Improving the Stability of CeO2 Catalyst by Rare Earth Metal Promotion and Molecular Insights in the Dimethyl Carbonate Synthesis from CO2 and Methanol with 2-Cyanopyridine

The unmatched efficiency of the direct dimethyl carbonate (DMC) synthesis from CO 2 and methanol over CeO 2 catalysts in the presence of an organic dehydrating agent (2-cyanopyridine, 2-CP) was recently reported with high DMC yield (>90%) in both batch and continuous operations. However, the CeO 2 catalyst gradually deactivates in the time scale of days due to suggested surface poisoning by 2-picolinamide (2-PA) produced by hydration of 2-CP. This work seeks active and stable CeO 2 -based catalysts and aims to understand the material factors influencing the catalytic performance. Surface modification of CeO 2 by the addition of rare earth metal (REM) was found to be effective for improving the catalyst stability. Surface basicity and reducibility of the Ce 4+ species play important roles in preventing catalyst deactivation by stabilizing the reactive methoxy species in comparison to the poisoning species (2-PA or species alike). This has been evidenced by in situ attenuated total reflection infrared spectroscopy. CeO 2 materials promoted with 1 wt % rare earth metals (La, Gd, and Pr) greatly enhanced the catalyst stability while retaining the high catalytic activity of CeO 2 . Among them, 1 wt % Pr promotion to CeO 2 was the most effective, affording 35% higher DMC yield in comparison to that of bare CeO 2 after 150 h on stream under the optimized reaction conditions of 30 bar and 120 °C.