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Abstract:
The promoting effect of cobalt on the catalytic activity of a NiCoO Dry Methane Reforming (DMR) catalyst was studied by a combination ofin situK beta X-ray Emission Spectroscopy (XES) and K beta-detected High Energy Resolution Fluorescence Detected X-ray absorption spectroscopy (HERFD XAS). Following the calcination process, Ni XES and K beta-detected HERFD XAS data revealed that the NiO coordination in the NiCoO catalyst has a higher degree of symmetry and is different than that of pure NiO/gamma-Al2O3. Following the reductive activation, it was found that the NiCoO/gamma-Al(2)O(3)catalyst required a relatively higher temperature compared to the monometallic NiO/gamma-Al(2)O(3)catalyst. This finding suggests that Co is hampering the reduction of Ni in the NiCoO catalyst by modulation of its electronic structure. It has also been previously shown that the addition of Co enhances the DMR activity. Further, the K beta XES spectrum of the partly reduced catalysts at 450 degrees C reveals that the Ni sites in the NiCoO catalyst are electronically different from the NiO catalyst. Thein situX-ray spectroscopic study demonstrates that reduced metallic Co and Ni are the primary species present after reduction and are preserved under DMR conditions. However, the NiCo catalyst appears to always be somewhat more oxidized than the Ni-only species, suggesting that the presence of cobalt modulates the Ni electronic structure. The electronic structural modulations resulting from the presence of Co may be the key to the increased activity of the NiCo catalyst relative to the Ni-only catalyst. This study emphasizes the potential ofin situX-ray spectroscopy experiments for probing the electronic structure of catalytic materials during activation and under operating conditions.
