Lean Exhaust Gas Conditions Research Articles

Supercritical flow synthesis of PtPdFe alloyed nanoparticles with enhanced low-temperature activity and thermal stability for propene oxidation under lean exhaust gas conditions

Supercritical flow technology was used for the one step production of PtPd and PtPdFe nanoparticles supported on high surface area γ-Al2O3.

DeNOx Abatement over Sonically Prepared Iron-Substituted Y, USY and MFI Zeolite Catalysts in Lean Exhaust Gas Conditions.

Iron-substituted MFI, Y and USY zeolites prepared by two preparation routes—classical ion exchange and the ultrasound modified ion-exchange method—were characterised by micro-Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet (UV)/visible diffuse reflectance spectroscopy (UV/Vis DRS). Ultrasound irradiation, a new technique for the preparation of the metal salt suspension before incorporation to the zeolite structure, was employed. An experimental study of selective catalytic reduction (SCR) of NO with NH3 on both iron-substituted reference zeolite catalysts and those prepared through the application of ultrasound conducted during an ion-exchange process is presented. The prepared zeolite catalysts show high activity and selectivity in SCR deNOx abatement. The MFI-based iron catalysts, especially those prepared via the sonochemical method, revealed superior activity in the deNOx process, with almost 100% selectivity towards N2. The hydrothermal stability test confirmed high stability and activity of MFI-based catalysts in water-rich conditions during the deNOx reaction at 450 °C.

Influence of single- and double-flame spray pyrolysis on the structure of MnOx/γ-Al2O3and FeOx/γ-Al2O3catalysts and their behaviour in CO removal under lean exhaust gas conditions

Manganese and iron oxides on alumina prepared by two-nozzle flame synthesis show improved CO-oxidation activity due to minimized composite formation.

Effect of Hydrogen-Enriched Gas as a Reductant on the Performance of a Lean NOx Trap Catalyst for a Light-Duty Diesel Engine

Direct-injection diesel engines have become prime candidates for future transportation needs owing to their high thermal efficiency. However, the increase in nitrogen oxides (NO x) within local high-temperature regions and the increase in particulate matter within the diffusion flame region during diesel combustion are problematic and must be resolved. The utilization of NO x-absorbing catalysts, based on the concept of NO x storage and release, is one of the most promising techniques able to reduce NO x emissions within net oxidizing gas conditions. This type of NO x removal system, called the lean NO x trap (LNT) catalyst, absorbs NO x under lean exhaust gas conditions and releases NO x under rich conditions. This technology provides the advantage of high NO x conversion efficiency; however, the correct amount of reducing agent must be supplied within the catalytic converter under appropriate conditions in order to guarantee a high NO x reduction efficiency. In this research, the performance characteristics of an LNT, using a hydrogen-enriched gas as a reductant, were examined via various injection strategies and rich exhaust gas conditions. Although the hydrogen concentration of hydrogen-enriched gas also affects the LNT performance, the composition of hydrogen-enriched gas was fixed as a similar composition to that for the ideal re-forming of diesel fuel. The NO x reduction efficiency is closely connected to the injection timing and duration of reductant flow. When the injection was introduced 1.5 s after throttling, the LNT NO x conversion was maximized. However, the LNT NO x conversion decreased when the injection timing was earlier or later than 1.5 s. Because the actual rich duration of the exhaust gas is limited at a specific point during the rich operation for 3 s, the LNT NO x conversion was maximized when the hydrogen-enriched gas was injected at the minimum air-to-fuel ratio observed at the LNT inlet. By optimizing the control of this flow, the system encounters only a 1.9 per cent fuel penalty while maintaining a 90 per cent NO x reduction efficiency.

연료 개질장치의 적용에 따른 디젤 LNT 환원성능 개선 특성

디젤엔진은 높은 열효율과 우수한 연비 성능 등의 장점을 가지고 있으나, 기화된 연료와 주변 공기가 혼합된 후 착화되는 과정을 거치기 때문에 이론 공연비 영역에서는 질소산화물(NOx) 배출이 증가되는 문제점을 가지고 있다. 최근 활발히 연구되고 있는 높은 정화 효율을 가진 LNT촉매는 희박 분위기 조건에서는 NOx를 흡장하게 되고 과농한 분위기에서는 환원 분위기 형성을 통하여 를 NOx저감시키게 된다. 희박 공연비에서 동작하는 디젤 엔진에서는 이러한 환원 과정을 이루기 위해 주기적으로 과농한 분위기를 형성해주어야만 하는데, 이러한 연구는 NOx저감을 위해 HC를 포함한 환원제의 농도를 제어하는 기술로서 본 연구에서는 디젤을 연료로 하는 수소농후가스 발생장치를 이용하여 LNT 촉매에 환원제로서 수소농후가스를 직접 공급하는 방식으로 LNT촉매의 NOx저감 특성을 파악하였다.

The influence of hydrogen-enriched gas on the performance of lean NO x trap catalyst for a light-duty diesel engine

Modern diesel engines have improved engine fuel economy and significantly reduced nitrogen oxides (NO x ) and particulate matter (PM) emissions achieved by advances in both combustion and exhaust aftertreatment technologies. Recently, it has been shown that the vehicle emissions can be further improved by several catalytic systems including fuel reformers and aftertreatment systems, such as the Lean NO x Trap (LNT). This NO x removal system, called LNT, absorbs NO x under lean exhaust gas conditions and releases NO x under rich conditions. This technology can provide high NO x conversion efficiency, but the right amount of reducing agent should be supplied into the catalytic converter under appropriate conditions. In this work, plasma reformer was used to supply a hydrogen-enriched gas as a NO x reductant. The plasma reforming is one of the most promising on-board reforming technologies, which allows reformates containing H 2 and CO to feed for LNT catalyst efficiently. Partial oxidation is induced by plasma in the fuel reformer and diesel fuel is converted into a hydrogen-enriched gas. The supplying strategy was focused on the maximization of NO x reduction efficiency varying both the total amount of hydrogen-enriched reformate and the ratio of oxygen molecules to in the reformer air-fuel mixture prior to processing at a fixed engine operating condition. The effect of exhaust gas temperature was also studied. The NO x reduction efficiency is closely connected to the amount of supplied fuel to the plasma reformer and the ratio of fuel/air feed rate. The LNT can reduce NO x efficiently with only a 2.6% fuel penalty.

Metal layered zeolite catalysts for NOx abatement in lean exhaust gas conditions

Metal layered ZSM-5 zeolites ion-exchanged with copper are effective catalysts in NOx abatement in lean automotive exhaust gas conditions. The effective ion-exchange level of Cu is above 100%, and some co-cations improve the catalytic activity. The thermal stability of the catalyst can be improved with Cr as a co-cation.

NO x abatement in lean exhaust gas conditions over metal substrated zeolite catalysts

Metal substrated ZSM-5 zeolites ion-exchanged with copper are effective catalysts in the elimination of nitrogen oxides from lean automotive exhaust gases when propene works as a reductant. Some co-cations improve the catalytic activity of Cu-ZSM-5. The critical temperature for the deactivation of Cu-ZSM-5 catalysts is around 700°C where the state of copper begins to change resulting in the decrease of the catalytic activity. The structure of the Cu-ZSM-5 zeolite collapses after thermal aging at temperatures above 800°C. However, the coexistence of chromium in the zeolite increases the thermal stability of Cu-ZSM-5 considerably.