Rational design of hierarchical zeolite encapsulating FeMnK architecture to enhance light olefins selectivity in Fischer-Tropsch synthesis

Construction of core-shell catalysts is generally considered as an effective strategy for regulating hydrocarbon distribution in Fischer-Tropsch synthesis. Rational design of core-shell catalysts to enhance olefins selectivity is greatly desirable but still challenging. Herein, a series of FeMnK@H-S-1(x) catalysts (FeMnK oxide encapsulated in hollow silicalite-1 zeolite) featured with hierarchical shell were elaborately fabricated by desilicationrecrystallization method in a mixed alkaline solution (x = NaOH/(TPAOH + NaOH)). Hierarchy factor was introduced to quantitatively describe variety of hierarchical zeolite encapsulating structures. In catalytic performance, it was found that the light olefins selectivity attained the maximum at 50.6% over FeMnK@H-S-1 (0.20) catalyst with space-time yield of light olefins up to 26.7 mu mol(C2)=(-C4)=.g(Fe)(-1).s(-1) and performed a mono tonicity increase relation with the hierarchy factor. Maximizing the hierarchy factor was beneficial to the formation of light olefins on the as-synthesized catalysts, which may result from the well coordination of shape selective function and transport efficiency due to the optimally orchestrated porosities. Additionally, the moderate H-2 activation capacity, relatively lower olefins desorption energy and the suppressed olefins secondary reaction over FeMnK@H-S-1(0.20) catalyst also contribute to the boosted light olefins selectivity. This study sheds new clues for rational catalyst design in direct light olefins synthesis from Fischer-Tropsch synthesis.

Automated summary

Constructing hierarchically structured FeMnK@H-S-1(x) catalysts can enhance light olefins selectivity in Fischer-Tropsch synthesis, with the hierarchy factor playing a key role in promoting light olefins formation. Maximizing the hierarchy factor benefits the coordination of shape selective function and transport efficiency, leading to boosted light olefins selectivity on the synthesized catalysts. Additionally, moderate H-2 activation capacity and suppressed olefins secondary reactions also contribute to the enhanced light olefins selectivity.