不同钴含量CoAPO-5分子筛的合成、表征及其催化环己烷氧化性能

用水热法合成了一系列不同含量钴掺杂的磷酸铝分子筛CoAPO-5. 合成的样品用X射线衍射(XRD), 扫描电镜(SEM), 紫外可见漫反射光谱(UV-Vis DRS), 热重分析(TG)仪和电感耦合等离子体发射光谱(ICP-AES)等进行了表征. XRD表征显示, 合成的CoAPO-5分子筛具有较高的结晶度, 分子筛晶胞参数与Co含量之间存在较好的对应关系. UV-Vis漫反射光谱显示合成的CoAPO-5分子筛具有骨架钴的特征三重峰; 焙烧后峰的强度降低, 表明分子筛骨架中Co2+可被氧化成Co3+. SEM表明该分子筛具有典型的AlPO4-5分子筛形貌特征. TG结果也表明Co2+进入了分子筛骨架, 分子筛具有较好的稳定性. 在环己烷氧化反应中CoAPO-5具有较好的催化性能, 环己烷转化率与环己酮选择性均较高; 随着分子筛中钴含量的增加, 环己烷的转化率增加.

Synthesis and Characterization of CoAPO-5 with different Cobalt Contents and Their Catalytic Performance for Cyclohexane Oxidation

Cobalt substituted molecular sieves (CoAPO-5) with different cobalt content were synthesized hydrothermally. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), thermogravimetric(TG) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that cobalt was incorporated into the framework of AlPO4-5 molecular sieves and the as-synthesized CoAPO-5 was highly crystalline and pure. There is a good linear relationship between the crystal cell parameters and the cobalt content in CoAPO-5. The UV-Vis intensity of Co(II) is significantly reduced through calcinations as Co(II) is oxidized to Co(III) during calcinations. The as-synthesized CoAPO-5 exhibited excellent performance for the oxidation of cyclohexane using molecular oxygen as oxidant. The conversion of cyclohexane and the ratio of cyclohexanol to cyclohexanone in the product increased as the cobalt content increased in CoAPO-5. At nCo/nP=0.04 the conversion of cyclohexane was 23.3%.