Pd/CNT-promoted Cusingle bondZrO2/HZSM-5 hybrid catalysts for direct synthesis of DME from CO2/H2

Authors: Meng-Hui Zhang, Zhi-Ming Liu, Guo-Dong Lin, Hong-Bin Zhang

Abstract:
A type of bi-functional hybrid catalyst of Pd-decorated CNT-promoted Cu-ZrO₂ admixed with HZSM-5 zeolite was developed, and displayed excellent performance for the direct synthesis of dimethyl ether (DME)from CO₂/H₂ via CH3OH in a single fixed-bed continuous flow reactor. Over a CuZr–PdCNTs/HZSM5 hybrid catalyst under reaction conditions of 5.0 MPa, 523K, V(H2)/V(CO2)/V(N2) = 69/23/8, GHSV= 25,000 mLSTP/(h g-hydr. catal.), the observed specific rate of CO₂ hydrogenation-conversion reached 0.39 mol/(s m²-Cu⁰-SA), which was 1.22 times that of the corresponding Pd/CNTs-free counterpart CuZr/HZSM-5. The addition of a minor amount of the Pd-decorated CNTs into the CuZr/HZSM-5 host catalyst caused little change in the apparent activation energy for CO₂ hydrogenation, but led to an increase of metal Cu exposed area (catalytically active Cu surface-sites closely associated with the CO₂ hydrogenation to methanol) and marked improvement of adsorption performance of the catalyst for H₂ and CO₂. The latter would help generate a micro-environment with higher concentration of active H and CO₂ adspecies at the surface of the functioning catalyst, thus increasing the rate of the surface hydrogenation reactions. The present study also demonstrated that combining the methanol-synthesis and methanol-dehydration-to-DME processes in heterogeneous “one-pot” reactions by using the bifunctional hybrid catalyst could indeed enhance the driving force for CO₂ hydrogenation conversion.

Keywords:
Pd-decorated CNTs
Pd-decorated CNT-promoted
Cu-ZrO₂/HZSM-5 hybrid catalysts
CO₂ hydrogenation
Direct DME synthesis

Published in: Applied catalysis A: General  (Volume 451, Pages 1-288, 31 January 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Pd/CNT-promoted Cusingle bondZrO2/HZSM-5 hybrid catalysts for direct synthesis of DME from CO2/H2

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