本文選題：密度泛函理論　切入點：化學(xué)鏈燃燒　出處：《華中科技大學(xué)》2015年碩士論文

【摘要】：目前,化石燃料燃燒中CO2減排的主要且切實可行的方式只有CCS路線。相比于傳統(tǒng)的能源密集型碳捕獲技術(shù),化學(xué)鏈燃燒是新型的具有CO2內(nèi)分離特點的清潔高效燃燒技術(shù)。其中氧載體是化學(xué)鏈燃燒技術(shù)的關(guān)鍵,Ni基氧載體被認(rèn)為是具有發(fā)展的氧載體之一。盡管已有大量實驗研究了Ni基氧載體在化學(xué)鏈燃燒中的氧化還原性能,但目前有關(guān)氣體分子對NiO反應(yīng)性的影響機理還不清楚,實驗過程中出現(xiàn)的一些現(xiàn)象未能得到合理解釋,缺乏微觀相互作用機理的深入研究。因此,在分子水平上研究NiO表面的反應(yīng)性能對Ni基氧載體的改性具有重要的理論和實際意義。本文基于密度泛函理論,系統(tǒng)的研究了CO在NiO(001)表面的吸附及氧化反應(yīng)機理,探究了氧對NiO還原過程的重要作用。通過計算結(jié)果與實驗所得參數(shù)的比較,SGGA+U方法可以準(zhǔn)確描述CO-NiO系統(tǒng)中的反應(yīng)。CO在NiO(001)潔凈表面和缺陷表面的吸附計算結(jié)果表明,CO在兩種表面上僅僅只是吸附,而沒有發(fā)生氧化反應(yīng)。為了揭示CO的氧化機理,本文著重研究了氧對CO和NiO(001)表面反應(yīng)的作用。結(jié)果表明氧空位對于O2分解成O原子的反應(yīng)表現(xiàn)出很高的表面反應(yīng)性;吸附于NiO(001)表面的活性氧原子和CO的反應(yīng)是生成CO2的重要反應(yīng)路徑之一。大量實驗表明,存在于氣體燃料中的H2S對Ni基氧載體的反應(yīng)性有明顯不利的影響,但其具體的影響微觀機理研究尚還欠缺。因此,H2S及其分解產(chǎn)物SH和S在N iO(001)兩種表面的吸附得到了詳細(xì)研究。結(jié)果發(fā)現(xiàn)H2S的吸附略強于CO,而SH在兩種表面的吸附均為強化學(xué)吸附。必須指出的是,S原子在潔凈表面會與鄰近的Ni和O原子反應(yīng)并成鍵,同時極大改變了NiO(001)表面的結(jié)構(gòu);而在氧空位處,S單原子則會完全替代失去的氧原子而填補空位。無論何種情況,NiO(001)表面的反應(yīng)性會降低。CO在預(yù)吸附S物質(zhì)的NiO(001)表面的吸附計算進一步證實了S物質(zhì)對氧載體反應(yīng)性的不利影響,結(jié)果表明NiO(001)表面的S物質(zhì)對CO具有明顯的排斥作用,阻礙了CO的吸附及氧化反應(yīng)。為了改善NiO氧載體的S中毒現(xiàn)象,本文研究了Cu摻雜對NiO(001)表面抗硫性的影響。結(jié)果表明,H2S,SH和S在Cu/N iO(001)表面的吸附均有減弱,其中對S的影響最為顯著。因此,Cu摻雜能有效提高NiO(001)潔凈表面的抗硫性。
[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).
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ038.1;O641.1

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本文編號：1724436