WO1997009523A1

WO1997009523A1 - Methods for improving the operation of a catalyzed engine

Info

Publication number: WO1997009523A1
Application number: PCT/US1996/014079
Authority: WO
Inventors: James M. Valentine; Jeremy D. Peter-Hoblyn; Barry N. Sprague
Original assignee: Clean Diesel Technologies, Inc.
Priority date: 1995-09-01
Filing date: 1996-08-29
Publication date: 1997-03-13
Also published as: AU7153696A

Abstract

The activity of catalytic engines is maintained over time, preferably while reducing emissions of pollutants. Platinum group catalysts deposit on the internal surfaces of the cylinder which make up the combustion chamber. In one embodiment, wherein the engines are equipped with particulate traps, through the use of mechanical modifications such as exhaust gas recirculation and engine timing modification, it is possible to reduce the emissions of NOx by significant amounts. In another embodiment, a multi-metal catalyst composition, comprising a combination of a platinum metal catalyst composition and at least one auxiliary catalyst metal, is added to the cylinder (as part of the fuel, separate injection, lubricating oil, or the combustion air) prior to combustion to provide catalyst metal to the cylinder and the exhaust system including a diesel trap to lower the balance point of the particulate trap (the temperature at which the rate of trap loading equals the rate of regeneration), while achieving the advantages of catalyst activity maintenance and preferably also lowering the emissions of carbon monoxide and unburned hydrocarbons.

Description

DESCRIPTION

METHODS FOR IMPROVING THE OPERATION OF A CATALYZED ENGINE

Technical Field

The invention provides improvements in the operation of internal combustion engines of the type including catalyzed part internal of the cylinder.

The art of internal combustion engines has developed to the extent that high quality ceramic cylinder parts, inserts and coatings are available to carry catalysts that can improve the combustion process and thereby provide improvements in efficiency and emissions. There are a number of practical problems remaining including the maintenance of catalytic activity and the balance which is struck between fuel efficiency, unburned hydrocarbon emissions and nitrogen oxide emissions.

There is a need for technology which addresses these problems and maintains the activity of ceramic catalyst support surfaces within cylinders of internal combustion engines over reasonable periods of time.

Background Art

U. S. Patent No. 4,646,707 describes an internal combustion engine having an insulated catalytic surface within the combustion chamber. In operation, fuel is injected into the combustion chamber at a time near maximum compression to impinge on the catalytic surface. Using a catalyst in this manner is said to decrease the production of soot.

U. S. Patent No. 4,811 ,707 describes a method for operating a catalytic ignition cyclic internal combustion engine wherein a catalytic surface is heated. After compression heating of the air, fuel is injected to impinge on the catalytic surface where it is rapidly vaporized and combusted. The catalyst surface is insulated from the cooled engine parts to maintain a high operating temperature.

In U. S. Patent No. 4,905.658 describes an engine using exhaust valves coated with a catalyst. In operation, an unthrottled internal combustion engine is operated with valves of this type by injecting fuel into compressed air prior to top dead center prior to contact with the catalyst on the valve face. A combustion pressure wave is said to be produced in the immediate vicinity of top dead center. The catalyst can be platinum or a base metal oxide.

The disclosures of these patents and those cited therein are incorporated herein by reference as illustrative of the type of engine construction and operation when this disclosure refers to a catalyzed engine. A problem with engines of this type is that the catalysts tend to lose their initial activity over time, due to poisoning (such as by sulfur) and catalyst loss. There is a present need for a technology which would maintain catalyst activity over time.

Disclosure of Invention

The invention relates to improvements in catalytic engines, particularly in maintaining the activity of catalytic engines over time, preferably while reducing emissions of pollutants. In one embodiment, the engines are equipped with particulate traps, but are made less essential by the invention due to the ability of the catalytic engines to reduce the production of particulates. In another embodiment, through the use of mechanical modifications such as exhaust gas • recirculation and engine timing modification, it is possible to reduce the emissions of NO_x by significant amounts.

The operation of catalytic engines is improved by introducing a platinum group catalyst into the cylinders during operation of the engine to deposit the catalyst on the internal surfaces of the cylinder which make up the combustion chamber.

In another embodiment, a multi-metal catalyst composition, comprising a combination of a platinum metal catalyst composition and at least one auxiliary catalyst metal, is added to the cylinder (as part of the fuel, separate injection, lubricating oil, or the combustion air) prior to combustion to provide catalyst metal to the cylinder and the exhaust system including a diesel trap to lower the balance point of the particulate trap (the temperature at which the rate of trap loading equals the rate of regeneration), while achieving the advantages of catalyst activity maintenance and preferably also lowering the emissions of carbon monoxide and unburned hydrocarbons.

The platinum group metal catalyst can be introduce into the cylinder in an manner effective, such as by adding it to the fuel in bulk storage, to the fuel in a tank associated with the engine, or by continuous or intermittent addition, such as by a suitable metering device, into: the fuel line leading to the engine or separate injection ports into the cylinders, or in the form of a vapor, gas or aerosol into the air intake, exhaust gases after the trap but before recirculation to the engine, or a mixing chamber or equivalent means wherein the exhaust gase are mixed with incoming air. The platinum group metal catalyst composition is preferably employed at a level of less than 1 part by weight of platinum group metal per million parts by ^•volume fuel (ppm). For the purposes of this description, all "parts per million" figures are on a weight to volume basis, i.e., grams/million cubic centimeters (which can also be expressed as milligrams/liter), and percentages are given by weight, unless otherwise indicated. The auxiliary catalyst metal composition preferably contains a metal selected from the group consisting of compounds of sodium, lithium, potassium, calcium, magnesium, cerium, iron, copper, manganese, and mixtures of these, can be employed to deliver the auxiliary catalyst metal at suitable levels, e.g., from about 1 to about 100 ppm and preferably 20 to 60 ppm of the catalyst metal in combination with the platinum group metal composition in diesel fuels. It is preferred to add the platinum group metal catalyst and the auxiliary catalyst metal to the fuel in amounts effective to reduce the balance point temperature of the trap by at least 50°C, and preferably by at least 150°C.

Detailed Description of the Preferred Embodiment

In this description, the term "catalytic engines" is meant to include those engines capable of being run on suitable fuels such as those identified in the patent disclosures above, e.g., "diesel fuel", as defined by the American Society of Testing and Management (ASTM) Standard Specification for Fuel Oils (designation D 396-86) or any of grade numbers 1-D, 2-D or4-D, as specified in ASTM D 975. More generally, diesel fuel can be a fuel oil No. 2 or No. 4_. petroleum distillates as well as alternative diesel fuels containing emulsified water or alcohols such as ethanol or methanol, very low sulfur fuels (less than 0.05% sulfur), diesel fuel blends with bioderived components (animal and vegetable fats and oils, fractions and derivatives), and the like, as long as they exhibit volatility and cetane number characteristics effective for the purpose. Diesel fuels will typically have a 90% distillation point within the range of 300° to 390°C and a viscosity of from 1 to 25 centistokes at 40°C.

Suitable particulate traps are known to the skilled worker for use in the embodiments of the invention which require them, and generally comprise an apparatus designed to trap or collect particulates which are present in the exhaust stream of a diesel engine. Such a trap can be made of any suitable material such as ceramic (for instance, a cordierite ceramic material), glass fiber, or metal. In addition, the trap can be coated with a catalytic material to facilitate regeneration. It is an advantage of the present invention that the traps are selectively catalyzed during operation.

Flow resistance to the exhaust increases in proportion to the efficiency of the diesel trap at collecting particulates, and a compromise must be made between trap efficiency and exhaust back pressure. One type of diesel engine particulate trap which is found to be effective at trapping particulates while still providing an acceptable compromise in terms of back pressure created are traps available under the trademarks Diesel filter or EX 51 100/17 from Corning Glass Corporation of Corning, New York.

Suitable diesel engine particulate traps are typically constructed of a gas permeable material, such as a ceramic. Traps can be configured to include at least two (and generally several) parallel gas channels longitudinally arranged in a honeycomb-type structure extending between what can be referred to as an upstream, or engine-side, face and a downstream, or exhaust-side, face. Each passage is plugged at one of its faces such that alternate faces of adjacent passages are plugged. In this way, exhaust entering the trap through a passag at its unplugged upstream face must pass through a wall into an adjacent passage in order to exit the trap from its unplugged downstream face. Particu¬ lates in the exhaust are then trapped or collected on the wall. Such a trap is described, for instance, in U.S. Patent 4,568,357 to Simon, the disclosure of which is incorporated herein by reference.

The particulate trap used in the methods of the invention can be one which is self regenerating, that is, trapped particulates are ignited by heat derive from the engine, usually from the hot exhaust gasses themselves. In order to reduce particulate buildup on the trap, it is desired that the particulates are combusted or "burned off' the trap in order to free the surface thereof for further collection of particulates. Under normal conditions, and without the use of a catalyst, temperatures of from over about 500°C up to about 600°C, and sometimes more, are required to combust the particulates and, thus, regenerate the trap. Since a four stroke diesel engine produces exhaust gases which are typically exhausted at an average temperature of between about 400°C and 500°C, and which only occasionally reach temperatures in excess of 600°C, the exhaust gas temperature is too low to lead to reliable trap regeneration. A two-stroke diesel engine produces exhaust gases at an even lower temperature, which rarely exceeds 600°C, making reliable trap regeneration even less likely.

Platinum group metals include platinum, palladium, rhodium, ruthenium, osmium, and iridium. Compounds including platinum, palladium, and rhodium, especially compounds of platinum alone or in combination with rhodium and/or palladium compounds are preferred in the practice of this invention since the vapor pressure of these metals is sufficiently high to facilitate the desired reduction of carbon monoxide emissions.

The platinum group metal catalyst compositions can be of the type which are soluble in nonpolar hydrocarbon fuels, soluble in polar fuels such as those including methanol, ethanol, or other lower alkyl alcohols, or soluble in fuels having polar and nonpolar components such as emulsified fuels and gasohol. The platinum group metal catalyst compositions can be formulated according to the teachings below or as known to the art generally, to have the degree of stability necessary to assure that the platinum group metal catalyst composition • is subjected to the heat of combustion in the combustion chamber within a cylinder of a diesel engine to release the platinum group metal catalyst into the exhaust gases which transport it to the exhaust system wherein it is deposited in the trap along with the particulates and any auxiliary catalyst metal.

The platinum group metal catalyst compositions can be fuel-soluble, fuel- soluble but water-sensitive, or water-soluble, as will be described below. The platinum group metal catalyst compositions are typically added in amounts effective to provide concentrations of the platinum group metal relative to the fuel of less than 1 part per million (ppm) When employed, the auxiliary catalytic metal compositions are preferably used in amounts to provide concentrations of from about 1 to about 100 ppm of the metal.

The platinum group metal catalyst is preferably present in the diesel fuel i an amount effective upon combustion of the diesel fuel to provide sufficient platinum group metal in the exhaust system to lower the emissions of unburned hydrocarbons and carbon monoxide. This will be less than about 1 ppm, based on the weight of the catalyst metal, and will preferably be within the range of fro about 0.05 to about 0.5 ppm, and most preferably in the range of from 0.10 to 0.30 ppm.

NO_x can be reduced by exhaust gas recirculation or setting the injection timing of a diesel engine (for instance retarded or set during manufacture of the engine) in a manner designed to reduce the nitrogen oxides emissions from the engine after combustion of a diesel fuel.

It is believed that the closer to top dead center (i.e., point of greatest pressure in the cylinder during the combustion process) at which the timing is set, the greater the reduction of NO_x emissions achieved. However, the injection timing should be set at that level sufficient to reduce nitrogen oxides levels to •those desired generally according to either preset arbitrary limits or those required by various regulatory authorities. For instance, in some jurisdictions, it is required that diesel engines (notably new engines) emit no more than 4 grams per brake horsepower-hour (gm/BHP-hr) of nitrogen oxides. Although not always possible, reduction of NO_x levels to no greater than about 4 gm/BHP-hr is, therefore, desired.

Preferably, injection timing can be retarded by between about 0.5° and about 8° to secure the advantages of the present invention. More particularly, the engine timing can be retarded between about 2° and about 6° in order to achieve satisfactory reductions in nitrogen oxides levels without compromising fuel consumption or CO or unburned hydrocarbon emissions to a level beyond that for which at least partial compensation is possible. If, for example, the injection timing is initially set at 18° before top dead center, practice of this invention dictates that it is preferably retarded, by which is meant injection occur closer in time to top dead center, to about 17.5° to about 10°, more preferably about 16° to about 12°, before top dead center.

The injection timing can be set by retarding the timing of the engine durin maintenance or at any other time when access to the engine is possible. In the alternative, the injection timing can be set by having it initially set at the desired level during manufacture or otherwise prior to placing the engine into operation.

In order to achieve further reductions in emissions of carbon monoxide and unburned hydrocarbons, a suitable oxidizer (either precatalyzed or catalyze by the operation of the invention), such as a matrix of extrudate or pellets of alumina or other refractory oxide, or a monolith having a surface of a refractory oxide or a metal matrix, can also be utilized. In this way, significant reductions in nitrogen oxides are obtained without the art-accepted tradeoffs associated therewith.

Fuel-Soluble Platinum Group Metal Catalyst Compositions

Preferred among the platinum group metal catalyst compositions are those which are soluble in the typical diesel fuel which is essentially a nonpolar hydrocarbon fuel, but can contain tramp moisture in amounts which would destabilize some fuel-soluble platinum group metal compositions. Among these are hydrocarbon-fuel-soluble organometal c platinum group metal coordination compounds. The compounds in this group are any of those disclosed for example in prior U.S. Patent Nos. 4,892,562 and 4,891 ,050 to Bowers and Sprague, 5,034,020 to Epperly and Sprague, 5,215,652 to Epperly, Sprague, Kelso and Bowers, and 5,266,083 to Peter-Hoblyn, Epperly, Kelso and Sprague, and WO 90/07561 to Epperly, Sprague, Kelso and Bowers. Reference can be made to these disclosures for details of preparation and purification. Where the application permits, a blend of these compounds can be used with one or more other platinum group metal compounds such as soaps, acetyl acetonates, alcoholates, β-diketonates, and sulfonates, e.g., of the type which will be described in more detail below. Preferably, the composition will be temperature stable, and substantially free of phosphorus, arsenic, antimony, or halides.

Advantageously, in fuels or systems where some tramp water may be present, the platinum group metal catalyst composition will also be substantially insensitive to water, as evidenced by a partition ratio sufficient to maintain signifi cant preferential solubility in the fuel. The relative solubility of the composition in the diesel fuel and water is important since there is often a substantial amount o water admixed in with fuel, and any piatinum group metal catalyst composition which separates from the fuel can precipitate out or be lost as a coating on fuel system walls. The relative solubility of the composition in the fuel is referred to ^•herein as the "partition ratio" and can be expressed as the ratio of the amount in milligrams per liter of composition which is present in the fuel to the amount which is present in the water. This can most easily be determined in a 100 milliliter (ml) sample which is 90% fuel and 10% water. By determining the amount of composition in the fuel and the amount in the water, the partition ratio can be readily determined.

The organic nature of the platinum group metal compositions of this type provides solubility in nonpolar hydrocarbon fuels such as diesel fuel, thereby facilitating the introduction of the composition into the combustion chamber of an internal combustion engine. High fuel solubility maintains the platinum in the fuel and inhibits its precipitation or plating out in the fuel tank or fuel lines prior to introduction into the combustion chamber. In uses where the composition is intended for long-term storage either in an additive formulation or in the final fuel, high fuel solubility and stability in solution are important. In uses where the composition as part of an additive is mixed with the fuel shortly before introduction into the engine, lesser stabilities can be effective.

Temperature stability of the composition is important in many practical and operational contexts. In a commercial setting, a fuel additive is often packaged and stored in a building or in a delivery truck for extended periods of time during which the additive can be exposed to temperature vaπations and extremes. If the breakdown temperature of the composition is not sufficiently high (i.e., if the composition is not temperature stable at the temperatures to which it is expected to be exposed), then the packaged composition as part of an additive will quickly break down and become virtually useless. Moreover, breakdown of the composition after mixing with the fuel will render the composition insoluble in the fuel, since the solubility is provided by the ^■organic functional groups. Such loss of solubility will cause the composition to precipitate and not reach the combustion chamber, as discussed above. This becomes important when the additive is mixed into the fuel in advance of the fuel being provided to the fuel system of the engine (as opposed to a separate additive reservoir on the vehicle, with mixing occurring immediately prior to combustion), as desired.

Typically, the breakdown temperature of the platinum group metal catalyst composition should be at least about 40°C, preferably at least about 50°C, in order to protect against most temperatures to which it can be expected to be exposed. In some circumstances, it will be necessary that the breakdown temperature be no lower than about 75°C.

The organic nature of the preferred platinum group metal catalyst compositions helps to maintain them in solution in an organic solvent which provides a convenient diluent and can have functional properties, thereby preventing "plating out" of the platinum group metal catalyst composition in the packaging medium.

The platinum group metal catalyst composition should be substantially free from objectionable amounts (in some cases, traces) of compounds or functional groups containing, phosphorus, arsenic, antimony, and, especially, halogens (i.e., they should not contain a substantial amount of such functional groups) which have significant disadvantages like "poisoning" or otherwise reduc ing the effectiveness of the platinum group metal catalyst composition or any auxiliary catalyst metal composition employed. Halogens can have the additiona undesirable effect of rendering a platinum group metal more volatile, leading to its release from the exhaust system. A substantial amount of such functional groups is considered an amount effective to significantly reduces the effectiveness of the catalyst. Preferably, the purified platinum group metal catalyst composition contains no more than about 300 ppm of halogen nor more than 500 ppm (on a weight per weight basis) of phosphorus, arsenic, or antimony, more preferably no more than about 250 ppm of any of these. Most preferably, the additive contains no phosphorus, arsenic, or antimony.

Such objectionable functional groups can be minimized in several ways. The platinum group metal catalyst composition can be prepared in a process which utilizes precursors or reactant compositions having a minimum of such functional groups; or the composition can be purified after preparation. Many such methods of puπfication are known to the skilled worker.

One preferred method of preparing and purifying the fuel-soluble platinum group metal catalyst compositions is set forth in U. S. Patent No. 5,215,652 , the disclosure of which is incorporated herein by reference.

The preferential solubility of the composition in fuel as compared to water can be critical because if a substantial amount of the composition is dissolved in the water which may be present, the overall effectiveness of the composition is proportionally reduced. This partition ratio should be at least about 25 and is most preferably greater than about 50.

In order to reduce the water susceptibility of the platinum group metal catalyst composition, it is especially desired that the composition have at least one platinum group metal-to-carbon covalent bond. A platinum group metal-to-oxygen or platinum group metal-to-nitrogen bond can be acceptable, bu there must also be at least one metal to carbon bond. The preferred class of fuel soluble catalyst compositions, shown by formula (A) below, includes compounds where the platinum group metal exists in oxidation states II and IV Compounds in the lower (II) state of oxidation are preferred due to their function in generating the catalytic effect, preferably having at least one coordination site occupied by a functional group containing an unsaturated carbon-to-carbon bond. Most preferably, two or more of the coordination sites will be occupied by such functional groups since the stability and solubility in diesel fuel of compounds having such multiple functional groups are improved.

Occupation of one of more coordination sites with the following unsaturated functional groups has been found useful.

1 Benzene and analogous aromatic compounds such as anthracene and naphthalene

2. Cyclic dienes and homologues such as cylooctadiene, methyl cyclopentadiene, and cyciohexadiene.

3. Olefins such as nonene, dodecene, and polyisobutenes. 4 Acetylenes such as nonyne and dodecyne

These unsaturated functional groups, in turn, can be substituted with nonhalogen-substituents such as alkyl, carboxyl, ammo, nitro, hydroxyl, and alkoxyl groups. Other coordination sites can be directly occupied by such groups.

A preferred group of compositions is represented by the following general formula

(A) L¹MR¹R² wherein L¹ is either a single cyclic polyolefin or nitrogenous bidentate ligand or a pair of nitrogenous or acetylenic monodentate ligands, preferably cycloocta- dienyl; M is a platinum group metal, especially platinum itself; and R¹ and R² are each, independently, substituted or unsubstituted lower alkyl (e.g., 1-5 carbons) benzyl, nitrobenzyl, aryl, cyclopentadiene or pentamethyl cyclopentadiene, pref¬ erably benzyl, methyl and/or phenyl.

Exemplary of compounds are dipyridine platinum dibenzyl; bipyridine platinum dibenzyl; dipyridine palladium diethyl; cyclooctadiene platinum dimethyl; cyclooctadiene platinum diphenyl; cyclooctadiene platinum dibenzyl; cyclooctadiene platinum dinitrobenzyl; cyclooctadiene platinum methyl cyclopentadiene; norbomadiene platinum di-cyclopentadiene; dimethyl platinum cyclooctatetrene (which often assumes the formula dimethyl platinum cyclooctatetrene platinum dimethyl); and cyclooctadiene osmium bis (cyclopentadiene).

One group of compounds meeting the above general formula for the preferred coordination II compounds is defined as follows:

B

D(C=C)_X E(C=C) where M" represents the platinum group metal, with a valence of +2, where A, B, D, and E are groups such as alkyl, alkoxy, carboxyl, etc. described above ^•specifically or functionally as providing stability and fuel solubility, where (C=C)_X and (C=C)_y represent unsaturated functional groups coordinated with the platinum group metal, and where x and y are any integer, typically 1 to 5.

The most preferred platinum group coordination compounds according to the above general formula are those represented by the following formula:

(A.2.) X M"R₂

wherein X is a cyclooctadienyl ligand, M is a platinum group metal, and R is methyl, benzyl, phenyl, or nitrobenzyl. The R group can be any organic group which provides the requisite stability and can be substituted consistently with this objective.

Among other platinum group metal compounds, are the following

(B) 2, 2'-bis(N,N-dialkylamino)1 ,1 '-diphenyl metals, such as represente by the formula

wherein M is a platinum group metal; R, and R₂ are lower alkyl, e.g., from 1 to 1 carbons; and each n is, independently, an integer from 1 to 5. Representative o this group is 2,2'-bis(N,N-dimethylamino)1 ,1'-diphenyl palladium. (C) tetrakis (alkoxy carbonyl) metal cycloalkenes, as represented by the formula

M(C₄COOR₁)₄R₂

wherein M is a platinum group metal; R, is a lower alkyl, e.g., from 1 to 5 carbons, and R₂ is a cycloalkene having, e.g., from 5 to 8 carbons and from 2 to four unsaturations within the ring structure. Representative of this group is tetrakis (methoxy carbonyl) palladia cyclopentadiene.

(D) μ-diphenyl acetylene bis (r pentaphenyl cyclopentadiene) di metals as represented by the formula

(ΦC CΦ) (C₅ M)₂

wherein M is a platinum group metal and Φ is phenyl. Representative of this group is μ-diphenyl acetylene bis (η⁵-pentaphenyl cyclopentadiene) dipalladium.

(E) dialkyi dipyridyi metals of the formula

R¹

\ ; M (C₁₀H_{8 2})

R²

wherein M is a platinum group metal; and R, and R₂ are lower alkyl, e.g., having from 1 to 5 carbons. Representative of this group is diethyl dipyridyi palladium. (F) bis (π-allyl) metals of the formula

(R-C₃H₅)₂M

wherein M is a platinum group metal and R is hydrogen, aryl, or alkyl, e.g., one to ten carbons. Representative of this group is bis (phenyl allyl) palladium.

(G) compositions of the general formula

wherein L² is either a single cyclic polyolefin or nitrogenous bidentate ligand or a pair of nitrogenous or acetylenic monodentate ligands; M¹ is a platinum group metal, especially rhodium or iridium; and R³ is cyclopentadiene or pentamethyl cyclopentadiene. Exemplary of suitable compounds of the formula L²M¹R³ are cyclooctadiene rhodium cyclopentadiene; cyclooctadiene rhodium pentamethyl cyclopentadiene: norbomadiene rhodium pentamethyl cyclopentadiene; cyclooctadiene iridium cyclopentadiene; cyclooctadiene iridium pentamethyl cyclopentadiene; norbomadiene iridium cyclopentadiene; and norbomadiene iridium pentamethyl cyclopentadiene.

(H) compositions of the general formula

L³M²(C₄R⁴ ₄)

wherein L³ is either a single cyclic polyolefin or nitrogenous bidentate ligand or a pair of nitrogenous monodentate ligands; M² is platinum, palladium, rhodium, or iridium; and R⁴ is COOR⁵, wherein R⁵ is hydrogen or alkyl having from 1 to 10 •carbons, preferably methyl. Exemplary compounds have the structure

R⁴ I

__÷ C=C-R⁴

L³-M'

C=C-R⁴

R⁴

such as tetrakis (methoxy carbonyl) palladia cyclopentadiene (wherein L³ is cyclopentadiene, M² is palladium, and R⁴ is COOH₃).

(I) compositions of the general formula

L M³(COOR⁶)₂

or a dimer thereof, wherein L⁴ is a non-nitrogenous cyclic polyolefin ligand, preferably cyclooctadiene or pentamethyl cyclopentadiene; M³ is platinum or iridium; and R⁶ is benzyl, aryl, or alkyl, preferably having 4 or more carbons, most preferably phenyl. Exemplary of compounds having the general formula L⁴M³(COOR⁵)₂ are cyclooctadiene platinum dibenzoate dimer; and pentamethyl cyclopentadiene iridium dibenzoate. (J) compositions comprising a reaction product of [L⁵RhX]₂ and R⁷MgX wherein L⁵ is a non-nitrogenous cyclic polyolefin ligand, preferably cyclooctadiene or pentamethyl cyclopentadiene; R⁷ is methyl, benzyl, aryl, cyclo¬ pentadiene or pentamethyl cyclopentadiene, preferably benzyl or phenyl, and X is a halide. Although presently uncharacterized, it is believed that this reaction product assumes the formula L⁵RhR⁷.

Functional groups which are especially preferred for use as ligands L through L³ are neutral bidentate ligands such as cyclopentadiene, cyclooctadiene, pentamethyl cyclopentadiene, cyclooctatetrene, norbomadiene, o-toluidine, o-phenantholine, and bipyridine. Most preferred among monodentat ligands is pyridine.

Also useful in the present invention are any of the following compositions.

(K) palladium acetylene complexes having the general formula

wherein R⁸ is aryl or alkyl; and R⁹ is aryl, preferably phenyl. (L) metal allyl complexes having the general formula

M⁴(C₃H₅)_n or

M⁴(C₃H₄-R¹⁰)_n

wherein M⁴ is platinum group metal, especially rhodium or iridium; n is 2 for platinum and palladium, and 3 for rhodium, iridium, osmium and ruthenium; and R¹⁰ is hydrogen, aryl, or alkyl. One compound of this type is bis (phenyl allyl) palladium.

(M) platinum (IV) compositions having the general formula

R₃ ¹¹PtR¹²

wherein R¹¹ is aryl, alkyl or mixtures thereof, such as cyclopentadiene or pentamethyl cyclopentadiene; and R¹² is hydroxyl (-OH), acetylacetonate (-CH₂(COCH₃)₂), cyclopentadiene or pentamethyl cyclopentadiene (exemplary of which is trimethyl platinum hydroxide).

(N) compositions of the general formula

L⁶M⁵R¹³

wherein L⁶ is substituted or unsubstituted butadiene or cyclohexadiene; M⁵ is rhodium or iridium; and R¹³ is cyclopentadiene or pentamethyl cyclopentadiene (exemplary of which are butadiene rhodium cyclopentadiene and butadiene iridium cyclopentadiene.

Any of the above can be employed alone or in combination. Water-Sensitive and Water-Soluble Platinum Group Metal Catalyst Compositions

In addition to the highly fuel-soluble compounds that are stable in the presence of water, the invention makes use of platinum group metal catalyst compositions which would normally be taken up or destabilized by any water present. These platinum group metal catalyst compositions can be either simply water-sensitive or essentially water-soluble. Water-sensitive platinum group metal catalyst compositions are characterized as being instable in the presence of from about 0.01 to about 0.5% water, but having sufficient affinity for the fuel that when a water-functional composition is employed, they remain in the fuel and effective for their intended catalytic function. Among the platinum group metal catalyst compositions in this group are, alcoholates, sufonates, substituted and unsubstituted beta-diketonates and soaps selected from the group consisting of stearates, palmitates, taurates, tallates, napthanates, other fatty acid soaps, and mixtures of two or more of these.

The water-sensitive compounds typically exhibit partition ratios of from about less than 50, down to about 1. Compositions of this type having partition ratios as low as 40 and below, e.g., less than 25, and more narrowly less than 1 to 20, can be effective according to the invention. Also, essentially water-soluble platinum group metal catalyst compositions having partition ratios of less than 1 can be employed according to the invention.

To achieve stability in the presence of water, the fuels are formulated to include a water-functional composition selected from the group consisting of lipophilic emulsifiers, lipophilic organic compounds in which water is miscible, an mixtures of these, which can be added to the fuel as an additive including any catalyst compositions, as a discrete additive or as part of the bulk fuel. The preferred compounds or compositions have the capability of preventing frank separation of water from the fuel and maintain it tied up in the fuel, preferably in complete miscibility with a nonpolar fuel component or in droplets no larger than about 2 μ, and preferably smaller than about 1 μ in diameter, based on a weight average of droplet sizes. Discrete pockets or pools of water, where the uniform distribution of the platinum group metal catalyst composition within the fuel is disturbed, are preferably avoided.

In addition to the required components, it is preferred to employ a suitable hydrocarbon diluent such as any of the higher aliphatic alcohols (e.g., having over 3 carbons, i.e., from 3 to 22 carbons), tetrahydrofuran, methyl tertiarybutyl ether (MTBE), octyl nitrate, xylene, mineral spirits or kerosene, in an amount effective to provide a suitably pourable and dispersible mixture for additive compositions. Additionally, where the fuel contains a demulsifier, then an additional amount of emulsifier specifically intended to overcome the effects of such can be employed. Also, the use of additives known to the art as described above and in the references there cited, can be employed as the application calls for. Specifically, it is sometimes desirable to add one or more of corrosion inhibitors, cetane improvers, lubricity control agents, detergents, antigel compositions, and the like.

Consistent with the objective of controlling the tendency for water to render certain platinum group metal catalyst compositions inactive, there are instances where the overt addition of water can be beneficial. Overt addition of water, e.g., from about 1 to about 65%, can be accomplished without rendering the platinum group metal catalyst compositions inactive. This is a highly effective technique for reducing NO_x, as disclosed for example in U. S. Patent Application No. 08/114,206, filed August 30, 1993, by J. M. Valentine.

For example, fuel mixtures can be prepared as emulsions of diesel fuel and water, as mentioned above, but preferably including from about 5 to about 45% (more narrowly, 10 to 30%) water, for the purpose of controlling the amount of NO_x produced during combustion. These emulsions can include a platinum group metal catalyst composition in a relative amount effective to provide the metal at a concentration of from about 0.1 to about 1.0 ppm, to reduce the carbon monoxide and hydrocarbon emissions, and employing a lipophilic emulsifier at a ratio of from about 1:10,000 to about 1 :500,000 (more narrowly, from about 1 :50,000 to about 1 :250,000) based on the weight of the platinum group metal.

Also, there are instances wherein the use of complex emulsions (typically including a continuous hydrocarbon phase having dispersed therein droplets of water, which in turn have droplets of a lipophilic fluid dispersed therein). In one exemplary formulation of such a complex emulsion, the droplets of lipophilic fluid as the internally-dispersed phase can comprise the fuel additive, including the platinum group metal and the water-functional composition, e.g., a suitable emulsifier having the capability to maintain an emulsion of this type.

The emulsifiers effective for the complex emulsions will preferably contain a hydrophilic emulsifier such as higher ethoxylated nonyl phenols, salts of alkyl and alkyl ether sulfates, ethoxylated nonyl phenols with higher degrees of ethoxylation, higher polyethylene glycol mono- and di- esters, and higher ethoxylated sorbitan esters (e.g., higher in these contexts means from a lower level of 4-6 to about 10 or more). A fuel additive for use in preparing the comple emulsion preferably comprises a continuous hydrocarbon phase including a hydrophilic emulsifier at a concentration of from about 0.1 to about 10%, and a dispersed phase comprised of aqueous droplets having a platinum group metal catalyst composition dissolved or dispersed therein and a lipophilic emulsifier at concentration of from about 0.1% to about 10% based on the weight of platinum group metal in the additive composition, said lipophilic emulsifier being charaterized by oil solubility and water dispersibiiity. To better understand the above concept, the following exemplary procedure is presented: (1) The lipophilic emulsifier is added to the oil to be used ^•for the internal phase at a ratio of from about 0.1 to about 10% of the total composition. Platinum group metal catalyst compositions may be dissolved or dispersed in this oil as desired. (2) The combined oil/lipophilic emulsifier just described is added to a solution of the hydrophilic emulsifier in water with stirring to form an oil-in-water emulsion. The concentration of hydrophilic emulsifier in the water is also between about 0.1 and 10% of the total composition. Water- soluble or dispersible platinum group metal catalyst compositions may be dispersed in the water as needed. (3) The oil-in-water emulsion described in step 2 is then added to oil containing the lipophilic emulsifier at a ratio of 0.1 to 10% of the total composition to form the final oil/water-in-oii emulsion.

Among the lipophilic emulsifiers suitable as the water-functional composition are, preferably, those emulsifiers having an HLB of less than about 10, and more preferably less than about 8. The term "HLB" means "hydrophile- lipophile balance" and is determined, as known from the procedure developed by ICI Americas, Inc. of Wilmington, Delaware, from a test of the relative solubility or dispersibility of the emulsifier in water, with nondispersible being 1-4 and fully dispersible being 13.

The emulsifier can be anionic, nonionic or cationic. Among the preferred anionic emulsifiers are sodium or TEA petroleum sulfonates, sodium dioctyl sulfosuccinates, and ammonium or sodium isostearyol 2-lactylates. Among the preferred cationic emulsifiers are lower ethoxylated amines, oleyl imidazolines and other imidazoline derivatives. Among the preferred nonionic emulsifiers are alkanolamides including oleamide, oleamide DEA, and other similar compounds, lower ethoxylated alkyl phenols, fatty amine oxides, and lower ethoxylated sorbitan esters (e.g., lower in these contexts means from 1 to an upper level of from about 4-6). Functionally, materials meeting the following criteria can be effective individually and in combinations to stabilize the presence of water- senstive and water-soluble platinum group metal catalyst compositions in water- containing systems. Concentrations will be dependent on the exact formulation and the expected water content of the fuel, but concentrations of from about 0.01 to about 5%, based on the weight of the fuel as combusted, and assuming a water concentration of up to about 0.05%, are among those preferred. In some cases, it is more meaningful to express the concentration on the basis of the platinum group metal, and in this case it is preferably at a ratio of from about 10:1 to about 500,000:1 as compared to the weight of platinum group metal in the additive composition

It is sometimes preferred to employ a combination of emulsifiers, because the various hydrocarbons in the fuels interact differently with the same emulsifier. Often, individual emulsifiers are less effective than combinations due to interactions, including those between the fuel and the emulsifier. One exemplary combination of emulsifiers, referred to herein also as an emulsification system, which can be utilized comprises about 25% to about 85% by weight of an amide, especially an alkanolamide or n-substituted alkyl amme; about 5% to about 25% by weight of a phenolic surfactant; and about 0% to about 40% by weight of a difunctional block polymer terminating in a primary hydroxyl group. More narrowly, the amide can comprise about 45% to about 65% of the emulsification system; the phenolic surfactant about, 5% to about 15%; and the difunctional block polymer, about 30% to about 40% of the emulsification system.

Suitable n-substituted alkyl amines and alkanolamides are those formed by the condensation of, respectively, an alkyl amme and an organic acid or a hydroxyalkyl amme and an organic acid, which is preferably of a length normally associated with fatty acids. They can be mono-, di-, or triethanolamines and include any one or more of the following: oleic diethanolamide (oleamide DEA), cocamide diethanolamine, lauramide DEA, polyoxyethylene (POE) cocamide, cocamide monoethanolamine (MEA), POE lauramide DEA, oleamide DEA, linoleamide DEA. stearamide MEA. and oleic triethanolamine. as well as mixtures thereof. Such alkanolamides are commercially available, including those under trade names such as Clindrol 100-0, from Clintwood Chemical Company of Chicago, Illinois; Schercomid ODA, from Scher Chemicals, Inc. of Clifton. New Jersey; Schercomid SO-A. also from Scher Chemicals. Inc.; Mazamide®, and the Mazamide series from PPG-Mazer Products Corp. of Gurπee, Illinois; the Mackamide series from Mclntyre Group, Inc. of University Park, Illinois; and the Witcamide series from Witco Chemical Co. of Houston. Texas.

The phenolic surfactant can be an ethoxylated alkyl phenol such as an ethoxylated nonylphenol or octylphenol. Especially preferred is ethylene oxide nonylphenol, which is available commercially under the tradename Triton N from Union Carbide Corporation of Danbury, Connecticut and Igepal CO from Rhone-Poulenc Company of Wilmington, Delaware.

The block polymer which is an optional element of the emulsification system can comprise a nonionic, difunctional block polymer which terminates in a primary hydroxyl group and has a molecular weight ranging from about 1 ,000 to above about 15,000. Such polymers are generally considered to be polyoxyalkylene derivatives of propylene glycol and are commercially available under the tradename Pluronic from BASF-Wyandotte Company of Wyandotte, New Jersey. Preferred among these polymers are propylene oxide/ethylene oxide block polymers commercially available as Pluronic 17R1.

The emulsification system should be present at a level which will ensure effective emulsification of the water present, either alone or with a suitable lipophilic organic compound in which water is miscible (to be described in detail later). As an example, the emulsification system can be present at a level of at least about 0.05% by weight of the fuel to do so. Although there is no true upper limit to the amount of the emulsification system which is present, with higher levels leading to greater emulsification and for longer periods, there is generally no need for more than about 5.0% by weight, nor, in fact, more than about 3.0% by weight.

It is also possible to utilize a physical emulsion stabilizer in combination with the emulsification system noted above to maximize the stability of the emulsion. Use of physical stabilizers also provides economic benefits due to their relatively low cost. Although not wishing to be bound by any theory, it is believed that physical stabilizers increase emulsion stability by increasing the viscosity of immiscible phases such that separation of the oil/water interface is retarded. Exemplary of suitable physical stabilizers are waxes, cellulose products, and gums such as whalen gum and xanthan gum.

When utilizing both the emulsification system and physical emulsion stabilizers, the physical stabilizer is present in an amount of about 0.05% to about 5% by weight of the combination of chemical emulsifier and the physical stabilizer. The resulting combination emulsifier/stabiiizer can then be used at th same levels noted above for the use of the emulsification system.

The emulsifiers are preferably blended with the platinum group metal catalyst composition and the resulting blend is then admixed with the fuel and emulsified. To achieve a stable emulsion, especially when large amounts of water are intended, a suitable mechanical emulsifying apparatus, such as an in-line emulsifying device, can be employed. Preferred emulsion stabilities will for time periods of from about 10 days at a minimum to about 1 month or more. More preferably, the emulsion will be stable for at least 3 months.

Among the lipophilic organic compounds in which water is miscible, effective according to the invention, will be water-miscible, fuel-soluble -28- compounds such as butanol, butyl cellosolve (ethyleneglycol monobutyl ether), dipropylene-glycol moπometyl ether, 2-hexyl hexanol, diacetone alcohol, •hexylene glycol, and diisobutyl ketone. Functionally, materials meeting the following criteria can be effective: that they have a water miscibility of at least about 10 g of water per liter of the material, and be soluble in the fuel (when the material contains the 10 g of water) in an amount of about at least 10 g per liter of total fuel. Additionally, the water functional composition will preferably be characterized by hydroxy, ketone, carboxylic acid funtional group, ether linkage, amine group, or other polar functional groups that can serve as water acceptors on a hydrocarbon chain. Concentrations will be dependent on the exact formulation and the expected water content of the fuel, but concentrations of from about 0.01 to about 1.0%, based on the weight of the fuel as combusted, are among those preferred. In some cases, it is more meaningful to express the concentration on the basis of the platinum group metal, and in this case it is preferably at a ratio of from about 1 ,000:1 to about 500,000:1 relative the weight of platinum group metal in the additive composition.

In addition to the materials described above and in U.S. Patent No. 4,891 ,050 to Bowers, et al., U.S. Patent No. 5,034,020 to Epperly, et al., and U.S. Patent No. 5,266,093 to Peter-Hoblyn, et al., other platinum group metal catalyst compositions include commercially-available or easily-synthesized platinum group metal acetylacetonates, platinum group metal dibenzylidene acetoπates, and fatty acid soaps of tetramine platinum metal complexes, e.g., tetramine platinum oleate. In addition, there are the water soluble platinum group metal salts such as chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, iron chloroplatinate, magnesium chloroplatinate, manganese chloroplatinate, and cerium chloroplatinate, as well as any of those compounds identified or included within the description set forth by Haney and Sullivan in U. S. Patent No. 4,629,472. The platinum group metal catalyst compositions are effective to release catalytic platinum group metal in the combustion chamber, or when added to the exhaust gases, release the catalytic platinum group metal there.

Auxiliary Catalyst Metal Composition

In the second embodiment, the platinum group metal catalyst compositions can be employed with other catalytic metallic compositions utilized for improving economy, reducing emissions of pollutants such as hydrocarbons and carbon monoxide, and for improving the operation of particulate traps or oxidation catalysts. Among the useful metallic compositions are organometallic salts of manganese, magnesium, calcium, iron, copper, cerium, sodium, lithium and potassium, which can be employed at suitable levels, e.g., from about 1 to about 100 ppm and preferably 20 to 60 ppm of the catalyst metal in combination with the platinum group metal catalyst in diesel fuels. Among these are the alcoholates, sufonates, beta-diketonates and soaps, e.g., selected from the group consisting of stearates, palmitates, laurates, tallates, napthanates, other fatty acid soaps, and mixtures of two or more of these, of copper, calcium, magnesium, manganese, iron, cerium, sodium, lithium and potassium compounds as are known as fuel soluble and useful fuel additives. Some, such as set forth in the above citations, are known as useful for reducing the temperature at which diesel traps can be regenerated. However, unlike the prior art, the invention permits them to achieve their known function while the emissions of hydrocarbons and carbon monoxide are reduced. Moreover, the invention reduces the balance point sufficiently low to permit NO_x reduction by modifying engine timing or exhaust gas recirculation without the concern for increased particulates which would normally be associated with those techniques. Among the lithium and sodium compounds are organometallic compounds and complexes as well as the salts of lithium and sodium respectively, with ^•suitable organic compounds such as alcohols or acids, e.g., aliphatic, alicyclic and aromatic alcohols and acids. Exemplary of particular salts are the lithium and sodium salts of tertiary butyl alcohol and mixtures of these. Other lithium and sodium organic salts are available and suitable for use to the extent that they are fuel-soluble and are stable in solution. While not preferred, inorganic salts can also be employed to the extent that they can be efficiently dispersed in the fuel, such as in a stable emulsion or otherwise.

Among the specific sodium compounds are: the salts of sulfonated hydrocarbons, for example sodium petroleum sulfonate, available as Sodium Petronate from Witco Chemical (Na0₃SR, R = alkyl, aryl, arylalkyl, and R is a hydrocarbon having greater than three carbons); sodium alcoholates, for example sodium t-butoxide and other fuel- soluble alkoxides (NaOR, wherein R is an alkyl, e.g., from 3 to 22 or more carbons; and sodium napthenate (sodium salts of napthenic acids derived from coal tar and petroleum). Among the specific lithium compounds are the lithium analogs of the above sodium compounds.

Among the specific cerium compounds are: cerium III acetylacetonate, cerium III napthenate, and cerium octoate and other soaps such as stearate, neodecanoate, and octoate (2-ethylhexoate). Many of the cerium compounds are trivalent compounds meeting the formula: Ce (OOCR)₃, wherein R = hydrocarbon, preferably C₂ to C₂₂, and including aliphatic, alicyclic, aryl and alkylaryl.

Among the specific copper compounds are: copper acetylacetonate, copper napthenate, copper tallate, and copper soaps of C₄ to C₂₂ fatty acids, including stearate, laurate, palmitate, octoate, neodecanoate and mixtures of any of these. Fatty acids for these compounds can be derived from any animal or vegetable fat or oil, or fraction thereof, as well as from mineral oils. These copper compounds are divalent compounds, with the soaps meeting the formula: Cu(OOCR)₂ • In addition, complexes formed by reacting or otherwise contacting copper compounds with various organic substrates to form a organometallic complexes as disclosed by patents such as U. S. Patent No. 4,664,677, U. S. Patent No. 5,279,627, U. S. Patent No. 5,348,559, U. S. Patent No. 5,360,549, U. S. Patent No. 5,376,154, International Publication Number WO 92/20764, and the various references cited in them, can be employed.

Among the specific iron compounds are- ferrocene, ferric and ferrous acetyl-acetonates, iron soaps like octoate and stearate (commercially available as Fe(lll) compounds, usually), iron pentacarbonyl Fe(CO)₅ ,ιron napthenate, and iron tallate.

Among the specific managanese compounds are: methylcyciopentadienyl manganese tricarbonyl (CH₃C₅H₄ MN (CO)₃ , as described for example in U. S. Patent No. 4,191 ,536 to Niebylski; manganese acetylacetonate, II and III valent; soaps including neodecanoate, stearate, tallate, napthenate and octoate.

The calcium and magnesium compounds can have the same anions as the copper compounds, but will also include a wider range of sulfonates and overbased sulfonates.

The catalyst compositions can be included in a lubricating oil or fuel additive composition which will preferably include a solvent which is soluble in the fuel. The fuel additive compositions may also contain other additives, such as detergents, antioxidants, and cetane improvers such as octyl nitrate which ar known as beneficial to engine performance, but the use of such is not an essential feature of the invention. The total amount of solvent and other additives used will depend on the dosage of platinum group metal catalyst composition required and on what is a convenient concentration to handle relative to the amount of fuel to be treated. Typically, solvent (plus other like additive) volumes of about 0.1 to about 40.0 liters/gram of platinum are acceptable.

Alternatively, the fuel additive composition can be provided at a ratio so as to provide a sufficient level of platinum group catalyst metal in a relatively short period of time, i.e., under about 10 hours, more preferably under about 5 hours. Effective levels to do so can range up to about 30 ppm, more advantageously, about 15 to about 25 ppm. These levels should be provided for about 0.5 to about 10 hours. Maintenance amounts to intermittently or continuously provide from about 0.1 to about 1.0 ppm can then be provided, to maintain superior activity.

Example 1

A platinum group metal catalyst composition in a fuel additive can have the following composition for mixture with diesel fuel at a dosage rate of 1:2600 by volume (0.15 ppm, Pt) or proportionally within the concentrations indicated above:

Component Parts

Pt (II) Diphenyl Cyclooctadiene 0.0928

Cordination Compound

Ethyl EDA-2 Detergent 23.32

Acetone 2.4

Toluene 0.46

K-1 kerosene 73.73

(Balance to 100.00) Exampie 2

Another diesel fuel additive containing a platinum group metal catalyst composition has the following formulation:

Component Parts

Pd Diphenyl Cyclooctadiene 0.0085

Cordination Compound

Pd(acetyl acetonate)₂ 0.0085

Ethyl D„-3 Octyl Nitrate 28.4

Ethyl EDA-2 Detergent 3.5

Xylene 2.6

Exxon LOPS Mineral Spirits 65.5

Example 3

Another diesel fuel additive containing a platinum group metal catalyst composition has the following formulation.

Component Parts

Pd(acetyl acetonate)₂ 0.017

Oleic Acid Diethanolamide 49.983

Kerosene 50.0

The above description is for the purpose of teaching the person of ordinary skill in the art how to practice the present invention, and it is not intended to detail all of those obvious modifications and variations of it which will become apparent to the skilled worker upon reading this description. It is intended, however, that all such obvious modifications and variations be included within the scope of the present invention which is defined by the foilowing ciaims. The claims cover the indicated components and steps in all arrangements and ^■sequences which are effective to meet the objectives intended for the invention, unless the context specifically indicates the contrary.

Claims

1. A method for improving the operation of a catalytic engine engine comprising: adding a platinum group metal composition to the cylinder of the catalytic engine in an amount effective to deposit caltalyst metal within the cylinder to maintain the activity of the catalyst.

2. A method according to claim 1 wherein platinum group metal catalyst is soluable in the fuel.

3. A method according to claim 1 wherein the platinum group metal catalyst composition is employed at a level sufficient to supply 0.05 to about 1.0 ppm of platinum group metal and an auxilliary catalyst metal compound is employed at a level effective to supply from about 1 to about 100 ppm of that metal, both based on the fuel combusted.

4. A method for according to claim 3 wherein: said auxiliary catalytic metal composition conatains at least one metal metal selected from the group consisting of calcium, magnesium, manganese, iron, sodium, lithium, potassium, and mixtures thereof.

5. A method of claim 1 wherein said diesel engine is modified by retarding engine timing or recirculating exhaust gas effectively to reduce NO_x emissions.

6. A method of claim 1 wherein the platinum group metal composition comprises a soap of a fatty acid, selected from the group consisting of stearates, palmitates laurates, tallates, napthanates, and mixtures of these.

7 . A method according to claim 5 wherein the platinum group metal catalyst composition is employed at a level sufficient to supply 0.05 to about 1.0 ppm of platinum group metal, and also provided is a cerium compound employed at a level effective to supply from about 1 to about 100 ppm of auxilliary catalyst metal, both concentrations based on the fuel combusted.

8. A method according to claim 1 wherein platinum group metal catalyst is present in the fuel.

9. A method according to claim 1 wherein platinum group metal catalyst is present in lubπcating oil.

10. A method according to claim 1 wherein platinum group metal catalyst is introduced into the cylinder with the combustion air.

11. A method according to claim 1 wherein platinum group metal catalyst is introduced into the cylinder through a dedicated injection port.

12. A method according to claim 1 wherein platinum group metal catalyst is introduced into the cylinder intermittently.