Spillover of Sorbed Species

This chapter focuses on spillover of sorbed species. The exchange of species from one position to another, either on the surface or through the bulk, has been well established. More unique is the mobilization of a sorbed species from one phase onto another phase where it does not directly adsorb. This has been defined as "spillover. Spillover may result in a spectrum of changes in the nonmetallic phase onto which it occurs. In the weakest sense, the spiltover species is transported across the surface of this phase as a two-dimensional gas. It may exchange with similar surface species.The spiltover species may react with the surface, which can result in the creation of surface defects and/or active sites. Further, the bulk of the solid may be transformed into a different structure. In each of these cases, the second phase is no longer an inert. It is not serving to promote the inherent activity on the first phase. The second phase is participating directly in the transport, exchange, and reaction with the spiltover species. In some cases it is able to become catalytically active on its own and thereby to participate directly in subsequent catalysis. The chapter discusses the types of phenomena associated with spillover, the spillover of species other than hydrogen, the aspect of spillover with the most significant catalytic implications, the implication of spillover to catalysis and other heterogeneous processes, the mechanism of spillover, and the nature of the surface and spiltover species.