论文部分内容阅读
采用自生压力的水热合成方法,以HMDA为模板剂,在160℃下,合成了4种杂原子ZSM-48型分子筛:B-ZSM-48,Ge-ZSM-48,Cr-ZSM-48和V-ZSM-48。实验结果表明,该类分子筛晶化条件变化范围较小,易和ZSM-5分子筛相伴生。晶化过程中,相对于晶体生长来说,成核是一个慢过程。在最佳合成的条件下,晶化速度的顺序为:B-ZSM-48>Ge-ZSM-48>Si-ZSM-48>V-ZSM-48>Cr-ZSM-48。杂原子对硅产生同晶取代并以畸变四面体配位方式占据分子筛骨架位置,使分子筛的孔道及骨架性质发生明显变化。尤其是非Ⅳ价态杂原子B和Cr,使分子筛骨架电性改变,从而导致孔道吸附性能、骨架酸性和对模板剂的束缚能力发生显著变化。
Four kinds of heteroatom ZSM-48 molecular sieves were synthesized by hydrothermal method with self-generated pressure and HMDA as template at 160 ℃: B-ZSM-48, Ge-ZSM-48, Cr-ZSM-48 and V-ZSM-48. The experimental results show that the crystallization range of this kind of molecular sieve has a small variation range and is easy to be associated with the ZSM-5 molecular sieve. In the crystallization process, nucleation is a slow process relative to crystal growth. Under the optimized conditions, the order of crystallization speed is: B-ZSM-48> Ge-ZSM-48> Si-ZSM-48> V-ZSM-48> Cr-ZSM-48. Heteroatoms produced isomorphous substitution of silicon and dominated molecular sieve framework with distorted tetrahedral coordination, which changed the pore and skeleton properties of molecular sieve significantly. In particular, the heteroatoms B and Cr, which are not IV valences, change the molecular structure of the molecular sieve, leading to significant changes in pore adsorption, backbone acidity and binding ability of the template.