Studies On Direct Conversion Of Syngas To C₂₊OH Over Cu-Fe/CNT Catalyst And Gasoline Fractions Over Zr-Zn/H-ZSM-5 Catalyst

Catalytic conversion of syngas to liquid fuels and high value-added chemicals is an important route for the utilization of non-oil-based carbon resources(coal,natural gas and biomass).A key scientific issue for the conversion of syngas is the selectivity control of the product.In this paper,based on the strategy of designing bifunctional catalysts for directly converting syngas to C2+OH and gasoline fractions,we prepared CuFe bimetallic catalysts and ZrZn oxides coupled zeolite catalysts,respectively,and studied the catalytic performance and’ correlation of the catalyst structure and performance.For the conversion of syngas to C2+OH,we developed the carbon nanotube-supported Cu-Fe bimetallic catalysts by different methods.Cu-Fe/CNT-co-imp catalyst was prepared by co-impregnation method.Cu-Fe/CNT-co-red-imm catalyst was prepared by co-reduction method.Cu/Fe/CNT-step-red-imm and Fe.Cu/CNT-step-red-imm catalysts were obtained by changing the reduction order of Cu and Fe salt solution,respectively.The relationship between the structure of four catalysts and their catalytic properties was investigated.Characterization results showed that the four fresh catalysts contained Cu2O and Fe3O4,which changed to CuO and FeO-Fe3O4 after 573 K under H2 reduction.During the reaction,FeO in the catalyst became ε-Fe2C,which indicated that Fe2C involved in the reaction and became the active phase of the reaction.The degree of proximity between Cu and Fe is different in the four catalysts,which resulted different catalytic performances.We found that Cu and Fe contact closest in the Cu-Fe/CNT-co-red-imm catalyst which was prepared by the co-reduction method,and this catalyst exhibited the highest selectivity to the C2+ alcohols.On the other hand,the catalysts contained less intimate contact of Cu and Fe showed higher selectivity to hydrocarbons.We speculate that the close contact between Cu and Fe favors coupling of CHxO and CHx intermediates formed on the Cu and Fe sites,thereby promoted the formation of higher alcohols.The TEM characterization of catalysts after reaction revealed that the catalyst structure was remained and relative stable.The stability of bimetallic structures may contribute to efficient synergies between Cu and Fe.In the second part,the production of gasoline fractions direct from syngas was performed by bifunctional catalysts coupling Zr-Zn hybrid oxides and H-ZSM-5 zeolite.We investigated the Zr/Zn molar ratio,the Si/Al ratio of H-ZSM-5 in Zr-Zn/H-ZSM-5 catalyst,the reaction temperature and stability of catalyst.We found that the increase in Zn contents was beneficial to improving the activity of the catalyst,but the selectivity of the gasoline fractions decreased.The Si/Al molar ratio also exhibited a significant influence on the catalytic performance.A proper ratio of Si/Al was 200.We speculate that a suitable acidity is necessary for selective formation of gasoline fractions from syngas.The reaction temperature has a great influence on the catalyst,a higher temperature was beneficial to the conversion of CO,but it is not conducive to the selective production of C5-11 gasoline fractions.Under a 100 hours test,the conversion under Zr-Zn(32:1)/H-ZSM-5(200)catalyst decreased slowly with time on stream.However,the selectivity of the C5-11 product remained unchanged.It is presumed that carbonization occurred on the catalyst,and some of the acid sites were clogged and the activity decreased.