不同加铝方式对SAPO-34分子筛合成及MTO催化性能的影响

在水热合成体系中,以三乙胺(TEA)和四乙基氢氧化铵(TEAOH)为混合模板剂,考察了在初始凝胶形成过程中铝源的加入方式对合成SAPO-34分子筛及甲醇制烯烃(MTO)催化性能的影响;通过X射线衍射(XRD)、扫描电子显微镜(SEM)、氮气等温吸附脱附(BET)、~(29)Si固体核磁(~(29)Si MAS NMR)、氨气程序升温脱附(NH_3-TPD)等方法对合成产物进行物性表征,并研究了其在甲醇转化制烯烃(MTO)反应中的催化性能。结果表明,随着首先加铝量的增加,粒径有逐渐变小的趋势,且逐渐出现板层状形貌的SAPO-34分子筛;同时,产物分子筛骨架中Si(4Al)配位结构的数量增加,强酸比例在逐渐增大,且酸密度增加;随着强酸比例和酸密度的提高,SAPO-34分子筛在MTO催化反应中的寿命逐渐延长,丙烯选择性逐渐增大而乙烯选择性逐渐减小。

Influence of the Manner of Adding Aluminum Source on the SAPO-34 Molecular Sieves Synthesis and the MTO Catalytic Properties

In hydrothermal synthesis system, with triethylamine(TEA) and tetraethyl ammonium hydroxide(TEAOH) as the mixed template agent, the influence of the manner of adding aluminum in the preparation of the initial gel on the SAPO-34 molecular sieves synthesis and the catalytic performances of methanol to olefins(MTO) reaction was investigated. The products were characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), Nitrogen isothermal adsorption stripping(BET), ²⁹Si MAS NMR and NH₃-TPD. The catalytic performances of methanol to olefins(MTO) were also investigated. The results showed that the particle size of SAPO-34 molecular sieve became smaller and the cubic morphology gradually turned into sheet-like, with the increased of the first addition amount of aluminum, and the proportion of Si(4Al) species in the as-synthesized SAPO-34 increased, the amount of strong acidity and the acid density also increased. The results also showed that the lifetime of SAPO-34 molecular sieve in MTO reaction is gradually extended, the ethylene selectivity decreases and the propylene selectivity increases with the increasing of the first addition amount of aluminum source.