Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA.
Langmuir. 2010 Jan 19;26(2):1260-70. doi: 10.1021/la902445c.
We report the mechanism of zeolite beta nucleation and growth at 120 degrees C in Al-containing solutions. Two solutions with molar compositions 1 SiO(2)/80 H(2)O/0.25 TEA(2)O/4 CH(3)CH(2)OH/(0.05 + Y) Na(2)O/Y Al(2)O(3), where Y is 0 and 0.01, were studied using attenuated total reflectance-Fourier transform spectroscopy, small angle scattering, and cryogenic-transmission electron microscopy. First, at room temperature, supersaturated silica self-assembles into primary particles (<3 nm). Upon heating the primary particles, the least stable ones aggregate into secondary particles. Some of the secondary particles are stable as spheroidal monomer particles, but others are unstable and aggregate into small clusters. After 4 days of heating, secondary particles are mostly composed of amorphous silica, but their density is similar to that of zeolite beta. All-silica secondary particles are stable in solution for extended periods of time (>100 days), and no all-silica zeolite beta product was obtained. On the other hand, after 6 days of heating solutions containing Al, we observe that Al-containing secondary particles aggregate into tertiary particles that have the structure of zeolite beta. We conclude that as silica reorganizes from amorphous into zeolite beta, Al-containing secondary particles become less stable (in the colloidal sense) and aggregate with tertiary particles.
我们报道了在含铝溶液中沸石β在 120°C 下成核和生长的机制。两种溶液的摩尔组成分别为 1SiO(2)/80H(2)O/0.25TEA(2)O/4CH(3)CH(2)OH/(0.05 + Y)Na(2)O/YAl(2)O(3)，其中 Y 为 0 和 0.01，使用衰减全反射傅里叶变换光谱、小角散射和低温传输电子显微镜进行了研究。首先，在室温下，过饱和的硅酸钠自组装成初级粒子（<3nm）。加热初级粒子时，最不稳定的初级粒子聚集成次级粒子。一些次级粒子以球形单体粒子稳定存在，但其他次级粒子不稳定，聚集成小簇。加热 4 天后，次级粒子主要由无定形硅组成，但它们的密度与沸石β相似。全硅次级粒子在溶液中稳定存在很长时间（>100 天），但没有得到全硅沸石β产物。另一方面，在含有 Al 的溶液加热 6 天后，我们观察到含 Al 的次级粒子聚集成具有沸石β结构的三级粒子。我们得出结论，随着硅酸钠从无定形重组为沸石β，含 Al 的次级粒子变得不太稳定（胶体意义上），并与三级粒子聚集。
