US20140274662A1

US20140274662A1 - Systems and Methods for Variations of ZPGM Oxidation Catalysts Compositions

Info

Publication number: US20140274662A1
Application number: US13/911,986
Authority: US
Inventors: Zahra Nazarpoor
Original assignee: Clean Diesel Technologies Inc
Current assignee: Clean Diesel Technologies Inc
Priority date: 2013-03-15
Filing date: 2013-06-06
Publication date: 2014-09-18
Also published as: WO2014145775A1; WO2014145775A8; US20140274663A1; US9511353B2

Abstract

The present disclosure refers to variation of compositions for catalytic converters free of platinum group metals, which may be employed to manufacture ZPGM oxidation catalyst systems, to remove main pollutants from exhaust of diesel engines, by oxidizing toxic gases. Suitable support oxides material may include ZrO₂, ZrO₂doped with lanthanide group metals, Nb₂O₅, Nb₂O₅—ZrO₂, Al₂O₃and Al₂O₃doped with lanthanide group metals, TiO₂and doped TiO₂may be used. Materials suitable for use as ZPGM catalysts include Lanthanum (La), Yttrium (Y), Silver (Ag), Manganese (Mn) and combinations thereof. The disclosed ZPGM DOC systems may include perovskite structures with the characteristic formulation ABO₃or related structures. A plurality of methods may be employed for production of ZPGM diesel oxidation catalyst systems substantially free of PGM, which may include a substrate, a washcoat, and an impregnation layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/791,721, filed Mar. 15, 2013, titled Methods for Oxidation and Three-way ZPGM Catalyst Systems and Apparatus Comprising Same and to U.S. Provisional Application No. 61/791,838, filed Mar. 15, 2013, titled Oxidation Catalyst Systems Compositions and Methods Thereof, and U.S. Provisional Application No. 61/791,963, filed Mar. 15, 2013, titled System and Method for Two Way ZPGM Oxidation Catalyst Systems, and U.S. Provisional Application No. 61/792,071, filed Mar. 15, 2013, titled ZPGM Catalyst Systems and Methods of Making Same, and U.S. Provisional Application No. 61/792,215, filed Mar. 15, 2013, titled ZPGM TWC Systems Compositions and Methods Thereof, the entireties of which are incorporated herein by reference as if set forth herein.

BACKGROUND

1. Field of the Disclosure
The present disclosure relates generally to catalytic systems, and more particularly to variation of compositions for catalytic converters which are free of any platinum group metals.
2. Background
A plurality of catalysts within catalytic converters are generally fabricated using a monolithic honeycomb skeleton made of metallic or ceramic materials, which may be coated with a ceramic substrate impregnated with Pt, Pd, and/or other platinum group metals (PGM) as the active catalysts. With the ever stricter standards for acceptable emissions, the demand on PGM continues to increase due to their efficiency in removing pollutants from exhaust. However, this demand, along with other demands for PGM, places a strain on the supply of PGM, which in turn drives up the cost of PGM and therefore catalysts and catalytic converters.
Accordingly, there is a need for improved cost efficient variation of sample composition, which may be used for manufacture catalyst systems that do not require PGM, and may be capable to work at low conversion temperatures having similar or better efficiency than existing oxidation catalysts, also for controlling air pollution and other environmental application.

SUMMARY

It is an object of the present disclosure to provide variation of compositions for production of Diesel Oxidation Catalyst (DOC), which are free of any platinum group metals, including but not limited to perovskite oxides.
Suitable variation of compositions for ZPGM catalyst, may produce improvements to oxidize carbon monoxide and hydrocarbons included in diesel exhaust gases, achieving similar or better efficiency than existing internal combustion engines oxidation catalysts, which employs PGM materials.
Materials suitable for use as ZPGM catalysts include Lanthanum (La), Yttrium (Y), Silver (Ag), Manganese (Mn) and combinations thereof. The disclosed ZPGM DOC systems may include perovskite structures with the characteristic formulation ABO₃or related structures.
The disclosed variation of compositions for ZPGM catalyst, may be used to prepare washcoat and overcoat material, forming an aqueous slurry, which may be used as coatings to fabricate ZPGM catalysts systems.
Suitable materials for use as substrates may include cordierite, metallic alloys, foams, microporous materials, zeolites or combinations.
Carrier metal oxide materials of use in catalysts containing one or more of the aforementioned combinations may also include ZrO₂, doped ZrO₂with Lanthanide group metals, Nb₂O₅, Nb₂O₅—ZrO₂, alumina and doped alumina, TiO₂and doped TiO₂.
A co-precipitation method may be employed for coating La—Mn or Y—Mn perovskite on suitable support oxide materials which may form part of the washcoat slurry and overcoat slurry. Washcoat or overcoat materials and ZPGM catalysts may be deposited on a substrate in a single step.
Additional element such as Ag for partial substitution of perovskite structure may be employed part of washcoat or overcoat via co-precipitation method. Additional element may also employed as impregnation component.
A variation of composition, carrier metal oxide and preparation method significantly influence the oxidation property of ZPGM catalyst.
These and other advantages of the present disclosure may be evident to those skilled in the art, or may become evident upon reading the detailed description of related embodiments, as shown in accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. In the figures, reference numerals designate corresponding parts throughout the different views.

FIG. 1 shows ZPGM catalyst system structures, according to an embodiment.

FIG. 2 shows light-off test results of a ZPGM catalyst system under exhaust lean condition, according to one embodiment.

FIG. 3 shows HC light-off test results of a ZPGM catalyst system under exhaust lean condition, according to one embodiment.

FIG. 4 shows HC light-off test results of a ZPGM catalyst system under exhaust rich condition, according to one embodiment.

DETAILED DESCRIPTION

The present disclosure is here described in detail with reference to embodiments illustrated in the drawings, which form a part here. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the present disclosure. The illustrative embodiments described in the detailed description are not meant to be limiting of the subject matter presented here.

DEFINITIONS

As used herein, the following terms may have the following definitions:
“Catalyst system” refers to a system of at least three layers, which may include at least one substrate, a washcoat, and an optional overcoat.
“Diesel oxidation catalyst” refers to a device which utilizes a chemical process in order to break down pollutants from a diesel engine in the exhaust stream, turning them into less harmful components.
“Substrate” refers to any suitable material for supporting a catalyst and can be of any shape or configuration, which yields sufficient surface area for deposition of washcoat.
“Co-precipitation” may refer to the carrying down by a precipitate of substances normally soluble under the conditions employed.
“Washcoat” refers to at least one coating including at least one oxide solid which may be deposited on a substrate.
“Overcoat” refers to at least one coating including one or more oxide solid which may be deposited on at least one washcoat.
“Perovskite” refers to a ZPGM catalyst, having ABO₃structure of material which may be formed by partially substituting element “A” and “B” base metals with suitable non-platinum group metals.
“Carrier material oxide” refers to materials used for providing a surface for at least one catalyst.
“Oxygen storage material” refers to materials that can take up oxygen from oxygen-rich feed streams and release oxygen to oxygen-deficient feed streams.
“ZPGM Transition Metal Catalyst” refers to at least one catalyst which may include at least one transition metal completely free of platinum group metals.
“Platinum group metals” refers to platinum, palladium, ruthenium, iridium, osmium, and rhodium, unless otherwise stated.
“Exhaust” refers to discharge of gases, vapor, and fumes created by and released at the end of a process, including hydrocarbons, nitrogen oxide, and carbon monoxide.
“Conversion” refers to the change from harmful compounds (such as hydrocarbons, carbon monoxide, and nitrogen oxide) into less harmful and/or harmless compounds (such as water, carbon dioxide, and nitrogen).
“T50” refers to the temperature at which 50% of a material is converted.
“R Value” refers to the number obtained by dividing the reducing potential by the oxidizing potential.
“Rich Exhaust” refers to exhaust with an R value above 1.
“Lean Exhaust” refers to exhaust with an R value below 1.

DESCRIPTION OF DRAWINGS

In the following detailed description, reference is made to the accompanying illustrations, which form a part hereof. On these illustrations, which are not to scale or to proportion, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative examples described in the detailed description, are not meant to be limiting. Other examples may be used and other changes may be made without departing from the spirit or scope of the present disclosure.
General Description of Variations of Compositions for ZPGM Oxidation Catalyst Systems
The present disclosure may employ methods for producing suitable variations of composition for diesel oxidation catalyst system. The ability of such materials to effectively treat internal combustion exhaust gases depends on the capability for oxidation of nitrogen oxide, carbon monoxide oxidation, and unsaturated and saturated hydrocarbon.
According to one embodiment, variation of composition for ZPGM catalyst, may be formed by using a suitable composition, such as perovskite, having the general formula ABO₃where components “A” and “B” may be any suitable non-platinum group metals. Materials suitable for use as catalyst, which may include, Lanthanum (La), Yttrium (Y), Silver (Ag), Manganese (Mn) and suitable combinations thereof.
Variation of compositions for ZPGM catalyst may also be formed by partially substituting element “A” of the structure with suitable non-platinum group metal in order to form a structure having the general formula A_1-xM_xBO₃, providing an improved, cost effective ZPGM diesel oxidation catalyst system for internal combustion engines, which may provide an alternative to PGM materials, based in low cost, thermal stability at high temperatures, and excellent oxidation properties.
System Configuration and Composition
FIG. 1 depicts ZPGM catalyst system 100 configurations, according to various embodiments. As shown in FIG. 1, ZPGM catalyst converters may include: a substrate 102, a washcoat 104, and an impregnation layer 106. Washcoat 104 may include at least support oxides material and may include ZPGM catalysts. Impregnation layers 106 may include the active oxidation ZPGM catalysts components.
According to an embodiment, ZPGM catalyst system 100 may include a perovskite structure having the general formula ABO₃or related structures resulting from the partial substitution of the A site. Partial substitution of the A site with M element will yield the general formula A_1-xM_xBO₃. “A” may include lanthanum, strontium, or mixtures thereof. “B” may include a single transition metal, including manganese, cobalt, chromium, or a mixture thereof. M may include silver, iron, cerium, niobium or mixtures thereof; and “x” may take values between 0 and 1. The perovskite or related structure may be present in about 1% to about 30% by weight.
Co-Precipitation Method for Preparation
In one embodiment, method for preparation may be a one-step process, wherein a ZPGM catalyst of ABO₃perovskite is precipitated on carrier metal oxide as washcoat 104. In this process, components of washcoat 104 including carrier metal oxide (CMO) and water may first undergo a milling process to form washcoat slurry. Milling process may take from about 10 minutes to about 10 hours, depending on the batch size, kind of material and particle size desired. Carrier metal oxide materials of use in catalysts containing one or more of the aforementioned combinations may also include ZrO₂, doped ZrO₂with Lanthanide group metals, Nb₂O₅, Nb₂O₅—ZrO₂, alumina and doped alumina, TiO₂and doped TiO₂. The co-precipitation process may start with first mixing nitrate solution of lanthanum or yttrium and manganese for a suitable amount of time at room temperature which may last from 1 hour to 5 hours. Afterwards, a silver nitrate solution may be added to the mixture of lanthanum (or yttrium) and manganese nitrate; then the solution may be mixed at room temperature for about 1 hour to 5 hours. When the mixture is ready, it may undergo metallization process by adding the ZPGM nitrate solution to washcoat slurry. Metallization process may last from 1 hour to 5 hours, followed by co-precipitation in presence of suitable compounds. Suitable compounds for co-precipitation of metal salts may include tetraethylammonium hydroxide, other tetraalkylammonium salts, ammonium acetate, ammonium citrate, sodium hydroxide, sodium carbonate and other suitable compounds known in the art.
After co-precipitation process, the aqueous slurry may be coated onto a suitable substrate 102 as washcoat 104, followed by a drying step, in which the washcoated substrate 102 may be dried at room temperature. Afterwards, the washcoated substrate 102 may undergo a firing stage, in which the washcoated substrate 102 may be fired at a temperature ranging from 600° C. to 800° C., for approximately 2 hours to 6 hours. In one embodiment, 750° C. for 4 hours. The resulting ZPGM catalyst system 100 has a perovskite structure A_1-xAg_xMnO₃, where A is Y or La.
Combination of Co-Precipitation and Impregnation Method for Preparation
In one embodiment, method for preparation may be a two-step process, wherein a part of ZPGM catalyst of ABO₃perovskite is precipitated on carrier metal oxide as washcoat 104 and other part of ZPGM catalyst may applied as impregnation component. In this process, components of washcoat 104 including carrier metal oxide (CMO) and water may first undergo a milling process to form washcoat slurry. Milling process may take from about 10 minutes to about 10 hours, depending on the batch size, kind of material and particle size desired. Carrier metal oxide materials of use in catalysts containing one or more of the aforementioned combinations may also include ZrO₂, doped ZrO₂with Lanthanide group metals, Nb₂O₅, Nb₂O₅—ZrO₂, alumina and doped alumina, TiO₂and doped TiO₂. The co-precipitation process may start with first mixing nitrate solution of lanthanum or yttrium and manganese for a suitable amount of time at room temperature which may last from 1 hour to 5 hours. When the mixture is ready, it may undergo metallization process by adding the ZPGM nitrate solution to washcoat slurry. Metallization process may last from 1 hour to 5 hours, followed by co-precipitation in presence of suitable compounds. Suitable compounds for co-precipitation of metal salts may include tetraethylammonium hydroxide, other tetraalkylammonium salts, ammonium acetate, ammonium citrate, sodium hydroxide, sodium carbonate and other suitable compounds known in the art. After co-precipitation process, the aqueous slurry may be coated onto a suitable substrate 102 as washcoat 104, followed by a drying step, in which the washcoated substrate 102 may be dried at room temperature. Afterwards, the washcoated substrate 102 may undergo a firing stage, in which the washcoated substrate 102 may be fired at a temperature ranging from 600° C. to 800° C., for approximately 2 hours to 6 hours. In one embodiment, 750° C. for 4 hours. The resulting ZPGM catalyst system 100 has a perovskite structure AMnO₃, where A is Y or La.
The preparation process may follow by impregnation method. The process may start with mixing step, where a silver nitrate solution may be added to water and the solution may be mixed for a suitable amount of time at room temperature which may last from 1 hour to 2 hours. When the Ag aqueous solution is ready, it may undergo impregnation process, where the mixture may be impregnated onto a previously washcoated substrate 102 with a perovskite structure AMnO₃, where A is Y or La. Subsequently, impregnated substrate 102 may be subjected to a drying process and a firing process. Firing process may last between 3 hours and 6 hours, and may be performed and a temperature between 600° C. and 800° C., preferably 750° C.
Example 1 is a ZPGM catalyst system 100, prepared by co-precipitation method and include substrate 102 and washcoat 104. Washcoat 104 includes at least a carrier material oxide, such as zirconia and ZPGM catalyst with perovskite structure. This catalyst system is free of any oxygen storage material. The milled zriconia slurry is mixed with aqueous solution of at least yttrium nitrate, silver nitrate and manganese nitrate, followed by precipitation by tetraethylammonium hydroxide. The pH of slurry adjusted to approximately neutral condition. The yttrium in washcoat 104 is present in about 10% to about 40%, by weight. The silver in washcoat 104 is present in about 1% to about 10%, by weight. The manganese in washcoat 104 is present in about 10% to about 30%, by weight. The washcoat 104 is deposited on the cordierite substrate 102 and then fired at about 750° C. which last about 4 hours. The resulting ZPGM catalyst system 100 has a perovskite structure Y_0.8Ag_0.2MnO₃.
Example 2 is a ZPGM catalyst system 100, prepared by co-precipitation method and include substrate 102 and washcoat 104. Washcoat 104 includes at least a carrier material oxide, such as alumina and ZPGM catalyst with perovskite structure. This catalyst system is free of any oxygen storage material. The milled alumina slurry is mixed with aqueous solution of at least lanthanum nitrate, silver nitrate and manganese nitrate, followed by precipitation by tetraethylammonium hydroxide. The pH of slurry adjusted to approximately neutral condition. The lanthanum in washcoat 104 is present in about 10% to about 40%, by weight. The silver in washcoat 104 is present in about 1% to about 10%, by weight. The manganese in washcoat 104 is present in about 10% to about 30%, by weight. The washcoat 104 is deposited on the cordierite substrate 102 and then fired at about 750° C. which last about 4 hours. The resulting ZPGM catalyst system 100 has a perovskite structure La_0.8Ag_0.2MnO₃.
Example #3 is a ZPGM catalyst system 100, prepared by combination of co-precipitation and impregnation method and include substrate 102 and washcoat 104 and impregnation layer 106. Washcoat 104 includes at least a carrier material oxide, such as zirconia and ZPGM catalyst with perovskite structure. This catalyst system is free of any oxygen storage material. The milled zirconia slurry is mixed with aqueous solution of at least yttrium nitrate and manganese nitrate, followed by precipitation by tetraethylammonium hydroxide. The pH of slurry adjusted to approximately neutral condition. The yttrium in washcoat 104 is present in about 10% to about 40%, by weight. The manganese in washcoat 104 is present in about 10% to about 30%, by weight. The washcoat 104 is deposited on the cordierite substrate 102 and then fired at about 750° C. which last about 4 hours. Afterward, silver may impregnated on washcoated substrate 102, following by firing at about 750° C. which last about 4 hours. The silver in impregnation layer 106 is present in about 1% to about 10%, by weight. The resulting ZPGM catalyst system 100 has a perovskite structure YMnO₃doped with Ag.
Example #4 is a ZPGM catalyst system 100, prepared by combination of co-precipitation and impregnation method and include substrate 102 and washcoat 104 and impregnation layer 106. Washcoat 104 includes at least a carrier material oxide, such as alumina and ZPGM catalyst with perovskite structure. This catalyst system is free of any oxygen storage material. The milled alumina slurry is mixed with aqueous solution of at least yttrium nitrate and manganese nitrate, followed by precipitation by tetraethylammonium hydroxide. The pH of slurry adjusted to approximately neutral condition. The yttrium in washcoat 104 is present in about 10% to about 40%, by weight. The manganese in washcoat 104 is present in about 10% to about 30%, by weight. The washcoat 104 is deposited on the cordierite substrate 102 and then fired at about 750° C. which last about 4 hours. Afterward, silver may impregnated on washcoated substrate 102, following by firing at about 750° C. which last about 4 hours. The silver in impregnation layer 106 is present in about 1% to about 10%, by weight. The resulting ZPGM catalyst system 100 has a perovskite structure YMnO₃doped with Ag.
FIG. 2 shows the light-off test results 200 for the ZPGM catalyst system 100 of example #1. The light-off test is performed under exhaust lean condition and the hydrocarbon in feed stream is propylene. The test is performed by increasing the temperature from about 100° C. to 600° C. at a constant rate of 20° C./min. The light-off test results 200 show this catalyst is very active for NO conversion, as well as for CO and THC conversion under lean light off condition.
The T50 for CO may be at about 230° C. and T50 for HC may be at about 250° C. The NO conversion under lean condition may result as oxidation of NO to NO₂. Neither NH₃nor N₂O formed during reaction. The NO oxidation reach to about 43% conversion at temperature of 396° C.
FIG. 3 shows the HC light-off test results 300 for the ZPGM catalyst system 100 of example #1, example#2, example#3 and example#4 for a fresh sample. The lean light-off test is performed under exhaust lean condition and the hydrocarbon in feed stream is propylene. The test is performed by increasing the temperature from about 100° C. to 600° C. at a constant rate of 20° C./min. The HC light-off test results 300 comparison of example#1 and example#3 shows that the catalyst prepared by one step co-precipitation are more active oxidation catalyst compare to samples prepared by combination of co-precipitation and impregnation. The HC T50 for catalyst of example#1 and example#3 is about 250° C. and 443° C. respectively. Comparison of catalysts of example#1 and example#2 shows the effect of composition variation on oxidation activity. The catalyst of example#1 with Y—Ag—Mn—ZrO₂composition shows better HC conversion than catalyst of example#2 with La—Ag—Mn—Al₂O₃composition at the same lean condition. The HC T50 of example#2 is about 432° C. Comparison of example#3 and example#4 light off curves shows the improvement of oxidation property by using ZrO₂instead of Al₂O₃carrier metal oxide.
FIG. 4 shows the HC light-off test results 400 for the ZPGM catalyst system 100 of example #1, example#2, example#3 and example#4 for fresh sample. The light-off test is performed under exhaust rich condition. The hydrocarbon in feed stream is propylene. The test is performed by increasing the temperature from about 100° C. to 600° C. at a constant rate of 20° C./min. The HC light-off test results 400 compare the combination effect of variation of composition, variation of carrier metal oxide and variation of preparation method. The HC T50 for fresh catalyst of example#1 is 312° C. The HC T50 for fresh catalyst of example#4 is 351° C. However, the HC T50 for fresh catalyst of example#2 is 480° C. and the HC T50 for fresh catalyst of example#3 is 500° C.
While various aspects of production methods may be described in the present disclosure, other aspects and embodiments may be contemplated. The various aspects and embodiments disclosed here are for purpose of illustration, and are not intended to be limiting with the scope and spirit being indicated by the following claims.

Claims

What is claimed is:

1. A method for forming a zero platinum group metal (ZPGM) catalyst, comprising:

providing at least one substrate, wherein the at least one substrate is selected from the group consisting of cordierite, zeolite, and combinations thereof;

depositing by co-precipitation a washcoat suitable for deposition on the substrate, the washcoat comprising at least one oxide solid further comprising at least one carrier metal oxide and at least one first ZPGM catalyst; and

depositing by co-precipitation an overcoat suitable for deposition on the substrate, the overcoat comprising at least one second ZPGM catalyst;

wherein at least one of the first ZPGM catalyst and second ZPGM catalyst comprises at least one perovskite structured compound having the formula ABO₃, wherein A and B are selected from the group consisting of at least one of lanthanum, yttrium, silver, manganese, and combinations thereof; and

wherein the at least one carrier metal oxide comprises ZrO₂.

2. The method of claim 1, wherein the at least one carrier metal oxide further comprises at least one selected from the group consisting of TiO₂, doped TiO₂, alumina, doped alumina, doped ZrO₂, Nb₂O₅—ZrO₂, and combinations thereof.

3. The method of claim 1, wherein the substrate comprises at least one selected from the group consisting of metallic alloy, microporous material, and combinations thereof.

4. The method of claim 1, wherein the at least one perovskite structured compound is of the general formula A_1-xAg_xMnO₃, wherein x is from 0 to 0.5 and where A is yttrium or lanthanum.

5. The method of claim 1, further comprising depositing by co-precipitation an impregnation layer suitable for deposition on the substrate, the impregnation layer comprising at least one third ZPGM catalyst.

6. The method of claim 5, wherein silver is present in the impregnantion layer by about 1% to about 10% by weight.

7. The method of claim 1, wherein the at least one perovskite structured compound has the formula AgBO₃, wherein B is selected from the group consisting of at least one of lanthanum, yttrium, silver, manganese, and combinations thereof.

8. The method of claim 1, wherein the at least one substrate at least one metallic alloy, a foam, a microporous materials.

9. The method of claim 1, wherein a T50 conversion temperature for carbon monoxide is less than about 230 degrees Celsius.

10. The method of claim 1, wherein a T50 conversion temperature for hydrocarbons is less than about 250 degrees Celsius.

11. The method of claim 1, wherein the washcoat is fired at about 750° C. for about 4 hours.

12. The method of claim 1, wherein manganese is present in the washcoat by about 10% to about 30% by weight.

13. The method of claim 1, wherein yttrium is present in the washcoat by about 10% to about 40% by weight.

14. The method of claim 1, wherein oxidation of NO is about 43%.

15. The method of claim 1, wherein the oxidation of NO is at about 396° C.

16. The method of claim 1, where the overcoat is a slurry and is deposited in a single step.

17. The method of claim 1, where the washcoat is a slurry and is deposited in a single step.

18. The method of claim 1, wherein the NO conversion rate corresponds to the carrier material oxide.