KR102044604B1 - 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 diesel engine exhaust particulate matter and an ozone oxidation system of particulate matter using the same. According to this embodiment, a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure for low temperature combustion of diesel engine exhaust particulate matter using ozone is provided. According to the present invention, it is possible to construct a system in which PM combustion or DPF is efficiently regenerated in an environment where the exhaust gas temperature of a diesel vehicle is 100 to 300 ° C. or less.

Description

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

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

Diesel engines have high torque and high thermal efficiency, resulting in low CO ₂ emissions, and fuel efficiency is about 30% better than gasoline engines under excessive oxygen conditions. .

On the other hand, emissions from heat engines including diesel engines include 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 was announced by the World Health Organization as a Class 1 carcinogen in 2012, and the emission standards of diesel engines are being strengthened around the world. As the emission regulations of diesel cars continue to be strengthened, the limitation of current commercially available technologies is highlighted, and interest in harmful gas reduction technologies is increasing again to solve the problems.

Currently, commercially available PM emission suppression technology is a continuous regeneration trap (CRT) technology, which collects PM in a diesel particulate filter (DPF) and collects Pt catalyst or DPF front end coated with DPF. After converting NO contained in the exhaust gas into NO ₂ using Pt catalyst, NO ₂ continuously burns PM trapped in DPF at 250 ℃ or higher and removes PM continuously (regenerates DPF). On principle.

Currently commercially available CRT technology uses NO ₂ as an oxidizing agent, and PM combustion reaction by NO ₂ shows a visible reaction rate at temperatures above 250 ° C. In an operating environment in which the city is mainly driven, the temperature of the exhaust gas is not high enough to proceed with the PM combustion reaction by NO ₂ , so that PM accumulation and combustion do not occur continuously, and only PM accumulation occurs. When the PM is exposed to the high temperature (over 500 ° C) exhaust gas in the state of excessive accumulation of PM, the PM is burned at once, resulting in a problem of thermal damage of the DPF due to excessive heat generation.

The reason why PM's low temperature combustion technology is more urgently needed than the above-mentioned problems related to DPF durability is that “high fuel consumption low emission engines and automobiles” are required due to the improvement of energy efficiency and tightening regulations on carbon dioxide which are being promoted worldwide. . The high fuel efficiency technology of diesel engines is based on lean-burning systems, where oxygen is present in excess of fuel volume. This allows less fuel to be used more efficiently, achieving up to 30% higher fuel economy and relatively lower CO2 emissions than existing technologies. On the other hand, in the high fuel consumption operating conditions, the amount of fuel burned in the engine combustion chamber is small, and the heat generated from the combustion reaction is small, thereby reducing the temperature of the exhaust gas.

Hence, an exhaust gas condition is created in the current exhaust gas purification catalyst device having a high dependency on the exhaust gas temperature. As a solution to this problem, some of the fuel may be burned in the purifier in order to raise the temperature of the purifier to the level of emission reduction activity. However, this causes a problem that the fuel economy of the engine is lowered again.

Therefore, in order to improve the fuel efficiency of vehicles aiming at high fuel consumption and low emissions (that is, high fuel efficiency and high emission reduction efficiency), the exhaust gas purification system must show high emission reduction performance even at low temperatures around 150 ° C. do. The US Drive Workshop (2012), hosted by the US Department of Energy (DOE), emphasizes the need for low temperature operation of the exhaust gas purification unit and expresses it as “The 150 ℃ Challenge” and reduces emissions even at 150 ℃. It has been reported that there is a need for catalytic technology that shows performance. Regulations on CO2 emissions will be tightened in Korea. High fuel efficiency low emission technologies must be accompanied by a study to lower the operating temperature of CRTs to 150 ° C.

Ozone is a material that has a much higher oxidation capacity than oxygen, nitrogen dioxide, and hydrogen peroxide. It is a chemical species that has a detrimental effect on the environment and the human body. However, ozone is easily thermally decomposed at temperatures above 150 ° C. It is applied in various fields. Ozone, on the other hand, can burn various carbonaceous particulates, including diesel engine PM, even at low temperatures close to room temperature.

Therefore, studies on the combustion reaction of ozone-based diesel engine PM have been conducted by many domestic and foreign researchers, and it is known that the combustion performance of PM is sufficient in the environment below 250 ° C as expected. However, since the decomposition of ozone is accelerated above 150 ° C and consumed by reacting with nitrogen oxides, unburned hydrocarbons, and carbon monoxide contained in the exhaust gas in addition to PM, it is necessary to inject too much ozone for visible PM combustion. It is an obstacle to commercialization. (Y. Itoh, Y. Sakakibara, H. Shinjoh, RSC Adv. 4 (2014) 19144-19149)

In order to solve the above problems of the prior art, the present invention is to propose a perovskite catalyst for the low-temperature combustion of diesel engine exhaust particulate matter that can be effectively PM combustion even at low temperature conditions and ozone oxidation system using the same.

The present invention has been made to solve the problems of the prior art, there is provided a perovskite catalyst having an ABO ₃ or A ₂ BO ₄ structure for low-temperature combustion of diesel engine exhaust particulate matter using ozone.

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

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

The B site has 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 cold plasma reactor.

Low temperature combustion of the diesel engine exhaust particulate matter may be made within a range of 100 to 300 ℃.

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

According to the present invention, it is possible to construct a system in which PM combustion or DPF is efficiently regenerated in an environment where the exhaust gas temperature of a diesel vehicle is 100 to 300 ° C. or less.

1 is a diagram illustrating 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.
Figure 3 shows the result of measuring the ozone production concentration by changing the frequency of alternating current from 100 to 700 Hz at the primary AC voltage of 18 kV.
Figure 4 shows the conversion rate from NO to NO2 according to the ozone concentration at 25 ℃ and 150 ℃ temperature conditions.
Figure 5 shows the XRD results for the crystal structure analysis of the La _{1 - x} K _x FeO3 catalyst in the prepared catalyst.
6 shows a series of TPO reaction results.
7 shows ITO test results at 150 ° C. under low temperature conditions.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

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

In order to solve the problem of injecting too much ozone for visible PM combustion, it is possible to effectively accelerate the PM oxidation reaction at an ozone concentration of several hundred to several thousand ppm, which is an acceptable level of concentration. Consider matching the catalytic material.

In order to realize this, it is necessary to select an optimal oxidation catalyst that can exert a synergistic effect or reaction mechanism on the redox cycle of PM combustion by ozone. The selected catalyst is coated and applied on the DPF, and can be implemented by installing a mechanical device injecting a controlled amount of ozone at an appropriate temperature condition in front of the DPF.

Therefore, in the present invention, by using a low-temperature plasma system that operates with low power consumption, ozone is produced, and by matching the perovskite catalyst with respect to the injected ozone, a method of effectively burning PM even at low temperatures of 100 to 300 ° C is proposed. I would like to present.

More specifically, the present invention utilizes ozone generated through atmospheric pressure plasma as an oxidant by combustion of Particulate Matter (PM) in diesel engine exhaust gas, and has a peroxide sky structure of ABO ₃ or A ₂ BO ₄ having excellent PM oxidation ability. The low temperature combustion (100 ~ 300 ℃) of the PM is to be proposed by contacting the catalyst with PM.

There is a need for an apparatus capable of generating ozone for low temperature combustion of diesel engine exhaust PMs according to the invention. However, if a lot of energy is required for ozone generation, it is not suitable for a high fuel consumption engine, so an ozone generation system with low power consumption is needed. Ozone generation is easily realized through the oxidation reaction of oxygen or air in a dielectric barrier plasma (DBD) reactor, which is one of atmospheric pressure low temperature plasma method. The DBD plasma reactor has a very small power required for operating the reactor, and has been widely applied as a mobile source aftertreatment device such as an automobile. Oxygen or air necessary for ozone production may be supplied from an air compressor supplying air to the engine combustion chamber, and ozone having a desired concentration may be injected into the exhaust gas stream by controlling the magnitude of plasma discharge power.

In addition, a Corona Discharge plasma reactor may be used.

In terms of stability and energy efficiency of the low temperature plasma, a dielectric discharge plasma is preferred, but is not necessarily limited thereto.

Previous cases of PM combustion through ozone have been focused on ozone-only PM combustion experiments and engine application system design. However, there have been no cases of increasing the PM combustion efficiency by matching the ozone oxidation reaction with the catalyst for promoting it.

In the present invention, by using a perovskite (Perovskite) catalyst having an ABO ₃ or A ₂ BO ₄ structure having excellent redox capability, it was sought to improve the PM combustion efficiency through ozone at low temperatures.

In perovskite catalysts of ABO ₃ or A ₂ BO ₄ structure, A and B are cations, and A site is one of La, Pr, Ce, Sr, Ba, Li, K, and Mg or a mixture of two or more metals You can select to configure.

Preferably, the A site may be configured by using one of the above metals as a main component and partially replacing one part with one of the remaining metals.

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

If you do not "partial" part of La with K, the number of oxygen vacancies that can activate oxygen or ozone decreases dramatically, resulting in a decrease in oxidation activity. In other words, it is possible to increase the number of oxygen defects by substituting 'part' of La with K to increase the oxidation activity.

In addition, the A site may 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} . Where x is 0 <x <1.

In addition, the oxidation activity of one oxygen defect is determined according to the type of B site metal, and preferably, the activity of the oxygen defect when Mn is a B-position metal is increased.

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

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

Hereinafter, with reference to the drawings, the ozone production, the synthesis of perovskite catalyst according to this embodiment and the low temperature combustion process using the same will be described in detail. In the following perovskite catalyst is ABO ₃ Although a description will be given of having a structure, it will be understood that the A ₂ BO ₄ structure may be included in the scope of the present invention.

One) DBD plasma  Production of ozone through the reactor

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

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

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

2) ABO ₃  Structure Perovskite  Catalytic synthesis

Synthesis of the ABO ₃ catalyst was performed using an evaporation-to-dryness method. Aqueous metal acetate solutions of the A site and B site metals constituting the catalyst were prepared at a constant concentration, and the aqueous solutions were mixed according to the stoichiometric ratio of each component of the catalyst to be synthesized, followed by stirring at room temperature for 30 minutes. The stirred solution was evaporated to dryness at 30 rpm and 50 ° C. through a rotary evaporator to obtain a precipitate in the form of particles, followed by drying at 110 ° C. for 24 hours, first firing at 410 ° C., and secondary at 960 ° C. After calcination, an ABO ₃ type catalyst was prepared.

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) gases were used for the combustion reaction of PM. Each reaction gas was supplied to the 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 carried out under 250 ppm NO ₂ , 10% O ₂ , 2500 ppm O ₃ , and N ₂ balance 300 mL / min to confirm combustion behavior through ozone.

The reason why NO ₂ is used instead of NO as a reactant is to prevent the ozone injected into the NO oxidation reaction from being consumed. So in actual exhaust gas NO ₂ .rich the reaction conditions there is expected to be achieved without regard to the larger exhaust-gas temperature, the equilibrium concentration of NO to NO ₂ in the temperature by further injecting ozone to the processing unit after the introduction PM It is possible to oxidize in advance. Experimental results to demonstrate this are shown in (Example 2).

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

4) PM  Combustion reaction test conditions and methods

The PM + catalyst bed is prepared by preparing the PM and the catalyst at a mass ratio of 1: 0.33, 0.5, 1, or 2.5, and siC particles of 200 to 450 mesh to prevent local temperature rise in the fixed bed and to simulate SiC DPF environment. Was taken in the same volume as the PM + catalyst bed volume and mixed evenly for 10 minutes using a mortar and pestle. The prepared PM + catalyst bed was placed in the center of the quartz tube reactor, and ozone was injected 10 mm away from the front of the PM + catalyst bed and mixed with other gas components to react with PM. Catalytic reaction experiment was carried out at room temperature to about 650 ℃ 3 ℃ / min to confirm the PM combustion behavior according to the temperature change (Temperature Programmed Oxidation, hereinafter referred to as TPO) and isothermal for comparing the PM combustion rate in the low temperature section at 150 ℃ Isothermal Oxidation (ITO) was performed. The gas emitted after PM combustion reaction was analyzed by the NO _X analyzer and CO ₂ analyzer connected to the rear stage of the reactor to analyze the change of concentration of NO ₂ and CO ₂ .

Example

( Example  One) DBD plasma  Ozone Production Through Reactors

Figure 3 shows the result of measuring the ozone production concentration by changing the frequency of alternating current from 100 to 700 Hz at the primary AC voltage of 18 kV.

The ozone concentration in the stream flowing out of the DBD plasma reactor was 2,000 to 28,500 ppm (Before Dilution), and it was 200 to 2,850 ppm when diluted with other reaction gases (After Dilution). In this experiment, the power used by the reactor (primary power) is about 0.5 to 6.6 W, which is very low compared to the general power consumption or fuel consumption of devices such as automobile headlights and heaters. Therefore, it is expected that the fuel efficiency reduction of the vehicle caused by the installation of additional ozone generator will be very small.

( Example  2) NO - NO ₂ conversion  exam

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

Here, the temperature condition of 150 ℃ is the temperature of the ITO experimental conditions shown in Figure 7 of (Example 5), it is included in the temperature range of the low temperature region where 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. The final conversion rates are close to the equilibrium conversion rates determined at that temperature.

( Example  3) of the prepared catalyst XRD  analysis

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

The Ni peaks shown in the test results are derived from internal standard materials mixed at a weight corresponding to a mass ratio of 10% for each sample to correct the peak size between samples. From the XRD results presented, it can be seen that the catalysts produced as a whole consist of ABO ₃ crystals.

( Example  4) the prepared catalyst and PM In the presence of ozone PM  Combustion Test 1: TPO  Experiment result

6 shows a series of TPO reaction results.

6 in a perovskite catalyst of _{La 0 .75 K 0 .25 MnO 3} , La 0 .3 K 0 .7 FeO 3 and simulating the noble metal catalyst used in the CRT 2 wt.% Pt / Al2O 3 catalyst The results used were compared with each other.

The PM: catalyst ratio in the PM + catalyst bed was 1: 0.33, 2 wt.% Pt / Al ₂ O ₃ 1: 1 for perovskite catalysts. In the non-catalytic reaction experiment (No Catalyst) where no catalyst was used, it was confirmed that the combustion of PM proceeded at a low temperature range of 100 to 300 ° C. because ozone was used as the oxidant, but the combustion reaction proceeded at a high temperature above 400 ° C. Compared with, it can be seen that the size of combustion peak is much smaller.

La _{0 .3} K _{0 .7} to the low temperature combustion Peak of 100 ~ 300 ℃ When using FeO ₃ catalyst is larger than the interval in the absence of a catalyst Peak condition was observed. La _{0 .75} K _{0 .25} when using MnO ₃ catalyst standing became hence large combustion Peak observed at a low temperature range of 100 ~ 300 ℃ is burned all of the PM at a low temperature region has not already burning Peak observed at a high temperature zone . In addition, La _0.75 K _0.25 MnO ₃ is superior to 2 wt.% Pt / Al ₂ O ₃ , a commercial CRT simulation catalyst, when compared with the combustion performance at low temperature. These results show that the PM combustion reaction rate by ozone in the range of 100 ~ 300 ℃ can be effectively improved by using perovskite catalyst, and compared with the platinum (Pt) catalyst included in commercial CRT. It is shown that the effect can be greater. 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) the prepared catalyst and PM In the presence of ozone PM  Combustion Test 2: ITO  Experiment result

7 shows ITO test results at 150 ° C. under low temperature conditions.

The ITO test compares the PM combustion performance of the catalysts at the same initial PM concentration and reaction temperature, and thus can be called a more preferable catalytic performance comparison method 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 more than three times larger, and the slope of CO ₂ emission concentration decreases after the peak generation is steeper. That is, it can be said that the reaction rate of PM combustion by ozone is significantly improved by using a perovskite catalyst at a low temperature of 150 ° C. La _{0 .75} K _{0 .25} MnO ₃ , La _0.3 K _0.7 FeO _{3 When the} two catalysts were compared with each other, the former had a larger concentration of the initial CO ₂ emission peak and the slope of the peak reduction than 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)

ABO ₃ or A ₂ BO is coated on diesel diesel particulate filter (DPF) of a diesel engine which collects diesel exhaust particulate matter and burns the diesel exhaust particulate matter under low temperature conditions using ozone supplied from an atmospheric low temperature plasma reactor. Has ₄ structures,
The A site is selected from one of La, Pr, Ce, Sr, Ba, Li, K, and Mg, or a mixture of two or more metals, wherein the A site is based on one of the metals, and the main component is the remaining metal. Partially substituted with one of the
B site is selected from one of Mn, Fe, Co, Zr, Cr, Ti, Cu and V or a mixture of two or more metals,
Low temperature combustion of the diesel engine exhaust particulate matter is perovskite catalyst is made in the range of 100 to 200 ℃. delete delete delete The method of claim 1,
The B site has one of the metals as a main component, the main component is partially substituted with one of the remaining metal perovskite catalyst. The method of claim 1,
The ozone is perovskite catalyst is supplied through the oxidation reaction of oxygen or air in an atmospheric pressure cold plasma reactor. delete As ozone oxidation system of particulate matter,
An atmospheric low-temperature plasma reactor for supplying ozone generated through oxidation of oxygen or air; And
ABO ₃ or A ₂ BO ₄ structured perovskite catalyst is in contact with the collected diesel engine exhaust particulate matter, and the diesel engine exhaust particulate matter is burned under low temperature conditions by using ozone supplied from the atmospheric low temperature plasma reactor. Including particulate combustion reactors,
A site is selected from one of La, Pr, Ce, Sr, Ba, Li, K, and Mg or a mixture of two or more metals, wherein the A site is based on one of the metals, and the main component is the remaining metal. Partially substituted with one of the
B site is selected from one of Mn, Fe, Co, Zr, Cr, Ti, Cu and V or a mixture of two or more metals,
Low temperature combustion of the diesel engine exhaust particulate matter ozone oxidation system of the particulate matter is made in the range of 100 to 200 ℃. delete delete

Images