多级SAPO-34的合成及其在甲醇制烯烃反应中的催化性能

Hierarchical SAPO-34:Synthesis and Catalytic Performances in Methanol to Olefins

针对SAPO-34在甲醇制烯烃(MTO)催化过程中易于失活的问题,采用水热法合成了具有不同粒径及多级孔SAPO-34。详细研究了铝源、硅源对SAPO-34分子筛晶粒尺度的调控性能及二次模板剂对多级孔SAPO-34合成的影响。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外(FT-IR)、N2吸附-脱附,透射电子显微镜(TEM)以及NH3-TPD等手段对合成的材料进行了表征。结果表明采用不同铝源可以实现对SAPO-34粒径的有效调控,二次模板剂的引入可以在纳米SAPO-34晶粒内部创造出孔壁晶化的晶内介孔结构。在甲醇制烯烃的催化反应过程中,大颗粒SAPO-34具有较高的低碳烯烃的选择性,多级SAPO-34因为纳米化或介孔的引入使得微孔孔道有效缩短,提高了其在MTO催化反应过程中的稳定性,但是对低碳烯烃的选择性受到抑制,而对油品的选择性则因为外表面积的增大而显著增加。

SAPO-34 is prone to losing its activity during methanol to olefins （MTO）. Hierarchical SAPO-34 with different particles size was synthesized in a hydrothermal procedure. The factors controlling the size of SAPO-34 zeolite such as aluminum species and silicon species, and the effect of secondary template on the synthesis of hierarchical SAPO-34 were investigated in details. The as-synthesized samples were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared （FT-IR） spectroscopy, N2 adsorption-desorption, transmission electron microscopy （TEM）, and NH3-TPD techniques. The results displayed that the different silicon species can tailor the crystalline size effectively, Secondary template can give the as-synthesized SAPO-34 a mesopore structure with crystalline walls, which contributes to enhancing the thermostability, especially the hydrothermal stability during the MTO process. The catalytic performance of the as-synthesized SAPO-34 was investigated during the MTO, as compared with the referenced SAPO-34-R, hierarchical SAPO-34 displayed an excellent catalytic performance during the MTO by giving a prolonged catalytic life and an elevated selectivity for oil while a depressed olefins selectivity because of the shortened microporous channel length caused by the nanocrystallization or the introduced mesopore system.