Sorption enhanced CO₂ hydrogenation to formic acid over CuZn-MOF derived catalysts

A series of Cu-Zn@CNx catalysts incorporated with platinum group metal (PGM) elements, such as Ru, Pd, Pt, and Ir were synthesised via the hard template approach, where a metal-organic framework (MOF) is utilised as a hard template. The developed materials were capitalised for sorption-enhanced synthesis of formic acid from CO2. The pyrolysis process has proven effective in stabilising the metallic Cu in a carbon-nitrogen matrix environment. Moreover, the diverse PGM group metal promoters facilitate enhanced CO2 adsorption behaviour on the catalyst surface. Structure-activity relationship, catalyst lifetime and deactivation are established through rigorous analysis of fresh and spent catalyst materials with various analytical techniques, including XRD, Raman, BET, SEM, XPS, chemisorption, physisorption and HRTEM. The utilisation of water as a reaction medium has been found to alleviate thermodynamic constraints, thereby promoting enhanced formic acid formation. Furthermore, the promotional effect of doped metals is elucidated by utilising density functional theory (DFT) calculations and revealed that Ru-CZ exhibited the highest CO2 adsorption energy, concomitant with the experimental findings, wherein the Ru-CZ catalyst displayed an outstanding CO2 conversion rate of 12.91% with an impressive TON of 11 435.