TS-1分子筛酸性的固体核磁表征

Titanium molecular sieve TS\|1 is a very useful oxidation catalyst, which is environmentally benign. Many discussions on whether TS\|1 has acid sites have arisen just because it is a zeolite of the penstail family where a fraction of the Si IV ions are replaced by Ti Ⅳ ions to form a metallosilicate with no charge on the framework. In this paper, we report the characterization of acidity in TS\|1 zeolite using probe molecules and solid\|state MAS NMR technique. Trimethylphosphine is a sensitive probe molecule which can distinguish Brnsted and Lewis acid sites. The peak at -4.5 in \{\}\+\{31\}P MAS NMR spectra is attributed to Brnsted acid sites, while the peak at -62.2 is related to the physisorbed phosphine, and the peak at \{-33.7\} is assigned to Lewis acid sites by using trimethylphosphine as the probe molecule. An additional shoulder next to the peak at 33.7 convinces the existence of at least two different Lewis acidic species in TS\|1 zeolite. As evidenced by \{\}\+1H MAS NMR technique, there are few acid sites in TS\|1 zeolite. The results of \{\}\+1H MAS NMR spectra obtained using perfluorotributyl amine as a probe molecule demonstrate that most of the acid sites are located on the internal surface of the zeolite.