本文選題：SCR　切入點：V_2O_5　出處：《鄭州大學(xué)》2016年碩士論文

【摘要】：大氣中的主要污染物是氮氧化物(NO_x)。脫除NO_x技術(shù)中最成熟有效的是選擇性催化還原技術(shù)(SCR)。它的原理是在合適催化劑的條件下通過合適的溫度,利用還原劑把NO_x還原為N2和H2O。SCR催化劑是脫硝技術(shù)的核心,但是在工業(yè)生產(chǎn)中SCR催化劑會失活從而使脫硝的能力減弱,研究其失活機理從而設(shè)計出高活性的催化劑具有重要意義。本文建立了催化劑V_2O_5的晶體結(jié)構(gòu)模型。研究了催化劑V_2O_5與NH_3的吸附機理,以及煙氣中的堿金屬K和重金屬Pb使其失活的機理,最后結(jié)合化學(xué)反應(yīng)時的分子軌道理論,設(shè)計出了高效的催化劑。得到的結(jié)論如下:(1)NH_3分子在催化劑表面的吸附機理探究。重點分析了NH_3分子與2×2×1V_2O_5(001)表面作用的兩種機理模型:路易斯酸位的Top位和Bridge位以及布朗特酸位的吸附模型。NH_3在催化劑V_2O_5(001)表面路易斯酸位的Top位和Bridge位均發(fā)生化學(xué)吸附,在吸附過程中N原子上的電子轉(zhuǎn)移到了相鄰的H和襯底上,NH_3由中性分子分別變?yōu)閹?.896和0.931個正電荷的共價態(tài)NH_3分子;NH_3分子與2×2×1 V_2O_5(001)表面的布朗特酸位吸附作用后催化劑表面V-O鍵的鍵長變長,H與NH_3之間的距離也接近NH_3分子計算得到的鍵長;NH_3由吸附前的電中性分子變?yōu)閹д姷年栯x子。進一步分析了兩種吸附模型的原子態(tài)密度,說明襯底上的O原子以及H原子與吸附分子NH_3發(fā)生了較強的化學(xué)作用。(2)堿金屬K、堿金屬氯化物KCl和重金屬Pb在催化劑表面的失活機理的探究。建立作用模型,利用密度泛函理論(DFT)研究了其在催化劑表面的失活機理。計算了吸附前后的吸附能、鍵長變化以及Mulliken電荷布局數(shù)。通過分析可知,K、KCl和Pb均在V_2O_5(001)表面形成較強的化學(xué)吸附,吸附能分別為-0.0985、-0.170、-0.136Ha較NH_3與催化劑的吸附能-0.063Ha更負,說明其吸附作用較強。這些物質(zhì)會與還原性氣體NH_3產(chǎn)生競爭吸附,影響V_2O_5催化劑的脫硝性能。(3)新型高效催化劑的設(shè)計。通過前線軌道理論設(shè)計出兩大類六種可使V_2O_5催化活性增強的新型催化劑,一類是催化劑的活性位V原子被取代的催化劑模型:W@V-V_2O_5,Mo@V-V_2O_5,Nb@V-V_2O_5;另外一類是催化劑活性位的鄰位的V原子被取代的催化劑模型:W@鄰V-V_2O_5、Mo@鄰V-V_2O_5和Nb@鄰V-V_2O_5的催化劑。得出活性位被W和Mo取代的催化劑和活性位的鄰位被Nb取代的催化劑可以作為高效催化劑。
[Abstract]:The main pollutant in the atmosphere is the nitrogen oxide. The most mature and effective way to remove the NO_x is the selective catalytic reduction. Its principle is to pass through the appropriate temperature under the suitable conditions of the catalyst. Reducing NO_x to N2 and H2O.SCR catalysts by reducing NO_x is the core of denitrification technology. However, in industrial production, SCR catalyst will deactivate and the ability of denitrification will be weakened. It is of great significance to study the deactivation mechanism of the catalyst and to design a catalyst with high activity. In this paper, the crystal structure model of catalyst V_2O_5 is established, and the adsorption mechanism between V_2O_5 and NH_3 is studied. And the mechanism of alkali metal K and heavy metal Pb inactivation in flue gas. Finally, combining with the molecular orbital theory of chemical reaction, A highly efficient catalyst was designed. The results are as follows: the adsorption mechanism of NH_3 molecule on the catalyst surface. Two mechanisms models of the interaction between NH_3 molecule and 2 脳 2 脳 1V2O5 / 001) surface are emphatically analyzed: the Top site and Bridge site of the Lewis acid site and the Bridge site of the Lewis acid site. Adsorption model of Bronte acid site. Chemical adsorption of Top site and Bridge site of Lewis acid site on catalyst V _ 2O _ 5T _ (001). During the adsorption process, the electrons on the N atom were transferred to the adjacent H and the substrates from neutral molecules to covalent NH_3 molecules with 0.896 and 0.931 positive charges, respectively, and the Brownitic acid sites adsorbed on the surface of 2 脳 2 脳 1 V _ 2O _ 5 / 01). The distance between the bond length of V-O bond and NH_3 on the surface of the chemical agent is also close to that of the bond length NH _ 3 calculated by NH_3 molecule, which changes from electrically neutral molecules before adsorption to positive cations. The atomic density of states of the two adsorption models is further analyzed. It is shown that O atom on substrate and H atom have strong chemical interaction with adsorbed molecule NH_3. The mechanism of deactivation of alkali metal K, alkali metal chloride KCl and heavy metal Pb on the surface of catalyst is studied. The mechanism of deactivation on catalyst surface was studied by density functional theory (DFT). The adsorption energy, bond length change and Mulliken charge distribution number before and after adsorption were calculated. It was found that both KCl and Pb formed strong chemisorption on V _ 2O _ 5T _ (001) surface. The adsorption energy is -0.0985- 0.170U -0.136Ha, respectively, which is more negative than that of NH_3 and catalyst (-0.063Ha), indicating that the adsorptive energy of these substances is stronger than that of the catalyst. These substances can compete with the reductive gas NH_3. The design of new high activity catalyst for V_2O_5. Two kinds of six kinds of new catalysts which can enhance the catalytic activity of V_2O_5 were designed by the frontier orbital theory. One is the catalyst model where the active V atom of the catalyst is replaced by the V atom of the catalyst, the one is the model of the V atom replaced by the active site of the catalyst: W @ W @ next to V-V _ 2O _ 5 / V-V_2O_5, and the other is the catalyst model: W @ neighbor V _ V _ 2O _ 5M @ next to V-V_2O_5 and Nb@ V-V_2O_5. The active sites are found to be the active sites of the catalyst by the catalyst model: W @ next door V atom replaced by the catalyst model: W @ o V _ 2O _ 5i _ Mo @ next to V-V_2O_5 and Nb@ @ neighbor V-V_2O_5. The W and Mo substituted catalysts and the NB substituted catalysts with active sites can be used as high efficient catalysts.
【學(xué)位授予單位】：鄭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：O643.36

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