Catalytic formation of silanes on copper-silicon alloys

• Published in: Journal of catalysis Vol. 91; no. 1; pp. 44 - 53
• Main Authors: Frank, Timothy C., Kester, Keith B., Falconer, John L.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1985
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(85)90286-6

Areal rates of silane formation from CH 3Cl and silicon were measured in a differential batch reactor at atmospheric pressure and 520–620 K, on three clean, nonporous, silicon-containing surfaces. These surfaces were characterized with Auger spectroscopy by transferring them directly between UHV and atmospheric pressure, without exposure to air. On pure silicon, a long induction time was seen before steady-state reaction; the main products at steady-state were HSiCl 3 and CH 3HSiCl 2. On Cu 3Si and Cu 3Si containing 0.4 atm% Zn, the overall silane formation rates were an order of magnitude lower than on pure silicon. Copper catalyst, however, dramatically increased selectivity to 85% (CH 3) 2SiCl 2, the desired product for silicone production. Copper also decreased the induction time by increasing the rate of active-site formation. Zinc promoter in Cu 3Si further increased (CH 3) 2SiCl 2 selectivity to 95% without significantly changing activity. No induction time was seen with the Zn promoter. Silicon diffusion in Cu 3Si limited silane formation, and a mathematical model is presented. Reaction on Cu 3Si containing Zn was not limited by diffusion. These are the first measurements of silane direct-synthesis kinetics on Cu 3Si of known surface area, and they show directly that Cu 3Si provides an active surface for selective formation of (CH 3) 2SiCl 2. Rates and selectivities on the alloys were similar to those measured for higher-surface-area solids.