NOx Storage Capacity Research Articles

Pd-promoted WO3-ZrO2 for low temperature NOx storage

Pd-promoted ZrO2 and WO3-ZrO2 (W-Zr) were investigated for low temperature NOx adsorption and release. Pd-promoted W-Zr exhibited high NOx storage efficiency at short storage times, subsequently releasing ∼95% of the stored NOx upon thermal ramping to 350 °C. DRIFTS studies demonstrated that Pd increased nitrate formation relative to nitrite during NOx storage on both Pd-Zr and Pd-W-Zr. Moreover, Pd sites on Pd-W-Zr played a major role in NOx storage, the ad-species being readily removed by 350 °C. From NO- and CO-DRIFTS data, it is inferred that Pd on the acidic W-Zr support was present as mainly cationic species, and was therefore able to adsorb NO, whereas on ZrO2 Pd was not able to directly store NOx. Co-feeding CO with NO resulted in increased NOx storage capacity for Pd-W-Zr, which on the basis of DRIFTS measurements is attributed to the formation of Pd2+(CO)(NO) complexes.

High Performance of Mn-Doped MgAlOx Mixed Oxides for Low Temperature NOx Storage and Release

NOx storage-reduction (NSR) is a potential approach for the effective removal of NOx under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlOx) with high performance for low temperature NOx storage and release were derived from hydrotalcites precursors prepared by a facile coprecipitation method. The catalysts were characterized by X-ray diffraction (XRD), SEM, N2 adsorption-desorption, H2-TPR, FT-IR, and X-ray photoelectron spectroscopy (XPS) techniques. The Mn-doped MgAlOx catalysts exhibited high NOx storage capacity (NSC) at low temperature range (150–300 °C), which was related to their increased surface area, improved reducibility and higher surface Mn3+ content. The largest NSC measured, 426 μmol/g, was observed for NOx adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NOx adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NOx storage and release due to their ability to store NOx mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NOx removal rate of Mn15 sample can reach above 70% within the wide temperature range of 150–250 °C. Besides, the influence of CO2, soot, H2O and SO2 on NOx storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NOx storage capacity, NSR cycling performance, and resistance to CO2, soot, SO2 and H2O, the Mn-doped MgAlOx NSR catalysts have broad application prospects in NOx control at low temperatures.

NOx storage and reduction on Pt-supported BaTiO3 with alkali washing

In this paper, we prepared Pt/BaTiO3-x catalyst through modified the surface of BaTiO3 perovskite by NaOH aqueous solution and loaded Pt by incipient wetness impregnation method. A series of characterization techniques including XRD, BET and in situ IR was conducted to investigate the physical and chemical properties. We found that NOx storage capacity of the catalyst was significantly improved as the sample was washed in alkali for 2 h, meanwhile NOx conversion was optimal. The surface of the catalyst was modified by alkali washing process, and then Pt was loaded. Further calcination could enhance the interaction between Pt and Ba, which facilitate the formation of a reactive nitrite species during the adsorption process, thus increasing NOx storage reduction (NSR) activity.

Investigation of an irreversible NOx storage degradation Mode on a Pd/BEA passive NOx adsorber

Passive NOx adsorbers (PNAs) are a proposed solution for cold start NOx emissions, via low temperature NOx trapping and subsequent release at a temperature where downstream NOx reduction catalysts are active. Pd/zeolites have been reported to have significant NOx storage capacities. However, their real exhaust compatibility has not been completely evaluated. In this work, Pd/BEA was used to study the mechanism of an observed PNA degradation. NO adsorption, NO and CO co-adsorption and temperature programmed desorption/oxidation were performed on a series of differently aged Pd/BEA catalysts to evaluate the NOx storage capacity and desorption temperature. An irreversible NOx storage degradation mode caused by low temperature CO exposure was observed. H2 temperature programmed reduction results indicate this irreversible degradation can be attributed to the loss of Pd2+. Additionally, STEM images revealed Pd particle migration/agglomeration after hydrothermal aging and CO/H2 exposure. Larger particles, formed during CO exposure, lead to the irreversible degradation.

Improved NOx Storage/Release Properties of Ceria-Based Lean NOx Trap Compositions with MnOx Modification

Ceria/spinel-based lean NOx trap compositions with and without barium were modified with MnOx via incipient wetness impregnation. The effect of the MnOx layer on the aged materials (850 °C) as to the NOx storage and release properties was investigated via NOx adsorption (500 ppm NO/5% O2/balance N2) carried out at 300 °C in a dual-bed with a 1% Pt/Al2O3 catalyst placed upstream of the samples to generate sufficient amounts of NO2 required for efficient NOx storage. Subsequent temperature programmed desorption (TPD) experiments were carried out under N2 from 300 °C to 700 °C. The addition of MnOx to the barium free composition led to a slightly reduced NOx storage capacity but all of the ad-NOx species were released from this material at significantly lower temperatures (ΔT ≈ 100 °C). The formation of a MnOx layer between ceria/spinel and barium had a remarkable effect on ageing stability as the formation of BaAl2O4 was suppressed in favour of BaMnO3. The presence of this phase resulted in an increased NOx storage capacity and lower desorption temperatures. Furthermore, NOx adsorption experiments carried out in absence of the Pt-catalyst also revealed an unexpected high NOx storage ability at low NO2/NO ratios, which could make this composition suitable for various lean NOx trap catalysts (LNT) related applications.

NOx Oxidation and Storage Properties of a Ruddlesden-Popper-Type Sr3Fe2O7-δ-Layered Perovskite Catalyst.

The development of NOx-trapping catalysts for automobiles is highly desired to meet the current strict exhaust emission regulations. This study demonstrates that NOx oxidation and storage reactions proceed over Pt-free Sr3Fe2O7-δ with a Ruddlesden-Popper-type layered perovskite structure. Two types of Sr-Fe perovskite with oxygen storage capacity, namely, SrFeO3-δ and Sr3Fe2O7-δ, are studied as NOx-trapping catalysts. Sr3Fe2O7-δ shows higher NOx storage capacity than SrFeO3-δ; its activity is comparable to that of Pt/Ba/Al2O3 calcined at 1273 K. NOx temperature-programmed desorption and diffuse reflectance infrared Fourier transform experiments confirm the superior NOx-trapping ability of Sr3Fe2O7-δ over SrFeO3-δ. In addition, NO temperature-programmed reactions and O2 temperature-programmed desorption experiments reveal that these catalysts operate through a novel NO oxidation mechanism involving the consumption of their lattice oxygens and topotactic structural changes at a temperature of around 350-400 K. The reduction performance of trapped NOx on Pd-modified Sr-Fe perovskites is investigated by lean-rich cycle experiments using H2 as the reductant. Pd/Sr3Fe2O7-δ shows significantly high NOx removal efficiency over the entirety of each lean-rich period. Modifying Sr3Fe2O7-δ with Pd is also effective for NOx storage in the presence of H2O and CO2 and the regeneration of the catalyst following SOx sorption. Sr3Fe2O7-δ, with both NOx adsorption and NO oxidation capabilities, acts as a Pt-free NOx-trapping catalyst, exhibiting both high NOx storage capacity and high thermal tolerance.

Comparison of Pt-BaO/Al2O3 and Pt-CeO2/Al2O3 for NOx storage and reduction: Impact of cycling frequency

NOx reduction under net lean and near-stoichiometric conditions was carried out on Pt/Al2O3, Pt/CeO2/Al2O3 and Pt/BaO/Al2O3 washcoated monoliths to compare performance features and identify reaction pathways. The impact of the storage components (BaO, CeO2) on the NOx conversion and byproduct (NH3 and N2O) yields was quantified for a range of feed temperatures, reductant types (H2, and C3H6), O2 feed concentrations, and cycle times. The NOx storage functionality is essential for NOx reduction under net lean conditions while the oxygen storage functionality promotes NOx reduction for near-stoichiometric conditions. NOx conversion by H2 under lean conditions is dependent on the NOx storage capacity of the catalyst, with Pt/CeO2/Al2O3 and Pt/BaO/Al2O3 exhibiting the highest NOx conversion below and above 300 °C, respectively. High NOx conversion is achieved over Pt/CeO2/Al2O3 for anaerobic rich feeds at temperatures above 400 °C. Increasing the O2 feed concentration enhances NOx conversion over Pt/CeO2/Al2O3 below 400 °C but inhibits NOx conversion above 400 °C. The former is attributed to promotion of NO oxidation leading to NOx storage while the latter is attributed to O2 inhibition of NO decomposition/reduction. Shorter cycle times increase the NOx conversion with C3H6 as reductant over Pt/BaO/Al2O3 under lean conditions and over PCA for the near-stoichiometric feed. The findings confirm that improved NOx storage utilization is mainly responsible for NOx conversion enhancement. A ceria redox pathway has only a secondary effect on NOx conversion under excess O2.

Al2O3-supported Pt/Rh catalysts for NOx removal under lean conditions

In this work the reactivity of Pt-Rh NOx storage-reduction (NSR) catalysts in the reduction of NOx under lean conditions is investigated. It is found that significant amounts of NOx are stored on both Rh- and Pt-based samples at all the investigated temperatures (in the range 150–350 °C). Mostly chelating nitrites are adsorbed at the lowest investigated temperature (150 °C), while nitrates (both bidentate and ionic) at higher temperatures. However, at all temperatures nitrites prevail at the beginning of the storage phase, while nitrates represent the most abundant adsorbed species after prolonged contact. Pt-containing catalysts (either monometallic Pt or bimetallic Pt/Rh) show higher NOx storage capacity than the Rh monometallic sample, possibly due to the higher dispersion of Pt vs. Rh and/or to the higher oxidizing capability of Pt vs. Rh.The stored NOx species show relevant thermal stability, and decompose to NOx and O2 upon heating. In particular, nitrites disproportionate to gaseous NO and nitrates; these latter then decompose to NOx and O2. On the Rh-Ba/Al2O3 catalyst the disproportionation reaction is observed with a higher temperature onset if compared to the Pt-based samples. The analysis of the reactivity of the stored NOx species (probed by isotopic labeling experiments and reduction with H2 and NH3) showed the lower reactivity of the Rh-Ba/Al2O3 sample; however Rh shows activity in the ammonia decomposition reaction to N2 and H2, unlike Pt. The lower reactivity of the Rh-Ba/Al2O3 sample is also pointed out by experiments under cyclic lean-rich conditions. However, the presence of Rh increases the reactivity of the catalyst in the steam reforming of hydrocarbons, especially at high temperature, and accordingly the reactivity of the bimetallic Pt/Rh sample at high temperatures is higher than that of the Pt and Rh monometallic catalysts.

Efficient Pt/Ba/SnxCe1–xO2 Catalysts for High-Temperature Lean NOx Traps with High H2O and CO2 Tolerance

Herein, we investigate the De-NOx activity of Pt/Ba/SnxCe1–xO2 catalysts at high temperatures. Our results show that at high temperatures, their NOx storage capacity (NSC), linked to the quantity of highly dispersed BaCO3 species on the catalysts, determines the De-NOx activity instead of the NOx oxidation and reduction ability. Moreover, we identify that monodentate nitrate species are more stable than free ion nitrate species on the Ce-containing catalysts. Thus, the presence of monodentate nitrate species is beneficial to improve the H2O and CO2 tolerance by inhibiting the latter ones’ competitive adsorption on NOx storage sites. Compared with other catalysts, Pt/Ba/Sn0.8Ce0.2O2 possesses the larger amount of highly dispersed BaCO3 species, and especially, more monodentate nitrate species are formed on it during the NOx storage period. Thus, it exhibits the superior De-NOx performance with NOx removal percentage over 86% in the presence of H2O and CO2 at 350∼500 °C.

BaTi0.8B0.2O3 (B = Mn, Fe, Co, Cu) LNT Catalysts: Effect of Partial Ti Substitution on NOx Storage Capacity

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi0.8B0.2O3 lean NOx trap (LNT) catalyst has been analyzed. The BaTi0.8B0.2O3 catalysts were prepared using the Pechini’s sol–gel method for aqueous media. The characterization of the catalysts (BET, ICP-OES, XRD and XPS) reveals that: i) the partial substitution of Ti by Mn, Co, or Fe changes the perovskite structure from tetragonal to cubic, whilst Cu distorts the raw tetragonal structure and promotes the segregation of Ba2TiO4 (which is an active phase for NOx storage) as a minority phase and ii) the amount of oxygen vacancies increases after partial Ti substitution, with the BaTi0.8Cu0.2O3 catalyst featuring the largest amount. The BaTi0.8Cu0.2O3 catalyst shows the highest NSC at 400 °C, based on NOx storage cyclic tests, which is within the range of highly active noble metal-based catalysts.

The first non-precious metal passive NOx adsorber for cold-start applications

Co-SSZ-13 served as a non-PM passive NOx adsorber (PNA) was adopted for the first time, to the best of our knowledge, as a promising alternative to platinum-based NOx adsorbers. This Co-based catalyst has a NOx storage capacity of 27.3 μmol/gcat, which is 77% of that of Pd-SSZ-13. NOx is desorbed above 250 °C, which is appropriate for use downstream of the NH3-SCR catalyst. NO adsorption on Co-SSZ-13 resulted in the formation of dinitrosyl species, which are further converted into NO+ on the zeolite framework and nitrate species on Co2+. The strong interaction between Co2+ and NO is responsible for the high NOx storage capacity. In addition, conversion among the adsorbed species increases the NO desorption temperatures, which is important for the correct operation of PNA.

Tolerance and regeneration versus SO2 of Ba0.9A0.1Ti0.8Cu0.2O3 (A = Sr, Ca, Mg) LNT catalysts

In this paper, the tolerance and stability versus SO2 of Ba0.9A0.1Ti0.8Cu0.2O3 (A = Sr, Ca, Mg) perovskite-type catalysts for NOx storage application have been analyzed at 400 °C. Characterization results show that only strontium and magnesium are introduced into the perovskite structure. From those data, it can be concluded that the incorporation of Sr into the Ba0.9Sr0.1Ti0.8Cu0.2O3 catalyst promotes the generation of new NOx adsorption active sites. On the contrary, for Ba0.9Mg0.1Ti0.8Cu0.2O3 catalyst, copper is segregated from the catalyst lattice to the surface due to the incorporation of magnesium into the B site of the perovskite.The partial substitution of barium in Ba0.9Sr0.1Ti0.8Cu0.2O3 and Ba0.9Mg0.1Ti0.8Cu0.2O3 catalysts increases the NOx Storage Capacity (460 and 415 μmol/g.cat. in saturation conditions, respectively), stability and tolerance versus SO2 compared to the raw BaTi0.8Cu0.2O3 perovskite.

Effect of support preparation with different concentration precipitant on the NO storage performance of Pt/BaO/CeO2 catalysts

Abstract In this study, the CeO2 nanorods as the supports of Pt/BaO/CeO2 catalysts were synthesis by the alkali-assisted hydrothermal method in a solution containing different content of NaOH. Pt/BaO/CeO2 catalyst with 7.5M NaOH pre-added in the support preparation process showed higher NOx storage capacity and NOx removal efficiency than samples derived from other concentration NaOH. Moreover, even under shorter rich time (3s) and more lean-rich cycles (60), Pt/BaO/CeO2-7.5M still maintained above 80% NOx conversion from 250 to 450 °C, exhibiting good fuel economy and durability. A series of characterization techniques including XRD, N2-adsorption, TEM, XPS, Raman, H2-TPR, and NO2-TPD were conducted to investigate the physical, chemical properties. Combining the activity with the structure of catalysts, a linear relationship between the NOx storage capacity (NSC) of NSR catalysts and the amount of oxygen vacancies was drawn. Meanwhile, the strong synergetic effect among Pt and CeO2 attributed to the role of oxygen vacancies in anchoring the active component Pt, promoting the mobility of surface oxygen species, was also related to the NSC value of NSR catalysts. These results indicated that the oxygen vacancies were responsible for the excellent catalytic activity.

Positive effects of K+ in hybrid CoMn-K and Pd/Ba/Al2O3 catalysts for NOx storage and reduction

CoMn-K was mechanically mixed with a Pd/Ba/Al2O3 catalyst to enhance its NOx storage and reduction properties. The Pd/Ba/Al2O3 and CoMn-K mixture showed a synergetic effect with respect to NOx storage capacity and improved NOx reduction ability. The addition of K+ ions promoted the catalytic performance by increasing NO oxidation activity and therefore NOx storage via the creation of active surface oxygen species on the catalysts. The stored NOx reduction by H2 was also improved, being ascribed to the fact that Pd was mainly present as Pd0 due to the electronic interactions between Pd and K+ ions. NOx conversions and N2 selectivity at low temperatures (80–200 °C) could be further enhanced by assistance of non-thermal plasma in rich phase.

Investigation of Various Pd Species in Pd/BEA for Cold Start Application

A series of Pd/BEA catalysts with various Pd loadings were synthesized. Two active Pd2+ species, Z−-Pd2+-Z− and Z−-Pd(OH)+, on exchanged sites of zeolites, were identified by in situ FTIR using CO and NH3 respectively. Higher NOx storage capacity of Z−-Pd2+-Z− was demonstrated compared with that of Z−-Pd(OH)+, which was caused by the different resistance to H2O. Besides, lower Pd loading led to a sharp decline of Z−-Pd(OH)+, which was attributed to the ‘exchange preference’ for Z−-Pd2+-Z− in BEA. Based on this research, the atom utilization of Pd can be improved by decreasing Pd loading.

Strontium doping and impregnation onto alumina improve the NOx storage and reduction capacity of LaCoO3 perovskites

Here we report the effects of strontium doping of perovskites (La1-xSrxCoO3) on NOx storage and reduction (NSR) as well as the effects of supporting the perovskite onto an alumina support. The NSR capacity of La0.7Sr0.3CoO3 improved with strontium doping: this material displayed a good balance between NO oxidation capacity and adsorption sites accessibility. Increased accessibility was mainly due to the strontium oxide segregates. In addition, different loadings of La0.7Sr0.3CoO3 perovskite (10, 20, 30, 40 and 50%) were impregnated onto alumina in order to increase the exposed surface area of the perovskite. This had the effect of increasing the NSR capacity of the perovskite. The results of X-Ray diffraction, UV–vis–NIR spectroscopy, N2 adsorption-desorption, electron microscopy, and temperature programmed techniques, demonstrated that the cobalt ions preferably formed cobalt aluminate (CoAl2O4) in the case of low perovskite loadings (<20%). Meanwhile, a well-developed perovskite phase was observed with the higher loadings (>30%). The specific NO oxidation rate per gram of perovskite increased dramatically with the incorporation onto an alumina support. 30% LSCO/Al2O3 sample had an oxidation rate of 138 μmol min-1 (g LSCO)-1 at 350 °C, more than double the rate of the bulk La0.7Sr0.3CoO3 (49 μmol min−1 (g LSCO)−1). Likewise, the 30% LSCO/Al2O3 sample had a higher NOx storage capacity than its bulk counterpart at 400 °C: 306 vs. 115 μmol (g LSCO)−1. The higher oxidation capacity of the alumina-supported samples also facilitated the diffusion of the intermediate compounds from oxidation to adsorption sites. Impregnating alumina with perovskite could be used to improve the efficiency of perovskite mediated NOx removal in automobile applications. Furthermore, adding palladium onto optimum alumina-supported perovskite sample, i.e. 1.5% Pd-30% LSCO/Al2O3, resulted in a clear improvement in NOx storage and reduction capacity. This last sample demonstrated a nitrogen yield as high as 65%, an improvement over the model Pt-based NSR catalyst.

Enhancing low-temperature NOx storage and reduction performance of a Pt-based lean NOx trap catalyst

Two lean NOx trap (LNT) catalysts, Pt/BaO/CeO2 + Al2O3 and Pt/BaO/CeO2 − Al2O3, were prepared and compared for low-temperature (< 250 °C) NOx storage and reduction performance. The influence of the form of ceria on low-temperature NOx storage and reduction performance of LNT catalysts was investigated with the focus on NOx storage capacity, NOx reduction efficiency during lean/rich cycling, product selectivity and thermal stability. Inductively coupled plasma-atomic emission spectrometry (ICP-AES), Brunner–Emmet–Teller (BET), H2-pulse chemisorption and X-ray diffraction (XRD) were conducted to characterize the physical properties of LNT catalysts. NOx storage capacity and NOx conversion efficiency were measured to evaluate NOx storage and reduction performance of LNT catalysts. Pt/BaO/CeO2 − Al2O3 catalyst exhibits higher NOx storage capacity than Pt/BaO/CeO2 + Al2O3 catalyst in the temperature range of 150–250 °C. Meanwhile, Pt/BaO/CeO2 − Al2O3 catalyst shows better NOx conversion efficiency and N2 selectivity. XRD results indicate that the thermal stability of CeO2 − Al2O3 complex oxide is superior to that of pure CeO2. H2-pulse chemisorption results show that Pt/BaO/CeO2 − Al2O3 catalyst has higher Pt dispersion than Pt/BaO/CeO2 + Al2O3 catalyst over fresh and aged samples. The improved physical properties of Pt/BaO/CeO2 − Al2O3 catalyst are attributed to enhance the NOx storage and reduction performance over Pt/BaO/CeO2 + Al2O3 catalyst.

The influence of Pt loading and dispersion on the NOx storage and reduction performance of Pt/K2CO3/Co1Mg2Al1Ox catalysts

Abstract For NOx storage and reduction (NSR) catalysts, Pt is necessary for the NO oxidation during the lean stage and the NOx reduction during the rich stage. However, due to its high price, synthesis of NSR catalysts with low Pt loading is highly demanded. In this contribution, Pt/K2CO3/Co1Mg2Al1Ox as NSR catalysts with low Pt loadings (0.15, 0.33 and 0.59 wt%) were prepared via co-precipitation and incipient wetness impregnation methods. The optimal of K2CO3 loading was determined to be 15 wt% for both samples. The influence of Pt particle size and Pt dispersion on the NOx storage capacity and the NSR cycling performance of Pt/K2CO3/Co1Mg2Al1Ox were then systematically and comparatively investigated. It was demonstrated that the samples prepared by CP method can result in higher isothermal NOx storage capacity, and higher NOx removal rate and better cycle stability during lean-rich cycling tests. By increasing the Pt loading or extending the rich period duration, the overall NOx removal rate can be promoted and became more stable. No matter what method was used for loading Pt, the N2 selectivity of all catalysts was higher than 95%. The results also indicated the samples prepared by CP method were more resistant to the effects of SO2, CO2 and H2O. CO-pulse and HR-TEM analyses confirmed that the 0.59 Pt/Co1Mg2Al1Ox (CP) possesses smaller Pt particle size (1.30–1.32 nm) and higher Pt dispersion (65.41%), while the values for 0.59 Pt/Co1Mg2Al1Ox (IWI) was 2.66–2.71 nm and 31.90%, respectively. All results indicated that the CP method, which can effectively improve Pt dispersion and reduce the Pt particle size, is superior to the traditional IWI for the preparation of highly efficient low Pt loading NSR catalysts.

Highly enhanced soot oxidation activity over 3DOM Co3O4-CeO2 catalysts by synergistic promoting effect.

Three-dimensionally ordered macroporous (3DOM) Co3O4-CeO2 catalysts with controllable Co/Ce molar ratios synthesized by colloidal crystal template method were developed to catalyze the NOx-assisted soot oxidation for the first time, and the obtained 3DOM Co3O4-CeO2 catalysts exhibited highly enhanced soot oxidation activity. Detailed characterizations of 3DOM Co3O4-CeO2 catalysts revealed that the highly enhanced soot oxidation activity was originated from the synergistic promoting effect by combining the macroporous effect resulted from the unique 3DOM framework, the chemical nature associated with more Co3+ reactive sites, the surface enrichment of Ce species and the improved redox properties. Meanwhile, the high NOx storage and oxidation capacity resulted from the integrated respective merits of Co3O4 and CeO2 also accounted for the enhanced soot oxidation activity via NOx-assisted mechanism. Furthermore, the 3DOM Co3O4-CeO2 catalysts demonstrated strong stability because of the surface enrichment of Ce species improving the thermal stability and the robust 3DOM framework inhibiting the structural collapse, showing their potential applications under practical conditions.

Low Temperature NOx Adsorption Study on Pd-Promoted Zeolites

In this study Pd-promoted zeolites (BEA, FER, MFI and MOR) are synthesized and investigated for potential use in the low-temperature NOx adsorption. The catalysts are characterized by BET, XRD, UV–Vis and XRF, while the adsorption/desorption characteristics of the samples are investigated by NOx adsorption/TPD, with and without water in the feed. The nature of the adsorbed NOx species has been analyzed by operando FT-IR spectroscopy. Under dry conditions at 50 °C all the investigated zeolite frameworks are able to store significant amounts of NOx, up to 1 mmol/gcat for the MOR sample; the presence of Pd has not a significant impact on the amounts of the stored NOx. In fact, under dry conditions at 50 °C the zeolite frameworks oxidize NO to NO2, and store NOx from NO2 over the zeolitic support. FTIR data indicates that NOx are stored in the form of nitrosonium ion NO+ and nitrate ions; nitrosyl species formed on Al3+ and Pdn+ sites have also been observed, although to a lower extent. Evidences have also been provided for the existence of gaseous/weakly interacting species (mostly NO2) contained in the pores of the zeolites. Water inhibits NO oxidation over all investigated samples, resulting in a strong decrease in the NOx storage capacity. Still, appreciable amounts of NOx could be stored at 50 °C (up to 60 µmol/gcat for Pd/MFI) in the presence of water over the Pd-doped carriers.