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Heterogenous Catalysis of Silicon to Methylchlorosilanes

The Direct or Rochow Synthesis, of methylchlorosilanes is the basis of a multibillion-dollar silicone industry. Methyl Chloride reacts with silicon in the presence of copper based catalyst and small amounts of metallic promoters. These metallic promoters can change the distribution from primarily dimethyldichlorosilane, the most desirable product, to other species. Although an entire industry is founded on the production of these monomers, the catalytic structure of copper in the presence of promoter is not completely understood. A key goal is to provide a spectroscopic understanding of the Direct Synthesis that can be utilized in tailoring process conditions for optimized methylchlorosilane production.

Scientific goals: While plenty of data for silicon reaction mixtures exists in literature as ex situ studies, we, for the first time, can study these reaction mixtures in situ under actual Rochow Synthesis reaction conditions. The functional link between the model and industrial catalyst is made by comparing their surface chemistries, (i.e. their abilities to convert methyl chloride and silicon to methylchlorosilanes) through the use of ATR and GC instrumentation.

Specific goals of the research include:
• A detailing of the structure of the catalytically active surfaces of the industrial catalyst through comparison with well defined model surfaces.
• An understanding of the action of promoter additives, such as Sn and Zn on the dissociative adsorption of CH₃Cl on, and the desorption processes from, model and real catalysts.
• The elucidation of the surface bound reaction intermediates, their binding, and their stability on the industrial catalyst surface at industrial reaction conditions.

Longer term goals include investigations of model surfaces and on industrially manufactured catalyst materials utilizing infrared, low-energy-ion, and photoelectron spectroscopies, electron and atom diffraction, and scanning probe, and electron microscopies. The research strategy, that integrates results from model surfaces studied in vacuum and real catalyst studied in situ at Rochow Synthesis conditions, will give new scientifically and industrially relevant insight into the surface structure and reactivity of catalytically active reaction mixtures. A molecular-scale description of the Direct Synthesis reaction can have immediate consequences on the strategies to be applied in further development of the industrial catalysts.