Detection of Brønsted acid sites in zeolite HY with high-field 17O-MAS-NMR techniques
Detection of Brønsted acid sites in zeolite HY with high-field 17O-MAS-NMR techniques
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DOI：
10.1038/nmat1332
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发表时间：
2005-02
期刊：
影响因子：
41.2
通讯作者：
Luming Peng;Yun Liu;Namjun Kim;J. Readman;C. Grey
中科院分区：
文献类型：
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作者：
Luming Peng;Yun Liu;Namjun Kim;J. Readman;C. Grey
沸石的酸性和独特的孔结构在控制许多沸石基催化剂的活性和选择性方面起着重要作用。尽管27 Al、29 Si和1H NMR光谱是研究这些材料的标准分析工具，但由于17 O的天然丰度非常低，17 O-NMR研究就不那么常规了（0.037%）、相对较低的共振频率和较大的四极矩。在各种沸石中检测到骨架氧位的~（17）O-NMR共振，但是直接结合到布朗斯台德酸位点（Si-O（H）-Al）的氧的17 O-NMR共振仍然难以捉摸。在这里，我们报告的直接观察到这种共振在脱水沸石HY，通过使用高磁场强度。17 O-1H双共振NMR实验被用来明确地证明，17 O信号来自O附近的H原子。一个大的四极耦合常数，该网站的本地失真的措施，为6.6 MHz的确定，这是类似于在ab initiocalculations的沸石HY-样簇得到的，这个值下降到5 MHz的丙酮结合。本文提出的结果开辟了表征沸石酸性和研究H+吸附剂相互作用的方法。
The acidity and unique porous structures of zeolites play an important role in controlling the activity and selectivity of many zeolite-based catalysts,. Although27Al,29Si and1H NMR spectroscopy represent standard analytical tools with which to study these materials,,17O-NMR investigations are much less routine, owing to the very low natural abundance of17O (0.037%), its relatively low resonant frequency and its large quadrupole moment.17O-NMR resonances from framework oxygen sites in a variety of zeolites have been detected,,,,,,, but the17O-NMR resonance from oxygen directly bound to the Brønsted acid site (Si–O(H)–Al) has remained elusive. Here we report the direct observation of this resonance in dehydrated zeolite HY, by using high magnetic-field strengths.17O–1H double-resonance NMR experiments are used to prove unambiguously that the17O signal arises from O nearby H atoms. A large quadrupolar coupling constant, the measure of the local distortion of this site, of 6.6 MHz is determined, which is similar to that obtained inab initiocalculations of zeolite HY-like clusters; this value drops to 5 MHz on acetone binding. The results presented in this paper open up methods for characterizing zeolite acidity and investigating H+-sorbent interactions.