QUANTUM CHEMICAL STUDY OF THE EFFECT OF THE STRUCTURAL CHARACTERISTICS OF ZEOLITES ON THE PROPERTIES OF THEIR BRIDGING OH GROUPS .2.
QUANTUM CHEMICAL STUDY OF THE EFFECT OF THE STRUCTURAL CHARACTERISTICS OF ZEOLITES ON THE PROPERTIES OF THEIR BRIDGING OH GROUPS .2.
复制标题
DOI：
10.1021/j100411a028
复制
发表时间：
1986-09-25
影响因子：
--
通讯作者：
BERAN, S
中科院分区：
文献类型：
--
作者：
SENCHENYA, IN;KAZANSKY, VB;BERAN, S
采用 STO-3G 基组的非经验 SCF 方法和 CNDO/2 方法，使用 (OH) 3SiOHAl (OH) 3 和 (OH) 3SiOAl (OH) 3 模型团簇研究沸石几何特征对桥接 OH 基团性能的影响。两种方法定性地得出相同的结论，表明随着 SiOAl 角的增加以及 Si-O 和 Al-O 键长的减小，这些 OH 基团的质子夺取能降低。然而，具有扩大的 SiOAl 角和缩短的 Si-0 和 Al-O 键长的 OH 基团几乎不可能存在于真实的沸石结构中，其中同时存在具有较小 SiOAl 角和较长的 Si-O 和 Al-O 键长的正常桥接氧原子。然后质子迁移到具有更深势阱的正常位置。计算还表明，Si:A1 比例对 OH 基团酸性的影响比结构特征的影响更明显。
The nonempirical SCF method with a STO-3G basis set and the CNDO/2 method are employed to study the influence of the zeolite geometry characteristics on the properties of the bridgingOH groups using the (OH) 3SiOHAl (OH) 3 and (OH) 3SiOAl (OH) 3-model clusters. Both methods lead qualitatively to the same conclusion, indicating a decrease in the proton abstraction energy of these OH groups with increasing SiOAl angle and decreasing Si-O and Al-O bond lengths. The OH groups with enlarged SiOAl angles and shortened Si-0 and Al-O bond lengths could, however, hardly exist in real zeolite structures where normal bridging oxygen atoms with smaller SiOAl angles and longer Si-O and Al-O bond lengths are simultaneously present. The protons then migrate to normal positions with deeper potential wells. The calculations also revealed that the effectof the Si: A1 ratio on the acidityof the OH groups is somewhat more pronounced than thatof the structural characteristics.