Sustainable high-energy radiation powering selective CO2 reduction to CH3OH over atomic dual-metal-sites embedded metal-organic framework

Abstract

The efficient use of renewable high-energy radiation (X/γ-rays or accelerated e‒) as the energy input for the chemical transformation of carbon dioxide (CO2) and water to energy-rich fuels holds new promise for a carbon-neutral, sustainable energy economy; however, such processes are challenging to implement, and require the assistance of catalysts capable of sensitizing the secondary electron scattering and providing active metal sites to bind intermediates. Herein, we report that atomic Cu-Ni dual-metal-sites embedded in a metal-organic framework matrix enable efficient and selective (~ 98%) conversion of CO2 to CH3OH in irradiated aqueous solutions. The reaction is initiated by the direct generation of CO2•‒ radicals via aqueous electrons attachment, followed by a series of interfacial reactions. We showed that the UiO-66(Hf) matrix serves as a radiation sensitizer to break electron yield limitation in water radiolysis, dramatically promoting CO2 activation and conversion efficiency. With the synergistic metal centers and a hydroxyl radical scavenger, we achieved stable and selective CH3OH production over multiple irradiation cycles. Pulse radiolysis experiments with theoretical calculations revealed the transient kinetics occurred on the nanosecond timescale and cascade hydrogenation steps. Our study highlighted an unprecedented catalytic route to produce CH3OH with CO2 feedstock and introduced a desirable atomic structure to improve performance.

Direct time-resolved observation of surface-bound carbon dioxide radical anions on metallic nanocatalysts

“…The existence of CO 2 •− on metal electrodes, such as Au, Cu, and Ag, has been proposed based on the experimental Tafel slope analysis 17 – 21 . Besides, the critical role of CO 2 •− formed by hydrated electrons (e aq − ) attachment has recently been recognized by plasma or radiation-driven catalytic and nanodiamond-assisted photolytic CO 2 reduction 22 – 24 . Different catalytic systems have several rate-determining steps (RDS), such as initial electron transfer to CO 2 to form surface-bound CO 2 •− radicals, the first proton-coupled electron transfer, or the reduction of other bound intermediates 17 – 21 .…”