Co-Mo-K sulfide-based catalyst promoted by multi-walled carbon nanotubes for higher alcohol synthesis from syngas

Abstract

Using home-made multi-walled carbon nanotubes (CNT) as the promoter, sulfurized Co-Mo-K catalysts (denoted as CoiMojKk-x% CNT) were prepared by the co-precipitation method. Their catalytic performance for higher alcohol synthesis from syngas was evaluated and compared with that of the CNT-free counterpart (CoiMojKk). Appropriate incorporation of a minor amount of CNT into CoiMojKk led to a significant increase in CO conversion and selectivity for the higher alcohols. Under the reaction conditions of 5.0 MPa, 623 K, V(H-2): V(CO): V(N-2)=60:30:10, and GHSV=3 600 ml(g.h), the observed space-time-yield of total (C1-4) alcohols reached 241.5 mg/(g.h) with CO conversion of 21.6% over the Co1Mo1K0.3-10% CNT catalyst, which was 1.84 times that over Co1Mo1K0.3. Ethanol became the dominant product of the CO hydrogenation under the conditions mentioned above. The water-gas-shift (WGS) side reaction was inhibited to a greater extent over the CNT-promoted catalyst. The results of catalyst characterization indicated that the addition of a minor amount of CNT into the Co1Mo1K0.3 catalyst did not cause an obvious change in the apparent activation energy for the conversion of CO but led to an increase in the molar percentage of catalytically active Mo-species (Mo4+) in the total Mo amount at the surface of the functioning catalyst. Based on the temperature-programmed desorption results, it could be inferred that, under the conditions of the higher alcohol synthesis, there existed a considerably larger amount of reversibly adsorbed H-species on the CNT-promoted catalyst, which would generate a surface micro-environment with high stationary-state concentration of the adsorbed H-species on the catalyst and thus increase the rate of a series of surface hydrogenation reactions. In addition, high stationary-state concentration of adsorbed H-species on the surface of catalyst would effectively inhibit the WGS side reaction. These factors contribute considerably to the increase in the main product yield.