Investigating the adsorption and reaction behavior on stepped surfaces provides a way to study the influence that surface defects have on the catalytic activity of heterogeneous catalysts [1,2]. Here we describe an investigation of the adsorption and thermally induced reactions of C2H4 on the flat Rh(111), the stepped Rh(553) with 111-type facets at the steps, and the stepped Rh(223) with 100-type facets. We study the general influence of the steps as well as the dependence of the specific type of step-facet. The development of the surface species was followed at temperatures ranging from 100 K to 450 K by high resolution core level photoemission (HRCLS) applied to the adsorbate C1s and the substrate Rh 3d levels. C2H4 is known to adsorb intact on Rh(111) at 100K, to form ethylidyne (CCH3) upon heating to temperatures below room temperature, and to decompose at higher temperatures [3]. Monitoring how C2H4 overlayers deposited at 100K develop during annealing reveals a number of differences, which can be ascribed to reactions occurring in vicinity of the steps. Differences are also found between the two stepped surfaces demonstrating the influence of the specific step-type. We find lower temperature activation on the stepped surfaces for both formation and decomposition of ethylidyne even though the decomposition products give the same HRCLS signal suggesting the same product. Comparing the two vicinal surfaces we find that formation and decomposition of ethylidyne occurs at lower temperature on the Rh(223) than on the Rh(553) surface suggesting higher reactivity of the 100-type steps.
[1] H.S.Taylor Royal Soc. London A Vol. 108, No. 745. (May 1, 1925), pp. 105-111
[2] J. Greeley, J. K. Nørskov and M. Mavrikakis Ann.Rev.Phys.Chem. Vol 53 (2002) pp 319
[3] R.J. Koestner, M.A. Van Hove and G.A. Somorjai Surf. Sci. 121 (1982) pp 321
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