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 H^δ− and H^δ+ 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.