Effects of catalyst phase structure on the elementary processes involved in the synthesis of dimethyl carbonate from methanol and carbon dioxide over zirconia

In situ infrared spectroscopy has been used to investigate the synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide over tetragonal (t-ZrO2) and monoclinic zirconia (m-ZrO2. While similar species were observed for both catalyst phases, the dynamics of the elementary processes were different. The dissociative adsorption of methanol to form methoxide species was approximately twice as fast on m-ZrO2 as on t-ZrO2. CO2 insertion to form monomethyl carbonate, an intermediate in the synthesis of DMC, occurred more than order of magnitude more rapidly over m-ZrO. By contrast, the transfer of a methyl group from adsorbed methanol to monomethyl carbonate and the resulting formation of DMC proceeded roughly twice as fast over m-ZrO2. The observed patterns are attributed to the higher Bronsted basicity of hydroxyl groups and cus-Zr4+O2- Lewis acid/base pairs present on the surface of zirconia.