MgAPO-11分子筛的合成、表征及其催化正己烷裂解反应的动力学研究

Synthesis and Characterization of Magnesium-Substituted Aluminophosphate Molecular Sieves (MgAPO-11) and Their Kinetic Study of Catalytic Cracking of n-Hexane

以二异丙基胺为有机模板剂,采用静态水热法合成了具有不同镁含量的镁铝磷酸盐分子筛MgAPO-11,并利用X射线衍射、扫描电子显微镜、傅里叶变换红外光谱、魔角旋转核磁共振和电感耦合等离子体原子发射光谱等方法对其进行表征.当0<n(MgO):n(Al2O3)≤0.30:0.70时,杂原子镁同晶取代AlPO4-11分子筛上的部分骨架铝,合成的MgAPO-11分子筛具有AEL结构,结晶度和纯度较高.以正己烷为模型底物,评价了合成的MgAPO-11分子筛在烃类催化裂解反应中的催化活性.研究结果表明,MgAPO-11在450～550 oC具有中等催化活性,正己烷在MgAPO-11分子筛上的催化裂解反应以单分子反应为主,速率方程中的正己烷浓度项反应级数为1,表观速率常数与反应温度之间的关系可用Arrhenius公式表示.

Magnesium-substituted aluminophosphate molecular sieves（MgAPO-11） with various magnesium contents were synthesized by the static hydrothermal method using diisopropylamine as an organic template and characterized by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,magic-angle-spinning nuclear magnetic resonance,and inductively coupled plasma atomic emission spectroscopy.When n（MgO）/n（Al2O3） was in the range of 0–0.30/0.70,the MgAPO-11 molecular sieves with AEL structure and high crystallinity could be obtained.The heteroatoms Mg（II） were confirmed to isomorphously substitute for the framework atoms Al（III） of AlPO4-11 molecular sieves.The catalytic activity of the MgAPO-11 for hydrocarbon catalytic cracking was evaluated using n-hexane as a model substrate.The MgAPO-11 showed a moderate activity for n-hexane catalytic cracking conversion in the reaction temperature range of 450–550 oC.The reaction was first order in n-hexane.The dependence of the rate constant on temperature can be expressed in terms of the Arrhenius formula in the whole temperature range.Considering both the kinetic data and product distribution,it was concluded that the monomolecular protolytic mechanism prevailed for this cracking reaction.