Catalytic removal of SO2, NO and HCl from incineration flue gas over activated carbon-supported metal oxides

Activated carbon-supported copper, iron, or vanadium oxide catalysts were exposed to incineration flue gas to investigate the simultaneous catalytic oxidation of sulfur dioxide/hydrogen chloride and selective catalytic reduction of nitrogen oxide by carbon monoxide. The results show that AC-supported catalysts exhibit higher activities for SO₂ and HCl oxidation than traditional γ-Al₂O₃-supported catalysts and the iron and vanadium catalysts act as catalysts instead of sorbents, and can decompose sulfate with evolution of SO₃ and then regenerate for more SO₂ adsorption to take place. The AC-supported catalysts also display a high activity for NO reduction with CO generated from a flue gas incineration process and the presence of SO₂ in the incineration flue gas can significantly promote catalytic activity. Using CO as the reducing agent for NO reduction is more effective than using NH₃, because NH₃ may be partially oxidized in the presence of excess O₂ (12 vol%. in the incineration flue gas used) to form N₂, which can decrease the overall extent of NO reduction.     

Investigation of flue-gas treatment with O3 injection using NO and NO2 planar laser-induced fluorescence

Direct ozone (O₃) injection is a promising flue-gas treatment technology based on oxidation of NO and Hg into soluble species like NO₂, NO₃, N₂O₅, oxidized mercury, etc. These product gases are then effectively removed from the flue gases with the wet flue gas desulfurization system for SO₂. The kinetics and mixing behaviors of the oxidation process are important phenomena in development of practical applications. In this work, planar laser-induced fluorescence (PLIF) of NO and NO₂ was utilized to investigate the reaction structures between a turbulent O₃ jet (dry air with 2000 ppm O₃) and a laminar co-flow of simulated flue gas (containing 200 ppm NO), prepared in co-axial tubes. The shape of the reaction zone and the NO conversion rate along with the downstream length were determined from the NO-PLIF measurements. About 62% of NO was oxidized at 15d (d, jet orifice diameter) by a 30 m/s O₃ jet with an influence width of about 6d in radius. The NO₂ PLIF results support the conclusions deduced from the NO-PLIF measurements.     

Activity and characterization of Rh/Al2O3 and Rh-Na/Al2O3 catalysts for the SCR of NO with CO in the presence of SO2 and HCl

SO₂ and HCl are major pollutants emitted from waste incineration processes. Both pollutants are difficult to remove completely and can enter the catalytic reactor. In this work, the effects of SO₂ and HCl on the performance of Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts for NO removal were investigated in simulated waste incineration conditions. The characterizations of the catalysts were analyzed by BET, SEM/EDS, XRD, and ESCA. Experimental results indicated the 1%Rh/Al₂O₃ catalyst was significantly deactivated for NO and CO conversions when SO₂ and HCl coexisted in the flue gas. The addition of between 2 and 10 wt.% Na promoted the activity of the 1%Rh/Al₂O₃ catalyst for NO removal, but decreased the CO oxidation and BET surface area. The catalytic activity for NO removal was inhibited by HCl as a result of the formation of RhCl₃. Adding Na to the Rh/Al₂O₃ catalyst decreased the inhibition of SO₂ because of the formation of Na₂SO₄, which was observed in the XRD and ESCA analyses. SEM mapping/EDS showed that more S was residual on the surface of the Rh-Na/Al₂O₃ catalyst than Cl.     

Impacts of acid gases on mercury oxidation across SCR catalyst

A series of bench-scale experiments were completed to evaluate acid gases of HCl, SO₂, and SO₃ on mercury oxidation across a commercial selective catalytic reduction (SCR) catalyst. The SCR catalyst was placed in a simulated flue gas stream containing O₂, CO₂, H₂O, NO, NO₂, and NH₃, and N₂. HCl, SO₂, and SO₃ were added to the gas stream either separately or in combination to investigate their interactions with mercury over the SCR catalyst. The compositions of the simulated flue gas represent a medium-sulfur and low- to medium-chlorine coal that could represent either bituminous or subbituminous. The experimental data indicated that 5–50 ppm HCl in flue gas enhanced mercury oxidation within the SCR catalyst, possibly because of the reactive chlorine species formed through catalytic reactions. An addition of 5 ppm HCl in the simulated flue gas resulted in mercury oxidation of 45% across the SCR compared to only 4% mercury oxidation when 1 ppm HCl is in the flue gas. As HCl concentration increased to 50 ppm, 63% of Hg oxidation was reached. SO₂ and SO₃ showed a mitigating effect on mercury chlorination to some degree, depending on the concentrations of SO₂ and SO₃, by competing against HCl for SCR adsorption sites. High levels of acid gases of HCl (50 ppm), SO₂ (2000 ppm), and SO₃ (50 ppm) in the flue gas deteriorate mercury adsorption on the SCR catalyst.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

介质阻挡放电中气体成分对NOx脱除的影响

利用介质阻挡放电(DBD)产生低温等离子体进行烟气的脱硝实验,研究了在乙烯存在的条件下,温度和其他烟气成分对NO_x脱除率的影响。结果表明:随着温度的升高,NO脱除速率增快;模拟烟气中加入CO₂,在能量密度较低时,CO₂作为电负性分子会降低自由基的生成,导致NO的脱除率降低,随着能量密度的升高,CO₂对NO脱除的影响减小;模拟烟气中加入水后可以产生更多的OH、HO₂等自由基,促进NO的氧化;SO₂的加入会与自由基O反应,使初始反应中O与C₂H₄的反应速率减弱,从而影响了NO的氧化速率,但O₃、HO₂等强氧化自由基会优先与NO反应,因此SO₂的加入不会影响NO最终的脱除率。     

Cobenefit of SO3 reduction on mercury capture with activated carbon in coal flue gas

Parametric experiments were carried out to study the interactions of mercury, SO₃, and injected activated carbon (AC) in a coal flue gas stream. The levels of SO₃ vapor in flue gas were altered by individually varying flue gas temperature, moisture, or sodium fume injection in the flue gas. Meanwhile, mercury emissions with AC injection (ACI) upstream of an electrostatic precipitator (ESP) were evaluated under varied SO₃ concentrations. SO₃ measurements using a condensation method indicated that low temperature, high moisture content, and sodium fume injection in flue gas shifted SO₃ partitioning from the vapor to particulate phase, subsequently improving mercury capture with ACI. 0.08 g/m³ of DARCO^® Hg-LH injection only provided approximately 20% mercury reduction across the ESP in a bituminous coal flue gas containing 28 ppm SO₃, but mercury capture was increased to 80% when the SO₃ vapor concentration was lowered less than 2 ppm. Experimental data clearly demonstrate that elevated SO₃ vapor is the key factor that impedes mercury adsorption on AC, mainly because SO₃ directly competes against mercury for the same binding sites and overwhelmingly consumes all binding sites.     

Catalytic Ozonation by Manganese,Iron and Cerium Oxides on γ-Al2O3 Pellets for the Degradation of Organic Pollutants in Continuous Fixed-Bed Reactor

ABSTRACT

Heterogeneous catalytic ozonation is an efficient technology for degrading refractory organic pollutants in water. However, most studied heterogeneous catalysts for catalytic ozonation were powders, which were not practically available for continuous fixed-bed reactor in water treatment. In this work, manganese, iron and cerium oxides on γ-Al₂O₃ pellets were synthesized and used as heterogeneous catalysts for catalytic ozonation in a continuous fixed-bed reactor. Results showed that all the prepared metal oxides on γ-Al₂O₃ pellets exhibited facilitated catalytic ozonation for degrading refractory contaminates compared with ozonation alone and catalytic ozonation on pure γ-Al₂O₃ pellets. The cerium oxides supported on γ-Al₂O₃ pellets (CeO₂/γ-Al₂O₃) performed best catalytic performance with the COD removal efficiency of 64.3% and TOC removal efficiency of 41.7%. Moreover, the catalytic activity was further enhanced by the synergistic effect of the bimetallic oxides on γ-Al₂O₃ pellets (CeO₂-Fe₂O₃/γ-Al₂O₃). This study is expected to help to encourage further research and applications in AOPs based on the success of this work in designing heterogeneous catalysts available for continuous fixed-bed reactor.     

CO2 adsorption and activation over γ-Al2O3-supported transition metal dimers: A density functional study

Catalytic conversion of CO₂ to liquid fuels has the benefit of reducing CO₂ emission. Adsorption and activation of CO₂ on the catalyst surface are key steps of the conversion. Herein, we used density functional theory (DFT) slab calculations to study CO₂ adsorption and activation over the γ-Al₂O₃-supported 3d transition metal dimers (M₂/γ-Al₂O₃, M = Sc–Cu). CO₂ was found to adsorb on M₂/γ-Al₂O₃ negatively charged and in a bent configuration, indicating partial activation of CO₂. Our results showed that both the metal dimer and the γ-Al₂O₃ support contribute to the activation of the adsorbed CO₂. The presence of a metal dimer enhances the interaction of CO₂ with the substrate. Consequently, the adsorption energy of CO₂ on M₂/γ-Al₂O₃ is significantly higher than that on the γ-Al₂O₃ surface without the metal dimer. The decreasing binding strength of CO₂ on M₂/γ-Al₂O₃ as M₂ changes from Sc₂ to Cu₂ was attributed to decreasing electron-donation by the supported metal dimers. Hydroxylation of the support surface reduces the amount of charge transferred to CO₂ for the same metal dimer and weakens the CO₂ chemisorption bonds. Highly dispersed metal particles maintained at a small size are expected to exhibit good activity toward CO₂ adsorption and activation.     

Gas-phase elemental mercury capture by a V2O5/AC catalyst

Gas-phase elemental mercury (Hg⁰) capture by an activated coke (AC) supported V₂O₅ (V₂O₅/AC) catalyst was studied in simulated flue gas and compared with that by the AC. The study on the influences of V₂O₅ loading, temperature, capture time and flue gas components (O₂, SO₂, H₂O and N₂) shows that the Hg⁰ capture capability of V₂O₅/AC is much higher than that of AC. It increases with an increase in V₂O₅ loading and is promoted by O₂, which indicates the important role of V₂O₅ in Hg⁰ oxidation and capture; it is promoted slightly by SO₂ but inhibited by H₂O; it increases with an increase in temperature up to 150 °C when Hg desorption starts. X-ray photoelectron spectroscopy analysis and sequential chemical extraction experiments indicate that the main states of Hg captured on V₂O₅/AC are HgO and HgSO₄. Temperature programmed desorption experiments were also made to understand the stability of the Hg captured.     

Mo and Co doped V2O5/AC catalyst-sorbents for flue gas SO2 removal and elemental sulfur production

Flue gas SO₂ removal at 200 °C over Mo and Co doped V₂O₅/AC catalyst-sorbents and regeneration of the used catalyst-sorbents in H₂ at 380 °C in the same reactor are studied in this paper. Compared with V₂O₅/AC, the catalyst-sorbents containing Co show higher SO₂ uptake while the one containing Mo shows a slightly lower SO₂ uptake. Elemental sulfur is produced during H₂-regeneration of the used catalyst-sorbents when effluent gas of the regeneration is recycled back to the reactor. H₂-regeneration of the used V₂O₅/AC produces little elemental sulfur, but the Mo and Co doped ones show high elemental sulfur yields with an elemental sulfur selectivity of 50% for a catalyst-sorbent containing 2% V₂O₅, 0.5% MoO₃ and 0.5% CoO, V2Mo0.5 Co0.5/AC. Molybdenum and cobalt sulfides are likely formed in the regeneration, which catalyze the elemental sulfur formation but reduce the SO₂ uptake of the catalyst-sorbents in the subsequent SO₂ removal stage.     

SO2 and NO removal from flue gas over V2O5/AC at lower temperatures — role of V2O5 on SO2 removal

Supporting V₂O₅ onto an activated coke (AC) has been reported to significantly increase the AC's activity in simultaneous SO₂ and NO removal from flue gas. To understand the role of V₂O₅ on SO₂ removal, V₂O₅/AC is studied through SO₂ removal reaction, surface analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) techniques. It is found that the main role of V₂O₅ in SO₂ removal over V₂O₅/AC is to catalyze SO₂ oxidation through a VOSO₄-like intermediate species, which reacts with O₂ to form SO₃ and V₂O₅. The SO₃ formed transfers from the V sites to AC sites and then reacts with H₂O to form H₂SO₄. At low V₂O₅ loadings, a V atom is able to catalyze as many as 8 SO₂ molecules to SO₃. At high V₂O₅ loadings, however, the number of SO₂ molecules catalyzed by a V atom is much less, due possibly to excessive amounts of V₂O₅ sites in comparison to the pores available for SO₃ and H₂SO₄ storage.     

Reduction of NO by CO on Cu/ZrO2/Al2O3 catalysts: Characterization and catalytic activities

ZrO₂, γ-Al₂O₃ and ZrO₂/γ-Al₂O₃-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO₂/γ-Al₂O₃ matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO₂. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO₂.     

Removal of elemental mercury from simulated coal-combustion flue gas using a SiO2–TiO2 nanocomposite

A novel silica–titania (SiO₂–TiO₂) nanocomposite has been developed to effectively capture elemental mercury (Hg⁰) under UV irradiation. Previous studies under room conditions showed over 99% Hg⁰ removal efficiency using this nanocomposite. In this work, the performance of the nanocomposite on Hg⁰ removal was tested in simulated coal-fired power plant flue gas, where water vapor concentration is much higher and various acid gases, such as HCl, SO₂, and NO_x, are present. Experiments were carried out in a fix-bed reactor operated at 135 °C with a baseline gas mixture containing 4% O₂, 12% CO₂, and 8% H₂O balanced with N₂. Results of Hg speciation data at the reactor outlet demonstrated that Hg⁰ was photocatalytically oxidized and captured on the nanocomposite. The removal efficiency of Hg⁰ was found to be significantly affected by the flue gas components. Increased water vapor concentration inhibited Hg⁰ capture, due to the competitive adsorption of water vapor. Both HCl and SO₂ promoted the oxidation of Hg⁰ to Hg(II), resulting in higher removal efficiencies. NO was found to have a dramatic inhibitory effect on Hg⁰ removal, very likely due to the scavenging of hydroxyl radicals by NO. The effect of NO₂ was found to be insignificant. Hg removal in flue gases simulating low rank coal combustion products was found to be less than that from high rank coals, possibly due to the higher H₂O concentration and lower HCl and SO₂ concentrations of the low rank coals. It is essential, however, to minimize the adverse effect of NO to improve the overall performance of the SiO₂–TiO₂ nanocomposite.     

SO2 oxidation over the V2O5/TiO2 SCR catalyst

The effects of V₂O₅ loading of the V₂O₅/TiO₂ SCR catalyst on SO₂ oxidation activity were examined by infrared spectroscopy (DRIFT) and SO₂ oxidation measurement. Vanadium oxide added to the catalyst was found to be well dispersed over the TiO₂ carrier until covered with monolayer V₂O₅. The rate of SO₂ oxidation increased almost linearly with V₂O₅ loading below the monolayer capacity and attained saturation with further increase. The hydroxyl groups bonded to vanadium atoms, V–OH, might be altered by SO₂ oxidation. Both V=O and V–OH groups are likely involved in the adsorption and desorption of SO₂ and SO₃.     

Enhanced catalytic activity of Pt/Al2O3 on the CH4 SCR

In this study, we investigated the effect of mixing α-Al₂O₃ and γ-Al₂O₃ with a Pt catalyst on CH₄ selective catalytic reduction (SCR). Among the prepared catalysts, the Pt/α-Al₂O₃ catalyst was found to have the lowest catalytic activity, but the best adsorption characteristics for CH₄, which was used as the reductant. In contrast, the Pt/γ-Al₂O₃ catalyst was found to exhibit relatively high catalytic activity and moderate adsorption characteristics. To simultaneously enhance the catalytic activity and CH₄ adsorption characteristics, we developed a new catalyst, Pt/γ-Al₂O₃ + Pt/α-Al₂O₃, by mixing α-Al₂O₃ and γ-Al₂O₃ with a Pt catalyst. The catalytic activity test confirmed that mixing these catalysts led to enhanced catalytic activity.     

Deactivation and coke formation on palladium and platinum catalysts in vegetable oil hydrogenation

Deactivation of palladium and platinum catalysts due to coke formation was studied during hydrogenation of methyl esters of sunflower oil. The supported metal catalysts were prepared by impregnating γ-alumina with either palladium or platinum salts, and by impregnating α-alumina with palladium salt. The catalysts were reused for several batch experiments. The Pd/γ-Al₂O₃ catalyst lost more than 50% of its initial activity after four batch experiments, while the other catalysts did not deactivate. Samples of used catalysts were cleaned from remaining oil by repeated extractions with methanol, and the amount of coke formed on the catalysts was studied by temperature-programmed oxidation. The deactivation of the catalyst is a function of both the metal and the support. The amount of coke increased on the Pd/γ-Al₂O₃ catalyst with repeated use, but the amount of coke remained approximately constant for the Pt/γ-Al₂O₃ catalyst. Virtually no coke was detected on the Pd/α-Al₂O₃ catalyst. The formation of coke on Pd/α-Al₂O₃ may be slower than on the Pd/γ-Al₂O₃ owing to the carrier’s smaller surface area and less acidic character. The absence of deactivation for the Pt/γ-Al₂O₃ catalyst may be explained by slower formation of coke precursors on platinum compared to palladium.     

Mineralization of Ibuprofen and Humic Acid through Catalytic Ozonation

Advanced oxidation methods are used to remove traces of pharmaceuticals from aquatic environments. The application of a catalyst improves the total organic carbon removal during ozonation of pharmaceuticals in water. The aim of this study was to use MnO₂-CuO/ γ-Al₂O₃ catalyst for ozonation of ibuprofen (5 mgL^?1) and evaluate the effect of the presence of humic acid in the removal process. The presence of the catalyst increased the mineralization percentage of ibuprofen from 27% for noncatalytic ozonation to 55% in the presence of catalyst. The presence of humic acid increased noncatalytic mineralization by 10%. The reusability and stability of the catalyst, and its ability to adsorb reaction by-products were demonstrated.     

P123辅助SB粉溶胶制备大孔径介孔γ-Al2O3及其对甲基蓝的强化吸附性能

以硝酸解胶的工业拟薄水铝石SB粉溶胶为铝源、三嵌段共聚物P123为结构调节剂,采用溶剂蒸发诱导自组装法成功地制备了甲基蓝吸附性能显著增强的大孔径介孔γ-Al₂O₃。运用XRD、N₂吸附-脱附、TEM和UV-Vis对比研究了水热预处理SB粉溶胶与否对产物结构、织构性质、形貌和甲基蓝吸附性能的影响。结果表明,所制备的大孔径介孔γ-Al₂O₃具有优异的甲基蓝吸附性能并满足Langmuir吸附等温式,吸附300 mg·L-1的甲基蓝溶液60 min和3000 mg·L-1的甲基蓝溶液150 min时,其平衡吸附量分别高达267、1500 mg·g-1,远高于同一条件下SB粉焙烧产物γ-Al₂O₃的平衡吸附量150、1080 mg·g-1;水热预处理能增加产物的比表面积并提高其对甲基蓝的吸附速率,但对其均匀的介孔结构和平衡吸附量无显著影响。本研究为介孔氧化铝用于废水中甲基蓝等染料的吸附提供了新的契机。