KR20190071266A - Manufacturing method of decomposition catalyst for N2O abatement by adding mixed metal oxides in alumina support - Google Patents

Abstract

The present invention relates to a catalyst producing method capable of preventing the activity degradation of a catalyst caused by water, oxygen, and nitrogen oxides existing in exhaust gas in terms of a decomposition catalyst for removing nitrous oxide and, more specifically, to a catalyst producing method which is able to prevent activity degradation in a low temperature area and improve the poisoning resistance of a catalyst by impregnating noble metals after producing a catalyst carrier by adding a metal complex oxide comprising transition metal and rare earth metal to γ-Al_2O_3 used as a carrier in a conventional decomposition catalyst. The present invention: is able to provide a high conversion rate of nitrous oxide (N_2O) by effectively preventing the activity degradation of a catalyst generated by water, oxygen, and nitrogen oxide (NO) existing in exhaust gas; and improves the poisoning resistance of a catalyst while preventing the activity degradation of a noble metal catalyst in an area of a low temperature of 300 to 400°C.

Description

[0001] The present invention relates to a method for producing a N2O decomposition catalyst by adding a mixed metal oxide to an alumina support,

The present invention relates to a catalyst preparation method capable of preventing catalyst deactivation caused by moisture, oxygen and nitrogen oxides present in exhaust gas in a decomposition catalyst for removing nitrous oxide, and more particularly, A catalyst composite is prepared by adding a metal complex oxide composed of a transition metal and a rare earth metal or the like to γ-Al ₂ O ₃ used as a carrier in the decomposition catalyst and impregnated with a noble metal, To a method for producing a catalyst capable of improving the poisoning resistance of the catalyst.

As global warming causes serious problems of climate change, interest in greenhouse gases is increasing worldwide. In general, greenhouse gas carbon dioxide (CO ₂₎ and CH _4, N ₂ O, PFCs, HFCs, SF _6, etc. Non-CO ₂ may be divided into a greenhouse gas, in particular N ₂ O gas Of these, including the CO ₂ , The global warming potential (GWP) is about 310 times higher than that of other countries.

The Direct N2Odecomposition method, which is one of the representative techniques for reducing N ₂ O gas, is a method that can decompose N ₂ O effectively using only the catalyst and temperature without requiring expensive reductant. Many studies are under way.

Various catalysts have been used as direct pyrolysis catalysts, and noble metal catalysts such as Rh and Ru have been mainly studied at low temperature. Due to the high reducing properties of the noble metal catalyst, high N ₂ O decomposition efficiency can be achieved even at low temperatures.

However, exhaust gases actually emitted from industrial processes contain oxygen, moisture, and nitrogen oxides, which reduce catalyst activity. The noble metal catalysts are easy to manufacture and have been studied because they are easy to apply to a source through a wash coating on a molding or monolith structure. However, they are very vulnerable to catalyst inert gases such as moisture and oxygen, Studies on the effect of NO on N ₂ O decomposition catalysts on the N ₂ O sources are still lacking.

In the case of oxygen and water, since the reaction is performed in a form of competitive adsorption with the reactants, the activity of the catalyst is reduced, and it acts as a factor which hinders the reduction of N ₂ O. Further, unlike the case of oxygen and moisture, NO is strongly bound to the surface of the catalyst to lower the activity of the catalyst, so that the activity of the catalyst is irreversibly greatly reduced, and the initial performance is not recovered. This is because the NO adsorbed on the catalyst is not fully desorbed or decomposed under the condition that the decomposition reaction of N ₂ O is proceeded, which hinders the activity, and a higher temperature is required to escape the influence of NO on the catalyst.

Therefore, there is a continuing need for the development of catalysts that can minimize or overcome the effect of deactivation by inert gases contained in the flue-gases.

Patent No. 10-1550289

As described above, the present invention provides a method for preparing a catalyst capable of preventing catalyst deactivation caused by moisture, oxygen and nitrogen oxides (NO) present in the exhaust gas. In the decomposition catalyst capable of removing nitrous oxide (N ₂ O), the metal complex oxide and alumina are simultaneously used as the carrier, thereby preventing the deterioration of the activity of the noble metal catalyst in the low temperature region of 300 to 400 ° C., Poisoning resistance.

A method for producing an N ₂ O decomposition catalyst in which a mixed metal oxide is added to an alumina support according to an embodiment of the present invention includes the steps of: preparing a composite oxide containing cerium and zirconium; A step of preparing a catalyst carrier by mixing boehmite (AlO (OH) sol or γ-Al ₂ O ₃ ) into the composite oxide, impregnating the catalyst carrier with an aqueous solution of rhodium nitrate, and drying and calcining And the drying and firing steps include drying performed at about 100 ° C for at least 24 hours and firing performed at about 550 ° C for about 4 hours.

The step of preparing the composite oxide comprises: preparing a mixture by mixing an aqueous solution of cerium nitrate and an aqueous solution of zirconium nitrate; A coprecipitation step of adding a basic substance to the mixture to adjust pH to a range of 8.0 to 12.0 to precipitate; And a drying and firing step of performing a drying process and a firing process after the coprecipitation step, wherein the drying process is performed at about 100 ° C for at least 24 hours, and the firing process is performed at about 550 ° C for about 4 hours ≪ / RTI >

Wherein the molar ratio of cerium to zirconium is controlled in the range of 1:10 to 10: 1 in the course of producing the complex oxide, and the step of preparing the catalyst support comprises mixing the composite oxide with boehmite (AlO (OH) The sol may be mixed and then calcined, or the complex oxide may be directly mixed with the? -Al ₂ O ₃ .

If necessary, the mixture may further contain at least one rare earth metal such as praseodymium (Pr), lanthanum (La), or yttrium (Y) in an amount of 10 mol% or less.

In the step of impregnating the catalyst carrier with the aqueous solution of rhodium nitrate, it is preferable that the aqueous solution of rhodium is used so that rhodium as the impregnated metal can be impregnated in the range of 0.1 to 3.0 wt% based on the total catalyst, The Ce-Zr complex oxide added to alumina is preferably used in a range of about 10 to 50%, more preferably in a range of 10 to 30%, based on the total weight of the catalyst.

The mixed metal oxide on the alumina support a N2O decomposition catalyst is added in accordance with the present invention, high nitrous oxide to prevent moisture present in the exhaust gas, oxygen, and nitrogen oxide (NO), etc. The activity of the catalyst deterioration caused by effectively (N ₂ O) conversion rate,

Particularly, there is an effect of preventing a decrease in the activity of the noble metal catalyst in the low temperature region of 300 to 400 ° C, and at the same time, improving the poisoning resistance of the catalyst.

1 is a block diagram showing a process for producing a Rh / Al ₂ O ₃ -CeZr complex oxide catalyst for N ₂ O decomposition.
Figure 2 is when O ₂ in the reaction gas was observed compared to the N ₂ O conversion of the Rh-based catalysts are (SV: 10,000h ^-1, N ₂ O initial concentration: 500ppm, O ₂ concentration: 3%, total flow rate : 3 L / min).
Figure 3 when H ₂ O in the reaction gas was observed compared to the N ₂ O conversion of the Rh-based catalysts are (SV: 10,000h ^-1, N ₂ O initial concentration: 500ppm, H ₂ O concentration: 0.5%, Total flow rate: 3 L / min).
4 shows the result of comparative observation of the conversion of N ₂ O in the presence of NO in the reaction gas (SV: 10,000 h ^-1 , N ₂ O initial concentration: 500 ppm, total flow rate: 3 L / min).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Prior to the description, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed in accordance with the technical concept of the present invention.

Throughout this specification, when a member is "on " another member, this includes not only when the member is in contact with another member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including" an element, it is understood that it may include other elements as well, without departing from the other elements unless specifically stated otherwise.

The terms "first "," second ", and the like are intended to distinguish one element from another, and the scope of the right should not be limited by these terms. For example, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The catalyst according to the present invention, which can achieve the objects and effects of the present invention, can be prepared in two stages. First, the first step is to produce a Ce-Zr complex oxide. And a step of mixing a Ce-Zr complex oxide and then carrying a noble metal such as Rh to complete the catalyst (see FIG. 1).

Referring to FIG. 1, the process of preparing the CeZr complex oxide will be described in more detail.

First, in order to prepare a CeZr complex oxide, an aqueous solution of cerium nitrate and an aqueous solution of zirconyl nitrate are mixed in a stoichiometric ratio and stirred.

The pH of the mixed and stirred aqueous solution is adjusted to 8.0 to 12.0 so that co-precipitation occurs. At this time, the pH can be adjusted by using a basic solution such as NH ₄ OH or NaOH. If the pH is less than 8.0 or exceeds 12.0, co-precipitation due to chemical bonding does not occur or there is a problem of crystal growth. It is necessary to adjust to a range of 8.0 to 12.0.

Here, the ratio of Ce to Zr can be adjusted from 1: 10 to 10: 1, and the metal ratio can be adjusted by adjusting the initial concentration of the metal compound precursor aqueous solution or adjusting the pH at which the coprecipitation occurs.

In addition, Ce-Zr complex oxides can be prepared by mixing rare earth metals such as Praseodymium (Pr), Lantanum (La), and Yttrium (Y) in the range of 0 to 10% May be prepared by adding a single metal or a combination of two or more metals.

The coprecipitation can be performed at room temperature, and may be performed by heating to a temperature range of 90 DEG C or lower depending on the case, and the temperature (i.e., heating) is not particularly limited.

When the co-precipitation is completed and precipitation occurs, the precipitate produced through the coprecipitation, that is, the CeZr complex oxide, is recovered by washing and filtration. The recovered CeZr complex oxide is dried at about 100 ° C. for about 24 hours to remove excess water, and then calcined at about 550 ° C. for about 4 hours.

The Ce-Zr composite oxide thus prepared will be described in detail with reference to the Rh-based catalyst preparation method for N ₂ O decomposition to be provided in the present invention.

In order to prepare a Rh-based catalyst for N ₂ O decomposition, a CeZr complex oxide prepared by the above-mentioned method is uniformly mixed with γ-Al ₂ O ₃ to prepare a catalyst support.

Alumina used in the carrier produced is through the γ-Al ₂ O ₃ form, γ-Al ₂ O ₃ powder simply may be used by mixing, boehmite (Boehmite, AlO (OH)) firing after mixing with the .

The amount of the Ce-Zr compound oxide mixed with the alumina may be in the range of about 10 to 50%, and preferably in the range of about 10 to 30%.

The decomposition catalyst is prepared by impregnating an aqueous solution of rhodium nitrate with the Al ₂ O ₃ -CeZr composite oxide thus prepared. The amount of the aqueous solution of rhodium nitrate supported thereon is preferably adjusted so that the rhodium metal is impregnated in the range of 0.1 to 3.0 wt% of the total catalyst, and the drying and calcination are performed at about 100 DEG C for about 24 After drying for a period of time, it is preferable to undergo a firing process at about 550 DEG C for about 4 hours.

[ Example  1] Production of decomposition catalyst (Rh / Al ₂ O ₃ + CeZr )

1.5289 g of Ce (NO ₃ ) ₃ .6H ₂ O, 0.7681 g of ZrO (NO ₃ ) ₂ .xH ₂ O and 0.0468 g La (NO ₃ ) ₃ .xH ₂ O were added to 2 L of distilled water and stirred ? X? 6). Thereafter, the pH is increased to 10.1 using a 15 wt% NH ₄ OH aqueous solution so that a precipitate is formed.

The pH-adjusted solution was stirred for 3 hours at room temperature, and the precipitated material was filtered off using a vacuum filter. This procedure was repeated several times. The resulting composite was placed in a drier, dried at 110 ° C for 24 hours, and then calcined at 550 ° C for 4 hours.

The CeZr complex oxide thus obtained and 9 g of boehmite sol were mixed with 10 ml of distilled water, stirred for 3 hours, and then calcined at 550 ° C for 4 hours. The resulting Al ₂ O ₃ -CeZr powder was loaded with 0.89 ml of a small amount of rhodium nitrate, dried at 110 ° C. for 24 hours, and then calcined at 550 ° C. for 4 hours.

[ Comparative Example ] Catalyst Preparation (Rh / Al ₂ O ₃ , Rh / CeZr )

For comparison with the decomposition catalyst according to the present invention prepared in Example 1, Rh-impregnated catalysts were prepared on Al ₂ O ₃ or CeZr supports.

The Rh / Al ₂ O ₃ catalyst was prepared by loading a small amount of 0.89 ml of rhodium nitrate in 10 g of γ-Al ₂ O ₃ powder, drying the resulting material at 110 ° C. for 24 hours, and then calcining at 550 ° C. for 4 hours .

The Rh / CeZr catalyst was also prepared in the same manner as in the preparation of the Rh / Al ₂ O ₃ catalyst. A small amount of 0.89 ml of rhodium nitrate was loaded on 10 g of the CeZr complex oxide prepared above as a carrier, And then calcined at 550 DEG C for 4 hours.

[ Example 2]

In order to compare the basic performances of the catalysts prepared in Example 1 and Comparative Example, each catalyst was coated on a cordierite monolith having a size of 200 cells / in ² before the experiment. The reactor was located in the center of a stainless steel (SUS 316) tube reactor, which was designed to mount a 27 mm x 28 mm x 24 mm honeycomb.

Due to the size of the reactor diameter, a total of three furnaces were used to control the temperature inside the reactor precisely. A thermocouple was installed at the top and bottom of the catalyst to keep the catalyst temperature uniform.

The total flow rate of the reaction gas supplied to the reactor was fixed at 3 L / min, the concentration of nitrous oxide contained therein was kept constant at a concentration of 500 ppm, and the space velocity (GHSV) was maintained at 10,000 h ^-1 .

The concentration of nitrous oxide was analyzed using an on-line gas analyzer (Madur Polska, Sensonic IR-1) to analyze the components of the gas after the reaction.

catalyst N ₂ O conversion (%) 300 ° C 350 ℃ Comparative Example 1 Rh / Al ₂ O ₃ 68.3 93.4 Example 1 Rh / Al ₂ O ₃ -CeZr 96.5 97.7 Comparative Example 2 Rh / CeZr 91.2 97

Table 1 shows the N ₂ O conversion rates of the catalysts prepared in Example 1 and Comparative Example 1 when the reactor temperatures were 300 ° C. and 350 ° C., respectively.

In the absence of other inert gases, the N ₂ O conversion was not significantly different at 350 ° C when the alumina alone was used as the carrier and when the carrier contained Ce-Zr complex oxide. However, at 300 ° C At a low temperature of 95 ° C or more, the conversion rate of the catalyst containing Ce-Zr complex oxide and alumina (Example 1) was higher than 95%.

In addition, although the catalyst (Comparative Example 2) used as the carrier alone with the Ce-Zr composite oxide showed a high N ₂ O conversion rate of about 20% or more as compared with the catalyst used as the carrier alone (Comparative Example 1) Lt; ₂ > O conversion characteristics as compared with the catalyst of Example 1 (Example 1).

FIG. 2 shows the results of observing N ₂ O conversion according to reaction temperatures of the catalysts prepared in Example 1 and Comparative Example under the condition that 3 vol% of oxygen, which is an inert gas, was present. Lt; 0 > C.

If previously it did not exist the inert gas in Table 1 down to the reaction temperature is 375 ℃ Like before Ce-Zr catalyst comprises a composite oxide (Example 1) and or N ₂ in the catalyst (Comparative Example 2) used as the sole O conversion rate was significantly increased as compared with the catalyst (Comparative Example 1) in which only alumina was used alone.

This is interpreted to be due to the excellent oxygen storage properties of the Ce-Zr complex oxide and hence the improved oxidation-reduction potential.

FIG. 3 shows the results of measurement of N ₂ O conversion according to the reaction temperature change of each catalyst when H ₂ O as an inert gas exists at 1 vol%. As shown in FIG. 3, when the Ce-Zr composite oxide is contained in alumina (Example 1), the catalysts of Comparative Examples 1 and 2 are highly resistant to moisture, Significant reduction in conversion was observed.

The deactivation of these catalysts is believed to be caused by competitive adsorption of water, which is believed to minimize the effect of this synergy on the alumina and Ce-Zr complex oxides used as supports.

FIG. 4 shows the results of measuring the conversion of N ₂ O according to the reaction temperature of the catalysts in the presence of NO, which is an inert gas. In the case where NO is present at a reaction temperature of 375 ° C., and NO 3 is present at a concentration of 100 ppm and 300 ppm The conversion of N ₂ O was confirmed.

In general, when the reaction temperature rises to 375 ° C, the activity of the catalyst due to the inert gases such as oxygen and moisture is not so great, but the activity decrease due to NO occurs very seriously.

However, in the case of the catalyst using the carrier in which the Ce-Zr composite oxide prepared in the example of the present invention is contained in alumina, the catalytic activity is much lower than the other catalysts prepared in the comparative examples (Comparative Example 1 and Comparative Example 2) Respectively.

As can be seen from the results of FIG. 4, in the case of the catalyst prepared in Example 1, about 15% of all catalysts were present in the presence of NO at a concentration of 100 ppm or 300 ppm, compared with the catalyst using only alumina alone as a carrier (Comparative Example 1) And the conversion rate was high.

(Comparative Example 2) shows a reduction in activity of about 20% as compared with the catalyst containing only alumina (Comparative Example 1) in the case where only the Ce-Zr composite oxide is used as a carrier (Comparative Example 2) It is believed that the interaction between the alumina and the Ce-Zr complex oxide used as the carrier contributes greatly to the improvement of the resistance of the catalyst to the NO gas.

In particular, when used as a support, the ratio of the Ce-Zr compound oxide added to alumina is effective when it is in the range of 10 to 50%, and more preferably in the range of 10 to 30%.

The present invention is not limited to the above-described specific embodiment and description, and various changes and modifications may be made by those skilled in the art without departing from the scope of the present invention as claimed in the claims. And such modifications are within the scope of protection of the present invention.

Claims (8)

Preparing a composite oxide comprising cerium and zirconium;
The method comprising the composite oxide, a mixture of boehmite (AlO (OH) sol, or γ-Al ₂ O ₃ to obtain a catalyst carrier;
Impregnating the catalyst carrier with an aqueous solution of rhodium nitrate; And
Drying and calcining the alumina support, wherein the mixed metal oxide is added to the alumina support.
The method according to claim 1,
Wherein the step of preparing the composite oxide comprises:
Mixing a cerium nitrate aqueous solution and an aqueous zirconium nitrate solution to prepare a mixture;
A coprecipitation step of adding a basic substance to the mixture to adjust pH to a range of 8.0 to 12.0 to precipitate; And
And a drying and calcining step of performing a drying step and a calcining step after the coprecipitation step. The method for producing an N 2 O decomposition catalyst according to claim 1, wherein the mixed metal oxide is added to the alumina support.
3. The method of claim 2,
The drying process is carried out at about 100 < 0 > C for at least 24 hours,
Wherein the calcination is carried out at about 550 DEG C for about 4 hours, wherein the mixed metal oxide is added to the alumina support.
The method according to claim 1,
Wherein said drying and calcining step comprises calcining performed at about 100 ° C for at least 24 hours and at about 550 ° C for about 4 hours, wherein the mixed metal oxide is added to the alumina carrier.
The method according to claim 1,
Wherein the molar ratio of cerium to zirconium is controlled in the range of 1:10 to 10: 1.
The method according to claim 1,
Wherein the step of preparing the catalyst carrier comprises:
The composite oxide and the boehmite (AlO (OH)) sol are mixed and fired,
Wherein the mixed oxide is mixed with? -Al ₂ O ₃ , wherein the mixed metal oxide is added to the alumina carrier.
3. The method of claim 2,
Characterized in that the mixture contains at least one rare earth metal of Praseodymium (Pr), lanthanum (La) or yttrium (Y) in an amount of 10 mol% or less. To the N2O decomposition catalyst.
The method according to claim 1,
In the step of impregnating the catalyst support with an aqueous solution of rhodium nitrate, the aqueous rhodium nitrate solution is used so that the rhodium metal is impregnated in the range of 0.1 to 3.0 wt% based on the total catalyst. A method for producing an N2O decomposition catalyst.

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