KR20080097700A - Diesel nox reduction system and method - Google Patents

Abstract

A NOx reduction system and method is provided to produce H2 and CO as the reducing agent through the reforming of the injected fuel by fuel direct injection method in producing NOX stored in LNT catalyst. A NOx reduction method comprises a step for injecting some of fuel of the vehicle into an exhaust system; a step for passing the fuel and exhaust gas to the reforming catalyst; and a step of passing the gas passing through the reforming catalyst to the LNT catalytic unit. The reforming catalyst is the catalyst in which Pt and Rh are dipped into the alumina carrier. The LNT catalyst is the catalyst in which Pt and Rh are dipped into the alumina carrier.

Description

Vehicle NOx reduction method and apparatus {Diesel NOx reduction system and method}

1 schematically illustrates the LNT catalyst mechanism,

2 and 3 are measurements of the amount of H 2, CO produced in the process of designing a fuel reforming catalyst,

4 is a measurement diagram of the amount of H2 produced by HC16 reforming by a fuel reforming catalyst,

5 and 6 are measurements of the H 2 / CO ratio and other components according to HC 16 reforming by the fuel reforming catalyst,

7 schematically shows an experimental apparatus for measuring NOx reduction,

8 is a measurement diagram showing the effect of reducing NOx according to the present invention.

The present invention relates to a method and apparatus for reducing NOx emission of a diesel vehicle, and more particularly, to a method for reducing NOx emission including H2 and CO generation by fuel reforming and a NOx reduction step using the same; And a fuel reforming means mounted before the lean NOx catalyst means.

As the exhaust regulations are tightened, it is inevitable to apply aftertreatment technology because there is a limit to satisfy the regulation by only the harmful gas reduction technology inside the engine. In the case of gasoline engines, so-called three-way catalyst technology that simultaneously reduces CO, HC, and NOx is currently used, but it is difficult to meet the stricter ULEV regulations in the United States, so Lean NOx Trap (LNT) catalysts are used in lean combustion engines. Its application is strong, and diesel engines have high particulate matter (PM) and NOx emissions, so the reduction technology is needed first. A smoke filter (DPF trap) is being studied as a countermeasure for PM. Similarly LNT catalysts are being developed.

LNT catalyst refers to a catalyst that converts nitrogen and carbon dioxide by a catalyst by collecting NOx in a lean region and then discharging it in a rich region. The LNT catalyst has a conventional three-way catalyst function in the theoretical performance ratio, but functions as a NOx trap in the lean region to adsorb and store NOx. Ba, Sr, K, etc. are used as the NOx trap material, and in the lean region, NO is converted into NO2 by Pt and stored in the NOx trap, and NOx stored in the NOx trap is reduced to N2 when the air-fuel ratio is rich. FIG. 1 illustrates the NOx storage and regeneration process when Ba is included as a trap material.

In the lean fuel efficiency state, NO 2 is produced in the first reaction using an oxidation catalyst or the like.

NO + 1/2 O2 = NO2;

A second reaction occurs in the NOx trap, where NO2 is adsorbed to Ba (NO3) 2.

BaO + NO 2 + 1/2 O 2 = Ba (NO 3) 2;

After that, when the air-fuel ratio becomes rich and the temperature is appropriate, the nitrogen molecules occupied in the NOx trap become thermodynamically unstable and change into NO and NO2 as follows.

Ba (NO 3) 2 = BaO + 2NO + 3/2 O 2;

Ba (NO 3) 2 = BaO + 2NO 2 + 1/2 O 2;

The generated NO is converted to N2 and CO2.

NO + CO = 1/2 N2 + CO2;

In this case, the NOx trap material is generally constituted by mixing a NOx storage component with a conventional three-way catalyst. The NOx storage components are typically of the following types:

Alkaline earths: Ba (barium), Ca, Sr (strontium), Mg

Alkali metals: K (potassium), Na (sodium), Li, Cs (cesium)

Rare earth metals: La (lanthanum), Y (ytrium)

However, the conventional NOx trap means need to be further developed in terms of durability and low temperature activity. In order to further reduce NOx emission in the present concept, an object of the present invention is to generate H2 and CO as a reducing agent through reforming of fuel injected by the fuel direct injection method when regenerating NOx stored in an LNT catalyst, and thereby reducing NOx. It is to propose a method to apply to the regeneration process. By introducing such a fuel reforming step, the diesel oil as a reducing agent injected into the front end of the LNT catalyst is directly exposed to the LNT catalyst, which leads to complete oxidation, thereby solving problems due to exothermic heat, diesel oil consumption, and the like.

In addition, the present invention proposes an apparatus capable of significantly reducing NOx emissions by introducing a system for mounting a fuel reforming catalyst means before the LNT catalyst means from a catalytic point of view.

In order to achieve the above object, the present invention,

Injecting a portion of the vehicle fuel into an exhaust system;

Passing the fuel and exhaust gas through a reforming catalyst;

It is achieved by a vehicle NOx emission reduction method comprising passing the gas passed through the reforming catalyst to the LNT catalyst means.

The automobile fuel is characterized in that the diesel oil, the reforming catalyst is characterized in that the Pt, Pd and Rh is a catalyst impregnated in the alumina carrier.

In addition, the present invention,

In the automotive after-treatment apparatus including the LNT catalyst means,

Provided is a vehicle NOx emission reduction device further equipped with a fuel reforming catalyst in front of the LNT catalyst means.

The fuel reforming catalyst is characterized in that Pt, Pd and Rh are catalysts impregnated in the alumina carrier.

DETAILED DESCRIPTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but embodiments are not limited thereto. In addition, the LNT catalyst may be used interchangeably with the same concept as a NOx adsorber, a NOx storage / reduction catalyst (NSRC), or a NOx storage catalyst (NAC) that performs the same function.

1. Design of Fuel Reforming Catalyst

First, the inventors have loaded Pt, Pd and / or Rh into a γ-alumina carrier as a first attempt to implement an appropriate catalyst system, and then investigated the amount of H2 and CO produced by hydrodecane modification at elevated temperatures. FIG. 2 shows the results of the modified state of the aging catalysts at 750 ° C. for 3 hours, where Pt is unsuitable for partial oxidation, and Rh is reformed to H 2, Pd to CO. It was confirmed that it was excellent in the modification. After aging, Pd / Rh catalyst was found to be the most stable and excellent in H2 and CO production. Pd / Rh impregnated with gamma-alumina as a carrier in a weight ratio of 1: 1 was referred to as a reference fuel reforming catalyst (named DFC 1). Was selected. The present inventors have prepared three other fuel reforming catalysts (DFC 2-4, relative Rh loading increased gradually to 1.5, 2. 2.5 compared to DFC 1), increasing the temperature (200-800 ℃) Hydrodecane conversion in) was observed by GC-MS. 4 shows these results, and hydrodecane conversion, ie H2 and CO generation, appears to be large with increasing temperature and Rh loading. On the other hand, Figures 5 and 6 illustrate the analysis of the modified component, the higher the temperature, the higher the H2 / CO ratio, it can be seen that other components are reduced.

2. Selection of LNT Catalyst

Commercially available LNT catalysts are catalysts in which Pt and Rh are impregnated with gamma-alumina at 120 g / ft 3 in a 5: 1 ratio by weight.

3. The fuel reforming catalyst and the LNT catalyst were mounted on the engine dynamometer as shown in FIG. 7 to measure the NOx conversion rate (inlet temperature 340 ° C.). DFC + NSR means a system according to the invention in which a fuel reforming catalyst and an LNT catalyst are continuously installed, and NSR alone means a conventional conventional exhaust system without a fuel reforming catalyst. That is, it was confirmed that the NOx conversion rate was significantly improved over the entire cycle by the means according to the present invention in which the fuel reforming catalyst was mounted at the front end as compared to the NOx conversion rate by the LNT catalyst alone.

The inventors found that when the fuel reforming catalyst is placed in front of the LNT catalytic means, the NOx conversion rate is significantly improved. This result is considered that the large amount of H2 and CO produced by the fuel reforming catalyst is derived from the effective regeneration of the occluded NOx amount. As a result, the introduction of the concept of a fuel reforming catalyst allows LNT catalysts to effectively reduce NOx at relatively low temperatures, which not only provides improved NOx removal rates but also achieves the effect of low fuel consumption. .

Claims (6)

In the vehicle NOx emission reduction method, Injecting a portion of the vehicle fuel into an exhaust system; Passing the fuel and exhaust gas through a reforming catalyst; A method for reducing automobile NOx emissions comprising passing gas through a reforming catalyst to the LNT catalyst means. The method of claim 1, wherein the reforming catalyst is a catalyst in which Pt and Rh are impregnated in an alumina carrier. The method of claim 1 or 2, wherein the LNT catalyst is a catalyst in which Pt and Rh are impregnated in an alumina carrier. In the automotive after-treatment apparatus including the LNT catalyst means, Vehicle NOx emission reduction device further equipped with a fuel reforming catalyst in front of the LNT catalyst means. The apparatus for reducing vehicle NOx emissions according to claim 4, wherein the fuel reforming catalyst is a catalyst in which Pt, Pd, and Rh are impregnated in the alumina carrier. The apparatus for reducing vehicle NOx emissions according to claim 4 or 5, wherein the LNT catalyst is a catalyst in which Pt and Rh are impregnated in an alumina carrier.

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