JP5295654B2 - Exhaust purification catalyst and exhaust purification apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treatment catalyst capable of efficiently treating NOx in exhaust gas at a low temperature even in an excess oxygen atmosphere and an exhaust gas treatment apparatus using the catalyst. <P>SOLUTION: NOx in exhaust gas is efficiently treated at a low temperature even in an excess oxygen atmosphere by an exhaust gas treatment catalyst comprising a carrier including an anion part containing an element of Group XV or XVI after the third period and oxygen atoms and a cation part for compensating the electric charge and having a high solid acid strength and a noble metal element carried on the carrier and an exhaust gas treatment apparatus using the catalyst. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an exhaust purification catalyst provided with a metal-supported catalyst that supports a complex oxide having solid acidity for the purpose of denitration, and an exhaust purification apparatus using the same. More specifically, under lean combustion, hydrogen as a reducing agent reacts with NOx to generate ammonia, which is stably adsorbed at an acidic point on the surface of the carrier, and then between adsorbed ammonia and NOx. The present invention relates to an exhaust gas purification catalyst that converts NOx into harmless nitrogen by performing selective catalytic reduction, and an exhaust gas purification device using the same.

  In recent years, NOx in exhaust gas discharged from an internal combustion engine such as a power generation facility or an automobile to the atmosphere has been regarded as a problem from the viewpoint of controlling harmful emissions. Since NOx causes acid rain and photochemical smog, the movement to regulate the amount of emission worldwide has been strengthened. Since an internal combustion engine such as a diesel engine or a gasoline lean burn engine performs lean combustion, a large amount of oxygen is present in the exhaust gas. Of the harmful components present in the exhaust gas of the internal combustion engine, NOx is purified by the reduction reaction, but it is difficult to advance the reduction reaction in the exhaust gas having a high oxygen partial pressure. For this reason, various methods for purifying NOx in exhaust gas containing excess oxygen have been studied.

A denitration technique based on a catalytic reaction using ammonia as a reducing agent has been put into practical use for flue gas denitration in stationary thermal power boilers, sintering furnaces, coke ovens, and the like. In this denitration technology, the denitration reaction proceeds according to the reaction scheme shown by the following formula 1 even in oxygen-excess exhaust (see Non-Patent Document 1).

In addition to the above formula 1, the following formulas 2 and 3 have been proposed as a reaction under excess oxygen as a method for purifying NOx by introducing ammonia into the exhaust of an automobile (see Non-Patent Document 2). ). A method for purifying NOx by introducing ammonia into the exhaust gas of an internal combustion engine has also been proposed (see Patent Documents 1 and 2).

  Further, a method for purifying exhaust gas of an internal combustion engine by generating ammonia by hydrolysis of urea and supplying it to a NOx purification catalyst without directly using ammonia is proposed (Patent Document 3 and Non-Patent Document). 3).

  Further, as a method for purifying NOx contained in exhaust gas exhausted from a lean-burn internal combustion engine, NOx is adsorbed on the catalyst under lean conditions in which the oxygen concentration in the exhaust gas becomes excessive, and then the internal combustion engine is in rich conditions. By controlling the amount of NOx adsorbed on the catalyst under lean conditions by periodically forming a state of low oxygen in the exhaust gas and simultaneously synthesizing and supplying carbon monoxide. How to do is known. This method utilizes a state where the oxygen partial pressure is low, which is a rich condition, and a hydrogen gas is generated by a shift reaction between carbon monoxide and water vapor present in the exhaust gas on the catalyst, and is adsorbed on the catalyst. Low temperature purification is promoted by converting a part of NOx to ammonia (see Non-Patent Document 4).

Japanese Patent No. 3462580 Japanese Patent Publication No. 6-35816 JP 2004-313917 A “New Catalytic Chemistry” Second Edition, Sankyo Publishing, Eiichi Kikuchi, Koichi Segawa, Asahi Tada, Yuzo Imizu, Ei Hattori, p. 128-129 SAE 2004-01-0155 "Modeling an ammonia SCR DeNOx Catalyst: Model development and validation" SAE 2004-01-1944 “Feasibility study of urea systems on heavy duty commercial vehicles” “A NOx Reduction System Using Ammonia Storage-Selective Catalytic Reduction in Rich and Lean Positions”, 15. Aachener cholloium Fahrzeug-und Motorentennik 2006 p. 259-270

  However, the method of selectively reducing and removing NOx by directly using ammonia as described above has high denitration characteristics, but has several problems such as requiring additional equipment for introducing ammonia into the exhaust gas. have.

  For example, when using stored ammonia gas or ammonia water, a tank is required, and when adding to exhaust, an injection device is required. In addition, handling and storage of highly toxic and corrosive ammonia gas requires careful attention, and requires the use of corrosion resistant materials and safety equipment such as sensors. Therefore, the system becomes complicated and the system becomes larger and the cost increases.

  When considering ammonia as a reducing agent for purifying NOx, there is a problem of infrastructure maintenance. Considering the general circulation of ammonia, since ammonia is in a gaseous state at room temperature, the difficulty of handling becomes a problem. In particular, when ammonia is used on an automobile, it becomes a complicated system and is not realistic.

  In addition, when denitration is performed by producing ammonia by hydrolysis of urea, equipment such as a catalyst device that decomposes urea into ammonia is necessary. Since urea is easier to handle than ammonia, it is more realistic than using ammonia directly. However, the system is complicated by the urea tank, the injection device, and the like, and there are similar problems such as an increase in the size of the denitration device and an increase in cost.

  In particular, when the denitration technology using urea is used in a moving medium such as an automobile, it is necessary to develop an infrastructure that can stably replenish urea. In addition, it is necessary to periodically replenish urea to purify NOx, which is a burden on the user.

  On the other hand, a method of generating ammonia by making exhaust gas into a reducing atmosphere by combustion under rich conditions and reducing NOx using the generated ammonia is one of promising denitration techniques. In this method, ammonia can be produced on-board by the control of the internal combustion engine and the exhaust catalyst, so that no special tank or injection device is required.

  However, it is necessary to make rich combustion when ammonia is generated, and in order to increase the amount of ammonia to be generated, it is necessary to consume oxygen remaining in the exhaust gas by combustion, and it is necessary to use a large amount of fuel. It leads to decline. In addition, in rich combustion, incomplete combustion is likely to occur due to a lack of air (oxygen), and an increase in hydrocarbon components becomes a problem.

  In addition, rich combustion is not practical because it becomes extremely incomplete combustion when the internal combustion engine is not sufficiently warm, and is difficult to control, leading to hydrocarbon emission and unpleasant combustion noise. The shift reaction that generates hydrogen for generating ammonia does not proceed unless the temperature is at least about 150 ° C. even if a catalyst is used. Therefore, ammonia generation at low temperatures is a problem, and purification is difficult. is there.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust purification catalyst capable of efficiently purifying NOx in exhaust gas at a low temperature even under an oxygen-excess atmosphere, and exhaust using the same. It is to provide a purification device.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, a carrier having high solid acid strength composed of an anion portion containing an element of group 15 or 16 after the third period and an oxygen atom, and a cation portion for compensating for the charge, and the carrier is supported on this carrier. According to the exhaust purification catalyst composed of the noble metal element and the exhaust purification apparatus using the exhaust purification catalyst, it is possible to efficiently purify NOx in the exhaust at a low temperature even in an oxygen-excess atmosphere. The headline and the present invention were completed.

That is, in the catalyst carrier surface of this invention, with H 2 _O presence or H _{2 O} generated conditions, the generation of NH ₃ by generating OH groups is promoted on the surface, thereby improving the purification performance of NOx. This OH group is produced by actively providing bridging oxygen produced by substituting the metal of the cation part with a metal having a lower valence, or bridging oxygen found in phosphoric acid or sulfate on the catalyst support. These bridging oxygens generate surface OH groups by reaction with H ₂ O as shown in FIG. 1, and due to the contribution of Bronsted acid, the equilibrium of ammonia production in the system is generated. Migrate to A remarkable NOx purification effect can be obtained by direct reduction of NOx to NH ₃ or indirect reduction of byproduct NH ₃ . More specifically, the present invention provides the following.

  The exhaust purification catalyst according to claim 1 is an exhaust purification catalyst used for purifying NOx in exhaust exhausted from an internal combustion engine and excessively containing oxygen, and is an element of Group 15 or Group 16 after the third period. And a carrier having a high solid acid strength comprising an anion portion containing oxygen atoms and a cation portion for compensating for a charge, and a noble metal element supported on the carrier.

  The exhaust purification catalyst according to claim 2 is the exhaust purification catalyst according to claim 1, wherein the anion portion is composed of a compound containing phosphorus oxide or sulfur oxide.

  The exhaust purification catalyst according to claim 3 is the exhaust purification catalyst according to claim 1 or 2, wherein the anion portion is an ortho type monomer or a polyacid type condensed to a dimer or more. Features.

  The exhaust purification catalyst according to claim 4 is the exhaust purification catalyst according to any one of claims 1 to 3, wherein the anion portion is pyrophosphoric acid.

  The exhaust purification catalyst according to claim 5 is the exhaust purification catalyst according to any one of claims 1 to 4, wherein the cation portion is mainly selected from the group consisting of tin, cerium, titanium, and zirconium. It is composed of a metal element.

  The exhaust purification catalyst according to claim 6 is the exhaust purification catalyst according to claim 5, wherein the metal element constituting the cation part is an alkaline earth element, a transition metal element, a group 13 element, and a rare earth gold element. It is characterized by being partially substituted by at least one element selected from the group consisting of elements having a valence lower than that of the metal element.

  The exhaust purification catalyst according to claim 7 is the exhaust purification catalyst according to any one of claims 1 to 6, wherein the noble metal element includes at least one of platinum and palladium.

  An exhaust emission control device according to claim 8 is an exhaust purification device used for purification of NOx in exhaust gas exhausted from an internal combustion engine and excessively containing oxygen, hydrogen supply means for supplying hydrogen into the exhaust gas, An exhaust purification catalyst according to any one of claims 1 to 7, wherein the exhaust purification catalyst according to any one of claims 1 to 7 is used to purify NOx contained in the exhaust using hydrogen supplied from the hydrogen supply means.

  The exhaust emission control apparatus according to claim 9 is the exhaust purification apparatus according to claim 8, wherein the hydrogen supply means performs a fuel reforming reaction, a fuel pyrolysis reaction, a fuel electrolysis reaction, or a fuel plasma reaction. It is a means for generating hydrogen by using it.

  An exhaust emission control device according to claim 10 is the exhaust emission control device according to claim 8 or 9, wherein the hydrogen supply means supplies hydrogen at a temperature of 70 ° C to 180 ° C at which hydrogen reducing ability is exhibited. It is characterized by being.

  The exhaust emission control device according to claim 11 is the exhaust purification device according to any one of claims 8 to 10, wherein the internal combustion engine is a compression ignition type internal combustion engine, and the fuel used is light oil. And

According to the present invention, even under a high-concentration oxygen atmosphere, a high NO conversion can be obtained at a low temperature of 70 ° C. to 180 ° C., and excellent NOx purification performance can be exhibited. When the output of the internal combustion engine is high, the amount of NO emission is large, and when the temperature of the exhaust gas is low, purification is difficult. Therefore, the present invention is considered to work effectively. As shown in the examples described later, for example, in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ (Pt: 1.0 mass%), NO is about 20% ammonia in the presence of 10% oxygen. And NO conversion of about 90% can be achieved.

  Hereinafter, embodiments of the present invention will be described in detail.

<Exhaust gas purification catalyst>
The exhaust purification catalyst of the present invention is used for purifying NOx in exhaust exhausted from an internal combustion engine and excessively containing oxygen. Specifically, a carrier having high solid acid strength composed of an anion portion containing an element of Group 15 or Group 16 after the third period and an oxygen atom, and a cation portion for compensating the charge, And a supported noble metal element.

[Carrier: Anion part]
The anion portion includes a group 15 or group 16 element after the third period and an oxygen atom. Preferably, it is composed of a compound containing phosphorus oxide or sulfur oxide, and is an ortho type monomer or a polyacid type condensed to a dimer or higher. Specifically, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, ultraphosphoric acid, orthosulfuric acid, pyrosulfuric acid, polythionic acid, sulfurous acid and the like are exemplified. Of these, pyrophosphate is particularly preferred.

  According to the exhaust purification catalyst having the anion portion having the above composition, the network structure of oxide ions constituting the anion portion is not changed by the metal element substitution of the cation portion described later, so that excellent NOx purification is achieved. Retain activity. The constituent compound of one network constituting the anion portion has a tetrahedral structure, and exhibits a higher catalytic activity than an octahedral structure such as molybdic acid or tungstic acid. It is considered that the unique electron transfer derived from the compound structure of the form contributes to the improvement of the catalytic activity.

[Carrier: Cation part]
The cation part compensates the charge of the exhaust purification catalyst by the combination with the anion part. The cation portion is preferably composed mainly of at least one metal element selected from the group consisting of tin, cerium, titanium, and zirconium. More preferably, the metal element constituting the cation portion is at least one element selected from the group consisting of an alkaline earth element, a transition metal element, a group 13 element, and a rare earth gold element, and more preferably than the metal element. It is partially substituted by a low valence element.

[Noble metal elements]
As the noble metal element, a noble metal element conventionally used in a purification catalyst can be used, but preferably contains at least one of platinum and palladium. According to the exhaust purification catalyst in which these platinum / palladium is supported on the carrier, excellent NOx purification performance can be exhibited.

[Preparation method]
The method for preparing the exhaust purification catalyst of the present invention is not particularly limited. For example, it can be prepared by using a conventionally known incipient wetness method. Specifically, after preparing a powder containing a predetermined amount of an oxide of a group 15 or group 16 element after the third period and a metal element constituting a cation part, the powder is dried under a predetermined condition, and then the predetermined condition is satisfied. The carrier is prepared by baking at An exhaust purification catalyst can be prepared by mixing a predetermined amount of a noble metal element compound with the prepared carrier, supporting the noble metal element using an incipient wetness method, and then treating it in air under predetermined conditions.

[Function and effect]
According to the present invention, even under a high-concentration oxygen atmosphere, a high NO conversion can be obtained at a low temperature of 70 ° C. to 180 ° C., and excellent NOx purification performance can be exhibited. The reason why a high NO conversion rate can be achieved at a low temperature in spite of being in a high concentration oxygen atmosphere is considered to be the progress of several denitration reactions. The main reaction mechanism will be described below.

  The exhaust purification catalyst of the present invention is composed of a carrier composed of an anion portion made of a specific oxide and a cation portion made of a metal, and a noble metal supported on the carrier. Then, a part of the cation portion of the metal is replaced with a low-valent metal to form a solid solution, whereby electron donating properties are exhibited and the noble metal on the support is activated. For this reason, the oxygen adsorption ability is lowered, and conversely, the hydrogen adsorption ability is improved, whereby ammonia and nitrogen are efficiently generated using nitrate ions as intermediate species. About this point, it is clear from the observation result of the catalytic reaction by the exhaust purification catalyst of the present invention that ammonia production has been confirmed on the catalyst surface. Further, the oxide ion exhibits an effect of promoting the activation of the supported metal by the substitutional solid solution of the metal cation part.

  The produced ammonia does not burn even in an oxygen atmosphere at low temperatures. Therefore, the generated ammonia is stably adsorbed on the acid sites expressed on the catalyst by the water vapor generated by the combustion of the introduced hydrogen or the water vapor present in the exhaust gas. In the exhaust purification catalyst of the present invention, the metal cation site is substituted and dissolved by a low-valent metal, and therefore the Bronsted acid point is expressed by adsorption of water vapor. For this reason, ammonia and NO adsorbed at this acid point react with each other, so that a high conversion rate can be obtained at a low temperature.

<Exhaust gas purification device>
The exhaust gas purification apparatus of the present invention is used for purifying NOx in exhaust gas exhausted from an internal combustion engine and excessively containing oxygen. Specifically, a hydrogen supply unit that supplies hydrogen into the exhaust gas, and the exhaust purification catalyst that purifies NOx contained in the exhaust gas by using hydrogen supplied from the hydrogen supply unit.

[Internal combustion engine]
In a compression ignition type internal combustion engine using light oil as fuel, lean combustion is performed, so that the exhaust gas is at a low temperature (70 to 180 ° C.) and contains a large amount of oxygen and NOx. Therefore, the exhaust purification device of the present invention including the exhaust purification catalyst having an excellent purification activity for NOx in oxygen-excess exhaust is suitably used for a compression ignition type internal combustion engine using light oil as fuel. .

[Hydrogen supply means]
The hydrogen supply means is not particularly limited, and examples thereof include supply using a hydrogen tank. Preferably, means for generating hydrogen using a fuel reforming reaction, a fuel pyrolysis reaction, a fuel electrolysis reaction, or a fuel plasma reaction is employed as the hydrogen supply means. Among these, those that supply hydrogen at a temperature of 70 ° C. to 180 ° C. at which hydrogen reducing ability is expressed are more preferably employed.

[Function and effect]
Since the exhaust purification apparatus of the present invention includes the exhaust purification catalyst, NOx is efficiently produced at a low temperature of 70 ° C. to 180 ° C. even under a high concentration oxygen atmosphere by the action of the exhaust purification catalyst as described above. Clean well.

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

<Example 1>
As shown in Tables 1 to 3, an oxide powder catalyst composed of an anion portion made of an oxide such as phosphoric acid and a cation portion made of metal is prepared by a preparation method as shown below. Evaluation was performed by the following evaluation method.

[Catalyst preparation 1]
First, a carrier of a phosphoric acid compound MP ₂ O ₇ (M: Sn, Ti, Zr, Ce) was prepared. Specifically, oxide powder composed of phosphoric acid and a cation part was mixed at a predetermined mixing ratio. About tin, the support | carrier was prepared by performing baking of 650 degreeC x 2.5 hours after drying at 300 degreeC x 24 hours. Regarding titanium, a carrier was prepared by drying at 120 ° C. for 2.5 hours and then baking at 500 ° C. for 2.5 hours. Zirconium was dried at 200 ° C. for 3 hours, treated at 400 ° C. for 1 hour, and then fired at 900 ° C. for 12 hours to prepare a carrier. Similarly, cerium was prepared by carrying out drying at 200 ° C. for 3 hours and firing at 600 ° C. for 15 minutes. All treatments were performed in air.

Each prepared carrier was subjected to X-ray diffraction (XRD) measurement, and it was confirmed from the measurement results that a single-phase product was obtained. After confirmation, platinum dinitrodiamine was used as a starting material so that 1% by mass of platinum was supported on the carrier. Specifically, after supporting platinum by the incipient wetness method, a Pt / MP ₂ O ₇ (M: Sn, Ti, Zr, Ce) catalyst was obtained by treating in air at 500 ° C. for 2 hours. .

[Selective reduction activity evaluation]
As activity evaluation, evaluation using reactive gas (NO: 1000 ppm, H ₂ : 4000 ppm, O ₂ : 10%, N ₂ : balance, flow rate: 30 mL / s) was performed. Specifically, the above reaction gases of 70 ° C., 100 ° C., 140 ° C., and 180 ° C. are circulated under predetermined conditions with respect to 0.1 g of each catalyst prepared above (the space velocity is about 10,000 h ⁻¹ ). FT-IR spectroscopic measurement using a gas cell for NO and NO ₂ contained in the gas before and after the reaction (using SPECTRUM 2000 manufactured by PerkinElmer, 5 scans at 900-3900 cm ⁻¹ with MCT detector, resolution Was determined by 0.5 cm ⁻¹ ) to obtain the NO conversion rate. The results are shown in Table 1.

  As shown in Table 1, in any of the catalysts, a high NO conversion rate was obtained at a low temperature of 70 ° C. to 180 ° C. When a tetravalent element was selected and evaluated for the cation metal species of the phosphate compound used as the carrier, it was found that there was not much difference in activity.

  Next, cerium was selected as the cation part, and the catalytic activity was evaluated when sulfate was used as the carrier instead of phosphate. The sulfate carrier was prepared by impregnating and supporting an aqueous solution of platinum dinitrodiamine on a commercially available cerium sulfate (manufactured by Wako Pure Chemical Industries, Ltd.). The platinum loading and the heat treatment after loading were performed under the same conditions as described above. Furthermore, a sulfate in which cerium was partially substituted with iron was also prepared in the same manner as described above. Moreover, the same activity evaluation as the above was performed about each prepared catalyst. The results are shown in Table 2.

As shown in Table 2, the NO conversion rate was not significantly different from that of the phosphoric acid compound, and a high NO conversion rate was obtained at a low temperature of 70 ° C to 180 ° C. As a point feature, the improvement of the _{N 2} selectivity is observed, whereas the _{N 2} selectivity at 100 ° C. in _CeP 2 _{O 7} support was _{25%, Ce (SO 4)} 2 in 35% It became. Moreover, it turned out that the activity of a sulfate falls by partially substituting cerium with iron.

<Comparative Example 1>
As Comparative Example 1, a catalyst using a single oxide of tin as a carrier was prepared and evaluated for activity. As the tin oxide, a commercially available reagent grade (manufactured by Wako Pure Chemical Industries, Ltd.) was used. Further, a catalyst was prepared in which a part of tin was partially substituted and dissolved by + trivalent scandium. The preparation was performed by adding a predetermined amount of scandium oxide to the above tin oxide and heating and baking at 800 ° C. for 12 hours. The results are shown in Table 3.

  As shown in Table 3, in the evaluation of the activity of the catalyst using the oxide of tin alone as a support, good results were not obtained. Further, the activity of a catalyst in which a part of tin was partially substituted by solid solution with + trivalent scandium was almost the same as that of an unsubstituted catalyst.

<Example 2>
For the phosphate of Example 1, a catalyst was prepared by fixing the cation portion to tin and partially replacing it with a low-valent metal, and evaluating the activity.

[Catalyst preparation 2]
Manganese, iron, nickel, and indium were used as replacement metals. Phosphate was prepared by solid phase reaction. Ammonium phosphate, which is a phosphoric acid starting material, and an oxide serving as a cation part were used, and after a predetermined amount of the starting material was mixed in an agate mortar, it was baked at 650 ° C. for 3 hours. Thereafter, platinum was supported by the same method as described above, and heat treatment was performed.

[Selective reduction activity evaluation]
The NO selective reduction characteristics were evaluated by the same method as in Example 1. The results are shown in Table 4.

As shown in Table 4, the catalyst in which a part of tin was substituted with a 3d transition metal such as manganese, iron, nickel, etc. showed better reduction characteristics than the unsubstituted one, whereas it was substituted with indium. On the contrary, the activity of the catalyst decreased. That is, it was found that the activity of the above-described sulfuric acid compound was reduced by partial substitution of the cation part, whereas the phosphoric acid compound showed the opposite tendency. In addition, SnP ₂ O ₇ is known to exhibit proton conductivity by replacing tetravalent Sn sites with trivalent indium, but the NO conversion rate decreases conversely by indium replacement. As a result, it was confirmed that the active hydrogen supplied from the proton conductor does not contribute much to the reduction of NO.

With respect to the platinum-supported catalyst in which the Sn site of SnP ₂ O ₇ was substituted with Fe, the temperature-programmed desorption spectra of NH ₃ , O ₂ , and H ₂ were measured and compared with those of the unsubstituted catalyst. The temperature programmed desorption spectrum of NH ₃ was performed by the following method. The catalyst 0.1g was charged into the reaction tube, pretreated He gas flow under 450 ° C. As a switching After heating for 1 h, the circulation gas is cooled to 100 ° C. in NH ₃ from He, to adsorb the NH ₃ . Thereafter, the reaction gas was switched to He again, and the desorption spectrum in the range of 100 to 550 ° C. was evaluated by a gas chromatograph (manufactured by Shimadzu Corporation, GC-8A) at a temperature rising rate of 5 ° C./min. Temperature-programmed desorption spectrum of O ₂ is _{O 2} gas flow under, treated 1 hour before at 450 ° C., The temperature was lowered to 50 ° C., the flowing gas was switched from _{O 2} in the He (50 ° C. for 30 minutes Retention). Thereafter, similarly, a desorption spectrum in the range of 50 to 550 ° C. was evaluated at a heating rate of 5 ° C./min. The temperature-programmed desorption spectrum of H _{2 was} the same as that of O ₂ , but the carrier gas at the time of spectrum measurement was changed from He to Ar.

The temperature programmed desorption spectra of NH ₃ , O ₂ and H ₂ are shown in FIGS. From the temperature-programmed desorption spectra of NH ₃ shown in FIGS. 2 and 3, it was found that a new peak appeared around 250 ° C. due to the substitution of Fe, and the solid acidity was improved. Moreover, from the temperature-programmed desorption spectra of O ₂ and H ₂ shown in FIGS. 4 to 7, it was confirmed that the adsorption ability of O ₂ was weakened by substitution of Fe, and conversely, the adsorption ability of H ₂ was strengthened, These were considered to contribute to the formation of NH ₃ when oxygen was excessive.

The reaction gas used in the evaluation contained 10% oxygen, but even in the presence of 10% oxygen, ammonia slip was confirmed in the FT-IR spectrum in the catalyst substituted with the transition metal. However, with the low activity Pt / Sn _0.9 In _0.1 P ₂ O ₇ , only a small ammonia peak was observed. Further, for each of Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ and Ce (SO ₄ ) ₂ support after the reaction gas at 140 ° C. was circulated, the diffuse reflection infrared was used using the FT-IR apparatus. The measurement by spectroscopy (DRIFTs) was performed by scanning 50 scans at 1000 to 4000 cm ⁻¹ . The results are shown in FIGS. As shown in FIGS. 8 and 9, an ammonia peak was observed in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ , and an ammonia absorption peak was also confirmed in the Ce (SO ₄ ) ₂ carrier. It was.

<Example 3>
Since ammonia slip was observed in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ prepared in Example 2, an ammonia calibration curve was prepared in the gas cell FT-IR, and the reaction gas temperature was 140 ° C. The oxygen concentration dependence of ammonia selectivity was evaluated. For comparison, the same evaluation was performed on the Sn _0.9 In _0.1 P ₂ O ₇ support. The results are shown in FIGS.

It was confirmed that about 20% of NO was converted to ammonia even in the region where the oxygen concentration was 10%. On the other _hand, the Sn _0.9 In _0.1 P 2 _{O 7} carrier, although the generation of ammonia by the oxygen content of 10% were only slightly observed, because they exhibit a high _{N 2} selectivity, resulting ammonia The reduction of NO was suggested.

Therefore, for the Sn _0.9 In _0.1 P ₂ O ₇ supported catalyst, the adsorbed species generated in the reaction process when the oxygen amount was 1% was evaluated by the FT-IR diffuse reflection spectrum. The results are shown in FIG. As shown in FIG. 12, peaks of adsorbed species of NO ₂ ⁻ and NH ₄ ⁺ were observed, and it was found that the reduction of NOx proceeds by the above reaction mechanism.

<Comparative example 2>
As Comparative Example 2, a platinum-based catalyst using molybdate (H ₃ PMo ₁₂ O ₄₀ · nH ₂ O: HPM) and tungstate (H ₃ PW ₁₂ O ₄₀ · nH ₂ O: HPW) as a support was prepared. The characteristics were evaluated. Since the specific surface areas of molybdate and tungstate are low, these were supported on TiO ₂ (reference catalyst TIO-1 distributed by the Catalysis Society of Japan). The loading was performed by impregnating each aqueous solution of TiO ₂ with TiO ₂ (the loading amount of the poly acid salt was 10% by mass with respect to the carrier) and then drying at 120 ° C. for 3 days. Next, platinum was supported in the same manner as in Example 1. The evaluation results are shown in Table 5.

  As shown in Table 5, both Pt / HPM and Pt / HPW were found to have very low NO reduction activity. From this result, good NO reduction ability is not obtained only by the polyacid network, and the cation part and polyacid compound form (for example, tetrahedron in phosphoric acid, octahedron in molybdenum / tungstic acid) have catalytic activity. It was thought to have contributed.

<Reference Example 1>
Since it was thought that the feature of the present invention was caused by the surface characteristics of the catalyst support, an attempt was made to introduce orthosulfate groups on the surface of a normal metal oxide. ZrO ₂ reference support (ZRO-3) distributed by the Catalytic Society of Japan and (NH ₄ ) ₂ SO ₄ were mixed with Zr such that S was in an atomic ratio of 10: 1, and then calcined at 600 ° C. for 3 hours. As a result, a ZrO ₂ carrier having sulfate ion groups introduced on the surface was prepared. Platinum was supported by the same method as in Example 1. Here, as a comparison, untreated ZrO ₂ was similarly loaded with platinum, and the activity was evaluated by the same method as in Example 1. The results are shown in Table 6.

As shown in Table 6, ZrO ₂ whose surface was modified with sulfate ions showed higher activity than that of untreated. As described above, it is considered that sulfate ions are bound to Zr which is partially positively charged (see, for example, M. Bensitel et al., Materials Chemistry and Physics, 19 (1988), 147-156). It has been confirmed that sulfate ions composed of tetrahedral units contribute not only to compounds but also to the catalytic activity not only in the adsorbed species state.

Moreover, about both catalysts, the diffuse reflection spectrum in 100 degreeC was measured by FT-IR. The diffuse reflection spectrum measurement results are shown in FIGS. In the case of surface modification, the peaks of adsorbed species attributed to NO ₂ ⁻ and NH ₄ ⁺ were observed, whereas in the untreated one, the peak of NO ₃ ⁻ alone was observed. It was also suggested that the reduction of NO progressed by the same mechanism as in Example 3 in the surface-modified catalyst.

It is a figure for demonstrating the ammonia promotion mechanism of this invention. It is a temperature-programmed desorption spectrum diagram of NH ₃ in Pt / SnP ₂ O ₇ . It is a temperature-programmed desorption spectrum diagram of NH ₃ in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ . It is a temperature-programmed desorption spectrum diagram of O ₂ in Pt / SnP ₂ O ₇ . It is a temperature-programmed desorption spectrum diagram of O ₂ in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ . It is a temperature-programmed desorption spectrum of H ₂ in Pt / SnP ₂ O ₇ . It is a temperature-programmed desorption spectrum diagram of H ₂ in Pt / Sn _0.9 Fe _0.1 P ₂ O ₇ . It is a FT-IR diffuse reflectance spectrum of the _{Pt / Sn 0.9 Fe 0.1 P 2} O 7 after the reaction gas flow. Ce after the reaction gas flow _{(SO 4)} is a FT-IR diffuse reflectance spectrum of the ₂ carrier. It is a diagram showing the oxygen concentration dependency of the ammonia selectivity of _{Pt / Sn 0.9 Fe 0.1 P 2} O 7. Is a diagram showing the oxygen concentration dependency of the ammonia selectivity of _{Pt / Sn 0.9 In 0.1 P 2} O 7. Is a FT-IR diffuse reflectance spectrum of the _{Pt / Sn 0.9 In 0.1 P 2} O 7 after the reaction gas flow. Is a FT-IR diffuse reflectance spectrum of the Pt / ZrO ₂ (surface modification). Pt / ZrO ₂ is a FT-IR diffuse reflectance spectrum of the (untreated).

Claims (10)

An exhaust purification device used for purifying NOx in exhaust exhausted from an internal combustion engine and containing oxygen excessively,
A hydrogen supply means for supplying hydrogen into the exhaust, and an exhaust purification catalyst for purifying NOx contained in the exhaust using the hydrogen supplied from the hydrogen supply means,
The exhaust purification catalyst includes a carrier having a high solid acid strength comprising a group 15 or group 16 element after the third period, an anion portion containing an oxygen atom, and a cation portion for compensating the charge, and the carrier. Composed of noble metal elements supported on
The exhaust gas purification apparatus , wherein the cation portion is mainly composed of at least one metal element selected from the group consisting of cerium, titanium, and zirconium. The metal element constituting the cation part is at least one element selected from the group consisting of alkaline earth elements, transition metal elements, group 13 elements, and rare earth elements, and an element having a lower valence than the metal element The exhaust purification device according to claim 1, wherein the exhaust purification device is partially replaced by An exhaust purification device used for purifying NOx in exhaust exhausted from an internal combustion engine and containing oxygen excessively,
A hydrogen supply means for supplying hydrogen into the exhaust, and an exhaust purification catalyst for purifying NOx contained in the exhaust using the hydrogen supplied from the hydrogen supply means,
The exhaust purification catalyst includes a carrier having a high solid acid strength comprising a group 15 or group 16 element after the third period, an anion portion containing an oxygen atom, and a cation portion for compensating the charge, and the carrier. Composed of noble metal elements supported on
The cation portion is mainly composed of tin,
Tin constituting the cation portion is partially substituted with an element having at least one element selected from the group consisting of an alkaline earth element, a transition metal element, and a rare earth element and having a lower valence than tin. An exhaust emission control device characterized by the above. The exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the anion portion is composed of a compound containing phosphorus oxide or sulfur oxide. 5. The exhaust emission control device according to claim 1, wherein the anion portion is an ortho type monomer or a polyacid type condensed to a dimer or more. The exhaust emission control device according to any one of claims 1 to 5, wherein the anion portion is pyrophosphoric acid. The exhaust emission control device according to any one of claims 1 to 6, wherein the noble metal element includes at least one of platinum and palladium. The hydrogen supply means, the reforming reaction of the fuel, the thermal decomposition reaction of the fuel, either electrolysis reaction of the fuel, or by using a plasma reaction of the fuel from claim 1, characterized in that the means for generating hydrogen 7 Or an exhaust emission control device. The exhaust gas purification apparatus according to any one of claims 1 to 8 , wherein the hydrogen supply means supplies hydrogen at a temperature of 70 ° C to 180 ° C at which hydrogen reducing ability is exhibited. The exhaust emission control device according to any one of claims 1 to 9 , wherein the internal combustion engine is a compression ignition type internal combustion engine, and the fuel used is light oil.

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