N2O DECOMPOSITION CATALYST

Abstract

Provided are: a catalyst containing a carrier including SiO.sub.2 and Al.sub.2O.sub.3 and an iron element carried on the carrier, having a total amount of desorbed pyridine of 100 mol or more with respect to 1 g catalyst within the range of 150 C. inclusive to 450 C. exclusive in the TPD spectrum, and configured to promote the decomposition reaction of nitrogen monoxide and nitric monoxide; and a method of reducing nitrogen monoxide and nitric monoxide in a gas containing water and/or a sulfur oxide, nitrogen monoxide, and nitric monoxide, the method comprising bringing a gas and a reductant into contact with the catalyst to decompose nitrogen monoxide and nitric monoxide, the gas containing water and/or a sulfur oxide, nitrogen monoxide, and nitric monoxide.

Claims

1. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein in a TPD spectrum, a total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. is 100 mol or more per 1 g of the catalyst, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

2. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein in a TPD spectrum, a ratio of a pyridine desorption amount at a peak top present in a range of 150 C. or higher and lower than 450 C. to a pyridine desorption amount at a peak top present in a range of 450 C. or higher and 800 C. or lower is more than 1, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

3. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein in a TPD spectrum, a ratio of a total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. to a total amount of pyridine desorbed in a range of 450 C. or higher and 800 C. or lower is 0.9 or more, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

4. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein in a TPD spectrum, a temperature at a peak top in a range of 450 C. or higher and 800 C. or lower is 490 C. or higher and 650 C. or lower, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

5. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein a saturated adsorption amount of pyridine is 100 mol or more per 1 g of the catalyst, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

6. A catalyst comprising: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support, wherein a crystallite size is 20 nm or more, and the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

7. A catalyst comprising: an organic structure-directing agent (OSDA)-free zeolite; and an iron element supported on the organic structure-directing agent (OSDA)-free zeolite, the catalyst is configured to promote a decomposition reaction of nitrous oxide or a decomposition reaction of nitrous oxide and nitric oxide.

8. The catalyst according to claim 1, wherein even after being exposed to gas containing 20% of H.sub.2O and 20 ppm of SO.sub.2 at 530 C. for 70 hours, a NO.sub.2 decomposition rate is 60% or more and NO decomposition rate is 90% or more under a condition of 450 C.

9. A catalyst element comprising: a substrate; and the catalyst according to claim 1 that covers the substrate.

10. A method of reducing nitrous oxide or nitrous oxide and nitric oxide from gas containing at least one selected from water and sulfur oxide and nitrous oxide or from gas containing at least one selected from water and sulfur oxide, nitrous oxide, and nitric oxide, the method comprising: bringing the gas containing at least one selected from water and sulfur oxide and nitrous oxide or the gas containing at least one selected from water and sulfur oxide, nitrous oxide, and nitric oxide and a reducing agent into contact with the catalyst according to claim 1 to decompose nitrous oxide or nitrous oxide and nitric oxide.

11. The method according to claim 10, wherein in the gas, a content of the water is 10% or more and a content of the sulfur oxide is 15 ppm or more.

12. An exhaust gas treatment device comprising: a reactor that accommodates the catalyst according to claim 1; a first supply line that is configured such that gas to be treated flows into the reactor; a second supply line that is configured such that a reducing agent flows into the reactor; and an exhaust line that is configured such that gas flows out from the reactor, wherein the gas to be treated is gas containing at least one selected from water and sulfur oxide and nitrous oxide or gas containing at least one selected from water and sulfur oxide, nitrous oxide, and nitric oxide.

13. The exhaust gas treatment device according to claim 12, wherein in the gas to be treated, a content of the water is 10% or more and a content of the sulfur oxide is 15 ppm or more.

14. An ammonia fuel engine comprising the exhaust gas treatment device according to claim 12.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0110] FIG. 1 is a diagram showing an example of an ammonia multi-fuel engine into which an exhaust gas treatment system is incorporated.

[0111] FIG. 2 is a diagram showing the example of the ammonia multi-fuel engine into which the exhaust gas treatment system is incorporated.

[0112] FIG. 3 is a diagram showing TPD spectra of catalysts A to F.

[0113] FIG. 4 is a diagram showing N.sub.2O decomposition rates of the catalysts A to F with respect to the temperature.

[0114] FIG. 5 is a diagram showing NO decomposition rates of the catalysts A to F with respect to the temperature.

[0115] FIG. 6 is a diagram showing a catalytic reaction rate of N.sub.2O with respect to a pyridine desorption amount w at 150 C. to 450 C.

[0116] FIG. 7 is a diagram showing TPD spectra of catalysts G, H, and J to N.

[0117] FIG. 8 is a diagram showing N.sub.2O decomposition rates of the catalysts G, H, and J to N with respect to the temperature.

[0118] FIG. 9 is a diagram showing NO decomposition rates of the catalysts G, H, and J to N with respect to the temperature.

[0119] FIG. 10 is a diagram showing N.sub.2O decomposition rates of catalysts J2 and G2 with respect to the temperature.

[0120] FIG. 11 is a diagram showing NO decomposition rates of the catalysts J2 and G2 with respect to the temperature.

[0121] FIG. 12 is a diagram showing N.sub.2O decomposition rates of catalysts J, J.sub.H, K, K.sub.H, G, and G.sub.H with respect to the temperature.

[0122] FIG. 13 is a diagram showing NO decomposition rates of the catalysts J, J.sub.H, K, K.sub.H, G, and G.sub.H with respect to the temperature.

[0123] FIG. 14 is a diagram showing N.sub.2O decomposition rates of catalysts O, P, Q, R, and S with respect to the temperature.

[0124] FIG. 15 is a diagram showing NO decomposition rates of the catalysts O, P, Q, R, and S with respect to the temperature.

DESCRIPTION OF EMBODIMENTS TO CARRY OUT THE INVENTION

[0125] A N.sub.2O decomposition catalyst according to the present invention contains: a support containing SiO.sub.2 and Al.sub.2O.sub.3; and an iron element supported on the support.

[0126] In the support, SiO.sub.2 and Al.sub.2O.sub.3 may be contained as a mixture or may be contained as a composite material.

[0127] Examples of the composite material of SiO.sub.2 and Al.sub.2O.sub.3 include aluminosilicate (xM.sub.2O.Math.yAl.sub.2O.sub.3.Math.zSiO.sub.2.Math.nH.sub.2O).

[0128] Specific examples of the aluminosilicates include mullite (3Al.sub.2O.sub.3.Math.2SiO.sub.2 to 2Al.sub.2O.sub.3.Math.SiO.sub.2); kaolinite (Al.sub.4Si.sub.4O.sub.10(OH).sub.s); illite ((K,H.sub.3O)(Al,Mg, Fe).sub.2(Si,Al).sub.4O.sub.10[(OH).sub.2,(H.sub.2O)]); zeolite; and feldspar ((Na,K,Ca,Ba)Al(AI,Si)Si.sub.2O.sub.8) such as sodium aluminosilicate, potassium aluminosilicate, or calcium aluminosilicate.

[0129] Examples of the zeolite include: natural zeolites such as amicite, analcime, barrerite, bellbergite, bikitaite, boggsite, brewsterite, brewsterite-Sr, brewsterite-Ba, chabazite, chabazite-Ca, chabazite-Na, chabazite-K, chiavennite, clinoptilolite, clinoptilolite-K, clinoptilolite-Na, clinoptilolite-Ca, cowlesite, dachiardite, dachiardite-Ca, dachiardite-Na, edingtonite, epistilbite, erionite, erionite-Na, erionite-K, erionite-Ca, faujasite, faujasite-Na, faujasite-Ca, faujasite-Mg, ferrierite, ferrierite-Mg, ferrierite-K, ferrierite-Na, garronite, gaultite, gismondine, gmelinite, gmelinite-Na, gmelinite-Ca, gmelinite-K, gobbinsite, gonnardite, goosecreekite, gottardiite, harmotome, heulandite, heulandite-Ca, heulandite-Sr, heulandite-Na, heulandite-K, hsianghualite, kalborsite, laumontite, levyne, levyne-Ca, levyne-Na, lovdarite, maricopaite, mazzite, merlinoite, mesolite, montesommaite, mordenite, mutinaite, natrolite, offretite, pahasapaite, partheite, paulingite, paulingite-Na, paulingite-K, paulingite-Ca, perlialite, phillipsite, phillipsite-Na, phillipsite-K, phillipsite-Ca, pollucite, roggianite, scolecite, stellerite, stilbite, stilbite-Ca, stilbite-Na, terranovaite, thomsonite, tschernichite, tschortnerite, wairakite, weinebeneite, willhendersonite, or yugawaralite; and synthetic zeolite such as A-type (LTA-type) zeolite, X-type (FAU-type) zeolite, LSX-type (FAU-type) zeolite, beta-type (BEA-type) zeolite, ZSM-5-type (MFI-type) zeolite, ferrierite-type (FER-type) zeolite, mordenite-type (MOR-type) zeolite, L-type (LTL-type) zeolite, Y-type (FAU-type) zeolite, MCM-22-type (MWW-type) zeolite, offretite/erionite-type (O/E-type) zeolite, AEI-type zeolite, AEL-type zeolite, AFT-type zeolite, AFX-type zeolite, CHA-type zeolite, EAB-type zeolite, ERI-type zeolite, KFI-type zeolite, LEV-type zeolite, LTN-type zeolite, MSO-type zeolite, RHO-type zeolite, SAS-type zeolite, SAT-type zeolite, SAV-type zeolite, SFW-type zeolite, TON-type zeolite, or TSC-type zeolite.

[0130] Among these, as the support used in the present invention, zeolite is preferable, synthetic zeolite is more preferable, and the BEA-type zeolite is still more preferable.

[0131] A ratio of SiO.sub.2 to Al.sub.2O.sub.3(SiO.sub.2/Al.sub.2O.sub.3 molar ratio) is preferably 1 or more, more preferably 5 or more, still more preferably 10 or more, and still more preferably 20 or more. As the ratio of SiO.sub.2 increases, the durability of the catalyst tends to increase. Therefore, the upper limit of the SiO.sub.2/Al.sub.2O.sub.3 molar ratio is not particularly limited as long as the catalyst can be produced and, for example, is preferably 100, more preferably 60, and still more preferably 55.

[0132] The synthetic zeolite can be obtained, for example, by mixing a silica source, an alumina source, an alkali source, a solvent, an organic structure-directing agent (OSDA), a surfactant, and the like to obtain a starting reaction mixture, causing a hydrothermal reaction to occur with the starting reaction mixture under high temperature and high pressure in an autoclave. The synthetic zeolite obtained using this method contains an organic component derived from OSDA. The organic component can be removed by subsequent sintering.

[0133] Some synthetic zeolite can be obtained through a hydrothermal reaction without using OSDA. Further, one synthetic zeolite can be obtained using a mechanochemical treatment or a vapor synthesis method without using OSDA. The synthetic zeolite obtained without using OSDA (hereinafter, referred to as OSDA-free zeolite) does not contain an organic component derived from OSDA. In the present invention, the OSDA-free zeolite can be preferably used. The SiO.sub.2/Al.sub.2O.sub.3 molar ratio in the OSDA-free zeolite is preferably 1 or more, more preferably 5 or more, and still more preferably 8 or more. The upper limit of the SiO.sub.2/Al.sub.2O.sub.3 molar ratio in the OSDA-free zeolite is, for example, preferably 50, more preferably 45, and still more preferably 40.

[0134] An iron element is supported on the support in the form of Fe, Fe(III), Fe(II), Fe(II,III), or the like. Fe(III), Fe(II), or Fe(II,III) may be in the form of iron oxide, iron oxyhydroxide, iron hydroxide, or the like. The support may be in a from where iron fine particles or fine particles of an iron compound (for example, iron oxide) are attached to the support or may be in a form where cations of an element forming the support exchange (ion exchange) with cations of iron. In the decomposition reaction of N.sub.2O, the supported iron element may be in the form of high-valence iron such as Fe(IV), Fe(V), Fe(VI), or the like.

[0135] The amount of the iron element supported is preferably 0.1 wt % or more, more preferably 1 wt % or more, still more preferably 2 wt % or more, and still more preferably 3 wt % or more in terms of Fe.sub.2O.sub.3 with respect to the support. The upper limit of the amount of the iron element supported is not particularly limited as long as the iron element can be supported and is, for example, preferably 10 wt % and more preferably 7 wt % in terms of Fe.sub.2O.sub.3 with respect to the support. A method of supporting the iron element on the support is not particularly limited. For example, a method of infiltrating the support with an aqueous solution or a suspension liquid of an iron compound and subsequently perforning drying/sintering.

[0136] In the N2O decomposition catalyst according to the present invention, optionally, another metal element may be supported on the support, and/or another metal element may be further supported on another support.

[0137] Examples of the other metal element include copper group elements (Cu, Ag, Au), platinum group elements (Pt, Rh, Pd, Ru, and the like), transition metal elements (Co, Ni, and the like other than Fe), and base metal elements (V, Mo, W, and the like) for which a function of promoting the decomposition reaction of N.sub.2O or a function of promoting the decomposition reaction of N.sub.2O and the decomposition reaction of NO can be expected. Examples of the other support on which the other metal element is supported include supports containing SiO.sub.2, Al.sub.2O.sub.3, SiO.sub.2Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2, TiO.sub.2SiO.sub.2, and SiC.

[0138] The N2O decomposition catalyst according to the present invention has acid sites derived from an OH group or the like. The properties of the acid sites can generally be observed by a method known as a pyridine-TPD method. In the pyridine-TPD method, for example, a hydrogen flame ionization detector (FID) can be used as a detector. Pyridine is adsorbed on the acid sites. Pyridine can be adsorbed on the acid sites of both an outer surface and an inner surface of pores of the catalyst. It is generally understood that, as the temperature at which the adsorbed pyridine desorbs increases, the acid strength of the acid sites increases. In addition, it is also said that pyridine desorbed at a high temperature is derived from an acid site affected by diffusion, that is, an acid site on the inner surface of the pores (Nakano et al., Measurement of Acidity of Various Zeolites by Temperature-Programmed Desorption Method, Toyo Soda Research Report, Vol. 29, No. 1 (1985), pp. 3-11). It is said that the effective molecular diameter of pyridine is 5.8 (refer to Anderson et al. J. Catal., 58, 114 (1979)). The total amount of acid sites can be determined by the saturated adsorption amount of pyridine. When pyridine is adsorbed and subsequently is heated at a certain rate (20 C./min), the acid strength distribution of the acid sites can be determined by a distribution of the amounts of pyridine desorbed at respective temperatures (this distribution will also be referred to as a TPD spectrum). In the present invention, the adsorption of pyridine can be performed at room temperature to 150 C. and preferably at 150 C.

[0139] In a TPD spectrum of the N.sub.2O decomposition catalyst according to the present invention, a ratio of a total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. to a total amount of pyridine desorbed in a range of 450 C. or higher and 800 C. or lower is preferably 0.9 or more, more preferably 0.98 or more, still more preferably 1 or more, and still more preferably 1.1 or more. The upper limit of the ratio of the total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. to the total amount of pyridine desorbed in a range of 450 C. or higher and 800 C. or lower is not particularly limited as long as the catalyst can be produced.

[0140] In the TPD spectrum of the N.sub.2O decomposition catalyst according to the present invention, the total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. is preferably 100 mol or more, more preferably 200 mol or more, still more preferably 250 mol or more, and still more preferably 300 mol or more per 1 g of the catalyst. The upper limit of the total amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. is not particularly limited as long as the catalyst can be produced.

[0141] In the TPD spectrum of the N.sub.2O decomposition catalyst according to the present invention, the total amount of pyridine desorbed in a range of 450 C. or higher and 800 C. or lower is preferably 1000 mol or less, more preferably 800 mol or less, and still more preferably 500 mol or less per 1 g of the catalyst. The lower limit of the total amount of pyridine desorbed in a range of 450 C. or higher and 800 C. or lower is not particularly limited as long as the catalyst can be produced.

[0142] In the TPD spectrum of the N.sub.2O decomposition catalyst according to the present invention, a value of a L peak (a pyridine desorption amount at a peak top present in a range of 150 C. or higher and lower than 450 C.) is more than a value of a H peak (a pyridine desorption amount at a peak top present in a range of 450 C. or higher and 800 C. or lower). That is, a ratio of the value of the L peak to the value of the H peak is preferably more than 1, more preferably 1.12 or more, still more preferably 1.2 or more, still more preferably 1.4 or more, and most preferably 1.6 or more. The upper limit of the ratio of the value of the L peak to the value of the H peak is not particularly limited as long as the catalyst can be produced.

[0143] In the TPD spectrum of the N.sub.2O decomposition catalyst according to the present invention, the lower limit of a temperature at which the H peak appears (temperature at a peak top in a range of 450 C. or higher and 800 C. or lower) is preferably 490 C., more preferably 510 C., and still more preferably 530 C., and the upper limit thereof is preferably 650 C., more preferably 620 C., still more preferably 600 C., and still more preferably 580 C.

[0144] In the N.sub.2O decomposition catalyst according to the present invention, it is preferable that the saturated adsorption amount of pyridine is large. In the N2O decomposition catalyst according to the present invention, the saturated adsorption amount of pyridine is preferably 100 mol or more, more preferably 200 mol or more, still more preferably 500 mol or more, and still more preferably 700 mol or more per 1 g of the catalyst. In the N.sub.2O decomposition catalyst according to the present invention, the upper limit of the saturated adsorption amount of pyridine is not particularly limited as long as the catalyst can be produced, and is, for example, preferably 2000 mol and more preferably 1500 mol per 1 g of the catalyst. The saturated adsorption amount of pyridine can be measured at 150 C.

[0145] In the N.sub.2O decomposition catalyst according to the present invention, it is preferable that a crystallite size is large. In the N.sub.2O decomposition catalyst according to the present invention, the crystallite size is preferably 5 nm or more, more preferably 10 nm or more, still more preferably 20 nm or more, and still more preferably 30 nm or more. In the N.sub.2O decomposition catalyst according to the present invention, the upper limit of the crystallite size is not particularly limited as long as the catalyst can be produced, and is, for example, preferably 100 nrn and more preferably 80 nm. The crystallite size can be measured using an X-ray diffraction method (for example, refer to JIS H 7805 or JIS R 7651).

[0146] In the N.sub.2O decomposition catalyst according to the present invention, it is preferable that, even after being exposed to gas containing 20% of H.sub.2O and 20 ppm of SO.sub.2 at 530 C. for 70 hours, a NO.sub.2 decomposition rate and NO decomposition rate are high. In the N.sub.2O decomposition catalyst according to the present invention, it is preferable that, even after being exposed to gas containing 20% of H.sub.2O and 20 ppm of SO.sub.2 at 530 C. for 70 hours, a NO.sub.2 decomposition rate is 60% or more and NO decomposition rate is 90% or more under a condition of 450 C.

[0147] The catalyst according to the present invention having the pyridine adsorption properties has excellent water resistance and/or sulfur oxide resistance and has a high function of promoting the decomposition reaction of N.sub.2O or the decomposition reaction of N.sub.2O and NO.

[0148] The N2O decomposition catalyst alone according to the present invention can promote not only the reduction reaction of N.sub.2O but also the reduction reaction of NO or NO.sub.2 in gas. The N.sub.2O decomposition catalyst according to the present invention can be used in combination or together with a well-knowncatalyst (denitration catalyst) configured to reduce NO or NO.sub.2. By using the N2O decomposition catalyst according to the present invention in combination or together with the denitration catalyst, nitrogen oxide (NO, NO.sub.2, N.sub.2O) in exhaust gas can be more effectively reduced.

[0149] Examples of the reduction reaction of NO or NO.sub.2 by ammonia include those represented by the following formulae.

4NO+4NH.sub.3+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O

NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O

6NO.sub.2+8NH.sub.3.fwdarw.7N.sub.2+12H.sub.2O

[0150] Examples of the reduction reaction of nitrous oxide by ammonia include those represented by the following formulae.

3N.sub.2O+2NH.sub.3.fwdarw.4N.sub.2+3H.sub.2O

[0151] Depending on a well-known molding method, the N.sub.2O decomposition catalyst according to the present invention can be molded in a shape of a sphere, a Raschig ring, a Berl saddle, a Paul ring, a honeycomb, a plate, a corrugated shape, or the like. In addition, a catalyst element including: a substrate having a desired shape; and the N2O decomposition catalyst according to the present invention that covers the substrate may be adopted. Examples of the substrate include a honeycomb substrate, a corrugated substrate, and a lath substrate (such as expanded metal, punched metal, or wire netting).

[0152] An exhaust gas treatment device according to the present invention includes: a reactor that accommodates the N.sub.2O decomposition catalyst or the catalyst element according to the present invention; a first supply line that is configured such that gas to be treated flows into the reactor; a second supply line that is configured such that a reducing agent flows into the reactor; and an exhaust line that is configured such that gas flows out from the reactor. The N.sub.2O decomposition catalyst or the catalyst element according to the present invention can be accommodated in the reactor to form a fixed bed, a fluidized bed, or a moving bed. In the exhaust gas treatment device according to the present invention, the gas to be treated is gas containing at least one selected from water and sulfur oxide and nitrous oxide or gas containing at least one selected from water and sulfur oxide, nitrous oxide, and nitric oxide. In the gas to be treated, the content of water is preferably 10% or more and/or the content of sulfur oxide is preferably 15 ppm or more.

[0153] Examples of the gas to be treated used in the present invention include exhaust gas of a coal-fired fluidized bed boiler, exhaust gas of an ammonia fuel marine engine, and exhaust gas of an ammonia fueled gas turbine. In addition to sulfur oxide (SOx) and/or water (H.sub.2O) and nitrous oxide and/or nitric oxide, the gas to be treated used in the present invention may further include nitrogen dioxide, carbon monoxide, carbon dioxide, hydrogen, hydrocarbon, oxygen, or nitrogen.

[0154] FIG. 1 is a diagram showing an example of an ammonia fuel engine including the exhaust gas treatment device according to the present invention. Not only a reducing agent (for example, ammonia or urea) 6 but also diluted air (not shown) or the like are added to gas exhausted from a cylinder 1 of the ammonia multi-fuel engine (ammonia fuel engine) through an exhaust manifold 5. The mixed gas of the exhaust gas and the reducing agent flow into a catalyst reactor 2 including a fixed bed 8 into which the N.sub.2O decomposition catalyst according to the present invention is charged. Mainly N2O and NOx in the fixed bed 8 into which the N.sub.2O decomposition catalyst is charged are decomposed to be chemically changed into N.sub.2 and H.sub.2O. The gas exhausted from the catalyst reactor rotates a turbine 12 in a turbocharger, flows out from the turbocharger, and is exhausted out from the system through an exhaust pipe 15. Due to the rotation of the turbine 12, a compressor 13 that is provided in the same shaft as the turbine 12 in the turbocharger rotates. The compressor 13 compresses air 3 that is taken in. The compressed air is supplied to the cylinder 1 through an intake manifold 14 of the ammonia multi-fuel engine. Fuel 4 is combusted in the cylinder. In FIG. 1, the fuel is supplied to the cylinder after being mixed with the compressed air. In a diesel engine, fuel can be injected into a cylinder.

[0155] FIG. 2 is a diagram showing another example of the ammonia fuel engine including the exhaust gas treatment device according to the present invention. Gas exhausted from the cylinder 1 of the ammonia multi-fuel engine (ammonia fuel engine) through the exhaust manifold 5 rotates the turbine 12 in the turbocharger. Due to the rotation of the turbine 12, the compressor 13 that is provided in the same shaft as the turbine 12 in the turbocharger rotates. The compressor 13 compresses air 3 that is taken in. The compressed air is supplied to the cylinder 1 through the intake manifold 14 of the ammonia multi-fuel engine. Fuel 4 is combusted in the cylinder. In FIG. 2, the fuel is supplied to the cylinder after being mixed with the compressed air. In a diesel engine, fuel can be injected into a cylinder. Not only the reducing agent (for example, ammonia or urea) 6 but also diluted air (not shown) or the like are added to the gas flowing out from the turbocharger. The mixed gas of the exhaust gas and the reducing agent flow into a catalyst reactor 2 including the fixed bed 8 into which the N2O decomposition catalyst according to the present invention is charged. Mainly N.sub.2O and NOx in the fixed bed 8 into which the N2O decomposition catalyst is charged are decomposed to be chemically changed into N.sub.2 and H.sub.2O. The gas exhausted from the catalyst reactor is exhausted out to the system through the exhaust pipe 15.

[0156] The method according to the present invention is to reduce nitrous oxide or nitrous oxide and nitric oxide from the gas to be treated. The method according to the present invention includes bringing the gas to be treated and the reducing agent into contact with the catalyst or the catalyst element according to the present invention to decompose nitrous oxide or nitrous oxide and nitric oxide. From the viewpoint of the catalyst lifetime, the content of water in the gas to be treated is preferably small and more preferably is less than 30%. The method according to the present invention exhibits a sufficient effect for the gas to be treated where the content of water is large, for example, for the gas to be treated where the content of water is 1% or more or the gas to be treated where the content of water is 10% or more. From the viewpoint of the catalyst lifetime, the content of sulfur oxide (SOx) in the gas to be treated is preferable small, more preferably 300 ppm or less, and still more preferably 250 ppm or less. The method according to the present invention exhibits the sufficient effect for the gas to be treated where the content of SOx is large, for example, for the gas to be treated where the content of SOx is 1 ppm or more, the gas to be treated where the content of SOx is 5 ppm or more, or the gas to be treated where the content of SOx is 15 ppm or more.

[0157] The content of nitrous oxide in the gas to be treated is not particularly limited and is preferably 1 ppm or more and 1000 ppm or less and more preferably 10 ppm or more and 500 ppm or less. The content of nitric oxide in the gas to be treated is not particularly limited and is preferably 1 ppm or more and 1000 ppm or less and more preferably 5 ppm or more and 500 ppm or less. In the gas to be treated, the content of water and/or the content of sulfur oxide is preferably 15 ppm or more.

[0158] Sulfur dioxide (SO.sub.2) is likely to cause a side reaction represented by the following formula to occur. The N2O decomposition catalyst according to the present invention can suppress the progress of the side reaction (in the present application, this property will be referred to as sulfur oxide resistance).

2SO.sub.2+O.sub.2.fwdarw.2SO.sub.3

[0159] Water (H.sub.2O) is produced by the reducing reaction of nitrogen oxide. When a large amount of water is present in the system, dealumination of the support is likely to occur. The N.sub.2O decomposition catalyst according to the present invention can suppress the progress of the dealumination (in the present application, this property will be referred to as water resistance).

[0160] In the method according to the present invention, the gas to be treated and the reducing agent can be brought into contact with the N.sub.2O decomposition catalyst or the catalyst element using a well-known method. For example, a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, or a simulated moving bed reactor can be used for the contact.

[0161] The temperature during the contact is preferably 200 to 950 C., more preferably 300 to 700 C., and still more preferably 400 to 500 C. A pressure during the contact may be the same as the atmosphere or may be higher than the atmospheric pressure. When the pressure is higher than the atmospheric pressure, an increase of a frequency (adsorption rate) at which nitrous oxide, nitric oxide, and the reducing agent are brought into contact with the catalyst can be expected.

[0162] Examples of the reducing agent used in the present invention include: a nitrogen-based reducing agent such as ammonia or urea; a hydrocarbon-based reducing agent such as methane, ethane, propane, propylene, methanol, or dimethylethyl; hydrogen; and carbon monoxide. Among these, a nitrogen-based reducing agent is preferable, and ammonia or urea is more preferable. The amount of the reducing agent is not particularly limited as long as it is sufficient for decomposing nitrous oxide or nitrous oxide and nitric oxide in the gas. For example, when the reducing agent is ammonia, the amount of the reducing agent is preferably 0.67 to 1.2 moles with respect to 1 mole of the total amount of nitrous oxide and nitric oxide. Using a well-known vaporizer, ejector, or the like, the reducing agent can be added to and mixed with the gas to be treated. In flue gas of ammonia fuiel, the amount of ammonia remaining in the flue gas can also be set by adjusting the combustion rate of the ammonia fuel.

[0163] Hereinafter, the present invention will be described using examples in more detail. Note that these examples are merely exemplary of the present invention, but the scope of the present invention is not limited thereto.

Catalyst Production Example 1

(Impregnation Step <Ion Exchange>)

[0164] 60 g of BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 13.2 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was dehydrated using a suction filter to which filter paper (No. 5C) was attached. A predetermined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 500 C. for 5 hours. The sintered product was pulverized using a planetary ball mill to obtain a powdered Fe-supported zeolite catalyst A.

(Pyridine-TPD Method)

[0165] An adsorption tube was filled with a predetermined amount (12.5 mg) of the catalyst. As a result, as a pre-treatment, helium was blown at 30 cc/min, and the catalytic bed temperature was kept at 450 C. for 1 hour. After that the catalytic bed temperature was decreased to 100 C. or lower. Next, helium was blown at 10 cc/mm, and pyridine was injected into the catalytic bed inlet side of the adsorption tube in a state where the catalytic bed temperature was maintained at 150 C. The pyridine amount on the catalytic bed outlet side was determined by GC-FID. When a fluctuation in the pyridine amount was stopped (assuming that the adsorption at 150 C. was saturated), the injection of pyridine was stopped. 30 minutes after stopping the injection of pyridine, the catalytic bed temperature was increased at a rate of 20 C./min. The pyridine amount on the catalytic bed outlet side in 150 C. to 800 C. was determined by GC-FID, and the TPD spectrum was recorded. The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst A are shown in FIG. 3 and Table 1. The crystallite size of the Fe-supported zeolite catalyst A was 14.8 nm.

(Coating Step)

[0166] Pure water was poured into the Fe-supported zeolite catalyst A, and the solution was subsequently stirred to obtain a catalyst slurry. A honeycomb substrate was coated with the catalyst slurry in a coating amount of 70 g/m.sup.2. The catalyst slurry was dried at 120 C. for 2 hours and was sintered at 500 C. for 2 hours to obtain a honeycomb catalyst A.

Catalyst Production Example 2

[0167] A powdered Fe-supported zeolite catalyst B and a honeycomb catalyst B were obtained using the same method as that of Catalyst Production Example 1, except that the BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was changed to BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=28). The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst B are shown in FIG. 3 and Table 1.

Catalyst Production Example 3

[0168] A powdered Fe-supported zeolite catalyst C and a honeycomb catalyst C were obtained using the same method as that of Catalyst Production Example 1, except that the BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was changed to BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=7.5). The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst C are shown in FIG. 3 and Table 1.

Catalyst Production Example 4

[0169] 60 g of CHA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=24) was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 13.2 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was filtered using a suction filter to which filter paper (No. 5C) was attached. A predetermined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 500 C. for 5 hours. The sintered product was pulverized using a planetary ball mill to obtain powder.

[0170] This powder was poured into 2000 ml of an aqueous solution containing 13.2 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O), and the above-described operation was further performed twice (an ion exchange step was performed three times in total) to obtain a powdered Fe-supported zeolite catalyst D. The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst D are shown in FIG. 3 and Table 1.

[0171] A honeycomb catalyst D was obtained using the same method as that of Catalyst Production Example 1, except that the Fe-supported zeolite catalyst A was changed to the Fe-supported zeolite catalyst D.

Catalyst Production Example 5

[0172] A powdered Fe-supported zeolite catalyst E and a honeycomb catalyst E were obtained using the same method as that of Catalyst Production Example 1, except that the BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was changed to MFI-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=30). The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst E are shown in FIG. 3 and Table 1.

Catalyst Production Example 6

[0173] A powdered Fe-supported zeolite catalyst F and a honeycomb catalyst F were obtained using the same method as that of Catalyst Production Example 1, except that the BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was changed to BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=24). The TPD spectrum, the pyridine desorption amount, and the like of the Fe-supported zeolite catalyst F are shown in FIG. 3 and Table 1.

TABLE-US-00001 TABLE 1 Catalyst A Catalyst B Catalyst C Catalyst D Catalyst E Catalyst F CatalystSupport Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite SiO.sub.2/Al.sub.2O.sub.3 25 28 7.5 24 30 24 Structure Type BEA BEA BEA CHA MFI BEA Amount of Fe Supported (wt % in terms of Fe.sub.2O.sub.3] 3.7 4.3 4.3 5.0 2.8 3.9 TPD Spectrum Pyridine Desorption Amount w at 150 C. to 450 C. [mol/g] 265 223 157 4 109 135 Pyridine Desorption Amount s at 450 C. to 800 C. [mol/g] 251 236 236 13 294 122 Desorption Amount w/Desorption Amount s [] 1.06 0.94 0.67 0.31 0.37 1.11 L Peak Value/H Peak Value [] 1.43 1.29 1.58 0.83 0.41 1.51 Pyridine Saturated Adsorption Amount [mol/g] 605 617 333 80 493 294

Test Example 1

[0174] Each of the above-described honeycomb catalysts A to F was attached to a reaction tube. Simulant gas having a composition ratio shown in Table 2 was caused to flow at AV=the amount of gas/the geometric surface area of the catalyst=25 Nm/hr, and the reaction tube was set to 400 C., 450 C., and 500 C. At each of the temperatures, a N.sub.2O decomposition rate and a NO decomposition rate were measured. The results are shown in FIGS. 4 and 5. In particular, the N.sub.2O decomposition rates and the NO decomposition rates of the catalysts A and B at 400 to 500 C. were high.

TABLE-US-00002 TABLE 2 Composition Ratio of Simulant Gas NO 34 ppm N.sub.2O 120 ppm NH.sub.3 114 ppm SO.sub.2 113 ppm O.sub.2 4% CO.sub.2 16% H.sub.2O 10% N.sub.2 Balance

Test Example 2

[0175] Plural kinds of powdered Fe-supported zeolite catalysts and honeycomb catalysts B were obtained using the same method as that of Catalyst Production Example 1, except that the support kind, the support amount, the sintering temperature, the sintering time, the co-catalyst addition, the SiO.sub.2/Al.sub.2O.sub.3 ratio, and the like were changed. The amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. was measured by the pyridine-TPD method. The N.sub.2O decomposition rate was measured using the same method as that of Test Example 1. Based on the measurement result, the catalytic reaction rate was calculated assuming that the N.sub.2O decomposition rate at 500 C. was a first-order reaction. The results are shown in FIG. 6. It can be seen that, as the amount of pyridine desorbed in a range of 150 C. or higher and lower than 450 C. increases, the catalytic reaction rate (Nnhr) tends to increase.

Catalyst Production Example 7

[0176] 60 g of BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=25) was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 9.1 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was dehydrated using a suction filter to which filter paper (No. 5C) was attached. A predetermined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 500 C. for 5 hours. The sintered product was pulverized using a planetary ball mill to obtain a powdered Fe-supported zeolite catalyst G. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst G are shown in FIG. 7 and Table 3.

[0177] Pure water was poured into the Fe-supported zeolite catalyst G, and the solution was subsequently stirred to obtain a catalyst slurry. A honeycomb substrate was coated with the catalyst slurry in a coating amount of 70 g/m.sup.2. The catalyst slurry was dried at 120 C. for 2 hours and was sintered at 500 C. for 2 hours to obtain a honeycomb catalyst G.

Catalyst Production Example 8

[0178] A powdered Fe-supported zeolite catalyst H was obtained using the same method as that of Catalyst Production Example 7, except that 9.1 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O) was changed to 13.2 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O) and the temperature during the sintering was changed from 500 C. to 600 C. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst H are shown in FIG. 7 and Table 3.

[0179] A honeycomb catalyst H was obtained using the same method as that of Catalyst Production Example 7, except that the Fe-supported zeolite catalyst G was changed to the Fe-supported zeolite catalyst H.

Catalyst Production Example 9

[0180] 60 g of BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=10) having a large crystallite size was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 26.4 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was dehydrated using a suction filter to which filter paper (No. 5C) was attached. A predetermined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 600 C. for 5 hours. The sintered product was pulverized using a planetary ball mill to obtain a powdered Fe-supported zeolite catalyst J. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst J are shown in FIG. 7 and Table 3.

[0181] Pure water was poured into the Fe-supported zeolite catalyst J, and the solution was subsequently stirred to obtain a catalyst slurry. A honeycomb substrate was coated with the catalyst slurry in a coating amount of 70 g/m.sup.2. The catalyst slurry was dried at 120 C. for 2 hours and was sintered at 500 C. for 2 hours to obtain a honeycomb catalyst J.

Catalyst Production Example 10

[0182] A powdered Fe-supported zeolite catalyst K and a honeycomb catalyst K were obtained using the same method as that of Catalyst Production Example 9, except that the BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=10) was changed to BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=12) having a large crystallite size. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst K are shown in FIG. 7 and Table 3.

Catalyst Production Example 11

[0183] A powdered Fe-supported zeolite catalyst L was obtained using the same method as that of Catalyst Production Example 9, except that 26.4 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O) was changed to 18.2 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O) and the temperature during the sintering was changed from 600 C. to 500 C. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst L are shown in FIG. 7 and Table 3.

[0184] A honeycomb catalyst L was obtained using the same method as that of Catalyst Production Example 9, except that the Fe-supported zeolite catalyst J was changed to the Fe-supported zeolite catalyst L.

Catalyst Production Example 12

[0185] A powdered Fe-supported zeolite catalyst M and a honeycomb catalyst M were obtained using the same method as that of Catalyst Production Example 9, except that 26.4 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O) was changed to 18.2 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O). The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst M are shown in FIG. 7 and Table 3.

Catalyst Production Example 13

[0186] A powdered Fe-supported zeolite catalyst N was obtained using the same method as that of Catalyst Production Example 9, except that the temperature during the sintering was changed from 600 C. to 500 C. The TPD spectrum, the pyridine desorption amount, the crystallite size, and the like of the Fe-supported zeolite catalyst N are shown in FIG. 7 and Table 3.

[0187] A honeycomb catalyst N was obtained using the same method as that of Catalyst Production Example 9, except that the Fe-supported zeolite catalyst J was changed to the Fe-supported zeolite catalyst N.

TABLE-US-00003 TABLE 3 Catalyst Catalyst Catalyst Catalyst Catalyst Catalyst Catalyst J K L M N G H CatalystSupport Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite SiO.sub.2/Al.sub.2O.sub.3 10.5 11.9 9.9 9.9 10.5 24.7 24.8 Structure Type BEA BEA BEA BEA BEA BEA BEA Amount of Fe Supported (wt % in terms of Fe.sub.2O.sub.3] 5.3 5.9 3.8 3.7 5.4 1.2 2.6 TPD Spectrum Pyridine Desorption Amount w at 150 C. to 450 C. 432.1 445.5 504.3 504.0 461.6 280.0 287.0 [mol/g] Pyridine Desorption Amount s at 450 C. to 800 C. 124.9 228.9 442.1 381.1 361.9 348.0 239.0 [mol/g] Desorption Amount w/Desorption Amount s [] 3.46 1.95 1.14 1.32 1.28 0.80 1.20 L Peak Value/H Peak Value [] 3.03 2.47 1.76 2.06 2.10 1.30 1.85 Pyridine Saturated Adsorption Amount [mol/g] 847 856 1216 1031 1063 657 594 Crystallite Size [nm] 59.0 63.8 67.1 61.6 68.7 14.6 14.5

Test Example 3

[0188] Each of the above-described honeycomb catalysts G, H, and J to N was attached to a reaction tube. Simulant gas having a composition ratio shown in Table 4 was caused to flow at AV=the amount of gas/the geometric surface area of the catalyst=25 Nm/hr (SV=the amount of gas/the amount of the catalyst=20000 hr.sup.1), and the reaction tube was set to 350 C., 400 C., and 450 C. At each of the temperatures, a N.sub.2O decomposition rate and a NO decomposition rate were measured. The results are shown in FIGS. 8 and 9. When the honeycomb catalysts J to N having a large crystallite size and a large desorption amount w were compared to the honeycomb catalysts G and H, both of the N.sub.2O decomposition rate and the NO decomposition rate were high.

TABLE-US-00004 TABLE 4 Composition Ratio of Simulant Gas NO 450 ppm N.sub.2O 180 ppm NH.sub.3 570 ppm SO.sub.2 15 ppm O.sub.2 13% H.sub.2O 15% N.sub.2 Balance

Catalyst Production Example 14

[0189] A honeycomb catalyst G2 was obtained using the same method as that of Catalyst Production Example 7, except that the coating amount was changed from 70 g/m.sup.2 to 140 g/m.sup.2.

Catalyst Production Example 15

[0190] A honeycomb catalyst J2 was obtained using the same method as that of Catalyst Production Example 9, except that the coating amount was changed from 70 g/m.sup.2 to 140 g/m.sup.2.

Test Example 4

[0191] Each of the above-described honeycomb catalysts G2 and J2 was attached to a reaction tube. Simulant gas having a composition ratio shown in Table 4 was caused to flow at AV=25 Nm/hr and 8.3 Nm/hr, and the reaction tube was set to 350 C., 400 C., and 450 C. At each of the temperatures and each of the flow rates, a N.sub.2O decomposition rate and a NO decomposition rate were measured. The results are shown in FIGS. 10 and 11. The N.sub.2O decomposition rate of the honeycomb catalyst J2 at AV 25 Nm/hr was the same as the N.sub.2O decomposition rate of the honeycomb catalyst G2 at AV 8.3 Nm/hr. These results can be shown that the N.sub.2O decomposition rate constant of the honeycomb catalyst J2 was about 3 times the N.sub.2O decomposition rate constant of the honeycomb catalyst G2.

Catalyst Production Example 16

[0192] Honeycomb catalysts G.sub.H, J.sub.H, and K.sub.H were obtained by performing a hydrothermal treatment on the honeycomb catalysts G, J, and K under conditions shown in Table 5 for 70 hours.

Test Example 5 (Evaluation of Water Resistance/SOx Resistance)

[0193] Each of the above-described honeycomb catalysts G, J, K, G.sub.H, J.sub.H, and K.sub.H was attached to a reaction tube. Simulant gas having a composition ratio shown in Table 4 was caused to flow at AV=25 Nm/hr, and the reaction tube was set to 350 C., 400 C., and 450 C. At each of the temperatures, a N.sub.2O decomposition rate and a NO decomposition rate were measured. The results are shown in FIGS. 12 and 13. It can be seen that, in the honeycomb catalyst according to the present invention, even after the hydrothermal treatment, the N.sub.2O decomposition rate and the NO decomposition rate were maintained to be 60% or more and 90% or more, without a significant decrease, that is, the water resistance and the sulfur oxide resistance are excellent.

TABLE-US-00005 TABLE 5 Hydrothermal Treatment Conditions NO 0 ppm N.sub.2O 0 ppm NH.sub.3 0 ppm SO.sub.2 20 ppm O.sub.2 20% H.sub.2O 20% N.sub.2 Balance Temperature 530 C. AV 12.5 Nm/hr SV 10000 hr.sup.1

Catalyst Production Example 17

[0194] 60 g of OSDA-free BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=10) was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 18.2 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was dehydrated using a suction filter to which filter paper (No. 5C) was attached. A predetennined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 500 C. for 5 hours. After the calcined product was pulverized by a planetary ball mill, the pulverized product was charged into pure water and then stirred to obtain a catalyst slurry. A honeycomb substrate was coated with the catalyst slurry in a coating amount of 70 g/m.sup.2. The catalyst slurry was dried at 120 C. for 2 hours and was sintered at 500 C. for 2 hours to obtain a honeycomb catalyst O. The same test as that of Test Example 3 was performed on the honeycomb catalyst O. The results are shown in FIGS. 14 and 15.

Catalyst Production Example 18

[0195] 60 g of OSDA-free BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=10) was poured into 2000 ml of an aqueous solution heated to 80 C. and containing 26.4 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O). Next, in a state where the temperature was kept at 80 C., the mixture was stirred for 3 hours to obtain a slurry. The slurry was dehydrated using a suction filter to which filter paper (No. 5C) was attached. A predetermined amount of pure water was poured to clean the cake on the filter paper. The cleaned cake was dried at 110 C. for 12 hours and then sintered at 600 C. for 5 hours. After the calcined product was pulverized by a planetary ball mill, the pulverized product was charged into pure water and then stirred to obtain a catalyst slurry. A honeycomb substrate was coated with the catalyst slurry in a coating amount of 70 g/m.sup.2. The catalyst slurry was dried at 120 C. for 2 hours and was sintered at 500 C. for 2 hours to obtain a honeycomb catalyst P. The same test as that of Test Example 3 was performed on the honeycomb catalyst P. The results are shown in FIGS. 14 and 15.

Catalyst Production Example 19

[0196] A powdered Fe-supported zeolite catalyst Q was obtained using the same method as that of Catalyst Production Example 18, except that the temperature during the sintering was changed from 600 C. to 500 C. A honeycomb catalyst Q was obtained using the same method as that of Catalyst Production Example 18, except that the Fe-supported zeolite catalyst P was changed to the Fe-supported zeolite catalyst Q. The same test as that of Test Example 3 was performed on the honeycomb catalyst Q. The results are shown in FIGS. 14 and 15.

Catalyst Production Example 20

[0197] A powdered Fe-supported zeolite catalyst R and a honeycomb catalyst R were obtained using the same method as that of Catalyst Production Example 18, except that the OSDA-free BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=10) was changed to BEA-type zeolite (SiO.sub.2/Al.sub.2O.sub.3 ratio=12). The same test as that of Test Example 3 was performed on the honeycomb catalyst R. The results are shown in FIGS. 14 and 15.

Catalyst Production Example 21

[0198] A powdered Fe-supported zeolite catalyst S and a honeycomb catalyst S were obtained using the same method as that of Catalyst Production Example 18, except that 26.4 g of iron(III) nitrate nonahydrate (Fe.sub.2(NO.sub.3).sub.3.Math.9H.sub.2O) was changed to 18.2 g of iron(II) sulfate heptahydrate (FeSO.sub.4.Math.7H.sub.2O). The same test as that of Test Example 3 was performed on the honeycomb catalyst S. The results are shown in FIGS. 14 and 15.

Catalyst Production Example 22

[0199] A honeycomb catalyst P2 was obtained using the same method as that of Catalyst Production Example 18, except that the coating amount was changed from 70 g/m.sup.2 to 140 g/m.sup.2. The same test as that of Test Example 4 was performed on the honeycomb catalyst P2. The N.sub.2O decomposition rate of the honeycomb catalyst P2 at AV 25 Nm/hr was the same as the N.sub.2O decomposition rate of the honeycomb catalyst G2 at AV 8.3 Nm/hr. These results can be shown that the N.sub.2O decomposition rate constant of the honeycomb catalyst P2 was about 3 times the N.sub.2O decomposition rate constant of the honeycomb catalyst G2.

Catalyst Production Example 23

[0200] A honeycomb catalysts P.sub.H was obtained by performing a hydrothermal treatment on the honeycomb catalyst P under conditions shown in Table 5 for 70 hours. The same test as that of Test Example 5 was performed on the honeycomb catalyst P.sub.H. It can be seen that, in the honeycomb catalyst P, even after the hydrothermal treatment (honeycomb catalyst P.sub.H), the N.sub.2O decomposition rate and the NO decomposition rate were maintained to be 60% or more and 90% or more, without a significant decrease. That is, the water resistance and the sulfur oxide resistance were excellent.

REFERENCE SIGNS LIST

[0201] 1: engine cylinder [0202] 2: catalyst reactor [0203] 3: air [0204] 4: fuel [0205] 5: exhaust manifold [0206] 6: reducing agent [0207] 7: temperature controller [0208] 8: N.sub.2O decomposition catalyst fixed bed [0209] 12: turbine [0210] 13: compressor [0211] 14: intake manifold [0212] 15: exhaust pipe