Methods and processes of coating zero-PGM catalysts including with Cu, Mn, Fe for TWC applications

Abstract

Variations of coating processes of CuMnFe ZPGM catalyst materials for TWC applications are disclosed. The disclosed coating processes for CuMnFe spinel materials are enabled in the preparation ZPGM catalyst samples according to a plurality of catalyst configurations, which may include an alumina only washcoat layer coated on a suitable ceramic substrate, and an overcoat layer with or without an impregnation layer, including CuMnFe spinel and doped Zirconia support oxide, prepared according to variations of disclosed coating processes. Activity measurements are considered under variety of lean condition to rich condition to analyze the influence of disclosed coating processes on TWC performance of ZPGM catalysts for a plurality of TWC applications. Different coating processes may substantially increase thermal stability and TWC activity, providing improved levels of NO.sub.x conversion that may lead to cost effective manufacturing solutions for ZPGM-TWC systems.

Claims

1. A process for making a catalytic system, comprising: providing a substrate; applying a washcoat to said substrate, wherein the substrate comprises alumina; applying an overcoat to said washcoat, said overcoat comprising at least one support oxide comprising doped ZrO.sub.2; applying to said overcoat at least one layer of CuMn spinel; and wherein the catalytic system is free of platinum group metals; and wherein the doped ZrO.sub.2comprises Nb.sub.2O.sub.5ZrO.sub.2.

2. The process of claim 1, wherein the CuMn spinel has a general formula of Cu.sub.xMn.sub.1-xFe.sub.2O.sub.4, where x is less than 0.9 and greater than 0.1.

3. The process of claim 2, wherein x is 0.5.

4. The process of claim 3; wherein the catalytic system's conversion of NO.sub.x is greater than 49%.

5. The process of claim 1, wherein the CuMn spinel is impregnated.

6. The process of claim 5; wherein the catalytic system's conversion of NO.sub.x is greater than 89%.

7. The process of claim 1, wherein the catalytic system's HC T.sub.50 is less than or equal to 61 C.

8. The process of claim 1, wherein the catalytic system's NO.sub.xT.sub.50 is less than or equal to 55 C.

9. The process of claim 1, wherein the substrate comprises ceramics.

10. The process of claim 1, wherein the catalytic system's conversion of NO.sub.x increases with an increasing amount of CuMn spinel.

11. The process of claim 1, wherein the catalytic system's NO/CO cross over increases with an increasing amount of CuMn spinel.

12. The process of claim 1, wherein the catalytic system's catalytic performance under lean conditions increases with an increasing amount of CuMn spinel.

13. The process of claim 1, wherein engine performance under lean conditions increases with an increasing amount of CuMn spinel.

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 place upon illustrating the principles of the disclosure. In the figures, reference numerals designate corresponding parts throughout the different views.

(2) FIG. 1 shows a catalyst configuration for fresh and aged ZPGM catalyst samples prepared using coating process referred as coating process Type 1, according to an embodiment.

(3) FIG. 2 illustrates a catalyst configuration for fresh and aged ZPGM catalyst samples prepared using coating process referred as coating process Type 2, according to an embodiment.

(4) FIG. 3 depicts catalyst performance for fresh ZPGM catalyst samples prepared using coating process Type 1, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and space velocity (SV) of about 40,000 h.sup.1, according to an embodiment.

(5) FIG. 4 shows catalyst performance for fresh ZPGM catalyst samples prepared using coating process Type 2, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h.sup.1, according to an embodiment.

(6) FIG. 5 illustrates NO.sub.x conversion comparison for fresh ZPGM catalyst samples prepared using coating processes Type 1 and Type 2, according to an embodiment.

(7) FIG. 6 depicts catalyst performance for hydrothermally aged ZPGM catalyst samples prepared using coating process Type 2, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h.sup.1, according to an embodiment.

DETAILED DESCRIPTION

(8) 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

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

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

(11) Zero platinum group (ZPGM) catalyst refers to a catalyst completely or substantially free of platinum group metals.

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

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

(14) Washcoat refers to at least one coating including at least one oxide solid that may be deposited on a substrate.

(15) Overcoat refers to at least one coating that may be deposited on at least one washcoat or impregnation layer.

(16) Milling refers to the operation of breaking a solid material into a desired grain or particle size.

(17) Impregnation refers to the process of imbuing or saturating a solid layer with a liquid compound or the diffusion of some element through a medium or substance.

(18) Calcination refers to a thermal treatment process applied to solid materials, in presence of air, to bring about a thermal decomposition, phase transition, or removal of a volatile fraction at temperatures below the melting point of the solid materials.

(19) Treating, treated, or treatment refers to drying, firing, heating, evaporating, calcining, or mixtures thereof.

(20) Spinel refers to any of various mineral oxides of magnesium, iron, zinc, or manganese in combination with aluminum, chromium, copper or iron with AB.sub.2O.sub.4 structure.

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

(22) R-value refers to the number obtained by dividing the reducing potential by the oxidizing potential of materials in a catalyst.

(23) Rich condition refers to exhaust gas condition with an R-value above 1.

(24) Lean condition refers to exhaust gas condition with an R-value below 1.

(25) Three-way catalyst (TWC) refers to a catalyst that may achieve three simultaneous tasks: reduce nitrogen oxides to nitrogen and oxygen, oxidize carbon monoxide to carbon dioxide, and oxidize unburnt hydrocarbons to carbon dioxide and water.

(26) T.sub.50 refers to the temperature at which 50% of a material is converted.

Description of the Drawings

(27) The present disclosure may provide material compositions including CuMnFe spinel on support oxide, coating process, and their influence on TWC performance to develop suitable catalytic layers, which may ensure the identification of a coating process, capable of providing high chemical reactivity, and thermal and mechanically stability for ZPGM catalysts. Aspects that may be treated in present disclosure may show improvements in the process for overall catalytic conversion capacity for a plurality of ZPGM catalysts, which may be suitable for TWC applications.

(28) ZPGM Catalyst Configuration, Material Composition, and Preparation

(29) As catalyst performance parameters may be translated into the physical catalyst structure, different coating methods may be used to achieve desired coating properties and an effective level of catalytic performance. A plurality of synthesis method may be used in present disclosure.

(30) FIG. 1 shows catalyst configuration 100 which may be used for coating of CuMnFe spinel as powder to prepare ZPGM catalyst samples. In present disclosure, CuMnFe spinel structure may be prepared using the general formulation Cu.sub.xMn.sub.1-xFe.sub.2O.sub.4, where X may be variable of different molar ratios within a range of about 0.1<X<0.9, in which X may preferably have a value of 0.5. Accordingly, in this configuration, washcoat (WC) layer 102 may be alumina only, coated on suitable ceramic substrate 104. Overcoat (OC) layer 106 may include Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4 spinel bulk powder which may be prepared separately and subsequently added to milled doped Zirconia support oxide for coating on alumina-based WC layer 102. In present disclosure, Niobium-Zirconia support oxide may be used as support oxide in catalyst configuration 100.

(31) FIG. 2 depicts catalyst configuration 200 which may be employed for impregnation of CuMnFe spinel on doped Zirconia support oxide to prepare ZPGM catalyst samples. In present disclosure, CuMnFe impregnation solution may be prepared using the general formulation Cu.sub.xMn.sub.1-xFe.sub.2O.sub.4, where X may be variable of different molar ratios within a range of about 0.1<X<0.9, in which X may preferably have a value of 0.5. In this configuration, WC layer 102 may be alumina only, coated on suitable ceramic substrate 104. Impregnation (IMP) layer 202 including Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4 spinel may be added to OC layer 106 of doped Zirconia support oxide. In present disclosure, Niobium-Zirconia support oxide may be used as support oxide in catalyst configuration 200.

(32) Fresh ZPGM catalyst samples may be hydrothermally aged, employing about 10% steam/air or fuel flow at a plurality of temperatures within a range from about 800 C. to about 1,000 C. for a plurality of aging times.

(33) Standard light-off test may be performed for ZPGM catalyst samples, per disclosed coating processes, under steady state condition at a selected R-value as verification for the influence of coating processes on TWC activity.

(34) The NO/CO cross over R-value of ZPGM catalyst samples, per disclosed coating processes, may be determined and analyzed by performing isothermal steady state sweep test.

(35) TWC Standard Light-Off Test Procedure

(36) TWC standard light-off test under steady state condition may be performed employing a flow reactor in which temperature may be increased from about 100 C. to about 500 C. at a rate of about 40 C./min, feeding a standard TWC gas composition of about 8,000 ppm of CO, about 400 ppm of C.sub.3H.sub.6, about 100 ppm of C.sub.3H.sub.8, about 1,000 ppm of NO.sub.x, about 2,000 ppm of H.sub.2, about 10% of CO.sub.2, about 10% of H.sub.2O, and about 0.70% of O.sub.2. The average R-value is about 1.2, at space velocity (SV) of about 40,000 h.sup.1.

(37) Isothermal Steady State Sweep Test Procedure

(38) The isothermal steady state sweep test may be done employing a flow reactor at inlet temperature of about 450 C., and testing a gas stream at 11-point R-values from about 2.00 (rich condition) to about 0.80 (lean condition) to measure the CO, NO.sub.x, and HC conversions.

(39) The SV in the isothermal steady state sweep test may be adjusted at about 40,000 h.sup.1. The gas feed employed for the test may be a standard TWC gas composition, with variable O.sub.2 concentration in order to adjust R-value from rich condition to lean condition during testing. The standard TWC gas composition may include about 8,000 ppm of CO, about 400 ppm of C.sub.3H.sub.6, about 100 ppm of C.sub.3H.sub.8, about 1,000 ppm of NO.sub.x, about 2,000 ppm of H.sub.2, about 10% of CO.sub.2, and about 10% of H.sub.2O. The quantity of O.sub.2 in the gas mix may be varied to adjust Air/Fuel (A/F) ratio within the range of R-values to test the gas stream.

(40) The following examples are intended to illustrate the scope of the disclosure. It is to be understood that other procedures known to those skilled in the art may alternatively be used.

EXAMPLES

Example #1

Coating Process Type 1, CuMnFe Spinel Bulk Powder/Nb2O5ZrO2 Support Oxide

(41) Example #1 may illustrate preparation of fresh and aged ZPGM catalyst samples of catalyst configuration 100 employing coating process here referred as coating process Type 1. Aged catalyst samples may be prepared by hydrothermal aging employing about 10% steam/air at a plurality of temperatures within a range from about 800 C. to about 1,000 C. for about 4 hours. In this embodiment, hydrothermally aged samples may be preferably aged at 900 C. for about 4 hours.

(42) Preparation of WC layer 102 may start by milling alumina to make slurry. Suitable loading of alumina may be about 120 g/L. Alumina slurry may be subsequently coated on ceramic substrate 104 and fired at about 550 C. for about 4 hours. Preparation of OC layer 106 may start by milling Nb.sub.2O.sub.5ZrO.sub.2 support oxide with water separately to make slurry. Then, CuMnFe solution may be prepared by mixing the appropriate amount of Cu nitrate solution (CuNO.sub.3), Mn nitrate solution (Mn(NO.sub.3).sub.2), and Fe nitrate solution (Fe(NO.sub.3).sub.3) with water to make solution at appropriate molar ratio for Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4, according to formulation Cu.sub.xMn.sub.1-xFe.sub.2O.sub.4, in which X may take value of 0.5. Subsequently, CuMnFe solution may be precipitated using an appropriate amount of base solution to adjust pH of slurry at desired level. Then, slurry may undergo filtering and washing with distilled water, followed by drying, and subsequently, calcination at selected temperature of about 600 C. for about 5 hours to prepare fine grain powder of Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4. CuMnFe spinel powder may then be mixed with slurry of Nb.sub.2O.sub.5ZrO.sub.2 support oxide. Suitable loading of OC layer 106 may be about 120 g/L. Then, slurry of CuMnFe solution and Nb.sub.2O.sub.5ZrO.sub.2 support oxide may be coated on top of WC layer 102 and fired at about 600 C. for about 5 hours. Subsequently, fresh ZPGM catalyst samples may be hydrothermally aged, according to an embodiment.

(43) TWC standard light-off test under steady state condition may be performed for fresh and aged ZPGM catalyst samples, per disclosed coating process Type 1, at average R-value of about 1.2, at SV of about 40,000 h.sup.1, at rate of about 40 C./min for temperature increase, and testing a TWC gas stream to verify the influence of coating process on TWC activity. In present disclosure, standard light-off test may be performed for fresh ZPGM catalyst samples.

(44) The NO/CO cross over R-value of fresh and aged ZPGM catalyst samples, per disclosed coating process Type 1, may be determined by performing isothermal steady state sweep test at inlet temperature of about 450 C., and testing a gas stream at 11-point R-values from about 2.0 (rich condition) to about 0.8 (lean condition) to measure the CO, NO.sub.x, and HC conversions. SV in the isothermal steady state sweep test may be adjusted at about 40,000 h.sup.1.

Example #2

Coating Process Type 2, IMP of CuMnFe Spinel on Nb2O5ZrO2 Support Oxide

(45) Example #2 may illustrate preparation of fresh and aged ZPGM catalyst samples of catalyst configuration 200 employing coating process here referred as coating process Type 2. Aged catalyst samples may be prepared by hydrothermal aging employing about 10% steam/air at a plurality of temperatures within a range from about 800 C. to about 1,000 C. for about 4 hours. In this embodiment, hydrothermally aged samples may be preferably aged at 900 C. for about 4 hours.

(46) Preparation of WC layer 102 may start by milling alumina to make slurry. Suitable loading of alumina may be about 120 g/L. Alumina slurry may be subsequently coated on ceramic substrate 104 and fired at about 550 C. for about 4 hours. Preparation of OC layer 106 may start by milling Nb.sub.2O.sub.5ZrO.sub.2 support oxide with water separately to make slurry. Slurry of Nb.sub.2O.sub.5ZrO.sub.2 support oxide may then be coated on WC layer 102 and fired at about 550 C. for about 4 hours. Suitable loading for OC layer 106 may be about 120 g/L. Subsequently, an IMP layer 202 of CuMnFe spinel may be prepared. Accordingly, CuMnFe solution may be prepared by mixing the appropriate amount of Cu nitrate solution (CuNO.sub.3), Mn nitrate solution (Mn(NO.sub.3).sub.2), and Fe nitrate solution (Fe(NO.sub.3).sub.3) with water to make solution at appropriate molar ratio for Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4, according to formulation Cu.sub.xMn.sub.1-xFe.sub.2O.sub.4, in which X may take value of about 0.5. Then, Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4 spinel solution may be impregnated on OC layer 106 of Nb.sub.2O.sub.5ZrO.sub.2 support oxide and fired at about 600 C. for about 5 hours. Subsequently, fresh ZPGM catalyst samples may be hydrothermally aged, according to an embodiment.

(47) TWC standard light-off test under steady state condition may be performed for fresh and aged ZPGM catalyst samples, per disclosed coating process Type 2, at average R-value of about 1.2, at SV of about 40,000 h.sup.1, at rate of about 40 C./min for temperature increase, and testing a TWC gas stream to verify the influence of coating process on TWC activity. In present disclosure, standard light-off test may be performed for fresh ZPGM catalyst samples.

(48) The NO/CO cross over R-value of fresh and aged ZPGM catalyst samples, per disclosed coating process Type 2, may be determined by performing isothermal steady state sweep test at inlet temperature of about 450 C., and testing a gas stream at 11-point R-values from about 2.0 (rich condition) to about 0.8 (lean condition) to measure the CO, NO.sub.x, and HC conversions. SV in the isothermal steady state sweep test may be adjusted at about 40,000 h.sup.1.

(49) Analysis of Influence of Variations of Coating Processes on TWC Performance

(50) The improvements in NO.sub.x, CO, and HC conversions when applying different coating processes may be confirmed with the results from standard light-off test for fresh ZPGM catalyst samples prepared per example #1 and example #2.

(51) For fresh ZPGM catalyst samples prepared using coating process Type 1, per example #1, NO.sub.x T.sub.50 occurs at about 494 C., CO T.sub.50 takes place at about 309 C., and HC T.sub.50 occurs at about 4760 C. For fresh ZPGM catalyst samples prepared using coating process Type 2, per example #2, NO.sub.x T.sub.50 occurs at about 439 C., CO T.sub.50 takes place at about 283 C., and HC T.sub.50 occurs at about 415 C.

(52) A comparison of results of NO.sub.x, CO, and HC T.sub.50 indicates and verifies that fresh ZPGM catalyst samples per example #2 are more effective than fresh ZPGM catalyst samples per example #1since they exhibit lower temperatures T.sub.50 for all TWC conversion. This improvement is more significant for NO.sub.x and HC conversions. Impregnation of CuMnFe reduces NO.sub.x and HC T.sub.50 about 55 C. and about 61 C., respectively.

(53) FIG. 3 shows catalyst performance 300 for fresh ZPGM catalyst samples prepared using coating process Type 1, per example #1, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h.sup.1, according to an embodiment.

(54) In FIG. 3, conversion curve 302 (solid line with circle) and conversion curve 304 (solid line with square) respectively show isothermal steady state sweep test results for NO.sub.x conversion and CO conversion.

(55) As may be seen in FIG. 3, for fresh ZPGM catalyst samples, NO/CO cross over R-value takes place at the specific R-value of 1.37, where NO.sub.x and CO conversions are about 98.00%, respectively.

(56) Activity at about stoichiometric condition for fresh ZPGM catalyst samples, per coating process Type 1, may be observed at R-values of 1.05. At R-value of 1.05, NO.sub.x conversion is about 24.80%, and CO conversion is about 99.70%. At R-value of 1.10, NO.sub.x and CO conversions are about 49.40% and about 99.50%, respectively.

(57) FIG. 4 depicts catalyst performance 400 for fresh ZPGM catalyst samples prepared using coating process Type 2, per example #2, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h.sup.1, according to an embodiment.

(58) In FIG. 4, conversion curve 402 (solid line with circle) and conversion curve 404 (solid line with square) respectively depict isothermal steady state sweep test results for NO.sub.x conversion and CO conversion.

(59) As may be seen in FIG. 4, for fresh ZPGM catalyst samples, NO/CO cross over R-value takes place at the specific R-value of 1.19, where NO.sub.x and CO conversions are about 98.80%, respectively.

(60) Activity at about stoichiometric condition for fresh ZPGM catalyst samples, per coating process Type 2, may be observed at R-values of 1.05. At R-value of 1.05, NO.sub.x conversion is about 70.40%, and CO conversion is about 99.50%. At R-value of 1.10, NO.sub.x and CO conversions are about 89.90% and about 99.30%, respectively.

(61) It may also observed from FIG. 3 and FIG. 4 that fresh ZPGM catalyst samples, per example #2, show significant improvement of NO.sub.x conversion, under all region of R-value from lean to stoichiometric and to rich conditions, when compare with NO.sub.x of fresh ZPGM catalyst samples, per example #1. At R-value of 1.05, about 24.80% NO.sub.x conversion levels may be noted for fresh ZPGM catalyst samples, per example #1, while about 70.40% NO.sub.x conversion levels may be noted for fresh ZPGM catalyst samples, per example #2. Results from FIG. 3 and FIG. 4 verify the influence that variations of coating processes may have on TWC performance, showing that fresh ZPGM catalyst samples including IMP layer 202 of Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4 provide significant improvement on TWC performance, especially NO.sub.x conversion.

(62) FIG. 5 illustrates NO.sub.x conversion comparison 500 for fresh ZPGM catalyst samples prepared using coating processes Type 1 and Type 2, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h1, according to an embodiment.

(63) In FIG. 5, conversion curve 502 (solid line with circle), and conversion curve 504 (solid line with square) respectively illustrate NO.sub.x conversion results for coating processes Type 1, per example #1, and Type 2, per example #2.

(64) As may be seen in FIG. 5, for fresh ZPGM catalyst samples, coating process with IMP layer, Type 2, exhibits higher level of influence on activity in NO.sub.x conversion than coating process with OC layer of ZPGM, Type 1. At R-value of 1.10 (rich condition close to stoichiometric condition), NO.sub.x conversions for coating process Type 1 and coating process Type 2 are about 49.40% and about 89.90%, respectively. It may be noted that coating process Type 2 shows activity improvement compared with coating process Type 1. Comparison of NO.sub.x conversions may indicate that the observed difference in NO.sub.x conversion for fresh ZPGM catalyst samples prepared using coating process Type 1 and Type 2 may be related to the level of dispersion of CuMnFe spinel on support oxide.

(65) FIG. 6 shows catalyst performance 600 for hydrothermally aged ZPGM catalyst samples prepared using coating process Type 2, per example #2, under isothermal steady state sweep condition, at inlet temperature of about 450 C. and SV of about 40,000 h.sup.1, according to an embodiment.

(66) In FIG. 6, conversion curve 602 (solid line with circle) and conversion curve 604 (solid line with square) respectively depict isothermal steady state sweep test results for NO.sub.x conversion and CO conversion.

(67) As may be seen in FIG. 6, for hydrothermally aged ZPGM catalyst samples, NO/CO cross over R-value takes place at the specific R-value of 1.34, where NO.sub.x and CO conversions are about 94.60%, respectively.

(68) Activity at about R-value of 1.20 for hydrothermally aged ZPGM catalyst samples, per coating process Type 2, may be observed for NO.sub.x conversion of about 84.40% and for CO conversion of about 96.60%, which indicates catalyst is still active after aging ZPGM catalyst samples, although the activity decreased compared with fresh ZPGM catalyst samples of Type 2, per example #2.

(69) Hydrothermally aged ZPGM catalyst samples prepared using coating process Type 1, per example #1, do not show a NO/CO cross over R-value. As may be noted, deactivation in hydrothermally aged ZPGM catalyst samples, per example #2, is not significant as in hydrothermally aged ZPGM catalyst samples, per example #1, indicating better thermal stability of ZPGM sample of Type 2, per example #2.

(70) According to principles in present disclosure, use of different coating processes may bring about different influence on TWC performance, as may be observed from the results of the disclosed coating processes in example #1 and example #2. In present disclosure, coating process Type 2, per example #2 which includes impregnation of CuMnFe spinel, shows higher level of influence on catalytic activity and thermal stability than coating process Type 1, per example #1, which includes OC of ZPGM component using powder of CuMnFe spinel. Fresh ZPGM catalyst samples, per example #1 and example #2, including Cu.sub.0.5Mn.sub.0.5Fe.sub.2O.sub.4 spinel on Nb.sub.2O.sub.5ZrO.sub.2 support oxide may exhibit suitable TWC performance when employed in ZPGM catalysts for a plurality of TWC applications, leading to a more effective utilization of ZPGM catalyst materials in TWC converters.