Platinum-Enriched Multi-Zone Catalyst for CNG Engine Exhaust Gas Treatment

Abstract

A three-way catalyst article and its use in an exhaust system for a compressed natural gas engine are disclosed. A catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising a substrate having an axial length L, an inlet end, and an outlet end, a first catalyst region starting at the inlet end and extending over a length less than the axial length L, the first catalyst region including a first platinum component, a second catalyst region starting at the outlet end and extending over a length less than the axial length L, the second catalyst region including a second palladium component, and a third catalyst region including a third rhodium component.

Description

Technical Field

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

Background Art

[0002] Compressed natural gas (CNG) consists of a single hydrocarbon, mainly methane, which results in much lower CO2 production per energy unit, and CNG is used as one clean energy alternative to conventional gasoline and diesel fuels. In addition to this, CNG is also favored in the market due to its abundant supply and relatively low price. Therefore, in recent years, CNG engines have attracted increasing attention in the automotive market, especially for large vehicles operating with CNG engines operating under stoichiometric calibration. Even when operating under CNG, automotive exhaust emissions are inevitable, which usually consist of typical pollutants such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (「NO x 」), and a three-way catalyst (TWC), which is a conventional gasoline emission catalyst, is usually applied to control exhaust emissions from CNG engines.

[0003] Palladium (Pd) and rhodium (Rh) are widely used in TWC formulations to reduce harmful emissions in gasoline vehicles. Similar Pd-Rh TWCs are commonly used in stoichiometric CNG engine applications and typically contain relatively high Pd loadings. However, in recent years, due to increasing demand in the market, the prices of these precious metals have risen and become even more expensive. On the other hand, due to more stringent environmental regulations globally, the automotive industry is being forced to put even more precious metals into catalytic converters. On the one hand, platinum (Pt) has become a more attractive candidate for gasoline applications due to its relatively low cost, and today, the price of Pd is still almost twice that of Pt. Therefore, while desiring to maintain equivalent catalytic performance, there are significant financial incentives regarding how to introduce Pt into the catalyst formulation or at least partially replace Pd. In the past, when simply replacing Pd with Pt on existing Pd-Rh TWC formulations, typically inferior performance was observed, especially when increasing the replacement ratio.

[0004] To meet increasingly stringent laws and achieve cost reduction, as a result, Pt utilization in CNG applications is widely noted in the market. This research brings a new approach in catalyst design, and this novel Pt-enriched TWC design not only exhibits improved emissions control performance but also provides significant cost reduction through optimization of the placement of Pt and Pd in multiple catalyst regions as described in the present invention. SUMMARY OF THE INVENTION

[0005] One aspect of the present disclosure is a catalytic article for treating exhaust gas from a compressed natural gas (CNG) engine, the catalytic article comprising a substrate having an axial length L, an inlet end, and an outlet end; a first catalytic region beginning at the inlet end and extending over less than the axial length L, the first catalytic region including a first platinum component; a second catalytic region beginning at the outlet end and extending over less than the axial length L, the second catalytic region including a second palladium component; and a third catalytic region including a third rhodium component.

[0006] The present invention also encompasses an exhaust system for a CNG engine comprising the catalytic article of the present invention.

[0007] The present invention also encompasses treating exhaust gas from a CNG engine, particularly exhaust gas from a stoichiometric CNG engine. The method includes contacting the exhaust gas with the catalytic article of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Fig. 1a

Fig. 1b

Fig. 1c

Fig. 1d

Fig. 1e

Fig. 2a

Fig. 2b

[0009] The present invention is directed to the catalytic treatment of combustion exhaust gases, such as those produced by stoichiometric CNG engines, and related catalyst articles and systems. More specifically, the present invention relates to a Pt-containing TWC that improves the emission control performance for CH4 and NO in a vehicle exhaust system. The present invention also reduces the cost of the catalyst by substituting Pd with Pt. x The present invention also reduces the cost of the catalyst by substituting Pd with Pt.

[0010] One aspect of the present disclosure is a catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, the catalyst article comprising a substrate having an axial length L and including an inlet end and an outlet end, a first catalyst region beginning at the inlet end and extending over a length less than the axial length L, the first catalyst region including a first platinum component, a second catalyst region beginning at the outlet end and extending over a length less than the axial length L, the second catalyst region including a second palladium component, and a third catalyst region including a third rhodium component.

[0011] The first catalyst region The first catalyst region can include a first Pt component of 0.1 to 300 g / ft. 3 Preferably, the first catalyst region can include a first Pt component of 10 to 200 g / ft. 3 More preferably, the first catalyst region can include a first Pt component of 15 to 150 g / ft. 3 In some embodiments, the first catalyst region can further include a first Pd component, and the weight ratio of Pd in the first catalyst region to Pt in the first catalyst region can be less than 1:1, preferably less than 1:2, more preferably 1:3, 1:5, 1:8, 1:10, or 1:20 or less.

[0012] Alternatively, the first catalyst region may essentially not contain other PGM components other than the first Pt component.

[0013] The first catalyst region can further include a first oxygen storage capacity (OSC) material, a first alkali metal component or alkaline earth metal component, and / or a first inorganic oxide.

[0014] The first OSC material can be cerium oxide, zirconium oxide, a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the first OSC material includes a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. The ceria-zirconia mixed oxide can further include dopants such as lanthanum oxide, neodymium oxide, praseodymium oxide, yttrium oxide, etc. The first OSC material can function as a carrier material for the first Pt component. In some embodiments, the first OSC material includes a ceria-zirconia mixed oxide and an alumina-ceria-zirconia mixed oxide.

[0015] The first inorganic oxide is preferably an oxide of an element of 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 oxide, neodymium oxide, praseodymium oxide, yttrium oxide, and mixed oxides or composite oxides thereof. Particularly preferably, the first inorganic oxide is alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxide. More preferably, the first inorganic oxide is alumina, lanthanum / alumina composite oxide, or magnesia / alumina composite oxide. One particularly preferred first inorganic oxide is alumina or lanthanum-alumina.

[0016] The first OSC material and the first inorganic oxide can have a weight ratio of 10:1 or less, preferably 8:1 or less or 5:1 or less, more preferably 4:1 or less, and most preferably 3:1 or less.

[0017] Alternatively, the first OSC material and the first 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, and most preferably 4:1 to 1:4.

[0018] The loading amount of the first OSC material in the second catalyst region may be less than 2 g / in 3 In some embodiments, the loading amount of the first OSC material in the first catalyst region is 1.5 g / in 3 or less, 1.2 g / in 3 or less, 1 g / in 3 or less, 0.8 g / in 3 or less, or 0.7 g / in 3 or less.

[0019] 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 supported in an amount of 0.1 to 15% by weight, more preferably 1.5 to 10% by weight, based on the total weight of the first catalyst region.

[0020] 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.

[0021] In some embodiments, the first catalyst region is substantially free of the first alkali metal or alkaline earth metal. In further embodiments, the first catalyst region is substantially free of or does not contain the first alkali metal or alkaline earth metal.

[0022] In some embodiments, the first catalyst region may extend over 10 to 90%, 20 to 80%, or 30 to 70% of the axial length L. Alternatively, the first catalyst region may extend over 35% to 65% of the axial length L. Preferably, it extends over 40% to 65%, more preferably 45% to 65% of the axial length L.

[0023] Alternatively, the first catalyst region can be 99% or less, 95% or less, 90% or less, or 85% or less of the axial length L. Alternatively, in certain embodiments, the first catalyst region can be 50% or less, 40% or less, 30% or less, or 20% or less of the axial length L.

[0024] The first catalyst region may further contain a first rare earth metal component such as lanthanum, neodymium, praseodymium, yttrium, gadolinium, scandium, or a mixture thereof. These rare earth metal components can be introduced as dopants or mixed as physical mixtures / blends such as in oxide form.

[0025] 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 - 3.5 g / in 3 and preferably 0.6 - 3 g / in 3 or 0.7 - 2.5 g / in 3 It can be.

[0026] The second catalyst region The second catalyst region can contain a second Pd component of 0.1 - 150 g / ft 3 Preferably, the second catalyst region can contain a second Pd component of 5 - 120 g / ft 3 more preferably a second Pd component of 10 - 90 g / ft 3 It can contain. In some embodiments, the second catalyst region can further contain a second Pt component, and the weight ratio of Pt to Pd in the second catalyst region in the second catalyst region is less than 1:1, preferably less than 1:2, more preferably 1:3 or less, 1:5 or less, 1:8 or less, 1:10 or less, or 1:20 or less.

[0027] Alternatively, in certain embodiments, the weight ratio of Pd in the second catalyst region to Pt in the second catalyst region can be less than 1:1, preferably less than 1:2, more preferably at least 1:3, 1:5, 1:8, 1:10 or 1:20.

[0028] Alternatively, the second catalyst region may essentially contain no other PGM components other than the second Pd component.

[0029] The second catalyst region may further contain a second oxygen storage capacity (OSC) material, a second alkali metal component or alkaline earth metal component, and / or a second inorganic oxide.

[0030] The second OSC material can be cerium oxide, zirconium oxide, a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the second OSC material includes a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. In addition, the second OSC material may further contain one or more of dopants such as lanthanum, neodymium, praseodymium, yttrium, etc. Further, the second OSC material can function as a carrier material for the second Pd component and / or (and / r) the second Pt component. In some embodiments, the second OSC material includes a ceria-zirconia mixed oxide and an alumina-ceria-zirconia mixed oxide.

[0031] The ceria-zirconia mixed oxide can have a weight ratio of zirconium dioxide to cerium dioxide of at least 50:50, preferably higher than 60:40, more preferably higher than 65:35. Alternatively, the ceria-zirconia mixed oxide can also have a weight ratio of cerium dioxide to zirconium dioxide of less than 50:50, preferably less than 40:60, more preferably less than 35:65.

[0032] The second OSC material (e.g., ceria-zirconia mixed oxide) can be 10-90 wt%, preferably 20-90 wt%, more preferably 30-90 wt% based on the total washcoat loading of the second catalyst region.

[0033] The loading of the second OSC material in the second catalyst region can be less than 2 g / in 3 In some embodiments, the loading of the second OSC material in the second catalyst region is 1.5 g / in 3 or less, 1.2 g / in 3 or less, 1 g / in 3 or less, 0.8 g / in 3 or less, or 0.7 g / in 3 or less.

[0034] The second alkali metal or alkaline earth metal is preferably barium, strontium, a mixed oxide or composite oxide thereof. Preferably, barium or strontium, when present, is in an amount of 0.1-15 wt%, more preferably 1.5-10 wt% based on the total weight of the second catalyst region.

[0035] Even more preferably, the second alkali metal or alkaline earth metal is strontium. Strontium, when present, is preferably in an amount of 0.1-15 wt%, more preferably 1.5-10 wt% based on the total weight of the second catalyst region.

[0036] Also, 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 0.1-15 wt%, more preferably 1.5-10 wt% based on the total weight of the second catalyst region. Even more preferably, the second alkali metal or alkaline earth metal is a composite oxide of barium and strontium.

[0037] 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.

[0038] In some embodiments, the second catalyst region is substantially free of a second alkali metal or alkaline earth metal. In further embodiments, the second catalyst region is substantially free of or does not contain a second alkali metal or alkaline earth metal.

[0039] The second inorganic oxide is preferably an oxide of an element of 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 alumina, zirconia, magnesia, silica, lanthanum, yttrium, neodymium, praseodymium oxides, and mixed oxides or composite oxides thereof. Particularly preferably, the second inorganic oxide is alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxide. One particularly preferred second inorganic oxide is alumina or lanthanum-alumina.

[0040] 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.

[0041] Alternatively, the second OSC material and the second inorganic oxide can have a weight ratio of 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.

[0042] In some embodiments, the second catalyst region can extend over 10% - 90%, 20% - 80%, or 30% - 70% of the axial length L. Alternatively, the second catalyst region can extend over 35% - 65% of the axial length L. Preferably, it extends over 40% - 65%, more preferably 45% - 65% of the axial length L.

[0043] Alternatively, the second catalyst region can be 99% or less, 95% or less, 90% or less, or 85% or less of the axial length L.

[0044] Preferably, the total length of the second region and the first region is equal to or greater than the axial length L.

[0045] The second catalyst region can overlap with the first catalyst region by 1 to 80 percent, preferably 1 to 60 percent, more preferably 1 to 50 percent, 1 to 30 percent, 1 to 20 percent, or even 1 to 15 percent of the axial length L. Alternatively, the total length of the second catalyst region and the first catalyst region may be equal to the axial length L. In another alternative, the total length of the second catalyst region and the first catalyst region may be less than the axial length L, for example, 95% or less, 90% or less, 80% or less, or 70% or less of the axial length L.

[0046] In some embodiments, the first catalyst region can be directly supported / deposited on the substrate. In certain embodiments, the second catalyst region can be directly supported / deposited on the substrate.

[0047] The second catalyst region may further include a second rare earth metal component such as lanthanum, neodymium, praseodymium, yttrium, gadolinium, scandium, or combinations thereof. These rare earth metal components can be introduced as dopants or mixed as physical mixtures / blends such as in oxide form.

[0048] The total washcoat loading of the second 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. Alternatively, the total washcoat loading of the first catalyst region can be 0.5 to 3.5 g / in 3 It may be, preferably 0.6 to 3 g / in 3 Or 0.7 to 2.5 g / in 3 It can be.

[0049] The third catalyst region The third catalyst region can contain a third Rh component of 0.1 to 30 g / ft 3 Preferably, the third catalyst region contains a third Rh component of 0.5 to 15 g / ft 3 More preferably, it can contain a third Rh component of 1 to 10 g / ft 3

[0050] The third catalyst region may further contain a third PGM component, a third oxygen storage capacity (OSC) material, a third alkali metal component or alkaline earth metal component, and / or a third inorganic oxide.

[0051] The third PGM component can include platinum, palladium, or a mixture thereof.

[0052] Alternatively, the third catalyst region may essentially not contain other PGM components other than the third Rh component.

[0053] The third OSC material can be cerium oxide, zirconium oxide, a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. More preferably, the third OSC material includes a ceria-zirconia mixed oxide, an alumina-ceria-zirconia mixed oxide, or a combination thereof. In addition, the third OSC material may further contain one or more of dopants such as lanthanum, neodymium, praseodymium, yttrium, etc. Further, the third OSC material may function as a carrier material for the third Rh component and / or the third PGM component. In some embodiments, the third OSC material includes a ceria-zirconia mixed oxide and an alumina-ceria-zirconia mixed oxide.

[0054] ​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, 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, more preferably less than 35:65.

[0055] The third OSC material (e.g., ceria-zirconia mixed oxide) can be 10 - 90 wt%, preferably 25 - 75 wt%, more preferably 30 - 60 wt% based on the total washcoat loading of the third catalyst region.

[0056] The loading of the third OSC material in the third catalyst region can be less than 2 g / in 3 In some embodiments, the loading of the third OSC material in the second catalyst region is 1.5 g / in 3 or less, 1.2 g / in 3 or less, 0.9 g / in 3 or less, 0.8 g / in 3 or less, or 0.7 g / in 3 or less.

[0057] The total washcoat loading of the third catalyst region can be less than 3.5 g / in 3 preferably 3.0 g / in 3 or less, 2.5 g / in 3 or less, or 2 g / in 3 or less.

[0058] The third alkali metal or alkaline earth metal is preferably barium, strontium, their mixed oxides or composite oxides. Preferably, when barium or strontium is present, the amount of barium or strontium is 0.1 - 15 wt%, more preferably 3 - 10 wt% based on the total weight of the third catalyst region.

[0059] The third alkali metal or alkaline earth metal is more preferably strontium. Strontium, when present, is preferably present in an amount of 0.1 to 15% by weight, more preferably 1.5 to 10% by weight, based on the total weight of the third catalyst region.

[0060] Also, the third 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 1.5 to 10% by weight, based on the total weight of the third catalyst region. The third alkali metal or alkaline earth metal is more preferably a composite oxide of barium and strontium.

[0061] 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.

[0062] In some embodiments, the third catalyst region is substantially free of the third alkali metal or alkaline earth metal. In further embodiments, the third catalyst region is substantially free of or does not contain the third alkali metal or alkaline earth metal.

[0063] The third inorganic oxide is preferably an oxide of an element of 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 oxide, neodymium oxide, praseodymium oxide, yttrium oxide, and mixed oxides or composite oxides thereof. Particularly preferably, the third inorganic oxide is alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxide. One particularly preferred third inorganic oxide is alumina or lanthanum-alumina.

[0064] The third OSC material and the third inorganic oxide can have a weight ratio of 10:1 or less, preferably 8:1 or less or 5:1 or less, more preferably 5:1 or less, and most preferably 4:1 or less.

[0065] Alternatively, the third OSC material and the third inorganic oxide can have a weight ratio of 10:1 to 1:10, preferably 8:1 to 1:8, or more preferably 5:1 to 1:5, or most preferably 4:1 to 1:4.

[0066] The third catalyst region can extend over 100 percent of the axial length L. Alternatively, the third catalyst region can be less than the axial length L, for example, 95% or less, 90% or less, 80% or less, or 70% or less of the axial length L. In certain embodiments, the third catalyst region can extend from the inlet end. In other embodiments, the third catalyst region can extend from the outlet end. In some embodiments, the third catalyst region can be supported / deposited directly on the substrate.

[0067] In some embodiments, the first Pt component in the first catalyst region can be at least 50%, 60%, 70%, or even 80% of the total Pt loading in the catalyst article.

[0068] In certain embodiments, the (weight) ratio of the total Pt loading to the total Pd loading is at least 1:5, at least 1:4, at least 1:3, at least 2:5, or 1:2.

[0069] Configurations of the first catalyst region, the second catalyst region, and the third catalyst region The second catalyst region may overlap with the first catalyst region by 1 to 80 percent, preferably 1 to 60 percent, more preferably 1 to 50 percent, 1 to 30 percent, 1 to 20 percent, or even 1 to 15 percent of the axial length L (see, for example, FIGS. 1b and 1c; the first catalyst region may cover the second catalyst region, or the second catalyst region may cover the first catalyst region). Alternatively, the total length of the second catalyst region and the first catalyst region may be equal to the axial length L (see, for example, FIGS. 1a and 2a). In yet another alternative, the total length of the second catalyst region and the first catalyst region may be less than the axial length L, for example, 95% or less, 90% or less, 80% or less, or 70% or less of the axial length L (see, for example, FIG. 1d).

[0070] In one aspect of the present invention, the various configurations of the catalyst article including the first catalyst region, the second catalyst region, and the third catalyst region can be prepared as follows.

[0071] FIG. 1a shows an embodiment according to the present invention, in which the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is equal to the axial length L. The third catalyst region extends to 100% of the axial length L and covers the first catalyst region and the second catalyst region as an upper layer.

[0072] FIG. 1b shows an embodiment according to the present invention, in which the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is greater than the axial length L. The third catalyst region extends to 100% of the axial length L and covers the first catalyst region and the second catalyst region as an upper layer.

[0073] FIG. 1c shows a modification of FIG. 1b.

[0074] Figure 1d shows an embodiment according to the present invention, in which the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is less than the axial length L. The third catalyst region extends to 100% of the axial length L and covers the first catalyst region and the second catalyst region as an upper layer.

[0075] Figure 1e shows an embodiment according to the present invention, in which the third catalyst region extends to 100% of the axial length L as a bottom layer, the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is equal to (it may also be greater than or less than) the axial length L.

[0076] Figure 2a shows an embodiment according to the present invention, in which the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is equal to (it may also be greater than or less than) the axial length L. The third catalyst region extends from the inlet end by less than 100% of the axial length L.

[0077] Figure 2b shows an embodiment according to the present invention, in which the first catalyst region extends from the inlet end by less than 100% of the axial length L, and the second catalyst region extends from the outlet end over less than 100% of the axial length L. The total length of the second catalyst region and the first catalyst region is equal to (it may also be greater than or less than) the axial length L. The third catalyst region extends from the outlet end by less than 100% of the axial length L.

[0078] Substrate Preferably, the substrate is a flow-through monolith.

[0079] The substrate can have a length of less than 200 mm, preferably 60 - 160 mm.

[0080] The flow-through monolith substrate has a first surface and a second surface, and defines a longitudinal direction therebetween. 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 surfaces of the walls defining each channel). Each of the plurality of channels has an opening in the first surface and an opening in the second surface. To avoid doubt, the flow-through monolith substrate is not a wall-flow filter.

[0081] The first surface is typically at the inlet end of the substrate, and the second surface is at the outlet end of the substrate.

[0082] The channels can be of a constant width, and each of the plurality of channels can have a uniform channel width.

[0083] Preferably, in a plane orthogonal to the longitudinal direction, the monolith substrate has 300 - 900 channels per square inch, preferably 400 - 800 channels. For example, on the first surface, the density of the open first channels and the closed second channels is 600 - 700 channels per square inch. These channels can have a cross-section that is rectangular, square, circular, elliptical, triangular, hexagonal, or other polygonal shape.

[0084] The monolith substrate acts as a carrier for holding a catalyst material. Suitable materials for forming the monolith 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 monolith substrates are well known in the art.

[0085] It should be noted that the flow-through monolithic substrate described herein is a single component (i.e., a single brick). Nevertheless, when forming an emissions treatment system, the substrate used can be formed by adhering together a plurality of channels or, as described herein, by adhering together a plurality of smaller substrates. Such techniques are well known in the art, along with suitable casings and configurations for emissions treatment systems.

[0086] In embodiments where the catalyst article of the present invention includes a ceramic substrate, the ceramic substrate can 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 aluminosilicates (such as cordierite and spodumene), or a mixture or mixed oxide of any two or more of these. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0087] In embodiments where the catalyst article of the present invention includes a metal substrate, the metal substrate can be made of any suitable metal, particularly heat-resistant metals and metal alloys such as titanium and stainless steel, and ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0088] Another aspect of the present disclosure is directed to a method for treating vehicle exhaust gas from a CNG engine containing NO x , CO, and HC (methane) using the catalyst article described herein. The test catalysts made according to this method exhibit improved catalyst properties compared to conventional TWCs (having the same or similar PGM loadings) (see, for example, Examples 1-3 and Tables 2-4).

[0089] Another aspect of the present disclosure is directed to a system for treating vehicle exhaust gas from a CNG engine, including the catalyst article described herein, along with a conduit for transferring exhaust gas through the system.

[0090] Definition As used herein, the term "region" typically refers to an area on a substrate obtained by drying and / or firing a washcoat. A "region" can be disposed or carried on a substrate, for example, as a "layer" or a "zone". The area or arrangement on a substrate is generally controlled during the process of applying a washcoat to the substrate. A "region" typically has a distinct boundary or edge (i.e., it is possible to distinguish one region from another using conventional analytical techniques).

[0091] Typically, a "region" has a substantially uniform length. The reference to "substantially uniform length" in this context refers to a length that does not deviate by more than 10% from its average value (e.g., the difference between the maximum length and the minimum length), preferably does not deviate by more than 5% from its average value, and more preferably does not deviate by more than 1% from its average value.

[0092] Each "region" preferably has a substantially uniform composition (i.e., there is no substantial difference in the composition of the washcoat when comparing one part of the region to another part of the same region). Substantially uniform composition in this context refers to a material (e.g., a region) where the difference in composition is 5% or less, usually 2.5% or less, and most commonly 1% or less when comparing one part of the region to another part of the same region.

[0093] As used herein, the term "zone" refers to a region 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).

[0094] The total length of the substrate is the distance between its inlet end and its outlet end (e.g., both ends of the substrate).

[0095] Any reference in this specification to a "zone disposed at the inlet end of the substrate" refers to a zone disposed or carried on the substrate that is closer to the inlet end of the substrate than to the outlet end of the substrate. Thus, the midpoint of the zone (i.e., the point at half its length) is closer to the inlet end of the substrate than to the outlet end of the substrate. Similarly, any reference in this specification to a "zone disposed at the outlet end of the substrate" refers to a zone disposed or carried on the substrate that is closer to the outlet end of the substrate than to the inlet end of the substrate. Thus, the midpoint of the zone (i.e., the point at half its length) is closer to the outlet end of the substrate than to the inlet end of the substrate.

[0096] When the substrate is a wall flow filter, generally, any reference to a "zone disposed at the inlet end of the substrate" refers to a zone disposed or carried on the substrate that (a) is closer to the inlet end (e.g., the open end) of the inlet channel of the substrate than to the closed end (e.g., the blocked or plugged end) of the inlet channel, and / or (b) is closer to the closed end (e.g., the blocked or plugged end) of the outlet channel of the substrate than to the outlet end (e.g., the open end) of the outlet channel.

[0097] Thus, the midpoint of the zone (i.e., the point at half its length) is (a) closer to the inlet end of the inlet channel of the substrate than to the closed end of the inlet channel and / or (b) closer to the closed end of the outlet channel of the substrate than to the outlet end of the outlet channel.

[0098] Similarly, when the substrate is a wall flow filter, any reference to a "zone disposed at the outlet end of the substrate" refers to a zone disposed or carried on the substrate that (a) A zone where it is closer to the outlet end (e.g., the open end) of the substrate outlet channel than to the closed end (e.g., the blocked or sealed end) of the outlet channel, and / or (b) Refers to a zone where it is closer to the closed end (e.g., the blocked or sealed end) of the substrate inlet channel than to the inlet end (e.g., the open end) of the inlet channel.

[0099] Therefore, the midpoint of the zone (i.e., the point at half of its length) is such that (a) it is closer to the outlet end of the substrate outlet channel than to the closed end of the outlet channel, and / or (b) it is closer to the closed end of the substrate inlet channel than to the inlet end of the inlet channel.

[0100] When the washcoat is present on the wall of the wall flow filter (i.e., the zone is within the wall), the zone can satisfy both (a) and (b).

[0101] The term "washcoat" is well-known in the art and generally refers to an adhesive coating applied to a substrate during the production of a catalyst.

[0102] The acronym "PGM", as used herein, 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.

[0103] The term "mixed oxide", as used herein, generally refers to a mixture of oxides in a single phase, as conventionally known in the art. The term "composite oxide", as used herein, generally refers to a composition of oxides having two or more phases, as conventionally known in the art.

[0104] As used herein, the phrase "consisting essentially of" limits the scope of a feature to include a specific material or step and any other materials or steps that do not materially affect the basic characteristics of that feature, such as trace impurities. The phrase "consisting essentially of" encompasses the phrase "consisting of".

[0105] As used herein, the phrase "substantially free of" when referring to a material typically means that the material is present in small amounts, such as 5 wt% or less, preferably 2 wt% or less, more preferably 1 wt% or less, in the context of the contents of a region, layer, or zone. The phrase "substantially free of" encompasses the phrase "free of".

[0106] As used herein, the phrase "essentially free of" when referring to a material typically means that the material is present in trace amounts, such as 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less, in the context of the contents of a region, layer, or zone. The phrase "essentially free of" encompasses the phrase "free of".

[0107] Any reference herein to the amount of a dopant expressed as wt% and in particular to the total amount refers to the weight of the carrier material or its refractory metal oxide.

[0108] The term "loading" as used herein refers to a measured value in units of g / ft on a metal weight basis. 3

[0109] The following examples are merely illustrative of the invention. Those skilled in the art will recognize many variations that are within the spirit and scope of the invention and the claims.

Examples

[0110] Materials All materials were commercially available and were obtained from known sources unless otherwise noted.

[0111] Catalyst 1 (Comparative Example) Catalyst 1 is a typical Pt-Pd-Rh ternary with three catalyst regions in a bilayer structure as shown in Figure 1a.

[0112] The first catalyst region: The first catalyst region starting at the inlet end consists of Pt and Pd supported on a washcoat of the first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading of the first region is about 2.4 g / in 3 and the Pt loading is 11 g / ft 3 and the Pd loading is 23 g / ft 3 was.

[0113] Next, using standard coating procedures, this washcoat was coated from the inlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils) and dried at 100°C.

[0114] The second catalyst region: The second catalyst region starting at the outlet end consists of Pt and Pd supported on a washcoat, and the washcoat is the same as the washcoat used in the first catalyst region.

[0115] Next, using standard coating procedures, this washcoat was coated from the outlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100°C, and fired at 500°C for 45 minutes.

[0116] The third catalyst region: The third catalyst region consists of Rh supported on a washcoat of the second CeZr mixed oxide and La-stabilized alumina. The washcoat loading of the third region is about 1.3 g / in 3 and the Rh loading is 4 g / ft 3 was.

[0117] Next, using a standard coating procedure, the washcoat was coated from each end face of the ceramic substrate including the first catalyst region and the second catalyst region from above. The target coating depth for each application amount was 50% of the length of the substrate, dried at 100°C, and fired at 500°C for 45 minutes.

[0118] Catalyst 2 (comparative example) Catalyst 2 is a Pt-Pd-Rh ternary catalyst having three catalyst regions with a bilayer structure.

[0119] First catalyst region: The first catalyst region starting at the inlet end consists of Pd supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pd loading amount is 34 g / ft 3 was.

[0120] Next, using a standard coating procedure, the washcoat was coated from the inlet face of the ceramic substrate with a coating depth targeting 67% of the substrate length (400 cpsi, wall thickness 4.3 mils) and dried at 100°C.

[0121] Second catalyst region: The second catalyst region starting at the outlet end consists of Pt supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pt loading amount is 34 g / ft 3 was.

[0122] Next, using a standard coating procedure, the washcoat was coated from the outlet face of the ceramic substrate with a coating depth targeting 33% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100°C, and fired at 500°C for 45 minutes.

[0123] Third catalyst region: The third catalyst region consists of Rh supported on a washcoat of a second CeZr mixed oxide and La-stabilized alumina. The washcoat loading amount of the third region is about 1.3 g / in 3 and the Rh loading amount is 4 g / ft 3 .

[0124] Next, using standard coating procedures, the washcoat was coated from each end face of the ceramic substrate including the first and second catalyst regions from above, and the target coating depth for each application amount was 50% of the length of the substrate. It was dried at 100 °C and fired at 500 °C for 45 minutes.

[0125] Catalyst 3 Catalyst 3 is a Pt-Pd-Rh ternary catalyst having three catalyst regions with a double-layer structure.

[0126] First catalyst region: The first catalyst region starting at the inlet end consists of Pt supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pt loading amount is 34 g / ft 3 .

[0127] Next, using standard coating procedures, the washcoat was coated from the inlet face of the ceramic substrate with a coating depth targeting 33% of the length of the substrate (400 cpsi, wall thickness 4.3 mils) and dried at 100 °C.

[0128] Second catalyst region: The second catalyst region starting at the outlet end consists of Pd supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pd loading amount is 34 g / ft 3 .

[0129] Next, using standard coating procedures, this washcoat was coated from the exit face of the ceramic substrate at a coating depth targeting 67% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100°C, and fired at 500°C for 45 minutes.

[0130] Third catalyst region: The third catalyst region consists of Rh supported on a washcoat of a second CeZr mixed oxide and La-stabilized alumina. The washcoat loading in the third region was about 1.3 g / in 3 and the Rh loading was 4 g / ft 3 It was.

[0131] Next, using standard coating procedures, this washcoat was coated from each end face of the ceramic substrate including the first and second catalyst regions from above, and the target coating depth for each application amount was 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0132] Catalyst 4 (comparative example) Catalyst 4 is a Pd-Rh ternary catalyst having three catalyst regions with a double-layer structure.

[0133] First catalyst region: The first catalyst region starting at the inlet end consists of Pd supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading in the first region was about 2.4 g / in 3 and the Pd loading was 34 g / ft 3 It was.

[0134] Next, using standard coating procedures, this washcoat was coated from the inlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils) and dried at 100°C.

[0135] Second catalyst region: The second catalyst region starting at the outlet end consists of Pd supported on a washcoat, and the washcoat is the same as the washcoat in the first catalyst region.

[0136] Then, using standard coating procedures, this washcoat was coated from the outlet surface of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100 °C, and fired at 500 °C for 45 minutes.

[0137] Third catalyst region: The third catalyst region consists of Rh supported on a washcoat of a second CeZr mixed oxide and La-stabilized alumina. The washcoat loading in the third region is about 1.3 g / in 3 and the Rh loading was 4 g / ft 3 was.

[0138] Then, using standard coating procedures, this washcoat was coated from each end surface of the ceramic substrate including the first catalyst region and the second catalyst region from above, and the target coating depth for each application amount was 50% of the substrate length, dried at 100 °C, and fired at 500 °C for 45 minutes.

[0139] Catalyst 5 (comparative example) Catalyst 5 is a Pt-Rh ternary catalyst having three catalyst regions with a double-layer structure.

[0140] First catalyst region: The first catalyst region starting at the inlet end consists of Pt supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading in the first region is about 2.4 g / in 3 and the Pt loading was 34 g / ft 3 was.

[0141] Next, using standard coating procedures, this washcoat was coated from the inlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils) and dried at 100°C.

[0142] Second catalyst region: The second catalyst region starting at the outlet end consists of Pt supported on the washcoat, and the washcoat is the same as the washcoat in the first catalyst region.

[0143] Next, using standard coating procedures, this washcoat was coated from the outlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100°C, and fired at 500°C for 45 minutes.

[0144] Third catalyst region: The third catalyst region consists of Rh supported on a washcoat of a second CeZr mixed oxide, La-stabilized alumina. The washcoat loading amount in the third region is about 1.3 g / in 3 and the Rh loading amount was 4 g / ft 3 at that time.

[0145] Next, using standard coating procedures, this washcoat was coated from each end face of the ceramic substrate including the first and second catalyst regions from the top, and the target coating depth for each application amount was 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0146] Catalyst 6 (comparative example) Catalyst 6 is a Pt-Pd-Rh ternary catalyst having three catalyst regions with a double-layer structure.

[0147] First catalyst region: The first catalyst region starting at the inlet end consists of Pd supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading of the first region is about 2.4 g / in 3 and the Pd loading is 34 g / ft 3 .

[0148] Next, using standard coating procedures, this washcoat was coated from the inlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils) and dried at 100 °C.

[0149] Second catalyst region: The second catalyst region starting at the outlet end consists of Pt supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading of the first region is about 2.4 g / in 3 and the Pt loading is 34 g / ft 3 .

[0150] Next, using standard coating procedures, this washcoat was coated from the outlet face of the ceramic substrate at a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100 °C, and calcined at 500 °C for 45 minutes.

[0151] Third catalyst region: The third catalyst region consists of Rh supported on a washcoat of a second CeZr mixed oxide, La-stabilized alumina. The washcoat loading of the third region is about 1.3 g / in 3 and the Rh loading is 4 g / ft 3 .

[0152] Next, using standard coating procedures, the washcoat was coated from each end face of the ceramic substrate including the first catalyst region and the second catalyst region from the top, and the target coating depth for each application amount was 50% of the length of the substrate, dried at 100 °C, and fired at 500 °C for 45 minutes.

[0153] Catalyst 7 Catalyst 7 is a Pt-Pd-Rh ternary catalyst having three catalyst regions with a bilayer structure.

[0154] First catalyst region: The first catalyst region starting from the inlet end is composed of Pt supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pt loading amount is 34 g / ft 3 was.

[0155] Next, using standard coating procedures, the washcoat was coated from the inlet face of the ceramic substrate with a coating depth targeting 50% of the length of the substrate (400 cpsi, wall thickness 4.3 mils) and dried at 100 °C.

[0156] Second catalyst region: The second catalyst region starting from the outlet end is composed of Pd supported on a washcoat of a first CeZr mixed oxide, La-stabilized alumina, and an alkali metal promoter. The washcoat loading amount of the first region is about 2.4 g / in 3 and the Pd loading amount is 34 g / ft 3 was.

[0157] Next, using standard coating procedures, the washcoat was coated from the outlet face of the ceramic substrate with a coating depth targeting 50% of the substrate length (400 cpsi, wall thickness 4.3 mils), dried at 100 °C, and fired at 500 °C for 45 minutes.

[0158] Third Catalytic Region: The third catalytic region consists of Rh supported on a washcoat of a second CeZr mixed oxide and La-stabilized alumina. The washcoat loading amount of the third region is about 1.3 g / in 3 and the Rh loading amount is 4 g / ft 3 .

[0159] Next, using standard coating procedures, this washcoat was coated from each end face of the ceramic substrate including the first and second catalytic regions from above, and the target coating depth for each application amount was 50% of the length of the substrate. It was dried at 100 °C and calcined at 500 °C for 45 minutes.

[0160] Catalyst 8 Catalyst 8 is a Pt-Pd-Rh ternary catalyst having a double-layer structure in three catalytic regions, which is the same as Comparative Catalyst 1 except for the PGM loading amount. Both the first and second catalytic regions have the same Pt loading amount of 4 g / ft 3 and the same Pd loading amount of 8 g / ft 3 , and in the third region has an Rh loading amount of 1 g / ft 3 .

[0161] Example 1: Light-Off Performance Test in Synthetic Catalytic Activity Test The catalytic performance test was carried out on Comparative Catalyst 1, Comparative Catalyst 2, and Catalyst 3 using simulated exhaust gas with perturbations having the compositions shown in Table 1 under the following conditions.

[0162]

Table 1

[0163] The catalytic performance test was carried out by setting the gas flow rate to a space velocity of 40,000 / hr, increasing the temperature from 100 °C to 550 °C at a heating rate of 10 °C / min, and analyzing the gas composition after passing through the catalyst. Lower T 50(Temperature at 50% conversion) means better catalyst performance. Comparative Catalyst 1, Comparative Catalyst 2, and Catalyst 3 were aged in an oven at 850 °C for 36 hours with 10% H2O in air.

[0164] As shown in Table 2, the temperature at 50% conversion for CH4 and NO x was significantly lower for Catalyst 3 compared to the temperatures of Comparative Catalysts 1 and 2.

[0165]

Table 2

[0166] Example 2: Procedure and Results of CNG Vehicle Test Comparative Catalyst 1, Comparative Catalyst 2, and Catalyst 3 were also evaluated for emission control performance under the world light vehicle test cycle (WLTC) using a lightweight CNG vehicle equipped with a 1.6L engine. The catalysts were aged on a gasoline engine bench under the conditions of SBC860 for 73 hours.

[0167] As shown in Table 3, from the emission results of the CNG vehicle, Catalyst 3 showed CH4 emissions equivalent to those of Comparative Catalyst 2 and much lower NO x emissions compared to Comparative Catalysts 1 and 2.

[0168]

Table 3

[0169] Example 3: CNG Bench Test Procedure and Results The catalyst performance test was conducted on a natural gas engine under the World Harmonized Transient Cycle (WHTC). The WHTC test was considered a reliable method for emission evaluation for engine operation. For each catalyst, the WHTC tests were carried out in the low-temperature and high-temperature states, and the emissions were measured downstream of the catalyst. The final WHTC emission value is the sum of the WHTC in the low-temperature state and the high-temperature state, accounting for 14% and 86% respectively.

[0170] In the WHTC test, the aftertreatment system consists of two bricks with a layout of comparison catalysts 4, 5, 6, or catalyst 7 upstream and catalyst 8 downstream. The following systems were tested for their catalyst performance. System 1: Comparison catalyst 4 + Catalyst 8 System 2: Comparison catalyst 5 + Catalyst 8 System 3: Comparison catalyst 6 + Catalyst 8 System 4: Catalyst 7 + Catalyst 8

[0171] The components were aged in an oven under the conditions of 850 °C for 36 hours using 10% H2O in air. The emission results in the natural gas engine for Systems 1 - 3 are shown in Table 4. The results show that System 4 has the lowest NO x emission of 275 mg / kwh, and when catalyst 7 is replaced with any one of comparison catalysts 4 - 6, the NO x emission increases significantly. The CO emissions and CH4 emissions from all of Systems 1 - 3 have a large margin within the range of China VI regulations.

[0172]

Table 4

Claims

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

2. The catalyst article according to claim 1, wherein the first catalyst region extends over 10 to 90 percent of the axial length L.

3. The catalyst article according to claim 1, wherein the second catalyst region extends over 10 to 90 percent of the axial length L.

4. The catalyst article according to claim 1, wherein the second catalyst region overlaps with the first catalyst region over 1 to 80 percent of the axial length L.

5. The catalyst article according to claim 1, wherein the total length of the second catalyst region and the first catalyst region is equal to the axial length L.

6. The catalyst article according to claim 1, wherein the total length of the second catalyst region and the first catalyst region is less than the axial length L.

7. The catalyst article according to claim 1, wherein the third catalyst region extends over 100 percent of the axial length L.

8. The catalyst article according to claim 1, wherein the third catalyst region extends over less than 100 percent of the axial length L.

9. The catalyst article according to claim 1, wherein the first catalyst region further comprises a first OSC material, a first alkali metal component or alkaline earth metal component, a first inorganic oxide, and / or a first rare earth component.

10. The catalyst article according to claim 1, wherein the second catalyst region further comprises a second platinum component, a second OSC material, a second alkali metal component or alkaline earth metal component, a second inorganic oxide, and / or a second rare earth component.

11. The catalyst article according to claim 1, wherein the third catalyst region further comprises a third platinum group metal (PGM) component, a third OSC material, a third alkali metal component or alkaline earth metal component, and / or a third inorganic oxide.

12. The catalyst article according to claim 11, wherein the third PGM component is Pd, Pt, or a combination thereof.

13. The catalyst article according to claim 1, wherein the first Pt component in the first catalyst region is at least 50% of the total Pt supported in the catalyst article.

14. The catalyst article according to claim 1, wherein the substrate is a flow-through monolith.

15. An exhaust treatment system for treating a flow of CNG exhaust gas, comprising a catalyst article according to any one of claims 1 to 14.

16. 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 14.

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