Patent Application
20140302983
N/A
1. Technical Field
This disclosure relates generally to catalytic converters, and, more particularly, to materials of use in catalyst systems.
2. Background Information
Emissions standards seek the reduction of a variety of materials in exhaust gases, including unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO). In order to meet such standards, catalyst systems able to convert such materials present in the exhaust of any number of mechanisms are needed.
To this end, there is a continuing need to provide materials able to perform in a variety of environments, which may vary in a number ways, including oxygen content and the temperature of the gases undergoing treatment.
Materials suitable for use as catalyst include Niobium (Nb), Zirconium (Zr), and combinations thereof. Methods for preparing catalysts containing these materials may use Niobium Oxalate and/or Niobium Pentoxide as a niobium source.
Support materials of use in catalysts containing one or more of the aforementioned combinations may include Cerium Oxide, Alumina, Lanthanum doped alumina,Titanium Oxide, Zirconia, and Ceria/Zirconia (CZO).
Numerous other aspects, features and advantages 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 invention. In the figures, any reference numerals designate corresponding parts throughout different views.
Disclosed here are catalyst materials that may be of use in the conversion of exhaust gases, according to an embodiment.
The present disclosure is here described in detail with reference to embodiments illustrated in the drawings, which form a part hereof. In the drawings, which are not necessarily to scale or to proportion, similar symbols typically identify similar components, unless context dictates otherwise. 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 herein.
As used here, the following terms have the following definitions:
“Exhaust” refers to the discharge of gases, vapor, and fumes that may include hydrocarbons, nitrogen oxide, and/or carbon monoxide.
“R Value” refers to the number obtained by dividing the reducing potential by the oxidizing potential.
“Rich Exhaust” refers to exhaust with an R value above 1.
“Lean Exhaust” refers to exhaust with an R value below 1.
“Conversion” refers to the chemical alteration of at least one material into one or more other materials.
“Catalyst” refers to one or more materials that may be of use in the conversion of one or more other materials.
“Carrier Material Oxide (CMO)” refers to support materials used for providing a surface for at least one catalyst.
“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.
“Three Way Catalyst (TWC)” refers to a catalyst suitable for use in converting at least hydrocarbons, nitrogen oxide, and carbon monoxide.
“Oxidation Catalyst” refers to a catalyst suitable for use in converting at least hydrocarbons and carbon monoxide.
“Wash-coat” refers to at least one coating including at least one oxide solid that may be deposited on a substrate.
“Over-coat” refers to at least one coating that may be deposited on at least one wash-coat or impregnation layer.
“Zero Platinum Group (ZPGM) Catalyst” refers to a catalyst completely or substantially free of platinum group metals.
“Platinum Group Metals (PGMs)” refers to platinum, palladium, ruthenium, iridium, osmium, and rhodium.
A catalyst in conjunction with a sufficiently lean exhaust (containing excess oxygen) may result in the oxidation of residual HC and CO to small amounts of carbon dioxide (CO2) and water (H20), where equations (1) and (2) take place.
2CO+O2→2CO2 (1)
2CmHn+(2m+½n)O2→2mCO2+nH2O (2)
Although dissociation of NO into its elements may be thermodynamically favored, under practical lean conditions this may not occur. Active surfaces for NO dissociation include metallic surfaces, and dissociative adsorption of NO, equation (3), may be followed by a rapid desorption of N2, equation (4). However, oxygen atoms may remain strongly adsorbed on the catalyst surface, and soon coverage by oxygen may be complete, which may prevent further adsorption of NO, thus halting its dissociation. Effectively, the oxygen atoms under the prevailing conditions may be removed through a reaction with a reductant, for example with hydrogen, as illustrated in equation (5), or with CO as in equation (6), to provide an active surface for further NO dissociation.
2NO→2Nads+20ads (3)
Nads+Nads→N2 (4)
Oads+H2→H2O (5)
Oads+CO→CO2 (6)
Materials that may allow one or more of these conversions to take place may include ZPGM catalysts, including catalysts containing Niobium(Nb), Zirconium(Zr) and combinations thereof. Catalysts containing the aforementioned metals may include any suitable Carrier Material Oxides, including Cerium Oxides, Aluminum Oxides, Titanium Oxides, doped aluminum oxide, doped ceria, fluorite, zirconium oxide, doped zirconia, titanium oxide, tin oxide, silicon dioxide, zeolite, and combinations thereof. ZPGM Catalyst may include any number of suitable OSMs, including cerium oxide, zirconium oxide, lanthanum oxide, yttrium oxide, lanthanide oxides, actinide oxides, and combinations thereof. Catalysts containing the aforementioned metals, Carrier Material Oxides, and/or Oxygen Storage Materials may be suitable for use in conjunction with catalysts containing PGMs. Catalysts with the aforementioned qualities may be used in a washcoat or overcoat, in ways similar to those described in US 20100240525.
Catalysts containing Nb and Zr may promote the chemisorption of C3H6 by an acidic attack on the hydrocarbon double bond, as in equation (7)
CH2═CH—CH3+H+→(CH3-CH—CH3)+ (7)
Catalysts containing Nb and Zr may exhibit resistance to SO2 poisoning, may display enhanced oxidative properties, may display high permanent Brønsted acidity, may exhibit higher thermal stability, and/or may promote the formation of reaction intermediates at temperatures below 150° C.
Catalyst Preparation
Catalysts similar to those described above may be prepared by co-precipitation. Co-precipitation may include the preparation of a suitable metal salt solution, where precipitate may be formed by the addition of a suitable base, including but not limited to Tetraethyl Ammonium Hydrate, NH4OH, (NH4)2CO3, other tetraalkylammonium salts, ammonium acetate, and ammonium citrate. This precipitate may be formed over a slurry including at least one suitable carrier material oxide, where the slurry may include any number of additional suitable Carrier Material Oxides, and may include one or more suitable Oxygen Storage Materials. The slurry may then undergo filtering and may undergo washing, where the resulting material may be dried and may later be fired. The resulting catalyst may then be subjected to an aging process.
Metal salt solutions suitable for use in the co-precipitation process described above may include solutions of Niobium Pentoxide (Nb2O5) and Niobium Oxalate (NbC2O4) in any suitable solvent, including but not limited to Sulfuric Acid (H2SO4).
The catalyst may also be formed on a substrate, where the substrate may be of any suitable material, including cordierite. The washcoat may include one or more carrier material oxides and may also include one or more OSMs. Nb, Zr, and combinations thereof may be precipitated on said one or more carrier material oxides or combination of carrier material oxide and oxygen storage material, where the catalyst may be synthesized by any suitable chemical technique, including solid-state synthesis and co-precipitation. The milled catalyst and carrier material oxide may then be deposited on a substrate, forming a washcoat, where the washcoat may undergo one or more heat treatments.
XRD Analysis
Catalysts containing Nb and Zr include: Type 1 Catalysts, prepared from a NbC2O4 precursor and having a ZrO2:Nb2O5 molar ratio of about 6:1; Type 2 Catalysts, prepared from a Nb2O5 precursor and having a ZrO2:Nb2O5 molar ratio of about 6:1; Type 3 Catalysts, prepared from a NbC2O4 precursor and having a ZrO2:Nb2O5 molar ratio of about 1:6.
A Type 1 Catalyst is prepared from a Niobium Oxalate source such that the niobium content in the catalyst is 10-20 wt %, the ZrO2:NbO5 molar ratio is of about 6:1, and the Alumina:Ceria ratio is of about 60:40. The catalyst is prepared through co-precipitation using suitable base such as Tetraethyl Ammonium Hydrate, NH4OH, (NH4)2CO3, other tetraalkylammonium salts, ammonium acetate, or ammonium citrate. The pH was adjusted at neutral condition. The resulting precipitae cake was filtered, washed several times and dried overnight at 120° C. The powder was then grinded and fired at 700° C. for 4 hours. The resulting catalyst is found to have a BET surface area of 70.3 m2/g and has a behavior similar to Type 1 Catalyst 502.
A Type 2 Catalyst is prepared from a Niobium Pentoxide source such that the niobium content in the catalyst is 10-20 wt %, the ZrO2:NbO5 molar ratio is of about 6:1, and the Alumina:Ceria ratio is of about 60:40. The catalyst is prepared through co-precipitation using suitable base such as Tetraethyl Ammonium Hydrate, NH4OH, (NH4)2CO3, other tetraalkylammonium salts, ammonium acetate, or ammonium citrate. The pH was adjusted at neutral condition. The resulting precipitae cake was filtered, washed several times and dried overnight at 120° C. The powder was then grinded and fired at 700° C. for 4 hours. The resulting catalyst is found to have a BET surface area of 56.1 m2/g and has a behavior similar to Type 2 Catalyst 504.
A Type 3 Catalyst is prepared from a Niobium Oxalate source such that the niobium content in the catalyst is 10-20 wt %, the ZrO2:NbO5 molar ratio is of about 1:6, and the Alumina:Ceria ratio is of about 60:40. The catalyst is prepared through co-precipitation using suitable base such as Tetraethyl Ammonium Hydrate, NH4OH, (NH4)2CO3, other tetraalkylammonium salts, ammonium acetate, or ammonium citrate. The pH was adjusted at neutral condition. The resulting precipitae cake was filtered, washed several times and dried overnight at 120° C. The powder was then grinded and fired at 700° C. for 4 hours. The resulting catalyst is found to have a BET surface area of 62.9 m2/g and has a behavior similar to Type 3 Catalyst 506.
