| AVS 55th International Symposium & Exhibition | |
| In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference | Wednesday Sessions |
| Session IS+NS+TR-WeA |
| Session: | In Situ Microscopy and Spectroscopy – Interfacial Science and Catalysis |
| Presenter: | S. Wehner, Universität Bayreuth, Germany |
| Authors: | S. Wehner, Universität Bayreuth, Germany S. Karpitschka, Universität Bayreuth, Germany P. Hoffmann, Hahn-Meitner-Institut Berlin, Germany Y. Burkov, Technische Universität Cottbus, Germany D. Schmeißer, Technische Universität Cottbus, Germany H.R. Brand, Universität Bayreuth, Germany J. Küppers, Universität Bayreuth, Germany |
| Correspondent: | Click to Email |
The catalytic CO oxidation on Iridium(111) and Palladium(111) surfaces was investigated experimentally under ultrahigh vacuum (UHV) conditions using photoelectron emission microscopy (PEEM) to visualize surface species. The underlying reaction-diffusion system based on the Langmuir-Hinshelwood mechanism was analyzed numerically. The effect of noise on this bistable surface reaction was examined for both surfaces. In a surface science experiment the effects on product formation detected by mass spectroscopy and the development of spatio-temporal patterns on the surface were explored. The influence of noise on the reaction rates and the formation of spatio-temporal patterns on the surface was analyzed by superposing noise of Gaussian white type on the feed gas composition, characterized by the molar fraction of CO Y (variance (ΔY)2), which represents multiplicative and additive noise. CO- and oxygen-covered regions are visible in PEEM images on both surfaces as brighter resp. darker areas as a consequence of their work function contrast. In the Iridium case islands of the adsorbate, corresponding to the globally stable branch, are formed in a background of the other adsorbate. The long transient times are the result of the extremely slow domain wall motion of these islands (around 0.05 µm s-1). For small noise only a few islands nucleate and grow until they merge and finally fill the whole surface. With increasing noise the number of islands increases and their maximum size decreases. At constant ΔY the island wall velocity and the number of islands increases when Y approaches the hysteresis boundary. The island density increases with noise, but the wall velocity is independent of applied ΔY. In the Palladium case quasi-periodic breakdowns of the CO2 with an interval of some thousands of seconds are recorded. These breakdowns are connected with very large patterns on the surface. Their domain wall motion is very fast (about 10 µm s-1). This long quasi-periodic behavior vanishes, already when small noise is superposed. For larger noise the CO oxidation reaction on both surfaces shows bursts and switching in the product CO2 rate and the recorded PEEM images.