Patent Application
20130217566
1. Field of the Invention
Embodiments of the present invention generally relate to supported catalysts containing precious group metals and, more particularly, to engine exhaust catalysts containing palladium and gold, and methods of production thereof.
2. Description of the Related Art
Many industrial products such as fuels, lubricants, polymers, fibers, drugs, and other chemicals would not be manufacturable without the use of catalysts. Catalysts are also essential for the reduction of pollutants, particularly air pollutants created during the production of energy and by automobiles. Many industrial catalysts are composed of a high surface area support material upon which chemically active metal nanoparticles (i.e., nanometer sized metal particles) are dispersed. The support materials are generally inert, ceramic type materials having surface areas on the order of hundreds of square meters/gram. This high specific surface area usually requires a complex internal pore system. The metal nanoparticles are deposited on the support and dispersed throughout this internal pore system, and are generally between 1 and 100 nanometers in size.
Supported catalysts are quite useful in removing pollutants from vehicle exhausts. Vehicle exhausts contain harmful pollutants, such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx), that contribute to the “smog-effect” that have plagued major metropolitan areas across the globe. Catalytic converters containing supported catalysts and particulate filters have been used to remove such harmful pollutants from the vehicle exhaust. While pollution from vehicle exhaust has decreased over the years from the use of catalytic converters and particulate filters, research into improved supported catalysts has been continuing as requirements for vehicle emission control have become more stringent and as vehicle manufacturers seek to use less amounts of precious metal in the supported catalysts to reduce the total cost of emission control.
The prior art teaches the use of supported catalysts containing palladium and gold as good partial oxidation catalysts. As such, they have been used extensively in the production of vinyl acetate in the vapor phase by reaction of ethylene, acetic acid and oxygen. See, e.g., U.S. Pat. No. 6,022,823. As for vehicle emission control applications, U.S. Pat. No. 6,763,309 speculates that palladium-gold might be a good bimetallic candidate for increasing the rate of NO decomposition. The disclosure, however, is based on a mathematical model and is not supported by experimental data. There is also no teaching in this patent that a palladium-gold system will be effective in treating vehicle emissions that include CO and HC.
U.S. patent application Ser. No. 11/624,116 and U.S. patent application Ser. No. 11/624,128 disclose engine exhaust catalysts containing palladium and gold that have been proven to be effective in treating vehicle emissions that include CO and HC. The process disclosed in these patent applications for producing palladium-gold catalysts involves contacting of a support material such as alumina with metal salt solutions containing palladium and gold, and reducing the palladium and gold ions to metal particles in situ and in the presence of the support material using suitable reducing agents.
In one embodiment, an emission control catalyst for treating an engine exhaust includes an oxide carrier; and palladium and gold particles supported on the oxide carrier, wherein the catalyst has a palladium to gold weight ratio in a range of about 0.5:1 to about 1:0.5. In another embodiment, the emission control catalyst includes a second oxide carrier having platinum and palladium particles.
One or more embodiments of the present invention provide methods for producing palladium-gold metal particles using a colloidal technique. A method for producing palladium-gold colloid, according to an embodiment of the present invention, includes the steps of adding a solution containing a phosphorus-based reagent and metal salt solutions containing palladium and gold to an aqueous solution and reducing palladium and gold ions within the aqueous solution. A method for producing a supported catalyst containing palladium-gold metal particles, according to an embodiment of the present invention, includes the steps of mixing a solution containing a phosphorus-based reagent and metal salt solutions containing palladium and gold to produce a palladium-gold colloid solution, and adding a support material to the palladium-gold colloid solution. The solution containing a phosphorus-based reagent in the embodiments of the present invention may be a solution of tetrakis (hydroxymethyl) phosphonium chloride (THPC).
An emission control catalyst for treating an engine exhaust, according to an embodiment of the present invention, includes a catalyst containing metal particles consisting essentially of palladium and gold, wherein such metal particles are formed using a compound containing phosphorus, such as THPC. The emission control catalyst may further comprise a platinum-based catalyst, such as a platinum-palladium catalyst, and the palladium-gold catalyst and the platinum-based catalyst are coated onto a substrate of the emission control catalyst as different layers on the substrate or onto different zones of the substrate.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, in various embodiments the invention provides numerous advantages over the prior art. However, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in the claims. Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in the claims.
In the exhaust system of
In the exhaust system of
In the exhaust system of
In the exhaust system of
Alternative configurations of the exhaust system includes the provision of SCR unit 107 and the ammonia slip catalyst 110 in the exhaust system of
As particulates get trapped in the particulate filter within the exhaust system of
Active regeneration is carried out by heating up the particulate filter 106 and oxidizing the particulates. At higher temperatures, NO2 assistance of the particulate oxidation becomes less important. The heating of the particulate filter 106 may be carried out in various ways known in the art. One way is to employ a fuel burner which heats the particulate filter 106 to particulate combustion temperatures. Another way is to increase the temperature of the exhaust stream by modifying the engine output when the particulate filter load reaches a pre-determined level.
The present invention provides catalysts that are to be used in the catalytic converter 104 shown in
In the configuration of
In the configuration of
In the configuration of
All of the configurations described above include a palladium-gold catalyst in combination with a platinum-based catalyst. The weight ratio of palladium to gold in the palladium-gold catalyst is about 0.05:1 to 20:1, preferably from about 0.5:1 to about 2:1. The palladium-gold catalyst may be promoted with bismuth or other known promoters. The platinum-based catalyst may be a platinum catalyst, a platinum-palladium catalyst, a platinum catalyst promoted with bismuth or other now promoters, or other platinum-based catalysts (e.g., Pt—Rh, Pt—Ir, Pt—Ru, Pt—Au, Pt—Ag, Pt—Rh—Ir, Pt—Ir—Au, etc.). When a platinum-palladium catalyst is used as the platinum-based catalyst, the weight ratio of platinum to palladium in this catalyst is about 0.05:1 to 20:1, preferably from about 2:1 to about 4:1.
In addition, the platinum-based catalyst is situated so that it encounters the exhaust stream prior to the palladium-gold catalyst. By positioning the platinum-based catalyst relative to the palladium-gold catalyst in this manner, the inventors have discovered that HC inhibition effects on the oxidation activity of the palladium-gold catalyst are reduced to sufficient levels so that the overall catalytic performance is improved. In the configurations of
A hydrocarbon absorbing material may be added to the emission control catalyst. Preferably, the hydrocarbon absorbing material is added to the emission control catalyst so that it encounters exhaust stream prior to the palladium-gold catalyst. By positioning the hydrocarbon absorbing material relative to the palladium-gold catalyst in this manner, the inventors have discovered that HC inhibition effects on the oxidation activity of the palladium-gold catalyst are reduced to sufficient levels so that the overall catalytic performance is improved. In the configuration shown in
In the method described above, THPC functions as both a reducing agent and a stabilizer during the production of the palladium-gold colloid. As a result, agglomeration of metal particles was not observed even at higher metal concentrations, e.g., on the order of 0.01 M. Therefore, a large amount of active catalyst material can be synthesized without employing large volumes of the host liquid, which includes water and sodium hydroxide.
As observed, the method produces palladium-gold particles having a narrow composition range such that the relative amounts of palladium to gold within each particle are consistent from particle to particle. In addition, THPC is relatively low in cost and so the colloid method may provide a cost effective method of palladium-gold catalyst production. Another advantage of the method is that the catalyst metal particles are prepared before they are placed on the support material. This allows the catalyst metal particles to be characterized and controlled more easily. Still another advantage of the method is that it can be carried out in an aqueous solution. As a result, unlike alcohol-based colloidal techniques, heating is not required for reduction of the metal ions in the solution.
A commonly used metric for measuring catalytic efficiency of catalysts is the temperature at which 50% conversion of CO or hydrocarbons such as C3H6 is observed. For simplicity, this temperature will be referred to herein as the T50 temperature. The T50 temperatures of catalysts differ depending on the conditions under which the conversion of CO into CO2 is observed. Therefore, they are determined under conditions that simulate the actual operating conditions of the catalyst as closely as possible. The T50 temperatures have been determined under simulated exhaust conditions, which were as follows. A gas mixture having the composition: 1000 ppm CO, 350 ppm hydrocarbons (C3H6/C3H8=7:3), 450 ppm NO, 10% O2, and 10% CO2 (10%), and He (balance) is supplied into a fixed bed flow reactor containing 15 mg (80-100 mesh size) of catalyst powder mixed with 85 mg of α-Al2O3 (80-100 mesh size) at a total flow rate of 300 cc/min. The reactor is heated from room temperature to 300° C. at 10° C./minute. As the reactor is heated, CO conversion (oxidation) was measured by use of mass spectrometry as a function of temperature. Hydrocarbon conversion (oxidation) was also measured as a function of temperature by use of mass spectrometry.
Table 1 presents experimental data on the T50 temperatures of sample palladium-gold catalysts prepared using the THPC colloid method according to embodiments of the present invention (Examples 1-4) and control catalysts prepared using the incipient wetness impregnation method (Control 1-4). Comparing Examples 1-4 with the respective Controls 1-4 in Table 1 above, the T50 conversion temperatures are lower for the sample palladium-gold catalysts prepared using the THPC colloid method according to embodiments of the present invention.
Analysis of the sample palladium-gold catalysts using STEM and EDX, (experimental error is estimated to be about 10%) indicates that the THPC colloid method described herein produces palladium-gold particles with good uniformity in composition, and as observed, all of the particles formed are Pd—Au alloys (no single-component particles were observed). Also, phosphorus was observed in the sample palladium-gold catalysts after elemental analysis. The third palladium-gold catalyst sample (Example 3) was observed to have an atomic composition for gold ranging between 25%-45%, with an average composition of 36%, compared to a targeted value of 39%. The fourth palladium-gold catalyst sample (Example 4) was observed to have an atomic composition for gold ranging between 21%-46%, with an average composition of 26%, compared to a targeted value of 24%. In addition, the analysis of the sample palladium-gold catalysts using STEM and EDX showed that the majority of the palladium-gold nanoparticles have a size range of 1 to 5 nanometers. For the two palladium-gold catalyst samples discussed above (Examples 3 and 4), all particles analyzed showed alloying of the palladium and gold, and most of the particles ranged from 1-5 nanometers in size, with only a few rare instances of particles larger than 6 nanometers in size, which suggests that particle clustering or agglomeration was, for the most part, not present. The results of the analysis of the two samples show that the THPC colloid method produces palladium-gold particles whose composition is fairly uniform and close to the targeted composition.
The preparation methods for Controls 1-4 were as follows.
Add 6.15 mL of H2O to a 20 mL vial. Add 2.925 g of Ml-386 alumina powder to the vial with mixing. Add 0.15 mL of 100 mg Pd/mL Pd(NO3)2 and 0.60 mL of 100 mg Au/mL HAuCL4 to the vial with mixing. The resulting slurry is then mixed periodically for 20 min, dried at 130° C. for 15 hours, and then ground to a fine powder using a mortar and pestle. The powder is then calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 6.00 mL of H2O to a 20 mL vial. Add 2.910 g of MI-386 alumina powder to the vial with mixing. Add 0.30 mL of 100 mg Pd/mL Pd(NO3)2 and 0.60 mL of 100 mg Au/mL HAuCL4 to the vial with mixing. The resulting slurry is then mixed periodically for 20 min, dried at 130° C. for 15 hours, and then ground to a fine powder using a mortar and pestle. The powder is then calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 5.80 mL of H2O to a 20 mL vial. Add 2.890 g of MI-386 alumina powder to the vial with mixing. Add 0.50 mL of 100 mg Pd/mL Pd(NO3)2 and 0.60 mL of 100 mg Au/mL HAuCL4 to the vial with mixing. The resulting slurry is then mixed periodically for 20 min, dried at 130° C. for 15 hours, and then ground to a fine powder using a mortar and pestle. The powder is then calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 5.30 mL of H2O to a 20 mL vial. Add 2.840 g of MI-386 alumina powder to the vial with mixing. Add 1.00 mL of 100 mg Pd/mL Pd(NO3)2 and 0.60 mL of 100 mg Au/mL HAuCL4 to the vial with mixing. The resulting slurry is then mixed periodically for 20 min, dried at 130° C. for 15 hours, and then ground to a fine powder using a mortar and pestle. The powder is then calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
The preparation methods for Examples 1-4 were as follows.
Add 20 mL of water to a 100 mL flask. Add 1.65 mL of 5M NaOH to the flask, stirring for 1 minute. Add 0.330 mL of 80% THPC to the flask, stirring for 2 minutes. Bubble formation is observed in this step. Mix 0.25 mL of 100 mg Pd/mL Pd(NO3)2 with 1 mL 100 mg Au/mL HAuCL4. Add the mixture to the flask, stirring for 5 minutes. The mixture is observed to turn into a deep dark color during stirring. The resulting mixture after stirring is the Pd—Au (0.5% Pd, 2% Au) colloid solution and this colloid solution is used in preparing Example 1.
Add 20 mL of water to a 100 mL flask. Add 2 mL of 5M NaOH to the flask, stirring for 1 minute. Add 0.434 mL of 80% THPC to the flask, stirring for 2 minutes. Bubble formation is observed in this step. Mix 0.5 mL of 100 mg Pd/mL Pd(NO3)2 with 1 mL 100 mg Au/mL HAuCL4. Add the mixture to the flask, stirring for 5 minutes. The mixture is observed to turn into a deep dark color during stirring. The resulting mixture after stirring is the Pd—Au (1% Pd, 2% Au) colloid solution and this colloid solution is used in preparing Example 2.
Add 20 mL of water to a 100 mL flask. Add 2.4 mL of 5M NaOH to the flask, stirring for 1 minute. Add 0.573 mL of 80% THPC to the flask, stirring for 2 minutes.
Bubble formation is observed in this step. Mix 0.833 mL of 100 mg Pd/mL Pd(NO3)2 with 1 mL 100 mg Au/mL HAuCl4. Add the mixture to the flask, stirring for 5 minutes. The mixture is observed to turn into a deep dark color during stirring. The resulting mixture after stirring is the Pd—Au (1.67% Pd, 2% Au) colloid solution and this colloid solution is used in preparing Example 3.
Add 20 mL of water to a 100 mL flask. Add 3.85 mL of 5M NaOH to the flask, stirring for 1 minute. Add 0.921 mL of 80% THPC to the flask, stirring for 2 minutes. Bubble formation is observed in this step. Mix 1.667 mL of 100 mg Pd/mL Pd(NO3)2 with 1 mL 100 mg Au/mL HAuCl4. Add the mixture to the flask, stirring for 5 minutes. The mixture is observed to turn into a deep dark color during stirring. The resulting mixture after stirring is the Pd—Au (3.34% Pd, 2% Au) colloid solution and this colloid solution is used in preparing Example 4.
Add 23.2 mL of 0.5% Pd, 2% Au colloid solution to a 100 mL flask while stirring. Add 4.875 g of MI-386 alumina powder to the flask, and then stir the mixture for 18 hours. The mixture is then filtered and dried at 130° C. for 3 hours, and then ground to a fine powder using a mortar and pestle. The powder is calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 23.93 mL of 1% Pd, 2% Au colloid solution to a 100 mL flask while stirring. Add 4.85 g of MI-386 alumina powder to the flask, and then stir the mixture for 18 hours. The mixture is then filtered and dried at 130° C. for 3 hours, and then ground to a fine powder using a mortar and pestle. The powder is calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 24.81 mL of 1.67% Pd, 2% Au colloid solution to a 100 mL flask while stirring. Add 4.817 g of MI-386 alumina powder to the flask, and then stir the mixture for 18 hours. The mixture is then filtered and dried at 130° C. for 3 hours, and then ground to a fine powder using a mortar and pestle. The powder is calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
Add 27.44 mL of 3.34% Pd, 2% Au colloid solution to a 100 mL flask while stirring. Add 4.733 g of MI-386 alumina powder to the flask, and then stir the mixture for 18 hours. The mixture is then filtered and dried at 130° C. for 3 hours, and then ground to a fine powder using a mortar and pestle. The powder is calcined in air at 500° C. for 2 hours using a heating ramp rate of 8° C./min.
While particular embodiments according to the invention have been illustrated and described above, those skilled in the art understand that the invention can take a variety of forms and embodiments within the scope of the appended claims.
This application is a continuation of Ser. No. 12/030,793, filed Feb. 13, 2008; which application is a continuation-in-part of U.S. patent application Ser. No. 11/624,116, filed Jan. 17, 2007, and U.S. patent application Ser. No. 11/624,128, filed Jan. 17, 2007, now U.S. Pat. No. 7,709,414. The entire contents of both applications are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12030793 | Feb 2008 | US |
| Child | 13671414 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11624116 | Jan 2007 | US |
| Child | 12030793 | US | |
| Parent | 11624128 | Jan 2007 | US |
| Child | 11624116 | US |
