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

Abstract

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.

Keywords: carbon dioxide fixation; cerium oxide; heterogeneous catalysis; non-reductive CO2 transformation; organic carbonate.