Catalytic conversion of silicon tetrachloride to trichlorosilane for a poly-Si process

Hydrogenation of silicon tetrachloride (SiCl ₄) to trichlorosilane (SiHCl ₃) using carbon-based catalysts is studied. The results show that surface functional groups that result from the defect sites of the carbon catalysts play an important role in producing SiHCl ₃. Because the metal-carbon composites obtained by treating sucrose and transition metals at high temperature in the N ₂ flow have more defect sites, they display an increased SiHCl ₃ yield. Elemental analysis of the catalyst and reaction results demonstrate that there is a very good correlation between the SiHCl ₃ yield and the amount of deposited silicon during the induction time, and the SiHCl ₃ yield and the accumulated amount of deposited Si species rapidly change initially and then reach a stable value. Hydrogenation of SiCl ₄ to SiHCl ₃ in metal-grade silicon (mg-Si) powder is known to give a higher equilibrium conversion of SiCl ₄. In a similar way, by introducing Si powder into the catalyst bed, a higher SiHCl ₃ yield can be obtained. It is important to retard the reverse reaction rate of HCl and SiHCl ₃ to increase the SiHCl ₃ yield; therefore, the HCl concentration in the product stream should be reduced as soon as it is formed on the catalyst surface during the hydrogenation of SiCl ₄. Consequently, the Si-doped metal-carbon composite catalyst shows a higher SiHCl ₃ yield than that of the physically-mixed catalyst and mg-Si powder. These results offer a quite promising potential for developing a stable and effective SiCl ₄ hydrogenation catalyst and can promote a deeper understanding of this important poly-Si industry reaction.