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

In the Mu''ller-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.