KR20050093531A - Rubidium containing nox trapping catalyst - Google Patents

Abstract

The present invention relates to a NOx trap catalyst containing rubidium. Specifically, in a NOx trap catalyst composed of a platinum component, a support, and a NOx adsorption component, the NOx adsorption component is a rubidium metal component alone, or a rubidium metal component and barium, strontium. It relates to a NOx trap catalyst consisting of a mixture of metal components selected from the group consisting of, calcium and cesium.

The NOx trap catalyst of the present invention has a smaller desorption tendency in a high temperature lean atmosphere than a conventional NOx trap catalyst, and is resistant to SOx and can be used as a NOx trap catalyst having excellent NOx purification rate.

Description

NOB trap catalyst containing rubidium {Rubidium containing NOx TRAPPING CATALYST}

The present invention relates to a NOx trap catalyst containing rubidium.

At present, countries are making various efforts to prevent global warming. Of these, carbon dioxide regulations are expected to be tightened. At present, the generation of carbon dioxide during combustion through the internal combustion engine is inevitable, and for this purpose, the application of diesel engines and lean burn engines to generate less carbon dioxide is being actively expanded.

However, when the diesel engine and the lean burn engine are used, there is a problem about NOx emission due to operation in a lean environment. Thus, reducing NOx from lean burn engines and partial lean burn engines, such as gasoline direct injection, as well as from diesel exhaust, traps and accumulates NOx under lean burn engine operating conditions and is stoichiometric or rich. It is required to release and reduce NOx under engine operating conditions. Lean run cycles are typically 1 minute to 3 hours, and rich run cycles are typically short (1-5 seconds) to conserve as much fuel as possible. Short and frequent regeneration lasts for a long time but is advantageous over less frequent regeneration.

The operation of the NOx trap catalyst is a collection of basic steps, which are shown in Schemes 1-5 below. In general, NOx trap catalysts should exhibit both oxidation and reduction actions. In an oxidizing environment, NO is oxidized to NO ₂ (Scheme 1), which is an important step for NOx storage. At low temperatures, this reaction usually uses noble metals such as Pt as catalyst. The oxidation process then continues, incorporating oxygen atoms while further oxidizing NO ₂ to nitrates (Cat. 2). Even when NO ₂ is used as the NOx source, almost no nitrate is formed without precious metals. The noble metal has a dual action of oxidation and reduction, in which case Pt catalyzes the release of NOx by first introducing a reducing agent such as CO (carbon monoxide) or HC (hydrocarbon) (Scheme 3). This allows some NOx storage points to be recovered, but is not involved in reducing NOx at all. The released NOx is then further reduced to gas N ₂ in a rich environment (Scheme 4 and 5). NOx emissions can be caused by fuel injection even in a pure oxidizing environment. However, a rich state is necessary to efficiently reduce the released NOx by CO. Temperature spikes can also lead to NOx emissions, since base metal nitrate is less stable at high temperatures. NOx trap catalysts operate cyclically. Non-noble metal compounds are thought to undergo carbonate / nitrate conversion as the dominant pathway during lean / rich operation. Sulfur poisoning of the NOx trap catalyst is shown in Schemes 6 and 7. In Scheme 6, S occupies a point for NOx, and in Scheme 7, SOx replaces CO ₃ or NOx.

NO ₂ NO oxidation

NO + 1 / 2O ₂ → NO ₂

NOx storage as nitrate

2NO ₂ + MCO ₃ + 1 / 2O ₂ → M (NO ₃ ) ₂ + CO ₂

NOx emission

M (NO ₃ ) ₂ + 2CO → MCO ₃ + NO ₂ + NO + CO ₂

N ₂ NOx reduction to

NO ₂ + CO → NO + CO ₂

2NO + 2CO → N ₂ + 2CO ₂

SOx poisoning process

SO ₂ + 1/2 O ₂ → SO ₃

SO ₃ + MCO ₃ → MCO ₄ + CO ₂

(In the schemes 2, 3 and 7, M represents a divalent non-noble metal cation, preferably Ba.)

In order to show the optimal activity of the NOx trap as described above, as shown in Figure 1, the adsorption of NOx in the Lean atmosphere should be easy and desorption should not occur until the Rich conversion. In addition, rapid NOx desorption occurs during the Rich conversion, requiring full regeneration of the NOx trap material.

However, currently used NOx trap materials have the following limitations. Firstly, desorption occurs at high temperature Lean atmosphere, which lowers NOx purification rate. Secondly, NOx trap material is generally weak to heat, so NOx storage capacity is significantly decreased when exposed to high temperature. Finally, competition for trap between NOx and SOx in presence of SOx Adsorption reactions occur and SOx desorption becomes more difficult than NOx.

SUMMARY OF THE INVENTION An object of the present invention is to provide a NOx trap catalyst which is less prone to desorption in a high temperature lean atmosphere and resistant to SOx.

In order to achieve the above object, the present invention is a NOx trap catalyst consisting of a platinum component, a support and a NOx adsorption component, wherein the NOx adsorption component is a rubidium metal component alone, or a rubidium metal component and barium, strontium, calcium and cesium It provides a NOx trap catalyst consisting of a mixture of metal components selected from the group consisting of.

Hereinafter, the present invention will be described in detail.

The NOx trap catalyst is based on a three way catalyst (TWC), which is composed of a platinum component, a support, and a NOx adsorption component.

The present invention is characterized by the NOx adsorption component, wherein the NOx adsorption component consists of a rubidium metal component alone or a mixture of a rubidium metal component and a metal component selected from the group consisting of barium, strontium, calcium and cesium. Preferably, the NOx adsorption component is a mixture or composite metal oxide consisting of a mixture of a metal oxide selected from the group consisting of barium, strontium, calcium and cesium, and rubidium metal oxide, and most preferably, a mixture of barium oxide and rubidium oxide. Mixture or composite metal oxide.

The NOx adsorption component of the present invention solves the limitation of the conventional NOx adsorption component. Specifically, the desorption tendency is greatly reduced in the high temperature lean atmosphere, thereby reducing the reduction of NOx purification rate, having stability against heat, and thus reducing the reduction of the NOx storage capacity at high temperature exposure. Finally, in the presence of SOx, NOx, SOx The reduction of NOx purification rate by competitive adsorption reaction to the liver trap was reduced.

The present invention includes a platinum component. As shown in FIG. 1, the platinum component oxidizes NO generated under lean conditions and converts the NO into NO ₂ , and in the oxygen rich process (rich transient), NOx desorbed to the NOx adsorption component is carbon dioxide, water, In order to perform the role of converting to nitrogen or the like, one consisting of platinum alone or one containing platinum group metal component in platinum is used. The platinum group metal component may be selected from the group consisting of palladium, rhodium, ruthenium, iridium and osmium components and mixtures thereof.

The present invention includes the use of rubidium as the NOx trap material and a support consisting of a high surface area refractory oxide support. The support uses one or more selected from the group consisting of alumina, silica, titania and zirconia compounds, preferably activated alumina, silica, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chroma and Use is selected from the group consisting of alumina-ceria.

In addition, the NOx trap catalyst of the present invention can be prepared by a conventional method in the art, in particular in the production of NOx adsorption components in a certain weight ratio of a metal component and a rubidium metal component selected from the group consisting of barium, strontium, calcium and cerium Mix. Example, the active alumina to Pt-MEA (mono ethanol amine) and impregnated with a Rh-Pt nitrate to-Rh- after producing alumina sufficient H ₂ O in the barium, strontium, calcium, and certain metal components selected from rubidium and cerium After the input dispersion by weight ratio, the prepared Pt-Rh-alumina was further added and dispersed.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the present invention is not limited to the contents of the present invention.

Example 1 Preparation of NOx Trap Catalyst 1

The NOx trap catalyst consisting of NOx adsorption component BaO and Rh ₂ O was prepared by the following method.

NOx trap catalyst is composed of bottom and top two layer catalyst.

-Bottom

A. Impregnated Pt-Rh-alumina was prepared by impregnating 70 g of alumina powder with 2 g of Pt and 0.6 g of Rh, and dispersing 16 g of ZrO ₂ , 45 g of CeO ₂ , 25 g of BaO and 25 g of Rb ₂ O in sufficient H ₂ O. The prepared Pt-Rh-alumina was further added. The particle size of the slurry was then adjusted by the ball milling method to a size suitable for coating on cordierite honeycomb.

B. The slurry prepared above was coated on cordierite honeycomb, dried at 130 ° C. to 150 ° C. for about 10 minutes, and calcined at 530 ° C. to 550 ° C. for about 40 minutes.

-Top

A. Pt-impregnated alumina was prepared by impregnating 20 g of alumina powder with 1 g of Pt, and then dispersed in sufficient H ₂ O with 4 g of ZrO ₂ , 10 g of CeO ₂ , and 20 g of zeolite. The particle size of the slurry was then adjusted by the ball milling method to a size suitable for coating on cordierite honeycomb.

B. The slurry was coated on a honeycomb with the bottom coating completed, dried at 130 ° C. to 150 ° C. for about 10 minutes, and calcined at 530 ° C. to 550 ° C. for about 40 minutes.

Comparative Example 1 Preparation of NOx Trap Catalyst 1

Example 1 A NOx trap catalyst was prepared in the same manner as in Example 1, except that Cs ₂ O was used instead of Rb ₂ O at the bottom.

Comparative Example 2 Preparation of NOx Trap Catalyst 2

Example 1 A NOx trap catalyst was prepared in the same manner as in Example 1, except that Rb ₂ O was used as the total amount of BaO at the bottom.

Experimental Example 1 Measurement of Purification Rate of a NOx Trap Catalyst 1

(1) catalyst evaluation

The NOx trap catalyst prepared in Examples 1 and 2 was deteriorated prior to catalyst evaluation. At this time, the deterioration conditions were carried out in a box furnace for 6 hours at 750 ℃.

After the deterioration, the catalyst evaluation was carried out at Engine Dyno.

At this time, the engine used a 2.0L DOHC Sonata, and the test mode was performed in the PLB-5 mode (see Fig. 2). Specifically, the initial PLB-5 mode was pre-treated with a Rich atmosphere for 120 seconds in the Lean 60 It is a mode to measure NOx trap catalyst activity in 8 operations for 2 seconds and Rich 2 seconds. In addition, the space velocity was 21,000 1 / hr, the fuel sulfur content was 0 ppm, and the Lean / Rich time was 60/2 (second). Finally, the purification rate of the NOx trap catalyst was measured at 350, 400, and 450 ° C.

In addition, in order to measure the purification rate of HC for the NOx trap catalyst of the present invention, the experiment was carried out in the same manner as described above.

(2) results

① NOx purification rate of NOx trap catalyst at catalyst inlet temperature 350, 400, 450 ℃

The NOx purification rate results of the NOx trap catalyst at the catalyst inlet temperatures of 350, 400, and 450 ° C are shown in FIG. 4. In addition, the real-time NOx according to the experiment mode is shown in FIG. As can be seen, it can be seen that the purification rate of the NOx trap catalyst at 350 ° C is superior to that of the NOx trap catalyst (Example 1) of the present invention compared to the NOx trap catalysts of Comparative Examples 1 and 2. In particular, it can be seen that the NOx trap catalyst of Example 1 exhibits a purification rate of 95% or more during the Rich process, and thus has better performance.

-NOx purification rate of NOx trap catalyst at catalyst inlet temperature of 400 ℃

As shown in Fig. 4, the NOx purification rate at 400 ° C shows the same result as the NOx purification rate at 350 ° C.

-NOx purification rate of NOx trap catalyst at catalyst inlet temperature of 450 ℃

As shown in FIG. 4, the NOx purification rate was shown to be excellent in the order of Example 1> Comparative Example 1> Comparative Example 2, but it is different from the results of the catalyst inlet temperatures 350 and 400 ° C. This indicates that the NOx adsorption capacity decreases with increasing temperature and the purification rate decreases due to desorption.

As shown in Figure 4 it can be seen that the NOx purification rate is improved from 350 ℃ to 400 ℃, it can be seen that the NOx purification rate is reduced at 450 ℃. At this time, it can be seen that the tendency to decrease is the smallest NOx trap catalyst of Example 1, so the desorption phenomenon with increasing temperature.

The purification rate of HC was measured in comparison with the result for the NOx purification rate. The results are shown in FIG. As shown in Figure 5, it can be seen that the HC purification rate of the NOx trap catalyst of Example 1, Comparative Example 1 and Comparative Example 2 is improved as the catalyst inlet temperature increases. As shown in FIG. 4, this is caused by the desorption phenomenon due to the temperature rise, which supports the result of FIG.

Experimental Example 2 Measurement of Purification Rate of the NOx Trap Catalyst 2

In order to determine the resistance to SOx, the space velocity used a fuel having a sulfur content of 100 ppm at 42,000 1 / hr, and the other experimental method was performed in the same manner as in Experiment 1. Finally, the NOx purification rate of the NOx trap catalyst was measured at 350, 400, 450, and 500 ° C.

The NOx purification rate of the NOx trap catalyst for each catalyst inlet temperature is shown in FIG. 6. As shown in FIG. 6, the NOx purification rate of the fuel without sulfur content of FIG. 4 shows a tendency to decrease, but it can be seen that the performance of the NOx trap catalyst of Example 1 of the present invention is superior to that of Comparative Example 1. In addition, it can be seen that the same result is obtained even by increasing the catalyst inlet temperature.

As described above, the NOx trap catalyst of the present invention is composed of a NOx adsorption component consisting of a mixture of a metal component such as barium and a metal component of rubidium or cesium, and thus has a low desorption tendency in a high temperature lean atmosphere. It is resistant to, and can be used as a better NOx trap catalyst.

1 is a view schematically showing the action of the NOx trap catalyst,

2 is a graph showing a PLB-5 test mode of Experimental Example 1 of the present invention;

3 is a graph of experimental data according to the actual test mode showing the NOx purification rate of the NOx trap catalyst at the catalyst inlet temperature of 400 ° C. when the fuel sulfur content is 0 ppm and the space velocity 21,000 1 / hr.

4 is a graph showing the NOx purification rate of the NOx trap catalyst at a catalyst inlet temperature of 350, 400, and 450 ° C when the content of fuel sulfur is 0 ppm and a space velocity of 21,000 1 / hr.

5 is a graph showing the purification rate of HC of the NOx trap catalyst at the catalyst inlet temperatures 350, 400, and 450 ° C. when the content of fuel sulfur is 0 ppm and the space velocity 21,000 1 / hr according to the present invention.

Figure 6 is a graph showing the NOx purification rate of the NOx trap catalyst according to the content of fuel sulfur at the space velocity 42,000 1 / hr, catalyst inlet temperature 350, 400, 450, 500 ℃ in the present invention.

Claims (8)

A NOx trap catalyst comprising a platinum component, a support and a NOx adsorption component, wherein the NOx adsorption component comprises a rubidium metal component. A NOx trap catalyst comprising a platinum component, a support, and a NOx adsorption component, wherein the NOx adsorption component is a mixture of a metal component selected from a group consisting of barium, strontium, calcium, and cesium and a rubidium metal component. . The NOx trap catalyst according to claim 2, wherein the NOx adsorption component is a mixture or complex oxide consisting of a mixture of a metal oxide and a rubidium metal oxide selected from the group consisting of barium, strontium, calcium and cesium. 4. The NOx trap catalyst according to claim 3, wherein the NOx adsorption component is a mixture or complex oxide consisting of a mixture of barium oxide and rubidium oxide. The NOx trap catalyst according to claim 1 or 2, wherein the platinum component is composed of platinum alone or further comprises platinum as a platinum group metal component. 6. The NO x trap catalyst of claim 5, wherein the platinum group metal component is selected from the group consisting of palladium, rhodium, ruthenium, iridium and osmium components and mixtures thereof. The NOx trap catalyst according to claim 1 or 2, wherein the support is one or more selected from the group consisting of alumina, silica, titania and zirconia compounds. The NOx trap catalyst according to claim 7, wherein the support is selected from the group consisting of activated alumina, silica, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chroma and alumina-ceria.