Boosting CO2 Hydrogenation to Formic Acid Through Secondary Metal Promotion in Fe3O-Based MOF Catalysts.

Metal-organic framework (MOF) catalysts are promising platforms for hydrogen energy systems, enabling CO2 conversion to formic acid (HCOOH), a liquid organic hydrogen carrier (LOHC) for hydrogen storage and release. Density functional theory (DFT) calculations (M06-2X/6-31G(d)/LANL2DZ) are performed to investigate CO2 hydrogenation on PCN-250(Fe) clusters featuring frustrated Lewis pair (FLP) sites formed by linker removal. The full hydrogenation pathway, including H2 adsorption, activation, and HCOOH formation, is explored, with HCOOH formation identified as the rate-determining step. Activation barriers from large and small cluster models are consistent (10.0 and 9.4 kcal mol-1). Secondary metal substitution at the Fe2MO node is screened using first- and second-row transition metals (Mn-Zn and Tc-Cd). Results show electronic effects dominate first-row metals, whereas steric effects govern second-row systems. Kinetic volcano analysis identifies Cu(II) and Ru(III) as optimal catalysts for efficient CO2 hydrogenation, supporting rational design of MOF-based hydrogen storage and conversion systems for sustainable energy applications.