Critical role of sodium migration in iron-based FT- zeolite tandem catalyst system for syngas hydrogenation to gasoline

Exploration the role of promotor in the Fischer-Tropsch zeolite (FTO-ZEO) tandem catalyst systems is of paramount importance in improving the selectivity of target products. Herein, by varying the contents of Na promotor in xNa-FeOx, the evolution of Na in FTO-ZEO system during reaction and the resultant catalytic performance for FT synthesis have been investigated. When the content of Na falls in the range of 0.5–5 %, the syngas conversion performance on bare FeOx catalysts reaches a performance-platform period, while that on tandem catalysts show a volcano-like trend. With a set of control experiments, it is speculated that there is a migration process of Na from xNa-FeOx to the H-ZSM-5 moiety. The changed acidity of H-ZSM-5 causes the transformation of products toward higher carbon alkanes and aromatics in the gasoline range with a selectivity of 71.5 %. This work makes an important progress by showing the phenomenon of Na migration during reaction, which puts forward the influence of promoters on FTO-ZEO system and gives a new insight of zeolites modification.