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 degrees 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. (C) 2009 Elsevier Inc. All rights reserved.