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Mn-Promoted Co/TiO2 Catalysts: Quantitative Analysis of Cobalt Polymorphs and Stacking Faults and Its Effect on
Danial Farooq1,2, Lucy Costley-Wood1,2, Sebastian Stockenhuber1,2
1Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
ACS Catalysis
|February 26, 2026
Summary
Manganese promotion in cobalt catalysts enhances Fischer-Tropsch synthesis for net-zero fuels by altering cobalt crystal structures. This study quantifies how manganese influences cobalt polymorphs and stacking faults, optimizing selectivity for valuable products.
Area of Science:
- Catalysis, Materials Science, Chemical Engineering
- Focus on heterogeneous catalysis and materials characterization for sustainable chemical production.
Background:
- The transition to net-zero emissions requires efficient circular economy strategies, including X-to-liquid (XTL) technologies like Fischer-Tropsch (FT) synthesis.
- Cobalt catalysts are crucial for FT, but their performance depends on polymorphic structures (FCC, HCP) and cobalt carbide (Co2C) formation.
- Understanding structure-performance relationships is key to optimizing FT catalysts for renewable feedstocks.
Purpose of the Study:
- To quantitatively analyze cobalt polymorphs and stacking faults in Mn-promoted Co/TiO2 FT catalysts.
- To correlate structural features with catalytic performance, particularly alcohol and olefin selectivity.
- To elucidate the role of manganese in modulating cobalt's polymorphic transformation and carbide formation.
Main Methods:
- In situ powder X-ray diffraction (XRD) and X-ray Diffraction Computed Tomography (XRD-CT) on spent catalysts.
- Supercell simulations to model stacking fault probabilities and determine proportions of faulted FCC and HCP domains.
- Analysis across a range of manganese loadings (0-5%).
Main Results:
- Increased Mn loading reduced stacking faults in FCC while increasing them in HCP, promoting HCP domain formation.
- The 3% Mn-loaded catalyst showed significantly higher HCP content and Co2C formation.
- Higher HCP and Co2C content correlated with the highest selectivity for alcohols and olefins.
Conclusions:
- Manganese promotion facilitates a transformation from FCC to HCP cobalt, and subsequently to Co2C, driven by stacking sequences and metal-support interactions.
- Mn stabilizes Co particles, enhances dispersion, and crucially modulates polymorph distribution and stacking faults, altering catalytic behavior.
- Characterizing stacking faults is vital for designing efficient FT catalysts for carbon-neutral fuel production via engineered polymorphic and interfacial structures.
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