KR20190046529A - Perovskite catalyst for low temperature combustion of Particulate Matter emitted in diesel engine and ozone oxidation system using the same - Google Patents

Abstract

The present invention discloses a perovskite catalyst for low temperature combustion of particulate matters emitted in a diesel engine and an ozone oxidation system of particulate matters using the same. According to an embodiment, provided is the perovskite catalyst having an ABO_3 or A_2BO_4 structure for low temperature combustion of particulate matters emitted in the diesel engine using ozone. Through the present invention, it is possible to construct a system in which PM combustion or DPF regeneration is efficiently performed in an environment where an exhaust gas temperature of a diesel vehicle is 100 to 300°C.

Description

TECHNICAL FIELD The present invention relates to a perovskite catalyst for low temperature combustion of particulate matter discharged from a diesel engine and an ozone oxidation system for particulate matter using the same.

The present invention relates to a perovskite catalyst for low temperature combustion of diesel particulate matter (PM) and an ozone oxidation system for particulate matter using the same.

The diesel engine has a high torque, high thermal efficiency, low CO ₂ emission, and the fuel efficiency is about 30% higher than that of the gasoline engine under the oxygen excess condition, and it has attracted attention as a very effective power source to cope with exhaustion problem of fossil fuel and regulation of carbon dioxide emission .

Meanwhile, exhaust gas from the heat engines including diesel engines includes carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO _x ) and particulate matter (PM) as the main causes of environmental pollution. Emissions are regulated.

In addition, the emission of diesel vehicles has been announced by the World Health Organization (WHO) as a Class I carcinogen in 2012 and is strengthening the emission standards for diesel engines worldwide. As the diesel emission regulations of diesel cars continue to tighten, limitations on commercialized technologies have been limited, and the interest in harmful gas reduction technology is increasing again to solve the problems.

Currently, commercialized PM emission suppression technology is a continuous regeneration trap (hereinafter referred to as CRT) technology. PM is captured in a diesel particulate filter (DPF), and Pt catalyst or DPF sheathed The NO contained in the exhaust gas is converted into NO ₂ by using Pt catalyst, and then the NO ₂ captures the PM trapped in the DPF at a temperature of 250 ° C or higher, thereby continuously removing PM (regenerating the DPF) simultaneously with the trapping of PM Principle.

The present CRT technology uses NO ₂ as an oxidizing agent, and the PM combustion reaction by NO ₂ shows a visible reaction rate at a temperature of 250 ° C. or more. However, in a cold start environment immediately after the start of the vehicle The PM accumulation and combustion do not occur consecutively, and the accumulation of PM continues only in the operating environment in which the driving of the city is mainly performed, since the temperature of the exhaust gas is not sufficiently high to progress the PM combustion reaction by NO ₂ . When the PM is excessively accumulated in the exhaust gas at a high temperature (500 ° C or higher) in a state where the PM is accumulated, the PM is burned all at once, and the DPF is thermally damaged due to excessive heat.

The reason why the low temperature combustion technology of PM is more urgent than the problems related to the DPF durability mentioned above is that the "high fuel consumption low emission engine and automobile" is required due to the improvement of the energy efficiency and the regulation of the carbon dioxide emission, . The fuel-efficient technology of diesel-engine cars is based on the lean-burn method, which has an excess of oxygen compared to the amount of fuel. This allows less fuel to be used more efficiently, achieving a fuel economy as high as 30% compared to existing technologies and achieving relatively low CO2 emissions. On the other hand, under the high fuel consumption operating condition, the amount of the fuel burned in the engine combustion chamber is small, and the heat generated from the combustion reaction is small, so that the temperature of the exhaust gas becomes low.

Thus, current exhaust gas purification catalytic apparatuses that are highly dependent on the exhaust gas temperature are provided with unfavorable exhaust gas conditions. In order to solve this problem, a method of burning a part of the fuel in the purifier is used in order to raise the temperature of the purifier to a level showing exhaust gas reducing activity. However, this causes a problem that the fuel consumption of the engine is lowered again.

Therefore, in order to improve the fuel efficiency of the vehicle with the goal of low fuel consumption (that is, high fuel efficiency and high exhaust gas reduction efficiency), the exhaust gas purification system should exhibit high exhaust gas reduction performance even at a low temperature of about 150 ° C do. The US Drive Workshop (2012), hosted by the US Department of Energy (DOE), calls the "150 ° C Challenge" with an emphasis on the need to operate the exhaust gas purifier at low temperatures, Catalytic technology that exhibits high performance is required. In Korea, regulations on carbon dioxide emissions will be strengthened, and studies on lowering the operating temperature of CRT to 150 ℃ should be accompanied by high fuel consumption low emission technology.

Ozone is a substance that has a much higher oxidizing power than oxygen, nitrogen dioxide and hydrogen peroxide. It is a chemical species that has harmful effects on the environment and human body, but it is easily pyrolyzed above 150 ℃. And the like. On the other hand, ozone can burn various carbon phase particulate matter including diesel engine PM at low temperature condition close to room temperature.

Therefore, research on the combustion reaction of diesel engine PM using ozone has already been carried out by many domestic and overseas researchers, and it is known that PM has a sufficient combustion performance in an environment below 250 ° C as expected. However, since the thermal decomposition of ozone accelerates at 150 ° C or higher, it is consumed by reacting with nitrogen oxides, unburned hydrocarbons, carbon monoxide, and the like contained in the exhaust gas in addition to PM, so that a large amount of ozone is injected for visible PM combustion It is becoming an obstacle to commercialization. (Y. Itoh, Y. Sakakibara, H. Shinjoh, RSC Adv., 4 (2014) 19144-19149)

In order to solve the problems of the prior art described above, the present invention proposes a perovskite catalyst for low temperature combustion of particulate matter emitted from a diesel engine, which can effectively burn PM even under low temperature conditions, and an ozone oxidation system using the perovskite catalyst.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems of the prior art, and provides a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure for low temperature combustion of particulate matter discharged from a diesel engine using ozone.

In the ABO ₃ or A ₂ BO ₄ structure, the A site is preferably selected from a mixture of one or more metals selected from La, Pr, Ce, Sr, Ba, Li, K and Mg.

The A site preferably has one of the metals as a main component and the main component is partially substituted with one of the remaining metals.

In the ABO ₃ structure, B site may be selected from a mixture of one or more metals of Mn, Fe, Co, Zr, Cr, Ti, Cu and V.

The B site may have one of the metals as a main component, and the main component may be partially substituted with one of the remaining metals.

The ozone may be supplied through an oxidation reaction of oxygen or air in an atmospheric low temperature plasma reactor.

The low-temperature combustion of the particulate matter discharged from the diesel engine can be carried out within a range of 100 to 300 ° C.

According to another aspect of the present invention, there is provided an ozone oxidation system for particulate matter, comprising: an atmospheric-pressure low-temperature plasma reactor for supplying ozone generated through an oxidation reaction of oxygen or air; And a particulate matter burning reactor filled with a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure and burning diesel engine exhaust particulate matter using ozone supplied from the DBD reactor under a low temperature condition, / RTI >

It is possible to construct a system in which regeneration of PM combustion or DPF is efficiently performed in an environment where exhaust gas temperature of a diesel vehicle is 100 to 300 ° C or less.

1 is a view showing a configuration of a DBD plasma reactor for generating ozone to be used for PM low-temperature combustion according to the present embodiment.
2 is a schematic diagram of a PM combustion reactor according to a preferred embodiment of the present invention.
FIG. 3 shows the results of measuring the ozone production concentration while varying the AC frequency from 100 kHz to 700 Hz at a primary AC voltage of 18 kV.
4 shows the conversion of NO to NO2 according to the ozone concentration at 25 DEG C and 150 DEG C temperature conditions.
FIG. 5 shows the XRD results for the crystal structure analysis of the La _{1 - x} K _x FeO 3 catalyst in the prepared catalyst.
Figure 6 shows the results of a series of TPO reactions.
7 shows the results of the ITO test at 150 ° C, which is a low-temperature temperature condition.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Hereinafter, the present invention will be described in detail with reference to embodiments thereof.

In order to solve the problem of introducing too much ozone for the visible PM burning, it is necessary to increase the amount of ozone to effectively oxidize the PM oxidation reaction at an ozone concentration of several hundred to several thousand ppm Consider matching the catalytic material.

In order to realize this, an optimal oxidation catalyst capable of giving a reaction mechanism or a kinetic synergy effect to the redox cycle of PM combustion by ozone should be selected. This selected catalyst can be implemented by coating on the DPF and installing a mechanical device to inject a controlled amount of ozone into the front of the DPF at appropriate temperature conditions.

In the present invention, ozone is produced using a low-temperature plasma system operated at a low power consumption and the PM burning can be effectively performed even at a low temperature of 100 to 300 ° C by matching the perovskite catalyst with the injected ozone I want to present it.

More particularly, the present invention relates to a method of burning Particulate Matter (PM) in a diesel engine exhaust gas, wherein ozone generated through atmospheric plasma is used as an oxidizing agent, and a perovskite structure having an ABO ₃ or A ₂ BO ₄ structure (100 ~ 300 ℃) of PM by contacting the catalyst with PM.

There is a need for a device capable of generating ozone for low temperature combustion of diesel engine exhaust PM according to the present invention. However, when a large amount of energy is required to generate ozone, it is not suitable for a high-fuel engine, so an ozone generating system having a low power consumption is needed. The generation of ozone is easily achieved through the oxidation reaction of oxygen or air in a dielectric barrier plasma (DBD) reactor, which is one of the atmospheric pressure low temperature plasma systems. Such a DBD type plasma reactor has a very small power required for operating the reactor, and has been applied variously as a post-treatment apparatus such as an automobile. Oxygen or air required for ozone production can be supplied from an air compressor that supplies air to the engine combustion chamber, and the desired concentration of ozone can be injected into the exhaust gas flow by controlling the magnitude of the plasma discharge power.

In addition, a corona discharge plasma reactor may be used.

The dielectric discharge plasma is preferable in view of the stability of the low-temperature plasma and the energy efficiency, but is not limited thereto.

Previous studies on PM combustion through ozone have been conducted focusing on PM combustion experiments using only ozone and engine system design. However, there has never been reported a case where the ozone oxidation reaction and the catalyst for promoting the ozone oxidation are matched to increase the PM combustion efficiency.

In the present invention, a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure having excellent oxidation-reduction ability was used to increase the PM combustion efficiency through ozone at a low temperature.

In the perovskite catalyst of the ABO ₃ or A ₂ BO ₄ structure, A and B are cations and A site is a mixture of one or more of La, Pr, Ce, Sr, Ba, Li, As shown in FIG.

Preferably, the A site is composed of one of the above metals as a main component, and a part of the metal is partially substituted with one of the remaining metals.

For example, K, which is known to be effective for PM burning, can be mixed with La as its main component (eg, La _{1 - x} K _x FeO ₃ ). Where the fraction (x) of K is a value between 0 and 1.

If the part of La is not partially replaced with K, the oxidation activity is lowered because the number of oxygen vacancies capable of activating oxygen or ozone is sharply reduced. That is, by increasing the number of oxygen defects by replacing a part of La with 'K' partly, the oxidation activity can be increased.

In addition, the A site can be determined in various combinations such as La _x K _{1 -x} , La _x Sr _{1 -x} , La _x Ce _{1 -x} , La _x Li _{1 -x,} or Ce _x Li _{1 -x} . Here, x is 0 < x < 1.

Further, the oxidation activity of one oxygen vacancy is determined depending on the kind of the B site metal, and preferably, the activity of oxygen defects is high when Mn is a B site metal.

In the perovskite catalyst of the ABO ₃ or A ₂ BO ₄ structure, the B site can be selected from a mixture of one or more of Mn, Fe, Co, Zr, Cr, Ti, Cu and V or a mixture of two or more metals.

The B site may be one of Mn, Fe, Co, Zr, Cr, Ti, Cu and V, or a mixture of these metals at a certain ratio. For example, B site can be determined in various combinations such as Cu _x V _{1 -x} , Co _x Fe _{1 -x} , and the like. Here, x is 0 < x < 1.

Hereinafter, ozone production according to the present embodiment, synthesis of a perovskite catalyst, and a low temperature combustion process using the same will be described in detail with reference to the drawings. Hereinafter, the perovskite catalyst is referred to as ABO ₃ Structure, but it should be understood that the A ₂ BO ₄ structure can also be included in the scope of the present invention.

One) DBD plasma  Production of ozone through reactor

1 is a view showing a configuration of a DBD plasma reactor for generating ozone to be used for PM low-temperature combustion according to the present embodiment.

SUS mesh and Cu rod were used as the electrode of the plasma reactor and Quartz tube was used as the dielectric. The power supplier used for the power supply has a frequency range of 50 Hz to 1 Khz, a primary voltage range of 0 to 15 Kv, a maximum power of 300 W, and a voltage supplied to the plasma reactor using an oscilloscope (Tektronix TDS 220) The current was observed.

O ₂ (99.99%) 30 ml / min was flowed to the front of the plasma reactor, and the ozone concentration was controlled through voltage and frequency control. The generated ozone was mixed with the NO ₂ / O ₂ / N ₂ gas flow and injected into the PM combustion reactor. The concentration of ozone applied to the reaction was 100 to 3,000 ppm after being diluted with the NO ₂ / O ₂ / N ₂ gas ).

2) ABO ₃  Structural Perovskite  Catalyst synthesis

The evaporation-to-dryness method was used for the synthesis of the ABO ₃ catalyst. The aqueous solutions of metal acetate of A site and B site metal constituting the catalyst were prepared at a constant concentration, and the aqueous solutions were mixed according to the stoichiometric ratio of the constituent elements of the catalyst to be synthesized, followed by stirring at room temperature for 30 minutes. The stirred solution was evaporated and dried at 30 rpm and 50 ° C through a rotary evaporator to obtain granular precipitates. The precipitates were dried in air at 110 ° C for 24 hours, first calcined at 410 ° C, and secondarily calcined at 960 ° C And then calcined to produce an ABO ₃ type catalyst.

3) PM  Combustion reactor

2 is a schematic diagram of a PM combustion reactor according to a preferred embodiment of the present invention.

NO ₂ (5000 ppm, N ₂ balance), O ₂ (99.99%), O ₃ and N ₂ (balance) gas were used for combustion reaction of PM. Each reaction gas was supplied to a PM combustion reactor after adjusting the flow rate through a pressure regulator and a mass flow controller (Brooks instrument 5800E series). The reaction gas was subjected to 250 ppm NO ₂ , 10% O ₂ , 2500 ppm O ₃ and N ₂ balance at 300 mL / min to confirm combustion behavior through ozone.

The reason for using NO ₂ instead of NO as the reactant is to prevent the exhausted ozone from being consumed in the NO oxidation reaction. In the actual exhaust gas, the NO ₂ .rich reactant condition is expected to be realized without significantly affecting the exhaust gas temperature. By additionally injecting ozone into the inlet of the PM post-treatment apparatus, NO is increased to NO ₂ It can be oxidized in advance. Experimental results that can prove this are shown in (Example 2).

The PM combustion reactor was a continuous fixed bed reactor, and a fixed bed (hereinafter referred to as PM + catalyst bed) in which a PM and a catalyst were uniformly mixed was charged in the middle of the quartz tube reactor, Respectively. The reaction temperature was measured by placing a thermocouple at the front of the PM + catalyst bed and controlling the reaction temperature using a heating furnace equipped with a PID controller. In the downstream of the reactor, a NO _x analyzer (Thermo Fisher 42i-HL) and a CO ₂ analyzer (Teledyne T360M) were connected in parallel to enable real-time online gas composition analysis.

4) PM  Conditions and method of combustion reaction test

In order to simulate the SiC DPF environment, the PM + catalyst bed was prepared by mixing the PM and the prepared catalyst at a mass ratio of 1: 0.33, 0.5, 1, or 2.5, Was taken in the same volume as the PM + catalyst bed volume and mixed for 10 minutes using a mortar. The prepared PM + catalyst bed was placed in the middle of the quartz tube reactor, and the ozone injection was performed at a distance of 10 mm from the front of the PM + catalyst bed, and then mixed with other gas components to react with PM. The catalytic reaction experiments were carried out using a temperature programmed oxidation (TPO) test to ascertain the PM combustion behavior with temperature change from room temperature to about 650 ° C at 3 ° C / min and an isothermal Isothermal Oxidation (ITO) was performed. After the PM combustion gas discharged was to analyze the change in concentration of NO _2, CO ₂ through the NO _X analyzer and CO ₂ analyzer connected to the rear end of the reactor.

Example

( Example  One) DBD plasma  Ozone production through reactor

FIG. 3 shows the results of measuring the ozone production concentration while varying the AC frequency from 100 kHz to 700 Hz at a primary AC voltage of 18 kV.

The ozone concentration in the outflow from the DBD plasma reactor was 2,000 ~ 28,500 ppm (Before Dilution) and 200 ~ 2,850 ppm after dilution with other reaction gas (After Dilution). In this experiment, the power (primary power) used by the reactor is about 0.5 ~ 6.6 W, which is very low when compared to the typical power consumption or fuel consumption of devices such as automotive headlights and heaters. Therefore, it is expected that the decrease of the fuel efficiency of the vehicle caused by the installation of the additional ozone generator is very small.

( Example  2) NO - NO ₂ conversion  exam

4 shows the conversion of NO to NO ₂ according to ozone concentration at 25 ° C and 150 ° C temperature conditions.

Here, the temperature condition of 150 ° C is the temperature of the ITO test condition shown in FIG. 7 of Example 5, and is included in the temperature region of the low temperature region in which the catalytic activity of the ozone + perovskite combination according to the present invention is confirmed.

100, 250, a result of the combustion of 500 ppm NO with O ₃ of 100 ~ 2,500 ppm, relative to the O ₃ concentration while increasing the NO conversion rate was the result of convergence of about 90% at more than a predetermined O ₃ concentration. These final conversion rates are close to the equilibrium conversion rate determined at that temperature.

( Example  3) XRD  analysis

FIG. 5 shows XRD results for the crystal structure analysis of the La _{1 - x} K _x FeO ₃ catalyst in the prepared catalyst.

The Ni peak in the test results is derived from an internal reference material mixed at a mass ratio of 10% per sample in order to correct the peak-to-sample peak size. From the XRD results, it can be seen that the catalysts prepared as a whole are composed mostly of ABO ₃ crystals.

( Example  4) PM In the presence of ozone PM  Combustion test 1: TPO  Experiment result

Figure 6 shows the results of a series of TPO reactions.

In FIG. 6, a 2 wt.% Pt / Al ₂ O ₃ catalyst simulating a noble metal catalyst used for perovskite catalysts La _{0 .75} K _{0 .25} MnO ₃ , La _{0 .3} K _{0 .7} FeO ₃ and CRT The results were compared with each other.

PM + PM at the catalyst Bed: catalyst ratio, if pepper lobe of kite catalyst 1:. 0.33, 2 wt% Pt / Al2O 3 was 1: 1. It was confirmed that the combustion of PM was progressed in a low temperature range of 100 to 300 ° C. because ozone was used as an oxidizing agent in the catalyst-free catalytic reaction experiment (No Catalyst), but the combustion reaction proceeding at a high temperature of 400 ° C. or higher It is found that the size of the combustion peak is small.

When La _{0 .3} K _{0 .7} FeO ₃ catalyst was used, it was observed that the low temperature combustion peak at 100 to 300 ° C was larger than the corresponding section Peak in the no catalyst condition. When La _{0 .75} K _{0 .25} MnO ₃ catalyst was used, the combustion peak was observed at 100-300 ° C, and the PM was already burned in the low temperature region and the combustion peak was not observed in the high temperature region . In addition, it can be confirmed that La _0.75 K _0.25 MnO ₃ is significantly superior to 2 wt.% Pt / Al ₂ O ₃ , which is a commercial CRT catalyst, when compared with combustion performance at low temperature. These results show that the use of perovskite catalysts can effectively improve the rate of PM combustion by ozone at 100-300 ° C. and can be improved more than when using Pt catalysts contained in commercial CRTs The effect can be larger. This means that the perovskite catalyst is more suitable catalysts for PM combustion reaction by ozone than the noble metal catalyst such as _{La 0 .75 K 0 .25 MnO 3} .

( Example  5) PM In the presence of ozone PM  Combustion test 2: ITO  Experiment result

7 shows the results of the ITO test at 150 ° C, which is a low-temperature temperature condition.

In the ITO experiment, the PM burning performance of the catalysts is compared with the initial PM concentration and the reaction temperature, so that the catalyst performance comparison test method is more preferable in terms of kinetics.

Perovskite than's catalyst _{(La 0 .75 K 0 .25 MnO} 3, La 0 .3 K 0 .7 FeO 3) When using the ozone supply only is catalyst-free catalytic reaction condition (No Catalyst) that are not used The initial CO ₂ emission peak is greater than 3 times, and the slope at which the CO ₂ emission concentration decreases after the peak occurs is more steep. That is, by using perovskite catalyst, it can be said that the rate of PM combustion reaction by ozone is remarkably improved at a low temperature of 150 ° C. La _{0 .75} K _{0 .25} MnO ₃ , and La _0.3 K _0.7 FeO ₃ , the former exhibits both the initial CO ₂ emission peak concentration and the peak decreasing slope compared to the latter, Like La _{0 .75} K _{0 .25} MnO ₃ in the PM combustion reaction with ozone, can make boindago superior catalytic activity concluded.

Claims (10)

A perovskite catalyst with ABO ₃ or A ₂ BO ₄ structure for low temperature combustion of diesel particulate emissions from ozone. The method according to claim 1,
In the ABO ₃ or A ₂ BO ₄ structure, the A site is selected from a mixture of one or more metals selected from La, Pr, Ce, Sr, Ba, Li, K, and Mg. 3. The method of claim 2,
Wherein the A site comprises one of the metals as a main component and the main component is partially substituted with one of the remaining metals. The method according to claim 1,
In the ABO ₃ structure, the B site is selected from a mixture of one or more of Mn, Fe, Co, Zr, Cr, Ti, Cu, 5. The method of claim 4,
Wherein the B site comprises one of the metals as a main component and the main component is partially substituted with one of the remaining metals. The method according to claim 1,
Wherein the ozone is supplied through an oxidation reaction of oxygen or air in an atmospheric low temperature plasma reactor. The method according to claim 1,
Wherein the low temperature combustion of the particulate matter discharged from the diesel engine is performed within a range of 100 to 300 占 폚. As an ozone oxidation system for particulate matter,
An atmospheric pressure low temperature plasma reactor for supplying ozone generated through oxidation reaction of oxygen or air; And
And a particulate matter burning reactor charged with a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure and burning diesel engine exhaust particulate matter under low temperature using ozone supplied from the DBD reactor. 9. The method of claim 8,
Wherein the temperature of the particulate matter combustion reactor is in the range of 100 to 300 占 폚. 9. The method of claim 8,
In the ABO ₃ or A ₂ BO ₄ structure, A site is selected from a mixture of one or more metals selected from La, Pr, Ce, Sr, Ba, Li, K, and Mg,
B site is selected from a mixture of one or more of the metals Mn, Fe, Co, Zr, Cr, Ti, Cu and V;

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