The review paper summarizes major developments in vehicular emissions regulations and technologies in 2013. First, the paper covers the key regulatory developments in the field, including proposed light-duty (LD) criteria pollutant tightening in the US; and in Europe, the continuing developments towards real-world driving emissions (RDE) standards. Significant shifts are occurring in China and India in addressing their severe air quality problems. The paper then gives a brief, high-level overview of key developments in fuels. Projections are that we are in the early stages of oil supply stability, which could stabilize fuel prices. LD and HD (heavy-duty) engine technology continues showing marked improvements in engine efficiency. Key developments are summarized for gasoline and diesel engines to meet both the emerging NOx and GHG regulations. HD engines are or will soon be demonstrating 50% brake thermal efficiency using common approaches. NOx control technologies are then summarized, including SCR (selective catalytic reduction) systems and SCR filter developments. Emphasis is on low-temperature deNOx and integration of components and control. Diesel PM (particulate matter) reduction technologies are evolving around the behavior of ash deposits and SCR integration. Filters for direct injection gasoline applications are developing very rapidly, and in some cases the back pressure, light-off characteristics, and emissions reductions are very similar to standard three way catalysts (TWCs). Oxidation catalysts mainly involve developments towards stubborn problems, like low-temperature performance with exhaust with high hydrocarbon and CO, and methane oxidation. Finally, the paper discusses some key developments in gasoline gaseous emission control, focusing on matching engine calibration with emissions system characteristics; and on lean burn gasoline emissions control. CITATION: Johnson, T., "Vehicular Emissions in Review," SAE Int. J. Engines 7(3):2014, doi:10.4271/2014-01-1491. 2014-01-1491 Published 04/01/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-1491 saeeng.saejournals.org 1207 This paper is posted on this website with permission from SAE International. It may not be shared, downloaded, duplicated, or transmitted in any manner without prior written permission from SAE.

https://www.corning.com/media/worldwide/cet/documents/SAE_2014-01-1491.pdf

Vehicular Emissions in Review

Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust control. It is a challenge to improve performance and reduce the cost of DOCs, while also to avoid interference of hydrocarbons and sintering of platinum metals at high temperatures. We present here an indium-doped Co 3 O 4 uniform nanorod catalyst whose catalytic performance in CO, C 3 H 6 , and even NO oxidation is comparable to platinum-group DOCs in diesel exhaust. No obvious deactivation was observed in long-term stability tests under simulated diesel exhaust conditions. These indium-doped Co 3 O 4 nanorods might open a promising pathway towards low-cost efficient diesel exhaust control systems. Characterization results indicated that lattice oxygen could be much more easily abstracted by hydrogen or carbon monoxide from indium-doped Co 3 O 4 than from Co 3 O 4 and the physical mixture Co 3 O 4 and In 2 O 3 . The presence of indium with its large cation radius could influence the chemical status of surface/chemisorbed oxygen in Co 3 O 4 -In 2 O 3 nanorods, thereby increasing the mobility of lattice oxygen involved in the catalytic oxidation reaction. The reaction mechanism of catalytic oxidation of CO and C 3 H 6 were evaluated based on kinetic and FTIR studies. For CO oxidation, activated CO 3 * reduced by adsorbed CO* in an irreversible step to generate the final product of CO 2 could be considered as the kinetically-relevant step. DRIFT spectroscopy confirmed that only stable carbonate species were observed over Co 3 O 4 -In 2 O 3 nanorods that might be further reduced by CO to form CO 2 . For C 3 H 6 oxidation, the incorporation of activated oxygen (O*) into anion vacancy of catalyst surface was the kinetically-relevant step, while the active sites on catalyst surface should be totally covered by the intermediates of C 3 H 6 or its generated species, which actually acted as the most abundant surface intermediates (MASI). DRIFT spectroscopy confirmed that C 3 H 6 and its related intermediates like formate, acetate, and acetone species would be formed over Co 3 O 4 -In 2 O 3 nanorods.

Indium-doped Co3O4 nanorods for catalytic oxidation of CO and C3H6 towards diesel exhaust

NO, NO2 and N2O emissions over a SCR using DOC and DPF systems with Pt reduction

The HC and CO oxidation activity of Pt/Al2O3, Pd/Al2O3 and Pd-Pt/Al2O3 catalysts was compared under three exhaust-gas model conditions typical for stoichiometric gasoline as well as lean burn diesel by means of temperature programed conversion tests on laboratory test benches. In order to understand the differences in emission reduction performance, the impact of gas mixture composition was systematically studied with a particular focus on methane and formaldehyde conversion. The catalysts used in this study were prepared by incipient wetness impregnation of Al2O3 followed by washcoating on ceramic honeycombs, and were pre-treated in an equal manner before each activity test. Distinct differences in pollutant conversion were observed over the three catalysts under the investigated conditions. Pd-based monometallic and bimetallic catalysts revealed the lowest temperature for CH4 oxidation ( Under stoichiometric gasoline conditions, Pt had the highest activity for methane oxidation whereas Pd/Al2O3 and Pd-Pt/Al2O3 hardly convert methane below 500 °C. Unsaturated HCs and CO on the other hand were converted at lower temperature over Pd containing monometallic and bimetallic catalysts in comparison to Pt/Al2O3, showing once again the multiple and complex effects generated by variations in exhaust gas mixture and catalyst composition.

PGM based catalysts for exhaust-gas after-treatment under typical diesel, gasoline and gas engine conditions with focus on methane and formaldehyde oxidation

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.

https://www.mdpi.com/2073-4344/11/3/404/pdf

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

Computer simulation is now considered to be a crucial stage in the design of automotive catalysts due to the increasing complexity of modern aftertreatment systems. The resulting models almost invariably include surface reaction kinetics that are measured under controlled conditions similar to those found on a vehicle. Repeatability of the measurements used to infer surface reaction rates is fundamental to the accuracy of the resulting catalyst model. To achieve the required level of repeatability it is necessary to ensure that the catalyst sample in question is stable and that its activity does not change during the test phase. It is therefore essential that the catalyst has been lightly aged, or ‘de-greened’ before testing begins. It is also known that the state of the catalyst's surface prior to testing has an impact on its subsequent light-off performance and that test history can play an important role in catalyst activity. Suitably pre-treating the catalyst surface can ensure that a reference point is reached prior to a light-off test. The work summarised in this paper includes a study of both the de-greening phase and the state of the catalyst's surface on its activity, with the aim of developing a robust test protocol that provides repeatable kinetic data under realistic operating conditions. To establish a protocol for initial stabilisation of new catalyst samples a series of tests were conducted on catalysts that had been thermally aged at 600°C and 750°C respectively until the sample exhibited stability. The activity of the sample was assessed by repeating identical CO light-off tests following each period of time in the oven. A period of 8 hours at 750°C was found to sufficiently stabilise the sample. In the pre-treatment study an investigation into the effect of several pre-treatment protocols on CO light off was carried out on a three-way catalyst of commercial formulation in order to establish a robust protocol to ensure test repeatability. The investigation focused on pre-treating the catalyst sample in hydrogen, oxygen or nitrogen environments at specified conditions of flow and temperature. Following pre-treatment, identical CO light-off tests were performed in order to assess the respective influences of each pre-treatment. A trend of lower light off temperatures was observed for all pre-treatment strategies on the first of two consecutive light-off temperature ramps with a notable increase in light off temperature observed on the second ramp. As a result of this study a pre-treatment protocol was established. The protocol involves treating the catalyst sample in flowing nitrogen up to 600° C using a temperature ramp of 15°C/min.

/pdf/performance-characterisation-of-a-range-of-diesel-oxidation-1fyshrbrrn.pdf

Performance Characterisation of a Range of Diesel Oxidation Catalysts: Effect of Pt:Pd Ratio on Light Off Behaviour and Nitrogen Species Formation

The Effect of De-greening and Pre-treatment on Automotive Catalyst Performance

The performance optimization of automotive catalysts has been the focus of in-depth research for many years as the automotive industry has endeavoured to reduce the emission of toxic and pollutant gases generated from internal combustion engines. Just as the emissions from diesel and gasoline combustion vary, so do the emissions from the combustion of alternative fuels such as ethanol, with variation in both quantity and chemical composition. In particular, when ethanol is contained in the fuel, ethanol and acetaldehyde are present in the exhaust gas stream, and these are two compounds which the catalytic converter has not traditionally been designed to manage. The aim of the study outlined in this paper was to assess the performance of various catalyst formulations when subjected to a representative ethanol exhaust gas mixture. Three automotive catalytic converter formulations were tested, including a fully platinum sample, a palladium/rhodium three-way catalyst sample and a fully palladium sample. Initi...

Performance and characteristics of platinum, palladium/rhodium and palladium automotive catalysts when subjected to ethanol, acetaldehyde and a synthetic E85 exhaust gas mixture

This work investigated and modelled the performance and characteristics of automotive catalytic converter formulations when subjected to a synthetic exhaust gas mixture representative of that emitt...

/pdf/characterisation-and-modelling-of-the-reactions-in-a-three-53utmpktgq.pdf

Claire McAtee

Papers

Performance Characterisation of a Range of Diesel Oxidation Catalysts: Effect of Pt:Pd Ratio on Light Off Behaviour and Nitrogen Species Formation

The Effect of De-greening and Pre-treatment on Automotive Catalyst Performance

Performance and characteristics of platinum, palladium/rhodium and palladium automotive catalysts when subjected to ethanol, acetaldehyde and a synthetic E85 exhaust gas mixture

Characterisation and Modelling of the Reactions in a Three-Way PdRh Catalyst in the Exhaust Gas from an Ethanol-Fuelled Spark-Ignition Engine