Catalytic de-halogenation of alkyl halides by copper surfaces

Abstract

The interplay of halogenated compounds with metal surfaces has been the focus of many experimental and theoretical studies. These investigations have mainly aimed to illustrate the potential dual role of transition metals and their oxides in mediating formation of toxic halogenated aromatics as well as their catalytic-assisted decomposition over these surfaces. An initial and prominent step in conversion of these precursors into heavier halogenated aromatics signifies their dissociative adsorption on metallic species readily present in the combustion media. This contribution represents a systematic computational study to examine thermo-kinetic parameters underlying rupture of Cl/BrC bonds in halogenated model compounds (namely; 2-chloropropane, chloromethane, chloroethyne, chloropropene, chlorobenzene, 2-bromopropane, bromomethane, bromoethyne, bromopropene, and bromobenzene) over the Cu(100) surface. These compounds adapt very weak physisorbed molecular states evidenced by marginal adsorption energies and minimal structural changes, in reference to their gas phase molecules. The calculated reaction barriers for Cl/Br-C bond fissions are scattered in the range of 8.3–37.2 kcal mol−1. Stronger ClC bonds in reference to BrC bonds (in the gas phase) translate into higher corresponding reaction barriers for the former. The calculated reaction rate constants and activation energies reveal faster rate for the decomposition of the brominated species. Our calculations of the activation energies correlate very well with analogues experiment values.