Nanoparticle catalysts consist of hundreds or thousands of atoms with structures that are essentially unknown. First-principles-based quantum mechanical calculations on this scale of substance would be prohibitively expensive to perform. Consequently, it has become common to use studies of small clusters at the subnano scale to gain insight into the chemical reactivity of nanoparticle catalysts. Recent theoretical and experimental investigations, however, have found that hydrogen reactivity on small Pt clusters is sensitive to the charge states of the clusters. This finding is in contrast to expectations about the reactivity of nanoparticles and casts doubt on whether small clusters can indeed be used to model realistic catalysts. The present case study for Pt clusters provides a systematic analysis of the charge sensitivity of the key catalytic properties for hydrogenation and clarifies the conditions for which a subnanoscale model may be expected to provide meaningful insights into the behavior of nanoparticle catalysts.
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