Drake Ian J, Zhang Yihua, Gilles Mary K, Teris Liu C N, Nachimuthu Ponnusamy, Perera Rupert C C, Wakita Hisanobu, Bell Alexis T
Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USA.
J Phys Chem B. 2006 Jun 22;110(24):11665-76. doi: 10.1021/jp058244z.
Aluminum coordination in the framework of USY and ZSM-5 zeolites containing charge-compensating cations (NH4+, H+, or Cu+) was investigated by Al K-edge EXAFS and XANES. This work was performed using a newly developed in-situ cell designed especially for acquiring soft X-ray absorption data. Both tetrahedrally and octahedrally coordinated Al were observed for hydrated H-USY and H-ZSM-5, in good agreement with 27Al NMR analyses. Upon dehydration, water desorbed from the zeolite, and octahedrally coordinated Al was converted progressively to tetrahedrally coordinated Al. These observations confirmed the hypothesis that the interaction of water with Brønsted acid protons can lead to octahedral coordination of Al without loss of Al from the zeolite lattice. When H+ is replaced with NH4+ or Cu+, charge compensating species that absorb less water, less octahedrally coordinated Al was observed. Analysis of Al K-edge EXAFS data indicates that the Al-O bond distance for tetrahedrally coordinated Al in dehydrated USY and ZSM-5 is 1.67 angstroms. Simulation of k3chi(k) for Cu+ exchanged ZSM-5 leads to an estimated distance between Cu+ and framework Al atoms of 2.79 angstroms.
通过铝K边扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）研究了含有电荷补偿阳离子（NH4+、H+或Cu+）的超稳Y型（USY）和ZSM-5沸石骨架中的铝配位情况。这项工作是使用专门为获取软X射线吸收数据而新开发的原位池进行的。对于水合的H-USY和H-ZSM-5，观察到了四面体配位和八面体配位的铝，这与27Al核磁共振分析结果吻合良好。脱水后，水从沸石中解吸，八面体配位的铝逐渐转化为四面体配位的铝。这些观察结果证实了以下假设：水与布朗斯特酸质子的相互作用可导致铝的八面体配位，而不会使铝从沸石晶格中损失。当H+被NH4+或Cu+取代时，即吸收较少水的电荷补偿物种，观察到的八面体配位的铝较少。对铝K边EXAFS数据的分析表明，脱水的USY和ZSM-5中四面体配位的铝的Al-O键长为1.67埃。对Cu+交换的ZSM-5的k3chi(k)模拟得出Cu+与骨架铝原子之间的估计距离为2.79埃。
