How is CO2 hydrogenated to ethanol on metal–organic framework HKUST-1? Microscopic insights from density-functional theory calculations†

Abstract

Thermocatalytic hydrogenation of CO₂ to multi-carbon chemicals (C₂₊) has received considerable interest to reduce CO₂ footprint and mitigate global warming. Comprising Cu paddle-wheel clusters, a metal–organic framework (MOF) namely HKUST-1 has been experimentally reported as a promising catalyst for CO₂ hydrogenation to ethanol under ambient conditions with the assistance of non-thermal plasma (NTP). Yet, there lacks microscopic understanding of the active center, reaction pathway and product selectivity. In this study, we conduct density-functional theory calculations to quantitatively and explicitly elucidate the fundamental mechanism involved. NTP is revealed to be responsible for H₂ dissociation, while the defective HKUST-1 with exposed Cu atoms accounts for highly selective CO₂ hydrogenation to ethanol via facile *CHOH–CO coupling, with *CHOH adsorbed on the Cu atoms and CO from the gas phase. The strong binding between the carbonyl C atoms in C₂ intermediates and Cu atoms, and the high stability of *CH₃CHOH intermediate, contribute to the higher selectivity of ethanol over acetaldehyde and ethylene, respectively. From bottom-up, this computational study provides deep microscopic insights into the catalytic mechanism of CO₂ hydrogenation to C₂ products on HKUST-1, and it will facilitate the design of new MOFs for efficient CO₂ conversion and other important chemical transformations.