K2CO3-Promoted CuCl Catalyst for the Direct Synthesis of Trimethoxysilane from Si and CH3OH

Abstract CuCl is the most widely used Cu-based catalyst for the direct synthesis of trimethoxysilane (HSi(OCH3)3, M3) from Si and CH3OH. However, achieving higher Si conversion and M3 selectivity over CuCl remains a challenge. In this study, we developed a K2CO3-promoted CuCl catalyst (K2CO3–CuCl), prepared via ball milling, which demonstrated a notably high M3 selectivity (92.6%) and Si conversion (77.3%) at 240 °C. This performance exceeded that of CuCl without a promoter under the same conditions. In the ball-milled K2CO3–CuCl catalyst, the promoter helps preserve low-valence Cu species, facilitating the formation of the key Cu3Si active phase during high-temperature activation. In the presence of methanol (CH3OH), a K3Cu5O4 composite oxide was generated, suppressing aggregation of active components and further enhancing catalytic performance. K2CO3 contributed to redox interconversion during the reaction. The K2CO3-containing environment helped preserve or regenerate Cu(I)-containing species. Additionally, K2CO3 neutralized the byproduct hydrogen chloride (HCl), helping to prevent catalyst poisoning. These findings provide deeper insight into the reaction mechanism and into the rational design of more efficient catalysts.