HEAT-RESISTANT RUTHENIUM COMPOSITE AND USE THEREOF AS CATALYST FOR NOX STORAGE AND REDUCTION

Abstract

Disclosed is a heat-resistant ruthenium composite and, more particularly, to a heat-resistant ruthenium composite, a catalyst using same, and an exhaust system, the heat-resistant ruthenium composite being composed of a matrix including a plurality of cores therein, wherein ruthenium is present in a metal state in the core and a Ru complex oxide including Ru perovskite (PV) is contained in the matrix.

Claims

1. A heat-resistant ruthenium composite comprising a matrix in which a plurality of cores is embedded, wherein the core contains ruthenium in a metallic state, and the matrix comprises Ru composite oxide containing Ru PV (perovskite).

2. The heat-resistant ruthenium composite of claim 1, wherein the Ru composite oxide comprises Ru PV (perovskite) having a ARuO.sub.3 structure and a Ru mixed oxide having a AA′RuBOx structure, wherein A and A′ are individually an alkali metal, wherein B is a transition metal or Mg.

3. The heat-resistant ruthenium composite of claim 2, wherein the A element is Ba, La, Sr, Zr, or Ca, and the B element is Fe, Mn, Ni, Co, or Mg.

4. A catalyst comprising the heat-resistant ruthenium composite of claim 1, wherein the catalyst is supported on a carrier, wherein the catalyst is used in an application of NO.sub.x Storage and Reduction (NSR) or Lean NO.sub.x Trap (LNT).

5. An internal combustion engine exhaust system comprising the catalyst of claim 4.

6. The internal combustion engine exhaust system of claim 5, further comprising a catalyst component selected from the group consisting of optional catalyst reduction (SCR) catalysts, particulate filters, SCR filters, NOx adsorbent catalysts, ternary catalysts, and oxidation catalysts, and combinations thereof.

7. A method of manufacturing a heat-resistant ruthenium composite, the method comprising: a step of mixing a precursor of an A-type alkali metal consisting of Ru metal powder or nano-particle powder (Ru/RuOx), Ba, La, Sr, Zr, and Ca, and a B-type precursor consisting of Mg, Fe, Mn, Ni, and Co; and a step of thermally treating the resulting mixture in air.

8. The method of claim 7, wherein the precursor is selected from among hydroxide, carbonate, nitrate, and metal oxides.

Description

DESCRIPTION OF DRAWINGS

[0007] FIG. 1 schematically shows a ruthenium composite according to the present disclosure.

[0008] FIG. 2 is an XRD result for the ruthenium composite prepared in Example.

[0009] FIG. 3 shows that the NOx conversion rate was tested for the catalysts prepared in Examples. It is confirmed that the conversion rate is significantly improved in the NSR catalyst containing the ruthenium complex.

[0010] FIG. 4 shows the catalyst measurement results of Examples.

[0011] FIG. 5 is a worldwide harmonized light vehicles test cycle (WLTC) results after engine aging for the catalyst prepared in Example.

[0012] FIG. 6 is an investigation of the volatility of Ru itself in the Ru complex.

BEST MODE

[0013] Perovskite is generally a metal oxide having the chemical structure of ABO.sub.3. Ru PV refers to ruthenium oxide having a perovskite structure of Formula ARuO.sub.3 (Alkali metal such as A: Ba, La, Sr, Zr, Ca, etc.). Ru composite oxide including Ru PV is defined as a concept including Ru mixed oxide including formula AA′RuBO.sub.X [X=2 to 15] (A, A′: Alkali metals such as Ba, La, Sr, Zr, Ca, B: a transition metal such as transition metals such as Fe, Mn, Ni, Co, etc., or Mg) in addition to Ru PV. According to the present disclosure, the heat-resistant ruthenium composite includes a substrate of a Ru composite oxide, and has a structure containing a plurality of metallic ruthenium as a core in the substrate. The Ru composite oxide includes a Ru mixed oxide having an AA′RuBOx structure as well as Ru PV having an ARuO.sub.3 structure. According to the present disclosure, it is determined that the core holds the metallic ruthenium, and the metallic ruthenium may contact the reaction gas through a plurality of pores present in the substrate and that the ruthenium may move to the surface of the substrate according to the reaction conditions, for example, lean or rich conditions.

[0014] In the present disclosure, the ruthenium composite may also be understood as a solid ruthenium solution and may also be referred to as a composition because it includes a Ru PV and a Ru mixed oxide. In the present disclosure, the core of the ruthenium composite is characterized by using a Ru-nano powder to maintain Ru in a metallic state. These ruthenium complexes can be applied as NOx storage and reduction catalysts due to their excellent NOx storage-De-NOx ability and excellent Passiveness (NOx.fwdarw.NH.sub.3 conversion rate), and N.sub.2 selectivity. In the present embodiment, N.sub.2 selectivity means a tendency for NOx to switch to preferred N.sub.2, not unwanted N.sub.2O.

Example 1: Preparation of Ruthenium Complex

[0015] Ru metal powder or nano-particle powder with a diameter of 5 nm to 5 micrometers (commercially referred to as Ru sponge) (Ru/RuOx), A type (Ba, La, Sr, Zr, Ca, etc. alkali metal) precursor, B-type (transition metal such as Fe, Mn, Ni, Co, or Mg) precursors were mixed, and ball-milled. A solid solution was prepared by heat treatment in a furnace ranging from 700° C. to 1300° C. In this case, the A-type or B-type precursor may be in the form of hydroxide, carbonate, nitrate, or oxide. After heat treatment, if necessary, the surface area may be adjusted by milling.

[0016] FIG. 2 is an XRD result for the ruthenium composite prepared by heat treatment at 1000° C. and 1250° C. in Example 1 in particular, confirming the Ru core embedded in the BaSr—RuMg-Ox substrate. It can be seen that the solid solution contains Ru PV and various Ru mixed oxides.

Example 2: Preparation of NSR (NOx Storage and Reduction) Catalyst

[0017] After impregnating the platinum group (Pt/Pd/Rh) component on modified alumina, ceria, and zirconia, and then thermally (500° C.) fixing and milling to prepare a powder, and then mixing the powder with the Ba, Sr, and MgO components, which are NOx storage components, in distilled water to complete the slurry was applied to complete the NSR comparative catalyst (referred to as reference). For Reference, a ruthenium composite (referred to as RUSS-1) prepared by heat treatment at 800° C. in Example 1 was kneaded to prepare an NSR catalyst (Ref.+RUSS-1) according to the present disclosure. A ruthenium composite (referred to as RUSS-2) prepared by heat treatment at 1100° C. in Example 1 was mixed as a Reference to prepare an NSR catalyst (Ref.+RUSS-2) according to the present disclosure. When manufacturing a system containing Ru SS-1 and Ru SS-2, the platinum group components contained in the Reference were reduced by 16% so that they could be manufactured at the same unit cost as the Reference. On the other hand, in this Example, the Reference and the powder of Example 1 were kneaded and performed, but of course, it may be implemented by applying to a substrate in a layered form.

Example 3: Preparation of LNT (Lean NOx Trap) or NA (NOx Adsorption) Catalyst

[0018] The LNT catalyst was prepared in a conventional method to complete the LNT comparative catalyst. The LNT catalyst (LNT Ru SS-3), according to the present disclosure, was prepared by mixing the ruthenium complex (referred to as Ru SS-3) containing La(RuMg)Ox prepared in Example 1 into LNT. Meanwhile, an LNT+w/o Ru(BaSrMgOx) system was prepared by mixing a BaSrMgOx solid solution, which was prepared similarly to Example 1 but did not include Ru, into an LNT comparison catalyst. When manufacturing a system containing Ru SS-3, the platinum group components contained in the Reference were reduced by 16% so that it could be manufactured at the same unit cost as the Reference.

[0019] The following table summarizes the catalyst systems completed in Examples 2 to 3.

TABLE-US-00001 TABLE 1 Catalysts Pt/Pd/Rh % Ru System-1 Reference (Ref.) 100% — (NSR) Ref. + Ru SS-1  84% .circle-solid. Ref. + Ru SS-2  84% .circle-solid. System-2 LNT 100% — (LNT/NA) LNT + w/o Ru 100% — (BaSrMgOx) LNT + Ru SS-3  84% .circle-solid.

[0020] FIG. 3 shows that the NOx conversion rate was tested for the catalysts prepared in Example 2, and it is confirmed that the conversion rate is significantly improved in the NSR catalyst containing the ruthenium complex.

[0021] FIG. 4 shows the catalyst measurement results of Example 3, and according to the results, in the case of a solid solution not containing ruthenium, it can be confirmed that the NOx storage and reduction performance is greatly reduced.

[0022] The present disclosure shows that a ruthenium composite is provided to improve the high temperature durability of Ru, and a composite using ruthenium, which is cheaper than other platinum group elements, can be applied as a part of the catalyst component of NSR, LNT, DOC, and TWC.

[0023] The results of performing worldwide harmonized light vehicles test cycle (WLTC) after engine aging on the catalyst prepared in Example 2 are summarized in FIG. 5.

[0024] It may be seen that the CO oxidation capability and the de-NOx capabilities of the Ru composite, according to the present disclosure, were significantly improved compared to Reference, and thus the Ru composite showed increased durability at a high temperature of engine aging.

[0025] Finally, the volatility of Ru itself in the Ru complex was investigated.

[0026] According to FIG. 6, ICP analysis results are shown after hydrothermal aging at 600 to 850° C. for 25 hours for the powder prepared in Example 1, and the high temperature stability of Ru through Ru complex formation according to the present disclosure may be confirmed.