Fabrication of hierarchical ZnSAPO-34 by alkali treatment with improved catalytic performance in the methanol-to-olefin reaction

A series of hierarchical ZnSAPO-34 zeolites were synthesized by treatment with different concentrations of tetraethylammonium hydroxide (TEAOH) solutions. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), temperature-programmed desorption, Fourier transform infrared, and N2 adsorption and desorption techniques and studied as catalysts for the methanol to olefin reaction. The characterization results reveal that the crystal size of ZnSAPO-34 is greatly reduced compared with the parent SAPO-34 owing to the incorporation of Zn. Hierarchical pores with the sizes up to the macropore level in the ZnSAPO-34 zeolites are created with the post-treatment of TEAOH. The acid strength and the amounts of the strong acid of the hierarchical ZnSAPO-34 zeolites decrease after the post-treatment because TEAOH preferentially extracts Si species from the zeolite. The hierarchical ZnSAPO-34 zeolites exhibit superior catalytic performance than that of the parent ZnSAPO-34, owing to the shortened transportation distance and the appropriate acidity of the treated samples.