Comparative study of higher alcohols synthesis over alumina and activated carbon-supported alkali-modified MoS_2 catalysts promoted with group Ⅷ metals

摘要

Potassium modified molybdenum sulfide catalysts promoted with nickel, cobalt, and rhodium were prepared using alumina or activated carbon as support to obtain highly dispersed MoS_2-based catalysts for higher alcohols synthesis. The N_2 adsorption study indicates a fall in textural characteristics of the catalysts compared to pure supports and this effect is more pronounced in activated carbon-based catalysts. The XRD phase analysis indicated the existence of promoted and un-promoted MoS_2 phases. The addition of rhodium resulted in an enhanced dispersion of smaller sized Mo particles. The TPR studies revealed that the addition of promoters such as, Ni, Co, and Rh improved the reducibility of the catalyst and shifts the reduction temperature of Mo~(+6) to lower temperature. Rh-promoted MoS_2 sites were revealed from DRIFT study of adsorbed CO over the Rh-promoted catalysts. Raman spectroscopy revealed the formation of Ni-Mo-S and Co-Mo-S phases in Ni and Co-promoted MoS_2 catalysts. The performance of these catalysts was tested for higher alcohols synthesis under similar conditions at 320 °C, 8.3 MPa (1200 psi g) and 3.6 m~3 (STP)/(kg of cat./h) and H_2 to CO molar ratio of 1. The Ni-promoted catalyst showed activity towards the formation of hydrocarbons over that of alcohols. The addition of Co to the Ni-Mo-K/Al_2O_3 catalyst improved the activity towards the formation of alcohols and hydrocarbons. The activity of Rh-promoted catalysts for higher alcohol synthesis was much higher than that obtained over the rhodium-free catalysts. The total alcohols space time yield and higher alcohols selectivities are significantly higher over the catalysts supported on activated carbon supported catalysts.