Modeling of the NO x trap and experimental validation using ultra-fast NO x analyzers

The present paper employs and validates a NO _x trap model which attempts an optimum compromise between complexity and predictive accuracy. It is shown that using the same set of kinetic data, the model is able to predict the storage rates and the maximum storage amounts as function of temperature. Moreover, the model predicts with reasonable accuracy the NO breakthrough during rich-mode regeneration and the spontaneous/thermal NO₂ release when the temperature is increased in a saturated catalyst. The experimental findings highlight the importance of transient O₂ adsorption/desorption phenomena which are incorporated in the model. The use of ultra-fast responding NO/NO _x analyzers was necessary for the study and modeling of the transient operation following inlet composition switches.     

Coarsening of Pt Particles in a Model NO x Trap

The effects of temperature and atmosphere on the coarsening of Pt particles in a model NO _x trap (Pt/BaO/Al₂O₃) were examined by XRD, TEM, and CO chemisorption. The main finding, that the most significant particle growth occurs at elevated temperatures under oxidizing conditions, is relevant to NO _x trap durability.     

NO x abatement by catalytic traps: on the mechanism of NO x trapping under automotive conditions

Topics in Catalysis - NO x adsorption was measured with a barium based NO x storage catalyst at an engine bench equipped with a lean burn gasoline direct injection engine (GDI). In order to study...     

Reduction of NO2 stored in a commercial lean NO x trap at low temperatures

Isothermal storage of NO₂ and subsequent reduction with different reducing agents (H₂, CO or H₂ + CO) in a lean NO _x trap catalyst was tested by Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR) experiments at temperatures representative of automotive “cold-start” conditions (<200 °C) using a commercial NO _x trap catalyst. Results from the TPR experiments revealed that no reduction of stored NO₂ to N₂ was observed at 100–180 °C, and at 200 °C 10% reduction only of NO₂ to N₂ was measured. A special affinity of H₂ to form NH₃ was observed during the reduction of stored NO₂. The formation of NH₃ increases with increasing amount of stored NO₂ and decreases with increasing storage temperature. Direct relation exists between the amount of adsorbed and/or stored NO₂ and the formation of H₂O and NH₃.     

Removal of so x and NO x from flue gas with ceria

Ceria (CeO₂) is considered as one of materials for the simultaneous removal of SO_x and NO_x from flue gas. Ceria was coated on honeycomb and tested for adsorption of SO₂ and reduction of NO with ammonia. Experimental results showed the characteristics similar to copper oxide but reactivity for NO reduction was higher in broader temperature range compared with the latter.     

The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

Mechanistic Considerations of the NO x Source and the Reducing Agent for Lean NO x Reduction over H-ZSM-5

This study focuses on the reaction mechanism for lean NO _x reduction by propane. In particular the role of the NO _x -source, i.e. NO or NO₂, for the SCR mechanism has been studied by transient experiments using in-situ FTIR spectroscopy and the results are discussed in relation to isopropylamine and ammonia as reducing agents.     

Investigation of NO adsorption and NO/O2 co-adsorption on NO x -storage-components by DRIFT-spectroscopy

Topics in Catalysis - NO adsorption and NO/O2 co-adsorption on CeO2 at different temperatures was studied by DRIFT-Spectroscopy. The results indicate that this oxide plays an important role in...     

Supported heteropolyacids for NO x storage and reduction

Topics in Catalysis - TiO2 and SnO2 were studied as possible supports for HPW in order to produce a new type of sorbent for NO x trap applications. SnO2 was synthesised by various inorganic methods...     

A NO x trap for low-temperature lean-burn-engine applications

A NO _x trap that uses only high-surface-area alumina as the NOx-storage material appears to provide significant advantages over the conventional baria-based trap for exhaust-gas after-treatment in low-temperature exhaust (∼250 °C) characteristic of light-duty diesel-powered vehicles operating at low speed/load conditions. In particular, an alumina trap provides better low-temperature NO _x conversion and also allows more efficient de-sulfurization than a baria-based trap in laboratory evaluations. Both of these features are ascribed to the difference in basicity of the NO _x -storage materials, which leads to thermally less stable nitrate (nitrite) and sulfate compounds in the case of alumina compared to conventional traps with high levels of alkali or alkaline-earth metal oxides. Further studies, extending the laboratory experiments to engine and vehicle evaluations, are still needed, however, in order to fully assess the true potential of the alumina trap. Article note George Graham—retired     

Selective Lean NO x Reduction over Metal Oxides

The present state of knowledge of NO _x reduction under lean conditions over metal oxides is summarized in this review, with an emphasis on the reaction mechanism. Although a number of nitrogen-containing intermediates have been observed and implied, including organic nitro, nitrite, cyanide, isocyanate, and ammonia, there is yet definitive observation that confirms the relevance of these to the principal reaction pathway. Individual component in a mixed oxide catalyst can participate at different stages of the NO _x reduction reaction. The nitrogen production efficiences for different oxide based catalysts are summarized, and their relationship to the nature of the catalyst is discussed.     

An Improved Model for NO x -Storage Catalysts

The physically based isothermal model of a monolith NO _x storage catalyst (NSC), proposed in Schmeißer et al. (Top Catal 42–43:77, 2007), has been further developed and adjusted to experimental results from Schmeißer et al. (Top Catal 42–43:15, 2007). It now describes all relevant reactions basically known from a three way catalyst, including several inhibition effects, over a wide concentration and temperature range. The different dynamics of NO _x storage and regeneration can be very well modeled by the build-up and break-open of a diffusion hindering nitrate shell around the (nano-size) Ba storage particles. The NSC-behavior under periodic lean-/rich-operation is well represented, even starting with the initially completely regenerated catalyst, moving towards cyclic steady state. Furthermore, the model gives insight into the periodic change of the nitrate distribution along the catalyst length. It turned out, however, that not all of the reaction rates determined under steady state conditions could be used for the simulation of the periodic storage/regeneration behavior. In particular it was necessary to increase the rate of the NO-oxidation during periodically lean conditions by a factor of 3.6. This can be explained by the build-up of a deactivating oxidation layer during steady state operation under lean conditions.     

Synthesis of Hexaaluminogallate Catalysts for NO x Reduction

BaCo(Al,Ga)₁₁O₁₉with β-alumina structure was found to be an effective catalyst for NO_xreduction and successfully synthesized by the coprecipitation method using metal nitrates and ammonium carbonate. Anisotropic BaCo(Al,Ga₁₁O₁₉particles crystallized at 1100 °C for 2 h through the coprecipitation method. BaCo(Al,Ga)₁₁O₁₉supported on a cordierite honeycomb had the NO_xremoval activity with methane over 500 °C in the presence of excess oxygen.     

Steam effect on NO x reduction over lean NO x trap Pt–BaO/Al2O3 model catalyst

The effect of steam on NO _x reduction over lean NO _x trap (LNT) Pt–Ba/Al₂O₃ and Pt/Al₂O₃ model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using CO and C₃H₈ as reductants, respectively. Compared to dry atmosphere, steam promoted NO _x reduction; however, under rich conditions the primary reduction product was NH₃. The results of NO _x reduction and NH₃ selectivity versus temperature, combined with temperature programmed reduction of stored NO _x over Pt–BaO/Al₂O₃ suggest that steam causes NH₃ formation over Pt sites via reduction of NO _x by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C₃H₈/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO, but also the stored NO _x contributed to NH₃ formation. The NH₃ formed under these conditions could be effectively trapped by a downstream bed of Co²⁺ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO _x reduction, leading to improved NO _x storage efficiency.     

ANN modeling applied to NO x reduction with octane in a new microreactor

A silver/alumina catalyst was tested for its NO _x reduction activity during oxygen-rich conditions and during variation in the input parameters (nitric oxide, octane and oxygen). The experimental data using the microreactor was investigated by means of artificial neural networks (ANN).     

Study of Ammonia Formation During the Purge of a Lean NO x Trap

The aim of this work was to study the formation of ammonia during the regeneration step of a commercial lean NO _x Trap catalyst in real conditions. Experiments were carried out on an engine test bench equipped with 2.2 L common rail diesel engine. The after-treatment system was composed of a commercial NSR monolith catalyst with a volume of 2.2 L. This material was composed of platinum, palladium and rhodium, as active components, with barium oxide and alumina as storage component and support, respectively. Catalytic measurements were carried out at 280 °C. Particular attention has been paid to formation of ammonia during the purge using hydrogen and CO as reducing agents. The time dependency of the extent of ammonia formation and the influence of hydrogen concentration were carefully examined. It was observed that the temperature rose in the first step of the regeneration process, after the switch in rich conditions, due to the occurrence of exothermic oxidation (H₂/O₂, CO/O₂) accompanied with the releasing of available vacant noble metal sites which may provide a route for H₂ and NO dissociation and/or subsequent surface reactions leading to the ultimate formation of ammonia. It was found that ammonia formation strongly depends on the purge duration and on the concentration of the reducing agent available during the purge.     

Development of Catalysts for Diesel Particulate NO x Reduction

While diesel vehicles feature high fuel economy with low CO₂ emissions, further suppression of particulate matter (PM) and NO _x in the exhaust stream is demanded worldwide. We have been working to develop a new diesel particulate-NO _x reduction (DPNR) system to decrease both PM and NO _x emissions by combining the NO _x storage-reduction catalyst for direct injection gasoline engines with the most advanced engine control technologies. This paper describes the development of the DPNR system, a post-treatment technology for PM and NO _x , which was achieved through a combination of catalysis and engine control technologies.     

火电厂NO_x排放在线监测研究

针对现有NOx排放在线监测系统无法准确、完整反映火电厂脱硝设备及排污状况动态变化的问题,建立了一种远程NOx排放实时在线监测系统,分析了系统的构成、数据采集及主要计算指标,并全面展示了系统的应用功能。火电厂NOx排放在线监测系统在采集火电厂侧烟气排放CEMS数据的基础上,全面采集了脱硝系统的设备运行数据,统计分析更加准确;系统以脱硝工艺流程实时展示单台机组的脱硝状态,配合关键指标刷新监测及数据超限报警进行全面NOx排放在线监测;采用统计报表平台实现实时数据及统计指标的及时处理;实时数据库与关系数据库相结合的数据存储方式保证了平台监测数据的透明、公开、公正。目前火电厂NOx在线监测系统已在某发电集团得到应用,实现下属火电机组污染物排放的实时监管,完成污染物排放数据的统计和分析,促进节能减排。