Advancing CO2 hydrogenation to formic Acid: DFT insights into Frustrated Lewis Pair−Functionalized UiO−67 catalysts

Abstract

In this study, we explore the potential of metal–organic frameworks (MOFs) as catalysts for converting CO2 into valuable chemicals. The focus is on integrating frustrated Lewis pairs (FLPs) within the UiO−67 framework. We investigated 12 distinct functionalized FLP moieties (X = −BF2, −BCl2, −BBr2, −BH2, −B(CH3)2, −B(CF3)2, −B(CN)2, −B(NO2)2, −B(OH)2, −B(NH2)2, −B(OCH3)2, and −B(N(CH3)2)2 to determine their ability to activate small molecules within heterogeneous catalysis using density functional theory (DFT). This study reveals two critical stages in the CO2 conversion process with H2 in UiO−67−X. First, the initial heterolytic cleavage of H2 at the FLP site, and second, the subsequent hydrogenation of CO2. The latter involves the addition of a hydride and a proton. Our findings demonstrate that these modifications facilitate efficient dissociation of H2 into Hδ− and Hδ+ with energy barriers ranging from 0.12 to 0.87 eV and CO2 hydrogenation barriers spanning from 0.61 to 1.90 eV. Notably, the −B(CH3)2 functional group exhibited superior effectiveness in CO2 hydrogenation to formic acid (HCOOH; FA). This enhanced activity correlates directly with FLP acidity and the Gibbs free energy changes in H2 dissociation reaction. It highlights the significant influence of FLP−assisted heterolytic dissociation of H2 in the CO2 conversion process. The results of this study do more than introduce metal-free heterogeneous FLPs within MOFs. They also establish a clear link between the functional group composition, FLP acidity, and catalytic efficiency. These insights offer a valuable theoretical foundation for the design of advanced UiO−67−X catalysts. They open up possibilities for transforming greenhouse gases into valuable chemical products, contributing to sustainable chemical synthesis.