Search Results (14)

In addition to SCR systems, lean NO_X traps (LNTs) are also used for exhaust aftertreatment of lean burn internal combustion engines to sustainably reduce NO_X emissions. Modern LNTs consist of different functional compounds to maximize the performance during NO_X storage and regeneration. Based on the material analysis of a serial production LNT, PGM loaded BaO, Al₂O₃, MgAl₂O₄, and CeO₂ were identified as the main base materials. In this paper, the NO_X storage capacity (NSC) of these compounds is investigated both as single catalysts and as physical mixtures to identify possible synergistic effects. Therefore, commercially available support materials were loaded with Platinum and tested in granular form under realistic conditions. To optimize the performance by reducing the diffusion pathways for NO_X molecules during storage, PGM, BaO, and Ceria were combined in a composite by the incipient wetness impregnation of alumina. As a result, the temperature dependent NSC of the commercial LNT could be reached with the Pt/Rh/Ba₁₀Ce₂₅/Al₂O₃ infiltration composite, while reducing the oxygen storage capacity by about 45%. Without the additional Rhodium coating, the low-temperature NSC was insufficient, highlighting the important contribution of this precious metal to the overall performance of LNTs. Full article

Particulate mass concentration is a crucial parameter for characterising air quality. The diesel particulate filter (DPF) is the primary technology used to limit vehicle particle emissions, but it needs periodic cleaning, a process called regeneration. This study aims to assess the impact of active DPF regeneration on the performance and emissions of Euro 5 and 6 vehicles. The study examined both carbon dioxide (CO₂) and pollutant (nitrogen oxides (NO_x) and particle number (PN)) emissions for eight vehicles tested in the laboratory and on the road. Apart from the DPF, a wide range of emission control systems was covered in this experimental campaign, including exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), lean NO_x trap (LNT) and selective catalytic reduction (SCR) catalyst, revealing the different impacts on NO_x emissions. The regeneration frequency and duration were also determined and used to calculate the K_i factor, which accounts for the emissions with and without regeneration, weighted over the distance driven between two consecutive regeneration events. Based on these outcomes, representative emission factors (EF) were proposed for the regeneration phase only and the complete regeneration interval. In addition, the effect of regeneration on efficiency was estimated and compared with other energy consumers. The results indicated a significant impact of DPF regeneration on CO₂, NO_x and PN emissions, higher in the case of driving cycle testing in the laboratory. The relevant mechanisms behind the elevated emission levels were analysed, focusing on the regeneration period and the test phase following immediately after. The calculation of the K_i factor and the comparison with the official values revealed some weaknesses in its application in real-world conditions; to overcome these, new NO_x EF values were calculated, depending on the emission control system. It was revealed that Euro 6 vehicles equipped with SCR could comply with the applicable limits when considering the complete regeneration interval. Finally, it was indicated that the DPF regeneration impact on vehicle efficiency is similar to that of driving with the air conditioning (A/C) system and headlights on. Full article

The net oxidising atmosphere of lean burn engines requires a special after-treatment catalyst for NO_x removal from the exhaust gas. Lean NO_x traps (LNT) are such kind of catalysts. To increase the efficiency of LNTs at low temperatures platinised perovskite-based infiltration composites La_0.5Sr_0.5Fe_1-xM_xO_3-δ/Al₂O₃ with M = Nb, Ti, Zr have been developed. In general, platinum based LNT catalysts show an undesired, hazardous formation of N₂O in the lean operation mode due to a competing C₃H₆-selective catalytic reduction (SCR) at the platinum sites. To reduce N₂O emissions an additional Rh-coating, obtained by incipient wetness impregnation, besides the Pt coating and a two-layered oxidation catalyst (2 wt.% Pd/20 wt.% CeO₂/alumina)-LNT constitution, has been investigated. Though the combined Rh-Pt coating shows a slightly increased NO_x storage capacity (NSC) at temperatures above 300 °C, it does not decrease N₂O formation. The layered oxidation catalyst-LNT system shows a decrease in N₂O formation of up to 60% at 200 °C, increasing the maximum NSC up to 176 µmol/g. Furthermore, the NSC temperature range is broadened compared to that of the pure LNT catalyst, now covering a range of 250–300 °C. Full article

The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NO_x and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NO_x under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NO_x trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NO_x and soot abatement strategies. The main focus of this review is on combined technologies for NO_x removal (i.e., LNT–SCR) and for the simultaneous removal of NO_x and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems. Full article

This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH₃ and N₂O. The NOx, N₂O, and NH₃ emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH₃ and N₂O is observed in both Diesel and gasoline light-duty vehicles, whereby NH₃ emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH₃ emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N₂O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles. Full article

Vehicular pollution has become a major problem in urban areas due to the exponential increase in the number of automobiles. Typical exhaust emissions, which include nitrogen oxides (NO_x), hydrocarbons (HC), carbon monoxide (CO), soot, and particulate matter (PM), doubtless have important negative effects on the environment and human health, including cardiovascular effects such as cardiac arrhythmias and heart attacks, and respiratory effects such as asthma attacks and bronchitis. The mitigation measures comprise either the use of clean alternative fuels or the use of innovative technologies. Several existing emission control technologies have proven effective at controlling emissions individually, such as selective catalytic reduction (SCR) and lean NO_x trap (LNT) to reduce NO_x and diesel particulate filter (DPF) specifically for PM abatement. These after-treatment devices are the most profitable means to reduce exhaust emissions to acceptable limits (EURO VI norms) with very little or no impact on the engine performances. Additionally, the relative lack of physical space in which to install emissions-control equipment is a key challenge for cars, especially those of small size. For this reason, to reduce both volume and cost of the after-treatment devices integrated catalytic systems (e.g., a sort of a “single brick”) have been proposed, reducing both NO_x and PM simultaneously. This review will summarize the currently reported materials for the simultaneous removal of NO_x and soot, with particular attention to their nature, properties, and performances. Full article

The behavior and operation parameters were analyzed for the hybrid LNT-SCR (Lean NO_x-Trap–Selective Catalytic Reduction) system with advanced catalyst formulations. Pt-Ba-K/Al₂O₃ was used as an NSR (NO_x Storage and Reduction) or LNT catalyst effective in NO_x and soot simultaneous removal whereas Cu-SAPO-34 with 2 wt.% of copper inside the structure was the small pore zeolite employed as the SCR catalyst. Under alternating and cyclic wet conditions, feeding volumetric concentrations of 1000 ppm of NO, 3% of O₂, 1.5% of water, 0.3% of CO₂, and H₂ as a reductant, the NO_x-conversion values were above 95% and a complete mineralization to nitrogen was registered using θ ≤ 3 (20 s of regeneration) and a hydrogen content between 10,000 and 2000 ppm in the whole temperature range tested. An excess of hydrogen fed (above 1% v/v) during the rich phase is unnecessary. In addition, in the low temperature range below 250 °C, the effect is more noticeable due to the further ammonia production and its possible slip. These results open the way to the scale up of the coupled catalytic technologies for its use in real conditions while controlling the influence of the operation map. Full article

The transport sector is one of the main sources air pollutants. Different exhaust after-treatment systems have been implemented over the years to control the emissions of criteria pollutants. However, while reducing the emissions of the target compounds these systems can lead to the emissions of other pollutants and/or greenhouse gases such as NH₃ or N₂O. Following the implementation of the Real Driving Emissions (RDE) test procedure in the EU, vehicles have been equipped with more complex after-treatment configurations. The impact that these technologies may have on the emissions of non-regulated pollutants during real-world driving have not been evaluated until now. In the current study we present the on-road emissions of a series of non-regulated pollutants, including NH₃, N₂O, CH₄ and HCHO, measured with a portable FTIR from a series of Euro 6d, Euro 6c and Euro 6d-TEMP, gasoline diesel and compressed natural gas (CNG) vehicles during real-world testing. The obtained results show that it is possible to measure N₂O, NH₃, CH₄ and HCHO during on-road operation. The results also highlight the importance of the measurement of the emissions of these pollutants during real-world driving, as the emissions of NH₃ (a particulate matter precursor) and those of N₂O and CH₄ (green-house gases) can be high from some vehicle technologies. NH₃ emissions were up to 49 mg/km for gasoline passenger cars, up to 69 mg/km for the CNG light-commercial vehicle and up to 17 mg/km a diesel passenger car equipped with a selective catalytic reduction system (SCR). On the other hand, N₂O and CH₄ emissions accounted for up to 9.8 g CO₂ eqv/km for a diesel passenger car equipped with a combination of diesel oxidation catalysts (DOC), lean NO_x traps (LNT), SCR and possibly an ammonia slip catalyst ASC. Full article

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO₂ emissions than stoichiometric gasoline engines. However, NO_x reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NO_x storage and reduction (NSR), also known as lean NO_x trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NO_x emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NO_x removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO₃) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NO_x from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO₂ conversion, NO_x storage capacity, and NO_x reduction efficiency is addressed. Furthermore, the NO_x removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al₂O₃) in the absence and presence of SO₂ and H₂O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted. Full article

Lean nitric oxide (NO_x)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NO_x. The combination of LNT and SCR catalysts improves overall NO_x removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H₂, C₃H₆, and the combination of CO + H₂ were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH₃-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH₃ and NO). The combination of CO and H₂ was especially detrimental to SCR activity and to NH₃ oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH₃ oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu²⁺/CuOH⁺ ratio in favor of the monovalent CuOH⁺ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters. Full article

Tailpipe emissions of a pool of 13 Euro 6b light-duty vehicles (eight diesel and five gasoline-powered) were measured over an extensive experimental campaign that included laboratory (chassis dynamometer), and on-road tests (using a portable emissions measurement system). The New European Driving Cycle (NEDC) and the Worldwide harmonised Light-duty vehicles Test Cycle (WLTC) were driven in the laboratory following standard and extended testing procedures (such as low temperatures, use of auxiliaries, modified speed trace). On-road tests were conducted in real traffic conditions, within and outside the boundary conditions of the regulated European Real-Driving Emissions (RDE) test. Nitrogen oxides (NO_X), particle number (PN), carbon monoxide (CO), total hydrocarbons (HC), and carbon dioxide (CO₂) emission factors were developed considering the whole cycles, their sub-cycles, and the first 300 s of each test to assess the cold start effect. Despite complying with the NEDC type approval NO_X limit, diesel vehicles emitted, on average, over the WLTC and the RDE 2.1 and 6.7 times more than the standard limit, respectively. Diesel vehicles equipped with only a Lean NO_X trap (LNT) averaged six and two times more emissions over the WLTC and the RDE, respectively, than diesel vehicles equipped with a selective catalytic reduction (SCR) catalyst. Gasoline vehicles with direct injection (GDI) emitted eight times more NO_X than those with port fuel injection (PFI) on RDE tests. Large NO_X emissions on the urban section were also recorded for GDIs (122 mg/km). Diesel particle filters were mounted on all diesel vehicles, resulting in low particle number emission (~10¹⁰ #/km) over all testing conditions including low temperature and high dynamicity. GDIs (~10¹² #/km) and PFIs (~10¹¹ #/km) had PN emissions that were, on average, two and one order of magnitude higher than for diesel vehicles, respectively, with significant contribution from the cold start. PFIs yielded high CO emission factors under high load operation reaching on average 2.2 g/km and 3.8 g/km on WLTC extra-high and RDE motorway, respectively. The average on-road CO₂ emissions were ~33% and 41% higher than the declared CO₂ emissions at type-approval for diesel and gasoline vehicles, respectively. The use of auxiliaries (AC and lights on) over the NEDC led to an increase of ~20% of CO₂ emissions for both diesel and gasoline vehicles. Results for NO_X, CO and CO₂ were used to derive average on-road emission factors that are in good agreement with the emission factors proposed by the EMEP/EEA guidebook. Full article

A high-throughput (HT) screening platform developed at hte with the application focus on automotive catalysis is described. hte HT units are configured for performing steady-state testing, as well as dynamic tests with fast feed switches, such as lean/rich excursions for the evaluation of NO_x storage capacity and efficiency of lean NO_x traps (LNT), ammonia storage capacity for selective catalytic reduction (SCR), evaluation of oxygen storage capacity (OSC), as well as lambda sweep tests for screening of three-way catalysts (TWC). Even though catalysts are screened on a rather small scale (~100 mg powder), experience showed that dosing rather complex gas mixtures in concentrations close to that found in real exhaust for the given application is mandatory to generate relevant data. The objective of this work is to give additional insight into HT technology. In the industrial research laboratory, HT screening has matured to become a reliable approach for rapid screening of both reaction parameter spaces, as well as material properties relevant for exhaust gas catalyst development. Due to the speed of optimized screening involving 48 parallel reactors, automated handling of primary data is an imported requirement. Software for data reduction, like estimation of light-off temperature, needs to be robust and handle results for diverse sample libraries in an unattended fashion. In combination with the statistical design of experiment and multivariate data analysis, HT testing has become a valuable enhancement to automotive catalyst development. Full article

An impedimetric NO_x dosimeter based on the NO_x sorption material KMnO₄ is proposed. In addition to its application as a low level NO_x dosimeter, KMnO₄ shows potential as a precious metal free lean NO_x trap material (LNT) for NO_x storage catalysts (NSC) enabling electrical in-situ diagnostics. With this dosimeter, low levels of NO and NO₂ exposure can be detected electrically as instantaneous values at 380 °C by progressive NO_x accumulation in the KMnO₄ based sensitive layer. The linear NO_x sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NO_x sorption-dependent conductivity of the KMnO₄-based material is obtained by the novel eTPD method that combines electrical characterization with classical temperature programmed desorption (TPD). The NO_x loading amount increases proportionally to the NO_x exposure time at sorption temperature. The cumulated NO_x exposure, as well as the corresponding NO_x loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NO_x concentration information from the signal derivative or (2) during the short-term thermal NO_x release. Full article

Sensors that detect directly and in situ the status of automotive exhaust gas catalysts by monitoring the electrical properties of the catalyst coating itself are overviewed. Examples included in this review are the in-situ determination of the electrical impedance of three-way catalysts based on ceria-zirconia solutions and of lean NO_x traps of earth-alkaline based coatings, as well as approaches to determine the ammonia loading in Fe-SCR-zeolites with electrical ac measurements. Even more sophisticated approaches based on interactions with electromagnetic waves are also reviewed. For that purpose, metallic stick-like antennas are inserted into the exhaust pipe. The catalyst properties are measured in a contactless manner, directly indicating the catalyst status. The radio frequency probes gauge the oxygen loading degree of three-way catalysts, the NO_x-loading of lean NO_x traps, and the soot loading of Diesel particulate filters Full article