Preparation of Cu+/SiO2-ZrO2 catalysts for the 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 Brønsted acid sites. When the CuCl2/SiO2-ZrO2 catalyst is calcined at 300–550°C 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 Brönsted 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°C exhibits excellent activity in the oxidative carbonylation of methanol; under the conditions of 140°C, 2.4 MPa and a CO/O2 ratio of 2, the conversion of methanol and the selectivity to DMC reach 10.0% and 79.4%, respectively.