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1.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
2.
Reaction activities of several developed catalysts for NO oxidation and NO x (NO + NO 2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co 3O 4 based catalysts are the most active ones for both NO oxidation and NO x reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co 3O 4 catalyst, the effects of calcination temperatures, SO 2 concentration, optimum SV for 50% conversion of NO to NO 2 were determined. Also, Co 3O 4 based catalysts (Co 3O 4-WO 3) exhibit significantly higher conversion than all the developed DeNO x catalysts (supported/unsupported) having maximum conversion of NO x even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N 2O formation over Co 3O 4-WO 3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N 2O over all the catalysts. The effect of SO 2 concentration on NO x reduction is found to be almost negligible may be due to the presence of WO 3 that resists SO 2 oxidation. 相似文献
3.
The adsorption of HCN on, its catalytic oxidation with 6% O 2 over 0.5% Pt/Al 2O 3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N 2O, NO and NO 2, and some residual adsorbed N-containing species were oxidized to NO and NO 2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N 2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 °C. Furthermore, the temperature of maximum HCN conversion to N 2O is located between 200 and 250 °C, while raising the reaction temperature increases the proportion of NO x in the products. The co-feeding of H 2O and C 3H 6 had little, if any effect on the total HCN conversion, but C 3H 6 addition did increase the conversion to NO and decrease the conversion to NO 2, perhaps due to the competing presence of adsorbed fragments of reductive C 3H 6. Evidence is also presented that introduction of NO and NO 2 into the reactant gas mixture resulted in additional reaction pathways between these NO x species and HCN that provide for lean-NO x reduction coincident with HCN oxidation. 相似文献
4.
The release and reduction of NO x in a NO x storage-reduction (NSR) catalyst were studied with a transient reaction analysis in the millisecond range, which was made possible by the combination of pulsed injection of gases and time resolved time-of-flight mass spectrometry. After an O 2 pulse and a subsequent NO pulse were injected into a pellet of the Pt/Ba/Al 2O 3 catalyst, the time profiles of several gas products, NO, N 2, NH 3 and H 2O, were obtained as a result of the release and reduction of NO x caused by H 2 injection. Comparing the time profiles in another analysis, which were obtained using a model catalyst consisting of a flat 5 nmPt/Ba(NO 3) 2/cordierite plate, the release and reduction of NO x on Pt/Ba/Al 2O 3 catalyst that stored NO x took the following two steps; in the first step NO molecules were released from Ba and in the second step the released NO was reduced into N 2 by H 2 pulse injection. When this H 2 pulse was injected in a large amount, NO was reduced to NH 3 instead of N 2. A only small amount of H2O was detected because of the strong affinity for alumina support. We can analyze the NOx regeneration process to separate two steps of the NOx release and reduction by a detailed analysis of the time profiles using a two-step reaction model. From the result of the analysis, it is found that the rate constant for NOx release increased as temperature increase. 相似文献
5.
In this paper, the effect of CO 2 and H 2O on NO x storage and reduction over a Pt–Ba/γ-Al 2O 3 (1 wt.% Pt and 30 wt.% Ba) catalyst is shown. The experimental results reveal that in the presence of CO 2 and H 2O, NO x is stored on BaCO 3 sites only. Moreover, H 2O inhibits the NO oxidation capability of the catalyst and no NO 2 formation is observed. Only 16% of the total barium is utilized in NO storage. The rich phase shows 95% selectivity towards N 2 as well as complete regeneration of stored NO. In the presence of CO 2, NO is oxidized into NO 2 and more NO x is stored as in the presence of H 2O, resulting in 30% barium utilization. Bulk barium sites are inactive in NO x trapping in the presence of CO 2·NH 3 formation is seen in the rich phase and the selectivity towards N 2 is 83%. Ba(NO 3) 2 is always completely regenerated during the subsequent rich phase. In the absence of CO 2 and H 2O, both surface and bulk barium sites are active in NO x storage. As lean/rich cycling proceeds, the selectivity towards N 2 in the rich phase decreases from 82% to 47% and the N balance for successive lean/rich cycles shows incomplete regeneration of the catalyst. This incomplete regeneration along with a 40% decrease in the Pt dispersion and BET surface area, explains the observed decrease in NO x storage. 相似文献
6.
In this work, a kinetic model is constructed to simulate sulfur deactivation of the NO x storage performance of BaO/Al 2O 3 and Pt/BaO/Al 2O 3 catalysts. The model is based on a previous model for NO x storage under sulfur-free conditions. In the present model the storage of NO x is allowed on two storage sites, one for complete NO x uptake and one for a slower NO x sorption. The adsorption of SO x is allowed on both of these NO x storage sites and on one additional site which represent bulk storage. The present model is built-up of six sub-models: (i) NO x storage under sulfur-free conditions; (ii) SO 2 storage on NO x storage sites; (iii) SO 2 oxidation; (iv) SO 3 storage on bulk sites; (v) SO 2 interaction with platinum in the presence of H 2; (vi) oxidation of accumulated sulfur compounds on platinum by NO 2. Data from flow reactor experiments are used in the implementation of the model. The model is tested for simulation of experiments for NO x storage before exposure to sulfur and after pre-treatments either with SO 2 + O 2 or SO 2 + H 2. The simulations show that the model is able to describe the main features observed experimentally. 相似文献
7.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
8.
A series of 1 wt.%Pt/ xBa/Support (Support = Al 2O 3, SiO 2, Al 2O 3-5.5 wt.%SiO 2 and Ce 0.7Zr 0.3O 2, x = 5–30 wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO x trapping (100 s). Catalysts were treated at 700 °C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO 2-TPD. At high temperature (400 °C) in the absence of CO 2 and H 2O, the NO x storage capacity increased with the catalyst basicity: Pt/20Ba/Si < Pt/20Ba/Al5.5Si < Pt/10Ba/Al < Pt/5Ba/CeZr < Pt/30Ba/Al5.5Si < Pt/20Ba/Al < Pt/10BaCeZr. Addition of CO 2 decreased catalyst performances. The inhibiting effect of CO 2 on the NO x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO 2 and H 2O were present in the inlet gas, a cumulative effect was observed at low temperatures (200 °C and 300 °C) whereas mainly CO 2 was responsible for the loss of NO x storage capacity at 400 °C. Finally, under realistic conditions (H 2O and CO 2) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO x uptake in the 200–400 °C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO 2 competition for the storage sites. 相似文献
9.
The selective catalytic reduction (SCR) of nitrogen oxides (NO x) by propane in the presence of H 2 on sol–gel prepared Ag/Al 2O 3 catalysts (0.5–5 wt.% Ag) was investigated. It was confirmed that hydrocarbon-assisted SCR of NO x is remarkably enhanced by co-feeding hydrogen to a lean exhaust gas mixture (λ>1), attaining considerable activity within a wide temperature window (470–825 K). The samples had marginal activity at 575 K without co-fed H 2, but achieved up to 60% NO x conversion in the presence of H 2 at a space velocity of 30,000 h −1. NO 2 as NO x feed component is not converted to N 2 by C 3H 8 to a substantial extent under lean conditions. This points to an activation route of NO through direct conversion to adsorbed nitrite/nitrate or to a dissociation of NO over Ag 0, formed through short-term reduction by H 2. The nature of Ag species was characterized by X-ray diffraction, temperature-programmed reduction, pulse thermoanalytical measurements, electron microscopy and FTIR spectroscopy. It could be shown that Ag 2O nano-sized clusters are predominantly present on all samples, whereas formation of silver aluminate could not be confirmed. Nano-sized Ag 2O clusters can reversibly be reduced/reoxidized by H 2. A silver loading higher than 2 wt.% leads to a part of Ag 2O particles, which are thermally decomposed during calcination at 800 K or higher. The catalytic role of this metallic silver is still unclear. Formal kinetic analysis of catalytic data revealed that the activation energy of the overall reaction is significantly lowered in the presence of H 2. The presence of water does not change the activation energy. It is concluded that hydrogen reduces the nano-sized Ag 2O clusters to Ag 0 on a short-term scale. Zero-valent silver promotes a dissociation pathway of NO x conversion. The fact that more oxidized ad-species (nitrite/nitrate) are observed in the presence of H 2 is attributed to a dissociative activation of gas-phase oxygen on Ag 0. 相似文献
10.
The effect of different reducing agents (H 2, CO, C 3H 6 and C 3H 8) on the reduction of stored NO x over PM/BaO/Al 2O 3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO 2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H 2 and CO have a relatively high NO x reduction efficiency compared to C 3H 6 and especially C 3H 8 that does not show any NO x reduction ability except at 350 °C over Pd/BaO/Al 2O 3. The type of precious metals affects the NO x storage-reduction properties, where the Pd/BaO/Al 2O 3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al 2O 3 catalyst shows a high reduction ability but a relatively low NO x storage capacity. 相似文献
11.
Combined effect of H 2O and SO 2 on V 2O 5/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2, H 2O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2O and reactants (NO and/or NH 3). Although SO 2 promotes the SCR activity of the V 2O 5/AC catalyst in the absence of H 2O, it speeds the deactivation of the catalyst in the presence of H 2O. The dual effect of SO 2 is attributed to the SO 42− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C. 相似文献
12.
The formation and stability of BaAl 2O 4 and BaCeO 3 in Pt-Ba/Al 2O 3 and Pt-Ba/CeO 2 based NO x storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO 3. The formation of BaAl 2O 4 started above 850 °C, whereas the formation of BaCeO 3 was already observed at 800 °C and was faster than that of BaAl 2O 4. The stability of BaAl 2O 4 and BaCeO 3 in various liquid and gaseous atmospheres was different. BaAl 2O 4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO 3) 2 and γ-alumina in the presence of HNO 3, whereas BaCeO 3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO 3 was transformed to Ba(NO 3) 2/CeO 2 in the presence of NO 2/H 2O at 300–500 °C. Also, the presence of CO 2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NO x-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts. 相似文献
13.
Phase changes in high temperature treated (>900 °C) 8 or 20 wt% BaO supported on γ-Al 2O 3 model lean NO x trap (LNT) catalysts, induced by NO 2 and/or H 2O adsorption, were investigated with powder X-ray diffraction (XRD), solid state 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and NO 2 temperature programmed desorption (TPD) experiments. After calcination in dry air at 1000 °C, the XRD and solid state 27Al MAS NMR results confirm that stable surface BaO and bulk BaAl 2O 4 phases are formed for 8 and 20 wt% BaO/Al 2O 3, respectively. Following NO 2 adsorption over these thermally treated samples, some evidence for nanosized Ba(NO 3) 2 particles are observed in the XRD results, although this may represent a minority phase. However, when water was added to the thermally aged samples after NO 2 exposure, the formation of bulk crystalline Ba(NO 3) 2 particles was observed in both samples. Solid state 27Al MAS NMR is shown to be a good technique for identifying the various Al species present in the materials during the processes studied here. NO 2 TPD results demonstrate a significant loss of uptake for the 20 wt% model catalysts upon thermal treatment. However, the described phase transformations upon subsequent water treatment gave rise to the partial recovery of NO x uptake, demonstrating that such a water treatment of thermally aged catalysts can provide a potential method to regenerate LNT materials. 相似文献
14.
For the first time, the coupling of fast transient kinetic switching and the use of an isotopically labelled reactant ( 15NO) has allowed detailed analysis of the evolution of all the products and reactants involved in the regeneration of a NO x storage reduction (NSR) material. Using realistic regeneration times (ca. 1 s) for Pt, Rh and Pt/Rh-containing Ba/Al 2O 3 catalysts we have revealed an unexpected double peak in the evolution of nitrogen. The first peak occurred immediately on switching from lean to rich conditions, while the second peak started at the point at which the gases switched from rich to lean. The first evolution of nitrogen occurs as a result of the fast reaction between H 2 and/or CO and NO on reduced Rh and/or Pt sites. The second N 2 peak which occurs upon removal of the rich phase can be explained by reaction of stored ammonia with stored NO x, gas phase NO x or O 2. The ammonia can be formed either by hydrolysis of isocyanates or by direct reaction of NO and H 2. The study highlights the importance of the relative rates of regeneration and storage in determining the overall performance of the catalysts. The performance of the monometallic 1.1%Rh/Ba/Al2O3 catalyst at 250 and 350 °C was found to be dependent on the rate of NOx storage, since the rate of regeneration was sufficient to remove the NOx stored in the lean phase. In contrast, for the monometallic 1.6%Pt/Ba/Al2O3 catalyst at 250 °C, the rate of regeneration was the determining factor with the result that the amount of NOx stored on the catalyst deteriorated from cycle to cycle until the amount of NOx stored in the lean phase matched the NOx reduced in the rich phase. On the basis of the ratio of exposed metal surface atoms to total Ba content, the monometallic 1.6%Pt/Ba/Al2O3 catalyst outperformed the Rh-containing catalysts at 250 and 350 °C even when CO was used as a reductant. 相似文献
15.
Catalytic reduction of NO by propene in the presence of oxygen was studied over SnO 2-doped Ga 2O 3–Al 2O 3 prepared by sol–gel method. Although SnO 2-doped Ga 2O 3–Al 2O 3 gave lower NO conversion than Ga 2O 3–Al 2O 3 in the absence of H 2O, the activity was enhanced considerably by the presence of H 2O and much higher than that of Ga 2O 3–Al 2O 3. The presence of SnO 2 and Ga 2O 3–Al 2O 3 species having intimate Ga–O–Al bondings was found to be essential for the promotional effect of H 2O. The promotional effect of H 2O was interpreted by the following two reasons. The first one is the removal of carbonaceous materials deposited on the catalyst surface by H 2O. The other is the selective inhibition by H 2O of the reaction steps resulting in propene oxidation to CO x without reducing NO. 相似文献
16.
The role of a multifunctional catalyst for de-NO x process has been investigated. The NO x storage capacity of H 3PW 12O 40·6H 2O (HPW) was improved by the presence of a noble metal (Pt, Rh or Pd). Both HPW and noble metal were deposited on a specific support (based on Zr–Ce or Zr–Ti). The presence of noble metal in several oxidation states, as evidenced by TPR and IR, involves the possibility of forming different catalytic sites: (i) M 0 (zero-valent metal) and perhaps (ii) (metal–H) δ+ from specific interactions between noble metal and the HPW proton. Supports were also able to adsorb and activate NO x and to generate cationic catalytic sites (M x+). These cationic sites seem to be the clue for their important activity toward NO x reduction. This catalyst presents an outstanding resistance to SO 2 poisoning which can be related to NO and NO 2 absorption mechanism in HPW. The use of alternating short cycles of lean/rich mixtures allows us optimising the performance of this catalytic system in terms of both NO x reduction capacity and NO x storage efficiency: up to 48 and 84%, respectively (with a 2% CO + 1% H 2 mixture for reducing). Experimental results sustain two hypotheses: first, HPW-metal-support catalyst includes several (independent) catalytic functions required for a de-NO x process to occur and second, the formation of oxygenate active species must be indispensable for NO x reduction into nitrogen. 相似文献
17.
A mean field model, for storage and desorption of NO x in a Pt/BaO/Al 2O 3 catalyst is developed using data from flow reactor experiments. This relatively complex system is divided into five smaller sub-systems and the model is divided into the following steps: (i) NO oxidation on Pt/Al 2O 3; (ii) NO oxidation on Pt/BaO/Al 2O 3; (iii) NO x storage on BaO/Al 2O 3; (iv) NO x storage on Pt/BaO/Al 2O 3 with thermal regeneration and (v) NO x storage on Pt/BaO/Al 2O 3 with regeneration using C 3H 6. In this paper, we focus on the last sub-system. The kinetic model for NO x storage on Pt/BaO/Al 2O 3 was constructed with kinetic parameters obtained from the NO oxidation model together with a NO x storage model on BaO/Al 2O 3. This model was not sufficient to describe the NO x storage experiments for the Pt/BaO/Al 2O 3, because the NO x desorption in TPD experiments was larger for Pt/BaO/Al 2O 3, compared to BaO/Al 2O 3. The model was therefore modified by adding a reversible spill-over step. Further, the model was validated with additional experiments, which showed that NO significantly promoted desorption of NO x from Pt/BaO/Al 2O 3. To this NO x storage model, additional steps were added to describe the reduction by hydrocarbon in experiments with NO 2 and C 3H 6. The main reactions for continuous reduction of NO x occurs on Pt by reactions between hydrocarbon species and NO in the model. The model is also able to describe the reduction phase, the storage and NO breakthrough peaks, observed in experiments. 相似文献
18.
In this work, we investigated the activity and stability of Ag–alumina catalysts for the SCR of NO with methane in gas streams with a high concentration of SO 2, typical of coal-fired power plant flue gases. Ag–alumina catalysts were prepared by coprecipitation–gelation, and dilute nitric-acid solutions were used to remove weakly bound silver species from the surface of the as prepared catalysts after calcination. SO 2 has a severe inhibitory effect, essentially quenching the CH 4-SCR reaction on this type catalysts at temperatures <600 °C. SO 2 adsorbs strongly on the surface forming aluminum and silver sulfates that are not active for CH 4-SCR of NO x. Above 600 °C, however, the reaction takes place without catalyst deactivation even in the presence of 1000 ppm SO 2. The reaction light-off coincides with the onset of silver sulfate decomposition, indicating the critical role of silver in the reaction mechanism. SO 2 is reversibly adsorbed on silver above 600 °C. While alumina sites remain sulfated, this does not hinder the reaction. Sulfation of alumina only decreases the extent of adsoption of NO x, but adsorption of NO x is not the limiting step. Methane activation is the limiting step, hence the presence of sulfur-free Ag–O–Al species is a requirement for the reaction. Strong adsorption of SO 2 on Ag–alumina decreases the rates of the reaction, and increases the activation energies of both the reduction of NO to N 2 and the oxidation of CH 4, the latter more than the former. Our results indicate partial contribution of gas phase reactions to the formation of N 2 above 600 °C. H 2O does not inhibit the reaction at 625 °C, and the effect of co-addition of H 2O and SO 2 is totally reversible. 相似文献
19.
The catalytic activity of Pt on alumina catalysts, with and without MnO x incorporated to the catalyst formulation, for CO oxidation in H 2-free as well as in H 2-rich stream (PROX) has been studied in the temperature range of 25–250 °C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2 wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15 wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al 2O 3. A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15 wt.% Mn operating at 139 °C and λ = 2. The effect of the presence of 5 vol.% CO 2 and 5 vol.% H 2O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO 2 in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnO x content. 相似文献
20.
NO x reduction with NO 2 as the NO x gas in the absence of plasma was compared to plasma treated lean NO x exhaust where NO is converted to NO 2 in the plasma. Product nitrogen was measured to prove true chemical reduction of NO x to N 2. With plasma treatment, NO as the NO x gas, and a NaY catalyst, the maximum conversion to nitrogen was 50% between 180 and 230 °C. The activity decreased at higher and lower temperatures. At 130 °C a complete nitrogen balance could be obtained, however between 164 and 227 °C less than 20% of the NO x is converted to a nitrogen-containing compound or compounds not readily detected by gas chromatograph (GC) or Fourier transform infrared spectrometer (FT-IR) analysis. With plasma treatment, NO 2 as the NO x gas, and a NaY catalyst, a complete nitrogen balance is obtained with a maximum conversion to nitrogen of 55% at 225 °C. For γ-alumina, with plasma treatment and NO2 as the NOx gas, 59% of the NOx is converted to nitrogen at 340 °C. A complete nitrogen balance was obtained at these conditions. As high as 80% NOx removal over γ-alumina was measured by a chemiluminescent NOx meter with plasma treatment and NO as the NOx gas. When NO is replaced with NO2 and the simulated exhaust gases are not plasma treated, the maximum NOx reduction activity of NaY and γ-alumina decreases to 26 and 10%, respectively. This is a large reduction in activity compared to similar conditions where the simulated exhaust was plasma treated. Therefore, in addition to NO2, other plasma-generated species are required to maximize NOx reduction. 相似文献
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