(47h) CO2 Hydrogenation to C2+ Chemicals on a Metal-Organic Framework (HKUST-1): Mechanistic Investigation

Thermocatalytic hydrogenation of CO₂ to high value-added multicarbon (C₂₊) chemicals has received considerable interest to reduce CO₂ footprint and mitigate global warming. With readily tunable structures and functionalities, metal-organic frameworks (MOFs) possess an unprecedentedly large degree of design flexibility and provide an ideal platform to catalyze CO₂ hydrogenation. With Cu paddle-wheel like structure, HKUST-1 has been experimentally reported as a promising catalyst for ethanal production under ambient conditions. Since Cu paddle-wheel is common in MOFs, mechanistic understanding of catalytic mechanism on HKUST-1 would provoke the exploration of more MOFs for C₂₊ chemical production.

In this work, we conduct a theoretical investigation into the mechanism for CO₂ hydrogenation on HKUST-1 through density-functional theory computations. Several atomic models with different structural configurations are considered and a defective HKUST-1 with one 1,3,5-benzene tricarboxylate (BTC) linker removed is identified for facile CO-CHOH coupling via Eley-Rideal mechanism for ethanol production. Intriguingly, only one of the dual Cu atoms is found to serve as an active site for C-C coupling, with the other one as an adsorption site for H atom. Furthermore, the defective HKUST-1 enables coupling of COCHOH and CO intermediates to generate the second C-C bond, which leads to the formation of isopropanol. From bottom-up, this work provides deep microscopic insights into C-C coupling on HKUST-1 and might facilitate the development of new MOFs for efficient CO₂ hydrogenation to C₂₊ chemicals.