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为了研究氢化芳烃的微观结构,进一步认识和理解氢化芳烃在催化裂化过程中的反应特性。以四氢萘为模型化合物,利用基于密度泛函理论的量子化学从头计算方法,对四氢萘的几何结构和电子结构进行了系统研究,得到了四氢萘不同位置C-H键和C-C键的键长、键级、键能以及电子云密度、前线轨道分布等微观结构信息。发现四氢萘结构具有轴对称特性,苯环上的C-C键和C-H键要远比环烷环的C-C键和C-H键稳定。由于受苯环的影响,会使得其环烷环上不同位置的C-C键的键长、键级和键能均具有明显差异,也导致环烷环上不同位置C-H键的键长、键级和键能有较明显的差异,具体表现为:对C-C键而言,与苯环相连的C-C键的键长较短,键级较高,键能也明显较高,而苯环β位C-C键的键能则明显较低;对C-H键而言,与苯环β位环烷碳原子上的C-H键相比,苯环α位环烷碳原子上的C-H键的键能明显较低。电子云分布计算结果能够较好地给出的这些C-C键和C-H键结构特征差异的原因。前线轨道计算结果表明,在催化裂化过程中,苯环α位环烷碳原子上的C-H键和β位C-C键较易受到催化剂酸性中心的进攻,是酸催化反应的位点。这些计算结果对于认识与理解氢化芳烃的反应特性具有一定的基础性理论意义。
In order to study the microstructure of hydrogenated aromatics, we further understand and understand the reaction characteristics of hydrogenated aromatics in the catalytic cracking process. Using tetralin as a model compound, the geometrical and electronic structures of tetrahydronaphthalene were systematically studied by ab initio calculations based on density functional theory. The bonds of CH bond and CC bond at different positions of tetralin were obtained. Long, key-level, bond energy and electron cloud density, front orbital distribution and other microstructure information. It was found that the tetralin structure has an axisymmetric structure. The C-C bond and C-H bond on the benzene ring are much more stable than the C-C bond and the C-H bond on the naphthenic ring. Due to the influence of the benzene ring, the bond length, the bond order and the bond energy of the CC bonds in different positions on the naphthenic ring are obviously different, and the bond length, the bond order and the bond order of the CH bonds at different positions on the naphthenic ring For the CC bond, the bond length of the CC bond to the benzene ring is shorter, the bond level is higher, the bond energy is significantly higher, and the CC bond at the β position of the benzene ring Of the bond energy is significantly lower; for the CH bond, benzene ring β-carbon atom on the CH bond compared to benzene ring α-carbon atoms on the CH bond bond was significantly lower. The calculation results of the electron cloud distribution can give a good illustration of the differences in the structural characteristics of these C-C bonds and C-H bonds. The frontal orbital calculations show that the C-H bond and the C-C bond at the β-position of the benzene ring are more susceptible to attack by the acid sites of the catalyst during the catalytic cracking process, which is the site of the acid-catalyzed reaction. These results have some basic theoretical significance for understanding and understanding the reaction characteristics of hydrogenated aromatic hydrocarbons.