KR20060017186A - Catalyst for purifying nitrogen oxides from diesel vehicles and a process for purifying nitrogen oxides using said catalyst - Google Patents

Abstract

The present invention relates to a catalyst for purifying nitrogen oxides and a method for purifying nitrogen oxides using the same, and more particularly, V _X -P _Y- (consisting of vanadium (V), phosphorus (P), and a substance having a hydroxyl group on its surface. Hydroxyl-containing substance) _Z- catalyst for purifying nitrogen oxides comprising 95 to 99.99% by weight of _Z carrier and 0.01 to 5% by weight of platinum (Pt) has a low NOx conversion rate of 95% or more and a conversion rate of 70% or more to N ₂ at a low temperature of 200 ° C or lower. Because it can reduce nitrogen oxide, NOx can be purified even when the temperature of exhaust gas at the beginning of car driving is low due to the high activity of the catalyst. Since hydrogen is used as a reducing agent, there is no environmental pollution problem even if the reducing agent leaks into the atmosphere. It is very useful for purifying the nitrogen oxides emitted from diesel vehicles because it does not deteriorate in the atmosphere of water vapor and SOx.

Catalyst for nitrogen oxide purification, hydrogen reduction, selective reduction, diesel vehicle

Description

Catalyst for purifying nitrogen oxides from diesel vehicles and a process for purifying nitrogen oxides using said catalyst}

Figure 1 shows the nitrogen oxide purification capacity of the catalyst according to the type of material used as a carrier (Alumina (○), silica (◇), ZSM-5 (▽), TiO ₂ (□) and V-Al ₂ O ₃ (●)),

Figure 2 shows the nitrogen oxide purification capacity of the Pt / V-Al ₂ O ₃ catalyst when the NO concentration is reduced by half under the same conditions as in Figure 1 (NO conversion rate (●) and conversion to N ₂ (■)) ,

Figure 3 shows the nitrogen oxide purification ability under the Pt (○), Pd (□), Rh (△) and Ru (◇) catalyst supported on the carrier V-Al ₂ O ₃ ,

4 shows nitrogen under a catalyst supporting Rh (□), Co (Δ), Sn (◇), Pd (▽), Mg (●) and Ce (▲) on Pt / V-Al ₂ O ₃ (o). Shows oxide purification ability,

Figure 5 shows the nitrogen oxide purification ability of the carrier V-Al ₂ O ₃ ,

Figure 6 shows the ability to purify the nitrogen oxides when the x value is changed to 5 (○), 10 (□) and 20 (△) in Pt / P ₁₀ V _x (Al ₂ O ₃ ) ₅₀ catalyst.

The present invention is composed of vanadium (V), phosphorus (P) and 95 to 99.99% by weight of a V _X -P _Y- (hydroxyl group) _Z carrier and 0.01 to 5% by weight of platinum (Pt) It relates to a catalyst for purifying nitrogen oxides containing% and a method for purifying nitrogen oxides using the same.

Nitrogen oxides emitted from diesel vehicles (lean-NOx, hereinafter called lean nitrogen oxides) coexist with large amounts of oxygen, making it very difficult to purify them, which is causing enormous environmental and human harm worldwide. Nitrogen oxides in urban areas, which are the main culprit of photochemical smog and acid rain, are mostly emitted from diesel cars without purification catalysts.

As a method for purifying lean nitrogen oxide, conventionally, (i) a method of selectively reducing nitrogen oxides under a catalyst using a reducing agent such as a hydrocarbon or an alcohol, ii) a method of directly decomposing under a catalyst without a reducing agent, iii) a plasma or a plasma A method of removing by using a hybrid system consisting of and a catalyst, i) a method of storing nitrogen oxide in the form of a metal nitrate in a basic oxide such as BaO, and then reducing it to a platinum (Pt) catalyst when the storage is saturated. Iii) Various methods have been studied, including other methods of electrochemical removal. However, all of these methods have disadvantages and thus have not been put to practical use as a technique for purifying lean nitrogen oxides.

First, the method of i) selectively reducing nitrogen oxides using a reducing agent is preferably a hydrocarbon constituting diesel fuel as a reducing agent, but there is a disadvantage in that the purification efficiency of nitrogen oxides is not high yet. As the reducing agent of nitrogen oxides, the most efficient materials presently release ammonia during ammonia or pyrolysis. If toxic ammonia and urea are used as reducing agents, they cause another environmental problem if they leak into the atmosphere. There is a disadvantage in that it is necessary to periodically inject into the vehicle and the nitrogen oxide is reduced, the temperature is relatively high, so the temperature of the exhaust gas is low, the nitrogen oxide can not be purified at the beginning of the vehicle operation.

In addition, the method of ii) of directly decomposing nitrogen oxides using a catalyst is the most ideal but very low in efficiency since no reducing agent is used, and the method of iii) using a plasma or a plasma / catalyst hybrid system is electrically Because of the high cost of operation, the structure of the purification device is complicated, the purification efficiency of nitrogen oxide has not reached the level of practical use.

On the other hand, the NOx storage-reduction method described in iii), which stores nitrogen oxides in basic oxides under excess air conditions and reduces them with platinum catalysts under air lean conditions, is developed by Toyota Motor Corp. of Japan and its lean-burn gasoline car This technology has been applied to, and is currently considered as one of the most promising methods for the purification of nitrogen oxides emitted from diesel vehicles. However, this method is not applicable to automobiles using diesel fuel containing sulfur because the basic oxide used for the storage of nitrogen oxides is easily reacted with sulfur oxides (SOx) to lower the activity. Diesel fuels generally contain sulfur, and gasoline sold in Europe is known to contain sulfur. In order to prevent the basic oxides from reacting with the sulfur component, studies are currently being conducted to add a second component that is resistant to sulfur, but when the additive is added, the NOx storage capacity of the basic oxide is lowered. In addition to these problems, the NOx storage-reduction method also requires the development of engines as well as catalysts to purify nitrogen oxides, since automobile engines must be operated periodically in excess and lean conditions.

Several attempts have been made, including electrochemical and photochemical removal of other lean nitrogen oxides, but the potential for practical use is very low.

Therefore, nitrogen oxide can be purified even in the early stage of driving a car with low exhaust gas temperature, so it has excellent activity even at low temperature of about 100 ℃, and has a wide range of temperature because the temperature of exhaust gas changes greatly according to the driver's habit. It is resistant to SOx and water vapor, does not cause deactivation due to carbon deposition on the surface of catalyst, and reduces nitrogen oxides to harmless nitrogen rather than nitrous oxide (N ₂ O), which destroys ozone layer and causes greenhouse effect. In addition, it is urgent to develop a catalyst for purifying nitrogen oxides that can use diesel fuel or a material obtained by reforming diesel fuel as a reducing agent for the driver's convenience.

Therefore, the present invention has excellent activity even at a low temperature of about 100 ° C., and even if the reducing agent leaks into the air, there is no problem of environmental pollution, and it does not deteriorate even in the atmosphere of water vapor and SOx. It is an object to provide a useful catalyst for purifying nitrogen oxides.

In order to achieve the above object, the present invention is 95 to 99.99% by weight of a V _X -P _Y- (hydroxy group holding material) _Z carrier composed of vanadium (V), phosphorus (P) and a material having a hydroxyl group on the surface (Pt) It provides a catalyst for purifying nitrogen oxides containing 0.01 to 5% by weight.

The present invention also impregnates a solution containing vanadium (V) and phosphorus (P) in a material having a hydroxy group on its surface, or a vanadium (V) and phosphorus (P) and a material having a hydroxy group on its surface. It provides a method for preparing the catalyst for purifying nitrogen oxides comprising the step of preparing a V _X -P _Y- (hydroxy group holding material) _Z carrier by coprecipitation of a solution containing the impregnated with platinum (Pt).

In addition, the present invention provides a method for purifying nitrogen oxides, characterized in that to reduce the diesel vehicle exhaust nitrogen oxides to hydrogen at a temperature of 50-400 ℃ in the presence of the catalyst for nitrogen oxide purification.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

Substances that can be used to reduce nitrogen oxides are chemicals containing C, H and O atoms in molecules such as hydrocarbons, alcohols, carbon monoxide and ammonia. In particular, since hydrogen dissociative adsorption occurs well under a metal catalyst even at low temperatures, when nitrogen is used as a reducing agent, nitrogen oxides can be reduced at low temperatures. Hydrogen can be easily obtained by reforming diesel fuel mounted on a vehicle. Fuel cells that produce electricity by producing hydrogen from hydrocarbons such as gasoline or methanol are systems that obtain hydrogen through reforming reactions.

Using diesel fuel directly as a reducing agent is ideal because there is no need to charge a separate device or reducing agent externally, but it is efficient in terms of using reducing agent because not all components of diesel fuel have activity as reducing agent of nitrogen oxides. Can not do it. Pt / alumina catalyst, the C ₃ H ₈ is, Pt / silica catalyst, just as C ₃ H ₆ are excellent denitration reducing agent generally have a good activity but has a particular reducing agent, particular catalyst. Therefore, the use of diesel fuel as a direct reducing agent is simply to burn most of the fuel components with carbon dioxide, so it is necessary to modify and use the specific components such as hydrogen.

When hydrogen is used as a reducing agent, not only can nitrogen oxide be removed at low temperatures as described above, but also can be directly obtained in a vehicle through a reforming reaction of diesel fuel, thereby eliminating the need to periodically recharge the reducing agent. Accordingly, the present inventors have determined that hydrogen is the most promising reducing agent for the removal of lean nitrogen oxides, and have completed the present invention by developing a catalyst in which platinum is supported on a carrier having high activity in the hydrogen reducing agent.

In Pt / V _X -P _Y- (hydroxy group holding material) _Z , which is a catalyst for purifying nitrogen oxides of the present invention, the hydroxyl group holding material is alumina, silica, zeolite, mesoporous (mesoporous) material MCM-41 and SBA-15 or It is a substance having a hydroxyl group on its surface, such as titania. The catalyst for purifying nitrogen oxides of the present invention has a carrier of V _X -P _Y- (hydroxy group) obtained by adding x moles and y moles of vanadium (V) and phosphorus (P) components to z moles of a substance having such a surface hydroxyl group. Substance) _Z is obtained by impregnating platinum (Pt) in an appropriate amount. In this case, phosphorus is not an essential ingredient, but may be added, but vanadium must be included.

The preparation of the carrier, V _X -P _Y- (hydroxy group-bearing substance) _Z , is not limited to impregnation obtained by impregnating and baking the vanadium and phosphorus components in the surface hydroxyl group-bearing particles, and the hydroxy group-bearing substance precursor, vanadium and It can also be prepared by co-precipitation while putting the phosphorus precursor solution together. That is, V _X -P _Y- (hydroxy group-bearing substance) _{Z, which} is a carrier supporting the catalyst of the present invention, refers to a bicomponent or ternary metal oxide composed of a surface hydroxy group-bearing substance and a vanadium or phosphorus component regardless of the preparation method. . The amount of vanadium component added to the surface hydroxy group-bearing substance is precisely determined by the number of surface hydroxy groups, but in approximately a molar ratio of atoms, Z / X is 4-200, preferably 10-40, and the phosphorus component is Z / Y is 2-1000 by molar ratio.

In particular, the catalyst for purifying nitrogen oxides of the present invention is composed of 95 to 99% by weight of the carrier, V _X -P _Y- (hydroxy group-bearing substance) _Z, and 0.01 to 5% by weight of platinum supported. At this time, when the content of platinum is less than 0.01% by weight or more than 5% by weight, there is a problem in that the activity of the catalyst is rather deteriorated.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

As shown in FIG. 1, alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zeolite (ZSM-5), and titania (TiO) are used as carriers of the platinum catalyst to remove lean nitrogen oxides when hydrogen is used as a reducing agent. ₂ ) of the alumina is the best. In particular, when the vanadium (V) component is added to the alumina carrier, the nitrogen oxides can be reduced with higher efficiency. In addition, except for reducing the concentration of nitrogen oxide in half, the lean nitrogen oxide reduction ability of the Pt / V-Al ₂ O ₃ catalyst was confirmed under the same conditions as in FIG. 1, and as shown in FIG. do.

As the hydroxyl group-bearing material usable in the present invention, the above-described alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zeolite (ZSM-5) or titania (TiO ₂ ) and the like can be used. Explain.

As a result of confirming that the V-Al ₂ O ₃ carrier impregnated with vanadium (V) in alumina functions as a good carrier for precious metals other than platinum, palladium (Pd), rhodium (Rh) or ruthenium ( Catalysts made of noble metals such as Ru) showed low nitrogen oxide reduction ability at most temperatures, and only the combination of platinum and V-Al ₂ O ₃ carriers showed high activity in the nitrogen oxide reduction reaction by hydrogen.

In addition, as a result of investigating the role of the promoter or additive for increasing the activity of the catalyst by tracely impregnating other catalyst components in the Pt / V-Al ₂ O ₃ catalyst, rhodium (Rh) and palladium (Pd) as shown in FIG. NO conversion and conversion to N ₂ when a catalyst was prepared by impregnating metal components such as cobalt (Co), tin (Sn), magnesium (Mg) and selenium (Ce) with platinum to a V-Al ₂ O ₃ carrier. All of this was reduced compared to the Pt / V-Al ₂ O ₃ catalyst.

In addition, when platinum was loaded while changing the amount of vanadium (V) component impregnated with alumina, the NO conversion increased as the ratio of Al / V decreased from 32 to 12 based on the molar ratio of atoms, and then the ratio of Al / V increased to 12 In the following cases, the NO conversion rate gradually decreased. That is, the average conversion rate of nitrogen oxide was highest when the Al / V ratio was around 12.

According to the Journal of Catalysis, 191 (2000), 384, vanadium (V) is present as vanadil ions (VO ²⁺ ) in combination with the surface hydroxyl group of alumina at low contents. The formation of a two-dimensional vanadate and the increase of the amount of vanadium (V) further results in the formation of V ₂ O ₅ oxide particles. When present, the conversion of nitrogen oxides is high, and this vanadiyl ion is one of the reactive active sites. The addition of other metals to the Pt / V-Al ₂ O ₃ catalyst results in a lower NO conversion because the access of the reactants to vanidyl ions is blocked by the added metal component.

Since the Pt / V _X -P _Y- (hydroxy group-bearing substance) _Z catalyst of the present invention is made only of a material having strong resistance to SOx, the activity is not reduced in the SOx atmosphere. Platinum is already known to be resistant to SOx as an SO ₂ oxidation catalyst, and vanadium oxide is also widely used as one of the main components of the fixed source NOx purification catalyst containing SOx because it is resistant to SOx.

In addition, the Pt / V _X -P _Y- (hydroxy group-bearing substance) _Z catalyst of the present invention is not affected by water vapor. The exhaust gas of diesel vehicles contains more than 10% water vapor. The effects of water vapor on Pt / V-Al ₂ O ₃ catalysts at a reaction temperature of 160 ° C show that the NO conversion and the conversion to N ₂ are 0-10%. It can be seen that it does not change significantly under the atmosphere.

In addition, diesel vehicle exhaust contains a large amount of oxygen of about 5-10%. This is the result of supplying air to the engine in excess of stoichiometric requirements to improve the combustion efficiency of the fuel. This makes it very difficult to reduce nitrogen oxides which are weaker than oxygen and present in much lower concentrations. However, the Pt / V _X -P _Y- (hydroxy group-containing substance) _Z catalyst of the present invention is not affected by oxygen in the oxygen concentration range of 5-10%. Generally, the activity of the catalyst decreases as the oxygen concentration increases. The conversion of the catalyst according to the present invention to NO and N ₂ is within 10% and 4% of the variation in the oxygen concentration of 5-10%, respectively. The catalyst of the present invention is not limited to the oxygen concentration because the variation of the conversion rate generated when the oxygen concentration increases also disappears by increasing the amount of reducing agent hydrogen by increasing the amount of oxygen, thereby keeping the ratio of oxygen and hydrogen constant. It is possible to purify lean nitrogen oxide with high efficiency.

In addition, the catalyst for purifying nitrogen oxides of the present invention impregnates a solution containing vanadium (V) and phosphorus (P) in a material having a hydroxyl group on the surface, or a material containing hydroxy group, vanadium (V) and Preparing a V _X -P _Y- (hydroxy group-containing substance) _Z carrier by coprecipitation of a solution containing phosphorus (P) and impregnating platinum (Pt) with the carrier (second step) Is manufactured.

In the preparation of the catalyst according to the present invention, phosphorus is not an essential ingredient, so it is not necessary to add it, but vanadium must be included. However, if the carrier of the catalyst according to the present invention, V _X -P _Y- (OH group holding material) _Z is prepared by the coprecipitation method, it is preferable to add the phosphorus component, which does not add the phosphorus component, If only vanadium precursor is used, coprecipitation efficiency is not high. Thus, the phosphorus used in the present invention facilitates coprecipitation but does not reduce the performance of the catalyst at all.

The present invention also provides a method for purifying nitrogen oxides for reducing diesel vehicle exhaust nitrogen oxides flowing at a space velocity of 20,000-200,000 h ⁻¹ to hydrogen at a temperature of 50-400 ° C. in the presence of the catalyst for purifying nitrogen oxides.

At this time, hydrogen as a reducing agent is preferably supplied at a concentration of 500-20,000 ppm.

Hereinafter, examples of the present invention will be described in detail through examples. However, the present invention is not limited by the following examples.

<Example 1>

Impregnated K ₂ PtCl ₄ solution in Al ₂ O ₃ , SiO ₂ , ZSM-5, TiO ₂ and V-Al ₂ O ₃ with an Al / V ratio of 12 and dried at 100 ° C. for 2 hours, and at 500 ° C. for 5 hours. Calcined to prepare a catalyst having a Pt content of 0.25% by weight. At this time, V-Al ₂ O ₃ was obtained by impregnating VOSO ₄ aqueous solution in Al ₂ O ₃ , dried at 120 ℃ for 2 hours and calcined at 500 ℃ for 5 hours.

0.2 g of the obtained catalyst was placed in a U-shaped quartz tube reactor, and a mixed gas consisting of 1000 ppm NO, 3% O ₂ , 4000 ppm H ₂ , and the remaining He was added to the reactor at a flow rate of 140 ml / min (space velocity: 84000 h ⁻¹ ). NO reduction reaction was investigated while flowing. At this time, the N ₂ concentration of the reactor outlet gas was analyzed by gas chromatography using molecular sieve 5A separation tube, and the H ₂ and N ₂ O concentrations were respectively analyzed using Porapak Q separation tube. NO conversion and conversion to N ₂ were obtained.

[Equation 1]

[Equation 2]

As a result, as shown in FIG. 1, alumina is the best carrier of the hydroxy group-bearing metal oxide, and when the vanadium component is added to the alumina, the NO conversion rate is 96% or more over a wide temperature range from 100 ° C to 210 ° C. The conversion to N ₂ was also maintained at over 60% up to 310 ° C. Since NO is reduced at such a low temperature, NO ₂ is hardly produced and only converted to N ₂ and N ₂ O.

<Example 2>

The concentration of NO in the reaction gas was 500 ppm and the other experimental conditions were performed in the same manner as in Example 1 to investigate the activity of the Pt / V-Al ₂ O ₃ (Pt 0.25 wt.%, Al / V ratio 12) catalyst. As a result, as shown in FIG. 2, when the NO concentration was 500 ppm, the NO conversion of the Pt / V-Al ₂ O ₃ catalyst reached 100% in the temperature range of 140-160 ° C., and the conversion to N ₂ also showed 91%. It was.

<Example 3>

Exemplary experimental conditions the same as in Example 1 in a V-Al ₂ O ₃ of the Al / V ratio 12 manufactured by making the catalyst supporting 0.25% by weight of Pd, Rh and Ru precious metal each embodiment the activity of the NO reduction reaction in Example 1 This was compared with the activity of Pt / V-Al ₂ O ₃ catalyst. As a result, as shown in FIG. 3, the Pd, Rh and Ru catalysts supported on V-Al ₂ O ₃ had a NO conversion of approximately 40%, and a conversion to N ₂ was also very low, of 40% or less.

<Example 4>

Pt and other metals were simultaneously supported by impregnation in V-Al ₂ O ₃ having an Al / V ratio of 12 prepared in Example 1 to form Pt-metal / V-Al ₂ O _{3 to} form a Pt / V-Al ₂ O ₃ catalyst. The effect of metal additives on the temperature was investigated. Experimental conditions were the same as in Example 1, and Rh, Pd, Co and Sn were 0.05 wt% and Mg and Ce were respectively 0.1 wt% in the added metal. As a result, FIG. 4 were lower both the Pt / V-Al ₂ conversion to NO conversion and N ₂ the addition of these metals to the O ₃ catalyst, as shown in, it was also narrow effective temperature range. The results were similar when these metals were added at different concentrations.

This metal component is added by being because the active site (active site) active sites of metal components in the respective present together V-Al ₂ O ₃ on the Pt the carrier V-Al ₂ O ₃ is added to the reaction conversion rate is decreased by being It was interpreted as decreasing. In particular, as shown in FIG. 4, most catalysts show double peaks in the form of increasing-decreasing-increasing-decreasing NO conversion with increasing temperature, which means that the active point of the reaction is at least two sites.

<Example 5>

0.2 g of the carrier V-Al ₂ O ₃ (Al / V ratio 12) was put into the reactor and the activity of the NO reduction reaction was investigated under the experimental conditions of Example 1. As a result, as shown in Figure 5, the carrier V-Al ₂ O ₃ showed a significant activity in the NO reduction reaction. In other words, the NO conversion was about 61% at 210 ° C and the conversion to N ₂ was 50%.

Therefore, the reason why Pt / V-Al ₂ O _{3, which} is one of the catalysts according to the present invention, is excellent in a wide temperature range is that active sites are activated at different temperatures on the catalyst main component Pt and the carrier.

<Example 6>

0.2 g of the Pt / V-Al ₂ O ₃ catalyst prepared in Example 1 was placed in a reactor, and a mixed gas consisting of 1000 ppm NO, 3% O ₂ , 4000 ppm H ₂ , 0-10% water vapor, and the rest He was 140 The effect of water vapor at 160 ° C. was investigated while feeding the reactor at a flow rate of ml / min. As a result, the NO conversion was 93, 90, 90, 88% at the vapor concentrations of 0, 3, 7, and 10%, respectively, and the conversion to N ₂ was 65, 60, 60, 58%, and N ₂ O, respectively. 28, 30, 30, 30%.

Therefore, even if water vapor is present in the reaction gas up to 10%, the activity of the catalyst is not significantly reduced, it can be seen that the conversion to N ₂ O slightly increases when water vapor is present.

<Example 7>

The effect of vanadium content on the Pt / V-Al ₂ O ₃ catalyst was investigated by varying the Al / V ratio to 32, 16, 12, 8 and controlling the amount of vanadium component supported on the alumina. Experimental results at 120 ℃ under the experimental conditions of Example 1, when the Al / V ratio was changed to 32, 16, 12, 8, the NO conversion was 22.0, 37.7, 100, 81.2%, respectively, the conversion to N ₂ was 10.4, 14.9, 60.2, 42.8% of the catalyst activity was the highest in the Al / V ratio 12.

<Example 8>

Hydroxy group-containing materials such as MCM-41, SBA-15, ZSM-5, silica and titania were impregnated with VOSO ₄ aqueous solution (hydroxy group-containing substance / vanadium ratio = 12), dried at 100 ° C. and calcined at 700 ° C. for 5 hours. Next, Pt was supported by 0.25% to prepare various Pt / V- (hydroxy group-bearing substance) catalysts. As a result of investigating the activity of the catalyst thus prepared and the Pt / (hydroxy group-containing substance) catalyst without V added under the experimental conditions of Example 1, the NO conversion rate and the conversion rate to N ₂ at 160 ° C. were shown in Table 1 below. The addition of the vanadium component to the catalyst greatly enhanced the activity of the catalyst.

 Pt / V-MCM-41 (Pt / MCM-41)  Pt / V-SBA-15 (Pt / SBA-15)  Pt / V-ZSM-5 (Pt / ZSM-5)  Pt / V-SiO₂                                                                                                    (Pt / SiO₂)  Pt / V-TiO₂                                                                                                    (Pt / TiO₂)   NO conversion rate (%)       95 (62)       93 (60)      98 (71)     94 (64)     89 (58) % Conversion to N ₂       58 (34)       55 (31)      83 (52)     64 (38)     56 (37)

Example 9

0.2 g of Pt / V-Al ₂ O ₃ prepared in Example 1 was placed in a reactor, and the concentration of O ₂ was changed to investigate the activity of the catalyst. As a result, when the O ₂ concentration changed to 0, 3, 5, 7, 10%, the NO conversion was 40.0, 99.1, 96.7, 93.4, 89.5% at 120 ° C, respectively, and the conversion to N ₂ was 16.0, 73.3, 72.7, As the concentration of O ₂ increased from 3 to 10%, NO conversion decreased by 9.6% and N ₂ decreased by 4.2%. In particular, when the O ₂ concentration is 0, the NO conversion rate and the conversion rate to N ₂ are the lowest, and thus it can be seen that O ₂ is required to effectively reduce NO.

<Example 10>

The V _X -P _Y- (Al ₂ O ₃ ) _Z carrier was prepared by coprecipitation and Pt / VP-Al ₂ O ₃ catalyst was prepared by carrying 0.25 wt% of Pt. Carrier _{V X -P Y - (Al 2} O 3) Z is _{Al (NO 3) 3 .9H 2} O and H ₃ PO ₄ mixed solution V ₂ O ₅ solution was added slowly to aqueous ammonia dissolved in, maintaining pH 9.5 with aqueous ammonia After aging for 12 hours with stirring, centrifugation and washing were carried out, dried at 110 ° C, and calcined at 700 ° C. Experimental conditions were the same as in Example 1 to investigate the activity of the catalysts in which the value of Y was fixed to 10, Z to 50 and X was changed to 5, 10 and 20, and as shown in FIG. Has the highest activity.

As described above, using a Pt / V _X -P _Y- (hydroxy group-containing substance) _Z catalyst of the present invention to reduce the lean nitrogen oxide discharged from diesel vehicles to hydrogen 95% of the NO conversion at a very low temperature As described above, nitrogen oxides can be removed with a high efficiency of conversion of N ₂ to 70% or more, and the catalyst is composed of a component that is not resistant to SOx and is resistant to SOx even in a vapor atmosphere, and is not poisoned by SOx. As a main component of the catalyst, it is not necessary to add other metals other than platinum as cocatalysts, which makes it cheaper and easier to manufacture than three-way catalysts for gasoline cars, and also uses hydrogen, a clean material that does not contain carbon, as a reducing agent. Due to the deactivation of the catalyst caused by the catalyst and no environmental pollution caused by the reducing agent, Which it is very useful in purifying NOx.

Claims (6)

95 to 99.99% by weight of V _X -P _Y- (hydroxy group holding material) _Z carrier and 0.01 to 5% by weight of platinum (Pt) consisting of vanadium (V), phosphorus (P) and a substance having a hydroxyl group on the surface Nitrogen oxide purification catalyst. The catalyst for purifying nitrogen oxides of claim 1, wherein the hydroxy group-bearing material is selected from the group consisting of alumina, silica, zeolite, MCM-41, SBA-15 and titania. The catalyst for purifying nitrogen oxides of claim 1, wherein the ratio of Z / X is 4-200 based on the number of moles of atoms, and the ratio of Z / Y is 2-1000. Impregnating a solution containing vanadium (V) and phosphorus (P) in a material having a hydroxy group on the surface, or coprecipitating a solution containing vanadium (V) and phosphorus (P) with a material having a hydroxyl group on the surface Preparing a V _X -P _Y- (hydroxy group bearing) _Z carrier to obtain a Impregnating platinum (Pt) on the carrier A method for producing the catalyst for purifying nitrogen oxides of claim 1, comprising: A method for purifying nitrogen oxides, comprising reducing the diesel vehicle exhaust nitrogen oxides to hydrogen at a temperature of 50-400 ° C. in the presence of the catalyst for purifying nitrogen oxides of claim 1. The method for purifying nitrogen oxides according to claim 5, wherein the hydrogen is supplied at a concentration of 500-200,000 ppm.

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