超微NaY分子筛的合成(Ⅰ)──添加轻稀土离子的影响

Synthesis of Ultrafine Zeolite NaY(Ⅰ) Effect of Light Rare Earth Ions Additive

导向剂的陈化时间和反应胶的晶化温度可以影响 Na Y分子筛的晶化行为 .随导向剂陈化时间的增加 ,Na Y分子筛的晶化速度加快 ,晶粒尺寸减小 ;随晶化温度的升高 ,Na Y分子筛的晶化速度加快 ,但晶粒尺寸增加 .而向合成体系中添加轻稀土离子 (L n3+)对 Na Y分子筛的晶化行为影响更为明显 .与未添加稀土离子时相比较 ,在一定的稀土离子添加量范围内 [n(L n3+) / n(Al3+) <0 .2 ],Na Y分子筛的晶化速度明显加快而晶粒尺寸显著减小 ,同时所合成出的 Na Y分子筛的 n(Si O2 ) / n(Al2 O3)比也有较大的提高 .添加稀土离子使合成体系中形成异晶晶种的 L n(OH) 3微晶 ,从而进一步引发 Na Y分子筛的成核 .

Ultrafine zeolite NaY was hydrothermally crystallized with silica sol and Al_2(SO_4)_2 as source materials via optimizing synthesis conditions and adding light rare earth ions(Ln 3+) to the synthesis batch. The crystallization performance of NaY could be affected by the aging time of nucleation Si-Al gel and the crystallization temperature of reaction Si-Al gel. With increasing the aging time(2—7 d) of nucleation gel, the crystallization rate of zeolite NaY increased whereas the average crystal size of zeolite NaY decreased. When elevating the crystallization temperature(363—383 K) of reaction gel, both the crystallization rate and the average crystal size of zeolite NaY increased. Nevertheless, the crystallization performance of zeolite NaY was more remarkably affected by the addition of Ln 3+ ions in the synthesis batch. The crystallization rate and the n(SiO_2)/n(Al_2O_3) ratio obviously increased while the average crystal size greatly reduced when zeolite NaY was crystallized in the presence of Ln 3+ ions, comparing with that in the absence of Ln 3+ ions. It was found that, with the amount of the added Ln 3+ ions increasing, the average crystal size of zeolite NaY decreased followed by increasing, while the crystallization rate and the SiO_2/Al_2O_3 ratio in framework changed in the opposite direction. The optimal amount of Ln 3+ additive appears to be in the range of n(Ln 3+)∶n(Al 3+)=0.05∶1—0.1∶1 in mole. In the case, the as-synthesized NaY zeolites had the smallest average crystal sizes(<100 nm), the highest n(SiO_2)/n(Al_2O_3) ratio(>5.7) and the shortest crystallization time(<36 h). The role of the added Ln 3+ ions was proposed to be that there formed the micro-crystalline Ln(OH)_3 under the synthesis conditions, which may present additional area to initiate the nucleation of zeolite NaY.