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The chemical state of the Cu promoter (1 wt %) in a Cu-promoted Cr-stabilized iron oxide based water−gas shift catalyst has been studied by in-situ X-ray absorption fine structure (XAFS) at 380 °C and elevated pressures, which is close to the conditions typically applied in industrial processes. The Cu promoter enhances the activity of the catalyst. In this study, the catalyst has been studied as fresh, after use for 2000 h, and after a further wash with an aqueous solution of ammonia. In all three cases, CuO and CuFe2O4-like phases are present; the used catalyst also contains some metallic Cu. X-ray absorption spectroscopy (XAS) shows that upon exposure to a typical feed gas for high-temperature shift containing CO, CO2, H2, and water, both the CuO and the CuFe2O4-phases are reduced to metallic Cu at 250 °C; Cr is present as Cr3+ and is slowly incorporated in the Fe3O4 matrix upon further heating to 380 °C and pressurizing to 12 or 24 bar. Washing a used catalyst with an aqueous solution of ammonia primarily removes the metallic Cu but also some CuO and CuFe2O4. Despite the fact that the Cu content in the catalyst after washing with ammonia varies, the activity is the same as that for the unwashed and fresh catalysts. This indicates that only a smaller part, estimated to <0.1 wt %, of the Cu is required to obtain the full promoter effect. These results indicate that the active sites for the water−gas shift reaction are provided by the magnetite surface and are promoted by metallic Cu.

The effect of Mn addition on the catalytic performances of Fischer-Tropsch synthesis was investigated using a series of Co/TiO 2 catalysts prepared by two different preparation methods; incipient wetness impregnation (IWI) and homogeneous deposition precipitation (HDP). Mn was loaded using two different procedures in order to investigate its interaction with Co and TiC>2. Several characterization techniques, mainly XRD, XPS and TPR, were used to elucidate the Co oxidation state and dispersion and to estimate the Mn location. Fischer-Tropsch synthesis carried out at 1 bar of pressure showed an improvement of the catalytic performance in the Mn-promoted HDP catalyst, whereas no promotion effect was found in Mn-promoted IWI catalyst. This difference can be explained by a different Co-Mn interaction.

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