Research On Selective Production Of Liquid Hydrocarbon Fuels Over Rare-earth Metal Modified Catalysts

In order to protect China's limited fossil resources and sustainable economic development,it is imperative to study the clean and efficient utilization of fossil fuels.Relatively speaking,China has abundant coal resources but a lack of oil and gas resources,which resulted in the China's energy comsumption structure dominated by coal.Gasification technology can be applied to convert fossil fuels into synthesis gas,and synthesis gas can be made into environmentally-friendly and high-efficiency liquid hydrocarbon fuels via Fischer-Tropsch synthesis,which is of great significance to solve China's energy strategical safety problems,promote the sustainable development of society and environment as well as improve the utilization of fossil energy.Therefore,the highly efficient catalysts for selective production of liquid hydrocarbon fuels were studied in this paper.Firstly,selective Fischer-Tropsch synthesis was carried out over a series of Co/H-?catalysts to investigate the influence of rare-earth metal ions promotion on the synthesis of gasoline-range hydrocarbons(GRHs,C₅–C₁₂ hydrocarbons).H-?zeolite was doped with rare-earth metal ions,specifically Y³⁺,Ce³⁺and La³⁺,by an ion-exchange method.It was found that the addition of Y³⁺improved the dispersion of active components over the Co/H-?catalyst,while doping with Ce³⁺,having the ability to change its valence state as well as the number of oxygen vacancies of the support,enhanced the catalyst reducibility.However,the addition of La³⁺tended to cause agglomeration of the active particles due to its large ionic radius.Performance tests showed that the Co/Y-?and Co/Ce-?catalysts achieved higher CO conversions.Due to the moderate acidity and the enhanced CO-metal bonding,the Co/Y-?catalyst exhibited optimal GRHs selectivity of49%with a yield of 41.4%at 260°C,2 MPa,H₂/CO=2,and 1064 h^-1.Then the influence of Y³⁺content on the selectivity of jet fuel range hydrocarbons(C₈–C₁₆hydrocarbons)was further explored.H-?zeolite was modified by several times of Y³⁺ion exchange,which was applied to prepare a series of Co/Y-?-x?x=1,2,3,4?catalysts.As the structural auxiliaries,the addition of Y³⁺improved the dispersion and reducibility of Co₃O₄particles,and resulted in the decreased average diameter of active Co particles as well as the increased active surface area for CO hydrogenation,thus enhancing the reaction activity and remarkably affecting Fischer-Tropsch synthesis product distribution.The increasing Y³⁺ion additives made the total acidity of Co/H-?catalysts cut down,which promoted the generation of jet fuel and lessened the selectivity of C₁–C₄ gaseous hydrocarbons.The selectivity and yield of C₈–C₁₆ hydrocarbons over Co/Y-?-3 catalyst with the proper Y³⁺content?0.99 wt%?achieved the highest values of 41.2%and 34.5%.After that,the effect of Y₂O₃-Co/H-?catalysts with different yttrium oxide contents on production distribution of selective Fischer-Tropsch synthesis was investigated.The Y₂O₃-Co/H-?catalysts were prepared to load the active metal cobalt and rare earth metal yttrium oxide on the H-?zeolite through step impregnation method.The product distribution was dramatically changed by the addition of yttrium oxide.Performance tests showed that the 3Y₂O₃-Co/H-?catalyst with the yttrium metallic content of 2.65 wt%promoted the production of C₈–C₁₆hydrocarbons,and achieved the best C₈–C₁₆ hydrocarbons selectivity of 42.8%with a yield of36.7%,which was attributed to its high dispersity of active components as well as the appropriate pore structure and acidity.