纳米NaY分子筛的合成

Synthesis of nanoparticle NaY molecular sieve

在合成NaY分子筛时,向合成体系中添加少量的吐温系列表面活性剂(吐温20,吐温40,吐温60)可以显著地降低分子筛的晶粒尺寸。这是由于吐温系列表面活性剂在体系的强碱作用下发生皂化反应,生成聚氧乙烯山梨酸糖醇酐和酸钠皂,有利于降低NaY分子筛的表面能。但棕榈酸钠和硬脂酸钠在高含量Al3+的合成体系中,会形成不溶于水的棕榈酸铝和硬脂酸铝,因此,吐温40和吐温60在合成纳米分子筛中的作用不如吐温20。在添加吐温20合成纳米分子筛时,较适宜的合成条件为:晶化温度90℃,晶化时间17h,吐温20的添加量n(吐温20)/n(Al2O3)=0 2%。产品的粒度约75nm,产率≥92%,硅铝比为3 46。

The size of NaY crystal particles could be reduced by adding a small amount of Tween surfactants (Tween-20, Tween-40, Tween-60) into the system during synthesis of nanoparticle NaY. This is probably because that Tween surfactants is saponified due to high pH of the synthetic system to form polyoxyethylene sorbitancarboxylic anhydride and hard soap. It was found that Tween 20 is superior to either Tween-40 or Tween-60 as a surfactant against aggregation of little particles. When a little amount of Tween-20 was added (n(Tween-20)/n(Al_2O_3)=0.2%) at appropriate crystallization temperature (90 ℃) and crystallization time (17 h), the diameter of NaY crystal decreased from (220 nm) to about 75 nm, with yield of over 92% and SiO_2/Al_2O_3 of 3.46.