Novel multi-regin catalyst for CNG engine exhaust gas treatment with improved ammonia leakage control

Abstract

This invention provides a catalytic article useful for treating exhaust gas emissions from compressed natural gas (CNG) engines. [Solution] A three-way catalytic converter article and its use in an exhaust system for a compressed natural gas engine are disclosed. A catalytic converter article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising: a base material having an axial length L and including an inlet end and an outlet end; a first catalytic region beginning at the outlet end and extending over less than the axial length L, comprising a first PGM component; and a second catalytic region beginning at the inlet end and comprising a second PGM component, wherein the first PGM component comprises palladium, platinum, or a combination thereof, and the second PGM component comprises rhodium.

Description

[Technical Field]

[0001] The present invention relates to a catalytic article useful for treating exhaust gas emissions from compressed natural gas (CNG) engines. [Background technology]

[0002] Compressed natural gas (CNG) is a single hydrocarbon, primarily methane, which results in much lower CO2 production per unit of energy, and CNG is used as a clean energy alternative to conventional gasoline and diesel fuels. In addition, CNG is also favored in the market due to its abundant supply and relatively low price, and in recent years, CNG engines have attracted increasing attention in the automotive market, particularly for heavy vehicles powered by CNG engines operating under stoichiometric calibration. Even when operating under CNG, vehicle exhaust emissions are unavoidable, which typically consist of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). x Ammonia (NH3) consists of typical pollutants such as ), and conventional gasoline exhaust catalysts, three-way catalysts (TWCs), are typically applied to exhaust emissions from CNG engines. However, ammonia (NH3) is recognized as a byproduct during the operation of three-way catalysts (TWCs) across stoichiometric CNG engines, which leads to new pollutant emission problems such as the formation of secondary inorganic aerosols and deterioration of air quality. Therefore, attempts have been made to control ammonia emissions using ammonia slip catalysts (ASCs), which is also a typical emission control approach in large diesel aftertreatment systems.

[0003] Despite advances in catalysts for stoichiometric CNG engine antitreatment systems, ammonia leakage control typically relies on oxidation catalysts, or oxidation catalysts combined with selective catalytic reduction (SCR) functionality, including molecular sieve zeolites as support materials in catalyst designs, such as those described in China Publication No. 109261200 and International Publication No. 2018 / 11552. However, in the design of NH3 slip control, there has been little effort across TWC designs aimed at solving ammonia emissions for stoichiometric CNG engines without any molecular sieve zeolites containing oxidation catalysts or SCR functional catalysts. To meet increasingly stringent emission regulations (such as China VI regulations for large CNG engines requiring NH3 < 10 ppm), reducing NH3 emissions is also a system emission challenge that requires greater attention. This work has led to new approaches in catalyst design, which address HC, CO, NO x In addition to transforming typical contamination control methods, the present invention can simultaneously provide a solution for ammonia leakage control through a novel and optimized TWC design having multiple catalytic regions, as described in this invention. [Overview of the Initiative]

[0004] One aspect of the present disclosure relates to a catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising: a substrate having an axial length L and including an inlet end and an outlet end; a first catalyst region beginning at the outlet end and extending over less than the axial length L, comprising a first PGM component; and a second catalyst region beginning at the inlet end and comprising a second PGM component, wherein the first PGM component comprises palladium, platinum, or a combination thereof, and the second PGM component comprises rhodium.

[0005] The present invention also encompasses an exhaust system for a CNG engine, including the catalyst article of the present invention.

[0006] The present invention also encompasses treating the exhaust gas from a CNG engine, particularly treating the exhaust gas from a stoichiometric CNG engine. The method includes contacting the exhaust gas with the catalyst article of the present invention.

Brief Description of the Drawings

[0007] [Figure 1] The configurations of Comparative Catalysts 1 and 4 are shown, where the first catalyst region extends as a bottom layer over 100% of the axial length L, and the second catalyst region extends as an upper layer over 100% of the axial length L. [Figure 2a] An embodiment according to the present invention is shown, where the first catalyst region extends less than 100% of the axial length L from the outlet end, and the second catalyst region extends less than 100% of the axial length L from the inlet end. The total length of the second and first catalyst regions is greater than the axial length L. [Figure 2b] An embodiment according to the present invention is shown, where the first catalyst region extends less than 100% of the axial length L from the inlet end, and the second catalyst region extends 100% of the axial length L from the outlet end. The total length of the second and first catalyst regions is greater than the axial length L. [Figure 2c] The configuration of Comparative Catalyst 3 is shown, where the first catalyst region extends less than 100% of the axial length L from the inlet end, and the second catalyst region extends less than 100% of the axial length L from the outlet end. The total length of the second and first catalyst regions is greater than the axial length L. [Figure 2d] An embodiment according to the present invention is shown, where the first catalyst region extends less than 100% of the axial length L from the outlet end, and the second catalyst region extends less than 100% of the axial length L from the inlet end. The total length of the second and first catalyst regions is less than or equal to the axial length L. [Figure 2e] An embodiment according to the present invention is shown, where the second catalyst region extends less than 100% of the axial length L from the inlet end, and the first catalyst region extends less than 100% of the axial length L from the outlet end. The total length of the second and first catalyst regions is greater than the axial length L, and the first catalyst region partially covers the second catalyst region. [Figure 3a]An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is greater than the axial length L. A third catalyst region extends from the outlet end to less than 100% of the axial length L. [Figure 3b] An embodiment of the present invention is shown, in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the outlet end to 100% of the axial length L and covers the first catalyst region. A third catalyst region extends to 100% of the axial length L and is located on top of the first and second catalyst regions as an upper layer. [Figure 3c] An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is less than or equal to the axial length L. A third catalyst region extends to 100% of the axial length L and overlaps the first and second catalyst regions as an upper layer. [Figure 3d] An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is less than the axial length L. A third catalyst region extends from the outlet end to less than 100% of the axial length L. [Figure 3e] An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is less than the axial length L. A third catalyst region extends from the inlet end to less than 100% of the axial length L. [Figure 3f]An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is greater than the axial length L. A third catalyst region extends to 100% of the axial length L and overlaps the first and second catalyst regions as an upper layer. [Figure 3g] An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total length of the second and first catalyst regions is greater than the axial length L. A third catalyst region extends from the outlet end to less than 100% of the axial length L. [Figure 4] An embodiment of the present invention is shown in which a first catalyst region extends from the outlet end to less than 100% of the axial length L, and a second catalyst region extends from the inlet end to less than 100% of the axial length L. The total lengths of the second and first catalyst regions may be less than the axial length L, equal to the axial length L, or greater than the axial length L. A third catalyst region extends from the inlet end to less than 100% of the axial length L, and a fourth catalyst region extends from the outlet end to less than 100% of the axial length L. The total lengths of the third and fourth catalyst regions may be less than the axial length L, equal to the axial length L, or greater than the axial length L. The first and second catalyst regions constitute the bottom layer, and the third and fourth catalyst regions constitute the upper layer. [Modes for carrying out the invention]

[0008] This invention relates to catalytic treatment of combustion exhaust gases, such as those produced by stoichiometric CNG engines and other engines, and related catalytic articles and systems. More specifically, this invention relates to the suppression of ammonia emissions and NO in vehicle exhaust systems. x This invention relates to the simultaneous processing of CO and HC. The process of the present invention also reduces process execution time and reduces catalyst costs.

[0009] One aspect of the present disclosure relates to a catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising: a substrate having an axial length L and including an inlet end and an outlet end; a first catalyst region beginning at the outlet end and extending over less than the axial length L, comprising a first PGM component; and a second catalyst region beginning at the inlet end and comprising a second PGM component, wherein the first PGM component comprises palladium, platinum, or a combination thereof, and the second PGM component comprises rhodium.

[0010] First catalytic region The first PGM component can be selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), and mixtures thereof. In some embodiments, the first PGM component may be Pd, Pt, or a mixture thereof. In other embodiments, the first PGM component may be Pd. In yet other embodiments, the first PGM component may be Pd and Rh, or Pt, Pd, and Rh. In certain embodiments, the first PGM component may be Pt and Rh.

[0011] If the first PGM component contains Pd, the first catalyst region is 0.1 to 300 g / ft 3 It may contain palladium. Preferably, the first catalyst region contains 10 to 200 g / ft 3 Palladium, more comfortably 20-150 g / ft 3 It can contain palladium.

[0012] The first catalyst region may further include a first oxygen storage capacity (OSC) material, a first alkali metal or alkaline earth metal component, and / or a first inorganic oxide.

[0013] The first OSC material may be cerium oxide, zirconium oxide, ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the first OSC material includes ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. The ceria-zirconia mixed oxide may further contain dopants such as lanthanum, neodymium, praseodymium, or yttrium oxide. The first OSC material may function as a carrier material for a first PGM component (e.g., as a first PGM carrier material). In some embodiments, the first OSC material includes ceria-zirconia mixed oxide and alumina-ceria-zirconia mixed oxide.

[0014] The first inorganic oxide is preferably an oxide of an element from Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The first inorganic oxide is preferably selected from the group consisting of alumina, zirconia, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxide, and mixed oxides or composite oxides thereof. Particularly preferred is the first inorganic oxide being alumina, lanthanum-alumina, zirconia, or a magnesia / alumina composite oxide. Even more preferred is the first inorganic oxide being alumina, a lanthanum / alumina composite oxide, or a magnesia / alumina composite oxide. One particularly preferred first inorganic oxide is alumina or lanthanum-alumina.

[0015] The weight ratio of the first OSC material to the first inorganic oxide can be 10:1 or less, preferably 8:1 or 5:1 or less, more preferably 4:1 or less, and most preferably 3:1 or less.

[0016] Alternatively, the weight ratio of the first OSC material to the first inorganic oxide can be 10:1 to 1:10, preferably 8:1 to 1:8, more preferably 5:1 to 1:5, and most preferably 4:1 to 1:4.

[0017] The first alkali metal or alkaline earth metal is preferably barium or strontium, and their mixed oxides or composite oxides. Preferably, when barium or strontium is present, it is filled with an amount of barium or strontium of 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the first catalyst region.

[0018] Preferably, barium or strontium is present as BaCO3 or SrCO3. Such materials can be implemented by any method known in the art, for example, incipient wetness impregnation or spray drying.

[0019] In some embodiments, the first catalyst region can extend over 20 to 99%, 40 to 99%, or 50 to 99% of the axial length L. Alternatively, the first catalyst region can extend over 30 to 90 percent of the axial length L. Preferably, it can extend over 40 to 90 percent, more preferably 50 to 90 percent of the axial length L (see, for example, FIGS. 2a, 2b, 2d, 2e, 3a - 3g, and 4).

[0020] Alternatively, the first catalyst region can be 99%, 95%, 90%, or 85% or less of the axial length L.

[0021] The total washcoat loading of the first catalyst region is less than 3.5 g / in 3 Preferably less than 3.0 g / in 3 Or less than 2.5 g / in 3 It can be less. Alternatively, the total washcoat loading of the first catalyst region can be 0.5 to 3.5 g / in 3 Preferably, 0.6 to 3 g / in 3 Or 0.7 to 2.5 g / in 3 It can be.

[0022] The second catalyst region The second PGM component may further include platinum, palladium, or a mixture thereof. In some embodiments, the second PGM component may be Pd and Rh. In other embodiments, the second PGM component may be Pt and Rh.

[0023] In some embodiments, the second catalyst region is substantially free of PGM metals other than rhodium. In further embodiments, the second catalyst region is essentially free of PGM metals other than rhodium.

[0024] The second catalyst region may further include a second oxygen storage capacity (OSC) material, a second alkali metal or alkaline earth metal component, and / or a second inorganic oxide.

[0025] The second catalytic region has a maximum of 25 g / ft 3 It may contain rhodium. Preferably, the second catalyst region contains 1 to 20 g / ft 3 Comfortably 3-15g / ft 3 It may contain rhodium.

[0026] The second OSC material may be cerium oxide, zirconium oxide, ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the second OSC material includes ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. In addition, the second OSC material may further include one or more dopants such as lanthanum, neodymium, praseodymium, and yttrium. Furthermore, the second OSC material may function as a carrier material for the second PGM component. In some embodiments, the second OSC material includes ceria-zirconia mixed oxide and alumina-ceria-zirconia mixed oxide.

[0027] The ceria-zirconia mixed oxide can have a weight ratio of zirconia dioxide to ceria dioxide of at least 50:50, preferably higher than 60:40, and more preferably higher than 65:35. Alternatively, the ceria-zirconia mixed oxide can also have a weight ratio of ceria dioxide to zirconia dioxide of less than 50:50, preferably less than 40:60, and more preferably less than 35:65.

[0028] The second OSC material (e.g., ceria-zirconia mixed oxide) may be 10 to 90% by weight, preferably 20 to 90% by weight, and more preferably 30 to 90% by weight, based on the total wash coat load of the second catalyst region.

[0029] The amount of the second OSC material supported in the second catalyst region is 2 g / in. 3 It may be less than 1.5 g / in. In some embodiments, the amount of the second OSC material supported in the second catalyst region is 1.5 g / in. 3 , 1.2g / in 3 , 1g / in 3 , 0.8g / in 3 , or 0.7g / in 3 The following applies:

[0030] The second alkali metal or alkaline earth metal is preferably barium, strontium, a mixed oxide or composite oxide thereof. Preferably, if present, the amount of barium or strontium is 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the second catalyst region.

[0031] The second alkali metal or alkaline earth metal is more preferably strontium. If present, strontium is preferably present in an amount of 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the second catalyst region.

[0032] Furthermore, the second alkali metal or alkaline earth metal is preferably a mixed oxide or composite oxide of barium and strontium. Preferably, the mixed oxide or composite oxide of barium and strontium is present in an amount of 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the second catalyst region. The second alkali metal or alkaline earth metal is more preferably a composite oxide of barium and strontium.

[0033] Preferably, barium or strontium exists as BaCO3 or SrCO3. Such materials can be produced by any method known in the art, for example, by initial wetting impregnation or spray drying.

[0034] In some embodiments, the second catalyst region is substantially free of the second alkali metal or second alkaline earth metal. In further embodiments, the second catalyst region is substantially free of the second alkali metal or second alkaline earth metal, or does not contain the second alkali metal or second alkaline earth metal.

[0035] The second inorganic oxide is preferably an oxide of an element from Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The second inorganic oxide is preferably selected from the group consisting of oxides of alumina, zirconia, magnesia, silica, lanthanum, yttrium, neodymium, praseodymium, and mixed or composite oxides thereof. Particularly preferred are alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxides. One particularly preferred second inorganic oxide is alumina or lanthanum-alumina.

[0036] The second OSC material and the second inorganic oxide can have a weight ratio of 10:1 or less, preferably 8:1 or less, more preferably 5:1 or less, and most preferably 4:1 or less.

[0037] Alternatively, the weight ratio of the second OSC material to the second inorganic oxide can be 10:1 to 1:10, preferably 8:1 to 1:8, more preferably 5:1 to 1:5, and most preferably 4:1 to 1:4.

[0038] The second catalyst region can extend over 100 percent of the axial length L (see, for example, Figures 2b and 3b). In some embodiments, the second catalyst region can extend over 20–99%, 40–99%, or 50–99% of the axial length L. Alternatively, the second catalyst region can extend over 30–90 percent, preferably 40–90 percent, and more preferably 45–85 percent of the axial length L (see, for example, Figures 2a, 2d, 2e, 3a, 3c–3g, and 4).

[0039] Alternatively, the second catalytic region may be 99%, 95%, 90%, or 85% or less of the axial length L.

[0040] Preferably, the total length of the second region and the first region is equal to or greater than the axial length L.

[0041] The second catalyst region can overlap the first catalyst region by 0.1 to 99 percent, preferably 5 to 90 percent, and more preferably 40 to 80 percent, of the axial length L. Alternatively, the total length of the second and first catalyst regions can be equal to the axial length L. In yet another alternative, the total length of the second and first catalyst regions can be less than the axial length L, for example, 95%, 90%, 80%, or 70% or less of the axial length L.

[0042] In some embodiments, the first catalyst region may be directly supported / deposited on the substrate. In certain embodiments, the second catalyst region may be directly supported / deposited on the substrate.

[0043] The total wash coat load in the second catalyst region is 3.5 g / in. 3 Less than 3.0 g / in3 Less than 2.5 g / in 3 It may be less than 0.5-3.5 g / in. Alternatively, the total wash coat load in the first catalyst region may be 0.5-3.5 g / in. 3 Preferably, 0.6 to 3 g / in 3 Or 0.7-2.5 g / in 3 It is possible.

[0044] Third catalytic region The catalyst article may further include a third catalyst region.

[0045] The third catalyst region may further include a third PGM component, a third oxygen storage (OSC) material, a third alkali or alkaline earth metal component, and / or a third inorganic oxide.

[0046] The third PGM component can be selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof. In some embodiments, the third PGM component may be palladium, rhodium, or a mixture thereof. In other embodiments, the third PGM component may be platinum, rhodium, or a mixture thereof.

[0047] The third OSC material may be cerium oxide, zirconium oxide, ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the third OSC material includes ceria-zirconia mixed oxide, alumina-ceria-zirconia mixed oxide, or a combination thereof. In addition, the third OSC material may further include one or more dopants such as lanthanum, neodymium, praseodymium, and yttrium. Furthermore, the third OSC material may function as a carrier material for the third PGM component. In some embodiments, the third OSC material includes ceria-zirconia mixed oxide and alumina-ceria-zirconia mixed oxide.

[0048] The ceria-zirconia mixed oxide can have a weight ratio of zirconia dioxide to ceria dioxide of at least 50:50, preferably higher than 60:40, and more preferably higher than 65:35. Alternatively, the ceria-zirconia mixed oxide can also have a weight ratio of ceria dioxide to zirconia dioxide of less than 50:50, preferably less than 40:60, and more preferably less than 35:65.

[0049] The third OSC material (e.g., ceria-zirconia mixed oxide) may be present in an amount of 10-90% by weight, preferably 25-75% by weight, and more preferably 30-60% by weight, based on the total wash coat load of the third catalyst region.

[0050] The amount of the third OSC material supported in the third catalytic region is 1.5 g / in. 3 It may be less than 1.2 g / in. In some embodiments, the amount of third OSC material supported in the second catalyst region is 1.2 g / in. 3 , 1.0g / in 3 , 0.9g / in 3 , 0.8g / in 3 , or 0.7g / in 3 The following applies:

[0051] The total wash coat load in the third catalyst region is 3.5 g / in. 3 Less than 3.0 g / in 3 Below 2.5g / in 3 , or 2g / in 3 It is possible.

[0052] The third alkali or alkaline earth metal is preferably barium, strontium, or a mixture or composite oxide thereof. Preferably, if present, the amount of barium or strontium is 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the third catalyst region.

[0053] The third alkali or alkaline earth metal is more preferably strontium. If present, strontium is preferably present in an amount of 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the third catalyst region.

[0054] Furthermore, the third alkali or alkaline earth metal is preferably a mixed oxide or composite oxide of barium and strontium. Preferably, the mixed oxide or composite oxide of barium and strontium is present in an amount of 0.1 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the third catalyst region. The third alkali or alkaline earth metal is more preferably a composite oxide of barium and strontium.

[0055] Preferably, barium or strontium exists as BaCO3 or SrCO3. Such materials can be produced by any method known in the art, for example, by initial wetting impregnation or spray drying.

[0056] In some embodiments, the third catalyst region is substantially free of a third alkali metal or a third alkaline earth metal. In further embodiments, the third catalyst region is substantially free of or does not contain a third alkali metal or a third alkaline earth metal.

[0057] The third inorganic oxide is preferably an oxide of an element from Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The third inorganic oxide is preferably selected from the group consisting of alumina, zirconia, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxide, and mixed or composite oxides thereof. Particularly preferred are alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxides. One particularly preferred third inorganic oxide is alumina or lanthanum-alumina.

[0058] The third OSC material and the third inorganic oxide may have a weight ratio of 10:1 or less, preferably 8:1 or 5:1 or less, more preferably 5:1 or less, and most preferably 4:1 or less.

[0059] Alternatively, the third OSC material and the third inorganic oxide may have a weight ratio of 10:1 to 1:10, preferably 8:1 to 1:8, more preferably 5:1 to 1:5, or most preferably 4:1 to 1:4.

[0060] The third catalyst region can extend over 100 percent of the axial length L (see, for example, Figures 3b, 3c, and 3f). Alternatively, the third catalyst region may be less than the axial length L, for example, 95%, 90%, 80%, or 70% or less of the axial length L (see, for example, Figures 3a, 3d, 3e, 3g, and 4). In some embodiments, the third catalyst region can begin at the outlet end. In other embodiments, the third catalyst region can begin at the inlet end.

[0061] Fourth catalytic region The catalyst article may further include a fourth catalyst region.

[0062] The fourth catalyst region may further include a fourth PGM component, a fourth oxygen storage (OSC) material, a fourth alkali or alkaline earth metal component, and / or a fourth inorganic oxide.

[0063] The fourth PGM component can be selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof. In some embodiments, the fourth PGM component may be Pd, Rh, or mixtures thereof.

[0064] The fourth catalyst region may have the same or similar composition as the third catalyst region.

[0065] The fourth catalyst region may have an axial length less than L, for example, 95%, 90%, 80%, or 70% or less of the axial length L.

[0066] Alternatively, either the fourth or third catalyst region can extend over 30 to 70 percent of the axial length L. Preferably, it can extend over 40 to 60 percent of the axial length L, more preferably over 45 to 55 percent, and most preferably, the total length of the fourth and third catalyst regions is greater than or equal to the axial length L (see, for example, Figure 4).

[0067] The catalyst articles of the present invention may contain further components known to those skilled in the art. For example, the compositions of the present invention may further contain at least one binder and / or at least one surfactant. If a binder is present, a dispersible alumina binder is preferred.

[0068] Base material Preferably, the substrate is a flow-through monolith.

[0069] The base material may be less than 200 mm in length, preferably 60 to 160 mm.

[0070] The flow-through monolith substrate has a first surface and a second surface, with a longitudinal direction defined between them. The flow-through monolith substrate has a plurality of channels extending between the first surface and the second surface. The plurality of channels extend in the longitudinal direction and provide a plurality of inner surfaces (e.g., the surface of the wall defining each channel). Each of the plurality of channels has an opening on the first surface and an opening on the second surface. To avoid misunderstanding, the flow-through monolith substrate is not a wall flow filter.

[0071] The first surface is typically located at the inlet end of the substrate, and the second surface is located at the outlet end of the substrate.

[0072] A channel may have a fixed width, and each of multiple channels may have a uniform channel width.

[0073] Preferably, in a plane perpendicular to the longitudinal direction, the monolithic substrate has 300 to 900 channels per square inch, preferably 400 to 800 channels. For example, on a first surface, the density of open first channels and closed second channels is 600 to 700 channels per square inch. The channels may have cross-sections that are rectangular, square, circular, elliptical, triangular, hexagonal, or other polygonal shapes.

[0074] The monolithic substrate acts as a carrier for holding the catalyst material. Suitable materials for forming the monolithic substrate include ceramic-like materials such as cordierite, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, or zirconium silicate, or porous refractory metals. Such materials and their use in the manufacture of porous monolithic substrates are well known in the art.

[0075] It should be noted that the flow-through monolithic substrates described herein are single components (i.e., a single brick-like mass). Nevertheless, when forming an exhaust treatment system, the substrates used may be formed by bonding multiple channels together, or by bonding multiple smaller substrates together, as described herein. Such techniques, along with suitable casings and configurations for exhaust treatment systems, are well known in the art.

[0076] In embodiments of the present invention in which the catalyst article includes a ceramic substrate, the ceramic substrate may be made of any suitable refractory material, such as alumina, silica, ceria, zirconia, magnesia, zeolite, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicate and metalloid aluminosilicate (such as cordierite and spodumene), or a mixture or mixed oxide of two or more of these. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0077] In embodiments of the present invention in which the catalyst article includes a metal substrate, the metal substrate may be made of any suitable metal, particularly heat-resistant metals and metal alloys such as titanium and stainless steel, as well as ferrite alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0078] Another aspect of this disclosure is the use of the catalyst articles described herein, NO x This invention relates to a method for treating vehicle exhaust gases from CNG engines containing CO, HC (methane), and ammonia. Test catalysts prepared according to this method exhibit improved catalytic properties compared to conventional TWCs (with the same or similar PGM loads), and also show particularly improved performance in controlling ammonia emissions over a wide lambda range (see, for example, Examples 1-2 and Tables 2-6).

[0079] Another aspect of this disclosure relates to a vehicle exhaust gas treatment system that includes catalytic articles described herein, along with conduits for transporting exhaust gases through the system. In some embodiments, the system does not include an ammonia slip catalyst (ASC).

[0080] definition As used herein, the term “region” typically refers to an area on a substrate obtained by drying and / or firing a wash coat. A “region” may be arranged or supported on the substrate as, for example, a “layer” or “zone.” The area or arrangement on the substrate is generally controlled during the process of applying the wash coat to the substrate. A “region” typically has a clear boundary or border (i.e., it is possible to distinguish one region from another using conventional analytical techniques).

[0081] Typically, the “region” has substantially uniform length. In this context, “substantially uniform length” means a length that does not deviate by more than 10% from its mean (e.g., the difference between the maximum and minimum lengths), preferably more than 5% from its mean, and more preferably more than 1% from its mean.

[0082] Each “region” preferably has a substantially uniform composition (i.e., there is no substantial difference in the composition of the wash coat when comparing one part of a region with another part of that region). In this context, a substantially uniform composition means a material (e.g., a region) where, when comparing one part of a region with another part of that region, the difference in composition is 5% or less, usually 2.5% or less, and most commonly 1% or less.

[0083] As used herein, the term “zone” refers to an area having a length less than the total length of the substrate, such as a length of 75% or less of the total length of the substrate. A “zone” typically has a length of at least 5% (e.g., 5% or more) of the total length of the substrate (i.e., a substantially uniform length).

[0084] The total length of the substrate is the distance between its inlet end and its outlet end (for example, both ends of the substrate).

[0085] Any reference to “zone located at the inlet end of the substrate” as used herein refers to a zone located or supported on the substrate such that the inlet end of the substrate is closer than the outlet end of the substrate. Therefore, the midpoint of the zone (i.e., the point halfway along its length) is closer to the inlet end of the substrate than to the outlet end of the substrate. Similarly, any reference to “zone located at the outlet end of the substrate” as used herein refers to a zone located or supported on the substrate such that the outlet end of the substrate is closer than the inlet end of the substrate. Therefore, the midpoint of the zone (i.e., the point halfway along its length) is closer to the outlet end of the substrate than to the inlet end of the substrate.

[0086] When the substrate is a wall flow filter, generally any reference to "the zone located at the inlet end of the substrate" refers to a zone located or supported on the substrate. (a) Zones and / or zones where the inlet end (e.g., open end) of the substrate inlet channel is closer than the closed end (e.g., blocked or sealed end) of the inlet channel. (b) A zone in which the closed end of the outlet channel of the substrate (e.g., a blocked or sealed end) is closer than the outlet end of the outlet channel (e.g., an open end).

[0087] Therefore, the midpoint of the zone (i.e., the point at half its length) is (a) closer to the inlet end of the substrate inlet channel than to the closed end of the inlet channel, and / or (b) closer to the closed end of the substrate outlet channel than to the outlet end of the outlet channel.

[0088] Similarly, if the substrate is a wall flow filter, any reference to "the zone located at the outlet end of the substrate" is a zone located on or supported on the substrate, (a) Zones and / or where the exit end (e.g., open end) of the exit channel of the substrate is closer than the closed end (e.g., blocked or sealed end) of the exit channel. (b) A zone in which the closed end of the substrate's inlet channel (e.g., a blocked or sealed end) is closer than the inlet end of the inlet channel (e.g., an open end).

[0089] Therefore, the midpoint of the zone (i.e., the point at half its length) is (a) closer to the exit end of the substrate's exit channel than to the closed end of the exit channel, and / or (b) closer to the closed end of the substrate's inlet channel than to the inlet end of the inlet channel.

[0090] If the washcoat is present on the wall of the wall flow filter (i.e., the zone is within the wall), then the zone may satisfy both (a) and (b).

[0091] The term "wash coat" is well known in the art and typically refers to an adhesive coating applied to a substrate during the manufacturing of a catalyst.

[0092] As used herein, the acronym "PGM, platinum group metal" refers to "platinum group metals." The term "platinum group metals" generally refers to metals selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt, preferably metals selected from the group consisting of Ru, Rh, Pd, Ir, and Pt. Generally, the term "PGM" preferably refers to metals selected from the group consisting of Rh, Pt, and Pd.

[0093] As used herein, the term “mixed oxide” generally refers to a mixture of oxides in a single phase, as is conventionally known in the art. As used herein, the term “composite oxide” generally refers to a composition of oxides having two or more phases, as is conventionally known in the art.

[0094] Where used herein, the expression “essentially consists of” limits the scope of a feature to include a specific material or process, and any other material or process that does not substantially affect the fundamental properties of that feature, such as trace impurities. The expression “essentially consists of” encompasses the expression “consists of.”

[0095] When used herein with respect to materials, the expression “substantially absent” typically means that the material is present in small amounts, for example, 5% by weight or less, preferably 2% by weight or less, and more preferably 1% by weight or less, in relation to the contents of an area, layer, or zone. The expression “substantially absent” encompasses the expression “absent.”

[0096] When used herein with respect to materials, the expression “essentially not present” typically means that the material is present in trace amounts, for example, 1% by weight or less, preferably 0.5% by weight or less, and more preferably 0.1% by weight or less, in relation to the contents of an area, layer, or zone. The expression “essentially not present” encompasses the expression “not present.”

[0097] Where used herein, any amount of dopant expressed as a weight percentage, particularly a total amount, refers to the weight of the carrier material or its refractory metal oxide.

[0098] As used herein, the term "loading capacity" refers to g / ft based on the weight of the metal. 3 It refers to the measured value in that unit.

[0099] The following examples are merely illustrative of the present invention. Those skilled in the art will recognize many modifications that fall within the spirit and scope of the claims of the present invention. [Examples]

[0100] material All materials are commercially available and, unless otherwise noted, were obtained from known suppliers.

[0101] Catalyst 1 (Comparative Example) Catalyst 1 is a typical ternary (Pd-Rh) catalyst having a bilayer structure in two catalytic regions, as shown in Figure 1. The bottom layer consists of Pd supported on a wash coat of a first CeZr mixed oxide, La-stabilized alumina, and Ba promoter. The amount of wash coat supported in the first catalytic region is approximately 2.2 g / in. 3 The Pd load is 128 g / ft 3 The following was observed: Using a standard coating procedure, a wash coat was applied to each end face of the ceramic substrate with a target coating depth of 50% of the substrate length (400 cpsi, wall thickness 4.3 mil), dried at 100°C, and fired at 500°C for 45 minutes.

[0102] The upper layer consists of a second CeZr mixed oxide and Rh supported on a wash coat of La-stabilized alumina. The wash coat load of the second layer is approximately 1.3 g / in. 3 The Rh load is 7g / ft 3 Next, using a standard coating procedure, this second wash coat was applied to each end face of the ceramic substrate, including the bottom layer, with a target coating depth of 50% of the substrate's length, dried at 100°C, and fired at 500°C for 45 minutes.

[0103] Catalyst 2 (Comparative Example) First catalytic region: Catalyst 2 is a ternary (Pd-Rh) catalyst having two catalytic regions as shown in Figure 2c. The first catalytic region, which begins at the inlet end, consists of a first CeZr mixed oxide, La-stabilized alumina, and Pd supported on a wash coat of Ba promoter. The amount of wash coat supported in the first region is approximately 2.2 g / in. 3 The Pd load is 128 g / ft 3 That was the case.

[0104] Next, using a standard coating procedure, the wash coat was applied from the entrance surface of the ceramic substrate to a target coating depth of 80% of the substrate length (400 cpsi, wall thickness 4.3 mils), and dried at 100°C.

[0105] Second catalytic region: A second catalyst region beginning at the outlet end, comprising a second CeZr mixed oxide and Rh supported on a wash coat of La-stabilized alumina. The amount of wash coat supported in the second region is approximately 1.3 g / in. 3 The Rh load is 7g / ft 3 That was the case.

[0106] Next, using a standard coating procedure, the second wash coat was applied to the exit end face of the ceramic substrate containing the first catalyst region, with a target coating depth of 80% of the substrate's length, dried at 100°C, and fired at 500°C for 45 minutes.

[0107] Catalyst 3 First catalytic region: Catalyst 3 was prepared according to the present invention in two catalyst regions, as shown in Figure 2a. The first catalyst region, beginning at the outlet end, consists of a first CeZr mixed oxide, La-stabilized alumina, and Pd supported on a wash coat of Ba promoter. The wash coat load of the first region is approximately 2.2 g / in 3 The Pd load is 128 g / ft 3 That was the case.

[0108] Next, using a standard coating procedure, the wash coat was applied from the exit surface of the ceramic substrate to a target coating depth of 80% of the substrate length (400 cpsi, wall thickness 4.3 mil), and dried at 100°C.

[0109] Second catalytic region: The second catalyst region, starting at the inlet end, consists of a second CeZr mixed oxide and Rh supported on a wash coat of La-stabilized alumina. The amount of wash coat supported in the second region is approximately 1.3 g / in. 3 The Rh load is 7g / ft 3 That was the case.

[0110] Next, using a standard coating procedure, the second wash coat was applied to the inlet end face of the ceramic substrate containing the first catalyst region, with a target coating depth of 80% of the substrate's length, dried at 100°C, and fired at 500°C for 45 minutes.

[0111] Catalyst 4 (Comparative Example) First catalytic region: Catalyst 4 is a commercially available ternary (Pd-Rh) catalyst having two catalytic regions in a bilayer structure as shown in Figure 1. The first catalytic region, which serves as the bottom layer, consists of Pd supported on a wash coat of a first CeZr mixed oxide, La-stabilized alumina, and Sr promoter. The amount of wash coat supported on the bottom layer is approximately 2.2 g / in. 3 The Pd load is 124 g / ft 3 That was the case.

[0112] Using a standard coating procedure, this wash coat was applied to each end face of the ceramic substrate with a target coating depth of 50% of the substrate length (400 cpsi, wall thickness 4.3 mil), dried at 100°C, and fired at 500°C for 45 minutes.

[0113] Second catalytic region: The second catalyst region, which serves as the upper layer, consists of a second CeZr mixed oxide and Rh supported on a wash coat of La-stabilized alumina. The amount of wash coat supported in the upper layer is approximately 1.3 g / in. 3 The Rh load is 7g / ft 3 That was the case.

[0114] Next, using a standard coating procedure, the second wash coat was applied to each end face of the ceramic substrate, including the first catalyst region, to a target coating depth of 50% of the substrate's length, dried at 100°C, and fired at 500°C for 45 minutes.

[0115] Example 1 - Improved catalyst performance Catalyst performance tests were conducted on comparative catalyst 1, comparative catalyst 2, and comparative catalyst 3 using simulated exhaust gases having the compositions shown in Table 1, under the following conditions.

[0116] [Table 1]

[0117] In the catalyst performance test, the gas flow rate was set to a space velocity of 60,000 / hour, the temperature to 430°C, and the gas composition was analyzed after passing through the catalyst to measure ammonia emissions and conversion rates. Lower ammonia emissions and higher conversion rates indicate better catalyst performance. The lambda value was controlled by adjusting the O2 concentration. The lambda value was 0.994 when the O2 concentration was 0.6%, which is calculated based on conventional methods. Comparative catalyst 1, comparative catalyst 2, and catalyst 3 were oven-aged for 100 hours at 950°C in 10% H2O air.

[0118] [Table 2]

[0119] [Table 3]

[0120] [Table 4]

[0121] As shown in Table 2, catalyst 3 showed significantly improved ammonia emission control performance compared to comparative catalysts 1 and 2 through optimization of the PGM layer structure (see, for example, the ammonia emissions of 591 ppm and 637 ppm to 159 ppm related to lambda at 0.985) (resulting in ammonia reductions of 73% and 75%, respectively). Catalyst 3 also showed improved NO emissions compared to comparative catalysts 1 and 2, as shown in Tables 3 and 4. x And CH4 exhibits improved performance, and NO x The conversion of CH4 and other components has been significantly improved.

[0122] Example 2 - Improved catalyst performance Catalyst performance tests were conducted on catalyst 3 and comparative catalyst 4 under conditions using simulated exhaust gas with the composition shown in Table 1.

[0123] In the catalyst performance test, the gas flow rate was set to a space velocity of 60,000 / hour, the temperature to 550°C, and the gas composition was analyzed after passing through the catalyst to measure ammonia emissions and conversion rate. Lambda was controlled by adjusting the O2 concentration. Catalyst 3 and comparative catalyst 4 were oven-aged for 100 hours at 950°C with 10% H2O in air.

[0124] [Table 5]

[0125] [Table 6]

[0126] As shown in Table 5, catalyst 3 exhibited significantly lower ammonia emissions than comparative catalyst 4 (see, for example, the ammonia emissions of 502 ppm to 135 ppm associated with lambda at 0.963) (a 73% reduction in ammonia emissions). Catalyst 3 also showed significantly improved performance in CH4 conversion, as shown in Table 6.

Claims

1. A catalytic article for treating exhaust gas from a compressed natural gas (CNG) engine, A base material having an axial length L and comprising an inlet end and an outlet end, A first catalyst region beginning at the outlet end and extending over an axial length less than L, comprising a first catalyst region containing a first PGM component, A second catalyst region beginning at the aforementioned inlet end, comprising a second catalyst region containing a second PGM component, The first PGM component comprises palladium, platinum, or a combination thereof. A catalyst article wherein the second PGM component contains rhodium.

2. The catalyst article according to claim 1, wherein the first catalyst region extends over 20 to 99 percent of the axial length L.

3. The catalyst article according to claim 1 or 2, wherein the second catalyst region extends over 20 to 100 percent of the axial length L.

4. The catalyst article according to any one of claims 1 to 3, wherein the second catalyst region overlaps with the first catalyst region.

5. The catalyst article according to claim 4, wherein the second catalyst region overlaps with the first catalyst region over 5 to 90 percent of the axial length L.

6. The catalyst article according to claim 5, wherein the second catalyst region overlaps with the first catalyst region over 40 to 80 percent of the axial length L.

7. The catalyst article according to any one of claims 1 to 6, wherein the second catalyst region essentially does not contain any PGM metals other than rhodium.

8. The second catalyst region has a maximum of 25 g / ft ３ A catalyst article according to any one of claims 1 to 7, comprising rhodium.

9. The catalyst article according to any one of claims 1 to 8, wherein the first catalyst region further comprises rhodium.

10. The catalyst article according to any one of claims 1 to 9, wherein the first PGM component comprises palladium.

11. The first catalyst region is 0.1 to 300 g / ft ３ The catalyst article according to claim 10, comprising palladium.

12. The catalyst article according to any one of claims 1 to 11, wherein the first catalyst region further comprises a first oxygen storage capacity (OSC) material, a first alkali metal or alkaline earth metal component, and / or a first inorganic oxide.

13. The catalyst article according to claim 12, wherein the first OSC material is selected from the group consisting of cerium oxide, zirconium oxide, ceria-zirconia mixed oxide, and alumina-ceria-zirconia mixed oxide.

14. The catalyst article according to claim 13, wherein the first OSC material comprises the ceria-zirconia mixed oxide.

15. The catalyst article according to any one of claims 12 to 14, wherein the first inorganic oxide is selected from the group consisting of alumina, zirconia, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxide, and mixed oxides or composite oxides thereof.

16. The catalyst article according to claim 15, wherein the first inorganic oxide is alumina, lanthanum / alumina composite oxide, or magnesia / alumina composite oxide.

17. The catalyst article according to any one of claims 12 to 16, wherein the first alkali metal or alkaline earth metal is barium or strontium.

18. The catalyst article according to claim 17, wherein the barium or strontium is present in the first catalyst region in an amount of 0.1 to 15% by weight, based on the total weight of the first catalyst region.

19. The catalyst article according to any one of claims 1 to 18, wherein the second catalyst region further comprises a second oxygen storage capacity (OSC) material, a second alkali metal or alkaline earth metal component, and / or a second inorganic oxide.

20. The catalyst article according to claim 19, wherein the second OSC material is selected from the group consisting of cerium oxide, zirconium oxide, ceria-zirconia mixed oxide, and alumina-ceria-zirconia mixed oxide.

21. The catalyst article according to claim 20, wherein the second OSC material comprises the ceria-zirconia mixed oxide.

22. The catalyst article according to any one of claims 19 to 21, wherein the second inorganic oxide is selected from the group consisting of alumina, zirconia, magnesia, silica, lanthanum, yttrium, neodymium, praseodymium oxide, and mixed oxides or composite oxides thereof.

23. The catalyst article according to claim 22, wherein the second inorganic oxide is alumina, lantana / alumina composite oxide, or magnesia / alumina composite oxide.

24. The catalyst article according to any one of claims 19 to 23, wherein the second alkali metal or alkaline earth metal is barium or strontium.

25. The catalyst article according to any one of claims 19 to 22, wherein the second catalyst region substantially does not contain the second alkali metal or the second alkaline earth metal.

26. A catalyst article according to any one of claims 1 to 25, further comprising a third catalyst region.

27. The catalyst article according to claim 26, wherein the third catalyst region begins at the outlet end and extends over a length less than the axial length L.

28. The catalyst article according to any one of claims 1 to 27, wherein the substrate is a flow-through monolith or a wall-flow filter.

29. The catalyst article according to any one of claims 1 to 28, wherein the first catalyst region is directly supported / deposited on the substrate.

30. The catalyst article according to any one of claims 1 to 28, wherein the second catalyst region is directly supported / deposited on the substrate.

31. An exhaust treatment system for treating the flow of exhaust gas from a CNG engine, comprising a catalytic article according to any one of claims 1 to 30.

32. A method for treating exhaust gas from a CNG engine, comprising contacting the exhaust gas with a catalyst article according to any one of claims 1 to 30.

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