Nitrogen incorporation in SAPO-34: How urea etching improves catalyst lifetime and selectivity

Abstract

Urea etching of SAPO-34 offers an effective route to enhance its catalytic performance in the methanol-to-olefins (MTO) process. This work examines the effects of nitrogen doping and mesoporosity enhancement on SAPO-34's physicochemical and catalytic properties through combined experimental and theoretical methods, including XRD, FTIR, HR-XPS, NH₃-TPD, molecular dynamics (MD) simulations, and performance testing. HR-XPS confirms successful nitrogen incorporation, showing increased CN and NC species with reduced CSi and NSi bonds. XRD and FE-SEM reveal decreased crystallinity and particle size, contributing to higher surface area and mesoporosity. NH₃-TPD indicates moderated strong acid sites and increased weak acid sites, optimizing the acidity profile for improved ethylene selectivity and coke resistance. MD simulations show that nitrogen doping stabilizes methanol conversion steps and suppresses coke precursor formation, prolonging catalyst life. Catalytic tests demonstrate that urea-etched SAPO-34 (SP-UN) surpasses conventional SAPO-34 (SP), achieving higher ethylene selectivity (57.42 %), sustaining high selectivity for over 420 min, and exhibiting slower deactivation. The synergy of framework stabilization, balanced acidity, and enhanced diffusion properties significantly boosts SAPO-34's efficiency and durability in MTO applications.