Energy-Saving CO₂ Hydrogenation Using Light

Supported by Saudi Aramco – KAIST CO₂ management center, Professor Hyunjoo Lee’s research team developed light-assisted CO₂ hydrogenation by investigating metal-CO₂ interaction upon light irradiation.

Metal nanoparticles loaded onto supports have been investigated as heterogeneous catalysts for thermal CO₂ hydrogenation. When light is irradiated on the metal catalyst, hot electrons can be generated, helping the surface reaction. Inter-band transitions, which occurs by ultraviolet light, are typically observed on precious metals. The input energy is quite high in this case, and photo-excitation by visible light would be more desired. Recently, it was reported that adsorbates on the metal surface can also absorb light, generating hot electrons. If the electrons on the adsorbates can be excited by visible light, the surface reaction would be accelerated by shining light with weak energy.

Herein, CO₂ hydrogenation on Ru nanoparticles was greatly promoted by light irradiation. The DFT calculation showed that the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreased from 8.5 eV in free CO₂ to 2.4 eV in CO₂ adsorbed on the Ru surface. By investigating the dependency on light intensity and light wavelength, it was confirmed that hot electrons were generated upon light irradiation, enhancing the surface reaction. Very weak light energy such as a laser pointer (532 nm) could enhance the surface reaction. As a result, the light-assisted CO₂ hydrogenation reduced energy consumption by 63%, comparing to the case without light irradiation. Additionally, the reaction can be easily turned on and off by turning on or off the lamp. This unique property can be potentially used to produce methane fuel from CO₂ and H₂ on-site using minimized energy.

This study entitled “Energy-Efficient CO₂ Hydrogenation with Fast Response Using Photoexcitation of CO₂ Adsorbed on Metal Catalysts” was published in the journal ‘Nature Communication’ on August 2, 2018.