JP3546908B2 - Ammonia purification catalyst device - Google Patents

Description

（実施例１−１）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に、モデルガスの流れ方向の上流側に熱処理Ｐｄ触媒を２ｃｃ充填し、下流側にＰｔ触媒を２ｃｃ充填して本実施例の触媒装置とした。
【００４１】
そして表１に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^-1の条件で反応管に導入し、触媒入口ガス温度を５００℃から５０℃まで変化させたときの触媒出口ガス組成を測定した。モデルガス中にはＮＯを含み、アンモニアからも僅かにＮＯ_x が生成するため、参考例と同じ計算式によりＮＯとＮＨ₃ の転化率を求めた。その結果を表３に示す。
【００４２】
（実施例１−２）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に、モデルガスの流れ方向の上流側にＺｎ添加Ｐｄ触媒を２ｃｃ充填し、下流側にＰｔ触媒を２ｃｃ充填して本実施例の触媒装置とした。
そして表１に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^-1の条件で反応管に導入し、触媒入口ガス温度を５００℃から５０℃まで変化させたときの触媒出口ガス組成を測定した。モデルガス中にはＮＯを含み、アンモニアからも僅かにＮＯ_x が生成するため、参考例と同じ計算式によりＮＯとＮＨ₃ の転化率を求めた。その結果を表３に示す。
【００４３】
（実施例１−３）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に、モデルガスの流れ方向の上流側に熱処理Ｚｎ添加Ｐｄ触媒を２ｃｃ充填し、下流側にＰｔ触媒を２ｃｃ充填して本実施例の触媒装置とした。
そして表１に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^-1の条件で反応管に導入し、触媒入口ガス温度を５００℃から５０℃まで変化させたときの触媒出口ガス組成を測定した。モデルガス中にはＮＯを含み、アンモニアからも僅かにＮＯ_x が生成するため、参考例と同じ計算式によりＮＯとＮＨ₃ の転化率を求めた。その結果を表３に示す。
【００４４】
（実施例１−４）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に、モデルガスの流れ方向の上流側にＣｅＯ₂ −Ｐｄ触媒を２ｃｃ充填し、下流側にＰｔ触媒を２ｃｃ充填して本実施例の触媒装置とした。
そして表１に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^-1の条件で反応管に導入し、触媒入口ガス温度を５００℃から５０℃まで変化させたときの触媒出口ガス組成を測定した。モデルガス中にはＮＯを含み、アンモニアからも僅かにＮＯ_x が生成するため、参考例と同じ計算式によりＮＯとＮＨ₃ の転化率を求めた。その結果を表３に示す。
【００４５】
（実施例２）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に、モデルガスの流れ方向の上流側から下流側に向かって第１触媒、Ｐｄ触媒及びＰｔ触媒をそれぞれ１ｃｃずつこの順に充填し、本実施例の触媒装置とした。
そして表２に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^−１の条件で反応管に導入し、触媒入口ガス温度を６００℃から５０℃まで変化させたときの触媒出口ガス組成を測定し、触媒入口ガス組成との比較からアンモニアのＮ_２ への転化率を求めた結果を表３に示す。また、触媒出口ガスの組成を質量分析計により分析し、各温度における生成物の組成変化を調査した結果を図４に示す。
【００４６】
【表２】

（比較例）
内径１５ｍｍ、長さ３００ｍｍの石英製反応管に第１触媒を４ｃｃ充填して本比較例の触媒装置とした。
【００４７】
そして表１に示すモデルガスを、空間速度ＳＶ＝１０万ｈｒ^-1の条件で反応管に導入し、触媒入口ガス温度を５００℃から５０℃まで変化させたときの出口ガス組成を測定した。モデルガス中にはＮＯを含み、アンモニアからも僅かにＮＯ_x が生成するため、参考例と同じ計算式によりＮＯとＮＨ₃ の転化率を求めた。その結果を表３に示す。
【００４８】
（評価）
【００４９】
【表３】

表３より、参考例、実施例１−１、実施例１−２、実施例１−３及び実施例１−４の触媒装置は、４００℃以下の温度領域において、アンモニアを比較例に比べて高い転化率でＮ₂ に転化できることが明らかである。さらに、参考例に比べて実施例１−１〜４の触媒装置の方が優れた結果を示し、熱処理Ｐｄ触媒、Ｚｎ添加Ｐｄ触媒、熱処理Ｚｎ添加Ｐｄ触媒及びＣｅＯ₂ −Ｐｄ触媒を用いるのが好ましいこともわかる。
【００５０】
また実施例２の触媒装置では、６００℃以下の温度範囲で高い添加率を示していることもわかる。
さらに図４より、実施例２の触媒装置では、１５０℃以上の温度範囲において発生するのは無害なＮ_２ とＨ_２ Ｏのみであり、ＮＯ_ｘ を全く発生していないことから、アンモニアは全てＮ_２ に転化されていることが明らかである。
【００５１】
【発明の効果】
すなわち本発明のアンモニア浄化用触媒装置によれば、低温域から高温域まで広い温度範囲において、ＮＯ_ｘ をほとんど再生成することなくアンモニアを無害なＮ_２ に転化することができる。
【図面の簡単な説明】
【図１】Ｐｄ触媒の各温度におけるアンモニア浄化後の生成物の生成量を示すグラフである。
【図２】Ｐｔ触媒の各温度におけるアンモニア浄化後の生成物の生成量を示すグラフである。
【図３】第１触媒の各温度におけるアンモニア浄化後の生成物の生成量を示すグラフである。
【図４】実施例２の触媒装置の各温度におけるアンモニア浄化後の生成物の生成量を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ammonia purification catalyst device used for efficiently purifying ammonia contained in exhaust gas discharged from an internal combustion engine or the like.
[0002]
[Prior art]
Oxidation and NO of CO and HC in exhaust gas discharged from internal combustion engines such as automobiles_xConventionally, a three-way catalyst has been used as an exhaust gas purifying catalyst for purifying the exhaust gas by performing the reduction simultaneously. As such a three-way catalyst, for example, a coat layer made of γ-alumina is formed on a heat-resistant carrier substrate made of cordierite or the like, and a catalytic noble metal such as platinum (Pt) or rhodium (Rh) is formed on the coat layer. Are widely known.
[0003]
In this three-way catalyst, the air-fuel ratio (A / F) is controlled to a stoichiometric air-fuel ratio (A / F = 14.6), and CO, HC and NO contained in exhaust gas burned at this air-fuel ratio are controlled._xIs purifying at the same time.
However, under the actual driving conditions of the vehicle, acceleration and deceleration are frequently repeated when driving in an urban area, and as a result, the air-fuel ratio may not necessarily be the stoichiometric air-fuel ratio but may slightly deviate from the stoichiometric air-fuel ratio. For example, during acceleration, a large amount of fuel is supplied, so that the air-fuel ratio becomes smaller than 14.6, resulting in a so-called rich atmosphere. At the time of deceleration, the air-fuel ratio becomes larger than 14.6 due to a decrease in the amount of supplied fuel, and a so-called lean atmosphere is obtained.
[0004]
In a rich atmosphere, NO in exhaust gas_xIs reduced on the catalyst by reducing substances such as CO and HC contained in the exhaust gas. However, NO_xIs N₂Most preferably, the reduction reaction proceeds further depending on conditions, depending on the conditions.₃) May occur.
On the other hand, in a lean atmosphere, CO and HC in exhaust gas are oxidized and purified by excess oxygen, but NO_xHas the problem that it is discharged without being reduced. Therefore, ammonia is added to the exhaust gas in a lean atmosphere, and NO_xIt has also been considered to purify and purify (JP-A-3-140147). However, it is difficult to control the amount of added ammonia,_xIf more than the equivalent is added, excess ammonia may be discharged to the atmosphere.
[0005]
Therefore, it is conceivable to install a catalyst capable of purifying ammonia downstream of the three-way catalyst in the exhaust gas channel. Oxidizes ammonia to N₂As an industrial denitration catalyst to be used, for example, as described on page 248 of “Catalysis Course 7 (Basic Industrial Catalyst Reaction)” (published by Kodansha),₂O₅-TiO₂Catalysts are known.
[0006]
[Problems to be solved by the invention]
But V₂O₅-TiO₂For the catalyst, SV = 10000 hr^-1At a small space velocity of exhaust gas, high activity can be obtained in a wide temperature range, but as in the case of automobile exhaust gas, SV = 10,000 hr.^-1If the space velocity is higher than, sufficient activity cannot be obtained. Therefore V₂O₅-TiO₂Even if the catalyst is used as an ammonia purification catalyst for automobile exhaust gas, purification of ammonia becomes insufficient.
[0007]
Also, by oxidizing ammonia, N₂In the case of purification by conversion to NO, depending on the type or condition of the catalyst, the oxidation reaction proceeds too much and NO_xMay occur.
The present invention has been made in view of such circumstances, and even in the case of exhaust gas having a large space velocity, such as automobile exhaust gas, efficiently removes ammonia that may be contained in the exhaust gas in a wide temperature range.₂It is an object of the present invention to provide a novel catalyst device capable of converting and purifying a catalyst.
[0008]
[Means for Solving the Problems]
The feature of the ammonia purifying catalyst device of the invention according to claim 1 that solves the above problem is an ammonia purifying catalyst device for purifying ammonia contained in exhaust gas,At least palladium supported on a porous carrier containing alumina 800 ~ 1500 A heat-treated Pd catalyst and a Pt catalyst having at least platinum supported on a porous carrier, and a heat-treated Pd catalyst and a Pt catalyst are arranged in this order from the upstream side to the downstream side of the exhaust gas channel. didIt is in.
[0009]
The feature of the ammonia purifying catalyst device of the invention according to claim 2 is an ammonia purifying catalyst device for purifying ammonia contained in exhaust gas,A Zn-added Pd catalyst in which at least palladium and zinc are supported on a porous carrier containing alumina, and a Pt catalyst in which at least platinum is supported on a porous carrier. Zn-added Pd catalyst and Pt catalyst were arranged in this orderIt is in.
A feature of the ammonia purifying catalyst device of the invention according to claim 3 is an ammonia purifying catalyst device for purifying ammonia contained in exhaust gas, wherein at least palladium is supported on a porous carrier containing ceria. CeO _Two -A Pd catalyst and a Pt catalyst in which at least platinum is supported on a porous carrier, and CeO flows from the upstream side to the downstream side of the exhaust gas flow path. _Two -The Pd catalyst and the Pt catalyst are arranged in this order.
[0010]
Alumina, which is relatively inexpensive, can be used as the porous carrier for the Pd catalyst. In this case, it is desirable to heat-treat the Pd catalyst in an oxidizing atmosphere containing water. Further, the Pd catalyst desirably contains zinc. As the porous carrier of the Pd catalyst, ceria (CeO) was used instead of the alumina carrier.₂) Can also be used. Further, it is desirable that ceria contains zirconia. When ceria is used as the porous carrier, sufficient performance can be obtained without the need for heat treatment in an oxidizing atmosphere containing water or addition of zinc as in the case of using alumina as the porous carrier.
[0011]
AndClaim 4The feature of the ammonia purification catalyst device of the invention described in is an ammonia purification catalyst device for purifying ammonia contained in exhaust gas, wherein the zeolite supports at least one metal selected from iron, cobalt, nickel and copper. A first catalyst, a Pd catalyst in which at least palladium is supported on a porous carrier, and a Pt catalyst in which at least platinum is supported on a porous carrier. The first catalyst, the Pd catalyst, and the Pt catalyst are arranged in this order.
[0012]
Claim 4In the ammonia purification apparatus described in the above, it is preferable that at least one metal selected from iron, cobalt, nickel and copper supported on the zeolite in the first catalyst is supported by an ion exchange method.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 show the relationship between the temperature of the incoming gas and the concentration of each component in the outgoing gas when ammonia is brought into contact with a Pd catalyst in which Pd is supported on alumina and a Pt catalyst in which Pt is supported on alumina. . In the case of a Pd catalyst, N₂Conversion peak to about 350 ° C and gradually NO_xHas been generated. On the other hand, with a Pt catalyst, N₂Conversion peak to 350 ° C._xHas been generated.
[0014]
The present invention pays attention to such a difference depending on the type of the catalyst, and oxidizes ammonia efficiently by optimizing the arrangement order to form N 2_Two And NO_x Was found to be able to suppress the generation of.
That is,Of the present inventionIn the ammonia purification catalyst device, ammonia is oxidized upstream of the exhaust gas_Two A catalyst having a high maximum conversion temperature at which the conversion rate at which the gas is converted to a maximum is disposed, and a catalyst having a low maximum conversion temperature is disposed downstream of the exhaust gas passage. Therefore, in a low temperature region of the exhaust gas, the ammonia is hardly purified by the upstream catalyst and is mainly purified by the downstream catalyst._xIs prevented from being regenerated. On the other hand, in the high temperature region of exhaust gas, ammonia is mainly purified by the upstream_Two And almost no reaction occurs on the downstream catalyst and NO_x Is prevented from being regenerated.
[0015]
Conversely, if a catalyst having a low maximum conversion temperature is disposed upstream of the exhaust gas flow path and a catalyst having a high maximum conversion temperature is disposed downstream of the exhaust gas flow path, ammonia flows upstream in a low temperature range of the exhaust gas. Most of the gas is oxidized and converted to nitrogen by the catalyst, but in the high temperature region of the exhaust gas, the oxidation reaction of ammonia proceeds too much with the catalyst on the upstream side and NO_xIs regenerated. In other words, in the configuration opposite to the present invention, the effect of the downstream catalyst cannot be obtained and NO_xIs discharged.
[0016]
In the invention according to claim 1,A Pd catalyst is arranged on the upstream side of the exhaust gas channel, and a Pt catalyst is arranged on the downstream side. In the Pd catalyst, as shown in FIG._Two The maximum conversion temperature is about 400 ° C. NO above about 350 ° C_x Is generated. On the other hand, in the case of the Pt catalyst, as shown in FIG._Two The maximum conversion temperature is about 200 ° C., and above about 350 ° C., NO_x Rapidly increases. 1 to 3 show SV = 100,000 hours, respectively.^-1It was measured at a high space velocity.
[0017]
ThereforeClaim 1In the catalyst device described in 1 above, in a low temperature range of less than about 350 ° C., a part of ammonia is converted to N by the Pd catalyst on the upstream side._Two And most of the ammonia is converted to N2 mainly by the Pt catalyst on the downstream side._Two And purified. In the case of Pd catalyst, NO_x Is not generated, and NO is generated at a temperature lower than about 350 ° C. even in the downstream Pt catalyst._x Generation hardly occurs.
[0018]
On the other hand, in the temperature range around 350 ° C., most of the ammonia is_Two Converted to NO_x Is slightly produced. On the downstream side, there is almost no ammonia in the exhaust gas._x Generation hardly occurs.
When an alumina carrier is used for the Pd catalyst, heat treatment is performed in an oxidizing atmosphere containing water. As a result, although the reason is unknown, the ammonia N_Two The conversion rate to is further improved.
[0019]
The heat treatment is performed in an oxidizing atmosphere containing water, and the amount of water must be at least 1% by volume. If the content is less than 1% by volume, the N₂It is not expected to improve the conversion rate to Although the upper limit of the water content is not particularly limited, a range of 10% or less is appropriate considering the easiness of adding water to the processing gas.
The oxidizing atmosphere includes an air atmosphere, an oxygen gas atmosphere, and the like. Regarding the degree of the oxidizing atmosphere, the oxygen concentration is at least 1% by volume, preferably the oxygen concentration is 4% by volume or more. If the oxygen concentration is less than 1% by volume, N₂It is not expected to improve the conversion rate to Note that since the atmosphere contains 20% by volume of oxygen, it is convenient to use an atmosphere in which water is added to the atmosphere in an amount of about several% by volume.
[0020]
As a heat treatment condition, it is desirable to perform the treatment at a temperature of 800 to 1500 ° C., preferably at a temperature of about 1000 ° C. for at least one hour. If the heat treatment temperature is lower than 800 ° C., N₂It is not possible to expect an increase in the conversion rate to 1500 ° C., and if it exceeds 1500 ° C., the activity is reduced by sintering of the carrier.
The Pd catalyst using alumina as the porous carrier preferably contains zinc. By including zinc, the ammonia N₂The effect of further improving the conversion rate to methane is obtained. Further, by performing a heat treatment in an oxidizing atmosphere containing water as described above, the N 2₂The conversion rate to is further improved.
[0021]
The content of zinc is preferably in the range of 0.05 to 1 mol per liter of Pd catalyst. If the amount is less than 0.05 mol / L, the effect of improving the activity cannot be obtained. If the amount is more than 1 mol / L, the effect is saturated and the cost is increased.
When ceria is used as the porous support of the Pd catalyst, it is desirable to add at least 1% by volume or more of zirconia to ceria. This improves the heat resistance of the ceria carrier. The amount of zirconia to be added is 5 to 75% by volume, preferably 10 to 50% by volume. When the added amount of zirconia exceeds 75% by volume, the effect of ceria decreases, and when the added amount of zirconia is 5% by volume or less, improvement in thermal stability of ceria cannot be expected.
[0022]
Claim 4The invention described inOn the upstream sideFurther, a first catalyst, which supports at least one metal selected from iron, cobalt, nickel and copper on the zeolite, is disposed. As a method for supporting the metal, an ion exchange method is preferable.
In this first catalyst, as shown in FIG._Two At about 400 ° C._Two And NO_x Does not occur at all. Therefore, in the catalyst device according to the third aspect, in a low temperature range of less than about 350 ° C., ammonia is purified by the same mechanism as the catalyst device described above, and NO_x Generation hardly occurs.
[0023]
On the other hand, at about 350 ° C. to 400 ° C., ammonia is first converted to N by the first catalyst.₂And further converted to N with a Pd catalyst.₂And purified. In the case of Pd catalyst, NO_xIs hardly generated, and the Pt catalyst on the downstream side has almost no ammonia in the exhaust gas._xGeneration hardly occurs. In a high temperature range of about 400 ° C. or more, ammonia is mostly N 1 in the first catalyst.₂To be purified by conversion to NO_xThere is no generation of
[0024]
ThereforeClaim 4In the catalyst device for purifying ammonia described in (1), ammonia is converted to N over a wide temperature range of about 100 to 600 ° C._Two And purified, and NO_x Also generatesIs prevented.
[0025]
The amount of Pd supported on the porous carrier is preferably in the range of 0.1 to 20 g per liter of the porous carrier. If the amount of Pd carried is less than 0.1 g, the ability to purify ammonia is low and is not practical. If the amount is more than 20 g, the effect is saturated and the cost is increased. A particularly preferred range is from 0.5 to 3 g. As a method for supporting Pd, a method used in the production of a conventional three-way catalyst such as an impregnation method and an adsorption method can be used, and there is no particular limitation.
[0026]
The Pd catalyst can carry other catalytic metals such as Rh in addition to Pd. The amount of Pd is preferably in the range of 1/2 to 1/10 of the amount of Pd as long as the action of Pd is not impaired. In particular, since Rh has an effect of preventing sintering of Pd, it is particularly preferable to carry it together with Pd.
Alumina, silica, titania, silica-alumina and the like can be used as the porous carrier referred to in the Pt catalyst. Among them, alumina capable of maintaining a high specific surface area up to a high temperature range is particularly desirable.
[0027]
The amount of Pt carried on the porous carrier is preferably in the range of 0.1 to 20 g per liter of the porous carrier. If the carried amount of Pt is less than 0.1 g, the purification ability of ammonia is low and it is not practical. Even if carried more than 20 g, the effect is saturated and the cost is increased. A particularly preferred range is from 0.5 to 3 g. As a method for supporting Pt, a method used in the production of conventional three-way catalysts such as an impregnation method and an adsorption method can be used, and there is no particular limitation.
[0028]
The Pt catalyst can also carry other catalytic metals such as Rh and Pd in addition to Pt. The loading amount is preferably in the range of 1/2 to 1/10 of the Pt amount as long as the action of Pt is not impaired. In particular, since Rh has an effect of preventing sintering of Pt, it is particularly preferable to carry it together with Pt.
Examples of the zeolite referred to as the first catalyst include ZSM-5, mordenite, ferriolite, and the like. From the results of experiments, it is considered that ZSM-5 is optimal in terms of high-temperature durability, resistance to poisoning, and the like.
[0029]
In the first catalyst, at least one metal selected from iron, cobalt, nickel and copper supported on the zeolite is preferably supported by an ion exchange method.
As the ion exchange amount of at least one metal selected from iron, cobalt, nickel and copper in the first catalyst, it is preferable that the ion exchange position of the zeolite be ion-exchanged by 50% or more. If the amount of ion exchange is less than 50%, the activity is low and the N₂It is difficult to convert to It is particularly desirable that the ion-exchangeable position is 100% ion-exchanged.
[0030]
As a method of using the ammonia purification catalyst device of the present invention, there is a method of loading and using a plurality of types of monolith catalysts in one catalytic converter. The respective catalysts may be arranged adjacent to each other, or may be arranged at intervals depending on mounting conditions. It is desirable that the catalyst device of the present invention be disposed downstream of the conventional three-way catalyst in the exhaust gas flow path. By doing so, the NO by the three-way catalyst_xCan be purified by the reduction of ammonia. In this case, it is preferable to supply air (oxygen) into the exhaust gas on the upstream side of the catalyst device of the present invention. As a result, the exhaust gas becomes an oxidizing atmosphere, and ammonia is further reduced to N.₂It is easy to convert to
[0031]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
(Preparation of Pd catalyst)
Alumina (BET surface area 100m)²/ G) from 2 to 4 mm in diameter. The pellet carrier was impregnated with a predetermined amount of an aqueous solution of palladium nitrate having a predetermined concentration, dried at 110 ° C. for 24 hours, and then reduced at 450 ° C. for 5 hours in a nitrogen gas stream containing 20% hydrogen gas to obtain a Pd catalyst. . The supported amount of Pd is 2 g per liter of pellet carrier.
[0032]
FIG. 1 shows the reactivity of ammonia with the Pd catalyst.
(Preparation of heat-treated Pd catalyst)
Alumina (BET surface area 100m)²/ G) from 2 to 4 mm in diameter. The pellet carrier was impregnated with a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration, dried at 110 ° C. for 24 hours, and then reduced at 450 ° C. for 5 hours in a nitrogen gas stream containing 20% of hydrogen gas. At this time, the supported amount of Pd is 2 g per liter of pellet carrier.
[0033]
This catalyst was subjected to a heat treatment of heating at 1000 ° C. for 5 hours in a nitrogen gas stream containing 4% by volume of oxygen and 3% by volume of water to obtain a heat-treated Pd catalyst.
(Preparation of Zn-added Pd catalyst)
Alumina (BET surface area 100m)²/ G) from 2 to 4 mm in diameter. After impregnating the pellet carrier with a predetermined amount of an aqueous solution of zinc acetate having a predetermined concentration and calcining in air at 150 ° C. for 1 hour, impregnating a predetermined amount of an aqueous solution of palladium nitrate with a predetermined concentration, and drying at 110 ° C. all day and night, The reduction treatment was performed at 450 ° C. for 5 hours in a nitrogen gas stream containing 20% of hydrogen gas. At this time, the supported amount of Pd was 2 g per liter of pellet support, and the supported amount of Zn was 0.25 mol per liter of pellet support.
[0034]
(Preparation of heat-treated Zn-added Pd catalyst)
The Zn-added Pd catalyst was heat-treated at 1000 ° C. for 5 hours in a nitrogen gas stream containing 4% by volume of oxygen and 3% by volume of water to obtain a heat-treated Zn-added Pd catalyst.
(CeO₂-Preparation of Pd catalyst)
As the porous carrier, a pellet carrier having a diameter of 2 to 4 mm and comprising a solid solution of 50% by volume of zirconia and 50% by volume of ceria was used. The pellet carrier was impregnated with a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration, dried at 110 ° C. for 24 hours, and then reduced at 450 ° C. for 5 hours in a nitrogen gas stream containing 20% of hydrogen gas. At this time, the supported amount of Pd is 2 g per liter of pellet carrier.
[0035]
(Preparation of Pt catalyst)
Alumina powder (BET surface area 100m²/ G) from 2 to 4 mm in diameter. The pellet support is impregnated with a predetermined amount of a dinitrodiammineplatinum nitric acid aqueous solution having a predetermined concentration, dried at 110 ° C. for 24 hours, and then subjected to a reduction treatment at 450 ° C. for 5 hours in a nitrogen gas stream containing 20% of hydrogen gas to remove the Pt catalyst. Obtained. The supported amount of Pt is 2 g per liter of pellet support.
[0036]
FIG. 2 shows the reactivity of ammonia with the Pt catalyst.
(Preparation of first catalyst)
H-type ZSM-5 (SiO₂/ Al₂O₃= 40) The powder was immersed in an aqueous solution of copper nitrate containing 0.2% by weight of copper atoms and subjected to ion exchange overnight. It was washed with a dilute ammonia solution, dried at 110 ° C., and calcined at 700 ° C. for 5 hours to prepare a first catalyst. The ion-exchangeable positions of the zeolite are 70% ion-exchanged with copper.
[0037]
FIG. 3 shows the reactivity of ammonia by the first catalyst.
(Preparation of denitration catalyst)
Specific surface area 50m²/ G TiO₂Add a certain concentration of vanadyl oxalate (VOC)₂O₄) Impregnated with a predetermined amount of an aqueous solution, dried at 120 ° C for 1 day, and calcined in air at 600 ° C for 1 hour.₂O₅-TiO₂A denitration catalyst was prepared. The amount of vanadium is TiO₂0.02 mol per liter of powder volume.
[0038]
(Reference example)
In a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm, 2 cc of a Pd catalyst was filled on the upstream side in the flow direction of the model gas, and 2 cc of a Pt catalyst was filled on the downstream side, to obtain a catalyst device of this reference example.
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1Was introduced into the reaction tube under the following conditions, and the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. was measured. The model gas contains NO, and the ammonia contains a slight amount of NO._x Is generated. From the comparison between the catalyst inlet gas composition concentration and the outlet gas composition concentration, NO and NH_Three Was determined.
[0039]
NH of incoming gas₃Concentration + NO concentration of incoming gas = A, NH of outgoing gas₃Assuming that concentration + NO concentration of outgas = B, conversion rate = (A−B) × 100 / A
Table 3 shows the results.
[0040]
[Table 1]

(Example 1-1)
A reaction tube made of quartz having an inner diameter of 15 mm and a length of 300 mm was filled with 2 cc of the heat-treated Pd catalyst on the upstream side in the flow direction of the model gas and 2 cc of the Pt catalyst on the downstream side, to obtain a catalyst device of this example.
[0041]
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1Was introduced into the reaction tube under the following conditions, and the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. was measured. The model gas contains NO, and the ammonia contains a slight amount of NO._x GeneratesReference exampleNO and NH by the same formula_Three Was determined. Table 3 shows the results.
[0042]
(Example 1-2)
In a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm, 2 cc of a Zn-added Pd catalyst was filled on the upstream side in the flow direction of the model gas, and 2 cc of a Pt catalyst was filled on the downstream side to obtain a catalyst device of this example.
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1Was introduced into the reaction tube under the following conditions, and the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. was measured. The model gas contains NO, and the ammonia contains a slight amount of NO._x GeneratesReference exampleNO and NH by the same formula_Three Was determined. Table 3 shows the results.
[0043]
(Example 1-3)
In a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm, 2 cc of the heat-treated Zn-added Pd catalyst was filled on the upstream side in the flow direction of the model gas, and 2 cc of the Pt catalyst was filled on the downstream side to obtain a catalyst device of this embodiment. .
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1Was introduced into the reaction tube under the following conditions, and the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. was measured. The model gas contains NO, and the ammonia contains a slight amount of NO._x GeneratesReference exampleNO and NH by the same formula_Three Was determined. Table 3 shows the results.
[0044]
(Example 1-4)
In a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm, CeO was placed on the upstream side in the model gas flow direction._Two -2 cc of Pd catalyst was filled, and 2 cc of Pt catalyst was filled on the downstream side to obtain a catalyst device of this example.
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1Was introduced into the reaction tube under the following conditions, and the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. was measured. The model gas contains NO, and the ammonia contains a slight amount of NO._x GeneratesReference exampleNO and NH by the same formula_Three Was determined. Table 3 shows the results.
[0045]
(Example 2)
Into a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm, the first catalyst, the Pd catalyst, and the Pt catalyst were filled in order of 1 cc from the upstream side to the downstream side in the flow direction of the model gas in this order, and the catalyst of the present embodiment was filled. The device.
Then, the model gas shown in Table 2 was converted to a space velocity SV = 100,000 hr.^-1And the catalyst outlet gas composition when the catalyst inlet gas temperature was changed from 600 ° C. to 50 ° C. was measured.₂Table 3 shows the results obtained for the conversion rate to OH. FIG. 4 shows the result of analyzing the composition of the catalyst outlet gas by a mass spectrometer and examining the composition change of the product at each temperature.
[0046]
[Table 2]

(Comparative example)
A catalyst device of this comparative example was filled with 4 cc of the first catalyst in a quartz reaction tube having an inner diameter of 15 mm and a length of 300 mm.
[0047]
Then, the model gas shown in Table 1 was converted to a space velocity SV = 100,000 hr.^-1, And the outlet gas composition was measured when the catalyst inlet gas temperature was changed from 500 ° C. to 50 ° C. The model gas contains NO, and the ammonia contains a slight amount of NO._x GeneratesReference exampleNO and NH by the same formula_Three Was determined. Table 3 shows the results.
[0048]
(Evaluation)
[0049]
[Table 3]

From Table 3,Reference Example, Example 1-1, Example 1-2, Example 1-3, and Example 1-4Has a higher conversion of ammonia in a temperature range of 400 ° C. or lower than that of the comparative example._Two It is clear that it can be converted to further,Reference exampleThe catalyst devices of Examples 1-1 to 4 showed superior results as compared with those of Example 1-1._Two It can also be seen that it is preferable to use a -Pd catalyst.
[0050]
Also, it can be seen that the catalyst device of Example 2 shows a high addition rate in a temperature range of 600 ° C. or lower.
Further, as shown in FIG. 4, in the catalyst device of Example 2, it is harmless that N is generated in a temperature range of 150 ° C. or more.₂And H₂O only, NO_xDoes not generate any ammonia, all of the ammonia is N₂It is evident that it has been converted to
[0051]
【The invention's effect】
That is, according to the ammonia purification catalyst device of the present invention, NO in a wide temperature range from a low temperature range to a high temperature range._xHarmless ammonia with almost no regeneration of ammonia₂Can be converted to
[Brief description of the drawings]
FIG. 1 is a graph showing the amount of product produced after purification of ammonia at each temperature of a Pd catalyst.
FIG. 2 is a graph showing the amount of product generated after ammonia purification at each temperature of a Pt catalyst.
FIG. 3 is a graph showing the amount of product generated after purification of ammonia at each temperature of a first catalyst.
FIG. 4 is a graph showing the amount of product generated after purifying ammonia at each temperature of the catalyst device of Example 2.

Claims (4)

An ammonia-purifying catalyst device for purifying ammonia contained in exhaust gas, comprising a heat-treated Pd catalyst comprising at least palladium supported on a porous carrier containing alumina and heat-treated at 800 to 1500 ° C. in an oxidizing atmosphere , A Pt catalyst comprising at least platinum supported on a porous carrier, wherein the heat-treated Pd catalyst and the Pt catalyst are arranged in this order from the upstream side to the downstream side of the exhaust gas flow path . Catalyst device. An ammonia purification catalyst device for purifying ammonia contained in exhaust gas, comprising a Zn-added Pd catalyst in which at least palladium and zinc are supported on a porous carrier containing alumina, and at least platinum supported on a porous carrier. And a Pt catalyst comprising: a Zn-added Pd catalyst and a Pt catalyst arranged in this order from the upstream side to the downstream side of the exhaust gas flow path ; A ammonia purification catalyst apparatus for purifying ammonia contained in exhaust gas, CeO ₂ formed by carrying at least palladium on a porous support including ceria -A Pd catalyst and a Pt catalyst in which at least platinum is supported on a porous carrier, and the CeO ₂ flows from the upstream side to the downstream side of the exhaust gas flow path. -A catalyst device for purifying ammonia , wherein a Pd catalyst and the Pt catalyst are arranged in this order . An ammonia purification catalyst device for purifying ammonia contained in exhaust gas, comprising: a first catalyst in which zeolite supports at least one metal selected from iron, cobalt, nickel, and copper; And a Pt catalyst having at least platinum supported on a porous carrier. The first catalyst, the Pd catalyst, and the Pt catalyst are arranged from the upstream side to the downstream side of the exhaust gas passage. Are arranged in this order.

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