NOx Adsorber Catalyst Research Articles

Pd-Doped SSZ-13 for Low-T NOx Adsorption: an Operando FT-IR Spectroscopy Study

In this study, mechanistic aspects of NO adsorption/desorption over a home-made Pd/SSZ-13 passive NOx adsorber (PNA) catalyst are investigated. Operando FT-IR spectroscopy and microreactor experiments are performed to envisage the performance of the catalyst and the pathway involved in NO adsorption, with particular emphasis to the impact of species such as C3H6 and CO. In the absence of C3H6 and CO, NO is observed to adsorb as nitrosyls (anhydrous and hydrated) over both Pd2+ and Pd+ species, and as nitrates. 80 μmolNOx/gcat (NO/Pd molar ratio of 0.8) are adsorbed. The stability of nitrosyls is higher in comparison to the nitrates in that the former initially dehydrate and further decompose at elevated temperatures (> 300 °C) leading to the evolution of NO. The presence of CO and C3H6 negatively affects the amounts of NO adsorbed (53 and 45 μmolNOx/gcat, respectively) due to the reduction of Pd sites. CO admission to the catalyst forms a variety of carbonyl species over Pd2+, Pd+ and Pd0 sites which upon NO admission are readily displaced and NO is adsorbed as hydrated/anhydrous nitrosyls of Pdn+. The nitrosyls so formed exhibit lower thermal stability in comparison to nitrosyls observed in the absence of CO and decompose below 300 °C. The addition of C3H6 leads to the apparent formation of oxidized species like acetone, acrolein and acetates, besides propylene adsorption. The NO adsorption in the presence of C3H6 leads to the formation of Pdn+(NO)(X) complexes; upon heating the decomposition of this complexes is observed at low temperatures along with propylene and water desorption. Formation of organic nitro-compounds is also observed that decompose at higher temperatures.

NOx and Hydrocarbon Trapping and Conversion in a Sequential Three-Zone Monolith: Spatiotemporal Features

The spatiotemporal features of the multifunctional monolithic lean hydrocarbon NOx trap (LHCNT), for eliminating NOx (x = 1 and 2) and ethylene (C2H4), are examined using spatially resolved mass spectrometry (SpaciMS), spanning the sequentially positioned passive NOx adsorber (PNA; Pd/SSZ-13), hydrocarbon trap (HCT; Pd/BEA), and oxidation catalyst (OC; Pt/Al2O3–CeO2). The overall LHCNT performance is captured in temporal trapping efficiency profiles, which show the integral NO and C2H4 uptake followed by delayed NO release along with NO and ethylene oxidation. Spatially resolved transient concentration profiles spanning uptake, release, and conversion of NO, H2, and C2H4, alone or as mixtures in feeds containing H2O, provide detailed insight into the transient coupling not attainable with effluent concentration monitoring alone. The PNA serves as the primary zone for NO uptake, followed by the OC and HCT. NO oxidation to NO2 occurs during NO uptake in the PNA due to Pd(II) reduction, while more extensive oxidation occurs in the OC at higher temperature. C2H4 uptake and oxidation occur in each of the functions with oxidation occurring the earliest (lowest temperature) in the OC. NO uptake in the PNA and HCT is negligibly affected by H2 but protracted oxidation of H2 during the temperature ramp delays NO release, suggesting persistence of NO bound on Pd(I). Both the PNA and HCT exhibit excellent C2H4 uptake, which diminishes in the presence of NO. Spatially resolved concentration data reveal several interesting features, such as high-temperature, sequential NO oxidation (by O2 to NO2) and C2H4 oxidation (by NO2 to NO + CO2) in the PNA. Simulated warmup experiments reveal that the LHCNT NO trapping is enhanced with C2H4 addition but that a reduction in space velocity may be needed to improve performance. A previously developed PNA model predicts satisfactorily the main features of spatially resolved NO and NO + C2H4 data.

Nanostructure and reactivity of soot produced from a turbodiesel engine using post injection

Post injection is commonly used for triggering regeneration of exhaust aftertreatment devices such as diesel particulate filters and NOx adsorber catalysts. Post injection is also a method to reduce engine-out particulate matter (PM) emissions while maintaining efficiency, to reduce or potentially eliminate exhaust aftertreatment. This study explores post injection in a light duty multi-cylinder turbodiesel engine to reduce PM. The impact of post injection dwell and duration on soot reduction and reactivity are investigated in this study. Soot samples were collected from the engine exhaust and subjected to analyses of oxidative reactivity and nanostructure of the primary soot particles. Close-coupled post injections conditions reduce soot emissions by 11–21%, while long-dwell post injection conditions reduce soot emissions by 28–33%. The reaction rate constants of soot collected from close-coupled post injection conditions decrease by 10–13% compared to baseline condition, while the reaction rate constants of soot collected from long dwell post injection conditions increase by 37–39% compared to the baseline condition. The difference in soot reactivity indicates fuel from the post injection interacts with the main injection flame. Moreover, with the increase of injection dwell and post injection size, soot surface oxygen content and amorphous carbon content increase. This explains the change in reactivity of soot from different injection dwells. Primary soot particle and particle aggregate sizes do not vary much with post injection. Soot from post injection conditions show shrinking-core-type oxidation without graphene layer rearrangement.

Reduce NOx Emissions by Adsorber-Reduction Catalyst on Lean Burn Engine

The effect of a new catalyst system composed of traditional three way catalyst converter and adsorber-reduction catalysis converter on the emission characteristics and BSFC ( Breake Specific Fuel Consumption- BSFC ) of a lean burn gasoline engine operated were investigated in this paper under different schemes of catalyst converter arrangement and different speeds and loads. The results show that the position of Three Way Catalyst is before the NOx adsorber Catalyst was the best scheme of catalyst converter arrangement. Which has the highest converter efficiency of reduction NOx emission in lean burn gasoline engine. The effects of speed on the exhaust emission and BSFC were also related to the ratio of lean burn time to rich burn time and the absolute value of both time of the adsorber-reduction catalyst converter. The load of the engine was the main influential factor to the exhaust emission characteristics and BSFC of lean burn gasoline engine, and the more load of the engine was, the more NOx emission, the less NOx conversion rate (C NOx ) and the better BSFC were.

Analysis Research of Technology Schemes of Reduction NOx Emission in Lean Burn Gasoline Engine

The lean burn technology has been paid attention recently by more and more people because the economics and emission of the gasoline engine can been improved extensively by lean burn technology. However, the reduction of NOx emission is quite small because of the rich oxygen. The different combination schemes of NOx adsorber and Three Way Catalyst were adopted in this paper and experiments of reduction NOx emission have been studied in an modified EFI 16 valves lean burn gasoline engine . The experiment results show that the scheme of the position of Three Way Catalyst is before the NOx adsorber Catalyst was the best scheme of reduction NOx emission in lean burn gasoline engine.

Spatially-Resolved Calorimetry: Using IR Thermography to Measure Temperature and Trapped NOX Distributions on a NOX Adsorber Catalyst

Spatial- and time-resolved temperature distributions over a Pt/Ba/Al2O3 model NOX storage/reduction (NSR) catalyst were measured using infra-red thermography. The heat generated during regeneration was correlated to surface nitrate reduction, thereby revealing the concentration of surface nitrates at specific locations along the catalyst. The results demonstrate that there is more nitrate formation at upstream positions relative to downstream, or from front to back of the catalyst, with short trapping times. However, as more NOX was trapped on the catalyst during longer trapping times, it was found that the largest amount of NOX was trapped slightly downstream of the inlet, evolving to a local maximum in amount trapped. Applying infrared (IR) thermography to this system resulted in a spatially resolved calorimetry method via the correlation of temperature to the distribution of sorbed nitrate species along the catalyst.

The Use of NOxAdsorber Catalysts on Diesel Engines

NO x adsorber catalysts (NACs) can be applied in lean-burn gasoline and diesel engines to reduce NO x emissions. Typically NACs are formulated using platinum as an oxidation catalyst, barium as a storage component and rhodium for NO x reduction. There has been intense research to optimise these catalysts for use on diesel engines aimed at increasing their efficiency, durability, sulfur tolerance and operating temperature window. This paper describes these developments and outlines the current level of knowledge of NO x adsorber catalyst systems using results from small-scale laboratory tests as well as engine-bench work.

Phenomenology of NOx Adsorber Catalysts

Lean phase operation of lean NOx adsorbers or lean NOx traps (LNTs) is analyzed using data from highly controlled isothermal bench-flow experiments on Pt/K/Al2O3 catalysts. Simulated diesel exhaust was used for inflow in the experiments. Pt promotes the oxidation of NO, the primary component of engine-out NOx, to NO2 which is more easily adsorbed and stored as KNO3. While the presence of Pt was found to be essential for capturing the NOx from the exhaust, it was seen that the NOx storage efficiency did not increase indefinitely with increasing Pt loading. Pt loading at a given temperature of operation is optimal when the rate of NO oxidation to NO2 is nearly equal to the NO2 adsorption rate at the sorbent sites. The NOx storage efficiency seems to be kinetically limited at lower temperatures and equilibrium limited at higher temperatures. When the lean/NOx capture operation was started from a fully regenerated condition, the NOx storage efficiency under most conditions was found to be independent of the reductant mixture used for regenerating the catalyst. The experiments also indicate the possibility of a significant NOx reduction reaction even under the highly oxidizing conditions. This reduction reaction seems to be of fractional order and is more significant at lower temperatures. More detailed analysis of the outflow from the reactor using Fourier-Transform-Infrared (FTIR) spectroscopy is being planned to identify the final product of this reduction reaction.

A compact solid SCR system for NOx reduction in passenger cars and light duty trucks

Apart from the NOx adsorber catalyst, which has already been introduced in series for direct injection spark ignition engines, SCR technology represents an interesting solution for reducing NOx emissions from diesel vehicles. However, this requires a reductant such as urea as an additional operating medium. From today’s point of view, a wide-scale provision of the frequently discussed aqueous urea solution does not appear feasible in the short term. Therefore, the use of a solid reductant such as ammonium carbamate, with its considerably lower space requirements, presents an interesting alternative for individual motor vehicles. This article describes the solid SCR system developed by FEV Motorentechnik GmbH, as well as the first vehicle tests.

Investigation of an NOx adsorber catalyst used with a passenger car diesel engine

The use of an NOx adsorber catalyst, which has already become a standard component in direct-injection spark-ignition engines, poses a special challenge in diesel engines. This article presents the results of experiments on an NOx adsorber catalyst in a passenger car diesel engine carried out by the Lehrstuhl fur Verbrennungskraftmaschinen of the RWTH Aachen in cooperation with FEV Motorentechnik GmbH.

Progress in the development of NOx adsorber catalysts for DI gasoline engines

In this article by Engelhard Technologies, recent progress in NOx trap emission control for lean-burn gasoline engines is described on the basis of defined performance criteria. The influence of different ageing conditions on the maximum temperature stability of NOx adsorbers is presented. The maximum temperature stability and the operating temperature range of current NOx adsorbers require the use of a close-coupled pre-catalyst. For series application, the maximum temperature load of the adsorbers must be limited in order to guarantee durability.