The Fischer-Tropsch reaction is of great importance in the industrial synthesis of hydrocarbon fuels and as such has motivated a large number of studies on the microscopic processes underlying the reaction. However, while the adsorption and interaction of the two reactants, carbon monoxide and hydrogen, on model catalyst surfaces has been investigated in detail for decades, several fundamental questions still remain, in particular that of the nature of the precursor species [1]. In addition, CO and H have been shown to segregate into different domains on single crystal surfaces [2-4], raising the question whether the reaction only takes place at the interface of these domains.Here we investigate the co-adsorption of CO and H on Ru(0001) using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) with the aim to gain a more detailed understanding of the forces driving the formation of the precursor state in the Fischer-Tropsch reaction. CO and H co-adsorbed at 77 K show a largely unordered structure in STM, while subsequent annealing to 150-300 K results in dense CO islands compressed and separated by H atoms that decrease in size with increasing annealing temperature. Interestingly, further annealing to 300-350 K gives rise to a mixed phase of CO and H in a 1:1 ratio. XPS measurements confirm a change in bonding geometry upon annealing. We believe that studying the transition from a segregated to a mixed phase is an important step in the understanding of the microscopic process of the reaction. [1] R. A. van Santen, A. J. Markvoort, I. A. W. Filot, M. M. Ghouri, E. J. M. Hensen, Phys.Chem. Chem. Phys. 15, 17038 (2013).[2] D. E. Peebles, J. A. Schreifels, J. M. White, Surf. Sci. 116, 117 (1982).[3] B. Riedmuller, D. C. Papageorgopoulos, B. Berenbak, R. A. van Santen, A. W. Kleyn, Surf. Sci. 515, 323 (2002).[4] I. M. Ciobica, A. W. Kleyn, R. A. van Santen, J. Phys. Chem. B 107, 164 (2003).

Mixed structures of CO and H on Ru(0001) as precursor states for Fischer-Tropsch synthesis

248th National Meeting (2014)

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