Raman and XPS Investigation of Copper Promoted Transition Metal Doped Ferrites – High Temperature Water Gas Shift Activity
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In our previous studies, we introduced a variety of metal ions (M = Cr, Mn, Co, Ni, Cu, Zn, and Ce) into iron oxide (spinel lattice) and screened for effectiveness for a high-temperature WGS reaction. The idea was to stimulate the ferrite formation via doping with certain foreign cations and to promote the Fe3+ „\ Fe2+ redox couple. In the present study, the role of copper on the shift activity of various transition metal doped catalysts is being investigated. The WGS feed condition were chosen to mimic conditions found in a membrane reactor. For this purpose, various copper doped modified ferrite catalysts were prepared using ammonia assisted coprecipitation method. The prepared catalysts were characterized by using TPR, Raman Mossbauer and X-ray photo electron spectroscopic techniques and evaluated for WGS reaction in the temperature region 400-550 oC and at a stream to CO ratio 3.5 which the conditions used in our membrane reactor. Interestingly, our shift activity findings reveal that copper act as a promoter for the transition metal doped ferrites expect for the Fe/Ce catalyst. While, Cu acts as an inhibitor for the Fe/Ce catalyst. TPR results suggest that addition of Cu to Fe/Ce catalyst promotes the transformation of magnetite to wustite phase to a much lower temperature (starts at 200 oC). This leads to the formation of FeO during the activation of the catalyst which decreases the catalytic activity. Mossbauer spectra of activated and spent catalysts after the WGS reaction reveal that the addition of Cu creates structural distortions in octahedral sites and promotes the WGS activity. In order to find out more about effect of Cu on transition metal doped ferrites in a molecular level, Raman and XPS studies are performed over the activated and used catalysts. These results will be presented in this study.