JP2010203328A - Exhaust emission control device for thermal engine, exhaust emission control method and nox elimination catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device and an exhaust emission control method for a thermal engine eliminating NOx in exhaust gas in an oxygen excess atmosphere with high elimination performance using CO, and to provide an NOx elimination catalyst used for the same. <P>SOLUTION: The exhaust emission control device for the thermal engine equipped with the NOx elimination catalyst reducing and eliminating nitrogen oxides (NOx) in exhaust gas using CO as reducer is disposed in an exhaust gas channel of the thermal engine discharging exhaust gas in an atmosphere containing CO and NOx and oxygen excessive from stoichiometric quantity. The NOx elimination catalyst includes a porous carrier and catalyst activating component carried on the porous carrier, and includes NOx elimination function by containing Ir and at least one kind selected from Au, Rh and Pd as the catalyst activating component. <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) using carbon monoxide (CO) 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 a heat engine, 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 purification performance using CO.

  That is, the exhaust gas purification apparatus for a heat engine of the present invention is disposed in an exhaust gas flow path of a heat engine that contains CO and NOx and exhausts exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount, and uses 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) in the exhaust gas, wherein the NOx purification catalyst is supported on a porous carrier and the porous carrier The catalytically active component includes Ir and at least one selected from Au, Rh, and Pd.

  Ir, Au, Rh, and Pd are difficult to form sulfates, and therefore the NOx purification performance is hardly reduced by the S component even if SOx is contained in the exhaust gas.

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 the exhaust gas contains O ₂ , CO, and NO, 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 present invention, NOx contained in exhaust gas from a heat engine operated in an excessive oxygen atmosphere can be efficiently purified using CO, and NOx and CO emissions of the heat engine can be suppressed. it can.

The figure which shows NOx purification activity about the various NOx purification catalyst from which a catalyst active component differs. The figure which shows NOx purification activity about the various NOx purification catalyst from which a catalyst active component differs. The figure which shows NOx purification activity by SOx presence or absence about various NOx purification catalysts from which a catalyst active component differs. The figure which shows NOx purification activity about the various NOx purification catalyst from which a catalyst active component differs. The figure which shows NOx purification activity about the various NOx purification catalyst from which a catalyst active component differs. The figure which shows the change of NOx purification activity with respect to the amount of active component addition about the various NOx purification catalyst from which a catalyst active component differs. The figure which shows the change of NOx purification activity with respect to the CO density | concentration in exhaust gas about a NOx purification catalyst. For NOx purification catalyst, it shows a change in the NOx purification activity by C ₃ H ₆ whether in the exhaust gas. (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.

  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. The exhaust gas from the boiler contains CO in addition to NOx.

  Regarding the purification of NOx, if the reduction reaction of the following formula (3) proceeds, NOx is reduced and purified. 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 present inventors have determined that NOx purification includes a porous carrier, Ir as a catalytically active component supported on the porous carrier, and at least one selected from Au, Rh, and Pd. It has been clarified that the use of a catalyst effectively purifies NOx using CO as a reducing agent. By combining Ir with Au, Rh, and Pd, the NOx purification performance particularly at 280 ° C. or higher is improved. The reason for this is not clear, but it is believed that Ir and Au, Rh, and Pd interact with each other to activate Ir. When Ir and Pt are combined, NOx is not effectively purified. Probably because CO oxidation by Pt proceeds.

  By containing Ir and at least two or more selected from Au, Rh, and Pd, NOx is further effectively purified. It is thought that Au, Rh, and Pd coexist and interact to increase Ir activation dramatically.

  In the case of a catalyst using Ir and at least one or more selected from Au, Rh, and Pd as catalytic active components, the NOx purification performance may be higher when SOx is contained in the exhaust gas. is there. Although the reason is not clear, it is thought that Ir is activated by SOx.

The porous support is preferably a metal oxide containing Si, in addition to _{SiO 2, SiO 2 -Al 2 O} 3, silicalite, zeolite or the like. By using a metal oxide containing Si, the SOx resistance performance of the carrier is enhanced. TiO ₂ can also be considered as a carrier having SOx resistance, but when TiO ₂ is used, the NOx purification performance tends to be lowered. This is probably because the state of Ir changes.

  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.

  If Nb is further contained in the catalyst using Ir and at least one selected from Au, Rh, and Pd as the catalytic active component, the NOx purification performance is improved. Although the reason is not clear, it is expected that Ir and Nb form a composite oxide to activate Ir.

  If a catalyst using Ir and at least one selected from Au, Rh, and Pd as a catalytic active component is further contained at least one selected from S, P, and Cl, the NOx purification performance is improved. . I think that it is because ionization of Ir is promoted. By containing at least one selected from S, P, and Cl, high NOx purification activity is exhibited even when SOx is not present in the reaction gas.

  The amount of S, P, and Cl contained in the catalyst is desirably 0.05 or more and 500 or less in terms of metal in terms of a molar ratio to Ir. If the amount of S, P, and Cl contained is less than 0.05 in terms of metal relative to Ir in terms of metal, the effect of inclusion is insufficient, while the molar ratio exceeds 500 relative to Ir. And poisoning to Ir occurs.

  The supported amount of Ir as the catalytically active component is preferably 0.000005 mol part or more and 1.0 mol part or less, more preferably 0.0003 mol part or more and 0.3 mol part in terms of element with respect to 2 mol part of the porous support. It is as follows. When the amount of Ir supported is less than 0.00005 mol part, the effect of supporting is insufficient. On the other hand, when the amount exceeds 1.0 mol part, the specific surface area of the active ingredient itself decreases and the catalyst cost increases. 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 amounts of Au, Rh, and Pd contained as the catalyst component are each preferably 0.15 or more and 3 or less in terms of metal in terms of molar ratio with respect to Ir. If the amounts of Au, Rh, and Pd contained are less than 0.15 in terms of metal, respectively, in terms of metal, the content effect is insufficient. When the amounts of contained Au, Rh, and Pd are 0.10 to 0.15 in terms of metal, respectively, in terms of metal, a dramatic improvement in activity is observed. On the other hand, if the molar ratio with respect to Ir exceeds 3, Ir is deactivated, and the catalyst cost is further increased.

  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 can be used. . 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 NOx 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. A catalyst component can be uniformly supported by preparing it by a co-impregnation method using an impregnation liquid in which Ir, Au, Rh, and Pd are present in the same solution.

  The shape of the NOx purification catalyst can be appropriately adjusted depending on 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 a honeycomb shape, cordierite is optimal as the base material. However, when there is a risk that the catalyst temperature may increase, a base material that does not easily react with the catalytically active component, such as a metal honeycomb mainly composed of Fe, etc. It is preferable to use a substrate. Alternatively, the honeycomb may be formed with only the porous carrier and the catalytically active component.

  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, it is preferable that a CO amount adjusting means for adjusting the CO amount contained in the exhaust gas contacting the NOx purification catalyst is disposed in the front stage of the NOx purification catalyst. The CO amount adjusting means includes means for adjusting the CO amount by changing the combustion state of the heat engine. Further, for example, it is conceivable to inject CO into the exhaust gas passage to adjust the CO amount. This CO amount adjusting means increases the amount of CO that contacts 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 further to arrange a CO inlet in the exhaust gas flow path between the NOx purification catalyst and the NOx purification catalyst. By adjusting the amount of CO in contact with the NOx purification catalyst by this CO amount adjusting means, the NOx purification reaction can be promoted.

  The above-mentioned CO amount adjusting means may be arranged in front of the NOx purification catalyst so that the amount of CO flowing into the NOx purification catalyst is at least twice as much as the molar ratio with respect to the amount of NOx in contact with the catalyst. preferable.

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

  In the case of a catalyst using Ir and at least one selected from Au, Rh, and Pd as a catalytic active component, the NOx purification performance may be higher when SOx is contained in the exhaust gas. Therefore, when SOx is not present in the exhaust gas, it is preferable to arrange an SOx amount adjusting means for adjusting the SOx amount contained in the exhaust gas that contacts the NOx purification catalyst, in front of the NOx purification catalyst. The SOx amount adjusting means adjusts the SOx amount by injecting SOx into the exhaust gas flow path, and is made possible by adding, for example, SOx gas or sulfuric acid. The amount of SOx in contact with the NOx purification catalyst is preferably 1 ppm or more and 500 ppm or less. If it is 1 ppm or less, the effect of SOx does not appear, and if it is 500 ppm or more, SOx poisons the catalyst and the NOx purification rate decreases. By controlling the amount of SOx present in the exhaust gas in this way, the NOx reduction reaction using CO as a reducing agent easily proceeds.

In the case of a catalyst using Ir and at least one selected from Au, Rh, and Pd as the catalytic active component, the NOx purification performance may be higher when the exhaust gas contains hydrocarbons. In that case, it is preferable to arrange the hydrocarbon amount adjusting means for adjusting the amount of hydrocarbon in contact with the NOx purification catalyst before the NOx purification catalyst. The means for adjusting the amount of hydrocarbon includes means for adjusting the amount of hydrocarbons by changing the combustion state of the heat engine. Further, for example, it is conceivable to adjust the amount of hydrocarbons by injecting hydrocarbons into the exhaust gas passage. . With this hydrocarbon amount adjusting means, the amount of hydrocarbon in contact with the NOx purification catalyst is increased. The hydrocarbon is not particularly limited as long as it is composed of hydrogen and carbon, but CH ₄ , C ₃ H ₆ , C ₂ H ₄ , C ₂ H ₂ , C ₃ H _{8 and the} like are preferable.

When the amount of CO or hydrocarbon flowing into the NOx purification catalyst is less than the amount capable of purifying NOx in the exhaust gas, NOx is reduced using NH ₃ as a reducing agent before or after the NOx purification catalyst. A catalyst, that is, an NH ₃ denitration catalyst may be disposed. 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, hydrocarbon, NH ₃ as a reducing agent. 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, if it is not necessary to make the air-fuel ratio rich, the combustion state of the heat engine is adjusted, and the air-fuel ratio of the exhaust gas flowing into the CO, NOx purification catalyst is not intermittently switched from the stoichiometric to rich state. It is preferable to always 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, means for adjusting the amount of CO by injecting CO into the exhaust gas passage becomes unnecessary.

  A CO and NOx sensor may be provided after the NOx purification catalyst. The CO, NOx sensor measures the amount of CO, NOx contained in the subsequent stage of the NOx purification catalyst, that is, the amount of CO, NOx remaining without being purified by the NOx purification catalyst. The amount of CO flowing into the CO, NOx purification catalyst is adjusted according to the measurement result of the CO, NOx amount by the CO, NOx sensor. As a result of measuring with the CO and NOx sensors, when a large amount of NOx remains behind the NOx purification catalyst and almost no CO remains, the above-mentioned CO amount adjusting means is arranged in the front stage of the NOx purification catalyst, Adjustment is made so that the amount of CO flowing into the NOx purification catalyst increases. On the other hand, as a result of measurement by the CO, NOx sensor, if the amount of NOx is so small that it cannot be measured after the CO, NOx purification catalyst, the amount of CO flowing into the NOx purification catalyst may be reduced. In addition to the CO amount adjusting means, the amount of CO flowing into the NOx purification catalyst can be adjusted by adjusting the combustion state of the heat engine. Thus, by measuring the CO and NOx amount in the latter stage of the NOx purification catalyst with the CO and NOx sensor, it is possible to maintain high NOx purification activity, reduce the outflow of CO to the atmosphere, and remain without being purified. It is possible to determine the optimum amount of CO to be added to reduce the amount of CO and NOx.

〔Example〕
Examples of the present invention will be described below.

(Preparation method of NOx purification catalyst)
A commercially available SiO ₂ (silica) powder (Fuji Silysia, CARiActG-3) was impregnated with a mixed solution of an Ir nitrate solution (Fluya Metal) and chlorinated Au acid (Tanaka Kikinzoku), and then dried at 120 ° C. And calcined at 600 ° C. for 1 h. Ir and Au were added in amounts of 0.3 mmol and 0.08 mmol with respect to 2 mol of silica, respectively. This catalyst is referred to as Example catalyst 1. Further, Example Catalysts 2 and 3 were prepared in the same manner as Example Catalyst 1 except that Rh nitrate and Pd nitrate (both made by Tanaka Kikinzoku) were used instead of chlorinated Au acid, and the same active component loading was obtained. It was. The same Ir, except that a mixed solution of an Ir nitrate solution, a mixed solution of Au chloride and Pd nitrate, and a mixed solution of Ir solution of nitrate, Au chloride and Rh nitrate are used, Example catalysts 4 and 5 were obtained in which the addition amount of Au was the same and the addition amount of Pd and Rh was the same as that of Au in terms of metal elements.

  Further, as a comparative example catalyst, a comparative example catalyst 1 which was prepared in the same manner as in Example catalyst 1 but did not contain Au was prepared. 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) having a capacity of 0.9 c.c. was fixed in a quartz glass reaction tube. This reaction tube was introduced into an electric furnace, and the heating was controlled so that the gas temperature introduced into the reaction tube was 240 ° C to 350 ° 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%, SO ₂ : 4 ppm, 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 of Example Catalysts 1 to 5 and Comparative Example Catalyst 1 were evaluated. FIG. 1 shows the NOx purification rate. It was confirmed that the example catalysts 1 to 3 showed a higher NOx purification rate than the comparative example catalyst 1. In particular, the difference at 280 ° C. or higher is remarkable. The catalyst examples 4 and 5 combining Ir, Au and Pd, and Ir, Au and Rh further increase the NOx purification rate. Therefore, it is clear that a high NOx purification rate can be obtained by using any one of Au, Pd, and Rh, or two or more, in addition to Ir, as the catalytic active component.

  As a comparative example catalyst, a comparative example catalyst 2 was prepared in the same manner as in Example catalyst 1, but without containing Ir and containing only Au as the active component. Similarly, Comparative Catalysts 3 and 4 containing no Ir, only Pd and only Rh as active components were prepared. Table 2 shows a list of prepared catalysts.

(Study results)
In the catalyst performance evaluation method shown in Example 1, the NOx purification rates of Comparative Examples Catalysts 2 to 4 were evaluated. FIG. 2 shows the NOx purification rate. It was confirmed that Comparative Catalysts 2 to 4 had almost no NOx purification activity. Therefore, it is clear that Au, Pd, and Rh exhibit NOx purification activity by coexisting with Ir.

(SOx coexistence effect)
In the evaluation method used in Example 1, the NOx purification activity of Example Catalysts 1, 2, 5, and Comparative Example Catalyst 1 was evaluated using the same evaluation method except that SOx was not included in the reaction gas. FIG. 3 shows the NOx purification activity at 310 ° C. Even when SOx is not present in the reaction gas, the NOx purification activity of the example catalysts 1, 2, and 5 is higher than that of the comparative example catalyst 1, but the NOx purification activity of the example catalysts 1, 2, and 5 when SOx coexists. Increases dramatically. Therefore, it is clear that the SOx coexistence in the reaction gas exhibits higher NOx purification activity.

(Nb addition effect)
Example catalyst 6 was prepared by the same preparation method as Example catalyst 1 except that Nb sol was added to the mixed solution of Ir nitrate and Au chloride to form an impregnation solution when the active ingredient was supported on the silica support. Obtained. Nb contained in Example Catalyst 6 was equimolar with Ir.

(Study results)
Regarding the Example catalysts 1 and 6, the NOx purification activity was evaluated by the evaluation method used in Example 1. FIG. 4 shows the NOx purification activity. From FIG. 4, it is clear that the NOx purification rate is further increased by containing Nb.

(S, P, Cl addition effect)
Example catalyst 7 was obtained by the same preparation method as Example catalyst 1 except that sulfuric acid was further added to the mixed solution of Ir nitrate and Au chloride to form an impregnation solution when the active ingredient was supported on the silica carrier. It was. S contained in Example catalyst 4 was set to 25 in a molar ratio with respect to Ir. Further, Example Catalysts 8 and 9 were prepared in the same manner as Example Catalyst 4 except that phosphoric acid and hydrochloric acid were used in place of sulfuric acid, and the same P and Cl loadings were obtained. The same preparation as in Example Catalyst 7, except that sulfuric acid was added to a mixed solution of Ir nitrate, Au chloride and phosphoric acid, and hydrochloric acid was added to a mixed solution of Ir nitrate, Au chloride and phosphoric acid. Example catalysts 10 and 11 were obtained by the above method. The amounts of P, Cl and S contained in the catalyst examples 10 and 11 were all set to 25 in molar ratio to Ir.

  Table 4 shows a list of prepared catalysts.

(Study results)
With respect to Example Catalysts 1 and 11 to 11, the NOx purification activity by the reaction gas containing no SOx used in Example 3 was evaluated. FIG. 5 shows the NOx purification activity. From FIG. 5, it is clear that the inclusion of one or more of S, P, and Cl shows a high NOx purification activity even if SOx does not coexist in the reaction gas.

(Au, Pd, Rh addition amount)
With respect to Example Catalysts 1 to 3, the NOx purification activity when the addition amount of Au, Pd, and Rh was changed was evaluated. FIG. 6 shows the NOx purification rate when the addition amount of Au, Pd, and Rh is changed with respect to Ir at a molar ratio. From FIG. 6, when the addition amount of Au, Pd, and Rh is 0.15 or more and 3 or less, respectively, the NOx purification activity is higher than that of Ir alone. In particular, it can be seen that when the added amounts of Au, Pd, and Rh are each 0.15 in terms of molar ratio to Ir, the NOx purification activity is dramatically increased.

In order to evaluate the influence of the CO concentration, the composition of the model gas is NOx: 150 ppm, CO: 200 ppm to 1500 ppm, O ₂ : 3%, SO ₂ : 4 ppm, H ₂ O: 3%, N ₂ : balance, volume The NOx purification rate of Example catalyst 1 when the CO concentration was changed at a space velocity (F / V) of 30,000 / h was evaluated. FIG. 7 shows the change in the NOx purification rate with respect to the CO concentration at 310 ° C.

  Even when the CO concentration is 200 ppm, the NOx purification rate is 40% and is sufficiently high, but the NOx purification rate is 45 by increasing the CO concentration to 300 ppm or more, that is, a concentration that is twice or more that of NOx in terms of molar ratio. % Or more, 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 twice the molar ratio with respect to the NOx concentration.

(Coexistence effect of hydrocarbons)
Regarding Example catalyst 1, in the evaluation method used in Example 1, the NOx purification activity was evaluated using the same evaluation method except that the reaction gas contained 100 ppm of C ₃ H ₆ . FIG. 8 shows the NOx purification activity at 330 ° C. Even when C ₃ H ₆ is not present in the reaction gas, the NOx purification activity of the example catalyst 1 is sufficiently high, but the NOx purification activity of the example catalyst 1 is dramatically increased by the coexistence of C ₃ H ₆ . Therefore, it is clear that higher NOx purification activity is exhibited when hydrocarbons coexist in the reaction gas.

  Fig.9 (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 1 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 1 has high CO oxidation ability. In the evaluation method used in Example 1, when the catalyst inlet temperature was 310 ° C., the amount of CO discharged from the subsequent stage of the NOx purification catalyst was 150 ppm. In this case, as shown in FIG. 9B, simply arranging two example catalysts 2 does not provide a high NOx purification rate because less CO flows into the downstream NOx purification catalyst.

  Therefore, as shown in FIG. 9A, if a CO gas injection port is provided between the catalysts so that CO can also flow into the subsequent NOx purification catalyst, the NOx purification rate is improved.

FIG. 10 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 1, NH ₃ supply means, are arranged NH ₃ denitration catalyst (Ti-V-based catalyst). When the amount of NOx emitted from the boiler is extremely large or the amount of CO emitted from the heat engine is small, NOx can not be sufficiently purified by the catalyst of Example 1 alone, so an exhaust gas purification device as shown in FIG. 10 is used. To do. According to the purification apparatus shown in FIG. 10, high NOx purification performance can be obtained.

  FIG. 11 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, CO amount adjusting means (CO tank 3, CO inlet 4), CO sensor 2, 9, exhaust gas temperature sensor 5, NOx sensor. 7 and a control unit 8.

  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 exhaust gas temperature sensor 5 disposed near the inlet of the NOx purification catalyst 6. 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 1 and the exhaust gas purification device, and controls them to appropriate combustion conditions and purification conditions.

  The amounts of NOx and CO discharged into the atmosphere are always measured by the NOx sensor 7 and the CO sensor 9 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 1 to increase the CO concentration (CO amount) in the exhaust gas of the boiler 1, or Control is performed to inject CO from the CO tank 3 into the exhaust gas passage. 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. On the other hand, when the CO sensor 9 determines that the amount of CO is large, the control unit 8 performs control to change the combustion state of the boiler 1 and performs control to reduce the CO concentration in the exhaust gas of the boiler 1.

  Therefore, according to this exhaust gas purification apparatus and purification method, CO and NOx emissions 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.

1 Boiler 2, 9 CO sensor 3 CO tank 4 CO inlet 5 Exhaust gas temperature sensor 6 NOx purification catalyst 7 NOx sensor 8 Control unit

Claims (20)

It contains CO and NOx, and is placed 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, and reduces nitrogen oxides (NOx) in the exhaust gas using CO as a reducing agent. An exhaust gas purification apparatus for a heat engine equipped with a NOx purification catalyst for purification,
The NOx purification catalyst has a porous carrier and a catalytically active component supported on the porous carrier, and the catalytically active component is Ir, and at least one selected from Au, Rh, and Pd An exhaust gas purification apparatus for a heat engine characterized by comprising:   2. The exhaust gas purification apparatus for a heat engine according to claim 1, wherein the catalytically active component includes Ir and at least two or more selected from Au, Rh, and Pd.   The exhaust gas purifying apparatus for a heat engine according to claim 1 or 2, wherein the exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount contains SOx.   The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 3, wherein the porous carrier is a metal oxide containing Si.   The exhaust gas of a heat engine according to any one of claims 1 to 4, wherein Au, Rh, and Pd contained in the catalyst are each in a molar ratio of 0.15 to 3 with respect to Ir. Purification equipment.   6. The exhaust gas purification apparatus for a heat engine according to claim 1, further comprising Nb as the catalytic active component.   The exhaust gas purification apparatus for a heat engine according to any one of claims 1 to 6, wherein the catalyst contains at least one selected from S, P, and Cl.   The CO amount adjusting means according to any one of claims 1 to 7, wherein a plurality of the purification catalysts are arranged in an exhaust gas flow path, and a CO amount in the exhaust gas is adjusted in an exhaust gas flow path between the catalyst and the catalyst. An exhaust gas purifying device for a heat engine, characterized by comprising:   9. The CO amount adjustment according to claim 1, wherein the CO amount is adjusted such that the CO amount in contact with the purification catalyst is at least twice the molar ratio with respect to the NOx amount in contact with the catalyst. An exhaust gas purifying apparatus for a heat engine, characterized in that means is arranged.   10. The exhaust gas purifying apparatus for a heat engine according to claim 1, wherein a hydrocarbon amount adjusting means for adjusting a hydrocarbon amount in the exhaust gas is disposed upstream of the purification catalyst. The exhaust gas of a heat engine according to any one of claims 1 to 10, 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 purification catalyst. Purification equipment.   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 and catalytic activity carried on the porous carrier And a catalytically active component containing Ir and at least one selected from Au, Rh, and Pd.   13. The NOx purification catalyst according to claim 12, wherein Au, Rh, and Pd contained in the catalyst are 0.15 or more and 3 or less in molar ratio to Ir.   The NOx purification catalyst according to claim 12 or 13, further comprising Nb as a catalytic active component.   15. The NOx purification catalyst according to claim 12, wherein the catalyst contains at least one selected from S, P, and Cl.   Using a NOx purification catalyst containing as a catalytically active component a porous carrier, Ir supported on the porous carrier, and at least one selected from Au, Rh, and Pd, CO as a reducing agent, An exhaust gas purification method for a heat engine, characterized by reducing and purifying NOx in the exhaust gas in an oxygen atmosphere that is in excess of the stoichiometric amount discharged from the heat engine.   The exhaust gas purification method for a heat engine according to claim 16, wherein Au, Rh, and Pd contained in the catalyst are each in a molar ratio of 0.15 to 3 with respect to Ir.   18. The exhaust gas purification method for a heat engine according to claim 16, further comprising Nb as a catalytic active component.   The exhaust gas purification method for a heat engine according to any one of claims 16 to 18, wherein the catalyst includes at least one selected from S, P, and Cl.   20. The combustion state of the heat engine according to any one of claims 16 to 19, wherein the amount of CO flowing into the purification catalyst is 3 times or more in molar ratio with respect to the amount of NOx in contact with the catalyst. An exhaust gas purification method for a heat engine, characterized by disposing CO amount adjusting means for adjusting the CO amount so that

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