A novel zone catalyst for CNG engine exhaust gas treatment with improved ammonia emission control

Abstract

A three-way catalyst article and its use in an exhaust system for a compressed natural gas engine is disclosed. A catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, the catalyst article comprising: a substrate including an inlet end, an outlet end and having an axial length L; a first catalyst region beginning at the outlet end and extending over less than the axial length L, the first catalyst region comprising a first zeolite; and a second catalyst region beginning at the inlet end, the second catalyst region comprising a second Platinum Group Metal (PGM) component, a second Oxygen Storage Capacity (OSC) material, and a second inorganic oxide, the second PGM component being selected from the group consisting of palladium, platinum, rhodium, or a combination thereof.

Description

[Technical field]

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

[0002] CNG is composed of simple hydrocarbons, mainly methane, and produces much less CO2 per unit of energy. And CNG has been used as a clean energy alternative to traditional gasoline and diesel fuels. CNG is also preferred in the market due to its abundant supply and relatively low price. Therefore, in recent years, CNG engines have attracted more and more attention in the automobile market, especially for heavy vehicles that operate with CNG engines under stoichiometric calibration. Even when operating under CNG, automobile exhaust gas is unavoidable, which is usually composed of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides "NO". x " and conventional gasoline exhaust catalysts such as three-way catalysts (TWC) are usually applied to control exhaust gas from CNG engines. However, ammonia (NH3) is a typical pollutant that is not ammonia, but ammonia, and NO x It has been recognized as a by-product when using TWC on stoichiometric CNG engines to reduce CO2 emissions. Therefore, NH3 brings new pollutant emission problems such as secondary inorganic aerosol formation, which may lead to deterioration of air quality. To better control NH3 emissions, China's VI regulations for large CNG engines set NH3 emission limits as low as 10 ppm.

[0003] To meet China's VI regulations and control NH3 emissions, other researchers have attempted to use ammonia slip catalysts (ASC), which is a typical emission control approach in heavy-duty diesel (HDD) aftertreatment systems. However, due to different compositions in fuel sources (diesel vs. CNG) and different operating conditions (lean vs. stoichiometric), typical ASC designs do not work at all for NH3 emission control for stoichiometric CNG engines. Therefore, there remains a need for improved NH3 emission control catalysts specifically designed to treat exhaust gas emissions from stoichiometric CNG engines. Summary of the Invention

[0004] One aspect of the disclosure is a catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising: a substrate including an inlet end, an outlet end and having an axial length L; a first catalyst region beginning at the outlet end and extending over less than the axial length L, the first catalyst region comprising a first zeolite; and a second catalyst region beginning at the inlet end, the second catalyst region comprising a second platinum group metal (PGM) component, a second oxygen storage capacity (OSC) material, and a second inorganic oxide, the second PGM component being selected from the group consisting of palladium, platinum, rhodium, or a combination thereof.

[0005] The present invention also includes an exhaust system for a CNG engine that includes the catalytic article of the present invention.

[0006] The present invention also encompasses treating exhaust gas from a CNG engine, particularly a stoichiometric CNG engine, comprising contacting the exhaust gas with a catalytic article of the present invention. [Brief description of the drawings]

[0007] [Figure 1]Illustrated are configurations of TWC-1, TWC-2, TWC-3, and TWC-4 in which a first catalyst region is a bottom layer that extends 100% of the axial length L, and a second catalyst region is a top layer that extends 100% of the axial length L. [Figure 2a] 1 illustrates an embodiment according to the present invention in which the first catalyst region extends from the outlet end less than 100% of the axial length L, and the second catalyst region extends from the inlet end 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. [Figure 2b] 1 illustrates an embodiment according to the present invention in which the first catalyst region extends from the outlet end less than 100% of the axial length L, and the second catalyst region extends from the inlet end 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. [Figure 2c] 1 illustrates an embodiment according to the present invention in which the first catalyst region extends from the outlet end less than 100% of the axial length L, and the second catalyst region extends from the inlet end 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. [Figure 2d] 1 illustrates an embodiment according to the present invention in which a first catalyst region extends from the outlet end less than 100% of the axial length L, and a second catalyst region extends from the inlet end 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. [Figure 2e] 1 illustrates an embodiment according to the present invention in which the first catalyst region extends from the outlet end less than 100% of the axial length L, and the second catalyst region extends from the inlet end 100% of the axial length L. The total length of the second and first catalyst regions is greater than the axial length L, and the second catalyst region overlies the first catalyst region. [Figure 3a] 1 illustrates an embodiment according to the present invention, where a first catalyst region extends less than 100% of the axial length L from the outlet end and a 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 equal to the axial length L. A third catalyst region extends less than 100% of the axial length L from the inlet end. [Figure 3b] 1 illustrates an embodiment according to the present invention, where a first catalyst region extends less than 100% of the axial length L from the outlet end and a 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 equal to the axial length L. A third catalyst region extends less than 100% of the axial length L from the inlet end and partially covers the first catalyst region. [Figure 3c] 1 illustrates an embodiment according to the present invention in which a first catalyst region extends less than 100% of the axial length L from the outlet end and a second catalyst region extends less than 100% of the inlet end configuration, axial length L. The total length of the second and first catalyst regions is equal to or less than the axial length L. A third catalyst region extends 100% of the axial length L and overlaps the first and second catalyst regions as an upper layer. [Figure 3d] 1 illustrates an embodiment according to the present invention in which a first catalyst region extends less than 100% of the axial length L from the outlet end and a second catalyst region extends less than 100% of the axial length L from the inlet end configuration. The total length of the second and first catalyst regions is greater than the axial length L. The third catalyst region extends to 100% of the axial length L. [Figure 3e] 1 illustrates an embodiment according to the present invention in which a first catalyst region extends less than 100% of the axial length L from the outlet end and a second catalyst region extends less than 100% of the axial length L in the inlet end configuration. The total length of the second and first catalyst regions is greater than the axial length L. A third catalyst region extends less than 100% of the axial length L from the inlet end. [Figure 4]1 illustrates an embodiment according to the present invention, in which the first catalyst region extends less than 100% of the axial length L from the outlet end and the third catalyst region extends less than 100% of the axial length L from the inlet end. The total length of the first and second catalyst regions can be less than, equal to, or greater than the axial length L. The second catalyst region extends less than 100% of the axial length L from the inlet end and the fourth catalyst region extends less than 100% of the axial length L from the outlet end. The total length of the second and fourth catalyst regions can be less than, equal to, or greater than the axial length L. The second and fourth catalyst regions constitute a bottom layer and the third and first catalyst regions constitute a top layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention relates to the 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, the present invention relates to the control of ammonia emissions and the reduction of NOx in vehicle exhaust systems. x The process of the present invention also reduces process run times and reduces catalyst costs.

[0009] One aspect of the disclosure is a catalyst article for treating exhaust gas from a compressed natural gas (CNG) engine, comprising: a substrate including an inlet end, an outlet end and having an axial length L; a first catalyst region beginning at the outlet end and extending over less than the axial length L, the first catalyst region comprising a first zeolite; and a second catalyst region beginning at the inlet end, the second catalyst region comprising a second platinum group metal (PGM) component, a second oxygen storage capacity (OSC) material, and a second inorganic oxide, the second PGM component being selected from the group consisting of palladium, platinum, rhodium, or a combination thereof.

[0010] The first catalytic region The first zeolite may be a silica-containing zeolite, such as a siliceous zeolite, also referred to as an aluminosilicate zeolite, a metal-substituted aluminosilicate zeolite, an aluminophosphate (AIPO) zeolite, a metal-substituted (MeAIPO) zeolite, a silicoaluminophosphate (SAPO), or a metal-substituted silicoaluminophosphate (MeAPSO), or a modified zeolite with Zr, P. The zeolite is preferably an aluminosilicate or a silicoaluminophosphate (SAPO) zeolite. More preferably, the zeolite is an aluminosilicate.

[0011] The zeolite may be a microporous or non-microporous zeolite, preferably the zeolite has a framework type selected from the group consisting of: ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, AST, ASV, ATT, BCT, BEA, BEC, BOF, BOG, BRE, CAN, CDO, CFI, CGS, CHA, -CHI, CON, DAC, DDR, DFT, EAB, EDI, EPI, ERI, FER, GIS, GOD, IHW, ITE, ITW, LEV, KFI, MER, MFI, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON. Each of the three letter codes above represents a framework type according to the "IUPAC Commission on zeolite Nomenclature" and / or the "structure Commission of the international Zeolite Association". More preferably, the first zeolite has a framework type selected from AEI, BEA, CHA, FER, FAU, MFA. In some embodiments, the first zeolite can be AEI, BEA, FER, or CHA. In further embodiments, the first zeolite can be AEI or CHA. In yet further embodiments, the first zeolite can be AEI. In another further embodiment, the first zeolite can be CHA. Generally, the first zeolite can have a silica to alumina ratio (SAR) of 2 to 500, preferably 4 to 250, more preferably 8 to 150. In some embodiments, the first zeolite is AEI or CHA with a SAR range of 8 to 40. In a further embodiment, the first zeolite is AEI or CHA having a SAR range of 10-30.

[0012] In some embodiments, the first catalyst region can further comprise a first PGM component selected from the group consisting of Pd, Pt, Rh, and combinations thereof. In further embodiments, the first PGM component can be Pt. In certain embodiments, the loading of the first PGM component is between 0.1 and 50 g / ft 3 Or 0.1 to 25 g / ft3 Or 0.1 to 15 g / ft 3 It could be.

[0013] In other embodiments, the first catalytic region can further comprise a first transition metal, which can be selected from the group consisting of Fe, Cu, Co, Mn, Ni, Zn, Ce, Mo, Ag, and any combination of two or more. In further embodiments, the first transition metal can be selected from Ce, Mn, Cu, Co, Ni, or Fe, and any combination of two or more. In yet other embodiments, the first transition metal can be Cu and / or Fe. In certain embodiments, the first transition metal is 0.01-20 wt%, preferably 0.1-15 wt%, more preferably 0.5-10 wt%, based on the weight of the first zeolite.

[0014] In some embodiments, the first catalyst region can extend over 10-50%, 10-40%, or 10-30% of the axial length L. Alternatively, the first catalyst region can extend over 20-50%, or 20-40% of the axial length L.

[0015] The total washcoat loading of the first catalyst region was 3.5 g / in 3 Less than 3.0 g / in 3 Less than or equal to 2.5g / in 3 Alternatively, the total washcoat loading of the first catalyst region can be between 0.5 and 3.5 g / in 3 , preferably 0.6 to 3 g / in 3 Or 0.7 to 2.8 g / in 3 It could be.

[0016] Second catalytic region In some embodiments, the second PGM components can be Pd and Rh, while in other embodiments, the second PGM components can be Pt and Rh.

[0017] 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 of dopants such as lanthanum, neodymium, praseodymium, yttrium, etc. Furthermore, the second OSC material may function as a support material for the second PGM component. In some embodiments, the second OSC material includes ceria-zirconia mixed oxide and alumina-ceria-zirconia mixed oxide.

[0018] The ceria-zirconia mixed oxide may 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 may 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.

[0019] The second OSC material (eg, 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.

[0020] The loading of the second OSC material in the second catalyst region is 2 g / in 3 In some embodiments, the loading of the second OSC material in the second catalytic region can be less than 2 g / in 3 , 1.5g / in 3 , 1.2g / in 3 , 1.0g / in 3 , or 0.8 g / in 3 The following is the result.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In some embodiments, the second catalytic region can further comprise a second alkali or alkaline earth metal.

[0025] The second alkali or alkaline earth metal is preferably barium, strontium, a mixed oxide or a composite oxide thereof. Preferably, the barium or strontium, if present, is in an amount of 0.1 to 15 wt. %, more preferably 3 to 10 wt. %, barium or strontium, based on the total weight of the second catalytic region.

[0026] It is even more preferred that the second alkali or alkaline earth metal is strontium, which, when present, is preferably present in an amount of from 0.1 to 15 wt %, more preferably from 3 to 10 wt %, based on the total weight of the second catalyst region.

[0027] 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 to 15% by weight, more preferably 3 to 10% by weight, based on the total weight of the second catalyst region. More preferably, the second alkali metal or alkaline earth metal is a composite oxide of barium and strontium.

[0028] Preferably, the barium or strontium is present as BaCO3 or SrCO3. Such materials can be prepared by any method known in the art, such as incipient wetness impregnation or spray drying.

[0029] In some embodiments, the second catalytic region is substantially free of a second alkali metal or a second alkaline earth metal, hi further embodiments, the second catalytic region is substantially free or free of a second alkali metal or a second alkaline earth metal.

[0030] In some embodiments, the second catalyst region can extend over 50-90%, 50-80%, or 50-70% of the axial length L. Alternatively, the second catalyst region is between 60 and 90 percent of the axial length L, preferably between 60 and 80 percent of the axial length L.

[0031] Alternatively, the second catalytic region may be less than or equal to 90%, 85%, 80%, or 75% of the axial length L.

[0032] In some embodiments, the second catalytic region may overlap the first catalytic region. In further embodiments, the second catalytic region may overlap the first catalytic region over 5-40% of the axial length L. Preferably, the total length of the second and first regions is equal to or greater than the axial length L. In certain embodiments, the total length of the first and second catalytic regions is equal to 100% L. In other embodiments, the total length of the first and second catalytic regions is less than 100% L, e.g., less than or equal to 99%, 95%, 85%, or 80% of the axial length L.

[0033] In some embodiments, the first catalytic region may be supported / deposited directly on the substrate. In certain embodiments, the second catalytic region may be supported / deposited directly on the substrate.

[0034] The total washcoat loading of the second catalyst region was 3.5 g / in 3 Less than 3.0 g / in 3 Less than or equal to 2.5g / in 3 Alternatively, the total washcoat loading of the first catalyst region can be between 0.5 and 3.5 g / in 3 , preferably 0.6 to 3 g / in 3 Or 0.7 to 2.8 g / in 3 It could be.

[0035] The third catalytic area The catalyst article may further include a third catalyst region. In some embodiments, the third catalyst region may begin at the inlet end and extend over less than the axial length L.

[0036] The third catalyst region may further comprise a third PGM component, a third oxygen storage capacity (OSC) material, a third alkali or alkaline earth metal component, and / or a third inorganic oxide.

[0037] The third PGM component may 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 mixtures thereof. In other embodiments, the third PGM component may be platinum, rhodium, or mixtures thereof.

[0038] 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 of dopants such as lanthanum, neodymium, praseodymium, yttrium, etc. Furthermore, the third OSC material may function as a support material for the third PGM component. In some embodiments, the third OSC material includes ceria-zirconia mixed oxide and alumina-ceria-zirconia mixed oxide.

[0039] The ceria-zirconia mixed oxide may 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 may 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.

[0040] The third OSC material (eg, 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.

[0041] The loading of the third OSC material in the third catalytic region is 2 g / in 3 In some embodiments, the loading of the third OSC material in the second catalytic region can be less than 2.0 g / in 3, 1.5g / in 3 , 1.2g / in 3 , 1.0g / in 3 , or 0.8 g / in 3 The following is the result.

[0042] The total washcoat loading of the third catalyst region was 3.5 g / in 3 Less than 3.0 g / in 3 Below 2.5g / in 3 , or 2g / in 3 It could be.

[0043] The third alkali or alkaline earth metal is preferably barium, strontium, a mixed oxide or a composite oxide thereof. Preferably, the barium or strontium, if present, is in an amount of 0.1 to 15 wt. %, more preferably 3 to 10 wt. %, barium or strontium, based on the total weight of the third catalytic region.

[0044] Even more preferably, the third alkali or alkaline earth metal is strontium, which, when present, is preferably present in an amount of from 0.1 to 15 wt %, more preferably from 3 to 10 wt %, based on the total weight of the third catalytic region.

[0045] Also, 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 catalytic region. More preferably, the third alkali or alkaline earth metal is a composite oxide of barium and strontium.

[0046] Preferably, the barium or strontium is present as BaCO3 or SrCO3. Such materials can be prepared by any method known in the art, such as incipient wetness impregnation or spray drying.

[0047] In some embodiments, the third catalytic region is substantially free of a third alkali metal or a third alkaline earth metal, hi further embodiments, the third catalytic region is substantially free or free of a third alkali metal or a third alkaline earth metal.

[0048] 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, neodymium, praseodymium, 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.

[0049] The third OSC material and the third inorganic oxide can 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.

[0050] 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.

[0051] The third catalyst region can extend over 100 percent of the axial length L. (See, e.g., FIGS. 3c and 3d). Alternatively, the third catalyst region can be less than the axial length L, such as 95%, 90%, 80%, or 70% or less of the axial length L (See, e.g., FIGS. 3a, 3b, 3e, 4). In some embodiments, the third catalyst region can begin at the outlet end.

[0052] The fourth catalytic region The catalyst article may further include a fourth catalyst region. In some embodiments, the fourth catalyst region may begin at the outlet end and may extend over less than the axial length L.

[0053] The fourth catalytic region may further comprise a fourth PGM component and a fourth inorganic oxide.

[0054] The fourth PGM component may be selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof. In some embodiments, the fourth PGM component may be platinum. In further embodiments, the fourth catalyst region is substantially free of PGM components other than Pt.

[0055] The fourth inorganic oxide is preferably an oxide of an element of group 2, group 3, group 4, group 5, group 13, and group 14. The fourth 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 preferably, the fourth inorganic oxide is alumina, lanthanum-alumina, zirconia, or magnesia / alumina composite oxide. One particularly preferred fourth inorganic oxide is alumina or lanthanum-alumina.

[0056] The fourth catalytic region can be less than the axial length L, for example, 95%, 90%, 80%, or 70% of the axial length L or less.

[0057] In some embodiments, the fourth catalyst region can extend over 10-50%, 10-40%, or 10-30% of the axial length L. Alternatively, the fourth catalyst region can extend over 20-50% or 20-40% of the axial length L (see, e.g., FIG. 4).

[0058] The catalyst article of the present invention may include additional components that are well known to those skilled in the art. For example, the composition of the present invention may further include at least one binder and / or at least one surfactant. When a binder is present, a dispersible alumina binder is preferred.

[0059] Base material Preferably, the substrate is a flow-through monolith.

[0060] The substrate can be less than 8 inches in length, preferably 4 to 7 inches.

[0061] The flow-through monolith substrate has a first surface and a second surface defining 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 longitudinally and provide a plurality of interior surfaces (e.g., surfaces of walls defining each channel). Each of the plurality of channels has an opening at the first surface and an opening at the second surface. For the avoidance of doubt, the flow-through monolith substrate is not a wall-flow filter.

[0062] The first surface is typically at an inlet end of the substrate and the second surface is at an outlet end of the substrate.

[0063] The channels may be of constant width, and each of the multiple channels may have a uniform channel width.

[0064] Preferably, in a plane perpendicular to the longitudinal direction, the monolith substrate has 300 to 900 channels per square inch, preferably 400 to 800 channels per square inch. For example, on the first face, the density of open first channels and closed second channels is 600 to 700 channels per square inch. The channels can have cross-sections that are rectangular, square, circular, oval, triangular, hexagonal, or other polygonal shapes.

[0065] The monolith substrate acts as a support to hold the catalytic 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.

[0066] It should be noted that the flow-through monolith substrates described herein are unitary components (i.e., a single brick-like mass). Nevertheless, when forming an emission treatment system, the substrates used may be formed by bonding together multiple channels, or by bonding together multiple smaller substrates as described herein. Such techniques, along with suitable casings and configurations of emission treatment systems, are well known in the art.

[0067] In embodiments in which the catalytic article of the present invention includes a ceramic substrate, the ceramic substrate may be made of any suitable refractory material, such as alumina, silica, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicates and metalloid aluminosilicates (such as cordierite and spodumene), or mixtures or mixed oxides of any two or more thereof. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0068] In embodiments in which the catalytic article of the present invention 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, and ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0069] In some embodiments, the first catalytic region can be located on a different substrate than the second (or optionally third) catalytic region. In certain embodiments, the first catalytic region and the fourth catalytic region can be on the same substrate, but on a different substrate than the second (or optionally third) catalytic region.

[0070] Another aspect of the present disclosure is a method for producing a NO x The present invention is directed to a method for treating vehicle exhaust gases from a stoichiometric CNG engine containing CO, HC (methane), and ammonia. Test catalysts made according to the present invention show significantly improved NH3 control performance compared to conventional TWCs (having the same or similar PGM loadings), and also show improved performance in ammonia emission control under a wide lambda range (see, e.g., Example 1 and Tables 1-2).

[0071] Another aspect of the present disclosure is directed to a system for treating vehicle exhaust gases comprising a catalyst article as described herein along with a conduit for transporting exhaust gas through the system. In some embodiments, the system does not include an ammonia slip catalyst (ASC).

[0072] definition The term "region" as used herein refers to an area on a substrate that is typically obtained by drying and / or calcining a washcoat. A "region" can be disposed or carried on a substrate as, for example, a "layer" or a "zone." The area or arrangement on the substrate is generally controlled during the process of applying the 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).

[0073] Typically, a "region" has a substantially uniform length. Reference to a "substantially uniform length" in this context refers to a length that does not deviate from its average value by more than 10% (e.g., the difference between the maximum and minimum length), preferably a length that does not deviate from its average value by more than 5%, and more preferably a length that does not deviate from its average value by more than 1%.

[0074] Each "region" preferably has a substantially uniform composition (i.e., there is no substantial difference in the composition of the washcoat when comparing one portion of the region to another portion of the region). Substantially uniform composition in this context refers to a material (e.g., region) that has a compositional difference of 5% or less, usually 2.5% or less, and most usually 1% or less, when comparing one portion of the region to another portion of the region.

[0075] As used herein, the term "zone" refers to a region having a length that is less than the entire length of the substrate, such as a length that is 75% or less of the entire length of the substrate. A "zone" typically has a length that is at least 5% (e.g., 5% or more) of the entire length of the substrate (i.e., a substantially uniform length).

[0076] The overall length of a substrate is the distance between its inlet end and its outlet end (eg, both ends of the substrate).

[0077] Any reference herein to a "zone disposed at the inlet end of a substrate" refers to a zone disposed on or supported by a substrate, which 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., a 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 herein to a "zone disposed at the outlet end of a substrate" refers to a zone disposed on or supported by a substrate, which 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., a point at half its length) is closer to the outlet end of the substrate than to the inlet end of the substrate.

[0078] 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 on or supported by the substrate, (a) a zone that is closer to the inlet end (e.g., an open end) of an inlet channel of the substrate than to the closed end (e.g., a blocked or plugged end) of the inlet channel; and / or (b) Refers to a zone that is closer to the closed end (e.g., blocked or plugged end) of an outlet channel of a substrate than to the outlet end (e.g., open end) of the outlet channel.

[0079] 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.

[0080] Similarly, where 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 on or carried by the substrate, (a) a zone that is closer to the outlet end (e.g., an open end) of the outlet channel of the substrate than to the closed end (e.g., a blocked or plugged end) of the outlet channel; and / or (b) Refers to a zone that is closer to the closed end (e.g., blocked or plugged end) of an inlet channel of a substrate than to the inlet end (e.g., open end) of the inlet channel.

[0081] Thus, the midpoint of the zone (i.e., the point at half its length) is (a) closer to the outlet end of the outlet channel of the substrate than to the closed end of the outlet channel, and / or (b) closer to the closed end of the inlet channel of the substrate than to the inlet end of the inlet channel.

[0082] If the washcoat is present on the wall of a wall-flow filter (ie, the zone is intramural), the zone may satisfy both (a) and (b).

[0083] The term "washcoat" is well known in the art and typically refers to an adherent coating that is applied to a substrate during the production of a catalyst.

[0084] 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. In general, the term "PGM" preferably refers to metals selected from the group consisting of Rh, Pt, and Pd.

[0085] The term "mixed oxide" as used herein generally refers to a mixture of oxides in a single phase, as is conventionally known in the art. The term "complex oxide" as used herein generally refers to a composition of oxides having two or more phases, as is conventionally known in the art.

[0086] As used herein, the phrase "consisting essentially of" limits the scope of a feature to include the specified materials or steps and any other materials or steps, e.g., trace impurities, that do not substantially affect the basic properties of the feature. "Consisting essentially of" encompasses the phrase "consisting of."

[0087] As used herein with respect to a material, the term "substantially free" typically means that the material is present in a small amount, e.g., 5% by weight or less, preferably 2% by weight or less, more preferably 1% by weight or less, in relation to the contents of a region, layer, or zone. The term "substantially free" encompasses the term "free."

[0088] As used herein with respect to a material, the term "essentially free" typically means that the material is present in trace amounts, e.g., 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, in the context of the contents of a region, layer, or zone. The term "essentially free" encompasses the term "free."

[0089] As used herein, any reference to an amount of dopant expressed as weight percent, particularly a total amount, refers to the weight of the support material or refractory metal oxide thereof.

[0090] As used herein, the term "loading" refers to g / ft2 on a metal weight basis. 3 Refers to the measurement in units of .

[0091] The following examples are merely illustrative of the present invention, and those skilled in the art will recognize many variations that are within the spirit and scope of the claims. EXAMPLES

[0092] material All materials are commercially available and were obtained from known sources unless otherwise stated.

[0093] TWC-1 TWC-1 is a typical ternary (Pt-Pd-Rh) catalyst with a double-layer structure in the two catalytic regions, as shown in Figure 1. The bottom layer consists of Pt and Pd supported on a first CeZr mixed oxide, La-stabilized alumina, and a washcoat of Sr promoter. The washcoat loading of the bottom layer is about 2.0 g / in. 3 The Pt loading is 30 g / ft 3 , Pd loading is 60g / ft 3 Using standard coating procedures, the washcoat was coated (400 cpsi, 4.3 mil wall thickness) from each end face of the ceramic substrate with a coating depth targeted to be 50% of the substrate length, dried at 100° C., and fired at 500° C. for 45 minutes.

[0094] The top layer is made of a second CeZr mixed oxide, Rh supported on a washcoat of La-stabilized alumina. The washcoat loading of the second layer is about 1.3 g / in. 3 The Rh loading is 10 g / ft 3 This second washcoat was then coated from each end face of the ceramic substrate containing the bottom layer using standard coating procedures with a coating depth targeted to be 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0095] TWC-2 TWC-2 is a typical ternary (Pt-Pd-Rh) catalyst with a double-layer structure in the two catalytic regions, as shown in Figure 1. The bottom layer consists of Pt and Pd supported on a first CeZr mixed oxide, La-stabilized alumina, and a washcoat of Sr promoter. The washcoat loading of the bottom layer is about 2.0 g / in. 3 The Pt loading is 18 g / ft 3 , Pd loading is 36g / ft 3 Using standard coating procedures, the washcoat was coated (400 cpsi, 4.3 mil wall thickness) from each end face of the ceramic substrate with a coating depth targeted to be 50% of the substrate length, dried at 100° C., and fired at 500° C. for 45 minutes.

[0096] The top layer is made of a second CeZr mixed oxide, Rh supported on a washcoat of La-stabilized alumina. The washcoat loading of the second layer is about 1.3 g / in. 3 The Rh loading is 6 g / ft 3 This second washcoat was then coated from each end face of the ceramic substrate containing the bottom layer using standard coating procedures with a coating depth targeted to be 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0097] TWC-3 TWC-3 is a typical ternary (Pt-Pd-Rh) catalyst with a double-layer structure in the two catalytic regions, as shown in Figure 1. The bottom layer consists of Pd supported on a first CeZr mixed oxide, La-stabilized alumina, and a Ba-promoter washcoat. The washcoat loading of the bottom layer is about 2.2 g / in 3 The Pt loading is 5 g / ft 3 , Pd loading is 47g / ft 3 Using standard coating procedures, the washcoat was coated (400 cpsi, 4.3 mil wall thickness) from each end face of the ceramic substrate with a coating depth targeted to be 50% of the substrate length, dried at 100° C., and fired at 500° C. for 45 minutes.

[0098] The top layer is made of a second CeZr mixed oxide, Pt and Rh supported on a washcoat of La-stabilized alumina. The washcoat loading of the second layer is about 1.3 g / in. 3 The Pt loading is 4g / ft 3 , Rh loading is 10g / ft 3 This second washcoat was then coated from each end face of the ceramic substrate containing the bottom layer using standard coating procedures with a coating depth targeted to be 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0099] TWC-4 TWC-4 is a typical ternary (Pt-Pd-Rh) catalyst with a double-layer structure in the two catalytic regions, as shown in Figure 1. The bottom layer consists of Pd supported on a first CeZr mixed oxide, La-stabilized alumina, and a Ba-promoter washcoat. The washcoat loading of the bottom layer is about 2.2 g / in. 3 The Pd loading is 24 g / ft 3Using standard coating procedures, the washcoat was coated (400 cpsi, 4.3 mil wall thickness) from each end face of the ceramic substrate with a coating depth targeted to be 50% of the substrate length, dried at 100° C., and fired at 500° C. for 45 minutes.

[0100] The top layer is made of a second CeZr mixed oxide, Pt and Rh supported on a washcoat of La-stabilized alumina. The washcoat loading of the second layer is about 1.3 g / in. 3 The Pt loading is 4.5 g / ft 3 , Rh loading is 9g / ft 3 This second washcoat was then coated from each end face of the ceramic substrate containing the bottom layer using standard coating procedures with a coating depth targeted to be 50% of the substrate length, dried at 100°C, and fired at 500°C for 45 minutes.

[0101] Comparative catalyst article 1 A catalyst with three catalytic regions was prepared (see, for example, FIG. 3a).

[0102] The first catalytic region The first catalytic region consisted of Pt supported on washcoated Si-stabilized alumina and alumina sol as a binder, with a total washcoat loading of approximately 2.1 g / in 3 The Pt loading is 5 g / ft 3 This catalytic area is the same as a typical NH3 oxidation catalyst coating applied in heavy duty diesel applications.

[0103] The washcoat for the first catalyst region was coated from the outlet end face of a ceramic substrate (400 cpsi, 4.3 mil wall thickness) using standard coating procedures with a targeted coating depth of 33% of the substrate length.

[0104] The second catalytic region The washcoat for the second catalyst region was the same as the TWC-2 bottom layer (approximately 2.0 g / in 3, Pt loading is 18g / ft 3 and Pd loading is 36g / ft 3 The washcoat was applied to the inlet end of the ceramic substrate containing the first catalytic region using standard coating procedures with a target coating depth of 67% of the substrate length.

[0105] The third catalytic area The washcoat of the third catalyst region was the same as the TWC-2 top layer (approximately 1.3 g / in 3 , Rh loading is 6g / ft 3 ), and the washcoat for the third catalyst region was also coated from the top, from the inlet end of the ceramic substrate containing the first and second catalyst regions, using a standard coating procedure with a targeted coating depth of 67% of the substrate length. The catalyst article was dried at 100° C. and calcined at 500° C. for 45 minutes.

[0106] Catalyst article 2 A catalyst with three catalytic regions was prepared (see, for example, FIG. 3a).

[0107] The first catalytic region The first catalytic region is comprised of Cu supported on a CHA-type zeolite having an SAR range of about 20-24 and a binder, with a total washcoat loading of about 2.0 g / in 3 The Cu loading was 3.3 wt% (based on the weight of CHA).

[0108] The washcoat for the first catalyst region was coated from the outlet end face of a ceramic substrate (400 cpsi, 4.3 mil wall thickness) using standard coating procedures with a targeted coating depth of 43% of the substrate length.

[0109] Second catalytic region The washcoat for the second catalyst region was the same as the TWC-4 bottom layer (approximately 2.2 g / in 3 , Pd loading is 24g / ft 3The second catalyst region washcoat was coated using standard coating procedures from the inlet end of the ceramic substrate containing the first catalyst region to a target coating depth of 57% of the substrate length.

[0110] The third catalytic area The washcoat of the third catalyst region was the same as the top layer of TWC-4 (approximately 1.3 g / in 3 , Pt loading is 4.5g / ft 3 and Rh loading is 9g / ft 3 ) and the washcoat for the third catalyst region was also coated from the top, from the inlet end of the ceramic substrate containing the first and second catalyst regions, using a standard coating procedure with a target coating depth of 57% of the substrate length. The catalyst was dried at 100°C and calcined at 500°C for 45 minutes.

[0111] Catalyst article 3 A catalyst having four catalytic regions was prepared (see, for example, FIG. 4).

[0112] The first catalytic region The first catalyst region consists of Cu supported on a CHA-type zeolite with a SAR range of about 20-24 and a binder. The total washcoat loading of this catalyst region is about 2.4 g / in. 3 The Cu loading was 3.3%.

[0113] The second catalytic region The washcoat for the second catalyst region was the same as the TWC-4 bottom layer (approximately 2.2 g / in 3 , Pd loading is 24g / ft 3 ) was.

[0114] The third catalytic area The washcoat of the third catalyst region was the same as the top layer of TWC-4 (approximately 1.3 g / in 3 , Pt loading is 4.5g / ft 3 and Rh loading is 9g / ft 3 ) was.

[0115] The fourth catalytic region The fourth catalytic region is made of Pt supported on an alumina and binder washcoat. The total washcoat loading of this catalytic region is about 1.0 g / in 3 The Pt loading is 3 g / ft 3 It was.

[0116] Coating sequence and depth The washcoat for the fourth catalyst region was coated from the outlet end of the ceramic substrate (400 cpsi, 4.3 mil wall thickness) using standard coating procedures with a coating depth targeted at 43% of the substrate length. The washcoat for the first catalyst region was coated from the outlet end of the ceramic substrate (400 cpsi, 4.3 mil wall thickness) containing the fourth catalyst region using standard coating procedures with a coating depth targeted at 43% of the substrate length.

[0117] The washcoat for the second catalyst region was coated from the inlet end of the ceramic substrate containing the first and fourth catalyst regions from above using a standard coating procedure with a coating depth targeted at 57% of the substrate length, and the washcoat for the third catalyst region was coated from the inlet end of the ceramic substrate containing the first, second and fourth catalyst regions from above using a standard coating procedure with a coating depth targeted at 57% of the substrate length. The catalyst article was dried at 100° C. and calcined at 500° C. for 45 minutes.

[0118] Catalyst article 4 A catalyst with three catalytic regions was prepared (see, for example, FIG. 3a).

[0119] The first catalytic region The first catalytic region is comprised of Pt supported on an AEI zeolite having an SAR range of about 17-22 and a binder. The total washcoat loading of this catalytic region is about 2.5 g / in 3 The Pt loading is 5 g / ft 3The washcoat for the first catalyst region was coated from the outlet end of a ceramic substrate (400 cpsi, 4.3 mil wall thickness) using standard coating procedures with a targeted coating depth of 33% of the substrate length.

[0120] The second catalytic region The washcoat for the second catalyst region was the same as the TWC-4 bottom layer (approximately 2.2 g / in 3 , Pd loading is 24g / ft 3 The second catalyst region washcoat was coated using standard coating procedures from the inlet face of the ceramic substrate containing the first catalyst region with a target coating depth of 67% of the substrate length.

[0121] The third catalytic area The washcoat of the third catalyst region was the same as the top layer of TWC-4 (approximately 1.3 g / in 3 , Pt loading is 4.5g / ft 3 and Rh loading is 9g / ft 3 ) and the washcoat for the third catalyst region was also coated from the top, from the inlet end of the ceramic substrate containing the first and second catalyst regions, using a standard coating procedure with a target coating depth of 67% of the substrate length. The catalyst was dried at 100°C and calcined at 500°C for 45 minutes.

[0122] Example 1 - Improved catalytic performance The catalytic performance of the following systems was tested with TWC-1 or TWC-3 placed upstream and TWC-2 or TWC-4 placed downstream. Comparative example system 1: TWC-1 + TWC-2 Comparative Example System 2: TWC-1 + Comparative Catalyst Article 1 Comparative example system 3: TWC-3 + TWC-4 System 4: TWC-3 + Catalyst Item 2 System 5: TWC-3 + Catalyst 3 System 6: TWC-3 + 4 catalytic articles

[0123] The catalyst performance test was conducted by a natural gas engine under a transient test cycle (WHTC). The WHTC test was considered a reliable method of emission evaluation for engine operation. Cold and hot WHTC tests were conducted for each catalyst to measure the post-catalyst emissions. The final WHTC emission value was the sum of the cold and hot WHTC, which accounted for 14% and 86%, respectively.

[0124] The emission results of the natural gas engine under the WHTC cycle for Comparative System 1 and Comparative System 2 are shown in Table 1. The results show that the NH3 emissions of Comparative Catalyst Article 1 and TWC-2 are comparable (32 ppm), and both do not meet the requirements of China VI (10 ppm). Therefore, Comparative Catalyst Article 1, which is a typical NH3 oxidation catalyst in HDD applications, does not work for NH3 emission control in stoichiometric CNG applications.

[0125] [Table 1]

[0126] The emissions of Comparative Example System 3 and Systems 4-6 are shown in Table 2. As shown in Table 2, the NH3 emissions from Comparative Example System 3 also exceeded the 10 ppm limit under China VI heavy vehicle regulations. When TWC-4 was replaced with any one of catalyst articles 2-4, the NH3 emissions were significantly reduced by about 80% reduction, and all pollutant emissions met China VI regulations.

[0127] [Table 2]

Claims

1. 1. A catalytic article for treating exhaust gases 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, the first catalyst region comprising a first zeolite; a second catalyst region beginning at the inlet end, the second catalyst region including a second Platinum Group Metal (PGM) component, a second Oxygen Storage Capacity (OSC) material, and a second inorganic oxide; The catalytic article, wherein the second PGM component is selected from the group consisting of palladium, platinum, rhodium, or combinations thereof.

2. The catalyst article of claim 1 , wherein the first catalyst region extends over 10 to 50 percent of the axial length L.

3. 3. The catalytic article of claim 1, wherein the second catalytic region extends over 50 to 90 percent of the axial length L.

4. The catalytic article of claim 1 or 2, wherein the second catalytic region overlaps the first catalytic region.

5. The catalytic article of claim 1 or 2, wherein the second catalytic region does not overlap the first catalytic region.

6. 3. The catalytic article of claim 1 or 2, wherein the first catalytic region further comprises a first PGM component selected from the group consisting of Pd, Pt, and Rh.

7. The catalytic article of claim 6 wherein the first PGM component is Pt.

8. The amount of the first PGM component supported is 0.1 to 50 g / ft ３ 3. The catalytic article of claim 1 or 2, wherein:

9. 3. The catalytic article of claim 1 or 2, wherein the first catalytic region further comprises a first transition metal selected from the group consisting of Fe, Cu, Mn, Co, Ni, Zn, and combinations thereof.

10. 10. The catalytic article of claim 9, wherein the first transition metal is Cu and / or Fe.

11. 11. The catalyst article of claim 10, wherein Cu is 0.01 to 20 wt. % based on the weight of the first zeolite.

12. The first catalyst region has a density of 0.5 to 3.5 g / in ３ 3. The catalyst article of claim 1 or 2 having a washcoat loading of

13. The catalytic article of claim 1 or 2, further comprising a third catalytic region.

14. The catalytic article of claim 1 or 2, further comprising a fourth catalytic region.

15. 3. An emissions treatment system for treating a CNG engine exhaust gas stream comprising the catalytic article of claim 1 or 2.

16. The emissions treatment system of claim 15 further comprising a TWC article upstream of the catalyst article.

17. A method for treating exhaust gas from a CNG engine, comprising contacting the exhaust gas with the catalytic article of claim 1 or 2.

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