NMR探针分子表征分子筛酸性的理论研究

用量子化学计算的方法，采用三甲基氧膦（TMPO）、吡啶和三甲基膦（TMP）3种探针分子，研究了工业上常用的3种分子筛H-Y、H-ZSM5、H-MOR的Bronsted酸强度，讨论了这3种探针分子化学位移与Bronsted相对酸强度的相关性，揭示了各种探针分子在表征Bronsted酸性上的适用性.

Characterization of Acidity of Zeolites by NMR Probe Molecules:A Theoretical Investigation

In this contribution, trimethylphosphine oxide (TMPO), pyridine and trimethylphosphine (TMP) were selected as NMR probe molecules to study the acid strength of several industrially used zeolites (H-Y, H-ZSM5 and H-MOR) theoretically. The relationship between chemical shifts of these probe molecules and acid strength of zeolites was revealed. In the meanwhile, the applicability of probe molecules on the characterization of Bronsted acidity was discussed. Since the ¹H, ¹⁵N and ³¹P chemical shift ranges of adsorbed D5-pyridine and TMP on the Bronsted acid sites in zeolites were relatively very smaller (i.e., δ 18.2 ~ 18.7, δ -191.0~-186.9, δ -8.7~-3.5 for ¹H, ¹⁵N and ³¹P, respectively), they were only used to detect the existence of acidic protons in the zeolites. However, the ³¹P chemical shift range of adsorbed TMPO ranges from δ 62.8 to δ 90.5, and it may be expected that the adsorbed TMPO were very sensitive to measure solid acid strengths of the zeolites catalysts, compared with the ³¹P NMR of adsorbed TMPO.