Patent Application
20170095801
Field of the Disclosure
This disclosure relates generally to catalyst materials, and more particularly, to catalyst material compositions having high oxygen storage capacity utilized within three-way catalysts (TWC) systems.
Background Information
Catalysts within catalytic converters have been used to decrease the pollution associated with exhaust from various sources, such as, automobiles, boats, and other engine-equipped machines. Significant pollutants contained within the exhaust gas of gasoline engines include carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx), among others.
Conventional gasoline exhaust systems employ three-way catalysts (TWC) technology and are referred to as three way catalyst (TWC) systems. TWC systems convert the CO, HC and NOx into less harmful pollutants. Typically, TWC systems include a substrate structure upon which promoting oxides are deposited. Bimetallic catalysts, based on platinum group metals (PGM), are then deposited upon the promoting oxides. PGM materials include Pt, Rh, Pd, Ir, or combinations thereof. Some conventional TWC systems have been developed to incorporate an oxygen storage material (OSM) that stores oxygen during the leaner periods of the engine operating cycle and then releases the stored oxygen during the richer periods of the engine operating cycle. These TWC systems exhibit more efficient conversion of the CO, HC and NOx within the exhaust gases into less harmful pollutants.
Although PGM catalyst materials are effective for toxic emission control and have been commercialized by the emissions control industry, PGM materials are scarce and expensive. This high cost remains a critical factor for wide spread applications of these catalyst materials. Therefore, there is a need to provide a lower cost TWC system exhibiting catalytic properties substantially similar to or better than the catalytic properties exhibited by TWC systems employing PGM catalyst materials.
The present disclosure describes Zero-PGM (ZPGM) catalyst material compositions with enhanced oxygen storage capacity (OSC) for improved performance of three-way catalyst (TWC) systems. Further, the present disclosure describes ZPGM catalyst material compositions having significantly high OSC stability properties after fuel cut aging, thereby making catalyst manufacturing independent of using PGM and rare earth metal oxides as oxygen storage materials (OSM) for TWC applications.
According to some embodiments, the ZPGM catalyst compositions are produced according to a catalyst configuration including a suitable substrate, a washcoat (WC) layer, an overcoat (OC) layer, and an impregnation (IMP) layer. In these embodiments, the layers within the catalyst configuration are produced by employing any of the conventional synthesis methods.
In some embodiments, the disclosed ZPGM catalyst compositions are configured to include a WC layer of Alumina, coated onto a suitable substrate. In these embodiments, the OC layer includes a plurality of support oxides, such as, MgAl2O4, Al2O3—BaO, Al2O3—La2O3, ZrO2—CeO2—Nd2O3—Y2O3, CeO2—ZrO2, CeO2, SiO2, Alumina silicate, ZrO2—Y2O3—SiO2, Al2O3—CeO2, Al2O3—SrO, TiO2-10% ZrO2, TiO2-10% Nb2O5, SnO2—TiO2, ZrO2—SnO2—TiO2, BaZrO3, BaTiO3, BaCeO3, ZrO2—Pr6O11, ZrO2—Y2O3, ZrO2—Nb2O5, Al—Zr—Nb, and Al—Zr—La, amongst others. Further to these embodiments, the OC layer includes Pr-doped Zirconia (ZrO2-10%Pr6O11) support oxide.
In some embodiments, the IMP layer within the ZPGM catalyst compositions is produced including a plurality of binary spinel structures. In these embodiments, exemplary binary spinel structures include aluminum, magnesium, manganese, gallium, nickel, copper, silver, cobalt, iron, chromium, titanium, tin, or mixtures thereof. Further to these embodiments, the IMP layer includes a Cu1Mn2O4 binary spinel structure. In these embodiments, the IMP layer of Cu1Mn2O4 spinel structure is coated onto the OC layer of doped Zirconia support oxide by an impregnation method to form the ZPGM catalyst.
In other embodiments, the disclosed ZPGM catalyst compositions are subjected to a standard isothermal oscillating OSC test, to assess/verify O2 and CO delay times. In these embodiments, different O2 and CO delay times under rich and lean conditions are obtained by selecting a range of time on stream times to characterize the OSC stability properties of fresh and aged ZPGM catalyst composition samples.
In some embodiments, the disclosed ZPGM catalyst compositions are subjected to a standard isothermal oscillating OSC test to assess/verify the OSC stability of aged ZPGM catalyst composition samples. In these embodiments, the oscillating OSC test measures a plurality of O2 and CO delay times under rich and lean conditions of the ZPGM catalyst material compositions.
In some embodiments, after the aging process the disclosed ZPGM catalyst compositions exhibits significantly higher catalytic activity and OSC stability. In these embodiments, the enhanced level of OSC stability properties can be attributed to the Cu—Mn spinel coated onto the OC layer of the doped Zirconia support oxide. Further to these embodiments, the disclosed ZPGM catalyst compositions represent an advantage for a new generation of ZPGM catalyst materials due to the lower catalyst cost of the disclosed ZPGM catalyst compositions and the associated impact of said lower catalyst cost. In these embodiments, disclosed ZPGM catalyst compositions demonstrate substantially similar or improved catalytic performance to conventional TWC systems while allow for the aforementioned reduction in catalyst costs.
Numerous other aspects, features, and benefits of the present disclosure may be made apparent from the following detailed description taken together with the drawing figures, which may illustrate the embodiments of the present disclosure, incorporated herein for reference.
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.
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.
As used here, the following terms have the following definitions:
“Substrate” refers to any material of any shape or configuration that yields a sufficient surface area for depositing a washcoat and/or overcoat.
“Washcoat” refers to at least one coating including at least one oxide solid that may be deposited on a substrate.
“Overcoat” refers to at least one coating that may be deposited on at least one washcoat or impregnation layer.
“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 NOx, CO, and hydrocarbons.
“Catalyst” refers to one or more materials that may be of use in the conversion of one or more other materials.
“Catalyst system” refers to any system including a catalyst, such as a PGM catalyst, or a
ZPGM catalyst a system, of at least two layers including at least one substrate, a washcoat, and/or an overcoat.
“Platinum group metals (PGM)” refers to platinum, palladium, ruthenium, iridium, osmium, and rhodium.
“Zero-PGM (ZPGM) catalyst” refers to a catalyst completely or substantially free of platinum group metals (PGM).
“Three-Way Catalyst” refers to a catalyst able of performing 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.
“Spinel” refers to any minerals of the general formulation AB2O4 where the A ion and B ion are each selected from mineral oxides, such as, magnesium, iron, zinc, manganese, aluminum, chromium, or copper, amongst others.
“Milling” refers to the operation of breaking a solid material into a desired grain or particle size.
“Impregnation” refers to the process of totally saturating a solid layer with a liquid compound.
“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.
“Oxygen storage material (OSM)” refers to a material able to take up oxygen from oxygen rich streams and able to release oxygen to oxygen deficient streams.
“Oxygen storage capacity (OSC)” refers to the ability of materials used as OSM in catalysts to store oxygen at lean and to release it at rich condition.
“Conversion” refers to the chemical alteration of at least one material into one or more other materials.
“Adsorption” refers to the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.
“Desorption” refers to the process whereby atoms, ions, or molecules from a gas, liquid, or dissolved solid are released from or through a surface.
“Extrapolation” refers to creating a tangent line at the end of the known data and extending it beyond that limit, based on calculations to predict the value of a variable by projecting past experience of known data.
“O2 delay time” refers to the time required to reach to 50% of the 02 concentration in feed signal.
“CO delay time” refers to the time required to reach to 50% of the CO concentration in feed signal.
“Time on-stream” refers to the actual time that a unit is operating in a process operation.
Description of the Drawings
The present disclosure describes Zero-PGM (ZPGM) catalyst material compositions with enhanced oxygen storage capacity for improved performance of three-way catalyst (TWC) systems. Further, the present disclosure describes hydrothermally aged (e.g., using fuel cut aging) ZPGM catalyst material compositions exhibiting significantly higher oxygen storage capacity (OSC) stability properties.
ZPGM Catalyst Configuration, Material Composition, and Preparation
In
Examples of materials suitable for use as OC layer 106 include support oxides, such as, MgAl2O4, Al2O3—BaO, Al2O3—La2O3, ZrO2—CeO2—Nd2O3—Y2O3, CeO2—ZrO2, CeO2, SiO2, Alumina silicate, ZrO2—Y2O3—SiO2, Al2O3—CeO2, Al2O3—SrO, TiO2-10% ZrO2, TiO2-10% Nb2O5, SnO2—TiO2, ZrO2—SnO2—TiO2, BaZrO3, BaTiO3, BaCeO3, ZrO2—Pr6O11, ZrO2—Y2O3, ZrO2—Nb2O5, Al—Zr—Nb, and Al—Zr—La, amongst others. In an example, OC layer 106 is implemented as a doped Zirconia (ZrO2-10% Pr6O11) support oxide.
In some embodiments, IMP layer 108 is produced using a plurality of binary spinel structures. In these embodiments, the binary spinel structures include aluminum, magnesium, manganese, gallium, nickel, copper, silver, cobalt, iron, chromium, titanium, tin, or mixtures thereof. In an example, IMP layer 108 is implemented as a binary spinel structure of copper (Cu) and manganese (Mn). In this example, the Cu-Mn spinel structure is produced using a general formulation CuxMn3-xO4 spinel, in which X preferably takes a value of about 1.0.
According to some embodiments, the preparation of ZPGM catalyst composition samples begins with the milling of alumina to produce a slurry. In these embodiments, the slurry of alumina is coated onto ceramic substrate 104 employing an alumina loading of about 120 g/L to form WC layer 102. In these embodiments, WC layer 102 is then fired at about 550° C. for about 4 hours. Further to these embodiments, OC layer 106 is separately produced by milling doped Zirconia support oxide with water to produce a slurry of doped Zirconia for coating onto WC layer 102 with a loading of about 120 g/L. In these embodiments, OC layer 106 is then fired at about 550° C. for about 4 hours.
In some embodiments, impregnation layer 108 is produced by mixing appropriate amounts of Cu nitrate and Mn nitrate solutions. In an example, the Cu nitrate solution used is about 23.6 wt % and the Mn nitrate solution used is about 40.8 wt %. In these embodiments, the Cu and Mn solutions are mixed for about 1 to 2 hours. Further to these embodiments, the mixture of Cu—Mn is then impregnated onto OC layer 106 using any suitable impregnation method. In some embodiments, the catalyst system configuration 100 is fired at a temperature within a range of about 550° C. to about 650° C., preferably at about 600° C. for about 5 hours.
In some embodiments, the ZPGM catalyst material compositions are aged using, for example, a fuel cut aging method at a temperature of about 800° C. for about 20 hours using a fuel gas. Examples of the components within the fuel gas include CO, O2, CO2, H2O and N2 used as an aging fuel feed, which runs at rich and lean modes.
Standard Isothermal Oscillating OSC Test Procedure
In some embodiments, the standard isothermal oscillating OSC test is performed on catalyst samples at a temperature of about 575° C. with a feed of either O2 with a concentration of about 4,000 ppm diluted in inert nitrogen (N2) simulating a lean cycle, or CO with a concentration of about 8,000 ppm of CO diluted in inert N2 simulating a rich cycle. In these embodiments, the isothermal oscillating OSC test is performed within a quartz reactor using a space velocity (SV) of 60,000 hr−1, ramping from room temperature to a temperature of about 575° C. under a dry N2 environment. Further to these embodiments, when the temperature of about 575° C. is reached, the isothermal oscillating OSC test is initiated by flowing O2 through the catalyst samples within the reactor. After about 240 seconds, the feed flow is switched to CO allowing CO to flow through the catalyst samples within the reactor for another 240 seconds. In some embodiments, OSC testing enables isothermal oscillating conditions, between CO and O2 flows, during the different times on stream. In these embodiments, O2 and CO are allowed to flow within an empty test reactor (before or after the OSC test) in order to establish test reactor benchmarks.
In some embodiments, the OSC stability properties of fresh and aged ZPGM catalyst material compositions are determined by using CO and O2 pulses under standard isothermal oscillating conditions. In these embodiments, the OSC test facilitates the determination of O2 and CO delay times for an extended number of rich and lean cycles to verify the OSC stability of the disclosed ZPGM catalyst material compositions. Further to these embodiments, the O2 and and CO delay times are the times required to reach 50% of the O2 and CO concentrations within the feed signal, respectively. The O2 and CO delay times are used as parameters for the determination of the oxygen storage capacity of the ZPGM catalyst composition samples.
OSC Stability Properties of Fresh ZPGM Catalyst Composition Samples
In some embodiments, O2 benchmark 202 (double-dot dashed graph) illustrates the results of flowing 4,000 ppm O2 through an empty test reactor, CO benchmark 204 (dashed graph) illustrates the result of flowing 8,000 ppm CO through the empty test reactor, O2 curve 206 (single-dot dashed graph) illustrates the result of flowing 4,000 ppm O2 through the test reactor including the disclosed ZPGM catalyst composition, and CO curve 208 (solid line graph) illustrates the result of flowing 8,000 ppm CO through the test reactor including the disclosed ZPGM catalyst composition.
In these embodiments, the O2 signal of the disclosed ZPGM catalyst composition does not reach the O2 signal of the empty operating test reactor, as illustrated by O2 curve 206 and O2 benchmark 202 respectively. These OSC test results indicate the storage of a significant amount of O2 within the disclosed ZPGM catalyst composition. Further to these embodiments, the measured O2 delay time is about 136.2 seconds. In these embodiments, the O2 delay time measured indicates the disclosed ZPGM catalyst composition exhibits significantly high OSC stability properties.
In other embodiments, the CO signal of the the disclosed ZPGM catalyst composition does not reach the CO signal of the empty operating test reactor, as illustrated by CO curve 208 and CO benchmark 204, respectively. These OSC results indicate the consumption of a significant amount of CO within the disclosed ZPGM catalyst composition due to oxidation reaction of CO with the stored O2 to produce CO2.
Further to these embodiments, the measured CO delay time is about 127.7 seconds. In these embodiments, the CO delay time measured illustrates the disclosed ZPGM catalyst composition material exhibits significantly high OSC stability properties.
In some embodiments, the measured O2 and CO delay times indicate the disclosed ZPGM catalyst compositions exhibit enhanced OSC stability properties. In these embodiments, the enhanced OSC stability properties are illustrated by the highly activated reversible O2 adsorption as well as the CO conversion that occurs under the isothermal oscillating conditions.
In some embodiments, the O2 delay time is illustrated as O2 delay time curve 302 (solid line graph) extended with dotted points for extrapolated values of time on stream as illustrated by extrapolated O2 delay time curve 306. In these embodiments, the CO delay time is illustrated as CO delay time curve 304 (dot-solid line graph) extended with dashed lines for extrapolated values of time on stream as illustrated by extrapolated CO delay time curve 308. Further to these embodiments, the extrapolated O2 and CO delay time values occur the after the end of the OSC stability test as illustrated by end of test mark 310. In these embodiments, there is not a significant decrease in O2 and CO delay time over time. Therefore, the O2 and CO delay time results indicate a significantly high OSC activity.
In some embodiments, the O2 delay time at the beginning of the oscillating OSC test cycle exhibits a delay time value of approximately 137 seconds. In these embodiments, the O2 delay after about 112 rich-lean cycles (at approximately 450 minutes of time on stream) indicates a value of about 121 seconds. Further to these embodiments, O2 delay time curve 302 can be used to calculate the amount of OSC at future point in time by extrapolation calculations to predict the trend-line of OSC stability behavior of O2 delay time curve 302 through about 3000 minutes of time on stream (approximately 750 cycles). In these embodiments, the extrapolated time delay curve is illustrated by extrapolated O2 delay time curve 306. Further to these embodiments, the prediction of O2 delay time for disclosed ZPGM catalyst compositions after approximately 750 rich-lean cycles is about 111 seconds.
In some embodiments, the CO delay time at the beginning of the oscillating OSC test cycle exhibits a delay time value of approximately 129 seconds. In these embodiments, the CO delay after 112 rich-lean cycles (at approximately 450 minutes of time on stream) indicates a value of about 112 seconds. Further to these embodiments, CO delay time curve 304 can be used to calculate the amount of OSC at future point in time by extrapolation calculations to predict the trend-line of OSC stability behavior of CO delay time curve 304 through about 3000 minutes of time on stream (approximately 750 cycles). In these embodiments, the extrapolated time delay curve is illustrated by extrapolated CO delay time curve 308. Further to these embodiments, the prediction of CO delay time for disclosed ZPGM catalyst compositions after approximately 750 rich-lean cycles is about 104 seconds.
In some embodiments, the oscillating OSC test results from about 112 rich-lean cycles, as illustrated by end of test mark 310, are used to extrapolate values and predict a trend-line to approximately 750 rich-lean cycles. The extrapolated values and associated predicted trend-line provide an indication the O2 and CO delay times that do not reduce significantly, and remain with a high percentage of OSC, thereby demonstrating the OSC stability of fresh ZPGM catalyst compositions.
In some embodiments, within oscillating OSC test 400 the CO conversion occurs due to the consumption of stored O2 from the OSC material during the lean cycles of oscillating OSC test 400. In these embodiments, CO conversion curve 402 illustrates conversion of CO over time on stream. Further to these embodiments, the oscillating OSC test results indicate that fresh ZPGM catalyst compositions exhibit a CO conversion of about 55% at the beginning of the cycle. In these embodiments, the oscillating OSC test results indicate a substantially similar steady rate of CO conversion for about 7.5 hours through approximately 112 rich-lean cycles. Further to these embodiments, the CO conversion decreases over the 112 rich-lean cycles from about 57% to about 48% conversion, as illustrated in CO conversion curve 402.
In some embodiments, test results of fresh ZPGM catalyst compositions indicated a high level of OSC stability properties during extended rich-lean cycles.
OSC Stability of Aged OSM Sample
In some embodiments, the O2 delay time is illustrated as O2 delay time curve 502 (solid line graph) extended with dotted points for extrapolated values of time on stream as illustrated by extrapolated O2 delay time curve 506. In these embodiments, the CO delay time is illustrated as CO delay time curve 504 (dot-solid line graph) extended with dashed lines for extrapolated values of time on stream as illustrated by extrapolated CO delay time curve 508. Further to these embodiments, the extrapolated O2 and CO delay times occur after the end of the OSC stability test as illustrated by end of test mark 510. In these embodiments, there is no significant O2 and CO delay times decrease over time. Therefore, the O2 and CO delay time results indicate a significantly high OSC activity.
In some embodiments, the O2 delay time at the beginning of the oscillating OSC test cycle exhibits a delay time value of approximately 71 seconds. In these embodiments, the O2 delay after about 112 rich-lean cycles (at approximately 450 minutes of time on stream) indicates a value of about 81 seconds. Further to these embodiments, slight increases of O2 and CO delay times occur over time.
In some embodiments, after aging the ZPGM catalyst compositions the measured O2 and CO delay times exhibit significantly high OSC stability, giving an indication that the OSC stability properties of disclosed ZPGM catalyst compositions are thermally stable.
The improved OSC stability properties of the disclosed ZPGM material compositions can be used in a large number of TWC catalyst applications with substantially similar or improved performance when compared to conventional TWC catalyst systems. The significantly high OSC stability properties after fuel cut aging of ZPGM catalyst compositions allow for the treating of exhaust gases produced by internal combustion engines, where lean and rich fluctuations in operating conditions produce high variations of exhaust pollutants.
The measured O2 delay time and CO delay times is an indication that the disclosed ZPGM catalyst material, exhibit enhanced OSC, (delay time above 136 seconds).
The results from multiple rich-lean cycles shows O2 and CO delay time does not reduce significantly and still keeps high percentage of OSC, indicating the stability of O2 and CO delay time of disclosed fresh ZPGM catalyst is still above 100 seconds.
OSC of disclosed ZPGM catalyst is thermally stable, aging the ZPGM material (under rich-lean aging mode) does not damage the OSC of spinel composition and disclosed ZPGM catalyst still exhibit stable O2 and CO delay time, indicating thermal stability of OSC of disclosed ZPGM composition.
While various aspects and embodiments have been disclosed, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
