JP2004290927A - Catalyst for use in cleaning exhaust gas and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for use in cleaning an exhaust gas, capable of stably maintaining a high cleaning performance with respect to HC, NOx and CO for a long period, and to provide a method of manufacturing such the catalyst. <P>SOLUTION: The exhaust gas cleaning catalyst is to clean a combustion exhaust gas containing HC, NOx, CO, SOx and O<SB>2</SB>. The catalyst comprises a zirconium oxide carrier consisting of zirconium oxide, and Pd, Cr, Ir and sulfate ions all carried by such the zirconium oxide carrier. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
【Technical field】
The present invention relates to an exhaust gas purifying catalyst that can purify combustion exhaust gas containing HC, NOx, CO, SOx, and O ₂ .
[0002]
[Prior art]
For example, when purifying combustion exhaust gas generated in a gas engine using a fuel gas containing methane as a main component such as city gas, a Pd-zeolite catalyst supporting Pd (palladium) on zeolite is widely used. Used. According to this Pd-zeolite catalyst, NOx in the combustion exhaust gas can be purified using methane in the combustion exhaust gas as a reducing agent.
Further, in the Pd-zeolite-based catalyst disclosed in Patent Document 1, not only Pd is supported on a zeolite carrier but also halogen is supported. In Patent Document 1, HC and NOx can be effectively purified, and 400 ° C. The catalyst provides excellent heat resistance and durability with little deterioration even when exposed to the high temperature combustion exhaust gas water vapor.
[0003]
Further, in the catalyst of Patent Document 2, a mixture of a sulfated zirconia carrier carrying Pd and a platinum zirconia carrier carrying platinum is used. In this Patent Document 2, NOx is effectively reduced. The present invention provides a catalyst that can be purified and has a stable catalytic activity for NOx over a long period of time even in combustion exhaust gas containing a large amount of water vapor.
[0004]
[Patent Document 1]
JP 2001-300320 A [Patent Document 2]
JP 2000-342972 A [0005]
[Problem to be solved]
However, in the catalysts of Patent Documents 1 and 2, the performance of purifying the combustion exhaust gas has been confirmed only for up to about 120 hours. Therefore, when used for a long time of about 1000 hours, sufficient purification performance may not always be obtained.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides an exhaust gas purifying catalyst capable of stably maintaining high purification performance for HC, NOx, and CO for a long period of time, and a method for producing the same. It is what we are going to offer.
[0007]
[Means for solving the problem]
A first invention relates to an exhaust gas purifying catalyst for purifying a combustion exhaust gas containing HC, NOx, CO, SOx and O ₂ ,
The catalyst for exhaust gas purification is characterized in that the catalyst has a zirconium oxide carrier made of zirconium oxide, and Pd, Cr, Ir and sulfate ions supported on the zirconium oxide carrier. 1).
[0008]
In the exhaust gas purifying catalyst of the present invention, the HC (hydrocarbon), NOx (nitrogen oxide), CO 2, and CO 3 are supported on the zirconium oxide carrier by supporting the respective catalyst components of Pd, Cr, Ir, and sulfate ions. It has high purification performance for HC, NOx and CO in combustion exhaust gas containing (carbon monoxide) and SOx (sulfur oxide).
Furthermore, the catalyst of the present invention can stably maintain the purification performance of HC, NOx, and CO for a long period of time, for example, 1000 hours or more by supporting the above-mentioned catalyst components.
[0009]
The high purification performance is considered to be caused particularly by the loading of the Pd, Cr and sulfate ions, and the maintenance of the purification performance for a long period of time is considered to be caused particularly by the loading of the Ir. The reasons are described below.
Regarding the purification of HC, it is considered that the fact that the Pd is supported on the zirconium oxide carrier has a great effect. That is, it is considered that HC in the combustion exhaust gas can be oxidized and purified by the presence of Pd.
It is considered that by supporting the sulfate ion on the zirconium oxide carrier, the purification action of HC by Pd can be activated, and the purification performance of HC can be improved.
[0010]
By the way, it is considered that the sulfate ion in the above catalyst disappears with the passage of time due to volatilization or the like. Therefore, it is considered that by supporting the Ir on the zirconium oxide carrier, SO ₂ contained in the combustion exhaust gas can be oxidized to SO ₃ and sulfate ions can be regenerated in the catalyst. Thus, it is considered that the disappearance of sulfate ions in the catalyst can be reduced. Therefore, it is considered that the high purification performance of HC by Pd can be maintained over a long period of time.
[0011]
Regarding the purification of NOx, the fact that the Pd and Cr were carried on the zirconium oxide carrier was considered to have a large effect. That is, the presence of the Cr oxidizes NO in the combustion exhaust gas to NO ₂ , and the NO ₂ reacts with the HC molecules converted by the presence of Pd to reduce the NO _2. Think you can. Thus, it is considered that the NOx can be purified.
Then, the presence of the Ir regenerates the sulfate ions, thereby maintaining the catalytic activity of the Pd. Therefore, it is considered that high purification performance can be maintained over a long period of time for NOx purification.
[0012]
Regarding the purification of CO, it is considered that the fact that the Pd is supported on the zirconium oxide carrier has the greatest effect. That is, it is considered that CO can be oxidized and purified by oxidizing CO into CO ₂ by the presence of Pd.
Then, since the sulfate ions are regenerated by the presence of the Ir, thereby maintaining the catalytic activity of the Pd, it is considered that high purification performance can be maintained for a long period of time even in the purification of CO.
In addition, it is considered that the presence of Cr also affects the purification of CO.
[0013]
The amount of Pd (palladium) supported is preferably 0.3 to 10.0% by weight based on the weight of the zirconium oxide (100% by weight). If the supported amount of Pd is less than 0.3% by weight, there is a possibility that the catalyst cannot sufficiently purify the HC, NOx and CO. On the other hand, if it exceeds 10.0% by weight, the particle size of Pd may increase when Pd is loaded on the zirconium oxide carrier, and this loading may be difficult.
[0014]
The amount of Ir (iridium) supported is preferably 0.3 to 10.0% by weight based on the weight of the zirconium oxide (100% by weight). If the supported amount of Ir is less than 0.3% by weight, the effect of regenerating the sulfate ion may not be sufficiently obtained. On the other hand, if the content exceeds 10.0% by weight, the purification action by Pd, Cr and the like may be adversely affected.
[0015]
The amount of Cr (chromium) supported is preferably 1.0 to 100.0% by weight based on the weight of the zirconium oxide (100% by weight). If the supported amount of Cr is less than 1.0% by weight, the effect of purifying NOx may not be sufficiently obtained. On the other hand, if it exceeds 100.0% by weight, there is a possibility that the purification action by Pd, Cr and the like may be adversely affected.
[0016]
The supported amount of the sulfate ion (SO ₄ ²⁻ ) is preferably 5.0 to 50.0% by weight, based on the weight of the zirconium oxide (100% by weight). If the amount of sulfate ion carried is less than 5.0% by weight, the catalyst may not be able to obtain a long-term stable purification performance. On the other hand, if it exceeds 50.0% by weight, there is a possibility that the purification action by Pd, Cr and the like may be adversely affected.
[0017]
A second invention is, HC, NOx, CO, to purify the combustion exhaust gas containing SOx and _{O 2,} Pd on zirconium oxide support comprising zirconium oxide, Cr, made by carrying Ir and sulfate ions exhaust In a method for producing a gas purification catalyst,
The zirconium oxide carrier is immersed in an aqueous solution containing Pd ions and sulfate ions, and then the zirconium oxide carrier is dried and fired, whereby an intermediate in which the Pd and sulfate ions are carried on the zirconium oxide carrier. And make
Next, the intermediate is immersed in an aqueous solution containing Cr ions and Ir ions, and then the intermediate is dried and fired, whereby the Pd, Cr, Ir and sulfate ions are supported on the zirconium oxide carrier. The present invention provides a method for producing an exhaust gas purifying catalyst, characterized by producing the above catalyst.
[0018]
In the present invention, an intermediate in which the above-mentioned Pd and the above-mentioned sulfate ion are supported on the above-mentioned zirconium oxide carrier is produced, and then, the above-mentioned intermediate is made to carry Cr and Ir to produce the above-mentioned catalyst. That is, in the present invention, the above catalyst components are carried step by step. Therefore, according to the present invention, each of the catalyst components can be effectively supported.
[0019]
In the first aspect, the catalyst may be used, for example, in the form of a powder and packed in a container having a predetermined shape. Further, the catalyst can be used after being formed into various shapes such as pellets and honeycomb structures.
In the first and second inventions, the combustion exhaust gas refers to an exhaust gas after combustion of fuel containing HC and air, and an exhaust gas in which a predetermined concentration of unburned oxygen remains. Means The HC may be CH ₄ (methane), and the combustion exhaust gas may be an exhaust gas obtained by burning a fuel gas containing CH ₄ with air.
[0020]
In the second invention, as the Pd ion, for example, those contained in palladium acetate, palladium nitrate, an aqueous amine solution, palladium sulfate and the like can be used. As the Cr ions, those contained in chromium acetate, chromium nitrate, chromium sulfate and the like can be used.
As the above-mentioned Ir ions, those contained in iridium chloride, aqueous ammine solution and the like can be used. As the sulfate ion, for example, those contained in sulfuric acid, ammonium sulfate, various kinds of metal sulfates, and the like can be used.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the above-described exhaust gas purifying catalyst of the present invention will be described.
The exhaust gas purifying catalyst of this embodiment purifies a combustion exhaust gas containing HC (hydrocarbon), NOx (nitrogen oxide), CO (carbon monoxide), SOx (sulfur oxide), and oxygen (O ₂ ). It is for doing. This catalyst has a zirconium oxide carrier composed of zirconium oxide, and Pd (palladium), Cr (chromium), Ir (iridium) and sulfate ions (SO ₄ ²⁻ ) supported on the zirconium oxide carrier. .
[0022]
(Invention)
In this example, the catalyst was manufactured as follows.
That is, first, the zirconium oxide carrier is immersed in an aqueous solution containing Pd ions and sulfate ions, and then the zirconium oxide carrier is dried and fired, so that the zirconium oxide carrier has Pd and sulfate ions supported thereon. The body was made.
[0023]
Specifically, a purity of 98 g was added by adding 100 g of zirconium hydroxide containing about 79% as zirconium oxide (manufactured by Mitsuwa Chemicals Co., Ltd.) and 2 g of palladium sulfate containing sulfate ions and Pd almost equally. It was immersed in a 10% by weight sulfuric acid solution for about 20 hours. The temperature of this aqueous solution was 80 ° C. Thereafter, the aqueous solution was filtered to remove the zirconium oxide, dried, and calcined at 550 ° C. for about 6 hours to produce the intermediate.
[0024]
Next, the intermediate is immersed in an aqueous solution containing Cr ions and Ir ions, and then the intermediate is dried and fired, whereby the Pd, Cr, Ir, and sulfate ions are supported on the zirconium oxide carrier. A catalyst was produced.
Specifically, 10 g of the above intermediate was immersed for about 20 hours in 150 ml of an aqueous solution containing 4.2 g of a tetraammine iridium hydroxide solution having an Ir concentration of 1.202% by weight and 2.3 g of chromium acetate. The temperature of this aqueous solution was also set to 80 ° C. Thereafter, the intermediate component was removed by evaporating the liquid component of the aqueous solution, dried, and calcined at 500 ° C. for about 5 hours to produce the catalyst.
In addition, each said baking was performed in the environment where oxygen exists, ie, in the air in this example.
[0025]
In this example, the catalyst produced as described above is referred to as (invention product), the conventional Pd-zeolite catalyst (comparative product 1), and the conventional Pd-Pt-sulfate zirconia catalyst (comparative product 2). , HC of the catalyst, NOx, CO, purification degree for the combustion exhaust gas containing SOx and _{O 2} were measured and compared.
[0026]
(Comparative product 1)
The Pd-zeolite-based catalyst of Comparative product 1 has 1.0% by weight of Pd supported on a zeolite carrier made of zeolite.
Specifically, first, 20 g of zeolite ("HSZ-620HOA" manufactured by Tosoh Corporation) was immersed in 300 ml of an aqueous solution containing 0.4 g of palladium acetate for about 20 hours. The temperature of this aqueous solution was also set to 80 ° C. Thereafter, the aqueous solution was filtered to remove the zeolite carrier, dried, and calcined in air at 500 ° C. for about 5 hours to produce the Pd-zeolite catalyst.
[0027]
(Comparative product 2)
The Pd-Pt-sulfuric acid zirconia catalyst of Comparative Product 2 is one in which Pd: 1.0% by weight and Pt: 0.2% by weight are supported on sulfated zirconia.
Specifically, first, 360 g of zirconium hydroxide (manufactured by Mitsuwa Chemicals, Inc.) containing about 79% of zirconium oxide and the remainder being water, and about 20 g in 400 ml of an aqueous solution in which 54 g of ammonium sulfate are dissolved. Soaked for hours. Thereafter, the aqueous solution was filtered to remove the zirconium oxide, dried, and calcined at 550 ° C. for about 6 hours to produce the sulfated zirconia.
[0028]
Then, this sulfated zirconia: 20 g, 60 ml of an aqueous solution containing 5.4 g of a palladium nitrate solution having a Pd concentration of 4.422 wt% and 3.0 g of an aqueous tetraammineplatinum solution having a Pt concentration of 1.957 wt%. For about 20 hours. The temperature of this aqueous solution was 80 ° C. Thereafter, the liquid component of the aqueous solution was evaporated to remove the sulfated zirconia, dried, and calcined at 500 ° C. for about 5 hours to produce the Pd-Pt-sulfated zirconia catalyst.
[0029]
The measurement of the degree of purification of each catalyst of the invention and comparative products 1 and 2 was performed by exposing each catalyst to combustion exhaust gas having an oxygen concentration of about 6% and contacting each catalyst with HC, HC in the combustion exhaust gas. The measurement was performed by measuring how much each concentration of NOx and CO decreased.
[0030]
The degree of purification of each catalyst was measured under the following conditions.
That is, the amount of each catalyst, and 1g, the composition of the combustion exhaust _{gas, CH 4: 1000ppm, NOx:} 500ppm, CO: 300ppm, SO 2: 40ppm, O 2: 6%, H 2 O: 13% ( (Estimated value from the composition of the combustion exhaust gas and the O ₂ concentration). The gas space velocity of the flow of the combustion exhaust gas was 10,000 ml / h · g, and the temperature of the combustion exhaust gas was 450 ° C.
Incidentally, HC in this example was a CH _4. Since it is considered that CH ₄ is most difficult to be decomposed among HCs, it is considered that the purifying action of other HCs can be estimated by measuring the result of CH ₄ .
[0031]
FIG. 1 shows the result of measurement of the invention product, FIG. 2 shows the result of measurement of the comparison product 1, and FIG. 3 shows the result of measurement of the comparison product 2. In each figure, the horizontal axis represents time (h), and the vertical axis represents conversion (%) indicating the purification performance of each catalyst.
[0032]
The conversion rate (%) is represented by the following equation: Conversion rate (%) = {1− (X _out )} / X _in × 100 (%). _{Here, X in} denotes HC, NOx, each concentration of CO in the combustion exhaust gas before the contact with the _{catalyst, X out} the HC in the combustion exhaust gas after contact with the catalyst, NOx, the CO Each concentration is represented.
The higher the conversion (%), the higher the purification performance of each of the catalysts.
[0033]
We know from results of the measurement, for the above-mentioned inventions, be used for about 1300 (h) also show a long period of time, is that CH 4, _NOx, purification performance of the CO is hardly lowered. That is, purification performance of CO is maintained substantially 100 (%), the purification performance of the CH ₄ and NOx were found that are high enough to over time.
[0034]
The reason for the CH ₄ and purification performance of NOx began to improve with time, in the above inventions, that by supporting the Ir along with being by supporting Pd and sulfate ions in a zirconium oxide support Is considered to have a significant effect. That is, since Ir can oxidize SO ₂ in the combustion exhaust gas to SO ₃ and regenerate the sulfate ions, not only the reduction of the purification action of HC by Pd but also the suppression of HC can be suppressed. It is thought that this is because the purifying action was further activated.
[0035]
On the other hand, for the comparative product 1, the purification performance of the CO, while maintaining almost 100 (%), for the purification performance of CH _4, almost clean while only 0.4 (h) about the short It turned out that the performance was gone. It was also found that the purification performance of NOx almost disappeared in a short time of only 0.8 (h).
[0036]
As for the comparative product 2, purification performance of the CO, while maintaining a high purification performance of about 95 (%), for the purification performance of CH _4, it had began to decrease with time I understood that. In addition, regarding the NOx purification performance, it was found that the purification performance was low from the beginning of the measurement, and the purification performance did not change much even after a lapse of time.
[0037]
From the above measurement results, the exhaust gas purifying catalyst in which the Pd, Cr, Ir, and sulfate ions are supported on the zirconium oxide carrier, which is the invention, has a higher HC content in the combustion exhaust gas than the conventional catalyst. Also, it was found that the purification performance for NOx was particularly excellent.
Further, it was found that the catalyst of the present invention can stably maintain the purification performance of HC, NOx, and CO for a long period of time of 1300 hours or more.
[0038]
In addition, the combustion exhaust gas contained H ₂ O as water vapor, but the presence of this H ₂ O did not reduce the purification performance of the catalyst. From this, it was found that the catalyst of the present invention can exhibit high purification performance even with respect to combustion exhaust gas containing H ₂ O as steam.
Although the temperature of the combustion exhaust gas was 450 ° C., it was found that the catalyst of the present invention can exhibit high purification performance even with such a high-temperature combustion exhaust gas.
[Brief description of the drawings]
FIG. 1 is a graph showing measurement results of purification performance performed on a catalyst (inventive product) in which Pd, Cr, Ir and sulfate ions are supported on a zirconium oxide carrier in the example, and the horizontal axis represents time (h). A graph showing the conversion rate (%) on the vertical axis.
FIG. 2 is a graph showing measurement results of purification performance performed on a Pd-zeolite-based catalyst (Comparative product 1) in the example, in which the horizontal axis represents time (h) and the vertical axis represents conversion (%). Graph shown.
FIG. 3 is a graph showing measurement results of purification performance performed on a catalyst in which Pd and Pt are supported on sulfated zirconia (Comparative product 2) in the example, in which the horizontal axis represents time (h) and the vertical axis represents time. 4 is a graph showing conversion (%).

Claims (2)

In an exhaust gas purifying catalyst for purifying a combustion exhaust gas containing HC, NOx, CO, SOx and O ₂ ,
An exhaust gas purifying catalyst, characterized in that the catalyst has a zirconium oxide carrier made of zirconium oxide, and Pd, Cr, Ir and sulfate ions supported on the zirconium oxide carrier. In order to purify combustion exhaust gas containing HC, NOx, CO, SOx and O ₂ , an exhaust gas purifying catalyst is produced by supporting Pd, Cr, Ir and sulfate ions on a zirconium oxide carrier made of zirconium oxide. In the method
The zirconium oxide carrier is immersed in an aqueous solution containing Pd ions and sulfate ions, and then the zirconium oxide carrier is dried and fired, whereby an intermediate in which the Pd and sulfate ions are carried on the zirconium oxide carrier. And make
Next, the intermediate is immersed in an aqueous solution containing Cr ions and Ir ions, and then the intermediate is dried and fired, whereby the Pd, Cr, Ir and sulfate ions are supported on the zirconium oxide carrier. A method for producing an exhaust gas purifying catalyst, comprising producing the above catalyst.

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