WO2009057959A2

WO2009057959A2 - A catalyst for treating exhaust gas of natural gas vehicles

Info

Publication number: WO2009057959A2
Application number: PCT/KR2008/006408
Authority: WO
Inventors: Seongho Lee; Hong-Seok Jung; Yong-Woo Kim; Seung-Hoon Oh
Original assignee: Sk Energy Co., Ltd.
Priority date: 2007-10-31
Filing date: 2008-10-30
Publication date: 2009-05-07
Also published as: CN101842561B; WO2009057959A3; KR100908049B1; MY171117A; KR20090044268A; CN101842561A

Abstract

The present invention relates to a catalyst for treating exhaust gas of natural gas vehicles, which can efficiently remove methane as a main ingredient contained in the exhaust gas. The catalyst for treating exhaust gas of natural gas vehicles has the excellent methane oxidation activity and also maintains the excellent catalytic activity even after the hydro thermal aging.

Description

[DESCRIPTION] [invention Title]

A CATALYST FOR TREATING EXHAUST GAS OF NATURAL GAS VEHICLES

[Technical Field]

The present invention relates to a catalyst for treating exhaust gas of natural gas vehicles, and more particularly, to a catalyst for treating exhaust gas, which can efficiently remove methane as a main ingredient contained in the exhaust gas of natural gas vehicles .

[Background Art]

A natural gas vehicle can be classified into a CNG type and an LNG type according to a fuel supply system. The CNG type uses gas compressed at a pressure of about 200 atmospheres and stored in a high-pressure vessel, and the LNG type uses cryogenic fuel having a temperature of approximately

-1301C. CNG (compressed natural gas) broadly means gas afforded from the depth of the ground, and typically inflammable gas containing hydrocarbon as a main ingredient . The CNG can be classified into oil field gas afforded from an oil field, coal field gas afforded from a coal field and water-soluble gas that exists in a dissolved state in water regardless of the genesis of coal and oil. The coal field gas and the water- soluble gas has methane as a main ingredient and also contains carbon dioxide, oxygen, nitrogen and the like, but since they can not be liquefied at room temperature under a high pressure, they are called as dry gas. The oil field gas contains propane, butane and the like as well as methane and since it can be liquefied at room temperature under a high pressure, it is called as wet gas. In case that CNG is used as fuel for vehicles, it can provide low cost and excellent economical efficiency, and also since it is mixed with air and then injected into a cylinder in mixed gas state, it can be maintained in a uniform status and thus completely burnt in an optimal fuel-air mixing ratio, thereby increasing combustion efficiency. Further, a CNG engine is very silent, and the CNG has a lower combustion speed than a gasoline engine and also has a high octane number, and thus it is free from knocking phenomenon .

Further, the CNG engine has excellent economical efficiency and also has advantages in the points of a high fuel efficiency, an engine oil injection ratio and a life span of engine and the like, compared with a gasoline engine. Since CNG has a low boiling point, it can be completely burnt in the cylinder so that oil is prevented from being washy and also carbon is hardly generated. Further, since an additive is not used, it is prevented that oil is contaminated with carbon or ashes, and also since CNG hardly contains a sulfur ingredient, metal corrosion phenomenon does not occur. Therefore, the CNG engine rarely causes air pollution and thus is hygienic, and also since the exhaust gas contains very little toxic CO, it hardly has smell and smoke.

However, these advantages of the natural gas vehicle are offset by exhausting unburned methane. The methane is a potential greenhouse gas having a long life span and shows a higher greenhouse effect than carbon dioxide. Due to environmental impact of the methane exhausted from the natural gas vehicle, it is expected that the emission regulation will be proposed sooner or later, and about 60% of the methane which is exhausted in the existing state of the natural gas vehicle should be treated by a low temperature post-treating apparatus and the like in order to conform with the strongest European regulation.

In addition, a product of a burning reaction of methane is carbon dioxide and water. It is known that carbon dioxide hardly exerts an effect on the reaction. But the water has an effect on activity of palladium impregnated in various supports such as alumina, zirconia and silica. Therefore, it is necessary to develop a catalyst for efficiently removing the methane contained in the exhaust gas of the natural gas vehicle, and also a catalyst for efficiently removing the methane with high catalytic activity, even though it is exposed to moisture or exposed to moisture under a high temperature .

[Disclosure] [Technical Problem]

An object of the present invention is to provide a catalyst for treating exhaust gas of natural gas vehicles, which can efficiently remove methane contained in the exhaust gas of the natural gas vehicles.

Another object of the present invention is to provide a catalyst for treating exhaust gas of natural gas vehicles, which has high methane removing performance and excellent catalytic activity even though it is exposed to moisture as a product of the methane oxidation reaction.

[Technical Solution] From a result of repeated studies to achieve the above objects, the inventors had found that, if one or more cocatalytic ingredients selected from cobalt and manganese are further used along with a palladium catalytic ingredient, the methane removing efficiency is improved and also high catalytic activity can be maintained even when a catalyst is exposed to moisture.

Therefore, the present invention provides a catalyst for treating exhaust gas of natural gas vehicles, in which one or more cocatalytic ingredients selected from cobalt and manganese are impregnated along with a palladium ingredient.

Hereinafter, the present invention will be described fully.

The present invention provides a catalyst for treating exhaust gas of natural gas vehicles, in which palladium (Pd) , and one or more cocatalysts selected from manganese (Mn) and cobalt (Co) are impregnated as catalyst active ingredients. A weight ratio of the palladium and cocatalyst is preferably 1:0.1-10, more preferably, 1:0.1-1. If the weight ratio of the cocatalytic ingredient with respect to palladium is larger than 10, the catalytic activity is deteriorated, and thus it is most preferable that the weight ratio of the cocatalytic ingredient is less than 1 in the aspect of catalytic activity. Further, moisture is generated as a reaction product during a process of oxidizing methane as a main ingredient of the exhaust gas in the natural gas vehicle. In case of a catalyst containing only palladium, if the catalyst is exposed to the moisture and a high temperature, its catalytic activity is remarkably reduced. The cocatalyst of the present invention functions to prevent the catalytic activity from being deteriorated even after hydro thermal aging. In case that a weight ratio of the cocatalytic ingredient with respect to the palladium is less than 0.1, the effect of preventing catalytic activity deterioration after the hydro thermal aging may be insignificant .

In case that cobalt (Co) is used as the cocatalyst, it is more preferable that a weight ratio of Pd: Co is 1:0.2-1, and in case that manganese (Mn) is used as the cocatalyst, it is more preferable that a weight ratio of Pd: Mn is 1:0.1-0.5. When the weight ratio of the cocatalyst is controlled within the above extent, it is possible to provide high methane oxidation activity in the fresh state and also provide excellent catalytic activity even under the condition of the hydro thermal aging.

The catalyst for treating exhaust gas of natural gas vehicles according to the present invention has a ceramic substrate on which a support and a catalytic active material are deposited. The ceramic substrate may have a honeycomb monolith structure formed of a heat-resistant ceramic material like cordierite. The support may include alumina, zirconia, silica, ceria and a mixture thereof. In the aspect of catalytic activity, it is preferable that the support is formed of alumina, or a mixture of alumina and one or more selected from zirconia, silica or ceria.

Preferably, an amount of the support washcoated on the ceramic substrate is 0.5 ~ 4g/in³. If the amount of the support is less than 0.5g/in³, catalyst performance is significantly deteriorated, and if the amount of the support is larger than 4g/in³, the catalyst performance is enhanced any more and also it is not facile to manufacture it.

Further, in the present invention, a content of the catalytic active material impregnated in the catalyst is in an extent of 0.1 ~ 20 weight% with respect to total weight of the support and the catalytic activation material. If the content is less than 0.1 weight%, catalyst performance is significantly deteriorated, and if the content is larger than

20 weight%, the catalyst performance is enhanced any more and it is disadvantage in the economical point of view.

According to the present invention, after the support is wash-coated on the substrate, the catalytic active material may be impregnated in the wash-coated substrate. Alternatively, after the catalytic active material is impregnated in the support, the support impregnating the catalytic active material may be wash-coated on the substrate.

The catalyst for treating exhaust gas of natural gas vehicle can be manufactured by a method comprising the steps of: preparing a wash-coated substrate by wash-coating a support selected from alumina, zirconia, silica, ceria and a mixture thereof on a ceramic substrate and then drying and calcining the ceramic substrate; and impregnating catalyst active ingredients by immerging the wash-coated substrate in a catalytic solution comprising palladium (Pd) , and one or more cocatalysts selected from manganese (Mn) and cobalt (Co) , and then drying and calcining the wash-coated ceramic substrate. The palladium (Pd) precursor used for preparing the catalytic solution includes palladium nitrate, palladium chloride, tetraamminepalladium chloride, and the like. The cobalt (Co) precursor includes cobalt nitrate, cobalt chloride and the like, and the manganese (Mn) precursor includes manganese nitrate, manganese chloride and the like.

The wash- coating of the support on the substrate, and the drying and calcining can be performed by typical methods in the art .

[Advantageous Effects]

The catalyst for treating exhaust gas of natural gas vehicles according to the present invention has the excellent methane oxidation activity and also maintains the excellent catalytic activity even after the hydro thermal aging. [Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 is a graph showing an evaluation result of activity of a methane oxidation catalyst impregnating Pd and Co as catalyst active ingredients.

Fig. 2 is a graph showing an evaluation result of activity of a methane oxidation catalyst impregnating Pd and Mn as catalyst active ingredients.

Fig. 3 is graph showing an evaluation result of catalytic activity after hydro thermal aging.

[Best Mode]

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings .

[Embodiments 1 to 4] Manufacturing of catalyst impregnating Pd and Co

Gamma alumina powder (SASOL, German, surface area:

210m²/gr, pore volume: 0.5cc/gr, specific gravity: 0.8g/cc) is mixed with a mixed solution of acetic acid and distilled water

(weight ratio of 1:3.5), and then uniform alumina slurry is prepared by grinding it using a wet ball mill for 12hours. A content of the gamma alumina powder in the slurry is 50 weight%, and an average particle size of the ground gamma alumina powder is 3/^n. Cordierite honeycomb monolith (lin³, 400 cpsi) is wash- coated with the alumina slurry so that an amount of the alumina washcoated is 2g/in³, dried for 2 hours at a temperature of 120 "C and then calcined for three hours at a temperature of 550^°C, thereby manufacturing the honeycomb monolith washcoated with alumina.

Catalytic solutions of 8Og are respectively prepared by dissolving Pd (NO₃ )₂ aqueous solution (10 weight%) as the Pd precursor and CO(NO_B)₂ ¹GH₂O as the Co precursor in distilled water so as to have each content as indicated in Table 1. And, the honeycomb monolith coated with alumina is immerged in each catalytic solution for 1 minute and then treated by air- blowing so as to remove residual solution. Then, the honeycomb monolith is dried for 2 hours at a temperature of 120^°C under atmospheric pressure and then calcined for four hours at a temperature of 600^°C, thereby manufacturing a catalyst impregnating Pd and Co.

[Embodiments 5 to 9] Manufacturing of catalyst impregnating Pd and Mn a catalyst impregnating Pd and Mn is prepared in the same way as the embodiment 1 except that catalytic solutions are respectively prepared by dissolving Pd (NO₃ )₂ aqueous solution (10 weight%) as the Pd precursor and Mn(NO₃) ₂-xH₂O (FW 178.95) as the Mn precursor in distilled water so as to have each content as indicated in Table 1.

[Comparative embodiments 1 to 2] Manufacturing of catalyst impregnating Pd and Mn

A catalyst is manufactured in the same way as the embodiment 7 except that Pd(NO₃) ₂ aqueous solution (10 weight%) is used as the Pd precursor.

Table 1

a: A content of a catalytic ingredient in a catalytic solution

[Test example 1] Evaluation of fresh catalytic activity The honeycomb monolith catalysts manufactured in the comparative embodiments 1 and 2 and the embodiments 1 to 8 are fixed in a catalyst reactor, and then methane (CH₄) oxidation experiment is performed.

Model gases having compositions as indicated in Table 2 are mixed in a controlled flow rate using MFC (mass flow controller) and then injected into the catalyst reactor. The flow rate of the model gases is 13.6 1/min and a space velocity is GHSV 50,00OhLr^"1. A thermocouple is provided at internal upper and lower sides of the catalyst reactor so as to control and measure a temperature, and a reaction temperature is in an extent of 150 ~ 600^°C, and a temperature is increased in stages at a heating rate of 5^°C/min, and then the catalytic activity is checked. Each concentration of NO, CO, CH₄ reaction gases after/before the reaction is detected through a gas analyzer. Table 2

Fig. 1 is a graph showing an evaluation result of activity of a methane oxidation catalyst impregnating only Pd of the comparative embodiments 1 and 2, and impregnating Pd and Co of the embodiments 1 to 4.

Referring to the result of Fig. 1, the catalyst in the embodiment 1 in which a weight ratio of Pd and Co is 1:2 has lower catalytic activity than the catalyst impregnating only Pd, but has higher catalytic activity than the catalysts in the embodiments 2 to 4. And the catalyst in the comparative embodiment 2 (2PA) has the excellent methane oxidation activity, but the catalyst in the embodiment 3 in which the weight ratio of Pd and Co is 1:0.5 has the most excellent catalytic activity in the view of a impregnating amount of Pd.

Fig. 2 is a graph showing an evaluation result of activity of a methane oxidation catalyst impregnating only Pd of the comparative embodiments 1 and 2, and impregnating Pd and Mn of the embodiments 5 to 8.

Referring to the result of Fig. 2, the catalyst in the embodiment 5 in which a weight ratio of Pd and Mn is 1:2 has lower catalytic activity than the catalyst impregnating only Pd, but the catalysts in the embodiments 6 to 8 has the excellent catalytic activity. And the catalyst in the comparative embodiment 2 (2PA) has the excellent methane oxidation activity, but the catalyst (PMA4) in the embodiment 8 in which the weight ratio of Pd and Mn is 1:0.2 has the most excellent catalytic activity in the view of a impregnating amount of Pd.

[Test example 2] Evaluation of catalytic activity after hydro thermal aging The methane oxidation performance of each catalyst of the comparative embodiments 1 and 2 and the embodiments 3 and 8 is evaluated in the same way as the test example 1 after hydrothermal aging (800^°C, 10%H₂O, 24 hours), and the result is illustrated in Fig. 3 From the results of Fig. 3, it can be understood that the catalysts impregnating only Pd in the comparative embodiments KlPA) and 2 (2PA) has the considerably deteriorated methane oxidation activity after the hydro thermal aging, and the catalysts in the embodiments 3 (PCA3) and 8 (PMA4) has the excellent methane removing efficiency.

Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for impregnating out the same purposes of the present invention. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims. [industrial Applicability]

The catalyst for treating exhaust gas of diesel LNG dual fuel vehicles according to the present invention has the excellent methane oxidation activity and also maintains the excellent catalytic activity even after the hydro thermal aging.

Claims

[CLAIMS!

[Claim l]

A catalyst for treating exhaust gas of natural gas vehicles, wherein palladium (Pd), and one or more cocatalysts selected from manganese (Mn) and cobalt (Co) are impregnated as catalyst active ingredients.

[Claim 2]

The catalyst according to claim 1, wherein a weight ratio of Pd and cocatalyst is 1:0.1-10.

[Claim 3]

The catalyst according to claim 2, wherein the weight ratio of Pd and cocatalyst is 1:0.1-1.

[Claim 4]

The catalyst according to claim 3, wherein a weight ratio of Pd and Co is 1:0.2-1.

[Claim 5]

The catalyst according to claim 3, wherein the weight ratio of Pd and Mn is 1:0.1-0.5.

[Claim 6] The catalyst according to claim 2, wherein the catalyst has a ceramic substrate on which a support selected from alumina, zirconia, silica, ceria and a mixture thereof, and a catalyst active ingredient are deposited. [Claim 7] The catalyst according to claim 6, wherein the catalyst for treating exhaust gas of natural gas vehicles can be manufactured by a method comprising the steps of: preparing a wash- coated substrate by wash- coating a support selected from alumina, zirconia, silica, ceria and a mixture thereof on a ceramic substrate and then drying and calcining the ceramic substrate,- and impregnating catalyst active ingredients by immerging the wash-coated substrate in a catalytic solution comprising palladium (Pd) , and one or more additive catalysts selected from manganese (Mn) and cobalt (Co) , and then drying and calcining the wash-coated ceramic substrate.