Water-Gas Shift Reaction on Ni–W–Ce Catalysts: Catalytic Activity and Structural Characterization

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• 作者：Fuzhen Zhao ; Zongyuan Liu ; Wenqian Xu ; Siyu Yao ; Anna Kubacka ; Aaron C. Johnston-Peck ; Sanjaya D. Senanayake ; Ai-Qing Zhang ; Eric A. Stach ; Marcos Fernández-García ; José A. Rodriguez
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：February 6, 2014
• 年：2014
• 卷：118
• 期：5
• 页码：2528-2538
• 全文大小：696K
• ISSN：1932-7455

文摘

The water-gas shift reaction (WGS, CO + H₂O 鈫?H₂ + CO₂) was studied over a series of W鈥揅e, Ni鈥揅e, and Ni鈥揥鈥揅e mixed-metal oxide catalysts. The structure of the catalysts and the WGS reaction intermediates were characterized using in situ techniques including X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), scanning transmission electron microscopy (STEM), and diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). XANES showed the existence of Ni²⁺ and W⁶⁺ inside the ceria lattices. The coexistence of Ni and W inside of ceria led to a large lattice strain, not seen for Ni鈥揅e and W鈥揅e, that facilitated the reduction of Ni鈥揥鈥揅e and gave this oxide special catalytic properties. A Ni_0.2W_0.1Ce_0.7O₂ catalyst displayed the highest catalytic activity among all the mixed oxides, followed by a Ni_0.2W_0.2Ce_0.6O₂ catalyst. Besides high activity, the Ni鈥揥鈥揅e catalysts also displayed the effective suppression of the methanation reaction (CO + 3H₂ 鈫?CH₄ + H₂O) under WGS conditions compared to W-free Ni鈥揅e catalysts. The introduction of W in the lattice of Ni鈥揅e favored the formation of O vacancies that facilitated the dissociation of water, preventing the dissociation of CO and the formation of methane. Because of the special chemical properties of Ni鈥揥鈥揅e, monodentate formates and carbonates, which could be chemically active species for the WGS reaction, appear on the surface of these catalysts. Synergistic interactions between Ni and W give Ni鈥揥鈥揅e unique structural and chemical properties not seen for W鈥揅e or Ni鈥揅e mixed-metal oxides.