摘要
应用X射线衍射 (XRD)、扫描电镜 (SEM )、红外光谱 (FT IR)、核磁共振 (NMR)和热重分析 (TGA)等表征手段研究了以HF 三乙胺复合模板剂合成SAPO 34分子筛的晶化历程 .结果表明 ,在晶化过程中有SAPO 5分子筛生成 ,而随着晶化时间的延长 ,SAPO 5逐渐消失 .通过SEM可以看出 ,SAPO 34的晶化在 6 0h内不断进行 ,直到生成晶面完美的SAPO 34分子筛晶体 .NMR研究表明 ,晶化过程中先生成磷酸铝结构 ,随后硅原子逐渐进入SAPO 34分子筛骨架 .对晶化不同时间的SAPO 34分子筛进行了甲醇制低碳烯烃反应的性能评价 ,发现晶化 12h的分子筛样品已经具有良好的催化性能 .
XRD, SEM, FT-IR, NMR and TGA were used to characterize the crystallization pro ce ss of the SAPO-34 molecular sieve synthesized using HF-triethylamine as the co mposite template. XRD results indicate that SAPO-5 molecular sieve appears at t he beginning of the crystallization and disappears gradually as the crystalliz ation continues. Pure SAPO-34 is obtained at the end of the crystallization pro cess (60 h). The presence of HF decreases the crystallization rate of SAPO-34 c ompared with the case without adding HF. SEM results show that the crystallizati on of SAPO-34 is a continual process and SAPO-34 crystals with perfect surface s are achieved at the end of the process. FT-IR results show that when the crys tallization time is 3 h, some SiO 4 tetrahedra are observed and the SAPO-34 mo lecular sieve appears. That is to say, the SAPO-34 can only be formed when Si O 4 tetrahedra are formed. NMR results indicate that the AlPO 4 structure is f i rst formed and when silicon atoms enter the structure, SAPO-34 is obtained. TG A results show that template molecules are gradually contained in the pore stru cture of SAPO-34 and at the beginning of the crystallization, the thermal deco mposition process includes the decomposition of chelated materials. SAPO-34 obt ained at 12 h already bears good catalytic performance for methanol-to-olefin and the molecular sieve samples with a longer crystallization time produce less isobutene because there is less SAPO-5 or no SAPO-5 in the samples.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2003年第11期849-855,共7页
关键词
SAPO—34分子筛
晶化
氟化氢
三乙胺
复合模板剂
甲醇
低碳烯烃
SAPO-34 molecular sieve, crystallization, hydrogen fluoride, triethylamine, com posite template, methanol, olefin
