Geometric and Electronic Structure of α-Oxygen Sites in Mn-ZSM-5 Zeolites
Geometric and Electronic Structure of α-Oxygen Sites in Mn-ZSM-5 Zeolites
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DOI：
10.1021/jp802915k
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发表时间：
2008-07
影响因子：
3.7
通讯作者：
D. Radu;P. Glatzel;A. Gloter;O. Stéphan;B. Weckhuysen;F. Groot
中科院分区：
文献类型：
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作者：
D. Radu;P. Glatzel;A. Gloter;O. Stéphan;B. Weckhuysen;F. Groot
结果表明，Mn-ZSM-5分子筛中α-氧位是由N2O分解产生的。催化活性在1 h内降至零，α-氧的形成量从初始N2O处理中每个Mn原子约30% α-氧位减少到后续循环中的约4%。催化活性与位于18 500 cm−1的UV - vis波段的强度相关，表明α-氧位点与Mn位点以扭曲的四方对称连接，相对于块体氧化物具有扩展的Mn−O键。扫描透射电镜与电子能量损失谱（STEM−EELS）结果表明，Mn位点在ZSM-5晶体上分布不均匀，其中大多数Mn原子位于距离晶体表面顶部~ 2nm处。x射线吸收光谱（XAS）表明，在反应条件下，Mn原子具有5倍配位，价态为~ 2.5，受N2O和NO处理的影响很小。
It is shown that α-oxygen sites are generated by the decomposition of N2O in ion-exchanged Mn-ZSM-5 zeolites. The catalytic activity decreases to zero in 1 h, and the amount of α-oxygen that is formed is reduced from ∼30% α-oxygen sites per Mn atom in the initial N2O treatment to a value of ∼4% in the subsequent cycles. The catalytic activity correlates with the intensity of a UV−vis band located at 18 500 cm−1, suggesting that the α-oxygen sites are linked to Mn sites with a distorted tetragonal symmetry with extended Mn−O bonds with respect to bulk oxides. Scanning transmission electron microscopy with electron energy loss spectroscopy (STEM−EELS) results indicate that the Mn sites are distributed unevenly over the ZSM-5 crystals, where most Mn atoms are found in the top ∼2 nm from the crystal surface. The X-ray absorption spectroscopy (XAS) spectra indicate that, under reaction conditions, the Mn atoms have a 5-fold coordination and a valence of ∼2.5, which is little affected by the N2O and NO treatmen...