On the possibility of AgZSM-5 zeolite being a partial oxidation catalyst for methane
On the possibility of AgZSM-5 zeolite being a partial oxidation catalyst for methane
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DOI：
10.1016/j.jcis.2009.01.015
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发表时间：
2009-05-01
影响因子：
9.9
通讯作者：
Nagao, Mahiko
中科院分区：
文献类型：
--
作者：
Kuroda, Yasushige;Mori, Toshinori;Nagao, Mahiko
在573K抽空的银离子交换HZSM-5沸石样品(Ag(H)ZSM-5)在573K以上的温度下对甲烷的部分氧化表现出显著的催化性能，超过了Ag/SiO_2中心点Al_2O_3和Ag/SiO_2催化剂的催化性能。红外光谱(IR)、X-射线吸收精细结构(XAFS)和氧气吸附测试表明，甲烷的部分氧化是由Ag+离子和小团簇Ag同时存在引起的。考虑到Ag2O(H=26kJ/mol)的生成热(每个氧原子)的大小，我们提出了这样的解释：在ZSM-5中形成的小的Ag金属团簇上活化的氧在小的Ag团簇上形成了一个表面氧化层，从而形成的物种在573K或更高的温度下同时容易分解，这样活化的银金属上的氧溢出并能与交换在ZSM-5中的Ag+离子活化的甲烷反应，从而导致了Ag(H)ZSM-5样品在甲烷部分氧化中的高催化活性。XAFS和IR数据也很好地证明了这一解释。预计这种材料在将天然气转化为更高附加值的化学品和燃料方面有潜力成为一种有前途的催化剂。(C)2009 Elsevier Inc.保留所有权利。
A silver-ion-exchanged HZSM-5 zeolite sample (Ag(H)ZSM-5) evacuated at 573 K exhibited prominent catalytic behavior in the partial oxidation of CH4 at temperatures above 573 K, exceeding the performance of Ag/SiO2 center dot Al2O3 and Ag/SiO2 catalysts. From the infrared (IR) and X-ray absorption fine structure (XAFS) spectra, as well as the dioxygen adsorption measurement, it was concluded that the simultaneous existence of Ag+ ions and small clusters of Ag particles leads to the partial oxidation of methane. Taking the magnitude of the formation enthalpy (per oxygen atom) of Ag2O (Delta H = 26 kJ/mol) into consideration, we propose the interpretation that the dioxygen activated on small Ag metal clusters formed in ZSM-5 elaborates a surface oxide layer on small Ag clusters and the thus-formed species is simultaneously and easily decomposed at 573 K or above, and the oxygen activated in this way on the Ag metal spills over and can react with methane that has been activated by the Ag+ ions exchanged in ZSM-5, resulting in the high catalytic activity of the Ag(H)ZSM-5 sample in the partial oxidation of methane. This interpretation is also well evidenced by XAFS and IR data. It is anticipated that this material has the potential to be a promising catalyst in the conversion of natural gas into higher value-added chemicals and fuels. (c) 2009 Elsevier Inc. All rights reserved.