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

Abstract

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 H₂ 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 (∼95%) at 250 °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.