CoAPO-5分子筛的水热合成研究

Hydrothermal synthesis of CoAPO-5 molecular sieve

以拟薄水铝石、质量分数85%的正磷酸、四水合醋酸钴为原料,N,N 二乙基乙醇胺为模板剂,水热法合成了CoAPO 5分子筛。考察了模板剂用量、晶化温度和晶化时间对水热法合成CoAPO 5的影响以及焙烧条件对CoAPO 5分子筛性状的影响。结果表明,模板剂用量对产物纯度有较大影响,R/Al2O3为1 25时,可在较宽的温度范围内(150～200℃)合成出CoAPO 5纯相。较高温度下晶化得到的晶体晶粒度较大,但过高的晶化温度又会导致杂质相的生成,同时晶化时间过长也将导致致密相杂质的生成,在200℃下晶化48h,能得到晶粒度达24 244nm的分子筛纯相。焙烧温度和时间决定CoAPO 5分子筛最终的物化性能,焙烧温度低于500℃不能有效去除模板剂,而高于600℃将导致分子筛骨架的破坏,Co2+向Co3+转化是一个逐渐转化的过程,550℃下焙烧10h,能较好地去除模板剂和结合水及实现Co2+的转化。

CoAPO-5 molecular sieve was hydrothermally synthesized using pseudo-boehmite, phosphoric acid (85%), tetrahydrate cobaltous acetate as raw material and N,N-diehtyl-ethanolamine as templating agent. The influences of N,N-diethyl-ethanolamine dosage, crystallization temperature, crystallization time and calcinations temperature on as-synthsized CoAPO-5 molecular sieve were investigated. The result showed that dosage of templating agent has remarkable influence on purity of as-synthsized CoAPO-5 molecular sieve. Pure CoAPO-5 was synthesized in wide temperature range (150-(200 ℃)) at R/Al_2O_3 of 1.25. Bigger grain size was obtained at higher crystallization temperature. However, higher temperature gave rise to occurrence of impurities. Product with grain size up to 24.244 nm was obtained after 48 hours of crystallization at 200 ℃. Calcination temperature and time have great influence on properties of final product. Templating agent could not be sufficiently removed at temperature below 500 ℃, while temperature exceeding 600 ℃ might result in collapse of the framework. The conversion from Co^(2+) to Co^(3+) was a gradual time-consuming process. Calcination at 550 ℃ in a muffle furnace for 10 hours could remove the templating agent and bond water and give a satisfactory result.