Modification and catalyst performance of ZSM-5 zeolite by treatment with TPAOH/NaOH mixed alkali

The composites with mesoporous and microporous structure were obtained by treatment of ZSM-5 zeolite in mixed alkali aqueous solution of tetrapropylammonium hydroxide and inorganic base NaOH. The products were characterized by XRD, N₂-adsorption/desorption, NH₃-TPD, SEM and so on. The results showed that the alkaline solution would cause the zeolite desilication and dealumination and either decreasing the TPA⁺/OH^- ratio or prolonging the alkali treatment time will cause reduction of micropore structure and increasement of mesopore amount increasingly while keeping the concentration of OH^- at a fixed value. And meanwhile, the treatment also changed the acidity of zeolite. Mixed alkali treatment with proper TPA⁺/OH^- ratio could preserve micropore structure to the maximum extent while formed the mesopore, reduce zeolite’s strong acid quantity and increase the selectivity of propylene when performanced on methanol-to-olefins (MTO) reaction. Compared with the inorganic base NaOH, the modification rate of zeolite by TPAOH was slower, milder and more controllable that could act as pore-growth moderator.