Trichloroethene Dechlorination Reactions on the PdCu(110) Alloy Surface: A Periodical Density Functional Theory Study of the Mechanism

Abstract

In the present work the dissociation of the trichloroethene on the PdCu(110) surface has been investigated by applying ab initio periodic density functional theory. The reaction steps, intermediates and transition states of this reaction have been identified. Two different mechanisms have been studied, starting from the most stable adsorption modes of trichloroethene (di-σ structures). Regarding the reaction path, all intermediate steps are exothermic. In addition, all activation energies are relatively small (<40 kJ mol−1). Therefore, this reaction is shown to be kinetically and thermodynamically favorable on this surface. From the intermediate steps of both mechanisms, it was possible to attain additional information about dechlorination reactions, for the other chloroethene molecules (dichloro and chloro). There is good evidence that the intermediates and transition states for the dechlorination reaction of these molecules have a similar configuration on the PdCu surface. A detailed study of the transition states indicated that the activation energy of the dissociation step increases with the rebonding energy of chlorine on the surface, which is a common fragment to all different transition states. This also confirms that these transition state are “early” ones. A simple kinetic model has been constructed with the elementary step rate constants evaluated from the calculations. The reactional system has been shown to be very complex. Most of all intermediates are present on the surface simultaneously, in accordance with experimental studies.