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

Abstract

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 “desilication-recrystallization” 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 µmolC2=-C4=.gFe−1.s−1 and performed a monotonicity 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 H2 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.