Encapsulating Ir nanoparticles into UiO-66 for photo-thermal catalytic CO2 methanation under ambient pressure

Photo-thermal catalysis provides a promising strategy for the efficient conversion of carbon dioxide (CO2) into value-added chemicals under mild conditions. Here, we successfully encapsulate iridium (Ir) nanoparticles of ca.1.5 nm into UiO-66, forming Ir@UiO-66 hybrids, as highly active catalysts for CO2 methanation under light irradiation. X-ray photoelectron spectroscopy (XPS) revealed that the electrons are transferred from UiO-66 to Ir nanoparticles, indicating a strong interaction between Ir nanoparticles and the UiO-66 host. Photoelectrochemical measurements indicated that the Ir nanoparticles could effectively facilitate the separation and transfer of photo-induced charge carriers in excited UiO-66, thus promoting H-2 cleavage and CO2 activation. As a result, Ir@UiO-66-2 showed an excellent methane (CH4) production rate of 19.9 mmol g(cat)(-1) h(-1) and high selectivity (similar to 95%) at 250 degrees C under light irradiation, far surpassing that in the dark. The in situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS) results revealed that formate (*HCOO) is the key intermediate in the CO2 methanation process, and light irradiation did not alter the reaction pathways while facilitating the conversion of *HCOO species, thus enhancing CH4 production. This study provides new strategies for the future design of catalysts for CO2 methanation under mild conditions.

Automated summary

Photo-thermal catalysis is a promising strategy for converting CO2 into value-added chemicals. In this study, Ir@UiO-66 hybrids were synthesized and used as catalysts for CO2 methanation under light irradiation. The results showed that the catalysts exhibited high activity and selectivity, with significantly improved methane production compared to the dark reaction. The study also revealed the key intermediate involved in the reaction and the role of light irradiation in promoting CH4 production.