Crystallite size effects in chemisorption on dispersed metals

In the elucidation of the crystallite size, 2R, of metals dispersed on inert supports, an assumption is made that n_p α R², where n_p is the chemisorption capacity of one particle. We have found that in many chemisorption studies the relation between n_p and R is more accurately given by n_p α R^D_c, ~1.8 < D^c < ~2.2. It is shown that some basic models of area-size relations can account for such D_c deviations from 2. These include small-size effects, size-dependent chemisorption stoichiometry, and the size-dependent ratio of the crystallographic planes.