Optimizing structural properties of zeolite support to enhance branched isomer yield in gasoline range in Fischer-Tropsch synthesis reaction

초록

In Fischer-Tropsch synthesis reaction using cobalt nano-catalyst, the role of zeolite nanosponge containing Br & Oslash;nsted-Lowry acid sites at mesopore walls was revealed to be important to enhance the yield of isomer hydrocarbon in gasoline range. The acid sites on the external surface where the product shows facile diffusion facilitate isomerization action and cracking. By performing systematic investigation, we confirmed that the yield of branched isomers in gasoline range (i-C5-11) gradually increases with increasing the external surface area of the MFI zeolite. This result indicates that the large external surface area is good for high dispersion of cobalt nanoparticles and high concentration of the external acid sites, consequently advantageous to form i-C5-11. Meanwhile, the i-C5-11 selectivity is varied significantly with respect to the acid concentration; the optimal Si/Al ratio, which determines the concentration of Br & Oslash;nsted-Lowry acid sites, was found to be 50, yielding a maximum i-C5-11 fraction of 25.6 %. Consequently, the zeolite MFI nanosponge synthesized using di-quaternary ammonium surfactant, with Si/Al = 50 is the most suitable supporting material for Co nanoparticles in Fischer-Tropsch synthesis reaction for the purpose producing high-value gasoline fuels.

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