TiO2(100)表面C和Cl2吸附反应的第一性原理计算

基于密度泛函理论的第一性原理从头算方法，建立金红石TiO2(100)表面吸附模型，计算了吸附能、电荷密度、态密度等参数，研究了加C促进TiO2氯化反应过程的行为机制。结果表明，Cl2单独在TiO2(100)表面吸附的过程为物理吸附，C和Cl2同时在TiO2(100)表面吸附的过程为化学吸附，加入C原子会促进Cl2解离及C?Cl键或Ti(5c)?Cl键的形成，含有C?O(2c)键的体系的稳定性高于含C?O(3c)的体系。C原子能够与O(2c)或O(3c)成键，削弱了Ti(5c)?O(2c)键的强度，使解离后的Cl原子更倾向于与TiO2(100)表面Ti(5c)成键或C原子成键，体系内Ti(5c)?Cl键的数量对体系的稳定性有一定影响。当体系存在一个解离后的Cl原子游离在真空层中，另一个Cl原子与C原子成键，体系的吸附能最高，为?5.25 eV，稳定性最低；当两个Cl原子分别与Ti(5c)和C形成Ti(5c)?Cl键和C?Cl键时，体系的吸附能为?6.75 eV；当两个Cl原子与表面Ti(5c)均形成Ti(5c)?Cl键时，体系的吸附能最低，为?7.78 eV，结构最稳定，此时该结构体系中C和O(2c)成键作用最强，更多的电子转移到Cl原子周围。表明加入C可削弱Ti?O键合结构，同时形成C?O(2c)双键，促使Cl2解离并在TiO2(100)表面吸附反应，对促进TiO2氯化反应进程发挥重要作用。

Adsorption and reaction of both C and Cl2 on TiO2(100) surface based on the first principles calculation

Based on the first principles ab initio method of density functional theory, the rutile TiO2(100) surface adsorption models were established. The mechanism of adding C to promote the chlorination process of TiO2 is revealed through the calculation and analysis of adsorption energy, charge density, state density. The simulated results indicated that the adsorption process of Cl2 on TiO2(100) surface was physical adsorption. The adsorption process of both C and Cl2 on TiO2(100) surface was chemical adsorption. The addition of C atom promoted the dissociation of Cl2, and the formation of C?Cl bond or Ti(5c)?Cl bond. Moreover, the stability of the system containing C?O(2c) bond was higher than that of the system containing C?O(3c) bond. The C atom can bond with O(2c) or O(3c), and weaken the strength of Ti(5c)?O(2c) bond. Thus, the dissociated Cl atom tended to bond with Ti(5c) on the surface of TiO2(100) or with C atom. It was found that the number of Ti(5c)-Cl bonds in the system had certain influence on the stability of the system. When one of the dissociated Cl atoms in the system was free, the other Cl atom bonded with C atom, and the adsorption energy of the system was the highest for ?5.25 eV, its stability was lowest. When the two dissociated Cl atoms form Ti(5c)?Cl bond and C?Cl bond with Ti(5c) respectively. The adsorption energy of the system was the second for ?6.75 eV. When two Cl atoms and surface Ti(5c) form Ti(5c)?Cl bond, the adsorption energy of the system was the lowest for ?7.78 eV and the structure was the most stable. At this point, the bond between C and O(2c) was the strongest in this structural system, and more electrons were transferred around the Cl atoms. It indicated that the addition of C can form the C?O(2c) double bond, promote the dissociation of Cl2, and adsorption reaction on the surface of TiO2 (100) which played an important role in improving the chlorination process of TiO2.