Effect of pore size on the performance of mesoporous zirconia-supported cobalt Fischer–Tropsch catalysts

Abstract

Mesoporous zirconia with different pore sizes have been prepared and investigated as supports of cobalt catalysts for Fischer–Tropsch synthesis (FTS). It was found that the F–T catalytic performances were closely correlated to the pore sizes of the mesoporous zirconia. The average crystalline sizes of Co₃O₄ grew with increasing the pore size. Furthermore, their reduction degrees were enhanced, in that the Co–ZrO₂ interaction decreased with the increase of pore size. The results from the catalyst testing showed that the FTS catalytic activity, C₅⁺ selectivity, C₁₈⁺ selectivity and the selectivity to C₁₂–C₁₈ paraffins were enhanced, whereas C₁ selectivity decreased with increasing pore size. Based on the systemic study on the effects of the pore sizes of mesoporous zirconia on FTS, it was shown that the Co/PMZ-12 catalyst supported on the large pore size mesoporous zirconia exhibited the largest cobalt oxide particle size, the highest reducibility, and thus showed the highest FTS catalytic activity, with especially good selectivity to C₁₂–C₁₈ paraffins as the main component of the clean diesel oil fraction. The result was attributed to the combination of two factors. One was the improvement of the reducibility of the cobalt catalyst, the control of re-adsorption of the α-alkene and chain growth derived from the large pore size and narrow pore size distribution of the mesoporous support. The other was that the cobalt catalyst supported on zirconia displayed a high FTS catalytic activity and C₅⁺ selectivity.