Catalytic conversion of silicon tetrachloride to trichlorosilane for a poly-Si process Ju Young Lee a , Woo Hyung Lee a , Yong-Ki Park a , Hee Young Kim a , Na Young Kang a , Kyung Byung Yoon b , Won Choon Choi a,n , O-Bong Yang c a Green Chemistry Division, Korea Research Institute of Chemical Technology, Republic of Korea b Department of Chemistry, Sogang University, Republic of Korea c School of Chemical Engineering, Chonbuk National University, Republic of Korea article info Article history: Received 11 August 2011 Received in revised form 20 February 2012 Accepted 5 June 2012 Available online 26 June 2012 Keywords: Poly-silicon Silicon tetrachloride Trichlorosilane Solar cell abstract 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. & 2012 Elsevier B.V. All rights reserved. 1. Introduction SiCl 4 is a major byproduct of polycrystalline silicon (poly-Si) production through the chemical vapor deposition (CVD) process of SiHCl 3 (Eq. (1)) [1]. Because a drastic increase in the production capacity of poly-Si in the solar cell industry is expected in the near future, finding an efficient process of converting SiCl 4 to SiHCl 3 is becoming more important economically, and the reac- tion of SiCl 4 to SiHCl 3 has become a focus of recent basic scientific and technological research. At present, there are two conversion processes, the hydrogenation of SiCl 4 in the presence of mg  Si (Eq. 2) and in the absence of mg  Si (Eq. (3)) [2]: 2SiHCl 3 -poly-Si þ SiCl 4 þ 2HCl, (1) 3SiCl 4 þ 2H 2 þ mg-Si-4SiHCl 3 , (2) SiCl 4 þ H 2 -SiHCl 3 þ HCl. (3) The former hydrogenation process (Eq. (2)) involves the use of mg  Si, SiCl 4 , and H 2 at reaction temperatures ranging from 600 to 700 1C and highly elevated pressures. This process has the drawback of purifying SiHCl 3 through a process that involves contamination due to the transition metal impurities of mg  Si. The latter hydrogenation process (Eq. (3)) involves a thermal reaction of SiCl 4 and H 2 at temperatures exceeding 1000 1C, and the main disadvantages of this process are the high energy consumption and undesirable chlorosilane products that result from the high reaction temperature [2]. Therefore, it is necessary to develop suitable catalysts that enable a reduction of the reaction temperature and do not bring impurities to the process. Some efficient catalysts have been reported. Transition metal silicides, formed by the reaction of the metal with SiCl 4  H 2 mixtures under hydrogenating reaction condi- tions, are known to allow a substantial lowering of the reaction temperature of the hydrogenation of SiCl 4 as compared with the uncatalyzed reaction [3–6]. Ingle and Peffley reported copper Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.solmat.2012.06.009 n Corresponding author. Tel.: þ83 42 860 7626; fax: þ83 42 860 7590. E-mail address: mrchoi@krict.re.kr (W.C. Choi). Solar Energy Materials & Solar Cells 105 (2012) 142–147