Mixed oxide

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

Insight into pathways of methylene blue degradation with H 2 O 2 over mono and bimetallic Nb, Zn oxides

Abstract: The aim of this work was to investigate the influence of surface properties of metal oxides (Nb2O5, ZnO and ZnNb2O6) on the type of reactive oxygen species (ROS) formed in contact with hydrogen peroxide, and to determine the effect of zinc addition to niobium pentoxide on the type of ROS formed and its activity in methylene blue degradation. The structure and surface properties of materials synthesized were characterized by nitrogen adsorption, XRD, XPS, SEM, SEM-EDX, DR UV–vis and FTIR techniques. The ability of metal oxides to generate superoxo and peroxo species upon treatment with H2O2 was documented and discussed in respect to the type of metal oxide used. It was found that the distortion of NbO6 species in bimetallic oxide influenced the interaction of this mixed oxide with hydrogen peroxide. The oxidative properties of reactive oxygen species formed on the surface of metal oxides were tested in degradation of methylene blue. The activity of niobium(V) oxide in this process was much higher than that of mixed oxide and ZnO. In order to identify the reaction pathways on the basis of determination of the reaction intermediates, the reaction mixtures were analyzed by ESI–MS. On the basis of the results obtained the mechanism of the dye degradation was discussed.

Guerbet condensation of methanol with n-propanol to isobutyl alcohol over heterogeneous bifunctional catalysts based on Mg–Al mixed oxides partially substituted by different metal components

Abstract: The synthesis of isobutyl alcohol ( i BuOH) from methanol (MeOH) and n -propanol (PrOH) through the Guerbet condensation has been studied in batch experiments using bifunctional heterogeneous systems based on a dehydrogenating/hydrogenating metal (Pd, Rh, Ni or Cu) and a basic Mg–Al mixed oxide derived from hydrotalcite-type (HT) precursors. Only copper-based systems showed appreciable performances. In particular, the Cu/Mg/Al mixed oxides catalysts obtained by the co-precipitation method offered the best results in terms of activity and selectivity, thus allowing to reduce pollution problems connected with the up to now adopted copper chromite. These co-precipitated systems were also tested in some preliminary experiments carried out in gas–solid phase in a flow reactor, thus confirming promising application perspectives.

Surface characterization and catalytic activity of sulfate-, molybdate- and tungstate-promoted Al2O3-ZrO2 solid acid catalysts

Abstract: Alumina–zirconia mixed oxide-supported sulfate-, molybdate- and tungstate-promoted solid acid catalysts were synthesized and characterized by various techniques. The Al–Zr hydroxide gel was obtained by a co-precipitation method from their corresponding nitrate salts by hydrolysis with aqueous ammonia. To the Al–Zr-hydrous mixed oxide support, aqueous solutions of sulfuric acid, ammonium heptamolybdate and ammonium metatungstate were added and the mixtures were refluxed at 110 °C, followed by evaporation of the water, drying and calcination at 650–750 °C. The surface and bulk properties of the catalysts were examined by using X-ray diffraction, BET surface area, TGA/DTA, ammonia-TPD and XPS techniques. The XRD results reveal that Al2O3–ZrO2 mixed oxide calcined at 650 °C is in amorphous or poorly crystalline state exhibiting broad diffraction lines due to tetragonal ZrO2 phase. At 750 °C calcination, a better crystallization of the zirconia tetragonal phase is observed. The XRD results further indicate that incorporation of alumina into zirconia stabilizes the tetragonal phase. The TGA–DTA studies provide information that there are at least two types of sulfate species with different thermal stabilities in the case of SO42−/Al2O3–ZrO2 catalyst. The TPD study reveals that the SO42−/Al2O3–ZrO2 catalyst exhibits an ammonia desorption peak maximum at 600 °C indicating super-acidic nature of the catalyst. The XPS peak intensities and the corresponding binding energies indicate that sulfate ion interacts with the support more strongly than other promoters. All characterization results provide information that the impregnated sulfate ions show a relatively strong influence on the physicochemical properties of the Al2O3–ZrO2 mixed oxide. The prepared catalysts were evaluated for acetylation of alcohols and amines with acetic anhydride in the liquid phase. In line with physicochemical characteristics, the SO42−/Al2O3–ZrO2 exhibits better product yields under very mild reaction conditions.