The chemical behaviour of 3-hexene on the Ru(0001) surface: a characterization by RAIRS

• Published in: Surface science Vol. 482-485; no. 1; pp. 107 - 113
• Main Authors: Garcia, A R, De Barros, R B, Ilharco, L M
• Format: Journal Article
• Language: English
• Published: 05.09.2000
• ISSN: 0039-6028

The chemical nature of Z-3-hexene/Ru(0001) bond at different temperatures was studied by reflection-absorption infrared spectroscopy (RAIRS). At 92 K and for low exposures (0.05 L) the results indicate that Z-3-hexene adsorbs non-dissociatively as a di- sigma complex. By annealing to 123 K, it dehydrogenates at the C sub alpha carbons (C sub 3 and C sub 4 , bonded to the surface), forming a hexyne di- sigma / pi complex in a mixture of rotational conformers. Upon thermal activation, this complex decomposes by breaking the C sub alpha -C sub beta (i.e., C sub 2 -C sub 3 and C sub 4 -C sub 5 ) bonds, yielding adsorbed ethylidyne. At 223 K, only this species and residual di- sigma / pi complex are present on the surface. A different decomposition path is proposed upon direct adsorption of Z-3-hexene at 223 K, since propylidyne appears to be formed on the surface, which implies breaking the C-C double bond with dehydrogenation. Since the behaviour of Z-3-hexene is identical to that of 3-hexyne, and rather different from 1-hexene, these results suggest that the decomposition of unsaturated hydrocarbons on clean Ru(0001) is determined by the position and not by the nature (double or triple bond) of the functionality.