JP2009297628A - APPARATUS AND METHOD FOR CLEANING EXHAUST GAS OF HEAT ENGINE AND NOx CLEANING CATALYST - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for cleaning the exhaust gas of heat engines which cleans NO<SB>x</SB>in the exhaust gas of an oxygen excessive atmosphere with a high NO<SB>x</SB>cleaning capability and an NO<SB>x</SB>cleaning catalyst used in them. <P>SOLUTION: An NO<SB>x</SB>cleaning catalyst cleaning NO<SB>x</SB>in exhaust gas by reduction with CO as a reducing agent is arranged in an exhaust gas passage of a heat engine emitting an exhaust gas of an atmosphere excessive in oxygen with respect to the stoichiometric quantity. The NO<SB>x</SB>cleaning catalyst comprises a porous support containing cerium (Ce) and catalytically active ingredients supported on the porous support and including at least one selected from silver (Ag), iridium (Ir), rhodium (Rh), platinum (Pt) and palladium (Pd) and cobalt (Co). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying apparatus, an exhaust gas purifying method, and an NOx purifying catalyst used therefor for purifying nitrogen oxides (NOx) in exhaust gas in an oxygen-excess atmosphere exhausted from a heat engine.

  In recent years, there has been an increase in the number of heat engines that operate under an oxygen-rich atmosphere, such as lean burn engines, diesel engines, gas turbines, chemical plants, etc., where the air-fuel ratio (ratio of air to fuel in the gas) is lean. Accordingly, a method for purifying nitrogen oxide (NOx) under excess oxygen is required.

  As a method of purifying NOx even under excess oxygen, a method of selectively catalytically reducing NOx on a titanium oxide catalyst using ammonia as a reducing agent has been proposed and applied to exhaust gas purification of boilers and gas turbines. (For example, refer to Patent Document 1).

  However, since ammonia has an irritating odor, there is a problem in safety, and further, the cost of ammonia itself is high.

  Therefore, a method for reducing and purifying NOx using a reducing agent such as hydrogen, carbon monoxide (CO), and hydrocarbon (HC) originally contained in the exhaust gas has been proposed.

  For example, Patent Document 2 describes a method of reducing and purifying NOx using a NOx purifying catalyst supporting rhodium (Rh) and silver on a porous carrier made of a metal oxide, and an excess of oxygen. The simultaneous removal of hydrocarbons, CO and NOx in exhaust gas containing benzene is described.

  Patent Document 3 describes that the reduction efficiency of NOx in exhaust gas containing oxygen is increased by incomplete combustion of hydrocarbons in exhaust gas.

  In Patent Document 4, when a NOx storage catalyst is used, when the air-fuel ratio is lean, NOx in the exhaust gas is once oxidized and trapped by the catalyst, and when a certain amount of NOx is trapped, the air-fuel ratio is stoichiometric or A technique for purifying trapped NOx by switching to rich is described.

  Furthermore, Patent Document 5 describes a purification device in which a hydrogen generation catalyst is installed in front of a NOx storage catalyst. Patent Document 5 describes that by using a hydrogen generation catalyst containing a noble metal, the steam reforming reaction proceeds and the activity is improved.

  However, Patent Documents 2 and 3 describe that NOx is reduced and purified using hydrocarbons, CO, or products during incomplete combustion, but the purification efficiency for NOx is not sufficient. Furthermore, NOx cannot be efficiently purified unless hydrocarbons are present in the exhaust gas. Further, according to the technique disclosed in Patent Document 4, although the NOx reduction efficiency is increased, it is necessary to make the air-fuel ratio rich, and engine control is indispensable, so that it is difficult to apply to plants such as boilers. . Furthermore, fuel consumption is reduced because a large amount of fuel is consumed when rich. Even in the technique disclosed in Patent Document 5, it is necessary to make the air-fuel ratio rich in order to cause the steam reforming reaction, and the same problems as in Patent Document 4 occur. Patent Documents 2 to 5 do not describe a method for dealing with the above problem.

Japanese Examined Patent Publication No. 52-22839 JP-A-8-998 JP-A-6-319953 JP 11-319564 A JP 2003-10646 A

  An object of the present invention is to provide an exhaust gas purification device for an exhaust gas, an exhaust gas purification method, and a NOx purification catalyst used therefor, which purify NOx in exhaust gas in an oxygen-excess atmosphere with high NOx purification performance.

  That is, the exhaust gas purification apparatus for a heat engine according to the present invention is disposed in an exhaust gas flow path of a heat engine that exhausts exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount, and the exhaust gas using carbon monoxide (CO) as a reducing agent. An exhaust gas purification apparatus for a heat engine comprising a NOx purification catalyst that reduces and purifies nitrogen oxides (NOx) therein, wherein the NOx purification catalyst contains cerium (Ce), and the porous carrier And a catalytically active component containing at least one selected from silver (Ag), iridium (Ir), rhodium (Rh), platinum (Pt) and palladium (Pd) and cobalt (Co). It is characterized by that.

  The exhaust gas purification method for a heat engine according to the present invention includes a porous support containing Ce, a catalyst supported on the porous support and containing at least one selected from Ag, Ir, Rh, Pt and Pd, and Co. Using a NOx purification catalyst having an active component, CO is used as a reducing agent to reduce and purify NOx in exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount discharged from the heat engine. .

  The NOx purification catalyst of the present invention is a NOx purification catalyst that reduces and purifies NOx in exhaust gas in an oxygen atmosphere in excess of the stoichiometric amount using CO as a reducing agent, a porous carrier containing Ce, It is supported on the porous carrier and comprises at least one selected from Ag, Ir, Rh, Pt and Pd, and a catalytically active component containing Co.

In the present invention, the stoichiometric amount means the amount of O ₂ and CO when O ₂ and CO contained in the exhaust gas react with each other without excess or deficiency.

When O ₂ , CO and NO are contained in the exhaust gas, the following equations (1) and (2) can be considered as reactions in these three gases.

2NO + 2CO → 2CO ₂ + N ₂ (1)
2CO + O ₂ → 2CO ₂ (2)
For example, when 1000 ppm of CO is present in the exhaust gas, if O ₂ is 500 ppm or less, CO remains even if the formula (2) is advanced over the formula (1), and the reaction of the formula (1) May be more likely to occur.

On the other hand, an oxygen atmosphere that is excessive than the stoichiometric amount means that the amount of oxygen that can be completely oxidized by CO when the formula (2) advances preferentially. That is, when 1000 ppm of CO is present in the exhaust gas, this means a case where O ₂ is greater than 500 ppm. In this case, if the formula (2) preferentially proceeds, all the CO is oxidized and the reaction of the formula (1) does not proceed.

  According to the exhaust gas purification method, exhaust gas purification device, and NOx purification catalyst of the present invention, NOx contained in exhaust gas from a heat engine operated in an excessive oxygen atmosphere can be efficiently purified using CO as a reducing agent. It is possible to suppress the NOx emission amount of the heat engine.

  Hereinafter, the present invention will be described in detail.

  In general, exhaust gas discharged from a boiler or the like is often in an oxygen atmosphere that is in excess of the stoichiometric amount. Since the exhaust gas from the boiler contains CO in addition to NOx, NOx is reduced and purified if the reduction reaction of the following formula (3) proceeds. However, since it is an oxygen atmosphere, in many cases, the combustion reaction of CO proceeds with priority, and the reaction of the formula (3) hardly proceeds.

NOx + CO → N ₂ , CO ₂ (3)
As a result of intensive studies, the inventors of the present invention have used a porous carrier containing cerium (Ce) as a NOx purification catalyst that purifies NOx in exhaust gas using CO as a reducing agent, and is supported on the porous carrier and silver. A NOx purification catalyst comprising at least one selected from (Ag), iridium (Ir), rhodium (Rh), platinum (Pt) and palladium (Pd) and a catalytic active component containing Co (cobalt) is used. Then, it was clarified that the reaction of the formula (3) proceeds and NOx is purified.

  Coexistence with at least one selected from Ag, Ir, Rh, Pt and Pd as a catalytically active component makes it easy for NOx to dissociate into N and O, and furthermore, high oxygen storage as a porous carrier. By using Ce having the capacity, O generated by dissociating NOx is easily taken into the porous carrier, and the dissociation reaction of NOx is promoted. O taken in the porous carrier is removed by CO according to the equation (6). Further, the reaction of the formula (4) proceeds, so that the reaction of the formula (5) easily proceeds.

NOx → N + O (4)
N + N → N ₂ (5)
O + CO → CO ₂ (6)
The porous carrier is not limited as long as it has an oxygen storage capacity with Ce, and for example, ceria (CeO ₂ ), ceria-zirconia (eg, Ce _0.1 Zr _0.9 O ₂ , Ce _0.3 Zr _0.7 O _2). , Ce _0.5 Zr _0.5 O ₂ , Ce _0.7 Zr _0.3 O ₂ , Ce _0.9 Zr _0.1 O ₂ ), etc., and at least one of praseodymium (Pr) and yttrium (Y) may be added thereto. Good.

  The porous carrier may be supported on the substrate. In this case, in order to improve the NOx purification performance, the loading amount of the porous carrier is preferably 50 g or more and 400 g or less with respect to 1 L of the base material. When the loading amount of the porous carrier is less than 50 g, the effect of the porous carrier becomes insufficient. On the other hand, when the loading amount exceeds 400 g, the specific surface area of the porous carrier itself is reduced, and this is the case when the substrate has a honeycomb shape. Clogging is likely to occur.

  The supported amount of Co as the catalytically active component is preferably 0.005 mol part or more and 2.5 mol part or less, more preferably 0.01 mol part or more and 2 mol part or less in terms of element with respect to 1.9 mol part of the porous carrier. It is as follows. When the amount of Co supported is less than 0.005 mol part, the effect of supporting is insufficient. On the other hand, when the amount exceeds 2.5 mol part, the specific surface area of the catalyst itself decreases and the activity tends to decrease. The amount of Ag supported as the catalytically active component is the same as that of Co described above. Here, the mol part means the content ratio of each component in terms of mol number. For example, when the loading amount of B component is 1 mol part with respect to 2 mol part of A component, the loading of B component is 1 with respect to A component 2 in terms of mol, regardless of the absolute amount of A component. Means that

  The supported amount of Ir as the catalytically active component is preferably 0.001 mol part or more and 0.5 mol part or less, more preferably 0.002 mol part or more and 0.00 mol part or less, in terms of element with respect to 1.9 mol part of the porous carrier. 4 mol parts or less. When the amount of Ir supported is less than 0.001 mol part, the effect of supporting is insufficient. On the other hand, when the amount exceeds 0.5 mol part, the specific surface area of the catalyst itself decreases and the catalyst cost increases. The supported amounts of the catalytically active components Rh, Pt, and Pd are the same as for Ir described above.

  The particle diameter of the catalytically active component Co is preferably 1 nm or less in order to promote the NOx purification reaction. Thereby, the catalytically active component can be highly dispersed, the surface area of the catalytically active component can be improved, and the catalytic performance peculiar to the fine particles can be expressed. The particle diameter of Co can be adjusted by controlling the raw material of the catalytic active component, the catalyst preparation temperature, the contact time between the porous carrier and the catalytic active component raw material during catalyst preparation, and the like.

  As a preparation method of the NOx 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. it can. Among them, an adjustment method using a chemical reaction is preferable, and the contact between the raw material of the catalytically active component and the porous carrier becomes strong, and sintering of the catalytically active component can be prevented.

As a starting material for the NOx purification catalyst, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonate compounds, organic compounds, metals, and metal oxides can be used. The catalytically active component Co is preferably prepared using a metal alkoxide, a carbonyl compound, or an organometallic compound such as Co (CO) ₃ NO as a starting material. For example, Co (Oi-C ₃ H ₇ ) ₂ , More preferably, Co ₄ (CO) ₁₂ is used as a starting material. By reacting these with OH groups on the porous carrier, Co can be uniformly dispersed and supported on the porous carrier.

  The shape of the NOx purification catalyst can be appropriately adjusted according to the application. For example, the honeycomb shape obtained by coating the NOx purification catalyst of the present invention on a honeycomb structure made of various materials such as cordierite, SiC, stainless steel, etc. First, pellets, plates, granules, powders, and the like can be mentioned. In the case of the honeycomb shape, cordierite is optimal as the base material. However, when there is a risk that the catalyst temperature may increase, it is preferable to use a base material that does not easily react with the catalytic active component, for example, a metal base material. . Alternatively, the honeycomb may be formed with only the porous carrier and the catalytically active component.

  When the flow rate of the exhaust gas contacting the NOx purification catalyst is F and the volume of the catalyst is V, the volume space velocity (F / V) is preferably 30000 / h or less. Thereby, a high NOx purification activity can be obtained, and a NOx purification reaction can be promoted.

  Adjust the amount of CO so that the amount of HC contained in the exhaust gas in contact with the NOx purification catalyst is equivalent to or less than the amount of CO in the exhaust gas in contact with the catalyst in terms of carbon atoms. It is preferable that the CO amount adjusting means or the HC amount adjusting means for adjusting the HC amount is disposed in front of the NOx purification catalyst. The CO amount adjusting means adjusts the CO amount by injecting CO into the exhaust gas flow path, and includes, for example, a CO tank and a CO inlet. The HC amount adjusting means reduces the HC amount relative to the CO amount, and is, for example, an HC adsorbent. By reducing the amount of HC relative to the amount of CO in this way, it becomes difficult for HC in the exhaust gas to come into contact with the NOx purification catalyst, and it is possible to prevent HC from being adsorbed by the catalytically active component of the catalyst, and CO is used as a reducing agent. The reduction reaction of NOx easily proceeds.

  The HC amount and CO amount may be adjusted by adjusting the combustion state of the heat engine.

  There are cases where the amount of CO flowing into the NOx purification catalyst is less than the amount capable of purifying all of the NOx in the exhaust gas. In that case, the CO amount adjusting means described above injects CO into the exhaust gas passage to increase the amount of CO in contact with the NOx purification catalyst.

  When the CO oxidation rate of the NOx purification catalyst is high, CO is consumed in the vicinity of the inlet of the NOx purification catalyst layer, so that the CO does not spread over the entire NOx purification catalyst, and the NOx purification reaction may not occur efficiently. . In this case, it is preferable to install a plurality of NOx purification catalysts along the exhaust gas flow path, and to further dispose the CO amount adjusting means in the exhaust gas flow path between the NOx purification catalyst and the NOx purification catalyst.

  The above-mentioned CO amount adjusting means may be arranged in the preceding stage of the NOx purification catalyst so that the amount of CO flowing into the NOx purification catalyst is three times or more in molar ratio with respect to the amount of NOx in contact with the catalyst. preferable. When the CO oxidation rate of the NOx purification catalyst is high, a part of CO is consumed in the vicinity of the inlet of the NOx purification catalyst layer, and CO does not reach the entire NOx purification catalyst. Thus, the NOx purification reaction can be promoted by adjusting the amount of CO in contact with the NOx purification catalyst by the CO amount adjusting means.

  The adjustment of the CO amount relative to the NOx amount may be performed by adjusting the combustion state of the heat engine.

When the amount of CO or HC flowing into the NOx purification catalyst is less than the amount capable of purifying all NOx in the exhaust gas, a catalyst that reduces NOx using NH ₃ as a reducing agent before or after the NOx purification catalyst That is, an NH ₃ denitration catalyst may be arranged. In this case, in front of the NH ₃ denitration catalyst, by placing the NH ₃ supply means having a NH ₃ tank and NH ₃ inlet, supplying the NH ₃ as a reducing agent to the catalyst. Thereby, NOx is reduced and purified by the NH ₃ denitration catalyst. As the NH ₃ denitration catalyst, for example, a catalyst using titanium oxide (TiO ₂ ) or zeolite as a carrier and containing vanadium (V), iron (Fe), molybdenum (Mo) or the like as active components can be used.

This NH ₃ denitration catalyst can be mixed and integrated with the NOx purification catalyst of the present invention, and NOx can be purified by introducing CO and NH ₃ as reducing agents. In this case, the space required for installing the catalyst can be reduced.

  The present invention can be suitably used for a heat engine that exhausts exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount. The present invention can also be used in a heat engine that discharges exhaust gas in an oxygen atmosphere (rich gas) that is equal to or less than the stoichiometric amount. In this case, the fuel added to the heat engine or the exhaust gas passage is used. This is likely to increase costs. Therefore, in particular, unless the air-fuel ratio needs to be rich, the combustion state of the heat engine is adjusted and the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst is not switched intermittently from the stoichiometric to rich state. It is preferable to maintain a lean state.

  When the amount of CO flowing into the NOx purification catalyst is less than the amount that can completely purify NOx in the exhaust gas, the amount of CO and NOx flowing into the NOx purification catalyst is adjusted by adjusting the combustion state of the heat engine. May be adjusted. In this case, the CO amount adjusting means for adjusting the CO amount by injecting CO into the exhaust gas passage becomes unnecessary.

  A NOx sensor may be provided after the NOx purification catalyst. The NOx sensor measures the amount of NOx contained in the subsequent stage of the NOx purification catalyst, that is, the amount of NOx remaining without being purified by the NOx purification catalyst. The amount of CO flowing into the NOx purification catalyst is adjusted according to the measurement result of the NOx amount by the NOx sensor. As a result of measurement by the NOx sensor, when a large amount of NOx remains in the subsequent stage of the NOx purification catalyst, the above-mentioned CO amount adjusting means is arranged in the previous stage of the NOx purification catalyst, and the exhaust flow before the NOx purification catalyst is arranged. Adjustment is made so that the amount of CO flowing into the NOx purification catalyst is increased by injecting CO into the passage. On the other hand, as a result of measurement by the NOx sensor, if the amount of NOx is so small that it cannot be measured after the NOx purification catalyst, the amount of CO injected by the CO amount adjusting means may be reduced. In addition to the CO amount adjusting means, the amount of CO flowing into the NOx purification catalyst can also be adjusted by adjusting the combustion state of the heat engine. Thus, by measuring the NOx amount at the latter stage of the NOx purification catalyst with the NOx sensor, high NOx purification activity can be maintained, CO outflow to the atmosphere can be reduced, and the amount of NOx remaining without being purified can be reduced. An optimum amount of CO to be reduced can be determined.

〔Example〕
Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Preparation method of NOx purification catalyst)
Commercially available CeO ₂ (Daiichi Rare Element Chemical Industries, Ltd., HS) was placed in a Schlenk flask, vacuum degassed at 200 ° C. for 9 hours, dehydrated THF (tetrahydrofuran) was added, and the Schlenk flask was added. CeO ₂ was suspended in THF under N ₂ . In addition, Co (Oi-C ₃ H ₇ ) ₂ , which is an alkoxide of Co, was placed in another Schlenk flask under N ₂ and dissolved in THF. Next, this Co solution was added to CeO ₂ suspended in THF and stirred for 15 h. Thereafter, the stirring was stopped, after removal of the THF by vacuum evacuation, 120 ° C. × 2h drying treatment, further 400 ° C. × 2h heat treatment of the catalyst active ingredients by performing Co is CeO ₂ that is supported in the catalyst in air A Co / CeO ₂ powder was obtained. The amount of Co added was 0.6 mmol in terms of metal element with respect to 1 g of CeO ₂ . Next, the obtained Co / CeO ₂ powder was impregnated with water in which Ag nitrate was dissolved in water, and subjected to a drying treatment at 120 ° C. for 2 hours and a heat treatment at 400 ° C. for 2 hours in the air. By the above method, Example catalyst 1 carrying Co and Ag with respect to CeO ₂ was obtained. The addition amount of Ag is, CeO ₂ is per 1g, was 0.1mmol in terms of metal element. Further, Example Catalysts 2 to 5 were obtained in the same manner as Example Catalyst 1 except that Ni, Ir, Rh, dinitrodiammine Pt, and Pd nitrate were used instead of Ag nitrate. The amount of Ir, Rh, Pt, and Pd added was 0.05 mmol in terms of metal element per gram of CeO ₂ .

On the other hand, Co / CeO ₂ obtained by the above method was used as Comparative Example Catalyst 1. Further, as Comparative Example Catalyst 2, a catalyst in which VO (on-C ₄ H ₉ ) ₃ was supported on CeO ₂ was prepared by the same method as Comparative Example Catalyst 1. Table 1 shows a list of prepared catalysts.

(Catalyst performance evaluation method)
In order to evaluate the performance of the catalyst, a NOx purification performance test was conducted under the following conditions.

A granular catalyst (diameter 0.75 mm to 1.5 mm) with a capacity of 4 c.c. was fixed in a reaction tube made of quartz glass. The reaction tube was introduced into an electric furnace, and the heating was controlled so that the gas temperature introduced into the reaction tube was 300 ° C. The gas introduced into the reaction tube was a model gas that simulates an exhaust gas having an oxygen atmosphere in excess of the stoichiometric amount. The composition of the model gas was NOx: 150 ppm, CO: 1500 ppm, O ₂ : 3%, H ₂ O: 3%, N ₂ : balance. The volume space velocity (F / V) was 30,000 / h.

  The NOx purification performance of the catalyst was determined by obtaining the NOx purification rate using the calculation formula shown below.

NOx purification rate (%) = ((NOx amount flowing into the catalyst) − (NOx amount flowing out from the catalyst))
÷ (NOx amount flowing into the catalyst) x 100

(Study results)
The NOx purification rates by CO of Example Catalysts 1 to 5 and Comparative Example Catalysts 1 and 2 were evaluated. FIG. 1 shows the NOx purification rate. It was confirmed that the NOx purification rates of Comparative Examples Catalysts 1 and 2 were 10% or less, while Example Catalysts 1 to 5 showed a high NOx purification rate of 15% or more.

  Therefore, it is clear that a high NOx purification rate can be obtained by using at least one selected from Ag, Ir, Rh, Pt and Pd and Co as the catalytic active component.

In Example 1, CeZrO powder (manufactured by Daiichi Rare Element Chemical Co., Ltd.), CeZrO powder to which Pr was added, and CeZrO powder to which Y was added were used instead of CeO ₂ . Example catalysts 6 to 8 in which Co and Ir were added to each powder were prepared by the preparation method. On the other hand, in Example 2, Co and Ir were added to each powder using the same preparation method as Example Catalyst 2 except that Al ₂ O ₃ (manufactured by Sasol) was used instead of CeO ₂ . Comparative catalyst 3 was prepared. Table 2 shows a list of prepared catalysts.

  FIG. 2 shows the NOx purification rate by CO for Example Catalysts 6 to 8 and Comparative Example Catalyst 3.

When at least one selected from Zr, Pr and Y as the porous carrier and Ce are included, it can be seen that the NOx purification rate reaches 25% and a high purification rate is exhibited. Comparative Example Catalyst 3 in which the porous carrier was Al ₂ O ₃ was only able to obtain a purification rate of 5%.

  Therefore, it is clear that Example Catalysts 6 to 8 containing at least one of Zr, Pr and Y and Ce as the porous carrier can obtain a high NOx purification rate.

In Example catalyst 2, Example catalyst 9 prepared using nitrate instead of metal alkoxide as the Co raw material for the catalytically active component was obtained. Table 3 shows Example catalyst 9. An aqueous Co nitrate solution was added to the CeO ₂ used in Example Catalyst 2 by an impregnation method, and then dried at 120 ° C. and calcined at 400 ° C. for ₂ hours to support Co on CeO ₂ . The Ir addition method and the Co and Ir loadings are the same as in Example Catalyst 2.

  FIG. 3 shows the NOx purification rate of the example catalyst 9 prepared by using the Co alkoxide as the NOx purification rate of the example catalyst 9. From FIG. 3, the NOx purification rate of Example Catalyst 9 prepared using nitrate was about 16%. Compared to Example Catalyst 2 using Co alkoxide as a raw material, the NOx purification rate was low. A high NOx purification rate was obtained.

In order to evaluate the effect of coexistence of hydrocarbons (HC) in the exhaust gas, the composition of the model gas is NOx: 150 ppm, CO: 1500 ppm, C ₃ H ₆ : 500 ppm, O ₂ : 3%, H ₂ O: 3% , N ₂ : The remainder, the volume space velocity (F / V) was set to 30,000 / h, and this model gas was used to evaluate the NOx purification rate by the catalyst examples 1, 2, and 4. FIG. 4 shows the NOx purification rate related to the presence or absence of C ₃ H ₆ .

When C ₃ H ₆ coexists in the exhaust gas, the NOx purification rates of the catalyst examples 1, 2, and 4 are 10% or less, which is greatly reduced.

  Therefore, the NOx purification catalyst of the present invention is preferably used in an atmosphere in which the amount of hydrocarbon (HC) flowing into the NOx purification catalyst is not more than the CO amount in terms of carbon atoms.

In order to evaluate the influence of CO concentration, the composition of the model gas is NOx: 150 ppm, CO: 250 ppm to 1500 ppm, O ₂ : 3%, H ₂ O: 3%, N ₂ : balance, and volume space velocity (F / Vx was set to 30,000 / h, and the NOx purification rate of Example catalyst 2 when the CO concentration was changed was evaluated. FIG. 5 shows the change in the NOx purification rate with respect to the CO concentration.

  Even when the CO concentration is 250 ppm, the NOx purification rate is 19% and is sufficiently high, but the NOx purification rate is 20% by increasing the CO concentration to 450 ppm or more, that is, a concentration three times or more that of NOx in terms of molar ratio. And a higher NOx purification rate is exhibited.

  Therefore, the NOx purification catalyst of the present invention is preferably used in an atmosphere in which the CO concentration is at least 3 times the molar ratio with respect to the NOx concentration.

In order to evaluate the effect of the volume space velocity (F / V), the composition of the model gas is NOx: 150 ppm, CO: 1500 ppm, O ₂ : 3%, H ₂ O: 3%, N ₂ : the balance, and the volume space The NOx purification rate of Example catalyst 2 when the volume space velocity (F / V) was changed at a speed (F / V) of 7500 / h to 45,000 / h was evaluated. FIG. 6 shows the change in the NOx purification rate with respect to the volume space velocity (F / V).

  Lowering the volume space velocity (F / V) and improving the NOx purification rate, and making the volume space velocity (F / V) 30000 / h or less, the NOx purification rate exceeds 20%, and the high NOx purification rate Will come to show.

  Therefore, the NOx purification catalyst of the present invention is preferably used in an atmosphere having a volume space velocity (F / V) of 30000 / h or less.

  Fig.7 (a) is a figure which shows typically the structure of one Embodiment of the exhaust gas purification apparatus of this invention. In this exhaust gas purifying apparatus, two example catalysts 2 are installed in an exhaust gas flow path of a boiler, and a CO gas inlet is disposed between the catalysts as a CO amount adjusting means. The catalyst of Example 2 has a high CO oxidation ability, and in the experiment where the data shown in FIG. 1 was acquired, the amount of CO discharged from the subsequent stage of the NOx purification catalyst was 0 ppm.

  On the other hand, as shown in FIG. 7B, simply arranging two example catalysts 2 will not improve the NOx purification rate because CO does not flow into the downstream NOx purification catalyst.

  Therefore, as shown in FIG. 7A, by providing the CO gas inlet between the catalysts, CO flows into the subsequent NOx purification catalyst, so that the NOx purification rate is improved.

FIG. 8 shows an embodiment of the exhaust gas purifying apparatus of the present invention. The exhaust gas purifying apparatus, along the flow of exhaust gas flow path of a boiler, NH ₃ inlet as for example catalyst 2, NH ₃ supply means, are arranged NH ₃ denitration catalyst (Ti-V-based catalyst). If the NOx emission from the boiler is very large, or if the CO emission from the heat engine is small, NOx cannot be sufficiently purified by the catalyst of Example 2 alone, so an exhaust gas purification device as shown in FIG. 8 is used. To do. According to the purification apparatus shown in FIG. 8, high NOx purification performance can be obtained.

  FIG. 9 shows an embodiment of the exhaust gas purifying apparatus of the present invention. The exhaust gas purification device is disposed in the exhaust gas flow path of the boiler 1, and includes a NOx purification catalyst 6, a CO amount adjusting means (CO tank 3, CO inlet 4), a CO sensor 2, a NOx purification catalyst inlet gas temperature sensor 5. A NOx sensor 7 and a control unit 8 are provided.

  Below, the exhaust gas purification method using this exhaust gas purification apparatus is demonstrated.

  The exhaust gas discharged from the boiler 1 has an oxygen atmosphere that is more than the stoichiometric amount, and contains CO and NOx in addition to oxygen. When the exhaust gas contacts the NOx purification catalyst 6, CO and NOx in the exhaust gas react to remove NOx.

  The temperature of the exhaust gas flowing into the NOx purification catalyst 6 is constantly monitored by the NOx purification catalyst inlet gas temperature sensor 5 disposed in the vicinity of the inlet of the NOx purification catalyst. The CO concentration of the exhaust gas is measured by the CO sensor 2. All signals from these sensors are input to the control unit 8. The control unit 8 evaluates the states of the boiler and the exhaust gas purification device, and controls them to appropriate combustion conditions and purification conditions.

  The amount of NOx discharged into the atmosphere is always measured by a NOx sensor 7 installed downstream of the NOx purification catalyst 6. When the NOx sensor 7 determines that the amount of NOx is large, the control unit 8 performs control to change the combustion state of the boiler to increase the CO concentration (CO amount) in the exhaust gas of the boiler, or the CO tank 3 to control the injection of CO into the exhaust gas flow path. By doing in this way, the amount of CO flowing into the NOx purification catalyst 6 can be increased, and the amount of NOx in the exhaust gas can be reduced.

  Therefore, according to this exhaust gas purification apparatus and purification method, the NOx emission amount can be effectively reduced with respect to a heat engine that exhausts exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount.

The figure which shows NOx purification activity by CO about various NOx purification catalysts from which a catalyst active component differs. The figure which shows NOx purification activity by CO about various NOx purification catalysts from which a carrier component differs. The figure which shows NOx purification activity by CO about what changed the raw material of a catalyst active component. For various NOx purifying catalyst, it shows the difference in NOx purification activity by the presence or absence of C ₃ H ₆ in the exhaust gas. The figure which shows the change of NOx purification activity by the CO density | concentration in waste gas about a NOx purification catalyst. The figure which shows the change of NOx purification activity by the volume space velocity (F / V) of exhaust gas about a NOx purification catalyst. (A) is a block diagram of a heat engine exhaust gas purification apparatus in which a CO inlet is provided between two NOx purification catalysts, and (b) is a heat engine exhaust gas in which two NOx purification catalysts are installed along an exhaust gas flow path. The block diagram of a purification apparatus. Diagram of the exhaust gas purifying apparatus of the heat engine provided with a NH ₃ denitration catalyst downstream of the NOx purifying catalyst. The figure which shows typically one embodiment of the exhaust gas purification apparatus of this invention.

Explanation of symbols

1 Boiler 2 CO sensor 3 CO tank 4 CO inlet 5 NOx purification catalyst inlet gas temperature sensor 6 NOx purification catalyst 7 NOx sensor 8 Control unit

Claims (16)

  It is arranged in the exhaust gas flow path of a heat engine that exhausts exhaust gas in an oxygen atmosphere that is more than the stoichiometric amount, and purifies by reducing nitrogen oxide (NOx) in the exhaust gas using carbon monoxide (CO) as a reducing agent. An exhaust gas purifying apparatus for a heat engine comprising a NOx purifying catalyst, wherein the NOx purifying catalyst is supported on the porous carrier containing cerium (Ce), silver (Ag), iridium (Ir) ), Rhodium (Rh), platinum (Pt), and palladium (Pd), and a catalytically active component containing cobalt (Co), and an exhaust gas purification apparatus for a heat engine.   2. The exhaust gas of a heat engine according to claim 1, wherein the porous carrier is a metal oxide containing at least one selected from zirconium (Zr), praseodymium (Pr), and yttrium (Y). Purification equipment.   The amount of CO is adjusted so that the amount of hydrocarbon (HC) in the exhaust gas in contact with the NOx purification catalyst is equivalent to or less than the amount of CO in contact with the catalyst in terms of carbon atoms. The exhaust gas purifying apparatus for a heat engine according to claim 1 or 2, wherein a CO amount adjusting means or an HC amount adjusting means for adjusting the HC amount is arranged.   The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 3, wherein the catalytically active component Co is prepared using an organometallic compound as a starting material.   5. The volume space velocity (F / V) is 30000 / h or less, where F is the flow rate of exhaust gas contacting the NOx purification catalyst and V is the volume of the catalyst. The exhaust gas purification apparatus for a heat engine according to any one of the preceding claims.   2. A plurality of NOx purification catalysts are disposed in an exhaust gas flow path, and a CO amount adjusting means for adjusting the CO amount in the exhaust gas is disposed in an exhaust gas flow path between the catalyst and the catalyst. The exhaust gas purifying device for a heat engine according to any one of claims 1 to 5.   The CO amount adjusting means for adjusting the CO amount so that the CO amount in contact with the NOx purification catalyst is 3 times or more in molar ratio with respect to the NOx amount in contact with the catalyst is provided. The exhaust gas purification apparatus for a heat engine according to any one of 1 to 6. The heat engine according to any one of claims 1 to 7, wherein an NH ₃ denitration catalyst that reduces and purifies NOx using NH ₃ as a reducing agent is disposed upstream or downstream of the NOx purification catalyst. Exhaust gas purification equipment.   The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 8, wherein a NOx sensor that measures the amount of NOx in the exhaust gas is disposed downstream of the NOx purification catalyst.   A NOx purification catalyst that reduces and purifies NOx in exhaust gas in an oxygen atmosphere in excess of the stoichiometric amount using CO as a reducing agent, comprising a porous carrier containing Ce, and supported on the porous carrier A NOx purification catalyst comprising: a catalytic active component containing at least one selected from Ag, Ir, Rh, Pt and Pd, and Co.   The NOx purification catalyst according to claim 10, wherein the porous carrier is a metal oxide containing at least one selected from Zr, Pr and Y.   Using a NOx purification catalyst comprising a porous support containing Ce, at least one selected from Ag, Ir, Rh, Pt and Pd supported on the porous support and a catalytically active component containing Co An exhaust gas purification method for a heat engine, characterized by reducing and purifying NOx in the exhaust gas in an oxygen atmosphere in excess of the stoichiometric amount discharged from the heat engine using CO as a reducing agent.   The exhaust gas purification method for a heat engine according to claim 12, wherein the porous carrier is a metal oxide containing at least one selected from Zr, Pr and Y.   The amount of HC flowing into the NOx purification catalyst is adjusted by adjusting the combustion state of the heat engine so as to be equivalent to or less than the amount of CO in terms of carbon atoms. Or the exhaust gas purification method for a heat engine according to 13,   The combustion state of the heat engine is adjusted so that the amount of CO flowing into the NOx purification catalyst is three times or more in molar ratio with respect to the amount of NOx. An exhaust gas purification method for a heat engine as described in 1.   16. The combustion state of the heat engine is adjusted so that the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst is always kept lean without being intermittently switched from stoichiometric to rich. The exhaust gas purification method for a heat engine according to claim 1.

Images