本文選題：氨選擇性催化還原 + 鐵鈰復合氧化物��； 參考：《大連理工大學》2017年博士論文

【摘要】：氮氧化物(NO_x)是主要的大氣污染物之一,其會對生態(tài)環(huán)境和人體健康產(chǎn)生不利影響。氨選擇性催化還原氮氧化物(NH3-SCR)技術是一種有效的NO_x去除技術,在固定源的煙氣脫硝和移動源的機動車尾氣NO_x去除領域均有良好的應用。針對商業(yè)V2O5-WO3/TiO2催化劑溫度窗口窄、高溫條件下N2選擇性差、成本高以及對環(huán)境造成二次污染等問題,本論文設計開發(fā)了高效且價格低廉的環(huán)境友好型鐵基復合氧化物催化劑。通過各種表征手段和理論計算分析了鐵基復合氧化物的物理化學性質(zhì),揭示了催化劑結構與NH3-SCR活性之間的構效關系,并采用原位紅外光譜技術及質(zhì)譜技術探討了催化劑上吸附物種的形成及其反應行為。取得的主要研究成果如下:(1)通過表面活性劑輔助法制備了一系列具有高比表面積的介孔鐵鈰復合氧化物(FexCe1-xOC2-δ)催化劑。XRD和Raman結果表明鐵摻雜到氧化鈰中可形成鐵鈰固溶體(Fe-O-Ce結構),導致了催化劑活性的提高及活化能的降低。其中,Fe0.4Ce0.6O2-δ催化劑的SCR反應活化能最低(26 kJ·mol-1)且催化性能最優(yōu)(在250到350℃反應溫度范圍內(nèi)NO_x轉化率大于80%)。XPS和DFT計算結果表明,Fe-O-Ce結構的形成促進了 Fe3+與Ce4+之間的電子相互作用,有利于增加催化劑的Lewis酸性位和提高催化劑的氧化還原性。當鐵添加量較少時(0x0.3),可通過空位補償機制形成鐵鈰固溶體且氧空位顯著增加,從而提高了催化劑的SCR反應活性。當鐵添加量較高時(1x ≥ 0.3),可通過間隙位補償機制形成鐵鈰固溶體同時出現(xiàn)間隙位Fe3+物種。間隙位Fe3+物種具有富電子性有利于NO氧化成NO2,改善鐵鈰催化劑的催化性能。(2)設計開發(fā)了在寬工作溫度窗口內(nèi)具有優(yōu)異NH3-SCR性能的鐵鎢復合氧化物(Fe1-xWxOδ)催化劑。其中,Feo.75W0.25Oδ催化劑活性最佳,在225至450℃溫度范圍內(nèi)NO_x轉化率可維持在90%以上。同時,該鐵鎢催化劑還具有較高的熱穩(wěn)定性和優(yōu)良的抗高空速能力。鎢物種的引入有利于形成較小顆粒的α-Fe2O3和FeWO4物種。FeWO4具有八面體[FeO6]/[WO6]結構可提供豐富的Br(?)nsted酸性位,有利于NH3吸附活化形成NH4+物種。結合DFT計算與XPS和UV-vis結果發(fā)現(xiàn),α-Fe2O3和FeWO4之間的界面電子相互作用促使電子從W6+位點轉移到Fe3+位點,有利于NO2活性物種的生成。因此,鐵鎢催化劑的高活性歸功于α-Fe2O3和FeWO4物種之間的協(xié)同作用。(3)采用原位紅外光譜技術探究了鐵鎢(FeW)催化劑的NH3-SCR反應機理。結果表明,在低溫區(qū)(≤250℃),NO2、配位NH3和NH4+為主要的吸附物種,它們之間反應形成的中間產(chǎn)物NO2(NH3)2和NO2(NH4+)2復合物可以與NO反應產(chǎn)生N2和H2O。因此,該FeW催化劑的低溫NH3-SCR遵循"快速SCR"反應路徑,其中NO氧化生成NO2是該反應的速控步驟。在高溫區(qū)(≥250℃),配位NH3和NH4+為主要的吸附物種而NO主要以氣態(tài)形成參與反應。配位NH3/NH4+物種和NO之間反應形成NH2NO中間物種,進一步反應以產(chǎn)生N2和H2O,遵循Eley-Rideal(E-R)反應機理。(4)通過紅外光譜和程序升溫等技術系統(tǒng)研究了硫化過程對FeW催化劑結構、反應性能以及機理的影響。在低溫區(qū)間內(nèi)(300℃),硫化作用抑制了 NH3-SCR活性,而在高溫(≥300℃)下反應活性沒有明顯變化。經(jīng)過硫化作用,FeW催化劑上形成了具有共價S=O鍵的硫酸鹽物種。結合TPD與原位紅外光譜測定的數(shù)據(jù)發(fā)現(xiàn),S=O共價雙鍵的強吸電子效應,增強了催化劑金屬物種的Lewis和Br(?)nsted酸性,有利于配位NH3、NH4+吸附物種和硝酸鹽的生成。在低溫區(qū),NO2的形成因硫化過程受阻導致"快速SCR"路徑被切斷,從而低溫SCR活性有所損失;在高溫區(qū),硝酸鹽吸附物種的形成,使SCR反應遵循 Langmuir-Hinshelwood 反應機理。
[Abstract]:Nitrogen oxide (NO_x) is one of the main atmospheric pollutants, which will have adverse effects on the ecological environment and human health. Ammonia selective catalytic reduction nitrogen oxide (NH3-SCR) technology is an effective NO_x removal technology. It has a good application in the field of fixed source flue gas denitrification and mobile vehicle exhaust NO_x removal in mobile vehicles. The V2O5-WO3/TiO2 catalyst has a narrow temperature window, low selectivity of N2 at high temperature, high cost and two pollution to the environment. This paper designed and developed a highly efficient and inexpensive environmentally friendly iron based composite oxide catalyst. The physicochemical properties of iron based composite oxides were analyzed by various characterization methods and theoretical calculations. The structure-activity relationship between the structure of the catalyst and the activity of NH3-SCR was revealed, and the formation and reaction of the adsorbed species on the catalyst were investigated by in situ infrared spectroscopy and mass spectrometry. The main results obtained were as follows: (1) a series of mesoporous iron with high specific surface area was prepared by the surfactant assisted method. The results of.XRD and Raman of the cerium complex oxide (FexCe1-xOC2- delta) catalyst show that iron doped to cerium oxide can form the iron cerium solid solution (Fe-O-Ce structure), which leads to the improvement of the activity of the catalyst and the reduction of the activation energy. Among them, the SCR reaction activation energy of the Fe0.4Ce0.6O2- delta catalyst is lowest (26 kJ. Mol-1) and the catalytic performance is optimal (at 250 to 350 degrees C). The conversion rate of NO_x within the temperature range is greater than 80%).XPS and DFT calculation results show that the formation of Fe-O-Ce structure promotes the electronic interaction between Fe3+ and Ce4+, is beneficial to increase the Lewis acidity of the catalyst and to increase the oxidation-reduction of the catalyst. When the amount of iron is less (0x0.3), the iron cerium solid solution can be formed by the vacancy compensation mechanism. As the oxygen vacancy increased significantly, the SCR reaction activity of the catalyst was increased. When the amount of iron was higher (1x > 0.3), the gap position compensation mechanism was used to form the iron cerium solid solution and the gap position Fe3+ species appeared at the same time. The gap position Fe3+ species had rich electron property, which was beneficial to NO oxidation to NO2 and improved the catalytic performance of the iron cerium catalyst. (2) design opening. The Fe / W composite oxide (Fe1-xWxO delta) catalyst with excellent NH3-SCR properties in a wide working temperature window has been developed. Among them, the Feo.75W0.25O delta catalyst has the best activity, and the NO_x conversion rate can be maintained over 90% at the temperature range of 225 to 450. The fe w catalyst has high thermal stability and excellent high air velocity resistance. The introduction of tungsten species is beneficial to the formation of smaller particles of alpha -Fe2O3 and FeWO4 species.FeWO4 with a eight body [FeO6]/[WO6] structure that provides a rich Br (?) nsted Acid position and is beneficial to NH3 adsorption and activation to form NH4+ species. The site transfer to the Fe3+ site is beneficial to the generation of NO2 active species. Therefore, the high activity of the iron tungsten catalyst is attributed to the synergism between the alpha -Fe2O3 and the FeWO4 species. (3) the mechanism of the NH3-SCR reaction of the iron tungsten (FeW) catalyst was investigated by in situ infrared spectroscopy. The results show that in the low temperature region (less than 250 degrees C), NO2, the coordination NH3 and NH4+ are the main factors. The adsorbed species, NO2 (NH3) 2 and NO2 (NH4+) 2 complex formed by the reaction between them, can react with NO to produce N2 and H2O., so the low temperature NH3-SCR of the FeW catalyst follows the "fast SCR" reaction path, in which NO oxidation produces NO2 is the speed control step. NO mainly takes part in the formation of the gaseous state. The reaction between the coordination NH3/NH4+ species and NO forms the intermediate species of NH2NO, and further reacts to produce N2 and H2O and follows the Eley-Rideal (E-R) reaction mechanism. (4) the effects of the vulcanization process on the structure, the reaction properties and the mechanism of the FeW catalyst are studied by the infrared spectrum and the temperature programmed system. In the low temperature range (300 degrees C), the vulcanization inhibits the NH3-SCR activity, but the reactive activity is not obviously changed at high temperature (> 300 degrees C). After the vulcanization, the sulfate species with covalent S=O bond is formed on the FeW catalyst. The strong electron absorption effect of the S=O covalent double bond is enhanced by the number of TPD and in situ infrared spectroscopy. The Lewis and Br (?) nsted acidity of the metal species of the catalyst is beneficial to the coordination of the ligand NH3, the NH4+ adsorbed species and the formation of nitrate. In the low temperature zone, the formation of the NO2 is blocked by the vulcanization process that causes the "fast SCR" path to be cut off, so that the low temperature SCR activity is lost; in the high temperature region, the nitrate adsorbed the species to follow Langmuir-Hinshelw. The reaction mechanism of ood.

【學位授予單位】：大連理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：X701

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