Influence of reduction-oxidation-reduction treatment on the structure and catalytic performance of Co-ZrO₂ for Fischer-Tropsch synthesis

Co-ZrO₂ precipitated catalyst is treated by reduction in H₂ at 400℃, Oxidation of the reduced catalyst in air at room temperature, and reduction again in H₂ at 250℃ or 400℃. The influence of this reduction-oxidation-reduction treatment on the properties of Co-ZrO₂ precipitated catalyst was investigated by TPR, N₂ physical sorption, H₂-TPD, XPS, XRD, and Raman spectra; the performance of treated catalysts in Fischer-Tropsch (F-T) synthesis was considered in both slurry phase and fixed bed reactors. The results showed that cobalt in the catalyst is in the form of Co₃O₄ with little change in particle sizes after the reduction-oxidation process. The concentration of cobalt on the catalyst surface is reduced a little after the treatment, but the amount of H₂ uptake is increased significantly. The reduction-oxidation treatment can lower the reduction temperature of surface cobalt species. As a result, the catalytic activity of Co-ZrO₂ for F-T-synthesis is improved and the selectivity to CH₄ is depressed by the reduction-oxidation treatment. Furthermore, the catalyst reduced at a relatively high temperature exhibits much better performance in the fixed bed reactor.