ZSM-5型分子筛的表面酸性与催化活性

合成了一批不同硅铝比的HZSM－5沸石分子筛，并用CO62 ,Fe^3 离子对其进行改性，测定了它们在醛氨缩合反应合成吡啶中的活性和选择性。对照它们的NH3－TPD，吡啶吸附红外光谱，研究了催化剂的表面酸性与醛氨缩合催化活性的关系。研究表明，硅铝比较小时，HZSM－5的酸中心较多，但过多的酸中心会引发其它的裂解反应和缩合反应，从而降低催化剂的活性和选择性；当硅铝比为120左右时，催化活性达到最大，吡啶碱产率达60％；若继续增大硅铝比，则无足够的酸中心进行反应，用Co^2 ,Fe^3 离子对HZSM进行改性，其B酸中心变化不明显，L酸中心减少，对氨气的吸附能力有所下降，从而保证了适当的酸中心暴露，有利于反应，采用CoZSM-5催化剂，吡啶碱产率可达78％。

Surface Acidity and the Catalytic Activity of ZSM-5 Zeolite

The surface acidity of various modified ZSM\|5 zeolites with different SiO\-2/Al\-2O\-3 ratios has been determined quantitatively by TPD and IR technique. The catalytic activity in condensation reaction of aldehydes and ammonia has been correlated with the acidity of the zeolite catalysts. It is found that excessive acid sites can lead to by\|reactions and reduce the activity and selectivity of the catalyst when the ratios of SiO\-2/Al\-2O\-3 is low. The catalytic activity achieves the top and the yield of pyridine base is 60% when the ratio is about 120. CoZSM\|5 and FeZSM\|5 have less Lewis acid sites than HZSM\|5. The reducing of Lewis acid sites will decrease the ability of NH\-3 adsorption. This phenomenon insure that the exploring of adequate acid sites is favorable to reacting with aldehydes. Using CoZSM\|5 catalyst, the yields of pyridine base can come up to 78%.