Hierarchical Mg/ZSM-5 catalysts for methanol-to-propylene reaction via one-step acid treatment

Abstract

One-step acid treatment for template- and solvent-free synthesized NaZSM-5 was developed to obtain hierarchical HZSM-5. Hierarchical Mg/ZSM-5 was obtained by the incipient impregnation method, which further increased the propylene yield of the methanol-to-propylene (MTP) reaction. The physicochemical properties of the samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), N2 adsorption–desorption, pyridine adsorption-IR (Py-IR) and NH3 temperature-programmed desorption (NH3-TPD). The results indicated that one-step acid treatment (250 °C, 12 h) could increase the SiO2/Al2O3 molar ratio from 29.43 to 53.33 and maintain the well-distributed state of acid sites. The blocked pore structure was opened to introduce additional mesoporosity. Additionally, NaZSM-5 was synchronously converted to HZSM-5, thereby avoiding ion-exchange procedures. Synchronization of dealumination, desodiation and introduction of the mesoporous structure was achieved in one step, providing a good matrix for further impregnation with Mg species. The obtained hierarchical Mg/ZSM-5 (0.3 M–MgO) showed low diffusion hindrance and reduction in external surface acid sites (especially Bronsted acid sites), affording high propylene selectivity (53.34%) and good resistance to carbon deposition (~ 0.77%) in the MTP reaction.