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    • 专利摘要:
    EXHAUST GAS CATALYST, EXHAUST SYSTEM FOR INTERNAL COMBUSTION ENGINES, AND METHOD FOR TREATMENT OF AN EXHAUST GAS FROM AN INTERNAL COMBUSTION ENGINE. Exhaust gas catalysts are described. An exhaust gas catalyst comprises a molecular sieve and a noble metal, and has an infrared spectrum having a characteristic absorption peak from 750 cm-1 to 1050 cm-1 in addition to the absorption peaks for the molecular sieve itself . The exhaust gas catalyst also comprises a molecular sieve and a noble metal, having more than 5 percent of the amount of noble metal located within the pores of the molecular sieve. The exhaust gas catalyst also comprises a first and a second molecular sieve catalyst. The first molecular sieve catalyst comprises a first noble metal and a first molecular sieve, and the second molecular sieve catalyst comprises a second molecular sieve and a noble metal. The first and second molecular sieves are different. The invention also includes exhaust systems comprising the exhaust gas catalysts, and a method for treating exhaust gas using the exhaust gas catalysts.
    公开号:BR112016012631B1
    申请号:R112016012631-9
    申请日:2014-12-08
    公开日:2021-05-04
    发明作者:Hai-Ying Chen；Raj Rao Rajaram；FIONA-MAIREAD McKENNA；Dongxia Liu
    申请人:Johnson Matthey Public Limited Company；
    IPC主号:
    专利说明:

    FIELD OF THE INVENTION
    [001] The invention relates to exhaust gas catalysts and their use in an exhaust system for internal combustion engines. FUNDAMENTALS OF THE INVENTION
    [002] Internal combustion engines produce exhaust gases that contain a variety of polluting substances, including nitrogen oxides (“NOx”), carbon monoxide, and unburned hydrocarbons, which are the subject of government legislation. Emission control systems are widely used to reduce the amount of these pollutants emitted into the atmosphere, and typically achieve very high efficiencies once they reach their operating temperature (typically 200°C and above). However, these systems are relatively inefficient below their operating temperature (the “cold start” period).
    [003] For example, implemented selective catalytic reduction (SCR) applications based on current urea to meet Euro v6b emissions require that the temperature at the urea dosing position be greater than about 180°C before the urea can be dosed and used to convert NOx. NOx conversion below 180°C is difficult to address using current systems, and future US and European legislation will emphasize low temperature NOx storage and conversion. This is currently achieved through warming strategies, but this has a detrimental effect on CO2 emissions.
    [004] As even more stringent national and regional legislation reduces the amount of pollutants that can be emitted from diesel or gasoline engines, reducing emissions during the cold start period is becoming a major challenge. Thus, methods to reduce the level of NOx emitted during cold start condition remains to be explored.
    [005] For example, US Published Patent Application No. 2012/0308439 teaches a cold start catalyst comprising (1) a zeolite catalyst comprising a base metal, a noble metal, and a zeolite, and (2) a platinum group metal supported catalyst comprising one or more platinum group metals and one or more inorganic oxide carriers.
    [006] Published PCT international patent application WO 2008/047170 describes a system in which NOx from lean exhaust gases is adsorbed at temperatures below 200°C and is subsequently thermally desorbed above 200°C. The NOx adsorbent is taught to consist of palladium and a cerium oxide or a mixed oxide or composite oxide containing cerium and at least one other transition metal.
    [007] Published US Patent Application No. 2011/0005200 teaches a catalyst system that simultaneously removes ammonia and enhances liquid NOx conversion by placing a selective ammonia selective catalytic reduction catalyst ("NH3-SCR") formulation downstream from poor NOx storage. The NH3-SCR catalyst is taught to adsorb the ammonia that is generated during the rich pulses in lean NOx storage. The stored ammonia then reacts with the NOx emitted from the upstream lean NOx storage, which increases the NOx conversion rate while depleting the stored ammonia.
    [008] Published international PCT patent application WO 2004/076829 describes an exhaust gas purification system that includes a NOx storage catalyst disposed upstream of an SCR catalyst. The NOx storage catalyst includes at least one alkali, alkaline earth, or rare earth metal that is coated or activated with at least one platinum group metal (Pt, Pd, Rh or Ir). A particularly preferred NOx storage catalyst is taught to include platinum coated cerium oxide and additionally platinum as an oxidation catalyst on an aluminum oxide based support. EP 1027919 describes a NOx adsorbent material comprising a porous support material such as alumina, zeolite, zirconia, titania, and/or lanthanum, and at least 0.1% by weight of precious metal (Pt, Pd and /or Rh). Platinum on alumina is exemplified.
    [009] As with any automotive process and system it is desirable to achieve even further improvements in exhaust gas treatment systems, particularly in cold starting conditions. We discovered an exhaust gas catalyst and system that can reduce cold start emissions during the low temperature period. The new exhaust gas catalyst also exhibits improved sulfur tolerance. SUMMARY OF THE INVENTION
    [0010] The invention is exhaust gas catalysts that are effective to adsorb NOx and hydrocarbons (HC) at or below a low temperature and to convert and release the adsorbed NOx and HC at temperatures above the low temperature. An exhaust gas catalyst comprises a noble metal and a molecular sieve, and has an infrared spectrum having a characteristic absorption peak in the range of from 750 cm-1 to 1050 cm-1 in addition to the absorption peaks for the molecular sieve in themselves. The exhaust gas catalyst also comprises a noble metal and a molecular sieve, having more than 5 percent of the amount of noble metal located within the pores of the molecular sieve. The exhaust gas catalyst also comprises a first and a second molecular sieve catalyst. The first molecular sieve catalyst comprises a first noble metal and a first molecular sieve, and the second molecular sieve catalyst comprises a second noble metal and a second molecular sieve, wherein the first and second molecular sieves are different. The invention also includes exhaust systems comprising exhaust gas catalysts, and a method for treating exhaust gases using exhaust gas catalysts. DETAILED DESCRIPTION OF THE INVENTION
    [0011] The exhaust gas catalysts of the invention are effective to adsorb NOx and hydrocarbons (HC) at or below a low temperature and to convert and release the adsorbed NOx and HC at temperatures above the low temperature. Preferably, the low temperature is in the range of about 200°C to 250°C, more preferably about 200°C.
    [0012] An exhaust gas catalyst of the invention comprises a noble metal and a molecular sieve. The exhaust gas catalyst has an infrared (IR) spectrum, which has a characteristic absorption peak in the range of from 750 cm-1 to 1050 cm-1, more preferably in the range of between 800 cm-1 and 1000 cm- 1, or in the range of 850 cm-1 to 975 cm-1. This characteristic absorption peak is in addition to the absorption peaks of an IR spectrum of the molecular sieve itself (ie, the unmodified molecular sieve).
    [0013] In another embodiment, the exhaust gas catalyst of the invention comprises a noble metal and a molecular sieve, in which some of the noble metal (more than 1 percent of the total added noble metal) in the gas catalyst exhaust is located inside the pores of the molecular sieve. Preferably more than 5 percent of the total amount of noble metal is located within the pores of the molecular sieve; and more preferably it may be greater than 10 percent or greater than 25% or greater than 50 percent of the total amount of noble metal that is located within the pores of the molecular sieve.
    [0014] In another embodiment, the exhaust gas catalyst of the invention comprises a noble metal and a molecular sieve, and has an infrared (IR) spectrum having a characteristic absorption peak in the range from 750 cm-1 to 1050 cm-1 (more preferably in the range of between 800 cm-1 and 1000 cm-1, or in the range of from 850 cm-1 to 975 cm-1.), and some of the noble metal (more than 1 percent of the total added noble metal, and preferably more than five percent of the total added noble metal) in the exhaust gas catalyst is located within the pores of the molecular sieve. More preferably, greater than 10 percent or greater than 25% or greater than 50 percent of the total amount of noble metal is located within the pores of the molecular sieve.
    [0015] The noble metal is preferably palladium, platinum, rhodium, gold, silver, iridium, ruthenium, osmium, or mixtures thereof; more preferably palladium, platinum, rhodium, or mixtures thereof. Palladium is particularly preferred.
    [0016] The molecular sieve can be any synthetic or natural molecular sieve, including zeolites, and is preferably composed of aluminium, silicon and/or phosphorus. Molecular sieves typically have a three-dimensional array of SiO4, AlO4, and/or PO4 that are held together by sharing oxygen atoms, but can also be two-dimensional structures as well. Molecular sieve structures are generally anionic, which are counterbalanced by the charge of make-up cations, typically alkaline and alkaline earth elements (eg, Na, K, Mg, Ca, Sr and Ba), ammonium ions, as well as protons.
    [0017] Preferably, the molecular sieve is selected from an aluminosilicate molecular sieve, a metal substituted aluminosilicate molecular sieve, an aluminophosphate molecular sieve, or a metal substituted aluminophosphate molecular sieve.
    Preferably, the molecular sieve is a small pore molecular sieve having a maximum ring size of eight tetrahedral atoms, a medium pore molecular sieve having a maximum ring size of ten tetrahedral atoms, or a molecular sieve of large pore with a maximum ring size of twelve tetrahedral atoms.
    [0019] If the molecular sieve is a small pore molecular sieve, it is preferably a molecular sieve that has the structure type of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, DPA, ATT, CDO, CHA, DOR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, as well as mixtures or intergrowths of any two or more. Most preferably, the small pore zeolite is AEI or CHA. Particularly preferred intergrowths of small pore molecular sieves include KFI-SIV, ITE-RHT, AEW-UEI, AEI-CHA and AEI-SAV. More preferably, the small pore molecular sieve is AEI or CHA, or an AEI-CHA intergrowth.
    [0020] If the molecular sieve is a medium pore molecular sieve, it is preferably a molecular sieve having the structure type of MFI, FER, MWW or EUO. If the molecular sieve is a large pore molecular sieve, it is preferably a molecular sieve having the structure types of CON, BEA, FAU, MOR or EMT.
    [0021] The exhaust gas catalyst can be prepared by any known means. For example, the noble metal can be added to molecular sieve to form the exhaust gas catalyst by any known means, the mode of addition is not considered to be particularly critical. For example, a noble metal compound (eg, palladium nitrate) can be supported on the molecular sieve by impregnation, adsorption, ion exchange, incipient moisture, precipitation, or the like. Other metals can also be added to the exhaust gas catalyst.
    [0022] Preferably, the exhaust gas catalyst further comprises a flux substrate or filter substrate. In one embodiment, the exhaust gas catalyst is coated onto the flux or filter substrate, and preferably deposited onto the flux or filter substrate using a reactive coating procedure to produce an exhaust gas catalyst system. exhaust.
    [0023] The flux or filter substrate is a substrate that is capable of containing catalyst components. The substrate is preferably a ceramic substrate or a metallic substrate. The ceramic substrate can be made of any suitable refractory material, eg alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates, metal aluminosilicates , (such as cordierite and spodumene), or a mixture or mixed oxide of any two or more thereof. Cordierite, a magnesium aluminum silicate, and silicon carbide are particularly preferred.
    [0024] Metallic substrates can be made of any suitable metal, and in particular heat resistant metals and metal alloys such as stainless steel and titanium, as well as ferritic alloys containing iron, nickel, chromium and/or aluminum in addition to others trace metals.
    [0025] The flux substrate is preferably a flux monolith with a honeycomb structure with many small, parallel thin-walled channels running axially through the substrate and extending along an inlet or an outlet of the substrate. The cross-section of the substrate channel can be of any shape, but is preferably square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular or oval.
    [0026] The filter substrate is preferably a monolith wall flow filter. The channels of a flow wall filter are alternately blocked, which allow the exhaust gas stream to enter a channel from the inlet, then flow through the channel walls, and out of the filter from a channel. different leading to the exit. Particles in the exhaust gas stream are thus trapped in the filter.
    [0027] The exhaust gas catalyst can be added to the through-flow substrate or filter substrate by any known means. A representative process for preparing the exhaust gas catalyst through a reactive coating procedure is set out below. It will be understood that the process below can be varied according to different embodiments of the invention.
    [0028] The preformed exhaust gas catalyst can be added to the through-flow substrate or filter by a reactive coating step. Alternatively, the exhaust gas catalyst can be formed on the through-flow and filter substrate by first reactive coating the unmodified molecular sieve onto the substrate to produce a molecular sieve coated substrate. Noble metal can then be added to the molecular sieve coated substrate, which can be performed by an impregnation procedure, or the like.
    [0029] The reactive coating procedure is preferably carried out by first liquid suspension of finely divided particles of the exhaust gas catalyst (or unmodified molecular sieve) in a suitable solvent, preferably water, to form the suspension. Additional components, such as transition metal oxides, binders, stabilizers, or promoters can also be incorporated into the suspension as a mixture of water-soluble or water-dispersible compounds. The suspension preferably contains from 10 to 70 percent by weight solids, more preferably from 20 to 50 percent by weight. Before forming the suspension, the exhaust gas catalyst particles (or unmodified molecular sieve) are preferably subjected to a size reduction treatment (eg milling) so that the average particle size of the solid particles is smaller. to 20 microns in diameter.
    The flux substrate or filter may then be dipped one or more times into the suspension or the suspension may be coated onto the substrate in such a way that the desired load of catalytic materials will be deposited on the substrate. If noble metal is not incorporated into the molecular sieve prior to reactive coating of the through-flow or filter substrate, the molecular sieve coated substrate is typically dried and calcined and then the noble metal can be added to the molecular sieve coated substrate by any known means, including impregnation, adsorption or ion exchange, for example, with a noble metal compound (eg, palladium nitrate). Preferably, the entire length of the through-flow substrate and filter is either coated with the suspension so that a reactive coating of the exhaust gas catalyst covers the entire surface of the substrate.
    [0031] After the through-flow substrate or filter has been coated with the exhaust gas catalyst, and impregnated with noble metal, if necessary, the coated substrate is preferably dried and then calcined by heating at an elevated temperature to form the substrate coated with exhaust gas catalyst. Preferably, calcination takes place at 400 to 600°C for approximately 1 to 8 hours.
    [0032] In an alternative embodiment, the through-flow substrate or filter is comprised of the exhaust gas catalyst. In this case, the exhaust gas catalyst is extruded to form the through-flow or filter substrate. The extruded exhaust gas catalyst substrate is preferably a through-flow honeycomb monolith.
    [0033] Extruded molecular sieve substrates and alveolar bodies, and processes for their production, are known in the art. See, for example, US Patent Nos. 5,492,883, 5,565,394, and 5,633,217 and US patent. No. Re. 34,804. Typically, the molecular sieve material is mixed with a permanent binder such as silicone resin and a temporary binder such as methyl cellulose, and the mixture is extruded to form a green honeycomb body, which is then calcined and sintered. to form the final molecular sieve flux monolith. The molecular sieve can contain the noble metal prior to extrusion so that an exhaust gas catalyst monolith is produced by the extrusion process. Alternatively, the noble metal can be added to a preformed molecular sieve monolith to produce the exhaust gas catalyst monolith.
    [0034] In a separate embodiment, the exhaust gas catalyst comprises a first molecular sieve catalyst and a second molecular sieve catalyst. The first molecular sieve catalyst comprises a first noble metal and a first molecular sieve. The second molecular sieve catalyst comprises a second noble metal and a second molecular sieve. The first and second molecular sieves are different. In this embodiment, the exhaust gas catalyst may comprise one or more additional molecular sieve catalysts (e.g., a third molecular sieve catalyst and/or a fourth molecular sieve catalyst), provided that the molecular sieve(s) additional are different than the first and second molecular sieves.
    [0035] The first noble metal and the second noble metal are independently selected from platinum, palladium, rhodium, gold, silver, iridium, ruthenium, osmium, or mixtures thereof; preferably, they are independently selected from palladium, platinum, rhodium, or mixtures thereof. Most preferably, the first noble metal and the second noble metal are both palladium.
    [0036] The first molecular sieve is preferably a small pore molecular sieve having the structure type of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DOR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, as well as mixtures or intergrowths of any two or more. Most preferably, the small pore zeolite is AEI or CHA. Particularly preferred intergrowths of small pore molecular sieves include KFI-SIV, ITE RTH, AEW-UEI, AEI-CHA and AEI-SAV. Most preferably, the small pore molecular sieve is AEI or CHA, or an AEI-CHA intergrowth.
    [0037] The second molecular sieve is preferably a medium or large pore molecular sieve. The medium pore molecular sieve is preferably a molecular sieve having the structure type of MFI, FER, MWW or EUO. The large pore molecular sieve is preferably a molecular sieve having the structure type CON, BEA, FAU, MOR or EMT. Most preferably, the large or medium pore molecular sieve is IMF or BEA.
    [0038] The exhaust gas catalyst can be prepared by processes well known in the prior art. The first molecular sieve catalyst and the second molecular sieve catalyst can be physically mixed to produce the exhaust gas catalyst. Preferably, the exhaust gas catalyst further comprises a through-flow substrate or filter substrate. In one embodiment, the first molecular sieve catalyst and the second molecular sieve catalyst are coated onto the throughflow and filter substrate or, and preferably, deposited onto the throughflow and filter substrate using a reactive coating to produce the exhaust gas catalyst system.
    [0039] Suitable through-flow or filter substrates are described above.
    [0040] The first molecular sieve catalyst and the second molecular sieve catalyst can be added to the through-stream substrate or filter substrate by any known means. A representative process for preparing the exhaust gas catalyst through a reactive coating procedure is set out below. It will be understood that the process below can be varied according to different embodiments of the invention. Furthermore, the order of addition of the first molecular sieve catalyst and the second molecular sieve catalyst to the through-flow substrate or filter substrate is not considered critical. Thus, the first molecular sieve catalyst can be coated with reactive coating on the substrate before the second molecular sieve catalyst or the second molecular sieve catalyst can be coated with reactive coating on the substrate before the first molecular sieve catalyst or both the first molecular sieve catalyst and the second molecular sieve catalyst may be wash coated onto the substrate simultaneously.
    [0041] The first preformed molecular sieve catalyst can be added to the through-flow substrate or filter substrate by a reactive coating step. Alternatively, the first molecular sieve catalyst can be formed on the through-flow substrate or filter substrate or by first washing substrate unmodified molecular sieve onto the substrate to produce a molecular sieve coated substrate. Noble metal can then be added to the molecular sieve coated substrate which can be achieved by an impregnation procedure, or the like.
    [0042] The reactive coating procedure is preferably carried out as described above. Preferably, the entire length of the through-flow substrate or filter substrate is coated with the first molecular sieve catalyst suspension so that a reactive coating of the first molecular sieve catalyst covers the entire surface of the substrate.
    [0043] After the through-flow substrate or filter substrate has been coated with the first suspension of molecular sieve catalyst, and impregnated with noble metal, if necessary, the coated substrate is preferably dried and then calcined by heating to a temperature high to form the molecular sieve catalyst coated substrate. Preferably, calcination takes place at 400 to 600°C for approximately 1 to 8 hours.
    [0044] The addition of the reactive coating of the second molecular sieve catalyst is preferably carried out according to the procedure described above. Preferably, the entire length of the through-flow substrate or filter is coated with the supported PGM catalyst slurry so that a reactive coating of the supported PGM catalyst covers the entire surface of the substrate.
    [0045] After the through-flow substrate or filter has been coated with both the first and second molecular sieve catalyst slurries, it is preferably dried and then calcined by heating at an elevated temperature to produce the exhaust gas catalyst . Preferably, calcination takes place at 400 to 600°C for approximately 1 to 8 hours.
    [0046] In an alternative embodiment, the through or filter flow is comprised of the first molecular sieve catalyst, the second molecular sieve catalyst, or both the first and second molecular sieve catalysts. In this case, the first, second, or both molecular sieve catalysts are extruded to form the through-flow or filter substrate. If not included in the extruded substrate, the first or second molecular sieve catalyst is coated onto the through-flow or extruded filter substrate. The extruded substrate is preferably a through-flowing alveolar monolith.
    [0047] Preferably, the exhaust gas catalyst comprises a first layer comprising the first molecular sieve catalyst and a second layer comprising the second molecular sieve catalyst. Typically, the first layer can be disposed on a substrate and the second layer is disposed on the first layer. Alternatively, the second layer can be disposed on a substrate and the first layer disposed on the second layer.
    [0048] In a separate embodiment, the exhaust gas catalyst comprises a first zone comprising the first molecular sieve catalyst and a second zone comprising the second molecular sieve catalyst. The first zone can be upstream of the second zone such that the first zone contacts the exhaust gas before the second zone, or, alternatively, the second zone can be upstream of the first zone such that the second zone contacts the zone the exhaust gas before the first zone. Preferably, the second zone is located upstream of the first zone so that the exhaust gas contacts the second molecular sieve catalyst prior to contacting the first molecular sieve catalyst. The two zones may be on the same catalyst component (or catalyst brick), or the first zone comprising the first molecular sieve catalyst may be located on a separate brick (or catalyst component) than the second zone comprising the second molecular sieve catalyst.
    [0049] The invention also includes an exhaust system for internal combustion engines comprising the exhaust gas catalyst. The exhaust system preferably comprises one or more additional after-treatment devices capable of removing pollutants from the exhaust gases of the internal combustion engine at normal operating temperatures. Preferably, the exhaust system comprises the exhaust gas catalyst and one or more other catalyst components selected from: (1) a selective catalytic reduction (SCR) catalyst, (2) a particulate filter, (3 ) an SCR filter, (4) a NOx adsorbing catalyst, (5) a three-way catalyst, (6) an oxidation catalyst, or any combination thereof. The exhaust gas catalyst is preferably a separate component from any of the above after-treatment devices. Alternatively, the exhaust gas catalyst can be incorporated as a component for any of the above after-treatment devices.
    [0050] These aftertreatment devices are well known in the art. Selective Catalytic Reduction (SCR) catalysts are catalysts that reduce NOx to N2 through reaction with nitrogen compounds (such as ammonia or urea) or hydrocarbons (lean NOx reduction). A typical SCR catalyst is comprised of a vanadia-titania catalyst, a vanadia-tungsta-titania catalyst, or a metal/zeolite catalyst such as iron/zeolite beta, copper/zeolite beta, copper/SSZ-13, copper/ SAPO-34, Fe/ZSM-5, or copper/ZSM-5.
    [0051] Particle filters are devices that reduce particles from the exhaust gases of internal combustion engines. Particle filters include catalyzed particle filters and bare (uncatalyzed) particle filters. Catalyzed particulate filters (for diesel and gasoline applications) include metal and metal oxide components (such as Pt, Pd, Fe, Mn, Cu and ceria) to oxidize hydrocarbons and carbon monoxide in addition to soot destruction trapped by the filter.
    [0052] Selective Catalytic Reduction Filters (SCRF) are single substrate devices that combine the functionality of an SCR filter and particles. They are used to reduce NOx and particulate emissions from internal combustion engines. In addition to the SCR catalyst coating, the particulate filter can also include other metals and metal oxide components (such as Pt, Pd, Fe, Mn, Cu and ceria) to oxidize the hydrocarbons and carbon monoxide in addition to destroying the soot trapped by the filter.
    [0053] NOx Adsorption Catalysts (NACs) are designed to adsorb NOx under lean exhaust conditions, release the adsorbed NOx under rich conditions, and reduce the NOx released to form N2. NACs typically include a NOx storage component (eg, Ca, Ba, Sr, Mg, K, Na, Li, Cs, La, Y, Pr and Nd), an oxidation component (preferably Pd), and an reducing component (preferably Rh). These components are contained in one or more brackets.
    [0054] Three-way catalysts (TWCs) are typically used in gasoline engines under stoichiometric conditions in order to convert NOx to N2, carbon monoxide to CO2, and hydrocarbons to CO2 and H2O in a single device.
    [0055] Oxidation catalysts, and in particular diesel oxidation catalysts (DOCs), are well known in the art. Oxidation catalysts are designed to oxidize CO to CO2 and gas phase hydrocarbons (HC) and an organic fraction of diesel particles (soluble organic fraction) to CO2 and H2O. Typical oxidation catalysts include platinum and optionally also palladium on a high surface area inorganic oxide support such as alumina, silica-alumina and a zeolite.
    [0056] The exhaust system can be configured so that the exhaust gas catalyst is situated close to the engine and the additional after-treatment device(s) are located downstream of the exhaust gas catalyst. Thus, under normal operating conditions, the engine exhaust gas first flows through the exhaust gas catalyst before contacting the after-treatment device(s). Alternatively, the exhaust system may contain valves or other means that direct the gas such that during the low temperature period (typically less than a temperature ranging from about 150 to 250°C, preferably 200°C, about as measured in the aftertreatment device(s), the exhaust gas is directed to contact the aftertreatment device(s) before flowing to the exhaust gas catalyst. Once the aftertreatment device(s) reaches operating temperature (about 150 to 250°C, preferably 200°C, as measured in the aftertreatment device(s), the gas flow exhaust is then redirected to contact the exhaust gas catalyst, before contacting the aftertreatment device(s). This ensures that the temperature of the exhaust gas catalyst remains low for a longer period of time, and thus improves the efficiency of the exhaust gas catalyst while simultaneously enabling the after-treatment device(s). reach operating temperature faster. US Patent No. 5,656,244, the teachings of which are hereby incorporated by reference, for example, teaches means for controlling the flow of exhaust gases during cold start and normal operating conditions.
    [0057] The invention also includes a method for treating exhaust gases from an internal combustion engine. The method comprises adsorbing NOx and hydrocarbons (HC) onto the exhaust gas catalyst at temperatures at or below a low temperature, converting and thermally desorbing NOx and HC from the exhaust gas catalyst at a temperature above the temperature low, and catalytically removing the desorbed NOx and HC in a catalyst component downstream of the exhaust gas catalyst. Preferably, the low temperature is in the range of about 200°C to 250°C, more preferably about 200°C.
    [0058] The catalyst component downstream of the exhaust gas catalyst is an SCR catalyst, a particulate filter, an SCR filter, a NOx adsorbing catalyst, a three-way catalyst, an oxidation catalyst, or combinations of the same.
    [0059] The following examples merely illustrate the invention. Those skilled in the art will recognize many variations which are within the spirit of the invention and scope of the claims. EXAMPLE 1: PREPARATION OF MOLECULAR SIEVE CATALYST WITH NOBLE METAL
    [0060] Palladium is added to a variety of different molecular sieves according to the following general procedure: The catalyst powder is prepared by wet impregnation of the molecular sieve using palladium nitrate as the precursor. After drying at 100°C, the samples are calcined at 500°C. The samples are then hydrothermally aged at 750°C in an air atmosphere containing 10% H2O. Pd loadings for all samples are 1% by weight. Examples of molecular sieve supported Pd catalysts are listed in Table 1. EXAMPLE 2: COMPARATIVE CATALYST PREPARATION
    [0061] Comparative catalyst 2A (Pd/CeO2) is prepared following the procedures reported in WO 2008/047170 by impregnating Pd onto a CeO2 support, and hydrothermally aged at 750°C in an air atmosphere containing 10% H2O. The Pd loading is 1% by weight. EXAMPLE 3: NOX STORAGE CAPACITY TEST PROCEDURES
    [0062] The catalyst (0.4 g) is maintained at the adsorption temperature of about 80°C for 2 minutes, in a gas mixture containing NO flowing at 2 liters per minute at an MHSV of 300 L * h-1 * g-1. This adsorption phase is followed by Temperature Programmed Desorption (TPD) at a rate of increase of 10°C/minute in the presence of the NO-containing gas until the bed temperature reaches about 400°C in order to remove the catalyst at all. NOx stored for further testing. The test is then repeated from a temperature of 100°C instead of 80°C; repeated once more from a temperature of 150°C; and again repeated from a temperature of 170°C.
    [0063] The gas mixture containing NO during both adsorption and desorption comprises 12% by vol. Of O2, 200 ppm of NO, 5% by vol. of CO2, 200 ppm of CO, 50 ppm of C10H22, and 5% by vol. of H2O.
    [0064] NOx storage is calculated as the amount of NO2 stored per liter of catalyst with reference to a monolith containing a catalyst charge of about 3 g/in3. The results with the different temperatures are shown in Table 1.
    [0065] The results in Table 1 show that all catalysts supported by molecular sieve, similar to Comparative Catalyst 2A, can store NOx at low temperatures. In general, small pore molecular sieve supported catalysts have greater NOx storage capacity at temperatures above 150°C; whereas catalysts supported with large pore molecular sieve have greater NOx storage capacity at temperatures below 100°C. EXAMPLE 4: NOx Storage Capacity Testing Procedures After Sulfur Exposure
    [0066] Catalysts of exhaust gases 1E, 1H, and 1K, together with comparative catalyst 2A, are subjected to a high level of sulphation, contacting them with a gas containing SO2 (100 ppm of SO2, 10% of O2, 5 % CO2 and H2O, equilibrium with N2) at 300°C to add about 64 mg of S per gram of catalyst. The NOx storage capacity of the catalysts before and after sulfation is measured at 100°C following the procedures of Example 3. The results are listed in Table 2.
    [0067] The results shown in Table 2 indicate that the flue gas catalysts of the invention retain a significant amount of storage capacity even after a high level of exposure to sulfur. In contrast, Comparative Catalyst 2A (Pd/ CeO2) loses almost all of its NOx adsorption capacity under the same sulfation conditions. The exhaust gas catalysts of the invention have much better tolerance to sulfur. EXAMPLE 5: PREPARATION AND EVALUATION OF MOLECULAR SIEVE SUPPORTED CATALYST WITH DIFFERENT PALLADIUM LOADS
    Palladium is added to different molecular sieves following the procedure of Example 1. The Pd charge is varied from 0.25 to 2% by weight. Samples are hydrothermally aged at 750°C in an atmosphere of air containing 10% H2O. The aged samples are then tested for their NOx storage capacities following the procedure in Example 3. The NOx storage capacities of the samples at various temperatures are listed in Table 3.
    [0069] The results in Table 3 show that increasing the load of Pd increases the storage capacity of NOx. EXAMPLE 6: PREPARATION OF PALLADIUM CATALYST SUPPORTED WITH MOLECULAR SIEVE MIXED
    [0070] Molecular sieve supported palladium catalysts are first prepared individually, following the procedures of Example 1. The catalysts are subsequently mixed together in a ratio of equivalents based on their weight. The mixed catalysts are then hydrothermally aged at 750°C in an air atmosphere containing 10% H2O. Examples of mixed catalysts are listed in Table 4. EXAMPLE 7: EVALUATION OF MIXED CATALYST
    [0071] Individual catalysts (0.2 g) and their mixtures (0.4 g) are maintained at the adsorption temperature of 80°C for 1 minute in a gas mixture containing NO flowing at 2 liters per minute to an MHSV of 300 L * h-1 * g-1. This adsorption step is followed by temperature programmed desorption (TPD) at an increase rate of 100°C/minute in the presence of the NO-containing gas until the bed temperature reaches about 400°C. The gas mixture containing NO during both adsorption and desorption comprises 12% by vol. of O2, 200 ppm of NO, 5% by vol. of CO2, 200 ppm of CO, 50 ppm of C10H22, and 5% by vol. of H2O.
    [0072] NOx storage capacities are calculated during 1 minute maintenance at 80°C as well as during the subsequent temperature ramp from 80 to 200°C. The results are summarized in Table 4.
    [0073] The results in Table 4 show that it is possible to optimize the storage capacity of NOx at different temperatures by combining different types of molecular sieve catalysts supported with noble metals. EXAMPLE 8: PALLADIUM CATALYST SUPPORTED WITH MOLECULAR SIEVE OF REACTIVE COATING
    Palladium catalyst powders supported with molecular sieve powder are prepared following the procedure of Example 1. Pd loadings are 1.4% by weight for all samples. Each of the powder samples is then suspended and mixed with an alumina binder. The mixture is coated onto a through-flow cordierite substrate to achieve a Pd load at 1,785 g/m3 (50 g/ft3). The coated catalyst is dried and then calcined by heat at 500°C for 4 hours. Examples of catalysts are listed in Table 5. EXAMPLE 9: PALLADIUM CATALYST SUPPORTED WITH MOLECULAR REACTIVE COATING SIEVE ALONG WITH A PLATINUM COMPONENT
    The washable coated catalysts in Example 8 are further coated with a second layer of alumina-supported Pt catalyst. Platinum nitrate is added to an aqueous suspension of alumina particles (ground to an average particle size of less than 10 microns in diameter) to form a Pt/alumina catalyst suspension. The Pt/alumina catalyst slurry is then coated onto the molecular sieve/Pt coated substrate to achieve a Pt loading of 892.5 g/m3 (25 g/ft3), and the final coated substrate is dried and then calcined by heating at 500°C for 4 hours. Examples of catalysts containing Pt are also listed in Table 5. EXAMPLE 10: PALLADIUM CATALYST SUPPORTED WITH MOLECULAR SIEVE MIXED REACTIVE COATING
    [0076] Molecular sieve supported palladium catalyst powders are prepared following the procedure of Example 1. Pd loadings are 1.4% by weight for all samples. Two selected powder samples are then suspended and blended in a 1:1 weight ratio, followed by the addition of alumina binding agent to the blended suspension. This mixture is coated onto a through-flow cordierite substrate to achieve a Pd load of 1,785 g/m3 (50 g/ft3). The coated catalyst is dried and then calcined by heat at 500°C for 4 hours. Examples of catalysts are listed in Table 5. EXAMPLE 11: PALLADIUM CATALYST SUPPORTED WITH MOLECULAR SIEVE REACTIVE COATING ALONG WITH A PLATINUM COMPONENT
    The washable coated catalysts in Example 10 are further coated with a second layer of alumina-supported Pt catalyst. Platinum nitrate is added to an aqueous suspension of alumina particles (ground to an average particle size of less than 10 microns in diameter) to form a Pt/alumina catalyst suspension. The Pt/alumina catalyst slurry is then coated onto the molecular sieve/Pd coated substrate to achieve a Pt loading of 892.5 g/m3 (25 g/ft3), and the final coated substrate is dried and then calcined by heating at 500°C for 4 hours. Examples of catalysts containing Pt are also listed in Table 5. EXAMPLE 12: EVALUATION OF WASHABLE COATED CATALYST
    [0078] All washable coated catalysts are tested on core samples (2.54 cm diameter x 7.62 in length) of the through-flow catalyst coated cordierite substrate. Catalyst cores are first aged under through-flow conditions in an oven under hydrothermal conditions (5% H2O, equilibrium air) at 750°C for 16 hours. The cores are then tested for catalytic activity in a laboratory reactor using a feed gas stream that is prepared by adjusting the mass flow of the individual exhaust gas components. The gas flow rate is maintained at 21.2 l min-1, resulting in a gas space velocity per hour of 30,000 h-1 (GHSV = 30,000 h-1).
    [0079] Catalysts are tested under lean conditions using a synthetic exhaust gas feed stream consisting of 200 ppm NO, 200 ppm CO, 50 ppm decane, 10% O2, 5% CO2, 5 % H2O and equilibrium with hydrogen (% by volume). The catalyst is exposed to the feed gas stream, first at an isothermal inlet gas temperature of 80°C for 100 seconds, after which the inlet gas temperature is increased to 650°C with an increased rate of 100° C/min.
    [0080] The NOx storage capacities of the catalysts at 80°C for 100 seconds and during the subsequent temperature ramp from 80 to 200°C are summarized in Table 5. Cumulative HC storage and conversion efficiency and the catalyst's cumulative CO conversion efficiency at temperatures below 200°C are also summarized in Table 5.
    [0081] The results in Table 5 show that supported catalysts of large pore molecular sieve have greater NOx storage capacity at low temperatures; considering small pore molecular sieve supported catalysts have greater NOx storage capacity at higher temperatures. Large pore molecular sieve supported catalysts also have higher HC storage and conversion efficiency. Comparison of results with mixed catalysts versus catalysts with the only corresponding type of molecular sieve component, mixed catalysts generally maintain high NOx storage capacity over a wider temperature window. EXAMPLE 13: ASSESSMENT OF CATALYST IN ZONES
    [0082] Zoned catalyst systems are evaluated by combining one-half the core length of a Pd/BEA bottom and Pt/Al2O3 top catalyst prepared in Example 9C and one-half the core length of a bottom of Pd/CHA and Pt/Al2O3 top catalyst prepared in Example 9A. The system of Example 13A places one half of the core from Example 9C, in front of one half of the core from Example 9A; whereas the system of Example 13B places one half of the core of Example 9A, in front of one half of the core of Example 9C. These systems are evaluated according to the same procedures as described in Example 12. The evaluation results are summarized in Table 5.
    [0083] The results in Table 5 show that zone systems, especially Example 11A, exhibit high NOx storage capacity over a much wider temperature range than the corresponding individual catalysts. TABLE 1: NOx storage capacity (g NO2/l)

    权利要求:
    Claims (11)
    [0001]
    1. Effective exhaust gas catalyst to adsorb NOx and hydrocarbons (HC) at or below a low temperature and to convert and release the adsorbed NOx and HC at temperatures above the low temperature, the exhaust gas catalyst characterized by the fact that comprising a first molecular sieve catalyst and a second molecular sieve catalyst, wherein the first molecular sieve catalyst comprises a first noble metal and a first molecular sieve, and the second molecular sieve catalyst comprises a second noble metal and a second molecular sieve, wherein the first molecular sieve is different from the second molecular sieve; wherein the first noble metal and the second noble metal are both palladium; wherein the first molecular sieve is a small pore molecular sieve selected from the structure type group consisting of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR , DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC , UEI, UFI, VNI, YUG and ZON, and intergrowths of two or more; wherein the second molecular sieve is a medium or large pore molecular sieve selected from the group consisting of BEA and MFI; and wherein more than 5 percent of the total amount of the first noble metal is located within the pores of the first molecular sieve and more than 5 percent of the total amount of the second noble metal is located within the pores of the second molecular sieve .
    [0002]
    2. Exhaust gas catalyst according to claim 1, characterized in that the small pore molecular sieve is selected from the group of structure type consisting of AEI and CHA.
    [0003]
    3. Exhaust gas catalyst according to claim 1, characterized in that the exhaust gas catalyst is coated on a through-flow substrate or filter.
    [0004]
    4. Exhaust gas catalyst according to claim 1, characterized in that the exhaust gas catalyst is extruded to form a through-flow substrate or filter.
    [0005]
    5. Exhaust gas catalyst according to claim 1, characterized in that the exhaust gas catalyst comprises a first layer comprising the first molecular sieve catalyst and a second layer comprising the second molecular sieve catalyst.
    [0006]
    6. Exhaust gas catalyst according to claim 1, characterized in that the exhaust gas catalyst comprises a first zone comprising the first molecular sieve catalyst and a second zone comprising the second molecular sieve catalyst.
    [0007]
    7. Exhaust gas catalyst according to claim 6, characterized in that the first zone comprising the first molecular sieve catalyst is located in a separate brick than the second zone comprising the second molecular sieve catalyst.
    [0008]
    8. Exhaust system for internal combustion engines, characterized in that it comprises the exhaust gas catalyst as defined in any one of claims 1 to 7 and a catalyst component selected from the group consisting of a reduction catalyst selective catalytic (SCR), a particulate filter, an SCR filter, a NOx adsorbing catalyst, a three-way catalyst, an oxidation catalyst, and combinations thereof.
    [0009]
    9. Method for treating an exhaust gas from an internal combustion engine, characterized in that the method comprises adsorption of NOx and hydrocarbons (HC) on the exhaust gas catalyst of any one of claims 1 to 7 on or below from a low temperature, the conversion and thermally desorption of NOx and HC from the exhaust gas catalyst at a temperature above the low temperature, and catalytically removing the desorbed NOx and HC in a catalyst component downstream of the gas catalyst of exhaust.
    [0010]
    10. Method according to claim 9, characterized in that the low temperature is in the range of 200°C to 250°C.
    [0011]
    11. Method according to any one of claims 9 or 10, characterized in that the second molecular sieve catalyst is located upstream of the first molecular sieve catalyst so that the exhaust gas contacts the second molecular sieve catalyst before contact with the first molecular sieve catalyst.
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    法律状态:
    2020-02-11| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-09-08| B07A| Application suspended after technical examination (opinion) [chapter 7.1 patent gazette]|
    2021-04-06| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-05-04| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 08/12/2014, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
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    US201361912839P| true| 2013-12-06|2013-12-06|
    US61/912,839|2013-12-06|
    PCT/US2014/069099|WO2015085305A1|2013-12-06|2014-12-08|An exhaust gas catalyst containing two different noble metal-molecular sieve catalysts|
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