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

Hydrogenation of silicon tetrachloride (SiCl4) to trichlorosilane (SiHCl3) 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 SiHCl3. Because the metal−carbon composites obtained by treating sucrose and transition metals at high temperature in the N2 flow have more defect sites, they display an increased SiHCl3 yield. Elemental analysis of the catalyst and reaction results demonstrate that there is a very good correlation between the SiHCl3 yield and the amount of deposited silicon during the induction time, and the SiHCl3 yield and the accumulated amount of deposited Si species rapidly change initially and then reach a stable value. Hydrogenation of SiCl4 to SiHCl3 in metal-grade silicon (mg−Si) powder is known to give a higher equilibrium conversion of SiCl4. In a similar way, by introducing Si powder into the catalyst bed, a higher SiHCl3 yield can be obtained. It is important to retard the reverse reaction rate of HCl and SiHCl3 to increase the SiHCl3 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 SiCl4. Consequently, the Si-doped metal−carbon composite catalyst shows a higher SiHCl3 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 SiCl4 hydrogenation catalyst and can promote a deeper understanding of this important poly-Si industry reaction.