NO Abatement Research Articles

Effects of Electrode Structure and Electron Energy on Abatement of NO in Dielectric Barrier Discharge Reactor

Electrode structure and electron energy effects on NO abatement were studied in two different structure DBD reactors. Final product analysis of NO abatement in coaxial cylinder dielectric barrier discharge (CC-DBD) and tubular multilayer dielectric barrier discharge (TM-DBD) reactors indicated that the electrode structure of TM-DBD was better under low O2 concentration conditions, but the result was opposite because the new NOx was produced in TM-DBD when O2 concentration was increasing. In addition, results of particle-in-cell with Monte Carlo collisions (PIC-MCC) simulation manifested that the largest and the average electron energy were 12.09 eV and 3.35 eV in TM-DBD reactor, respectively, while they were 5.25 eV and 2.96 eV in CC-DBD reactor, respectively. CC-DBD electrode structures are preferable for better NO abatement and no new NOx under oxygen-containing condition.

Study of innovative photocatalytic cement based coatings: The effect of supporting materials

For an ideal photocatalytic active building material, the substrate, on which the photocatalytic material is deposited, should neither interfere with nor affect its photocatalytic activity. In the present work, photocatalytic cement based coatings were immobilized on the surface of three different building substrates: gypsum, plywood and glass. The purpose was to investigate the effect of the substrates material on the photocatalytic activity of the corresponding end products against NO. In addition, the effect of the coatings composition and the selected illumination source (UV & Vis) on the material’s photocatalytic behavior was also studied. Results displayed a slightly higher photocatalytic activity for the cementitious coatings on the glass substrate compared to the ones obtained on gypsum and plywood substrates, Overall, both cement based coatings, with 5% w/w and 10% w/w photocatalyst (Mn doped TiO2), presented sufficient photocatalytic activity under either UV or Vis irradiation in the NO abatement. The latter (10% w/w) exhibited, as expected, a slightly better performance due to higher concentration, as monitored by the corresponding photocatalytic degradation rate parameters (n% and r) value.

Catalytic N2O decomposition and reduction by NH3 over Fe/Beta and Fe/SSZ-13 catalysts

Fe/zeolites are important N2O abatement catalysts, efficient in direct N2O decomposition and (selective) catalytic N2O reduction. In this study, Fe/Beta and Fe/SSZ-13 materials were synthesized via solution ion-exchange and used to catalyze these two reactions. The nature of the Fe species was probed with UV–vis, Mössbauer and EPR spectroscopies and H2-TPR. These characterizations collectively indicate that primarily isolated and dinuclear Fe sites are present in Fe/SSZ-13, whereas Fe/Beta contains higher concentrations of oligomeric FexOy species. H2-TPR results suggest that Fe-O interactions are weaker in Fe/SSZ-13, as evidenced by the lower reduction temperatures by H2 and higher extents of autoreduction during high-temperature pretreatments in inert gas. Kinetic measurements show that Fe/SSZ-13 has higher normalized reaction rates in catalytic N2O decomposition, thus demonstrating a positive correlation between reaction rate and Fe-O binding, consistent with O2 desorption being rate-limiting for this reaction. However, Fe/Beta was found to display higher reaction rates in catalyzing N2O reduction by NH3. This latter result indicates that larger active ensembles (i.e., oligomers) are responsible for this reaction, consistent with the fact that both N2O and NH3 need to be activated in this case.

ACTIVITY OF ALUMINA SUPPORTED Fe CATALYSTS FOR N2O DECOMPOSITION: EFFECTS OF THE IRON CONTENT AND THERMAL TREATMENT

The activity of Fe2O3/Al2O3 catalysts prepared by impregnation of Al2O3 with different amounts of Fe and calcination temperatures (650 and 900 oC) in the direct N2O decomposition reaction was studied. High calcination temperature was introduced to study the effect of “aging”, which are the conditions prevailing in the process-gas option for N2O abatement. The catalysts were characterized by BET, XRD, UV-DRS, and H2-TPR. The incorporation of Fe promotes the alumina phase transition (g-Al2O3 to a-Al2O3) when the catalysts are calcined at 900 oC, which is accompanied by a decrease in the specific area. The activity of the catalysts and the specific surface area depend on Fe loading and calcination temperature. It was found that highly dispersed Fe species are more active than bulk type Fe2O3 particles. We conclude that Fe2O3/Al2O3 catalysts prepared by impregnation method are active in the decomposition of N2O, to be used at low or high reaction temperatures (tail-gas or process-gas treatments, respectively), as part of nitric acid production plant.

Combustion measurements of type-1 pulverized coal flames operating under oxy-fired conditions

The present study addresses the impact of oxy-fired conditions on type-1 flames generated by an oxidant-staged burner operating with pre-dried lignite and applying wet flue-gas recirculation. Investigations were carried out in a laboratory facility where the combustion takes place in a furnace with a rated capacity of 0.40MWth. In-flame measurements were performed for oxy-fired conditions operating at three levels of secondary swirl number (1.15, 1.65, and 2.05), while overall O2 fraction upstream of the burner in oxy-firing was kept at 31vol%. One air-fired condition at 1.65 secondary swirl number was also investigated. Measurements of local gas temperature and gas species concentrations were performed using standard water-cooled probes with focus on the near burner region. Results showed evidence of radial flame stratification consistent with gradual O2 admixing to the central fuel jet. Lower temperatures on the flame axis were obtained under oxy-fired condition. In the same region, as a result of CO2 dissociation and/or gasification reactions by water vapor and CO2, higher CO concentrations were also monitored, which contributed to lower temperatures. Experimental data also suggested great potential for NO abatement through flame stratification due to type-1 flame pattern.

Abatement of NOX using compact high voltage pulse power supply: Towards retrofitting to automobile vehicle

The research work in this paper is based on generation of high voltage pulses using compact power supply sources for abatement of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> from the diesel engine exhaust. The high voltage source is made up of zero voltage switch cascaded with flyback converter to produce high voltage AC, a Cockroft-Walton voltage multiplier to generate high voltage DC and a rotary spark gap for the production of high voltage pulses of rise time in the range of nano seconds. The rectifier based power supply is validated by a 12 V battery supply. To corroborate the feasibility of proposed methodology in diesel operated vehicles, the experiments are conducted with a 12 V battery. Performance of various shapes of electrodes (cylindrical 5mm diameter, square 5 mm diagonal and hexagonal with vertex to vertex diameter of 5 mm) at different flow rates of 2 l/min, 4 l/min and 6 l/min are also examined.

Photocatalytic abatement of NOx pollutants in the air using commercial functional coating with porous morphology

Titanium dioxide is the most important photocatalyst used for purifying applications. The purpose of this study was to investigate the photocatalytic activity of the commercial product Protectam FN2, containing Evonik P25 titanium dioxide nanopowder, with regard to NO and NO2 abatement. Photocatalytic experiments on the photocatalytic coatings on concrete and plaster substrates were carried out in two types of flow reactors, namely one with laminar flow and another with ideally-mixed flow, under “real world conditions” of temperature, relative humidity, irradiation intensity and pollutant concentrations. The results showed that the photocatalytic process significantly reduced the concentration of both nitrogen oxides in the air. The reaction rate, i.e., the decrease in the concentration of NOx achieved in the steady-state for the inlet concentration of NO and NO2 of 0.1ppmv, which corresponds to highly polluted urban air, was up to 75 and 50μmolm−2h−1, respectively, at the flow rate of 3000cm3min−1 and relative humidity of 50%. Further, even two years after their application to the surface of concrete walls along a busy thoroughfare, the photocatalytic coating maintained high effectivity.

Atmospheric NOx removal: Study of cement mortars with iron- and vanadium-doped TiO2 as visible light–sensitive photocatalysts

Mortars made with Portland cement, two different calcium aluminate cements and air lime were chosen to incorporate photocatalytic additives, because they have large exposed surfaces that boost the photochemical oxidation (PCO) of atmospheric pollutants such as nitrogen oxides. TiO2 as reference catalyst, and two doped titania, Fe-TiO2 and V-TiO2, which were expected to increase the sensitivity of the additives towards the visible light, were studied. Cementing matrices, particularly air lime and high alumina cement mortars, yielded significant amounts of NO removal under the three illumination conditions studied (UV, solar and visible light), with high selectivity response for NO abatement (up to 60–80%) and low NO2 release. The presence of calcium carbonate has been shown to have a synergistic effect, enhancing the PCO of these mortars under different light sources.

Plasma-catalytic decomposition of nitrous oxide over γ-alumina-supported metal oxides

This work investigated the decomposition of dilute N2O from gas streams with various oxygen contents by using a plasma-catalytic process over metal oxide catalysts supported on γ-Al2O3. Among the metals explored (Ru, Co, Cu, V, etc.), Ru was found to be the best catalyst for the decomposition of N2O in a plasma-catalytic reactor, and most of the experiments were conducted with alumina-supported Ru. The effects of applied voltage, reaction temperature, O2 content, gas flow rate and initial N2O content on the decomposition efficiency and byproducts formation were examined. Compared to the catalyst-alone case, the presence of plasma enhanced the decomposition efficiency by 30–50%, depending on the operating condition. The increase in the oxygen content from 0 to 20% largely decreased the catalytic decomposition efficiency, whereas in the presence of plasma N2O could be successfully decomposed even at 20% O2 content. The decomposition efficiency was not a strong function of the initial N2O concentration in the range of 225–1800ppm, exhibiting pseudo first-order reaction kinetics. Without O2, there were negligible byproducts, but in the presence of O2, NO and NO2 were formed mainly due to the plasma-induced reactions between background molecules such as N2 and O2. The results obtained in this work showed the feasibility of plasma-catalytic process for the abatement of N2O.

Nitrous Oxide Abatement Coupled with Biopolymer Production As a Model GHG Biorefinery for Cost-Effective Climate Change Mitigation.

N2O represents ∼6% of the global greenhouse gas emission inventory and the most important O3-depleting substance emitted in this 21st century. Despite its environmental relevance, little attention has been given to cost-effective and environmentally friendly N2O abatement methods. Here we examined, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L for the abatement of N2O from a nitric acid plant emission. The process was based on the biological reduction of N2O by Paracoccus denitrificans using methanol as a carbon/electron source. Two nitrogen limiting strategies were also tested for the coproduction of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) coupled with N2O reduction. High N2O removal efficiencies (REs) (≈87%) together with a low PHBV cell accumulation were observed in both bioreactors in excess of nitrogen. However, PHBV contents of 38-64% were recorded under N limiting conditions along with N2O-REs of ≈57% and ≈84% in the ALR and BCR, respectively. Fluorescence in situ hybridization analyses showed that P. denitrificans was dominant (>50%) after 6 months of experimentation. The successful abatement of N2O concomitant with PHBV accumulation confirmed the potential of integrating biorefinery concepts into biological gas treatment for a cost-effective GHG mitigation.

Catalytic Abatement of Nitrous Oxide Coupled with Ethane Oxydehydrogenation over Mesoporous Cr/Al2O3 Catalyst

Waste nitrous oxide (N2O) was utilized as an oxidant for ethane oxydehydrogenation reaction at the temperature range from 450 °C to 700 °C over the mesoporous Cr/Al2O3 catalyst synthesized via the one-pot evaporation-induced self-assembly (EISA) method. The catalyst was characterized by X-ray diffraction, transmission electron microscopy, and nitrogen adsorption-desorption analysis. The obtained mesoporous material with favorable textural property and advantageous thermal stability was investigated as the catalyst for ethane oxydehydrogenation. It was found that the utilization of N2O as an oxidant for the oxydehydrogenation reaction of ethane resulted in simultaneous and complete N2O abatement. Moreover, the catalytic conversion of C2H6 to C2H4 was increased from 18% to 43% as the temperature increased from 450 °C to 700 °C. The increased N2O concentration from 5 vol % to 20 vol % resulted in an increased ethane conversion but decreased ethylene selectivity because the nonselective reactions occurred. Ethane was converted into ethylene with approximately 51% selectivity and 22% yield at 700 °C and N2O concentration of 10%. After a catalytic steady state was reached, no obvious decline was observed during a 15 h evaluation period.

Assessing the influence of the carbon source on the abatement of industrial N2O emissions coupled with the synthesis of added-value bioproducts

The continuous abatement of a synthetic N2O emission from a nitric acid plant coupled with the simultaneously production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer and the coenzyme Q10 (CoQ10) in a bubble column reactor (BCR) was tested using methanol, glycerol and a mixture of sodium acetate-acetic acid (Ac-HAc) as a carbon and electron donor source. The BCRs were inoculated with Paracoccus denitrificans and supplied with the carbon/electron donor at a loading rate of 139gCm−3d−1. High N2O removal efficiencies (81–91%) were achieved, with glycerol supporting the highest abatement. The PHBV cell content ranged from 25 to 53%, with highest accumulation in the culture obtained with methanol and Ac-HAc. However, the greatest PHBV productivities were observed in the BCRs operated with glycerol and Ac-HAc (21.7 and 33.5gPHBVm−3d−1, respectively). Glycerol supply induced the highest molar ratio (23%) of the homopolymer 3-hydroxyvalerate in the composition of PHBV. In addition, the specific cell content of CoQ10 ranged from 0.4 to 1mgg−1. This work constitutes, to the best of our knowledge, the first study combining N2O abatement with the simultaneous production of multiple bioproducts, which pave the way to the development of greenhouse gas biorefineries for climate change mitigation.

Optimization of cesium and potassium promoter loading in alkali-doped Zn0.4Co2.6O4|Al2O3 catalysts for N2O abatement

A series of potassium or cesium doped Zn0.4Co2.6O4|Al2O3 catalysts with different alkali loadings were prepared, characterized with respect to chemical composition (XRF), structure (XRD, RS) morphology (TEM), and the alkali promoter thermal stability. A strong beneficial effect on the deN2O activity of the Zn0.4Co2.6O4|Al2O3 catalyst (decrease in the T50% by about 80 °C) was observed for both promoters at different surface coverages. It was found that in comparison to a rather narrow range of optimal cesium loading (0.5–2 atoms/nm2) a comparable promotional effect of potassium doping was observed for a slightly wider surface concentrations (0.5–3 atoms/nm2). Such difference was attributed to surface dispersion of potassium over the alumina support and the spinel active phase, while cesium was found to be located mainly on the spinel phase. For practical applications, the superiority of potassium over cesium consist in fact that a similar beneficial effect is associated with much higher thermal stability in the temperature range of the catalyst deN2O operation and lower price of the promoter precursor.

CoOx and FeOx supported on ZrO2 for the simultaneous abatement of NOx and N2O with C3H6 in the presence of O2

MeOx/ZrO2 (Me=Co and Fe) catalysts were studied for the simultaneous selective catalytic reduction of NO and N2O in the presence of O2 using C3H6 as reducing agent (SCRsim). To give a better insight in the simultaneous process we investigated the reactions related to SCRsim (SCRN2O, SCRNO, N2O decomposition and C3H6 combustion) as well as the abatements in the absence of O2 (CRsim, CRN2O, CRNO).Catalytic results showed that, in the presence of O2 excess, CoOx/ZrO2 and FeOx/ZrO2 catalysts were scarcely active and unselective for the separate NO and N2O abatements with C3H6 and are ineffective for their simultaneous abatement. Because C3H6 preferentially reacted with O2, NO was poorly reduced and N2O was abated, at a temperature above that of complete C3H6 conversion, via both SCRN2O and decomposition. Conversely, in the absence of O2 in the feed, on both catalysts NO and N2O were efficiently reduced by C3H6, but undesired by-products formed.The activity for SCRsim strongly depended on the C3H6/O2 feeding ratio. With suitable feeding mixture O2 was completely consumed and the residual propene efficiently and simultaneously reduced NO and N2O, with negligible formation of by-products. In hydrothermal conditions both catalysts were slightly and reversibly deactivated.Characterization by XRD, UV–vis DRS and FTIR after catalytic experiments showed that dispersed Co2+ and Fe3+ species were stable on zirconia surface and that no significant segregation phenomena occurred in hydrothermal conditions.

Influence of preparation method on dispersion of cobalt spinel over alumina extrudates and the catalyst deN2O activity

A series of supported catalysts of the Co3O4 spinel active phase dispersed over alumina extrudates (9×25mm) was prepared by several methods (incipient wetness impregnation with Co(NO3)2 and CoCl2, with glycerol-assisted impregnation with Co(NO3)2, combustion synthesis, and two variants of spray deposition with Co(NO3)2 on pristine and ammonia soaked extrudates). The catalysts were characterized by XRF, XRD, RS, UV–vis, SEM/TEM/EDX, and their catalytic deN2O activity was investigated in the temperature programmed surface reaction (TPSR) mode. The relation between the spinel active phase particle size and its radial dispersion over the alumina extrudate and the deN2O activity was revealed and quantified. For the assessment of the active phase utilization, the N2O concentration profile across the extrudates was calculated using Thiele modulus and compared with the radial distribution of the spinel. It was shown that the dispersion of spinel active phase exhibits optimal profile when the sample is obtained in the presence of the organic components of the precursor mixture (glycerol or urea). The obtained results were discussed in the context of practical implications for the development of an efficient, low-cost catalyst for the N2O abatement.

High Selectivity of Visible-Light-Driven La-doped TiO2 Photocatalysts for NO Removal

Semiconductors mediated by rare earth metals (REMs) have attracted attention with regard to the degradation of pollutants. In order to enhance the visible response of TiO2, La-doped TiO2 (La-TO) photocatalysts with visible-light-driven capacity for NO removal were successfully synthesized in this study via a facile sol-gel method followed by calcination. A series of La-TiO2 samples with differing weight ratios were evaluated for their photocatalytic performances. It was found that 3% La integrated with TiO2 (in mass ratio) could enhance the removal efficiency of NO (up to 32%) under solar light, which is more than twice that seen with pure TiO2. The resulting products were characterized by a series of techniques, such as XRD, FTIR, UV-vis DRS, BET and (photo)electrochemical analysis. The results indicated that La-doped TiO2 can harvest visible light due to the relatively narrow band gap (from 2.98 to 2.75 eV). More importantly, La dopant improved electron-hole separation and suppressed charge carrier recombination, due to the synergistic effect. Furthermore, La-doped TiO2 increased the photo-oxidation efficiency of the transformation from NO to NO3–, owing to inhibition of the production of intermediate NO2 (0.02%). To the best of our knowledge, this study is the first time that La-doped TiO2 has been used to eliminate NO (at the ppb level) in the atmosphere. This study provides a facile and controllable route to fabricate La-TO photocatalyst for NO abatement with high selectivity of NO2 under visible light.

Controlling the atomic distribution in PtPd nanoparticles: thermal stability and reactivity during NO abatement.

In situ X-ray absorption spectroscopy and mass spectrometry measurements were employed to simultaneously probe the atom specific short range order and reactivity of Pd and PtPd nanoparticles towards NO decomposition at 300 °C. The nanoparticles were synthesized by a well controlled, eco-friendly wet chemical reduction of metal salts and later supported on activated carbon. Particularly for the bimetallic PtPd samples, distinct atomic arrangements were achieved using a seeding growth method, which allowed producing a random nanoalloy, or nanoparticles with Pt- or Pd-rich core. X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction provided additional insights on their electronic, morphological and long range order structural properties. The results revealed that the higher the thermal induced atomic migration observed within the nanoparticles during thermal treatments, the least were their reactivity for NO abatement.

Tailoring dual redox-acid functionalities in VOx/TiO2/ZSM5 catalyst for simultaneous abatement of PCDD/Fs and NOx from municipal solid waste incineration

A series of VOx/TiO2/ZSM5 were prepared in order to enhance the acid functionalities of commercially used VOx/TiO2 for the combined abatement of NO and o-dichlorobenzene (o-DCB, model molecule to simulate dioxins and furans) from the off-gases of a Municipal Solid Waste (MSW) incinerator plant. The catalysts have been prepared by wet impregnation varying the TiO2 content from 0 to 46%. VOx/TiO2 was also prepared as a reference sample.Combining catalysts characterization (N2 adsorption-desorption isotherms, XRD, TEM, NH3-TPD, H2-TPR and Raman) and activity data, we found that high TiO2 loading VOx/TiO2/ZSM5 catalyst, is highly suitable catalyst for dDiNOx process. The NO conversion is higher than the reference VOx/TiO2 catalyst partly due to higher amount of acid sites provided by the zeolite and partly due to Ti-V interaction, which is a key factor in the conversion of both o-DCB and NO. The TiO2 is heterogeneously dispersed over zeolite, but VOx dispersion is enhanced as the TiO2 content is increased, leading to a higher active polymeric species contribution, as in the sample V/46Ti/Z (confirmed by correlation between TOF and Ti-V interaction).

Biological Nitrous Oxide Abatement by Paracoccus denitrificans in Bubble Column and Airlift Reactors

Nitrous oxide (N2O), with a global warming potential 300 times higher than that of CO2, represents 6.2 % of the total greenhouse gas emission inventory worldwide. Furthermore, N2O is considered the most critical O3- depleting substance emitted in this XXI century. In spite of the environmental relevance of this pollutant, very little research on biotechnologies for the treatment of N2O emissions has been conducted. In this study, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L was evaluated for the abatement of N2O from industrial emissions from nitric acid plants along 62 days of operation. The systems were inoculated with a methylotrophic Paracoccus denitrificans strain (DSM 413) and continuously supplied with methanol as a carbon and electron donor source for the anoxic reduction of N2O. The simulated waste gas consisted of a N2 gas stream containing 1 ± 0.1 % of O2 and 3377 ± 312 ppmv of N2O at the inlet of theBCR and 1 ± 0.1 % of O2 with N2O concentration of 3617 ± 342 ppmv at the inlet of the ALR. This N2-laden stream was supplied at a constant flow rate of 110 ml min-1 in each reactor. The performance of the BCR was characterized by a steady state N2O removal efficiency (RE) of 87 ± 3 % with CO2 productions of 308 ± 36 gm-3 d-1 and total suspended solid (TSS) concentrations of 867 ± 109 mg L-1. On the other hand, the ALR showed a N2O RE of 88 ± 2 % with productions of CO2 of 346 ± 28 g m-3 d-1 and TSS concentrations of 874 ±88 mg L-1. This work constitutes, to the best of our knowledge, the first systematic study of a biotechnology for the continuous abatement of N2O from nitric acid plants.

Hydrazine-enhanced NO conversion in a pulsed corona discharge plasma (PCDP) reactor: Behaviors and mechanism

The NO conversion efficiency in a pulsed corona discharge plasma (PCDP) reactor in the presence of a new additive, hydrazine hydrate (N2H4·H2O), was studied, and the reaction mechanism was analyzed. The NO conversion efficiency reached 62.5%, and the NO conversion Energy Yield (EY) reached 20.9 gNO/kWh, which is higher than that obtained using water or ammonia additives under the same conditions. The predominant elementary reactions and radicals, as well as the mechanism by which the additive enhanced the NO conversion process, were determined by comparing experimental data with theoretical simulation results and by performing a sensitivity analysis. After the addition of N2H4·H2O, the N2H4 reacts with radicals generated in the PCDP reactor to form a large quantity of strongly reducing species with NH2 as the predominant component, which can directly reduce NO to N2 and effectively prevent the generation of N2O. Compared with the traditional PCDP-based De-NOx process in which nitric acid is generated by oxidation with an additional neutralization step required, this new PCDP-based De-NOx process with N2H4·H2O addition is superior because NO is mostly reduced to N2. The study provides a basis for the application of N2H4·H2O as a synergist to improve NO abatement in a PCDP reactor.