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

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 C1-4-alcohols, especially ethanol, from syngas. Over a Ni0.5Mo1K0.5-15%CNTs catalyst under the reaction conditions of 8.0 MPa and 593 K, 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 Ni0.5Mo1K0.5 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 H-2 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. (C) 2013 Elsevier B.V. All rights reserved.