Efficient diesel production over the iron-based Fischer-Tropsch catalyst supported on CNTs treated by urea/NaOH

- The relationship between FTS activity and pyrrolic N content of the supported catalyst is established.
- The synergy effect of the NaOH and urea combined treatment of the CNTs remarkably improves the FTS catalytic performance of the supported catalyst.
- High diesel selectivity and superior stability is obtained on Fe/CNTs-NaU.

Due to the complex control of nitrogen (N) species in functionalizing the carbon nanotubes (CNTs), the contribution of N species to catalysis is difficult to understand. In this study, we report a facile one-pot approach for the synthesis of N-doped CNTs with N present only in the pyrrolic form using a hydrothermal method and by tailoring the treatment conditions, the N content could reach 2.3 at.%. Then the N-doped CNTs are used as a support to prepare an iron-based Fischer-Tropsch synthesis (FTS) catalyst. The FTS activity and C5+ selectivity of N-doped CNTs supported iron catalyst increases with an increase of N content up to 2.1% but it decreases with higher pyrrolic N content. The enhanced FTS catalytic performance is attributed to increased electron conduction, electron donor effect and improved surface basicity due to the pyrrolic N incorporated into the carbon framework. Furthermore, a urea/NaOH co-treatment of CNTs is conducted and the treated CNTs is used as a support for preparing an iron catalyst. The results indicate that the synergistic modification effect of NaOH and urea effectively functionalizes the CNTs and leads to the incorporation of the pyrrolic N, to a high graphitization degree, to easy reduction, to a structural integrity and to a strong metal-support interaction of the supported iron catalyst. This results in an increased FTS activity, superior stability and remarkable diesel selectivity (52%). This synergistic effect shows the potential applications of carbon materials in the field of energy storage, carbon dioxide capture and catalysis, with appropriate functionalization.

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