ZSM-5分子筛酸性和晶体大小对醛氨缩合合成吡啶碱的影响

The Influence of Acidity and Crystal Size of ZSM-5 Catalyst on the Pyridine Bases Synthesis from the Chichibabin Condensation

针对Chichibabin醛氨缩合合成吡啶碱,用离子交换法制备具有相同酸性位类型,但Br?nsted(B)酸量不同的ZSM-5催化剂,并选择硅铝比接近但晶粒大小不同的H-ZSM-5分子筛,以及与ZSM-5具有相同MFI晶体结构的TS-1分子筛进行催化性能的比较。探讨了ZSM-5分子筛催化剂酸性、酸量和晶粒大小对反应活性、吡啶碱选择性和收率以及催化剂稳定性的影响。结果表明B酸位是进行醛氨缩合反应合成吡啶碱不可缺少的活性位,但酸强度较弱的末端硅羟基B酸位合成吡啶碱的活性较低;催化剂B酸含量越大,其进行醛氨缩合反应的初始活性和吡啶碱收率越高,催化剂失活越慢;小晶粒分子筛的初始活性、稳定性优于大晶粒分子筛,但合成吡啶碱的选择性和初始收率较低,这主要是因为与大晶粒分子筛相比,小晶粒分子筛具有更多的活性中心,特别是外表面活性中心,和相对较短的分子筛孔道。

For the pyridine bases synthesis with Chichibabin condensation, the ZSM-5 catalysts with the same type of acid site but different amounts of BrΦnsted （B） acid site were prepared by an ion-exchange method. The hydrogen type H-ZSM-5 catalysts with similar Si/Al ratio but different crystal sizes and TS-1, which has same MFI structure as ZSM-5, were selected for the comparison of the catalysis performance. The influences of type, amount of acid site and crystal size on the activity, pyridine bases selectivity and stability of the catalyst were investigated. The catalytic performances of these catalysts show that the B acid site is indispensable for the pyridine bases synthesis with Chichibabin condensation, while the activity of the terminal silanol hydroxyl groups, which is the B acid site with weak acid strength, has the lower activity for pyridine bases synthesis. The more amount of the B acid site in the catalyst, the higher initial activity and pyridine bases selectivity and the more stable of the catalyst for Chichibabin condensation. The catalyst with smaller crystal size is more stable and has larger aldehyde conversion than the larger one, but the selectivity and initial yield of pyridine bases of smaller crystal catalyst are lower than those of larger one, this is because that compared with larger crystal size catalyst, the catalyst with smaller crystal has larger amount of acid site, especial the acid site on the external surface, and shorter pore channels.