KR101266397B1 - After―treatment system for reducing nitrogen oxide in dimethylether fueled vehicles - Google Patents

Abstract

A post-treatment system for reducing nitrogen oxide according to an embodiment of the present invention, by placing the SR catalyst in front of the LNT catalyst, by using the reducing agent produced by the reforming reaction of dimethyl ether and SR catalyst for the reaction of the LNT catalyst, Nitrogen oxides can be reduced. In addition, since the reforming reaction of dimethyl ether and SR catalyst is endothermic, heat source and moisture from the outside are required, but energy loss of exhaust gas is not required because a separate heat source supply device is not required by using heat source and moisture present in the exhaust gas. Cost reduction and process simplification can be achieved.

Description

AFTER-TREATMENT SYSTEM FOR REDUCING NITROGEN OXIDE IN DIMETHYLETHER FUELED VEHICLES}

A post-treatment system for reducing nitrogen oxides in automobiles using dimethyl ether as a fuel is disclosed. More specifically, a post-treatment system is disclosed that can reduce nitrogen oxides (NOx) in the exhaust gas of automobiles using a complex system of SR-LNT catalysts.

Dimethyl ether (DME) is recognized as a clean fuel that can replace petroleum. DME can be produced from natural gas, coal, biomass and the like. DME has an oxygen content of 34.8% and a cetane number of about 55, making it a fuel for diesel engines. In addition, the problem of particulate matter (PM), which is a problem in diesel engines, can be solved, and in recent years, attention has been increased as an alternative fuel of diesel, such as excellent magnetization characteristics.

In addition, since dimethyl ether has properties similar to that of LPG, commercialization is advantageous because most existing infrastructures can be used. However, engines using DME have slightly lower NOx (Nitrogen Oxide) emissions than diesel engines, and emissions can be further reduced by applying exhaust-gas recirculation (EGR). However, due to the low calorific value of the DME, excessive use of EGR causes a decrease in output, so the rate of use of EGR is limited. After all, NOx reduction is an important challenge when using DME in diesel engines, and the recent European EURO6 passenger car regulation (0.08g / km, 2014) has almost reduced NOx emissions compared to the EURO5 regulation (0.18g / km). It is demanding that it be lowered to 1/2 level. Thus, aftertreatment devices for automobiles are required to meet more stringent NOx emission regulations.

Currently, as the NOx reduction catalyst, lean NOx trap (LNT), urea-SCR (selective catalytic reduction), HC-SCR and the like are very well known. Although urea-SCR catalysts have been commercialized mainly for large vehicles, the lack of infrastructure for supplying large volume urea-SCR systems and aqueous urea solutions requires an alternative to new aftertreatment systems. On the other hand, LNT catalysts developed mainly for small vehicles occupy NOx under lean operation conditions, and NOx adsorbed on the LNT catalyst by using reducing agents (H ₂ , CO, HC) obtained through post injection of fuel without a separate device. Can be effectively removed. However, LNT also uses fuel as a reducing agent, resulting in poor fuel economy.

Therefore, there is a need to supply an optimal reducing agent with high NOx purification efficiency. H ₂ is an optimal reducing agent of LNT, which has fast reactivity and excellent activity even at low temperatures. Currently, a study of Scheme 2, which reacts with D ₂ with H ₂ O to generate H ₂ , generates H ₂ and CO due to partial oxidation by reacting with O ₂ . Recently, the research to produce H ₂ using a low-temperature plasma and diesel fuel cracking catalyst (diesel fuel cracking catalyst) to improve the selectivity of H ₂ is made. In addition, since DME does not contain sulfur, the deactivation of the LNT catalyst due to sulfur poisoning, which is one of the causes of the degradation of the LNT catalyst performance, does not occur.

[Reaction Scheme 1]

CH ₃ OCH ₃ + 3H ₂ O → 6H ₂ + 2CO ₂

[Reaction Scheme 2]

CH ₃ OCH ₃ + 1 / 2O ₂ → 3H ₂ + 2CO

The reforming of DME into a steam reforming catalyst is being studied around copper-based / r-Al ₂ O ₃ catalysts to supply H ₂ to fuel cells. In order to increase the production rate of H ₂ , a transition metal is added to a copper-based catalyst, a zeolite having a high acid point instead of r-Al ₂ O ₃ , and a spinel structure have been studied. However, many problems have been reported, such as a decrease in the selectivity of H ₂ due to weakening of the thermal durability of the copper catalyst and side reactions.

There is provided a post-treatment system that can reduce the NOx in the exhaust gas of a vehicle by using a complex system of SR-LNT catalyst.

A post-treatment system for reducing nitrogen oxides according to an embodiment of the present invention includes a feed gas unit including exhaust gas discharged from an engine unit and dimethyl ether injected from an injector, and an SR catalyst reacting with the dimethyl ether. And a second catalyst part including a first catalyst part and an LNT catalyst reacting with a reducing agent generated by the reaction of the dimethyl ether and the SR catalyst.

In a post-treatment system for reducing nitrogen oxides according to one aspect of the present invention, the size of the SR catalyst and the LNT catalyst may be 1.0: 1 to 4.0: 1 for SR: LNT.

In the aftertreatment system for reducing nitrogen oxides according to one side of the present invention, the reducing agent may be H ₂ or CO.

In the aftertreatment system for reducing nitrogen oxides according to one side of the present invention, the SR catalyst can be prepared by the sol-gel method.

In the aftertreatment system for reducing nitrogen oxides according to one side of the present invention, the content of copper in the SR catalyst may be 1% by weight to 50% by weight.

In the aftertreatment system for reducing nitrogen oxides according to one aspect of the present invention, the SR catalyst further includes zinc as a promoter, and the zinc content may be 0 wt% to 10 wt%.

In the aftertreatment system for reducing nitrogen oxides according to one side of the present invention, dimethyl ether may be in the range of 0% to 5.0% of the flow rate of the feed gas included in the feed gas portion.

In a post-treatment system for reducing nitrogen oxides according to one aspect of the present invention, the catalyst is disposed before the first catalyst portion, and further includes a third catalyst portion including a diesel oxidation catalyst for oxidizing the hydrocarbon or carbon monoxide in the exhaust gas. can do.

In a post-treatment system for reducing nitrogen oxides according to one aspect of the present invention, the cell density of the carrier in the SR catalyst may be 100 cpsi (cell per square inch) ~ 1200 cpsi.

A post-treatment system for reducing nitrogen oxide according to an embodiment of the present invention, by placing the SR catalyst in front of the LNT catalyst, by using the reducing agent produced by the reforming reaction of dimethyl ether and SR catalyst for the reaction of the LNT catalyst, Nitrogen oxides can be reduced.

In addition, since the reforming reaction of dimethyl ether and SR catalyst is endothermic, heat source and moisture from the outside are required, but energy loss of exhaust gas is not required because a separate heat source supply device is not required by using heat source and moisture present in the exhaust gas. Cost reduction and process simplification can be achieved.

Furthermore, since dimethyl ether containing no sulfur is used, it is possible to prevent a decrease in activity of the LNT catalyst due to sulfur poisoning.

1 is a schematic diagram of a post-treatment system for reducing nitrogen oxides according to an embodiment of the present invention.
2 is a TEM photograph of a washcoat prepared by the sol-gel method according to an embodiment of the present invention.
3A shows the NOx purification rate according to the injection amount of the DME, FIG. 3B shows the DME slip concentration according to the injection amount of the DME, and FIG. 3C shows the NOx purification rate according to the injection time.
Figure 4a shows the H ₂ generation rate according to the type of SR catalyst according to an embodiment of the present invention, Figure 4b shows the NOx purification rate in the SR + LNT catalyst of the after-treatment system according to an embodiment of the present invention.
5A shows the generation rate of H ₂ according to the size of the SR catalyst, and FIG. 5B shows the NOx purification rate according to the size of the SR catalyst.
Figure 6a shows the generation rate of H ₂ according to the cell density of the SR catalyst carrier according to an embodiment of the present invention, Figure 6b shows the NOx purification rate according to the cell density of the SR catalyst carrier according to an embodiment of the present invention .
FIG. 7A shows the H ₂ generation rate when Zn is added to the SR catalyst of the aftertreatment system according to an embodiment of the present invention, and FIG. 7B shows Zn in the SR catalyst of the aftertreatment system according to an embodiment of the present invention. The NOx purification rate when added is shown.

Hereinafter, a post-treatment system capable of reducing nitrogen oxides according to an embodiment of the present invention will be described with reference to the following drawings.

1 is a schematic diagram of a post-treatment system for reducing nitrogen oxides according to an embodiment of the present invention.

Referring to FIG. 1, a post-treatment system for reducing nitrogen oxides according to an embodiment of the present invention includes a supply gas unit including exhaust gas discharged from the engine unit 100 and dimethyl ether injected from the injector 200. 300, the first catalyst part 400 including the SR catalyst reacting with the dimethyl ether and the second catalyst part 500 including the LNT catalyst reacting with a reducing agent generated by the reaction of the dimethyl ether and the SR catalyst. ).

In addition, the after-treatment system according to an embodiment of the present invention is disposed before the first catalyst unit, and further comprises a third catalyst unit 600 including a diesel oxidation catalyst for oxidizing the hydrocarbon or carbon monoxide in the exhaust gas. It may include.

Furthermore, the first catalyst unit 400, the second catalyst unit 500, and the third catalyst unit 600 may be canned by different catalyst devices, respectively, and connected to a series of systems, which is one embodiment of the present invention. It is included in the scope of the aftertreatment system which reduces nitrogen oxide according to an example.

Exhaust gas containing hydrocarbons, carbon monoxide, oxygen, nitrogen oxides, and the like is discharged from the engine unit 100. The discharged exhaust gas passes through the third catalyst unit 600 and then enters the first catalyst unit 400 together with the dimethyl ether injected from the injector 200 into the feed gas unit 300. Dimethyl ether introduced into the first catalyst unit 400 generates a reforming reaction with the SR catalyst to generate a reducing agent such as H ₂ and CO. The SR catalyst can be prepared by the sol-gel method.

Dimethyl ether undergoes a reforming reaction with the following SR catalyst to generate H ₂ , CO and the like. The supply gas including the exhaust gas and the dimethyl ether present in the supply gas unit 300 passes through the first catalyst unit 400 at a specific flow rate. Reforming of dimethyl ether and a SR catalyst can be carried out so that the selectivity for H ₂ is high, it is possible to change the supply amount and the temperature of the SR catalyst of dimethyl ether to enhance the selectivity of H _2. It is also possible to change the copper content in the SR catalyst. In addition, the cell density of the carrier in the SR catalyst may be 100 cpsi ~ 1200 cpsi. Preferably, the cell density of the carrier in the SR catalyst may be 200 cpsi ~ 600 cpsi.

The supply amount of dimethyl ether may range from 0% to 5.0% relative to the total flow rate of the feed gas. Preferably, the supply amount of the dimethyl ether may be 0.5% to 2.0% relative to the total flow rate of the feed gas. In order to increase the selectivity of the H ₂ , the copper content may be 1 wt% to 50 wt% of the total amount of the SR catalyst. Preferably, the copper content may be 5 wt% to 40 wt% of the total amount of the R catalyst. In addition, the SR catalyst may further include zinc as a promoter, and the zinc content may be 0 wt% to 10 wt%.

The reducing agent produced due to the reforming reaction of the dimethyl ether and the SR catalyst may be H ₂ or CO as described above. Such a reducing agent may be used in a reduction reaction with the LNT catalyst included in the second catalyst part 500. In particular, H ₂ is the most effective at low temperatures as a reducing agent of the LNT catalyst.

The temperature between the first catalyst unit 400 and the second catalyst unit 500 may be a temperature range of 300 ℃ to 450 ℃. The activation temperature of the catalyst may vary depending on the temperature between the first catalyst unit 400 and the second catalyst unit 500, and the activity of the catalyst may be directly related to the reduction of nitrogen oxides. As a result, in the aftertreatment system for reducing nitrogen oxides according to an embodiment of the present invention LNT by maintaining the temperature between the first catalyst unit 400 and the second catalyst unit 500 preferably 300 ℃ ~ 450 ℃ After the second catalyst unit 500 including the catalyst, nitrogen oxides may be reduced.

In addition, in order to reduce nitrogen oxides by the reduction reaction in the second catalyst part 500 including the LNT catalyst, the first catalyst part 400 and the second catalyst part 500 are spaced apart in a range of 5 mm to 10 mm. Can be arranged. The SR catalyst included in the first catalyst unit 400 and the LNT catalyst included in the second catalyst unit 500 may have an SR: LNT of 1.0: 1 to 4.0: 1. Preferably, the size of the SR catalyst included in the first catalyst unit 400 and the LNT catalyst included in the second catalyst unit 500 may be 1.0: 1 to 2.5: 1 of SR: LNT. The size ratio of the SR catalyst and the LNT catalyst may be appropriately selected according to the temperature between the first catalyst unit 400 and the second catalyst unit 500.

Accordingly, the post-treatment system for reducing nitrogen oxides according to an embodiment of the present invention, by placing the SR catalyst in front of the LNT catalyst by using a reducing agent produced by the reforming reaction of dimethyl ether and SR catalyst for the reaction of the LNT catalyst As a result, nitrogen oxides emitted can be reduced.

In addition, since the reforming reaction of dimethyl ether and SR catalyst is endothermic, heat source and moisture from the outside are required, but energy loss of exhaust gas is not required because a separate heat source supply device is not required by using heat source and moisture present in the exhaust gas. Cost reduction and process simplification can be achieved. In addition, since dimethyl ether which does not contain sulfur is used, it is possible to prevent the deactivation of the LNT catalyst due to sulfur poisoning.

Hereinafter, embodiments of the NOx purification rate due to the SR + LNT catalyst in the preparation and post-treatment system of the SR catalyst according to an embodiment of the present invention will be described in detail.

Explanation of Terms

The set temperature or the reference temperature means the temperature T1 at the front end of the SR catalyst, the temperature T2 at the front end of the SR catalyst or the front end of the LNT catalyst, and the temperature T3 at the rear end of the LNT catalyst, respectively.

SR catalyst refers to a catalyst used to modify dimethyl ether and LNT catalyst refers to a catalyst that reduces NOx.

SR + LNT catalyst is included in the aftertreatment system according to an embodiment of the present invention, and refers to a structure in which the SR catalyst is disposed at the front end of the aftertreatment system and then the LNT catalyst is disposed thereafter.

The sol-gel method is one of the methods for preparing the SR catalyst, which means that it is prepared in the following steps.

Steady-state condition means that the experiment was performed at a specific temperature, and transient condition means that the experiment was performed while continuously increasing the temperature.

Washcoat is a type of carrier that allows the catalyst to react more effectively, which means a thin coating of activated alumina.

Preparation of the catalyst

The SR catalyst was prepared directly by the sol-gel method, and the amount of Cu (copper) supported was 10, 20, 30%. As the LNT catalyst, a commercially available catalyst (Ordeg Co.) was used. A process for preparing the SR catalyst by the sol-gel method is as follows.

SR catalyst was dissolved in aluminum isopropoxide (Al [OCH (CH ₃ ) ₂ ], sigma Aldrich 99.9%) in 100 mL of H ₂ O at 60 ° C. and then copper precursor according to the respective copper content. ([Cu (NO ₃ ) ₂ 2.5H ₂ O], sigma Aldrich) was added. After 30 minutes, 10 mL of ethylene glycol was injected and stirred for 1 hour, HNO ₃ was added until pH = 2, followed by stirring for 1 hour. The suspension thus prepared was washed and then dried at 130 ° C. The washcoat was milled for 2 hours and calcined at 500 ° C. for 5 hours.

Then, to coat the washcoat on the carrier, the washcoat was put in H ₂ O, stirred for 2 hours, and then supported by the carrier (dip), taken out, and dried for 30 minutes in a 3L / min air atmosphere at a temperature of 200 ℃. The catalyst weight was measured before and after loading to load the same amount of washcoat onto the carrier. The catalyst was calcined (calcination) at 500 ° C. for 2 hours and reduced with H ₂ at 300 ° C. for 6 hours.

Experimental apparatus

In order to evaluate the reaction characteristics of SR catalyst and the NOx purification efficiency of SR + LNT catalyst, a laboratory scale atmospheric fixed bed model gas catalysis apparatus was used. In one embodiment, the catalytic reaction part used a cylindrical quartz tube having an internal diameter of 19 mm and a length of 350 mm, and the catalyst was fixed at the center of the reaction tube. The external heat source was supplied using an electric furnace. NOx purification rate measurement and DME slip concentration were measured by Fourier Transform Infrared Spectroscopy (MIDAC), and H ₂ production rate was measured by gas chromatograph (HP 6890).

SR  Due to catalyst H ₂ of Yield  How to measure

In one embodiment, the carrier is a honeycomb type of cordierite material having a cell density of 400 and 600 cpsi. Experiments to DME conversion and the H ₂ generation rate was measured both by the T2 to the set temperature. In the model gas reactor, the DME conversion rate of the catalyst is measured by measuring the gas concentration at the inlet and the outlet of the catalytic reaction part, and the conversion rate (%, conversion,%) = (([DME _in ]-[DME _out ]) / [DME _in ]) × 100 Obtained by the equation. Yield ratio of each reactant was obtained from the standard value before measurement, and production (%) = ((Yield of reaction gas / ((H ₂ + CO + CH ₄ + CO ₂ )) × DME Conversion rate (%)).

NOx  How to measure conversion

Evaluation of the NOx purification rate of the LNT catalyst was performed using one commercially available catalyst (18 mm diameter, 15 mm length, 400 cpsi). In the SR + LNT catalyst, one SR catalyst and one LNT catalyst were disposed 7 mm apart from the SR catalyst at the front and the LNT catalyst at the rear. Evaluation of the NOx conversion rate of SR + LNT catalyst was carried out with a total flow rate of 2 L / min of feed gas, SV was 28000h ^-1 , H ₂ O was 5%, O ₂ was 10%, CO ₂ was 0, 5%, N _The balance was supplied with ₂ gases. The temperature of the catalyst was carried out under transient conditions from 200 ° C. to 500 ° C. at 4 ° C./min. 0.7, 0.85, and 1% of DME were supplied as reducing agents, and the lean / rich time was 55/5 seconds, respectively. When tested with LNT catalyst alone, the SV (space velocity) is 28000 h ⁻¹ , and the SV of SR + LNT catalyst is 9500 h ⁻¹ (30 mm), 12000 h ⁻¹ (20 mm), and 17000 (10 mm) h ⁻¹ .

Hereinafter, the experimental results will be described with reference to FIGS. 2 to 7.

SR  Characteristics of the catalyst

Figure 2 is a TEM picture of the washcoat prepared by the sol-gel method according to an embodiment of the present invention. This is for observation of copper particle size and dispersibility of washcoats prepared by sol-gel method. Referring to (a) and (b) in FIG. 2, when the amount of Cu supported is large, it is advantageous to generate H ₂ , but too much amount of Cu reduces the dispersibility. In addition, the mixing of Zn as a cocatalyst of the Cu catalyst improves the Cu particle size and improves dispersibility. When Zn is mixed with 1% as a promoter of the SR catalyst using Cu30 / r-Al ₂ O ₃ , it can be seen that the particle growth of Cu is suppressed and particle dispersibility is increased.

The BET surface area decreased as the amount of Cu supported increased, because the surface area of r-Al ₂ O ₃ containing 30% Cu was relatively small. The addition of Zn resulted in a smaller BET surface area. On the other hand, the Cu surface area becomes larger as the amount of Cu supported. Comparing Cu29Zn1 / r-Al ₂ O ₃ catalyst with 1% Zn as cocatalyst with Cu30 / r-Al ₂ O ₃ , Cu29Zn1 / r-Al ₂ O ₃ catalyst suppresses the growth of Cu particles, The acidity was improved, resulting in a wider Cu surface area. On the other hand, the BET surface area of the Cu 25 Zn 5 / r-Al ₂ O ₃ catalyst to which Zn was added 5% was smaller than that of the Cu 30 / r-Al ₂ O ₃ catalyst. Therefore, it can be seen that the amount of Zn to increase the Cu surface area is 1% more advantageous than 5%.

LNT  Catalytic NOx  purification

3A shows the NOx purification rate according to the injection amount of the DME, FIG. 3B shows the DME slip concentration according to the injection amount of the DME, and FIG. 3C shows the NOx purification rate according to the injection time.

Referring to Figure 3a, the supply amount of DME is 0.7, 0.85, 1%. In the absence of the LNT catalyst, 1% DME was supplied to observe the NOx purification rate. LNT catalyst shows the most adsorption amount at 200 ° C, but relatively low NOx purification rate because of low reactivity of DME. When DME was supplied at 0.7, 0.85, and 1% at 350 ° C, the NOx purification rates were 60, 80, and 85%, respectively. In the case of 1% and 0.7% of DME supplied, the NOx purification rate at a temperature of 350 ° C. shows a difference of about 25%.

However, when the DME slip concentration is observed in FIG. 3B, the NOx purification rate is highest when DME 1% is supplied in all temperature ranges, but the DME slip concentration is also highest at 300 ° C. In addition, the NOx purification rate due to H ₂ generated by thermal decomposition of DME in the high temperature state without the catalyst was observed, but it can be seen that it does not affect the NOx purification rate at a temperature lower than 500 ° C.

3C shows the NOx purification rate when the lean / rich time is changed to 55/3, 55/5, 55/8 seconds when DME is supplied at 0.7%. The highest NOx purification was achieved at the highest DME feed rate of 55/8 seconds. As a result, the longer the injection amount and injection time of the DME used as a reducing agent increases the NOx purification rate, but it can be seen that the DME slip concentration also increases at the rear end of the LNT. Therefore, considering the fuel economy of the LNT and the DME slip, the amount of DME supplied to the SR + LNT system would be 0.7% and the lean / rich time 55/5 seconds.

SR  Due to catalyst DME  conversion

Figure 4a shows the H ₂ generation rate according to the type of SR catalyst according to an embodiment of the present invention, Figure 4b shows the NOx purification rate in the SR + LNT catalyst of the after-treatment system according to an embodiment of the present invention.

The size of the SR catalyst was twice that of the LNT catalyst and the same cell density was used at 400 cpsi. Referring to FIG. 4A, the H ₂ generation rates of the three types (Cu10, 20, 30 / r-Al ₂ O ₃ ) SR catalysts were 22%, 30%, and 58% at 350 ° C, respectively. The Cu 30 / r-Al ₂ O ₃ catalyst with the highest copper content has the highest H ₂ production rate. Since DME is hydrolyzed to methanol, and this methanol is again modified by copper to produce H ₂ , a higher copper content is advantageous for H ₂ formation. However, when the copper content is large, the dispersibility is deteriorated, so the copper content may be 30% by weight in an optimal range. However, in view of the generation of H ₂ , the optimal copper content in the SR catalyst is SR It may vary depending on the preparation of the catalyst.

Cu30 / r-Al ₂ O ₃ showed a high H ₂ generation rate of 400% or higher at 400 ° C., and the H ₂ production rate increased with increasing temperature. However, at a high temperature of 450 ° C., a phenomenon in which H ₂ production rate decreases and CO production rate increases due to a reverse water gas reaction is observed.

In the SR + LNT catalyst of the aftertreatment system according to an embodiment of the present invention, CO may be an excellent reducing agent together with H ₂ . The NOx purification rate in SR + LNT catalysts showed similar purification rates at 200 ° C and 250 ° C compared to the case where only LNT catalysts were used. However, NOx purification rate at 350 ℃ exhibited a _{Cu20 / r-Al 2 O 3} + LNT catalyst is 74%, Cu30 / r-Al 2 O 3 + LNT catalyst is 78%.

As a result, the NOx purification rate was about 20% higher at 350 ° C. compared with the SR + LNT catalyst of the aftertreatment system according to one embodiment of the present invention using only LNT catalyst. This can be seen that it is more advantageous to improve the NOx purification rate when H ₂ is produced as a reducing agent in the SR catalyst and supplied to the LNT catalyst than the DME is supplied to the LNT catalyst as the reducing agent.

In addition, the reaction of reforming DME to SR catalyst is advantageous for the generation of H ₂ as the temperature of the catalyst is higher, and it is expected to improve the NOx purification rate at SR + LNT catalyst at high temperature, but the adsorption of NO to the LNT catalyst at a temperature of 400 ° C. or higher. Since the amount was small, the NOx purification rate was reduced.

Figure 5a shows the production rate of H ₂ according to the size of the SR catalyst in the system of SR + LNT catalyst, Figure 5b shows the NOx purification rate according to the size of the SR catalyst.

As the SR catalyst, Cu30 / r-Al ₂ O ₃ having the highest production rate of H ₂ was used. The SR: LNT ratios are 0.6: 1, 1.3: 1, and 2: 1 and the cell density of the catalyst is 400 cpsi. Referring to FIG. 5A, the production rates of H ₂ were 5, 8, and 21% at 300 ° C., respectively, and 48, 64, and 72% at 400 ° C., respectively. As a result, it can be seen that the larger the size of the SR catalyst, the higher the production rate of H ₂ . This is because the reaction time with the catalyst in the reaction for reforming the DME to the SR catalyst has a longer residence time.

Referring to FIG. 5B, the NOx purification rate in three SR + LNT catalysts of different sizes is highest when SR: LNT = 1.3: 1 at a temperature of 350 ° C. or lower, and above the temperature, the NOx purification rate is SR: It can be seen that the highest when LNT = 2: 1.

Figure 6a shows the generation rate of H ₂ according to the cell density of the SR catalyst carrier according to an embodiment of the present invention, Figure 6b shows the NOx purification rate according to the cell density of the SR catalyst carrier according to an embodiment of the present invention .

Referring to FIG. 6A, the H ₂ production rate of the SR catalyst using 400 cpsi was 10, 40, and 60% H ₂ production rates at 300, 350, and 400 ° C., respectively. On the other hand, the H ₂ production rate of the SR catalyst using 600 cpsi showed 20, 50, 60% H ₂ production rate at 300, 350, 400 ℃, respectively. As such, it can be seen that the H ₂ production rate of the SR catalyst using 600 cpsi is higher than at 400 cpsi.

Referring to FIG. 6B, the NOx purification rates for the SR + LNT catalyst using 400 cpsi and 600 cpsi were 75 and 85%, respectively. The higher H ₂ production rate of SR catalyst with 600 cpsi of higher cell density resulted in higher NOx purification rate of SR + LNT catalyst with 600 cpsi. This is because 600 cpsi, which has a relatively high cell density, has a larger amount of support for the washcoat than 400 cpsi, which increases the chance of the catalyst reacting with the reaction gas.

FIG. 7A shows the H ₂ generation rate when Zn is added to the SR catalyst of the aftertreatment system according to an embodiment of the present invention, and FIG. 7B shows Zn in the SR catalyst of the aftertreatment system according to an embodiment of the present invention. The NOx purification rate when added is shown.

In order to increase the H ₂ production rate in the SR catalyst containing copper, Zn, a kind of transition metal, was mixed at 1% and 5% as a cocatalyst. SR catalyst was tested using Cu30, Cu29Zn1, Cu25Zn5 / r-Al ₂ O ₃ .

Referring to Figure 7a, the H ₂ production rate was 48, 54, 37% at 350 ℃, it was 59, 70, 51% at 400 ℃. The H ₂ production rate of the SR catalyst was found in the order of Cu 29 Zn 1> Cu 30> Cu 25 Zn 5 / r-Al ₂ O ₃ . This is because, as with the above results, the dispersibility of Cu was improved by mixing 1% of Zn to increase the surface area of Cu. Meanwhile, Cu25Zn5 / r-Al ₂ O ₃ containing 5% Zn exhibited a lower H ₂ generation rate than Cu30 / Al ₂ O ₃ , which means that when 5% Zn is mixed, the dispersibility of Cu is not increased. This is because the amount of Cu supported is less than that of Cu30 / r-Al ₂ O ₃ .

Referring to FIG. 7B, the purification rate of NOx was also shown in the order of Cu29Zn1>Cu30> Cu25Zn5 / r-Al ₂ O ₃ .

As a result, the Cu 30 / r-Al ₂ O ₃ catalyst having a copper content of 30% by weight in the SR catalyst prepared by the sol-gel method according to an embodiment of the present invention showed a high DME conversion rate, and the SR catalyst had a high temperature. As it increased, the H ₂ production rate increased, and at a temperature above 450 ° C., the H ₂ production rate decreased and the CO production rate increased due to the reverse water gas reaction.

In addition, DME conversion and H ₂ production rate were excellent as the catalyst size was larger, and the best when the cell density of the carrier was 600 cpsi, and Cu29Zn1 / r-Al ₂ O ₃ catalyst containing 1% Zn as a promoter was used. Best. In terms of NOx purification rate, SR + LNT catalyst using Cu29Zn1 / r-Al ₂ O ₃ catalyst (1.3: 1, 600 cpsi) showed excellent NOx purification rate above 300 ℃, and NOx purification compared to the case of using only LNT catalyst The rate has improved by more than about 20%.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

100: engine 200: injector
300: supply gas unit 400: first catalyst unit
500: second catalyst unit 600: third catalyst unit

Claims (9)

A feed gas unit providing a feed gas including exhaust gas discharged from an engine unit and dimethyl ether (DME) injected from an injector;
A first catalyst part including a steam reforming (SR) catalyst reacting with the dimethyl ether; And
A second catalyst part including an LNT (lean NOx trap) catalyst reacting with a H ₂ reducing agent or a CO reducing agent generated by the reaction of the dimethyl ether and the SR catalyst,
Size ratio of the SR catalyst and the LNT catalyst is 1.0: 1 to 1.5: 1,
Copper content in the SR catalyst is 1% by weight to 50% by weight,
The SR catalyst comprises zinc as a promoter and the content of zinc is greater than 0% by weight and no greater than 3% by weight,
Using waste heat of the exhaust gas as a heat source,
Post-treatment system to reduce NOx.
delete delete The method of claim 1,
The SR catalyst is a post-treatment system to reduce the nitrogen oxides produced by the sol-gel method.
delete delete The method of claim 1,
The dimethyl ether is a post-treatment system to reduce the nitrogen oxides in the range of 0% to 5.0% of the feed gas contained in the feed gas portion.
The method of claim 1,
And a third catalyst part disposed before the first catalyst part, the third catalyst part including a diesel oxidation catalyst that oxidizes hydrocarbons or carbon monoxide in the exhaust gas.
The method of claim 1,
A post-treatment system to reduce nitrogen oxides having a cell density of 100 cpsi to 1200 cpsi in the SR catalyst.

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