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Abstract

From the earliest days of heterogeneous catalysis, high surface area solids were extensively used for attaining largest possible densities of active sites and, correspondingly, for maximizing turnover. Since sites are active in the real sense of the word only if they are occupied by reactants, i.e., by molecules still to be converted, the relative fraction of pore volume occupied by reactants (the ?effectiveness factor?) is a key number for the efficiency of a catalyst in a given reaction. Its determination, so far generally based on reaction rate measurements with purposefully varied catalyst particles, remained to date a challenging task since it must be based on additional assumptions. The ?one-shot determination? of effectiveness factors by IR microimaging, here exemplified on considering the catalytic hydrogenation of benzene to cyclohexane by platinum dispersed on nanoporous glass, is shown to open up a promising route to overcome these limitations.