两步晶化法合成纳米SAPO-34分子筛及其催化性能

摘要

分别以拟薄水铝石、硅溶胶和磷酸为铝源、硅源和磷源,四乙基氢氧化铵为模板剂,采用两步水热晶化法合成出粒径为200～300 nm的纳米级SAPO-34分子筛.采用X射线衍射(XRD)、X射线荧光光谱(XRF)、29Si 、27Al、31P MAS NMR、SEM、BET和NH3-TPD等手段对合成的SAPO-34分子筛进行表征,并考察了纳米SAPO-34分子筛在固定床甲醇制取烯烃(MTO)反应中的催化性能.结果表明,通过控制两步水热晶化过程的条件可有效地调控SAPO-34分子筛的晶粒大小.当第一步和第二步晶化温度分别为130和180 ℃时,可得到200～300 nm的晶型完整的SAPO-34分子筛.合成的纳米级SAPO-34分子筛对MTO反应的C2～C4选择性可达92%,单程寿命接近10 h,显著优于传统方法合成的大粒径SAPO-34分子筛.%Nano-scaled SAPO-34 molecualr sieves with size in the range of 200-300 nm were synthesized by a two-step crystallization process, with pseudoboehmite, colloidal silica and H3PO4 as sources of aluminum,silicon and phosphorous and TEAOH as template. The prepared SAPO-34 zeolites was characterized by XRD,SEM, NH3-TPD, XRF, BET, 29Si , 27Al, 31p MAS NMR. And the catalytic performance of the SAPO-34 on the methanol-to-olefins (MTO) reactions was carried out on a fixed bed. The results show that the particle size of the SAPO-34 could be effectively modulated by the crystallization temperature of the two-step crystallization process. In particular, when the first and second crystallization were conducted at 130 and 180 ℃, cubic SAPO-34 with size in the range of 200-300 nm could be successfully synthesized. Compared with the microscaled SAPO-34 prepared by the traditional hydrothermal process, the nano-scaled SAPO-34 crystals synthesized show better performance in the MTO reaction and the selectivity of C(=2)-C(=4) and the lifetime for one-turn could attained about 92％ and 10 h, respectively.