Ferrosilicon alloy as both reactant and catalyst for hydrogenation of SiCl4: Thermodynamics, mechanism, and kinetics studies

Abstract

A novel reaction system utilizing FeSi_y (ferrosilicon alloy) as both catalyst and reactant was developed for converting silicon tetrachloride (STC) into trichlorosilane (TCS), the key precursor for polysilicon production. The thermodynamic results revealed that the FeSi₂ system is more favorable than FeSi, and the STC conversion increases with increasing pressure and H₂/STC ratio, with a one-pass conversion of silicon exceeding 80 %. The catalytic mechanism and active sites in STC-H₂-FeSi₂ system were further studied through DFT calculations. The calculated results confirm that FeSi₂ was the catalytic active sites, and transformed into FeSi during the reaction. A kinetic model based on the L-H mechanism was established, indicating that adsorption of STC on FeSi_y was the rate-determining step with the activation energy of 100.47 kJ/mol and the adsorption heat of H₂ and TCS of −76.33 and −31.70 kJ/mol, respectively. Based on this study, one can expect a great upgrade for the conventional silicon feedstock and copper catalyst process for TCS.