Base metal activated rhodium coatings for catalysts in three-way catalyst (TWC) applications

Abstract

Close-coupled catalysts (CCC) for TWC applications are disclosed. The novel CCCs are implemented using light-weighted ceramic substrates in which a thin coating employing a low loading of Iron (Fe)-activated Rhodium (Rh) material composition, with Iron loadings and an OSM of Ceria-Zirconia, are deposited onto the substrates. Different CCC samples are produced to determine and/or verify improved light-off (LO) and NO.sub.X conversion of the CCCs. Other CCC samples produced are a CCC including a standard (non-activated) Rh thin coating and a heavily loaded CCC with a single coating of Pd/Rh material composition. The CCC samples are aged under dyno-aging using the multi-mode aging cycle and their performance tested using a car engine with ports on the exhaust to measure the emissions, according to the testing protocol in the Environmental Protection Agency Federal Test Procedure 75. During testing, the thin coatings of Fe-activated Rh exhibit improved light-off and NO.sub.x conversion efficiency.

Claims

1. A catalytic system comprising: a ceramic substrate coated with Fe-activated Rh at a loading of about 90 g/L.

2. The catalytic system of claim 1, wherein the Fe-activated Rh is supported on a OSM comprising one selected from the group consisting of Cc, Zr, Nd, Pr, Y, and combinations thereof.

3. The catalytic system of claim 1, wherein the Fe is present at about 7% (w/w).

4. The catalytic system of claim 1, wherein the Rh is present at less than about 0.5% (w/w).

5. A catalytic system comprising: a ceramic substrate coated with Fe-activated Rh; wherein the Rh loadings are from about 1 g/ft.sup.3 to about 20 g/ft.sup.3 and the Fe loadings are from about 1 g/ft.sup.3 to about 20 g/ft.sup.3; and wherein the Fe-activated Rh is supported on a OSM.

6. The catalytic system of claim 5, wherein the Rh loadings are about 3 g/ft.sup.3.

7. The catalytic system of claim 5, wherein the Fe loadings are less than about 7 g/ft.sup.3.

8. The catalytic system of claim 5, wherein the Fe is present at about 7% (w/w).

9. The catalytic system of claim 5, wherein the Rh is present at less than about 0.5% (w/w).

10. The catalytic system of claim 5, wherein the OSM comprising one selected from the group consisting of Ce, Zr, Nd, Pr, Y, and combinations thereof.

11. The catalytic system of claim 5, wherein the OSM comprising a CeZr oxide.

12. The catalytic system of claim 5, wherein the OSM comprising a CeZr oxide having a fluorite phase.

13. The catalytic system of claim 5, wherein the Fe-activated Rh is applied at a loading of less than about 10 g/ft.sup.3.

14. The catalytic system of claim 5, wherein the Fe-activated Rh is applied at a loading of greater than about 3 g/ft.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 is a graphical representation illustrating comparison of isothermal light-off (LO) test results for NO.sub.X conversion associated with a catalyst sample including a light-weight substrate employing a single coating of 3 g/ft.sup.3 of Iron (Fe)-activated Rhodium (Rh) loading and a catalyst sample including a single coating of 9.8 g/ft.sup.3 of standard Rh loading, according to an embodiment.

(3) FIG. 2 is a graphical representation illustrating the cumulative NO.sub.X measurements obtained during the implementation of the Federal Test Procedure (FTP)-75 protocol to test catalyst samples including Fe-activated Rh and standard Rh loadings of about 9.8 g/ft.sup.3 and 9.8 g/ft.sup.3, respectively, according to an embodiment.

(4) FIG. 3 is a graphical representation illustrating the cumulative NO.sub.X measurements obtained during the implementation of the FTP-75 protocol to test catalyst samples including Fe-activated Rh and standard Rh loadings of about 9.8 g/ft.sup.3 and 9.8 g/ft.sup.3, respectively, as well as a standard catalyst sample including a multi-layer coating of Palladium (Pd)/Rh with a total loading of about 300 g/L, according to an embodiment.

DETAILED DESCRIPTION

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

(6) Definitions

(7) As used here, the following terms have the following definitions:

(8) Air to fuel ratio, or A/F ratio, or AFR refers to the mass ratio of air to fuel present in a combustion process.

(9) Catalyst refers to one or more materials that may be of use in the conversion of one or more other materials.

(10) Catalytic converter refers to a vehicle emissions control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (oxidation or reduction).

(11) Catalyst system refers to any system including a catalyst, such as, a PGM catalyst or a ZPGM catalyst of at least two layers comprising a substrate, a washcoat and/or an overcoat.

(12) Close-coupled catalyst refers to a catalyst located in close proximity to the exhaust manifold of the engine and reduces cold-engine emissions.

(13) Conversion refers to the chemical alteration of at least one material into one or more other materials.

(14) Conversion efficiency refers to the percentage of emissions passing through the catalyst that are converted to their target compounds.

(15) Federal Test Procedure 75 or FTP-75 refers to a city driving cycle during which a series of tests defined by the US Environmental Protection Agency (EPA) are conducted to measure tailpipe emissions and fuel economy of passenger cars.

(16) Lean condition refers to an exhaust gas condition with an R-value less than 1 and having excess oxidants.

(17) Light off refers to the time elapsed from an engine cold start to the point of 50 percent pollutant conversion.

(18) Oxygen storage material (OSM) refers to a material that absorbs oxygen from oxygen rich gas flows and further able to release oxygen into oxygen deficient gas flows.

(19) Platinum group metals (PGM) refers to platinum, palladium, ruthenium, iridium, osmium, and rhodium.

(20) R-value refers to the value obtained by dividing the total reducing potential of the gas mixture (in moles of Oxygen) by the total oxidizing potential of the gas mixture (in moles of Oxygen).

(21) Rich condition refers to an exhaust gas condition with an R-value greater than 1 and having excess reductants.

(22) Stoichiometric condition refers to an exhaust gas condition with an R-value equal to 1.

(23) Substrate refers to any material of any shape or configuration that yields a sufficient surface for depositing a washcoat layer and/or an overcoat layer.

(24) Support oxide refers to porous solid oxides, typically mixed metal oxides, which are used to provide a high surface area which aids in oxygen distribution and exposure of catalysts to reactants such as NO.sub.x, CO, and hydrocarbons.

(25) Three-Way Catalyst (TWC) refers to a catalyst able to perform the three simultaneous tasks of reduction of nitrogen oxides to nitrogen and oxygen, oxidation of carbon monoxide to carbon dioxide, and oxidation of unburnt hydrocarbons to carbon dioxide and water.

(26) Description of the Disclosure

(27) The present disclosure is directed to three-way catalyst (TWC) material compositions including light-weighted ceramic substrates in which a single, thin layer coating of Fe-activated Rhodium (Rh) is applied to the substrates to enable performance synergies with lower loadings of platinum group metals (PGM) material compositions within conventional TWC systems. Further, the present disclosure describes improved light-off catalytic behavior and steady-state conversion efficiency for cumulative emissions, specifically nitrogen oxide (NO.sub.X), for close-coupled catalysts (CCCs) including Fe-activated Rh. The improved light-off catalytic behavior and steady-state conversion efficiency for cumulative emissions are measured in comparison with the light-off catalytic behavior of conventional CCCs including coatings of PGM employing heavy loadings of material compositions that are applied onto ceramic substrates.

(28) As used herein, and as an illustrative example, loading of a washcoat is the mass of washcoat deposited on a substrate divided by a catalyst system volume. Loading of an overcoat or a component of the washcoat or the overcoat has a corresponding meaning about the weight of that layer or component divided by the volume of the catalyst system. As shown in Example 3.1 of R. E. Hayes and Stan T. Kolaczkowski, Introduction to Catalytic Combustion, 310-313(1997), a washcoat loading divided by the fraction of the volume of a reactor that is taken up by the washcoat is equal to the density of the washcoat, confirming the usage. In more detail, the washcoat area divided by the total area of a reactor produces a fraction equivalent to the volume of the washcoat divided by the volume of the reactor (in the example, 0.112). Dividing the loading of the washcoat (in the example, 170 g/L), by the aforementioned fraction, equals the weight of the washcoat divided by the volume of the washcoat, or the washcoat density. Consequently, the washcoat loading, (in the example, 170 g/L), equals the mass of the washcoat divided by the volume of the reactor. Accordingly, washcoat loading is the mass of washcoat deposited on the substrate divided by the catalyst system volume. As recognized by persons of ordinary skill in the art, expressing loading as a concentration refers to the mass of the loaded component or layer divided by the volume of a catalyst system.

(29) Production of Close-Coupled Catalyst Samples

(30) The present disclosure includes TWC systems employing CCC samples to determine the effect of using Fe-activated Rh coatings deposited onto light-weight ceramic substrates

(31) In some embodiments, a CCC sample, herein referred to as CCC Type 1A catalyst sample, including a Fe-activated Rh coating that is deposited onto a light-weight substrate is produced. In these embodiments, the substrate employed has dimensions of about 4.66 diameter, 3.58 length, 600 cells per square inch (CPSI), and 2.75 mil wall thickness. The deposition layer includes suitable loadings of Fe-activated Rh and suitable loadings of Iron (Fe), and a suitable oxygen storage material (OSM) composition, such as, for example Ceria (Ce), Zirconia (Zr), Neodymia (Nd), Praseodymia (Pr), Yttria (Y) mixed oxide, amongst others. Further to these embodiments, the deposition layer includes Fe-activated Rh loadings with a combined weight-percentage ranging from about 1 wt % to about 20 wt % of Fe. Still further to these embodiments, the catalyst sample of CCC Type 1A includes an Fe-activated Rh loading of about 3 g/ft.sup.3 Rh, an Fe loading of about 7.37 wt %, and the OSM for the remaining amount. In these embodiments, the OSM includes a Ceria-Zirconia mixed oxide with fluorite phases. Further to these embodiments, other OSMs are used including Ceria, or other Ceria-containing materials that may include additional oxides. In these embodiments, a total loading of about 90 g/L (approximately, 2548 g/ft.sup.3) is achieved with Fe-activated Rh loading of about 3 g/ft.sup.3, Fe loading of about 215 g/ft.sup.3, and OSM for the remaining amount.

(32) In other embodiments, a CCC sample, herein referred to as CCC Type 1C catalyst sample, including a Fe-activated Rh coating that is deposited onto a light-weight substrate is produced. In these embodiments, the substrate has similar dimension as the substrate used for CCC Type 1A, and the deposition layer includes suitable loadings of Fe-activated Rh and suitable loadings of Iron (Fe), and a suitable oxygen storage material (OSM) composition, such as, for example Ceria (Ce)-Zirconia (Zr)-Neodymia (Nd)-Praseodymia (Pr)-Yttria (Y) mixed oxide, amongst others. Further to these embodiments, the deposition layer includes Fe-activated Rh loadings with a combined weight-percentage ranging from about 1 wt % to about 20 wt % of Fe. Still further to these embodiments, the catalyst sample of CCC Type 1C includes a Fe-activated Rh loading of about 0.38 wt %, an Fe loading of about 7.37 wt %, and the OSM for the remaining amount. In these embodiments, the OSM includes a Ceria-Zirconia mixed oxide with fluorite phases. Further to these embodiments, other OSMs are used including Ceria, or other Ceria-containing materials that may include additional oxides. In these embodiments, a total loading of about 90 g/L (approximately, 2548 g/3) is achieved with Fe-activated Rh loading of about 9.8 g/ft.sup.3, Fe loading of about 215 g/ft3, and OSM for the remaining amount.

(33) In some embodiments, a CCC samples herein referred as CCC Type 1B catalyst sample, is produced. In these embodiments, the substrate has similar dimension as the substrate used for CCC Type 1A, and the CCC Type 1B catalyst sample includes a standard Rh coating deposited onto a suitable light-weight ceramic substrate. Further to these embodiments, a standard Rh loading of about 9.8 g/ft.sup.3 is employed to produce the Type 1B catalyst samples with a total loading of about 90 g/L. In these embodiments, the CCC Type 1B catalyst sample includes substantially similar OSM as CCC Type 1A and CCC Type 1C catalyst samples.

(34) In other embodiments, a sample of a conventional CCC, herein referred as a CCC Type 2 catalyst sample, is produced. In these embodiments, the CCC Type 2 catalyst sample includes a ceramic substrate on which a coating of platinum group metals (PGM) loadings is deposited. Further to these embodiments, a multi-layer coating of Palladium (Pd)/Rh, with a total loading of about 300 g/L (approximately, 8495 g/ft.sup.3), is deposited onto the ceramic substrate. In these embodiments, the s coating of Pd/Rh includes loading of about 50 g/ft.sup.3 Pd and about 9.8 g/ft.sup.3 Rh. Further to these embodiments, CCC Type 2 catalyst samples include OSM and Alumina for the remaining amount.

(35) Aging of Close-Coupled Catalyst Samples

(36) In some embodiments, as described in FIG. 1, the CCC Type 1A catalyst samples produced are aged at approximately 1000 C. for about 20 hours employing dyno-aging methodology and using the multi-mode aging cycle on an engine. In these embodiments and during the aging cycle, temperatures are monitored.

(37) In other embodiments, as described in FIGS. 2 to 3, CCC Type 1B, CCC Type 1C and CCC Type 2 catalyst samples produced are aged at approximately 950 C. for about 50 hours employing dyno-aging methodology and using the multi-mode aging cycle on an engine. In these embodiments and during the aging cycle, temperatures are monitored.

(38) Test Methodology

(39) In some embodiments, testing of the CCC samples is conducted using a car engine that includes ports added to the exhaust of the car engine to measure engine emissions according to the testing protocol requirements within the Environmental Protection Agency Federal Test Procedure75 (FTP-75), using a vehicle speed profile established for the dyno drive cycle. In these embodiments, a single roll chassis dynamometer is employed to conduct the FTP-75 tests. Further to these embodiments, the engine emissions that are continuously measured during the FTP-75 tests are compared to determine/verify improved performance levels of CCC Type 1C, CCC Type 1B, and conventional CCC Type 2 catalyst samples. In these embodiments, the effect of the single, thin coating of Fe-activated Rh is analyzed/determined by comparing the cumulative grams of NO.sub.X conversion that is measured downstream at the tail pipe for CCC Type 1C, CCC Type 1B, and conventional CCC Type 2 catalyst samples.

(40) Performance of Fe-Activated Rh Thin Coatings

(41) FIG. 1 is a graphical representation illustrating comparison of isothermal light-off (LO) test results for NO.sub.X conversion associated with a catalyst sample including a light-weight substrate employing a single, thin coating of 3 g/ft.sup.3 of Fe-activated Rh (CCC Type 1A) and a catalyst sample including a single coating of 9.8 g/ft.sup.3 of standard Rh loading (CCC Type 1B), according to an embodiment. In FIG. 1, the isothermal LO tests were performed at a temperature of 350 C. and space velocities within a range from about 20,000 hr-.sup.1 to about 180,000 hr-.sup.1. In FIG. 1, conversion performance 100 includes conversion curve 102 and conversion curve 104.

(42) In some embodiments, conversion curve 102 illustrates NO.sub.X conversion associated with a CCC Type 1A catalyst sample. In these embodiments, conversion curve 104 illustrates NO.sub.X conversion associated with a CCC Type 1B catalyst sample. Further to these embodiments, the catalytic activity of the CCC Type 1A and CCC Type 1B catalyst samples in FIG. 1 vary over the range of space velocities employed during the testing. In these embodiments, the CCC Type 1A catalyst sample exhibits a greater NO.sub.X conversion performance than the CCC type 1B catalyst sample. Further to these embodiments, the CCC Type 1A catalyst sample exhibits a stable catalytic behavior of about 100% NO.sub.X conversion within a range of space velocities from about 20,000 hr.sup.1 to about 100,000 hr.sup.1, while the CCC Type 1B catalyst sample exhibits a continuous decrease in NO.sub.X conversion (from about 90% to about 75% NO.sub.X conversion) within the same range of space velocities.

(43) In these embodiments, for increasing space velocities within a range from about 100,000 hr.sup.1 to about 180,000 hr.sup.1, the CCC Type 1A catalyst sample maintains a significantly high NO.sub.X conversion percentage rate within a slightly decreasing range from about 99% to 95%. Further to these embodiments, for increasing space velocities within a range from about 100,000 hr.sup.1 to about 180,000 hr.sup.1, the CCC Type 1B catalyst sample continues to exhibit a decreasing NO.sub.X conversion percentage rate within a range from about 75% to about 67%. In FIG. 1, a thin coating including an Fe-activated Rh loading of about 3 g/ft.sup.3 combined with Fe loadings, as previously described for a CCC Type 1A catalyst sample, exhibits a greater performance in NO.sub.X percentage conversion rate than a thin coating with a loading of 9.8 g/ft.sup.3 of standard Rh only, a CCC Type 1B catalyst sample.

(44) FIG. 2 is a graphical representation illustrating the accumulation of total NO.sub.X emissions obtained during the first 100 seconds of implementation of the Federal Test Procedure (FTP)-75 test protocol to test catalyst samples including Fe-activated Rh (CCC Type 1C) and standard Rh (CCC Type 1B) loadings of about 9.8 g/ft.sup.3 and 9.8 g/ft.sup.3, respectively, according to an embodiment. In FIG. 2, FTP-75 test results 200 include accumulation curve 202, accumulation curve 204, and vehicle speed curve 206.

(45) In some embodiments, accumulation curve 202 illustrates total NO.sub.X accumulation associated with CCC Type 1C catalyst samples. In these embodiments, accumulation curve 204 illustrates total NO.sub.x accumulation associated with CCC Type 1B catalyst samples. Further to these embodiments, vehicle speed curve 206 illustrates the vehicle speed profile used during the implementation of the FTP-75 test protocol for testing the aforementioned CCC samples.

(46) In some embodiments, the results measured during the FTP-75 test protocol are compared and verify that thin coatings including low loadings of Fe-activated Rh provide improved NO.sub.x conversion performance levels versus standard Rh applications. In these embodiments, the effects of the thin coatings including low loadings of Fe-activated Rh on NO.sub.X accumulation are analyzed during all cycles of the FTP-75 test protocol to verify improvements in NO.sub.x conversion efficiency. Further to these embodiments, the effects of the thin coatings including low loadings of Fe-activated Rh on NO.sub.X conversion are verified by comparing the accumulated grams of NO.sub.X for CCC Type 1C catalyst samples with the accumulated grams of NO.sub.X for CCC Type 1B catalyst samples, measured downstream at the tail pipe.

(47) In these embodiments, it is observed in FIG. 2 that the accumulation of NO.sub.X emissions after the gas stream exits both CCCs are substantially similar, at a level of about 0.025 accumulated grams of NO.sub.X, during the first 20 seconds of the FTP-75 test cold start. Further to these embodiments, it is further observed in FIG. 2 that the accumulation of NO.sub.X emissions after the gas stream exits both CCCs during the FTP-75 test post the 20 seconds time mark results in the accumulation of significantly more grams of NO.sub.X emissions associated with accumulation curve 204 as compared to the accumulation of grams of NO.sub.X emissions associated with accumulation curve 202. In these embodiments, CCC Type 1C catalyst samples including thin coatings employing low loadings of Fe-activated Rh exhibit improved NO.sub.X conversion as compared to CCC Type 1B catalyst samples including standard Rh applications.

(48) FIG. 3 is a graphical representation illustrating the accumulation of total NO.sub.X emissions obtained during the implementation of the FTP-75 test protocol to test catalyst samples including Fe-activated Rh (CCC Type 1C) and standard Rh (CCC Type 1B) loadings of about 9.8 g/ft.sup.3 and 9.8 g/ft.sup.3, respectively, as well as a standard catalyst sample including a multi-layer coating of Pd/Rh (CCC Type 2) with a total loading of about 300 g/L, according to an embodiment. In FIG. 3, FTP-75 test results 300 include accumulation curve 202, accumulation curve 204, vehicle speed curve 206, and accumulation curve 302.

(49) In some embodiments, accumulation curve 202 illustrates NO.sub.X accumulation associated with CCC Type 1C catalyst samples. In these embodiments, accumulation curve 204 illustrates NO.sub.X accumulation associated with CCC Type 1B catalyst samples. Further to these embodiments, accumulation curve 302 illustrates NO.sub.X accumulation associated with CCC Type 2 catalyst samples. Still further to these embodiments, vehicle speed curve 206 illustrates the vehicle speed profile used during the implementation of the FTP-75 test protocol for testing the aforementioned CCC samples. In FIG. 3, elements having identical element numbers from previous figures perform in a substantially similar manner.

(50) In some embodiments, the results measured during the FTP-75 test protocol are compared and verify that thin coatings including low loadings of Fe-activated Rh provide improved NO.sub.x conversion performance levels when compared to standard Rh applications as well as a standard catalyst samples employing multi-layer coatings of Pd/Rh. In these embodiments, the effects of the thin coatings including low loadings of Fe-activated Rh on NO.sub.X accumulation are analyzed during all cycles of the FTP-75 test protocol to verify improvements in conversion efficiency. Further to these embodiments, the effects of the thin coatings including low loadings of Fe-activated Rh on NO.sub.X conversion are verified by comparing the accumulated grams of NO.sub.X for the CCC Type 1C catalyst samples with the accumulated grams of NO.sub.X for CCC Type 1B catalyst samples and with the accumulated grams of NO.sub.X for CCC Type 2 catalyst samples, measured downstream at the tail pipe.

(51) In these embodiments, it is observed in FIG. 3 that the accumulation of NO.sub.X emissions after the gas stream exits the CCCs are substantially similar, at a level of about 0.025 accumulated grams of NO.sub.X, during the first 20 seconds of the FTP-75 test cold start. Further to these embodiments, it is further observed in FIG. 3 that the accumulation of NO.sub.X emissions after the gas stream exits all three CCCs during the FTP-75 test post the 20 seconds time mark results in the accumulation of more grams of NO.sub.X emissions associated with accumulation curve 204 and accumulation curve 302 as compared to the accumulation of grams of NO.sub.X emissions associated with accumulation curve 202. In these embodiments, during the post 20 seconds time mark portion of the FTP-75 test protocol, the heavily loaded CCC Type 2 catalyst samples exhibit a lower performance of NO.sub.x conversion as compared to the NO.sub.x conversion performance of the CCC Type 1B catalyst samples. Still further to these embodiments, during the FTP-75 test post the 200 s time mark both CCC Type 2 and CCC Type 1B catalyst samples exhibit a NO.sub.x conversion performance that is significantly lower than the NO.sub.x conversion performance exhibited by the CCC Type 1C catalyst sample, which maintains a stable conversion efficiency throughout the entire light-off portion of the FTP-75 test procedure.

(52) In other embodiments and in the third part (Bag 3) of the FTP-75 test procedure (not shown), the CCC Type 2 catalyst samples exhibit improved Bag 3 performance. However, even with extra Pd the CCC Type 2 catalyst samples exhibit a lower light-off performance than the CCC Type 1B catalyst samples as CCC Type 2 catalyst samples have about three times the coating mass of CCC Type 1B catalyst samples. In these embodiments, the accumulation of NO.sub.x emissions during the FTP-75 test procedure, illustrated in FIG. 3, indicates CCC Type 1C catalyst samples exhibit stable performance and conversion efficiency when compared to CCC Type 1B and CCC Type 2 catalyst samples. The CCC system including a thin coating employing low loadings of Fe-activated Rh of about 9.8 g/3 and further including loadings of Fe with CeZr OSM outperforms other catalysts (e.g., CCC Type 1B and CCC Type 2 catalyst samples) when their respective light-off and FTP-75 test procedure performances are compared. These results enable potential benefits, such as, for example reduced costs, improved NO.sub.x conversion, etc. when implemented within a plurality of TWC system applications.