Design And Performance Of Ni-based Catalysts For Hydro-conversion Of Fatty Acids To Alternative Aviation Fuel

Hydroconversion of fatty acids(FAs)into aviation fuel is an alternative way to solve the energy crisis.Ni/ZSM-5 bifunctional catalyst has been studied in recent years.However,the low activity and sintering of metal Ni,as well as the uncontrollable diffusion length in micropore and acid distribution of ZSM-5,favor secondary cracking reaction and weaken isomerization reaction,reducing the yield and performance of aviation fuel.In this paper,the Ni-Me^?+structure was designed to enhace the catalytic activity and stability.ZSM-5 zeolite with lamellar morphology was synthesized to improve the diffusion performance,and the HZSM-5 nanosheet was modified by chemical liquid deposition to inhibit the secondary cracking reaction and enhace the isomerization reaction.Ni/Al₂O₃ catalysts with different metal-support interactions and Ni surface site distributions synthesized by atomic layer deposition(ALD)and incipient-wetness impregnation(IW),respectively,were employed for the hydroconverison of oleic acid.It was found that the deoxygenation activity of Ni(ALD)/Al₂O₃ catalyst with high Ni step site content was 2.0 times of that of Ni(IW)/Al₂O₃ catalyst,and the stronger metal-support interaction of Ni(ALD)/Al₂O₃ catalyst result in the deactivation rate only 0.33 times of Ni(IW)/Al₂O₃catalyst.Using diffetent reducible oxides as the support,Ni based catalysts with different surface oxygen defect concentrations were synthesized by IW method.The results of oleic acid hydroconversion showed that the deoxygenation activity of Ni/Ce O2e O₂ catalyst with high oxygen vacancy concentration was 2.1 times higher than that of Ni/SiO₂ catalyst,indicating that oxygen vacancy promoted the deoxygenation of FAs.NiMeO_x catalysts with Ni-Me^?+(Zn,Mo,W)structure were synthesized by incipient-wetness co-impregnation.The synergy effect of NiMeO_x/SiO₂ catalysts on stearic acid deoxygenation was proposed.The deoxygenation activity of NiMeO_x/SiO₂ catalysts increaases with the increase of Me oxyphilicity.Compared with Ni/SiO₂ catalyst,the turnover frequency of stearic acid deoxygenation over NiWO_x/SiO₂ catalyst increased from 20.0 h^-1 to 58.3 h^-1.In addition,after three times cycles,the activity loss of NiWO_x/SiO₂ catalyst is less than 5%.Ni/ZSM-5 catalysts with different nanosheet thickness(3-200 nm)were synthesized by using dual-quaternary ammonium salt surfactant.The results of oleic acid hydroconverion suggested that as the nanosheet thickness decreased from 200 nm to 3 nm,the dispersion of Ni and the pore connectivity of the catalyst gradually increased.The yield of C₉-C₁₅ hydrocarbons increased from 2.8 wt%to 41.4 wt%,and the isomerization ratio increased from 0.50 to 0.75.The HZSM-5 nanosheet with 3 nm thickness was modifation by chemical liquid deposition(CLD)of SiO₂.Ni/ZSM-5 nanosheet catalysts with similar structure but different acid spatial distribution were synthesized.The experiment results suggested that external acid sites mainly favored the primary cracking of the deoxygenated products.Internal acid sites enhanced the isomerization and secondary cracking of the primary cracking products.The Si/Al=200 catalyst modified by CLD for once with weak external acid concentration(7.8?mol/g)and medium internal acid concentration(17.4?mol/g)further improved the iso/n-alkanes ratio(1.6 vs 0.75)with a high C₉-C₁₅ hydrocarbon yield of 39.6 wt%.The nanoshee structure is regulated to further improve the catalytic preformace.Self-pillared(SP)ZSM-5 zeolite with intergrown nanosheet structure was synthesized by using TBAOH as the structure-directing agent.The SP ZSM-5-supported Ni nanoparticles catalysts further increased the iso-/n-alkanes ratio(1.8 vs 1.6).The catalytic stability of the SP NiWO_x/ZSM-5 was about 2 times of that of SP Ni/ZSM-5.Morever,the SP NiWO_x/ZSM-5 displayed better recyclability after regeneration by calcination.