CoMo/TiO₂-Al₂O₃HDS催化剂的氟里昂气相改性研究

【作者】 凌岚；

【导师】 付贤智； 王绪绪；

【作者基本信息】 福州大学 ， 物理化学， 2002， 硕士

【摘要】 本文采用CFC-12气相预氟化载体法、CFC-12直接氟化法、NH₄F氯化法分别制备出含氟MoCo/Al₂O₃-TiO₂HDS催化剂，利用连续流动微反催化装置考察了三种方法所制催化剂的噻吩HDS反应活性，采用X射线粉末衍射（XRD）、氮气吸附、吡啶吸附IR光谱、H₂程序升温还原（TPR）、紫外漫反射光谱（DRS）和X射线光电子能谱（XPS）等方法表征了气相预氟化载体法所制MoCo/Al₂O₃-TiO₂催化剂的物化性能。结果表明，采用CFC-12预氟化载体法，在温度623～673K、时间50～60min和CFC-12浓度1～3O％下氟化得到的催化剂表现出优良的催化活性和良好的物化性质，反应活性显著优于未氟化、CFC-l2直接氟化和NH₄F氟化的催化剂。 根据CFC-12气相预氟化对催化剂的比表面、孔结构、晶相组成、表面酸性、还原情况、表面态等方面的影响探讨了CFC-12气相预氟化提高噻吩HDS活性的可能原因。CFC-12气相氟化法可克服NH₄F溶液氟化法部分破坏载体织构的缺点，保持了未氟化TiO₂-Al₂O₃载体的高比表面和合适的孔结沟；气相氟化可使催化剂表面L酸和B酸酸中心数目减少；用适当的温度、时间和CFC-12浓度气相预氟化载体可明显降低催化剂的还原温度；适当的气相氟化条件可减少正四面体Co（Ⅱ）的含量，即增多正八面体Co（Ⅱ）的含量，有利于“Co-Mo-S”活性相的形成；气相氟化可促进Mo、Co和Ti在Al₂O₃上分散，使之形成了较小的晶粒；F离子的强拉电子能力，可使Mo^Ⅵ离子处于相对缺电子状态，这种缺电子状态使Mo^Ⅵ易于接受硫化合物中的孤对电子，并保持高的硫化状态。上述影响使得CFC-12气相预氟化载体法所制的催化剂表现出较高的HDS活性。更多还原

【Abstract】 MoCo/Al2O3-TiO2 catalysts containing fluorine were prepared by pre-fluorination of the support with Freon gas (CFC-12), direct fluorination of MoCo/Al2O3-TiO2 with CFC-12, and pre-fluorination of the support with NH4F, and their HDS activity to thiophene were studied by a flow micro-reactor. The effect of pre-fluorination of the support by using CFC-12 on MoCo/Al2O3-TiO2 in the physical properties was studied by XRD, N2 adsorption, pyridine adsorption IR, TPR, DRS and XPS. The results showed that pre-fluorination of the support by using CFC-12 led to a remarkable enhancement of the catalytic activity of MoCo/Al2O3-TiO2 for hydrodesulfurization of thiophene. And this method was much better than the other two in the catalytic activity of MoCo/Al2O3-TiO2 for hydrodesulfurization of thiophene.The effect of pre-fluorination of the support by using CFC-12 on specific surface area, pore structure, crystalline form, surface acidity, reductive temperature and active phase was examined, and the reason leading to enhancement of the catalytic activity of MoCo/Al2O3-TiO2 for hydrodesulfurization of thiophene was proposed. It’s showed that pre-fluorination of the support by using CFC-12 compared to the impregnation of fluoride salt solution, brought no damage to the texture, e.g. surface area of the catalyst, keeping the appropriate specific surface area and pore structure of Al2C>3-TiO2 support. Pre-fluorination of the support by using CFC-12 decreased Lewis and BrOnsted acidic sites. The reductive temperature of MoCo/Al2O3-TiO2 catalyst was greatly reduced if the support was pre-fluorinated with suitable fluorination temperature, time and CFC-12 concentration. Appropriate fluorination condition also led to reduction of content of tetra-Co(II) viz. increase of octa-Co(II), which promoted formation of active phase i.e. Co-Mo-S. Pre-fluorination of the support improved dispersion of active phase. Strong pull of F" ion made Mo" relatively devoid uf electron, promoting the possibility for Movl to accept lone-pair electron of sulfide and keeping Movl high- sulfuration state. Above-mentioned effect led to remarkable enhancement of the catalytic activity of MoCo/Al2O3-TiO2更多还原