JP2013139757A - Exhaust emission control device for heat engine, exhaust emission control method and oxidation catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device or the like of a heat engine to purify CO, HC in an exhaust gas in an oxygen excess atmosphere with high purification performance.SOLUTION: The exhaust emission control device of the heat engine, which is provided with a CO, HC purification catalyst oxidizing and purifying CO or HC, is arranged in an exhaust flow path of the heat engine discharging the exhaust gas containing CO and HC and in an oxygen atmosphere excessive more than stoichiometric amount. The CO, HC purification catalyst has: a porous support of an inorganic compound; and at least one kind selected from Pt, Pd, Rh, Au, Ir, Ru, Os supported on the porous support as a catalytic active component. The porous support contains: Ce; and at least one kind selected from Pr, Nd, Gd, La.

Description

  The present invention relates to carbon monoxide (CO) and hydrocarbons (HC) in exhaust gas in an oxygen-excess atmosphere exhausted from internal combustion engines typified by diesel engines such as passenger cars and construction machinery and external combustion engines such as boilers and gas turbines. The present invention relates to an exhaust gas purification apparatus for a heat engine, an exhaust gas purification method, and a CO and HC oxidation catalyst used therefor.

  In recent years, internal combustion engines such as diesel engines and lean burn engines, where the air-fuel ratio (ratio of air in the gas to fuel) is lean, or external combustion that operates in an oxygen-rich atmosphere such as gas turbines and chemical plants As the number of engines increases, a method for highly oxidizing and purifying carbon monoxide (CO) and hydrocarbons (HC) under excess oxygen is required.

  As a method for oxidizing and purifying CO and HC, a method of oxidizing using noble metals such as platinum (Pt) and palladium (Pd) is known and applied to purification of exhaust gas discharged from a diesel engine or the like. (For example, refer nonpatent literature 1). However, the price of these noble metal raw materials is high, and it is necessary to suppress the use amount as much as possible. Moreover, there is a possibility that sintering may occur due to the heat load and the activity may be reduced.

Therefore, it has been considered to use an oxide having a high specific surface area such as aluminum oxide (Al ₂ O ₃ ) or cerium oxide (CeO ₂ ) as a carrier for the purpose of increasing the precious metal dispersion and improving the purification activity. (For example, refer nonpatent literature 2). In particular, CeO ₂ has a high affinity with noble metals and is unlikely to sinter. Further, CeO ₂ has an oxygen storage capacity (OSC (Oxygen Storage Capacity) capacity), and has an effect of promoting an oxidation reaction by a noble metal by storing oxygen on the catalyst surface. Therefore, in recent years, it is being applied to oxidation purification catalysts in general (Non-patent Document 3).

  Further, as a technique for providing an exhaust gas purification catalyst excellent in the purification of carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas in an oxygen-excess atmosphere, a carrier made of a porous material ( There are those that carry a composite oxide having lattice defects of i) platinum or palladium and (ii) at least one metal selected from lanthanum and rare earth metals and transition metals (see Patent Document 1, etc.) .

JP-A-6-205975

Supervised by Yuichi Murakami, catalyst degradation mechanism and prevention measures, Technical Information Association, 1995 Trends in elemental technology for clean diesel development, NTS, November 2008 Shinichi Matsumoto, Catalyst, 52, No. 21, 2010

  However, Patent Document 1 and Non-Patent Documents 2 and 3 describe that CO and HC are oxidized and purified, but the purification efficiency is not sufficient. Further, when the heat load is applied, the catalyst activity is reduced, so that the purification efficiency is further reduced. Patent Document 1 and Non-Patent Documents 1 to 3 do not describe a method for dealing with the above problem.

  An object of the present invention is to provide an exhaust gas purification apparatus and an exhaust gas purification method for a heat engine that purifies carbon monoxide (CO) and hydrocarbons (HC) in an exhaust gas in an oxygen-excess atmosphere exhausted from a heat engine without reducing efficiency. And it is providing the CO and HC oxidation catalyst used for it.

  In order to achieve the above object, the present invention includes CO and HC, and is disposed in an exhaust gas flow path of a heat engine that exhausts exhaust gas in an oxygen atmosphere always exceeding the stoichiometric amount. Alternatively, in the exhaust gas purification apparatus of a heat engine equipped with CO and HC purification catalyst that oxidizes and purifies HC, the CO and HC purification catalyst is an inorganic compound porous carrier and a catalytically active component on the porous carrier. And at least one selected from Pt, Pd, Rh, Au and Ir supported, and the porous support contains at least one selected from Pr, Nd, Gd and La and Ce .

  In addition, after the inflow of exhaust gas to the CO, HC purification catalyst is stopped, an oxygen-containing gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less is circulated to the CO, HC purification catalyst. Gas supply means is further provided.

  According to the present invention, CO and HC contained in exhaust gas from a heat engine operated in an excessive oxygen atmosphere can be efficiently purified, and CO and HC emissions of the heat engine can be highly suppressed. .

The figure which shows CO purification activity about various CO and HC purification catalysts from which a carrier component differs. The figure which shows HC purification activity about various CO and HC purification catalysts from which a carrier component differs. The figure which shows CO purification activity about the CO and HC purification catalyst from which catalyst pretreatment conditions differ. The figure which shows CO purification activity about various CO and HC purification catalysts from which a carrier component differs. The figure which shows CO purification activity about various CO and HC purification catalysts from which a carrier component differs. The figure which shows CO purification activity about various CO and HC purification catalysts from which the amount of carriers differs. 1 is a schematic configuration diagram of an exhaust gas purification apparatus according to a first embodiment of the present invention. The schematic block diagram of the exhaust gas purification apparatus which concerns on the 2nd Embodiment of this invention.

Hereinafter, the present invention will be described in detail. In general, exhaust gas discharged from internal combustion engines typified by diesel engines such as passenger cars and construction machines and external combustion engines such as boilers and gas turbines often has an oxygen atmosphere that is in excess of the stoichiometric amount. In addition, the exhaust gas from these internal combustion engines and external combustion engines may generally contain CO and HC. In the present invention, the stoichiometric amount means the amount of O ₂ , CO, and HC when O ₂ and CO, HC contained in the exhaust gas react with each other without excess or deficiency.

When O ₂ , CO and HC are contained in the exhaust gas, the following chemical formulas (1) and (2) are considered as reactions in these three gases.

For example, when 300 ppm of CO and C ₃ H ₆ are present in the exhaust gas, 150 ppm and 1350 ppm of O ₂ are required for the reactions of the chemical formulas (1) and (2) to proceed. An oxygen atmosphere in excess of the stoichiometric amount means that the amount of oxygen that can oxidize all CO and HC. That is, when 300 ppm of CO and C ₃ H ₆ are present in the exhaust gas, this means a case where O ₂ is higher than 1500 ppm (= 150 ppm + 1350 ppm).

  As a result of intensive studies, the present inventors have found that a porous support of an inorganic compound and platinum (Pt), palladium (Pd), rhodium (Rh), gold (Au) supported on the porous support as catalytic active components. ), Iridium (Ir), ruthenium (Ru) and osmium (Os) and at least one metal selected from the group consisting of cerium (Ce) and praseodymium (Pr). , CO and HC in exhaust gas are effectively purified by using a CO and HC purification catalyst containing at least one rare earth element selected from neodymium (Nd), gadolinium (Gd) and lanthanum (La) It was made clear that.

  The inorganic oxide containing Ce, at least one selected from Pr, Nd, Gd, and La used as a support component has a high OSC ability and increases the amount of oxygen accumulated on the catalyst surface. Therefore, it is thought that the oxidation reaction of CO and HC is promoted. Furthermore, the heat resistance performance of the CO and HC purification catalyst is enhanced. It is considered that heat resistance is enhanced by combining Ce with at least one selected from Pr, Nd, Gd, and La. For Ce, Pr, Nd, Gd, and La may be combined in two or more elements. Pt, Pd, Rh, Au, Ir, Ru, and Os used as catalytic active components have high CO and HC oxidation ability, and it is considered that the CO and HC oxidation ability is improved dramatically in combination with the improvement of the OSC ability of the catalyst. It is done.

The HC to be purified is not particularly limited as long as it is composed of hydrogen and carbon. Examples include CH ₄ , C ₃ H ₆ , C ₂ H ₄ , C ₂ H ₂ , C ₃ H _{8 and the} like.

  When the operation of the diesel engine or boiler is stopped, the inflow of exhaust gas to the CO and HC purification catalyst is also stopped. The gas (oxygen-containing gas) with an oxygen concentration of 10% or more and a water vapor concentration of 3% or less after the inflow of exhaust gas is stopped until the exhaust gas inflow to the CO and HC catalyst starts. If the catalyst is allowed to flow through the HC purification catalyst, the CO and HC purification performance by the catalyst when the operation of the diesel engine or the like is restarted is enhanced. The reason is not clear, but by circulating a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less to the catalyst, at least one selected from Pr, Nd, Gd, and La and Ce This is probably because oxygen donation to the support containing oxygen is promoted, and a large amount of active oxygen accumulates on the catalyst surface.

  Oxygen contained in the exhaust gas discharged from the heat engine is about 3% to 10%, and the oxygen concentration may decrease depending on the operating conditions. Further, the concentration of water vapor contained in the exhaust gas is 5% or more, and at this concentration, moisture adheres to the catalyst surface, which may cause a decrease in activity. Most exhaust gases contain nitrogen oxides (NOx) and sulfur oxides (SOx). When the inflow of exhaust gas to the CO and HC purification catalyst stops, NOx and sulfur content (S content) may remain on the catalyst surface. NOx and S may adhere to the precious metal contained in the CO and HC purification catalyst and poison the precious metal. Furthermore, when oxides of Ce and Pr, Nd, Gd, and La are contained in the catalyst, these oxides are generally basic, so that NOx and S components easily adhere to the catalyst, and the CO and HC purification activity of the catalyst. Tends to decrease. If a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less is circulated, the moisture, NOx, and S adsorbed on the catalyst surface can be effectively removed, and the activity increases. Conceivable.

  A gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less for flowing into the CO or HC purification catalyst is not particularly limited as long as the conditions are met. An example of a preferred gas is air. The air contains about 21% oxygen, and oxygen donation to the catalyst is sufficiently promoted. However, since the saturated water vapor pressure increases as the air temperature increases, the water vapor concentration may exceed 3% depending on the air temperature. Therefore, in such a case, it is preferable to perform a water vapor concentration lowering operation using a dehumidifying material. Air is a preferable gas from the viewpoint of maintaining the activity of the catalyst because the content of poisoning components of the catalyst such as NOx and SOx is small. Further, instead of air, a gas composed only of oxygen or a mixed gas of oxygen and an inert gas may be used. For example, a mixed gas composed of 15% oxygen gas and 85% nitrogen gas can flow into the CO and HC purification catalyst. The type of inert gas is not limited to nitrogen gas. In addition to nitrogen gas, helium gas or argon gas can also be used.

  If the temperature of the catalyst layer when flowing a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less is 300 ° C to 700 ° C, preferably 350 ° C to 500 ° C, the operation is resumed. The CO and HC purification performance at the start is further enhanced. It is considered that by setting the temperature of the catalyst layer to 300 ° C. or higher, the oxygen scavenging reaction of the support containing at least one selected from Pr, Nd, Gd, and La and Ce is promoted. Further, it is considered that CO, HC, moisture, NOx, and S adsorbed or adhered to the CO, HC purification catalyst can be scattered and the surface exposure amount of the active component of the catalyst is increased. On the other hand, if the gas temperature is 700 ° C. or higher, thermal aggregation of the active components of the CO and HC purification catalyst is likely to occur, and there is a possibility that the activity is reduced due to thermal degradation.

  The method of setting the catalyst layer to 300 ° C. or more and 700 ° C. or less is not particular. For example, the temperature of the catalyst layer during diesel engine operation can reach 400 ° C. In that case, since the temperature of the catalyst layer is about 400 ° C. for a while even after the operation is stopped, a method of introducing air before the temperature of the catalyst layer decreases can be considered. A method of raising the temperature of the catalyst layer with a heater is also conceivable. In addition, after the temperature of the catalyst layer falls from the range of 300 ° C or more and 700 ° C or less, the inflow of gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less to the CO, HC purification catalyst is continued. However, since the moisture adsorbed or adhered to the catalyst can be scattered, there is an effect of increasing the surface exposure amount of the active component of the catalyst.

There is no particular concern on the means for flowing a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less into the CO or HC purification catalyst. In the case where the heat engine is a diesel engine, a method may be considered in which air taken in from the engine intake port is directly injected into the CO and HC purification catalyst without injecting fuel. It is also conceivable that the gas supply means is installed upstream of the CO and HC purification catalyst in the exhaust gas flow path and flows into the CO and HC purification catalyst. Furthermore, it is conceivable to install a preparation means for adjusting the oxygen concentration of the gas flowing in by the gas supply means to 10% or more. Furthermore, storage means (for example, a tank filled with a gas composed of oxygen and an inert gas such as N ₂ ) filled with a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less is installed. It is also conceivable that the gas in the storage means flows into the CO and HC purification catalyst via the gas supply means.

  If the porous carrier used for the CO and HC purification catalyst contains a complex oxide consisting of at least one selected from Pr, Nd, Gd and La and Ce, the CO and HC purification performance will be further improved. Rise. This is probably because Ce and Pr, Nd, Gd, and La are combined to form a complex oxide that strengthens the interaction and increases the OSC performance of the catalyst.

  The total content of Pr, Nd, Gd, La contained in the porous carrier is 10% by weight or more and 70% by weight or less with respect to the sum of the weights of Ce, Pr, Nd, Gd, La in terms of metal elements. It is desirable to be. If the total content of Pr, Nd, Gd, and La is less than 10% by weight or 70% by weight or more with respect to the sum of the weights of Ce, Pr, Nd, Gd, and La, the OSC ability of the catalyst is considered to decrease. It is done.

By using an oxide with a high specific surface area as a porous carrier, Pt, Pd, Rh, Au, Ir, Ru, and Os are highly dispersed, and CO and HC purification performance is enhanced. In particular, when a complex oxide composed of Ce and Nd is used as a porous carrier, high CO and HC purification performance can be obtained stably. The specific surface area of the porous support used in the present invention is preferably in the range of 30~800m ² / g, in particular in the range of 50 to 400 m ² / g are preferred.

  When two or more selected from Pt, Pd, Rh, Au, Ir, Ru, and Os are contained as catalytic active components, the CO and HC purification performance after thermal deterioration is enhanced. The reason is not clear, but it is thought that aggregation of noble metals is suppressed by alloying the active ingredients. In particular, when Pt and Pd or Pt and Rh are combined, the heat resistance performance is enhanced.

  The total supported amount of catalytically active components Pt, Pd, Rh, Au, Ir, Ru, Os is preferably 0.00005 mol part to 1.0 mol part in terms of element with respect to 2 mol part of the porous carrier, more preferably 0.0003 mol part to 0.3 mol part. If the total supported amount of Pt, Pd, Rh, Au and Ir is less than 0.00005 mol part, the effect of supporting is insufficient, while if it exceeds 1.0 mol part, the specific surface area of the active ingredient itself decreases, and further the catalyst Cost increases. Here, “mol part” means the content ratio of each component in terms of mol number. For example, the loading amount of B component is 1 mol part with respect to 2 mol part of A component, regardless of the absolute amount of A component. Means that

  The porous carrier may be supported on the substrate. As the base material, cordierite that has been used conventionally, ceramics made of Si-Al-O, or heat-resistant metal substrates such as stainless steel are suitable. When a substrate is used, the amount of the porous carrier supported is preferably 100 g or more and 300 g or less with respect to 1 L of the substrate in order to improve the CO and HC purification performance. If it is 100 g or less, the dispersion of the noble metal is lowered and the catalytic activity is lowered. On the other hand, when the weight is 300 g or more, when the substrate has a honeycomb shape, problems such as clogging of the gas flow path are likely to occur.

  As a preparation method of the CO, HC purification catalyst, for example, a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, a vapor deposition method, a preparation method using a chemical reaction, or the like is used. be able to. In particular, by using a preparation method utilizing a chemical reaction, the contact between the raw material of the catalytically active component and the porous carrier is strengthened, and sintering of the catalytically active component can be prevented.

  As starting materials for the CO and HC purification catalyst, various compounds such as nitric acid compounds, chlorides, acetic acid compounds, complex compounds, hydroxides, carbonate compounds, organic compounds, metals, and metal oxides can be used. For example, when two or more selected from Pt, Pd, Rh, Au, Ir, Ru, and Os are combined as the active component of the catalyst, co-impregnation using an impregnating solution in which the active component is present in the same solution The catalyst component can be uniformly supported by preparing by the method.

  The shape of the CO and HC purification catalyst can be appropriately adjusted according to the application. For example, the honeycomb structure obtained by coating the honeycomb structure made of various base materials such as cordierite, Si-Al-O, SiC, and stainless steel with the CO and HC purification catalyst of the present invention, pellets, and plates , Granular, powdery and the like. In the case of a honeycomb shape, it is preferable to use a structure made of cordierite or Si—Al—O as the base material. It is preferable to use a material (for example, a base material such as a metal honeycomb mainly composed of Fe). Alternatively, the honeycomb may be formed with only the porous carrier and the catalytically active component.

  Hereinafter, examples and embodiments of the present invention will be described.

<CO and HC purification catalyst preparation method>
A cordierite honeycomb (400 cells / inc ² ) is coated with a slurry prepared by adding Ce-Pr-O powder (1st rare element, Pr / (Pr + Ce) = 10 wt%) and alumina sol to water Then, it was dried by circulating hot air of 150 ° C. for 30 minutes. Furthermore, the obtained sample was fired at 600 ° C. for 1 hour in the air in an electric furnace to coat a honeycomb of Ce-Pr-O coated with 140 g of Ce-Pr-O per liter of apparent volume of the honeycomb Got. The Ce-Pr-O coated honeycomb was impregnated with a dinitrodiammine Pt nitric acid solution, dried by flowing hot air at 150 ° C. for 30 minutes, and then fired at 600 ° C. for 1 hour in an electric furnace.

  As a result, Example Catalyst 1 containing 140 g of Ce—Pr—O per liter of honeycomb and 5 wt% of Pt in terms of elements with respect to Ce—Pr—O was obtained.

Similarly, instead of Ce-Pr-O, Ce-Nd-O (first rare element, Nd / (Nd + Ce) = 10% by weight), Ce-Gd-O (first rare element, Gd / (Gd + Ce) = 10 wt%), Ce-La-O (manufactured by the first rare element, La / (La + Ce) = 10 wt%), respectively Example catalysts 2, 3, and 4 were obtained by the method of Further, Comparative Example Catalyst 1 was obtained in the same manner as Example Catalyst 1 except that CeO ₂ (manufactured by First Rare Element) was used instead of Ce—Pr—O as a comparative example catalyst. Table 1 shows a list of prepared catalysts. In the case of evaluating the heat resistance performance, samples were prepared by heat-treating each catalyst in an electric furnace at 800 ° C. for 50 hours.

<Catalyst performance evaluation method>
In order to evaluate the performance of the catalyst, a CO and HC purification performance test was conducted under the following conditions. A honeycomb catalyst having a capacity of 6 c.c. was fixed in a reaction tube made of quartz glass. This reaction tube was introduced into an electric furnace, and the temperature of the gas introduced into the reaction tube was controlled to be 200 ° C to 500 ° C.

As pretreatment of the honeycomb catalyst, the temperature was raised to 500 ° C. while 4.5 L / min of 10% O ₂ —N ₂ gas was circulated. Thereafter, the catalyst temperature was lowered to around 50 ° C., and then the following performance evaluation test was performed.

The reaction gas introduced into the reaction tube is a composition simulating exhaust gas in an oxygen-excess atmosphere, NOx: 300 ppm, C ₃ H ₆ : 300 ppm, CO: 300 ppm, CO ₂ : 6%, O ₂ : 10%, H ₂ O : 6%, N ₂ : Residual.

  At this time, the CO and HC purification performance of the catalyst was estimated by the CO and HC purification rate shown in the following equation. The volume space velocity was 45,000 / h.

CO purification rate (%) = ((CO amount flowing into the catalyst)-(CO amount flowing out from the catalyst)) ÷ (CO amount flowing into the catalyst) × 100
HC purification rate _{(%) = ((C 3} H 6 amount flowing into the catalyst) - (C ₃ H ₆ amount flowing out from the catalyst)) ÷ (C ₃ H ₆ amount flowing into the catalyst) × 100
<Examination results>
The CO purification rates of the initial product and the heat-treated product of Example Catalysts 1 to 4 and Comparative Example Catalyst 1 were evaluated. Fig. 1 shows the CO purification rate at 200 ° C. Compared to Comparative Example Catalyst 1, all of the Example Catalysts 1 to 4 showed improved activity in both the initial product and the heat-treated product. In particular, the heat-treated product of Example Catalyst 2 showed high activity. Further, FIG. 2 shows the HC purification activity of the initial product of each catalyst. As in the case of the CO purification activity, the example catalysts 1 to 4 showed higher purification performance than the comparative example catalyst 1. From this result, it is clear that the CO and HC purification activity of the catalyst is enhanced by using an oxide containing Pr, Nd, Gd, and La in Ce as a support.

<O ₂ distribution effect>
Using the initial product of Example catalyst 2, the influence on the CO and HC purification activity due to the difference in the presence or absence of the O ₂ -containing gas flow was evaluated. When the activity is evaluated after standing under a reaction gas at room temperature (comparative example conditions), after setting the catalyst layer to 400 ° C. and flowing 10% O ₂ —N ₂ gas (without water vapor) for 5 minutes The case where the catalyst temperature was lowered to 100 ° C. and the activity was evaluated (Example conditions) was compared. The CO and HC purification activity was evaluated by raising the catalyst temperature from 100 ℃ to 400 ℃ while circulating the reaction gas. FIG. 3 shows the CO purification activity.

  Under the comparative example conditions, the catalyst temperature decreased when the catalyst temperature was increased. This is probably due to moisture adhering to the catalyst. Along with that, the CO purification activity decreased. This is probably because the active component of the catalyst was poisoned by HC and NOx adhering to the catalyst in addition to the decrease in the catalyst temperature. On the other hand, under the example conditions, no decrease in the catalyst temperature was observed, and high CO purification activity was exhibited.

  From the above results, until the reaction gas flow to the catalyst is finished and the reaction gas flow is started again, the catalyst temperature is raised and a gas containing 10% or more of oxygen and 3% or less of water vapor is circulated. It is clear that the purifying activity is increased by keeping.

  Regarding Example Catalyst 2, the content ratio of Ce and Nd was changed. FIG. 4 shows the CO purification activity at 200 ° C. of the catalyst after the heat treatment with respect to the Nd content ratio. It can be seen that when the Nd content is 10 wt% or more and 70 wt% or less, the CO purification activity exceeds 60%, indicating a high CO purification activity.

  For Example Catalysts 1 to 4 and Comparative Example Catalyst 1, the same preparations as Example Catalysts 1 to 4 and Comparative Example Catalyst 1 were carried out except that Pd was used as the active component in addition to Pt. 8 and Comparative Example catalyst 2 were obtained. Pt and Pd were added by impregnating a mixed solution of Pt and Pd instead of Pt solution. The amount of Pd added was 0.5 wt% with respect to the support. Table 2 shows a list of catalysts.

  FIG. 5 shows the CO purification activity at 200 ° C. after the heat treatment. It can be seen that Example Catalysts 5 to 8 have high performance with a CO purification activity of 70% or more.

<Amount of carrier>
In Example Catalyst 2, the CO purification activity when the amount of Ce—Nd—O support was changed was evaluated. FIG. 6 shows the CO purification activity of the initial product at 200 ° C. and 250 ° C. when the amount of Ce—Nd—O carrier is changed. FIG. 6 shows that when the amount of the Ce—Nd—O carrier is 100 g or more and 300 g or less with respect to 1 L of the honeycomb, the CO purification rate exceeds 90% and shows high CO purification activity.
<Gas supply means to CO, HC purification catalyst>
Next, an embodiment according to the exhaust gas purification apparatus of the present invention will be described with reference to the drawings. Here, an embodiment relating to means (gas supply means) for supplying a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less to the upstream side of the CO and HC purification catalyst will be mainly described.

  FIG. 7 is a schematic configuration diagram of the exhaust gas purifying apparatus according to the first embodiment of the present invention. The exhaust gas purifying apparatus shown in this figure purifies exhaust gas from the diesel engine 1 and includes a controller (control apparatus) 9 for controlling the engine 1 and the like.

  The diesel engine 1 includes a turbocharger (hybrid turbo) 7. The air in the combustion chamber (cylinder) 1 a is compressed by a piston 1 b to a high temperature, and fuel is supplied to the compressed air via a fuel injection device 2. And gaining power by spontaneous ignition. Further, the diesel engine 1 includes an intake valve 1c between the intake pipe 11 and the combustion chamber 1a, and an exhaust valve 1d between the combustion chamber 1a and the exhaust pipe 3. Although one intake / exhaust valve 1c, 1d is shown in FIG. 7, the number of each valve is not limited to this.

  The turbocharger 7 includes a compressor (compression device) 7a, a motor 7b, and a turbine 7c. The compressor 7a is installed in an intake pipe 11 connected to an intake device (not shown), and is driven by at least one of a motor 7b and a turbine 7c to compress intake air (atmosphere), which is compressed in the combustion chamber 1a. To supply. The motor 7b is for driving the compressor 7a, and an inverter device 8 is connected to the motor 7b. Inverter device 8 in the present embodiment converts DC power from battery (power storage device) 10 into AC power, supplies it to motor 7b, and drives and controls motor 7b based on a command from controller 9. The turbine 7c is installed in the exhaust pipe 3, receives the exhaust from the combustion chamber 1a, and rotationally drives the compressor 7a installed coaxially. Purifying catalysts 5 and 6 are installed on the outlet side of the turbine 7 c in the exhaust pipe 3, and the exhaust gas that has rotated the turbine 7 c is supplied to the purifying catalysts 5 and 6.

  The purification catalysts 5 and 6 oxidize and purify CO or HC in the exhaust gas (CO, HC purification catalyst), and are installed in the exhaust pipe 3 on the downstream side of the turbine 7c. In the present embodiment, as shown in FIG. 7, two types of purification catalysts (first purification catalyst 5 and second purification catalyst 6) are used. The embodiment catalyst 6 is used as the first purification catalyst 5 installed relatively upstream, and the embodiment catalyst 2 is used as the second purification catalyst 6 installed relatively downstream. . The shape of the purification catalysts 5 and 6 can be appropriately adjusted according to the application. For example, a honeycomb structure obtained by coating purification catalysts 5 and 6 on a honeycomb structure made of various base materials such as cordierite, Si-Al-O, SiC, stainless steel, pellets, plates, granules, Examples include powder.

  A filter (not shown) is installed on the downstream side of the purification catalysts 5 and 6, and particulate matter (particulate matter: PM) in the exhaust gas is collected by the filter.

In the exhaust gas purification apparatus of the present embodiment configured as described above, when the operation of the diesel engine 1 is stopped, the motor 7b is driven via the controller 9 and the inverter device 8, and the intake valve 1c and the exhaust valve 1d. And the intake pipe 11, the combustion chamber 1a, and the exhaust pipe 3 are communicated. Note that exhaust gas is present in the honeycomb flow paths of the example catalysts 6 and 2 when the operation of the engine 1 is stopped, and the O ₂ concentration is approximately 10% and the water vapor concentration is approximately 6%.

  When the motor 7b is driven as described above, the compressor 7a is driven, so that air is introduced into the combustion chamber 1a, the exhaust pipe 3, and the purification catalysts 5, 6 via the intake pipe 11. The temperature of the purification catalyst immediately after the engine is stopped is about 400 ° C., and air is introduced into the purification catalysts 5 and 6 through the compressor 7a, so that the air containing 21% oxygen is purified at about 400 ° C. Can be contacted. Furthermore, although depending on the temperature and humidity of the atmosphere, for example, when the temperature of the atmosphere is 25 ° C. and the humidity is 60%, the concentration of water vapor contained in the air is 1.9%, which is also preferable from the viewpoint of water vapor concentration. It becomes. When the water vapor concentration in the atmosphere is high, it is preferable to suppress the water vapor concentration to 3% or less by a preparation means such as a dehumidifying material.

  As a result of the above processing, the accumulation of oxygen on the surfaces of the purification catalysts 5 and 6 is promoted, and further, CO, HC, and moisture adhering to the catalyst surfaces are removed. Therefore, when the diesel engine 1 is started again. High CO and HC purification activity can be obtained.

  As a power source for the motor 7, a capacitor or an external power source may be used instead of the battery 10. In addition, in order to start the purification process after the exhaust gas inflow to the purification catalysts 5 and 6 has stopped reliably, a timer that measures the elapsed time after the engine stops is installed, and the measurement time of the timer reaches a predetermined value. It is good also as starting the atmospheric supply to the purification catalysts 5 and 6 when it does.

  FIG. 8 is a schematic configuration diagram of an exhaust gas purification apparatus according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same part as FIG. 7, and description is abbreviate | omitted. The exhaust gas purifying apparatus shown in this figure includes a gas tank 16, a pump 15, and a gas supply pipe 13.

  A gas tank (storage means) 16 stores a gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less. The gas to be filled in the gas tank 16 is not particularly limited as long as the above conditions are met. An example of a preferred gas is air. Further, instead of air, a gas composed only of oxygen or a mixed gas of oxygen and an inert gas may be used. The type of inert gas is not limited to nitrogen gas. In addition to nitrogen gas, helium gas or argon gas can also be used.

  The gas supply pipe 13 connects the gas tank 16 and the exhaust pipe 3, and the end of the gas supply pipe 13 on the exhaust pipe 3 side opens between the combustion chamber 1 a and the purification catalysts 5 and 6. A pump 15 is installed in the gas supply pipe 13. In the gas supply pipe 13 shown in FIG. 8, a check valve 19 is installed on the downstream side (discharge side) of the pump 15. The check valve 19 is closed so that gas does not flow into the exhaust pipe 3 while the pump 15 is stopped. The check valve 19 is opened when the discharge pressure of the pump 15 reaches a predetermined value, and the gas supply pipe 13 and the exhaust pipe are opened. 3 is communicated.

  The pump 15 is for supplying the gas in the gas tank 16 into the exhaust pipe 3 through the gas supply pipe 13 and is driven by the electric motor 17. An inverter device 18 is connected to the motor 17. The inverter device 18 converts DC power from the battery (power storage device) 10 into AC power, supplies the AC power to the motor 7 b, and drives and controls the motor 17 based on a command from the controller 9. Instead of the pump 15, a compressor may be used as in the embodiment shown in FIG.

  In this embodiment, the purification catalysts 5 and 6 also use the example catalyst 6 as the first purification catalyst 5 and use the example catalyst 2 as the second purification catalyst 6.

  In the exhaust gas purification apparatus of the present embodiment configured as described above, when the operation of the diesel engine 1 is stopped, the motor 17 is driven via the controller 9 and the inverter device 18. As a result, the pump 15 is driven, so that the gas in the gas tank 16 can be introduced into the purification catalysts 5 and 6 through the exhaust pipe 3. Therefore, also in the present embodiment, the accumulation of oxygen on the surfaces of the purification catalysts 5 and 6 is promoted, and further, CO, HC and moisture adhering to the catalyst surfaces are removed, so the diesel engine 1 is started again. High CO and HC purification activity can be obtained.

  As a gas storage means, a gas cylinder may be connected instead of the gas tank 16. In this case, since the gas in the storage means is sufficiently pressurized, the pump 15 may be omitted and the gas supply may be controlled by installing a valve device in the gas supply pipe 13. Further, instead of installing the gas tank 16, the end of the gas supply pipe 13 on the gas tank 16 side may be opened to the atmosphere, and the atmosphere may be introduced into the purification catalysts 5 and 6 after the engine 1 is stopped. In this case, a preparation means for suppressing the water vapor concentration to 3% or less as in the previous embodiment may be used.

  Further, as a power source for the motor 17, a capacitor or an external power source may be used instead of the battery 10. Further, in order to start the purification process after the exhaust gas inflow to the purification catalysts 5 and 6 has stopped reliably, a timer for measuring the elapsed time after the engine is stopped is installed, and the measurement time of the timer reaches a predetermined value. Then, the air supply to the purification catalysts 5 and 6 by the pump 15 may be started.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 1a ... Combustion chamber, 1b ... Piston, 1c ... Intake valve, 1d ... Exhaust valve, 2 ... Fuel injection device, 3 ... Exhaust pipe, 5 ... First purification catalyst, 6 ... Second purification catalyst, 7 ... Turbocharger, 7a ... compressor, 7b ... motor, 7c ... turbine, 8 ... inverter device, 9 ... engine controller, 10 ... battery, 13 ... gas supply pipe, 15 ... pump, 16 ... gas tank, 17 ... motor, 18 inverter device , 19 ... Check valve

Claims (15)

CO and HC purification catalyst that is disposed in the exhaust gas flow path of a heat engine that exhausts exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount in the oxidation reaction of CO and HC, and oxidizes and purifies CO or HC in the exhaust gas In an exhaust gas purification device for a heat engine comprising:
The CO, HC purification catalyst is a porous carrier of an inorganic compound, and at least one selected from Pt, Pd, Rh, Au, Ir, Ru, Os supported as a catalytic active component on the porous carrier. Have
An exhaust gas purification apparatus for a heat engine, wherein the porous carrier contains Ce and contains at least one selected from Pr, Nd, Gd, and La. The exhaust gas purification apparatus for a heat engine according to claim 1,
An exhaust gas purification apparatus for a heat engine, further comprising gas supply means for circulating an oxygen-containing gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less to the CO and HC purification catalyst. The exhaust gas purification apparatus for a heat engine according to claim 2,
The exhaust gas purification apparatus, wherein the gas supply means supplies the oxygen-containing gas to the CO and HC purification catalyst after the inflow of exhaust gas to the CO and HC purification catalyst stops. The exhaust gas purification apparatus for a heat engine according to claim 2 or 3,
The exhaust gas purifying apparatus for a heat engine, wherein the oxygen-containing gas further contains at least one selected from N ₂ , He, and Ar. In the exhaust gas purification apparatus for a heat engine according to any one of claims 2 to 4,
An exhaust gas purifying apparatus for a heat engine, wherein the oxygen-containing gas is air. The exhaust gas purification apparatus for a heat engine according to any one of claims 2 to 5,
The exhaust gas purifying apparatus for a heat engine, wherein the temperature of the purifying catalyst is 300 ° C or higher and 700 ° C or lower while the oxygen-containing gas is allowed to flow into the CO and HC purifying catalyst. The exhaust gas purification apparatus for a heat engine according to any one of claims 2 to 6,
An exhaust gas purification apparatus for a heat engine, further comprising a preparation means for adjusting an oxygen concentration of the oxygen-containing gas supplied to the gas supply means to 10% or more. The exhaust gas purification apparatus for a heat engine according to any one of claims 2 to 7,
The exhaust gas purifying apparatus for a heat engine, wherein the gas supply means is an electric compressor for compressing the atmosphere and supplying the compressed air to the heat engine. The exhaust gas purification apparatus for a heat engine according to any one of claims 2 to 7,
The exhaust gas purifying apparatus for a heat engine, wherein the gas supply means is an electric pump for supplying the oxygen-containing gas into a pipe line connecting the heat engine and the exhaust gas purifying apparatus. The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 9,
An exhaust gas purification apparatus for a heat engine, wherein the porous carrier contains a composite oxide composed of Ce and at least one selected from Pr, Nd, Gd, and La. The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 10,
The total weight of Pr, Nd, Gd, La contained in the porous carrier is 10 wt% or more and 70 wt% or less of the total weight of Ce, Pr, Nd, Gd, La in terms of metal elements Exhaust gas purification device for heat engine. The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 11,
An exhaust gas purification apparatus for a heat engine, wherein the CO, HC purification catalyst contains at least two or more selected from Pt, Pd, Rh, Au, Ir, Ru, Os as the catalytic active component. The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 12,
The exhaust gas purifying apparatus for a heat engine, wherein the porous carrier is supported on a base material and is contained in an amount of 100 g to 300 g with respect to the base material 1L. A CO and HC purification catalyst that oxidizes and purifies CO and HC in an oxygen atmosphere in excess of the stoichiometric amount,
A porous carrier of an inorganic compound;
Having at least one selected from Pt, Pd, Rh, Au, Ir, Ru, and Os supported as a catalytically active component on the porous support;
A CO, HC purification catalyst, wherein the porous carrier contains at least one selected from Pr, Nd, Gd, and La and Ce. A porous carrier of an inorganic compound, and at least one selected from Pt, Pd, Rh, Au, Ir, Ru, and Os supported as a catalytically active component on the porous carrier, the porous carrier In the exhaust gas purification method using a CO, HC purification catalyst containing at least one selected from Pr, Nd, Gd, La and Ce,
An exhaust gas characterized in that after the inflow of exhaust gas to the CO, HC purification catalyst stops, the gas having an oxygen concentration of 10% or more and a water vapor concentration of 3% or less is circulated to the CO, HC purification catalyst. Purification method.

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