以两亲性单季铵盐分子为模板剂合成的多级孔SAPO-34分子筛

设计合成两亲性的单季铵盐分子作为助结构导向剂，两亲性分子具有晶体生长抑制剂或者致孔剂作用，最终导向合成多级孔/小晶粒SAPO-34分子筛。助结构导向剂减少Si进入AlPO₄骨架，降低分子筛的强酸酸性。相较于传统的SAPO-34分子筛(CS)，添加助结构导向剂合成的多级孔SAPO-34颗粒尺寸较小，介孔孔体积较高，强酸酸性较弱，其在甲醇制烯烃反应中的双烯(乙烯和丙烯)选择性提高约4%，催化剂的寿命延长一倍。

Hierarchical SAPO-34 templated by amphiphilic single-quaternary-ammonium surfactants

The introduction of mesopores and downsizing of the crystals of SAPO-34 can enhance its diffusion efficiency, leading to high catalytic activity in methanol-to-olefin (MTO) reactions. Amphiphilic single-quaternary-ammonium molecules with different lengths of carbon chains (N⁺(CH₂CH₃)₃-C_nH_2n+1] Br^-], Cn-1N (n=4, 6, 8)) were designed and synthesized as co-structure directing agents. Due to the electrostatic interaction, amphiphilic molecules acted as crystal growth inhibitors or pore-forming agents, which resulted in the formation of hierarchical SAPO-34 (HS) zeolite with a smaller crystal size. When the carbon chain length was four (C4-1N), the hierarchical SAPO-34 zeolite (HS-4) was synthesized with a smaller crystal size and without other crystal phases. SAPO-34 zeolites with high mesopore volume (HS-6 and HS-8) were synthesized with C6-1N and C8-1N as co-structure directing agents. Without adding a co-structure directing agent, conventional SAPO-34 (CS) was synthesized. There were many tetrahedral particles in CS, which is the early morphology of the cubic particles. The results of the X-ray fluorescence spectrometer (XRF) and ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) indicated that Cn-1N molecules restrain Si atoms from incorporating into the AlPO₄ framework. The results of NH₃-temperature-programmed desorption (NH₃-TPD) proved the strong acid gradually decreases in the order of CS > HS-8 > HS-6 > HS-4. The diffusion behaviors of methanol molecules in HS-4, HS-6, and HS-8 were better than in CS. HS-4 showed excellent catalytic performance in MTO reaction:the selectivity of ethylene (C₂H₄) and propylene (C₃H₆) (84.4%) has improved by about 4% compared to that of CS (80.5%), and the catalyst lifetime of HS-4 was about two times the lifetime of CS. HS-6 also exhibited high selectivity of C₂H₄ and C₃H₆ (83.5%), and its lifetime was almost the same as HS-4. HS-8 had a high mesopore volume, but the higher strong acidity promoted hydrogen transfer reactions, leading to alkanes, aromatics, and coke, so the lifetime of HS-8 in MTO reaction was slightly prolonged.