铜铈掺杂六铝酸盐的脱硝性能

用共沉淀法制备用于脱除NO的六铝酸盐催化剂LaMxAl12-xO19(M =Cu,Ce,CuCe).用XRD、H2-TPR和BET对催化剂进行了结构和物性表征.用微型催化反应装置考察了催化剂在CO选择性催化还原NO中的活性.结果表明,Cu离子易于进入六铝酸盐晶格内,形成完整的六铝酸盐结构.Ce离子不易于进入六铝酸盐晶格内,主要以CeO2的形式存在.在CO+ NO条件下,3种催化剂都表现出较好的脱硝活性,LaCuCeAl10O19中由于Cu离子与Ce离子间产生协同作用,该催化剂的脱硝活性有所增加.加入SO2后,3种催化剂都有不同程度的失活现象发生,其中LaCuAl11O19催化剂受SO2中毒影响最严重,LaCuCeAl10O19催化剂的脱硝活性在三者中最好.     

Selective Reduction of Nitrogen Oxides In Combustion Flue Gases

The body of Information presented in this paper is directed to those Individuals concerned with the removal of NO_x in combustion flue gases. A catalytic process for the selective reduction of nitrogen oxides by ammonia has been investigated. Efforts were made toward the development of catalysts resistant to SO_x poisoning. Nitrogen oxides were reduced over various metal oxide catalysts in the presence or absence of SO_x(SO₂ and SO₃). Catalysts consisting of oxides of base metals (for example, Fe₂O₃) were easily poisoned by SO₃, forming sulfates of the base metals. A series of catalysts which are not susceptible to the SO_x poisoning has been developed. The catalysts possess a high activity and selectivity over a wide range of temperatures, 250—450°C. The catalysts were tested in a pilot plant which treated a flue gas containing 110-150 ppm NO_x, 660-750 ppm SO₂, and 40-90 ppm SO₃. The pilot plant was operated at 350°C and at a space velocity of 10,000 h^-1. The removal of nitrogen oxides was more than 90% for several months.

A mechanism of the NO-NH₃ reaction has also been investigated. It is found that NO reacts with NH₃ at a 1:1 mole ratio in the presence of oxygen and the reaction is completely inhibited by the absence of oxygen. The experimental data show that the NO-NH₃ reaction in the presence of oxygen is represented byNO + NH₃ + 1/4 O₂ = N₂ + 3/2 H₂O.     

固体超强酸和金属氧化物类催化剂上CH4-SCR还原NOx研究进展

由于还原剂甲烷价廉易得,甲烷选择性催化还原NO_x（简称CH₄-SCR）被认为是最有潜力替代NH₃-SCR的催化还原技术。现有的CH₄-SCR催化剂中,分子筛类催化剂因催化活性高而被广泛研究,但由于其水热稳定性不好,使得非分子筛负载的催化剂成为近年来的研究热点,其中主要包括固体超强酸和氧化物两大类。综述了这两类催化体系在催化活性、反应机理及掺杂改性等方面的研究现状,比较了各种催化剂的优缺点,并对CH₄-SCR的发展前景进行了展望。     

Catalytic Reduction of Nitrogen Oxides in Automobile Exhaust

The catalytic reduction of oxides of nitrogen from leaded automobile exhaust has been demonstrated to be technically feasible. These studies made with copper-containing catalysts are based upon the reducing nature of exhaust caused by the carbon monoxide present. The reaction involves 2 CO + 2 NO → + N₂ + CO₂ + 178.5 Kcal.     

Size Distribution of Particles That May Contribute to Soiling of Material Surfaces

ABSTRACT

This study investigated the effect of adding vanadium (V) to natural manganese oxide (NMO) in ammonia (NH₃) selective catalytic reduction (SCR). The addition of V to NMO decreased the catalytic activity at low temperatures by blocking the active site. However, the enhancement of catalytic activity was achieved by controlling NH₃ oxidation at high temperatures. From the NH₃ temperature programmed desorption and oxygen on/off test, it was confirmed that the amount of Lewis acid site and active lattice oxygen of the catalyst affects the catalytic performance at low temperature

IMPLICATIONS Recently, NMO and manganese oxide have been reported as SCR catalysts. They usually have only reported the reaction characteristics and catalytic activity on the NH₃ SCR over NMO or manganese/metal oxide catalysts. There are no studies about the effect of addition of V to NMO. Therefore, this study investigates the catalytic activity and reaction characteristics on the NH₃ SCR over NMO and V/NMO, and a new application is proposed based on the conclusions of this study.     

Manganese-cerium oxide (MnOx-CeO2) catalysts supported by titanium-bearing blast furnace slag for selective catalytic reduction of nitric oxide with ammonia at low temperature

A series of manganese-cerium oxide (MnO_x-CeO₂) catalysts supported by Ti-bearing blast furnace slag were prepared by wet impregnation and used for low-temperature selective catalytic reduction (SCR) of NO with NH₃. The slag-based catalyst exhibited high nitrogen oxide removal (deNO_x) activity and wide effective temperature range. Under the condition of NO = 500 ppm, NH₃ = 500 ppm, O₂ = 7–8 vol%, and total flow rate = 1600 mL/min, the Mn-Ce/Slag catalyst exhibited a NO conversion higher than 95% in the range of 180–260 °C. The activity of Mn/Slag catalysts was greatly enhanced with the addition of CeO₂. The results indicated that Ti-bearing blast furnace slag had suitable phase composition as good support of SCR catalyst.

Implications: Ti-bearing blast furnace slag is a kind of industrial waste in China. Much slag was underused and piling up, which could cause many environmental issues, such as enormous waste of titanium and groundwater and soil contamination by heavy metals in leachates. The utilization of slag as the support of SCR catalyst will not only make use of solid waste but also cut down the NO_x emitted from power plant.     

Study on the denitrification performance of FexLayOz/activated coke for NH3-SCR and the effect of CO escaped from activated coke at mid-high temperature on catalytic activity

Currently, activated coke is widely used in the removal of multiple pollutants from industrial flue gas. In this paper, a series of novel Fe_xLa_yO_z/AC catalysts was prepared by the incipient wetness impregnation for NH₃-SCR denitrification reaction. The introduction of Fe-La bimetal oxides significantly improved the denitrification performance of activated coke at mid-high temperature, and 4% Fe_0.3La_0.7O_1.5/AC exhibited a superior NO_x conversion efficiency of 90.1% at 400 °C. The catalysts were further characterized by BET, SEM, XRD, Raman, EPR, XPS, FTIR, NH₃-TPD, H₂-TPR, et al., whose results showed that the perovskite-type oxide of LaFeO₃ and oxygen vacancies were produced on the catalysts’ surfaces during roasting. Fe-La doping enhanced the amount of acid sites (mainly Lewis and other stronger acid sites) and the content of multifarious oxygen species, which were beneficial for NO_x removal at mid-high temperature. Moreover, it was investigated that the effect of released CO from activated coke at mid-high temperature on the NO_x removal through the lifetime test, in which it was found that a large amount of CO produced by pyrolysis of activated coke could promote the NO_x removal, and long-term escaping of CO on the activated coke carrier did not have a significant negative impact on catalytic performance. The results of the TG-IR test showed that volatile matter is released from the activated coke while TG results showed that the weight loss rate of 4% Fe_0.3La_0.7O_1.5/AC only was 0.0015~0.007%/min at 300–400 °C. Hence, 4% Fe_0.3La_0.7O_1.5/AC had excellent thermal stability and denitrification performance to be continuously used at mid-high temperature. Finally, the mechanisms were proposed on the basis of experiments and characterization results.

     

Effect of NOx Control Processes on Mercury Speciation in Utility Flue Gas

Abstract

The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NO_x control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NO_x control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH₃, has been evaluated. The influence of NH₃ on fly ash Hg reactions also is being investigated.     

柴油车尾气碳烟颗粒物催化燃烧催化剂的最新研究进展

柴油车尾气排放的碳烟颗粒已经引起了严重的环境污染问题,必须加以净化处理.柴油车碳烟颗粒的低温燃烧离不开高活性的催化剂.针对柴油车排放的碳烟颗粒物后处理方法中的催化氧化技术,总结了近年来几种主要类型的碳烟燃烧催化剂(贵金属催化剂、碱金属催化剂、单组分过渡金属氧化物催化剂、多组分混合氧化物催化剂和固定结构复合氧化物催化剂)的最新研究进展,并对该研究方向存在的主要问题和应用前景进行了探讨.     

Effect of the Mn oxidation state and lattice oxygen in Mn-based TiO2 catalysts on the low-temperature selective catalytic reduction of NO by NH3

TiO₂-supported manganese oxide catalysts formed using different calcination temperatures were prepared by using the wet-impregnation method and were investigated for their activity in the low-temperature selective catalytic reduction (SCR) of NO by NH₃ with respect to the Mn valence and lattice oxygen behavior. The surface and bulk properties of these catalysts were examined using Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Catalysts prepared using lower calcination temperatures, which contained Mn⁴⁺, displayed high SCR activity at low temperatures and possessed several acid sites and active oxygen. The TPD analysis determined that the Brönsted and Lewis acid sites in the Mn/TiO₂ catalysts were important for the low-temperature SCR at 80～160 and 200～350 °C, respectively. In addition, the available lattice oxygen was important for attaining high NO to NO₂ oxidation at low temperatures.

Implications: Recently, various Mn catalysts have been evaluated as SCR catalysts. However, there have been no studies on the relationship of adsorption and desorption properties and behavior of lattice oxygen according to the valence state for manganese oxides (MnO_x). Therefore, in this study, the catalysts were prepared by the wet-impregnation method at different calcination temperatures in order to show the difference of manganese oxidation state. These catalysts were then characterized using various physicochemical techniques, including BET, XRD, TPR, and TPD, to understand the structure, oxidation state, redox properties, and adsorption and desorption properties of the Mn/TiO₂ catalysts.     

Catalytic hydrolysis of urea from wastewater using different aluminas by a fixed bed reactor

In order to find an effective method for treating urea wastewater, the experiments on the hydrolysis of urea in wastewater were conducted in a fixed bed reactor with different aluminas (α-Al₂O₃, γ-Al₂O₃, and η-Al₂O₃) as catalysts respectively in contrast with inert ceramic particle. The results indicate that the three alumina catalysts show obvious catalytic activity for urea hydrolysis at 125 °C. The order of activity is η-Al₂O₃?>?γ-Al₂O₃?>?α-Al₂O₃, and the activity difference increases with increasing temperature. According to the characterization results, surface acidity has little impact on the activity of catalyst. However, it was found that surface basicity of alumina catalyst plays an important role in catalytic hydrolysis of urea, and the activity of catalyst may be also influenced by the basic strength. With η-Al₂O₃ as catalyst, the urea concentration in wastewater is reduced to 4.96 mg/L at a temperature of 165 °C. Moreover, the η-Al₂O₃ shows a good stability for urea hydrolysis. The hydrolysis of urea over η-Al₂O₃ catalyst can evidently reduce the reaction temperature and is promising to replace industrial thermal hydrolysis process.     

Co3O4/介孔分子筛催化剂对苯催化完全氧化的研究

分别以介孔分子筛MCM-41、MCM-48、SBA-15为载体,采用等体积浸渍法制备了氧化钴/介孔分子筛催化剂,利用N₂吸附、X射线衍射、程序升温还原等技术对催化剂进行了表征,考察了Co₃O₄的负载量及载体的孔结构对催化剂完全催化氧化苯的性能的影响。结果表明,Co₃O₄的负载量为20%时,催化剂的催化活性最好;载体的孔径和催化剂的可还原性能是影响催化活性的主要因素,催化剂活性顺序为Co₃O₄ /SBA-15> Co₃O₄ /MCM41> Co₃O₄ /MCM-48。     

富氧条件下选择性还原NO的复合催化剂体系

选择性催化还原法是净化稀燃汽车尾气中NOx 的最有效途径之一 ,单一催化组分或单一类型的催化剂很难满足实际需要 ,复合催化剂的研究成为必然趋势。本文介绍了复合催化体系的组合形式 ,回顾了国内外最近几年复合催化剂体系净化NOx 的研究成果 ,为将来设计新的复合催化体系提出了建议     

微量Pd对CrOx／ZrO2催化剂催化活性的影响

运用微反技术考察了ＣｒＯＸ负载型催化剂对ＣＯ＋Ｏ２和ＣＯ＋ＮＯ反应的催化活性。研究了微量Ｐｄ加和ＣｒＯＸ基双组元催化剂对上述反应的催化活性,中间产物Ｎ２Ｏ生成和Ｎ２生成的影响。     

氧化锰矿渣改性制备SCR脱硝催化剂

以锰酸钾生产过程中产生的氧化锰矿渣为原料,制备了一系列Mn基SCR脱硝催化剂。研究了活性炭、二氧化钛、以及含锰量的变化对催化剂的脱硝活性的影响。结果表明,直接由矿渣制备的催化剂和添加活性炭、二氧化钛制备的催化剂,其最大脱硝率分别为40%和78%。XPS表征发现催化剂中的锰元素存在多种氧化价态,活性炭的加入在一定程度上改变了不同价态之间的相对含量;在矿渣中加入硫酸锰后,发现总锰含量达到10%时,催化剂的最大脱硝率从78%降低至57%,XRD测试发现硫酸锰的加入导致S2O27-物种的生成,可能是引起催化剂活性下降的原因之一;而加入醋酸锰至总锰含量达到10%时,增大了催化剂的活性温度窗口,当总锰含量达到20%时,在空速10 000 h-1条件下,催化剂的最大脱硝率达到86.7%。     

Activities of different metal oxide catalysts on NO reduction and CO oxidation

A series of transition metal oxide catalysts (Zn, Ti, Cu, Ni, Fe and V) supported on Al₂O₃ and SiO2 were prepared using the incipient wetness impregnation method. Their performances on NO reduction and CO oxidation followed the sequence of TiO₂ > CuO/ZnO > CuO > ZnO. TiO₂ supported on SiO₂ was more active than that on Al₂O₃, while ZnO had the opposite performances. The activities of CuO/Al₂O₃ and ZnO/SiO₂ were both decreased with the calcination temperature increasing because the sintering and agglomerations of catalysts were occurred at high temperature.     

Comparison of titania nanotubes and titanium dioxide as supports of low-temperature selective catalytic reduction catalysts under sulfur dioxide poisoning

A series of iron–manganese oxide catalysts supported on TiO₂ and titanium nanotubes (TNTs) were studied for low temperature selective catalytic reduction (SCR) of NO with NH₃ in the presence of SO_2. The results showed that the specific surface area and the amount of Brønsted acid sites were highly correlated. The results also demonstrated that higher Mn⁴⁺/Mn³⁺ ratios and larger specific surface areas might be the main reasons for the excellent performance of MnFe-TNTs catalyst after SO₂ poisoning. The SO₂ poisoning effect could be minimized by reducing the GHSV, increasing the reaction temperature, or increasing the [NH₃]/[NO] molar ratio. The results also indicated that the formation of ammonium sulfate had a stronger effect on the NO conversion efficiency as compared to the formation of metal sulfate. Thus operating the low temperature SCR at above 230 ^oC to avoid the formation of ammonium sulfate would be the priority choice when SO₂ poisoning is a concerned issue.?Implications: Low-temperature selective catalytic reduction (SCR) has attracted increasing attention due to that it can reduce the energy consumption for the SCR process employed in industries such as steel plants and glass manufacturing plants. However, it also suffers from the sulfur dioxide (SO₂) poisoning problem. This study investigates the possibility of using titania nanotubes (TNTs) as the support of Mn/Fe bimetal oxide catalysts for low-temperature SCR to reduce the SO₂ poisoning. The results indicated that the MnFe-TNT catalyst can tolerate SO₂ for a longer time as compared with the MnFe-TiO₂ catalyst.     

Improving the activity of Mn/TiO2 catalysts through control of the pH and valence state of Mn during their preparation

In this study, the authors investigated the influence of the valence state of Mn on the efficacy of selective catalytic reduction using a Mn-based catalyst. The nitrogen oxides (NO_x) conversion rate of the catalyst was found to be dependent on the type of TiO₂ support employed and on the temperature, as the catalyst showed an excellent conversion of > 80% at a space velocity of 60,000 hr^?1 when the temperature was above 200 °C. Brunauer-Emmett-Teller, X-ray diffraction, and X-ray photoelectron spectroscopy analyses confirmed that catalyst displaying the highest activity contained the Mn⁴⁺ species and that its valence state was highly dependent on the pH during the catalyst preparation.

Implications Recently, various Mn catalysts have been evaluated as selective catalyst reduction (SCR) catalysts. However, in these previous studies, only the reaction characteristics and catalytic activity on the NH₃ SCR over Mn catalysts were evaluated. There have been no studies on the effect of pH during catalyst preparation. Therefore, in this study, the effect of pH during the catalyst preparation process was examined and a new application of the Mn catalysts was proposed based on the current findings.     

Study on the removal of elemental mercury from simulated flue gas by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>/AC at low temperature

Fe₂O₃ and CeO₂ modified activated coke (AC) synthesized by the equivalent-volume impregnation were employed to remove elemental mercury (Hg⁰) from simulated flue gas at a low temperature. Effects of the mass ratio of Fe₂O₃ and CeO₂, reaction temperature, and individual flue gas components including O₂, NO, SO₂, and H₂O (g) on Hg⁰ removal efficiency of impregnated AC were investigated. The samples were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Results showed that with optimal mass percentage of 3 % Fe₂O₃ and 3 % CeO₂ on Fe3Ce3/AC, the Hg⁰ removal efficiency could reach an average of 88.29 % at 110 °C. Besides, it was observed that O₂ and NO exhibited a promotional effect on Hg⁰ removal, H₂O (g) exerted a suppressive effect, and SO₂ showed an insignificant inhibition without O₂ to some extent. The analysis of XPS indicated that the main species of mercury on used Fe3Ce3/AC was HgO, which implied that adsorption and catalytic oxidation were both included in Hg⁰ removal. Furthermore, the lattice oxygen, chemisorbed oxygen, and/or weakly bonded oxygen species made a contribution to Hg⁰ oxidation.     

Sensitivity of tropospheric oxidants to global chemical and climate change

A photochemical model has been used to quantify the sensitivity of the tropospheric oxidants O₃ and OH to changes in CH₄, CO and NO emissions and to perturbations in climate and stratospheric chemistry. Coefficients of the form ∂1n[O₃]/∂1n[X] and ∂1n[OH]/∂1n[X], where [X] = flux of CH₄, CO, NO; stratospheric O₃ and H₂O have been calculated for a number of “chemically coherent” regions (e.g. nonpolluted continental, nonpolluted marine, urban) at low and middle latitudes. Sensitivities in O₃ and OH vary with regional emissions patterns and are nonlinear within a given region as [X] changes. In most cases increasing CH₄ and CO emissions will suppress OH (negative coefficients) and increase O₃ (positive coefficients) except in areas where NO and O₃ influenced by pollution are sufficient to increase OH. Stratospheric O₃ depletion will tend to decrease O₃ (except in high NO_x areas) and increase OH through enhanced u.v. photolysis. Increased levels of water vapor (one possible outcome of a global warming) will also decrease O₃ and increase OH. We conclude that in most regions, NO, CO and CH₄ emission increases will suppress OH and increase O₃, but these trends may be opposed by stratospheric O₃ depletion and climate change. A regional survey of OH and O₃ levels suggests that the tropics have a pivotal role in determining the earth's future oxidizing capacity.