Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

The nature of the nano-catalyzed hydrogenation of ethylene, yielding benchmark information pertaining to the concept of structure sensitivity/insensitivity and its applicability at the bottom of the catalyst particle size-range, is explored with experiments on size-selected Ptn (n=7–40) clusters soft-landed on MgO, in conjunction with first-principles simulations. As in the case of larger particles both the direct ethylene hydrogenation channel and the parallel hydrogenation–dehydrogenation ethylidyne-producing route must be considered, with the fundamental uncovering that at the 150K catalyzed by Ptn (n≥10) clusters, with maximum room temperature reactivity observed for Pt13 using a pulsed molecular beam technique. Structure insensitive behavior, inherent for specific cluster sizes at ambient temperatures, can be induced in the more active sizes, e.g. Pt13, by a temperature increase, up to 400K, which opens dehydrogenation channels leading to ethylidyne formation. This reaction channel was, however found to be attenuated on Pt20, as catalyst activity remained elevated after the 400K step. Pt30 displayed behavior which can be understood from extrapolating bulk properties to this size range; in particular the calculated d-band center. In the non-scalable sub-nanometer size regime, however, precise control of particle size may be used for atom-by-atom tuning and manipulation of catalyzed hydrogenation activity and selectivity. [Display omitted] •Ethylene hydrogenation performed on Pt7–Pt40 with temperature programmed and isothermal, pulsed techniques.•Structure sensitivity revealed for sub-nanometer particle sizes.•First-principles analysis deepens understanding of atomic size catalytic dependency.•Survey of the concept of structure sensitivity and its application to the nonscalable size regime.