Pure and mixed oxides

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.  

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Surface Vanadate, Molybdate and Tungstate Species The pure and mixed oxides and the salts of vanadium, molybdenum and tungsten in their higher oxidation states are used widely as heterogeneous catalysts, for selective oxidation as well as for acid catalysis. Similarly, supported chromia and rhenium oxides find wide application in different catalytic processes. 

Tb)-doped zirconia [85,90], gold, gold alloys and gold-oxide composites [87, 88], and pure and mixed oxides [89]. 

PHOTOLYTIC AND REDOX MECHANISMS FOR THE PHOTODECOMPOSITION OF ETHANOIC ACID ADSORBED OVER PURE AND MIXED OXIDES... 

Photolytic and Redox Mechanisms for the Photodecomposition of Ethanoic Acid Adsorbed over Pure and Mixed Oxides (M. Schiavello, V. Augugliaro, S. Coluccia, L. Palmisano, and A. Sclafani) 1 9... 

Wang and Willey (260) report the oxidation of methanol in SCCO2 over pure and mixed oxide (Fe, Si, and Mo) aerogel catalysts. Selective oxidation products of dimethyl ether, methyl formate, and formaldehyde were found from 200°C to 300°C, and the selectivity depended on the catalyst used. Pure iron oxide favored dimethyl ether (80% yield), low levels of iron oxide on silica favored... 

A flame reactor is an excellent means for preparing pure or mixed oxides in the form of nonporous particles. The absence of porosity allows an average homogeneous irradiation of the particles. The morphologies (spheres, polyhedra) and the particle sizes (usually with a narrow distribution) can be mastered by adjusting the temperature, the flow rates (H2 and 02), and the concentration(s) of the compound(s) employed to generate the oxide. In the particular case of Ti02, anatase samples whose rutile content is very low can be produced. Consequently, the effect of the surface area S on the photocatalytic activity can be determined, in principle. 

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. 

Wakao, N., M. Mishina, Y. Sakurai, and H. Shiota. 1982. Bacteria pyrite oxidation. I. The effect of the pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans on release of iron. J. Gen. Appl. Microbiol. 28 331-343. 

Fig. 2 Existence of pure and mixed iron oxides as a function of the partial pressure ratios H2O/H2 and C02/CO, respectively. The equilibrium con iosition of the producer gas after conversion is indicated with PI (pure iron oxide) and P2 (manganese iron...

Manganese oxides in natural systems are often complex minerals characterized by poor crystallinity and mixed oxidation states (McKenzie, 1989). In addition to being electron acceptors in the oxidation of As(III) to As(V), Mn oxides can also adsorb As. Direct evidence for adsorption of As by Mn oxides comes from laboratory experiments in which pure mineral phases have been used. 

IGC was used to determine the thermodynamic miscibility behavior of several polymer blends polystyrene-poly(n-butyl methacrylate), poly(vinylidene fluoride)-poly(methyl methacrylate), and polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases of the molten polymers, and Flory-Huggins interaction parameters were calculated. A generally consistent and realistic measure of the polymer-polymer interaction can be obtained with this technique. 

Figure 4. (A) TPR spectra of CO, from a defect-rich MgO thin film (a), various pure and mixed Au and Au Sr clusters (b)-(e), as well as from a thin Au-film grown on a defect-rich MgO thin film (f). The reactivity expressed as the number of formed COj molecules per cluster is shown for cluster sizes up to Au,. (B) Calculated snapshots of three different reaction mechanisms (ER, LHt, LHp) for the oxidation of CO on Au, adsorbed on an F center of an MgO(lOO) surface.

The adsorption energies (Eads) of the various species in reactions (1) - (4) are essential information for understanding methanol oxidation. The results are collected in Table 6, together with available experimental data. Calculations were done for two types of sites, on-top (t) and threefold hollow (h). Excepting H and OH, the species treated prefer the on-top site in both pure and mixed clusters. 

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 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... 

Bacelar-Nicolau P, Johnson DB (1999) Leaching of pyrite by acidophilic heterotrophic iron-oxidizing bacteria in pure and mixed cultures. Appl Environ Microbiol 65(2) 585-590... 

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 detailed kinetic study of oxidative dehydrogenation of propane, isobutane, n-butane (23 runs) and LPG (27 runs) was conducted over a wide range of partial pressures of pure and mixed hydrocarbons (0-0.3 atm), oxygen (0-0.2 atm) and steam (0.2-0.7) atm and temperature 600-670°C. Oxidation of Hj, CjHg, C H, CH and CO was also tested at 600-650°C. A set of reactions was selected based on the distribution of products ... 

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