Lean NO Research Articles

Thermal decomposition of dispersed and bulk-like NOx species in model NOx trap materials

The thermal decomposition of bulk Ba(NO3)2, Ba(NO3)2 impregnated on γ-Al2O3, and the release of NO2 stored on BaO/γ-Al2O3 are investigated by thermogravimetric analysis (TGA) and infrared spectroscopy (IR) as a function of baria loading. Two distinct weight loss events at ∼434°C and ≥545°C are observed on the γ-Al2O3 supported samples, corresponding to the decomposition of dispersed and bulk-like Ba(NO3)2 to BaO, respectively. Decomposition of dispersed phase having a temperature of 150°C lower than bulk Ba(NO3)2 is attributed to a strong interaction between dispersed BaO and alumina. Bulk-like phase shows a similar decomposition characteristics to bulk Ba(NO3)2 as BaO loading increases to 31.8%. The decomposition products vary from predominantly NO2 at low temperature (≤434°C) to NO at high temperature (≥545°C), consistent with the trend expected from the NO2↔NO+1/2O2 thermal equilibrium. As the total baria loading is increased, the amount of dispersed phase saturates at a baria loading of 14% (w/w) while the bulk-like phase increases without reaching saturation. Both phases can be regenerated on 15min exposure of corresponding BaO/Al2O3 to NO2 at room temperature. The release of these regenerated nitrates mimics the decomposition characteristics of impregnated Ba(NO3)2 on γ-Al2O3. X-ray powder diffraction and IR spectra show that the stored NO2 species gradually convert to a crystalline, bulk-like Ba(NO3)2 phase when aged at room temperature. These results are useful for optimizing BaO loading strategies for lean NOx trap catalyst.

Mechanistic study of the influence of surface acidity on lean NO 2 reduction by propane in HZSM-5

This study focuses on the mechanism of lean NO x reduction by propane, over acidic zeolites (HZSM-5), and the influence of surface acidity. In situ FTIR measurements of ammonia adsorption indicate a higher number of Brønsted acid sites for a sample with a low SiO 2/Al 2O 3 ratio. The activity for NO x reduction and the selectivity for N 2 formation correlate well with the Brønsted acidity. Step-response experiments with NO 2 and propane show the formation of surface-bound NO +, isocyanate, unsaturated hydrocarbons, and amine species. Formation of the latter two seems to be closely related to the Brønsted acidity. In the NO 2 reaction with propane, the NO + species seem to play a vital role, probably reacting with carbenium ions (from propane cracking) to form isocyanates, which may be hydrolysed to amine species. Step-response experiments with isopropylamine and NO 2 indicate a fast reaction, where the amine and NO + species react over Brønsted acid sites. Hence, amine species are possible reaction intermediates in the lean reduction of NO 2 by saturated hydrocarbons, such as propane, over HZSM-5.

Supported Bimetallic Pd‐Co Catalysts: Characterization and Catalytic Activity.

Abstract The aim of this contribution is to present a general overview about the effect of palladium addition to supported cobalt catalysts. First, the promotion of supported monometallic catalysts by the addition of a second component is described from a general point of view. Then, the properties of bimetallic Pd–Co supported on inorganic oxides are illustrated from the most relevant reports given in the literature. These works have been mainly performed on metallic catalysts under reducible atmospheres for important reactions like hydrogenation of butadiene, Fisher–Tropsch and methane activation under nonoxidative conditions. The last part is concentrated on Pd–Co zeolite-supported catalysts which have exhibited much more resistance to water vapor for lean NO x reduction by CH 4 than either Pd or Co monometallic loaded zeolites under net oxidizing conditions. Recent results about the synergism of cobalt and palladium in zeolites and sulfated zirconia are discussed in terms of the effects of catalyst preparation and pretreatment, type of support and gas phase composition on the selectivity and stability of these catalysts for the selective catalytic reduction (SCR) of NO by methane.

Novel Ag–Pd/Al 2O 3–SiO 2 for lean NO x reduction by C 3H 6 with high tolerance of SO 2

Activity test and in situ DRIFTS experiments were carried out on the selective catalytic reduction of NO x by propene over Ag (5 wt%)–Pd (0.01 wt%)/Al 2O 3 and Ag (5 wt%)–Pd (0.01 wt%)/Al 2O 3–SiO 2. The activity test results showed that the Ag–Pd/Al 2O 3–SiO 2 had a higher NO x conversion than Ag–Pd/Al 2O 3 in the presence of SO 2. The in situ DRIFTS results showed the SO 2 poisoned Ag–Pd (0.01 wt%)/Al 2O 3 surface inhibited the formation of enolic species and NO 3 - , which are reactive intermediates to form –NCO species. However, the SO 2 poisoned Ag–Pd (0.01 wt%)/Al 2O 3–SiO 2 surface can hardly affect the formation of enolic species, NO 3 - and –NCO species. The reaction mechanism of NO x reduction and the effect of adding SiO 2 are discussed based on these results.

LES studies of the flow in a swirl gas combustor

Environmental and other practical concerns have led to the development of compact gas turbine combustors burning lean mixtures leading to potentially low CO and NO x emissions. The compact design requires efficient atomization and mixing together with a compact premixed flame. Associated with these requirements are higher temperatures, increased heat transfer, and thermal load, thus increasing the danger of combustion instabilities (causing performance deterioration and excessive mechanical loads), and possible off-design operation. Numerical simulations of reacting flows are well suited to address these issues. To this end, large eddy simulation (LES) is particularly promising. The philosophy behind LES is to explicitly simulate the large scales of the flow and the thermochemistry, affected by boundary conditions whilst modeling only the small scales, including the interaction between the flow and the combustion processes. Here, we examine the flow and the flame in a model gas turbine combustor (General Electric’s lean premixed dry low NO x LM6000) to evaluate the potential of LES for design studies of engineering applications and to study the effects of the combustor confinement geometry on the flow and on the flame dynamics. Two LES models, a Monotone Integrated LES model with 1 and 2 step Ahrrenius chemistry, and a fractal flame-wrinkling LES model coupled to a conventional one-equation eddy-viscosity subgrid model, are used. Reasonable agreement is found when comparing predictions with experimental data and with other LES computations of the same case. Furthermore, the combustor confinement geometry is found to strongly affect the vortical flow, and hence also the flame and its dynamics.

Screening by Kinetic Monte Carlo Simulation of Pt−Au(100) Surfaces for the Steady-State Decomposition of Nitric Oxide in Excess Dioxygen

An ab initio-based kinetic Monte Carlo algorithm was developed to simulate the direct decomposition of NO over Pt and different PtAu alloy surfaces. The algorithm was used to test the influence of the composition and the specific atomic surface structure of the alloy on the simulated activity and selectivity to form N2. The apparent activation barrier found for the simulation of lean NO decomposition over Pt(100) was 7.4 kcal/mol, which is lower than the experimental value of 11 kcal/mol that was determined over supported Pt nanoparticles. Differences are likely due to differences in the surface structure between the ideal (100) surface and supported Pt particles. The apparent reaction orders for lean NO decomposition over the Pt(100) substrate were calculated to be 0.9 and -0.5 for NO and O2, respectively. Oxygen acts to poison Pt. Simulations on the different Pt-Au(100) surface alloys indicate that the turnover frequency goes through a maximum as the Au composition in the surface is increased, and the maximum occurs near 44% Au. Turnover frequencies, however, are dictated by the actual arrangements of Pt and Au atoms in the surface rather than by their overall composition. Surfaces with similar compositions but different alloy arrangements can lead to very different activities. Surfaces composed of 50% Pt and 50% Au (Pt4 and Au4 surface ensembles) showed very little enhancement in the activity over that which was found over pure Pt. The Pt-Pt bridge sites required for NO adsorption and decomposition were still effectively poisoned by atomic oxygen. The well-dispersed Pt(50%)Au(50%) alloy, on the other hand, increased the TOF over that found for pure Pt by a factor of 2. The most active surface alloy was one in which the Pt was arranged into "+" ensembles surrounded by Au atoms. The overall composition of this surface is Pt(56.2%)Au(43.8%). The unique "+" ensembles maintain Pt bridge sites for NO to adsorb on but limit O2 as well as NO activation by eliminating next-nearest neighbor Pt-bridge sites. The repulsive interactions between two adatoms prevent them from sharing the same metal atoms. The decrease in the oxygen coverage leads to a greater number of vacant sites available for NO adsorption. This increases the NO coupling reaction and hence N2 formation. The inhibition of the rate of N2 formation by O2 is therefore suppressed. The coverage of atomic oxygen decreases from 53% on the Pt(100) surface down to 19% on the "+" ensemble surface. This increases the rate of N2 formation by a factor of 4.3 over that on pure Pt. The reaction kinetics over the "+" ensemble Pt(56.2%)Au(43.8%) surface indicate apparent reaction orders in NO and oxygen of 0.7 and 0.0, respectively. This suggests that oxygen does not poison the PtAu "+" alloy ensemble. The activity and selectivity of the PtAu ensembles significantly decrease for alloys that go beyond 60% Au. Higher coverages of Au shut down sites for NO adsorption and, in addition, weaken the NO and O bond strengths, which subsequently promotes desorption as well as NO oxidation. The computational approach identified herein can be used to more rapidly test different metal compositions and their explicit atomic arrangements for improved catalytic performance. This can be done "in silico" and thus provides a method that may aid high-throughput experimental efforts in the design of new materials. The synthesis and stability of the metal complexes suggested herein still ultimately need to be tested.

Role of Pt-precursor on the performance of Pt/BaCO3/Al2O3·NOx storage catalysts

Monolith Pt/BaCO 3 /Al 2 O 3 NO x storage catalysts were prepared using one of the following platinum precursors for each catalyst: (i) hexachloroplatinic acid [H 2 Pt(Cl) 6 ], (ii) tetraammineplatinum hydroxide [Pt(NH 3 ) 4 (OH) 2 ], (iii) diammineplatinum nitrite [Pt(NH 3 ) 2 (NO 2 ) 2 ] and (iv) platinum nitrate [Pt(NO 3 ) 2 ]. The Pt dispersion is strongly affected by the interaction between the Pt complex and the BaCO 3 /γ-Al 2 O 3 surface during the Pt impregnation. The influence of the choice of platinum precursor on the catalytic performance of Pt/BaCO 3 /Al 2 O 3 NO x storage catalysts was studied. The precursors used in the preparation of the catalysts were: (i) hexachloroplatinic acid [H 2 Pt(Cl) 6 ], (ii) tetraammineplatinum hydroxide [Pt(NH 3 ) 4 (OH) 2 ], (iii) diammineplatinum nitrite [Pt(NH 3 ) 2 (NO 2 ) 2 ] and (iv) platinum nitrate [Pt(NO 3 ) 2 ]. The catalytic activity of the prepared catalysts was tested for continuous lean NO x reduction with C 3 H 6 , NO x storage and reduction, and NO 2 dissociation in a flow reactor. The reactor experiments show that the sample prepared using platinum nitrate is the most active catalyst followed by the catalyst prepared from tetraammineplatinum hydroxide. The catalyst prepared from hexachloroplatinic acid is more active for continuous NO x reduction, and NO x storage and reduction than the catalyst prepared from diammineplatinum nitrite, but deactivates faster during NO 2 dissociation than the catalyst prepared using diammineplatinum nitrite. In order to be able to predict mechanisms for the interaction between the platinum precursors and the BaCO 3 /Al 2 O 3 surface during the platinum impregnation, powder samples of γ-Al 2 O 3 , BaCO 3 and BaCO 3 precipitated on γ-Al 2 O 3 were studied using FTIR and zeta potential measurements. Additionally, XRD measurements were performed to verify the transformation of the barium precursor to BaCO 3 . The results from these studies show that up to 18% BaO content, the BaCO 3 /Al 2 O 3 surfaces contain domains of both BaCO 3 and Al 2 O 3 .

Supported bimetallic Pd–Co catalysts: characterization and catalytic activity

The aim of this contribution is to present a general overview about the effect of palladium addition to supported cobalt catalysts. First, the promotion of supported monometallic catalysts by the addition of a second component is described from a general point of view. Then, the properties of bimetallic Pd–Co supported on inorganic oxides are illustrated from the most relevant reports given in the literature. These works have been mainly performed on metallic catalysts under reducible atmospheres for important reactions like hydrogenation of butadiene, Fisher–Tropsch and methane activation under nonoxidative conditions. The last part is concentrated on Pd–Co zeolite-supported catalysts which have exhibited much more resistance to water vapor for lean NO x reduction by CH 4 than either Pd or Co monometallic loaded zeolites under net oxidizing conditions. Recent results about the synergism of cobalt and palladium in zeolites and sulfated zirconia are discussed in terms of the effects of catalyst preparation and pretreatment, type of support and gas phase composition on the selectivity and stability of these catalysts for the selective catalytic reduction (SCR) of NO by methane.

Novel nanocrystalline Ga–Al–Zn complex oxide: catalyst for simultaneous treatment of NPAC and lean NO x

Nanocrystalline Ga–Al–Zn complex-oxide (designated here as nano-GAZ) has been successfully synthesized using hydrothermal method. Using TEM, BET, FTIR, DTA–TGA, and XRD, synthesized nano-GAZ particles are shown as high-surface-area nanoparticles comprising typical spinel crystal structures. The nano-GAZ catalyst was tested as a new deNPAC catalyst, using pyridine as the model NPAC compound. The reaction results show that pyridine could be completely oxidized over nano-GAZ catalyst above 400 °C. Furthermore, NO formation was significantly decreased due to the excellent performance of the nano-GAZ catalyst for the selective catalytic reduction of NO x with hydrocarbon in the presence of excess oxygen. An optimal reaction temperature at around 440–500 °C was observed to achieve complete catalytic oxidation of pyridine with the lowest NO x formation. These results demonstrate a promising approach for dual-mitigation of NPAC and NO x pollutants using nano-GAZ catalyst.

Dynamics of storage and reaction in a monolith reactor: lean NO [formula omitted] reduction

The NO x storage and reduction performance of a series of supported Pt/BaO washcoated monolith catalysts is investigated ( y %Pt/ x %BaO/Al 2 O 3 ; y = 2 –2.6%; x = 0 –25%). Storage experiments over a range of exposure (storage) times and feed flow rates (space velocities) show the importance of the NO oxidation to NO 2 reaction. At high space velocities, kinetic limitations reduce the NO conversion and NO x trapping efficiency (fraction of NO x trapped). Higher trapping efficiencies are achieved at lower space velocities when the NO oxidation approaches the equilibrium conversion limit. The NO x trapping efficiency increases with barium loading, but the extent of increase depends on the exposure time. Cycle-averaged NO x conversions and N 2 selectivities exceeding 80% are achieved over a range of operating conditions, including cycle time, space velocity, and reductant (propylene) concentration. The NO x conversion exhibits a maximum at an intermediate cycle time, and the location and magnitude of the maximum depends on the barium loading. The conversion also achieves a maximum at an intermediate barium loading, indicating that increases in dynamic storage capacity of the catalyst do not guarantee improved reduction performance. The dependence of the trapping efficiency on the exposure (storage) time provides a good estimate for the lean storage time needed to achieve a prescribed cycle-averaged NO x conversion during cycling. The dependence of the cycle-averaged NO x conversion on barium loading parallels that of the short-time NO x storage, indicating the importance of the NO x trapping step in the overall monolith catalyst performance.

Development and optimization of NO x storage and reduction catalysts using statistically guided high-throughput experimentation

The interaction between reaction conditions and catalyst compositions for NO x storage and reduction (NSR) catalysts has been explored using a combination of high-throughput experimentation and experimental design. This was accomplished by varying the concentration of NO and O 2, the reducing agent concentration and identity, space velocity, and reactor temperature. All reaction conditions were varied simultaneously for a range of Pt, Ba, and Fe loadings on γ-Al 2O 3. It was found that most of the reaction conditions investigated affected the saturation NO x storage, the production of nitrous oxide, and the steady state lean NO x reduction. An empirical model was developed using response surface methodology to predict the saturation NO x storage and nitrous oxide production as a function of Pt, Ba, and Fe weight loading. This model was used to optimize the catalytic composition and a comparison between the model predictions and experimental results for the optimized catalysts are given. It was shown that high-throughput experimentation in combination with experimental design leads to more efficient use of experimental resources in addition to a more in depth understanding of catalytic systems.

Catalytic Properties of Ag/Al2O3Catalysts for Lean NOxReduction Processes and Characterisation of Active Silver Species

A study of the lean NOx reduction activity employing different reductants over Ag/Al2O3 samples prepared from reverse microemulsions or impregnation with EDTA-complexes is presented. A multitechnique approach is employed for characterisation of the samples and/or processes taking place in the course of the NOx-SCR reaction with propene and propane. Results by in situ-DRIFTS reveal that, for the propene reductant, silver provides a new path for hydrocarbon activation involving generation of adsorbed acrylate species as a partially oxidised active intermediate, in line with previous proposals for other non-noble metal systems. It is shown, mainly on the basis of XAFS studies, that active silver species are related to well dispersed silver aluminate-like phases with tetrahedral local symmetry and a relatively high disorder in the oxygen first shell.

The reactions of NO 2 and CH 3CHO with Na-Y zeolite and the relevance to plasma-activated lean NO x catalysis

We have examined the interaction of NO 2 and CH 3CHO with Na-Y zeolite under conditions relevant to low-temperature plasma-activated reduction of NO x . Acetaldehyde interacts weakly with the surface primarily via electrostatic and ion–dipole interactions and is not present at appreciable levels in the molecular adsorbed state at temperatures exceeding 350 K. The interaction of NO 2 with Na-Y zeolite produces various forms of adsorbed nitrogen oxide species that are primarily present in the form of nitrites and nitrates. The nitrites can be present in the nitrito (–O–N–O −) and nitro (–NO 2 −) configurations and nitrates in the (–NO 3 −) and nitrato (–O–NO 2 −) configurations. Reactions of NO 2 with a Na-Y zeolite surface containing pre-adsorbed acetaldehyde at room temperature are primarily limited to oxidation of the organic fragments and reduction of the surface nitrates to surface nitrites. Reactions of NO 2 on Na-Y zeolite surfaces containing a low coverage of acetaldehyde at temperatures >350 K produces a dehydrogenated surface adsorbed species that likely contains C, N and O. This deposit or adsorbate is also produced when the surface is directly dosed with nitromethane and isopropyl nitrate. The surface reactions seem to involve the Al and associated acid sites.

Continuous lean NOx reduction with hydrocarbons over dual pore system catalysts

In order to reduce CO2 emissions there is a trend towards an increased use of more fuel-efficient lean burn combustion engines and thus an increased need for deNOx catalysts for such engines. In this study a mechanical mixture of CoFER and HZSM-5 zeolites was studied as a dual pore system catalyst for the continuous lean reduction of NOx with isobutane as reducing agent. The degree of NOx conversion was found to be strongly dependent on the oxygen concentration in the gas mixture, and the highest degree of reduction was achieved with 10% O2. This optimum is explained by the need for NO2 as an intermediate for the catalyst to work efficiently, and that above a certain oxygen concentration O2 oxidises the hydrocarbon resulting in a lower reduction potential for NOx. At an operating temperature of 350°C the conversion of NOx to N2 was 52% under steady-state conditions, but the efficiency can be improved further by optimisation of the oxidising zeolite and of the mixing ratio of the two zeolites.

SCR of lean NO x with C 3H 8 over Co/MFI catalysts: dependence on synthesis condition of MFI and Co location

The effects of different synthesis conditions for MFI and the different locations of Co 2+ on MFI on the catalyst properties for the selective catalytic reduction of NO by C 3H 8 [C 3H 8–SCR] in the presence of excess oxygen were investigated, and the nature of Co 2+ was characterized by XRD, FTIR, H 2-TPR, XPS, and DTG. H 2-TPR shows that the exchanged Co ions in MFI are nonreducible even at 750 °C, while the reduction temperature of incorporated Co is at 690 °C. Three types of DTG peaks, which correspond to different temperatures for the thermal decomposition or disassociation of TPA, are observed in the differential thermogravimetric (DTG) analysis of the as-synthesized MFI prepared under different conditions, and are related well to C 3H 8–SCR of NO for three different types of Co sites in MFI: incorporated Co 2+ site and two different exchanged Co 2+ sites, respectively. The incorporated Co 2+ in MFI with the DTG peak temperature at 418 °C is almost inactive for C 3H 8–SCR of NO. For the Co 2+-exchanged MFI, the sample with a low Co 2+-exchange degree has a higher TOF for NO reduction than that having a higher Co 2+-exchange degree, indicating that at least two types of Co 2+ sites exist in the Co 2+-exchanged MFI sample. The corresponding DTG peak temperatures located at 455 and 481 °C show two types of exchanged Co ion sites having different surface energies for different activities for SCR of NO, with the Co 2+ site with higher surface energy having higher specific catalytic activity for NO reduction. The exchange degree and position of Co 2+ depend on the alkalinity of the hydrothermal synthesis condition and the sodium content of the resulting Co 2+-exchanged MFI.

Exploiting the synergy of titania and alumina in lean NO x reduction: in situ ammonia generation during the Pd/TiO 2/Al 2O 3–catalysed H 2/CO/NO/O 2 reaction

In situ DRIFTS, XPS, HREM, XRD, and reactor studies have been used to examine and elucidate the catalytic performance of Pd particles supported on TiO 2/Al 2O 3. These materials deliver 100% NO x conversion under demanding and technically relevant conditions (low temperature, high oxygen excess) in the presence of mixed H 2+CO reductant feeds. In particular, they are far superior to the corresponding Pd/TiO 2 and Pd/Al 2O 3 catalysts. It is shown that the synergy that operates between the titania and the alumina components involves the intrinsic surface chemistry of these oxides rather than formation of mixed oxide phases. Specifically, titania is critical for the formation of NCO on Pd while alumina promotes subsequent hydrolysis of NCO to ammonia, which then reduces NO x . At high temperature a second NO x reduction channel operates with Pd/TiO 2/Al 2O 3 which greatly extends the useful temperature range. This also involves in situ formation of ammonia—in this case directly from reaction between H 2and NO.

An in situ DRIFTS study of efficient lean NOx reduction with H2 + CO over Pd/Al2O3: the key role of transient NCO formation in the subsequent generation of ammonia

The catalytic reduction of NOx under oxygen rich conditions in the presence of mixed H2+CO reductant feeds occurs much more efficiently on Pd/Al2O3 than Pt/Al2O3 catalysts [Appl. Catal. B 35 (2002) 269]. In effect, CO promotes the former while poisoning the latter. Here in situ DRIFTS was used to investigate details of the reaction mechanisms on both these catalysts. Under various reaction conditions, nitrate, carbonate and bicarbonate species were observed in both cases. However, formate and isocyanate (NCO) species were observed only on the Pd/Al2O3 catalyst. Formate is shown to be spectator, whereas in contrast NCO shows significant reactivity. Although pre-adsorbed NCO is consumed in flowing NO+O2, its reactivity is much greater in H2+NO+O2. We propose that hydrolysis of NCO results in the formation of NH3 species, whose production is ultimately responsible for improved NOx reduction by Pd/Al2O3 in the presence of H2+CO.

Effects of sulfur in gasoline on NO x emission from vehicles equipped with lean NO x catalysis : Uchiyama, T. et al. JSAE Review, 2002, 23, (4), 423–427

Effects of sulfur in gasoline on NO x emission from vehicles equipped with lean NO x catalysis : Uchiyama, T. et al. JSAE Review, 2002, 23, (4), 423–427

Nature and catalytic role of active silver species in the lean NO x reduction with C 3H 6 in the presence of water

A study of the lean NO x reduction activity with propene in the presence of water over Ag/Al 2O 3 catalysts with different silver loadings (1.5–6 wt%) has been done using X-ray diffraction, ultraviolet–visible spectroscopy, transmission electron microscopy, and in situ diffuse reflectance infrared and X-ray absorption spectroscopies under reaction conditions. The catalysts were prepared by an impregnation method employing EDTA complexes that allow highly dispersed silver phases to be obtained, which are stabilized under reaction conditions by strong interactions with the support. It is shown that the active species corresponds to silver aluminate-like phases with tetrahedral local symmetry. The role of silver in the reaction mechanism is shown to be mainly in the activation of NO x and propene species. In particular, the silver entities have been found to offer a new reaction path for propene activation which involves generation of acrylate species as a partially oxidized active intermediate. Differences between two active catalysts containing 1.5 and 4.5 wt% of Ag suggest that optimization of the SCR activity can be related to the oxygen lability of the tetrahedral silver aluminate-like phase present in the catalyst. As postulated previously, the high nonselective propene oxidation activity of the highest loaded sample (with 6 wt% Ag) appears to be related to formation of metallic silver surface states at low reaction temperatures which are active for NO dissociation.

Effects of sulfur in gasoline on NO x emission form vehicles equipped with lean NO x catalysts

Effects of sulfur in gasoline on exhaust emissions were studied on vehicles equipped with several types of lean NO x catalysts. A lean NO x catalyst used in a newly launched vehicle was found to be regenerative during running. A catalyst of another vehicle using Na for NO x adsorption was confirmed to have higher sulfur proof performance.