Highly robust and efficient MnZnFe2O4 decorated fibrous KCC-SiO2 catalyst for the synthesis of light olefins from syngas

Abstract

The synthesis of light olefin products (C2–C4), including ethylene, propylene and butylene, has gained immense interest due to its importance in the petrochemical industry, as key building blocks to produce important chemicals such as polymers, solvents and drugs. Among the various non-petroleum synthesis approaches, Fischer–Tropsch synthesis (FTS) is considered as the most promising economically and environmentally-benign single process for the conversion of syngas to light olefins, over heterogeneous catalysts. In this study, a straightforward and green sonochemical route is designed and successfully applied to synthesize novel and robust catalysts: bare-MnZnFe₂O₄ NPs and KCC-SiO₂ fibrous nanospheres decorated with MnZnFe₂O₄ NPs. The prepared catalysts were exposed to industrially relevant FTS reaction and subjected to comprehensive structural and morphological characterization using XRD, SEM/TEM, EDS mapping, N₂-BET adsorption–desorption, H₂-TPR, XPS and Mössbauer spectroscopy analysis. The obtained FTS catalytic results demonstrated that compared with commonly reported iron-based catalysts, the KCC-SiO₂/MnZnFe₂O₄ core/shell NP catalyst displayed a high light olefin C2–C4 selectivity of 64.5% and an olefin/paraffin ratio of 3.4, while the pristine MnZnFe₂O₄ catalyst exhibited 57% C2–C4 selectivity and an O/P ratio of 7.1. Moreover, the CO conversion significantly improved from 54% for MnZnFe₂O₄ to a maximum value of 81.5% for the optimized KCC-SiO₂-supported MnZnFe₂O₄ catalyst. Notably, the produced catalysts displayed long-term stability for a period of 500 h while maintaining high FTS catalytic performance, showing potential FTS industrial application. The obtained high FTS activity for the developed KCC-SiO₂/MnZnFe₂O₄ catalyst is discussed in terms of the improved dispersion, textural properties, spinel redox properties and the unique architecture of the silica–spinel interface that facilitates the desorption of light olefins and suppresses the sequential hydrogenation to unfavourable kinds of paraffins.