In Situ Growth-etching Synthesis And Catalytic Performance Of Hierarchical SAPO-34 Zeolite

SAPO-34 zeolites are widely applied due to unique structure,moderate acidity and high hydrothermal stability.SAPO-34 zeolites are widely used in methanol-to-olefin（MTO）and selective catalytic reduction technology（SCR）.However,microporous SAPO-34 has the problem of rapid deactivation in MTO reaction.Synthesis methods have important effects on the structure and reactivity of Cu-SAPO-34 in SCR technology.Therefore,it is extremely important to develop a low-cost and facile synthesis method for hierarchical SAPO-34 and Cu-SAPO-34.Based on above background,the synthesis of hierarchical SAPO-34 and Cu-SAPO-34 was mainly studied in the following aspects:1.The hierarchical SAPO-34 zeolites were successfully synthesized via one-step hydrothermal synthesis approach with the assistance of excess triethylamine.The effects of TEA concentration in the synthesis system and crystallization time on the crystallinity,crystal morphology,structure,acidity and growth process of SAPO-34were investigated.The physicochemical properties of SAPO-34 with different TEA contents were characterized by XRD,SEM,FT-IR,N₂ adsorption/desorption,XRF,²⁹Si MAS NMR and NH₃-TPD,and the evolution of crystal morphologies was monitored by SEM.It was worth emphasizing that the catalytic lifetime and the selectivity of C₂H₄ plus C₃H₆in the methanol-to-olefin（MTO）reaction over the hierarchical SAPO-34 were about two-times as high as and improved more than 5%compared to that of the conventional counterpart,respectively.2.The microporous SAPO-34 zeolites were etched with a certain concentration of Na₂CO₃ solution and different mass percentages of Na₂CO₃ powder by alkaline solution treatment and solvent-free route,respectively.The effects of mass ratio,treatment temperature and treatment time on SAPO-34 were investigated.When the mass percentage of Na₂CO₃,treatment temperature and treatment time were 5%,100°C and 2 h,respectively,the MTO lifetime of SP34-5-100-2 was 1.5 times that of microporous SAPO-34,and the selectivity of C₂H₄ plus C₃H₆was increased by about4%.3.Cu-SAPO-34 catalysts were prepared by ion exchange and one-step synthesis using Cu（Ac）₂ and Cu-TEPA,respectively.The effects of exchange concentration,exchange time,Cu-TEPA and TEA content on Cu-SAPO-34 were investigated.NH₃-SCR technology was used to investigate catalytic performance of Cu-SAPO-34under one-step hydrothermal method.The results showed that 5.0 Cu-SAPO-34-1synthesized by one-step had better catalytic effect in NH₃-SCR technology.