Lower olefins (C2=-C4=) are crucial intermediates in chemical engineering industry for producing plastics, polymers, solvents, textiles and etc. Fischer-Tropsch synthesis to lower olefins (FTO) process as a non-oil-based route has attracted increasing attention in recent years. Fe catalyzed FTO has been recognized as a structure-sensitive reaction. However, the size effect shows different performance tendency on different supported catalysts. Therefore, fabricating bulk catalysts with changeable particle size would help to solely investigate the size effect of Fe phase. In this paper, nanoparticles assembled porous-Fe3O4 microspheres were synthesized via a PAA-mediated solvothermal method. Different from the traditional bulk iron catalysts, the porous-Fe3O4 microspheres had good mechanical stability and self-assembled pore structure. By tuning preparation parameters, a series of porous-Fe3O4 microspheres with different nanoparticle size (8.5-16.5 nm) but same microsphere diameter (300 nm) was obtained. N2 physisorption method showed that porous-Fe3O4 microspheres had large surface area and micro-, meso-pores coexisting. H2-TPR demonstrated that smaller particle size could be reduced easily with lower reduction temperature. The large surface area, abundant micro- and meso- porosity as well as favorable reducibility contributed to the enhanced catalytic performance compared with the traditional Fe bulk catalysts. Particularly, Fe3O4 with nanoparticle size of 9.9 nm showed the highest intrinsic activity (TOF), highest C2-C4= selectivity and O/P ratio. C5+ selectivity was higher for the smaller particles, while the opposite trend applied to CH4 selectivity. Moreover, it was found that the extent of Fe5C2 correlated positively with catalytic activity. So, particle size of bulk Fe catalysts played a crucial role in Fe5C2 formation and catalytic performance. These results shed light on the structure-performance relationship in FTO.

Porous-Fe3O4 microspheres with tunable size as catalysts for Fischer-Tropsch synthesis to lower olefins

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.