Searching for Microporous, Strongly Basic Catalysts: Experimental and Calculated 29Si NMR Spectra of Heavily Nitrogen-Doped Y Zeolites

被引:48
作者
Dogan, Fulya [1 ]
Hammond, Karl D. [2 ]
Tompsett, Geoffrey A. [2 ]
Huo, Hua [1 ]
Conner, W. Curtis, Jr. [2 ]
Auerbach, Scott M. [2 ,3 ]
Grey, Clare P. [1 ]
机构
[1] SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA
[2] Univ Massachusetts, Dept Chem Engn, Amherst, MA 01003 USA
[3] Univ Massachusetts, Dept Chem, Amherst, MA 01003 USA
关键词
AMINE-SUBSTITUTED ZEOLITES; GAUSSIAN-BASIS SETS; CORRELATED MOLECULAR CALCULATIONS; MESOPOROUS SILICON OXYNITRIDES; CHEMICAL-SHIFTS; WAVE-FUNCTIONS; ALKYLAMMONIUM FORMATION; DENSITY; NITRIDATION; ATOMS;
D O I
10.1021/ja9031133
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Nitrogen substituted zeolites with high crystallinity and microporosity are obtained by nitrogen substitution for oxygen in zeolite Y. The substitution reaction is performed under ammonia flow by varying the temperature and reaction time. We examine the effect of aluminum content and charge-compensating cation (H+/Na+/NH4+) on the degree of nitrogen substitution and on the preference for substitution of Si-O-Al vs Si-O-Si linkages in the FAU zeolite structure. Silicon-29 magic angle spinning (MAS) nuclear magnetic resonance (NMR) and H-1/Si-29 cross-polarization MAS NMR spectroscopy have been used to probe the different local environments of the nitrogen-substituted zeolites. Experimental data are compared to simulated NMR spectra obtained by constructing a compendium (>100) of zeolite clusters with and without nitrogen, and by performing quantum calculations of chemical shifts for the NMR-active nuclei in each cluster. The simulated NMR spectra, which assume peak intensities predicted by statistical analysis, agree remarkably well with the experimental data. The results show that high levels of nitrogen substitution can be achieved while maintaining porosity, particularly for NaY and low-aluminum HY materials, without significant loss in crystallinity. Experiments performed at lower temperatures (750-800 degrees C) show a preference for substitution at Si-OH-Al sites. No preference is seen for reactions performed at higher temperatures and longer reaction times (e.g., 850 degrees C and 48 h).
引用
收藏
页码:11062 / 11079
页数:18
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