弱酸性介质中合成B-ZSM-5型分子筛

在弱酸性介质中,用四丙基溴化铵、氟化铵合成了B-ZSM-5型分子筛。由于晶化过程中无碱金属氢氧化物等强碱参与,B-ZSM-5型分子筛原粉为铵型,灼烧除掉NH₃及有机模板剂后,直接转化为氢型,吸附吡啶后IR谱中有B酸和L酸中心存在。扫描电镜分析表明,B-ZSM-5分子筛晶体生长完美,晶体形貌随硼含量不同呈规律性变化。X射线衍射、红外光谱、X射线光电子能谱、差热分析等结果表明,硼原子位于ZSM-5分子筛骨架中。

Synthesis of B-ZSM-5 Zeolites in Slightly Acidic Medium

B-ZSM-5 type molecular sieve was synthesized by hydrothermal crystallization at 150-200ccccccccccccc from mixture containing NH4F and tetrapropyl-ammonium bromide (TPABr) as template. pH values were 5-7. Because of the lack of alkaline metal hydroxide, NH4-form precursors were obtained and H-form B-ZSM-5 was directly yielded after calcination. After adsorption of pyridin the IR spectra showed the presence of both Lewis and Bronsted acid sites. SEM analysis indicated that the formation of large B-ZSM-5 crystals and its growth were pe'r-fect. Si substitution by B led to a decrease of crystal size and of the length/width ratio. XRD, IR, XPS, DTA studies on B-ZSM-5 proved that boron atom did situate in ZSM-5 framework.