Case Studies Selected Oxide-Metal Systems

Case Studies Selected Oxide-Metal Systems 

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Case Studies Selected Oxide-Metal Systems... 

The structure of the review is organized as follows. In Section 6.2, we will address experimental aspects concerning apparatus developments and oxide nanolayer preparation methods, and briefly comment on the interplay between experimental and theoretical results. Section 6.3 constitutes the main body of this chapter, where we present case studies of selected oxide-metal systems. They have been chosen according to their prototypical oxide nanosystem behavior and because of their importance in catalysis. We conclude with a synopsis and a brief outlook speculating on future developments. 

Selective oxidation of aromatic amines to nitroso-derivatives with hydrogen peroxide and a catalyst is also studied [68, 69], In kinetic systems with transition metal complexes substrate oxidation is accompanied by H202 dissociation to H20 and 02. Therefore, in this case, the occurrence of chemical induction would be expected. 

Several catalytic systems have been recently studied for selective oxidation reactions. Transition metals on oxide supports have shown high activity and selectivity toward CO oxidation [59-63]. In general, a high activity and selectivity are achieved when the affinity of the metal toward CO is higher than that toward H2, and the support is able to supply mobile oxygen. In such cases, the selective... 

Patterson and coworkers [5-18] have reported detailed liuninescence studies of selected transition metal complex ions in a varietjr of different environments such as in single crystals, in host crystals and on surfaces. For example, for vanadium oxide on a Si02 substrate the vanadium oxide (d ) is present in low concentrations on the substrate and detailed information can be obtained from the luminescence spectra about the vanadium oxide system [5]. This is a case where charge transfer transitions are present. This d° system is the first example to be discussed in Sect. 3. 

The set of results from TPR is consistent with the interpretations made so far, based on other characterization techniques used. In aU cases, the reduction in tin oxides occurs at temperatures much lower than those in the literature, where values above 900 K are reported for Sn02 [59]. The selectivity of the preparation reaction leads to a close relationship between M and Sn atoms transition metal atoms generate atomic hydrogen by dissociative adsorption, these hydrogen atoms being able to reduce tin oxides closely related to transition metals. Thus, the reduction temperature of the transition metal is the one that controls the global reduction process. As Pt is the metal that can be reduced most easily, the PtSn-BM catalyst exhibits the highest reducibiUty (lower reduction temperature) of aU the bimetalUc systems studied. 

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