Diesel particulate filters mean less soot The emission regulations for diesel engines are becoming increasingly stricter worldwide, which makes modifications to the drive systems necessary. As a basic principle, MTU’s approach to achieve compliance is to reduce emission levels by means of internal engine enhancements. Depending on the specific emission limits, it may be possible to do without a diesel particulate filter altogether. However, there is a relationship between the production of soot particulates and nitrogen oxides when internal engine measures are used — if fewer soot particulates are produced during the combustion process, the quantity of nitrogen oxides increases, and vice versa. In situations where emission requirements are very strict, therefore, adding a diesel particu late filter is necessary, since it removes 90 percent or more of the soot particulates from the exhaust.

Chapter 10 Perspectives of the Automotive Industry on the Modeling of Exhaust Gas Aftertreatment Catalysts Daniel Chatterjee, Daniel Chatterjee MTU Friedrichshafen GmbH, Maybachplatz 1, 88045 Friedrichshafen, GermanySearch for more papers by this authorVolker Schmeißer, Volker Schmeißer Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this authorMarcus Frey, Marcus Frey Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this authorMichel Weibel, Michel Weibel Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this author Daniel Chatterjee, Daniel Chatterjee MTU Friedrichshafen GmbH, Maybachplatz 1, 88045 Friedrichshafen, GermanySearch for more papers by this authorVolker Schmeißer, Volker Schmeißer Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this authorMarcus Frey, Marcus Frey Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this authorMichel Weibel, Michel Weibel Daimler AG, Department GR/APE, HPC 010-G206, 70546 Stuttgart, GermanySearch for more papers by this author Book Editor(s):Prof. Dr. Olaf Deutschmann, Prof. Dr. Olaf Deutschmann Karlsruhe Institute of Technology (KIT), Institute for Chemical Technology and Polymer Chemistry, Engesserstr. 20, 76131 Karlsruhe, GermanySearch for more papers by this author First published: 23 November 2011 https://doi.org/10.1002/9783527639878.ch10Citations: 6 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Emission Legislation Exhaust Gas Aftertreatment Technologies Modeling of Catalytic Monoliths Modeling of Diesel Particulate Filters Selective Catalytic Reduction by NH3 (Urea-SCR) Modeling Diesel Oxidation Catalyst, Three-Way Catalyst, and NOx Storage and Reduction Catalyst Modeling Modeling Catalytic Effects in Diesel Particulate Filters Determination of Global Kinetic Parameters Challenges for Global Kinetic Models System Modeling of Combined Exhaust Aftertreatment Systems Conclusion References Citing Literature Modeling and Simulation of Heterogeneous Catalytic Reactions: From the Molecular Process to the Technical System RelatedInformation

Combination of an NOx storage and reduction catalyst (NSRC, called also lean NOx trap, LNT) and a catalyst for the selective catalytic reduction of NOx by NH3 (NH3-SCR) offers a potential to significantly increase the efficiency of NSRC-based exhaust gas aftertreatment systems. Under most situations the SCR catalyst is able to adsorb the NH3 peaks generated in the NSRC during the regeneration and utilise it for additional NOx reduction in the course of the consequent lean phase. This synergy becomes more important with the aged NSRC, where generally lower NOx conversions and higher NH3 yields in wider range of operating temperatures are observed (in comparison with the fresh or de- greened NSRC).In this paper we present global kinetic models for the NSRC (Pt/Ba/Ce/gamma-Al2O3 catalyst type) and NH3-SCR (Fe-ZSM5 catalyst type). The NSRC regeneration by a mixture of CO, H-2 and HC is considered with a differentiated activity and selectivity of individual reducing agents in the NOx reduction. The oxygen storage effects and NH3 oxidation reactions are also included in the NSRC model. A non-equilibrium spill-over of the adsorbed NH3 between the non-reactive and reactive sites is involved in the SCR model. The kinetic parameters are evaluated from transient lab experiments with synthetic gases, individually for the NSRC and SCR, and the models are then validated by engine test data.The performance of the NSRC+SCR system is simulated in dependence on temperature and rich phase length, and their effects on integral NOx conversions and NH3 yields are discussed. Defined periodic lean/rich operation is simulated as well as the test driving cycle FTP. The simulation results show that the added SCR can significantly improve the deNO(x) efficiency in a wide range of operating conditions. The mechanistic understanding and modelling of the relevant chemical and physical processes in the NSRC and SCR played a key role in the development of the combined NSRC+SCR system and enabled to bring this technology to series production within the BlueTec I system (2006).

A combined Diesel exhaust gas aftertreatment system is studied, consisting of the NO storage and reduction catalyst (NSRC, called also lean NOx trap, LNT) and the catalyst for selective catalytic reduction of NOx by NH3 (NH3-SCR). Most of the time the system is operated under prevailing fuel-lean conditions, enabling economical running of the engine. During this phase the NO), emissions are being adsorbed in the NSRC. However, short fuel enrichments need to be applied periodically for the NSRC regeneration (reduction of the stored NO). Ammonia produced in the NSRC as a by-product of the NOx reduction under controlled fuel-rich conditions is then adsorbed in the NH3-SCR reactor located downstream. The adsorbed NH3 is consequently utilised in selective NO3 reduction during the next fuel-lean period. The NSRC + SCR configuration thus eliminates the need for an external NH3 source (e.g., periodically re-filled urea solution tank) that is necessary in the case of the stand-alone SCR.Development of effective mathematical models for the NSRC and SCR catalysts is discussed. Dynamic measurements in a lab mini-reactor are performed separately for the industrial NSRC(PtRh/Ba/Ce/gamma-Al2O3 type) and SCR (Fe-ZSM type) catalyst samples. The experimental results are employed in the evaluation of rate parameters for the individual catalysts. Particular attention is given to the dynamic evolution of NH3 during the NSRC regeneration and its dependence on temperature and length of the enrichment period. Trends in NH3 selectivity with the NSRC ageing are discussed. Synergistic effects of the NSRC and NH3-SCR are then studied by simulations of defined lean/rich operation and engine test driving cycles. The combined NSRC + SCR system provides higher NO3 conversions in comparison with the stand-alone NSRC and it prevents undesired NH3 slip. The positive effects of the downstream SCR are most important at lower intermediate temperatures, and in the case of an aged NSRC that usually produces more NH3. (C) 2010 Elsevier B.V. All rights reserved.

A dynamic Mars-van Krevelen kinetic model that unifies Standard and Fast SCR reactions into a single redox approach is herein proposed for V-based catalysts for NOx removal from Diesel exhausts. Such a mechanistic model is consistent with the detailed catalytic chemistry proposed for the NH3-NO/NO2) reacting system in which NO2 disproportionates to fibrin nitrites and nitrates, nitrates are reduced by NO to nitrites in a key redox step, and nitrites react with NH3 to form N-2 via decomposition of unstable ammonium nitrite. Intrinsic kinetic parameters were estimated by global multiresponse nonlinear regression of 42 transient runs. The model accounts for stoichiometry, selectivity, and kinetics of the global SCR process, reproducing successfully both the steady-state and transient behaviors of the SCR reacting system over the full range (0-1) of NO2/NOx, feed ratios in the 175-425 degrees C temperature range. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 1514-1529, 2009

The activity and the mechanism of the main reactions in the NO/NO2–NH3 SCR reacting system were comparatively investigated over a Fe- and a Cu-promoted commercial zeolite catalyst for the aftertreatment of Diesel exhausts. A dynamic micro-kinetic model in close agreement with all the details of the SCR catalytic chemistry was also developed.

Heterogeneous ID model with global kinetics is proposed for industrial NO, storage and reduction catalyst (NSRC) on the basis of lab experiments in a mini-reactor in the temperature range 100-500 degrees C. The NOx reduction dynamics and selectivity towards N-2 or NH3 are modelled for three main reducing components present in the rich exhaust gas: CO, H-2, and unburned hydrocarbons (HCs). The following reactions are considered: CO, H-2 and HC oxidation, NOx reduction, NO/NO2 transformation, NO and NO2 storage, oxygen storage effects, water gas shift and steam reforming, and reduction of the stored NOx by H-2, CO and HC. Ammonia is formed mainly by the reaction of H-2 with NOx, but also by the water-assisted reaction of CO with NOx (formation and consequent hydrolysis of isocyanates). Inclusion of the latter route is necessary to explain the NH3 formation in CO-rich mixtures without H-2 at lower temperatures. At higher temperatures, water gas shift and steam reforming reactions enable in situ H-2 production from CO, HC and H2O. The formed ammonia subsequently reacts with oxygen and NOx deposited on the catalyst surface downstream, which results in NH3 wave travelling along the catalytic monolith.The highest NH3 yield is obtained around 200 degrees C, when the NH3 formation from the accumulated NOx is already ignited, while the ammonia consumption reactions are still relatively slow. At lower temperatures CO inhibits the NOx reduction by H-2 (i.e., the NH3 production). At higher temperatures the ammonia oxidation reactions become fast enough to eliminate most of the NH3 produced locally from the stored NOx. However, ammonia can be still observed after the completion of the regeneration, when it is formed steadily from the rich inlet gas containing NOx. Model results are confronted with the lab data, and calculated evolution of concentration profiles inside the monolith is discussed. The developed model is validated by engine test driving cycle data. (C) 2009 Elsevier B.V. All rights reserved.

A numerical model for a diesel oxidation catalyst (DOC) is presented. It is based on a spatially 1D, physical and chemically based modeling of the relevant processes within the catalytic monolith. A global reaction kinetic approach has been chosen to describe the chemical reactions. Water condensation and evaporation was also considered, in order to predict the cold start behavior. Reaction kinetic parameters have been evaluated from a series of laboratory experiments. A correlation between the kinetic parameters and the noble metal loading was developed. The model was used in combination with a SCR-Model to study the influence of changes of noble metal loading and DOC volume on the overall transient NOx performance of a DOC+DPF+SCR system.

We present a systematic study of the chemical steps in the NO/NO2–NH3 fast SCR reaction 2NH3+NO+NO2 → 2N2+3H2O over a commercial Fe-ZSM5 catalyst. The study is based on transient reaction experiments at realistic conditions for removal of NOx from mobile diesel exhausts. Its goal is to assess and critically evaluate the current ideas on the SCR mechanism, and also to establish to what extent the mechanistic pathways demonstrated for V-based catalysts also apply to Fe-promoted zeolites. Results show that the fast SCR reaction proceeds at low temperature via a global sequence involving NH4NO3 or related surface species as intermediates,2NO2+2NH3 → N2+NH4NO3+H2O,NO+NH4NO3 → NO2+N2+2H2O. Such a sequential scheme is the same as that proposed previously for the fast SCR chemistry over V-based catalysts and other zeolite catalysts and thus is considered a general mechanism. It explains all of the available observations for stoichiometry (e.g., optimum NO/NO2 unit molar ratio), selectivity (e.g., N2O from NH4NO3 decomposition), and kinetics (e.g., rate of fast SCR=rate of nitrate reduction by NO). We further show that the redox reaction between NO and nitrates is the rate-controlling step and is inhibited by ammonia. Remarkably, the same strongly enhanced deNOx activity observed in the fast SCR reaction also was observed in the absence of gaseous NO2 but in the presence of surface nitrates. We accordingly propose a general summary of the fast SCR chemistry over V-based and zeolite catalysts that emphasizes the key role of surface nitrates.

Decreasing emission limits lead to the development of combined aftertreatment systems, consisting of combinations of different catalyst technologies and particulate filters. Modeling such systems can contribute considerably in reducing development time and cost. The methodology for developing catalyst models is reviewed and models for the diesel oxidation catalyst (DOC) with hydrocarbon (HC) adsorption, the NOx storage and reduction catalyst (NSRC) and the urea-selective catalytic reduction system (urea-SCR) are developed. Applications for exhaust aftertreatment system modeling are shown.

We present a systematic study of the NH3-SCR reactivity over a commercial V2O5-WO3/TiO2 catalyst in a wide range of temperatures and NO/NO2 feed ratios, which cover (and exceed) those of interest for industrial applications to the aftertreatment of exhaust gases from diesel vehicles. The experiments confirm that the best deNO(x), efficiency is achieved with a 1/1 NO/NO2 feed ratio. The main reactions prevailing at the different operating conditions have been identified, and an overall reaction scheme is herein proposed.Particular attention has been paid to the role of ammonium nitrate, which forms rapidly at low temperatures and with excess NO2, determining a lower N-2 selectivity of the deNO(x) process. Data are presented which show that the chemistry of the NO/NO2-NH3 reacting system can be fully interpreted according to a mechanism which involves: (i) dimerization/disproportion of NO2 and reaction with NH3 and water to give ammonium nitrite and ammonium nitrate; (ii) reduction of ammonium nitrate by NO to ammonium nitrite; (iii) decomposition of ammonium nitrite to nitrogen. Such a scheme explains the peculiar deNO(x) reactivity at low temperature in the presence of NO2, the optimal stoichiometry (NO/NO2 = 1/1), and the observed selectivities to all the major N-containing products (N2, NH4NO3, HNO3, N2O). It also provides the basis for the development of a mechanistic kinetic model of the NO/NO2-NH3 SCR reacting system. (c) 2006 Elsevier B.V. All rights reserved.

We review herein the key mechanistic and kinetic features of the reactions involved in the NH3-NO/NO2 SCR system investigated by dynamic reactive experiments over a V-based commercial powdered catalyst, eventually leading to the proposal of an original redox scheme which accounts for stoichiometry, selectivity and intrinsic kinetics of the global SCR process.

A numerical model describing the ammonia based SCR process of NOX on zeolite catalysts is presented. The model is able to simulate coated and extruded monoliths. The development of the reaction kinetics is based on a study which compares the activity of zeolite and vanadium based catalysts. This study was conducted in a microreactor loaded with washcoat powder and with crushed coated monoliths. A model for the SCR reaction kinetics on zeolite catalysts is presented. After the parameterization of the reaction mechanism the reaction kinetics were coupled with models for heat and mass transport. The model is validated with laboratory data and engine test bench measurement data over washcoated monolith catalysts. A numerical simulation study is presented, aiming to reveal the differences between zeolite and vanadium based SCR catalysts.