FI116236B - Purification system for exhaust gases of diesel or gasoline engines, includes oxidation catalyst, particle separator, and nitrogen oxide adsorption catalyst - Google Patents

Abstract

An exhaust gas purification system includes an oxidation catalyst (3), a particle separator (4), and a nitrogen oxide adsorption catalyst (5). An independent claim is also included for a method of purifying exhaust gases of diesel or gasoline engines containing on average an excess of oxygen. The method involves passing the exhaust gases over the nitrogen oxide (NO x) catalyst of the inventive purification system. The regeneration of nitrates, sulfates and particles can be achieved by periodically adjusting the mixture ratio of the engine from lean to a ratio closer to stoichiometric. The lambda value is less than 1.2, preferably less than 1.15.

Description

116236 System and Method for Exhaust Gas Purification - This application is divided by application FI-20001608.

This invention relates to a system and method for purifying engine exhaust in heterogeneous conditions.

The lean blend engine (λ> 1, excess oxygen) was originally used in all heavy duty vehicles (lorries, locomotives, ships) and power plants because it can produce the energy needed to move with a significantly higher efficiency la than the small gasoline engine, for example. the best solution for demanding engines. The limited availability of fossil fuels, C02 emission targets and rising fuel prices have also driven the development of engine manufacturers. Recently, new types of direct fuel injection diesel and gasoline engines have been introduced that are competitive with efficient gasoline delta and driving characteristics in normal stoichiometric or rich (λ <1, oxygen stoichiometric or low) combustion conditions. Traditionally, diesel engine particle emissions have been higher than those of petrol cars, but the diesel emissions of today's diesel cars have already been reduced by engine technology. The new • · · 20 diesel engines (TDI, HDI) have significantly lower hydrocarbon emissions *; (HC), carbon monoxide (CO) and NOx levels than in petrol cars. The emission limit values will be tightened in accordance with a pre-determined timetable, in which the amount of particulate matter and NOx must be halved when switching from the present level by 2005: a particle limit of 0.025 g / km and a NOx of 0.25 g / km. Driving cycles emphasize urban driving in passenger cars and road driving in lorries due to their typical use. Buses have also used more urban driving simulations.

\\ Y The gaseous emissions (HC, CO) are readily purified by a conversion of more than 70% in a good oxidation catalyst, usually Pt or Pd, although the exhaust gas * Y temperature decreases with improved engine efficiency. For this reason, the catalysts: 30 are often mounted as close to the engine (CC = Closed Coupled) as possible under a Y-shaped body instead of being mounted (UF = Under Floor). The temperature difference is different. . the positions may be above 30-50 ° C. In passenger cars, the exhaust gas temperature immediately after the diesel engine is typically 150-250 ° C for urban and 250-350 ° C for highway 2 116236. For temperature and space reasons, a small starter catalyst is sometimes installed in the CC station and a larger main catalyst in the UF station.

Existing passenger and truck applications require a reduction, especially in NOx and particle emissions, which are difficult to eliminate with conventional catalysts. Gaseous adsorbent hydrocarbons can be oxidized from particle 5, but solid carbon black and inorganic compounds do not react much in the catalyst. In a 3-way catalyst, HC, CO, and NOx react simultaneously to harmless compounds, but the use of such a catalyst requires stoichiometric conditions and a return to a conventional gasoline engine. Because the diesel engine's operating principle and fuel differ from the petrol engine's 10, it cannot be used continuously in stoichiometry or in the rich. As petrol engines using direct injection and excess oxygen are becoming more common, the composition of emissions from gasoline and diesel engines is converging. In fact, lean gasoline exhaust gases have significantly higher soot emissions than conventional gasoline engines. Like emissions, fuel and engine quality are subject to tightening restrictions in Europe, the United States and Japan. This means, for example, that the sulfur content of petrol and diesel in Europe will be the same after 50 ppm. Other countries follow in the regulations with a slower schedule.

Reduction of nitrogen oxides in the catalyst has been promoted by using fuel or reducing agent injections into the exhaust system or cylinder, but the selectivity (20-30% NOx 'conversion) and catalyst durability are too poor.

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• · · Filters and alternatives for regeneration of soot in diesel exhaust gas have been developed: flame burners, electric heating and • * >> i>; catalyst-containing additives in the fuel or particle trap. The particle separators must be regenerated from the accumulated particles at regular intervals. ··· However, the combustion of soot particles requires a temperature above 600 ° C in the air. It is hoped that any inorganic compounds will go into the catalyst system:: *. through the process unchanged. The sulfates are derived from sulfur in the fuel and lubricant, which oxidizes to SC 4 and SC 3 to form sulfate in the catalyst and particles 30. Sulphate formation can be reduced by using low-sulfur fuels. ···. or catalyst which minimizes oxidation of SC> 2 to SO3. Sulphates on the surface of soot also increase the mass of the particles as they continue to collect water and * * absorbable compounds into the surface.

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A regenerable particle filter method is also disclosed, but requires the use of two parallel lines and a very complex control system (EP 0703 352 A3).

For the oxidation of soot in a filter, a method (CRT = Continuous Re-5 generated Trap) is disclosed in which NO2 formed in a forward Pt oxidation catalyst oxidizes soot in a subsequent filter at low temperatures (US 4,902,487). Particulate separators are widely used and their structure and material are developed to withstand demanding automotive applications. The resolution may easily be over 80-90%, but with virtually no reduction in nitrogen oxides. There are also drawbacks to large amounts of stinging NO 2, which is more harmful to health than NO near the source. It has been proposed to use a urea SCR (Selective Catalytic Reduction) catalyst after a Pt oxidation catalyst and particle trap (Automotive Engineering 25 (2000) no. 5, pp. 73-77), but in that case a separate, expensive demanding equipment for the urea tank 15, which cannot be used below 250 ° C.

One solution utilizes a dual cell catalyst system in which the aperture density of the first catalyst is lower than that of the latter catalyst to prevent blockage of the catalyst apertures (EP 0 875 667 A2). Such solutions seek to extend the residence time of the soot under conditions where it can burn, but it is estimated that less than 50% of the particles can be removed and the degree of removal is very dependent on flow rate and temperature in a cell-only system.

NOx-trap catalysts have been proposed for the removal of nitrogen oxides in direct injection gasoline vehicle targets (GDI = gasoline • ·,. Direct injection) based on ... 25 conditions that vary as planned between lean and rich. In this case, '* ··' NOx can adsorb to specially designed compounds for a longer lasting lean phase and be reduced to nitrogen during a short rich or stoichiometric peak. Typically, the length of the lean phase is more than 30 times the length of the rich phase. In this way it is possible to obtain fuel savings. However, the average consumption of the mixture is clearly lean and, at the same time ···, more than 70% of the nitrogen oxide emissions are removed (EP 0 560 991). Typical • · NOx adsorption compounds on a Pt catalyst include, for example, Ba, Sr, K, Na, Li, Cs, La, and Y. The petrol engine easily performs enrichments, with the disadvantage of • V ·· sulfur resistance and the resulting increase in fuel consumption.

35 The diesel engine runs best on a lean fuel-air mixture, but it has been shown in engine tests that the concentrates and NOx trap catalysts also function in the purification of 4,116,336 diesel fuels (Kramer et al. 1999, seminar "Abgas-nachbehandlung von Fahrzeugd" 16.6.1999, Haus der Technik, Aachen).

It is an object of the present invention to provide a system that is efficient in particle and NOx removal and is integrated with existing engine systems to achieve high conversions, particularly with respect to nitrogen oxides and particles.

According to the invention there is provided a system and a method for purifying the exhaust gases of an average oxygen-containing diesel or gasoline engine comprising NOx adsorption catalysts installed in one of each exhaust outlet of the cylinder or one in each exhaust outlet of two cylinders. This system is especially suited for thin petrol destinations (GDI). This system may also include a particle separator and / or another catalyst, such as an oxidation catalyst or a 3-catalyst catalyst.

In the system of the invention, NOx adsorption catalysts are installed in one exhaust outlet of each of the 15 engines or one in each combined exhaust outlet of two cylinders of the engine, and the system includes a control system for periodically adjusting engine or at least one cylinder ratio less than 1.2 NOx -::: 20 for the regeneration of adsorbent catalysts nitrates, sulphates and particles.

'; Fields of application of the invention include diesel, light gasoline and flue gas applications in mobile or stationary applications. The engines can be free-breathing or 'turbocharged' and the fuel injection is direct-injection in both diesel and gasoline cars. The systems of the invention may also be used in other engines or fuels where the conditions can be controlled as described below.

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The concept may also consist of three functional units with one or more oxidation catalysts, one or more particle separators and one or more NOx adsorption catalysts.

In accordance with the invention, there is also provided an average system for purifying exhaust gas of I * · * '· oxygen-containing diesel or gasoline engines comprising three functional units which are an oxidation catalyst, a particle separator and a NOx adsorption catalyst for reducing the exhaust gas content of the exhaust gas. , carbon monoxide, nitrogen oxides and particles.

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The functional units may be an oxidation catalyst, a particle separator and an NOx adsorption catalyst, or an NOx adsorption catalyst, a particle separator and an oxidation catalyst, or an NOx adsorption catalyst, an oxidation catalyst, respectively.

According to an embodiment of the invention, the exhaust outlet of each cylinder of the engine is connected to a connecting duct where said functional units are mounted.

According to another embodiment, an NOx adsorption catalyst is installed in the exhaust outlet of each cylinder of the engine, the outlet channels being connected to a connecting channel where an oxidation catalyst and a particle separator are mounted.

The system of the invention may also include two or more subsystems mounted in parallel, each containing said three functional units.

According to the invention, the purification of the exhaust gas is carried out under heterogeneous conditions, wherein regeneration of the sulfates of the NOx adsorption catalyst, reduction of nitrates and combustion of the particles is carried out using a lean mixture and a rich mixture. Hereby, the ratio of the duration of the lean to rich stages is preferably greater than 3, and particularly preferably more than 10. The enrichment and lean stages may be of different situations and purpose depending on the duration and the mixture ratio.

: V 20 Heterogeneous conditions provide several simultaneous advantages in the enrichment stage, namely nitrate reduction, S-regeneration and enrichment heat - *: ··: Increasing age helps in particle combustion and S-regeneration.

A preferred NOx adsorption catalyst contains platinum and / or '···' rhodium as the catalytic metal and at least one of Ba, Sr, La, Y, Ce, Zr and optionally at least one of Li, Na, K, Rb, Cs , Be, Mg, • ·: Ca. Said elements may be in the form of oxide, sulfate, nitrate, aluminate or metal. Preferably they are in the oxide form.

Said oxidation catalyst preferably contains platinum and / or ·· as the catalytic metal. palladium.

. . Preferred excipients in the oxidation catalyst and the NOx adsorption catalyst are those containing at least one of the following oxides: alumina, zeolite, aluminosilicate, silica and titanium dioxide.

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According to the invention there is also provided a process for the purification of exhaust gases of an average oxygen-containing diesel or gasoline engine, wherein the exhaust gas to be purified is passed through a system according to the invention described above.

According to the invention there is further provided a process for the purification of the exhaust gases of an average oxygen-containing diesel and gasoline engine, wherein the exhaust gases to be purified are passed through a NOx adsorption catalyst, wherein sulfate regeneration is achieved using a lean-rich blend 10.

According to the invention, enrichments of different durations can be used for the regeneration of nitrates, sulfates and particles, whereby the regeneration of sulfates and particles is preferably used for a longer period of time than the regeneration of nitrates.

According to the invention there is further provided a process for the purification of exhaust gases on average in oxygen-containing diesel and gasoline engines, wherein the exhaust gases to be purified are passed through a NOx adsorption catalyst, wherein regeneration of nitrates, sulfates and particles is achieved by preferably less than 1.2 and more preferably less than 1.15. In connection with this method, fuel may be injected into the engine or exhaust system prior to the NOx adsorption catalyst, whereby the mixture ratio is substantially stoichiometric or rich with a λ value of less than 1.1, preferably ». ., Additionally 1 or less than 1 and more preferably between 0.97 and 1.00.

The invention will now be described in more detail with reference to the accompanying drawings, in which * »· I · • ·, ··. Figure 1 shows a system according to the invention, Figure 2 shows another system according to the invention, ·. Fig. 3 shows a third system according to the invention, Fig. 4 shows a fourth system according to the invention, and Figs. 5-9 graphically show the results obtained from laboratory tests.

nm: According to the invention, the functional units may be arranged in a different order according to the object conditions and the conversion requirements. Figures 1-4 illustrate, by way of example, some preferred systems of the invention.

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In Figures 1-4, A denotes air and F denotes fuel.

Figure 1 illustrates a system in which the units are arranged in the order in which the raw exhaust gas 2 from the engine 1 first enters the oxidation catalyst 3, next into the particulate trap 4, and finally the purified NOx 5 adsorbent catalyst 5 exits. in terms of generation.

Figure 2 shows another system in which the units are arranged in the order in which the raw exhaust gas 2 from the engine 1 first enters the NOx adsorption catalyst 5, then the particulate trap 4, and finally the purified oxidant 6 from the oxidation boiler 10.

Figure 3 shows a system in which each cylinder is provided with its own NOx adsorption catalyst. Because it is difficult for a diesel engine to provide rich exhaust conditions, the latest engine control systems can use cylinder-specific A / F control and step-by-step enrichment in different cylinders 15 at different times. The 4-cylinder 7, 8, 9, 10 engines have their own NOx adsorption catalyst 5 "mounted in the exhaust pipe from each cylinder. Modern control systems and engines (common trail, turbocharged) allow you to adjust λ individually for each cylinder. Most of the time, all cylinders are lean to collect nitrogen oxides in NOx -: 'j': 20 adsorption catalysts Periodically, at intervals of about 0.5 to 10 min, a cylinder-specific jv concentrate (λ <1) is made to reduce the nitrates in the NOx adsorption catalyst to nitrogen.

• ·. Enrichment is not done simultaneously on all cylinders. However, since the cylinders 8-10 parallel to the enrichment cylinder 7, * * 11 are lean, the composition of the mixture in the interconnector 12, however, is lean, where the oxidation boiler, lithium 3 can function and the particulate trap 4 collects solids . The amount of soot '···' in diesel engine exhaust gas can be significantly better controlled per cylinder compared to the case where the entire mixture is enriched. Particle Trap: 4 is regenerated from carbon black with NO2 by allowing the mixture to remain at

It is thin on some cylinders.

Figure 4 shows a system in which the functional units are also arranged in two parts on different cylinders 7 and 8 and 9 and 10, each having a complete system according to the invention including an oxidation catalyst 3 ', a particle trap 4' and NOx adsorption catalyst 5 '. In this case, about half the smaller volumes for catalysts and traps can be used, allowing them to be placed as close to the engine as possible. The concentration of concentrates is considerably weaker in two cylinders than in the entire engine, and in this way the NOx adsorption catalyst can be regenerated from nitrates, sulphates or particles. In a one or two cylinder system, the diesel engine can be enriched in such a way that the temperature also rises sufficiently high to decompose the sulfates into hydrogen sulphide in the rich phase and the soot burns back when the oxygen concentration is abruptly increased. A similar system can also be used for lean gasoline targets (GDI), whereby the particle trap can also be omitted and the oxidation catalyst is replaced by a 3-carbon catalyst.

With the system of the invention, nitrogen oxides can be removed in a lean condition and prevent the entry of harmful NO2 formed in current oxidation catalysts into the open air. The objective is to reduce the oxides of nitrogen to λ: η during the reduction peak to <1. Even though nitrate reduction would not work under certain conditions, the decomposing nitrates and the catalyst desorb mainly NO instead of NO2, which is already a considerable advantage in the system. If the blend ratio becomes 15 stoichiometric or almost stoichiometric in NOx adsorption catalyst, the decomposition temperature of nitrates is clearly reduced compared to normal diesel conditions, whereby such desorption is possible. Depending on the NOx adsorption materials, the temperature is between 150 and 400 ° C.

Since the high NO 2 / C ratio is required for the combustion of soot and the reaction selectivity is poor, most of the NO 2 comes through the particle trap in the system of Figure 1 and v; adsorbs on an NOx adsorption catalyst. Concentration peaks can sometimes be utilized to raise the temperature, which results in additional combustion temperature of the particles: i *: For the combustion of soot, a rich mixture is not advantageous, but immediately thereafter the surface temperature of the filter is still high and as the oxygen concentration in the gas rapidly increases, the particles react even with oxygen (> 500 ° C) to form, gaseous compounds.

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By placing the particulate trap closest to the engine, a higher * temperature can be utilized and the NOx adsorption catalyst can be operated at the highest possible running speeds:> t>: (Fig. 2). The order of the particle separator and the oxidation catalyst may also be reversed. This system can also make enrichment peaks that are enriched to such an extent that a large amount of nitrates decompose, form NO 2 in the oxidation catalyst, and efficiently burn particles at high NO 2 / C ratios. If the particle separator is after the NOx adsorption catalyst, NO 2 can be trapped in the particle trap by allowing the mixture to be lean for a sufficient period of time, e.g.

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The soot, C (s), accumulated in the particulate separator or system, is regenerated by a thermal or catalytic reaction in which, in the normal exhaust, NO 2 acts primarily as an oxidant:

C (s) + NO 2 -> COx (g) + NO (g) (+ N 2 (g))> 230 ° C

5 C (s) + O 2 → CO 2 (g)> 500 ° C

wherein the oxygen and NO 2 are in the gas phase or adsorbed on the surfaces.

In the system of the invention, the particle separator can be any filter or particle separator system made of ceramic, SiC or metal. The separator can be of cellular, rod-type, foam, 10-porous plate, wire mesh, silencer or cyclone type. A particle separator is a place where the particles remain long enough to be oxidized to carbon oxides and water. The resolution may have been enhanced electrostatically and combustion with an additional source of heat (burners, electric heating). Fuel or catalytic additive catalysing soot combustion may also be used in the system to reduce the soot ignition temperature. The particle trap can also be coated to provide a compact structure with an oxidation and / or NOx adsorption catalyst. The particle separator can be coated on the upstream side with an oxidation catalyst and on the upstream side with a NOx adsorption catalyst. The problem in this situation may be that the total geometric surface area for the catalyst materials is too low.

Since the NOx adsorption catalyst is a reasonably good oxidation catalyst under lean conditions, the system of the invention can be used in a suitable subject with two functional units, which are the NOx adsorption catalyst and the particle *: · *: separator. The NO 2 is then formed by allowing the mixture to be periodically prolonged; head lean. However, the regeneration of soot is relatively rare. In a two 25 unit system, the regeneration of soot can also be arranged in other ways as described herein.

With a cylinder-specific NOx adsorption catalyst, lean engines can be used; V; However, the system will grow even though the system contains several separate functional units. ropes and is therefore more expensive than normal. Experience has shown that the '' 30 enrichment of diesel engines is known to be difficult, with problems with combustion failure and abundant particle formation. By concentrating only one cylinder at a time, clearly less enrichment is required and when mixed with the exhaust gas from the other cylinders, the excess hydrocarbon, CO, hydrogen, and particles burn thermally, in the oxidation catalyst and in the particle separator. The particle separator placed in front of the NOx adsorption catalyst 10 116236 removes the formed particles and only gaseous reducing agents such as CO, hydrocarbons, reach the NOx adsorption catalyst during the reduction peak. The particle separator, on the other hand, regenerates as the NC / IIa mixture is again lean.

5 Cylinder-specific NOx adsorption catalysts allow the removal of accumulated sulfates much more easily than with a complete system, since in one cylinder the enrichment does not interfere with engine operation and runnability compared to the situation where the enrichment would be done in the exhaust. The decomposition of stable sulfates (such as BaSO 4) may require a temperature above 600 ° C under sufficiently long reducing conditions. When the enrichment is carried out in a single cylinder line alone at different times with others, the desorbable H2S reacts thermally or at the surface of the catalyst back to SO2, which is less odorous to hydrogen sulfide, in the oxygen-containing exhaust gas. When the temperature of the enrichment cylinder exhaust gas 11 (Figure 3) is high enough for sulfate decomposition, the temperature in the combined exhaust gas 12 is sufficiently high for the hydrogen sulfide to react in the oxidation catalyst to SC 4. The enrichment peaks are normally very short, 0.1 to 5 s, and the length of the lean phase, e.g., 15 to 180 s.

The temperature of diesel exhaust gases decreases as the efficiency of new engine types continues to increase. Cylinder-specific catalysts can be positioned closer to the engine, and the catalyst diameter remains more reasonable than in a situation where exhaust gas from all cylinders would flow through a single catalyst. Alternatively, if a 4-cylinder car requires a total of 2.0 liters of NOx adsorption catalyst, approximately 0.5 liters of catalyst may be placed on each cylinder - *: ··. Because each catalyst receives only one cylinder exhaust gas, the diameter of the catalyst can be significantly reduced than, for example, a starter catalyst of the same size through which all exhaust gas flows. In the situation of the invention, the diameter of the catalyst approaches the diameter of the exhaust pipes, whereby the catalyst fits into a small space.

When using two separate lines, for example in a 4 or 6 cylinder engine, they can be used separately as complete systems. This is where the process of concentrating for nitrate decomposition, particle incineration and sulphate decomposition is much easier than in the overall system. Nitrates: Reduction already occurs at very low temperatures (up to <200 ° C). The main thing is to create a reducing circumstance. If the NOx concentrations in the crude emissions 35 are low, the NCVC ratio will remain low, which will also require additional heat generated in the enrichment of the system of the invention to burn the particles accumulated in the filter 11116236. In normal ΝΟχ-adsorption catalysts, the removal of sulfates is the most critical for the temperature requirement, and for this the temperature must be raised to at least 300 ° C, normally above 600 ° C. The division into two lines can be a critical factor without which the diesel engine system of the invention cannot be used due to the requirement for runnability and running smoothness.

It is possible to install the systems of the invention in different sizes so that the exhaust gases from one cylinder go to one system and the other to another larger system. In this case, the second system may be very small. The functional units according to the invention can be connected together, in parallel, by several combinations of the alternatives presented.

Developed, low-emission direct injection gasoline engines have encountered difficulties in increasing particle emissions. Particles can be generated in the combustion chamber, both lean and enriched, more than normal gasoline engine emissions. The system and method of the invention can also be used in those applications and, due to higher temperatures, the removal of particles and sulfates from the system occurs rapidly, often in normal running. A simple particle separator would prevent momentarily generated particles from entering the open air.

Since the diesel engine is more difficult to make concentrates (λ <1) than the petrol engine, the diesel engine blend ratio can be adjusted to near stoichiometric conditions. where the engine can be run normally for a short time. NOx-adsorption catalyst-. nitrates accumulated in the lithium can be regenerated by simultaneously injecting additional, 2 * fuel into the exhaust gas (exhaust or post injection into cylinders). In this way, NOx emissions in the engine remain lower than in engine enrichment 25 (λ <1). The raw emissions of NOx from combustion increase when compared to lean '···' transition to a stoichiometric and rich blend. As crude emissions rise, the requirement for NOx conversion also increases. By using a diesel engine: momentarily close to the stoichiometric but clearly lean, the raw emissions of nitrogen oxides and particulates can be considered reasonable. At that moment enrichment: v. 30 reducing conditions are done by fuel injection. From the point of view of reduction power, it may be necessary to make an enrichment peak of longer duration when using this method, since λ is now closer to 1 than in the previously described method. The reduction power depends on the duration of the enrichment step, the distance to the stoichiometric mixture. ' ·; and the composition of the reducing agents.

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Additional fuel injection may also be scheduled at a slightly different time than the motor horn injection for a slightly lean time. The additional injection may be to enhance the concentration slightly before or after the motor enrichment. It may be advantageous to make additional injection prior to engine enrichment, for example because in still clearly lean blend 5, fuel is cracked to reactive compounds at a lower temperature than when fed to a blend near the stoichiometer. This can be optimized e.g. temperature and reduction power. Additional injection can also be made by injecting fuel into the system just before the NOx adsorption catalyst. S-regeneration can also be achieved by using this method or by making a longer-lasting and sulfur-enriched enrichment. According to thermodynamic calculations, without further injection near the stoichiometric mixture, the decomposition temperature of the lean nitrates is clearly lowered, under which, under normal driving conditions, the NOx adsorption catalyst desorbs NO, which is a better environmental release than the normal Pt oxidation catalysts. Continuous or momentary enrichment with a diesel engine cannot reasonably be done by fuel injection, since oxygen is present in the exhaust at 5-16% under normal operating conditions. Then the amount of fuel needed would be so great that it would consume all of this oxygen before the nitrogen oxides would begin to reduce properly. Such a large amount of hydrocarbons is no longer properly burned in the catalysts and the injection causes an excessive increase in fuel consumption and a risk of emissions.

During the development of the system, an S-regeneration -... process was also developed for NOx adsorption catalysts, where S-regeneration was used instead of the usual long reduction treatment. were performed under heterogeneous lean-to-rich conditions that corresponded to the normal system-lean-to-lean timing and conditions except for the temperature, which had to be raised at that time. to the level required for the decomposition of the catalyst sulfates. Own: "25 women is a shorter phase of the rich phase compared to the lean phase. S-regeneration should be done in situations where the temperature is otherwise high due to driving conditions, e.g. motorway driving. Additional heat is achieved by moving the lean phase mixture closer to the stoichiometer.

The invention will now be further described by means of examples relating to laboratory tests performed.

The oxidation catalyst, NOx adsorption catalyst and particle trap, described in more detail below, were used in the systems and reference systems of the invention.

The oxidation catalyst used was an oxidation catalyst developed for diesel conditions where the specific surface area of the support was> 200 m / g fresh and the amount of support 13,132,636 on the surface of 50 μητη thin metal foil was about 50 m2 / g. The aperture density was 400 holes / inch. The support contained about 1.4% Pt, whereby the catalyst gave high activity at the same time from the NO in NO under diesel conditions for the oxidation of CO / HC and the oxidation of soot. A small amount of nitrogen oxides was also reduced under diesel conditions at 150-280 ° C in this Pt catalyst.

The support for the alumina-based NOx adsorption catalyst contained 10% Ba, 9% La, 17% Ce, 3% Zr, 1.8% K, 1.2% Mg, and 2.4% Pt. The aperture density was 500 holes / in2 and the metal foil thickness was 50 µm.

The ceramic honeycomb particle trap used in the experiments contained about 110 rei-10 coils / in2. The cell always had one end closed in the holes, whereby gas had to pass through the permeable wall of the porous exhaust gas. However, the size of the holes was so small that the particles remain at the inlet side of the filter at a resolution of more than 80%. As the number of particles increases, the pressure drop increases and the soot accumulated in the filter must be removed by incineration.

The systems were simulated under laboratory conditions that simulate the average exhaust emissions of low-emission diesel engines with deliberate enrichments to reduce adsorbed NOx. Although no particles were fed to the inlet and no resolution was measured, the purpose of the simulation was to investigate how the particle separator 20 used in normal passenger cars influences the flows and the passage of the enrichment peaks. The simulation is also comparable to the one performed on the motor because of the reaction of the particles with NO 2. it does not consume much NO 2 and does not affect the concentration present in the NOx adsorption catalyst.

Because of the problem of durability under real conditions, the activity of the samples was measured after being hydrothermally aged (10% water in air, about 4000 hr -1 in a sample) at 700 ° C for 20 hours. This resulted in a result that corresponds to the actual exhaust emissions required. Laboratory Tube Reaction ··· The composition of the inlet to the market was controlled by computer controlled mass flow controllers and analyzed by continuous NOx, CO, HC and O2: * 'analyzers. The conditions in the laboratory equipment were as shown in Table 1.

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Table 1 Inlet gas compositions used in the laboratory simulation

Compound__Fat 1__Wealthy 1__Fat 2__Wealthy 2 NO, ppm__500__1500 500__500 C3H6, ppm__500 1000__1000 3330 CO,% __ 0.05 6__01__1.0 H2,% __ 0.04 2__03__0.8 02,% __ 7 ___ 0J3__1.8 1, .8 H2Q,% 10__ ,% __ 10 10__10__10 S02, ppm__0 / 25 0 / 25__0__0 N2__the rest__the rest of the λ__045__0.84 1.08 0.99

Time, s__60 5 5__5__

Exhaust gases simulate the following conditions in diesel exhaust: 5 Lean 1: Normal diesel exhaust

Rich 1: Diesel engine instantaneous enrichment to rich (λ <1)

Lean 2: Mixture ratio shifted close to stoichiometric with diesel engine, but clearly lean: Rich 2: Shifted mixture ratio in exhaust to slightly rich Lean 2 - '•• v 10 conditions after injecting fuel into exhaust

Average activities were measured over 5 cycles between 150-600 ° C and 50 ° C.

<· ·. . Example 1

At constant temperatures, the laboratory performed cyclic activity tests in which the 15 lean 1 mixture of Table 15 was fed to the reactor for 60 s and the rich 1 mixture for 5 s. The results are shown in Figures 5 and 6, where the functional units are designated as follows: Oxi-cat = oxidation catalyst (length 30 mm, change 75,000 h'1, PF = particle separator (length 75 mm, change 30,000 h'1) and NSR = NOx Adsorption Catalyst (Length 47: mm, 48,000 h -1) The sample lengths and shifts were selected to correspond to 20 relatively normal conditions found in diesel vehicle exhaust and NOx-116236 adsorption catalysts, corresponding to adsorption capacities, oxidation capacities and flow dynamics.

The first set of tests, the results of which are shown in Figure 5, used an oxidation catalyst (control), a NOx adsorption catalyst (control) and a system in which the 5 particles and the NOx adsorption catalyst are placed in series. The results show that the Pt oxidation catalyst alone does not work but requires a NOx adsorption catalyst to achieve a higher NOx conversion in this type of cycle. Positioning the particle chelator in the front does not prevent NOx adsorption and access of the enrichment peaks to the ΝΟχ adsorption catalyst. 40% NOx conversion is already achieved at 200 ° C. 10 The maximum conversions in the simulation were over 80%.

In another set of tests, the results of which are shown in Figure 6, a system according to the invention was used, in which the oxidation catalyst, even the particulate and NOx adsorption catalyst, are arranged in series. The system has been shown to work well and, surprisingly, to provide improved high-temperature performance compared to the system without Pt oxidation catalyst. The result shows that placing the oxidation catalyst first downstream does not prevent NOx adsorption and reduction. The oxidation catalyst was deliberately chosen to be relatively small compared to the PF and NOx adsorption catalyst so as not to prevent the reductants from passing through the adsorption at the enrichment time used.

The NOx conversion level of the systems of Figures 5 and 6 was reduced by the continuous presence of 25 ppm SO2. The systems were completely regenerated by use. conditions above 600 ° C. The results of Figures 5 and 6 are measurements taken once with a regenerated system, demonstrating the sulfate resistance of the NOx adsorption catalysts and the overall system and the functionality of S regeneration. Regeneration of the S-25 was performed with the same gas mixtures at a timer of 60 s lean 1 and 5 s • · '* ··' rich 1. The regeneration was thus carried out under the exhaust gas conditions in which the system presented is otherwise used, whereby the best NOx adsorption catalysts operate. : still with more than 30% conversion. Generally, S-regeneration is carried out using a · long reducing step, with the risk of a high concentration of HaS in the exhaust gas.

: V. 30 The regeneration test showed the method to work. By using • · '.. • t heterogeneous conditions in S-regeneration, purely reducing treatment alone reduces

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'! * emissions. Under heterogeneous conditions, S regeneration is characterized by a shorter rich phase compared to a lean phase. If the NO adsorption catalyst to be used requires a high S-regeneration temperature, it may be best to increase the temperature by moving the lean phase mixture closer to the stoichiometry to a level sufficient to decompose the sulfates.

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Example 2 This example simulates the situation of Figure 3 with four NOx adsorption catalysts for each cylinder. The change in each of these catalysts was assumed to be the same 48,000'1 as in the situation where there was only one catalyst in the entire exhaust gas. The individual NSR catalyst outlet CO, HC, NOx and O2 concentrations at 11,200, 250 and 300 ° C were analyzed. We simulated a situation where the cylinders are synchronized for one minute in such a way that the 5 s enrichment phase (λ = 0.865) rotates smoothly across the different cylinders while the other cylinders are lean (λ = 1.447). The composition (λ = 1.30) of the exhaust gas 10 of Figure 7 at position 12 prior to the oxidation catalyst was then obtained. This gas mixture was used as an input in a simulation examining how the oxidation catalyst functions in the combined exhaust at 75,000 h -1. HC and CO ignited at about 225 ° C and HC concentrations below 100 ppm and CO concentrations below 500 ppm in the simulated mixture at 250 ° C. The results are shown in Figure 8. Simulation 15 showed how the gaseous CO and HC emissions can be kept low in the system of the invention when the cylinders are in the enrichment phase synchronously at different times. Based on the result, it can be concluded that a similar benefit can be achieved in reducing particle emissions. At the same time, the NOx conversions would be as in Figure 6, or even slightly better, since the NOx-20 conversions in the simulated gas mixture were still 10-20% still in the Pt oxidation catalyst at 200-300 ° C. This conversion of NOx ... can be calculated in addition to the conversion level of the NOx adsorption catalyst.

• * * • Example 3

Enrichment with diesel engine near stoichiometric composition and simultaneous enrichment with fuel injection were simulated in a laboratory reactor with - * .. * 25 l mixtures according to Table 1. A system according to the invention was used in which the oxidation catalyst '··' (Oxicat, 30 mm), the particle separator (PF, 75 mm) and the NOx adsorption catalyst (NSR, 47 mm) are arranged in series. In the first simulation, the mixture was alternated between lean 1 and lean 2 at 60 s / 5 s. In the second simulation, the lean 1 and rich 2 mixture was alternated at 60 s / 5 s and col. In 30 manne, the rich 2 phase duration was extended to 10 s. Enrichment by fuel injection was simulated in the blends so that the ratio of hydrocarbons to CO and hydrogen was significantly higher than in the case of engine enrichment (rich 1). The results are shown in Figure 9.

This simulation showed that the additional injection (lean 1 / lean 2) provided a clear improvement over the situation without the additional lean (lean 1 / lean 2). The conversion of NOx-17 116236 at 250-300 ° C improved from about 20% to nearly 50%, although the reduction peak duration was 5 s and the mixture was only slightly rich (λ = 0.99). The NOx conversion was more than 40% between 220-410 ° C. The conditions used in the simulation are reasonable for engine running and additional fuel consumption. The result also shows the difference in continuous NOx reduction with hydrocarbons, since the Pt catalyst has a narrow operating window between 200-300 ° C. The level of action was clearly lower at high temperatures than with higher enrichment (rich 1 alloy, λ = 0.86), but the exemplified embodiment provides a new possibility that is technically easier to accomplish by motor than Example 1. By extending the enrichment time with HC injection (ri-10 cas 2 mix) could be clearly improved. By optimizing the conditions (enrichment duration and λ value), it is likely to be possible to significantly increase the operating level.

* · I * · t «> · 1 · * ·

Claims (23)

1. A system for purifying the exhaust gases of diesel or gasoline engines, which contains on average an excess of oxygen, which system includes NOx adsorption catalysts, characterized by the fact that NOx adsorption catalysts (5 ', 5 ") have been mounted (5"). ) in each cylinder (7, 8, 9, 10) of the engine in the exhaust duct or one (5 ') in the combined exhaust duct of each engine's two cylinders'. (7, 8; 9, 10), and that the system includes a control system for controlling the electric power of the engine. * At least one cylinder's mixing ratio is periodically from lean closer to a stoichiometric ratio or to substantially stoichiometric or rich, the λ value being less than 1.2 for regeneration of NOx adsorption catalysts nitrates, sulphates and particles. System according to claim 1, characterized in that the system further includes a particle separator (4, 4 ') and / or an oxidation catalytic converter (3, 3'). System according to claim 1 or 2, characterized in that the system includes three functional units, which are a NOx adsorption catalytic (5 ', 5'), a particle separator (4, 4 ') and an oxidation catalytic (3, 3'). 4. A system according to any of the preceding claims, characterized in that the system includes a particle separator and that the NOx adsorption catalytic and / or oxidation catalytic converter is in the same construction as the particle separator. System according to claim 3, characterized in that the functional units in the direction of exhaust flow are in the order of the oxidation catalyst (3 '), the particle separator (4') and the NOx adsorption catalyst (5 '). System according to claim 3, characterized in that the functional units in the direction of exhaust gas flow are in the order NCVadsorption catalytic converter, particle separator and oxidation catalytic converter. 7. A system according to claim 3, characterized in that the functional units in the direction of flow of the exhaust gas are in the order NOx adsorption catalytic converter (5 "), oxidation catalytic converter (3) and particle separator (4). • f m. * 20 8. A system according to any of the preceding claims, characterized in that the particle separator and / or the oxidation catalytic converter are mounted in the exhaust duct for the exhaust gases for each cylinder or in a combined exhaust duct for the exhaust gases from each two cylinders. . . 9. A system according to claim 1, characterized in that an NOx adsorption catalytic converter (5 ") has been mounted in the outlet duct for each cylinder (7, 8, 9, 10), which outlet ducts have been combined into a combined channel (12) into which the oxidation catalyst (3) and the particle separator (4) have been mounted. *; 10. A system according to any one of the preceding claims, characterized in that the regeneration of the sulfates, the reduction of the nitrates, and the combustion of the particles in the NOx adsorption catalytic acid are carried out using periodic lean mixing and rich mixing. 116236 11. A system according to claim 10, characterized in that the ratio of the thin / rich periods is more than 3, preferably above 10. System according to any of the claims above, characterized in that by means of the control system, the enrichment in the various cylinders is made at different times and / or the enrichments in the different cylinders are made periodically between each other at different times. A system according to any of the preceding claims, characterized in that the NOx adsorption catalyst contains as a catalytic metal platinum and / or rhodium and at least one of the following substances: Ba, Sr, La, Y, Ce, Zr and optionally at least one the following substances: Li, Na, K, Rb, Cs, Be, Mg, Ca. System according to any of the preceding claims, characterized in that the oxidation catalytic converter (3, 3 ') contains as a catalytic metal platinum and / or palladium. 15. A process for cleaning off the exhaust gases of diesel or gasoline engines, which contain, on average, an excess of oxygen, characterized in that the exhaust gases to be cleaned are passed through a system according to any of claims 1-14. 15 The method according to claim 15, characterized in that periodic blend and rich blend are used, the ratio of lean / rich periods lasting over 3, preferably above 10. :; Process according to claim 15 or 16, characterized in that different enrichments are used for the regeneration of the nitrates, sulphates and particles. Suitable for the regeneration of the sulfates and particles for a longer period of time than for the regeneration of the nitrates. • » 18. A process according to claim 15, characterized in that the exhaust gases to be: purified are passed through a NOx adsorption catalytic wherein the regeneration of the sulphates is effected using periodic lean rich mixture, the ratio of: between lean / rich periods being over 3, preferably above 10. 19. A process according to claim 15, characterized in that the exhaust gases to be purified are passed through a NOx adsorption catalytic, wherein regeneration of the nitrates, sulphates and particles is effected by periodically regulating the engine's mixing ratio from lean. closer to a stoichiometric ratio, the λ- [* value being preferably less than 1.2 and more preferably less than 1.15. 20. A process according to claim 19, characterized in that fuel is injected into the engine or exhaust pipe prior to the NOx adsorption catalytic, the mixing ratio being substantially stoichiometric or rich, the λ value being less than 1.1, preferably 1 or less than 1, and more preferably in the range of 0.97-1.00. 21. A method according to claim 20, characterized in that the additional injection of fuel into the engine or exhaust pipe is carried out at different times than the engine enrichment. 5 Method according to claim 21, characterized in that the extra injection is performed before the enrichment. 23. A method according to claim 21, characterized in that the additional injection is performed after the engine enrichment.