Abstract
The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept. Here we report on the nature of nano-catalysed ethylene hydrogenation, investigated through experiments on size-selected Ptn (n=8–15) clusters soft-landed on magnesia and first-principles simulations, yielding benchmark information about the validity of structure sensitivity/insensitivity at the bottom of the catalyst size range. Both ethylene-hydrogenation-to-ethane and the parallel hydrogenation–dehydrogenation ethylidyne-producing route are considered, uncovering that at the <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to structure insensitivity found for larger particles. The onset of catalysed hydrogenation occurs for Ptn (n≥10) clusters at T>150 K, with maximum room temperature reactivity observed for Pt13. Structure insensitivity, inherent for specific cluster sizes, is induced in the more active Pt13 by a temperature increase up to 400 K leading to ethylidyne formation. Control of sub-nanometre particle size may be used for tuning catalysed hydrogenation activity and selectivity.
Highlights
The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept
In quest of appraising the applicability of the fundamental concept of structure sensitivity/insensitivity to nanoscale catalysts, founded on the basis of observations made at larger size scales, we focus here on the hydrogenation of ethylene catalysed by size-selected platinum nanoclusters containing between 7 and 40 Pt atoms supported on an MgO(100)/Mo(100) surface, which is inactive for ethylene hydrogenation
We begin with temperature programmed reaction (TPR) experiments, starting from the low temperature adsorption of the two reactants (H2 and C2H4) where all reaction pathways are quenched
Summary
The sensitivity, or insensitivity, of catalysed reactions to catalyst structure is a commonly employed fundamental concept. This smaller amount of negative excess charge on most of the atoms of the Pt10 cluster compared with the Pt9 case, are found to influence binding sites, adsorption energies and consequent reaction pathways on the adsorbed clusters as well as demonstrating that, in this size-range, even the addition of a single atom, while not changing the basic geometric structure, can drastically alter the electronic properties of a cluster.
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