ZSM-5分子筛物化性能的差异对其催化性能的影响

Correlation between the physicochemical and catalytic properties of ZSM-5 zeolites

通过调变RNH2/Si O2摩尔比值合成出硅铝比相近而晶粒大小不同的ZSM-5分子筛。用XRD、SEM分析样品的相对结晶度和形貌;用STPD法测量其表面酸性。表征的结果发现:在相同的合成条件下,ZSM-5分子筛的物化性能随着初始凝胶中RNH2/Si O2比值的变化而发生显著变化。以甲醇为模型化合物,考察其物化性能的差异对催化性能的影响。研究结果发现小晶粒的ZSM-5分子筛对C5+和芳香烃的选择性高,催化活性好,而大晶粒的ZSM-5分子筛对对二甲苯的选择性高。研究的结果显示由ZSM-5分子筛的物化性能可以预测其催化性能。

ZSM-5 zeolites with different physicochemical and catalytic properties were synthesized with different RNH2/Si O2 ratios. The samples were characterized by XRD and SEM.The acidity was measured by stepwise temperature-programmed desorption（STPD）of ammonia. It was found that the physicochemical and catalytic properties of ZSM-5 significantly changed with various RNH2/Si O2 ratios. Methanol conversion reaction was carried out over the two samples to evaluate the correlation between the physicochemical and catalytic properties of H-ZSM-5 zeolites. In contrast to large crystallites, the aggregated H-ZSM-5 consisting of small crystallites showed high selectivities for C5＋, aromatics and catalytic activity.However, the aggregated H-ZSM-5 consisting of large crystallites showed high selectivities for p-xylene. These results indicate that the physicochemical properties of H-ZSM-5 significantly affects the catalytic activity in MTG reaction and the catalytic properties could be somewhat predicted from these physicochemical properties.