Removal characteristics of PCDDs/Fs from municipal solid waste incinerator by dual bag filter (DBF) system

A dual bag filter (DBF) system was developed for the removal of dioxins (PCDDs/Fs) emitted from a municipal solid waste incinerator (MSWI). A 2000 N m³/h capacity DBF pilot plant was designed, manufactured, and operated with actual MSWI flue gases. The result showed that pressure drop of the filter bag is the most important variable in PCDDs/Fs removal by the DBF system. Removal efficiency of PCDDs/Fs decreased as pressure drop increased in the first bag filter of the DBF system. On the contrary, removal efficiency of PCDDs/Fs increased as the pressure drop of the second bag filter increased. Pressure drop ranges for the most effective operation in the filter bag were 150–200 mm H₂O and 170–200 mm H₂O for first and second bag filter, respectively. The emission of PCDDs/Fs after removal by the DBF system was below 0.05 ng-TEQ/ N m³, when pressure drop of the second bag filter was operated near 200 mm H₂O. Activated carbon consumption was also less in case of DBF (40 mg/N m³) as compared to SBF which discharged about 100 mg/N m³.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of preparation methods for V<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript> aerogel catalysts on the selective catalytic reduction of NO with NH<Subscript>3</Subscript>

A series of V₂O₅-TiO₂ aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO₂. The main variables in the sol-gel method were the amounts of V₂O₅ and when the vanadium precursor was introduced. V₂O₅-TiO₂ xerogel and V₂O₅/TiO₂ (P-25) were also prepared for comparison. The V₂O₅-TiO₂ aerogel catalysts showed much higher surface areas and total pore volumes than V₂O₅-TiO₂ xerogel and impregnated V₂O₅/TiO₂ (P-25) catalysts. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H₂ (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O₂ was studied over these catalysts. Among various V₂O₅-TiO₂ catalysts, V₂O₅ supported on aerogel TiO₂ showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility and monomeric and polymeric vanadia surface species. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

NO – oxygen scavenger or reaction intermediate in the decomposition of N2O?

Nitric oxide and nitrogen dioxide were found during the thermal desorption of surface species left on Fe-ferrierites after the decomposition of nitrous oxide. This demonstrates the formation of surface NOx species during N₂O decomposition. Repeated decomposition and subsequent desorption of surface species confirm the active role of surface NOx species. Addition of NO up to a fraction of 0.1 times the amount of N₂O increased the decomposition of nitrous oxide as well as the amount of surface NOx species. The use of nitrous oxide labeled with ¹⁸O demonstrated that the zeolite oxygens participate in the reaction and that the presence of NO enhances this participation.     

Application of computational fluid dynamics analysis for improving performance of commercial scale selective catalytic reduction

The performance of commercial scale selective catalytic reduction (SCR) system is strongly dependant upon the degree of mixing between NH₃ and NOx or NH₃ concentration distribution at the catalyst layer according to the reaction kinetics of SCR catalysts. Insufficient mixing of the reduction agent and NOx mass flow necessitates an uneconomically large catalyst volume and high NH₃ slip to meet the required NOx emission values. The effective methodology which can increase the performance of commercial scale SCR through improving NH₃ concentration distribution at the catalyst layer using computational fluid dynamics (CFD) analysis was suggested and applied to the real operations. The operation results have shown that the performance of commercial SCR was improved from 54.4% to 74.8% as NH₃ concentration deviation at the catalyst layer was reduced from 23.6% to 8.6%. It is established that the increase of NH₃ concentration uniformity at the catalyst layer contributes to improvement of performance of commercial scale SCR.     

NOx storage properties of Pt/Ba/Al model catalysts prepared by different methods: Beneficial effects of a N2 pre-treatment before hydrothermal aging

The influence of a pre-treatment at 700 °C, either under a O₂/N₂ mixture or only under N₂, and followed by a hydrothermal aging at 700 °C under wet air, was studied for Pt/Ba/Al NSR model catalysts prepared by different methods: (i) successive impregnation of Ba and Pt, (ii) co-addition of Pt and Ba and (iii) barium precipitation followed by Pt impregnation. The catalysts were evaluated by NOx storage capacity measurements and were characterized by N₂ adsorption, XRD, CO₂-TPD, H₂ chemisorption and H₂-TPR. The pre-treatment under N₂ largely improves the NOx storage performance in the whole studied temperature range (200–400 °C), with or without H₂O and CO₂ in the inlet gas. The better NOx storage properties of the catalysts treated under N₂ before aging are due to: (i) a higher NO oxidation activity (mainly linked to a higher platinum dispersion), (ii) a higher number of NOx storage sites resulting from a higher barium dispersion, and consequently to (iii) a higher Pt-Ba proximity.     

The preparation of V2O5/TiO2 catalyst supported on the ceramic filter candle for selective reduction of NO

In order to prepare the catalytic filters based on V₂O₅/TiO₂ for the removal of NO_x and participate simultaneously from the flue gas stream, the experimental study was carried out. The effective method to support TiO₂ layer in the pore of the commercial ceramic filter element was developed. TiO₂ layer was supported on the filter element by three methods; impregnation with Ti solution, sol-gel dip coating and sol-gel centrifugal coating. As the model test to check the catalytic activity, NO reduction in the oxidizing stream was investigated. The catalytic filter prepared by applying the centrifugal force showed the best NO conversion more than 90% when the face velocity was 0.02 m/sec. This was a very promising result for the application of catalytic filter for the flue gas control at high temperature. The supporting methods by the impregnation and dip coating were not recommended because the TiO₂ layer was concentrated in the exterior layer of the filter element. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

Lean NOx Trap Chemistry Under Lean-Gasoline Exhaust Conditions: Impact of High NOx Concentrations and High Temperature

The primary technical barrier to deployment of fuel saving lean gasoline engines is NOx emissions control. We conducted automated flow reactor experiments on a commercial LNT catalyst to identify opportunities and challenges associated with the higher temperatures and higher NOx concentrations expected in lean gasoline applications. Overall NOx conversion was quite high at low to moderate temperatures, but dropped off at high temperatures. The decrease in NOx conversion with temperature was worse for higher inlet NOx concentrations. As expected from equilibrium considerations, the catalyst stored more NOx under higher gas phase NOx concentrations, but that NOx was rapidly released during the rich phase and slipped out of the catalyst before it could be converted to N₂ by incoming reductant. This rich phase NOx release was the primary factor limiting performance of the catalyst at high temperatures, and resulted in significant spikes of NOx that would likely exceed any not-to-exceed regulated emissions levels. N₂O production was also significant, and increased with NOx concentration. The catalyst made very little NH₃ at high temperatures. NH₃ yield was significant at the lowest operating temperature studied, but it decreased with increasing NOx concentration.     

FTIR study of NO, C3H6 and O2 adsorption and interaction on gold modified MCM-41 materials

This paper is devoted to the detailed FTIR study of the adsorption, co-adsorption, and interaction of all the reagents used in NO HC-SCR process addressed to lean-burn engines with the surface of new gold catalysts based on ordered mesoporous materials. Gold was introduced into silicate and niobiosilicate matrices by the impregnation (Au/MCM-41 and Au/NbMCM-41, respectively) and via co-precipitation with siliceous and niobium sources (AuNbMCM-41). The in situ FTIR study allowed the estimation of the possible chemisorption of the reagents and their interaction towards intermediates, depending on the chemical composition of the catalyst and the way of gold introduction. It has been found that propene is chemisorbed, but not, NO, on gold species at room temperature. Chemisorbed C₃H₆ interacts with NO only in the presence of oxygen excess. Oxygen oxidizes NO to NO₂, the latter interacts with chemisorbed propene towards carboxylates (1570 cm⁻¹) and NO₂ is reduced to N₂O. At higher temperatures carboxylates interact with gaseous NO to carbonate, N₂O, CO and CO₂. The presence of niobium in the NbMCM-41 matrix enhances the oxidative properties of the catalysts and as a consequence the interaction between intermediates in NO reduction with propene in the oxygen excess. The co-precipitated AuNbMCM-41 exhibits higher NOx storage properties than the impregnated one.     

Effects of Hydrogen Peroxide Residuals on Biologically Active Filters

The objective of this research was to obtain a better understanding of the effects of hydrogen peroxide (H₂O₂) residuals on the biological removal of certain biodegradable components in biologically active filters. Data were collected at lab scale using two parallel anthracite/sand filters. Both filter influents (dechlorinated tap water) were dosed with a biodegradable organic matter (BOM) cocktail, and one filter received additionally H₂O₂ at an influent concentration of approximately 1 mg/L. Measured parameters included carboxylic acids and hydrogen peroxide residuals. The results showed that the presence of H₂O₂ residuals (～ 1 mg/L) did not lead to a major inhibition of the biological removal of acetate and formate anions. After a period of biological acclimatization (colonization), H₂O₂ was removed rapidly within the biological filter, probably as a result of its reaction with the biomass or with catalase produced by certain bacteria.     

The reactivity of V2O5-WO3-TiO2 catalyst supported on a ceramic filter candle for selective reduction of NO

For realizing the environmental issues and constituting an economical treatment system, a catalytic filter based on V₂O₅/TiO₂ supported on tubular filter elements has many advantages by removing NO_x and particulate simultaneously from flue gas. In order to improve the activity of a catalytic filter based on V₂O₅/TiO₂ supported on a commercial high temperature filter element (PRD-66), the promoting effects of WO₃ were investigated in an experimental unit. PRD-66 presented very good properties for SCR catalyst carrier since it contains much active material such as A1₂O₃ SiO{om2}, and MgO whose contributions were remarkable. For additional catalyst carrier, TiO₂ particles were coated in the pores of PRD-66 with relatively good distribution of the particle size less than 1 μm, by a coating process applying centrifugal force. WO₃, in the V₂O₅-WO₃-TiO₂/PRD-66 catalytic filter system, increased the SCR activity significantly and broadened the optimum temperature window. The catalytic filter shows the maximum NO conversion of more than 95% for NO concentration of 700 ppmv at face velocity of 0.02 m/sec, which is comparable to the current commercial catalytic filters of plate form.     

Effective combination of non-thermal plasma and catalyst for removal of volatile organic compounds and NOx

A plasma/catalyst hybrid reactor was designed to overcome the limits of plasma and catalyst technologies. A two-plasma/catalyst hybrid system was used to decompose VOCs (toluene) and NOx at temperature lower than 150 °C. The single-stage type (Plasma-driven catalyst process) is the system in which catalysts are installed in a non-thermal plasma reactor. And the two-stage type (Plasma-enhanced process) is the system in which a plasma and a catalyst reactor are connected in series. The catalysts prepared in this experiment were Pt/TiO₂ and Pt/Al₂O₃ of powder type and Pd/ZrO₂, Pt/ZrO₂ and Pt/Al₂O₃ which were catalysts of honeycomb type. When a plasma-driven catalyst reactor with Pt/Al₂O₃ decomposed only toluene, it removed just more 20% than the only plasma reactor but the selectivity of CO₂ was remarkably elevated as compared with only the plasma reactor. In case of decomposing VOCs (toluene) and NOx using plasma-enhanced catalyst reactor with Pt/ZrO₂ or Pt/Al₂O₃, the conversion of toluene to CO₂ was nearly 100% and about 80% of NOx was removed. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Preparation of bao-pbo-nd2o3-tio2 powders by hydrothermal synthesis

Homogeneous and nano-sized BPNT [(Ba_1-xPb_x)Nd₂Ti₅O₁₄] powders were prepared under various hydrothermal conditions. Crystallinity and homogeneity of the synthetic powders were investigated. The microwave dielectric properties of the filters prepared with hydrothermal powders were compared with those of the filters prepared with conventional powders. The microwave dielectric properties of the filter prepared with the hydrothermal powders were also better than those of the filter manufactured with the conventional powders. The dielectric constant, quality constant and temperature coefficient of resonance frequency of hydrothermally prepared filter under optimum condition and measured at 3.5 GHz around were about 93, 6067 and 0 ppm/°C, respectively.     

Promoted Fe/ZSM-5 catalysts prepared by sublimation: de-NOx activity and durability in H2O-rich streams

Fe/ZSM-5 catalysts with an Fe/Al ratio 1:0, were prepared by sublimation of FeCl3 into H/ZSM-5. They display high activity and durability for the selective catalytic reduction of NOx to N2, both in dry and wet gas flows. These catalysts have now been modified by exchanging a second cation into the zeolite. Mere neutralization of zeolite protons by Na⁺ lowers the selectivity for NOx reduction to N2, but the cations Ce₃ ⁺ and La₃ ⁺ act as true catalyst promoters. With isobutane as the reductant in a simulated vehicular emission gas, almost 90% of NOx is reduced to N2 at 350°C over the La-promoted catalyst. The presence of 10% H2O in the feed does not impair the catalyst performance at high temperature; in the temperature region below 350°C it even increases the N2 yield. The beneficial effect of La is due to its lowering of the catalyst activity for the undesired combustion of the hydrocarbon. No signs of zeolite destruction are evident after 100 h TOS in a wet gas flow at 350°C. Carbonaceous deposits causing a slight deactivation are easily removed in an O2/He flow at 500°C; this in situ regeneration fully restores the original activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

NO reduction by CH4over La2O3: temperature‐programmed reaction and in situ DRIFTS studies

The chemistry between NO _x species adsorbed on La₂O₃ and CH₄ was probed by temperature‐programmed reaction (TPR) as well as in situ DRIFTS. During NO reduction by CH₄ in the presence of O₂, NO ₃ ^- does not appear to activate CH₄, thus either an adsorbed O species or an NO ₂ ^- species is more likely to activate CH₄. In the absence of O₂, a different reaction pathway occurs and NO^- or (N₂O₂)^2- species adsorbed on oxygen vacancy sites seem to be active intermediates, and during NO reduction with CH₄ unidentate NO ₃ ^- , which desorbs at high temperature, behaves as a spectator species and is not directly involved in the catalytic sequence. Because reaction products such as CO₂ or H₂O as well as adsorbed oxygen cannot be effectively removed from the surface at lower temperatures, steady‐state catalytic reactions can only be achieved at temperatures above 800 K, even though formation of N₂ and N₂O from NO was observed at much lower temperature during the TPR experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the reaction of iron blast furance slag/hydrated lime sorbents with SO2 at low temperatures: effects of sorbent preparation conditions

Sorbents highly reactive towards SO₂ have been prepared from iron blast furnace slag and hydrated lime under different hydration conditions. The reaction of the dry sorbents with SO₂ has been studied under the conditions similar to those in the bag filters in the spray-drying flue gas desulfurization system. The reaction was well described by a modified surface coverage model which assumes the reaction rate being controlled by chemical reaction on sorbent grain surface and takes into account the effect of sorbent Ca molar content and the surface coverage by product. The effects of sorbent preparation conditions on sorbent reactivity were entirely represented by the effects of the initial specific surface area (S_g0) and the Ca molar content (M⁻¹) of sorbent. The initial conversion rate of sorbent increased linearly with increasing S_g0, and the ultimate conversion increased linearly with increasing S_g0M⁻¹. The initial conversion rate and ultimate conversion of sorbent increased significantly with increasing relative humidity of the gas. Temperature and SO₂ concentration had mild effects on the initial conversion rate and negligible effects on the ultimate conversion.     

Adsorption/desorption of NOx on MnO2/ZrO2 oxides prepared in reverse microemulsions

A series of MnO₂/ZrO₂ mixed oxides were prepared in reverse microemulsions for NOx adsorption and abatement. The results show that the amount of NOx adsorbed was increased with increasing MnO₂ content in various MnO₂/ZrO₂ samples. The maximum uptake value of NOx was 27.66 mg NOx/g adsorbent on the 40% Mn–Zr sample at 200 °C with NOx initial adsorption rate as 2.63 mg/(g adsorbent min). TPD results show that the complete desorption of NOx was easily obtained by heating the sample to 450 °C, and the temperature for the complete desorption can be further decreased to 210 °C by adding carbon monoxide into the argon desorption streams. Furthermore, water vapor was found to reduce NOx adsorption capacity because of its stronger competitive adsorption with NOx species. It is noteworthy that a small amount of sulfur dioxide could significantly increase the initial rate of NOx adsorption although it slightly decreased the NOx adsorption capacity.     

Cs2.5H0.5PWO40/SiO2 as addition self-humidifying composite membrane for proton exchange membrane fuel cells

In this paper, we first reported a novel self-humidifying composite membrane for the proton exchange membrane fuel cell (PEMFC). Cs_2.5H_0.5PWO₄₀/SiO₂ catalyst particles were dispersed uniformly into the Nafion^® resin, and then Cs_2.5H_0.5PWO₄₀-SiO₂/Nafion composite membrane was prepared using solution-cast method. Compared with the H₃PWO₄₀ (PTA)_, the Cs_2.5H_0.5PWO₄₀/SiO₂ was steady due to the substitute of H⁺ with Cs⁺ and the interaction between the Cs_2.5H_0.5PWO₄₀ and SiO₂. And compared with the performance of the fuel cell with commercial Nafion^® NRE-212 membrane, the cell performance with the self-humidifying composite membrane was obviously improved under both humidified and dry conditions at 60 and 80 °C. The best performance under dry condition was obtained at 60 °C. The self-humidifying composite membrane could minimize membrane conductivity loss under dry conditions due to the presence of catalyst and hydrophilic Cs_2.5H_0.5PWO₄₀/SiO₂ particles.     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Performance of a catalytically activated ceramic hot gas filter for catalytic tar removal from biomass gasification gas

Silicon carbide-based filter elements were catalytically activated to provide filter elements for catalytic tar removal from biomass-derived syngas. The filter element support was coated with CeO₂, CaO–Al₂O₃ and MgO with a specific surface of 7.4, 15.9 and 21.9 m²/g synthesized by exo-templating with activated carbon. Doping of a MgO coated filter element with 60 wt% NiO has led to an increase of the specific surface from 0.15 to 0.21 m²/g, whereas in case of a MgO–Al₂O₃ coated filter element a decrease from 1.18 to 0.91 m²/g was found. An increase of the NiO loading from 6 to 60 wt% on a MgO coated filter element resulted in an increase of the naphthalene conversion from 91 to 100% at 800 °C and a face velocity of 2.5 cm/s at a naphthalene concentration of 5 g/Nm³ in model biomass gasification gas. In case of a MgO–Al₂O₃ coated filter element with 60 wt% NiO in addition to complete naphthalene conversion in the absence of H₂S, a higher conversion of 66% was found in the presence of 100 ppmv H₂S compared to 49% of the MgO–NiO coated filter element. After scaling up of the catalytic activation procedure to a 1520 mm long filter candle, which shows an acceptable differential pressure of 54.9 mbar, 58 and 97% naphthalene conversion was achieved in the presence and absence of H₂S, respectively. The calculated WHSV value of 209.6 Nm³ h⁻¹ kg⁻¹ indicates the technical feasibility of a further increase of the catalytic performance by an increase of the NiO loading.