In this work, size-selected metal sulfide (MxSy: M = Mo, Fe) clusters are deposited onto metal surfaces using mass-selected cluster deposition as model “inverse” catalysts for the study of CO/CO2 hydrogenation and N2 activation, respectively. The control over the stoichiometry of clusters and the oxidation state of the metal centers enables the study of atomic level details such as identification of active sites, interfacial electron transfer and the role of sulfur vacancies. Results of recent work on alkali (K) promoted Mo6S8 clusters deposited on Au (111) surface and characterized by XPS and thermal desorption measurements will be presented. This work was motivated by DFT calculations which predicted that K-atoms promote CO2 activation for hydrogenation to methanol via direct participation in CO2 binding and charge transfer to the Mo6S8 cluster (Liu and Liu, ACS Catal. 2015, 5, 1004-1012). Thermal desorption measurements show that compared to the bare Au(111) surface, the presence of Mo6S8 clusters leads to a higher K-atom coverage (∼4x) and the resulting K/Mo6S8/Au(111) surface exhibits a CO2 desorption peak above room temperature (∼450 K) that scales with cluster coverage. In contrast, CO2 only binds weakly to the Mo6S8/Au (111) surface without co-deposited K-atoms (≦ 160 K). These results suggest strong interactions between K-atoms and the clusters, as well as a promotional effect of K-atoms for strengthening CO2 binding on Mo6S8/Au (111) surfaces. Results of initial studies of the generation and application of size-selected iron sulfur clusters (FexSy; x ≦ 4, y ≦ 6) for small molecule activation and hydrogenation will also be presented.

Preparation and activity studies of supported metal sulfide clusters

256th National Meeting (2018)

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