Bonding of Saturated Hydrocarbons to Metal Surfaces

The adsorption of octane on Cu(110) was studied by x-ray absorption and x-ray emission spectroscopy, in combination with spectrum calculations in the framework of density functional theory, as a model system for alkane adsorption on transition metals. Significant electron sharing between the adsorbate and metal surface and involvement of both bonding and antibonding C-H molecular orbitals in the molecule-metal bond was found. The calculations were extended to the case of octane adsorbed on Ni(110), and the position of the metal $d$ band was found to be important for the bonding. The results were generalized to show that this is important for the efficiency as an alkane dehydrogenation catalyst.

Figure 1

Experimental and theoretical symmetry-resolved XES and XAS spectra of $n$ octane adsorbed on Cu(110). The spectra are projected along the three high-symmetry directions of the surface. The alignment of the $n$-octane molecule on the surface is shown in the inset.

Figure 2

A schematic figure showing the interaction between the C-H orbitals and the metal $d$ band, which leads to a strong mixing of molecular orbitals.

Figure 3

Charge density difference plotted along the C-H plane (top) and the CuH plane (bottom).

Figure 4

The calculated local $p$ density of states projected onto the out of plane ($p_z$) direction for octane on Cu and Ni.