Preparation of a Novel Copper Catalyst in Terms of the Immiscible Interaction Between Copper and Chromium
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Preparation of a Novel Copper Catalyst in Terms of the Immiscible Interaction Between Copper and Chromium Satoshi Kameoka Æ Mika Okada Æ An Pang Tsai
Received: 19 April 2007 / Accepted: 10 September 2007 / Published online: 29 September 2007 Springer Science+Business Media, LLC 2007
Abstract Based on the metallurgical point of view, we aimed to design a new form of copper catalysts with high thermal stability and activity. Delafossite CuCrO2 has been studied as a precursor for copper catalyst. The CuCrO2 was reduced to fine dispersion of Cu and Cr2O3 particles with porous structure by the treatment in H2 at 600 C, which exhibited much higher activity and thermal stability for steam reforming of methanol (SRM) than those of the CuO and/or Cr2O3 catalysts. Sintering of Cu particles was significantly suppressed even after H2 reduction at 600 C. Moreover, the CuCrO2 can be regenerated by calcination in air at 1,000 C where the activity is also restored completely even after sintering at high temperatures. Fine porous structure generated by the reduction of CuCrO2 and immiscible interaction between Cu and Cr2O3 are important in stabilizing of copper nanoparticles. Based on these findings, we propose that the CuCrO2 is an effective precursor for a high performance copper catalyst. Keywords CuCrO2 Delafossite Immiscible Porous structure Thermal stability Reversible Methanol steam reforming
1 Introduction Copper-based catalysts are extensively studied due to their good catalytic performance in several reactions such
S. Kameoka (&) M. Okada A. P. Tsai Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan e-mail: [email protected]
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as steam reforming of methanol and water gas shift reaction [1, 2]. Difficulty of homogeneous dispersion of Cu particles on supports and poor thermal stability have been the major drawbacks [3]. To overcome these problems, catalytic performance of copper-based catalysts has been improved by combination with the metal oxides such as ZnO [3–5], Cr2O3 [5, 6], Fe2O3 [7, 8], and CoO [9]. However, roles of the oxides in the improved copperbased catalysts have not been sufficiently understood. According to the binary alloy equilibrium phase diagrams, Cu and M (M = Fe, Cr, Co, etc.) are neither form compounds nor mutually dissolve in the solid state, i.e., Cu and M are immiscible [10]. Recently, we have found that copper catalysts with fine dispersion of copper particles and high thermal stability can be directly prepared from a spinel CuFe2O4 in which the combination of Cu with Fe is important [7, 11]. High catalytic performance is ascribed to the reduction of the spinel CuFe2O4 and the subsequent immiscible interaction between Cu and Fe [7]. The origin of high catalytic performance is due to the formation of a composite structure induced by reductive decomposition of the CuFe2O4 where nano-scale copper particles homogenously dispersed within the porous Fe3O4 matrix [11]. With understanding o
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