An efficient Ni–Mo–K sulfide catalyst doped with CNTs for conversion of syngas to ethanol and higher alcohols

Authors:  Ji-Jie Wang, Jian-Rong Xie, Yan-Hui Huang, Bing-Hui Chen, Guo-Dong Lin, Hong-Bin Zhang

Abstract:
A type of Ni–Mo–K sulfide catalyst doped with CNTs for conversion of syngas to ethanol and higher alcohols was developed, and displayed high activity and selectivity for direct synthesis of C_1–4-alcohols, especially ethanol, from syngas. Over a Ni_0.5Mo₁K_0.5–15%CNTs catalyst under the reaction conditions of 8.0 MPa and 593K, the S(total oxy.) reached 64.1% (CO2-free), with the corresponding STY(total oxy.) being 113 mg h⁻¹ g⁻¹. Ethanol was the dominant product, with S(EtOH) and STY(EtOH) reaching 33.1% (CO₂-free) and 55.6 mg h⁻¹ g⁻¹, respectively. This STY(EtOH)-value was 1.47 times that (37.9 mg h⁻¹ g⁻¹) of the CNTs-free counterpart under the same reaction conditions. Addition of a minor amount of CNTs to the sulfurized Ni_0.5Mo₁K_0.5 catalyst caused little change in the Ea for the hydrogenation–conversion of syngas. Appropriately reducing CNT’s grain-size could improve its capability to adsorb hydrogen, thus increasing CO hydrogenation–conversion, yet did not influence selectivity of the products. The present work demonstrated that CNTs as promoter function through their adsorbing/activating H₂ to generate a surface micro-environment with higher stationary-state concentration of H-adspecies on the functioning catalyst. This resulted in a dramatic increase, at the surface of the functioning catalyst, of the molar percentage of catalytically active Mo⁴⁺/Mo⁵⁺ species in the total amounts of surface Mo. On the other hand, those active H-species adsorbed at the CNTs surface could be readily transferred to NiiMojKk active sites via the CNT-assisted hydrogen spillover. The aforementioned two factors both were conducive to increasing the rate of hydrogenation conversion of syngas.

Keywords:
Multiwalled carbon nanotubes
CNT-doped Ni–Mo–K sulfide catalyst
Higher alcohol synthesis
Ethanol synthesis
Syngas

Published in: Applied catalysis A: General   (Volume 468, Pages 1-474, 5 November 2013)

Publisher: Elsevier  

ISSN Information: 0926-860X

An efficient Ni–Mo–K sulfide catalyst doped with CNTs for conversion of syngas to ethanol and higher alcohols

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