AVS 54th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP3
Surface Reaction of (CH3S)2 /Rh(100) Depending on Adsorption Coverage Studied by XPS and NEXAFS

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Session: Surface Science Poster Session
Presenter: O. Sumi, Nagoya University, Japan
Authors: O. Sumi, Nagoya University, Japan
T. Nomoto, Nagoya University, Japan
S. Yagi, Nagoya University, Japan
K. Soda, Nagoya University, Japan
H. Namatame, Hiroshima University, Japan
M. Taniguchi, Hiroshima University, Japan
Correspondent: Click to Email

The automobile exhaust catalysts oxidize and/or reduce the exhaust gases, such as CO, CxHy and NOx. As know as Sulfur Poisoning, the sulfur-containing molecules that originate from fuels affect the reactivity of noble metals (Rh, Pt and Pd), which are capital components of the catalysts. There are some reports that Rh has the highest resistance to the Sulfur Poisoning among those noble metals. However there are a few reports that have an interest in adsorption reaction of sulfur-containing molecules at low temperature. Therefore it is important to investigate the reaction mechanism. In this report, we reveal the surface reaction of dimethyl disulfide (DMDS) on the Rh(100) surface using XPS and NEXAFS techniques. The clean Rh(100) single crystal was cooled down to 90 K and subsequently exposed to DMDS. DMDS coverage was controlled to 0.44 ML, 0.32 ML and multilayer. As a result of the XPS spectra at 0.44 ML, DMDS molecules are decomposed into methanethiolate and atomic S at 90 K. Methanethiolate is generated by the dissociation of S-S bond and partial methanthiolate dissociates into atomic S and methyl. After heating up to 170 K, XPS results indicate that some of methanethiolate desorbs. At 0.32 ML, DMDS molecules are also decomposed into methanethiolate and atomic S at 90 K. However the ratio of atomic S has increased and methanethiolate does not desorb but dissociates into atomic S at 170 K. These results indicate that the surface reaction depends on initial DMDS coverage. Polarization dependent S K-edge NEXAFS spectra for submonolayer at 90 K show that the peak intensity of σ*(S-C) at 90° is larger than that of 20°. This results indicates that the coordination angle of σ*(S-C) should be almost lying on Rh(100) surface.