弱酸性介质中Ga-ZSM-5型分子筛的合成与鉴定

Synthesis and Characterization of Ga-ZSM-5 Zeolite in a Slightly Acidic Medium

近年来,Ga-ZSM-5型分子筛的合成与催化性能已有报道,但对Ga是否位于ZSM-5型沸石晶格中这一重要问题则显得证据不足。由于以往的合成均在NaOH等碱性介质中进行,重复性和产品的结晶度不能令人满意。本文报道在弱酸性介质中,NH4F存在下,Ga-ZSM-5型分子筛的合成。这种新的合成途径,克服了在碱性介质中合成的缺点。用多种手段研究了Ga-ZSM-5型分子筛结构与性能的关系,为Ga对ZSM-5沸石骨架的同晶取代提供了充分的证据。

Ga-ZSM-5 zeolite was synthesized by hydrothermal crystallization at 150--200℃ from a mixture countaining NH_4F and tetrapropylammonium bromide as template at pH 5--7. NH_4-form precursors were obtained and converted to H-form Ga-ZSM-5 after calcination. Ga-ZSM-5 zeolite was characterized by means of XRD, SEM and electron microprobe analysis, IR, XPS and DTA, which showed that the gallium atoms were situated in the zeolite framework.