| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS2-WeM |
| Session: | Chemisorption on Metal & Oxide Nanoparticles |
| Presenter: | Jeppe Vang Lauritsen, Aarhus University, Denmark |
| Authors: | A. Tuxen, Aarhus University, Denmark S. Porsgaard, Aarhus University, Denmark H. Goebel, Aarhus University, Denmark F. Besenbacher, Aarhus University, Denmark J.V. Lauritsen, Aarhus University, Denmark |
| Correspondent: | Click to Email |
The atomic and electronic structure of MoS2 nanoclusters is of considerable interest due to the catalytic application of MoS2 in e.g. hydrotreating catalysis of crude oil and in photocatalysts and hydrogen evolution reactions. Previous atom-resolved STM results have shown in great detail that both the overall morphology and in particular the edge structure of MoS2 nanoclusters, which are known to contain the most catalytically active sites for hydrotreating and H2 dissociation, adopt a structure which is very dependent on the conditions under which the cluster are kept. Under sulfiding conditions, atom-resolved STM images show that the MoS2 nanoclusters expose fully sulfide edges, whereas activation by H2 or mixed H2/H2S exposures show that sulfur vacancies and S-H form on the cluster edges reflecting the MoS2 catalyst in its active state. To dynamically follow such structural changes at the MoS2 edges induced e.g. by hydrotreating reaction conditions we have here combined high-resolution x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) studies of single-layer MoS2 nanoclusters with a well known structure. The XPS studies done on well-characterized samples reveal a set of edge specific core level shifts in the Mo3d photoemission peak that can be uniquely associated with the fully sulfide edges, edge with S vacancies or fully reduced edges. The XPS fingerprint thus allows us to dynamically follow changes between the catalytically active states of MoS2 when exposed to sulfiding of sulforeductive conditions. Preliminary in-situ XPS results on the same MoS2 samples obtained under a 10-2 torr H2 atmosphere on the Ambient Pressure X-ray Photoelectron Spectroscopy on beamline 11.0.2 of the Advanced Light Source Berkeley show a characteristic sequence of sulfur reduction steps on the catalytically interesting edges followed by decomposition of MoS2 at higher temperatures. The present studies thus successfully shows that XPS in combination with STM can be successfully used as a tool to characterize the chemistry of highly dispersed active sites of well-defined nanoclusters, such as the active edges on MoS2.