Superior pillared clay catalysts for selective catalytic reduction of nitrogen oxides for power plant emission control

Fe(3+)-, Cr(3+)-, Cu(2+)-, Mn(2+)-, Co(2+)-, and Ni(2+)-exchanged Al2O3-pillared interlayer clay (PILC) or TiO2-PILC catalysts are investigated for the selective catalytic reduction (SCR) of nitric oxide by ammonia in the presence of excess oxygen. Fe(3+)-exchanged pillared clay is found to be the most active. The catalytic activity of Fe-TiO2-PILC could be further improved by the addition of a small amount of cerium ions or cerium oxide. H2O and SO2 increase both the activity and the product selectivity to N2. The maximum activity on the Ce-Fe-TiO2-PILC is more than 3 times as active as that on a vanadium catalyst. Moreover, compared to the V2O5-WO3/TiO2 catalyst, the Fe-TiO2-PILC catalysts show higher N2/N2O product selectivities and substantially lower activities (by approximately 85%) for SO2 oxidation to SO3 under the same reaction conditions. A 100-hr run in the presence of H2O and SO2 for the CeO2/Fe-TiO2-PILC catalyst showed no decrease in activity.     

TiO2纳米管催化活性再生处理技术简

采用H₂O₂、Fe₂（SO₄）₃和Fenton溶液对失活的TiO₂纳米管进行再生处理,重点考察了3种溶液的浓度和处理时间等对再生效果的影响,初步分析了经处理后TiO₂纳米管催化活性得到再生或增强的机理。结果表明,经H₂O₂溶液处理后TiO₂催化活性能得到有效再生,经Fe₂（SO₄）₃和Fenton溶液处理后其催化活性不仅得到再生,还能显著增强,这与H₂O₂和Fenton的强氧化作用,及进入TiO₂纳米管的Fe³⁺的阻止电子-空穴对再复合作用有关。     

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.     

改进钒基SCR脱硝催化剂的抗碱金属中毒性能

以锐钛矿型二氧化钛和钛钨粉(5%WO3-TiO2)为载体,制备了系列钒和钨负载量不同的钒钛催化剂,考察碱金属和碱土金属(钾、钠和钙)对催化剂在氨选择性催化还原(NH3-SCR)氮氧化物反应中催化活性的影响。钾、钠和钙对钒钛催化剂的中毒影响大小顺序为钾钠钙。提高钒钛催化剂中钒的含量可显著提高催化剂的SCR活性和抗碱金属中毒性能,但高钒负载量(4.5%V2O5)造成催化剂氮气选择性明显下降,氧化亚氮生成显著增加。钨的添加有利于提高钒钛催化剂的低温活性和抗碱金属中毒性能,对氮气选择性无明显影响。     

Catalytic oxidation for air pollution control

Bench-scale experiments have been conducted to evaluate a series of titania-supported Pt-Pd (as oxides) catalysts in the presence and absence of MoO₃ and Fe₂O₃ additives for their effectiveness in the complete catalytic oxidation of volatile organic compounds (VOCs) in air likely to be found in waste gases. Under oxidizing conditions, all of the catalysts promoted the complete oxidation of VOCs to CO₂ and H₂O. 99 % Conversion was achieved with a C₂H₄-C₂H₆ gas mixture in air at temperatures between about 160–450 °C and at a space velocity of 20,000 h^?1. Oxidation activity for the titania supported catalysts were found to decrease in the order Pt-Pd-Mo-Fe > Pt-Pd-Mo > Pt-Pd-Fe > Pt-Pd. However, the addition of MoO₃ and Fe₂O₃ increase the catalyst activity and reduce the reaction temperature for the complete destruction. Ageing was also performed in order to study the stability of the most active catalyst. Pt-Pd-Mo-Fe (as oxides) on titania catalyst is effective in oxidizing a wide range of volatile organic compounds at relatively low temperatures (220–405 °C) and and at a space velocity of 40,000 h^?1 and is resistant to poisoning by halogenated and amine volatile organic compounds.     

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.     

用于气态零价汞转化的催化剂研究

零价汞的高效去除是燃煤烟气汞污染控制过程中的关键环节。为了促进烟气中的零价汞转化为易于去除的氧化态汞,分别考察了在有HCl存在时,几种过渡金属氧化物(Cu、Fe、Mn、Co和Zr)对零价汞氧化的催化作用,以筛选出性能较好的催化组分;为提高催化剂的抗SO2性能,分别尝试了利用几种金属元素(Sr、Ce、W和Mo)对催化剂进行掺杂改性的方法。结果表明,锰氧化物的催化作用最好,其最佳使用温度在573 K左右;SO2对零价汞的催化氧化有明显抑制作用,在无SO2及1 400 mg/m3SO2时锰催化剂对零价汞催化氧化效率分别为93%和78%。而Mo改性的锰氧化物催化剂的抗硫性能大幅提高,在1 400 mg/m3SO2存在的情况下其对零价汞的催化氧化效率可达到90%以上,较其他改性元素高。     

Use of carbon-based composites to enhance performance of TiO<Subscript>2</Subscript> for the simultaneous removal of nitrates and organics from aqueous environments

The simultaneous photocatalytic removal of nitrate from aqueous environment in presence of organic hole scavenger using TiO₂ has long been explored. However, the use of unmodified TiO₂ in such reaction resulted in non-performance or release of significant amount of undesirable reaction products in the process, a problem that triggered surface modification of TiO₂ for enhanced photocatalytic performance. Previous studies focused on decreasing rate of charge carrier recombination and absorption of light in the visible region. Yet, increasing active sites and adsorption capacity by combining TiO₂ with a high surface area adsorbent such as activated carbon (AC) remains unexploited. This study reports the potential of such modification in simultaneous removal of nitrates and oxalic acid in aqueous environment. The adsorptive behaviour of nitrate and oxalic acid on TiO₂ and TiO₂/AC composites were studied. The Langmuir adsorption coefficient for nitrate was four times greater than that of oxalic acid. However, the amount of oxalic acid adsorbed was about 10 times greater than the amount of nitrate taken up. Despite this advantage, the materials did not appear to produce more active photocatalysts for the simultaneous degradation of nitrate and oxalic acid. The photocatalytic activity of TiO₂ and its carbon-based composites was improved by combination with Cu₂O particles. Consequently, 2.5 Cu₂O/TiO₂ exhibited the maximum photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, while selectivity stood at 45.7, 12.4 and 41.9% for NH₄⁺, NO₂^? and N₂, respectively. For the carbon based, 2.5 Cu₂O/TiO₂-20AC showed removal of 12.7% nitrate and 80.3% oxalic acid and achieved 21.6, 0 and 78.4% selectivity for NH₄⁺, NO₂^? and N₂, respectively. Using the optimal AC loading (20 wt%) resulted in significant decrease in the selectivity for NH₄⁺ with no formation of NO₂^?, which unveils that selectivity for N₂ and low/no selectivity for undesirable products can be manipulated by controlling the rate of consumption of oxalic acid. In contract, no nitrate reduction was observed with Cu₂O promoted TiO₂-T and its TiO₂-(T)-20AC, which may be connected to amorphous nature of TiO₂-T and perhaps served as charge carrier trapping sites that impeded activity.     

Sorption of chlorimuron-ethyl on montmorillonite clays: effects of exchangeable cations,pH, and ionic strength

Sorption interaction of chlorimuron-ethyl with montmorillonite clays was investigated under varied types of exchangeable cation, pH, and ionic strength conditions. Chlorimuron-ethyl sorption on bentonites exhibited pronounced cation dependency, and the sorption ability increased as the sequence Ca²⁺- < Na⁺- < Al³⁺- < Fe³⁺-bentonite, due to different sorption mechanisms, whereas the cation dependency was influenced by the clay type and much weaker for montmorillonites. The decrease of pH at the range of 4.0–6.0 prominently increased sorption of chlorimuron-ethyl on all cation-exchanged montmorillonite clays, and nearly a neglected sorption (about 2 %) can be observed at pH over 7.0. In the presence of CaCl₂, sorption of chlorimuron-ethyl on Fe³⁺-bentonite was promoted because of complexion of Ca²⁺ and the surface of Fe³⁺-bentonite. However, as the concentration of CaCl₂ increased, chlorimuron-ethyl sorption on Ca²⁺- and Fe³⁺-exchanged bentonite decreased, suggesting that Ca bridging was not the prevailing mechanism for sorption of chlorimuron-ethyl on these clays. Furthermore, chlorimuron-ethyl sorption was relatively sensitive to pH, and the change of pH may obscure effect of other factors on the sorption, so it was quite necessary to control pH at a constant value when the effect of other factor was being studied.     

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.     

Incinerating Volatile Organic Compounds with Ferrospinel Catalyst MnFe2O4: An Example with Isopropyl Alcohol

Abstract

This paper concerns the incineration of isopropyl alcohol (IPA) using the ferrospinel catalyst MnFe₂O₄. It covers the preparation of the ferrospinel catalyst, the screening of catalytic activity, catalytic incineration testing, and 72-hr decay testing of the catalyst. The experimental results of catalyst screening reveal that the Mn/Fe catalyst is the best of five prepared catalysts (chromium/iron [Cr/Fe], manganese/iron [Mn/Fe], zinc/iron [Zn/Fe], nickel/iron [Ni/Fe], and pure magnetite [Fe₃O₄]). In tests of the catalytic incineration system used to convert IPA, 98% conversion was obtained at a space velocity of 24,000 hr^?1, an oxygen (O₂) content of 21%, 1700 ppm of IPA, and a reaction temperature of 200 °C.     

Influence of Fe and mn ions on the incorporation of radioactive 35SO2 by sulfate aerosols

The rate of incorporation of radiolabeled sulfur dioxide has been determined in submicron sized ammonium sulfate droplet aerosols with and without catalytic metal ions (Fe³⁺, Mn²⁺). The sulfate droplets were generated by nebulizing solutions with a multiple jet Collison nebulizer and aged up to 30 min in a 10 m³ plug-flow reaction duct. Radiolabeled ³⁵SO₂ was metered into purified air to provide a concentration of 5 ppm.Three different atmospheres were studied: SO₂ in purified air, SO₂ in the presence of ammonium sulfate aerosol (1 mg m⁻³, 1 μm MMAD), and SO₂ in the presence of ammonium sulfate aerosol containing Fe³⁺ and Mn²⁺ ions. No measurable SO₂ conversion was detected in samples from atmospheres without the catalytic metal ions. A net SO₂ conversion rate equivalent to 0.02 % h⁻¹ was observed in the presence of Fe³⁺ and Mn²⁺ ions.     

Superior photodecomposition of pyrene by metal ion-loaded TiO2 catalyst under UV light irradiation

Background

The photocatalytic degradation of pyrene under UV (125?W Hg-Arc, 10.4?mW/cm²) irradiation of TiO₂ aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu²⁺, Fe³⁺, Ag⁺, and Au³⁺, etc. As the reduction potential of these metals lies below the conduction band (CB) position (?0.1?eV) of TiO₂, the photoexcited electron transfer occurs more readily and reduces electron?Chole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO₂ because of rapid Fermi energy equilibrium between the CB of TiO₂ and its surface adsorbed metal ions.

Results and discussion

The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni²⁺ having more negative reduction potential (?0.25?eV) than the CB of TiO₂ imparts negligible co-catalytic activity to TiO₂ photoreaction. It also revealed that loading of Au³⁺ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe⁺³ and Au³⁺ ions gradually increases from 0.1 to 2?wt.%, the pyrene photodecomposition rate also become faster.     

高压电弧放电处理偶氮染料废水

用高压电弧放电产生的低温等离子体对含偶氮染料的废水进行了处理,以甲基橙为例研究了电压幅值、处理时间、溶液初始浓度、溶液初始pH值、投加Fe^2＋和Fe^3＋对染料脱色的影响。实验结果表明,甲基橙浓度为50mg／L时其降解率随时间和电压幅值的增加而增加。溶液初始浓度对染料去除效果影响较为明显,同等条件下初始浓度越低降解率越高。酸性条件下有利于低温等离子体处理甲基橙。Fe^2＋和Fe^3＋对低温等离子体降解甲基橙有一定的催化作用。电压8kV处理3min,Fe^2＋为20mg／L时去除率由89．64％增至99．72％。Fe2（SO4）,的最佳投加量为5mg／L（以Fe^3＋计）,而FeCl,的最佳投加量为80mg／L（以Fe^3＋计）。     

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.     

Cu/La共掺杂TiO2光催化氧化水中的氨氮

采用水解-沉淀法制备了Cu/La共掺杂纳米TiO2催化剂,利用XRD、XPS和BET技术对其进行表征,并考察了在紫外灯下,共掺杂TiO2对氨氮的光催化氧化工艺条件。物相结构和比表面积测试结果表明,共掺杂催化剂具有较好的锐钛矿晶型,孔径分布为4～8 nm,Cu/La共掺杂TiO2La以La3+,Cu是以Cu2+、Cu+的形式掺杂进入TiO2的晶格。光催化实验表明:所得改性光催化剂对氨氮的去除及焦化废水的处理均具有较高的催化活性。     

燃煤烟气低温SCR脱硝中试研究

低温选择性催化还原(SCR)脱硝是国内外脱硝技术研发的热点,但目前主要集中在实验室小试范围,无法完全反映催化剂在实际烟气中的运行状况。在30 t/h循环流化床燃煤锅炉脱硫除尘装置后建设了2 000~5 000 m3/h的SCR脱硝中试装置,经系统研究发现,中试使用的蜂窝式催化剂对SO2和NO具有很强的吸附能力,且反应温度、喷氨速率和气体空速均会影响催化脱硝效率。为期5 d的连续运行实验结果表明,催化剂的脱硝效率一直稳定在30%~50%,并未发现明显的失活,这证明设计除雾除尘器、较大的混合器、混合器与反应器间较长的管路均有利于缓解催化剂因SO2、H2O和飞灰中的碱性金属导致的失活。     

New Fe-immobilized natural bentonite plate used as photo-Fenton catalyst for organic pollutant degradation

Novel photo-Fenton catalysts were prepared by immobilizing iron species on commercial bentonite plates via two methods: (1) ion exchange reaction (Fe³⁺ vs. Na⁺) by aqueous suspension powder-clay/FeCl₃ followed by plate preparation, and (2) forced hydrolysis of Fe(NO₃)₃ onto a prefabricated clay plate. The last method led to a more photo-active Fe-oxide/bentonite plate. This material allowed, at a non-adjusted initial pH of 5.5 and in the presence of H₂O₂, the total degradation of resorcinol and 55% mineralization in 80 and 100 min of irradiation, respectively. The reached degradation percentages were correlated to the presence of dissolved iron, demonstrating that in these processes, the homogeneous photo-Fenton reactions were mainly responsible for the resorcinol elimination.Likewise, in slurry system, where clay has normally an increased surface area, there was no increase in activity because of a reduced leached iron probably due to the diminished light penetration in the suspension. Despite the lower surface area, in comparison to that of the slurry, the clay plates have the advantage, as heterogeneous photo-catalysts, that separation of the reaction media after treatment is not needed, and thus, a potential use for batch and continuous reaction systems is proposed.     

光纤传导可见光降解亚甲基蓝

针对浓度大、色度高的印染废水难以处理的情况,选用加入光纤的光催化体系进行研究。采用溶胶凝胶法制备了Ag+/TiO2粉体光催化剂,用固体紫外可见光谱、X射线衍射对其进行表征。选用亚甲基蓝溶液作为目标降解物,评价了Ag+/TiO2在可见光下的光催化活性。分别考察了加入石英芯侧光光纤与塑料侧光光纤反应体系下,催化剂量、光纤数量、光照强度和pH值等因素对亚甲基蓝降解实验的影响。结果表明,选用20 mg/L的亚甲基蓝,采用催化剂量为11.67 g/L,500根侧光光纤,300 W的外部光源,pH值约为11时,光催化降解效果最佳,均能达到90%以上。     

The effects of manganese precursors on Mn-based/TiO2 catalysts for catalytic reduction of NO with NH3

Manganese acetate (MnAc) and manganese nitrate (MnN) were employed as precursors for the preparation of MnAc)/TiO2, Mn (N)/TiO2, Mn(Ac)-Ce/TiO2, and Mn(N)-Ce/TiO2 by impregnation. These complexes were used as catalysts in the low-temperature selective catalytic reduction of NO with NH3. The influence of manganese precursors on catalyst characteristics, the reduction activity, and the stability of the catalysts to poisoning by H2O and SO2 were studied. Experiments showed that Mn(N) produced MnO2 with large grain sizes in Mn(N)/TiO2 catalyst. On the contrary, Mn(Ac) led to highly dispersed and amorphous Mn2O3 in Mn (Ac)/TiO2 catalyst, which had better catalytic activity and stability to SO2 at low temperatures. The doping of cerium reduced the differences in catalytic performance between the catalysts derived from different Mn precursors.