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O: Oberflächenphysik

O 55: Epitaxie und Oberfl
ächenreaktionen

O 55.3: Vortrag

Mittwoch, 9. März 2005, 11:15–11:30, TU EB107

A Theoretical study of Nanoporous Carbon for Styrene Catalysis — •Johan M. Carlsson¹, Suljo Linic², and Matthias Scheffler¹ — ¹Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin — ²Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-2136, USA

Dehydrogenation of Ethylbenzene(EB) to produce Styrene is one of the most important processes in chemical industry. Iron-oxide is widely used as catalyst, but it has recently been proposed that Nanoporous carbon (NPC) deposited on the surface is the actual active material for this reaction. We have therefore studied how motives present in NPC, can change an inert graphene sheet into a chemically active NPC. Our Density Functional Theory (DFT) calculations shows that undercoordinated C-atoms surrounding a vacancy tend to rebind next-nearest neighbours (NNN) forming a larger pore like, structure in the graphene sheet. The strain in the lattice prevent the NNN to form proper sp²-bonds, such that the defects lead to local curvature and lattice contraction. The cohesive energy of such a defective graphene sheet is comparable to perfect nanotubes in spite of the large E_form for the individual defects. This suggests that NPC may concist of graphitic sheets with a significant amount of defects frozen in during growth. The presence of these defects may leave dangling bonds and perturbs the π-band such that a defect state appears close to E_F. Subsequent calculations for oxidation of NPC has confirmed that the vacancies has an increased activity towards adsorption of O₂. These oxidized vacancies furthermore appears promissing as an active sites for oxidative dehydrogenation of EB.