DFT study on the accommodation and role of La species in ZSM-5 zeolite
DFT study on the accommodation and role of La species in ZSM-5 zeolite
复制标题
La物种在ZSM-5沸石中的容纳和作用的DFT研究
DOI：
10.1016/j.micromeso.2011.01.007
复制
发表时间：
2011-07
影响因子：
5.2
通讯作者：
Tian, Huiping
中科院分区：
文献类型：
--
作者：
Li, Yanfeng;Zhu, Jiqin;Liu, Hui;Wang, Peng;He, Peng;Tian, Huiping
对镧改性ZSM-5分子筛中镧的位置和结构进行了理论研究。研究了镧离子加入后ZSM-5沸石酸性质的变化机理，以及镧种类对ZSM-5沸石水热稳定性的影响。基于优化的聚类模型和热力学分析表明，引入的镧离子位于对称的六元氧环中，Al位于直道中的T11位，并以La(OH)2+的形式存在，直至典型的烃裂解温度为950K。La(OH)2+中的羟基与晶格氧之间存在弱的分子内氢键，进一步证实了这种结构。同样，我们发现引入镧离子将强Brønsted酸位（Si-OH-Al）转化为弱Brønsted酸位。因此，弱Brønsted酸位的O-H伸展频率为3742和3762cm−1，以Si-OLa (OH) 2-Al的形式存在。研究结果还表明，引入镧离子后，ZSM-5分子筛的Al-O键增强，空间位阻增加，酸性减弱，分子内氢键减弱，从而提高了分子筛的水热稳定性。最后，我们扩展了我们的研究，考虑了镧的种类对ZSM-5沸石失活速率的影响。
Theoretical investigations on the location and structure of lanthanum species in lanthanum-modified ZSM-5 zeolites were carried out. The mechanism of change in the acid properties of the ZSM-5 zeolite after addition of lanthanum cations, and the influence of lanthanum species on the hydrothermal stability of the ZSM-5 zeolite were also studied. Based on optimized cluster models and thermodynamic analyses it is demonstrated that the introduced lanthanum cations lie in the symmetrical six-membered oxygen rings with Al situated at T11 sites in the straight channels and exist as La(OH)2+up to a typical hydrocarbon cracking temperature of 950K. This structure is further confirmed by the existence of weak intramolecular hydrogen bonds between the hydroxyls in La(OH)2+species and the lattice oxygens. Similarly, we found that the introduced lanthanum cations transformed the strong Brønsted acid sites (Si–OH–Al) into the weak Brønsted acid sites. Accordingly, the weak Brønsted acid sites have O–H stretching frequencies of 3742 and 3762cm−1and are in the form Si–OLa(OH)2–Al. Our results also suggest that the hydrothermal stability of the ZSM-5 zeolite is improved by introducing lanthanum cations due to the strengthened Al–O bond, increased steric hindrances, weakened acidity and weak intramolecular hydrogen bonds. Finally, we extended our investigation by considering the influence of the lanthanum species on the deactivation rate of the ZSM-5 zeolite.
登录
查看更多内容
影响因子：
3.3
作者：
Hyun Sook Park and;K. Seff
通讯作者：
Hyun Sook Park and;K. Seff
DOI：
10.1016/0144-2449(95)00161-1
发表时间：
1996-04
期刊：
Zeolites
影响因子：
--
作者：
T. Sano;N. Yamashita;Y. Iwami;K. Takeda;Y. Kawakami
通讯作者：
T. Sano;N. Yamashita;Y. Iwami;K. Takeda;Y. Kawakami
影响因子：
7.3
作者：
L. A. Pine;P. Maher;W. A. Wachter
通讯作者：
L. A. Pine;P. Maher;W. A. Wachter
影响因子：
5.3
作者：
M. Rokosz;A. Kucherov;H. Jen;M. Shelef
通讯作者：
M. Rokosz;A. Kucherov;H. Jen;M. Shelef
影响因子：
6.7
作者：
Yi-Ling Luo;Xiaohong Wan;Yuki Ito;S. Takami;M. Kubo;A. Miyamoto
通讯作者：
Yi-Ling Luo;Xiaohong Wan;Yuki Ito;S. Takami;M. Kubo;A. Miyamoto