Temperature-programmed Combustion Research Articles

Study on Oxidation Activity of CuCeZrOx Doped with K for Diesel Engine Particles in NO/O2

CuCeZrOx and KCuCeZrOx catalysts were synthesized and coated on the blank diesel particulate filter (DPF) substrate and a particulate matter (PM) loading apparatus was used for soot loading. The catalytic performances of soot oxidation were evaluated by temperature programmed combustion (TPC) test and characterization tests were conducted to investigate the physicochemical properties of the catalysts. The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy. The results demonstrated that CuCeZrOx catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu0.9Ce0.05Zr0.05Ox over which the maximum soot oxidation rate decreased to 410 °C. Characterization tests have shown that catalysts containing 90% Cu have uniformly distributed grains and small particle sizes, which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot. The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K. The maximum particle oxidation rate can be easily realized at such a low temperature as 347°C.

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1-20 ng/g) by wet chemistry is challenging. Combustion-trapping techniques have been shown to be an appropriate alternative. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O2 stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H2O, CO2, SO2, etc. The O2 carrier gas, including combustion products and elemental Hg, is then purged into a 40% (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO3/1HCl (v/v), 25 mL/min O2 flow rate, and a dynamic temperature ramp rate (15 °C/min for 25-150 and 600-900 °C; 2.5 °C/min for 150-600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81-102%) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80-120%. This protocol has the advantages of a short sample processing time (∼3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.

NO and C Oxidation with Pt Recovered From Spent Catalytic Converters

Several powder samples obtained from a spent catalytic converter, which contained approximately 1.1% w/w of platinum (Pt), were subjected to a leaching process to assess the relationships between the amount of recovered Pt, the time, and the temperature of the leaching process. The leached powder samples were characterized by X-ray fluorescence (XRF), which showed that the amount of recovered Pt increased linearly with increasing temperature. Our best recovery results (nearly 85% recovery) were reached at a temperature of 100°C, that was applied for 1 h. In the second step of the process, the leached solution was exposed to 100°C for 1 h and then run through ion exchange column with two basic resins: Amberlite-IRA 400 and 900. The aim of this second stage was to eliminate the impurities that originated from the first stage. The purity of the recovered Pt was higher when the process was carried out with the macroreticular matrix resin. Two 2-wt% Pt/Al2O3 catalyst powder samples were synthesized via incipient wetness impregnation, either using recovered platinum or an aqueous hydrogen hexachloroplatinate solution. The activity of these catalysts toward carbon and NO oxidation was assessed using a temperature-programmed combustion (TPC) plant. Results showed that the Tp values (peak combustion temperatures) of carbon oxidation were 555 and 560°C for the commercial Pt and the recovered Pt catalysts, respectively. When the catalysis of NO to NO2 is considered, both catalysts showed similar performances. They both reached their highest conversion (~61%) at 310°C without the production of nitrous oxide.

Soot Combustion over Lanthanum Cobaltites and Related Oxides for Diesel Exhaust Treatment

This paper reports a comparative study of a series of La1−x(M)xCoO3 (M = Ce and Sr) perovskites and the related M′Ox (M′ = La, Co, Ce, and Sr) sample oxides. These catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), temperature-programmed desorption (TPD) of oxygen, temperature-programmed reduction (TPR) by hydrogen, and temperature-programmed combustion (TPC) of soot. In the presence of perovskite-type catalysts, the soot oxidation was promoted, showing a shift of CO2 peaks toward lower temperature compared to the non-catalytic process. In addition, the catalytic activity of these perovskites was found to follow the trend La0.8Ce0.2CoO3 > La0.9Ce0.1CoO3 > La0.9Sr0.1CoO3 > La0.8Sr0.2CoO3 ≈ LaCoO3. A mechanism was proposed with an attack of soot by surface oxygen species, which migrate from the perovskite surface. The generation of CO (or carbonyl groups) as an intermediate and the possible formation of carbonate species over the most basic compounds are also discussed.

Pd substitution effects on perovskite catalyst activity for methane emission control

Perovskite-type oxides of the LaBO 3 and LaB 0.9Pd 0.1O 3 series (where B = Cr, Mn, Fe) have been prepared and characterized by X-ray diffraction (XRD), BET specific surface area, and field emission scanning electron microscope (FESEM) techniques. The activity of the reference perovskites, LaBO 3, and the new versions (with Pd introduction at the B-site) towards the combustion of methane, was evaluated in a Temperature Programmed Combustion (TPC) apparatus. Perovskite-type oxide containing Mn and Pd at the B-site was found to provide the best results. The half-conversion temperature of methane over the LaMn 0.9Pd 0.1O 3 catalyst was 425 °C, compared to 485 °C for LaMnO 3, with a W/F = 0.12 g s/cm 3. On the basis of a Temperature Programmed Desorption (TPD) analysis of oxygen as well as catalytic combustion runs, the prevalent activity of the LaMn 0.9Pd 0.1O 3 catalyst could be explained by its capability to deliver a higher amount of intrafacial oxygen. This catalyst was then deposited on cordierite monoliths in a γ-Al 2O 3 supported form (catalyst weight percentage 15%) and tested in a lab-scale test rig under realistic conditions. Half methane conversion ( T 50) was achieved at 340 °C (Gas Hourly Space Velocity (GHSV) = 10 000 h −1), almost the same T 50 value as the commercial 4 wt% Pd/γ-Al 2O 3 catalyst, but with a six-times lower amount of the expensive noble metal.

Household oven self-cleaning surfaces via catalytic thermal oxidation

The present work is aimed at developing oven walls with self-cleaning properties, via catalytically enhanced thermal oxidation of soiling material within the standard range of household oven, temperatures, i.e. up to 300 °C. Some saturated fatty acids, e.g. myristic (tetradecanoic), palmitic (hexadecanoic) and stearic (octadecanoic) acids, were selected as single soiling compounds to investigate their thermal degradation behaviour under different operating conditions. MnCr 2O 4, LaFeO 3 and CeO 2 were chosen as oxidative catalysts and synthesized by the “Solution Combustion Synthesis” (SCS) method. The catalytic activity towards fatty acids was tested in a temperature programmed combustion (TPC) apparatus. The Ozawa method was adopted to calculate the activation energy for the catalytic combustion of palmitic acid on, e.g. ceria showing a very low value of 50 kJ/mol compared to the 90 kJ/mol for the non-catalytic combustion. The prepared catalysts were then deposited on steel sheet samples coated with commercial enamel by in situ spray pyrolysis. The obtained catalytic layers were characterized by SEM–EDS analysis to assess their integrity and adhesion to enamel and the obtained phases. The self-cleaning performance of the coated sample activity was measured in a standard oven, by performing a cooking cycle simulation (250 °C for 60 min; soiling by olive oil and pork lard); the weight loss and aesthetic appearance were benchmarked versus a bare, non-catalytic enamel surface. The CeO 2 catalyst showed the best adhesion properties as well as the best performances towards the combustion of the three selected fatty acids, whereas the MnCr 2O 4 catalyst provided the best performance towards both the pork lard and the olive oil catalytic combustion with fat removal per cycle of about 18% and 40%, respectively.

Lanthanum cobaltite catalysts for diesel soot combustion

This paper deals with the preparation (by solution combustion synthesis), the characterization (by XRD, AAS, BET, FESEM, XPS and TPD/R analyses), the catalytic activity evaluation (in a temperature-programmed combustion microreactor), and the conception of a possible reaction mechanism of a series of nano-structured soot combustion catalysts based on La–Co substoichiometric or alkali metal-substituted perovskites (La0.9CoO3, La0.9Na0.1CoO3, La0.9K0.1CoO3, La0.9Rb0.1CoO3), whose performance has been compared with that of the standard LaCoO3. Significant catalytic activities have been measured in the 350–450°C range, even after a specific thermal ageing protocol (at 850°C for 16h in the presence of water) or repeated combustion cycles (up to 9). The La0.9Rb0.1CoO3 catalyst has been found to allow the best compromise between satisfactory catalytic activity and stability. This catalyst has been then deposited on an SiC wall-flow trap, submitted to the same ageing treatment and then tested on a diesel engine bench (trap loading and regeneration inducing a temperature increase due to the catalytic combustion of the on purpose post-injected fuel). The presence of the catalyst in the wall-flow trap has enabled both a more complete regeneration and a significant reduction of the regeneration time compared to that of a non-catalytic trap, even after ageing, with a consequent potential saving of post-injected fuel.

Catalytic removal of methane over thermal-proof nanostructured catalysts for CNG engines

Five spinel-type catalysts AB2O4 (Co0.8Cr2O4, CoCr2O4, MnCr2O4, MgFe2O4 and CoFe2O4) were prepared and characterized by XRD, BET and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a Temperature Programmed Combustion (TPC) apparatus. The half conversion temperature of methane over the Co0.8Cr2O4 catalyst was 369 °C with a W/F = 0.12 g s/cm3. On the basis of Temperature Programmed Desorption (TPD) of oxygen as well as of catalytic combustion runs, the prevalent activity of the Co0.8Cr2O4 catalyst could be explained by its higher capability to deliver suprafacial chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of Pd, deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and Co0.8Cr2O4 catalysts enables half methane conversion at 340 °C (GHSV = 10,000 h−1), a performance similar to that of conventional 4 wt% Pd-γ Al2O3 catalysts but guaranteed with just a four-fold lower amount of noble metal. Both the catalysts in powder and the monolith hosting the Co0.8Cr2O4 + 1 wt% Pd catalyst, submitted to a thermal ageing treatment in air at 700 °C for 12 h, displayed a negligible deactivation.

Effects of Minerals on the Release of Nitrogen Species from Anthracite

Experiments have been carried out to investigate the effects of minerals on nitrogen species emission including NO and its precursors from a high rank coal during temperature-programmed combustion by TG/EGA method at 10°C/min. Sodium was found to be an excellent catalyst for the reduction of NO and HCN evolution due to its higher catalysis of sodium on the char-NO reaction. However, iron can induce an increase of NO release. Calcium and titanium additives can be classified as inactive constituents because of their weak catalysis on HCN and NO emission. All the metallic additives can promote NH3 emission except sodium. Parent coal has higher fractions of nitrogen release as NO and NH3 and lower fraction of nitrogen release as HCN than demineralized coal, which can be attributed to the catalysis of indigenous minerals in parent coal.

An evaluation of stability by thermogravimetric analysis of digestate obtained from different biowastes

Research was carried out with the aim of monitoring anaerobic digestion processes using thermal analysis with the aid of mass spectrometry so as to define the stability of the digestate obtained. Three different systems were investigated under varying conditions. The digestion of waste sludge from a pharmaceutical industry (PI) and the digestion of cattle manure (CM) were evaluated under mesophilic conditions. The co-digestion of a mixture of primary sludge (PS) and the organic fraction of municipal solid wastes (OFMSW) was studied under thermophilic conditions. Temperature-programmed combustion tests were carried out to investigate the degree of stabilization of samples throughout the digestion processes. The derivative thermogravimetry (DTG) profiles obtained for the mesophilic digestion of PI waste showed a decrease at low temperatures and an increase at high temperatures in the intensity of the peaks recorded as the stabilization process proceeded. These results are in accordance with those obtained by the present authors in their previous work on the mesophilic digestion of primary sludge and OFMSW. In contrast, the DTG profiles obtained from the stabilization process of CM and thermophilic codigestion of PS and OFMSW showed a reduction in peaks at high temperatures. When the stabilization products obtained from CM by anaerobic digestion and by composting processes were compared, it was observed that the composting process was capable of further decomposing materials readily oxidized at low temperatures and increasing the presence of structurally more complex substances. The evolution of the differential thermal analysis (DTA) signal recorded simultaneously showed considerable similarity to the mass/charge ( m/ z) signal 44 registered by the mass spectrometer. The use of mass spectrometry helped to clarify the inner workings of the digestion process.

High catalytic activity of SCS-synthesized ceria towards diesel soot combustion

Nano-sized particles of ceria with high surface area were processed by solution combustion synthesis (SCS) and their catalytic activity towards combustion of carbonaceous materials was compared with that obtained by simple thermal decomposition of cerium nitrate, exhibiting the same specific surface area. These two kinds of ceria powders were tested by DTA and temperature-programmed combustion of diesel soot and a commercial carbon.Ceria processed by SCS was found to be more active than its counter part since it could decrease significantly both the combustion activation energy (from 115 to 111kcal/mol) and the TPC-plot peak temperature of diesel soot (from 466 to 405°C).The mechanism of the catalytic reaction of combustion was investigated by TPD/R experiments. Likewise other combustion catalysts acting as oxygen pumps, ceria can exchange limited amounts of oxygen even below 300°C, the SCS-synthesized one showing a superior O2 release at low temperatures (≤450°C). Moreover, the SCS-ceria exhibited a microstructure (i.e. a foam of nano-sized crystals) particularly suitable for maximizing the number of contact points between catalyst and carbon. Finally, the effect of specific aging protocols (thermal treatment at 600°C for 96h) in the presence of potentially deactivating species present in diesel exhaust gases (SO2 and water) was also studied showing that the here proposed material suffers from less significant ageing than Ce(NO3)3-derived ceria.

CNG engines exhaust gas treatment via Pd-Spinel-type-oxide catalysts

Four spinel-type catalysts AB 2O 4 (CoCr 2O 4, MnCr 2O 4, MgFe 2O 4 and CoFe 2O 4) were prepared and characterized by XRD, BET, TEM and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a temperature-programmed combustion (TPC) apparatus. Spinel-type-oxides containing Cr at the B site were found to provide the best results. The half-conversion temperature of methane over the CoCr 2O 4 catalyst was 376 °C with a W/ F = 0.12 g s/cm −3. On the basis of temperature-programmed oxygen desorption (TPD) analysis as well as of catalytic combustion runs, the prevalent activity of the CoCr 2O 4 catalyst could be explained by its higher capability to deliver suprafacial, weakly chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of palladium deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and CoCr 2O 4 catalysts enables half methane conversion at 330 °C (GHSV = 10,000 h −1), a performance similar to that of conventional 4 wt% Pd-γ-Al 2O 3 catalysts but enabled with just a four-fold lower amount of noble metal.

Supported gold catalysts for CO oxidation

Catalysts containing gold clusters dispersed on different oxide supports (CeO 2, ZrO 2, La 2O 3) were developed as alternative materials to platinum group metals (PGM), widely used in catalytic exhaust gas treatment. The catalysts were prepared by the innovative combustion synthesis method (SCS) and then characterized by XRD, BET, TEM and SEM-EDS analyses, whereas their catalytic activity towards CO oxidation was tested in a temperature programmed combustion (TPC) apparatus. Combustion synthesis allowed to achieve in a single step 5–25 nm Au clusters supported on nanostructured metal oxides powders. Significant catalytic activities were measured in the range 150–250 °C which has to be regarded as a good basis for further development. A more lengthy classical precipitation method at pH 8 was indeed also applied to the preparation best performing catalyst (2 wt.% Au-La 2O 3) thereby getting better results in a fresh state but practically equal after prolonged ageing (800 °C for 5 h). TPR analyses were carried out to elucidate the nature of the support-gold synergism of the 2 wt.% Au-La 2O 3 catalyst, which appears to be dominated by the size of the gold clusters.

La–Li–Cr perovskite catalysts for diesel particulate combustion

Nano-structured bulk Li-substituted La–Cr perovskites (La 0.8Cr 0.9Li 0.1O 3, La 0.8Cr 0.8Li 0.2O 3, La 0.8Cr 0.7Li 0.3O 3) were prepared (by combustion synthesis), characterized (by XRD, AAS, BET, SEM, TEM, TPD/R, XPS analyses), tested (in a temperature-programmed combustion TPC microreactor and in a DSC analyzer) in comparison with the reference LaCrO 3. The progressive increase in the Li content of the catalysts induces an increase in the catalytic activity owing to the enhancement of the amount of weakly chemisorbed oxygen O − species (even exceeding 1200 μmol/g), key players in the soot oxidation mechanism. However, beyond 20% Cr substitution with Li, part of this latter metal got segregated as LiCrO 2. The best single-phase catalyst (La 0.8Cr 0.8Li 0.2O 3) was already active well below 350 °C. Catalytic traps were prepared by in situ combustion synthesis within cordierite (CORNING) and SiC (IBIDEN) wall-flow filters on the basis of the above catalysts and tested on real diesel exhaust gases in an engine bench, fully confirming the encouraging results obtained on powder catalysts.

Studies on the redox properties of chromite perovskite catalysts for soot combustion

This paper deals with the preparation (by combustion synthesis), the characterization (by XRD, AAS, BET, SEM, TEM, TPD/R, and XPS analyses), the catalytic activity testing (in a temperature-programmed combustion microreactor and in a DSC analyzer), and the assessment of the reaction mechanism of a series of nanostructured soot combustion catalysts based on La–Cr substoichiometric or alkali-metal-substituted perovskites (La 0.9CrO 3, La 0.8CrO 3, La 0.9Na 0.1CrO 3, La 0.9K 0.1CrO 3, La 0.9Rb 0.1CrO 3, La 0.8Cr 0.9Li 0.1O 3), whose performance is compared with that of the standard LaCrO 3. Some conclusions are drawn concerning the role of each single constituting element on the activity of the most promising catalyst, La 0.8Cr 0.9Li 0.1O 3, which is already active well below 400 °C. The role of weakly chemisorbed O − surface species in particular is pointed out as crucial for the soot combustion process. This indicates the way for the development of new, more active catalysts, possibly capable of delivering amounts of these oxygen species even higher than those obtained (about 700 μmol / g) for the most active Li-substituted lanthanum chromite catalyst developed.

Evaluation of digestate stability from anaerobic process by thermogravimetric analysis

A study aimed to monitor the anaerobic digestion process using thermal analysis to define the stability of the digestate obtained was conducted. The mesophilic digestion of primary sludge (PS), of the organic fraction of municipal solid wastes (OFMSW), and of a mixture of these two biowastes was evaluated. Temperature-programmed combustion tests were carried out to investigate the stabilization degree of samples throughout the digestion process. The DTG profile obtained from combustion in an oxidizing atmosphere for the samples analysed showed, as a common result, reduction at low temperatures together with an increase at high temperatures (around 500 °C) of the intensity of the rate of loss of mass as the stabilization process evolved. In all digestate samples the DTA signal showed energy release at high temperatures (around 500 °C) which was not present in feed samples. This study shows that thermogravimetry may offer a means of ascertaining the stabilization degree reached by the organic matter under the anaerobic digestion process.

Comparison between the reactivity of coal and synthetic coal models ☆

A mixture of carbon compounds was pyrolysed under an inert atmosphere at different temperatures in a fixed bed reactor. The resultant chars were characterised in terms of texture and thermal behaviour. Textural characterisation of the chars was carried out by N 2 and CO 2 adsorption isotherms at −196 and 0 °C, respectively. Char isothermal reactivity in air at 500 °C, and in CO 2 at 1000 °C, was performed in a thermogravimetric analyser (TGA). Temperature-programmed combustion tests under 20% oxygen in argon were also performed in the TGA linked to a mass spectrometer (TGA/MS). The results showed that char textural properties do not always relate well to their reactivity. Not only do physical properties (e.g. surface area, porosity) but also chemical properties (e.g. active sites concentration and distribution) play an important role in the reaction of carbonaceous material and oxidant. On the other hand, in terms of chemical composition the chars obtained from the mixture of carbon compounds were very similar to the chars produced under the same experimental conditions by a high volatile bituminous coal. The fact that carbon compounds are well known makes it easier to obtain knowledge about the functional groups present in synthetic char, and to study the mechanisms of heterogeneous reactions such as the reduction of NO with carbon.

Nickel doped hydrotalcites as catalyst precursors for the partial oxidation of light paraffins

A series of Ni, Mg and Al containing hydrotalcite-type precursors was synthesised (Ni X Mg 72− X Al 28, X=10–72) by coprecipitation at low supersaturation at pH 8±0.2 at 60–70°C. Their calcination at 900°C in air resulted in the formation of solids consisting of spinel and divalent metal oxide phases. The catalyst activation was studied by temperature programmed reduction (TPR). Ni 2+ in the divalent metal oxide phase could be reduced in all samples, with the reduction temperatures increasing with decreasing Ni content, but only in the sample without Mg the Ni 2+ in the spinel phase were reducible. The Ni dispersion determined from the TPR results was higher for the catalysts with a lower Ni content and decreased for higher Ni contents. Catalytic tests were carried out at 700°C and at 800°C for 240 min using a C 3H 8/O 2/He-mixture at a gas hourly space velocity (GHSV) of 900 dm 3 g −1 h −1. High values for the conversion of C 3H 8 (≥73%) as well as for the selectivities to CO (≥88%) and H 2 (≥69%) were observed for all the catalysts at both reaction temperatures. At lower temperatures and with higher Ni content, these values were lower, whereas the conversion of O 2 was found to be almost complete in all experiments. The carbon content of the spent catalysts was determined by temperature programmed combustion (TPC) using thermogravimetry (TG). The tendency towards carbon formation was found to be higher at lower temperatures and for higher Ni contents. On the basis of activity, selectivity and resistance against coke formation, the Ni containing catalyst with the lowest Ni content was found to be the best catalyst.

Effect of the grinding behaviour of coal blends on coal utilisation for combustion

Grinding of a high volatile bituminous coal was performed in three comminution devices: Raymond Mill (RM), Rolls Crusher (RC) and Ball Mill (BM). The pulverised samples were sieved to obtain four particle size fractions, and temperature-programmed combustion (TPC) was used for the evaluation of their combustion behaviour. In addition, three coals of different hardness and rank were mixed in various proportions in order to compare the combustibility characteristics of the binary coal blends with those of the individual coals. The effect of coal blending on grindability was also studied. It was found that grindability was non-additive especially when coals of very different Hardgrove Grindability Index (HGI) were blended. The combustion studies also suggested that there exists an interaction between individual coals when they are burnt as a blend.

The effect of the textural properties of bituminous coal chars on NO emissions

NO is the primary product of the oxidation of char nitrogen, and in some combustion processes the NO can be reduced on the char surface to give N 2O and/or N 2. In this study a range of bituminous coals (low, medium and high volatile matter content) were pyrolysed in a fixed bed reactor at various heating rates. Textural characterisation was carried out by measuring true (He) and apparent (Hg) densities and N 2 (−196°C) and CO 2 (0°C) adsorption isotherms. Pore volume distributions and surface areas were obtained for the chars studied. A thermogravimetric analyser coupled to a quadrupole mass spectrometer (TG-MS) was used to study the combustion behaviour of the samples and the nitrogen compounds evolved during temperature-programmed combustion. Results are discussed in terms of the influence of both textural properties and reactivity on NO emissions and on the heterogeneous reduction of NO.