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

作者：Crampton Andrew S; Roetzer Marian D; Ridge Claron J; Yoon Bokwon; Schweinberger Florian F; Landman Uzi; Heiz Ueli^*

来源：Surface Science, 2016, 652: 7-19.

DOI：10.1016/j.susc.2016.02.006

• Platinum
• Ethylene hydrogenation
• Model catalysis
• Structure sensitivity
• Clusters
• DFT calculations

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 <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to the structure insensitivity found for larger particles. In this size-regime, the chemical properties can be modulated and tuned by a single atom, reflected by the onset of low temperature hydrogenation at T > 150 K catalyzed by Pt-n (n >= 10) clusters, with maximum room temperature reactivity observed for Pt-13 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. Pt-13, by a temperature increase, up to 400 K, which opens dehydrogenation channels leading to ethylidyne formation. This reaction channel was, however found to be attenuated on Pt-20, as catalyst activity remained elevated after the 400 K step. Pt-30 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.

• 出版日期2016-10