JP2008043947A - Dual bed catalytic system for nitrogen oxide removal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent dual bed catalytic system for NO<SB>x</SB>removal composed of Ag/Al<SB>2</SB>O<SB>3</SB>and a ZSM-5 zeolite catalyst. <P>SOLUTION: The dual bed catalytic system of the invention is characterized in that the catalytic system includes silver (Ag)-carrying alumina (Al<SB>2</SB>O<SB>3</SB>) containing silver (Ag) of 1 to 5% by weight and alumina (Al<SB>2</SB>O<SB>3</SB>) of 95 to 99% by weight and zeolite (ZSM-5) containing copper (Cu) of 0 to 5% by weight and zeolite (ZSM-5) of 95 to 100% by weight, in that the silver (Ag)-carrying alumina (Al<SB>2</SB>O<SB>3</SB>) and the zeolite (ZSM-5) are stacked and contained in a range of 4:1 to 1:4 by weight, in that the silver (Ag)-carrying alumina (Al<SB>2</SB>O<SB>3</SB>) is located at the front end of the catalytic group, whereas the zeolite (ZSM-5) is located at the back end of the catalytic group, and in that the catalytic system further contains a hydrocarbon compound of 6 to 16 carbons as a reducing agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a double-layer catalyst system for removing nitrogen oxides, and more particularly, to a double-layer catalyst system for removing nitrogen oxides containing silver (Ag) -supported alumina (Al ₂ O ₃ ) and zeolite (ZSM-5). .

Automobiles that use light oil as fuel, due to their characteristics, have relatively few problems with CO and hydrocarbons in exhaust gas, but particulate matter (PM) and nitrogen oxides (NOx) cause environmental problems such as causing disease. In Europe and other developed countries, regulations are being tightened.
Europe has adopted environmental regulations roughly classified by EURO-IV and V, and the United States by SUVLE and ZEV. Such regulations cannot be satisfied by engine improvements alone. Therefore, it has become necessary to develop exhaust gas aftertreatment technology along with engine improvements.

  Currently, the technology for removing PM is being developed mainly by DPF (Diesel Particulate Filter) developed by Johnson Matthey, Engelgard, Umicore and others. As a technique for removing NOx, there is DPNR (Diesel Particulate NOx Reduction) recently developed by Toyota Motor Corporation. This can reduce PM and NOx at the same time, but it is necessary to operate intermittently under an overload condition, and is vulnerable to sulfur contained in the fuel.

In Europe, urea (or ammonia) SCR technology is expected to be the most promising technology in terms of practical application, but the injector must be installed directly in the car, supplying urea like a gas station There is a problem that it is necessary to construct a basic facility that can be used.
As a technique for solving such a problem, HC-SCR technology using diesel fuel of a light oil vehicle as a reducing agent has attracted attention. Clearaire's Longview and Lonestar have developed HC-SCR catalyst technology that can easily improve existing vehicles, but with low activity and fuel limitations.

Recently known HC-SCR catalysts include Ag / Al ₂ O ₃ , such as Burch et al. [S. Satokawa, J. et al. Shibata, K .; Shimizu, A.A. Satsuma, T .; Hattori, Appl. Catal. B42 (2003) 179. , R.A. Burch, J. et al. P. Breen, C.I. J. et al. Hill, B.B. Krutzsch, B.R. Konrad, E .; Jobson, L.M. Cider, K.C. Eranen, F.M. Klingstedt, LE. According to Lindfors, Capoc6 meeting (2003)], the Ag / Al ₂ O ₃ catalyst has excellent activity under conditions of 350 ° C. or higher using a system using a long-chain hydrocarbon such as n-octane as a reducing agent. Can be obtained, Niwa [T. Nakatsuji, R.A. Yaskawa, K .; Tabata, K .; Ueda, M .; Niwa, Appl. Catal. B, 17 (1998) 333] is a NOx removal study on a diesel engine with secondary fuel injection using Ag / Al ₂ O ₃ as a catalyst and applied to a gasoline lean-burn engine or diesel engine. I confirmed that I was able to.
However, there is still a problem in terms of activity for reducing NOx with N ₂ .
JP 2001-327838 A JP 2001-212464 A S. Satokawa, J. et al. Shibata, K .; Shimizu, A.A. Satsuma, T .; Hattori, Appl. Catal. B 42 (2003) 179 R. Burch, J. et al. P. Breen, C.I. J. et al. Hill, B.B. Krutzsch, B.R. Konrad, E .; Jobson, L.M. Cider, K.C. Eranen, F.M. Klingstedt, LE. Lindfors, Capoc6 meeting (2003) T.A. Nakatsuji, R.A. Yaskawa, K .; Tabata, K .; Ueda, M .; Niwa, Appl. Catal. B, 17 (1998) 333

The inventor of the present invention has a problem with the conventional Ag / Al ₂ O ₃ catalyst as described above, that it shows almost no deNOx activity for reducing NOx with N ₂ at 300 ° C. or lower, and even at 350 ° C. or higher. As a result of studying that there are still points to be improved in terms of activity, a single-bed catalytic system using only a conventional Ag / Al ₂ O ₃ catalyst (ZED-5) was developed as a single-bed catalytic system. When produced in a dual bed catalytic system using Ag / Al ₂ O ₃ , it shows excellent activity even at 300 ° C., even when only Ag / Al ₂ O ₃ catalyst is used at 350 ° C. or higher. It was confirmed that the activity of NO to N ₂ could be increased by 20% or more, and the present invention was completed.

The object of the present invention is to provide an excellent double-layer catalyst system comprising Ag / Al ₂ O ₃ and ZSM-5 zeolite catalyst for NOx removal.

The present invention relates to silver (Ag) -supported alumina (Al ₂ O ₃ ) containing 1 to 5% by weight of silver (Ag) and 95 to 99% by weight of alumina (Al ₂ O ₃ ), copper (Cu) 0 to 5% by weight and zeolite (ZSM-5) including 95 to 100% by weight of zeolite (ZSM-5).

In the present invention, the silver (Ag) -supported alumina (Al ₂ O ₃ ) and zeolite (ZSM-5) are laminated, and the silver (Ag) -supported alumina (Al ₂ O ₃ ) and zeolite (ZSM-5) are 4 : It is characterized by being contained in the range of 1-1: 4 weight ratio.

The silver (Ag) -supported alumina (Al ₂ O ₃ ) is located at the front end of the catalyst base, and the zeolite (ZSM-5) is located at the rear end of the catalyst base, and has 6 to 16 carbon atoms. A hydrocarbon compound in the range of is further included as a reducing agent.

In the double layer catalyst system comprising Ag / Al ₂ O ₃ and ZSM-5 of the present invention, NOx is reduced with N 2 when dotecan (n-detecan) is used as a reducing agent as a diesel oil stimulant. DeNOx activity is superior to single layer Ag / Al ₂ O ₃ catalyst, especially when only conventional Ag / Al ₂ O ₃ is used, the activity is enhanced by 40% or more even at 300 ° C., where almost no activity is confirmed. In addition to the above, even at 350 ° C. or higher, a significant increase in activity can be confirmed as compared with the single layer Ag / Al ₂ O ₃ catalyst.
Therefore, the double-layer catalyst system containing Ag / Al ₂ O ₃ and ZSM-5 can be used more widely as an industrial catalyst that reduces nitrogen oxides emitted from several types of fixed and mobile sources at 300 ° C. or higher.

  Since the present invention contains silver-supported alumina and zeolite, the removal efficiency of nitrogen oxides is superior to the case where an existing silver-supported alumina catalyst or zeolite is used alone. Even under low-temperature (300 ° C.) conditions which are hardly shown, high nitrogen oxide removal activity is exhibited.

The double layer catalyst system of the present invention has a structure in which silver supported alumina (hereinafter, Ag / Al ₂ O ₃ ) and zeolite (ZSM-5) are laminated.
The stacked double-layer catalyst system of the present invention includes the order of packing the catalyst constituting the catalyst, the packing ratio, the Ag content of the Ag / Al ₂ O ₃ catalyst, the type of metal ions supported on the ZSM-5 zeolite catalyst, and It has a technical configuration that shows different activity results depending on the content, and that the catalyst can be blended to suit each application site.

In the Ag / Al ₂ O ₃ catalyst, the nitrogen oxide removal activity [deNOx activity (NOx reduced by N ₂ )] varies depending on the Ag content. At this time, the Ag content is 1 to 5% by weight, preferably 2 to 2% by weight. A range of 3% by weight is suitable. When the Ag content is less than 1% by weight, the nitrogen oxide removal activity is weak. When the Ag content exceeds 5% by weight, the improvement degree of the nitrogen oxide removal activity does not increase obviously. Can be adjusted differently. The content of alumina (Al ₂ O ₃ ) in the Ag / Al ₂ O ₃ catalyst is adjusted in the range of 95 to 99% by weight.

In the stacked double-layer catalyst system of the present invention, the activity of the ZSM-5 zeolite catalyst varies depending on the type of metal supported, and the activity varies depending on the content of the supported metal.
Further, the ZSM-5 zeolite catalyst may support copper, and at this time, the supported amount of copper is 0 to 5% by weight, preferably 2 to 5% by weight, most preferably about 4.66% by weight, At this time, the removal activity of nitrogen oxides is good. If the amount of copper supported exceeds 5% by weight, the effect of improving the nitrogen oxide removal activity tends to decrease. Zeolite is contained in an amount of 95 to 100% by weight depending on the copper content.

In the double layer catalyst system for removing nitrogen oxides of the present invention, the removal activity of nitrogen oxides varies depending on the ratio of silver-supported alumina and zeolite, but the ratio of silver-supported alumina and zeolite is in the range of 4: 1 to 1: 4 by weight. Preferably, it is contained in a 2: 1 weight ratio.
Although the removal activity of nitrogen oxides differs depending on the packing order of the silver-supported alumina and the zeolite, it is preferable that the silver-supported alumina is located at the front end of the catalyst base and the zeolite is located at the rear end of the catalyst base.
The double-layer catalyst system for removing nitrogen oxides of the present invention preferably contains a hydrocarbon compound as a reducing agent, and as the hydrocarbon compound, a long-chain hydrocarbon compound having 6 to 16 carbon atoms is preferably used. Specifically, alkanes having 10 to 16 carbon atoms can be used. These can be used in a mixed state, and diesel oil is often used as the reducing agent.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not necessarily limited to an Example.
As seen in Table 1 below to make a double layer catalyst system consisting of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5 catalyst, AgNO in γ-Al ₂ O ₃ (BET = 204 m ₂ / g). ₃ is used as a precursor, and impregnated with an Ag content of 1, 2, ₃ , 5 weight ratio, Cu / ZSM-5 is produced by a wet ion exchange method, and the Cu content is determined by the number of ion exchanges. Three kinds of catalysts were manufactured by adjusting the amount of supported Cu. These physicochemical properties are as shown in Table 1.

First, 2% by weight of γ-Al ₂ O ₃ and Cu / ZSM-5 catalyst were mounted at the front end in a 2: 1 weight ratio to produce a double layer catalyst system.
[Experimental Example 1]
In order to measure the nitrogen oxide removal efficiency of the double layer catalyst system produced in Example 1, it was pretreated at 550 ° C. with He balance, 10% O ₂ for 1 hour, 1000 ppm NO, 10% O ₂ , 5% H ₂ O, 540 ppm of diesel oil stimulant (n-C ₁₂ H ₂₆ ) as a reducing agent was injected at 200 to 500 ° C. at a space velocity of 30,000 h ^−1. The deNOx reaction was carried out, the nitrogen oxide removal ratio was converted to nitrogen removal ratio, and the results depending on the reaction temperature are shown in FIG.
In order to quantitatively analyze N2 produced after the reaction, a packed column (molecular sieve 5A) was installed in on-line GC (HP6890).

Example 2 was conducted to evaluate the effect of nitrogen oxide removal efficiency on the packing sequence of a double layer catalyst system composed of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5.
First, Cu / ZSM-5 3.37% by weight at the front end and Ag / γ-Al ₂ O ₃ 2% by weight at the rear end are attached at a 1: 1 weight ratio, and second, Ag / γ at the front end. -Al ₂ O ₃ 2 wt% and Cu / ZSM-5 3.37 wt% at the rear end were mounted at a 1: 1 weight ratio, and finally the Cu / ZSM-5 catalyst 3.37 wt% and Ag / γ -al ₂ O ₃ catalyst 2 wt% physically mixed to measure the removal activity of nitrogen oxides. The measurement method was the same as in Experimental Example 1, and the results of activity measurement are shown in FIG.

Example 3 was performed in order to evaluate the influence of the packing ratio of the double layer catalyst system composed of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5 on the removal efficiency of nitrogen oxides.
Ag / γ-Al ₂ O ₃ 2 wt% at the front end and Cu / ZSM-5 3.37 wt% or 4.66 wt% at the rear end in a 1: 2 weight ratio, 1: 1 weight ratio, and 2: 1 A stack type double layer catalyst experiment was carried out by weight. The measurement method is the same as in Experimental Example 1, and the experimental results are shown in FIGS.

Example 4 is the same as that of HZSM-5 in which copper was not ion-exchanged in order to confirm optimal copper in a double layer catalyst system composed of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5. Four types of Cu / ZSM-5 catalysts containing 91 wt%, 3.37 wt%, 4.66 wt% copper were applied to the double layer catalyst system.
After removing 2% by weight of Ag / γ-Al ₂ O _{3 at the} front end and packing the four types of ZSM-5 catalysts based on the copper content in a 2: 1 weight ratio at the rear end, the nitrogen oxide removal activity Was measured.
The measurement method is the same as in Experimental Example 1, and the measurement results are shown in FIG.
[Experimental Example 5]

Example 5 carries 1, 2, 3 and 5% by weight of silver to confirm the optimum silver content in a double layer catalyst system consisting of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5. The four types of Ag / γ-Al ₂ O ₃ catalysts applied were applied to the double layer catalyst system.
The four types of Ag / γ-Al ₂ O ₃ catalysts are fixed, a Cu / ZSM-5 catalyst is fixed to the rear end, and the contents of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5 are set to 2: Activity was measured after packing at 1 weight ratio. The measurement method is the same as in Experimental Example 1, and the measurement results are shown in FIG.
[Comparative Examples 1-5]

Ag / _γ-Al 2 _{O 3} and Cu / ZSM-5 bilayers catalyst system 2 each catalyst Ag / _γ-Al 2 _{O 3} contained in weight percent consisting of Metropolitan and Cu / ZSM-5 catalyst 3.37 Taking the weight% as a reference substance, the synthesis was performed in the same manner as in Example 1, and the activity was measured in the same manner as in Experimental Example 1 in order to confirm the removal efficiency of these nitrogen oxides. It was shown in 1-6.
In addition, in order to confirm the superiority of the double layer catalyst system composed of Ag / γ-Al ₂ O ₃ and Cu / ZSM-5, three different double layer catalyst systems were synthesized.

First, Ag / γ-Al ₂ O ₃ and Cu / Y catalyst are mounted in a 2: 1 weight ratio, and second, Ag / γ-Al ₂ O ₃ and Fe / ZSM-5 catalyst are in a 2: 1 weight ratio. At last, Ag / γ-Al ₂ O ₃ and G / ZSM-5 catalyst were mounted in a 2: 1 weight ratio to form a reactive group.
Cu / Y was produced by a wet ion exchange method, and Fe / ZSM-5 was produced by a solid phase ion exchange method with FeCl ₃ in a condition free of moisture. These physicochemical properties are shown in Table 1 below.
The removal efficiency of nitrogen oxides in the three-layer double-layer catalyst system is shown in FIG. The measurement method is the same as in Experimental Example 1.

In order to confirm the usefulness of the method of removing nitrogen oxides by nitrogen using a double layer catalyst system in the present invention, the results of Examples and Comparative Examples were compared.
As can be seen from FIG. 1, a double-layer catalyst system in which Cu / ZSM-5, Fe / ZSM-5, and Cu / Y catalyst are mounted on the rear end of 2 wt% Ag / γ-Al ₂ O ₃ is constructed, and deNOx activity is achieved. Evaluated.
Other bilayer catalyst system it is seen that all low activity compared to 2 wt% Ag / _Al 2 _{O 3} to the combination of 4.66 wt% Cu / ZSM-5.
In the case of the H / ZSM-5 catalyst, an improved catalytic activity was confirmed at 300 ° C. compared to 2 wt% Ag / γ-Al ₂ O ₃ which is a single layer catalyst. The CuY catalyst was superior to the 2 wt% Ag / γ-Al ₂ O ₃ single layer catalyst at 350 ° C. or lower, but the activity was observed to be much lower at 350 ° C. or higher.

As can be seen from FIG. 2, as a result of evaluating the influence of the packing order on the removal efficiency of nitrogen oxides, the activity that was not seen with the Ag / γ-Al ₂ O ₃ catalyst was seen at 300 ° C. regardless of the packing order. When the Ag / γ-Al ₂ O ₃ was attached to the front end and the Cu / ZSM-5 catalyst was attached to the rear end, it was confirmed that the activity was considerably improved even at 350 ° C. or higher compared to other cases. From the results using the Fe / ZSM-5 catalyst, superior deNOx activity was observed at all measured temperatures.

3 and 4, it can be confirmed that the deNOx activity shows many differences depending on the packing ratio, in particular, Ag / γ-Al ₂ O _{3 at} the front end and 2: 1 weight of Cu / ZSM-5 at the rear end. When experimented with a ratio, it was confirmed that all deNOx activities increased above 300 ° C. Even when the Cu content was different, 2: 1 showed the most excellent activity.

As can be seen from FIG. 5, the activity was measured at a low temperature depending on the Cu content, and the deNOx activity was most excellent at 300 ° C. with 4.66 wt% Cu / ZSM-5, and at 350 ° C. or higher, It was observed that the effect of content was small. In the case of the ZSM-5 catalyst in which Cu was not ion-exchanged, the catalytic activity was greatly improved at 300 ° C. compared to 2 wt% Ag / γ-Al ₂ O ₃ which is a single layer catalyst.

As can be seen from FIG. 6, at 300 ° C., the activity tendency was almost similar except for the case where a 1 wt% Ag / γ-Al ₂ O ₃ catalyst was placed at the front end, and at 400 ° C. or higher, 5 wt% Ag / γ- It was confirmed that the activity of the Al ₂ O ₃ catalyst was greatly reduced. Therefore, a more preferable effect can be expressed when the supported amount of silver is about 2 to 3% by weight.

A graph showing the deNOx activity of a double layer catalyst system packed with Ag / Al ₂ O ₃ and Cu / ZSM-5, Cu / Y, Fe / ZSM-5 or H / ZSM-5 catalyst in a 2: 1 ratio. is there. Here, F is a front end catalyst, R is a rear end catalyst, Ag (2.00) is 2 wt% Ag / γ-Al ₂ O ₃ , Cu (4.66) is 4.66 wt% Cu / ZSM-5, Cu / Y (8.17) means 8.17 wt% Cu / Y and Fe (1.96) means 1.96 wt% Fe / ZSM-5. ₃ is a graph showing deNOx activity according to packing order of a double layer catalyst system of 3.37 wt% Cu / ZSM-5 and 2 wt% Ag / γ-Al ₂ O ₃ . Where F is the front end catalyst, R is the rear end catalyst, Ag (2.00) is 2 wt% Ag / γ-Al ₂ O ₃ , and Cu (3.37) is 3.27 wt% Cu / ZSM-5 Means. Is a graph showing a 2 _{wt% Ag / γ-Al 2 O} 3 ( front) and 3.37 wt% Cu / ZSM-5 (rear end) of the deNOx activity by packing ratio of double layer catalyst system. Where F is the front end catalyst, R is the rear end catalyst, Ag (2.00) is 2 wt% Ag / γ-Al ₂ O ₃ , and Cu (3.37) is 3.27 wt% Cu / ZSM-5 Means. Is a graph showing a 2 _{wt% Ag / γ-Al 2 O} 3 ( front) and 4.66 wt% Cu / ZSM-5 deNOx activity by packing ratio of double layer catalyst system of (rear end). Where F is the front end catalyst, R is the rear end catalyst, Ag (2.00) is 2 wt% Ag / γ-Al ₂ O ₃ , and Cu (4.66) is 4.66 wt% Cu / ZSM-5. Means. Is a graph showing a 2 _{wt% Ag / γ-Al 2 O} 3 ( front) and x wt% Cu / ZSM-5 (rear end) of the deNOx activity by copper content of double layer catalyst system. Here, F is a front end catalyst, R is a rear end catalyst, Ag (2.00) is 2 wt% Ag / γ-Al ₂ O ₃ , and Cu (x) is x wt% Cu / ZSM-5. is a graph showing the deNOx activity by silver supported amount of double layer catalyst system of x _{wt% Ag / γ-Al 2 O} 3 ( front) and 4.66 wt% Cu / ZSM-5 (the rear end). Where F is the front end catalyst, R is the rear end catalyst, Ag (x) is x wt% Ag / γ-Al ₂ O ₃ , and Cu (4.66) is 4.66 wt% Cu / ZSM-5. To do.

Claims (5)

Silver (Ag) -supported alumina (Al ₂ O ₃ ) comprising 1 to 5% by weight of silver (Ag) and 95 to 99% by weight of alumina (Al ₂ O ₃ ), 0 to 5% by weight of copper (Cu) and zeolite (ZSM-5) Zeolite (ZSM-5) containing 95 to 100% by weight and a double layer catalyst system for removing nitrogen oxides. The silver (Ag) on alumina _(Al 2 _{O 3)} and zeolite (ZSM-5) is according to claim 1 nitrogen oxide bilayer catalyst system for the removal of, wherein a stacked. _2. The nitrogen oxide removing method according to claim 1, wherein the silver (Ag) -supported alumina (Al ₂ O ₃ ) and the zeolite (ZSM-5) are contained in a weight ratio of 4: 1 to 1: 4. Double layer catalyst system. _2. The nitrogen according to claim 1, wherein the silver (Ag) -supported alumina (Al ₂ O ₃ ) is located at the front end of the catalyst base and the zeolite (ZSM-5) is located at the rear end of the catalyst base. Double layer catalyst system for oxide removal.   The double-layer catalyst system for removing nitrogen oxides according to any one of claims 1 to 4, further comprising a hydrocarbon compound having 6 to 16 carbon atoms as a reducing agent.

Images