Heterogeneous catalysis deviation

The structures of metal oxides and mixed oxides are often relatively simple, so that many features of reaction, such as the properties and dispositions of extended imperfections (Section 9.4.), can be characterized more easily than for more complex sohds. The ability of these compounds to deviate from stoichiometry does, however, increase interpretational difficulties. Topotactic behaviour, arising from structures based on simple ions, is important in formulating mechanisms [87], The surface chemistry and interface reactions of oxides are also of importance in heterogeneous catalysis and metal oxidations. 

The classical model of solid acid and bifimctional heterogeneous catalysis basically assumed that the acid catalyzed reactions followed the laws known for liquid acids. It also assumed that catalysis over bifunctional catalysts, exposing both metal sites and acid sites, could be described by assuming simple additivity, reaction intermediates were thought to shuttle fi equently between metal sites and acid sites. More recent research has, however, shown that both assumptions are inadequate. Some reactions which are not catalyzed by liquid acids are fast over solid acids, moreover bifimctional catalysts display substantial deviations fi"om the additivity model. 

In heterogeneous catalysis, the chemical shift is usually simply interpreted as electron gain or loss. But this interpretation is not always correct. For metal nanoparticles, electron redistribution or band narrowing can occur resulting in an deviation... 

Firstly, is a kinetic expression, a rate law, such as, e.g., the Langmuir-Hinshelwood-Hougen-Watson rate expressions in heterogeneous catalysis, and as such has no universal applicability. It is derived on the basis of mass action kinetics and does reduce to the fundamental thermodynamic Nemst equation for i = 0, thus q = 0. ° Nevertheless, experimental deviations can be expected as with any other, even most successful, rate expression. 

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