分子筛催化剂结晶度和硅铝比的X射线分析

用Ｘ射线衍射法测定分子筛催化剂的硅铝比（ＳｉＯ２／Ａｌ２Ｏ３）是通过准确测定分子筛晶体的点阵常数来完成的。分子筛晶格骨架中，硅氧四面体（ＳｉＯ４）中ＳｉＯ键长小于铝氧四面体（ＡｌＯ４）中ＡｌＯ的键长，分子筛晶体的组成不同，其晶胞的点阵常数将随之变化。点阵常数与硅铝比的变化关系可用经验公式表达。测定分子筛晶体的点阵常数采用内标法，该法比化学分析法要简便、快捷。由于分子筛催化剂的不稳定性，用Ｘ射线衍射法测定结晶度和硅铝比，必须对分析样品进行稳定性处理。为了保证测量精度，应严格控制测试条件，以减少各种因素的影响。用积分计数法测量结晶度，其结果优于峰高法和半高宽法。ＣＲＣ１分子筛催化剂随老化处理温度的升高和时间的增长而降低，分子筛的点阵常数则随之减小，硅铝比则随之增大。在老化温度为７５０℃以下进行处理时，结晶度和硅铝比的变化不太明显。

DETERMINATION OF CRYSTALLINITY AND SiO_2/Al_2O_3 VALUE OF MOLECULAR SIEVES BY X RAY DIFFRACTION METHOD

The measurement of crystallinity and SiO_2/Al_2O _3 value of molecular sieves by using X ray powder diffraction method depends on the determination of lattice constant of crystallite of molecular sieves.The lattice constant changed with the crystalline structure of molecular seive.The measuring temperature and the relative humidity have great effects on measured results of lattice constant. So the measuring temperature should be strictly controlled in measuring SiO_2/Al_2O_3 value.The experimental result showed that the integrated intensity mode is better than the peak height intensity mode and peak height peak width intensity mode in measuring crystallinity.The relationship between lattice constant with SiO_2/Al_2O_3 can be expressed by an experimental formula. The crystallinity and SiO_2/Al_2O_3 value for CRC 1 molecular sieve catalysts changed at different ageing conditions.