In situ x-ray absorption of Co/Mn/TiO2 catalysts for Fischer-Tropsch synthesis

The reduction behavior of Co/TiO2 and Co/Mn/TiO2 catalysts for Fischer−Tropsch synthesis has been investigated by soft X-ray absorption spectroscopy (XAS). In situ XAS measurements of the L2,3 edges of Co and Mn have been carried out during reduction treatments of the samples in H2 at a pressure of 2 mbar and at temperatures up to 425 °C. The changes of Co and Mn 3d valences and the symmetries throughout the reduction have been determined by comparison with theoretical calculations based on the charge transfer multiplet code. Furthermore, bulk Co3O4 has been reduced under the same conditions to evaluate the effect of TiO2 as a support on the reducibility of Co oxides. The average Co valence at the various temperatures has been determined from a linear combination of the reference spectra. It was found that the unsupported Co3O4 was easily reduced to Co0 at 425 °C, whereas the Co3O4 supported on TiO2 catalysts was only reduced to a mixture of CoO and Co0, even after 12 h reduction at 425 °C. The presence o...