In-Situ Infrared Spectroscopic Study of the Dynamics of Protons in the Cages of Zeolites

用原位透射红外光谱法系统地研究了H型分子筛笼中小分子与羟基的相互作用。本研究的主要目的是阐明分子筛催化过程中发生的基本过程，从而从分子水平上对分子筛的酸性有一个基本的认识。(1)弱碱性小分子间的相互作用：研究了H_2、O_2、N_2等双原子分子和He、Ar、Kr、H_3等稀有气体与典型H型分子筛H-MOR、H-Y和H-ZSM-5的相互作用。除了He之外，这些分子与酸性OH基团形成氢键。结果表明，利用红外光谱数据可以表征分子筛的酸性。(2)N_2作为分子筛酸中心探针分子的特性：揭示了N_2可以作为分子筛酸中心探针分子。详细考察了N_2作为探针的特性。由于N_2是一种很弱的碱性分子，不发生化学反应，因此它是一种很好的新型探针分子，它只探测强酸中心，而不改变酸性中心的固有性质。并与近年来广泛使用的CO探针进行了比较。(3)活性分子在沸石酸中心上的吸附和反应：以H_2，^<18>O为吸附剂，发现水吸附的红外吸收带主要是氢键吸附。采用快速扫描红外光谱法跟踪了甲醇转化为二甲醚以及水与酸性羟基之间的H/D交换反应的动力学过程。

The interaction between small molecules and hydroxyl groups in the cages of H-form zeolites was systematically investigated by means of in-situ transmission infrared spectroscopy. The main purpose of this research is to clarify the fundamental processes taking place in zeolite catalysis, which would give the fundamental understanding of the acidity of zeolites at molecular level.(1) The Interaction between small and weakly basic molecules : The interaction of diatomic molecules such as H_2, O_2, and N_2, and rare gases such as He, Ar, Kr and Xe with the representative H-form zeolites, H-MOR,H-Y and H-ZSM-5 were investigated. These molecules except for He form hydrogen bonding with the acidic OH groups. It was revealed out that we can characterize the acidity of the zeolites using the IR data of the interaction.(2) The characteristics of N_2 as a probe molecules of the acid sites in zeolites : We have revealed out that N_2 can be used as the probe of acid sites. The characteristic of N_2 as the probe was examined in detail. Since N_2 is very weak base and unreactive, it serves as an excellent new type of the probe molecule that probes only the strong acid sites without changing the intrinsic nature of the acid sites. Its nature was compared with that of CO that has been widely used as the probe recent years.(3) The absorption and reaction of the reactive molecules on the acid sites of zeolites : By using H_2, ^<18>O as absorbate, the main feature of the IR bands observed for the water adsorption was conclusively attributed to the H-bonded adsorption. The dynamic processes of the methanol conversion to dimethyl ether and the H/D exchange reaction between water and the acidic hydroxy groups were followed by means of rapid-scanning FT-IR spectroscopy.