Toward Understanding the Formation of Coke during the MCS Reaction: A Theoretical Approach

In the Müller–Rochow process, where CH₃Cl reacts with silicon to form methylchlorosilanes, copper is used as a catalyst. To provide insight into mechanisms leading to coke formation in the process, the interactions and decomposition of CH₃Cl with four different surface orientations of copper were investigated by means of density functional theory. CH₃Cl adsorbs weakly on the different surfaces, and decomposition occurs preferentially by splitting the C–Cl bond, leaving CH₃ and Cl on the surface. Dehydrogenation of CH₃ can be considered as a key step toward coke formation as the presence of CH₂ can lead to C–C bond coupling or further dehydrogenation. All surfaces investigated, Cu(100), Cu(111), Cu(410) and Cu(221), show that CH₂ formation is thermodynamically favorable relative to gaseous CH₃Cl, and the path with lowest energy barriers is found for the Cu(410) surface.