TPD study for direct synthesis of methylchlorosilanes

Abstract

Temperature programmed desorption (TPD) was performed to obtain information about the role of silicon, catalyst (copper), and promoters (zinc and tin), and to characterize the active sites for the formation of silanes. Use of infrared spectroscopy allowed rapid analysis of the gas-phase product composition. During TPD where methyl chloride was used as an adsorbate, methyl chloride (MeCl), hydrogen chloride (HC1), methane (CH4) and silanes were produced from contact masses. Although dimethyldichlorosilane (DMDC), methyltrichlorosilane (MTCS), methyltrichlorosilane (MTCS), trimethylchlorosilane (TMCS) and dimethylchlorosilane (DMCS) were produced during the direct reaction, tetrachlorosilane (QCS), trichlorosilane (TCS), methyltrichlorosilane (MTCS), and methyldichlorosilane (MDCS) were the major silanes observed during the TPD. Zinc promotion to silicon-copper contact mass (CuSi mass) increased the production of TCS, while tin promotion decreased the production of silanes having H atom, and increased the production of MTCS. Copromotion of 0.5 wt% zinc and 0.2 wt% tin increased the MTCS production further; however, the copromotion of zinc (0.5 wt%) and tin containing a small amount of tin (0.01 wt%) produced QCS as a major silane product. The silicon sites having two or three surface species such as CH3, Cl and H were proposed as the active sites responsible for the formation of silanes, and the silicon sites of = SiCl2 and =Si(CH3)Cl were the most abundant under the steady state condition.