Full-spectrum light-assisted thermocatalytic CO2 hydrogenation to formic acid over a highly hydrophobic MOF-based triphase catalyst

Abstract

The practical application of CO2 hydrogenation is often hindered by the conflicting phase requirements for CO2 reduction (gas-solid) and water oxidation (liquid-solid) in conventional two-phase systems. To address these limitations, a gas-solid-liquid triphase microenvironment was constructed using PdAg@NH2-UiO-66-SHP, in which PdAg nanoparticles were integrated with NH2-UiO-66 followed by hydrophobic modification with phenylsilane. Under full-spectrum light irradiation at 60 °C and 1 MPa (CO2:H2 = 1:1), in the presence of 1 mL TEOA in 30 mL H2O the optimized catalyst achieved a HCOOH production rate of 2258 μmol g−1 h−1 with >99% selectivity, approximately twice that obtained under dark conditions. The enhanced performance is attributed to the cooperative effects of the hydrophobic interface, PdAg nanoparticles, and light excitation. The hydrophobic microenvironment facilitates the accessibility of gaseous CO2 and H2 to the catalyst surface, while PdAg nanoparticles promote H2 activation and light-induced charge-transfer processes. In-situ DRIFTS, photoelectrochemical measurements, and DFT calculations further reveal the formation and evolution of key HCOO* intermediates and provide mechanistic insight into the light-assisted reaction pathway. These results demonstrate the effective integration of interfacial gas transport, bimetallic H2 activation, and light-assisted thermal catalysis for selective CO2 hydrogenation to HCOOH.