Controlled reduction of spinel material for highly selective syngas aromatization over bifunctional catalysts

Directly converting syngas to aromatics allowed fossil fuel and biomass to provide high-value chemicals. Combining MnFe2O4 spinel material with ZSM-5 zeolite made obtaining a highly selective and stable bifunctional catalyst possible to overcome the present challenge in severe operating conditions and low aromatics content in liquid products. The precisely controlled catalyst exhibited an aromatics selectivity of 63.1 % at CO conversion of 38.3 %, leading to the content of aromatics in C-5(+) being higher than 95 %, ensuring that most liquid products are aromatic hydrocarbon (dominated by C-6 similar to C-12 aromatics), which were significant for the separation and practical application in the syngas conversion process. Characterizations provided evidence of the partially reduced spinel material forming the tiny Fe5C2 particles as main active sites in CO conversion, and the formed olefins were further transformed into aromatics on acid sites of ZSM-5 zeolites. The results fully proved that the precise control of the content and proximity of each component was of great significance for the catalytic performance. Benefiting from the stable structure and potassium promoter, the reduction degree of the spinel material was controllably altered, achieving a significant improvement in aromatics selectivity. Moreover, the long-term stable reaction performance of the optimal catalyst indicated excellent application prospects for selectively converting syngas to aromatics. Thus, this work provided an idea to realize the aromatic production from syngas conversion by precisely controlling the exposure of the active centers.