In situ X‐Ray Absorption of Co/Mn/TiO₂ Catalysts for Fischer—Tropsch Synthesis.

Abstract

The reduction behavior of Co/TiO 2 and Co/Mn/TiO 2 catalysts for Fischer-Tropsch synthesis has been investigated by soft X-ray absorption spectroscopy (XAS). In situ XAS measurements of the L 2,3 edges of Co and Mn have been carried out during reduction treatments of the samples in H 2 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 Co 3 O 4 has been reduced under the same conditions to evaluate the effect of TiO 2 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 Co 3 O 4 was easily reduced to Co 0 at 425°C, whereas the Co 3 O 4 supported on TiO 2 catalysts was only reduced to a mixture of CoO and Co 0 , even after 12 h reduction at 425°C. The presence of Mn further retards the reduction of the supported Co 3 O 4 particles. The Mn III ions were easily reduced to MnO at temperatures lower than 300°C , and they remained in this oxidation state even after further temperature increase. In addition, catalytic tests in the Fischer-Tropsch synthesis reaction at a pressure of 1 bar indicate that the selectivity of these catalysts might be related to the extent of Co reduced after the activation treatment (i.e., the reduction with H 2 ).

The LUCIA beamline at SOLEIL

“…6(a) shows the Mn L 2,3edge spectra obtained for MnO and MnO 2 . They are consistent with those published using conventional grating monochromators (Morales et al, 2004;Chang et al, 2005;Thakur et al, 2008), although the resolution is lower in the case of the MGM. Fig.…”

Enhancement Effect of Noble Metals on Manganese Oxide for the Oxygen Evolution Reaction

“…Generally, the spectral weight shifts to higher energies when manganese is more oxidized, but the scans also reflect changes in the local bonding environment with a rich multiplet structure, consistent with earlier studies. 41,42 As prepared, the MnO x phases of the catalysts with and without noble metals are indistinguishable and best match a mixture of the Mn 3 O 4 and Mn 2 O 3 reference powder spectra, as can be seen in Figure 2b. However, after they have been electrochemically oxidized under OER conditions (1.65 V versus RHE; see the methods for details), we observe significant changes in the spectra.…”

Atomic structure of cobalt-oxide nanoparticles active in light-driven catalysis of water oxidation

“…Co ligand environment was further studied with soft X-ray measurements at the cobalt L-edge and the oxygen K-edge, both being more informative with respect to metal ligands [65,[84][85][86].…”