Catalytic properties and structure of zirconia catalysts for direct synthesis of dimethyl carbonate from methanol and carbon dioxide

Article abstract of DOI:10.1006/jcat.2000.2854

Dimethyl carbonate (DMC) is a nontoxic substitute for dimethyl sulfate and phosgene, which are toxic and corrosive methylating or carbonylating agents, and is considered to be an option to meet the oxygenation specifications for transportation fuels. Selective synthesis of DMC from methanol and CO₂ proceeded effectively on a ZrO₂ catalyst prepared by the calcination of zirconium hydroxide at 673 K. DMC formation highly depended on the structure of the catalyst. The activity was maximum at 673 K, and then it decreased with the calcination temperature at > 773 K. XRD showed that the bulk of ZrO₂ had a mainly tetragonal structure, but near its surface, the monoclinic phase was major and the tetragonal phase was minor. TPD of coadsorbed CO₂ and NH₃ indicated that a neighboring acid-base site is present on ZrO₂. The amount of the site corresponded to the activity of DMC formation, suggesting that the neighboring acid-base site was active for DMC formation. The methoxy carbonate species was the reaction intermediate causing high selectivity of DMC formation.