A series of oxideized CO-K-Mo/γ-Al2O3 catalyst samples,prepared by impregnating oxidized K-Mo/γ-Al2O3 samples with an aqueous solution of calculated Co(NO3)2 and then calcining in air at temperatures of 350℃，500...A series of oxideized CO-K-Mo/γ-Al2O3 catalyst samples,prepared by impregnating oxidized K-Mo/γ-Al2O3 samples with an aqueous solution of calculated Co(NO3)2 and then calcining in air at temperatures of 350℃，500℃65℃ and 800℃ respectively,were sulfided and then investigated for the activity in the synthesis of mixed alcohols from CO hydrogenation under conditions of p=5.0MPa,T=350℃ and GHSV=4800h^-1 .The results demonstrate that the addition of cobalt promoter is favorable to the formation of higher alcohols and the opimum calcination temperatures after impregnating with Co^2+ are about 500-650℃.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℃ ,cobalt exists as Co3O4 specties 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℃,Co component interacts with the K-Mo-O species and destroys the long-range order of the K-Mo-O spectes 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℃,Co component exists mainly as CoAl2O4 species,most of which cannot be sultided during sulfidation.展开更多
A series of rhodium-modified Mo-K/Al2O3 catalyst samples was prepared by varying the rhodium loading between 0 and 1.0 wt% and maintaining molybdenum and potassium contents as constants.The structures of the samples w...A series of rhodium-modified Mo-K/Al2O3 catalyst samples was prepared by varying the rhodium loading between 0 and 1.0 wt% and maintaining molybdenum and potassium contents as constants.The structures of the samples were charaterized by techniques of XRD.LRS.TPR,XPS and EXAFS and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas,It was found that.in the oxidic rhodium-modified samples.a strong interaction of the rhodium modifier with the supported K-Mo-O species occurs.This interaction facilitates the sulfidation and reduction of the supported oxo-molybdenum and leads to a decrease in the size of the molybdenum species and stabilization of the cationic rhodium species on the samples during sulfidation.Upon sulfidation.The sulfided molybdenum species in the rhodium-free sample is manly present as large pateches of MoS2-like slabs with their basal sulfur planes interacting with the support surface.With the modirication of rhodium to the samples.The supported MoS2-like species becomes highly dispersed.as revealed by the decrease in the average size of the sulfided molybdenum species.The interaction of the rhodium species with the molybdenum somponent may cause the basal planes of the MoS2-like species to become oriented perpendicular to the support surface due to favorable bonding of the MoS2edge planes to the support through Mo-O-Al bonds.In comparison with the sulfided sample free of rhodium.the properties of the rhodium-modified samples for alcohol synthesis from synthesis gas are much improved.It most probably results from the synergic interaction of the rhodium with the molybdenum species that gives rise to the appearance of the catalytically active surfaces of sites.The co-existence of cationic and metallic rhodium stabilized by this interaction may be responsible for the increased selectivity for the formation of C2+ alcohols.展开更多
文摘A series of oxideized CO-K-Mo/γ-Al2O3 catalyst samples,prepared by impregnating oxidized K-Mo/γ-Al2O3 samples with an aqueous solution of calculated Co(NO3)2 and then calcining in air at temperatures of 350℃，500℃65℃ and 800℃ respectively,were sulfided and then investigated for the activity in the synthesis of mixed alcohols from CO hydrogenation under conditions of p=5.0MPa,T=350℃ and GHSV=4800h^-1 .The results demonstrate that the addition of cobalt promoter is favorable to the formation of higher alcohols and the opimum calcination temperatures after impregnating with Co^2+ are about 500-650℃.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℃ ,cobalt exists as Co3O4 specties 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℃,Co component interacts with the K-Mo-O species and destroys the long-range order of the K-Mo-O spectes 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℃,Co component exists mainly as CoAl2O4 species,most of which cannot be sultided during sulfidation.
文摘A series of rhodium-modified Mo-K/Al2O3 catalyst samples was prepared by varying the rhodium loading between 0 and 1.0 wt% and maintaining molybdenum and potassium contents as constants.The structures of the samples were charaterized by techniques of XRD.LRS.TPR,XPS and EXAFS and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas,It was found that.in the oxidic rhodium-modified samples.a strong interaction of the rhodium modifier with the supported K-Mo-O species occurs.This interaction facilitates the sulfidation and reduction of the supported oxo-molybdenum and leads to a decrease in the size of the molybdenum species and stabilization of the cationic rhodium species on the samples during sulfidation.Upon sulfidation.The sulfided molybdenum species in the rhodium-free sample is manly present as large pateches of MoS2-like slabs with their basal sulfur planes interacting with the support surface.With the modirication of rhodium to the samples.The supported MoS2-like species becomes highly dispersed.as revealed by the decrease in the average size of the sulfided molybdenum species.The interaction of the rhodium species with the molybdenum somponent may cause the basal planes of the MoS2-like species to become oriented perpendicular to the support surface due to favorable bonding of the MoS2edge planes to the support through Mo-O-Al bonds.In comparison with the sulfided sample free of rhodium.the properties of the rhodium-modified samples for alcohol synthesis from synthesis gas are much improved.It most probably results from the synergic interaction of the rhodium with the molybdenum species that gives rise to the appearance of the catalytically active surfaces of sites.The co-existence of cationic and metallic rhodium stabilized by this interaction may be responsible for the increased selectivity for the formation of C2+ alcohols.
