KR20210039131A - Catalyst for removal of nitrogen oxides and method for producing the same - Google Patents

Abstract

The present invention relates to a selective reduction catalyst capable of removing nitrogen oxides with carbon monoxide as a reducing agent, and a method for preparing the same. The catalyst includes 0.1-3.0 parts by weight of rhodium and 1.0-3.0 parts by weight of lanthanum based on 100 parts by weight of an alumina carrier, and is obtained by the method including the steps of: weighing rhodium and lanthanum while supporting the same on the alumina carrier, drying and baking. The catalyst shows enhanced conversion and adsorption of nitrogen oxides into nitrosyl species capable of reacting with carbon monoxide on the surface of reduced rhodium, and thus can remove nitrogen oxides with a high conversion ratio and selectivity. In addition, the catalyst has enhanced oxygen transportability, and thus can remove the remaining carbon monoxide effectively even with a low concentration of oxygen in exhaust gas.

Description

Catalyst for nitrogen oxide removal and its manufacturing method {CATALYST FOR REMOVAL OF NITROGEN OXIDES AND METHOD FOR PRODUCING THE SAME}

The present invention relates to a catalyst for removing nitrogen oxides and a method for producing the same, and more particularly, to a selective reduction catalyst capable of removing nitrogen oxides using carbon monoxide as a reducing agent and a method for producing the same.

Recently, among the major air pollutants that cause environmental pollution, a method of removing nitrogen oxides, which is a source of fine dust and discharges the largest amount, has been actively discussed. These nitrogen oxides are discharged from various fixed and mobile pollution sources based on combustion, and various technologies are being developed as a method of removing nitrogen oxides.

Traditionally, technologies for controlling nitrogen oxides include denitrification control technology during combustion, which controls conditions during combustion, and flue gas denitration control technology, which controls nitrogen oxides contained in exhaust gas after combustion by a reduction reaction. Typical denitrification control technologies during combustion include Lean NOx burner, Overfire Air, and FGR, but there is a disadvantage that the nitrogen oxide control efficiency is only 50% or less. Therefore, flue gas denitration technology is a technology that must be used in order to meet the standards on nitrogen oxide regulations that are being strengthened.

Among the flue gas denitration technologies, selective catalyst reduction (SCR), which is the most efficient in terms of economic and technical aspects, is the most widely used. The selective catalytic reduction method is divided into ammonia-based SCR using aqueous ammonia, ammonia or urea, and other non-ammonia-based SCRs according to the type of reducing agent.

Among them, ammonia-based SCR is a method that uses ammonia as a reducing agent. As an example that can remove more than 90% of nitrogen oxides generated from fixed pollutants, BACT (Best Available Control Technology) is commercialized. If the device is required and ammonia, which is a reducing agent, is oxidized and the reducing agent becomes insufficient, the reduction reaction of nitrogen oxides does not proceed smoothly. In addition, when sulfur oxide is included in the exhaust gas, it reacts with ammonia and moisture to form ammonium sulfate, thereby corroding the downstream equipment or blocking the active point of the catalyst.

For this reason, currently, alternative studies on non-ammonia-based SCR are being conducted very actively, and examples of using hydrocarbon, hydrogen, or carbon monoxide as a reducing agent are known.

The method of removing nitrogen oxides using a hydrocarbon as a reducing agent in the non-ammonia SCR is called a three way catalyst (TWC), and is used limitedly to an emission source such as a vehicle using gasoline as a fuel, and incomplete oxidation of the catalyst is achieved. It has the disadvantage of producing a by-product called carbon monoxide by reacting with oxygen or moisture.

Among other non-ammonia-based SCRs, the method of removing nitrogen oxides using hydrogen as a reducing agent exhibits high activity at a low reaction temperature of 150 ℃ or less, but the temperature range showing excellent activity is very narrow, and is active by carbon monoxide and moisture. It exhibits lowered and low N ₂ selectivity.

Meanwhile, in the case of the method of removing nitrogen oxides by using carbon monoxide as a reducing agent among other non-ammonia-based SCRs, there is an advantage that there is no injection of an additional reducing agent because carbon monoxide contained in the exhaust gas can be used, and carbon monoxide and nitrogen oxides are included in the exhaust gas. Since it has an advantage that can be applied in various combustion facilities, it is envy as a method that can compensate for the disadvantages of non-ammonia-based SCR using hydrocarbons or hydrogen as well as ammonia-based SCR described above, and the reaction is as follows. 1].

[Formula 1]

2CO + 2NO → 2CO ₂ + N ₂

As an example of a non-ammonia-based SCR using carbon monoxide as a reducing agent, Korean Patent Application No. 10-2017-0145646 discloses _{an Ir-based deNO x} catalyst capable of increasing the removal efficiency of _{NO x present in exhaust gas even at a low temperature of 180°C.} And a manufacturing method thereof is disclosed, and in Korean patent application No. 10-2007-0134191, nitrogen in the exhaust gas is used as a reducing agent without a separate reducing agent in the exhaust gas composition condition of a diesel or lean-burn engine. A composite catalyst for removing oxides is disclosed.

However, most of the SCR catalysts that remove nitrogen oxides using carbon monoxide as a reducing agent, including the above patents, have a low nitrogen removal rate and low selectivity when converting nitrogen oxides, so there is a need for improvement and also removes excess carbon monoxide. There is a problem that secondary pollution may occur due to the need for excessive oxygen. The inventors of the present invention have come to the present invention after continuing research on a catalyst for removing nitrogen oxides using carbon monoxide as a reducing agent by paying close attention to the problems of these prior arts.

Korean Patent Application No. 10-2017-0145646 Korean Patent Application No. 10-2007-0134191

An object of the present invention is a catalyst capable of removing nitrogen oxides with high conversion and selectivity by using carbon monoxide in the exhaust gas as a reducing agent without injecting a separate reducing agent, and also capable of sufficiently removing excess carbon monoxide with only low concentration oxygen in the exhaust gas, and the like. It is to provide a manufacturing method.

In the process of researching and developing a catalyst related to the above problem, the inventors of the present invention have carried out simultaneous drying and firing of a rhodium (Rh) precursor and a lanthanum (La) precursor to prepare a rhodium-based catalyst. The conversion and adsorption of nitrosyl species that can react with this carbon monoxide is promoted, so that nitrogen oxides can be removed with high conversion and selectivity, and the oxygen transfer ability of the catalyst is improved, so that only low concentration of oxygen in the exhaust gas is spared. It was found that carbon monoxide of can be effectively removed, and it was confirmed that it can be achieved by controlling the conditions for the manufacturing process and quantitative control of the precursor and the content of each component. The gist of the present invention based on the recognition and knowledge of the above-described problem is the same as described in the claims below.

(1) As a catalyst for removing nitrogen oxides used to remove nitrogen oxides using carbon monoxide as a reducing agent, removing nitrogen oxides comprising 0.1 to 3.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum based on 100 parts by weight of the alumina support For rhodium-lanthanum/alumina catalyst.

(2) The rhodium-lanthanum/alumina catalyst of (1), wherein the rhodium surface reacts with carbon monoxide and nitrogen oxide in a reduced state.

(3) The rhodium-lanthanum/alumina catalyst of (2), wherein the nitrogen oxide reacts with carbon monoxide after being adsorbed as nitrosyl species on the reduced rhodium surface.

(4) The rhodium-lanthanum/alumina catalyst of (3) above, characterized in that the ^{reduced rhodium ratio (Rh 0} /Rh _total ) is maintained at 35% or more during the carbon monoxide pre-reaction.

(5) The specific surface area of the catalyst is 148.82 to 184.99 m ² /g, the lattice size is 8.59 to 10.12 ÅA, and the average pore size is 11.51 to 12.14 nm. /Alumina catalyst.

(6) A method for producing a rhodium-lanthanum/alumina catalyst for removing nitrogen oxides, characterized in that 0.1 to 1.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum are quantified and supported at the same time, followed by drying and firing, based on 100 parts by weight of an alumina support. .

(7) The method for producing a rhodium-lanthanum/alumina catalyst for removing nitrogen oxides of (6), wherein the alumina support is gamma alumina (γ-Al ₂ O _{3 ).}

(8) The rhodium precursor is rhodium hydroxide (Rh(OH) ₂ ) The method for producing a rhodium-lanthanum/alumina catalyst for removing nitrogen oxides of (6).

(9) The lanthanum precursor is a rhodium-lanthanum/alumina catalyst for removing nitrogen oxides of (6), characterized in that _{lanthanum nitrate hydrate (LaN 3} O _{9 ).}

(10) The process of sintering the rhodium precursor and the lanthanum precursor on the alumina support is performed at a temperature of 400° C. for 4 hours. The method for preparing a rhodium-lanthanum/alumina catalyst for removing nitrogen oxides of (6).

(11) A method of removing nitrogen oxides by contacting the exhaust gas in which carbon monoxide and nitrogen oxides are mixed with the catalyst according to any one of claims 1 to 5.

(12) The method of removing nitrogen oxides of (11), wherein the step of contacting the exhaust gas with the catalyst is performed in the presence of oxygen and moisture.

According to the present invention, carbon monoxide and nitrogen oxide can be simultaneously removed at a removal rate of 80 to 100% in a temperature range of 210 to 300°C by reacting carbon monoxide and nitrogen oxide on the reduced rhodium surface. In addition, by removing nitrogen oxides using carbon monoxide in the exhaust gas as a reducing agent without injecting a separate reducing agent, it can be applied to various processes in which carbon monoxide and nitrogen oxides in the exhaust gas are discharged, and it is advantageous in terms of economy and technology.

1A and 1B are diagrams showing the removal rates of carbon monoxide and nitrogen oxides of catalysts prepared by the methods of Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2 depending on whether rhodium and lanthanum were supported.
2A and 2B are diagrams showing removal rates of carbon monoxide and nitrogen oxides of catalysts prepared by the methods of Preparation Example 1, Comparative Preparation Example 5, and Comparative Preparation Example 6 according to the loading time of rhodium and lanthanum.
3A and 3B are diagrams showing DRIFT analysis results using FT-IR for catalysts prepared by the methods of Preparation Example 1 and Comparative Preparation Example 1. FIG.
4A and 4B are diagrams showing the correlation result of the ratio of reduced rhodium through XPS analysis in the catalyst prepared by the method of Preparation Example and Comparative Preparation Example excluding Comparative Preparation Example 2;

Hereinafter, preferred embodiments of the present invention will be described in detail. In describing the present invention, when it is determined that a detailed description of a related known technology may obscure the subject matter of the present invention, a detailed description thereof will be omitted. Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

The present invention discloses a catalyst for removing nitrogen oxides used to remove nitrogen oxides using carbon monoxide as a reducing agent and a method for preparing the same, and a method for removing nitrogen oxides and carbon monoxide contained in exhaust gas using such a catalyst. It will be explained as.

The catalyst is a rhodium, lanthanum, and alumina three-way catalyst, and is prepared by supporting a rhodium precursor and a lanthanum precursor on an aluminum support, followed by drying and firing.

The rhodium (Rh) is an active point at which carbon monoxide and nitrogen oxide react, and pre-adsorption of carbon monoxide is induced, and preferably, 0.1 to 1.0 parts by weight of rhodium is supported with respect to 100 parts by weight of the alumina carrier. Rhodium is a precious metal-based active metal, and it is preferable to minimize the cost in terms of cost as long as it can achieve catalytic activity.In the present invention, the above-described carbon monoxide and carbon monoxide and the above-described carbon monoxide and It is characterized by having a resolution of 80% or more at ^{210 o} C or more of nitrogen oxides.

In more detail with respect to the role of the rhodium as an active point for reacting carbon monoxide and nitrogen oxide, the rhodium surface reacts with carbon monoxide and nitrogen oxide in a reduced state, and in this case, the nitrogen oxide is the reduced rhodium surface. After being adsorbed as a nitrosyl species, it reacts with carbon monoxide. In connection with such a reactor operation, in order to have a resolution of more than 80% of carbon monoxide and nitrogen oxide at 210 ^{o C or higher as described above, it is necessary to maintain a reduced rhodium ratio (Rh 0} /Rh _total ) of 35% or more during the carbon monoxide pre-reaction. desirable.

The lanthanum (La) maximizes the conversion and adsorption of nitrogen oxides to nitrosyl species during the carbon monoxide pre-reaction by increasing the oxygen transfer capacity of the catalyst to form a ratio of reduced rhodium to 35% or more, preferably alumina. It is preferable that it is supported in an amount of 1.0 to 3.0 parts by weight of lanthanum based on 100 parts by weight of the carrier. If the lanthanum content is less than 1.0 part by weight, the proportion of reduced rhodium upon pre-adsorption of carbon monoxide is formed to 35% or less, so that the decomposition capacity of carbon monoxide and nitrogen oxide falls to 80% or less. Although the decomposition capacity of carbon monoxide is partially increased, the decomposition capacity of nitrogen oxides decreases, which is not preferable.

When preparing the catalyst, as a precursor material, for example, gamma alumina (γ-Al ₂ O _{3 ) may be used as an alumina carrier, rhodium hydroxide (Rh(OH) 2} ) may be used as a rhodium precursor, and lanthanum precursor may be used as a lanthanum precursor. Nitrate hydrate (LaN ₃ O ₉ ) may be used, respectively.

To describe the catalyst manufacturing process in more detail, first, a rhodium precursor of rhodium hydroxide (Rh(OH) ₂ ) and a lanthanum precursor of lanthanum nitrate hydrate (LaN ₃ O ₉ ) on a _{gamma alumina (γ-Al 2} O _{3) support} Is dissolved in the aqueous solution. The content of each component is calculated as 0.1 to 3.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum based on the weight of the alumina carrier.

In this case, it is preferable that the rhodium precursor and the lanthanum precursor are simultaneously supported. According to this simultaneous support, the reduced rhodium formation rate is increased to 35% or more, thereby maximizing conversion and adsorption of nitrogen oxides to nitrate species, thereby exhibiting the decomposition power of carbon monoxide and nitrogen oxides by 80% or more.

Next, a gamma-alumina carrier is quantitatively added to the aqueous solution in which the rhodium precursor and the lanthanum precursor are dissolved, sufficiently mixed to form a slurry, and dried by stirring and heating using a vacuum evaporator. In order to continue to remove the residual moisture, it is sufficiently dried in a dryer for at least one day to completely remove the moisture contained in the micropores.

Thereafter, when drying of the sample is completed, it is calcined in an air atmosphere to complete the catalyst. In this case, the sintering of the dried sample is performed by heat treatment at 400° C. for 4 hours in an air atmosphere. This firing process may be performed in various known types of furnaces such as a tube type furnace, a convection type furnace, and a grate type furnace, and is not particularly limited.

The rhodium-lanthanum/alumina catalyst prepared by the above method has its specific surface area, crystallite size, and average pore diameter in relation to the physicochemical properties of the removal rate of carbon monoxide and nitrogen oxides. It has a significant correlation, and specifically, ^{in order to have a resolution of 80% or more at 210 o} C or more, the specific surface area of the catalyst of the catalyst is 148.82 ~ 184.99m ² /g, the lattice size is 8.59 ~ 10.12 ÅA, the average pore size is 11.51 It is preferably controlled in the range of ~ 12.14 nm.

In this case, the catalyst has the ability to simultaneously remove carbon monoxide and nitrogen oxides, and specifically, when carbon monoxide is pre-adsorbed, the active point, rhodium, is reduced using oxygen in the catalyst to reduce the proportion of reduced rhodium to 35% or more. At this time, nitrogen oxides in the reduced rhodium increase conversion and adsorption to nitrosyl species, so that the resolution of carbon monoxide and nitrogen oxides at a temperature of ^{210 to 300 o C can be obtained as 80% or more.}

Optionally, in the process of removing nitrogen oxides using the catalyst according to the present invention, at least 0 to 0.5 vol.% of oxygen and 0 to 8 vol.% of moisture may be further included in the exhaust gas including carbon monoxide and nitrogen oxides. In this case, oxygen is used to remove excess carbon monoxide after the reaction, and when it is present in an amount of 0.5 vol.% or more, carbon monoxide, which is a reducing agent, reacts faster with the injected oxygen than with the oxygen in the catalyst to reduce the rhodium. Inhibition, and moisture acts to inhibit through competition reactions with carbon monoxide. Therefore, when oxygen and moisture are present in excess of the preceding value, the decomposition capacity of carbon monoxide and nitrogen oxides may be reduced to 80% or less. In the present invention, since the required amount of oxygen and moisture in each application is minimally required within the above concentration range, and various combustion sources or pollutants contain most of the oxygen and moisture in the above concentration range in the exhaust gas itself, substantially oxygen And separate supplementation for moisture may become unnecessary.

On the other hand, the performance evaluation of the catalyst prepared according to the present invention is, for example, carbon monoxide 6,000 ppm, nitrogen monoxide 60 ppm, nitrogen dioxide 3 ppm, oxygen 5000 ppm, moisture 6 vol.%, and the catalyst under reaction conditions maintained at an likelihood rate of ^{160,000 hr -1.} It may be to check the carbon monoxide and nitrogen oxide removal rates of. Under these reaction conditions, the present invention may have a conversion rate of 80% or more at a reaction temperature of 210 to 300°C. In addition, it may be to perform FT-IR (Fourier Transform Infrared Spectrometer) analysis to confirm the reaction characteristics of removing carbon monoxide and nitrogen oxides. In addition, when carbon monoxide is pre-adsorbed, XPS (X-ray Photoelectron Spectroscopy) analysis may be performed to determine the reduction ratio of rhodium.

Hereinafter, the present invention will be described in more detail based on preferred embodiments of the present invention. However, the technical idea of the present invention is not limited or limited thereto, and may be modified and variously implemented by those skilled in the art.

Manufacturing Example 1

_{Rhodium hydroxide (Rh(OH) 2} ) and lanthanum nitrate hydrate (LaN ₃ O ₉ ) are converted into 0.1 parts by weight of rhodium and 3.0 parts by weight of lanthanum in 100 parts by weight of a gamma alumina carrier, and then quantified and dissolved in distilled water at room temperature. Subsequently, the rhodium and lanthanum aqueous solutions prepared above are added to a gamma alumina carrier to prepare a slurry form. In this case, commercially available products obtained from various manufacturers to control the specific surface area, crystallite size, and average pore diameter of the catalyst as summarized in [Table 3] below. Of gamma alumina was used. Thereafter, the prepared slurry was stirred and heated at 65°C using a vacuum evaporator, dried at 103°C for more than 24 hours to completely remove moisture contained in the micropores, and then in an air atmosphere at ^{a temperature of 400°} C for 4 hours. During firing to prepare a catalyst.

Manufacturing Example 2

It was prepared in the same manner as in Preparation Example 1, except that 0.5 parts by weight of the rhodium was quantified in 100 parts by weight of the gamma alumina carrier.

Manufacturing Example 3

It was prepared in the same manner as in Preparation Example 1, except that 1.0 part by weight of the rhodium was quantified in 100 parts by weight of the gamma alumina carrier.

Manufacturing Example 4

It was prepared in the same manner as in Preparation Example 1, except that the rhodium was quantified to 3.0 parts by weight in 100 parts by weight of the gamma alumina carrier.

Manufacturing Example 5

It was prepared in the same manner as in Preparation Example 1, except that the rhodium was quantified to 5.0 parts by weight in 100 parts by weight of the gamma alumina carrier.

Manufacturing Example 6

It was prepared in the same manner as in Preparation Example 1, except that 1.0 part by weight of the lanthanum was quantified in 100 parts by weight of the gamma alumina carrier.

Manufacturing Example 7

It was prepared in the same manner as in Preparation Example 1, except that it was quantified as 5.0 parts by weight of lanthanum in 100 parts by weight of the gamma alumina carrier.

Comparative Production Example 1

A rhodium/alumina catalyst was prepared in the same manner as in Preparation Example 1, except that only 0.1 part by weight of the rhodium was quantified in 100 parts by weight of the gamma alumina support.

Comparative Production Example 2

A lanthanum/alumina catalyst was prepared in the same manner as in Preparation Example 1, except that only 3.0 parts by weight of lanthanum was quantified in 100 parts by weight of the gamma alumina support.

Comparative Production Example 3

It was prepared in the same manner as in Preparation Example 1, except that the gamma alumina carrier 100 parts by weight was quantified as 0.05 parts by weight of the rhodium.

Comparative Production Example 4

It was prepared in the same manner as in Preparation Example 1, except that 0.5 parts by weight of lanthanum was quantified in 100 parts by weight of the gamma alumina carrier.

Comparative Production Example 5

After preparing lanthanum/alumina in the same manner as in Preparation Example 1 by using 100 parts by weight of the gamma alumina carrier as 3.0 parts by weight of the lanthanum, and then adding 0.1 parts by weight of rhodium to 100 parts by weight of the lanthanum/alumina that was subsequently prepared. A rhodium/lanthanum/alumina catalyst was prepared in the same manner as in 1.

Comparative Production Example 6

Lanthanum/rhodium/alumina was prepared in the same manner as in Preparation Example 1 by using 3.0 parts by weight of lanthanum to 100 parts by weight of rhodium/alumina of Comparative Preparation Example 1.

Comparative Production Example 7

The alumina carrier of Preparation Example 1 was used as alpha alumina, and was prepared in the same manner as in Preparation Example 1.

The types of catalysts according to the above-described Preparation Example are shown in [Table 1] below, and the types of catalysts according to Comparative Preparation Examples are shown in [Table 2] below.

division Rhodium content
(Based on 100 parts by weight of the carrier) Lanthanum content
(Based on 100 parts by weight of the carrier) Form of catalyst Manufacturing Example 1 0.1 3.0 Rhodium-lanthanum
/Gamma alumina (A) Manufacturing Example 2 0.5 3.0 Rhodium-lanthanum/gamma alumina (A) Manufacturing Example 3 1.0 3.0 Rhodium-lanthanum/gamma alumina (A) Manufacturing Example 4 3.0 3.0 Rhodium-lanthanum/gamma alumina (A) Manufacturing Example 5 5.0 3.0 Rhodium-lanthanum/gamma alumina (A) Manufacturing Example 6 0.1 1.0 Rhodium-lanthanum/gamma alumina (A) Manufacturing Example 7 0.1 5.0 Rhodium-lanthanum/gamma alumina (A)

division Rhodium content
(Based on 100 parts by weight of the carrier) Lanthanum content
(Based on 100 parts by weight of the carrier) Form of catalyst Comparative Production Example 1 0.1 0 Rhodium/gamma alumina (A) Comparative Production Example 2 0 3.0 Lanthanum/gamma alumina (A) Comparative Production Example 3 0.05 3.0 Rhodium-lanthanum/gamma alumina (A) Comparative Production Example 4 0.1 0.5 Rhodium-lanthanum
/Gamma alumina (A) Comparative Production Example 5 0.1 3.0 Rhodium/lanthanum
/Gamma alumina (A) Comparative Production Example 6 0.1 3.0 Lanthanum/Rhodium
/Gamma alumina (A) Comparative Production Example 7 0.1 3.0 Rhodium-lanthanum/alpha alumina (A)

Example 1 In order to evaluate the removal rate of carbon monoxide and nitrogen oxides according to the presence or absence of rhodium and lanthanum in the catalyst of the present invention, an experiment was performed to remove nitrogen oxides using carbon monoxide as a reducing agent, and the above preparation was performed according to the presence or absence of rhodium and lanthanum. Example 1, Comparative Preparation Example 1 and Comparative Preparation Example 2 are compared, and the results of carbon monoxide and nitrogen oxide removal rates are shown in FIGS. 1A and 1B.

In this case, the temperature of the reactor was maintained at a rate of 200 to 300°C, 6,000 ppm of carbon monoxide, 60 ppm of nitrogen monoxide, 3 ppm of nitrogen dioxide, 5,000 ppm of oxygen, 6 vol.% of moisture, and 160,000 hr ^-1 .

In this case, in order to confirm the removal rate of carbon monoxide as a reducing agent and nitrogen oxide as a reactant, a non-dispersive infrared gas analyzer (ZKJ-2, FUJI Electronic CO.) was used for carbon monoxide, and a non-dispersive infrared gas analyzer (non-dispersive infrared gas analyzer) among nitrogen oxides Uras10E, Hartman & Braun Co.) was used, and for nitrogen monoxide, a non-dispersive infrared gas analyzer (ULTRAMAT 6, Simens Co.) was used. In addition, nitrogen dioxide was measured through a detection tube (9L, Gas Tec. Co.) at the outlet of the main reactor.

Referring to FIG. 1, in Preparation Example 1 in which both rhodium and lanthanum were supported, the conversion rate of carbon monoxide and nitrogen oxides was greater than or equal to 88% at a reaction temperature ^{of 210 to 300 o C.} On the other hand, Comparative Preparation Example 1 to which only rhodium was added ^{exhibited a carbon monoxide conversion rate of 100% at 275 to 300 o} C, but at a temperature below that, it showed a conversion rate of 80% or less, and an overall nitrogen oxide conversion rate of 60% or less. I got it. In addition, Comparative Preparation Example 2 in which only lanthanum was added had an overall efficiency of 50% or less. Therefore, according to the present invention, when both rhodium and lanthanum are supported on gamma alumina, an optimal catalyst can be prepared.

Example 2

In the catalyst prepared according to Preparation Example 1, the specific surface area, crystallite size, and average pore size of rhodium-lanthanum/alumina prepared using gamma alumina according to various samples A to E pore diameter) is shown in Table 3 below, and the correlation between the physicochemical properties and removal performance of rhodium-lanthanum/alumina is shown.

division A B C D E BET (m ² /g) 184.99 148.82 125.01 87.32 112.42 Crystallite size (ÅA) 8.59 10.12 5.71 16.87 7.36 Average pore diameter (nm) 11.51 12.14 6.44 14.81 8.10 Carbon monoxide removal rate at 210 ^{o C (%)} 100.00 94.51 41.25 30.47 60.29 Nitrogen oxide removal rate at 210 ^{o C (%)} 88.00 81.57 10.24 37.93 62.50

From [Table 3], it can be seen that alumina applied to the production of a rhodium-lanthanum/alumina catalyst should basically have a specific surface area ^{of 148.82 m 2 /g or more.} In addition, the lattice size should be in the range of 8.59 ~ 10.12 ÅA, and the average pore size should be in the range of 11.51 ~ 12.14 nm, it can be seen that it is preferable for the carbon monoxide and nitrogen oxide removal reaction.

Example 3

In order to evaluate the removal rate of carbon monoxide and nitrogen oxides according to the time of carrying lanthanum in the catalyst of the present invention, an experiment was performed to remove nitrogen oxides using carbon monoxide as a reducing agent. And Comparative Preparation Example 6 is compared, and the removal rates of carbon monoxide and nitrogen oxides are shown in FIGS. 2A and 2B. The experiment was the same as in Example 1.

Referring to FIG. 2, the best carbon monoxide and nitrogen oxide removal rates can be confirmed in the catalyst prepared in Preparation Example 1 prepared by simultaneously supporting rhodium and lanthanum on gamma alumina. Therefore, according to the present invention, an optimal catalyst can be prepared when rhodium and lanthanum are simultaneously supported on gamma alumina.

Example 4

In order to evaluate the removal rate of carbon monoxide and nitrogen oxides according to the content of rhodium and lanthanum in the catalyst of the present invention, an experiment was performed to remove nitrogen oxides using carbon monoxide as a reducing agent. According to the content of rhodium, the carbon monoxide and nitrogen oxide removal rates were shown in [Table 4] by comparing Preparation Example 1, Preparation 2, Preparation 3, Preparation 4, Preparation 5 and Comparative Preparation Example 3, and lanthanum content According to the comparison of Preparation Example 1, Preparation Example 5, Preparation Example 6 and Comparative Preparation Example 4, the carbon monoxide and nitrogen oxide removal rates are shown in [Table 5]. The experiment was the same as in Example 1.

When 0.1 parts by weight or more of rhodium was supported on the alumina carrier and 1.0 parts by weight or more of lanthanum was supported, the decomposition power of carbon monoxide and nitrogen oxides was exhibited. Rhodium is a precious metal-based active metal, and it is preferable to minimize it in terms of cost as long as it can achieve catalytic activity, so when it is supported in 5.0 parts by weight, the decomposition capacity of carbon monoxide and nitrogen oxides appears to be 80% or more, but it is not preferable in terms of cost. Can not do it. In addition, when the lanthanum content is increased from 3.0 parts by weight to 5.0 parts by weight, the decomposition capacity of carbon monoxide is partially improved, but the decomposition capacity of nitrogen oxides is partially reduced, which is not preferable. ^{For example, in order to exhibit 80% or more resolution at 210 to 300 o} C depending on the content of rhodium or lanthanum, it can be seen that it is preferable when supported by 0.1 to 3.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum on an alumina support.

reaction
Temperature
(℃) Carbon monoxide removal rate (%) Nitrogen oxide removal rate (%) Manufacturing Example 1 Manufacturing example
2 Manufacturing example
3 Manufacturing example
4 Manufacturing example
5 Comparative Production Example
3 Manufacturing example
One Manufacturing example
2 Manufacturing example
3 Manufacturing example
4 Manufacturing example
5 Comparative Production Example
3 300 100 100 100 100 100 100 96.83 97 99 100 100 84.54 275 100 100 100 100 100 100 100 100 100 100 100 91.40 250 100 100 100 100 100 94.51 100 100 100 100 100 83.67 225 100 100 100 100 100 76.99 91 100 100 100 100 65.98 210 100 100 100 100 100 44.12 88 100 100 100 100 31.69 200 26 36.51 48.51 74 79 11.59 12.70 24 37 64 65 67

Reaction temperature(℃) Carbon monoxide removal rate (%) Nitrogen oxide removal rate (%) Manufacturing example
One Manufacturing example
5 Manufacturing example
6 Comparative Production Example
4 Manufacturing example
One Manufacturing example
5 Manufacturing example
6 Comparative Production Example
4 300 100 100 100 100 96.83 87.55 91.58 61.77 275 100 100 100 94.83 100 96.55 100 76.21 250 100 100 100 91 100 94.51 100 69.51 225 100 100 100 88 91 81.58 100 51.27 210 100 88.52 100 48.51 88 81.58 82.12 31.6 200 26 7.89 31 0 12.70 6.58 12.58 0

Example 5

In order to confirm the reaction characteristics of the catalyst of the present invention, DRIFT analysis was performed using FT-IR, and the comparison between Preparation Example 1 and Comparative Preparation Example 1 is shown in FIGS. 3A and 3B.

Specifically, FT-IR 660 Plus (JASCO) was used to perform DRIFT analysis. For the reflectance analysis of the solid, a Diffuse Reflectance (DR) 400 acessory was used, and a spectra was collected using a KBr window as a plate for DR measurement. After filling the DR with 0.3g of the catalyst pulverized to 100 μm or less, the temperature was raised to 300℃ at 10℃/min in an air atmosphere for removal and activation of moisture and impurities on the catalyst surface, and then maintained for 30 minutes and lowered to 250℃. After that, 1,000 ppm of carbon monoxide was adsorbed for 1 hour. After confirming the process of the catalyst surface reaction while adsorbing 1,000 ppm of nitrogen monoxide for 1 hour, desorption of adsorbed species remaining on the catalyst surface for 1 hour in an air atmosphere was confirmed.

Looking at the DRIFT analysis shown in FIG. 3, it was possible to confirm the same reactive action on the catalyst surfaces of Preparation Example 1 and Comparative Preparation Example 1. First, when carbon monoxide, which is used as a reducing agent, is adsorbed for 1 hour ^{, carbon monoxide is adsorbed from rhodium (Rh 2+} ) on the surface of the catalyst and reacts with oxygen in the catalyst to convert it into carbon dioxide, so that the rhodium surface is reduced and the reduced rhodium (Rh ^It can be seen that carbon monoxide is adsorbed to 0 ). After that, when the reactant nitrous oxide is adsorbed for 1 hour, it can be seen that nitrogen monoxide is converted and adsorbed to nitrosyl ^{species (NO +) on the reduced rhodium surface.} After that, it can be seen that the adsorbed species are reduced by reacting the nitrosyl species, which is a convertible adsorbed species of carbon monoxide and nitrous oxide, adsorbed on the reduced rhodium surface. Finally, when all the carbon monoxide adsorbed on the reduced rhodium surface reacted and desorbed, it was confirmed that the _{rhodium surface was oxidized again and the nitrogen monoxide continuously injected was finally converted into nitrate (NO 3} ^{−) species.} Therefore, it can be confirmed that the reaction proceeds in the reduced rhodium when carbon monoxide and nitrogen oxide react on the surface of the catalyst, and it can be confirmed that nitrogen monoxide must be converted and adsorbed into nitro disappearance in order to participate in the reaction.

In this case, Preparation Example 1 confirmed that the reaction rate of carbon monoxide and nitrogen oxide in the reduced rhodium was further increased. In addition, as mentioned in Example 4, since the catalyst of Preparation Example 1 is very excellent in reducing ability, it is judged that the reaction activity and reaction rate are increased because it can further form a reduced rhodium surface when carbon monoxide is adsorbed.

Example 6

As can be seen in Example 5, in order for carbon monoxide and nitrogen oxides in the catalyst to react, reduced rhodium must be formed. Therefore, in the present invention, XPS analysis was performed to confirm the ratio of the reduced rhodium of the catalysts according to Preparation Example 2 and Comparative Preparation Example excluding Comparative Preparation Example 2 in which rhodium was not supported, and lanthanum was supported for each Preparation Example and Example. Table 6 shows the values for ^{the reduced rhodium ratio (Rh 0} /Rh _total ) according to the presence or absence, rhodium content, lanthanum content, and supporting positions of rhodium and lanthanum. 4 shows the correlation between the reduced rhodium ratio (Rh ⁰ /Rh _total ) and the reaction activity at ^{210 o C.} As a method for checking the proportion of reduced rhodium, in the same manner as in the carbon monoxide pre-adsorption reaction of Example 5, 1,000 ppm of carbon monoxide containing no oxygen was injected into nitrogen for 1 hour, and the reaction was performed using only oxygen in the catalyst. ^{Referring to FIG. 4, it was confirmed that the reduced rhodium ratio (Rh 0} /Rh _total ) must be present at 35% or more in order for the resolution of carbon monoxide and nitrogen oxides to be 80% or more.

catalyst Reduced Rhodium Ratio (Rh ⁰ /Rh _total ) Manufacturing Example 1 42.33 Manufacturing Example 2 48.54 Manufacturing Example 3 51.24 Manufacturing Example 4 59.11 Manufacturing Example 5 62.51 Manufacturing Example 6 37.51 Manufacturing Example 7 43.78 Comparative Production Example 1 14.84 Comparative Production Example 3 28.52 Comparative Production Example 4 29.34 Comparative Production Example 5 28.69 Comparative Production Example 6 19.14 Comparative Production Example 7 29.99

Claims (12)

As a catalyst for removing nitrogen oxides used to remove nitrogen oxides using carbon monoxide as a reducing agent, rhodium for nitrogen oxide removal comprising 0.1 to 3.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum based on 100 parts by weight of an alumina carrier- Lanthanum/alumina catalyst.
The rhodium-lanthanum/alumina catalyst according to claim 1, wherein the rhodium surface reacts with carbon monoxide and nitrogen oxides in a reduced state.
The rhodium-lanthanum/alumina catalyst according to claim 2, wherein the nitrogen oxide reacts with carbon monoxide after being adsorbed as nitrosyl species on the reduced rhodium surface.
The rhodium-lanthanum/alumina catalyst according to claim 3, wherein the reduced rhodium ratio (Rh ⁰ /Rh _total ) is maintained at 35% or more during the carbon monoxide pre-reaction.
The method of claim 1, wherein the catalyst has a specific surface area of 148.82 to 184.99 m ² /g, a lattice size of 8.59 to 10.12 ÅA, and an average pore size of 11.51 to 12.14 nm. catalyst.
Rhodium-lanthanum/alumina catalyst for removing nitrogen oxide, characterized in that 0.1 to 3.0 parts by weight of rhodium and 1.0 to 3.0 parts by weight of lanthanum are quantified and supported at the same time, followed by drying and firing, based on 100 parts by weight of the alumina support.
The method of claim 6, wherein the alumina carrier is gamma alumina (γ-Al ₂ O ₃ ).
The method of claim 6, wherein the rhodium precursor is rhodium hydroxide (Rh(OH) ₂ ).
The method of claim 6, wherein the lanthanum precursor is lanthanum nitrate hydrate (LaN ₃ O ₉ ).
[7] The method of claim 6, wherein the firing of the rhodium precursor and the lanthanum precursor on the alumina support is performed at a temperature of 400° C. for 4 hours.
A method for removing nitrogen oxides by contacting the exhaust gas in which carbon monoxide and nitrogen oxides are mixed with the catalyst according to any one of claims 1 to 5.
The method of claim 11, wherein the step of contacting the exhaust gas with the catalyst is performed in the presence of oxygen and moisture.

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