Comparative Study between 2‐Furonitrile and 2‐Cyanopyridine as Dehydrants in Direct Synthesis of Dialkyl Carbonates from CO2 and Alcohols over Cerium Oxide Catalyst

The shift of equilibrium by removing water with nitrile dehydrants is crucial for CeO2‐catalyzed synthesis of dialkyl carbonates from CO2 and alcohols. Two nitriles – 2‐cyanopyridine and 2‐furonitrile – were previously found as effective dehydrants, yet their detailed comparison as well as exploration of potential of 2‐furonitrile remain insufficient. Herein, the performance of 2‐cyanopyridine and 2‐furonitrile was compared in the synthesis of various dialkyl carbonates. 2‐furonitrile was found to be superior to 2‐cyanopyridine in the synthesis of dialkyl carbonates from CO2 and bulky or long‐chain (≥C3) alcohols. Namely, the yield of diisopropyl carbonate (up to 50 %) achieved using CeO2 and 2‐furonitrile is comparable to or even higher than previously reported ones. Meanwhile, 2‐cyanopyridine acted as a better dehydrant than 2‐furonitrile in the synthesis of dimethyl carbonate and diethyl carbonate. The adsorption experiments and density functional theory calculations have indicated that the better performance of 2‐furonitrile compared to 2‐cyanopyridine in the synthesis of dialkyl carbonates from bulky or long‐chain alcohols is due to the weaker interaction of 2‐furonitrile with the CeO2 surface. Such weak interaction of 2‐furonitrile offers a larger reaction field on the catalyst surface for both CO2 and alcohols. Which is better? The performance of 2‐cyanopyridine and 2‐furonitrile as a dehydrant has been compared in the CeO2‐catalyzed direct synthesis of dialkyl carbonates from CO2 and various alcohols. The affinity of nitrile dehydrant and CeO2 as well as bulkiness of alkyl chain in alcohols are important factors.