Structure of Co-K-Mo/γ-Al2O3 catalysts and their catalytic activity for mixed alcohols synthesis

A series of oxidized Co-K-Mo/gamma-Al2O3 catalyst samples, prepared by impregnating oxidized K-Mo/gamma-Al2O3 samples with an aqueous solution of calculated CO(NO3)(2) and then calcining in air at temperatures of 350 degrees C, 500 degrees C, 650 degrees C and 800 degrees C, respectively, were sulfided and then investigated for the activity in the synthesis of mixed alcohols from CO hydrogenation under conditions of P=5.0 MPa, T=350 degrees C and GHSV=4800 h(-1). The results demonstrate that the addition of cobalt promoter is favorable to the formation of higher alcohols and the optimum calcination temperatures after impregnating with Co2+ are about 500-650 degrees C. The structure of Co and Mo species on the oxidized and sulfided samples was determined by X-ray diffraction (XRD), laser Raman spectrum (LRS) and extended X-ray absorption fine structure (EXAFS). For oxidized sample calcined at 350 degrees C, cobalt exists as Co3O4 species and covers the surface of K-Mo-O species, the structure of K-Mo-O species is the same as that in K-Mo/Al2O3 sample. The interaction between cobalt and K-Mo-O species is relatively weak. After sulfidation, cobalt exists as sulfide crystallites with an octahedral coordinated structure, and molybdenum as MoS2 crystallites. For oxidized samples calcined at 500-650 degrees C, Co component interacts with the K-Mo-O species and destroys the long-range order of the K-Mo-O species gradually. After sulfidation, Co tends to exist as a sulfide with tetrahedral coordinated structure and Mo still as MoS2 crystallites. For oxidized sample calcined at 800 degrees C, Co component exists mainly as CoAl2O4 species, most of which cannot be sulfided during sulfidation. (C) 1999 Elsevier Science B.V. All rights reserved.