NO Abatement Research Articles

The catalytic activity of FeOx/ZrO2 for the abatement of NO with propene in the presence of O2

FeOx/ZrO2 samples, prepared by impregnation with Fe(NO3)3, were characterised by means of DRS, XRD, FTIR, redox cycles and volumetric CO adsorption. Volumetric CO adsorption, combined with FTIR, showed that 45% of iron in the sample containing 2.8Featomsnm−2 was capable of forming iron carbonyls. DRS evidenced Fe2O3 on samples with Fe-content≥2.8atomsnm−2. The selective catalytic reduction of NO with C3H6 in the presence of O2 was studied with a reactant mixture containing NO=4000ppm, C3H6=4000ppm, O2=2%. The dependence on iron-content suggests that only isolated iron, prevailing in dilute FeOx/ZrO2, is active for NO reduction, whereas iron on the surface of small oxide particles, prevailing in concentrated FeOx/ZrO2, is active for C3H6 combustion.

The role of the global system design in the abatement of NO x in a boiler

The role of the global system design in the abatement of NO x in a boiler

Abatement of NO 3–N concentration in agricultural waters by narrow buffer strips

The performance of narrow buffer strips in abating the NO 3–N concentrations in the water coming from cropland was tested in an experiment carried out on the low plains of the Veneto Region (northeast Italy). The buffer was composed of a 5-m wide grass strip and a 1-m wide row of trees. Maize and wheat were cultivated in the neighbouring field during the monitoring period (December 1997–June 1999). Four experimental conditions were monitored, deriving from a combination of two levels of crop N fertilisation and two sizes of buffer trees. The narrow buffer was very effective in abating NO 3–N concentrations, allowing water to be discharged with a concentration always below 2 ppm. Its zone of influence might be bigger than its simple width. The abatement was also efficient during winter. Tree size showed no evident effect on the reduction of the concentration.

Copper Aluminate Catalysts for Abatement of NO with Propylene or Ammonia in Presence of Excess Oxygen.

To abate NO in exhaust, a series of copper-aluminate catalysts were prepared by calcination at high temperature with high surface area support. Variables were Cu loadings and calcination temperatures. Characterization results show that a copper aluminate phase is formed with spinel type structure through high calcination temperature and copper loading. The activity and stability for NO reduction were studied in a lab. scale reactor in the presence of excess oxygen. The reducing agent was C3H6 or NH3. The catalyst, calcined at high temperature showed enhanced activity in the presence of C3H6, but copper aluminate species, formed by calcination at high temperature, have no effect on NO conversion when NH3 is used as the reducing agent. Engine dynamometer test showed that C3H6 is more effective than C2H5OH to abate nitric oxide with 10 wt.% copper loaded aluminate catalysts.

Abatement technologies for N2O emissions in the adipic acid industry

Adipic acid (AA) is the main intermediate in nylon 6, 6 that is manufactured by polymerization condensation of AH salt (hexamethylenediammonium adipate). Adipic acid is also an intermediate in the production of polyester-polyol, a material used in polyurethane.Annual production capacity of AA for 1998 was estimated to be 2.3 million metric tons and about 80% of that AA is used to manufacture nylon 6, 6. Almost all AA is produced by nitric acid oxidation of KA oil, a mixture of cyclohexanone and cyclohexanol.The reaction of nitric acid oxidation unavoidably generates nitrous oxide. The N2O emission coefficient for Japan's AA plant is approximately 0.25 kg-N2O/kg-AA. If the N2O output from all adipic acid plants is calculated using the N2O emission coefficient described above and the world's AA production capacity then we obtain a figure of 576,250 metric tons per year, but if we calculate only that which will be clearly reduced by 1999–2000, a reduction of ca. 80% has already been achieved. This is because the N2O abatement equipment of the major AA manufacturers is scheduled to have completed startup by 1999–2000.The main technologies used to reduce nitrous oxide in the adipic acid industry are catalytic decomposition and thermal destruction. These methods convert nitrous oxide into nitrogen and oxygen. Catalytic decomposition operates at about 500°C and thermal destruction operates at and over 1000°C. Using these reduction technologies allows the adipic acid manufacturers to reduce N2O emissions by 90% or more.

No abatement with CH4 in the presence of O2 on H-ZSM5 with Si/Al = 15-200: The dependence of activity on the proton concentration

The abatement of NO with methane in the presence of oxygen was studied on commercial H-ZSM5 samples with Si/Al = 15–200 in a conventional flow apparatus. H-ZSM5 samples were used in the acid form or after exchanging protons with sodium ions to various extents. Their catalytic activity was compared with that of commercial H-mordenite and H-Y. On all H-ZSM5 catalysts, reaction rates R NO and \(R_{{\text{CH}}_{\text{4}} }\) (molecules s−1 g−1) increased proportionally to the proton concentration, showing that either all protons or a constant fraction of them were equally active. On sodium-exchanged H-ZSM5 samples with Si/Al = 15–17, both R NO and \(R_{{\text{CH}}_{\text{4}} }\) nearly exponentially increased with the proton concentration. Conversely, on sodium-exchanged H-ZSM5 with Si/Al = 50, both R NO and \(R_{{\text{CH}}_{\text{4}} }\) linearly increased with the proton concentration. At lower Si/Al ratios, replacing the H-ZSM5 protons with sodium ions partly inactivated the remaining protons.

The catalytic activity of CuO x/ZrO 2 for the abatement of NO with propene or ammonia in the presence of O 2

Samples CuO x /ZrO 2 (0.1–8.4 Cu atoms nm −2) were prepared by adsorption or impregnation methods. The characterisation of samples by means of XPS, XRD, DRS, ESR, IR and volumetric adsorption of CO, showed copper dispersion up to 2.5 atoms nm −2, and the presence of CuO in samples with higher Cu content. The selective catalytic reduction of NO with propene or ammonia in the presence of excess oxygen, was studied in a flow apparatus with reactant mixtures of various composition (NO : C 3H 6 : O 2 = 0–4000 ppm : 100–2000 ppm : 0–3.5%; and NO : NH 3 : O 2 = 0–700 ppm : 700 ppm : 3.6%). With both propene and ammonia, CuO x /ZrO 2 catalysts containing up to 2.5 Cu atoms nm −2 were active, selective and stable as a function of the time on stream. On all catalysts, with ammonia as reducing agents, up to 523 K, NO conversion equalled NH 3 conversion leading to 100% selectivity. With both propene and ammonia, NO molecules that were converted to N 2 per Cu atom and per second were nearly independent of the Cu content up to 2.5 Cu atoms nm −2.

Abatement of N2O in the selective catalytic reduction of NOx on platinum zeolite catalysts upon promotion with vanadium

The selectivity to N2O during the selective catalytic reduction of NOx on platinum-containing zeolite catalysts is reduced by incorporation of vanadium into the catalyst.

Combustion Kinetics of Light Hydrocarbons in the Presence of Nitrogen Oxide

An experimental analysis of the interactions between different hydrocarbons and NO is reported. All the experiments have been carried out in a perfectly stirred reactor, operated isothermally in the temperature range 1050-1250 K, with stoichiometric ratios ranging between 1.0 and 1.3. It has been found that, close to the higher temperature values investigated, the NO conversion as a function of the stoichiometric ratio shows a maximum around 1.15-1.20, both in the case of pure methane and methane-ethane mixtures in the feed. Moreover, the addition of NO significantly enhances the system reactivity at the lower temperatures investigated. The ethane content in the feed plays a different role depending upon the temperature value considered. At the lowest temperatures investigated the larger the amount of ethane, the higher the NO abatement, while at the higher temperatures the methane-ethane mixtures always show a larger NO conversion than that of pure methane. However, when increasing the ethane content in the feed, the NO conversion decreases. Finally, various detailed kinetic models (with particular reference to that developed by Miller and Bowman [Prog. Energy Combust. Sci. 1989, 15, 287]) have been discussed and used to interpret the experimental results.

Simultaneous removal of nitrogen oxides and fly-ash from coal-based power-plant flue gases

Catalytic filters are, in principle, capable of performing shallow-bed dust filtration plus a catalytic reaction, promoted by a catalyst deposited in their inner structure. Such a feature may allow potential cost reduction in several environmental applications and particularly in flue-gas treatment of pressurised fluidised-bed coal combustors (e.g. fly-ash removal+selective catalytic reduction of NO x with NH 3). Lab-scale V 2O 5·TiO 2(anatase)-deposited filters were prepared, characterised and tested for their activity towards the SCR reaction. The effect on NO conversion of operating temperature, superficial feed velocity and amount of deposited catalyst was determined. Results were interpreted on the grounds of a specific model, taking into account the mass transfer and reaction kinetics taking place inside the filter. Wide operating margins were found in which nearly complete NO abatement was achieved with negligible by-product release (N 2O, unreacted ammonia) for superficial velocities typical of the industrial practice (5–65 m h −1).

The selective catalytic reduction of NO x with CH 4 on Mn-ZSM5: A comparison with Co-ZSM5 and Cu-ZSM5

The abatement of NO with CH 4 in the presence of O 2 was studied on Mn-ZSM5 (Mn percent exchange 2 to 75%), prepared from Na-ZSM5 by the ion-exchange method. Samples were characterised by FTIR, ESR and magnetic measurements. Both ESR and magnetic measurements showed that all manganese was present as Mn II. FTIR showed the formation of carbonyls (one type only, on manganese equivalent sites). The intensity of bands from carbonyls was almost proportional to the manganese content. The selectivity for NO abatement, reaction orders in O 2, NO or CH 4, and apparent activation energy were independent of the manganese content, suggesting that the same surface complexes were formed on all Mn-ZSM5 catalysts. On Mn-ZSM5, turnover frequencies (molecules s −1 Mn-atom −1) for both NO abatement and CH 4 reaction were nearly independent of the manganese content and close to the relevant values on Co-ZSM5 (previously investigated in our laboratory), but substantially higher than those on Cu-ZSM5 (Cu percent exchange 98%, studied for a comparison). On Mn-ZSM5, Co-ZSM5 and Cu-ZSM5, the adsorption at RT of NO+O 2 or NO 2 caused the formation of nitrates. The normalised intensity (per atom) of monodentate nitrate bands (∼1520 and ∼1320 cm −1) was (i) independent of the metal content, (ii) the same in Mn-ZSM5 and Co-ZSM5, and (iii) much higher in Mn-ZSM5 and Co-ZSM5 than in Cu-ZSM5. On all these catalysts, NO abatement rates were proportional to the concentration of these monodentate nitrates. On FTIR evidence, these species reacted with methane at the same temperature at which the various catalysts were active. These findings suggest a role of monodentate nitrates in the SCR reaction.

Adducts of nitric oxide with cobaltous tetraphenylporphyrin and phthalocyanines: potential nitric oxide sorbents

Cobaltous tetraphenylporphyrin (Co(II) TPP) and cobaltous phthalocyanine (Co(II) Pc) complexes were studied in a variety of solvents, including water. The imidazole and nitrosyl adducts were synthesized and characterized by UV-Vis spectrophotometry and electron spin resonance spectroscopy. The imidazole adducts were subsequently exposed to nitric oxide to study the competitive interactions between nitrosyl and imidazole ligands in these cobaltous compounds. This is important, since it has been suggested that aqueous solutions of cobaltous porphyrins and phthalocyanines can serve as denitrification agents when bound to an immobilized imidazole modified silica gel (IMSG) substrate. Our results indicate that while nitric oxide binds both Co(II) TPP and Co(II) Pc in organic solvents in the absence of a bound imidazole ligand, it will not bind when imidazole is axially bound to the cobalt ion. Neither Co(II) TPP nor Co(II) Pc are water soluble and both will dimerize in water. A water soluble NO sorbent which does not dimerize in water would be ideal for removing NO from flue gas streams. The Co(II) PcTs(IMSG) appears to meet these requirements. Preliminary results indicate that aqueous suspensions of Co(II) PcTs(IMSG) are capable of NO removal from a gas stream passed through these suspensions and may thus be suitable candidates for further development as NO sorbents for NO abatement.

Supported oxides: Preparation, characterization and catalytic activity of CrO x/ZrO 2, MoO x/ZrO 2 and VO x/ZrO 2

In the paper, we review the preparation and the characterization of CrO x /ZrO 2, MoO x /ZrO 2 and VO x /ZrO 2. Catalysts were prepared by various methods (equilibrium adsorption, impregnation or mechanical mixing) and characterized by XRD, XPS, ESR and FTIR techniques. In the paper, we also review the catalytic activity of the ZrO 2 supported systems for propene hydrogenation (CrO x /ZrO 2 and MoO x /ZrO 2), propane or isobutane dehydrogenation (CrO x /ZrO 2), abatement of NO with H 2, propane, or propene (CrO x /ZrO 2), abatement of NO with NH 3 (VO x /ZrO 2). In selected cases, in order to assess the influence of the support on the catalytic activity, we compare the activity of the MeO x /ZrO 2 samples with that of the same MeO x on other supports.

Low-temperature conversion of NO x to N 2 by zeolite-fixed ammonium ions

The selective catalytic reduction (SCR) of NO x in oxygen excess is reported to proceed with good efficiency by NH 4 + ions fixed to zeolites at temperatures as low as 373 K. The reaction starts with almost complete reduction of NO x to N 2 under consumption of NH 4 + ions thereby converting the zeolite into its H + form. The consumed NH 4 + ions can easily be replenished at reaction temperature by admission of gaseous ammonia. A key step of the reaction sequence is the oxidation of NO to NO 2 by O 2 which is catalyzed by the zeolite. Both properties of the zeolite, namely, its storage capacity for NH 3 (in the form of NH 4 + ions) and its oxidation capability for NO allow the abatement of NO x in exhaust gases at low temperatures and in the presence of oxygen without permanent addition of a reductant. This process is named catalytic low temperature conversion (CLTC) of NO x .

What Overall Nitrogen Kinetics can Teach us about Optimizing Catalytic NO Abatement Reactors

Due to the competition of chemical reactions, respectively favorable or defavorable to appropriate performance of finite size catalytic converters, optimum NO conversion may become noticeably dependent on the residence time (or GHSV) of the gaseous reactants. Model computations, required then to assess the optimum temperature-concentrations-residence time relationship, need an appropriate kinetic subroutine. In the present default of detailed, intrinsic catalytic kinetics, it is shown that overall experimental rates, suitably chosen to match the experimental observations, constitute a promising bias as a surrogate chemical subroutine, since, provided they have been determined at conditions identical to the industrial application, (i) they implicitely account for co-controlling physical transport phenomena and (ii) they allow for very acceptable trend predictions even with simple, one dimensional modeling calculations. This is illustrated for three typical cases: (i) NO reduction in gasoline engine exhaust by three-way catalysts, (ii) selective catalytic NO reduction with ammonia (SCR) and (iii) selective NO reduction by hydrocarbons on ZSM5-Cu catalysts in the presence of excess oxygen.

Catalytic activity of Co-ZSM-5 for the abatement of NO x with methane in the presence of oxygen

The abatement of NO with CH 4 in the presence of oxygen ([NO] = [CH 4] = 1000 or 4000 ppm, [O 2] = 0 to 2%, by volume) was studied on Co-ZSM-5 catalysts (Co content 0.29 to 4.1 wt.-%), prepared from H-ZSM-5 or Na-ZSM-5 by the ion-exchange method. On all samples, the amount of CO and NO adsorbed at room temperature was proportional to the cobalt content (CO/Co⋍ 0.5 and NO/Co⋍ 1.6), with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the adsorption was only slightly higher than that on Co-ZSM-5 with Co 2.0 wt.-%. Infrared spectroscopy (FTIR) showed the formation of carbonyls (one type only, on cobalt equivalent sites), cobalt mononitrosyls (two types) and dinitrosyls (two types). The intensity of bands from carbonyls and nitrosyls was about proportional to the cobalt content, with the exception of the Co-ZSM-5 sample with Co 4.1 wt.-%, on which the bands were roughly as intense as in the sample with Co 2.0 wt.-%. In the Co-ZSM-5 sample with Co 4.1 wt.-%, after heating with O 2 at 773 K, or after its use in catalysis, diffuse reflectance spectroscopy (DRS) showed the presence of Co 3O 4, not detected by X-ray diffraction. In the presence of O 2, the NO reduction rate was proportional to the Co content, except for the sample containing Co 4.1 wt.-%. The CH 4 oxidation rate was proportional to the Co content, in the entire range of Co concentrations. The selectivity of catalysts for NO abatement (selective catalytic reduction, SCR), was nearly independent of Co content but was markedly lower on the sample with Co 4.1 wt.-%. The results suggest that only Co II ions exchanged in the framework of the ZSM-5 matrix are active in CO and NO adsorption and in the SCR reaction, whereas also the cobalt of the dispersed Co 3O 4 phase contributes to CH 4 oxidation with O 2.

Photocatalytic property of titanium silicate zeolite

Titanium silicate zeolite was prepared by treating a dealuminated ZSM-5 zeolite with the vapor of titanium tetrachloride, and characterized by means of XRD, FT-IR, XPS, UV-Vis and photoluminescence spectroscopies. By the introduction of titanium, the zeolite had a unique absorption phenomenon and an emission band and became sensitive to UV irradiation. The obtained titanium silicate zeolites showed catalytic activity for abatement of NO at room temperature under UV irradiation.

Selective catalytic reduction of nitrogen oxide by use of the Ljungstroem air heater as reactor: a case study

A new NO abatement strategy proposes the use of the Ljungstroem air heater of the power plant as a chemical reactor, covering the air heater elements with a catalyst. A simple model has been developed to predict the performance of such a catalyst air heater. The model calculations are based on kinetic data obtained by laboratory scale experiments. The comparison of the calculated results with preliminary experimental data of a full-scale installed catalyst air heater proves the validity of the approach chosen. The catalyst air heater provides substantial NO reduction potential without requiring major modifications of existing power plant equipment.

Nitrous Oxide Formation and Destruction by Industrial No Abatement Techniques Including Scr

Systematic investigations on N2O emission from full scale stationary combustion units, equipped with primary or secondary NO control techniques, are scarce or inexistent. Recent results obtained from laboratory scale studies are presented, from which it appears that fuel staging, selective non catalytic NO reduction with ammonia and selective catalytic NO reduction in the presence of ammonia, should be considered as potential sources of nitrous oxide emission enhancement. For the two mentioned gas phase NO abatement techniques (fuel staging and NCSR), this N2O emission enhancement is clearly linked with a decrease of the temperature, a result that might have been expected from the known gas phase reactions of N2O formation and destruction. Production of N2O from NCSR is more important than from fuel staging, and increases with ammonia concentration; this probably is related to the fact that ammonia yields N2O precursors (NH, NH2) readily by its decomposition. Separate injection of pure NO or NH3 suggests that N2O is a product of the interaction of those two reactants, whereas NO also is formed as a primary ammonia decomposition product in the presence of oxygen. A kinetic investigation of N2O formation from SCR has been made. It is shown that catalytic decomposition of neat ammonia yields both NO and N2O, the former as a primary product (from adsorbed ammonia and solid bound oxygen), the latter as a secondary product (from NO and adsorbed ammonia). Both NO and N2O subsequently undergo catalytic decomposition. In the presence of molecular oxygen, another NO formation (from O2 and adsorbed ammonia) manifests itself at somewhat higher temperatures, creating the well known optimum temperature window . Comparative tests conducted on a number of metal oxides, tend to show that high efficiency for NO decomposition is often related to high production of N2O within the temperature window .

In-furnace reduction of NO x during the parallel-flow moving-bed combustion of surplus activated sludge char by an active use of self-evolved ammonia

A novel approach is proposed for the abatement of NO x from moving-bed combustion of surplus activated sludge containing large amounts of organic nitrogen compounds. The primary feature of the proposed low-NO x combustion technique is that self-evolved NH 3 from the initial pyrolysis of the sludge is actively utilized for in-furnace reduction of NO x produced during combustion. Although NH 3, HCN, NO x and N 2 were detected as the gaseous nitrogen compounds in the initial pyrolysis, the main ingredient of these products was NH 3 at temperatures between 750 and 1000 K. The NH 3 injected into the parallel-flow moving-bed combustor was found to be extremely potent for the abatement of NO x only at air-fuel stoichiometric ratios of 1.05-1.3 but had a negative effect at the other ratios.