School of Energy and Power Engineering, Changsha University of Science and Technology

基于密度泛函理论(DFT),在M06-2X/6-311G(d)基组水平下,研究了钙和羟基在焦炭还原N2O过程中的作用。采用了Zigzag焦炭模型及钙和羟基修饰后的焦炭模型对N2O还原反应过程进行模拟。结果表明:整个反应过程分为三个阶段,N2O的吸附、N2的析出以及C(O)配合物的解吸,三种模型的决速步均位于C(O)配合物解吸阶段;动力学结果表明,随着反应温度升高,反应速率常数增大,温度升高对N2O-C反应有促进作用;根据传统过渡态理论(TST)计算得到,原始Zigzag焦炭模型及钙和羟基修饰后的焦炭模型异相还原N2O的反应活化能分别为450.1kJ/mol,420.4kJ/mol和406.3kJ/mol,表明钙和羟基对焦炭还原N2O均有促进作用;钙和羟基促进焦炭还原N2O反应的机理不同,钙吸附到焦炭表面,向焦炭转移电子使焦炭带有更多的负电荷,增加了焦炭边缘活性位点的反应活性,决速步的能垒降低,整个反应的放热增加,羟基修饰后整个反应的放热减少,并且N2O—C反应路径发生改变,解吸产物由CO转变为CO2,降低了焦炭表面含氧配合物的解吸能垒,促进了焦炭对N2O的还原。

The effects of Ca and OH on the heterogeneous reduction of N2O by char were investigated based on density functional theory (DFT) at the M06-2X/6-311G(d) level. The pris-tine Zigzag model and Ca- or OH-decorated Zigzag model were selected in this study. The entire reaction process is divided into three stages: adsorption of N2O, desorption of N2, and desorption of C(O) complexes. The rate-limiting steps of the three models all located in the desorption of C(O) complexes. The kinetic results show that the reaction rate constant increases with increas-ing temperature, indicating that the increasing temperature promotes the N2O-C reaction. Ac-cording to the traditional transition state theory (TST), the reaction activation energies of heter-ogeneous reduction of N2O by the pristine Zigzag model, Ca- or OH-decorated Zigzag model are 450.1 kJ/mol, 420.4 kJ/mol and 406.3 kJ/mol respectively, indicating that Ca and OH facili-tates the reduction of N2O. The mechanisms of the promotional effect of Ca and OH are differ-ent. For the Ca-decorated Zigzag char model, the adsorption of Ca on the surface of char results in more negative charge due to the electron transfer from Ca to char, thereby increasing the reac-tivity of the active sites at the edge of the char. The energy barrier of the rate-limiting step after Ca-decoration decreases, but the heat release in the overall reaction process increases. However, after OH decoration, the heat release reduces in the overall reaction process and the N2O—C re-action pathway is changes. For the OH-decorated Zigzag model, the desorption product is CO2 rather than CO, reducing the desorption energy barrier of the oxygen-containing complexes on the char surface and promoting the reduction of N2O by char.

湖南省 教 育 厅 优 秀 青 年 项 目 (20B041)、湖 南 省 自 然 科 学 基 金 面 上 项 目 (2023JJ30047)和 长 沙 理 工 大 学 研 究 生 科 研 创 新 项 目(CXCLY2022097).

尹艳山,邓文鹏,陶建航,等.钙和羟基影响焦炭还原 N2O 的量子化学研究[J].煤炭转化,2023,46(6):12-22

DOI:10.19726/j.cnki.eb-cc.202306002.YIN Yanshan,DENG Wenpeng,TAO Jianhang,et al.Quantum chemistry study on effect of calcium and hydroxyl group on reduction of N2O by char[J].Coal Conversion,2023,46(6):12-22