用固体核磁共振研究HZSM-35分子筛的酸性

Acidity Characterization of HZSM-35 Zeolite by Solid-State NMR

分别采用氘代吡啶和三甲基膦为探针分子,利用高分辨固体核磁共振技术研究了HZSM-35分子筛与探针分子之间的相互作用以及分子筛的酸性.结果表明,探针分子氘代吡啶能够进入分子筛的十元环孔道和八元环孔道,但需在300℃下长时间吸附才能扩散到八元环开口的孔穴中.吸附氘代吡啶后的1H MAS NMR谱和吸附三甲基膦后的31P MAS NMR谱表明,这两种孔道中均具有两种酸强度不同的B酸位,并且B酸的数量多于L酸的数量.

The accessibility and acidity of HZSM-35 zeolite were studied by high-resolution solid-state MAS NMR spectroscopy after adsorption of deuterated pyridine or trimethylphosphine as probe molecules. The results showed that the probe molecules could enter both the ten-membered ring （10-MR） channels and eight-membered ring （8-MR） cavities. However, the diffusion into the 8-MR cavities was very slow and it took a long time to reach the adsorption equilibrium at 300℃. After adsorption of deuterated pyridine, ^1H MAS NMR spectra showed that there were two types of Br6nsted acidic sites with different strength in both the 10-MR channels and 8-MR cavities, After adsorption of trimethylphosphine, the ^31p MAS NMR spectra indicated that there were Lewis acidic sites in HZSM-35 zeolite, but their strength and amount were less than the Bronsted acidic sites.