化学链燃烧中镍基氧载体表面反应性的密度泛函研究

发布时间：2018-04-09 02:23

本文选题：密度泛函理论　切入点：化学链燃烧　出处：《华中科技大学》2015年硕士论文

【摘要】：目前,化石燃料燃烧中CO2减排的主要且切实可行的方式只有CCS路线。相比于传统的能源密集型碳捕获技术,化学链燃烧是新型的具有CO2内分离特点的清洁高效燃烧技术。其中氧载体是化学链燃烧技术的关键,Ni基氧载体被认为是具有发展的氧载体之一。尽管已有大量实验研究了Ni基氧载体在化学链燃烧中的氧化还原性能,但目前有关气体分子对NiO反应性的影响机理还不清楚,实验过程中出现的一些现象未能得到合理解释,缺乏微观相互作用机理的深入研究。因此,在分子水平上研究NiO表面的反应性能对Ni基氧载体的改性具有重要的理论和实际意义。本文基于密度泛函理论,系统的研究了CO在NiO(001)表面的吸附及氧化反应机理,探究了氧对NiO还原过程的重要作用。通过计算结果与实验所得参数的比较,SGGA+U方法可以准确描述CO-NiO系统中的反应。CO在NiO(001)洁净表面和缺陷表面的吸附计算结果表明,CO在两种表面上仅仅只是吸附,而没有发生氧化反应。为了揭示CO的氧化机理,本文着重研究了氧对CO和NiO(001)表面反应的作用。结果表明氧空位对于O2分解成O原子的反应表现出很高的表面反应性;吸附于NiO(001)表面的活性氧原子和CO的反应是生成CO2的重要反应路径之一。大量实验表明,存在于气体燃料中的H2S对Ni基氧载体的反应性有明显不利的影响,但其具体的影响微观机理研究尚还欠缺。因此,H2S及其分解产物SH和S在N iO(001)两种表面的吸附得到了详细研究。结果发现H2S的吸附略强于CO,而SH在两种表面的吸附均为强化学吸附。必须指出的是,S原子在洁净表面会与邻近的Ni和O原子反应并成键,同时极大改变了NiO(001)表面的结构;而在氧空位处,S单原子则会完全替代失去的氧原子而填补空位。无论何种情况,NiO(001)表面的反应性会降低。CO在预吸附S物质的NiO(001)表面的吸附计算进一步证实了S物质对氧载体反应性的不利影响,结果表明NiO(001)表面的S物质对CO具有明显的排斥作用,阻碍了CO的吸附及氧化反应。为了改善NiO氧载体的S中毒现象,本文研究了Cu掺杂对NiO(001)表面抗硫性的影响。结果表明,H2S,SH和S在Cu/N iO(001)表面的吸附均有减弱,其中对S的影响最为显著。因此,Cu掺杂能有效提高NiO(001)洁净表面的抗硫性。
[Abstract]:At present, the CCS route is the main and feasible way to reduce CO2 emission in fossil fuel combustion.Compared with traditional energy-intensive carbon capture technology, chemical chain combustion is a new clean and efficient combustion technology with the characteristics of internal separation of CO2.Among them, oxygen carrier is the key of chemical chain combustion technology and Ni-based oxygen carrier is considered to be one of the developed oxygen carriers.Although a large number of experiments have been conducted to study the redox properties of Ni-based oxygen carriers in chemical chain combustion, the mechanism of the effect of gas molecules on the reactivity of NiO is not clear, and some phenomena in the experimental process have not been properly explained.There is a lack of deep research on the mechanism of microcosmic interaction.Therefore, it is of great theoretical and practical significance to study the surface reaction properties of NiO on the molecular level for the modification of Ni-based oxygen carriers.Based on density functional theory, the mechanism of CO adsorption and oxidation on NiO001) surface was studied systematically, and the important role of oxygen in NiO reduction process was investigated.By comparing the calculated results with the experimental parameters, we can accurately describe the adsorption of carbon monoxide on the clean surface and defect surface of CO-NiO system. The results show that CO is only adsorbed on the two surfaces.There was no oxidation reaction.In order to reveal the oxidation mechanism of CO, the effect of oxygen on the surface reaction of CO and NiO001) was studied.The results show that the oxygen vacancy exhibits a high surface reactivity to the decomposition of O _ 2 into O atoms, and the reaction of active oxygen atom and CO adsorbed on the surface of nio _ (001) is one of the important reaction pathways for the formation of CO2.A large number of experiments show that H _ 2S in gaseous fuels has a significant adverse effect on the reactivity of Ni-based oxygen carriers, but the study of its specific microcosmic mechanism is still lacking.Therefore, the adsorption of H _ 2S and its decomposition products SH and S on nio _ (001) has been studied in detail.The results show that the adsorption of H _ 2S is slightly stronger than that of CO, while the adsorption of SH on both surfaces is strong chemisorption.It must be pointed out that the S atom reacts and binds with adjacent Ni and O atoms on the clean surface, which greatly changes the structure of the surface of NiOC001), while at the oxygen vacancy, the single S atom completely replaces the lost oxygen atom and fills the vacancy.In any case, the reactivity of NiO001) surface will decrease. The calculation of adsorption of CO on the surface of NiO001) further confirms the adverse effect of S on the reactivity of oxygen carrier.The results show that the S substance on the surface of NiO001) has obvious repulsive effect on CO, which hinders the adsorption and oxidation of CO.In order to improve the S poisoning of NiO oxygen carrier, the effect of Cu doping on the surface sulfur resistance of NiO001) was studied.The results show that the adsorption of H _ 2S _ 2O _ SH and S on the surface of Cu/N iOO _ (001) is weakened, and the influence of S on S is the most significant.Therefore, Cu doping can effectively improve the sulfur resistance of the clean surface of NiO001).
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ038.1;O641.1

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