KR20210041998A - Low-temperature de-NOx catalyst using ceria-alumina complex support and manufacturing method thereof - Google Patents

Abstract

The present invention discloses a low-temperature de-NOx catalyst using a ceria-alumina composite support and a method for manufacturing the same. According to the present invention, provided is a low-temperature de-NOx catalyst using a ceria-alumina composite support, manufactured by impregnating a noble metal and a metal oxide in a ceria-alumina composite support synthesized by treating a ceria precursor and an alumina precursor in a predetermined mass ratio through a co-precipitation method.

Description

TECHNICAL FIELD [0001] Low-temperature de-NOx catalyst using ceria-alumina complex support and manufacturing method thereof.

The present invention relates to a low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support and a method for preparing the same, and more particularly, an optimum of a ceria-alumina composite support used for NOx removal at a low temperature of 200 °C or less. It relates to the synthesis method and, in addition, to the optimal synthesis method of precious metals and metal oxides.

With the application of high fuel efficiency technology (lean combustion engine) to reduce the fuel consumption of automobiles, it is difficult to remove NOx, which is one of the harmful substances in exhaust gas.

This is because the amount of air introduced during combustion increases, and the amount of NOx produced itself increases, and the temperature of the exhaust gas is lowered, which is not suitable for the activation temperature of the existing catalyst.

In addition, in order to keep pace with accelerating environmental regulations, it is important to secure the NOx removal capability in the'cold-start' section.

According to the survey, it can be confirmed that the amount of NOx discharged from the cold start section is greater than the amount of NOx discharged during normal driving. The cold start section refers to the initial stage of start-up and refers to a driving condition in which the temperature of the exhaust gas purification device is insufficient.

In order to improve this problem, the development of a catalyst capable of efficiently removing NOx at a low temperature, specifically below 200 °C, and an adsorption and removal factor are being sought.

Existing Lean NOx Trap (LNT) is a carrier made of porous materials such as alumina, metal oxides using adsorption-active materials such as barium oxide, and precious metals that are responsible for NOx oxidation or reduction catalysts such as platinum, It consists of 3 parts.

However, in order to enhance the NOx removal efficiency above, it is necessary to be able to remove NOx even under low temperature conditions, and lowering the desorption temperature as well as enhancing the adsorption capacity for NOx at low temperatures is an important improvement direction.

If the adsorption capacity for NOx at low temperature is low, NOx slip phenomenon occurs frequently below the catalytic activity temperature, and the very high desorption temperature is another disadvantage of the existing LNT catalyst, which is disadvantageous in regeneration during low temperature operation. Therefore, by introducing various kinds of elements, the performance is improved. Among them, the introduction of ceria with excellent oxygen storage capacity (OSC) helps to oxidize nitrogen monoxide, thereby increasing the NOx storage performance. It has excellent redox properties and is advantageous when reducing stored NOx.

According to the prior art, ceria was additionally supported on an inorganic carrier and used, or ceria was physically mixed with other inorganic oxides such as alumina, silica, or zirconia with high thermal stability.

Ceria is an inorganic oxide having a high surface area, and can serve as a support by itself, but since its thermal stability is not high, it is not suitable to be used alone as a support for automobile exhaust gas purification catalysts.

According to the paper on the surface area depending on the firing temperature of ceria, the surface area of about 130 m ² /g was maintained when fired at 600 °C, and the surface area continued to decrease at higher temperatures, and the surface area was 46 m when fired at 800 °C. ² /g was recorded [M. Eberhardt et al., Topics in Catalysis 30-31 (2004) 135].

Conventionally, there are cases in which ceria is additionally impregnated with a noble metal, barium oxide, etc. in an inorganic carrier, but when the carrier is impregnated with a certain level or more, the surface area characteristics of the catalyst decrease, and the adsorption performance of the catalyst may decrease.

Korean Patent Registration 10-1621110

In order to solve the above problems of the prior art, the present invention is a ceria-alumina composite that can improve the thermal stability of the carrier and increase the oxygen storage capacity and oxidation-reduction ability of ceria when an inorganic carrier and ceria are mixed and used. To propose a low-temperature nitrogen oxide removal catalyst using a support and a method for producing the same.

In order to achieve the above object, according to an embodiment of the present invention, as a low-temperature nitrogen oxide removal catalyst, a ceria precursor and an alumina precursor are treated by a coprecipitation method at a preset mass ratio to obtain a ceria-alumina composite support. A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support prepared by impregnating a noble metal and a metal oxide is provided.

The ceria precursor may include one of cerium chloride (CeCl ₃ ), cerium sulfate (Ce(SO ₄ ) ₂ ) and cerium nitrate hydrate (Ce(NO ₃ ) ₃ 6H ₂ O).

The alumina precursor may include one of aluminum chloride (AlCl ₃ ), aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) and aluminum nitrate hydrate (Al(NO ₃ )9H ₂ O).

The mass ratio of the ceria precursor and the alumina precursor may be 1:3 to 1:5.

The ceria-alumina composite carrier may be synthesized by dissolving the alumina precursor and then introducing the ceria precursor after a predetermined time elapses and dissolving for a predetermined time again.

The ceria-alumina composite support may be synthesized by stirring, washing, filtering, and sintering at a preset temperature to obtain a precipitate through pH adjustment after the dissolution.

The noble metal includes at least one of platinum, palladium, rhodium, and iridium, and the metal oxide includes an oxide including at least one of magnesium, calcium, strontium, barium, sodium, potassium, rubidium, cesium, iron, and copper. I can.

After the precursor of the noble metal is first impregnated with the ceria-alumina composite carrier and dried, the precursor of the metal oxide may be impregnated and fired.

The precursor of the noble metal includes (NH ₄ ) ₂ PtCl ₄ , and the precursor of the metal oxide is a copper oxide precursor of copper nitrate hydrate (Cu(NO ₃ ) ₂ ·3H2O) and a barium oxide precursor of barium acetate ((CH ₃ COO) ₂ Ba).

The mass ratio of the precursor of the copper oxide and the barium oxide may be 1:1.

According to another aspect of the present invention, as a method for preparing a catalyst for removing nitrogen oxides at a low temperature, after dissolving the alumina precursor in distilled water, after a preset time elapses, the ceria precursor is introduced and dissolved again for a preset time, and through pH adjustment. Obtaining a precipitate and preparing a ceria-alumina composite carrier through drying, washing, filtering, and firing; Impregnating a noble metal precursor into the ceria-alumina composite carrier; And impregnating at least one metal into the ceria-alumina composite carrier impregnated with the noble metal using one or more metal oxide precursors through co-impregnation. A method is provided.

According to the present invention, ceria can have a relatively high surface area even at a high temperature by synthesizing ceria with alumina by a coprecipitation method, and it is possible to simultaneously increase the oxygen storage capacity and oxidation-reduction capacity of ceria.

In addition, according to the present invention, since ceria exists as a carrier, it is possible to avoid deterioration in performance of surface area characteristics through impregnation.

Furthermore, the catalyst is synthesized by co-impregnating the ceria-alumina composite support formed through the co-precipitation method with additional precious metals and metal oxides, thereby increasing the adsorption capacity of NOx compared to the existing LNT catalyst and lowering the desorption temperature. There is this.

1 is a view showing a synthesis process of a ceria-alumina composite carrier according to the present embodiment.
Figure 2 shows the results of the _{H 2} -TPR experiment from 50 °C to 600 °C.
3 shows the gas composition change under conditions in which nitrogen monoxide and oxygen coexist from 50 °C to 600 °C in order to evaluate the nitrogen monoxide oxidation ability.
4 is a diagram showing comparison of NOx storage efficiency according to temperature of two catalysts through the above calculation method.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

According to a preferred embodiment of the present invention, a ceria-alumina composite carrier is synthesized through a coprecipitation method instead of impregnating ceria into alumina.

The co-precipitation method is a treatment method in which a precipitate precursor containing metal ions is uniformly precipitated at the same time.

1 is a view showing a synthesis process of a ceria-alumina composite carrier according to the present embodiment.

Referring to FIG. 1, the ceria precursor and the alumina precursor are dissolved in a solvent in a predetermined order (step 100).

As a precursor of ceria, cerium chloride (CeCl ₃ ), cerium sulfate (Ce(SO ₄ ) ₂ ), cerium nitrate hydrate (Ce(NO ₃ ) ₃ 6H ₂ O) may be used, and cerium nitrate hydrate is preferably used. I can.

As a precursor of alumina, aluminum chloride (AlCl ₃ ), aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), aluminum nitrate hydrate (Al(NO ₃ )9H ₂ O), etc. may be used, and preferably aluminum nitrate hydrate is used. I can.

In step 100, the ceria precursor and the alumina precursor are dissolved in a preset mass ratio.

The mass ratio of the ceria precursor and the alumina precursor is a variable that can affect surface area properties and catalyst properties.

According to this embodiment, the mass ratio of the alumina precursor and the ceria precursor may be 1:1 to 9:1, preferably 4:1 to 5:1, and more preferably 4:1.

When performing the co-precipitation method, the dissolution sequence and dissolution time of the ceria precursor and the alumina precursor introduced into distilled water may be considered as factors that may affect the surface area characteristics of the composite carrier.

The alumina precursor may be dissolved after the ceria precursor is first dissolved, or the ceria precursor may be dissolved after the alumina precursor is first dissolved, and the precursor may be introduced into distilled water at the same time.

According to this preferred embodiment, a method of dissolving the alumina precursor and then introducing the ceria precursor after a preset time has elapsed (for example, after 3 hours) and dissolving the alumina precursor for a preset time is used.

Table 1 shows the BET surface area (m ² /g), pore volume, and pore diameter of _{Al 2} O ₃ and CeO ₂ according to the present embodiment.

BET surface area
(m ² /g) Pore volume
(cm ³ /g) Pore diameter
(nm) Al ₂ O ₃ 294 0.26 5.6 Al1Ce1 204 0.29 4.6 Al2Ce1 212 0.27 5.5 Al4Ce1 299 0.20 5.8 Al9Ce1 271 0.18 5.4 Ce1Al2 239 0.16 3.6 Ce1Al4 204 0.22 4.2 Ce1Al2(co) 190 0.16 3.8 CeO ₂ 55 0.10 4.6

Referring to Table 1, in the case of dissolving the alumina precursor first and dissolving the ceria precursor, in the experiment in which the mass ratio of the alumina and the ceria precursor was changed to 1:1, 2:1, 4:1 and 9:1, 4: In the case of 1, it can be seen that the BET surface area is the largest. In addition, looking at the case where the mass ratio of the alumina and the ceria precursor is 4:1 in the precipitation sequence, when the alumina precursor is first dissolved and the ceria precursor is dissolved (Al4Ce1), the BET surface area is more than the reverse case (Ce1Al4). You can see a big one.

In order to obtain a precipitate from the alumina precursor and the ceria precursor, the pH is adjusted with NaOH and stirring is performed (step 102).

In step 102, the pH required to obtain a precipitate from each precursor is determined in the range of 10.0 to 11.0, and the stirring speed is maintained at 300 rpm.

After the stirring is completed, a precipitate is obtained through washing and filtering (step 102).

In step 104, even when washing and filtering are performed, agitation is performed at 300 rpm to prevent the filtering speed from being slowed down by the precipitate as much as possible.

After sufficiently washing proceeds, a precipitate is obtained through filtering without stirring.

The precipitate is dried in an oven at 110 °C for 12 hours to remove moisture (step 106).

In order to activate the dried precipitate into a ceria-alumina composite carrier, firing is performed (step 108).

The activation firing temperature of the composite carrier according to the present embodiment may be 600 °C and proceeds for 4 hours.

The firing atmosphere is a factor that can change the surface area characteristics. Gas flowing during firing may be selected from nitrogen, argon, carbon dioxide, air, and the like, and firing is preferably carried out in an air atmosphere.

Precious metal and metal oxide impregnation

Precious metals and metal oxides were impregnated using the ceria-alumina composite carrier synthesized by the above method.

The impregnation of precious metals and metal oxides uses continuous impregnation and co-impregnation methods.

Platinum, palladium, rhodium, iridium, and the like may be used as the noble metal, preferably platinum, and (NH ₄ ) ₂ PtCl ₄ as a platinum precursor.

Metal oxides were used to store NOx, and magnesium, calcium, strontium, barium, sodium, potassium, rubidium, cesium, iron, copper, and the like may be used, preferably barium and copper oxides.

_{Table 2 below shows the NO 2} adsorption ability when the ceria-alumina composite carrier is synthesized, the sedimentation sequence is performed at different mass ratios in the order of alumina and ceria, and then impregnated with platinum and barium.

Adsorption capacity
(mmol/g) Pt2-Ba20-Al 0.99 Pt2-Ba20-Al2Ce1 0.83 Pt2-Ba20-Al4Ce1 1.04 Pt2-Ba20-Al9Ce1 0.90

Table 2 shows the adsorption capacity of the synthesized catalyst to NOx by impregnating the support with Pt and Ba corresponding to the LNT catalyst after synthesizing a support having the same precipitation sequence and different ratios of Al and Ce. Referring to Table 3, _{when comparing the adsorption capacity when flowing a gas of 10% NO 2} /He balance composition, when the mass ratio of alumina and ceria precursor was 4:1, the adsorption capacity was the highest compared to other mass ratios. I can confirm.

Barium and copper oxide precursors are barium acetate ((CH ₃ COO) ₂ Ba) and copper nitrate hydrate (Cu(NO ₃ ) ₂ ·3H ₂ O), respectively.

The mass of each precursor is a variable that can affect catalyst properties, and the precious metal can be adjusted to 0.5, 1, 2 wt%, etc. based on the mass of the total catalyst, and preferably 2 wt%.

The metal oxide can be adjusted to 5, 10, 20 wt%, etc. of the total mass of the catalyst, and preferably 20 wt%.

The mass ratio of the precursor of the copper oxide and the barium oxide can be adjusted to 2:1, 1:1, 1:2, and preferably 1:1.

The copper oxide and barium oxide precursors were dispersed and impregnated together or individually in 1.5 mL or 1.2 mL of distilled water, and this sequence may affect the catalyst properties. Preferably, the platinum precursor was impregnated first, followed by successive copper and barium oxide. The precursor was co-impregnated.

Specifically, after dispersing the platinum precursor in 1.5 mL of distilled water, impregnating 1 g of ceria-alumina composite support at 0.25 mL increments, drying at 110 °C was repeated 6 times, and then dried at 110 °C for 12 hours, Next, the copper and barium oxide precursors were dispersed in 1.2 mL of distilled water, co-impregnated with 0.2 mL each of the same ceria-alumina composite carrier, and dried 6 times, followed by drying at 110 °C for 12 hours.

The catalyst after impregnation was completed was calcined for activation, and proceeded at 600 °C for 2 hours. The calcination atmosphere may be selected from nitrogen, argon, carbon dioxide, air, etc. as variables that can affect catalyst properties, and sintering was preferably performed under an air atmosphere.

Catalyst property evaluation

In order to compare the activity of the catalysts, a reduction experiment (H ₂ -TPR) according to the elevated temperature using hydrogen was conducted.

The nomenclature of the catalyst is divided into three parts: noble metal catalyst, metal oxide, and support. When the metal oxide part and the support part consist of two or more, each element is marked with a dash (-).

2 is a result of _{H 2} -TPR experiment from 50 °C to 600 °C. The initial reduction of the Pt/Ba/Al catalyst corresponding to the existing LNT material recorded the highest point at 218 °C, and the higher reduction recorded the highest point at 514 °C, and it was confirmed that the degree of reduction at high temperatures was greater.

The initial reduction of the Pt/Ba/Al-Ce catalyst in which the carrier was replaced with a ceria-alumina composite carrier reached a peak at 176 °C and higher reduction was observed around 450 °C. Compared with Pt/Ba/Al, the amount of reduction at low temperature increases and the reduction start temperature is lower.

_{Finally, looking at the H 2} -TPR of the Pt/Cu-Ba/Al-Ce catalyst, the reduction temperature at low temperature was the lowest among the three catalysts and the largest size. Therefore, it can be seen that the catalyst having the highest activity at low temperature is Pt/Cu-Ba/Al-Ce.

In particular, the Pt/Cu-Ba/Al-Ce catalyst shows the highest point in the amount of reduction near 200 °C, so it can be confirmed that its utilization is high for NOx removal at low temperatures below 200 °C.

In order to measure the specific surface area of the support and the catalyst, nitrogen adsorption analysis was performed, and the results are shown in Table 3.

Support and catalyst Specific surface area
(m ² /g) Pore volume
(cm ³ /g) Al 294 0.25 Al-Ce 289 0.23 Pt/Ba/Al 197 0.11 Pt/Cu-Ba/Al-Ce 163 0.16

Referring to Table 3, the specific surface area and pore volume of the alumina carrier and the ceria-alumina composite carrier were not significantly different. However, after impregnation of the catalyst and metal oxide, it can be seen that the specific surface area and pore volume of both catalysts are greatly reduced. Through this, it can be seen that the surface area characteristics are reduced as the carrier is impregnated.

3 shows the gas composition change under conditions in which nitrogen monoxide and oxygen coexist from 50 °C to 600 °C in order to evaluate the nitrogen monoxide oxidation ability.

3A shows a change in gas composition through temperature increase after adsorption of nitrogen monoxide for Pt/Ba/Al, FIG. 3B for Pt/Ba/Al-Ce, and FIG. 3C for Pt/Cu-Ba/Al-Ce.

Since barium oxide has a higher affinity for nitrogen dioxide than for nitrogen monoxide, the oxidizing ability for nitrogen monoxide at low temperatures is important to increase the adsorption capacity.

In the experiment, a gas in an atmosphere of 50 °C to 200 ppm NO/10% O ₂ /N ₂ was flowed for 30 minutes, and then the temperature was raised to 600 °C while flowing a gas of the same composition.

Referring to FIG. 3, when comparing the nitrogen monoxide adsorption section (10 to 40 minutes) at 50 °C, it can be seen that adsorption is hardly achieved through the rapid recovery of the concentration of NOx in Pt/Ba/Al. .

Next, in Pt/Ba/Al-Ce, since the concentration of NOx recovered slowly compared to Pt/Ba/Al, it can be seen that adsorption took place a little more. This is thought to be due to the high oxygen storage capacity and oxidation-reduction capacity of ceria, which is present as a carrier. Lastly, in the Pt/Cu-Ba/Al-Ce catalyst, it can be seen that the most adsorption occurred as the concentration of NOx was recovered most slowly compared to the previous two catalysts during the nitrogen monoxide adsorption period (10 to 40 minutes).

When comparing the results of analyzing the degree of oxidation of nitrogen monoxide through elevated temperature after 30 minutes of adsorption, first, Pt/Ba/Al and Pt/Ba/Al-Ce corresponding to the existing LNT catalyst showed almost the same trend, and the amount of adsorbed was Pt/Ba/Al-Ce appeared to be more, and the temperature range in which the adsorption capacity increased due to oxidation was similar. However, Pt/Cu-Ba/Al-Ce showed a different tendency from the previous two catalysts, and the nitric oxide slip phenomenon was notable difference from 200 °C or higher. This is a phenomenon in which nitrogen monoxide, which is weakly bound to copper oxide, falls off as the temperature increases.After the nitrogen monoxide slip, an additional adsorption phenomenon due to nitrogen monoxide oxidation was observed in the higher temperature region, and desorption was not possible at temperatures above 450 °C. Seemed to happen.

The temperature at which desorption occurs is lowered by near 100 °C compared to Pt/Ba/Al or Pt/Ba/Al-Ce.

Adsorption performance evaluation

The adsorption capacity of the Pt/Ba/Al catalyst corresponding to the conventional LNT catalyst and the Pt/Cu-Ba/Al-Ce catalyst according to the temperature was compared.

The adsorption capacity was compared through the NOx storage efficiency (hereinafter, NSE, the difference between the inflow NOx and the exhaust NOx compared to the inflow NOx), and the formula for calculating the NOx storage efficiency is as follows.

4 is a view showing a comparison of NSE according to temperature of two catalysts through the above calculation method.

Referring to FIG. 4, first, when comparing the NSE according to the temperature of the Pt/Ba/Al catalyst, it can be seen that it is considerably lower at a low temperature and higher as the temperature rises. Next, when comparing the NSE according to the temperature of the Pt/Cu-Ba/Al-Ce catalyst, it can be seen that the adsorption efficiency increased considerably at low temperatures, especially in the initial section, and decreased with time.

At 250 °C, it can be seen that the NSE decreased by a small width due to the preceding NOx slip phenomenon, and at 350 °C, the highest NSE was recorded, indicating that there was almost no amount of NOx discharged until about 15 minutes. Based on these results, it can be confirmed that the Pt/Cu-Ba/Al-Ce catalyst is advantageous for NOx adsorption at low temperature and the adsorption efficiency is the best in the high temperature region of 350 °C.

The above-described embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art who have ordinary knowledge of the present invention will be able to make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes and additions It should be seen as falling within the scope of the following claims.

Claims (11)

In the low-temperature nitrogen oxide removal catalyst,
A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite carrier prepared by impregnating a noble metal and metal oxide into a ceria-alumina composite carrier synthesized by treating a ceria precursor and an alumina precursor by a coprecipitation method at a preset mass ratio. The method of claim 1,
The ceria precursor is a ceria-alumina composite carrier comprising one of _{cerium chloride (CeCl 3} ), cerium sulfate (Ce (SO ₄ ) ₂ ) and cerium nitrate hydrate (Ce (NO ₃ ) ₃ 6H _{2 O)} Low-temperature nitrogen oxide removal catalyst. The method of claim 1,
As the alumina precursor, aluminum chloride (AlCl ₃ ), aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) and aluminum nitrate hydrate (Al(NO ₃ )9H ₂ O) using a ceria-alumina composite support Low-temperature nitrogen oxide removal catalyst. The method of claim 1,
A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support having a mass ratio of the alumina precursor and a ceria precursor of 3:1 to 5:1. The method of claim 1,
The ceria-alumina composite support is a low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support that is synthesized by dissolving the alumina precursor and then dissolving the ceria precursor for a preset period of time after dissolving the alumina precursor. . The method of claim 5,
The ceria-alumina composite support is a low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support that is synthesized by stirring, washing, filtering and sintering at a preset temperature to obtain a precipitate through pH adjustment after the precipitation. The method of claim 1,
The noble metal includes at least one of platinum, palladium, rhodium, and iridium,
The metal oxide is a low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support comprising an oxide containing at least one of magnesium, calcium, strontium, barium, sodium, potassium, rubidium, cesium, iron, and copper. The method of claim 7,
A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support in which the precursor of the noble metal is first impregnated with a ceria-alumina composite support and dried, and then the precursor of the metal oxide is impregnated and fired. The method of claim 8,
The precursor of the noble metal includes (NH ₄ ) ₂ PtCl ₄ , and the precursor of the metal oxide is a copper oxide precursor of copper nitrate hydrate (Cu(NO ₃ ) ₂ ·3H2O) and a barium oxide precursor of barium acetate ((CH ₃ COO) A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support comprising _{2 Ba).} The method of claim 9,
A low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite carrier having a mass ratio of the precursor of the copper oxide and the barium oxide of 1:1. In the low-temperature nitrogen oxide removal catalyst manufacturing method,
After dissolving the alumina precursor in distilled water, after a preset time elapses, the ceria precursor is introduced and dissolved again for a preset time, and a precipitate is obtained through pH adjustment, and a ceria-alumina composite is carried out through drying, washing, filtering and firing. Preparing a carrier;
Impregnating a noble metal precursor into the ceria-alumina composite carrier; And
A method for preparing a low-temperature nitrogen oxide removal catalyst using a ceria-alumina composite support comprising the step of impregnating at least one metal into the ceria-alumina composite support impregnated with the noble metal by using one or more metal oxide precursors through co-impregnation. .

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