Modulating the Pore Hydrophobicity and Electronic Structure of Cerium MOFs for Enhanced Dimethyl Carbonate Production from CO2 and Methanol without Dehydrants

Abstract

The one-step synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and CO₂ plays an important role in carbon neutrality, but it is still far from practical application due to the undesirable use of dehydrants and the lack of rational design of efficient catalysts. Herein, the model of a CeO₂-like cerium metal–organic framework (MOF) UiO-66-Ce-NH₂ was chosen to introduce a series of hydrophobic perfluoroalkyl groups into the –NH₂ group in the channel of the MOFs by postsynthesis modification to create a hydrophobic reaction environment and remove water molecules during the reaction process, thereby avoiding the need for additional dehydrants, denoted as UiO-66-Ce-F_x (x = 3, 5, 7, 11, and 15). As a result, the catalytic performance of UiO-66-Ce-F_x was significantly improved. Among them, UiO-66-Ce-F₁₁ exhibited the highest DMC formation rate of 408.25 mmol g^–1 h^–1 without additional dehydrants, which was about 13 times higher than that of unmodified UiO-66-Ce-NH₂. Importantly, to the best of our knowledge, this has reached the highest level among currently reported catalysts for the one-step synthesis of DMC from MeOH and CO₂ in batch reactors. Mechanistic studies have shown that the highly efficient catalytic performance is attributed to the synergistic effect of the hydrophobicity and electron-rich capability of the fluorides in the MOF pores. On one hand, the introduction of hydrophobic fluorides creates a hydrophobic reaction site, which accelerates the transfer of water generated in real time during the reaction out of the reaction site, thereby promoting the forward reaction kinetically. On the other hand, the electron-rich fluorides optimize the electronic structure of the Ce sites, enhancing the thermodynamic adsorption and activation of the substrates CO₂ and MeOH. In the present work, a facile post-modification strategy to realize the synergistic promoting effect of thermodynamics and kinetics of one-step synthesis of DMC from CO₂ and MeOH will offer a whole new strategy to design high-efficiency catalysts for one-step synthesis of DMC.