Pure and mixed metal oxides

Pure and mixed metal oxides have been widely investigated as Lewis acid and/or Lewis base for the reaction epoxides with CO to form the corresponding cyclic carbonates. Bhanage et al. [31] investigated several kinds of basic metal oxides (MgO, CaO, ZnO, ZrO, La Oj, CeO, Al Oj and K CO ) for the reactions of EO and PO with CO to the corresponding cyclic carbonates and for the transesterification reactions of the cyclic carbonates with methanol to DMC and the corresponding glycols. The catalytic performance of the various metal oxides for the synthesis of PC (express in Yp ) was (54.1%) >MgO (32.1%) > ZrO (10.9%) > K CO (8.7%) =... 

A novel continuous approach for the synthesis and characterization of pure and mixed metal oxide systems applied in heterogeneous catalysis... 

The various processes for the catalytic reaction are similar. The factor that makes the difference is the choice of catalyst, which in turn affects the temperature regime needed to trigger the decomposition of nitrous oxide. In the literature, numerous works illustrate the several classes of catalysts appropriate for this reaction [9a, k] noble metals (Pt, Au), pure or mixed metal oxides (spinels, perovskite-types, oxides from hydrotalcites), supported systems (metal or metal oxides on alumina, silica, zirconia) and zeolites. 

In general, metal chlorides or metal alkoxides were used as metal oxide precursors that, when contacted with alcoholic solutions of a variety of block copolymers, formed mesostructured solids. To limit the rates of hydrolysis and condensation, the above mixtures were simply allowed to stand in air for variable times (1—30 days), whereby moisture was absorbed, thus providing a "controlled" source of water. High surface area (100— 800 m /g), thermally robust, mesoporous (3-12 nm pore diameter maxima) samples of pure and mixed metal... 

The most recently developed anode for the cathodic protection of steel in concrete is mixed metal oxide coated titanium mesh The anode mesh is made from commercially pure titanium sheet approximately 0-5-2mm thick depending upon the manufacturer, expanded to provide a diamond shaped mesh in the range of 35 x 75 to 100 x 200 mm. The mesh size selected is dictated by the required cathode current density and the mesh manufacturer. The anode mesh is supplied in strips which may be joined on site using spot welded connections to a titanium strip or niobium crimps, whilst electrical connections to the d.c. power source are made at selected locations in a suitably encapsulated or crimped connection. The mesh is then fitted to the concrete using non-metallic fixings. 

The applications of IR spectroscopy in catalysis are many. For example, IR can be used to directly characterize the catalysts themselves. This is often done in the study of zeolites, metal oxides, and heteropolyacids, among other catalysts [77,78], To exemplify this type of application, Figure 1.11 displays transmission IR spectra for a number of Co Mo O (0 < x < 1) mixed metal oxides with various compositions [79]. In this study, a clear distinction could be made between pure Mo03, with its characteristic IR peaks at 993, 863, 820, and 563 cm-1, and the Mo04 tetrahedral units in the CoMo04 solid solutions formed upon Co304 incorporation, with its new bands at 946 and 662 cm-1. These properties could be correlated with the activity of the catalysts toward carburization and hy-drodenitrogenation reactions. 

The reaction of metal oxide in powders in the presence of solid carbon. Carbides are obtained by closely mixing metal oxide powders with carbon, and heating, again as with the pure metals, at temperatures... 

This transformation is carried out by intimately mixing metal oxide powders with carbon, again as with the pure metals, at temperatures between 1500-2300 K, with or without the presence of a hydrocarbon gas. The reactions of oxides with carbon are thermodynamically favored, but high temperatures are again needed because the transformations are limited by diffusion. The direct transformation of oxides to carbides is economically advantageous over the use of metals since the need to separately reduce the oxide phases is avoided. Wide application is found for the commercial production of carbides of molybdenum, tungsten, and tantalum. 

The first Raman spectra of bulk metal oxide catalysts were reported in 1971 by Leroy et al. (1971), who characterized the mixed metal oxide Fe2(MoC>4)3. In subsequent years, the Raman spectra of numerous pure and mixed bulk metal oxides were reported a summary in chronological order can be found in the 2002 review by Wachs (Wachs, 2002). Bulk metal oxide phases are readily observed by Raman spectroscopy, in both the unsupported and supported forms. Investigations of the effects of moisture on the molecular structures of supported transition metal oxides have provided insights into the structural dynamics of these catalysts. It is important to know the molecular states of a catalyst as they depend on the conditions, such as the reactive environment. 

Pure and Mixed Oxides. The specific heat and magnetic susceptibility of ReOj have been measured and the results shown to agree closely with the corresponding parameters calculated from the free electron model with ReOa behaving as a simple metal. ... 

Thin films of mixed metal oxides are usually obtained from a mixture of two different kinds of alkoxide precursors. However, this method suffers from problems with stoichiometry control since extensive efforts must be made to control the vapor phase concentration of two precursors with often dissimilar vapor pressures. Also of importance here is the near impossible task of matching rates of hydrolysis/oxidation to give pure , non-phase segregated films, i.e., those having a homogeneous composition and structure. In an effort to solve these problems, research effort has been aimed at single-source precursors, i.e., those containing both aluminum and silicon. 

There are some excellent review articles on different aspects of mesostructured materials, such as synthesis, properties, and applications. " Extensive research effort has been devoted to the exploitation of new phases (lamellar, cubic, hexagonal structures), expansion of the pore sizes (about 2-50 nm are accessible), and variable framework compositions (from pure silica, through mixed metal oxides to purely metal oxide-based frameworks, and inorganic-organic hybrid mesostructures). Another research focus is on the formation of mesostructured materials in other morphologies than powders, e.g. monolithic materials and films, which are required for a variety of applications including, but not limited to, sensors (based on piezoelectric mass balances or surface acoustic wave devices), catalyst supports, (size- and shape-selective) filtration membranes or (opto)electronic devices. The current article is focused... 

The kinetics of the oxidations of trans-[Tc(dppe)X2] (X = Cl , Br ) by Co(III) amine complexes have been investigated in pure and mixed DMF and CH3CN solvent systems, with an observed increase in the rate constant with DMF concentrations. The rate constants for the reductions of three metal carbonyl dimers [M2,M = Mn(CO)5, CpMo(CO)3, and Co(CO)4] by [Re(CO)5r in THF (measured using infrared stopped-flow spectroscopy) do not parallel the reduction... 

In this study, it has been demonstrated that elementally pure amorphous metal oxide thin films of Zr, Ti, and Mn may be prepared photochemically from thin film precursors at room temperature by our method. By using these and other compounds which are compatible were able to prepare amorphous mixed metal oxides. In the case of thin films of Pb(ZrxTii.x)03 thermal annealing studies indicated that the polycrystalline tetragonal phase of Pb(Zro.48Tio.52)03 could be produced from the amorphous films. 

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