Patent Application
20160361710
Field of the Disclosure
This disclosure relates generally to zero-PGM (ZPGM) catalyst materials, and more particularly, to reversible redox properties of spinel-based oxide materials for use in a plurality of catalyst applications.
Background Information
Conventional gasoline exhaust systems employ three-way catalysts (TWC) technology and are referred to as TWC systems. TWC systems convert the toxic CO, HC and NOx into less harmful pollutants. Typically, TWC systems include a substrate structure upon which a layer of supporting and sometimes promoting oxides are deposited. Catalysts, based on platinum group metals (PGM), are then deposited upon the supporting oxides. Conventional PGM materials include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), or combinations thereof.
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 widespread applications of PGM catalyst materials. As changes in the formulation of catalysts continue to increase the cost of TWC systems, the need for catalysts of significant catalytic performance has directed efforts toward the development of catalytic materials capable of providing the required synergies to achieve greater catalytic performance. Additionally, compliance with ever stricter environmental regulations and the need for lower manufacturing costs require new types of TWC systems. Therefore, there is a continuing need to provide TWC systems exhibiting catalytic properties substantially similar to or exceeding the catalytic properties exhibited by conventional TWC systems employing high PGM catalyst materials.
The present disclosure describes zero-platinum group metals (ZPGM) material compositions including binary spinel oxide powders to develop suitable ZPGM catalyst materials. Further, the present disclosure describes the reduction/oxidation (redox) reversibility of the aforementioned ZPGM catalyst materials. These ZPGM catalyst materials can be used for a variety of catalyst applications, such as, for example oxygen storage material (OSM) applications, and ZPGM and ultra-low loading synergized-PGM (SPGM) three-way catalyst (TWC) systems, amongst others.
In some embodiments, the ZPGM catalyst materials include binary spinel oxide compositions, which are synthesized using conventional synthesis methodologies to produce spinel oxide powders. In these embodiments, the binary spinel oxide composition is implemented as copper (Cu)-manganese (Mn) spinel oxide compositions. Further to these embodiments, the Cu—Mn spinel oxide is produced using a general formulation CuXMn3-XO4 spinel in which X is a variable representing molar ratios within a range from about 0.01 to about 2.99. In an example, X takes a value of about 1.0 for a stoichiometric CuMn2O4 spinel oxide powder.
In some embodiments, the redox behavior of the Cu—Mn spinel oxide powder is analyzed within oxidation-reduction environments to determine the redox property of the Cu—Mn spinel oxide powder. In these embodiments, functional testing and chemical characterization of Cu—Mn spinel powder are conducted to assess the structure stability of the spinel phase to redox reactions. Further to these embodiments, the Cu—Mn spinel powders are characterized after the oxidation-reduction reactions employing XRD, XPS, and TPR analyses.
The results confirm the significant redox reversibility of the Cu—Mn spinel oxide. In other words, the Cu—Mn spinel oxide, which is free of PGM and rare-earth (RE) metals, exhibits an improved redox property that can enable catalyst materials in bulk powder format for the development of a plurality of TWC systems and other catalyst applications.
In one aspect, the present invention provides a zero-platinum group metal catalytic composition comprising a binary Cu—Mn spinel of the formula CuxMn3-xO4, wherein X is a number from 0.01 to 2.99, and wherein the composition is reducible to form metal Cu and MnO, and then oxidizable to form said binary Cu—Mn spinel. In a preferred embodiment, the catalytic composition the binary Cu—Mn spinel is CuMn2O4.
In one embodiment, a concentration of Cu1+ in the composition is greater than that of Cu2+ when the binary Cu—Mn spinel is in a reduced state.
In a preferred embodiment, the composition is in the form of a powder.
In some embodiments, the binary Cu—Mn spinel of the composition exhibits a crystalline size of about 26 nm following reduction.
In one embodiment, the binary Cu—Mn spinel has been reduced to form metal Cu and MnO.
In one aspect of the invention, the catalytic composition may be used in a catalytic converter.
Another aspect of the invention is directed to a method of removing pollutants from a gas stream comprising:
a) contacting an exhaust stream comprising one or more of NOx, CO, or HC with a catalytic composition comprising a binary Cu—Mn spinel of the formula CuxMn3-xO4, wherein X is a number from 0.01 to 2.99, and wherein the step of contacting results in a reduction of one or more of NOx, CO, or HC in the exhaust stream, and in a reduction of the Cu—Mn spinel to Cu metal and MnO; and
b) oxidizing the catalytic composition following step b) to form a binary Cu—Mn spinel of the formula CuxMn3-xO4.
In one embodiment, step a) is carried out a temperature from about 130° C. to 335° C., and in particular, at a temperature that is about 225° C. to 230° C.
In one embodiment, the method may include a step c) in which steps a) and b) are repeated at least once. In some embodiments, the catalytic composition has been subjected at least once to steps a) and b), and exhibits a crystalline size of about 26 nm.
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.
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.
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.
Definitions
As used here, the following terms have the following definitions:
“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.
“Catalyst” refers to one or more materials that may be of use in the conversion of one or more other materials.
“Lattice matching” refers to a matching of a unit cell of an unknown material against a database of known materials represented by their respective standard unit cells to determine the unknown materials lattice parameters and identify the unknown material.
“Lattice parameter or Lattice constant” refers to the physical dimension of unit cells in a crystal lattice. Lattices in three dimensions have three lattice constants, referred to as a, b, and c. However, in the special case of cubic crystal structures, all of the constants are equal and only referred to a.
“Platinum group metals (PGM)” refers to platinum, palladium, ruthenium, iridium, osmium, and rhodium.
“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, for example magnesium, iron, zinc, manganese, aluminum, chromium, titanium, cobalt, nickel, or copper, amongst others.
“Temperature-programmed reduction (TPR)” refers to a technique for the characterization of solid materials often used in the field of heterogeneous catalysis to find the most efficient reduction conditions, in which a catalyst is subjected to a programmed temperature rise, while a reducing gas mixture is flowed over it.
“Three-way catalyst (TWC)” refers to a catalyst that performs 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.
“X-ray diffraction (XRD) analysis” refers to analytical technique for identifying crystalline material structures, including atomic arrangement, crystalline size, and imperfections in order to identify unknown crystalline materials (e.g., minerals, inorganic compounds).
“X-ray photoelectron spectroscopy (XPS) analysis” refers to a surface-sensitive quantitative spectroscopy technique that measures the elemental composition at the parts per thousand range, empirical formula, chemical state, and electronic state of the elements that exist within a material.
The present disclosure describes zero-platinum group metals (ZPGM) material compositions including binary spinel oxide powders to develop suitable ZPGM catalyst materials. Further, the present disclosure describes a reduction-oxidation (redox) stability and reversibility of the aforementioned ZPGM catalyst materials. These ZPGM catalyst materials can be used for a variety of catalyst applications, such as, for example oxygen storage material (OSM) applications, and ZPGM and ultra-low loading synergized-PGM (SPGM) three-way catalyst (TWC) systems, amongst others.
ZPGM Catalyst Material Composition and Preparation
In some embodiments, the ZPGM catalyst materials include binary spinel oxide compositions, which are synthesized using conventional synthesis methodologies to produce spinel oxide powders. In these embodiments, the binary spinel oxide composition is implemented as copper (Cu)-manganese (Mn) spinel oxide compositions. Further to these embodiments, the Cu—Mn spinel oxide is produced using a general formulation CuXMn3-XO4 spinel in which X is a variable representing molar ratios within a range from about 0.01 to about 2.99. In an example, X takes a value of about 1.0 for a stoichiometric CuMn2O4 spinel oxide powder. In these embodiments, bulk powder of CuMn2O4 spinel is produced as described in U.S. patent application Ser. No. 13/891,617. Further to these embodiments, bulk powder Cu—Mn spinel is calcined at a plurality of temperatures within a range from about 600° C. to about 1000° C.
X-ray Diffraction Analysis for CuMn2O4 Spinel Phase Formation
In some embodiments, XRD spectrum 102 illustrates diffraction peaks of bulk powder Cu—Mn spinel. In these embodiments, a single phase CuMn2O4 spinel is produced, as illustrated by spectral lines 104. Further to these embodiments, no additional diffraction peaks or no secondary phase could be identified, and only CuMn2O4 spinel oxide is observed after calcination step at suitable temperatures.
In
Redox Behavior of Cu—Mn Spinel Oxide
In some embodiments, the Cu—Mn spinel oxide powder is subjected to a redox reaction to determine the phase stability of the aforementioned Cu—Mn binary spinel oxide after the redox reaction.
Reversibility and Stability Analysis of CuMn2O4 Spinel After Redox Condition
In some embodiments and referring to full reduction reaction process 202, points 204 and 206 illustrate a nitrogen (N2) feeding gas, at an initial temperature of about 100° C., into the flow reactor until the reactor temperature, increased at a ramping rate of 10° C./min, reaches about 600° C. at point 206. In these embodiments, isothermal reduction reaction 208 illustrates, starting at point 206, the reducing feed gas having about 0.5% CO at an isothermal temperature of about 600° C. for about 2 hours, at point 210. Further to these embodiments, points 210 and 212 illustrate the beginning and ending of a cooling step wherein the flow reactor is cooled from about 600° C. to about 100° C. while continuously purging N2 gas into the reactor to retain the reduction state of the Cu—Mn spinet oxide powder. Still further to these embodiments, the Cu—Mn spinel oxide powder after complete reduction is characterized by means of an XRD analysis to detect the phase changes as a result of full reduction condition process.
In other embodiments, reduction-oxidation reaction process 214 is carried out, after the full reduction reaction process 202 described above, at point 210, isothermal oxidation reaction 216 illustrates feeding of an oxidation gas at isothermal condition having about 0.5% O2 at about 600° C. for about 2 hours, until point 218. In these embodiments, points 218 and 220 illustrate the initial and final of a cooling step wherein the flow reactor is cooled from about 600° C. to about 100° C. while purging inner N2 gas into the reactor to complete the reduction-oxidation condition process of the Cu—Mn spinel oxide powder. Further to these embodiments, the Cu—Mn spinel oxide powder is characterized by means of an XRD analysis to detect the phases formed as a result of the complete reduction-oxidation cycle.
In some embodiments, XRD spectrum 302 illustrates diffraction peaks products formed after full reduction of a Cu—Mn spinel oxide powder. In these embodiments, spectral lines 304 illustrates a phase of Cu metal produced after full reduction of the Cu—Mn spinel oxide powder. Further to these embodiments, spectral lines 306 illustrates a separate phase of MnO produced after full reduction of the Cu—Mn spinel oxide powder.
In some embodiments and referring to
In some embodiments, XRD spectrum 402 illustrates diffraction peaks of spinel phases produced after reduction-oxidation of a Cu—Mn spinel oxide powder. In these embodiments and after the reduction-oxidation condition process, the pure CuMn2O4 spinel oxide phase is retained, as illustrated by spectral lines 104, which are the same spectral lines of the pure Cu—Mn spinel oxide powder before reduction, as illustrated by XRD spectrum 102. Further to these embodiments, the probing of the CuMn2O4 spinel oxide powder under reduction-oxidation condition process confirms that Cu—Mn spinel oxide powder is full reversible after reduction-oxidation reactions.
In some embodiments and referring to
In some embodiments, H2-TPR testing is performed employing a reducing gas mixture of about 10% H2 diluted in argon (Ar). In these embodiments, the Cu—Mn spinel oxide powder samples at various stages of redox reaction (e.g., fresh, after full reduction reaction and after reduction-oxidation reaction cycle) is heated up at a temperature programmed ramp of 10° C./min up to a temperature of about 950° C., with a dwell time of about 3 minutes. Further to these embodiments, the detailed reduction reaction and redox reaction conditions are described in
In some embodiments, TPR spectrum 502 confirms that fresh Cu—Mn spinel oxide powder exhibits full reduction of the spinel oxide to Cu metal and MnO at a temperature of about 229° C. during H2-TPR testing. In these embodiments, TPR spectrum 504 confirms that, at the TPR of the full reduced spinel oxide powder, no reduction peak is observed during H2-TPR testing. Further to these embodiments, TPR spectrum 506 confirms that spinel after reduction-oxidation exhibits full reduction of the spinel oxide to Cu metal and MnO at a temperature of about 248° C. that is substantially similar to fresh Cu—Mn spinel illustrated in TPR spectrum 502.
In some embodiments, the integration of the area under the associated curve provides the total hydrogen consumption (mL/g spinel) that occurs during H2-TPR testing. In these embodiments, H2 consumption of TPR spectrum 502 is about 141.9 mL/g, for TPR spectrum 504 is about 7.1 mL/g, and for TPR spectrum 506 is about 149.1 mL/g. Further to these embodiments, the H2 consumption of fresh spinel and spinel after redox reaction exhibit very close numbers, which suggests that the Cu—Mn spinel structure is reversible to redox reactions.
In some embodiments, reversibility curves 602 and 604 illustrate that Cu2+ cations are reduced to Cu1+ cations and are then further re-oxidized back to Cu2+ cations. In these embodiments, in a fresh Cu—Mn spinel the Cu2+ concentration is higher than the Cu1+ concentration, therefore majority of Cu cations in spinel oxide is in form of Cu2+. Further to these embodiments and after full reduction reaction, the Cu1+ concentration is higher than the Cu2+ concentration, thereby indicating that majority of the Cu cations are reduced to Cu1+. Still further to these embodiments and after re-oxidation (complete redox cycle) of the spinel oxide powder, the Cu—Mn spinel oxide powder exhibits again a higher concentration of Cu2+ than Cu1+ concentration, thereby indicating re-oxidation of Cu1+ to Cu2+. In these embodiments, the oxidation state of Cu within the Cu—Mn spinel oxide powder resulting from the XPS analysis confirms that the Cu—Mn spinel exhibits a reversible oxidation state property.
In summary, based on the XRD, TPR, and XPS analyses, the Cu—Mn spinel oxide powder decomposes to Cu metal and MnO during full reduction cycle and retains its spinel structure and property after re-oxidation (redox cycle). Further, the consumption of H2 during the H2-TPR testing of the Cu—Mn spinel oxide powder confirms the reversible redox property of the Cu—Mn spinel after the reduction-oxidation cycle. Still further, the reversible redox property of the Cu—Mn spinel oxide powder is confirmed by the reproduction of Cu2+ cations resulting from the XPS analysis after the reduction-oxidation condition process. The XRD, TPR, and XPS analyses verify the significant oxidation-reduction stability of the Cu—Mn spinel oxide. As such, the Cu—Mn spinel oxide, free of PGM and rare-earth metals, can enable catalyst materials in bulk powder format for the development of a plurality of TWC systems and other catalyst applications.
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.
This application claims priority to U.S. Provisional Application Ser. No. 62/175,956, filed Jun. 15, 2015, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62175956 | Jun 2015 | US |
