Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1994-04-14
1995-12-19
Straub, Gary P.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502305, 502350, 4232391, B01J 2334
Patent
active
054768284
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a catalyst comprising a metal on a porous support, and to a method of making such a catalyst. The invention also relates to a method of reduction using the catalyst.
BACKGROUND OF THE INVENTION
The natural gas industry has long sought a way in the presence of excess oxygen of removing oxides of nitrogen from flue gas, which may typically be at 375-425 K and may contain 13-14 volume % water vapor, 5-6% oxygen, 6-7% carbon dioxide and 100 ppm nitric oxide. Oxides of nitrogen can also arise in flue gas in other industries where combustion occurs and in petrol motor car exhausts. It is desirable to convert these compounds into harmless compounds before they are released into the atmosphere.
EP-B-256590 discloses a titanium/vanadium catalyst on a silica carrier for reducing nitrogen oxides in the presence of ammonia to nitrogen and water. This is stated in the EP-B to be only 64% effective at 423 K even at a gas hourly space velocity (explained later) of 10000, which is too low a throughput for some large-scale industries.
Further catalysts for this reaction are disclosed in Catalysis Today 7 (1990) 157-165, (copper salts on carbon supports), Ind Eng Chem Prod Res Dev 20 (1981) 301-304 (molybdenum on titania/zirconia/alumina/silica, International Chemical Engineering 15 (July 1975) 546-549 (Pt, CuO--Cr.sub.2 O.sub.3, CuO, V.sub.2 O.sub.5, NiO, Fe.sub.2 O.sub.3, MnO--Cr.sub.2 O.sub.3, MoO.sub.3, Co.sub.3 O.sub.4, MnO.sub.2, Cr.sub.2 O.sub.3 and WO.sub.3), and Bulletin of Chemical Society of Japan 54 (1981) 3347-3350 (Mn.sub.2 O.sub.3 and Mn.sub.2 O.sub.3 --Co.sub.3 O.sub.4 in 1 mm particles from calcined carbonate-precipitated nitrate solution), the last-named suffering from slow partially irreversible poisoning by sulphur dioxide.
Wakker and Gerritsen, Proc American Chemical Society, Division of Fuel Chemistry 35(1) (1990) 170 discloses a catalyst of MnO supported on gamma-alumina, the MnO being obtained by impregnating the alumina in manganese acetate, sulphate, nitrate or oxalate solution, drying, optionally calcining, and reducing with hydrogen at 600.degree. C. This catalyst can remove H.sub.2 S from hot reactor gases. However, it cannot reduce oxides of nitrogen.
A similar catalyst (manganese acetate or nitrate solution impregnated into steam-activated carbonised peat and calcined in 2% oxygen) was disclosed for reducing NO with ammonia at the International Symposium on Carbon, TsuKuba, 1990, page 590 of the Extended Abstracts. This catalyst can successfully reduce NO below 425 K but its activity decreases irreversibly above that temperature. This is a serious problem since it cannot be guaranteed that the temperature of a flue in an industrial process (such as petrochemical cracking) will not accidentally rise above 425 K.
DESCRIPTION OF THE INVENTION
According to the present invention, a process of preparing a catalyst for the reduction of nitrogen oxide comprises applying a manganese compound in solution to a porous carrier, removing the solvent, and subjecting the carrier (including the manganese compound) to a heat treatment at from 550 K to 850 K characterised in that said heat treatment tends to oxidise Mn(II) and in that the porous carrier is inorganic. The heat treatment is preferably in the presence of at least 0.01 or 0.03 atmospheres oxygen, more preferably at least 0.05 atmospheres, for example at least 0.1 atmospheres. The oxygen presence is most conveniently the air, or may be 1/2 atmosphere or more, such as pure oxygen.
The heat treatment may be performed at from 720 K, more preferably from 750 K, and preferably at up to 830 K, more preferably up to 800 K. The preferred duration of the heat treatment depends on the temperature, as follows:
The upper time limits may be exceeded but there is no advantage. Beforehand, if proceeding above 625 K, it preferably takes at least 1 hour from passing 525 K to passing 625 K.
The porous inorganic carrier, which preferably comprises silica or alumina or both, may be loaded with titanium dioxide or tungsten trioxide or both
REFERENCES:
patent: 4003854 (1977-01-01), Skvortsov et al.
patent: 4966882 (1990-10-01), Kato et al.
Kapteijn Freek
Singoredjo Lydia
British Technology Group Limited
Dunn Jr. Thomas G.
Straub Gary P.
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