Metal oxide bulk doping catalytic activity

In catalysis, oxides with well defined acidic and basic properties are used in different forms that have found application in numerous catalytic applications in the gas-solid and liquid-solid heterogeneous catalysis [3, 46, 47], Among the most used oxide materials in catalysis, we And (i) bulk oxides (one component metal oxides) (ii) doped and moditied oxides (iii) supported metal oxides (dispersed active oxide component onto a support oxide component) (iv) bulk and supported binary metal oxides to quaternary metal oxides (mixed oxide compositions) (v) complex oxides (e.g., spinels, perovskites, hexa-aluminates, bulk and supported hydrotalcites, pillared clays, bulk and supported heteropolyacids, layered silicas, etc.). 

Perovskites form the matrix for the next paperthere is ample evidence for the catalytic activity of Pt in this structure. When incorporated in p.p.m. in (La,Pb)Mn03 there were doubts about the ionic or metallic nature of the Pt. The extent to which Pt was in the surface or in the bulk was also in question. This field has been investigated by Johnson et al. who applied XPS and identified Pt and Pt species. Activities in catalysis were compared for Pt and Pt by synthesizing another perovskite, BaPtOa. Then for CO oxidation Pt turned out to be twice as active as metallic Pt. The very high catalytic activity of the Pt-doped Lao. Pbo.3 MnOa perovskite was then attributed to surface enrichment e.g. 70-fold) of Pt ". ... 

Pd-doped catalysts have been produced by USS [82]. The fingerprint of Pd adopting the octahedral coordination of Fe in LaFeo,95Pdo,o503 has been observed in the XANES spectra of the material prepared by spray synthesis (27m /g) similarly to the preparation by the amorphous citrate method (14m /g) [17,82]. In contrast, the flame-made material of the same composition (22m /g) exposed metallic Pd particles on LaFeOs similarly to preparation by solution combustion. The different nature of the Pd species obtained by changing the synthesis method dramatically influences their catalytic performance, since PdO nanoparticles exposed at the surface of the mixed oxide exhibit catalytic activity, whereas Pd—O species in the bulk of the mixed oxide are inactive, at least in the case of methane oxidation [27]. In contrast to LaFeOs, LaMnOs did not allow Pd to adopt the octahedral coordination irrespective of synthesis method. Therefore, the coordination of Pd strongly depends on both the composition of the perovskite-type oxide and the synthesis method. 

Metal oxides, either bulk, doped, supported or mixed, are widely used as catalysts in chemical industry. Catalytic behavior of these materials, in terms of activity and selectivity, is related to their acid/base properties. 

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