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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 0.5 Mo 1 K 0.5 –15%CNTs catalyst under the reaction conditions of 8.0 MPa and 593 K, the S (total oxy.) reached 64.1% (CO 2 -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% (CO 2 -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 0.5 Mo 1 K 0.5 catalyst caused little change in the E a 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 Mo 4+ /Mo 5+ 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 Ni i Mo j K k active sites via the CNT-assisted hydrogen spillover. The aforementioned two factors both were conducive to increasing the rate of hydrogenation conversion of syngas. |
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