Catalytic behaviors, metallic oxides

K-absorption edges in study of, 12 149 structure of, and magnetism, 3 27 Catalytic behaviors, metallic oxides, 29 240 Catalytic converter automotive, 24 71, 72 single-bed, 24 72, 74 design of, 24 75-77, 83-86 dual-bed, 24 73... 

Promotion of the Rates of C— O Bond Hydrogenation by the Oxide-Metal Interface CO hydrogenation catalysis has benefited greatly from the rediscovery of the unique catalytic behavior of oxide-metal interfaces first observed by Schwab [92]. The effect is commonly referred to as strong metal-support interaction, or SMSI (see also reference [93]). Tauster et al. [94, 95] reported large enhancement... 

Many investigators have also measured the trace metal content of asphalts (68). The catalytic behavior of vanadium has prompted studies of the relation between vanadium content and an asphalt s sensitivity to oxidation (viscosity ratio). The significance of metals in the behavior of asphalts is not yet well understood or defined. 

Although catalytic wet oxidation of acetic acid, phenol, and p-coumaric acid has been reported for Co-Bi composites and CoOx-based mixed metal oxides [3-5], we could find no studies of the wet oxidation of CHCs over supported CoO catalysts. Therefore, this study was conducted to see if such catalysts are available for wet oxidation of trichloroethylene (TCE) as a model CHC in a continuous flow fixal-bed reactor that requires no subsequent separation process. The supported CoOx catalysts were characterized to explain unsteady-state behavior in activity for a certain hour on stream. 

Complex Base-Metal Oxides Complex oxide systems include the mixed oxides of some metals which have perovskite or spinel structure. Both the perovskites and the spinels exhibit catalytic activity toward cathodic oxygen reduction, but important differences exist in the behavior of these systems. 

The [Co(CN)5]3 complex is an effective catalyst for some reactions, particularly the isomerization of alkenes. Newer and more efficient catalysts have been developed for some of the processes, but the catalytic behavior of the pentacyanocobalt(II) ion is also significant from a historical perspective. In reactions such as that shown in Eq. (22.10), two Co2+ ions increase one unit in oxidation state, instead of the more common situation in which one metal ion increases by two units in oxidation state. The cobalt complex also reacts with CIT3I, Cl2, and H202, which are indicated as X-Y in the equation... 

Thus far, we have discussed the properties of the metal oxide, the surface structures, and their acid-base behavior. In the concluding section, we shall discuss some important catalytic reactions occurring on oxide surfaces. 

Activities and Catalytic Behaviors of Various Metallic Oxides"... 

Catalysts prepared from iridium neutral binary carbonyl compounds and several supports have been studied extensively. Small Ir (x = 4, 6) clusters supported on several oxides and caged in zeolite, and their characterization by EXAFS, have been prepared [159, 179, 180, 194-196]. The nuclearity of the resulting metallic clusters has been related with their catalytic behavior in olefin hydrogenation reactions [197]. This reaction is structure insensitive, which means that the rate of the reac-hon does not depend on the size of the metallic particle. Usually, the metallic parhcles are larger than 1 nm and consequently they have bulk-like metallic behavior. However, if the size of the particles is small enough to lose their bulk-like metallic behavior, the rate of the catalytic reaction can depend on the size of the metal cluster frame used as catalyst. 

Alkaline earth metal oxides have been used as solid base catalysts for a variety of organic transformations. Excellent reviews by Tanabe 4) and Hattori 2,3,7) provide detailed information about the catalytic behavior of alkaline earth metal oxides for several organic reactions of importance for industrial organic synthesis. In this section, we describe in detail reactions that have been reported recently to be catalyzed by alkaline earth metal oxides. 

You have now learned about how to use DFT calculations to compute the rates of individual activated processes. This information is extremely useful, but it is still not enough to fully describe many interesting physical problems. In many situations, a system will evolve over time via many individual hops between local minima. For example, creation of catalytic clusters of metal atoms on metal oxide surfaces involves the hopping of multiple individual metal atoms on a surface. These clusters often nucleate at defects on the oxide surface, a process that is the net outcome from both hopping of atoms on the defect-free areas of the surface and in the neighborhood of defects. A characteristic of this problem is that it is the long time behavior of atoms as they move on a complicated energy surface defined by many different local minima that is of interest. 

Studies on the nature of the interaction between the dispersed metal oxide species and the support have shown that their catalytic behavior and their acid-base properties are strongly affected by the inductive effect of the metal ions in the solids [187,188]. It has also been established in the literature that the support influences... 

Various results have been also published indicating that metal or metal oxides supported on Ti02 nanotubes have different characteristics than when supported over conventional Ti02 particles or other type of supports. We briefly mention here some selected examples, because in principle different characteristics indicate also possible differences in the catalytic behavior. 

Oxidation with N2O. In the evaluation of the catalytic data, we first compare the catalytic behavior of the metal molybdates with that of Mo03/Si02. Data obtained for this catalyst eailier (7) under the present conditions aie also included in Figure 2 and the appropriate tables. The conversion of ethane on Mo03/Si02 at 823 K was... 

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