Effect of pretreatment conditions of Si-CuCl mixtures on the rate and selectivity in the reaction of silicon with methanol using copper(I) chloride catalyst

The reaction of silicon with methanol was carried out in a fixed-bed flow reactor using copper(I) chloride as a catalyst. The rate of the reaction and the selectivity for trimethoxysilane greatly depends on the preheating conditions of the Si-CuCl mixture prior to feeding methanol. When the preheating temperature was above 623 K. trimethoxysilane was formed with selectivities around 65%, the remainder being tetramethoxysilane. The XRD and EPMA studies revealed that the Cu₃Si phase was scattered on the silicon surface upon heating the Si-CuCl mixture above 623 K. When the preheating temperature was below 553 K, the rate of the reaction was faster than that for higher preheating temperatures, and the selectivity for trimethoxysilane was very high (>98%). In this case, however, no evidence for the Cu₃Si phase was obtained. Pits on the silicon surface are formed upon the reaction with methanol. When the pretreatment temperature is high (723 K), the number of pits is close to that of the Cu₃Si patches which were present before starting the reaction. The number does not change with reaction time. This indicates that silicon atoms are consumed only around the areas where the Cu₃Si patches are located. The number of pits was far greater in the reaction with lower preheating temperatures (<513 K) compared with that with higher preheating. The kinetics of the reaction also depended on the preheating temperature of the Si-CuCl mixtures.