High Temperature Water Gas Shift Reaction over Nanocrystalline Copper Codoped-Modified Ferrites

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• 作者：Gunugunuri K. Reddy ; Kapila Gunasekera ; P. Boolchand ; Junhang Dong ; Panagiotis G. Smirniotis
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 21, 2011
• 年：2011
• 卷：115
• 期：15
• 页码：7586-7595
• 全文大小：1184K
• 年卷期：v.115,no.15(April 21, 2011)
• ISSN：1932-7455

文摘

Nanocrystalline metal (M)-modified ferrite catalysts codoped with copper in atomic ratios Fe/M/Cu = 10/1/0.25 are synthesized and investigated for the high temperature water gas shift (WGS) reaction. The metal modifiers considered in the present work include M = Cr, Ce, Ni, Co, Mn, and Zn. The goal of the present work is to elucidate the role of Cu-codoping in the M-modified ferrites (Fe:M) for the WGS reaction. Interestingly, our shift activity results reveal that Cu act as a promoter for the modified ferrite catalysts, M = Cr, Ni, Co, Mn, and Zn, but it acts as an inhibitor for the case of cerium. XRD measurements indicate that there is a formation of solid solution of type Fe_0.875M_0.1Cu_0.025 (M = Cr, Ce, Ni, Co, Mn, and Zn) in the case of all copper doped-modified ferrites during the activation of the catalysts except for the case of cerium. The activated catalyst Fe/Ce/Cu shows magnetite and wustite phases in the XRD pattern. Cell parameter measurements show that Cu enters into the magnetite structure during the activation and leads to lattice expansion. Temperature-programmed reduction measurements inferred that Cu selectively promotes the reduction of hematite (Fe₂O₃) to magnetite (Fe₃O₄) in all modified ferrite catalysts. The addition of Cu to the Fe:Ce catalyst decreases significantly the reduction temperature of surface ceria, first, the transition temperature of hematite to magnetite, and, finally, the transition of magnetite to wustite. M枚ssbauer spectroscopic studies show changes both in the internal magnetic field and in the isomer shift parameters upon Cu-codoping, consistent with a lattice expansion of the magnetite phase. Our XRD and M枚ssbauer effect results suggest that Cu enters at M-modified octahedral sites in magnetite during activation of the catalysts and, in general, promotes the WGS activity.