Patent Application
20210229078
This disclosure relates generally to diesel oxidation catalysts for the treatment of exhaust gas emissions from diesel engines, and more particularly, to sulfur-resistant synergized platinum group metals (SPGM) catalyst systems with low platinum group metals (PGM) loading, according to a catalyst structure including at least two distinct layers.
Diesel oxidation catalysts (DOCs) include PGM deposited on a metal support oxide. DOCs are used in treating diesel engine exhaust to reduce nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) gaseous pollutants. The DOCs reduce the gaseous pollutants by oxidizing them.
Conventional catalytic converter manufacturers utilize a single PGM catalyst within their diesel exhaust systems. Since a mixture of platinum (Pt) and palladium (Pd) catalysts within the PGM portion of a catalytic system offer improved stability, the catalytic converter manufacturing industry has moved to manufacturing Pt/Pd-based DOCs.
In diesel engines, the sulfur present in the exhaust gas emissions may cause significant catalyst deactivation, even at very low concentrations due to the formation of strong metal-sulfur bonds. The strong metal-sulfur bonds are created when sulfur chemisorbs onto and reacts with the active catalyst sites of the metal. The stable metal-adsorbate bonds can produce non-selective side reactions which modify the surface chemistry.
Current attempts to solve this problem have led manufacturers to produce catalyst systems with improved sulfur resistance. Typically, these catalyst systems are manufactured by using high loadings of PGM. Unfortunately, utilizing high loadings of PGM within catalyst systems increases the cost of the catalyst systems because PGMs are expensive. PGMs are expensive because they are scarce, have a small market circulation volume, and exhibit constant fluctuations in price and constant risk to stable supply, amongst other issues.
Accordingly, as stricter regulatory standards are continuously adopted worldwide to control emissions, there is an increasing need to develop DOCs with improved properties for enhanced catalytic efficiency and sulfur poisoning stability.
The present disclosure describes synergized PGM (SPGM) catalysts with low PGM loading for diesel oxidation catalyst (DOC) applications.
It is an object of the present disclosure to describe embodiments of SPGM catalyst systems having a high catalytic activity and resistance to sulfur poisoning. In these embodiments, a catalytic layer of 5 g/ft1 of PGM active components is synergized with Zero-PGM (ZPGM) catalyst compositions including a pseudobrookite structure in a separate catalytic layer. In some embodiments, the disclosed 2-layer SPGM catalysts can provide catalyst systems exhibiting high oxidation activity as well as sulfur resistance.
According to some embodiments in the present disclosure, the disclosed SPGM DOC systems can be configured to include a washcoat (WC) layer of ZPGM material compositions deposited on a plurality of support oxides of selected base metal loadings. In these embodiments, the WC layer can be formed using a YMn2O5 pseudobrookite structure deposited on doped ZrO2 support oxide.
In further embodiments, a second layer of the disclosed SPGM DOC system is configured as an overcoat (OC) layer. The OC layer includes a plurality of low PGM material compositions on support oxides. In these embodiments, the OC layer can be formed using an alumina-type support oxide which is metalized using a low loading PGM solution, such as a platinum (Pt) and palladium (Pd) solution, to form a alumina-type support oxide/low loading PGM slurry. The alumina-type support oxide/low loading PGM slurry is then deposited onto the WC layer, and subsequently calcined.
In other embodiments, the disclosed SPGM catalysts for DOC application are subjected to a DOC/sulfur test methodology to assess/verify significant NO oxidation activity and resistance to sulfur poisoning. In these embodiments, DOC light-off tests are performed to confirm synergistic effects of ZPGM catalytically active materials in the layered SPGM configuration. Further to these embodiments, the sulfur resistance and NO oxidation of disclosed SPGM catalyst samples are confirmed under a variety of DOC conditions at space velocity (SV) of about 54,000 h−1, according to a plurality of steps in the test methodology.
Still further to these embodiments, the combined catalytic properties of the layers in SPGM catalyst systems can provide more efficiency in NO oxidation and more stability against sulfur poisoning.
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 here 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:
“Catalyst” refers to one or more materials that may be of use in the conversion of one or more other materials.
“washcoat” refers to at least one coating including at least one oxide solid that may be deposited on a substrate.
“Substrate” refers to any material of any shape or configuration that yields a sufficient surface area for depositing a washcoat and/or overcoat.
“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 NOR, CO, and hydrocarbons.
“Zero PGM (ZPGM) catalyst” refers to a catalyst completely or substantially free of platinum group metals.
“Synergized PGM (SPGM) catalyst” refers to a PGM catalyst system which is synergized by a ZPGM compound under different configuration.
“Catalyst system” refers to any system including a catalyst, such as, a PGM catalyst or a ZPGM catalyst of at least two layers comprising a substrate, a washcoat and/or an overcoat.
“Diesel oxidation catalyst (DOC)” refers to a device which utilizes a chemical process in order to break down pollutants from a diesel engine or lean burn gasoline engine in the exhaust stream, turning them into less harmful components.
“Pseudobrookite” refers to a ZPGM catalyst, having an AB2O5 structure of material which may be formed by partially substituting element “A” and “B” base metals with suitable non-platinum group metals.
“Incipient wetness (IW)” refers to the process of adding solution of catalytic material to a dry support oxide powder until all pore volume of support oxide is filled out with solution and mixture goes slightly near saturation point.
“Metallizing” refers to the process of coating metal on the surface of metallic or non-metallic objects.
“Conversion” refers to the chemical alteration of at least one material into one or more other materials.
“Poisoning or catalyst poisoning” refers to the inactivation of a catalyst by virtue of its exposure to lead, phosphorus, or sulfur in an engine exhaust.
The present disclosure is directed to a diesel oxidation catalyst (DOC) system configuration. The DOC configuration includes a 2-layer catalyst having a washcoat (WC) layer of Zero-PGM (ZPGM) catalyst and an overcoat (OC) layer. The overcoat (OC) layer is a low loading PGM catalyst. This 2-layer catalyst improves the conversion rate of NOx, HC, and CO contained with the exhaust gases emitted from the diesel engine.
In some embodiments, SPGM catalyst samples are implemented including WC layer 102 that comprises a pseudobrookite oxide structure of AB2O5 deposited on a support oxide. In these embodiments, OC layer 104 is implemented including one or more PGM material compositions deposited on support oxide.
Example materials suitable to form pseudobrookites with the general formula of AB2O5 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), and niobium (Nb). Suitable support oxides that can be used in WC and OC layers include zirconia (ZrO2), any doped ZrO2 including doping such as lanthanide group metals, niobium pentoxide, niobium-zirconia, alumina-type support oxide, titanium dioxide, tin oxide, zeolite, silicon dioxide, or mixtures thereof, amongst others. PGM material compositions include platinum, palladium, ruthenium, iridium, and rhodium, either by themselves, or combinations thereof of different loadings.
In an example, a ZPGM catalyst used in a WC layer of a SPGM catalyst structure includes YMn2O pseudobrookite composition deposited on a doped ZrO2 support oxide.
In some embodiments, preparation of the WC layer begins with preparation of a Y—Mn solution. In these embodiments, preparation of the Y—Mn solution includes mixing Y nitrate solution with Mn nitrate solution and water to produce a solution at the appropriate molar ratio. In an example, a Y:Mn molar ratio of 1:2 is used.
In other embodiments, the Y—Mn nitrate solution is added to doped ZrO2 powder using a conventional incipient wetness (IW) technique forming a Y—Mn/doped ZrO2 slurry. In these embodiments, the Y—Mn/doped ZrO2 slurry is dried and calcined at about 750° C. for about 5 hours. Further to these embodiments, the calcined Y—Mn/doped ZrO2 powder is then ground to fine grain for producing, for example, YMn2O5/doped ZrO2 powder. In an example, YMn2O5/doped ZrO2 powder is subsequently milled with water to produce a slurry. In the example, the slurry is then coated onto a suitable substrate for calcination at about 750° C. for about 5 hours. A substrate coated and calcined in this matter forms a WC layer.
In some embodiments, the PGM catalyst used in the OC layer includes a PGM solution of platinum (Pt) and palladium (Pd) nitrates deposited on an alumina-type support oxide.
In an example, the preparation of the OC layer includes milling of doped Al2O3 support oxide. In this example, the milled doped Al2O3 support oxide is mixed with water to form aqueous slurry. Further to this example, the doped Al2O3 support oxide slurry is metallized by a solution of Pt and Pd nitrates with a total loading of PGM within about 5 g/ft3, preferably about 4.5 g/ft3 of Pt and about 0.25 g/ft3 of Pd. Subsequently, the OC layer is deposited onto the WC layer and calcined at about 550° C. for about 4 hours.
DOC LO and Sulfation Test Methodology
In some embodiments, a DOC/sulfur test methodology can be applied to SPGM catalyst systems as described in
In
In some embodiments, DOC test methodology 200 begins with DOC LO test 210. The DOC LO test is performed employing a flow reactor with flowing DOC gas composition of about 100 ppm of NO, about 1,500 ppm of CO, about 4% of CO2, about 4% of H2O, about 14% of O2, and about 430 ppmC1 of mixed hydrocarbon, while temperature increases from about 100° C. to about 340° C., at SV of about 54,000 h−1. Subsequently, at about 340° C., isothermal soaking under DOC condition 220 is conducted for about one hour to stabilize catalyst performance at about 340° C. At the end of this time period, at point 230, testing under soaking at isothermal sulfated DOC condition 240 begins by adding a concentration of about 3 ppm of SO2 to the gas stream for about 4 hours. At the end of this time period, at point 250, the sulfation process is stopped when the amount of SO2 passed to catalyst is about 0.9 gS/L (grams of sulfur per liter) of substrate. Subsequently, the flowing gas stream is allowed to cool down to about 100° C., at point 260. After this point, DOC test methodology 200 continues by conducting another cycle of test steps including DOC LO test 210, isothermal soaking under DOC condition 220 for about one hour, and sulfated DOC condition 240, flowing about 3 ppm of SO2 for about 2 hours in the gas stream, until reaching a total SO2 passed to catalyst of about 1.3 gS/L of substrate at point 270, when sulfation of the gas stream is stopped. Finally, the catalyst activity of the SPGM catalyst sample is determined by another DOC LO and soaking after a total of about 6 hours of sulfation soaking NO conversion and sulfur resistance are compared at the end of the test for all the DOC conditions (e.g., before and after sulfation, in the test methodology).
In other embodiments, DOC test methodology 200 begins with DOC LO test 210, which is conducted employing a flow reactor with flowing DOC gas composition of about 100 ppm of NO, about 1,500 ppm of CO, about 4% of CO2, about 4% of H2O, about 14% of O2, and about 430 ppmC1 of mixed hydrocarbon, while temperature increases from about 100° C. to about 340° C., at SV of about 54,000 h−1. Subsequently, at about 340° C., isothermal soaking under DOC condition 220 is conducted for about one hour to stabilize catalyst performance at about 340° C. At the end of this time period, at point 230, testing under soaking at isothermal sulfated DOC condition 240 begins by adding a concentration of about 5.8 ppm of SO2 to the gas stream, for about 6 hours. At the end of this time period, at point 250, the sulfation process is stopped when the amount of SO2 passed to the catalyst is about 2.6 gS/L of substrate. Subsequently, the flowing gas stream is allowed to cool down to about 100° C., at point 260. DOC test methodology 200 continues by conducting another cycle of test steps including DOC LO test 210, isothermal soaking under DOC condition 220 for about one hour, and sulfated DOC condition 240, flowing about 5.8 ppm of SO2 for about 6 hours in the gas stream, until reaching a total SO2 passed to catalyst of about 5.2 gS/L of substrate at point 270, when sulfation of the gas stream is stopped. Finally, the catalyst activity of the SPGM catalyst sample is determined by another DOC LO and soaking after a total of about 12 hours of sulfation soaking. NO conversion and sulfur resistance are compared at the end of the test for all the DOC conditions (e.g., before and after sulfation, in the test methodology).
Catalyst Activity of SPGM System Before and After Sulfation Conditions
In
In
In
In
The test results of
Sulfur Resistance of SPGM Catalyst
In
In
In
The results achieved during testing of the SPGM catalyst samples in the present disclosure confirm that SPGM catalyst systems produced to include a layer of low amount of PGM catalyst material added to a layer of ZPGM catalyst material are capable of providing significant improvements in sulfur resistance. As observed in
The diesel oxidation properties of the disclosed 2-layer SPGM catalyst systems indicate that under lean conditions the chemical composition is more efficient as compared to conventional DOC systems.
While various aspects and embodiments have been disclosed, other aspects and embodiments can 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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14726807 | Jun 2015 | US |
| Child | 16841955 | US |
