Cobalt Loading Effects on the Physico-Chemical Properties and Performance of Co Promoted Alkalized MoS2/CNTs Catalysts for Higher Alcohols Synthesis

An extensive study of Higher Alcohol Synthesis (HAS) from synthesis gas using cobalt (Co) promoted alkalized MoS2 catalysts supported on Carbon NanoTubes (CNTs) is reported. Up to  5wt.% of Co is added to the 15wt.% Mo-wt.%K/ CNTs by incipient wetness impregnation method. Most of the metal particles were homogeneously distributed inside the tubes and the rest on the outer surface of the CNTs. The catalysts are extensively characterized by different methods and    the activity and selectivity of the catalysts were assessed in a fixed bed micro-reactor. Temperature Programmed Reduction (TPR) tests showed that addition of cobalt decreased the second TPR peak temperature from 801 to 660oC. The diffraction peaks that represent the characteristic K-Mo-O phase (i.e. K2Mo2O7, K2MoO4, K2Mo7O20, KMo4O6, and K0.33MoO3; these species can enhances formation of higher alcohols) were observed in the X- Ray Diffraction (XRD) patterns of unpromoted Mo-K/CNTs and to a greater extent in the XRD patterns of Co-promoted Mo-K/CNTs catalysts.    Co addition to Mo-K/CNTs not only increased the number of surface sites, but also decreased      the average active metal particle sizes from 7.53 to 5.33 nm and increased the percentage dispersion from 51.1 to 68.2%. Among the catalysts with different Co loadings, catalyst with 5 wt.% Co showed the highest %CO conversion of  38.8%. The total alcohol selectivity reached a maximum of 59.7 wt.% on the catalyst promoted with 3 wt.% cobalt. The catalyst with 3 wt.% Co exhibited selectivity of 41.65 wt.% towards higher alcohols.