Feature ArticleKinetic modelling of temperature-programmed reduction of cobalt oxide by hydrogen

- A 5-steps reduction mechanism for Co3O4 was proposed.
- The promoter improved the reducibility of Co3O4 while it had little effect on CoO.
- Reduction difficulties follow the order: Ru-Co-La/Al2O3 < Ru-Co/Al2O3< Co/Al2O3.
- High crystallinity increases the difficulty of reducing Co3O4 instead of intermediates.
- The interaction between CoO and Al2O3 to form CoAl2O4 was modelled.

The reduction activities and mechanisms of cobalt-based catalysts are of great interest to industry and researchers, due to their applications in Fischer-Tropsch synthesis. Here, we investigated the reduction of alumina‐supported cobalt catalysts by hydrogen using temperature-programmed reduction. We propose a five-step reduction mechanism that incorporates both amorphous and crystalline Co3O4, and includes the interaction between CoO and the Al2O3 support. Based on our proposed mechanism, we developed a kinetic model of the reduction process. The modelling results of catalysts promoted with ruthenium and lanthanum in contrast with un-promoted catalyst clearly show that the promoter improves reducibility of the catalyst. The effect of Co3O4 crystallinity was also investigated by the reduction of fresh in comparison of pre-oxidised catalyst. We conclude that high crystallinity significantly increases the difficulty of reducing Co3O4. The interaction between CoO and Al2O3 under reduction conditions to form CoAl2O4 was quantitatively simulated. The kinetic modelling confirms that the support plays an important role in catalyst reduction via the interaction between the catalyst and the support. Those kinetic modelling results are supported by in situ X-ray diffraction studies of the reduction process.

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