Single-metal Oxides

Single metal oxides have shown that they could be a suitable alternative to precious metals. However, the active phase and the supporting oxide must be 

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Meta/ Oxides. The metal oxides aie defined as oxides of the metals occurring in Groups 3—12 (IIIB to IIB) of the Periodic Table. These oxides, characterized by high electron mobiUty and the positive oxidation state of the metal, ate generally less active as catalysts than are the supported nobel metals, but the oxides are somewhat more resistant to poisoning. The most active single-metal oxide catalysts for complete oxidation of a variety of oxidation reactions are usually found to be the oxides of the first-tow transition metals, V, Cr, Mn, Fe, Co, Ni, and Cu. 

The role of defects in heterogeneous catalysis, including the role of CS planes which form near the catalyst operating temperature in single metal oxides such... 

This technique is used industrially to produce powders for the fabrication of ceramics [29]. Mainly single-metal oxides arc made in this way, but it is claimed that MnFc204. NiFciOa, NiAl204, dopant-stabilized zirconium oxide and titanates can be obtained. Powders of surface area up to 20 m2g l can be produced. The powder is usually in the form of aggregates of 0.2-... 

Single metal oxides AI2O3, Sn02, TiOa, Zr02, La203, Fe304 and Ag20... 

Single metal oxides Alkaline earth and alkali metal oxides (MgO, CaO, SrO, BaO) Rare earth oxides (La203, Yh02) Transition metal oxides (Th02, Zr02, ZnO, Ti02)... 

The light-off curves for acetone combustion over the catalysts based on the single Mn and Co oxides are presented in Fig. 1, and the corresponding values of the temperature T50 at which the acetone conversion reaches 50% are included in Table 1. It is clear from these results that the behaviour of the alumina-supported single metal oxides contrasts strongly with that of the silica-supported ones. The performance of Mn/Si-823 is very similar to the one of Co/Si-823 in accordance with the tendency of the respective unsupported Mn and Co oxides for this reaction... 

Phase diagrams can also be used as an aid for material selection of oxide compounds that can be used at high temperature. Examination of diagrams (summarized in Tables 2-5) reveals that oxide compounds with melting temperatures above 1800°C are predominantly single metal oxides (e.g., A1203 or Ti02) or binary oxides... 

When single metallic oxide catalysts such as magnesium oxide supported on wood charcoal are used at a temperature of 420° to 430° C., a mixture of butanol, ethyl acetate, and aldehyde is obtained from ethanol. When manganese carbonate or zinc oxide supported on wood charcoal is used at 450°, ethanol decomposes into only butanol and aldehyde.65... 

C. J. Heyes, J. G. Irwin, H, A. Johnson, and R.L. Moss, "The Catalytic Oxidation of Organic Air Pollutants. Part 1. Single Metal Oxide Catalysts", J. Chem. Tech. Biotechnol.. 1982,22, 1025-1033. 

In no case was the formation of perovskite-like materials evidenced by means of XRD. Also, reactivity tests did not give any improvement with respect to the single metal fluorides the activity substantially turned out to be an average of that one of the single metal oxides. In the case of the CeF4/AgF mixture, we identified the Agp2 phase that is formed after AgF oxidation by Ce and... 

A new design of photocatalyst, double loading of ceriiun and titaniiun oxides on silica, was examined for the non-oxidative direct methane coupling. In the present method, both highly dispersed cerium and titanium oxide species coexisting on silica were obtained. This provided totally larger number of photoactive sites than that for the system of single metal oxide on silica. 

The decomposition of HCFC-22 (CHCIF2) by a series of acidic single and dual component metal oxides has been studied by Li et al. [70], Initial studies over single metal oxides showed the order of reactivity ... 

Electron-richer dM compounds can also be considered as H2-activating alternatives to compounds with the unfavorable dM configuration. In the case of the bis-dppm bridged Rh(I)Ir(-I) complex 14, the d d configuration has been found to result in a metal-metal bonded species in which the coordination around the rhodium center is similar to that in planar homovalent d compounds. [47] The kinetic product of dihydrogen addition to 14 is consistent with the occurrence of a single-metal oxidative addition to the Rh(I) (Scheme 12). This kinetic product is thermally unstable and reductively eliminates methane from the iridium center. The overall reaction constitutes a clear example of bimetallic cooperation, since the oxidative addition to one center provokes a reductive elimination in the other metal. 

Other d d ° complexes containing Ir(I)-Ag(I) and Ir(I)-Cu(I) metal cores have been reported to react with dihydrogen. [48] The structures deduced for the products of these reactions are also those expected from single-metal oxidative additions to the lr(l) centers. 

Mixed metal oxides are used quite often in industrial partial oxidation reactions, examples being Bi Oj-MoOj for the oxidation of propene to acrolein and V O -MoOj for oxidation of benzene to maleic anhydride. Some mixed oxides also are quite active deep oxidation catalysts, a good example being MnOj-CuO. The difficulties in understanding mixed oxides are of course more formidable than they are for single metal oxides. It is a well-established empirical fact that mixed oxides behave quite differently than as individual oxides in most catalytic reactions. This situation is further complicated by the often dramatic effect of promoters, such as alkali metal oxides that are added to the catalyst intentionally. 

Several inexpensive colorants compatible with a wide variety of polymers have a simple chemical structure - they are single metal oxides. For convenience, we have listed the four most commonly used examples in Table 1, along with several properties of interest, such as compliance with food contact applications and cost. 

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