A high-temperature electrostatic precipitator (ESP) is a good solution for hot gas cleaning to ensure the long-term stability of the production system in many energy-consuming industries. The high-carbon fly ash particles in the gasification of coal pyrolysis process are typical particles with low resistivity. In this paper, the characteristics of the coal pyrolysis furnace fly ash (ash A) were compared with coal-fired power plant fly ash (ash B). The effects of their characteristics on particle removal were compared in a wire-plate ESP. The particle collection efficiency was found to decrease with increasing temperature. From 363 to 523 K, the collection efficiencies of both ash samples were as high as above 95%. However, at 623 and 723 K, the collection efficiency of ash A was obviously lower than ash B. A method of enhancing particle removal was proposed by particle conditioning to reduce the occurrence of particle re-entrainment, and the fine calcium carbonate powders were used as the conditioning particles to improve the collection efficiency. When the ratio in mass was 1:1, the particle collection efficiency of ash A increased from 93.5% to 99.2% at 623 K by particle conditioning in the ESP. The optimal effect of conditioning occurred compared with different mix proportion because the resistivity of mixing particles was 1.01 × 108 Ω·cm, within the scope of normal resistivity for good operation of ESP.

In this work, the partitioning of hazardous trace elements among air pollution control devices in five ultra-low-emission coal-fired power plants was investigated. Results showed that most of the trace elements were enriched in fly ash at 58.0–93.3% (Hg), 75.2–95.3% (As), 78.2–94.9% (Cd), 79.4–96.6% (Se), 73.8–89.2% (Cr), and 86.5–99.5% (Pb). A low-low temperature electrostatic precipitator (LLT-ESP) and electric fabric filter (EFF) greatly increased the relative enrichment factors of Hg, As, and Se in fly ash up to 0.78–1.23, 0.85–1.04, and 0.83–0.99, respectively. In the wet flue gas desulfurization (WFGD) system, the concentrations of trace elements in fine fractions were much higher than those in coarse fractions. Large amounts of Hg (2.17–168 μg/kg), Se (21.3–357 μg/kg), and Cd (44.1–839 μg/kg) in wastewater needed special treatment to satisfy the discharge standard. The wet electrostatic precipitator (WESP) system removed hazardous trace elements mainly by capturing fine particles in the flue gas, and a small amount of hazardous trace elements (0.2–26%) were retained in the washing water. The concentrations of Hg in the fine particulates captured by WESP were 16.8–60.1 times of those in the fly ash, which could reach up to 17.5 mg/kg. The application of selective catalytic reduction + LLT-ESP/EFF + WFGD + WESP could effectively control the emission of hazardous trace elements in coal-fired power plants.

A wet electrostatic precipitator (ESP) is considered as an effective technology for the control of dust and acid mist after wet flue gas desulfurization. In this study, a lab-scale wet ESP was designed to investigate dust collection with residual SO2 in the flue gas. Results showed that dust collection efficiency was reduced in the presence of SO2. This finding is attributed to the sulfuric acid aerosol formation during the corona discharge process. An exponential increase of the aerosol number concentration was observed with the increasing applied voltage, which could be 2 orders of magnitude higher than that without corona discharge. Fractional aerosol size distribution indicated that the aerosol penetration ratio was extremely low, in the size range of 0.1–1.0 μm. The formation of sulfuric acid aerosol could only be detected when the specific energy density exceeded a threshold value. Dust collection efficiency decreased by 13.5% when the SO2 concentration increased from 0 to 25 ppm as a consequence of aerosol formation.

•Coupling plasma with Ce-doped catalysts enhanced plasma oxidation of ethyl acetate.•La0.9Ce0.1CoO3+δ catalyst showed the highest removal efficiency and COx selectivity.•Ce-doped catalysts generated more surface adsorbed oxygen species for oxidation.•Combining plasma with Ce-doped catalysts reduced the formation of by-products.In this work, plasma-catalytic oxidation of low concentration ethyl acetate (100 ppm) over La1-xCexCoO3+δ (x = 0, 0.05, 0.1, 0.3 and 0.5) perovskite catalysts was carried out in a coaxial dielectric barrier discharge (DBD) reactor. The effects of Ce-doping on the removal of ethyl acetate and COx (x = 1 and 2) selectivity in the plasma-catalytic oxidation process were investigated as a function of specific energy density (SED). Compared to the plasma reaction without a catalyst, the presence of the LaCoO3 catalyst in the plasma enhanced the removal of ethyl acetate and COx selectivity. The use of the Ce-doped catalysts further enhanced the performance of the plasma-catalytic oxidation process. The highest removal efficiency of ethyl acetate (100%) and COx selectivity (91.8%) were achieved in the plasma-catalytic oxidation of ethyl acetate over the La0.9Ce0.1CoO3+δ catalyst at a SED of 558 J L−1. The interactions between Ce and LaCoO3 resulted in an increased specific surface area (by 17.1%–68.6%) and a reduced crystallite size (by 13.5%–68.2%) of the Ce-doped LaCoO3 catalysts compared to pure LaCoO3, which favours the oxidation of ethyl acetate in the plasma process. Compared to the LaCoO3 catalyst, the Ce-doped perovskite catalysts showed higher content (maximum 54.9%) of surface adsorbed oxygen (Oads) and better reducibility, both of which significantly contributed to the enhanced oxidation of ethyl acetate and intermediates in the plasma-assisted surface reactions. The coupling of plasma with the Ce-doped catalysts also reduced the formation of by-products including NO2 and N2O. The possible reaction pathways involved in the plasma oxidation process have been discussed.Download high-res image (157KB)Download full-size image

•Characteristics of fly ash from a glass furnace were studied.•Properties of particle removal in ESP were studied at various temperatures.•The method “particle conditioning” was proposed and applied in industrial tests.•Mechanism of particle conditioning was preliminarily discussed.The flue gas generated from glass furnaces contains particles with high concentrations of alkali metals and hazardous heavy metals, which could reduce the lifespan of selective catalytic reduction (SCR) catalysts and lead to catalyst deactivation. Removing the particles before SCR could improve system operation reliability and reduce nitric oxides (NOx) emission. In this paper, the characteristics of fly ash from glass furnaces and the particle removal properties in the electrostatic precipitator (ESP) from 363 K to 623 K were studied. The particle collection efficiency was found to decrease with increasing temperature. A method of enhancing particle removal was proposed and tested through particle conditioning in a lab-scale experiment. In order to change the characteristics of the fly ash, calcium carbonate powders were used as conditioning particles and the particle collection efficiency increased from 65.8% to 87.6% at 623 K. This method was further applied in an industrial high-temperature ESP for a glass furnace. When the ratio in mass between the particles from the glass furnace and from the conditioning proportion was 1:1.5, the particle collection efficiency of the ESP was improved significantly and the outlet particle concentrations decreased from 103.23 mg/Nm3 to 39.25 mg/Nm3.Download high-res image (154KB)Download full-size image

•Effects of water droplet humidification on electric agglomeration were examined.•A novel sampling method was developed for agglomerated particle observation.•A theory of particle electric agglomeration modes was proposed.Electric agglomeration is a useful method to improve fly-ash particle collection efficiency in traditional electrostatic precipitators (ESPs) by increasing particle diameter and achieving particle pre-charging. In this study, a laboratory agglomerator, which consisted of a pre-charging region and a static mixer, was designed and tested for fine particle agglomeration. The pre-charging provided both positive and negative discharges in parallel channels. Fine water droplets were used to enhance particle agglomeration and collection efficiency in a downstream small ESP. The operating effects were evaluated under various applied voltages and droplet concentrations. Experimental results showed that the presence of water droplets effectively improved coal-fired particle agglomeration, pre-charging, and collection in the ESP. The total number collection efficiency improved from 53.91% to 86.02% compared with the condition without the agglomerator. In addition, a novel sampling method was used to observe agglomerated particles using scanning electron microscopy, and theoretical adhesive force analysis supported the proposal of a series of power-plant particle electric agglomeration modes.

•A novel method is proposed to modify the properties of metal oxide catalyst.•High catalytic efficiency is obtained by low O2 concentration plasma treatment.•Amorphous state Mn-O-Ce structure is formed by plasma preparation method.•The correlation of surface absorbed oxygen and Ce3+ species is obtained.•The correlation of catalytic activity and surface absorbed oxygen is obtained.Non-thermal plasma with different O2 concentration in discharge atmosphere was applied to synthesize manganese and cerium mixed-oxides catalysts, which were compared in NO oxidation activity. Discharge atmosphere displayed a crucial influence on the performance of the catalysts prepared by plasma. Relatively low O2 concentration in discharge atmosphere allows synthesizing manganese-cerium oxides catalysts in a moderate environment and therefore is favorable for better physicochemical properties which lead to superior catalytic behavior. The best catalyst was obtained by treatment with 10% O2/N2 plasma and presented over 80% NO conversion in the temperature range of 275–325 °C, whereas catalyst prepared in pure O2 discharge atmosphere had the same activity with a catalyst prepared by calcinations. A correlation between the surface properties of the plasma prepared catalysts and its catalytic activity in NO oxidation is proposed. The amount of the surface adsorbed oxygen has an obvious linear correlation with the amount of Ce3+, the H2 consumption at low temperatures and the catalytic performance. The superior catalytic performance is mainly attributed to the stronger interaction between manganese oxides and ceria, and the formation of poorly crystallized Mn-O-Ce phase in the catalyst which resulted from the slow decomposition of nitrates and organics during plasma treatment. Catalysts prepared in relatively low O2 concentration have large specific surface area and is abundant in Ce3+ species and active oxygen species. The study suggests that plasma treatment with proper discharge gas components is a promising method to prepare effective manganese- cerium oxides catalyst for NO oxidation.Download high-res image (79KB)Download full-size image

•V-Ce(SO4)2/Ti shows better low-T activity for standard SCR than commercial V-W/Ti.•Sodium resistance of V-Ce(SO4)2/Ti is enhanced.•V-Ce(SO4)2/Ti shows excellent durability in the presence of SO2 and H2O at 350 °C.•A redox mechanism accounting for the promoting effects is proposed.A series of V-Ce(SO4)2/Ti catalysts for selective catalytic reduction (SCR) of NO with ammonia are prepared by impregnation method. Low temperature SCR activity and alkali resistance of the optimal V-0.5Ce(SO4)2/Ti sample are found to be better than on the commercial V-W/Ti catalyst. Also, V-0.5Ce(SO4)2/Ti shows an excellent durability in the presence of SO2 and H2O, indicating to have prospects for the industrial application.Based on catalysts characterization and in-situ DRIFTS studies, a higher proportion of surface active oxygen generated by the introduction of Ce and a much faster H2 reduction point out the improved redox properties of V-0.5Ce(SO4)2/Ti, which results in a stronger NO oxidative activation and is confirmed by a more abundant formation of surface NO+ and NO3− species. When exposed to SCR conditions where both NH3 and NO are present, this enhanced NO activation can produce more reactive nitrite and/or NO+ intermediates which then readily react with adsorbed NH3 and decompose to N2 and H2O, accounting for the improved SCR activity of V-0.5Ce(SO4)2/Ti at low temperatures.The addition of Ce(SO4)2 also provides abundant reactive acid sites and adsorbed NH3 species thus increase. Even after Na poisoning, adequate surface acidity and redox properties still remain. Furthermore, relatively higher contents of V-OH are preserved owing to the interaction between Na and OSO, acting as a protection for the active sites. These promotional effects contribute to the better alkali resistance of V-0.5Ce(SO4)2/Ti. Therefore, all the results suggest that V-0.5Ce(SO4)2/Ti is a promising candidate as a catalyst for NH3-SCR in coal-fired power plants, especially under high Na-content conditions.Download high-res image (108KB)Download full-size image

•Novel hierarchical MnOx/TiO2 nanofiber catalysts were synthesized.•Catalysts were fabricated by combining electrospinning and hydrothermal growth.•Hierarchical structures were comprised of TiO2 nanofibers and MnOx nanoparticles.•As-synthesized samples displayed high oxidation performance on acetone.•The structure–activity relationships of hierarchical nanofibers was revealed.A novel hierarchical MnOx/TiO2 composite nanofiber was fabricated by combining the electrospinning technique and hydrothermal growth method. The synthesized nanomaterial, which comprised primary TiO2 nanofibers and secondary MnOx nanoneedles, was further investigated for complete catalytic oxidation of volatile organic compounds for the first time, and this presented high-oxidation performance on low-concentration acetone. The morphological, structural, physicochemical characterization, and catalytic performance analyses demonstrated that the highest catalytic activity was achieved from the obtained MnOx/TiO2 nanofiber catalyst with 30 wt.% manganese loading. This finding can be ascribed to the synergistic effect of the specific hierarchical nanofibrous morphology, the abundant surface-adsorbed oxygen, the superior redox property, and the sufficient specific surface.Download high-res image (151KB)Download full-size image

In China, industry is responsible for 88.15% of the sulfur dioxide emissions, of which coal-fired power plants account for around 35.62%. Moreover, over 90% of power plant had installed FGD implementers. On the road to an optimal economic emission control, this article develops an ILP algorithm to optimize the sorting SO2 emission control technology costs, based on a detailed database that contains large amounts of information for 1,966 thermal power plants, such as unit installed capacity and annual generating capacity, coal consumption, sulfur content, emission control technologies, operation duration and geographical location. The results demonstrate that the total operating costs will increase along with emission abatement. When the average desulfurization efficiency reaches 95%, 98% and 99%, the total operating cost in China is 54.4 billion CNY, 64.8 billion CNY and 78.6 billion CNY, respectively. Under the scenario that every power plant reaches the SO2 emission limitation, the total operating cost of following the least-cost retrofitting laws could reduce by 5.05% to 15.31% nationwide. Finally, the study suggests that desulfurization equipment with high removal efficiency should be installed primarily in larger units, and policymakers could develop cost-effectiveness control strategies for coal-fired power plants using the results of this paper.

•An updated industrial VOCs emission inventory was developed for 2011–2013 in China.•Variations in regions and source characteristics were investigated and analyzed.•Scenario were set to project industrial VOCs emissions for the year 2020, 2030 and 2050, which present the potential of the emissions reduction.The temporal trends of industrial volatile organic compound (VOC) emissions was comprehensively summarized for the 2011 to 2013 period, and the projections for 2020 to 2050 for China were set. The results demonstrate that industrial VOC emissions in China increased from 15.3 Tg in 2011 to 29.4 Tg in 2013 at an annual average growth rate of 38.3%. Guangdong (3.45 Tg), Shandong (2.85 Tg), and Jiangsu (2.62 Tg) were the three largest contributors collectively accounting for 30.4% of the national total emissions in 2013. The top three average industrial VOC emissions per square kilometer were Shanghai (247.2 ton/km2), Tianjin (62.8 ton/km2), and Beijing (38.4 ton/km2), which were 12–80 times of the average level in China. The data from the inventory indicate that the use of VOC-containing products, as well as the production and use of VOCs as raw materials, as well as for storage and transportation contributed 75.4%, 10.3%, 9.1%, and 5.2% of the total emissions, respectively. ArcGIS was used to display the remarkable spatial distribution variation by allocating the emission into 1 km × 1 km grid cells with a population as surrogate indexes. Combined with future economic development and population change, as well as implementation of policy and upgrade of control technologies, three scenarios (scenarios A, B, and C) were set to project industrial VOC emissions for the years 2020, 2030, and 2050, which present the industrial VOC emissions in different scenarios and the potential of reducing emissions. Finally, the result shows that the collaborative control policies considerably influenced industrial VOC emissions.

A series of Ce–Nb oxide catalysts were synthesized at different calcination temperatures for the selective catalytic reduction (SCR) of NO with NH3 and the reaction pathway and reactive species were investigated in detail. The SCR reaction pathway over the Ce–Nb catalysts followed both the Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism, where the former contributed more especially at high reaction temperatures. Lewis acidity was found to be catalytically important in the Eley–Rideal mechanism. NO2 and monodentate nitrate were the main reactive species in the Langmuir–Hinshelwood mechanism. The catalyst calcined at lower temperatures exhibited higher catalytic activity at low temperatures but lower activity at high temperatures. With the increase in calcination temperature, the catalyst surface was gradually covered with niobium oxide species, resulting in the enhancement of total acidity but the decline of redox ability, along with the decrease in the contribution of the Langmuir–Hinshelwood mechanism to the SCR reaction.

The relationship between the molecular structure of V2O5/TiO2 catalysts and the reactivity of SO2 oxidation was investigated. The dispersion state and surface properties of supported vanadia over V2O5/TiO2 catalysts were studied with various experimental techniques. Isolated vanadia species were dispersed on the TiO2 surface as Ti–O–V bonds at VOx coverage far below the monolayer. Polymeric vanadia species were then formed through the V–O–V bonds as the VOx coverage increased. SO2 temperature-programmed desorption and in situ diffuse reflectance infrared Fourier transform spectroscopy were conducted to study the interaction between SO2 and V2O5/TiO2. On the V2O5/TiO2 catalysts, the turnover frequency of SO2 oxidation was almost constant with increased VOx coverage under the condition of constant temperature. VO was demonstrated to play a critical role in the SO2 adsorption and oxidation. A possible reaction mechanism was established in this study.

•Electrode optimization of high-temperature ESP was investigated.•The variety of electrodes to particle collection at different temperature was discussed.•The effect of electrode configuration for particles of different sizes was investigated.This study investigated the influence of electrode configuration on corona discharge and particle collection from 300 K to 900 K. Electrodes of different shapes (rod, saw, and screw), diameters (3, 5, and 8 mm), and intervals (55, 110, and 165 mm) were tested in an experimental-scale electrostatic precipitator (ESP). Results showed that a high current was generated with a saw electrode and increased the particle collection efficiency, particularly for fine particles (diameter smaller than 0.1 μm), with the best particle collection efficiency being 99.8% at 300 K. However, with an increase in temperature, the rod electrode obtained an applied voltage higher than those of other electrode types and, as a result, generated relatively high particle collection efficiencies at 700 K and 900 K. Increasing the electrode diameter from 3 mm to 5 mm improved the applied voltage, whereas increasing this diameter from 5 mm to 8 mm reduced the discharge current. Among electrodes with different diameters, the electrode with a diameter of 5 mm achieved the best particle collection efficiency (87.4%) at 900 K. The applied voltages of the electrodes with different intervals were almost similar, but the discharge currents varied significantly. The best particle collection efficiencies were achieved by the electrode with an interval of 55 mm at 300 K and 500 K, but at 700 K and 900 K, the electrode with an interval of 110 mm obtained the best result. The interval between electrodes should be expanded with an increase in temperature to avoid the offsetting of electric field between neighboring electrodes.

A series of copper- and manganese-containing ordered mesoporous carbons (OMCs) were synthesized for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The results demonstrated that NO conversion can be greatly improved by the addition of Cu or Mn. In addition, Cu and Mn had a synergetic effect and the optimal catalytic performance was obtained over the bimetallic catalyst Cu5Mn5-OMC. N2 sorption, small-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm the ordered mesoporous structures. Wide-angle XRD results showed that in the bimetallic catalysts some Cu ions were substituted by Mn ions, resulting in lattice contraction by the formation of a solid solution. X-ray photoelectron spectroscopy (XPS) results indicated that the O–CO groups and chemisorbed oxygen species increased with the addition of Cu or Mn. Temperature-programmed desorption of CO/CO2 and NH3 (CO/CO2-TPD and NH3-TPD) results verified that the acidity of the catalyst was enhanced by the addition of Cu and Mn and the bimetallic catalyst Cu5Mn5-OMC had the strongest acidity. Temperature-programmed reduction of H2 (H2-TPR) results showed that Cu5Mn5-OMC had the strongest oxidizing capacity. Based on the above analysis, a possible synergetic catalytic effect was proposed through the electron transfer between Cu and Mn ions.

A controllable strategy to fabricate novel hierarchical V2O5/TiO2 nanofiber catalysts was proposed. The catalysts, which comprised primary TiO2 nanofibers and secondary V2O5 nanoparticles, were fabricated by combining electrospinning and hydrothermal growth. The controllable synthesis process and possible formation mechanism were also demonstrated through a series of time-dependent experiments. The hierarchical V2O5/TiO2 nanofiber catalysts were further applied in the oxidation of volatile organic compounds for the first time and were found to present a high oxidation performance for acetone. The morphological, structural, chemical characterization and catalytic performance analyses illustrated the highest catalytic activity was obtained from the synthesized V2O5/TiO2 nanofiber catalyst with 5 wt% V2O5. This finding could be attributed to the combined effect of the specific hierarchical nanofibrous morphology, abundant oxygen vacancies, and appropriate vanadium concentration.

•The particle collection in a high temperature ESP was studied.•The voltage–current characteristic of the ESP was highly affected by temperature.•The mechanism of particle migration and collection in ESP was discussed.An experimental-scale electrostatic precipitator (ESP) was built to investigate the characteristics of corona discharge, particle migration, and particle collection at various temperatures ranging from 300 K to 900 K. The variations in particle collection efficiencies and migration velocities with temperature, applied voltage, current density, energy consumption density, particle concentration, and flue gas velocity were obtained. Both onset and spark voltages decreased with an increase in temperature and resulted in a decrease in particle collection efficiency and particle migration velocity. At the same voltage, a large current was generated at high temperature; particle charging was enhanced, and high particle collection efficiencies and particle migration velocities were obtained. At the same current and energy consumption densities, the particle collection efficiencies decreased because of the low electric field intensity. The increase in particle concentration was favorable to particle collection and improved the particle migration velocities. The increase in flue gas velocity reduced the particle collection efficiencies and had minimal influence on the particle migration velocities.

China owns the world’s largest capacity of coal-fired power units. By the end of 2012, the capacity of installed national thermal power has been 819.68 million kilowatts. The latest standard requires that newly built power plants emit SO2 in no more than 100 mg/m3 and the emission of old ones be lower than 200 mg/m3 while in some key areas the emission should be controlled under 50 mg/m3. So by the end of 2012, 90 % of the active coal-fired units have been equipped with flue gas desulfurization devices. Among the desulfurization methods adopted, limestone-gypsum wet flue gas desulphurization accounts for 92 %, causing the problem of fine droplets in the exhaust gas after defogger, which may even form “gypsum rain.” At present, sampling methods are widely used at home and abroad, such as magnesium ion tracer method, modified magnesium ion tracer method and chemical analysis. In addition, some scholars use aerodynamic methods, such as ELPI, to measure the diameter distribution and concentration. The methods mentioned above all have their own demerits, such as the inability to on-line, continuous measurements and the need of prolonged measuring time. Thus, in this paper some potential optical on-line methods are presented, such as Fraunhofer diffraction pattern analysis and wavelength-multiplexed laser extinction. Also brought up are their measuring scope and merits. These methods have already been utilized to measure small liquid droplets and their demonstrations and evaluations are as well stated. Finally, a 3D imaging method based on digital holographic microscope is proposed for in-line measurement of size and concentration of slurry droplets. The feasibility of this method is demonstrated by preliminary experimental investigation.

An experimental study on the regeneration of deactivated SCR catalysts was carried out using a microwave-assisted method containing three steps of washing with mixed liquid of ethanol and water, impregnating, and drying. After the regeneration treatment, NO conversion at 320 °C increased from 39 to 90 % and vanadium content increased by 62.2 %, which were much higher than those regenerated by the traditional method. The more impregnated vanadium was due to the fact that the rapid evaporation of mixed liquid inside the catalyst channels led to the enlargement of surface areas by creating more pores on the catalysts. Meanwhile, with the increasing concentrations of ethanol, the heating rate of the mixed liquid increased, and the volume after complete evaporation of the mixed liquid was gradually reduced. Since higher heating rate and lager volume after the liquid evaporation could help to create more pores, therefore, when the volume ratio of ethanol/mixed solution was 20 %, the catalyst obtained the maximum specific surface area, which significantly increased to ca. 123 % compared with the deactivated catalyst. In addition, the catalyst dried by microwave exhibited better catalytic activity than that dried in conventional oven. Therefore, this method showed great potential in industrial applications.

This invited review highlights recent progress in the various classes of heterogeneous catalysts for methane combustion. These combustion catalysts provide a high-efficiency, clean energy source for natural gas vehicles and power plants. This review examines bimetallic systems, and a variety of oxides including single metal oxides, perovskites, spinels, and hexaaluminates. Noble metal mixed oxides exhibit superior catalytic activity due material-specific supports, additives, preparation methods, poisoning, regeneration and surface structure. Kinetic aspects, mechanisms, and the latest studies concerning density functional theory modelling are discussed in conjunction with particle oxidation/reduction mechanisms. The extensive background knowledge on the methane combustion reaction provided by this review provides guidance for researchers with interests ranging from the field of heterogeneous catalysis to the engineering of new high performance materials in environmental and chemical engineering.

A series of CuCeOx nanofiber catalysts with different Cu/(Cu + Ce) molar ratios were synthesized by an electrospinning method. The catalysts were evaluated for acetone oxidation at different temperatures (100–280 °C) with a GHSV of 79000 ml g−1 h−1. The results showed that nanofiber catalysts possessed better catalytic performance than catalysts prepared by urea-nitrate combustion and sol–gel methods. An appropriate Cu/(Cu + Ce) molar ratio could greatly improve the activity of the nanofiber catalysts, and a significant improvement of the activity was obtained on the Cu0.50Ce0.50Ox nanofiber catalyst (∼100% acetone conversion at 270 °C). Characteristic analysis of prepared catalysts suggested (1) a special nanofibrous morphology with large specific surface area; (2) abundant oxygen vacancies and (3) cerium ions with unusual oxidation states were the main factors that would affect catalytic activity of CuCeOx nanofibers catalysts.

Pulsed corona discharge is an efficient method on NO oxidization, and the investigation of the oxidization process is significant both for model validation and industrial application. In-situ visualization of NO and OH in pulsed corona discharge was performed by planar laser-induced fluorescence (PLIF) in this work. Two dimensional NO oxidization and OH consumption were studied under different conditions. Some significant results were obtained for mixing behaviors of NO oxidization process. The NO oxidization rate and OH consumption increased by 22% and 40%, respectively, as the Re number of additional gas flow increased from 1379 to 4138. The OH utilization ratio was defined to describe the effect of OH radicals on NO oxidization process. It is demonstrated that OH plays an important role on NO oxidization. The NO reaction and OH consumption zone has a good consistent.Highlights► Two dimensional NO and OH distribution under different mixing conditions were carried out by planar laser-induced fluorescence. ► The OH utilizaition ratio was defined to describe the effect of OH radicals on NO oxidization process. ► Two dimensional NO oxidization rate distribution shows that the NO oxidization rate increased by 22% due to well mixing between background gas and addition gas.

The effect of gas–liquid phase compositions on NO and NO2 absorption into ammonium-sulfite and bisulfite solutions is investigated. Preliminary experiment results indicate that the concentrations of (NH4)2SO3 or NH4HSO3 solution and the molar ratio for HSO3− to the total solution concentrations all have significant impact on NO2 and NO absorption rates. While the solution concentration is constant, the absorption of NOx mixture is strongly related to the ratio NO2/NOx. The absorption rate of NO is primarily affected by NO2 inlet concentration, and the NO absorption rate reaches the maximum value in (NH4)2SO3 solution with the increase of NO2 inlet concentration, which is determined by the reaction of NO and NO2 with SO32− as well as NO formation. Moreover, when the solution is NH4HSO3 the best ratio of NO2/NO for the maximum value of the NO absorption rate becomes less or smaller. Meanwhile, the presence of NO in the gas phase is also favorable to the absorption rate of NO2 in ammonium-sulfite or bisulfite solutions. The total results suggest that the coexistence of NO and NO2 in the flue gas could enhance the absorption of each other to some extent.Research highlights► NO2 and NO absorption rates in (NH4)2SO3 are higher than them in NH4HSO3 solution. ► NO absorption rate is primarily affected by NO2 inlet concentration. ► The presence of NO in gas phase is favorable to NO2 absorption. ► The coexistence of NO and NO2 enhance the absorption of each other to some extent.

The reactive adsorption of NO2 over activated carbon (AC) was investigated at 50 °C. Both the NO2 adsorption and its reduction to NO were observed during the exposure of AC to NO2. Temperature programmed desorption (TPD) was then performed to evaluate the nature and thermal stability of the adsorbed species. Adsorption and desorption processes have been proposed based on the nitrogen and oxygen balance data. The micropores in AC act as a nano-reactor for the formation of –C(ONO2) complexes, which is composed by NO2 adsorption on existing –C(O) complexes and the disproportionation of adsorbed NO2. The generated –C(ONO2) complexes are decomposed to NO and NO2 in the desorption step. The remaining oxygen complexes can be desorbed as CO and CO2 to recover the adsorptive and reductive capacity of AC.

The naphthalene decomposition in a corona radical shower discharge (CRS) was investigated, with attention paid to the influences of voltage and initial naphthalene density. The OH emission spectra were investigated so as to know the naphthalene decomposing process. The by-products were analyzed and a decomposing theory in discharge was proposed. The results showed that higher voltage and relative humidity were effective on decomposition. The initial concentration affected the decomposing efficiency of naphthalene. When the initial naphthalene density was 17 mg/m3, the decomposition rate was found to be 70% under 14 kV. The main by-products were carbon dioxide and water. However, a small amount of carbonic oxide, 1,2-ethanediol and acetaldehyde were found due to the incomplete oxidization.

The mass transfer and kinetics of NOx absorption into (NH4)2SO3 solution, the main compound of an ammonia-based wet flue gas desulfurization process, have been investigated in a double-stirred reactor. Under the experimental conditions, the gas−liquid reaction between NOx and the (NH4)2SO3 solution without O2 coexisting is controlled mainly by the gas film because the (NH4)2SO3 concentration is higher than 0.05 mol/L. In this case, the absorption rate of NOx is found to be zero-order with respect to the (NH4)2SO3 concentration. The inlet partial pressure and the oxidation degree (Φ = NO2/NOx) have an apparent effect on the absorption rate of NOx. In this research, a simplified mathematical calculated model is applied to the simulation of the absorption process. The experimental results demonstrate that the orders of the reaction with respect to the concentration of NOx (NO2* or NO*) in the gas phase and the reaction rate constants of NOx (NO2* or NO*) with (NH4)2SO3 are all a function of the oxidation degree. A kinetic equation for total NOx absorption as a function of the oxidation degree can be obtained, and the calculated value fits the experimental data well.

Iron leaching from fly ash has been investigated under simulated ammonia-based wet flue gas desulfurization conditions to determine the effects of the reaction temperature, initial pH value, liquid/solid ratio, and vibration frequency. The experimental results indicated that the ferric ion concentration in solution increased with the increase of the temperature and vibration frequency and the decrease of the pH value and liquid/solid ratio. The kinetics of iron leaching can be expressed as diffusion combined with a surface chemical reaction model. The reaction path can be described by the equation: 1 − (1 − α)1/3 = kt. The apparent activation energy was estimated to be about 20.01 kJ/mol. Such a value of the activation energy indicates that the leaching of iron under experimental conditions is controlled by both chemical reaction and diffusion.

•A comprehensive model for ESPs was developed and validated.•Characteristics of the corona-electrostatic field in ESP were identified.•Typical charging and transport behaviors of fine particles in ESP were studied.•Effects of operation parameters on ESP performances were analyzed and discussed.In this work, an integrated numerical model is presented and validated to investigate the particle charging and transport behaviors in a wire-plate electrostatic precipitator (ESP). Calculations of gas flow, electrostatics field and particle motions are coupled in the model, and the influences of electro-hydrodynamics (EHD) flows are also taken into account. The dynamic charging process of particles was treated with separate field and diffusion charging rates, and the trajectories of particles in the ESP were tracked with a Lagrangian-type method. Numerical results show that electric field strengths and charging ion densities varied largely in the computational domain, and inlet particles were initially charged primarily by diffusion charging mechanism. The particles were then charged to a near-saturation state in the discharging zone, while their transverse velocities showed considerable fluctuations along the trajectories. Numerical results indicate that particles with diameter between 0.2 and 1 μm normally exhibited lowest average transverse velocities, and longer residential time could slightly improve the transverse velocities for all sizes of particles. Moreover, increasing voltages could greatly improve the acquired charges and collecting performances for particles larger than 1 μm, while higher ion current value was more effective in achieving higher collection efficiencies for sub-micron particles.

Selective catalytic reduction (SCR) of NO and NO2 with ammonia was investigated over activated carbon-supported vanadium oxide (V2O5/AC) catalyst. The results show that high activity and selectivity could be achieved in wide range of temperatures and space velocities. NOx conversion to N2 increases with increasing NO2/NOx ratio, and the increase vanishes gradually with increasing temperature. An increase of NOx conversion to N2 from 26% to 94% can be achieved at a temperature as low as 150 °C without the formation of NH4NO3. The results of temperature programmed desorption (TPD) and infrared (IR) spectrometry experiments show that NH4NO3 could be deposited on the catalyst at 100 °C and decomposed to NH3, N2O, and NO around 130 °C. To explain the observed behaviors, AC involved NO2-SCR process was proposed, in which NH4NO3 is reduced to N2 by AC instead of NO. This process shows better reactivity at lower temperatures.Graphical abstractDownload high-res image (301KB)Download full-size imageHighlights► NO2 is adsorbed on V2O5/AC to form nitrogen complexes, decomposed around 130 °C. ► V2O5/AC shows high activity and selectivity. ► NOx conversion to N2 increase with increasing NO2/NOx ratio, especially at 150 °C. ► NH4NO3 could be deposited on the catalyst at 100 °C and decomposed around 130 °C.

A combination of theoretical and experimental methods, including DFT calculation, BET, Raman spectroscopy, NH3-TPD, H2-TPR and XPS, has been used to elucidate the mechanism of lead deactivating effect on the V2O5 based SCR catalyst. The theoretical calculations have shown that the doping of lead atom will cause the great change of the surface electronic property. Each lead atom will influence two active sites, resulting in the decrease of the acid formability and reducibility of the catalyst surface. The NH3-TPD and H2-TPR experiments have shown the decrease of acid site amount and reducibility, which is in accordance with the calculation result. The BET result has also shown the physical influence caused by the doping of lead compound. The NO conversion experiment has confirmed the deactivation effect of lead on the V2O5 based catalyst.Graphical abstractDownload high-res image (365KB)Download full-size imageHighlights► The lead-doping will cause the great change of the surface electronic property. ► Each lead atom will influence two active sites. ► Lead doping results in the decrease of the acid formability of the catalyst surface. ► The doping of lead results in the decrease of surface reducibility. ► The doping of lead compound also influences the physical properties.

A Ce–Cu–Ti complex oxide catalyst for the selective catalytic reduction of NO with NH3 was prepared by coprecipitation method. XRD and H2–TPR reveal that the strong interaction between Ce and Cu results in the production of a new active oxygen species with high reducibility at low temperatures. Compared with Ce–Ti oxide catalyst, the Ce–Cu–Ti oxide catalyst produces better performance at the temperatures lower than 350 °C and higher SO2-resistent ability. H2O will reduce the SCR activity of Ce–Cu–Ti catalyst at low temperatures while promoting the catalyst performance at temperatures more than 350 °C.Download full-size imageResearch Highlights►The Ce–Cu–Ti oxide catalyst exhibits high activity in a wide temperature range. ►The Ce–Cu–Ti oxide catalyst performs better than Ce–Ti oxide at low temperatures. ►The Ce–Cu–Ti oxide catalyst has higher SO2 resistance than Ce–Ti oxide catalyst. ►H2O will promote the catalyst performance at the temperatures more than 350 °C.

H2O inhibits the SCR performance of the Ce-Cu-Ti (CCT) oxide catalyst at low temperatures, while it promotes SCR performance at high temperatures above 300 °C. A combination of experiments and DFT calculations was applied to study this phenomenon. NH3 adsorption profiles showed that the presence of H2O would greatly decrease the NH3 adsorption amount, especially the weakly adsorbed NH3 part. The DFT calculations of H2O and NH3 adsorption on the CCT catalyst showed that the presence of H2O would compete with NH3 to be adsorbed on the catalyst. NH3 oxidation experiments indicated that NH3 oxidation at high temperatures decreases with the addition of 10% H2O. The DFT calculation also indicated that H2O would inhibit NH3 oxidation. The inhibition effect of H2O at low temperatures could be attributed to the competing adsorption of H2O with NH3. The promotional effect of H2O at high temperatures was due to the inhibition of NH3 oxidation.Graphical abstractHighlights► H2O inhibits the SCR performance of the Ce-Cu-Ti-O catalyst at low temperatures. ► H2O enhances the NO conversion of the Ce-Cu-Ti-O catalyst at high temperatures. ► The presence of H2O would greatly decrease the NH3 adsorption amount. ► NH3 oxidation at high temperatures decreases with the addition of 10% H2O.

The relationship between the molecular structure of V2O5/TiO2 catalysts and the reactivity of SO2 oxidation was investigated. The dispersion state and surface properties of supported vanadia over V2O5/TiO2 catalysts were studied with various experimental techniques. Isolated vanadia species were dispersed on the TiO2 surface as Ti–O–V bonds at VOx coverage far below the monolayer. Polymeric vanadia species were then formed through the V–O–V bonds as the VOx coverage increased. SO2 temperature-programmed desorption and in situ diffuse reflectance infrared Fourier transform spectroscopy were conducted to study the interaction between SO2 and V2O5/TiO2. On the V2O5/TiO2 catalysts, the turnover frequency of SO2 oxidation was almost constant with increased VOx coverage under the condition of constant temperature. VO was demonstrated to play a critical role in the SO2 adsorption and oxidation. A possible reaction mechanism was established in this study.

A series of Ce–Nb oxide catalysts were synthesized at different calcination temperatures for the selective catalytic reduction (SCR) of NO with NH3 and the reaction pathway and reactive species were investigated in detail. The SCR reaction pathway over the Ce–Nb catalysts followed both the Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism, where the former contributed more especially at high reaction temperatures. Lewis acidity was found to be catalytically important in the Eley–Rideal mechanism. NO2 and monodentate nitrate were the main reactive species in the Langmuir–Hinshelwood mechanism. The catalyst calcined at lower temperatures exhibited higher catalytic activity at low temperatures but lower activity at high temperatures. With the increase in calcination temperature, the catalyst surface was gradually covered with niobium oxide species, resulting in the enhancement of total acidity but the decline of redox ability, along with the decrease in the contribution of the Langmuir–Hinshelwood mechanism to the SCR reaction.

A series of copper- and manganese-containing ordered mesoporous carbons (OMCs) were synthesized for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The results demonstrated that NO conversion can be greatly improved by the addition of Cu or Mn. In addition, Cu and Mn had a synergetic effect and the optimal catalytic performance was obtained over the bimetallic catalyst Cu5Mn5-OMC. N2 sorption, small-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm the ordered mesoporous structures. Wide-angle XRD results showed that in the bimetallic catalysts some Cu ions were substituted by Mn ions, resulting in lattice contraction by the formation of a solid solution. X-ray photoelectron spectroscopy (XPS) results indicated that the O–CO groups and chemisorbed oxygen species increased with the addition of Cu or Mn. Temperature-programmed desorption of CO/CO2 and NH3 (CO/CO2-TPD and NH3-TPD) results verified that the acidity of the catalyst was enhanced by the addition of Cu and Mn and the bimetallic catalyst Cu5Mn5-OMC had the strongest acidity. Temperature-programmed reduction of H2 (H2-TPR) results showed that Cu5Mn5-OMC had the strongest oxidizing capacity. Based on the above analysis, a possible synergetic catalytic effect was proposed through the electron transfer between Cu and Mn ions.