Metal oxide-adsorbate interactions surface relaxation

These difficulties have stimulated the development of defined model catalysts better suited for fundamental studies (Fig. 15.2). Single crystals are the most well-defined model systems, and studies of their structure and interaction with gas molecules have explained the elementary steps of catalytic reactions, including surface relaxation/reconstruction, adsorbate bonding, structure sensitivity, defect reactivity, surface dynamics, etc. [2, 5-7]. Single crystals were also modified by overlayers of oxides ( inverse catalysts ) [8], metals, alkali, and carbon (Fig. 15.2). However, macroscopic (cm size) single crystals cannot mimic catalyst properties that are related to nanosized metal particles. The structural difference between a single-crystal surface and supported metal nanoparticles ( 1-10 nm in diameter) is typically referred to as a materials gap. Provided that nanoparticles exhibit only low Miller index facets (such as the cuboctahedral particles in Fig. 15.1 and 15.2), and assuming that the support material is inert, one could assume that the catalytic properties of a... 

In order to understand the reactivity of ceria surfaces and the interaction of it with metal particles or adsorbates, it is of fundamental interest to know its surface structure and the extent or type of defects present. Even though the film may be an oriented single crystal, there is still the question of whether the surface is terminated in oxygen anions, Ce cations, a mixture or in defects associated with the termination. Charge neutrality, interfacial relaxation and dielectric discontinuities may modify the properties of an oxide surface. Also the ability of the surface to adsorb or give up oxygen, as well as the structure, clustering and reactivity of defects may be expected to depend upon the surface orientation and structure. 

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