Single crystals site-activity relationship

In the concluding section, consideration will be given to the relationship between studies on single crystals and the behaviour of particulate catalysts, especially with respect to the relevance of one to the other. A very old concept in catalysis is that of the active site . This concept recently has come again to the forefront of research in this area and consideration of the possibility of directly observing the active site will be given in the final section. 

The aim of many surface science experiments is to provide the fundamental detail of a reaction over a well-characterized single crystal surface in order to establish structure-reactivity relationships. Supported catalytic particles, on the other hand, may have various exposed surface facets along with defect sites. A choice then has to be made as to which single crystal surface will provide the most accurate representation of the active surface facets of the support particles. In order to address the similarities or differences in the rate over ideal surfaces and those over supported particles, Kelly and Goodmanl l compared the rate of methane formation from CO and H2 catalyzed by an Ni(lOO) single crystal with that over a supported catalyst taken under the same conditions (see Fig. 2.12). 

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