CATALYST FOR REMOVING NITROGEN OXIDES

Abstract

A catalyst for removing nitrogen includes an LNT catalyst and a Cu/CeO.sub.2 catalyst physically mixed with the LNT catalyst.

Claims

1. A catalyst for removing nitrogen oxides, comprising: a lean NO.sub.x trap (LNT) catalyst; and a Cu/CeO.sub.2 catalyst physically mixed with the LNT catalyst.

2. The catalyst for removing nitrogen oxides of claim 1, wherein a weight ratio of the LNT catalyst and the Cu/CeO.sub.2 catalyst is 1:3 to 3:1.

3. The catalyst for removing nitrogen oxides of claim 1, wherein a Cu content of the Cu/CeO.sub.2 catalyst is 1 to 5 wt %.

4. The catalyst for removing nitrogen oxides of claim 1, wherein the LNT catalyst includes at least one selected from the group consisting of Pt, Ba, and Ce.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a view showing a removal principle of nitrogen oxide in a typical LNT catalyst.

[0018] FIG. 2 is a view showing a method of synthesizing Cu/CeO.sub.2 according to an exemplary embodiment of the present disclosure.

[0019] FIG. 3 is a view showing a structure of a reaction device used in an evaluation of the present disclosure.

[0020] FIG. 4 is a view showing evaluation of a purification performance while differentiating an application method of Cu/CeO.sub.2 to an LNT catalyst.

[0021] FIG. 5 is a view showing a measurement of purification efficiency while varying a Cu content of a mixed Cu/CeO.sub.2 catalyst.

[0022] FIG. 6 is a view showing a measurement of purification efficiency while varying a mixture ratio of an LNT catalyst and Cu/CeO.sub.2.

[0023] FIG. 7 is a view showing a measurement of a NO.sub.x storage speed for various catalyst combinations.

[0024] FIG. 8 is a view showing a measurement of NO oxidation performance for various catalyst combinations.

[0025] FIG. 9 is a view showing a measurement of a H.sub.2 generation amount for various catalyst combinations.

[0026] FIG. 10 is a view showing a measurement of a H.sub.2 generation amount under a lean/rich condition.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Now, an LNT catalyst according to an exemplary embodiment of the present disclosure will be described in detail with reference to accompanying drawings.

[0028] FIG. 1 is a view showing a removal principle of a nitrogen oxide in a typical LNT catalyst. The LNT catalyst is mainly used in a diesel engine vehicle as the NO.sub.x removal catalyst through lean/rich control. In the typical LNT catalyst, NO is oxidized into NO.sub.2 in a lean atmosphere on a noble metal catalyst and stored to a Ba site. Next, stored NO.sub.x in a rich atmosphere is reduced to N.sub.2 by the reaction with reducing agents gases of H.sub.2, CO, and HC.

[0029] However, in a case of a current commercial LNT, NO.sub.x purification performance appears in the temperature range of 250-350 C. However, according to introduction of a real driving emission (RDE), the NO.sub.x purification performance requires introduction of an excellent LNT catalyst at the low temperature (150-200 C.).

[0030] To improve the NO.sub.x purification performance at low temperature, it is necessary to improve both NO.sub.x storage amount and reduction efficiency at low temperatures. Therefore, it is necessary to improve the purification performance by adding a functional material for improving the low temperature NO.sub.x storage and the reduction to the existing LNT catalyst.

[0031] Accordingly, the LNT catalyst according to an exemplary embodiment of the present disclosure improves the low temperature NO.sub.x purification performance by applying a non-noble metal catalyst (Cu/CeO.sub.2) to the present LNT catalyst.

[0032] It is described in detail below.

[0033] The LNT catalyst according to an exemplary embodiment of the present disclosure improves the low temperature purification performance by mixing a non-noble metal catalyst (Cu/CeO.sub.2) with the existing LNT catalyst.

[0034] FIG. 2 is a view showing a method of synthesizing Cu/CeO.sub.2 according to an exemplary embodiment of the present disclosure.

[0035] The Cu/CeO.sub.2 catalyst according to the present disclosure is manufactured by impregnating Cu to the CeO.sub.2 supporting member, and the catalyst is dried at 110 C. for 5 hours or more and then heated for 5 hours while increasing the temperature to 500 C. with a 5 C./min ramping rate in a furnace.

[0036] The manufactured Cu/CeO.sub.2 catalyst is mixed with an LNT catalyst (1 wt % Pt/10 wt % Ba/CeO.sub.2) and the NO.sub.x purification performance is evaluated.

[0037] The NO.sub.x purification performance is evaluated in an experimental condition as shown in Table 1 below by using a reaction apparatus shown in FIG. 3.

TABLE-US-00001 TABLE 1 Lean Rich Duration (min) 12 2 Space velocity (mLg.sub.cat.sup.1h.sup.1 120,000 120,000 NO (ppm) 200 200 O.sub.2 (%) 8 CO (%) 2 H.sub.2O (%) 5 5 Ar Balance Balance

[0038] That is, in a catalyst activation evaluation with the conditions as in Table 1, 0.1 g of a powder type of catalyst is filled in a quartz reaction tube, a 1% H.sub.2/Ar gas is flowed therein, and a pretreatment is performed at 500 C. for 1 hour, and then the lean/rich conditions are repeated, and the NO.sub.x purification performance is evaluated according to the reaction temperature.

[0039] First, the purification performance is evaluated while differentiating the application method of the Cu/CeO.sub.2 method to the LNT catalyst, and a result thereof is shown in FIG. 4.

[0040] Referring to FIG. 4, the performance of the catalyst in which Cu/CeO.sub.2 is physically mixed with the LNT catalyst is excellent compared with a single usage of the LNT catalyst or Cu/CeO.sub.2. Also, as confirmed through FIG. 4, when mixing Cu with the LNT catalyst by a precipitation method, the purification performance is reduced compared to the cases of the physical mixing or the usage alone.

[0041] The purification efficiency is measured while differentiating the Cu content of the mixed Cu/CeO.sub.2 catalyst, and is shown in FIG. 5. Referring to FIG. 5, when the Cu content of Cu/CeO.sub.2 is 1-5 wt %, the improvement of the low temperature performance below 300 C. is effective.

[0042] Also, the purification efficiency is measured while differentiating a mixture ratio of the LNT catalyst and Cu/CeO.sub.2, and the result thereof is shown in FIG. 6. Referring to FIG. 6, the low temperature performance is improved when the mixture ratio of the LNT and Cu/CeO.sub.2 catalyst is a 3:1-1:3 weight ratio range, and particularly the best performance appears at a 1:1 ratio.

[0043] A NO.sub.x purification rate according to the temperature of LNT (1 wt % Pt/10 wt % Ba/CeO.sub.2)+5 wt % Cu/CeO.sub.2 catalyst is measured and shown in Table 2. The total catalyst amount is equally maintained in the experiment conditions of Table 2 below. That is, in each experimental example, the contents of (1) LNT: 100 mg, (2) Cu/CeO.sub.2: 100 mg, (3) LNT-Cu: 100 mg, and (4) LNT+Cu/CeO.sub.2: 50 mg+50 mg are evaluated.

TABLE-US-00002 TABLE 2 NO.sub.x NO.sub.x storage NO.sub.x reduction Temperature conversion efficiency efficiency ( C.) Catalyst (%) (%).sup.a (%).sup.b 150 LNT 11.8 25.6 32.4 Cu/CeO.sub.2 15.9 40.6 30.8 LNT-Cu 17.8 47.6 32.4 LNT + Cu/CeO.sub.2 40.0 61.7 59.4 200 LNT 27.2 33.0 53.9 Cu/CeO.sub.2 21.0 43.6 42.8 LNT-Cu 27.8 52.4 46.9 LNT + Cu/CeO.sub.2 68.0 75.8 85.4 250 LNT 61.8 64.5 88.8 Cu/CeO.sub.2 38.7 59.3 68.4 LNT-Cu 37.9 62.7 55.7 LNT + Cu/CeO.sub.2 82.1 85.7 93.6 300 LNT 68.5 76.0 91.2 Cu/CeO.sub.2 49.0 59.0 75.5 LNT-Cu 35.1 63.2 51.3 LNT + Cu/CeO.sub.2 88.2 92.9 94.1 350 LNT 74.9 86.9 90.1 Cu/CeO.sub.2 42.4 53.0 70.9 LNT-Cu 33.1 61.6 49.2 LNT + Cu/CeO.sub.2 91.3 93.5 96.4 [00001]${}^a.Math.\frac{{\mathrm{NOx}}^{\mathrm{stored}}}{{\left({\mathrm{NO}}^{i.Math..Math.n}\right)}_{\mathrm{Lean}}}100.Math..Math.\%$[00002]${}^b.Math.\frac{{\mathrm{NOx}}^{\mathrm{reduced}}}{{\mathrm{NOx}}^{\mathrm{to}.Math..Math.\mathrm{be}.Math..Math.\mathrm{reduced}}}100.Math.\%=\frac{\left[{\mathrm{NOx}}^{\mathrm{stored}}+{\left({\mathrm{NO}}^{i.Math..Math.n}\right)}_{\mathrm{Rich}}\right]-{\left({\mathrm{NOx}}^{\mathrm{out}}\right)}_{\mathrm{Rich}}}{{\mathrm{NOx}}^{\mathrm{stored}}+{\mathrm{NO}}_{\mathrm{Rich}}^{i.Math..Math.n}}100.Math.\%$

[0044] The following contents may be confirmed through Table 2. When evaluating the NO.sub.x purification efficiency by mixing the LNT+Cu/CeO.sub.2 catalyst at 1:1, the NO.sub.x storing amount and the reduction efficiency compared to the LNT catalyst is greatly improved in the 150-350 C. temperature range.

[0045] In addition, when Cu/CeO.sub.2 alone is used, the purification efficiency is low, and the LNT and Cu/CeO.sub.2 catalyst have to be mixed with each other to be effective.

[0046] In addition, when the LNT is manufactured by adding Cu by the precipitation method (LNT-Cu), the NO.sub.x purification efficiency was not improved due to a Pt-Cu alloy, the amount of the noble metal used in LNT+Cu/CeO.sub.2 is about 50% compared with that of the LNT catalyst, and it may be confirmed that the NO.sub.x purification performance is even better when the small amount of the noble metal is used.

[0047] Hereinafter, various performances of the LNT Cu/CeO.sub.2 catalyst are measured. FIG. 7 is a view showing a measurement of a NO.sub.x storage speed for various catalyst combinations. Referring to FIG. 7, it may be confirmed that an initial NO.sub.x storing speed of the catalyst in which the LNT+Cu/CeO.sub.2 are physically mixed is high compared with other cases.

[0048] FIG. 8 is a view showing a measurement of NO oxidation performance for various catalyst combinations. Referring to FIG. 8, it may be confirmed that the NO oxidation performance is increased when the Cu/CeO.sub.2 is mixed compared with the LNT catalyst. Therefore, the amount of low temperature NO.sub.x storage may be increased.

[0049] FIG. 9 is a view showing a measurement of a H2 generation amount for various catalyst combinations. H.sub.2 is generated by a following reaction formula.

Water Gas Shift Reaction: CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2

[0050] Through FIG. 9, it is confirmed that the H.sub.2 generation amount is increased in the Cu/CeO.sub.2 addition catalyst during the CO.sub.2/H.sub.2O injection.

[0051] FIG. 10 is a view showing a measurement of a H.sub.2 generation amount in a lean/rich condition. Referring to FIG. 10, when being evaluated in an exhaust gas simulation condition, the H.sub.2 generation amount is increased in the Cu/CeO.sub.2 addition catalyst in the rich period. The H.sub.2 gas is an excellent reducing agent for the low temperature NO.sub.x reduction, and it is predicted that the low temperature NO.sub.x purification rate would be excellent in the Cu/CeO.sub.2 addition catalyst because it is effective for improving the low temperature performance.

[0052] As described above, the catalyst according to the present disclosure improves the low temperature purification performance of nitrogen oxide by physically mixing the LNT catalyst and the Cu/CeO.sub.2 catalyst.

[0053] While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.