Surface species in direct liquid phase synthesis of dimethyl carbonate from methanol and CO 2 : an MCR-ALS augmented ATR-IR study.

The reaction mechanism of dimethyl carbonate (DMC) production over ZrO from CO and CHOH is well-known, but the level of understanding has not improved in the last decade. Most commonly, the reaction mechanism has been explored in the gas phase, whilst DMC production occurs in the liquid phase. To overcome this contradiction, we exploited ATR-IR spectroscopy to study DMC formation over ZrO in the liquid phase. A multiple curve resolution-alternate least square (MCR-ALS) approach was applied to spectra collected during the CO/CHOH interaction with the catalyst surface, leading to the identification of five pure components with their respective concentration profiles. CO and CHOH activation to carbonates and methoxide species was found to strongly depend on the reaction temperature. Low temperature prevents methanol dissociation leaving a catalyst covered with stable carbonates, whilst higher temperature decreases the stability of the carbonates and enhances the formation of methoxides. A reaction path involving the methoxide/carbonate interaction at the surface was observed at low temperature (≤50 °C). We propose that a different reaction path, independent of carbonate formation and involving the direct CO/methoxide interplay, occurs at 70 °C.