FTIR-TPD常压法研究沸石分子筛的表面酸性

采用高纯氮保护,用付立叶变换红外光谱-程序升温脱附(FTIR-TPD)代替传统的高真空法进行沸石分子筛表面酸性研究。其结果与传统的高真空法的文献值相符。吸附吡啶后的红外光谱证明在5A分子筛上同时存在B酸和L酸中心,而NaY型分子筛存在第三类酸中心。应用常压法进行FTIR-TPD研究时,应消除水对基线漂移的干扰,才能正确确定饱和吸附量时的吸光度值。

The Surface Acidity of Zeolite Molecular Sieve Investigated by FTIR-TPD Method Under Normal Pressure

The surface acidity of the zeolite molecular sieve was investigated under an atmosphere of highly purified nitrogen by the Fourier Transform Infrared Temperature Programmed Desorption (FTIR-TPD)method instead of the traditional method under high vacuum. The data obtained by this work are very consistent with those by the traditional method as reported in the literature. The experimental resuits show that after the 5A molecular sieve has adsorbed pyridine, the absorption bands at 1540 cm~(-1) and 1445 em~(-1)respectively demonstrate the existence of both Bronsted acid site and Lewis acid site, and the hydroxy group corresponding to the absorption band at 3640 cm~(-1) is the Br(?)nsted acid site which is able to supply a proton. It is also shown that after NaY molecular sieve has adsorbed pyridine, the absorption bands at 1442 cm~(-1) and 1592 cm~(-1)demonstrate the existence of the 3rd type acid site.In comparison with the high vacuum method, the present method is simple to perform and can provide much more data on surface characteristics. However, in order to determine the correct value of absorbanee under saturated adsorption, the influence of the base line departure, which might be caused by a trace of water existing in the N_2 gas, adsorbent and adsorbate, should be carefully eliminated.