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 CO₂ and methanol over CeO₂ 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 CeO₂ 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 for active and stable CeO₂-based catalysts and aims to understand the material factors influencing the catalytic performance. Surface modification of CeO₂ by the addition of rare earth metal (REM) was found effective to improve the catalyst stability. Surface basicity and reducibility of the Ce⁴⁺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 ATR-IR spectroscopy. CeO₂ materials promoted with 1 wt% rare earth metals (La, Gd, and Pr) greatly enhanced the catalyst stability while retaining the high catalytic activity of CeO₂. Among them, 1 wt% Pr promotion to CeO₂ was the most effective, affording 35% higher DMC yield in comparison to bare CeO₂ after 150 h time on stream under the optimized reaction condition of 30 bar and 120 °C.