The Active Site in High Surface Area Catalysts

FIGURE 9.5 Classification of the structure dependence of catalytic reactions. In each case, the transition state scaling lines for activation and removal are shown for two different sites. Below the transition state scaling fines, the resulting volcano types are shown. Case 1 both activation and removal exhibit structural dependence. Case 2 activation is independent of structure, but removal shows structural dependence. Case 3 activation is structure dependent but removal is not. Case 4 neither activation nor removal shows structural dependence. Adapted from Nprskov et al. (2008). (See insert for color representation of the figure.) 

3 THE ACTIVE SITE IN HIGH SURFACE AREA CATALYSTS 

The structure sensitivity of the reactivity of different facets translates directly into a dependence of the rate and selectivity of supported catalysts on the particle size, morphology, and defect density. 

Consider the case where there are two different facets, or possible active sites, m and n, on a nanoparticle catalyst. Assume for simplicity that the rate at each site can 

This shows that in order to compare the relative importance of different sites, we should compare the geometry probability-weighted activation energies  

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