Effects of individual promoters on the Direct Synthesis of methylchlorosilanes

The industrially relevant Direct Synthesis involves the reaction of methyl chloride with silicon in the presence of a copper catalyst (promoted with Zn, Sn, and P), termed the contact mass, to form methylchlorosilanes. In situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) coupled with flow reactor studies was used to help understand the relationship between the composition of the working catalytic surface and product selectivity during reaction (1 bar CH3Cl at 300 °C). Promotion of copper–silicon contact masses with Sn and Zn increased the selectivity of the reaction for dimethyldichlorosilane compared to P-promoted and copper–silicon (unpromoted) contact masses. Results showed that the rate of Si conversion associated with the Sn-promoted contact mass was higher than the Si conversion rate associated with the Zn and unpromoted contact masses. ATR-FTIR results suggested that Sn promotion led to a stabilization and relatively high concentration of surface methyl species. In contrast to Sn or Zn promotion, P promotion led to significant methyl fragmentation on the contact mass surface, consistent with its relatively low selectivity toward dimethyldichlorosilane.