A top-down approach to hierarchical SAPO-34 zeolites with improved selectivity of olefin

Abstract

A facile and effective fluoride post-treated route has been systematically applied for the preparation of hierarchical zeolite catalysts in three different SAPO-34 systems using morpholine, triethylamine and tetraethylammonium hydroxide as template, respectively. Secondary pores in SAPO-34 zeolite crystals are formed by etching with HF-NH4F containing solutions under ultrasonic condition. The samples were characterized by XRD, SEM, N2 adsorption-desorption, XRF, TG, 29Si MAS NMR and NH3-TPD techniques. The set of experimental data demonstrate that the organic templates impact the etching process by fluoride route, most probably the distribution of active sites, thus influence the catalytic properties. It is worth underline that the selectivity to C2H4 and C3H6 over the obtained hierarchical SAPO-34 catalysts in the methanol-to-olefin (MTO) reaction is improved as compared to the parent SAPO-34 catalysts, while an undesired diminished catalyst lifetime is observed for hierarchical SAPO-34 templated by morpholine and tetraethylammonium hydroxide.