Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1996-12-11
1999-11-30
Dunn, Thomas
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
4232135, 502 60, 502 64, 502 66, 502 73, 502 74, B01D 5356
Patent
active
059937645
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a catalyst for reducing nitrogen oxides in exhaust gas, more particularly to a catalyst for reducing nitrogen oxides by hydrocarbons in oxygen-rich exhaust gas, and to a process for reducing nitrogen oxides in exhaust gas, more particularly in exhaust gas containing hydrocarbons and an excessive amount of oxygen.
BACKGROUND ART
As a process for removing nitrogen oxides (hereinafter referred to as NOx) from oxygen-rich exhaust gas, ammonia denitration has been put into practical use. However, this process cannot be applied to small combustors because of two reasons: firstly it requires an ammonia source, and secondly release of excess ammonia can cause a secondary environmental pollution problem. It has been found recently, as is disclosed in Japanese Patent Laid Open Sho 63-100919, that NOx can selectively be reduced by hydrocarbons on a zeolite catalyst ion-exchanged with Cu or the like metal.
However, when hydrocarbons as the reducing agent have four or fewer carbons, this catalyst provides low selectivity (molar ratio of hydrocarbons used in NOx reduction to consumed hydrocarbons), and therefore low NOx conversion, in the presence of water vapor which is always contained in general exhaust gases.
Armor et al. reported (in Applied Catalysis B: Environmental, Vol. 1, p. L31) that NOx can selectively be reduced by methane on Co ion-exchanged ZSM-5 (MFI zeolite). However, it has been known that the catalyst is also deactivated to the level insufficient for practical use in the presence of water vapor. These problems of the conventional catalysts urged the search for an improved catalyst which is active even in presence of water vapor.
As a solution to the above-mentioned problems, NOx reduction process using BEA zeolite ion-exchanged with Co (Co-BEA) as a catalyst is proposed in Italian Patent Application No. MI93A2337.
The Co-BEA catalyst is improved substantially in the activity and durability at low temperature in an actual exhaust gas atmosphere containing water vapor etc. However, even this catalyst does not provide high NOx conversion when the exhaust gas temperature is as low as 350.degree. C., when NOx concentration in the exhaust is lower than about 100 ppm, or when the amount of effective hydrocarbons for NOx reduction is quite small in the exhaust. Therefore, a catalyst with higher activity and higher selectivity at low temperature and low NOx concentration has been sought for.
To meet the above-mentioned need, an object of the present invention is to provide a NOx reducing catalyst that is sufficiently active and durable at low temperature and low NOx and hydrocarbons concentrations even in exhaust gas containing water vapor and sulfur oxides (hereinafter referred to as SOx), etc., for use in reducing NOx in exhaust gases, such as those from natural gas combustion, which contain only small quantities of relatively lower hydrocarbons.
Another object of the invention is to provide a NOx reducing process using this catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the evaluation result for Ni-Co-BEA(1) catalyst.
FIG. 2 shows the result of durability test for the Ni-Co-BEA(6) catalyst.
DISCLOSURE OF INVENTION
To solve the above-mentioned problems, the inventors made substantial researches and found the following fact: when BEA zeolite is ion-exchanged with Co to have a Co/Al ratio (molar ratio; hereinafter, the same) between 0.2 and 0.6 and is loaded with at least one metal selected from among Ca, Sr, Ba, La, Mn, Ag and In, the oxidation activity of the resultant catalyst is enhanced moderately in a low temperature range without deteriorating the selectivity for NOx reduction, resulting in an increase in NOx reduction activity around 350.degree. C.
The inventors also found that, when the loading metal is selected from among Ca, Sr, Ba and Mn, NOx adsorption on the catalyst is promoted, resulting in a substantial increase in NOx conversion even at a low NOx concentration.
Furthermore, the inventors found that, when BEA zeolite is ion-e
REFERENCES:
patent: 3308069 (1967-03-01), Wadlinger et al.
patent: 4491637 (1985-01-01), Hartig et al.
patent: 4867954 (1989-09-01), Staniulis et al.
patent: 5149512 (1992-09-01), Li et al.
patent: 5260043 (1993-11-01), Li et al.
patent: 5443803 (1995-08-01), Mizuno et al.
patent: 5451385 (1995-09-01), Hansel et al.
Catalytic reduction of nitrogen oxides with methane in the presence of excess oxygen: a review, J.N. Armor, Catalysis Today 26 (1995) 147-158.
The effect of SO.sub.2 on the catalytic performance of Co-ZSM-5 and Co-ferrierite for the selective reduction of NO by CH.sub.4 in the presence of O.sub.2, Yuejin Li, John N. Armor, Applied Catalysis B: Envirnomental 5 (1995), L257-270, Air Products and Chemicals Inc.
Zeolite Molecular Sieves, Structures of Zeolites, pp 52-67.
Atlas of Zeolite Structure Types, W.M. Meier and D.H. Olson, 1992, pp450-469.
Selective Catalytic Reduction of Nitrogen Monoxide by Hydrocarbons in Oxidizing Atmosphere, YU-U et al., 67th CATSJ Meeting Abstracts: No. A2, vol. 33 1991.
Armor et al. "Catalytic Reduction of Nitrogen Oxides . . . " Applied Catalysis B: Environ. vol. 1, No. 4, L31-L40, Dec. 15, 1992.
Li, et al., "Catalytic reduction of nitrogen oxides with methane in the presence of excess oxygen", Applied Catalysis B: Environmental, 1 (1992) Amsterdam, pp. L31-L40.
Bellussi Giuseppe
Kokitsu Mikako
Ohtsuka Hirofumi
Okada Osamu
Sabatino Luigina Maria Flora
Dunn Thomas
Eniricerche S.p.A.
Osaka Gas Company Limited
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