Patent Application
20180290128
This disclosure relates generally to catalyst materials for diesel oxidation catalyst (DOC) systems, and more particularly, to pseudo-brookite catalyst materials having improved light-off (LO) performance and catalytic activity.
Diesel engines offer superior fuel efficiency. However, one of the technical obstacles to the broad implementation of diesel engines is the requirement for an additional lean nitrogen oxide (NOX) exhaust component within the overall diesel exhaust system. Conventional lean NOX exhaust components are expensive to manufacture and are key contributors to the premium pricing associated with diesel engine equipped vehicles. Unlike a conventional gasoline engine exhaust, in which equal amounts of oxidants (O2 and NOX) and reductants (CO, H2, and hydrocarbons) are available, diesel engine exhaust contains excessive O2 due to combustion occurring at much higher air-to-fuel ratios (>20). This oxygen-rich environment makes the removal of NOX much more difficult.
Conventional diesel exhaust systems employ diesel oxidation catalyst (DOC) technology and are referred to as diesel oxidation catalyst (DOC) systems. Typically, DOC 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.
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 DOC system exhibiting catalytic properties substantially similar to or better than the catalytic properties exhibited by DOC systems employing PGM catalyst materials.
The present disclosure describes Zero-PGM (ZPGM) catalyst materials for use in diesel oxidation catalyst (DOC) applications which include pseudo-brookite oxides expressed with a general formula of AB2O5, where both A and B sites are implemented as cations and the A and B sites can be interchangeable. Example materials that are suitable to form pseudo-brookite catalysts include, but are not limited to, silver (Ag), manganese (Mn), yttrium (Y), lanthanum (La), cerium (Ce), iron (Fe), praseodymium (Pr), neodymium (Nd), strontium (Sr), cadmium (Cd), cobalt (Co), scandium (Sc), copper (Cu), niobium (Nb), and tungsten (W). In some embodiments, the ZPGM pseudo-brookite catalyst materials, such as, YMn2O5 pseudo-brookite bulk powders, are produced by employing conventional synthesis methodologies.
In other embodiments, the A-site and/or B-site cations can be partially doped with base metals. In these embodiments, either A-site and/or B-site cations within the AB2O5 pseudo-brookite catalysts can be partially doped with a base metal including, but are not limited to, Sr, Ce, Fe, Co, Ni, and Ti, among others.
In an example, the A-site cation is substituted with Sr or Ce yielding pseudo-brookite compositions expressed with a general formula of (Y1-xAx)Mn2O5, where x=0.01 to 0.5. In another example, the B-site cation is substituted with Fe, Co, Ni, or Ti yielding pseudo-brookite compositions expressed with general formula of Y(Mn2-xBx)O5, where x=0.01 to 0.5.
In some embodiments, X-ray diffraction (XRD) analyses are used to analyze/measure the pseudo-brookite phase formation and the thermal stability of the different doped pseudo-brookite compositions. In these embodiments, the XRD data is then analyzed to determine if the structure of the various doped pseudo-brookite compositions remain stable. If the structure of any of the doped pseudo-brookite compositions becomes unstable, new phases will form within the ZPGM catalyst material. Further to these embodiments, different calcination temperatures will result in different doped pseudo-brookite phases.
In some embodiments, the XRD analyses indicate the disclosed doped pseudo-brookite catalysts are stable when calcined within a temperature range from about 800° C. to about 1000° C. using nitrate combustion methodology.
In some embodiments, the disclosed doped pseudo-brookite compositions are subjected to a DOC standard light-off (LO) test methodology to assess/verify catalyst activity. In these embodiments, DOC LO tests are performed by employing a flow reactor, at a space velocity (SV) of about 54,000 h−1. Further to these embodiments, the disclosed doped pseudo-brookite compositions exhibit higher NO oxidation catalyst activities when compared to bulk powder pseudo-brookite, thereby indicating improved thermal stability when using a dopant in an A-site cation or in a B-site cation within a pseudo-brookite catalyst.
In some embodiments, the disclosed doped pseudo-brookite compositions including a dopant in an A-site cation exhibit higher NO oxidation activity when compared to the disclosed doped pseudo-brookite compositions including a dopant in a B-site cation. In these embodiments, the disclosed doped pseudo-brookite catalysts can provide significantly improved ZPGM catalyst materials within DOC applications.
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 placed 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:
“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.
“Conversion” refers to the chemical alteration of at least one material into one or more other materials.
“Diesel oxidation catalyst (DOC)” refers to a device that utilizes a chemical process in order to break down pollutants within the exhaust stream of a diesel engine, turning them into less harmful components.
“Pseudobrookite” refers to a ZPGM catalyst, having AB2O5 structure of material which may be formed by partially substituting element “A” and “B” base metals with suitable non-platinum group metals.
“T50” refers to the temperature at which 50% of a material is converted.
“X-ray diffraction (XRD) analysis” refers to a rapid analytical technique for verifying crystalline material structures, including atomic arrangement, crystalline size, and imperfections in order to identify unknown crystalline materials (e.g., minerals, inorganic compounds).
“Zero platinum group metal (ZPGM) catalyst” refers to a catalyst completely or substantially free of platinum group metals.
The present disclosure describes Zero-PGM (ZPGM) catalyst materials with pseudo-brookite catalysts for use in diesel oxidation catalyst (DOC) applications. In some embodiments, pseudo-brookite catalysts are partially doped with suitable base metals in order to improve NO oxidation as well as to reduce DOC light off (LO) temperatures. In these embodiments, pseudo-brookite compositions include yttrium (Y) expressed with a general formula of YxMn2O5.
In other embodiments, the pseudo-brookite catalysts are expressed with a general formula of AB2O5, where both A and B sites are implemented as cations and the A and B sites can be interchangeable.
In these embodiments, A-site or B-site cations within the pseudo-brookite catalysts are substituted with a base metal including, but are not limited to, Sr, Ce, Fe, Co, Ni, and Ti, among others.
Further to these embodiments, the A-site cation is substituted with Sr or Ce yielding pseudo-brookite compositions expressed with a general formula of (Y1-xAx)Mn2O5, where x=0.01 to 0.5. Example formulas of the doped pseudo-brookite compositions are described in Table 1.
In further embodiments, the B-site cation is substituted with Fe, Co, Ni, or Ti yielding pseudo-brookite compositions expressed with general formula of Y(Mn2-xBx)O5 where x=0.01 to 0.5. Example formulas of the doped-pseudo-brookite compositions are described in Table 2.
Disclosed doped pseudo-brookite compositions are employed in the production of catalyst coatings for ZPGM catalyst systems.
ZPGM Pseudo-Brookite Material Composition and Preparation
In some embodiments, the disclosed ZPGM pseudo-brookite compositions are produced using a nitrate combustion methodology. In these embodiments, the preparation begins by mixing the appropriate amount of Y nitrate solution, Mn nitrate solution and water to produce a Y-Mn solution at an appropriate molar ratio (Y:Mn) of about 1:2 for an YMn2O5 pseudo-brookite catalyst. Further to these embodiments, the Y-Mn solution is then fired from about 300° C. to about 400° C. for nitrate combustion. In these embodiments, the firing produces a Y-Mn solid material. Further to these embodiments, the Y-Mn solid material is ground and then calcined at a range of temperatures from about 800° C. to about 1000° C., for about 5 hours. In these embodiments, the grinding and calcination produces a Y-Mn powder. The calcined Y-Mn powder is then re-ground to fine grain powder yielding an YMn2O5 pseudo-brookite catalyst.
In an example, the A-site doped pseudo-brookite compositions include a formula of Y0.9A0.1Mn2O5, where A=Ce or Sr. In this example, a nitrate combustion methodology as described above is employed. In some embodiments, the nitrate combustion methodology begins when the appropriate amount of Y nitrate solution, Ce nitrate (or Sr nitrate), and Mn nitrate solution are mixed with water to produce a Y-A-Mn solution at an appropriate molar ratio (Y:A:Mn) of about 0.9:0.1:2. In these embodiments, the Y-Mn solution is then fired from about 300° C. to about 400° C. for nitrate combustion. Further to these embodiments, the firing produces a Y-Mn solid material. In these embodiments, the Y-Mn solid material is ground and calcined at a range of temperatures from about 800° C. to about 1000° C., for about 5 hours. Further to these embodiments, the grinding and calcination produces a Y-Mn powder. The calcined Y-Mn powder is then re-ground to fine grain powder of doped pseudo-brookite compositions having a formula of Y0.9Ce0.1Mn2O5 or Y0.9Sr0.1Mn2O5.
In another example, the B-site doped pseudo-brookite compositions include formula of YMn1.9B0.1O5, where B═Fe, Co Ni, or Ti. In this example, a nitrate combustion methodology as described above is employed. In some embodiments, the nitrate combustion methodology begins when the appropriate amount of nitrate solution of Y, Mn, and a doped element, such as Fe, Co Ni, or Ti are mixed in order to produce a Y-Mn-B solution at an appropriate molar ratio (Y:Mn:B) of about 1:1.9:0.1. In these embodiments, the Y-Mn solution is then fired from about 300° C. to about 400° C. for nitrate combustion. Further to these embodiments, the Y-Mn material is ground and calcined at a range of temperatures from about 800° C. to about 1000° C., for about 5 hours. In these embodiments, the grinding and calcination produces a Y-Mn powder. The calcined Y-Mn powder is then re-ground to fine grain powder of doped pseudo-brookite composition having a formula of YMn1.9Fe0.1O5, YMn1.9Co0.1O5, YMn1.9Ni0.1O5, or YMn1.9Ti0.5O5.
In order to determine the phase formation and thermal stability of the disclosed doped pseudo-brookite compositions, X-ray diffraction (XRD) analyses are performed.
X-Ray Diffraction Analysis
In some embodiments, X-ray diffraction (XRD) analyses are used to analyze/measure the pseudo-brookite phase formation and the thermal stability of the different doped pseudo-brookite compositions. In these embodiments, the XRD data is then analyzed to determine if the structure of the various doped YMn2O5 pseudo-brookite remains stable. If the structure of any of the doped YMn2O5 pseudo-brookite compositions becomes unstable, new phases will form within the ZPGM catalyst material. Further to these embodiments, different calcination temperatures will result in different doped YMn2O5 pseudo-brookite phases.
In some embodiments, XRD patterns are measured on a powder diffractometer using Cu Ka radiation in the 2-theta range of about 15°-100° with a step size of about 0.02° and a dwell time of about 1 second. In these embodiments, the tube voltage and current are set to about 40 kV and about 30 mA, respectively. The resulting diffraction patterns are analyzed using the International Center for Diffraction Data (ICDD) database to identify phase formation. Examples of powder diffractometer include the MiniFlex™ powder diffractometer available from Rigaku® of Woodlands, Tex., USA.
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In some embodiments, the disclosed doped pseudo-brookite compositions are subjected to a DOC standard light-off (LO) test methodology to assess/verify catalyst activity.
DOC Standard Light-Off Test
In some embodiments, the DOC standard light-off (LO) test methodology is applied to bulk powder YMn2O5 pseudo-brookite, A-site doped pseudo-brookite compositions, and B-site doped pseudo-brookite compositions. In these embodiments, the LO test is performed employing a flow reactor in which temperature is increased from about 75° C. to about 400° C. at a rate of about 40° C./min to measure the CO, HC and NO conversions. Further to these embodiments, a gas feed employed for the test includes a composition of about 100 ppm of NOX, 1,500 ppm of CO, about 4% of CO2, about 4% of H2O, about 14% of O2, and about 430 ppm of C3H6, and a space velocity (SV) of about 54,000 h−1 or about 100,000 h−1. In these embodiments, during DOC LO test, neither N2O nor NH3 are formed.
In some embodiments, DOC LO tests are performed in order to determine the effect of the use of a dopant in an A-site within a pseudo-brookite catalyst.
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In other embodiments, DOC LO tests are performed in order to determine the effect of the use of a dopant in a B-site within a pseudo-brookite catalyst.
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In these embodiments, the bulk powder YMn2O5 pseudo-brookite exhibits high NO oxidation catalyst activity, which oxidizes NO up to 80% at a temperature of about 350° C. Further to these embodiments, Ni-doped pseudo-brookite compositions, Fe-doped pseudo-brookite compositions, and Co-doped pseudo-brookite compositions exhibit high NO oxidation catalyst activities. Ni-doped pseudo-brookite compositions oxidize NO at up to 73% at a temperature of about 350° C., Fe-doped pseudo-brookite compositions oxidize NO at up to 72% at a temperature of about 350° C., and Co-doped pseudo-brookite compositions oxidize NO at up to 75% at a temperature of about 350° C. In these embodiments, Ti-doped pseudo-brookite compositions do not exhibit NO oxidation activity. The absence of NO oxidation activity indicates the Ti dopant affects the activity of pseudo-brookite catalysts. This lack of activity is due to the absence of a pseudo-brookite phase at a calcination temperature of about 800° C.
In some embodiments, bulk powder YMn2O5 pseudo-brookite exhibits higher NO oxidation catalyst activities when compared to the disclosed doped pseudo-brookite compositions. In these embodiments, B-site doped pseudo-brookites do not increase NO oxidation of pseudo-brookite compositions. Further to these embodiments, Ni-doped pseudo-brookite exhibits slight improvement in LO temperature within the temperature range from about 265° C. to about 325° C. which allows improved NO conversion when compared to bulk powder pseudo-brookites.
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In some embodiments, DOC LO tests 400, 500, 600, and 700 indicate both the A-site partially substituted doped pseudo-brookite catalysts and the B-site partially substituted pseudo-brookite catalysts exhibit improvement of NO conversions and NO oxidation at lower LO temperatures. Such improvement is especially confirmed in A-site doped pseudo-brookite compositions.
In some embodiments, when calcination occurred at about 800° C. A-site substituted doped pseudo-brookite catalysts, such as Ce-doped pseudo-brookite compositions and Sr-doped pseudo-brookite compositions, exhibited higher NO conversion catalytic activities as compared to B-site substituted doped pseudo-brookite catalysts. In other embodiments, when calcination occurred at about 1000° C., both the A-site doped pseudo-brookite catalysts and the B-site doped pseudo-brookite catalysts exhibited higher NO conversion catalyst activities as compared to bulk powder YMn2O5 pseudo-brookites. Therefore, the disclosed doped pseudo-brookite catalysts can provide significantly improved ZPGM catalyst materials within DOC applications.
While various aspects and embodiments have been disclosed, other aspects and embodiments may be contemplated. The various aspects and embodiments disclosed here are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/055882 | 9/30/2016 | WO | 00 |
