Effect of surface sites of TiO2 support on the formation of cobalt-support compound in Co/TiO2 catalysts

This study has addressed the effect of surface sites (as Ti4+ and Ti3+) of TiO2 support on the formation of the cobalt-support compound on Co/TiO2 catalyst. A 20% cobalt was prepared on each TiO2 support having the different Ti4+/Ti3+ ratios covering on the surface (1.2, 1.3, 1.4, and 1.6). It can be concluded that the non-reducible compound as a Co-SCF preferred to form on the Co/TiO2 catalyst when the most proportional site of surface TiO2 became Ti4+. This is because the migration of cobalt cluster, which plays the significant role for creating Co-SCF, can be promoted by the increasing of Ti4+ sites resulting in the decrease of cobalt dispersion. The hyperfine patterns of ESR spectra demonstrated that the Co0(HxTiOy) was the simple chemical form of Co-SCF formed after standard reduction. Moreover, the structure of Co-SCF changed to be a higher non-uniform structure when the number of Ti4+ site on TiO2 surface increased. The possible mechanism to form this compound has also been discussed.