Formation of dimethyldichlorosilane (M2) in the Müller-Rochow process at the molecular level

In the Müller-Rochow process or direct process, CH₃Cl reacts with silicon, forming (CH₃)₂SiCl₂ (M2) as the dominant species with copper as catalyst. This complex and highly heterogeneous process takes place in a gas-solid stirred fluidized bed reactor. In this study, the formation of (CH₃)₂SiCl₂ on a Cu rich Cu-Si model has been investigated using density functional theory (DFT). The results show that the overall reaction is exoergic. Upon dissociation of CH₃Cl, the reaction proceeds first by interaction of CH₃ with Si followed by subsequent addition of Cl. The largest activation barrier is found for the second Si-Cl bond formation in which a weakly adsorbed (CH₃)₂SiCl₂ is formed. Compared to dehydrogenation of adsorbed CH₃ formed upon dissociation of CH₃Cl, formation of M2 is energetically favoured on a Si modified Cu(111) model.