undertaken in an endeavor to study the effect of the cobalt content on the structure and activity of Co–Al hydrotalcite-like materials as catalyst precursors for CO oxidation by varying the Co 2+ /Al 3+ atomic ratio, thermal treatment of the samples and the reaction temperature. The samples (Co 2+ /Al 3+ = 0.5, 1.5, 3.0) have been synthesized by the co-precipitation method. The unsupported Co 3 O 4 has been prepared according to the same procedure as the reference compound in order to reveal the role of Al 3+ ions presence. The physicochemical characterization of the uncalcined, hydrothermally treated, calcined and tested samples has been accomplished appropriately by ICP-AES, N 2 adsorption, Powder X-ray diffraction technique and Diffuse Reflectance Spectroscopy and H 2 -TPR measurements. The samples were examined by a number of heating–cooling cycles during the activity tests as a procedure to screen the most active catalyst precursor. It was established that the hydrotalcite-like structure of all uncalcined samples had been completely destroyed during the CO oxidation reaction. A concomitant phase transformation into poorly crystallized spinel-type Co 2+ (Co 3+ ,Al 3+ ) 2 O 4 mixed oxide occurred. This spinel-like mixed oxide phase is better organized in all samples after their calcination at 500 °C. The TPR examinations reveal concomitant presence of high-temperature reduced non-stoichiometric CoAl 2 O 4 . It was found out that the Co–Al mixed oxide, derived from the sample with the highest cobalt loading (Co 2+ /Al 3+ = 3.0) preserves a complete and prolonged CO oxidation ability even after cooling down to ambient temperature. On the contrary, the samples with ratios Co 2+ /Al 3+ = 0.5 and 1.5 as well as the Co 3 O 4 oxide deactivate more rapidly during the cycles. A hypothetic scheme is proposed for activation/deactivation of the catalysts. It is related to the oxygen ion-radicals O 2 x – stabilization by Al 3+ cation association with the Co 2+ /Co 3+ redox couple via anionic vacancy.

Method of producing monolithic catalyst for purification of exhaust gas

Abstract: A method of producing a monolithic three-way catalyst for the purification of exhaust gases of internal combustion engines. First, a mixed oxide coating is provided to a monolithic carrier by treating the carrier with a coating slip in which an active alumina powder containing cerium in oxide form is dispersed together with a ceria powder and then baking the treated carrier. Next, Pt, Rh and/or Pd are deposited on the oxide coating by a known thermal decomposition process. The addition of the ceria powder to the coating slip is effective in enhancing the CO, HC and NOx conversions and durability of the produced catalyst at high temperatures. Preferably the content of Ce in the active alumina powder is 1-5 wt%, and, in the coating after baking, Ce of the ceria powder amounts to 5-50wt% of the coating. Optionally a zirconia powdertoo may be added to the coating slip such that Zr of the zirconia powder amounts to 1-10 wt% of the coating.

Neutron diffraction studies of polycrystalline ni/mg/al mixed oxides obtained from hydrotalcite-like precursors

Abstract: The thermal decomposition of a synthetic hydrotalcite-type (HT) sample [Mg0.71Al0.29(OH)2(CO3)0.145·mH2O] has been investigated by neutron diffraction using a programmed temperature control facility. The evolution from HT phase to mixed oxide leading ultimately to the partial segregation of a spinel phase is reported. Structural modification ascribed to the interlayer water loss from the HT phase is accompanied by a reduction of the c-axis parameter and changes in the neutron powder pattern. The neutron diffraction patterns of five Mg/Ni/Al mixed oxides obtained from HT samples by calcination at 923 K were subjected to structural refinement by the Rietveld method. The model that best describes the refined data consists of a supercell with an a-axis twice that of the stoichiometric rock-salt type oxide, a certain degree of ordered cation vacancies in the octahedral sites, and partially occupied tetrahedral sites. Although the samples essentially show the typical patterns of a rock-salt type structure, the ...

Exploring the Structural and Electronic Properties of Pt/Ceria-Modified TiO2 and Its Photocatalytic Activity for Water Splitting under Visible Light

Abstract: In the past few years there has been intensive research focused on doping TiO2 with other metal oxides in order to synthesize a mixed metal oxide based semiconductor with modified band gap which can split water efficiently in visible light. In this study we modified titania–anatase powders through deposition of ceria nanoparticles on them. The formation of a mixed metal oxide at the CeOx/TiO2 interface was observed using transmission electron microscopy and near-edge X-ray absorption spectroscopy. UV–vis spectra show that this mixed metal oxide can absorb photons in the visible region due to the presence of stabilized Ce3+ in the mixed oxide phase. The addition of 0.5 wt % Pt imposes a significant chemical change on the ceria nanoparticles by substantially enhancing the concentration of Ce3+ and makes possible photocatalytic activity by providing an electron trap. When irradiated with visible light, 0.5 wt % Pt loaded on CeO2-modified TiO2 generates oxygen almost seven times more efficiently than a standa...