Effect of Isomorphic Substitution of Zirconium On Mesoporous Silica as Support for Cobalt Fischer-Tropsch Synthesis Catalysts

Isomorphic substituted mesoporous SBA-15 with zirconium at Zr/Si atomic ratios of 1/100, 1/50, 1/20, 1/8 and 1/3 have been successfully synthesized. It was demonstrated that the Zr4+ ions were introduced into the framework of SBA-15 with the hexagonal array of uniform tubular channel configuration intact until Zr/Si ratio of 1/20. Another sample of zirconium incipient wetness impregnated SBA-15 with Zr/Si ratio of 1/20 was prepared for comparison. These mesoporous materials were loaded with 10 wt % cobalt by incipient wetness impregnation and characterized by XRD, TEM, N2 absorption–desorption, UV-visible, H2-TPR, H2-TPD, O2 titration as well as XPS. It was shown that introduction of zirconium increased the density of surface cobalt, improved the cobalt reducibility and generated more available active sites with the low zirconium content (Zr/Si atomic ratio < 1/20). At the high zirconium content, strong interaction between the cobalt species and the surface of the support formed to decrease cobalt reducibility detected by XPS and H2-TPR. The catalytic performances of catalysts for FTS were tested in a fixed bed reactor, and the isomorphic substituted mesoporous SBA-15 with zirconium at Zr/Si ratio of 1/20 supported cobalt catalyst showed the best performance. -->