Preparation of Cu⁺/SiO₂-ZrO₂ catalysts for oxidative carbonylation of methanol to dimethyl carbonate

Silica-zirconia mixed oxide (SiO₂-ZrO₂) was synthesized by sol-gel method; with SiO₂-ZrO₂ as the support, CuCl₂/SiO₂-ZrO₂ catalyst was then prepared by ion-exchange and used in the liquid oxidative carbonylation of methanol to dimethyl carbonate (DMC). The results showed that the introduction of zirconium species into the amorphous silica leads to the formation of Si-O-Zr bonds and Brnsted acid sites. When the CuCl₂/SiO₂-ZrO₂ catalyst is calcined at 300℃~550℃ in an inert atmosphere, CuCl₂ is dispersed and bounded on the surface of SiO₂-ZrO₂ support; CuCl₂ can be auto-reduced to CuCl, which is then ion-exchanged with the surface Brnsted acid sites of the SiO₂-ZrO₂ support to form Cu⁺ species. As a result, most of copper remains to be highly dispersed on the surface of SiO₂-ZrO₂ and only a small amount of chlorine is left over. The CuCl₂/SiO₂-ZrO₂ catalyst calcined at 450℃ exhibits excellent activity in the oxidative carbonylation of methanol; under the conditions of 140℃, 2.4MPa and a CO/O₂ ratio of 2, the conversion of methanol and the selectivity to DMC reach 10.0% and 79.4%, respectively.