Combustion – Process of combustion or burner operation
Patent
1998-01-09
1999-05-04
Straub, Gary P.
Combustion
Process of combustion or burner operation
4232132, 4232135, 4232453, 422177, 422180, 502300, 502325, 502326, 502302, 502343, 502500, 502514, B01J 2300, B01J 3700, F01N 320, F23C 1100
Patent
active
058996788
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a catalyst for oxidation and reduction reactions. In addition, the invention relates to a new catalytic composition.
Combustion catalysts include, for example the generic catalysts present in car exhaust systems and which reduce the output of nitrogen oxides (NO.sub.x) and carbon monoxide (CO) gases as exhaust fume components which are discharged into the atmosphere. Conventionally such a car exhaust system consists of platinum together with rhodium. Whilst this catalyst is effective at converting nitrogen oxides and carbon monoxide to molecular nitrogen (N.sub.2) and carbon dioxide (CO.sub.2) platinum metal is expensive and thus increases the cost of the car exhaust catalyst manufacture.
Moreover the platinum/rhodium catalytic system does not become catalytically active until it reaches its characteristic "light off" temperature. Under laboratory conditions the light off temperature of the conventional Pt/Rh car catalyst is approximately 157.degree. C. However, under practical conditions the light off temperature under normal operating criteria is in the region of 200-250.degree. C. Increasing the temperature of the car catalyst to approximately 200-250.degree. C. requires a warming period of approximately 8-10 minutes during which the catalyst is ineffective and the undesirable NO.sub.x and CO gases are released into the atmosphere. There is therefore strong motivation to produce a car exhaust catalyst system which has a lower light off temperature.
Another disadvantage of the conventional platinum/rhodium car catalyst system is that if misfiring of the engine occurs (in which unspent fuel is available for combustion inside the exhaust system), the temperature of the catalyst may be raised as high as 550-600.degree. C. At these temperatures the conventional catalyst begins to deteriorate irreversibly.
One of the major research areas in vehicle exhaust catalysis is to develop a palladium based system as an alternative to the expensive platinum/rhodium system used in today's conventional car catalyst. However, to date major difficulties in achieving a palladium based catalyst to control vehicle exhaust emissions has been that the palladium metal is prone to reaction with oxygen at moderately high temperatures resulting in elution of the palladium metal from the catalyst washcoat, and also catalyst deactivation. Processes that invoke catalyst deactivation include 1) deposition of non-labile materials at the catalyst surface, 2) restructuring of the catalyst surface and in particular sintering of the supported metal function and 3) oxidation of the supported metal function through the chemical bonding of active species generated during the catalysis process. Deactivation of the catalyst through oxidation of the metal function renders a change in the metal character of the catalyst from its zero valent state to a localised state of positive charge.
UK Patent Application No. 9404802.2 discloses the use of a catalytic system for the catalysis of halogen replacement in halo-substituted hydrocarbons. The reaction catalyst is the removal of a halogen atom and its replacement by a hydrogen atom, and is therefore classified as an hydrogenation reaction.
It is known in chemistry that catalysts tend to catalyse only very specific reactions. In particular oxidation and hydrogenation reactions are viewed as being very different indeed.
Contrary to expectation, it has now been found that the catalyst disclosed in UK 9404802.2 is also effective in oxidation and combustion reactions.
The present invention therefore provides a catalyst for oxidation or combustion reactions, said catalyst comprising a catalytic metal selected from palladium, nickel, platinum, rhodium, silver, ruthenium, cobalt, iron, molybdenum and tungsten in combination with a material which is an electron donor or a precursor of an electron donor.
The function of the material is to stabilise the catalytic metal. Ideally the material should be able to stabilise the catalytic metal in it's zero oxidization state.
The material may b
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Cairns James
Hourd Andrew
Thomson James
Straub Gary P.
University Court of the University of Dundee
Vanoy Timothy C
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