Temperature-dependent ethylene dissociative adsorption on ruthenium

Abstract

The dissociative adsorption of ethylene onto Ru(111) at different temperatures was computed systematically at the first time. At 105 K, ethylene dissociative adsorption has the co-adsorbed CH2C*+2H* and CH3C*+H* as the first and second stable surface intermediates. At over 330 K, CH3C*+H* is converted back into CH2C* accompanied by H2 desorption and the subsequent dissociation of CH2C* into HCC*, HC*+C* and 2C*. The computed Arrhenius activation barriers of the dissociation of CH2CH2 (0.18 vs. 0.22 ± 0.04 eV) and CH3C (0.54 vs. 0.52 ± 0.04 eV) agree perfectly with the available experimental values, and CH3C* represents the most stable surface species. Under CO co-adsorption, the most stable surface species are the co-adsorbed CH3C*+H*+3CO*. It is found that CO co-adsorption promotes H2 desorption and stabilizes CH3C* by blocking the surface sites for dissociation and raises the dissociation barrier compared to the clean surface (0.78 vs 0.54 eV). Brønsted–Evans–Polanyi relationship between the activation Gibbs free energy barrier and reaction Gibbs free energy is found for CH2C*+2H*+nCO* = CH3C*+H*+nCO* and CH2C*+2H*+nCO* = HCC*+3H*+nCO* (n = 0–3). Ethylene adsorption has di-σ and π adsorption configurations in very close energy, and H2 has adsorption energy of about 0.90 eV.