CO2 hydrogenation activity and surface structure of zeolite-supported Rh catalysts Original Research Article

CO2 hydrogenation (H2/CO2=3, total pressure=3 MPa, 423 K) over Rh ion-exchanged Y-type zeolite catalysts (RhY) was studied. The RhY catalyst showed 10 times higher activity (as a turnover frequency) than a conventional impregnated SiO2-supported Rh catalyst (Rh/SiO2). Production of methanol was observed at 423 K over RhY. At first the Rh atoms were supported in a highly dispersed form in the zeolite cage. Then they began to aggregate under the reaction conditions, and moved outside the cage. The working state of Rh species was determined to be Rh metal particles (3.3 nm in diameter) located outside the cage; it was the same, regardless of the Rh loading (from 1 to 6 wt%). It was speculated that the high activity of the RhY catalyst was due to the zeolite cage, which played important roles to condense CO2 and to supply CO2 to the Rh sites outside the cage for the promotion of the reaction. Intense deactivation at 100 min was due to accumulation of produced water inside the zeolite cage, because it suppressed the CO2 reservoir inside the cage.