本文選題：選擇性催化還原　切入點(diǎn)：氮氧化物　出處：《浙江大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：隨著社會(huì)經(jīng)濟(jì)的迅速發(fā)展,能源消費(fèi)水平逐年上升,特別是京津冀、長(zhǎng)三角、珠三角等重點(diǎn)地區(qū),能源消費(fèi)強(qiáng)度遠(yuǎn)高于全國(guó)平均水平。高強(qiáng)度的能源特別是煤炭的消費(fèi)帶來了嚴(yán)重的環(huán)境污染問題。氮氧化物(NO_x)是一種主要的大氣污染物,其排放會(huì)造成酸雨、光化學(xué)煙霧等問題,給環(huán)境和人類健康帶來極大的影響。選擇性催化還原(SCR)技術(shù)是目前治理煙氣中氮氧化物最為高效的技術(shù)。催化劑是SCR技術(shù)的關(guān)鍵。SCR催化劑在我國(guó)推廣應(yīng)用面臨的一大挑戰(zhàn)在于其對(duì)鍋爐負(fù)荷的適應(yīng)性。我國(guó)燃煤電廠負(fù)荷波動(dòng)頻繁,在機(jī)組低負(fù)荷運(yùn)行時(shí),傳統(tǒng)的V2O5-WO3/TiO2催化劑低溫活性不足,導(dǎo)致氮氧化物排放超標(biāo)、氨逃逸增加、甚至引起環(huán)保設(shè)備的故障。傳統(tǒng)的應(yīng)對(duì)策略是采用省煤器旁路改造,這一方法成本高,而且會(huì)導(dǎo)致鍋爐熱效率降低。本文針對(duì)燃煤電廠全負(fù)荷脫硝的難題開展研究,提出了寬溫度窗口催化劑設(shè)計(jì)的理論依據(jù)并開發(fā)了系列寬溫度窗口 SCR催化劑配方,系統(tǒng)研究了催化劑的構(gòu)效關(guān)系,反應(yīng)機(jī)理,抗硫性能和促進(jìn)硫酸氫銨分解的機(jī)制,得到了適用于低溫實(shí)際煙氣條件下可長(zhǎng)時(shí)間穩(wěn)定運(yùn)行的寬溫度窗口催化劑。全文得到的主要結(jié)果如下:一、研究了寬溫度窗口脫硝催化劑的構(gòu)效關(guān)系。從SCR反應(yīng)機(jī)理出發(fā),采用具有良好氧化還原性能的氧化鈰作為催化劑氧化位點(diǎn)以及具有強(qiáng)酸性的氧化鈮作為酸性位點(diǎn),采用共沉淀法合成了系列鈰鈮復(fù)合氧化物SCR催化劑。當(dāng)Ce:Nb原子摩爾比為1:1時(shí),其在200～450℃C溫度區(qū)間內(nèi)具有80%以上的催化活性。研究建立了催化劑的結(jié)構(gòu)-理化性質(zhì)-催化活性的關(guān)聯(lián),揭示了不同價(jià)態(tài)的稀土/過渡金屬氧化物的摻雜可以產(chǎn)生短程活化作用,生成更多的配位不飽和氧物種,并首次發(fā)現(xiàn)了這種配位不飽和氧物種是決定低溫活性的關(guān)鍵因素。二、研究了催化劑表面的關(guān)鍵活性物種和反應(yīng)路徑。研究發(fā)現(xiàn)在催化劑表面,SCR反應(yīng)遵循Eley-Rideal機(jī)理和Langmuir-Hinshelwood機(jī)理。在L-H機(jī)理中,NO_2和單齒硝酸鹽物種具有良好的催化活性,而雙齒硝酸鹽以及橋式硝酸鹽則不具備反應(yīng)活性;而在E-R機(jī)理中,Lewis酸性位點(diǎn)起到主要作用。通過定量計(jì)算不同溫度區(qū)間內(nèi)L-H機(jī)理和E-R機(jī)理對(duì)反應(yīng)的貢獻(xiàn),發(fā)現(xiàn)L-H機(jī)理對(duì)反應(yīng)的低溫活性更為重要,而E-R機(jī)理則是主要負(fù)責(zé)高溫活性。根據(jù)前兩部分的研究?jī)?nèi)容提出了寬溫度窗口 SCR催化劑設(shè)計(jì)理論依據(jù),并制備了一系列的催化劑進(jìn)行驗(yàn)證,發(fā)現(xiàn)在250℃下的脫硝活性都顯著高于商業(yè)催化劑,而在400℃時(shí)活性都在97%以上,證實(shí)了該理論具有普遍適應(yīng)性。三、研究了催化劑抗SO_2中毒的機(jī)理。研究發(fā)現(xiàn)鈰鈮復(fù)合氧化物催化劑易受SO_2影響,200ppm SO_2的加入使得鈰鈮復(fù)合氧化物催化劑活性在20 h內(nèi)降低了接近40%,且該失活現(xiàn)象為不可逆現(xiàn)象;而氧化鐵的加入可有效提高鈰鈮催化劑抗SO_2中毒能力:20h后,催化活性依舊保持在92%左右。通過表征測(cè)試,發(fā)現(xiàn)在氧化鐵改性的催化劑表面所形成的硫酸鹽具有較低的熱穩(wěn)定性,同時(shí)與硫酸化后的鈰鈮復(fù)合氧化物催化劑相比,硫酸化后的鈰鈮鐵催化劑反應(yīng)中L-H比例依舊高達(dá)32%,遠(yuǎn)高于硫酸化后鈰鈮催化劑反應(yīng)中L-H比例(6%)。這說明低溫下氧化鐵的添加可有效保證L-H機(jī)理的進(jìn)行,因此提高了催化劑在低溫下抗SO_2中毒的能力。四、研究了催化劑表面硫酸氫銨分解的機(jī)理。針對(duì)SCR催化劑低溫區(qū)間內(nèi)硫酸氫銨沉積問題,制備了 TiSi復(fù)合載體,并研究了 TiSi復(fù)合載體對(duì)于硫酸氫銨在低溫下分解的促進(jìn)作用。研究發(fā)現(xiàn),當(dāng)硫酸氫銨負(fù)載在催化劑表面時(shí),銨物種主要以NH_4~+形式存在,而硫物種主要以雙齒硫酸鹽形式存在。硫酸氫銨在升溫過程中遵循如下的分解規(guī)律:低溫下NH_3首先釋放出來,硫物種則固定在催化劑表面;隨著溫度的進(jìn)一步升高,硫酸鹽開始分解為SO_2。與Ti載體相比,TiSi載體表面的硫酸氫銨中的NH_4~+更容易在較低溫度下分解并釋放出NH_3,而SO_4~(2-)具有較高的熱穩(wěn)定性。根據(jù)這一研究結(jié)果,設(shè)計(jì)了系列載體均可促使硫酸氫銨在較低溫度下分解�；诒菊撐牡难芯克_發(fā)的催化劑應(yīng)用于溫州電廠300MW機(jī)組,在35%和100%負(fù)荷下氮氧化物排放濃度均低于50 mg/m~3。
[Abstract]:With the rapid development of economy, energy consumption increased year by year, especially in Beijing Tianjin Hebei, Yangtze River Delta, Pearl River Delta and other key areas, the energy consumption intensity is much higher than the national average. High strength energy especially coal consumption brought serious environmental pollution. The nitrogen oxide (NO_x) is one of the major pollutants in the atmosphere, its emissions will cause acid rain, smog and other issues, a great impact to the environment and human health. The selective catalytic reduction (SCR) technology is currently the treatment of flue gas of nitrogen oxides in the most efficient technology. The catalyst is the key technology of SCR.SCR catalyst is its adaptability to boiler load in a big challenge the popularization and application in China. The frequent fluctuation of coal-fired power load in the low load operation of the unit, the V2O5-WO3/TiO2 catalyst activity at low temperature than conventional nitrogen oxide emissions exceed the standard result. , ammonia escape increases, even cause the failure of environmental protection equipment. The traditional strategy is the use of bypass reconstruction of economizer, the cost of this method is high, but also leads to a decrease in the thermal efficiency of the boiler. Aiming at the problem of coal-fired power plant full load denitrification research, puts forward the theoretical basis for a wide temperature window catalyst design and development a series of wide temperature window of SCR catalyst, structure-activity relationship, catalyst system and reaction mechanism of the sulfur resistance, and promote the mechanism of ammonium hydrogen sulfate decomposition, which are suitable to the actual conditions of flue gas in low temperature under long time stable wide temperature window catalyst run. The main results are as follows: first, this thesis. Effect on wide temperature window of denitration catalyst. Starting from the SCR reaction mechanism, the cerium oxide has good redox properties as catalysts for the oxidation of strong acid sites and oxygen Niobium as acidic sites, using a series of cerium niobium composite oxide SCR catalyst was synthesized by co precipitation method. When the Ce:Nb atom ratio is 1:1, with catalytic activity of more than 80% at 200~450 DEG C temperature range. The research establishes the relationship of catalyst structure physicochemical properties and catalytic activity, reveals different valence the rare earth doped transition metal oxides can produce short-range activation, generate more coordinatively unsaturated oxygen species, and for the first time found the coordinatively unsaturated oxygen species is a key factor in determining the low temperature activity. Two, studies the key active species and reaction path of catalyst surface. The study found that on the surface of the catalyst. SCR reaction follows the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism. In the mechanism of L-H, NO_2 and monodentate nitrate species has good catalytic activity, and bidentate nitrate and nitrate salt bridge Do not have the reaction activity; and in the E-R mechanism, Lewis acid sites play a major role. Through the calculation of different temperature range L-H mechanism and E-R mechanism of contribution to the reaction mechanism of L-H, found that activity in low temperature reaction is more important, and the mechanism of E-R is mainly responsible for the high temperature activity. According to the contents of the first two the author put forward a wide temperature window of SCR design based on the theory of catalyst, catalyst and preparation of a series of verification, found that the denitrification activity at 250 DEG C were significantly higher than that of the commercial catalyst, and at 400 degrees C activity in more than 97%, confirmed that the theory has universal adaptability. Three, study on the mechanism of resistance SO_2 poisoning catalyst. Study found that cerium niobium oxide catalyst susceptible to SO_2 200ppm because of the addition of SO_2 within 20 h by nearly 40% active cerium niobium composite oxide catalyst, and the deactivation phenomenon can not be Inverse phenomenon; and iron oxide could effectively improve the anti poisoning ability of cerium niobium catalyst SO_2 20h, catalytic activity still remained at around 92%. The characterization tests that sulfate formed in the catalyst surface iron oxide modified with low thermal stability, compared with cerium niobium composite oxide catalyst after sulfation cerium niobium iron catalyst, reaction of sulfated L-H in the proportion is still as high as 32%, far higher than the proportion of cerium niobium catalyst reaction after L-H sulfuric acid (6%). This shows that low temperature iron oxide addition can effectively ensure the L-H mechanism, so as to improve the ability of the catalyst under low temperature resistance to SO_2 poisoning. Four. Study on the mechanism of ammonium hydrogen sulfate catalyst surface decomposition. For the deposition of ammonium hydrogen sulfate SCR catalyst at low temperature range, the TiSi composite support was prepared, and the effects of TiSi composite carrier for ammonium hydrogen sulfate at low temperature Under the decomposition of the role. The study found that when ammonium hydrogen sulfate load on the surface of the catalyst, ammonium species mainly exists in the form of NH_4~+ and sulfur species mainly exist in the form of bidentate sulfate. Ammonium hydrogen sulfate in the heating process follow the decomposition rules as follows: low temperature NH_3 first released sulfur species is fixed at the surface of the catalyst; as the temperature increases, the sulfate decomposition of SO_2. and Ti compared to the carrier, the ammonium hydrogen sulfate TiSi carrier surface in NH_4~+ more easily in the low temperature decomposition and release of NH_3, and SO_4~ (2-) has high thermal stability. According to the results of this study, designed a series of carrier can promote the decomposition of ammonium hydrogen sulfate at low temperature. The development of this research based on the catalyst was applied in Wenzhou power plant 300MW unit, in the 35% and 100% load NOx concentrations were lower than 50 mg/m~3.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：X773;O643.3

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本文編號(hào)：1568173