A New Strategy for the Improvement of the N2 Adsorption Properties of Copper-Ion-Exchanged MFI-Type Zeolites at Room Temperature

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• 作者：Atsushi Itadani ; Masashi Tanaka ; Toshinori Mori ; Mahiko Nagao ; Hisayoshi Kobayashi ; Yasushige Kuroda
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：August 16, 2007
• 年：2007
• 卷：111
• 期：32
• 页码：12011 - 12023
• 全文大小：516K
• 年卷期：v.111,no.32(August 16, 2007)
• ISSN：1932-7455

文摘

A copper-ion-exchanged MFI-type zeolite, CuMFI, which exhibits an extremely efficient adsorption of thedinitrogen (N₂) molecule at room temperature, has been successfully prepared by ion exchange in an aqueoussolution of Cu(CH₃COO)₂ containing a component of NH₄CH₃COO. This ion-exchange method has uniquecharacteristics as follows; first, the copper ion exchange takes place exclusively on the ion-exchangeable sitethat acts as the active site for N₂ adsorption, and second, the extent of the reduction of the divalent copperion exchanged attains a high value of 88%. In addition, the CuMFI sample thus prepared exhibits a highefficiency for N₂ adsorption at 298 K where the monovalent copper ions act as adsorption sites; approximately86% of them are effective for N₂ adsorption. In this case, the heats of adsorption of N₂ were large, 87-60kJ mol^-1. These observations were rationalized as showing that the site-selective ion exchange with copperions occurs, accompanying acetate ligands by which the effect of the size is brought, and that the divalentcopper ions exchanged in this way can be reduced easily and efficiently to the monovalent ions; on thatoccasion the organic ligands incorporated in the ion-exchange process are decomposed, promoting the reductionof the copper ions. From the observations of photoluminescence spectra and X-ray absorption near-edgestructure spectra in the processes both before and after N₂ adsorption, it was deduced that the three-coordinatedmonovalent copper ions are active sites for N₂ adsorption at room temperature, which was also supported bythe results of both diffuse reflectance spectra and density functional theory calculations. The results obtainedare expected to provide significant information for the development of materials that function efficiently asN₂-fixation or N₂-activation catalysts as well as NO_x decomposition catalysts.