Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1999-06-16
2000-11-28
Dunn, Tom
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423212, 4232132, 502305, 502306, 502307, 502314, 502318, 502319, 502320, 502323, 502342, 502346, 502347, 502348, 502355, 502524, B01J 800, B01J 2300, B01J 2332, B01J 2348, B01J 2302
Patent
active
061531626
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the use of certain catalysts for reducing nitrogen oxides (NO.sub.x) and to a corresponding process. Nitrogen oxides primarily come from combustion off-gases, in particular from internal-combustion engines such as diesel engines.
The combustion of hydrocarbons with air as an oxidant gives rise, particularly with excess air and at high temperatures, to nitrogen oxides via oxidation of the nitrogen present in the air. Examples of such nitrogen oxides are NO, NO.sub.2, NO.sub.3, N.sub.2 O.sub.3, N.sub.2 O.sub.4 and N.sub.2 O.sub.5. Being pollutants, the nitrogen oxides are to be removed as completely as possible from the combustion off-gases, to avoid environmental pollution. While emissions from power stations and industry are progressively declining, owing to the use of off-gas treatment plants, abating the pollutant fraction in motor vehicle exhaust gases is becoming increasingly important, particularly given the increase in the number of motor vehicles.
Many solutions have been proposed for abating NO.sub.x emissions of motor vehicle engines. Effective solutions for abating the amounts of NO.sub.x must meet numerous criteria, particularly if catalysts are used, for example: low temperature and in the event of frequent load changes during operation
A number of catalysts for reducing nitrogen oxides have been proposed.
EP-A1-0 687 499 describes spinel catalysts made of a spinel comprising copper, zinc and aluminum, for reducing nitrogen oxides.
U.S. Pat. No. 3,974,255 describes a magnesium aluminate spinel catalyst coated with platinum. The catalyst is employed for reducing NO.sub.x in exhaust gases from internal-combustion engines.
EP-B1-0 494 388 describes a process for removing nitrogen oxides from an off-gas in which the catalyst used is a polyvalent metal phosphate, a polyvalent metal sulfate or a spinel aluminate of a transition metal of the 4th period of the Periodic Table of the Elements. In particular, a cobalt aluminate catalyst is described which is prepared by coprecipitation of cobalt nitrate and aluminum nitrate, followed by drying and calcination.
JP-A2-08024648 describes catalysts for removing nitrogen oxides from an off-gas. The catalyst, for example, has the composition Ag.sub.0.01 P.sub.0.01 Pr.sub.0.01 Cu.sub.0.2 Zn.sub.0.5 Al.sub.2.0, and Fe.sub.0.02 Co.sub.0.02 or 0.01% of MgO may also be present. The catalyst is prepared by the nitrates of Ag and Pr being mixed together with H.sub.3 PO.sub.4 and this mixture being introduced into oxide mixtures of Cu, Zn and Al in the presence of aqueous solutions of ammonia or ammonium carbonate or ammonium sulfate. The calcination is carried out at 500.degree. C. and 800.degree. C., respectively. The silver content of the catalysts is 0.67 wt %.
Also known are catalysts for the catalytic decomposition of dinitrogen monoxide (N.sub.2 O). DE-A1-42 24 881 describes a silver-containing aluminum oxide supported catalyst and a process for the catalytic decomposition of dinitrogen monoxide, either pure or present in gas mixtures, where dinitrogen monoxide is decomposed selectively without other nitrogen oxides being decomposed to a significant extent into the elements. The catalyst used may be in the form of copper/zinc/aluminum spinels which are doped with silver. This involves, for example, an aluminum oxide support being impregnated with a solution of copper nitrate and zinc nitrate, being dried, calcined and then being impregnated with a solution of silver nitrate, being dried and calcined.
It is an object of the present invention to provide improved catalysts, compared with known catalysts, for reducing NO.sub.x. In addition, a process for reducing NO.sub.x, particularly in exhaust gases from internal-combustion engines, is to be provided.
We have found that this object is achieved, according to the invention, by the use of a catalyst which comprises subgroup of the Periodic Table of the Elements or mixtures thereof,
based on the total weight of the components (a) to (e), which adds up to 100 wt %,
wherein, in each case, up to
REFERENCES:
patent: 3974255 (1976-08-01), Erickson et al.
patent: 5580534 (1996-12-01), Hartweg et al.
patent: 5750460 (1998-05-01), Hartweg et al.
Fetzer Thomas
Hartweg Martin
Kumberger Otto
Morsbach Bernd
Roitzheim Rolf-Dirc
BASF - Aktiengesellschaft
Daimler - Benz Aktiengesellschaft
Dunn Tom
Medina Maribel
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