Study of the Effect of Zn, Sn, and Pb Additives on the Direct Mechanochemical Synthesis of Tetramethoxysilane in the Presence of CuCl and CuO Catalysts

This article presents the results of our study on the direct mechanochemical synthesis of tetramethoxysilane in a high-pressure reactor using CuO and CuCl as catalysts and some promoters. The rate of the reaction of silicon with methanol in the presence of CuO is significantly lower than that in the presence of CuCl. A method for studying the influence of promoters (SnCl2, Zn, and PbCl2) on different process steps (formation of an active silicide and the reaction of silicon with methanol) has been proposed. It has been shown that the addition of 5000 ppm of SnCl2 [or the same amount of Sn as Sn(0)] improves the rate of the reaction between silicon and methanol in the presence of a low-active copper source (CuO) to the level provided by CuCl. Scanning electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy studies of the contact masses (CM) carried out at different steps of the process showed that tin promotes the reduction of CuO to Cu by silicon. The term "mechanochemical contact mass" was proposed because in traditional systems without in situ milling (fixed bed, slurry, and fluidization), the CMs are static, resulting in uneven formation of active reaction sites.