This disclosure relates generally to catalytic converters and, more particularly to catalytic converters which are free of any platinum group metals.
Emission standards for unburned contaminants, such as hydrocarbons, carbon monoxide and nitrogen oxide, continues to become more stringent. In order to meet such standards, Diesel oxidation catalysts, lean NOx traps and Continues regenerable traps are used in the exhaust gas lines of internal combustion engines. These catalysts promote the oxidation of unburned hydrocarbons and carbon monoxide as well as the oxidation of nitrogen oxides in the exhaust gas stream to reduce the engine generated pollutants. oxidation of NO to NO2 may be used for removal of carbon soot in continues regenerable trap. One of the major limitations of current catalysts is that the Platinum Group Metals (PGM) used in their fabrication have very high demand and increasing prices.
Therefore, there is a continuing need to provide cost effective catalyst systems that provide sufficient conversion so that HC, NOx, and CO emission standards can be satisfied.
Zero platinum group metals (ZPGM) catalyst systems are disclosed.
ZPGM catalyst may be formed by using a perovskite structure having the general formula ABO3 where components “A” and “B” may be any suitable non-platinum group metals. Materials suitable for use as catalyst include Yttrium, (Y), Lanthanum (La), Silver (Ag), Manganese (Mn) and suitable combinations thereof.
ZPGM catalyst may also be formed by partially substituting element “A” of the structure with suitable non-platinum group metal in order to form a structure having the general formula A1-xMxB2O3.
ZPGM catalyst may also be formed by using a mullite structure having the general formula of AB2O5 where components “A” and “B” may be any suitable non-platinum group metals. Materials suitable for use as catalyst include Yttrium, (Y), Lanthanum (La), Silver (Ag), Manganese (Mn) and suitable combinations thereof.
ZPGM catalyst may also be formed by partially substituting element “A” of the structure with suitable non-platinum group metal in order to form a structure having the general formula A1-xMxB2O5.
Suitable known in the art chemical techniques, deposition methods and treatment systems may be employed in order to form the disclosed ZPGM catalyst.
The present disclosure also pertains to a method of making a catalyst powder sample by precipitation of ZPGM catalyst on support materials.
Support materials of use in catalysts containing one or more of the aforementioned combinations may include ZrO2, doped ZrO2 with Lanthanid group metals, alumina and doped alumina, TiO2 and doped TiO2, Nb2O5, and Nb2O5-ZrO2, or a combinations thereof.
ZPGM catalyst systems may oxidize carbon monoxide, hydrocarbons and nitrogen oxides that may be included in diesel exhaust gases.
ZPGM catalyst systems may be used for NOx storage application.
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.
“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.
“T50” refers to the temperature at which 50% of a material is converted.
“Oxidation Catalyst” refers to a catalyst suitable for use in converting at least hydrocarbons and carbon monoxide.
“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.
Various example embodiments of the present disclosure are described more fully with reference to the accompanying drawings in which some example embodiments of the present disclosure are shown. Illustrative embodiments of the present disclosure are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present disclosure. This disclosure however, may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.
A catalyst in conjunction with a sufficiently lean exhaust (containing excess oxygen) may result in the oxidation of residual HC and CO to carbon dioxide (CO2) and water (H2O), where equations (1) and (2) take place.
2CO+O2→2CO2 (1)
2CmHn+(2m+/2n)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+2Oads (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 Yttrium (Y), Lanthanum (La), Manganese (Mn), Silver (Ag) and combinations thereof. Catalysts containing the aforementioned metals may include any suitable Carrier Material Oxides, including alumina and doped alumina, TiO2 and doped TiO2, ZrO2, doped ZrO2 with Lanthanid group metals, Nb2O5, Nb2O5-Zr02, Cerium Oxides, tin oxide, silicon dioxide, zeolite, and combinations thereof. Catalysts containing the aforementioned metals and Carrier Material Oxides 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.
According to an embodiment, ZPGM catalyst may include a perovskite structure having the general formula ABO3 or related structures resulting from the partial substitution of the A site. Partial substitution of the A site with M element will yield the general formula A1-xMxBO3. “A” may include, Yttrium, lanthanum, strontium, or mixtures thereof. “B” may include a single transition metal, including manganese, cobalt, chromium, or mixture thereof. M may include silver, iron, Cerium, niobium or mixtures thereof; and “x” may take values between 0 and 1. The perovskite or related structure may be present in about 1% to about 30% by weight.
For example, components created using a perovskite structure may be YMnO3 or LaMnO3, which follows the general formula ABO3. The “A” component may be partially substituted with another components such as, silver to form Y1-xAgxMnO3, which follows the formula A1-xMxBO3.
In another embodiment, ZPGM catalyst may include a Mullite-like structure having the general formula AB2O5 or related structures resulting from the partial substitution of the A site. Partial substitution of the A site with M element will yield the general formula A1-xMxB2O5. “A” may include, Yttrium, lanthanum, strontium, or mixtures thereof. “B” may include a single transition metal, including manganese, cobalt, chromium, or mixture thereof. M may include silver, iron, Cerium, niobium or mixtures thereof; and “x” may take values between 0 and 1.
For example, components created using a mullite-like structure may be YMn2O5 or LaMn2O5, which follow the general formula AB2O5. The “A” component may be partially substituted with another components such as silver to form Y1-xAgxMn2O5, which follows the general formula A1MxB2O5.
The co-precipitation technique may also be used for preparation of a mullite powder sample of formula A1-xMxB2O5on a zirconium oxide 108 as support material using a yttrium nitrate solution 102, a Manganese Nitrate Solution 104 and a Silver nitrate solution 106. In an embodiment, yttrium nitrate may be substituted by lanthanum nitrate. However, the Yttrium (or lanthanum) may have loading of 1 to 20 percentage by weight, while silver may have loading of 1 to 20 percentage by weight and manganese may have a loading of 1 to 30 percentage by weight. Appropriate amount of nitrate solution of all metal components may be added to a stabilizer solution. Some examples of compounds that can be used as stabilizer solutions may include polyethylene glycol, polyvinyl alcohol, poly(N-vinyl-2pyrrolidone)(PVP), polyacrylonitrile, polyacrylic acid, multilayer polyelectrolyte films, poly-siloxane, oligosaccharides, poly(4-vinylpyridine), poly(N,Ndialkylcarbodiimide), chitosan, hyper-branched aromatic polyamides and other suitable polymers. The weight ratio of metals to stabilizer may be varied from 0.5 to 2. The small amount of octanol solution may be used as de-foaming agent. The stabilized metal solution may then be precipited on zirconium oxide support by using ammonium hydroxide, tetraethyl ammonium hydroxide, other tetralkyl ammonium salts, ammonium acetate, ammonium citrate, or other suitable compounds. The precipitated slurry may then be aged for about 2 hours to about 4 hours at room temperature and PH between 8.0 and 10.0. The slurry may then be filtered and washed 122 using any conventional methods known in the art. The precipitated cake 124 may be dried overnight 126 at a temperature about 120° C. and may then be calcined 128 for about 4 hours at a temperature between 500° C. and 800 C, preferably 750° C. to produce (A1-xAgx)Mn2O5 130 powder supported on zirconium oxide, where A may be yttrium or lanthanum, and x=0 to 0.5.
In example #1, a perovskite powder sample of (Y1-xAgx)MnO3 where x=0.2 is prepared and tested under a simulated DOC condition. The feed stream may include 100 ppm NO, 1500 ppm CO, 430 pm C3H6 as feed hydrocarbon, 4% CO2, 4% H20 and 14% O2.
The light-off test shows that T50 for CO may be at about 232° C., T50 for HC may be at about 278° C. and T50 for NO may be at about 287° C. The NO conversion may be related to the oxidation of NO to NO2. NH3 or N20 were not formed under this exhaust condition. The decreasing of NO conversion at temperature above 320° C. may be related to desorption of NO stored initially by catalyst.
In
In example #2, A mullite powder samples of (La1-xAgx)Mn2O5 where x=0.5 may be prepared and tested under a simulated DOC condition. The feed stream may include 100 ppm NO, 1500 ppm CO, 430 pm C3H6 as feed hydrocarbon, 4% CO2, 4% H2O and 14% O2.
Despite the perovskite powder of example#1, the mullite powder sample of example#2 may not be active in oxidation of NO.