COLD START CATALYST, EXHAUST SYSTEM FOR INTERNAL COMBUSTION ENGINES, AND METHOD FOR TREATING EXHAUST GASES FROM AN INTERNAL COMBUSTION ENGINE

Description

"Cold Start Catalytic Converter, Exhaust System for Internal Combustion Engines, and Method for Treating Exhaust Gases from an Internal Combustion Engine" FIELD OF INVENTION

[001] The invention relates to a cold start catalyst and its use in an exhaust system for internal combustion engines. BACKGROUND OF THE INVENTION

[002] Internal combustion engines produce exhaust gases containing a variety of pollutants, including nitrogen oxides (NOx), carbon monoxide, and unburned hydrocarbons, which are the subject of government regulation. 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] As national and regional legislation further tightens to reduce 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 and hydrocarbons emitted during the cold start condition continue to be explored.

[004] For cold start hydrocarbon control, zeolite-based hydrocarbon capture components have been investigated. In these systems, the zeolite adsorbs and stores hydrocarbons during the start-up period and releases the stored hydrocarbons when the exhaust temperature is high enough to desorb hydrocarbons. The desorbed hydrocarbons are subsequently converted when the Petition 870160025133, dated 02 / 06 / 2016, page 11 / 31 / 17 downstream catalytic components reach their operating temperature.

[005] For the control of cold-start NOx, especially under lean combustion conditions, NOx storage and release catalysts have been studied. The catalysts adsorb NOx during the warm-up period and thermally desorb NOx at higher exhaust temperatures. Downstream catalysts, such as selective catalytic reduction (SCR) or NOx adsorption catalysts (NAC), effectively reduce the desorbed NOx to nitrogen.

[006] Typically, NOx adsorbent materials consist of inorganic oxides, such as alumina, silica, cerium oxide, zirconium dioxide, titania, or mixed oxides that are coated with at least one platinum group metal. International Application PCT 2008 / 047170 describes a system in which NOx from a lean exhaust gas 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 oxide compound containing cerium and at least one other transition metal.

[007] International Application PCT WO 2004 / 076829 describes an exhaust gas purification system that includes a NOx storage catalyst arranged upstream of an SCR catalyst. The NOx storage catalyst includes at least one alkaline, alkaline, 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 platinum additionally 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, zirconium, titanium, and / or lanthanum oxide, and at least 0.1% by weight of precious metal (Pt, Pd, Petition 870160025133, dated 02 / 06 / 2016, page 12 / 31 / 17 and / or Rh). Platinum on alumina is exemplified.

[008] In addition, Pat. Nos. 5,656,244 and 5,800,793 describe systems that combine a NOx storage / release catalyst with a three-way catalyst. The NOx adsorbent is taught to include oxides of chromium, copper, nickel, manganese, molybdenum, cobalt or, in addition to other metals, which are supported on alumina, mullite, cordierite, or silicon carbide. International PCT Application. Document WO 03 / 056150 describes a system that combines a low-temperature NO2 capture material and a soot filter. Low-temperature NO2 capture material is taught to be part of zeolites exchanged with common metal cations, with the selected zeolites being ZSM-5, ETS-10, Y-zeolites, beta zeolites, ferrierite, mordenite, titanium silicates and aluminum phosphates, and base metals selected from Mn, Cu, Fe, Co, W, Re, Sn, Ag, Zn, Mg, Li, Na, K, Cs, Nd and Pr.

[009] Unfortunately, the NOx adsorption capacity of such systems is not high enough, especially at high NOx storage efficiency. Because of increasing global legislation regulating the amount of NOx and hydrocarbons released into the atmosphere from internal combustion engines, the need for more effective exhaust gas cleaning under cold start conditions is ever-present. In order to overcome these problems, U.S. Appl. Bar. No. 2012 / 0308439 A1 describes a catalyst comprising Cold Start (1) a zeolite catalyst consisting of a base metal, a noble metal, and a zeolite, and (2) a supported platinum group metal catalyst comprising one or more platinum group metals and one or more inorganic oxide carriers. However, U.S. Appl. Bar. No. 2012 / 0308439 A1 requires a base metal component of the zeolite catalyst component.

[0010] As with any automotive system and Petition 870160025133, dated 02 / 06 / 2016, page 13 / 31 / 17 process, which is desirable to achieve even more improvements in exhaust gas treatment systems, particularly under cold start conditions. We have discovered a new cold start catalyst that provides improved exhaust gas cleanup from internal combustion engines. SUMMARY OF THE INVENTION

[0011] The invention is a cold-start catalyst that is effective for adsorbing NOx and hydrocarbons (HC) at or below a low temperature and for converting and releasing the adsorbed NOx and HC at temperatures above the low temperature. The cold-start catalyst comprises a molecular sieve catalyst and a supported platinum group metal catalyst. The molecular sieve catalyst essentially consists of a noble metal and a molecular sieve. The supported platinum group metal catalyst comprises one or more platinum group metals and one or more inorganic oxide carriers. The invention also includes an exhaust system comprising the cold-start catalyst, and a method for treating exhaust gases from an internal combustion engine using the cold-start catalyst.The cold start catalyst effectively reduces emissions during the cold start period through improved NOx storage and conversion, improved hydrocarbon storage and conversion, and improved CO oxidation. DETAILED DESCRIPTION OF THE INVENTION

[0012] The cold-start catalyst of the present invention comprises a molecular sieve catalyst and a supported platinum group metal catalyst. The cold-start catalyst is effective for adsorbing NOx and hydrocarbons (HC) at or below a low temperature and for converting and releasing the adsorbed NOx and HC at temperatures above the low temperature. Preferably, the low temperature is about Petition 870160025133, dated 02 / 06 / 2016, p. 14 / 31 / 17 of 200°C. The molecular sieve catalyst consists essentially of, and preferably is made up of, a noble metal and a molecular sieve. 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.

[0013] A molecular sieve can be any single or synthetic molecular sieve, including zeolites, and is preferably composed of aluminum, silicon, and / or phosphorus. Molecular sieves typically have a three-dimensional arrangement of SiO4, AlO4, and / or PO4 that are joined by sharing oxygen atoms, but can also be two-dimensional structures as well. The molecular sieve frameworks are generally anionic, which are counterbalanced by the offsetting charge, typically cations of alkali and alkaline earth elements (e.g., Na, K, Mg, Ca, Sr, and Ba), ammonium ions, and also protons.

[0014] The molecular sieve is preferably a small pore molecular sieve having a maximum ring size of eight tetrahedral atoms, a medium pore molecular sieve with a maximum ring size of ten tetrahedral atoms, or a large pore molecular sieve having a maximum ring size of twelve tetrahedral atoms. More preferably, the molecular sieve has a framework structure of AEI, MFI, EMT, ERI, MOR, FER, BEA, FAU, CHA, LEV, MWW, CON, EUO, or mixtures thereof.

[0015] The molecular sieve catalyst can be prepared by any known means. For example, the noble metal can be added to the molecular sieve to form the molecular sieve catalyst by any known means; the mode of addition is not considered to be particularly critical. For example, a noble metal compound (e.g., palladium nitrate) can be supported on the molecular sieve by Petition 870160025133, dated 02 / 06 / 2016, p. 15 / 31 / 17 impregnation, adsorption, ion exchange, incipient moisture, precipitation or similar.

[0016] The supported platinum group metal catalyst comprises one or more platinum group metals (PGMs) and one or more inorganic oxide carriers. The PGM may be platinum, palladium, rhodium, iridium, or combinations thereof, and more preferably platinum and / or palladium. The most commonly used inorganic oxide carriers include oxides from Groups 2, 3, 4, 5, 13, and 14 elements. Useful inorganic oxide carriers preferably have surface areas in the range of 10 to 700 m² / g, pore volumes in the range of 0.1 to 4 ml / g, and pore diameters of about 10 to 1000 Angstroms. The inorganic oxide carrier is preferably alumina, silica, titania, zirconia, cerium oxide, niobium, tantalum oxides, molybdenum oxides, tungsten oxides, or mixed oxides or oxides of compounds of any two or more of the same, for example silica-alumina, cerium oxide-zirconia or alumina-ceria-zirconia. Alumina and ceria are particularly preferred.

[0017] The supported platinum group metal catalyst can be prepared by any known means. Preferably, one or more platinum group metals are loaded onto one or more inorganic oxides by any known means to form the supported PGM catalyst; the mode of addition is not considered to be particularly critical. For example, a platinum compound (such as platinum nitrate) can be supported on an inorganic oxide by impregnation, adsorption, ion exchange, incipient moisture, precipitation, or the like. Other metals, such as iron, manganese, cobalt, and barium, can also be added to the supported PGM catalyst.

[0018] The cold start catalyst of the present invention can be prepared by processes well known in the prior art. The catalyst of Petition 870160025133, dated 02 / 06 / 2016, page 16 / 31 / 17 Molecular sieve and supported platinum group metal catalyst can be physically mixed to produce the cold start catalyst. Preferably, the cold start catalyst further comprises a flow substrate or filter substrate. In one embodiment, the molecular sieve catalyst and the supported platinum group metal catalyst are coated onto the filter substrate or flow through, and, preferably, deposited onto the filter substrate or flow through using a washable coating procedure to produce a cold start catalyst system.

[0019] The filter substrate or flow throughput is a substrate capable of containing catalyst components. The substrate is preferably a ceramic substrate or a metallic substrate. The ceramic substrate may be made of any suitable refractory material, for example, alumina, silica, titanium oxide, cerium oxide, zirconium dioxide, magnesium oxide, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates, metallic aluminosilicates (such as cordierite and spudomene), or a mixture of mixed oxides or any two or more of these. Cordierite, a magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0020] Metallic substrates may be made of any suitable metal, and in particular heat-resistant metals and metal alloys such as titanium and stainless steel, as well as ferritic stainless alloys containing iron, nickel, chromium, and / or aluminum, in addition to other trace metals.

[0021] The flow substrate is preferably a flow monolith having an alveolar structure with several thin-walled, small parallel channels running axially through the substrate and extending along an inlet or outlet of the substrate. The cross-section of the substrate channel can be of any shape, but is of Petition 870160025133, dated 02 / 06 / 2016, page 17 / 31 / 17 preference square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular or oval.

[0022] The filter substrate is preferably a monolithic flow-wall filter. The channels of a flow-wall filter are alternately blocked, which allows the exhaust gas stream to enter a channel from the inlet, then flow through the channel walls, and exit the filter from a different channel leading to the outlet. The particles in the exhaust gas stream are thus trapped in the filter.

[0023] The molecular sieve catalyst and the supported platinum group catalyst can be added to the flow stream or filter substrate by any known means. A representative process for preparing the cold-start catalyst using a washable coating procedure is set forth 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 molecular sieve catalyst and the supported PGM catalyst onto the flow stream or filter substrate is not considered critical. Thus, the molecular sieve catalyst can be subjected to reactive coating on the substrate before the supported PGM catalyst, or the supported PGM catalyst can be subjected to reactive coating on the substrate before the molecular sieve catalyst.

[0024] The pre-formed molecular sieve catalyst can be added to the filter substrate or stream-through of a reactive coating step. Alternatively, the molecular sieve catalyst can be formed over the stream-through filter or by first coating the unmodified molecular sieve reactive substrate 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 similar. Petition 870160025133, dated 02 / 06 / 2016, page 18 / 31 / 17

[0025] The reactive coating procedure is preferably carried out by forming a thick suspension of finely divided particles of molecular sieve catalyst (or unmodified molecular sieve) in a suitable solvent, preferably water, to form the flowable paste. Additional components, such as binders or stabilizers, may also be incorporated into the suspension as a mixture of water-soluble or water-dispersible compounds. The suspension preferably contains between 10 and 70 percent by weight of solids, more preferably between 20 and 50 percent by weight. Before forming the flowable paste, the unmodified molecular sieve catalyst (or molecular sieve) particles are preferably subjected to a size reduction treatment (vg, grinding) so that the average particle size of the solid particles is less than 20 microns in diameter.

[0026] The filter substrate or flow-through can then be dipped one or more times into the flow-through paste, or the flow-through paste can be coated onto the substrate in such a way that the desired load of catalytic materials will be deposited onto the substrate. If noble metal is not incorporated into the molecular sieve before reactive coating of the substrate by flow-through or filter, 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 (e.g., palladium nitrate). Preferably, the entire length of the filter substrate or flow-through paste is coated with the flow-through paste so that a washable coating of the molecular sieve catalyst covers the entire surface of the substrate.

[0027] After the flow substrate or filter was coated with the molecular sieve catalyst suspension, and impregnated with metal Petition 870160025133, dated 02 / 06 / 2016, page 19 / 31 / 17 noble, if necessary, the coated substrate is preferably dried and then calcined by heating to a high temperature to form the substrate coated with molecular sieve catalyst. Preferably, calcination occurs at 400 to 600°C for approximately 1 to 8 hours.

[0028] The addition of the supported PGM reactive coating catalyst is preferably carried out by first preparing a flowable paste of finely divided particles of the supported PGM catalyst in a suitable solvent, preferably water. Before forming the flowable paste, the supported PGM catalyst particles are preferably subjected to a size reduction treatment (e.g., grinding) so that the average particle size of the solid particles is less than 20 microns in diameter. Additional components, such as transition metal oxides, binders, stabilizers, or promoters, may be incorporated into the suspension as a mixture of water-soluble or dispersible compounds.

[0029] The sieve substrate coated with molecular catalyst can then be dipped one or more times into the fluid paste of supported PGM catalyst or the supported PGM catalyst suspension can be coated onto the sieve substrate coated with molecular catalyst such that the intended catalytic material will not be deposited onto the substrate.

[0030] Alternatively, a fluid paste containing only the inorganic oxide(s) can first be deposited onto the substrate coated with molecular sieve catalyst to form an inorganic oxide-coated substrate, followed by drying and calcination steps. The platinum group metal(s) can then be added to the inorganic oxide-coated substrate by any known means, including impregnation, adsorption, ion exchange, or a platinum group metal compound (such as platinum nitrate).

[0031] Preferably, the entire length of the filter substrate or throughflow is coated with PGM catalyst flow paste. Petition 870160025133, dated 02 / 06 / 2016, page 20 / 31 / 17 supported in such a way that a washable coating of the PGM-supported catalyst covers the entire surface of the substrate.

[0032] After the flow substrate, although or filter, was coated with the PGM-supported catalyst suspension, it is preferably dried and then calcined by heating to an elevated temperature to produce the cold-start catalyst. Preferably, calcination occurs at 400 to 600°C for approximately 1 to 8 hours.

[0033] In an alternative embodiment, the substrate flows through the filter or is comprised of the molecular sieve catalyst, and the supported platinum group metal catalyst is coated onto the molecular sieve catalyst substrate. In this case, the molecular sieve is extruded to form the filter substrate or flow-through, and the supported platinum group metal catalyst is coated onto the flow-through substrate or extruded molecular sieve catalyst. The extruded molecular sieve catalyst substrate is preferably a flowable honeycomb monolith.

[0034] Extruded molecular sieve substrates and honeycomb bodies, and processes for making them, are known in the art. See, for example, U.S. Pat. Nos. 5,492,883, 5,565,394, and 5,633,217 and U.S. Pat. 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 methylcellulose, and the mixture is extruded to form a green honeycomb body, which is then calcined and sintered to form the final molecular sieve monolith substrate. The molecular sieve may contain a noble metal prior to extrusion so that a noble metal / molecular sieve substrate (by flow or filter) monolith is produced by the extrusion process.

[0035] If a molecular sieve substrate monolith is formed, the molecular sieve substrate monolith is then subjected to a process of Petition 870160025133, dated 02 / 06 / 2016, page 21 / 31 / 17 impregnation, if necessary to load noble metal onto the molecular sieve monolith, followed by a washable coating step subjected to reactive coating for the PGM-supported catalyst.

[0036] The invention also includes an exhaust system for internal combustion engines, comprising the cold start catalyst. The exhaust system preferably comprises one or more additional after-treatment devices capable of removing pollutants from the engine exhaust combustion gases at normal operating temperatures. Preferably, the exhaust system comprises the cold start 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 adsorber catalyst, (5) a three-way catalyst, (6) an oxidation catalyst, or any combination thereof.

[0037] These post-treatment 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 (poor NOx reduction). A typical SCR catalyst is composed of a vanadium-titania catalyst, a vanadium-tungsta-titania catalyst, or a metal / zeolite catalyst such as iron / beta zeolite, copper / beta zeolite, copper / SSZ-13, copper / SAPO-34, Fe / ZSM-5, or copper / ZSM-5.

[0038] Particulate filters are devices that reduce particulate matter in the exhaust gases of internal combustion engines. Particulate filters include catalyzed particulate filters and bare particulate filters (non-catalyzed). 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, as well as destroy soot trapped by the filter. Petition 870160025133, dated 02 / 06 / 2016, page 22 / 31 / 17

[0039] Selective catalytic reduction (SCRF) filters are single-substrate devices that combine the functionality of an SCR and a particulate filter. They are used to reduce NOx and particulate emissions from internal combustion engines. In addition to the SCR catalyst coating, the particulate filter may also include other metals and metal oxide components (such as Pt, Pd, Fe, Mn, Cu, and ceria) to oxidize hydrocarbons and carbon monoxide in addition to destroying soot trapped by the filter.

[0040] Adsorption NOx catalysts (NACs) are designed to adsorb NOx under poor exhaust conditions, release the adsorbed NOx under rich conditions, and reduce the released NOx to form N2. NACs typically include a storage NOx component (e.g., Ca, Ba, Sr, Mg, K, Na, Li, Cs, La, Y, Pr, and Nd), an oxidation component (preferably Pd), and a reduction component (preferably Rh). These components are contained in one or more carriers.

[0041] 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.

[0042] Oxidation catalysts, and in particular diesel oxidation catalysts (DOCs), are well known in the art. Oxidation catalysts are designed to oxidize CO to the hydrocarbons CO2 and gas phase (HC) and an organic fraction of diesel particles (soluble organic fraction) in 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.

[0043] The exhaust system can be configured so that the cold start catalyst is located close to the engine and the additional after-treatment device(s) are located downstream of the cold start catalyst. Petition 870160025133, dated 02 / 06 / 2016, page 23 / 31 / 17 cold. Thus, under normal operating conditions, the engine exhaust gas flows first through the cold start catalyst before contacting the after-treatment device(s). Alternatively, the exhaust system may contain valves or other gas conduction means such that during the cold start period (below a temperature ranging from about 150 to 220°C, as measured at the after-treatment device(s)), the exhaust gas is directed to contact the after-treatment device(s) before flowing to the cold start catalyst. Once the after-treatment device(s) reaches operating temperature (approximately 150 to 220°C, as measured on the after-treatment device(s)), the exhaust gas flow is then redirected to contact the cold start catalyst before contacting the after-treatment device(s).This ensures that the temperature of the cold start catalyst remains low for a longer period of time, and thus improves the efficiency of the cold start catalyst, while simultaneously allowing the after-treatment device(s) to reach operating temperature more quickly. U.S. Pat. No. 5,656,244, the teachings of which are incorporated herein by reference, for example, teaches means for controlling the flow of exhaust gases during cold start and normal operating conditions.

[0044] The invention also includes a method for treating exhaust gases from an internal combustion engine. The method comprises adsorbing NOx hydrocarbons (HC) onto the cold start catalyst at temperatures at or below a low temperature, converting and thermally desorbing NOx and HC from the cold start catalyst at a temperature above the low temperature, and catalytically removing desorbed NOx and HC in a catalyst component downstream of the cold start catalyst. Preferably, the low temperature is about 200°C. Petition 870160025133, dated 02 / 06 / 2016, page 24 / 31 / 17

[0045] The downstream catalyst component of the cold start catalyst is an SCR catalyst, a particulate filter, an SCR filter, a NOx adsorbent catalyst, a three-way catalyst, an oxidation catalyst, or combinations thereof.

[0046] The following examples merely illustrate the invention. Skilled in the art will recognize many variations that are within the spirit of the invention and the scope of the claims. EXAMPLE 1: CATALYST PREPARATION Comparative Catalyst 1A: Pd-Fe / beta zeolite + Pt / Al2O3

[0047] Beta zeolite is added to an aqueous iron nitrate, followed by silica binder to form a fluid paste. The suspension is coated onto a through-flow cordierite substrate to achieve an iron loading of 6.783 g / m3 (190 g / ft3) of Fe, and the zeolite / Fe coated substrate is dried, and then calcined by heating at 500°C for 4 hours. Palladium is then added to the zeolite / Fe coated substrate by impregnation with an aqueous solution of Pd nitrate to achieve a Pd loading of 1.785 g / m3 (50 g / ft3), and the zeolite / Pd-Fe coated substrate is dried and then calcined by heating at 500°C for 4 hours.

[0048] Platinum nitrate is added to an aqueous flowable paste of alumina particles (ground to an average particle size of less than 10 microns in diameter) to form an alumina / Pt flowable catalyst paste. The alumina / Pt flowable catalyst paste is then coated onto the zeolite / Pd-Fe 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 to produce Catalyst 1A (containing 1.785 g / m3 (50 g / ft3) of Pd, 6.783 g / m3 (190 g / ft3) of Fe and 892.5 g / m3 (25 g / ft3) of Pt). Catalyst 1B: Pd / beta zeolite + Pt / Al2O3 Petition 870160025133, dated 02 / 06 / 2016, p. 25 / 31 / 17

[0049] Catalyst 1B is prepared in accordance with the procedure for Comparative Catalyst 1A, except that iron nitrate is not added. Example 2: TEST PROCEDURES

[0050] The catalysts are tested on core samples (2.54 cm x 8.4 cm) of a flow-through-flow coated cordierite substrate. The catalyst cores are first aged under flow-through conditions in a furnace under hydrothermal conditions (5% H2O, air equilibrium) 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 rate 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).

[0051] The catalysts are tested under poor conditions using a synthetic exhaust gas feed stream consisting of 200 ppm NO, 200 ppm CO, 500 ppm decane (on a C1 basis), 10% O2, 5% CO2, 5% H2O and the equilibrium nitrogen (% 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 at a ramp rate of 100°C / min.

[0052] The results in Table 1 show that catalyst 1B of the invention is comparable to Comparative Catalyst 1A, showing that the base metal can be removed from the zeolite component of the cold start catalyst without affecting its catalytic performance.

[0053] In summary, the cold start catalyst system of the invention performs several functions, including (1) storage and conversion of low-temperature NOx with high selectivity to N2; (2) Petition 870160025133, dated 02 / 06 / 2016, page 26 / 31 / 17 storage and conversion of low-temperature hydrocarbons; and (3) improved CO oxidation activity. Table 1. Comparison of Catalyst 1B and Comparative Catalyst 1a Catalyst 1B Comparative Catalyst 1A * NOx storage capacity at 80°C (g NO2 / L) 0.32 0.34 NOx capture efficiency at the 100 sec. end (%) 78 78 Cumulative NOx storage capacity below 200°C (g NO2 / L) 0.45 0.46 Cumulative HC storage and conversion efficiency below 200°C (%) 98 98 Cumulative CO conversion efficiency below 200°C (%) 44 45 Comparative Example

Claims

CLAIMS 1. An effective cold-start catalyst for adsorbing NOx and hydrocarbons (HC) at or below a low temperature and for converting and releasing the adsorbed NOx and HC at temperatures above the low temperature, the cold-start catalyst characterized in that it comprises: (1) a molecular sieve catalyst consisting essentially of a noble metal and a molecular sieve; and (2) a platinum group-supported metal catalyst comprising one or more platinum group metals and one or more inorganic oxide carriers; wherein the noble metal is palladium; wherein the molecular sieve is a small-pore molecular sieve with a maximum ring size of eight tetrahedral atoms; and wherein the low temperature is 200°C.

2. Cold start catalyst according to claim 1, characterized in that the molecular sieve has a structure selected from the group consisting of AEI, ERI, CHA, LEV and mixtures thereof.

3. Cold start catalyst according to any one of claims 1 or 2, characterized in that one or more platinum group metals is / are selected from the group consisting of platinum, palladium, rhodium, iridium and mixtures thereof.

4. Cold-start catalyst according to any one of claims 1 to 3, characterized in that one or more inorganic oxide carriers is / are selected from the group consisting of alumina, silica, titania, zirconia, ceria, niobium, tantalum oxides, molybdenum oxides, tungsten oxides and mixed oxides or composite oxides thereof. Petition 870200034029, dated 03 / 13 / 2020, page 9 / 28 2 / 3 5. Cold start catalyst according to any one of claims 1 to 4, characterized in that the cold start catalyst is coated onto a filter or throughflow substrate.

6. Cold-start catalyst according to claim 5, characterized in that the flow substrate is an alveolar monolith.

7. Cold-start catalyst according to any one of claims 1 to 4, characterized in that the molecular sieve catalyst is extruded to form a filter substrate or through-flow, and the supported platinum group metal catalyst is coated onto the through-flow substrate and is a honeycomb monolith of extruded molecular sieve catalyst.

8. Exhaust system for internal combustion engines, characterized in that it comprises a cold start catalyst as defined in any one of claims 1 to 7.

9. Exhaust system according to claim 8, characterized in that it further comprises a catalyst component selected from the group consisting of a selective catalytic reduction (SCR) catalyst, a particulate filter, an SCR filter, a NOx adsorbent catalyst, a three-way catalyst, an oxidation catalyst, and combinations thereof.

10. A method for treating exhaust gases from an internal combustion engine, characterized in that it comprises adsorbing NOx and HC onto the cold-start catalyst, as defined in any one of claims 1 to 7, below a low temperature, converting and thermally desorbing NOx and HC from the cold-start catalyst at temperatures above the low temperature, and catalytically removing the desorbed NOx and HC in a catalyst component downstream of the cold-start catalyst; wherein the low temperature is 200°C. Petition 870200034029, dated 03 / 13 / 2020, page 10 / 28 3 / 3 11. Method according to claim 10, characterized in that the downstream catalyst component of the cold start catalyst is selected from the group consisting of an SCR catalyst, a particulate filter, an SCR filter, a NOx adsorbent catalyst, a three-way catalyst, an oxidation catalyst and combinations thereof.