碱液后处理对纳米ZSM-5沸石孔道和酸度的影响

Effect of Alkaline Treatment on Pore and Acidity of Nano-ZSM-5 Zeolite

采用XRD、N2物理吸附、NH3-TPD以及TEM、IR和NMR手段,系统研究了NaOH碱液后处理对低硅铝比纳米ZSM-5沸石(Si/Al摩尔比为14.5、晶粒度为20～50 nm)孔道和酸度的影响.结果表明,在碱液中,低硅铝比纳米ZSM-5沸石主要发生限域脱硅,而且低硅铝比纳米ZSM-5沸石的碱液脱硅难度大于高硅铝比沸石.但在适当的碱液处理条件下(碱硅比为0.19～0.35,温度为60～80℃,处理时间为2～5 h)可以在其晶体内产生大量介孔,增加比表面积和孔容;同时增加弱酸和中强酸的浓度,并提高L酸比例.L酸的大量增加主要是由于产生了裸露的骨架铝(≡Alδ+),这与文献的观点有所不同.

Effect of alkaline treatment on pore and acidity of nano-sized ZSM-5 zeolite （ particle size = 20 - 50 nm, Si/A1 = 14.5 ） was investigated by XRD, N2-adsorption, NH3-TPD, TEM, IR and NMR methods. The results show that under alkaline environment, nano-ZSM-5 with low Si/A1 ratio mainly has restricted disilieation. And it is more difficult for ZSM-5 zeolite with low Si/A1 ratio to desilicate than that with high Si/A1 ratio. However, Under appropriate alkaline treatment conditions （[ OH]/[ SiO2 ] = 0.19-0.35, T = 60- 80 ℃, t = 2-5 h）, abun- dant mesopores can be created, which results in the surface areas and pore volume increased; at the same time, the concentration of weak and middle strong acid was increased, especially the proportion of Lewis acid sites. Different from the opinion in literature, we think that the increased Lewis acid sites were mainly caused by the naked frame- work aluminium （ =A1＋） , which were generated by alkaline treatment.