| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Division Poster Session |
| Presenter: | Mikhail Trought, Michigan Technological University |
| Authors: | M. Trought, Michigan Technological University E.J. Crumlin, Advanced Light Source, Lawrence Berkeley National Laboratory S. Nemsak, Advanced Light Source, Lawrence Berkeley National Laboratory K.A. Perrine, Michigan Technological University |
| Correspondent: | Click to Email |
The industrial synthesis of ammonia, known as the Haber-Bosch process1, 2, occurs at high temperatures and pressures where hydrogen (H2) and nitrogen (N2) react to produce ammonia (NH3). The dissociation of nitrogen is known as the rate-limiting step on the surface of an iron oxide catalyst.3-6 At equilibrium conditions, this reaction is well-known, however the surface transformations of the iron oxide single crystal surfaces have not been explored in the near-ambient pressure (intermediate) regime, which may allow for a better understanding of the role of the surface sites and transformations under pressure regimes between traditional surface science (in ultra-high vacuum) and reaction conditions (high pressures).
Synchrotron radiation ambient pressure-X-ray photoelectron spectroscopy (AP-XPS) was used to measure changes in the surface structure and oxidation states of single crystal Fe3O4(001) (magnetite) and α-Fe2O3(0001) (hematite) surfaces near-ambient pressure conditions. Adsorption of N2, H2, and O2 on single crystal Fe3O4(001) and α-Fe2O3(0001) surfaces was measured as a function of temperature and pressure to gain a better understanding of the fundamental surface reactions associated with ammonia formation. In particular, the shape and states in the valence band photoemission spectra were examined to measure the affect of oxidation and reduction of the surfaces.7 The valence band region helped to identify the states associated with the Fe2+ and Fe3+ cations in each compound highlighting the differences in structure between magnetite, hematite and the transformations that occurred due to the oxidative and reductive environments. The states present in the N1s, Fe2p and O1s regions complemented the changes in the valence band region observed on the iron oxide surfaces. The results reveal N2 adsorbs on Fe3O4(001) but not α-Fe2O3(0001). These studies give insight into the complexity of adsorption processes and surface transformations during heterogeneous catalysis that merge surface science experiments with reaction conditions.
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