Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 20: POSTER A

CPP 20.75: Poster

Montag, 24. März 2003, 19:00–21:00, ZEU/250

Adsorption and reaction of acetaldehyde on Co{1010}: identification of surface-bound paraldehyde and its configuration transition — •J. Gu¹, J.A. Schaefer¹, and D.A. King² — ¹Institut für Physik and Zentrun für Mikro- und Nanotechnologien, Technische Universität Ilmenau, D-98684, Ilmenau, Germany — ²Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK

We have employed reflection-absorption infrared spectroscopy (RAIRS) as the principal technique as well as temperature programmed desorption (TPD) as a diagnostic tool to study the adsorption and reaction of acetaldehyde (CH₃CHO) on Co{1010}. At 90 K, low acetaldehyde exposures lead to three adsorption species, η²(C,O)-(CH₃CHO),η³(C,C,O)-(CH₂CHO), and α-paraldehyde. At higher coverage, the fourth species, η¹(O)-(CH₃CHO), appears. The η³ (C,C,O)-(CH₂CHO) species is metastable, and with higher exposure or annealing the surface to 125 K, it transfers to η² (C,O)-(CH₃CHO). Further heating the crystal to 200 K, the η¹ (O)-(CH₃CHO) decomposes to CO, H and O adsorbates, while the α-paraldehyde species experiences a configuration transition from α-state to β-state; by 350 K, the β-paraldehyde dissociates to acetate fragments, and the η²(C,O)-(CH₃CHO) dehydrogenates to η²(C,O)-(CH₃CO). The η²(C,O)-(CH₃CO) species totally decomposes at 375 K, while the acetate fragments are still stable up to 500 K. TPD spectra reveal two CO desorption peaks at 390 K and 580 K, respectively.