Ba Loading Research Articles

Promotion of Ru or Ni on Alumina Catalysts with a Basic Metal for CO2 Hydrogenation: Effect of the Type of Metal (Na, K, Ba).

Ru and Ni on alumina catalysts have been promoted with a 10 wt% of alkali metal (K or Na) or alkaline earth metal (Ba) and tested in CO2 methanation. For the catalyst consisting of Ni and Ba, the variation of Ba loading while keeping Ni loading constant was studied. The promotion in terms of enhanced CH4 yield was found only for the addition of barium to 15 wt% Ni/Al2O3. In contrast, K and Na addition increased the selectivity to CO while decreasing conversion. For the Ru-based catalyst series, no enhancement in conversion or CH4 yield was attained by any of the alkaline metals. CO2 temperature-programed desorption (CO2-TPD) revealed that the amount of chemisorbed CO2 increased significantly after the addition of the base metal. The reactivity of COx ad-species for each catalyst was assessed by temperature-programed surface reaction (TPSR). The characterization revealed that the performance in the Sabatier reaction was a result of the interplay between the amount of chemisorbed CO2 and the reactivity of the COx ad-species, which was maximized for the (10%Ba)15%Ni/Al2O3 catalyst.

One-step synthesis of Ni/yttrium-doped barium zirconates catalyst for on-site hydrogen production from NH3 decomposition

On-site produced hydrogen from ammonia decomposition can directly fuel solid oxide fuel cells (SOFCs) for power generation. The key issue in ammonia decomposition is to improve the activity and stability of the reaction at low temperatures. In this study, proton-conducting oxides, Ba(Zr,Y) O3-δ (BZY), were investigated as potential support materials to load Ni metal by a one-step impregnation method. The influence of Ni loading, Ba loading, and synthesis temperature, of Ni/BZY catalysts on the catalytic activity for ammonia decomposition were investigated. The Ni/BZY catalyst with Ba loading of 20 wt%, Ni loading of 30 wt%, and synthesized at 900 °C attained the highest ammonia conversion of 100% at 600 °C. The kinetics analysis revealed that for Ni/BZY catalyst, the hydrogen poisoning effect for ammonia decomposition was significantly suppressed. The reaction order of hydrogen for the optimized Ni/BZY catalyst was estimated as low as −0.07, which is the lowest to the best of our knowledge, resulting in the improvement in the activity. H2 temperature programmed reduction and desorption analysis results suggested that a strong interaction between Ni and BZY support as well as the hydrogen storage capability of the proton-conducting support might be responsible for the promotion of ammonia decomposition on Ni/BZY. Based on the experimental data, a mechanism of hydrogen spillover from Ni to BZY support is proposed.

Ba–Al-decorated iron ore as bifunctional oxygen carrier and HCl sorbent for chemical looping combustion of syngas

Abstract The simultaneous high-temperature HCl removal and chemical looping combustion (CLC) of syngas over barium-decorated oxygen carriers (OCs) was investigated. An iron ore was coated with a layer of sorbent (5 wt%) containing Ba and Al compounds (molar ratios Al:Ba = 0.5, 2.0, 4.5, 8.0, 12) and used for model syngas combustion at 800 °C. It was found that the synthesized materials can effectively remove HCl from the syngas. The HCl removal capacity increased with the Ba loading, and the HCl breakthrough capacity can reach 0.0345 mmol/g for the OC with Al:Ba = 0.5, resulting in the formation of BaCl2. The conversion of Ba species into BaCl2 was 17.3%. Besides the HCl sorption, the coating with Ba and Al compounds enhanced the activity of lattice oxygen and improved the reducibility of OCs during CLC due to the Ba–Fe composite formed on the OCs surface. Compared to the iron ore, the combustion efficiencies of the coated OC with Al:Ba = 4.5 for CO and H2 increased from 62.2% and 87.2% to 99.6% and 95.9%, respectively. Through fluidized bed experiments and thermodynamic calculations, the feasibility of sorbent regeneration was demonstrated by treating OCs with a mixture of CO2 and H2O at 800–1000 °C. The HCl desorption rate increased with temperature and nearly complete sorbent regeneration (99.6%) could be achieved at 1000 °C. These findings demonstrate that Ba–Al-decorated iron ore can be used as bifunctional material in CLC process since it enables simultaneous high-temperature HCl removal and syngas combustion.

Role of Ba(O2)1−xOx species in improvement of selective oxidation activity of CoOx/CeO2−y

A series of Ba-doped CoOx/CeO2−y catalysts was prepared by co-precipitation followed by the deposition–precipitation method. The catalysts were investigated for selective oxidation (selox) of benzyl alcohol (B-ol) using tertiary butyl hydroperoxide (TBHP) without solvent and activity was compared with Co0.5/Ce0.5. The Ba loading has been optimized with time and temperature for selox reaction. The catalyst was characterized by various surface and bulk characterization techniques. The characterization study indicates that the synergistic interaction between Ba and CoCe could form more oxygen vacancies and peroxide species responsible for the activation of B-ol and TBHP. The formation of Ba(O2)1−xOx oxide (peroxide) was observed and could be responsible for the activation of B-ol. The optimum Ba doping enhances selectivity and yields benzaldehyde. However, the increase in Ba concentration on CoOx/CeO2−y could lead to the over-oxidation of B-ol to by-products.

Visible-light-induced degradation of Rhodamine B by Ba doped ZnO nanoparticles

In the present work, ZnO and Ba doped ZnO nanoparticles (Ba/ZnO) were synthesized by the sol-gel approach. The effects of Ba doping and calcination temperature on photodegradation of Rhodamine B (RhB) were examined under visible light irradiation. In the optimized synthesis conditions, 0.1% Ba loading, and 400 °C calcination temperature, the photocatalyst revealed considerable activity toward photodegradation of RhB. The photocatalytic process by optimal photocatalyst was further modeled and optimized by Response Surface Methodology. The maximum removal efficiency of 98.40% was obtained for catalyst dosage of 350 mg L−1, initial RhB concentration of 4.11 mg L−1, the irradiation time of 68 min, and pH 8. In addition, for 0.1% Ba/ZnO photocatalyst, the activity under visible light was near to UV-A light with a considerable reduction in photoluminescent spectra (PL) compared to neat ZnO. A comparison of PL spectra of RhB and RhB/0.1%Ba/ZnO showed considerable quenching of the light-emitting broad peak of RhB for the later confirming the photosensitizer effect of adsorbed RhB for efficient visible-light-driven degradation of dye.

Synthesis of modified layered double hydroxide of MgAl catalyst with Ba and Li for the biodiesel production

In this study, the layered double hydroxide of MgAl was synthesized and utilized as a catalyst for transesterification. The catalyst structure was modified by adding Ba and Li to improve biodiesel production yield and decrease the reaction temperature and time, methanol-to-oil ratio, and concentration catalyst. To this end, five hydrotalcite catalysts, including MgAl, MgAlBa, MgAl/Li20%, MgAl/Li40%, and MgAlBa/Li20%, were prepared and analyzed by XRD, FE-SEM, and EDX in terms of Hydrotalcite pattern, morphological structure, and distribution of the elements in the catalysts. Biodiesel samples were produced using sunflower oil, and hydrotalcite catalysts concerning the effects of temperature, reaction time, amount and the types of the catalysts, methanol-to-oil molar ratio, and Li, Ba loading ratio. The Taguchi method was used for experimental design and results analyzed with ANOVA method. The results demonstrated that the Li or/and Ba ratio, reaction time, temperature, and methanol-to-oil molar ratio had a significant effect on the yield. Furthermore, the produced biodiesel by MgAl/Li40 catalyst reaches to more than 90% yield in 8 h that was same as 10% MgAl catalyst but with lower reaction temperature (from 75 to 55 °C), catalyst amount (from 10 to 7%), and methanol-to-oil ratio (from 30:1 to 12:1). The ratio of divalent cations to trivalent cations in the hydrotalcite structure of MgAl and MgAlBa, the type of cations and their ratio were essential parameters in yield calculation of transesterification reaction. The ratio of divalent cations to trivalent cations in this work was 0.33. The reusability of the catalysts was tested by analyzing the viscosity of biodiesel production. The results showed that the viscosity of products with MgAl and MgAl/Li catalysts increased to 8 mm2/s and 23 mm2/s after two uses.

Modelling NOX Storage and Thermal Desorption: Is It Possible to Model the Effect of Changing the Catalyst Composition?

In this work, a series of model NOX storage catalysts with different Pt and Ba loadings (in the range 0–2 wt% and 0–20 wt%, respectively) have been studied for NOX storage and desorption. The samples have been characterised by in-situ DRIFTS to identify the nature of the stored species and by EXAFS to gather information about the Pt particle size. A correlation between the average Pt particle size and the Pt/Ba ratio has been found. A simple kinetic model for NOX storage and thermal desorption has been developed, which can reasonably capture the experimental results over a wide range of conditions. The fitting parameters have been optimised independently for each of the samples and have been found to be dependent on the catalyst’s structural properties (average Pt particle size, total Pt perimeter and Ba loading). The so found correlations have been introduced in the model, which can now be used to simulate the behaviour of catalysts with different Pt and Ba loadings as well as to optimise the catalyst composition for different applications.

Effect of doping on the performance of high-crystalline SrMnO3 perovskite nanofibers as a supercapacitor electrode

Perovskite oxides are promising multi-functional materials with enhanced physical and chemical properties. In this study, high-crystalline SrMnO3 perovskite oxide nanofibers have been successfully synthesized by sol–gel electrospinning followed by calcination at different temperatures, using polyvinylpyrrolidone as a sacrificial polymeric binder. The change in porosity and grain size with calcination temperature imparted a substantial effect on the electrochemical properties of the obtained SrMnO3 nanofibers. The SrMnO3 nanofiber electrode calcined at 700 °C exhibits an electrochemical capacitance of 321.7 F g−1 at a discharge current density of 0.5 A g−1. The effect of doping Ba/Ca on Sr, and Co/Fe/Ni on Mn, respectively, on the specific capacitance of SrMnO3 nanofibers is studied. 20 mol% Ba loading shows the best performance as a supercapacitor electrode with a specific capacitance of 446.8 F g−1 at a discharge current density of 0.5 A g−1. The nanofibers retained 87% its initial capacitance after 5000 successive cycles. The device fabricated using the nanofibers show an energy density of 37.3 W h kg−1 at a power density of 400 W kg−1, and it is retained as 15.7 W h kg−1 even at a high-power density of 8006 W kg−1, indicating the potential of this electrode material for high-rate charge/discharge operations in supercapacitors.

Oxidative coupling of methane over Ba-doped Y2O3 catalyst—Similarity with active site for direct decomposition of NO

A similarity of catalytically active sites for oxidative coupling of methane (OCM) and NO decomposition was investigated. Y2O3 prepared by different methods showed the activity for both reactions. However, no good correlation between the C2 (C2H6 and C2H4) yield for the OCM reaction and the NO decomposition activity was observed. Since the disagreement of the catalytic activity for both reactions was suspected to be due to the non-uniform surface morphological properties of Y2O3, detail experiments were performed for Ba-doped Y2O3 catalysts. It was noteworthy that the addition of Ba into Y2O3 prepared by precipitation method caused a significant increase in not only the C2 yield for the OCM reaction but also the NO decomposition activity. The order of the C2 yield for the OCM reaction over Ba/Y2O3 with different Ba loading was in good agreement with that for the NO decomposition, suggesting the similarity of the active sites for the OCM and NO decomposition reactions. XRD, FT-IR spectroscopy following methanol adsorption and 16O/18O isotopic exchange reaction revealed that the oxygen-deficient Y3+ sites interacting strongly with Ba play a beneficial role in O2 activation, leading to the activation of CH4 and NO molecules to form intermediate in the OCM and NO decomposition reactions.

Effect of barium and potassium promoter on Co/CeO2 catalysts in ammonia synthesis

The Co/CeO2 catalysts promoted with Ba or K were prepared to study the effect of promoter on the catalytic performance of ammonia synthesis. The results show that the presence of Ba or K promoter changes the properties of CeO2-supported Co catalysts including the surface area, the crystallite size and the morphology of CeO2, the reduction degree of cobalt species and the adsorption performance of hydrogen and nitrogen. As a consequence, the samples promoted with an appropriate amount of Ba show higher ammonia synthesis rates, while the catalysts with high Ba loading or K promoter all exhibit low catalytic activities.

Effect of barium loading on CaO derived from waste egg shell heterogeneous catalyst for canola oil biodiesel

The purpose of this research was to investigate the catalytic activity of Ba loading on calcium oxide (CaO) catalyst by varying the amount of barium added during the synthesis: 5-15 wt%. The waste egg shells were utilized as a CaO heterogeneous catalyst by calcined at 900 °C for 2 h. The Ba/CaO catalysts were prepared by impregnation method and were used as a catalyst in transesterification reaction of canola oil via microwave irradiation under microwave power 300 W. The characterization of catalyst and FAME composition of biodiesel were determined by X-ray fluorescence (XRF), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), and gas chromatography (GC-FID). The conditions of biodiesel production were operated at 60 °C, 3 wt% of catalyst loading, 9:1 methanol-to-canola oil ratio, and microwave irradiation power was 300W for 2 min. The experimental results found that, the waste egg shells consist mainly of CaCO3, which was decomposed to CaO more than 88 wt% after cacination step. The 15 wt% Ba/CaO catalysts exhibited the best catalytic performance with the FAME conversion higher than 97.68%.

Novel and facile synthesis of Ba-doped BiFeO3 nanoparticles and enhancement of their magnetic and photocatalytic activities for complete degradation of benzene in aqueous solution

In this work, Bi1-x Bax FeO3 (x=0.05, 0.1 and 0.2mol%) multiferroic materials as visible-light photocatalysts were successfully synthesized via a simple and rapid sol-gel method, at a low temperature and with rapid calcination. Ba loading brought about a distorted structure of BiFeO3 magnetic nanoparticles (BFO MNPs) consisting of small, randomly oriented and non-uniform grains, leading to increased surface area and improved magnetic and photocatalytic activities. Doping of Ba2+ into pure BFO (Bi1-x Bax FeO3, x=0.2mol%) greatly increased magnetic saturation to 3.0emu/g and significantly decreased the band-gap energy to 1.79eV, as compared to 2.1emu/g and 2.1eV, respectively, for pure BFO. Bi1-xBa xFeO3 of x=0.2mol% exhibited the greatest photocatalytic degradation effect after 60min of visible light irradiation, and reached 97% benzene removal efficiency, leading to production of a high concentration of carbon dioxide (CO2), with 93% and 82% reductions in chemical oxygen demand (COD) and total organic carbon (TOC), respectively. The identified major intermediate products of photodegradation enabled prediction of the proposed benzene degradation pathway. The enhanced photocatalytic activity of benzene removal is due to both mechanisms, photocatalytic and photo-Fenton catalytic degradation.

Surface-specific visible light luminescence from composite metal oxide nanocrystals

Low-coordinated surface elements on metal oxide nanoparticles represent the basis for a new concept of luminescent nanoparticles made of abundant, non-toxic, and thermally stable materials. This combined experimental and theoretical study describes the generation and stability of Ba-doped MgO nanoparticle surfaces and their optical absorption and luminescence dependence on Ba loading. It is demonstrated that the vapor phase growth process employed here represents a particularly robust synthesis approach for particle powders with reproducibly adjustable photoluminescence emission properties in the range between blue and yellow light. Moreover, this in-depth characterization also provides an understanding of the electronic and optical characteristics of this nanoparticulate material with a so far unnoticed potential for solid-state light applications that are based on down conversion of UV light.

Highly-enhanced water resistant and oxygen barrier properties of cross-linked poly(vinyl alcohol) hybrid films for packaging applications

Abstract To enhance the thermal stability and barrier properties of pure poly(vinyl alcohol) (PVA), five different cross-linked poly(vinyl alcohol)/boric acid (PVA/BA) hybrid films were prepared via a solution blending method, and their properties including barrier properties, thermal stability, transparency, and mechanical properties were investigated as a function of the BA content. The physical properties of the PVA/BA hybrid films were strongly dependent upon the chemical structure and morphology of the films originating from the amount of BA and change in degree of cross-linking. With increasing BA content, the size and amount of PVA crystallites decreased, whereas the cross-linking density increased, resulting in more compact packing of the molecules and lower free volume in the amorphous regions. The glass transition temperature and thermal stability were highly enhanced with increasing BA content. The oxygen transmission rate (OTR) of pure PVA decreased from 5.96 to 0.15 cc/m 2 day with increasing BA content and were greatly suppressed by 22.8% for 1% BA, 7.7% for 3% BA, and 2.5% for 3% BA, respectively, relative to pure PVA film. With increasing BA content, their water-resistant pressure and tensile strength increased with BA loading. All the hybrid films showed good transparency. These properties of the cross-linked PVA/BA hybrid films make them potential candidates for versatile applications as coatings, films, and packaging materials.

Dependence of the conductivity of polycrystalline Li0.33BaxLa0.56–2/3xTiO3 on Ba loading

Abstract The dependence of lithium ion conductivity on barium loading was investigated for Li 0.33 Ba x La 0.56–2/3 x TiO 3 (LBLT, 0 ≤ x ≤ 0.1) ceramics. The highest bulk conductivity, σ dc , of 1.24 × 10 − 3 S cm − 1 obtained for 0.25 mol.% Ba loading was slightly improved compared to that of non-doped Li 0.33 La 0.56 TiO 3 (1.18 × 10 − 3 S cm − 1 ). The intensities of the XRD patterns in the independent cubic and tetragonal reflections, i.e. , I c(100) and I t(101) , were analyzed; a larger I c(100) / I t(101) ratio corresponded to a larger σ dc . A possible reason for the only slight enhancement of the σ dc by a small loading of Ba is an increased volume fraction of the more highly conductive LBLT cubic phase.

In situ DRIFTS study of NOx adsorption behavior on Ba/CeO2 catalysts

A series of Ba/CeO2 catalysts with different Ba loading amounts were prepared by incipient wetness impregnation. Their NOx adsorption behaviors under NO and NO+O2 conditions were investigated by in situ DRIFTS. It was found that NOx was adsorbed and stored in the form of nitrites and nitrates on both Ba and Ce sites on the surface of the catalysts. The less thermally stable BaCO3 was suggested to be the main active phase for NOx trapping. Ceria served primarily as an oxygen supplier in the absence of O2, and the reaction from nitrites to nitrates on Ba sites was the key step in this case. In the presence of O2, however, gaseous O2 became the main oxygen source. The NOx adsorption capacity of the catalyst was dominated by the Ba content. Moreover, the stability of nitrites and nitrates formed on Ce sites was found to be lower than those formed on Ba sites which existed in the form of the ionic barium nitrate species.

Direct Decomposition of NO over Ba–Y2O3 Catalyst Prepared by Coprecipitation

Abstract The catalytic performance of Ba–Y2O3 prepared by a coprecipitation method for the direct decomposition of NO was investigated. Although Y2O3 catalyzed NO decomposition, its activity was increased by addition of Ba. The maximum NO decomposition activity was achieved on Ba–Y2O3 with 5 wt % Ba loading. XRD measurements revealed the formation of a solid solution of Ba and Y2O3 as well as BaCO3 small particles, when Ba loading was increased up to 5 wt %. From the comparison between the amount of CO2 desorption measured by temperature-programmed desorption of CO2 (CO2-TPD) and the NO decomposition activity of Ba–Y2O3, highly dispersed Ba species, which is initially present as BaCO3 small particles, on the catalyst surface act as catalytically active sites for NO decomposition. On the basis of in situ observation of surface species formed during NO decomposition by Fourier transform infrared (FT-IR) spectroscopy, we proposed that highly dispersed Ba species plays a role for the formation and adsorption of nitrite (NO2−) as reactive species for NO decomposition over Ba–Y2O3 catalyst.

Formation and removal of Ba-carbonates or carboxylates on Pt/BaO/γ-Al2O3 lean NOx traps

In addition to feed composition, the NOx storage capacity (NSC) of a Pt/BaO/γ-Al2O3 lean NOx trap (LNT) also depends on the chemical state of Ba prior to the start of the lean NOx exposure phase during which the NSC is measured. This state of Ba is a result of the history of the trap's cyclic exposures to lean and rich conditions and is a function of the feed composition and the time intervals of the exposures. We have systematically investigated the role of adsorbed CO2 on the NOx sorption process on traps with 20, 8 and 4wt.% Ba. This was accomplished through a sequence of NOx storage and regeneration cycles with CO2 and H2O in the feed followed by purge in Ar and then by NOx storage and regeneration without CO2 and H2O at 300°C. The amount of pre-adsorbed CO2 released during NOx storage upon the introduction of NO2+O2 correlated well with the amount of NOx stored on the trap with 20wt.% Ba but not on the traps with 8 and 4wt.% Ba loadings. These results were further investigated in DRIFTS sequential adsorption experiments for CO2, NO2+O2, H2 or NO2+O2, CO2, H2 at 300°C. The DRIFTS experiments showed that, similar to bulk vs. surface nitrate formation on samples with high vs. low Ba loading, CO2 adsorption forms either carbonates or carboxylates on high vs. low Ba loadings, respectively. Regeneration by H2 removed all NOx adsorbates and any carboxylates, but not the carbonates. Thus, the formation of carbonates slows the NOx storage process as NOx must compete with pre-adsorbed carbonates for adsorption sites after regeneration. In addition, comparison between the NOx breakthrough curves with 7% CO2 in the lean feed and with pre-adsorbed CO2 on the catalyst showed that the NOx storage before the slip occurs was intimately related to the oxygen spillover from Pt to the surrounding Ba and competition between CO2 and NOx for adsorption sites. These findings provide insights to further improve the LNT formulations by using optimum Ba loadings and dispersions targeted at increasing the zero NOx slip time after each fuel rich pulse.

Effect of barium loading on CuO x–CeO 2 catalysts: NO x storage capacity, NO oxidation ability and soot oxidation activity

A series of Ba–Cu–Ce catalysts were prepared by loading different amounts of Ba(Ac) 2 on the sol–gel-synthesized CuO x –CeO 2 mixed oxides. The activities of the catalysts for soot oxidation were evaluated in 1000 ppm NO/10% O 2/N 2 under loose contact conditions. The catalysts were characterized by XRD, BET, H2-TPR, in situ-DRIFTS and NO-TPO measurements. When Ba loading is between 6 and 10 mol.% of Cu + Ce, the catalysts exhibit an onset temperature ( T i) as low as 376 °C. NO is oxidized at Cu x+ and Ce x+ sites and then stored on the adjacent Ba species in form of barium nitrate. Ba(NO 3) 3 begins to decompose, releasing abundant NO 2 at around 370 °C under the driving of soot as the reductant. The nitrate-derived NO 2 and the NO-derived NO 2 initiate the soot combustion over the Ba-modified catalysts with a significantly lowered T i. The ternary catalysts lose their NO x storage capacity after hydrothermally aged at 800 °C for 10 h due to the formation of BaCeO 3. However, Ba restrains the sintering of (Cu,Ce)O x , resulting in relatively more favorable redox properties and thus higher activity for NO oxidation. The barium-modified catalysts show lower onset temperatures (470–480 °C) of soot oxidation than pure CuCe (509 °C) after aging.

‘Fast’ NOx storage on Pt/BaO/γ-Al 2O 3 Lean NOx Traps with NO 2 + O 2 and NO + O 2: Effects of Pt, Ba loading

NOx storage on Pt/BaO/γ-Al 2O 3 Lean NOx Traps (LNTs) has been studied with a particular focus on the NOx storage capacity (NSC) of these traps for the time up to which 1% of the inlet [NOx] escapes the trap. This complete or ‘fast’ NOx sorption capability of LNTs for appreciable amounts of time is what makes these catalysts useful for automotive NOx emission abatement. The fast NSC for LNT formulations with combinations of a range of Pt (0.6–6.3 wt.%) and Ba (4–20 wt.%) loadings was measured under various lean feed compositions including NO, NO 2 and NO + NO 2 as the NOx sources and presence and absence of 7%CO 2 and 7%H 2O. All the measurements were performed at 300 °C and at a space velocity of 30,000 h −1. The complex trends in the fast NSC due to various Pt, Ba loading combinations are explained with the help of a phenomenological model. The model addresses the trends in fast NSC primarily through combinations of NOx storage contributions in parallel pathways on Ba vicinal to Pt and Ba uninfluenced by Pt. We attribute the influence of Pt to the spillover of dissociated oxygen atoms from Pt to the vicinal Ba sites. This Pt–Ba synergy was found to play a dominating role in governing the fast NSCs of all the LNT samples especially in presence of CO 2, H 2O and CO 2 + H 2O in the lean feed. It was also found to be the prominent factor in limiting the fast NSC when NO and NO + NO 2 (with low NO 2/NO) were the NOx sources rather than NO 2. We propose that the NOx storage process on Ba vicinal to Pt involves a localized reaction front of NOx that travels through the catalyst bed with saturation of those sites. This process has no preference between NO and NO 2 as a precursor. CO 2 and H 2O affect through competition for both types of Ba sites available for NOx storage.