Systematic Theoretical Study of Ethylene Adsorption on δ-MoC(001), TiC(001), and ZrC(001) Surfaces

A systematic study of ethylene adsorption over delta-MoC(001), TiC(001), and ZrC(001) surfaces was conducted by means of calculations based on periodic density functional theory. The structure and electronic properties of each carbide pristine surface had a strong influence in the bonding of ethylene. It was found that the metal and carbon sites of the carbide could participate in the adsorption process. As a consequence of this, very different bonding mechanisms were seen on delta-MoC(001) and TiC(001). The bonding of the molecule on the TMC(001) systems showed only minor similarities to the type of bonding found on a typical metal like Pt(111). In general, the ethylene binding energy follow the trend in stability: ZrC(001) < TiC(001) < delta-MoC(001) < Pt(111). The van der Waals correction to the energy produces large binding energy values, modifies the stability orders and drives the ethylene closer to the surface but the adsorbate geometry parameters remain unchanged. Ethylene was activated on clearly defined binding geometries, changing its hybridization from sp(2) to sp(3) with an elongation (0.16-0.31 angstrom) of the C=C bond. On the basis of this theoretical study, delta-MoC(001) is proposed as a potential catalyst for the hydrogenation of olefins, whereas TiC(001) could be useful for their hydrogenolysis.