利用理論計算來探討 NO2 在Fe nano-sized cluster(Fe15)上的吸附過程與分解反應

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Title:	利用理論計算來探討 NO2 在Fe nano-sized cluster(Fe15)上的吸附過程與分解反應
Authors:	張書維
Contributors:	化學系應用化學研究所
Keywords:	二氧化氮分解反應
Date:	2010
Issue Date:	2011-11-02 13:16:58 (UTC+8)
Abstract:	此篇研究是利用Vienna ab initio simulation program (VASP)來探討NO2 於Fe nano-sized cluster 上之吸附及分解反應，其中在NO2 的吸附位置上我們找到了許多種的吸附方法，如Top、Bridge 和Hollow 等等的位置，得到吸附結構最好的為FeNO2(H-Fe6,6,7-μ3-N,O,O)，其吸附能量為-80.67 kcal/mol。而在NO2斷去其N─O鍵的反應過程，發現FeNO2(B-Fe6,7-μ2-N,O) 結構斷鍵時，其電子轉移現象最為明顯，因此能障是所有之中最大的，能障為53.11kcal/mol，但也是放熱最多的，而吸附能最好的 FeNO2(H-Fe6,6,7-μ3-N,O,O)，其斷鍵反應過程之電子轉移現象較不明顯，能障也較低，能障為35.10 kcal/mol，但是形成NO(a) + O(a)時為吸熱的結果。最後與NO2/Fe(111)的研究系統做了相互的比較，發現NO2 於Fe nano-sized cluster 的吸附能比Fe(111)的吸附能要高上一些，且所需克服的能障也比Fe(111)高上許多，不過整個實驗探討到最後還是有成功將NO2(g) + Fecluster 斷鍵成為NO(a) + O(a) + Fecluster。 We applied periodic density-functional theory (implemented in Vienna ab initio simulation package, VASP) to investigate the adsorption and dissociation of NO2 on a Fe nano-sized cluster. There are a lot of locations for NO2 adsorption such as top, bridge, and hollow sites…etc., and the most favorable adsorption configuration of NO2/Fe-cluster is the FeNO2(H-Fe6,6,7-η3-N,O,O) configuration, which has an adsorption energy of -80.67 kcal/mol. For the process of the first (ONO bond activation) nitrogen-oxygen bond scission, it is found that the adsorption structure, FeNO2(B-Fe6,7-η2-N,O), with the largest difference of its charge-density alteration, possesses the highest activation barrier of 53.11 kcal/mol and release a lot of heat. Another configuration of FeNO2(H-Fe6,6,7-η3-N,O,O), with the best adsorption behavior, has an exceptionally smaller charge-density difference alteration and lower energy barrier of ONO bond scission. However, it is an endothermic process to form the NO(a) + O(a). Furthermore, we also compare the potential–energy surfaces with that of the relevant study from our previous work of NO2/Fe(111) system. We found that, in general, the calculated adsorption energy and barrier height (ONO bond scission) for NO2/Fe-cluster system are slightly larger than NO2/Fe(111) counterpart, and the eventual product for NO2(g) + Fecluster reaction would be NO(a) + O(a) + Fecluster.
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