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C-O单键官能团在半焦-NO反应中的作用
赵彤
Subtype硕士
Thesis Advisor宋文立
2018
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword半焦,一氧化氮,密度泛函理论,反应机理,C-o单键
Abstract

本课题利用密度泛函理论计算,在分子尺度上研究了Zigzag边结构和Armchair边结构上的半焦-NO反应机理。同时讨论了C-O单键官能团以及分子边结构对半焦-NO反应的影响。在本文中建立了4条可能的反应路径,这些反应路径阐明了半焦局部结构与NO分子反应的化学过程以及反应过程中分子体系总能的变化情况。结果表明,半焦-NO反应的化学过程可以归纳为四个阶段:半焦边结构的活化,NO分子的化学吸附,异构化反应,以及气体分子的释放。其中半焦分子活化步骤以及释放CO或CO2分子的步骤是半焦-NO反应的控制步骤。而处于热力学有利过程之前的高能垒的半焦分子活化步骤是主要的控制步骤。根据半焦分子活化步骤的反应能垒,4条反应路径由易到难的顺序为:2b(带C-O单键官能团的Armchair边结构与NO的反应),1b(带C-O单键官能团的Zigzag边结构与NO的反应),2a(不带C-O单键官能团的Armchair边结构与NO的反应),1a(不带C-O单键官能团的Zigzag边结构与NO的反应)。NO分子的化学吸附能够放出大量的热量并供后续步骤利用。C-O单键官能团能够通过降低半焦分子活化步骤的能垒而使得反应路径更容易进行,进而促进半焦-NO反应。另一方面,在C-O单键官能团由于可以作为CO2分子前驱体的一部分而对CO2的释放有较高的选择性,本文中的C-O单键官能团均以CO2的形式释放。而且CO2的释放总是在半焦边结构上生成两个新的活性位点,这进一步促进了后续步骤的反应。Armchair边结构和Zigzag边结构的相对优势需是情况而定。Armchair边结构比起Zigzag半结构更容易脱氢活化,也更容易释放CO或CO2分子;但是NO分子在Zigzag边结构上化学吸附放出的热量要远大于在Armchair边结构上的吸附。;The reaction mechanism between char and nitric oxide (NO) on zigzag and armchair edge structures was studied, on molecular scale, based on density functional theory (DFT). The influence of C-O single bond group and edge structure on NO-Char reaction were studied. Four possible pathways were established to illustrate the chemical processes and the variation of the total energy of the molecular structures. The results show that, in NO-char reaction, there are four stages which include the activation of the char surface, the chemisorption of NO molecules, the isomerization reactions, and the release of gas molecules. The activation step and the steps which release carbon monoxide (CO) and carbon dioxide (CO2) are control steps in NO-char reaction. Where the activation step, which takes place before the thermodynamically favorable process, is the primary control step. Based on the reaction barriers of the activation steps, the priority of the pathways can be ranked from easy to hard as 2b (reaction between NO and armchair edge with C-O), 1b (reaction between NO and zigzag edge with C-O), 2a (reaction between NO and armchair edge without C-O), 1a (reaction between NO and zigzag edge without C-O). The exothermic chemisorption of NO molecules can release a great deal of energy which can be used by the subsequent reactions. The Carbon-Oxygen single bond groups (C-O single bond groups) could promote the NO-char reaction by lowering the barrier of activation. On the other hand, the C-O single bond group can favor the production of CO2 since it can be considered as a part of the precursor of CO2 molecule. In this work, all C-O single bond groups are released on the form of CO2 molecule. The release of CO2 always leave two new active sites on the edge structures of char, which further promote the subsequent steps. The superiorities of armchair and zigzag structures depend on the situation. The armchair edge is easier to activate (via dehydrogenation) and release CO or CO2 than zigzag edge, while chemisorption of NO on zigzag edge releases much more energy than that on armchair edge.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40717
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
赵彤. C-O单键官能团在半焦-NO反应中的作用[D]. 中国科学院大学,2018.
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