CA1190379A - Palladium catalyst promoted by tungsten - Google Patents
Palladium catalyst promoted by tungstenInfo
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- CA1190379A CA1190379A CA000404403A CA404403A CA1190379A CA 1190379 A CA1190379 A CA 1190379A CA 000404403 A CA000404403 A CA 000404403A CA 404403 A CA404403 A CA 404403A CA 1190379 A CA1190379 A CA 1190379A
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- internal combustion
- combustion engine
- palladium
- catalyst
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Abstract
ABSTRACT OF THE DISCLOSURE
There is disclosed a method of using an exhaust gas catalyst for treatment of exhaust gases developed by burning a hydrocarbon fuel or a fuel containing hydrocarbon and alcohol blends in an internal combustion engine. These exhaust gases contain varying amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon the operating conditions of an internal combustion engine. This specification teaches a method of using an improved catalyst composition in which a support medium is provided for supporting the catalyst system. This support medium has deposited thereon palladium and finely divided tungsten. Tungsten is present on the support media in a quantity such that tungsten is available to substantially all of the palladium on the support medium. In this manner, the palladium/tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without production of significant amounts of ammonia when the internal combustion engine is operating under fuel rich conditions.
There is disclosed a method of using an exhaust gas catalyst for treatment of exhaust gases developed by burning a hydrocarbon fuel or a fuel containing hydrocarbon and alcohol blends in an internal combustion engine. These exhaust gases contain varying amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon the operating conditions of an internal combustion engine. This specification teaches a method of using an improved catalyst composition in which a support medium is provided for supporting the catalyst system. This support medium has deposited thereon palladium and finely divided tungsten. Tungsten is present on the support media in a quantity such that tungsten is available to substantially all of the palladium on the support medium. In this manner, the palladium/tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without production of significant amounts of ammonia when the internal combustion engine is operating under fuel rich conditions.
Description
D~
PALLADIIJM CATALYST PROMOTED_BY TUNGSTEN
Tllis invention relates to the use of pal]adium ca-talysts.
No prior art search was conducted on the subject matter of this specification in the U.S. Patent Office or in any other search Eac:ility.
We are unaware of any prior art that is relevant to the catalyst system taught in thi.s specfication. The specific catalyst system taught is a palladium catalyst promoted by tungsten. The catalyst system has highly desirable characteristics in that it is effective in the catalytic oxidation of unburned hydrocarbons and the catalytic xeduction of oxides of nitrogen without significant production of ammonia when an internal combustion engine with which it is associated is operated under fuel rich (oxygen deficient) conditions.
The disclosure o the present specification teaches a catalyst formation which we consider to be unique.
This unique catalyst formation contains palladium and tungsten. The catalyst system find utility in the simultaneous control of carbon monoxide, unburned hydrocarbons and oxides of nitrogen under engine operating conditions which are on the fuel rich side of stoichiometric. Palladium is a catalyst material which is considerably less expensive than platinum, which has been known in the past for uses such as the catalyst system disclosed herein. Tungsten, of course, ls a base metal and is much less expensive than noble metals such as platinum and rhodium~
i ....
. . ..
As is well known to a skilled artisan, an internal combustion engine normal.ly associatecl with an au-tomobile will generally operate on both sides of a stoichiometic air/fuel ratio during various modes of engine operation~
For example, many engi.ne systems are designed to operate slightly fuel deficient during normal cruising modes of the vehicle. At such time, there is more alr present than is required to oxidize the fuel. '~herefore, the overa]l operating mode of the system is oxidizing and the catalyst materials present are operating under oxidizing conditions. In other modes of engine operation, for example, du:ring acceleration periods, internal combustion engines associated with automotive vehicles are normally operated on the rich side of stoichiometry. In this condition, there is more fuel present than air to oxidize the same. In such a case, the overall catalyst system is exposed to reduci.ng conditions because there is not sufficient oxygen available over the catalyst system.
The catalyst system of the present invention is one which under oxidiz.ing conditions is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide, and under reducing conditions is effective not only in the catalytic oxidation of unburned hydrocarbons and carbon monoxide, but also in the catalytic reduction of oxides of nitrogen without significant production of ammonia. The catalyst system of this specification has these excellent characteristics even though it is using materials substantially less expensive than a material such as platinum, which was previously us~ for this type of catalyst system.
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Another very siynificant advantage of the method of using the catalyst system of our invention is that the palladium and tungsten materials used are found in the United States. This lowers the dependency of the manufac-ture of catalyst systems on the availability of catalyst materials from foreign sources.
As mentioned above, p:Latinum generally was the material used in order to achieve the catalytic control of certain materials in exhaust gases~ ~Iowever, platinum has some characteristics which are undesirable in such control systems which are not found with the palladium/tungsten system taught herein. In general, under fuel rich conditions, that is, when the catalyst system is exposed to reducing conclitions, the platinum catalyst had good characteristics ~ith respect to the oxidation of unburned hydrocarbons. However, the platinum catalyst does not have good selectivity in the reduction of oxides of nitrogen~ By this we mean that the platinum catalyst produces a great amount of ammonia, rather than nitrogen gas, by the reduction of oxides of nitrogen.
The catalyst system of our invention does not have this side effect under reducing conditions of producing significant quantities of ammonia by the reduction of oxides of nitrogen.
This invention relates to the use of a palladium catalyst promoted by tungsten and, more particularly, to the use of such a catalyst for use as an exhaust gas catalyst for treatment of exhaust gases developed by burning a hyarocarbon fuel or fuels contai~ing hydrocarbons and alcohol blends in an internal combustion engine.
1~, , ;34~3i7~
In accordance with the present invention, an exhaust gas catalyst is provided for treatment of exhaust gases developed by burning a hydrocarbon fuel in an internal combustion engine. The exhaust gases contain various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine. The improved catalyst composition used in the exhaust yas treatment method is one which is deposited on a suppor-t medium and contains the following componen-ts. Finely divided tungsten is supported on the support media.
Palladium is also deposited on the support media. In a sequential impregnation of these materials, it is necessary that the tungsten be deposited prior to the palladium so that the palladium is not covered up. The tungsten is present on the support medium in quantities such that tunysten is available to substantially all of the palladium on the support medium so that the platinum/tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
It is understood by those skilled in the art that other catalyst materials, materials for protecting the catalyst materials, and materials for promoting the catalyst materials may also be present on the support medium to carry out those functions alrea~y well known to the skilled artisan.
By way of instruction and not by way of a limitation to the scope oE our invention, some particular details of a catalyst system falling within the scope of the method of o~ir invention are set forth herein. The support medium for the catalyst system may be a monolithic substrate, or ,it may be a pelletized substrate, or even a metallic substrate. Fox ~ L~q examp:Le, if a monolithic substrate is selected, it may be washcoated with 5 to 25 weight percent of the catalyst substrate of gamma alumina. Thereafter, finely divided tungsten from 0.2 to 5 weight percent of the washcoated substrate and 0.02 to 1.0 weight percent of palladium by weight of the washcoated substrate can be applied to the washcoated substrate.
The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, will best be understood from the following description of the specific embodiments when read in connection with the accompanying drawings, in Which Figure 1 is a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 0O18% by weight palladium and 8~ by weight gamma alumina;
Figure 2 i6 a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 4.2% by weight tungsten and 9% by weight gamma alumina; and Figure 3 is a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 0 J 15~ by weight palladium, 4.75% by weight tungsten and 9% by weight gamma alumina.
i , In order to disclose the method of using the catalyst sys-tem oE this invention, we desire tv demons-trate the catalytic activity of three different catalyst systems with respect to the effect of the redo~
ratio on the conversion efficiency of that catalyst system on oxides of nitrogen, carbon monoxide and unburned hydrocarbons. The three catalyst systems are demonstrated in Figures 1, 2 and 3~ The fi~st system is a palladium only catalyst, the second is a tungsten only catalyst, and the third is the combined palladium/
tungsten catalyst system in accordance with our invention.
To illustrate the manufacture of the catalyst system used in owr method, detailed instxuctions will be given for the manufacture of a catalyst system, namely one containing both palladium and tungstenO The palladium only or tungsten only catalyst system may be manufactured using the same general procedures simply by leaving out the palladium or the tungsten component as i~lustrated when the combined system is made.
The preparation of a catalyst system is as follows.
The resulting catalyst system will contain palladium, tungsten and gamma alumina. The preparation is initiated by coating a cordierite honeycomb substrate (400 square cells/square inches, 6 mil wall thickness) as available from Corning Glass Company with a gamma alumina washcoat. ~fter coating, with the gamma alumina, the substrate is calcined at 600C for a period of 3 to ~ hours. The completed substrate has approximately g~ by weight of the substrate of gamma alumina contained thereon.
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The tungsten is next impregnated on the gamma alumina coated substrate using a solution of H~WO~ in concentrated NH40H. This solution is dried on the coated substrate at a temperature of 130C and then calcined at 5 300C for a time period of 3 to 4 hours. The tungsten is placed ~y this process onto the substrate i~n a finely divided manner and makes up approximately 4.75% by weight of the substrate of tungsten.
The palladium is now impregnated onto the sub-strate using an acidic aqueous solution of palladium chloride (4~/vol. in concentrated HNO3) dried on the substrate at 130C and then calcined at 500C for a time period of 3 to 4 hours. Thi~ results in approximately 0.15% by weight of the substrate of palladium being applled to the substrate in a finely divided state. With the great excess of tungsten available on the substrate, the tungsten is present on the substrate in a quantity such that the tungsten is available to substantially all of the palladium on the support medium.
By having ~he tungsten closely available to the palladium, we believe the following happens. There is believed to be an interaction between palladium and tungsten resulting in possible PdWOX type surface complex formulatîon where x varies from 3 to 2 to 1, depending upon reduction tempPrature, time of reduction, and reducing gas mixture. The PdWOX type surface complex has significantly diferent catalytic properties than either palladium or WO3. Thus, under reducing conditions, s~ch catalyst provides activity for saturated hydrocarbons which is similar to platinum without producing high N~3 formation, a common product of NO reduction under reducing conditions over a Pt catalyst. The weight ratio of W/Pd could vary from 2 to 50, however, in the preferred limit it can very from 5 to 20 times greater amount~
]:E a PdWOX complex is presynthesized for deposi.tion on a substrate, then one can deposlt -this material on the washcoated substrate. In -this case, no excess of tungsten over palladlum is needed, and tungsten and palladium could be present in equal amounts on an atomic basis.
Al.though this preferred embodlment illustrated herein was prepared as out:lined above, there are a number of ways that a skilled artisan can vary the preparation. For example, instead of impregnating tungsten and gamma alumina in t~o consecutive steps with calcination therebetween, one can combine these steps in one. Also, the gamma alumina support need not be coated on a honeycornb, but may be in a different configuration such as alumina pellets as required for a desired application.
Reference is now made to Figures 1l ~ and 3 so that the benefits of the catalyst system in the method of this invention may be better understood.
In Figure 1 there is shown the effect of redox ratio on the conversion efficiency for oxides of nitrogen, carbon monoxide and unburned hydrocarbons over a palladium only catalyst on a gamma alumina coated substrate. This graph indicates that this catalyst normally maintains a respectable conversion efficiency : for unburned hydrocarbons and reduction of oxides of nitrogen as the redox potenti.al moves Erom less than one (fuel deficient) to more than one (fuel excess).
However, the significant thing to note about the 0 palladium only catalyst system is that the amount of ammonia produced as a percentage of the oxides of nitrogsn reduced is drastically increased as the redox potential moves from 1.0 toward 2.2. The significant amount oE ammonia produced i.s much more than can ~e 5 tolerated in such a system.
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,1 ,., a~ 3 In Figure 2 there is graphed the effect of the redox ratio on the conversion eff.iciency for oxides of nitrogen~ carbon monoxide and unburned hydrocarbons over a tungsten only catalyst system on a gar~ma alumina washcoat.
This graph indicates that the tungsten only system has almost no conversion efficiency in the reduction of oxides of nitrogen from a redox potential of 0.8 all the way to 2Ø This demonstrates that the tungsten only material has absolutely no eff.iciency for the conversion of oxides of 10 nitrogen.
In Figure 3 there ls seen the effect of redox ratio on the conversion efficiency for oxides of nitrogen, carbon monoxide and unburned hydrocarbons over a cataly~t system containing 0.15% by weight palladium, 4.75~ by weight tungsten on a gamma alumina washcoated substrate.
This graphical presentation is of interest because it shows that the efficiency of this catalyst remains high for the conversion of hydrocarbons even though one moves into the rich fuel region past a redox potential of 1Ø ~t also shows that the 02ides of nitrogen conversion rate is quite good in the rich region and actually increases as one goes to richer stoichiometric mixtures~ The thing of particular importance with ~li~ catalyst system is ~hat the ammonia produced as a percentage of the oxides of nitrogen con-verted remains very low and in some regions is nonexistant,For example, no ammonia is seen until a redox potential in excess of 1.4 is passed for this catalyst system and even at a redox potential greater than 1,8~ the amount of ammonia produced as a percentage of the o~ides of nitrogen converted is a relatively lo~ 10% when compared to appro~imately 55% at the same point for the palladium only catalyst system shown in Figure 1.
This low ammonia production is a s.ignif icant improvement because tungsten was added to palladium. The real interesting point is l:hat tungsten by itse:lf ha~ no apparent activity for the reductiorl of o~ide~ of nitrogen, 5 bu~ ye~: when this material i assoc:iated wi~h a palladium catalyst, the uniquely ~eneficial resul~ a~e achieved of permi~tin~ a signiicant conversion ~f oxides of nitrogen by l:he palladium~ungsten catalyst, yet the grea~ suppres-~ion and control of ~he amoun~ o:E ammonia produced as a 10 result o~ this conversion.
Ar~ther sign~ficant aspe.ct of the use of the palladi~n/
~ungs~en ca~alyst system wi:ll be under~tood after review o the ma~er ial contalned in Table 1 hereinbelow, TABI~ 1. EIYDROC:AP~BON CO~IERSIONS
I~Y CATALYSTS OF FI~S. 1, 2 & 3 CATAL YST
Pd W Pd-W
C3E~6C3H8 C3~6C3H8 C3E16 C3H8 R
1 ~ 0 1û0% 589~ 76% 0 100% ~8%
1.1 10û% 42~ 76% 0 100% ~5~3 1.2 1û0% 35% 73% ~ 10~% 80%
1.3 1~0% 27% 67% 0 100% 76%
1.4 100% ~3% 64% û 100% 70%
1.5 100% ~0% 58% 0 100% 67%
1.6 100% 18g 52% 0 1~0% 64 1.7 100% 17% JJ7~ 0 100% 61 lo~3 100%15S~ ~s1% 0 10096 58~6 --1 1 ~
The unique feature of using the cataly~t system as demonstratecl in 'rable 1 is that use of our catalyst system allows conversion of difficult to oxidize, saturated unburned hydrocarbons under oxy~en deficient conditions and simultaneously provides some oxides of nltrogen conversion with minimum ammonia formation as demonstrated in Figure 3. For example, Ta~le 1 shows that while a palladium only catalyst retains its efficiency in oxidizing C3H6, its ability to oxidize C3~8 drops off as R goes up from 1.0 to 1~8. At 1.8, its efficiency in this conversion is only 15%~ Table 1 also shows that tungsten has absolutely no abi]ity in converting ~3H~ in the range of R's from 1.0 to 1.8 The amazing point now is that when palladium and tungsten are used together, the conversion efficiency for C3H8 is drastically increased at an R of 1.0 and remains drastically increased over any conversion efficiency achieved on a palladium only catalyst regardless of the redox poterrtial at which the measurement is made. This effect is more than additive becaùse the tungsten by itself has no efficiency in the oxidation of C3H8, but when it is combined with palladium the over~ll efficiency of the palladium for this conversion is greatly enhanced~
In summation, we desire to point out some of the characteristics o~ the palladium/tungs-ten catalyst used with our method. Under reducing conditions, ~or example, with the redox potential equal to 1.8, the catalyst system converts 45% of the gross oxide of nitrogen and 41% of the net oxides of nitrogen. At this location, the ammonia formation measured as a percentage of the oxides of nitrogen converted is only 10~. From this measurement and the other data displayed in Figure 3, the following may be stated. In a vehicle application where an engine is operating slightly lean of stoichiometry, the palladium/tungsten containing catalyst used with the method of our invention will give high unburned hydrocarbons and carbon rnonoxide converslon. For example~ at ~=0.9 the unburned hydrocarbon and carbon monoxide conversions are approximately 96~ and 80% respectively. During rich -transients (~or e~ample, during an acceleration when more power is demanded) the engine will run rich, that is, the air/fuel ratio decreases from the set point oE
15.2-15.5 to approximately 1~.3 (e.g., R=1.8). Under these conditions, the palladium/tungsten catalyst system used with the method of our invention can convert approximately 40% of the oxides of nitrogen to nitrogen gas with a minimum ammonia formation. It should also be noted that even under such reclucing conditions the catalyst system used with the method of our invention is capable of converting over 85~ of the total unburned hydrocarbons.
It is understood that many different materials may find their way onto a catalyst substrate for particular use. For example, certain materials are put on the catalyst substrate in order to stabilize the gamma alumina catalyst washcoat~ Also, other washcoat materials such as zirconia or alpha alumina may be used ; and these also may have their stabilizing elements. As an additional matter, stabilizing elements may be present for stabilizing the catalyst materials under certain operating conditions, for example, under oxidizing or under reducin~ conditions. In a similar manner, materials may also find their way onto the catalyst substrate in order to promote the catalyst activity or to ensure the action o~ a stab~llzer material. The appended claims are not to be construed so as to eliminate such materials from the catalyst system used with the method of our invention. Our predominant invention is that the combination of palladium and tungsten has certain unique benefits. It is well within the scope of a ,skilled artisan to use the unique benefits of this catalyst system with other catalyst materials, promoters and stabilizers therefor.
Thus, the appended claims are to be interpreted ,~'i.~
as not excluding from their coverage the use of catalyst sys-tems which use pallacllum and. tungs-ten in the manner described in this specification, but use such materials iJl combination with other catalyst elements as well as promoters and stabilizers therefor.
While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spiri.t and scope of this invention.
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PALLADIIJM CATALYST PROMOTED_BY TUNGSTEN
Tllis invention relates to the use of pal]adium ca-talysts.
No prior art search was conducted on the subject matter of this specification in the U.S. Patent Office or in any other search Eac:ility.
We are unaware of any prior art that is relevant to the catalyst system taught in thi.s specfication. The specific catalyst system taught is a palladium catalyst promoted by tungsten. The catalyst system has highly desirable characteristics in that it is effective in the catalytic oxidation of unburned hydrocarbons and the catalytic xeduction of oxides of nitrogen without significant production of ammonia when an internal combustion engine with which it is associated is operated under fuel rich (oxygen deficient) conditions.
The disclosure o the present specification teaches a catalyst formation which we consider to be unique.
This unique catalyst formation contains palladium and tungsten. The catalyst system find utility in the simultaneous control of carbon monoxide, unburned hydrocarbons and oxides of nitrogen under engine operating conditions which are on the fuel rich side of stoichiometric. Palladium is a catalyst material which is considerably less expensive than platinum, which has been known in the past for uses such as the catalyst system disclosed herein. Tungsten, of course, ls a base metal and is much less expensive than noble metals such as platinum and rhodium~
i ....
. . ..
As is well known to a skilled artisan, an internal combustion engine normal.ly associatecl with an au-tomobile will generally operate on both sides of a stoichiometic air/fuel ratio during various modes of engine operation~
For example, many engi.ne systems are designed to operate slightly fuel deficient during normal cruising modes of the vehicle. At such time, there is more alr present than is required to oxidize the fuel. '~herefore, the overa]l operating mode of the system is oxidizing and the catalyst materials present are operating under oxidizing conditions. In other modes of engine operation, for example, du:ring acceleration periods, internal combustion engines associated with automotive vehicles are normally operated on the rich side of stoichiometry. In this condition, there is more fuel present than air to oxidize the same. In such a case, the overall catalyst system is exposed to reduci.ng conditions because there is not sufficient oxygen available over the catalyst system.
The catalyst system of the present invention is one which under oxidiz.ing conditions is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide, and under reducing conditions is effective not only in the catalytic oxidation of unburned hydrocarbons and carbon monoxide, but also in the catalytic reduction of oxides of nitrogen without significant production of ammonia. The catalyst system of this specification has these excellent characteristics even though it is using materials substantially less expensive than a material such as platinum, which was previously us~ for this type of catalyst system.
.~h .
a~3~
Another very siynificant advantage of the method of using the catalyst system of our invention is that the palladium and tungsten materials used are found in the United States. This lowers the dependency of the manufac-ture of catalyst systems on the availability of catalyst materials from foreign sources.
As mentioned above, p:Latinum generally was the material used in order to achieve the catalytic control of certain materials in exhaust gases~ ~Iowever, platinum has some characteristics which are undesirable in such control systems which are not found with the palladium/tungsten system taught herein. In general, under fuel rich conditions, that is, when the catalyst system is exposed to reducing conclitions, the platinum catalyst had good characteristics ~ith respect to the oxidation of unburned hydrocarbons. However, the platinum catalyst does not have good selectivity in the reduction of oxides of nitrogen~ By this we mean that the platinum catalyst produces a great amount of ammonia, rather than nitrogen gas, by the reduction of oxides of nitrogen.
The catalyst system of our invention does not have this side effect under reducing conditions of producing significant quantities of ammonia by the reduction of oxides of nitrogen.
This invention relates to the use of a palladium catalyst promoted by tungsten and, more particularly, to the use of such a catalyst for use as an exhaust gas catalyst for treatment of exhaust gases developed by burning a hyarocarbon fuel or fuels contai~ing hydrocarbons and alcohol blends in an internal combustion engine.
1~, , ;34~3i7~
In accordance with the present invention, an exhaust gas catalyst is provided for treatment of exhaust gases developed by burning a hydrocarbon fuel in an internal combustion engine. The exhaust gases contain various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine. The improved catalyst composition used in the exhaust yas treatment method is one which is deposited on a suppor-t medium and contains the following componen-ts. Finely divided tungsten is supported on the support media.
Palladium is also deposited on the support media. In a sequential impregnation of these materials, it is necessary that the tungsten be deposited prior to the palladium so that the palladium is not covered up. The tungsten is present on the support medium in quantities such that tunysten is available to substantially all of the palladium on the support medium so that the platinum/tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
It is understood by those skilled in the art that other catalyst materials, materials for protecting the catalyst materials, and materials for promoting the catalyst materials may also be present on the support medium to carry out those functions alrea~y well known to the skilled artisan.
By way of instruction and not by way of a limitation to the scope oE our invention, some particular details of a catalyst system falling within the scope of the method of o~ir invention are set forth herein. The support medium for the catalyst system may be a monolithic substrate, or ,it may be a pelletized substrate, or even a metallic substrate. Fox ~ L~q examp:Le, if a monolithic substrate is selected, it may be washcoated with 5 to 25 weight percent of the catalyst substrate of gamma alumina. Thereafter, finely divided tungsten from 0.2 to 5 weight percent of the washcoated substrate and 0.02 to 1.0 weight percent of palladium by weight of the washcoated substrate can be applied to the washcoated substrate.
The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, will best be understood from the following description of the specific embodiments when read in connection with the accompanying drawings, in Which Figure 1 is a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 0O18% by weight palladium and 8~ by weight gamma alumina;
Figure 2 i6 a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 4.2% by weight tungsten and 9% by weight gamma alumina; and Figure 3 is a graphical presentation of data on the effect of redox ratio on the conversion efficiency of oxides of nitrogen, carbon monoxide and hydrocarbons over a catalyst system containing 0 J 15~ by weight palladium, 4.75% by weight tungsten and 9% by weight gamma alumina.
i , In order to disclose the method of using the catalyst sys-tem oE this invention, we desire tv demons-trate the catalytic activity of three different catalyst systems with respect to the effect of the redo~
ratio on the conversion efficiency of that catalyst system on oxides of nitrogen, carbon monoxide and unburned hydrocarbons. The three catalyst systems are demonstrated in Figures 1, 2 and 3~ The fi~st system is a palladium only catalyst, the second is a tungsten only catalyst, and the third is the combined palladium/
tungsten catalyst system in accordance with our invention.
To illustrate the manufacture of the catalyst system used in owr method, detailed instxuctions will be given for the manufacture of a catalyst system, namely one containing both palladium and tungstenO The palladium only or tungsten only catalyst system may be manufactured using the same general procedures simply by leaving out the palladium or the tungsten component as i~lustrated when the combined system is made.
The preparation of a catalyst system is as follows.
The resulting catalyst system will contain palladium, tungsten and gamma alumina. The preparation is initiated by coating a cordierite honeycomb substrate (400 square cells/square inches, 6 mil wall thickness) as available from Corning Glass Company with a gamma alumina washcoat. ~fter coating, with the gamma alumina, the substrate is calcined at 600C for a period of 3 to ~ hours. The completed substrate has approximately g~ by weight of the substrate of gamma alumina contained thereon.
,~' t~`P~
The tungsten is next impregnated on the gamma alumina coated substrate using a solution of H~WO~ in concentrated NH40H. This solution is dried on the coated substrate at a temperature of 130C and then calcined at 5 300C for a time period of 3 to 4 hours. The tungsten is placed ~y this process onto the substrate i~n a finely divided manner and makes up approximately 4.75% by weight of the substrate of tungsten.
The palladium is now impregnated onto the sub-strate using an acidic aqueous solution of palladium chloride (4~/vol. in concentrated HNO3) dried on the substrate at 130C and then calcined at 500C for a time period of 3 to 4 hours. Thi~ results in approximately 0.15% by weight of the substrate of palladium being applled to the substrate in a finely divided state. With the great excess of tungsten available on the substrate, the tungsten is present on the substrate in a quantity such that the tungsten is available to substantially all of the palladium on the support medium.
By having ~he tungsten closely available to the palladium, we believe the following happens. There is believed to be an interaction between palladium and tungsten resulting in possible PdWOX type surface complex formulatîon where x varies from 3 to 2 to 1, depending upon reduction tempPrature, time of reduction, and reducing gas mixture. The PdWOX type surface complex has significantly diferent catalytic properties than either palladium or WO3. Thus, under reducing conditions, s~ch catalyst provides activity for saturated hydrocarbons which is similar to platinum without producing high N~3 formation, a common product of NO reduction under reducing conditions over a Pt catalyst. The weight ratio of W/Pd could vary from 2 to 50, however, in the preferred limit it can very from 5 to 20 times greater amount~
]:E a PdWOX complex is presynthesized for deposi.tion on a substrate, then one can deposlt -this material on the washcoated substrate. In -this case, no excess of tungsten over palladlum is needed, and tungsten and palladium could be present in equal amounts on an atomic basis.
Al.though this preferred embodlment illustrated herein was prepared as out:lined above, there are a number of ways that a skilled artisan can vary the preparation. For example, instead of impregnating tungsten and gamma alumina in t~o consecutive steps with calcination therebetween, one can combine these steps in one. Also, the gamma alumina support need not be coated on a honeycornb, but may be in a different configuration such as alumina pellets as required for a desired application.
Reference is now made to Figures 1l ~ and 3 so that the benefits of the catalyst system in the method of this invention may be better understood.
In Figure 1 there is shown the effect of redox ratio on the conversion efficiency for oxides of nitrogen, carbon monoxide and unburned hydrocarbons over a palladium only catalyst on a gamma alumina coated substrate. This graph indicates that this catalyst normally maintains a respectable conversion efficiency : for unburned hydrocarbons and reduction of oxides of nitrogen as the redox potenti.al moves Erom less than one (fuel deficient) to more than one (fuel excess).
However, the significant thing to note about the 0 palladium only catalyst system is that the amount of ammonia produced as a percentage of the oxides of nitrogsn reduced is drastically increased as the redox potential moves from 1.0 toward 2.2. The significant amount oE ammonia produced i.s much more than can ~e 5 tolerated in such a system.
,J~ !
,1 ,., a~ 3 In Figure 2 there is graphed the effect of the redox ratio on the conversion eff.iciency for oxides of nitrogen~ carbon monoxide and unburned hydrocarbons over a tungsten only catalyst system on a gar~ma alumina washcoat.
This graph indicates that the tungsten only system has almost no conversion efficiency in the reduction of oxides of nitrogen from a redox potential of 0.8 all the way to 2Ø This demonstrates that the tungsten only material has absolutely no eff.iciency for the conversion of oxides of 10 nitrogen.
In Figure 3 there ls seen the effect of redox ratio on the conversion efficiency for oxides of nitrogen, carbon monoxide and unburned hydrocarbons over a cataly~t system containing 0.15% by weight palladium, 4.75~ by weight tungsten on a gamma alumina washcoated substrate.
This graphical presentation is of interest because it shows that the efficiency of this catalyst remains high for the conversion of hydrocarbons even though one moves into the rich fuel region past a redox potential of 1Ø ~t also shows that the 02ides of nitrogen conversion rate is quite good in the rich region and actually increases as one goes to richer stoichiometric mixtures~ The thing of particular importance with ~li~ catalyst system is ~hat the ammonia produced as a percentage of the oxides of nitrogen con-verted remains very low and in some regions is nonexistant,For example, no ammonia is seen until a redox potential in excess of 1.4 is passed for this catalyst system and even at a redox potential greater than 1,8~ the amount of ammonia produced as a percentage of the o~ides of nitrogen converted is a relatively lo~ 10% when compared to appro~imately 55% at the same point for the palladium only catalyst system shown in Figure 1.
This low ammonia production is a s.ignif icant improvement because tungsten was added to palladium. The real interesting point is l:hat tungsten by itse:lf ha~ no apparent activity for the reductiorl of o~ide~ of nitrogen, 5 bu~ ye~: when this material i assoc:iated wi~h a palladium catalyst, the uniquely ~eneficial resul~ a~e achieved of permi~tin~ a signiicant conversion ~f oxides of nitrogen by l:he palladium~ungsten catalyst, yet the grea~ suppres-~ion and control of ~he amoun~ o:E ammonia produced as a 10 result o~ this conversion.
Ar~ther sign~ficant aspe.ct of the use of the palladi~n/
~ungs~en ca~alyst system wi:ll be under~tood after review o the ma~er ial contalned in Table 1 hereinbelow, TABI~ 1. EIYDROC:AP~BON CO~IERSIONS
I~Y CATALYSTS OF FI~S. 1, 2 & 3 CATAL YST
Pd W Pd-W
C3E~6C3H8 C3~6C3H8 C3E16 C3H8 R
1 ~ 0 1û0% 589~ 76% 0 100% ~8%
1.1 10û% 42~ 76% 0 100% ~5~3 1.2 1û0% 35% 73% ~ 10~% 80%
1.3 1~0% 27% 67% 0 100% 76%
1.4 100% ~3% 64% û 100% 70%
1.5 100% ~0% 58% 0 100% 67%
1.6 100% 18g 52% 0 1~0% 64 1.7 100% 17% JJ7~ 0 100% 61 lo~3 100%15S~ ~s1% 0 10096 58~6 --1 1 ~
The unique feature of using the cataly~t system as demonstratecl in 'rable 1 is that use of our catalyst system allows conversion of difficult to oxidize, saturated unburned hydrocarbons under oxy~en deficient conditions and simultaneously provides some oxides of nltrogen conversion with minimum ammonia formation as demonstrated in Figure 3. For example, Ta~le 1 shows that while a palladium only catalyst retains its efficiency in oxidizing C3H6, its ability to oxidize C3~8 drops off as R goes up from 1.0 to 1~8. At 1.8, its efficiency in this conversion is only 15%~ Table 1 also shows that tungsten has absolutely no abi]ity in converting ~3H~ in the range of R's from 1.0 to 1.8 The amazing point now is that when palladium and tungsten are used together, the conversion efficiency for C3H8 is drastically increased at an R of 1.0 and remains drastically increased over any conversion efficiency achieved on a palladium only catalyst regardless of the redox poterrtial at which the measurement is made. This effect is more than additive becaùse the tungsten by itself has no efficiency in the oxidation of C3H8, but when it is combined with palladium the over~ll efficiency of the palladium for this conversion is greatly enhanced~
In summation, we desire to point out some of the characteristics o~ the palladium/tungs-ten catalyst used with our method. Under reducing conditions, ~or example, with the redox potential equal to 1.8, the catalyst system converts 45% of the gross oxide of nitrogen and 41% of the net oxides of nitrogen. At this location, the ammonia formation measured as a percentage of the oxides of nitrogen converted is only 10~. From this measurement and the other data displayed in Figure 3, the following may be stated. In a vehicle application where an engine is operating slightly lean of stoichiometry, the palladium/tungsten containing catalyst used with the method of our invention will give high unburned hydrocarbons and carbon rnonoxide converslon. For example~ at ~=0.9 the unburned hydrocarbon and carbon monoxide conversions are approximately 96~ and 80% respectively. During rich -transients (~or e~ample, during an acceleration when more power is demanded) the engine will run rich, that is, the air/fuel ratio decreases from the set point oE
15.2-15.5 to approximately 1~.3 (e.g., R=1.8). Under these conditions, the palladium/tungsten catalyst system used with the method of our invention can convert approximately 40% of the oxides of nitrogen to nitrogen gas with a minimum ammonia formation. It should also be noted that even under such reclucing conditions the catalyst system used with the method of our invention is capable of converting over 85~ of the total unburned hydrocarbons.
It is understood that many different materials may find their way onto a catalyst substrate for particular use. For example, certain materials are put on the catalyst substrate in order to stabilize the gamma alumina catalyst washcoat~ Also, other washcoat materials such as zirconia or alpha alumina may be used ; and these also may have their stabilizing elements. As an additional matter, stabilizing elements may be present for stabilizing the catalyst materials under certain operating conditions, for example, under oxidizing or under reducin~ conditions. In a similar manner, materials may also find their way onto the catalyst substrate in order to promote the catalyst activity or to ensure the action o~ a stab~llzer material. The appended claims are not to be construed so as to eliminate such materials from the catalyst system used with the method of our invention. Our predominant invention is that the combination of palladium and tungsten has certain unique benefits. It is well within the scope of a ,skilled artisan to use the unique benefits of this catalyst system with other catalyst materials, promoters and stabilizers therefor.
Thus, the appended claims are to be interpreted ,~'i.~
as not excluding from their coverage the use of catalyst sys-tems which use pallacllum and. tungs-ten in the manner described in this specification, but use such materials iJl combination with other catalyst elements as well as promoters and stabilizers therefor.
While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spiri.t and scope of this invention.
"
,, ~, ~
...~. .1:'.
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method for treatment of exhaust gases from an internal combustion engine, the steps of:
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a support medium for supporting a catalyst system has deposits thereon comprising:
palladium; and finely divided tungsten, said tungsten being present on said support medium in quantities such that tungsten is available to substantially all of said palladium on the support medium so that said palladium/
tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a support medium for supporting a catalyst system has deposits thereon comprising:
palladium; and finely divided tungsten, said tungsten being present on said support medium in quantities such that tungsten is available to substantially all of said palladium on the support medium so that said palladium/
tungsten combination is effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
2. In a method for treatment of exhaust gases from an internal combustion engine the steps of:
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a catalyst support mdeiafor supporting a catalyst system has deposits theron comprising:
finely divided palladium; and finely divided tungsten, said tungsten being present on said catalyst support medium in a quantity such that tungsten is available to substantially all of said finely devided palladium on the catalyst support medium so that said palladium/tungsten combination is particularly effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a catalyst support mdeiafor supporting a catalyst system has deposits theron comprising:
finely divided palladium; and finely divided tungsten, said tungsten being present on said catalyst support medium in a quantity such that tungsten is available to substantially all of said finely devided palladium on the catalyst support medium so that said palladium/tungsten combination is particularly effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
3. The method of claim 1 or 2, wherein the support media is a gamma alumina coated monolithic substrate.
4. The method of claim 1 or 2, wherein the support media is gamma alumina pellets.
5. The method of claim 1 or 2, wherein the support media is a washcoated metallic substrate.
6. In a method for treatment of exhaust gases from an internal combustion engine, the steps of:
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a catalyst support medium for supporting a catalyst system has deposits thereon comprising:
0.02 to 1.0% by weight of the substrate of finely divided palladium; and from 2 to 50 times the weight of palladium present of finely divided tungsten, said tungsten being present on the said catalyst support medium in a quantity such that tungsten is available to substantially all of said finely divided palladium on the catalyst support medium so that said palladium/tungsten combination is particularly effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine; and passing said generated exhaust gases over an improved catalyst composition in which a catalyst support medium for supporting a catalyst system has deposits thereon comprising:
0.02 to 1.0% by weight of the substrate of finely divided palladium; and from 2 to 50 times the weight of palladium present of finely divided tungsten, said tungsten being present on the said catalyst support medium in a quantity such that tungsten is available to substantially all of said finely divided palladium on the catalyst support medium so that said palladium/tungsten combination is particularly effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
7. The method of claim 6, wherein the support media is a gamma alumina coated monolithic substrate.
8. The method of claim 6, wherein the support media is gamma alumina pellets.
9. The method of claim 6, wherein the support media is a washcoated metallic substrate.
10. The method of claim 6, wherein said finely divided tungsten is present from 5 to 20 times the weight of palladium present.
11. In a method for treatment of exhaust gases from an internal combustion engine, the steps of:
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine, and passing said generated exhaust gases over an improved catalyst composition in which a support medium for supporting a catalyst system has as adeposit thereon comprising:
a presynthesized PdWOX (x goes from 1 to 3), said presynthesized palladium/tungsten compound being effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
burning a hydrocarbon fuel or fuel containing hydrocarbon and alcohol blends in the internal combustion engine thereby to generate exhaust gases from the internal combustion engine containing various amounts of unburned hydrocarbons, carbon monoxide and oxides of nitrogen depending upon operating conditions of the internal combustion engine, and passing said generated exhaust gases over an improved catalyst composition in which a support medium for supporting a catalyst system has as adeposit thereon comprising:
a presynthesized PdWOX (x goes from 1 to 3), said presynthesized palladium/tungsten compound being effective in the catalytic oxidation of unburned hydrocarbons and carbon monoxide and the catalytic reduction of oxides of nitrogen without significant production of ammonia when the internal combustion engine is operating under fuel rich conditions.
12. The method of claim 11, wherein the support media is a gamma alumina coated monolithic substrate.
13. The method of claim ll, wherein the support media is gamma alumina pellets.
14. The method of claim 11, wherein the support media is a washcoated metallic substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US28475981A | 1981-07-20 | 1981-07-20 | |
| US284,759 | 1981-07-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1190379A true CA1190379A (en) | 1985-07-16 |
Family
ID=23091426
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000404403A Expired CA1190379A (en) | 1981-07-20 | 1982-06-03 | Palladium catalyst promoted by tungsten |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5824344A (en) |
| CA (1) | CA1190379A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105073250A (en) * | 2013-02-26 | 2015-11-18 | 庄信万丰股份有限公司 | Oxidation catalyst for internal combustion engine exhaust gas treatment |
-
1982
- 1982-06-03 CA CA000404403A patent/CA1190379A/en not_active Expired
- 1982-07-19 JP JP57125604A patent/JPS5824344A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105073250A (en) * | 2013-02-26 | 2015-11-18 | 庄信万丰股份有限公司 | Oxidation catalyst for internal combustion engine exhaust gas treatment |
| CN105073250B (en) * | 2013-02-26 | 2018-11-13 | 庄信万丰股份有限公司 | Oxidation catalyst for engine exhaust gas processing |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5824344A (en) | 1983-02-14 |
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