Pd-Decorated CNT-Promoted Pd-Ga2O3 Catalyst for Hydrogenation of CO2 to Methanol

摘要

A type of Pd-decorated CNT-promoted Pd-Ga catalysts was developed. The catalyst displayed excellent performance for CO2 hydrogenation to methanol. Under the reaction conditions of 5.0 MPa and 523 K, the observed specific reaction rate of CO2 hydrogenation reached 2.23 μmol s~(-1) (m~2-Pd)~(-1), which was 1.39 times that (1.60 μmol s~(-1) (m~2-Pd)~(-1)) of the non-promoted Pd-Ga host. The addition of a small amount of the Pd-decorated CNTs to the Pd-Ga host catalyst did not cause a marked change in the E_a of the CO2 hydrogenation reaction. The function of the CNT-promoter was mainly in increasing the molar percentage of the catalytically active Pd°-species in the total Pd-amount at the surface of the functioning catalyst, and in improving the capability of the catalyst to adsorb and activate H2 (one of the reactants). Compared to the "Herringbone-type" CNTs, the "Parallel-type" CNTs possess less active surface (with less dangling bonds), and thus, lower capacity for adsorbing H2, resulting in the rather limited promoter effect.