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1.
以256 m 2烧结机O 3氧化烧结烟气中NO过程为研究对象,采用CFD数值模拟方法考察了含O 3喷射气体与烧结烟气流动及NO低温氧化特性。通过与76步复杂反应机理的对比验证了11步简化机理的适用性,分析了反应温度、O 3/NO摩尔比以及O 3分布特性对NO氧化效率和不同价态NO x 转化率的影响规律。通过对简单结构反应器的模拟结果表明:NO 3稳定性较差,烟道内主要氧化产物为NO 2与N 2O 5;随反应温度升高,NO氧化效率基本保持不变,NO 2转化率提高且提升速率逐渐增大而N 2O 5呈相反规律;随O 3/NO摩尔比增大,NO氧化效率提高但提升速率逐渐减小,NO 2转化率先增大后在摩尔比高于1.25时开始减小,而各工况均产生N 2O 5且生成量逐渐增大,其原因为射流核心区可提供高O 3/NO摩尔比条件;通过优化O 3分布器结构改善O 3与烟气接触与混合条件,O 3与NO摩尔比为1.0、停留时间为0.87 s时NO氧化率可提高约12.8%,摩尔比为2.0、停留时间为1.73 s时N 2O 5转化率可提高约15.6%。 相似文献
2.
区别于还原法脱硝技术,臭氧氧化脱硝技术将NO氧化为易溶于水的NO 2和N 2O 5等,结合后续吸收工艺进行脱硝。臭氧氧化脱硝技术已经广泛应用于催化裂化、工业锅炉烟气NO x排放控制。结合臭氧氧化技术的工艺特点及反应动力学,分析了复杂烟气组分中NO氧化的选择性,重点关注臭氧与NO摩尔比、反应温度和停留时间等关键工艺参数对氧化产物组成的影响。通过阐述湿法与半干法脱硫工艺中的硫硝协同吸收原理,分析吸收剂、吸收气体组成、添加剂等因素对吸收效率的影响。在此基础上,提出臭氧氧化脱硝技术研究中存在的不足以及此技术未来的发展前景。 相似文献
3.
The gliding arc discharge, combined with a catalytic bed, has been applied for nitrous oxide processing in oxygen containing gases. It has been found that under conditions of the gliding arc, nitrous oxide in mixtures with oxygen or air not only decomposes to oxygen and nitrogen, but is also oxidised to nitric oxide. The overall conversion of nitrous oxide, as well as the degree of N 2O oxidation to NO were studied as a function of its initial concentration, flow rate, and discharge power. The overall N 2O conversion and degree of oxidation to NO decreased with increasing flow rate and initial N 2O concentration, and increased with increasing discharge power. The degree of N 2O oxidation to NO varied within 20–37%. The overall conversion and degree of N 2O oxidation increased when granular dielectric materials (TiO 2, SiO 2 (quartz glass), and γ-Al 2O 3) were introduced into the reaction zone. The energy efficiency and the overall conversion of N 2O were still further increased due to catalytic effects of a number of metal oxides (CuO, NiO, MnO 2, Fe 2O 3, Co 3O 4, ZrO 2) deposited on γ-Al 2O 3. The activity of the oxide catalysts within the active power range of 300–360 W decreased in the order: CuO>Fe 2O 3>NiO>MnO 2>Co 3O 4>ZrO 2. It has been concluded that the combined plasma-catalytic processing may be an efficient way for the reduction of N 2O emissions. 相似文献
4.
SO 2 and NO emitted from coal-fired power plants have caused serious air pollution in China. In this study, a test system for NO oxidation using O 3 is established. The basic characteristics of NO oxidation and products forms are studied. A separate test system for the combined removal of SO 2 and NO x is also established, and the absorption characteristics of NO x are studied. The characteristics of NO oxidation and NO x absorption were verified in a 35 t·h -1 industrial boiler wet combined desulfurization and denitrification project. The operating economy of ozone oxidation wet denitrification technology is analyzed. The results show that O 3 has a high rate and strong selectivity for NO oxidation. When O 3 is insufficient, the primary oxidation product is NO 2. When O 3 is present in excess, NO 2 continues to get oxidized to N 2O 5 or NO 3. The removal efficiency of NO 2 in alkaline absorption system is low (only about 15%). NO x removal efficiency can be improved by oxidizing NO x to N 2O 5 or NO 3 by increasing ozone ratio. When the molar ratio of O 3/NO is 1.77, the NO x removal efficiency reaches 90.3%, while the operating cost of removing NO x per kilogram is 6.06 USD (NO 2). 相似文献
5.
A systematic reactivity study of N 2O, NO, and NO 2 on highly dispersed CuO phases over modified silica supports (SiO 2–Al 2O 3, SiO 2–TiO 2, and SiO 2–ZrO 2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N 2O) to selective reductions by hydrocarbons (N 2O, NO, and NO 2) and oxidation (NO to NO 2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO 2–Al 2O 3 and SiO 2–ZrO 2, led to a better activity and selectivity of CuO for the reactions of N 2O, NO, and NO 2 reductions and N 2O decomposition than SiO 2–TiO 2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values. 相似文献
6.
The interaction of γ-Al 2O 3, taken as a model substance of tropospheric mineral dust, with N 2O, NO and NO 2 has been studied using kinetic and temperature-programmed desorption (TPD) mass-spectrometry in presence and absence of UV irradiation. At low surface coverages (<0.001 ML), adsorption of N 2O and NO 2 is accompanied by dissociation and chemiluminescence, whereas adsorption of NO does not lead to appreciable dissociation. Upon UV irradiation of Al 2O 3 in a flow of N 2O, photoinduced decomposition and desorption of N 2O take place, whereas in a flow of NO, only photoinduced desorption is observed. Dark dissociative adsorption of N 2O and NO and photoinduced N 2O dissociation apparently occur by a mechanism involving electron capture from surface F- and F +-centers. Photoinduced desorption of N 2O and NO may be associated with decomposition of complexes of these molecules with Lewis acid sites, V-centers or OH-groups. TPD of N 2O and NO proceeds predominantly without decomposition, while NO 2 partially decomposes to NO and O 2. 相似文献
7.
The kinetic model of the reduction of NO to N 2 with decane, developed based on the experimental data over Fe-MFI catalyst, has been applied for the oxidation of NO to NO 2 and reduction of NO 2 to N 2 with decane over Cu-MFI catalyst. The model fits well the experimental data of oxidation of NO as well as reduction of NO to N 2. Remarkable differences have been found in performance of Cu-MFI and Fe-MFI catalysts. While Fe-MFI is more active in oxidation of NO to NO 2, Cu-MFI exhibits much higher activity in the reduction of NO with decane. The kinetic model indicates that the significantly lower activity of Fe-MFI in comparison with Cu-MFI in transformation of NO x to nitrogen is due to higher rate of transformation of NO 2, formed in the first step by the oxidation of NO, back to NO instead to molecular nitrogen. 相似文献
8.
Reaction activities of several developed catalysts for NO oxidation and NO x (NO + NO 2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co 3O 4 based catalysts are the most active ones for both NO oxidation and NO x reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co 3O 4 catalyst, the effects of calcination temperatures, SO 2 concentration, optimum SV for 50% conversion of NO to NO 2 were determined. Also, Co 3O 4 based catalysts (Co 3O 4-WO 3) exhibit significantly higher conversion than all the developed DeNO x catalysts (supported/unsupported) having maximum conversion of NO x even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N 2O formation over Co 3O 4-WO 3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N 2O over all the catalysts. The effect of SO 2 concentration on NO x reduction is found to be almost negligible may be due to the presence of WO 3 that resists SO 2 oxidation. 相似文献
9.
Almost quantitative absorption of NO is achieved in nitric acid solutions containing sodium chlorite, sodium hypochlorite, or chlorine gas at temperatures up to 80°C and atmospheric pressure. Experiments are conducted by bubbling various mixtures of NO, NO 2 and O 2, with the balance N 2 into varying volumes of scrubbing solutions up to one dm 3. When scrubbing with acidic NaClO 2, a greenish yellow color is observed in the solution when the gaseous mixture is bubbled into the liquid containing the oxidizing compound. The color is due to the presence of ClO 2 gas, an intermediate active in the oxidation of NO. Results in acidic NaClO or Cl 2 show similar results, except the intermediate that actually promotes the oxidation is HClO. These intermediates were identified spectroscopically. Material balances, determined using ion chromatography, show that the only anions in solution at NO breakthrough are NO 3- and Cl -. 相似文献
10.
The infrared spectral performance of the N xO y species observed on oxide surfaces [N 2O, NO -, NO, (NO) 2, N 2O 3, NO +, NO 2- (different nitro and nitrito anions), NO 2, N 2O 4, N 2O 5, NO 2, and NO 3- (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N 2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N xO y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded. 相似文献
11.
The promoting effect of supported metals on alumina catalyst was investigated for the reduction of nitrogen monoxide in oxygen-rich atmospheres. For NO reduction with propene over impregnated CoO/A1 2O 3, the first reaction step was found to be the oxidation of NO to NO 2 probably catalyzed by dispersed cobalt species. The next reaction step, which is the reaction of NO 2 with propene to form N 2, was considered to take place on the alumina surface. Although the activity of impregnated FeO/A1 2O 3 was low because of the presence of large iron oxide particles catalyzing propene oxidation with dioxygen, FeO/A1 2O 3 prepared with sol-gel method showed excellent deNO x activity. 相似文献
12.
Nitric oxide and nitric dioxide compounds (NO x) present in stack gases from nitric acid plants are usually eliminated by selective catalytic reduction (SCR) with ammonia. In this process, small quantities of nitrous oxide (N 2O) are produced. This undesirable molecule has a high greenhouse gas potential and a long lifetime in the atmosphere, where it can contribute to stratospheric ozone depletion. The influence of catalyst composition and some operating variables were evaluated in terms of N 2O formation, using V 2O 5/TiO 2 catalysts. High vanadia catalyst loading, nitric oxide inlet concentration and reaction temperature increase the generation of this undesirable compound. The results suggest that adsorbed ammonia not only reacts with NO via SCR, but also with small quantities of oxygen activated by the presence of NO. The mechanism proposed for N 2O generation at low temperature is based on the formation of surface V–ON species which may be produced by the partial oxidation of dissociatively adsorbed ammonia species with NO + O 2 (eventually NO 2). When these active sites are in close proximity they can interact to form an N 2O molecule. This mechanism seems to be affected by changes in the active site density produced by increasing the catalyst vanadia loading. 相似文献
13.
The influence of ammonia and nitric oxide oxidation on the selective catalytic reduction (SCR) of NO by ammonia with copper/nickel and vanadium oxide catalysts, supported on titania or alumina have been investigated, paying special attention to N 2O formation. In the SCR reaction, the VTi catalyst had a higher activity than VAl at low temperatures, while the CuNiAl catalyst had a higher activity than CuNiTi. A linear relationship between the reaction rate of ammonia oxidation and the initial reduction temperature of the catalysts obtained by H 2-TPR showed that the formation rate of NH species in copper/nickel catalysts would be higher than in vanadia catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that copper/nickel catalysts presented ammonia coordinated on Lewis acid sites, whereas ammonium ion adsorbed on Brønsted acid sites dominated on vanadia catalysts. The NO oxidation experiments revealed that copper/nickel catalysts had an increase of the NO 2 and N 2O concentrations with the temperature. NO could be adsorbed on copper/nickel catalysts and the NO 2 intermediate species could play an important role in the reaction mechanism. It was suggested that the presence of adsorbed NO 2 species could be related to the N 2O formation. 相似文献
14.
The adsorption and coadsorption of selective catalytic reduction (SCR) reactants and reaction products on CuZSM-5-37 containing 11 wt.-% CuO have been studied by FTIR spectroscopy. The catalyst surface is characterized by both weak acidity and weak basicity as revealed by testing with probe molecules (CO 2, NH 3, H 2O). NO 2 adsorption results in formation of different kinds of nitrates. The same species are formed when NO is coadsorbed with oxygen at 180°C. NO adsorption at ambient temperature also leads to formation of nitrates as well as of Cu 2+NO species. In the presence of oxygen the latter are converted according to the scheme: NO → N 2O 3 → N 2O 4 → NO 2 → NO 3. It is concluded that the surface nitrates are important intermediates in the SCR process. They are thermally stable and resistant towards interaction with CO 2, N 2, O 2, and are only slightly affected by H 2O and NO. However, they posses a high oxidation ability and are fully reduced by propane at 180°C. It is concluded that one of the most important roles of oxygen in SCR by hydrocarbons is to convert NO x into highly active surface nitrates. 相似文献
15.
采用实验方法研究了不同尺寸滴管炉反应器内H 2O 2热分解氧化NO特性。对比了不同H 2O 2蒸发条件对NO氧化率的影响规律。分析了气体温度、H 2O 2溶液浓度、H 2O 2:NO摩尔比、NO初始浓度及气体流量对NO氧化率的影响。检测了氧化产物并分析了产物的生成路径。结果表明:H 2O 2的快速蒸发是其热分解氧化NO的前提。减小H 2O 2液滴尺寸或液膜厚度可加速H 2O 2蒸发与分解,提高NO氧化率,扩宽NO氧化的温度范围。保证蒸发速率可削弱H 2O 2浓度对NO氧化率的影响。当H 2O 2:NO < 10时,NO氧化率随H 2O 2:NO的增加而增加;当H 2O 2:NO>10时,NO氧化率几乎不随H 2O 2:NO变化。H 2O 2热分解对于较高浓度的NO具有更高的氧化效率。H 2O 2热分解氧化NO的主要产物为NO 2。HO 2·直接将NO氧化为NO 2,·OH则先将NO转化为HONO,然后进一步氧化为NO 2。 相似文献
16.
The pathway for selective reduction of NO x by methane over Co mordenite cataysts has been studied by comparing the rates of the individual reactions (NO oxidation, CH 4 oxidation, NO 2 reduction) with that of the combined reaction (NO + O 2 + CH 4). Co (+2) was exchanged into H-MOR and Na-MOR to give catalysts with different metal loading and number of support protons. Additionally, exchanged Co (+2) ions were precipitated with NaOH to produce dispersed cobalt oxide on Na-MOR. The NO oxidation rate is the same for ion exchanged Co (+2) ions in H-MOR and Na-MOR, but the rate of Co (+2) ions is much lower than that of cobalt oxide. NO oxidation equilibrium is obtained only for those catalysts with high metal loading, cobalt oxide or run at low GHSV. Under the conditions of selective catalytic reduction, methane oxidation by O 2 is low for all catalysts. The turnover frequency of Co on Na-MOR, however, is higher than that on H-MOR. The rate of NO 2 reduction to N 2 is directly proportional to the number of support acid sites and independent of the amount of Co. Comparison of the rates and selectivities for the individual reactions with the combined reaction of NO + O 2 + CH 4 indicates that there are two types of catalysts. For the first, the NO oxidation is in equilibrium and the rate determining step is reduction of NO 2. For these catalysts, the rate (and selectivity) for formation of N 2 is identical from NO + O 2 + CH 4 and NO 2 + CH 4. These catalysts have high metal loading and few acid sites. Nevertheless, the rate of N 2 formation increases with increasing number of protons. For the second type of catalyst, NO oxidation is not in equilibrium and is the rate limiting step. For these catalysts the rate of N 2 formation increases with increasing metal loading. Neither catalyst type, however, is optimized for the maximum formation of N 2. By using a mixture of catalysts, one with high NO oxidation activity and one with a large number of Brønsted acid sites, the rate of N 2 is greater than the weighted sum of the individual catalysts. The current results support the proposal that the pathway for selective catalytic reduction is bifunctional where metal sites affect NO oxidation, while support protons catalyze the formation of N 2. 相似文献
17.
The adsorption of HCN on, its catalytic oxidation with 6% O 2 over 0.5% Pt/Al 2O 3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N 2O, NO and NO 2, and some residual adsorbed N-containing species were oxidized to NO and NO 2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N 2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 °C. Furthermore, the temperature of maximum HCN conversion to N 2O is located between 200 and 250 °C, while raising the reaction temperature increases the proportion of NO x in the products. The co-feeding of H 2O and C 3H 6 had little, if any effect on the total HCN conversion, but C 3H 6 addition did increase the conversion to NO and decrease the conversion to NO 2, perhaps due to the competing presence of adsorbed fragments of reductive C 3H 6. Evidence is also presented that introduction of NO and NO 2 into the reactant gas mixture resulted in additional reaction pathways between these NO x species and HCN that provide for lean-NO x reduction coincident with HCN oxidation. 相似文献
18.
The behavior of the selective catalytic reduction of nitrogen oxides (NO x) assisted by a dielectric barrier discharge was investigated. The principal function of the dielectric barrier discharge in the present system is to generate ozone, which is continuously fed to a chamber where the ozone and NO-rich exhaust gas (NO forms the large majority of NO x) are mixed. In the ozonization chamber, a part of NO contained in the exhaust gas is oxidized to NO 2, and then the mixture of NO and NO 2 enters the catalytic reactor. The ozonization method proposed in this study was found to be more energy-efficient for the oxidation of NO to NO 2 than the typical nonthermal plasma process. The degree of NO oxidation was approximately equal to the amount of ozone added to the exhaust gas, implying that the decomposition of ozone into molecular oxygen was relatively slow, compared to its reaction with NO. When the exhaust gas was first treated by ozone to produce a mixture of NO and NO 2, a remarkable enhancement in the catalytic reduction of nitrogen oxides was observed. Neither NO 3 nor N 2O 5 was formed in the present system, but small amounts of ozone and N 2O (less than 5 ppm) were detected in the outlet gas. 相似文献
19.
以Al 2O 3、SiO 2和TiO 2为载体,采用凝胶-溶胶法和浸渍法制备铁基堇青石整体式催化剂,并对其丙烯选择性催化还原NO性能进行了研究。通过N 2物理吸附/脱附、XRD、SEM、H 2-TPR、Py-FTIR和原位DRIFTS技术对催化剂进行了表征。不同载体对催化剂的表面酸性、氧化还原性能、比表面积和表面形貌有显著影响,从而导致丙烯还原NO的催化活性明显差异。C 3H 6-SCR的催化活性按Fe/Al 2O 3/CM > Fe/SiO 2/CM > Fe/TiO 2/CM依次降低。在450℃的有氧条件下,在Fe/Al 2O 3/CM上催化C 3H 6还原NO效率可达到100%,这主要是因为较好的氧化还原性能和丰富的Lewis酸性位。基于原位的DRIFTS研究表明,Lewis酸性位的增加有助于促进形成NO 2/NO 3-物种,从而提高了催化性能。 相似文献
20.
NO conversion to N 2 in the presence of methane and oxygen over 0.03 at.%Rh/Al 2O 3, 0.51 at.%Pt/Al 2O 3 and 0.34 at.%Pt–0.03 at.%Rh/Al 2O 3 catalysts was investigated. δ-Alumina and precious metal–aluminum alloy phases were revealed by XRD and HRTEM in the catalysts. The results of the catalytic activity investigations, with temperature-programmed as well as steady-state methods, showed that NO decomposition occurs at a reasonable rate on the alloy surfaces at temperatures up to 623 K whereas some CH4 deNOx takes place on δ-alumina above this temperature. A mechanism for the NO decomposition is proposed herein. It is based on NO adsorption on the precious metal atoms followed by the transfer of electrons from alloy to antibonding π orbitals of NO(ads.) molecules. The CH4 deNOx was shown to occur according to an earlier proposed mechanism, via methane oxidation by NO2(ads.) to oxygenates and then NO reduction by oxygenates to N2. 相似文献
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