Titania interaction with metal particles

It was not until recently that Chen and Goodman probed the influence of the oxide support material on the intrinsic properties at the metal surface. By covering a titania support with one or two flat atomic layers of gold they eliminated, direct adsorbate-support interactions as well as particle size and shape effects. Their results definitively showed that the electronic properties at the metal surface changed due to charge transfer between the support and the metal. Furthermore, their comparison of one- and two-layer films highlighted the dependence of these effects on the thickness of the metal slab. 

Recently titania appeared as a non-conventional support for noble metal catalysts, since it was found to induce perturbations in their H2 or CO adsorption capacities as well as in their catalytic activities, This phenomenon, discovered by the EXXON group, was denoted "Strong Metal-Support Interactions" (SMSI effect) (1) and later extended to other reducible oxide supports (2). Two symposia were devoted to SMSI, one in Lyon-Ecully (1982) (3) and the present one in Miami (1985) (4) and presently, two main explanations are generally proposed to account for SMSI (i) either the occurence of an electronic effect (2,5-13) or (ii) the migration of suboxide species on the metal particles (14-20). The second hypothesis was essentially illustrated on model catalysts with spectroscopic techniques.lt can be noted that both possibilities do not necessarily exclude each other and can be considered simultaneously (21). 

With the surge in research on carbonaceous nanomaterials, the combination of these entities with metal oxide nanoparticles is enticing as the electronic properties of materials such as graphene may influence particle characteristics. For this reason, the interaction of titania nanoparticles with B- and N-doped graphene has been investigated recently in order to study the photodegradation of dye molecules by these composites. Anatase Ti02... 

In the Au/Al203/NiAl(100) system, hemispherical particles occur even at low coverage,7 unlike the situation with titania size distribution was narrow, and particles were stable to 600 K, implying low mobility of adsorbed atoms. Paradoxically, on alumina large particles migrate and coalesce faster than small ones, presumably because the metal-support interaction is weaker but with Au/FeO the diffusivity of atoms is higher due to a lower concentration of surface defects. 

The SPSDs of mixed oxides (initial and carbonized) depend strongly on pH (Figures 2.53, 2.55, and 2.56) since the electrostatic interactions between silica, titania, alumina, andpyrocarbon phases characterized by different points of zero charge, PZC are differently affected by pH (Figures 2.52 and 2.54). The studied characteristics of nanooxides can correlate with the adsorption of metal ions because of the common basis (structure of oxide particle surfaces and their behavior in the aqueous medium) of these phenomena. 

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