沸石分子筛上程序升温脱附谱的Monte　Carlo模拟研究　Ⅰ．模型的建立

MONTE CARLO SIMULATION OF TEMPERATURE-PROGRAMMED DESORPTION SEPCTRA OF ADSORBATES FROM ZEOLITES Ⅰ.Model

沸石分子筛因其特殊的孔道结构而致使其ＴＰＤ谱图的分析比其它催化剂更为困难，目前尚无一种切实可行的理论分析方法。本文发展了一种较为简单的模拟分子筛上ＴＰＤ谱图的ＭｏｎｔｅＣａｒｌｏ方法，模拟结果表明，在同一组脱附动力学参数下，沸石分子筛上的峰形和峰位置与其它催化剂都有明显的差异，并且峰温的差别与脱附活化能和指前因子有关。同时表明，对于普通催化剂可以根据峰最大时的覆盖度θ＿Ｍ来判断脱附级数，而对于沸石分子筛，θ＿Ｍ却随Ｅ＿ｄ线性变化。

he most important difference between zeolites and other catalysts appears to be the absence of free gas phase in the zeolite cavities.The gas phase terminates at the external surface of zeolite crystallites which contain the sorbed phase inside the channel,i.e. ,the adsorption and desorption of molecules take place at the external surface only.Taking into account of this characteristics of zeoltes,a Monte Carlo model for the simulation of temperature-programmed desorption(TPD) spectra from zeolites was developed,and the TPD spectra for different values of the activation energy and the pre-exponential factor for desorption were simulated.A comparison between the TPD spectra from zeolites and those from a flat surface was made. The result,showed that the peak-maximum temperature,T_M,for zeolites is higher than that for a flat surface for the same desorption kinetic parameters,and the shift of T_M,to higher temperature for zeolites is related to both the activation energy and the pre-exponential factor for desorption.