Unveiling the Pivotal Role of Ce Coordination Structures and Their Surface Arrangements in Governing 2-Cyanopyridine Hydrolysis for Direct Dimethyl Carbonate Synthesis from CO₂ and Methanol

Abstract

The direct synthesis of dimethyl carbonate (DMC) from CO 2 and methanol presents a promising alternative to conventional methods that use toxic chemicals, but its yield is limited by equilibrium. Coupling this reaction with 2-cyanopyridine (2-Cp) hydrolysis over CeO 2 -based catalysts was found to significantly boost the DMC yield by removing water. Our recent study has revealed that methanol is the key species being activated by surface Ce sites to produce DMC. The reactivity of surface methoxy species toward CO 2 varies greatly with their configuration, which is determined by the Ce coordination structures. A similar challenge remains in understanding the CeO 2 surface feature governing the hydrolysis of 2-Cp to 2-picolinamide (2-PA). Herein, CeO 2 nanocrystallites with well-defined (111), (110), and (100) surfaces were used to study the effects of Ce coordination structures and their arrangements in this reaction and coupled DMC synthesis. We found that the synergistic adsorption of 2-Cp via cyano-N and pyridine-N on (111) and (110) surfaces enables nucleophilic addition of lattice oxygen, producing imino-like N with stronger Lewis basicity, which in turn facilitates hydrolysis. The (111) surface outperforms the (110) surface due to its unique Ce coordination structure and arrangement, which allows more 2-Cp activation and easier 2-PA desorption. Notably, the (111)-enclosed octahedral CeO 2 used herein outperforms the reported pristine CeO 2 catalysts in this coupled reaction. In contrast, this synergistic adsorption/activation does not occur on the (100) surface, leading to low activity. These findings provide insights for designing CeO 2 -based catalysts for CO 2 conversion with alcohols and amines using 2-Cp as a dehydrant.

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