The above and other features of the present invention will be described with reference to certain exemplary embodiments thereof illustrated the attached drawings in which:
Reference will now be made in detail to the preferred embodiments of the present invention.
As discussed above, in a preferred aspect, the present invention provides dual bed catalytic systems for the reduction of NOx comprising Ag/Al2O3 and ZSM-5. The present systems have significantly improved NOx reducing efficiency compared with conventional systems comprising Ag/Al2O3 only or ZSM-5 only. More particularly, the present systems have excellent reducing activity at a low temperature at which NOx reduction is almost impossible with the conventional system using Ag/Al2O3 only.
A preferred system of the present invention may have a packing structure of Ag/Al2O3 and ZSM-5. Catalytic activity of a packed dual bed catalytic system may vary depending on the packing sequence of catalysts, packing ratio, Ag content of Ag/Al2O3, the kind and content of metal ions deposited in ZSM-5, etc. Thus, a customized catalyst system may be prepared depending on applications.
More specifically, deNOx activity varies depending on Ag content of Ag/Al2O3. A preferable Ag content is 1 to 5 wt %. More preferable Ag content is 2 to 3 wt %. If the Ag content is below 1 wt %, deNOx activity becomes poor. If the content exceeds 5 wt %, deNOx activity does not improve noticeably. Persons of ordinary skilled in the art would understand that Ag content can vary depending on the application of the catalyst. Preferable content of Al2O3 of Ag/Al2O3 is 95 to 99 wt %.
The catalytic activity of the packed dual bed catalytic system also depends on the kind of metal deposited in ZSM-5 and the content of the metal.
A preferable metal deposited in ZSM-5 is copper (Cu). Preferably, the amount of Cu is from 0 to 5 wt %. More preferably, it is 2 to 5 wt %. Most preferably, it is about 4.66 wt %. DeNox activity does not increase significantly, if the Cu amount exceeds 5 wt %. It shall be evident that the zeolite ZSM-5 content varies from 95 to 100 wt %.
DeNOx activity also depends on the ratio of Ag/Al2O3 to ZSM-5. A preferable ratio of Ag/Al2O3:ZSM-5 is about 4:1 to about 1:4 based on weight. A more preferable ratio is about 2:1. DeNOx activity also depends on packing sequence of Ag/Al2O3 and ZSM-5. Preferably, Ag/Al2O3 is located at the front part of the system with ZSM-5 located at the rear part thereof.
In a further preferred embodiment, the present dual bed catalytic systems may comprise a hydrocarbon compound as a reductant of NOx. Preferably, the hydrocarbon compound may have 6-16 carbon atoms. More preferably, it is a C10-C16 alkane. Also preferably, it can be a mixture of hydrocarbon compounds. Diesel oil can be used as the reductant.
Practical and presently preferred embodiments of the present invention are illustrated as shown in the following examples. However, it will be appreciated that those skilled in the art may, in consideration of this disclosure, make modifications and improvements within the spirit and scope of the present invention.
A dual bed catalytic system comprising Ag/γ-Al2O3 and Cu/ZSM-5 catalyst was prepared as shown in Table 1 below. AgNO3 was added as precursor to γ-Al2O3 (BET=204 m2/g) and impregnation was performed with an Ag content of 1, 2, 3 and 5 wt %. Cu/ZSM-5 was prepared by wet ion exchange. Three kinds of catalysts were prepared by varying Cu content. The physical and chemical properties of the catalysts are summarized in Table 1.
2 wt % Ag/γ-Al2O3 (front) and 4.66 wt % Cu/ZSM-5 (rear) were packed with the ratio of 2:1 based on weight to obtain a dual bed catalytic system.
In order to measure the NOx reducing efficiency of the dual bed catalytic system prepared in Example 1, the dual bed catalytic system was pretreated for 1 hour under the condition of 550° C., He balance and 10% O2. Then, 1000 ppm NO, 10% O2, 5% H2O and 540 ppm n-dodecane (n-C12H26) as a stimulant of diesel oil and reductant were injected. The deNOx reaction was performed at 200 to 500° C. at a space velocity of 30,000 h−1. The conversion ratio of NOx into N2 was calculated. The result is given in
On-line GC (HP 6890 series) was performed on a packed column (molecular sieve 5A) for the quantitative analysis of N2.
The effect of the packing sequence of the dual bed catalytic system comprising Ag/γ-Al2O3 and Cu/ZSM-5 on the NOx reducing efficiency was evaluated.
The mixture of 3.37 wt % Cu/ZSM-5 was packed at the front and 2 wt % Ag/γ-Al2O3 was packed at the rear side with the ratio of 1:1 based on weight. Then, 2 wt % Ag/γ-Al2O3 was packed at the front and 3.37 wt % Cu/ZSM-5 at the rear side with the ratio of 1:1 based on weight. Finally, 3.37 wt % Cu/ZSM-5 and 2 wt % Ag/γ-Al2O3 were physically mixed. NOx reducing activity was measured. The result is given in
The effect of the packing ratio of the dual bed catalytic system comprising Ag/γ-Al2O3 and Cu/ZSM-5 on the NOx reducing efficiency was evaluated.
2 wt % Ag/γ-Al2O3 (front) and 3.37 wt % or 4.66 wt % Cu/ZSM-5 (rear) were packed with the ratio of 1:2 based on weight, 1:1 based on weight and 2:1 based on weight. The results are given in
In order to find out the optimum Cu content of the dual bed catalytic system comprising Ag/γ-Al2O3 and ZSM-5, HZSM-5 with no Cu and Cu/ZSM-5 catalysts comprising 1.91 wt %, 3.37 wt % and 4.66 wt % of Cu were used to prepare dual bed catalytic systems.
2 wt % Ag/γ-Al2O3 (front) and ZSM-5 (rear) with different Cu content were packed with the ratio of 2:1 and NOx reducing activity was measured. The result is given in
In order to find out the optimum Ag content of the dual bed catalytic system comprising Ag/γ-Al2O3 and Cu/ZSM-5, silver (Ag) and Ag/γ-Al2O3 catalysts comprising 1, 2, 3 and 5 wt % of 4 silver were used to prepare dual bed catalytic systems.
Ag/γ-Al2O3 (front) and Cu/ZSM-5 (rear) were packed with the ratio of 2:1 based on weight of Ag/γ-Al2O3 to Cu/ZSM-5 based on weight. The result is given in
Catalytic systems were prepared using 2 wt % Ag/γ-Al2O3 and 3.37 wt % Cu/ZSM-5 as standard materials in the same manner as in Example 1. NOx reducing efficiency was measured in the same manner as in Experimental Example 1. The result is given in
Also, three kinds of other dual bed catalytic systems comprising Ag/Y-Al2O3 and Cu/ZSM-5 were prepared.
First, Ag/γ-Al2O3 and Cu/Y were packed with the ratio of 2:1 based on weight. Second, Ag/γ-Al2O3 and Fe/ZSM-5 were packed with the ratio of 2:1 based on weight. At last, Ag/γ-Al2O3 and H/ZSM-5 were packed with the ratio of 2:1 based on weight.
Cu/Y was prepared by wet ion exchange. Fe/ZSM-5 was prepared by solid state ion exchange with FeCl3 in the absence of moisture. Their physical and chemical properties are given in Table 1.
The NOx reducing efficiency of the three types of dual bed catalytic systems are given in
The NOx reducing efficiency of the dual bed catalytic systems of Examples and Comparative Examples was compared.
As shown in
The H/ZSM-5 catalyst showed improved catalytic activity at 300° C. compared with the single bed catalyst comprising 2 wt % Ag/γ-Al2O3. The CuY catalyst showed superior activity below 350° C. to the single bed catalyst comprising 2 wt % Ag/γ-Al2O3, but the activity decreased greatly over 350° C.
As shown in
As shown in
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As shown in
As described above, the present dual bed catalytic systems provide excellent deNOx activity, especially when using n-dodecane as a reductant than the single bed catalytic system comprising Ag/Al2O3. 40% or more improved activity can be attained at 300° C. at which little activity is observed when using Ag/Al2O3 only. Besides, a significantly improved activity is attained at 350° C. or above.
Thus, the present dual bed catalytic systems can be industrially applied for reducing nitrogen oxides emitted from a variety of non-moving and moving facilities, at 300° C. or above.
Preferred embodiments of the present invention have been described and illustrated, however, the present invention is not limited thereto, rather, it should be understood that various modifications and variations of the present invention can be made thereto by those skilled in the art without departing from the spirit and the technical scope of the present invention as defined by the appended claims.
Number | Date | Country | Kind |
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10-2006-0076274 | Aug 2006 | KR | national |