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首页> 美国政府科技报告 >Spin counting in dipolar coupled spin 1/2 systems by multiple quantum NMR spectroscopy in solids: Development of a single quantum propagator and its application to heterogeneous catalysis
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Spin counting in dipolar coupled spin 1/2 systems by multiple quantum NMR spectroscopy in solids: Development of a single quantum propagator and its application to heterogeneous catalysis

机译：固体中多量子核磁共振光谱法在偶极耦合自旋1/2系统中的自旋计数：单量子传播器的开发及其在多相催化中的应用

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The ideas behind the development and detection of multiple quantum coherence in ensembles of dipolar coupled spin 1/2 systems are developed. An rf pulse sequence for a single quantum propagator which creates multiple quantum coherence in steps of single quanta was developed and examined for use as a tool for spin counting in solids. Experimental details concerning the manipulations necessary to produce multiple quantum NMR spectra are presented. The multiple quantum (MQ) spin counting was applied to identify reaction intermediates in heterogeneous catalysis. Spin counting was shown to yield an upper limit of n = 6 for strongly bound, rigid intermediates C(sub m)H(sub n) in the reaction of ethylene over Ru/SiO(sub 2). The results eliminated the possibility of major components of such intermediates being polymer-like coke precursors. A precursor to 2-butene such as Ru-CH(sub 2)-CH(double bond)CH-CH(sub 2)-Ru was proposed as one possible intermediate which is in accord with the experimental observations. Another application of multiple quantum spin counting was performed in order to characterize the local structure of silica in supported Ru/SiO(sub 2) catalysts. Cab-O-Sil HS5 used as the support in silica supported ruthenium (Ru/SiO(sub 2)) catalysts was characterized via single and multiple quantum (MQ) (sup 1)H NMR spectroscopy. The samples were studied both in the presence and the absence of ruthenium. Single quantum spin counting of protons on a silica support with and without ruthenium metal indicated that the total number of hydroxyl groups decreased significantly with increasing reduction temperature over the range of 350--530 C. Two different components shown in static (sup 1)H NMR were found to reveal homogeneous and inhomogeneous broadening via spectral hole burning experiments. (sup 1)H MQ-NMR spin counting, based on the number of MQ coherences observed showed the existence of small clusters of proton spins on the silica surface.

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