Molecular iridium catalysts immobilized in metal-organic frameworks (MOFs) were positioned in the condensing chamber of a Soxhlet extractor for efficient CO2 hydrogenation. Droplets of hot water seeped through the MOF catalyst to create dynamic gas/liquid interfaces which maximize the contact of CO2, H-2, H2O, and the catalyst to achieve a high turnover frequency of 410 h(-1) under atmospheric pressure and at 85 degrees C. H/D kinetic isotope effect measurements and density functional theory calculations revealed concerted proton hydride transfer in the rate-determining step of CO2 hydrogenation, which was difficult to unravel in homogeneous reactions due to base-catalyzed H/D exchange.