| AVS 57th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS1-TuM |
| Session: | Catalysis on Metal and Alloy Surfaces |
| Presenter: | R. Denecke, Universität Leipzig, Germany |
| Authors: | R. Denecke, Universität Leipzig, Germany C. Wöckel, Universität Leipzig, Germany K. Fischer, Universität Leipzig, Germany S. Wickert, Universität Leipzig, Germany R. Streber, Universität Erlangen, Germany |
| Correspondent: | Click to Email |
Using high-resolution and time-dependent x-ray photoelectron spectroscopy (XPS) adsorption and reaction processes can be followed in-situ. From the data, adsorbed species as well as reaction intermediates and products can be determined and quantitatively analyzed. Time-dependent data allow for the determination of kinetic parameters.
We are applying this method to pyridine molecules adsorbed on flat and stepped Pt surfaces. Using a regularly stepped Pt(355) surface with (111) oriented terraces which are five atomic rows wide and (111) oriented monatomic steps, C 1s and N 1s core level data are recorded during adsorption at various temperatures. As additional parameter, the free Pt terrace width is varied by deposition of Ag atoms on the surface. At 300 K, they form rows along the step edges, thus effectively reducing the terrace width. Following the core level data while increasing the temperature with a fixed heating rate, temperature-programmed XPS data allow to follow the thermal reaction of the adsorbed species. The experiments have been performed at the synchrotron radiation facility BESSY II in Berlin .
Literature reports a temperature- and coverage-dependent reorientation of the pyridine molecules on Pt111) [1]. While at 300 K an upright molecule is proposed, the situation changes for low temperatures from flat-lying at low to upright at higher coverages. In line with these reports, we observe distinct changes in the core level binding energies and intensities. While at 200 K only one strong N 1s feature is observed for all coverages, there is a change from two features to one for 300 K. Here, the remaining feature is observed at a higher binding energy. Temperature-dependent data show the change from the low to the high energy feature. This is accompanied by respective changes in the C 1s data, thus suggesting again temperature- and coverage-dependent changes.
The presence of steps and especially their decoration by Ag changes the situation quite drastically. This manifests itself in changed binding energies and reaction schemes. From a comprehensive analysis a scheme for adsorption and thermal reaction of pyridine on Platinum surfaces is derived.
[1] S. Haq, D.A. King, J. Phys. Chem. 100 (1996) 16957.