K-Co-Mo/CNTs Catalyst Performance Study Of Low Carbon Alcohol

The preparation of higher mixed alcohols by syngas catalytic conversion is one of the important ways to clean utilization of coal resources.Higher alcohols can be used as alternative fuels,gasoline additives and basic chemical raw materials.Over the past few decades,researchers have developed a variety of synthetic alcohol catalytic systems.Among them,the alkali-promoted Mo-based catalyst has attracted much attention from researchers because of its excellent resistance to sulfur resistance and carbon deposition.The support plays an important role in the performance of the catalyst.Multi walled carbon nanotubes(MWCNTs)have attracted much attention due to their unique physical and chemical properties,such as the multi-layer wall structure of graphite like structure,high electrica]conductivity,and excellent ability of H2 adsorption and activation.On the basis of our previous work,a series of CNTs supported K-Co-Mo catalysts were prepared by a modified sol-gel method combined with incipient wetness impregnation.The relationship between the structure and catalytic performance was also discussed.The main conclusions are show as below:(1)A series of K-Co-Mo/CNTs catalysts with different Mo loading were prepared by sol-gel method combined with incipient wetess impregnation.The characterization results indicated that the as-prepared catalyst particles had a low crystallization degree,high dispersion and a uniform mesoporous structure.Some particles enters the carbon tubes and well dispersed on the inside surface.The main species of Mo in oxidation state are Mo6+ and Mo4+.The valence state of Co species was related to the Mo loading.When the catalyst with a Mo/CNTs weight ratio of 10%contained metal Co.With further increasing the Mo loading,the Co species mainly existed in the form of Co2+.H2-TPD results showed that the introduction of CNTs can significantly improve the adsorption and activation of H2,which may be related to the presence of sp2-C on the surface of CNTs.The activity testing results indicated that the K-Co-Mo/CNTs catalyst with a Mo/CNTs weight ratio of 30%showed the best catalytic performance for the higher alcohols synthesis after reduction at 525?.The STY of total alcohols was 141.7 g·kg-1·h-1,about 9 times as high as that of the unsupported sample and the alcohol selectivity increased up to 35.4%.In particular,the methanol production was.inhibited remarkably.Further increasing the Mo loading resulted in a decrease of catalytic performance,which may be related to the aggregation of the catalytic particles.(2)The K-Co-Mo catalysts with the same Mo loading were prepared by using CNTs and activated carbon(AC)as the support.The results showed that the active component of the catalyst has a low degree of crystallinity and a high degree of dispersion on the surface of both CNTs and AC support.The K-Co-Mo/CNTs catalysts have a homogeneous mesoporous structure,while the K-Co-Mo/AC catalyst has more microporous pores.The results of H2-TPD show that the peak of dissociatively chemisorbed hydrogen is shifted to the low temperature in the K-Co-Mo/CNTs catalyst compared with the K-Co-Mo/AC catalyst.That is,the interaction between the H-species and the CNTs support is weaker indicated a higher spillover capability of H-species.Furthermore,it was found that CNTs suopprt has a stronger ability to adsorb H-species because sp2-C sited on the surface of CNTs promoted the adsorption and activation of hydrogen.The results of the activity test showed that the selectivity of the K-Co-Mo/CNTs catalyst,especially the C2+alcohol content increased significantly when the H2/CO ratio of the synthesis gas decreased from 2 to 1.and the total alcohol STY decreased.Under the same reaction conditions,CNTs supported catalysts have more excellent properties of synthetic alcohols,which are related to their homogeneous mesoporous structure and excellent H adsorption and spillover capability.Under the condition of reaction temperature 553 K,pressure 5.0 MPa,space velocity 2400 h-1,H2/CO = 1,the selectivity of the K-Co-Mo/CNTs catalyst was 49.8%and the alcohol yield was 110.0 g·kg-1 h-1,C2+OH/MeOH reached 2.33,the comprehensive catalytic performance was excellent.