Bifunctional catalysts for selective ammonia oxidation

(54) Title: METHOD FOR TREATING EMISSIONS (57) Summary:

PRODUCED IN THE GAS CHAIN ​​OF

EXHAUST OF A BURNING VEHICLE

POOR OR DIESEL, CATALYST FOR THE

AMMONIA OXIDATION, AND, SYSTEM OF

TREATMENT FOR A CHAIN ​​OF

EXHAUST CONTAINING NOX.

(30) Unionist priority: 27/02/2008 us 12/038459,

02/27/2007 US 60/891835, 02/27/2007 US 60/891835, 02/27/2008 US

12/038459 (66) Internal Priority: 860446 (73) Holder (s): Basf Catalysts LLC (72) Inventor (s): Martins Dieterle, Matthew Tyler Caudle,

Stanley A. Roth, Wen-Mein Xue (74) Attorney (s): Momsen, Leonardos & Cia.

(86) International Order: pct US2OO8O55148 of 02/27/2008 (87) International Publication: wo 2008 / i06523of 04/09/2008

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Conversion of NH3Seletivity of N2 -Q- Conversion of NHSQ- Selectivity of N2 “METHOD FOR TREATING EMISSIONS PRODUCED IN THE EXHAUST GAS CHAIN ​​OF A POOR OR DIESEL BURNING VEHICLE, CATALYST FOR THE AMMONIA, EAT, AND SATISHAY OXIDATION AN EXHAUST CHAIN ​​CONTAINING_X”

CROSS REFERENCE TO RELATED ORDERS

This application claims priority benefit under 35 USC § 119 (e) for US Patent Application No. 60 / 891,835, filed February 27, 2007, and for US Patent Application No. 12 / 038,459, filed at February 27, 2008, which are incorporated herein, by reference, in their entirety.

TECHNICAL FIELD

Exhaust emission treatment systems and catalysts for internal combustion engines and methods for their manufacture and use as low-burn engines, including diesel engines and low-burn gasoline engines, are exposed.

FUNDAMENTALS

The exhaust of a diesel engine is a heterogeneous mixture, which contains not only gaseous emissions, such as carbon monoxide (“CO”), unburned or partially burned or oxygenated hydrocarbons (“HC”) and nitrogen oxides ("AT THE_X”), But also materials in condensed phase (liquids and solids) that constitute the so-called particulate materials or particulate matter. Often, the catalyst compositions and substrates, on which the compositions are arranged, are provided in diesel engine exhaust systems in order to convert certain or all of these exhaust components to harmless components. For example, diesel systems may contain one or more of a diesel oxidation catalyst, a soot filter and a NO reduction catalyst_X.

A technology for NO reduction_X proven, applied to stationary sources with poor exhaust conditions, is Selective Catalytic Reduction (SCR) for ammonia. In this process, NO_X (= NO + NO₂) is reacted with ammonia to form dinitrogen (N₂) by means of a catalyst typically composed of base metals. This technology is capable of reducing NO_X greater than 90%, and, therefore, it represents one of the best approaches for achieving the goals of NO reduction_X. SCR provides efficient NO conversions_X, as long as the exhaust temperature is within the active catalyst temperature range.

The reduction of the NO species_X for N₂ using NH₃ it is of interest to meet the NO emission targets_X in poorly burning engines. A consequence of using NH₃ it is the one under the conditions of incomplete conversion or fluctuations in exhaust temperature. NH₃can escape from the vehicle's exhaust. In order to avoid NH escape₃, a substoichiometric amount of NH₃ can be injected into the exhaust current, but there will be a conversion of NO_Xdecreased. Alternatively, NH₃ can be dosed in excess into the system in order to increase the NO conversion rate_X, but the exhaust needs to be further treated, so that the NH is removed₃ escaped or in excess. Even at a NH stoichiometric measurement₃, an increase in exhaust temperature can release the ammonia stored in the NO reduction catalyst_Xresulting in an NH escape₃. Conventional precious metal-based oxidation catalysts, such as platinum supported on alumina, can be very efficient in removing NH₃, but they produce N₂O and NO_X considerably as undesirable side products of the N product₂wanted. Thus, there is a need for a catalyst composition, which is active for the oxidation of NH₃, at temperatures as low as 225 ° C and which have a selectivity of N₂ in excess of about 60%, between 250 ° C and 400 ° C.

There is also a need for ammonia oxidation catalysts, which are stable against long-term thermal, chemical operation, and for the physical stress of normal vehicle operation, which includes temperatures up to about 450 ° C for a typical diesel application. In addition, a vehicle exhaust system can operate for short periods at temperatures above 800 ° C, for example, during the thermal regeneration of a particulate filter. It is important that an ammonia oxidation catalyst is stable, at acute thermal stress factors, in the same way. Due to this reason, accelerated curing conditions are identified, which simulate the cumulative effects of these long-term and acute stress factors on the activity of the catalyst. Such curing conditions involve exposing the catalyst to temperatures of 700 ° C to 800 ° C for between 5 and 50 hours, in the presence of up to 10% water vapor, in air.

SUMMARY

Aspects of the invention relate to catalysts, methods and systems for the treatment of exhaust gas. According to one or more embodiments of the invention, methods for treating emissions produced in the exhaust gas stream of a diesel vehicle are provided. A vehicle engine exhaust current is passed through an NO reduction catalyst_X. The exhaust gas stream, which leaves the NO reduction catalyst_X, which may contain ammonia, is passed through an oxidation catalyst. The oxidation catalyst comprises platinum, a second metal from one of the groups VB, VIB, VIIB, VIIIB, IB, or IIB of the Periodic Table, a refractory metal oxide, and a zeolite. The oxidation catalyst can be effective for removing ammonia, at temperatures below about 300 ° C, preferably below 250 ° C. The oxidation catalyst may not exhibit a significant decrease in ammonia removal efficiency in hydrothermal curing. According to one or more modalities, hydrothermal curing refers to curing a catalyst at temperatures up to about 700 ° C, specifically up to about 800 ° C, for up to 50 hours, for example, from about 5 to about 25 hours, in the presence of about 10% water vapor, in air.

Other embodiments of the invention are directed to catalysts for the oxidation of ammonia. The catalyst comprises two distinct metals, having a complementary function: A platinum component supported on a refractory metal oxide or zeolite; and a zeolite, on which a second metal, from one of the groups VB, VIB, VIIB, VIIIB, IB, or IIB of the Periodic Table, is supported. The second metal OP may be present on the zeolite as metal cations associated with the ion exchange sites in the zeolite structure. The supported platinum component provides a highly active and thermally stable ammonia oxidation function. The second metal supported on the zeolite provides an additional route for NH consumption₃ and NO_X through the selective catalytic reduction reaction, which serves to increase the selectivity of the catalyst for the production of N₂. The metal / zeolite component can also be designed to decompose N₂O, produced by the oxidation of NH₃ through the platinum / refractory metal oxide component, at low temperatures, to N₂, thus improving, even more, the selectivity of N₂. The oxidation catalyst must be effective for removing ammonia at temperatures below 300 ° C, preferably below 250 ° C. The oxidation catalyst must not exhibit a significant decrease in ammonia removal efficiency, in hydrothermal curing, at temperatures around 700 ° C. According to one or more modalities, the second metal is copper, present as copper (II) ions associated with ion exchange sites in the zeolite.

Other embodiments of the invention are directed to treatment systems for an exhaust stream containing NO_X. The treatment system comprises an upstream catalyst, which is effective in reducing NO_X; and a downstream oxidation catalyst being effective for the oxidation of ammonia. The oxidation catalyst comprises platinum, a second metal from one of the groups VB, VIB, VIIIB, IB or IIB of the Periodic Table, a refractory metal oxide, and a zeolite. The oxidation catalyst can be effective for removing ammonia at temperatures below about 300 ° C, preferably below 250 ° C. The oxidation catalyst may not exhibit a significant decrease in ammonia removal efficiency in hydrothermal curing.

According to one or more modalities, the catalysts used in the NO reduction catalyst methods or systems_Xcomprise an SCR catalyst, an LNT catalyst, or another catalyst for the destruction of NO_X, which results in the escape of ammonia from the NO reduction catalyst_X. In one or more embodiments, the NO reduction catalyst compositions_X and the oxidation catalyst are placed on separate substrates. In other embodiments, the NO reduction catalyst_X and the oxidation catalyst are arranged on the same substrate.

In one or more modalities, the platinum is distributed over the refractory metal oxide. Platinum can also be distributed over zeolite. In one or more embodiments, platinum is present in an amount in a range of about 0.1 g / 0.028 m³ at about 10 g / 0.028 m³, based on the total catalyst volume.

In one or more modalities, the metal from one of the groups VB, VIB, VIIB, VIIIB, IB or IIB of the Periodic Table is distributed over the zeolite. The metal can be distributed over the zeolite in an amount of between 0.1% and 5%, by weight, of the zeolite. In specific embodiments, the metal is copper or iron, or a mixture of both.

According to one or more modalities, the refractory metal oxide is selected from alumina, silica, zirconia, titania, ceria, and physical mixtures or chemical combinations thereof, including atomically doped combinations. In certain embodiments, the total load of the refractory metal oxide support on the substrate is between about 0.01 g / 16.40 cm³ and 2.0 g / 16.40 cm³ based on the volume of the total catalyst. In one or more modalities, the zeolite has one of the following crystal structures: CHA, BEA, FAU, MOR, MFI. In one embodiment, the molar ratio of silica to alumina in the zeolite is about 2 to about 250. In specific embodiments, the total charge of the zeolite on the substrate is between about 0.1 / 16.40 cm³ and 4.0 g / 16.40 cm³, based on the total catalyst volume. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic illustration of an emission treatment system modality;

Figure 2 shows the oxidation profile of NH₃ in steady state for two catalysts: Closed Symbols = 0.57% Pt over A1₂THE₃, catalyst load 0.5 g / 16.40 cm³, Pt load 5g / 0.028 m³, Open Symbols - 0.57 Pt on A12O3, catalyst charge 0.5 g / 16.40 cm³, Pt load 5 g / 0.028 m³ + 2.5 g / 16.40 cm³ beta zeolite with iron exchange (Fe - 1.1% measured as Fe2O₃, SAR = 30). NH₃ - 500 ppm, NO = 0, O₂ = 10% (as air), H₂O = 5%, balance = N₂, GHSV = 100,000 / hour. Solid lines are interpolations between data points;

Figure 3 shows the NH input concentration profile₃and the reactor temperature profile for the NH extinction experiment₃ pulse ramp for the assessment of NH oxidation₃ provisional. Gas composition: O₂ = 10%, H₂O = 5%, CO₂ = 5%, balance = N₂, GHSV = 100,000 / hour;

Figure 4 shows the instantaneous emission profile for a representative bifunctional ammonia oxidation catalyst, assessed by the pulse ramp extinction test. Catalyst = 1,8% by weight of Pt on A1₂THE₃, 1.0 g / 16.40 cm³, Pt load = 30 g / 0.028 m³ + 0.5 g / 16.40 cm³beta zeolite;

Figure 5 shows the instantaneous emission profile for a representative bifunctional ammonia oxidation catalyst, evaluated by the pulse ramp extinction test. Catalyst = 1.8% by weight of Pt over A1₂THE₃, 1.0 g / 16.40 cm³, Pt load = 30 g / 0.028 m³ + 0.5 g / 16.40 cm³beta zeolite;

Figure 6 shows selectivity for NO_X (= NO + NO₂) for a series of ammonia oxidation catalysts having different levels of beta zeolite with iron exchange in the catalyst, evaluated by the pulse ramp extinction test. The solid line is a linear fit of least squares to the data;

Figure 7 shows the fractional conversion of ammonia as a function of the amount of beta zeolite with iron exchange in the catalyst, for a series of bifunctional ammonia oxidation catalysts, assessed by the pulse ramp extinction test. The solid line is a linear fit of least squares to the data; and

Figure 8 shows the oxidation profile of NH₃ in steady state for two catalysts: Closed Symbols = 0.57% Pt over A1₂THE₃, catalyst load 0.5 g / 16.40 cm³, Pt load 5 g / 0.028 m³; Open Symbols = 0.57% Pt over A12O3, catalyst load 0.5 g / 16.40 cm³, Pt load 5g / 0.028 m³ + chabazite with copper exchange, catalyst charge = 2.5 g / 16.40 cm³(Copper = 2.5% measured as CuO, SAR = 30). NH3 = 500 ppm, NO = 0, O₂ = 10% (as air), H₂O = 5%, balance = N₂, GHSV = 100,000 / hour. Solid lines are linear interpolations between data points.

DETAILED DESCRIPTION

Before describing the various exemplary embodiments of the invention, it should be understood that the invention is not limited to the details of construction or process stages set out in the description that follows. The invention is capable of other modalities and of being practiced or of being executed in several ways.

As used in this report and in the appended claims, the singular forms "one", "one" and "o" include the various plural referents, unless the context clearly indicates otherwise. Thus, for example, the reference to "a catalyst" includes a mixture of two or more catalysts, and the like. As used herein, the term "reduce" means decrease in quantity and "decrease" means a decrease in quantity, caused by any means. When they appear in this, the terms "exhaust current" and the term "engine exhaust current" refer to the effluent from the engine as well as the effluent downstream of one or more other components of the catalyst system including, but not limited to, be limited to a diesel oxidation catalyst and / or a soot filter.

According to one or more embodiments of the invention, methods for treating emissions produced in the exhaust gas stream of a diesel or low-burn vehicle are provided.

In one embodiment, a vehicle engine exhaust current is passed through a NO reduction catalyst_X. The exhaust current, which leaves the NO reduction catalyst_X, which may contain ammonia, is passed through an oxidation catalyst. The oxidation catalyst comprises platinum, a second metal from one of the groups VB, VIB, VIIB, VIIIB, IB, or IIB of the periodic table, a refractory metal oxide, and a zeolite. The oxidation catalyst can be effective to remove ammonia at temperatures below about 300 ° C, preferably below 250 ° C. The oxidation catalyst may not exhibit a significant reduction in the efficiency of ammonia removal in curing at temperatures up to about 700 ° C, preferably up to about 800 ° C, for up to 50 hours, in the presence of about 10 % of water vapor in air.

The NO reduction catalyst_X of one or more modalities comprises a selective catalytic reduction (SCR) catalyst, a NO retention catalyst_X poor (LNT), or another catalyst for the destruction of NO_X, which results in a possible emission or escape of ammonia from the NO reduction catalyst_X.

The NO reduction catalyst_X and the oxidation catalyst composition can be arranged as a wash coating layer on the same or on different substrates. In addition, the SCR catalyst and the selective ammonia oxidation catalyst can be in the same catalyst housing or can be in different catalyst housing.

Other aspects are addressed to catalysts for the oxidation of ammonia. In one embodiment, the catalyst comprises two distinct materials having a complementary function; a platinum component supported on a refractory metal oxide or zeolite; and a zeolite, on which a second metal, from one of the groups VB, VIB, VIIB, VIIIB, IB or IIB of the Periodic Table, is supported. The second metal may be present on the zeolite as metal cations associated with ion exchange sites on the zeolite structure. The supported platinum component provides a highly active and thermally stable ammonia oxidation function. The second metal supported on the zeolite provides an additional path for NH consumption₃ and NO_X through selective catalytic reduction reaction, which serves to increase the selectivity of the catalyst for the production of N₂. The metal / zeolite component can be designed to decompose N₂O, produced by the oxidation of NH₃ by the refractory platinum / metal oxide component, at low temperatures, to N₂, in order to further improve N selectivity₂. The oxidation catalyst can be effective to remove ammonia at temperatures below 300 ° C, preferably below 250 ° C. The oxidation catalyst may not exhibit a significant decrease in ammonia removal efficiency by curing at temperatures up to 700 ° C, preferably up to 800 ° C, for up to 50 hours, in the presence of about 10% water vapor in air. According to one or more modalities, the second metal is copper, present as copper (II) ions, associated with ion exchange sites in the zeolite.

Other modalities are for treatment systems for an exhaust gas stream containing NO_X; and a downstream oxidation catalyst being effective in oxidizing ammonia. The oxidation catalyst comprises platinum, a second metal from one of the groups VB, VIB, VIIB, IIIB, IB, or IIB of the Periodic Table, a refractory metal oxide, and a zeolite. The oxidation catalyst can be effective to remove ammonia at temperatures below about 300 ° C, preferably below 250 ° C. The oxidation catalyst may not exhibit a significant decrease in ammonia removal efficiency by curing at temperatures up to about 700 ° C, preferably up to about 800 ° C, for up to 50 hours, in the presence of about 10% of water vapor in air.

The engine treatment system according to one or more modalities includes a metering system for metering ammonia, or an ammonia precursor, or a mixture of different ammonia precursors, either continuously, or at periodic intervals within the leakage current.

One embodiment of an emission treatment system according to the invention is shown schematically in Figure 1. As can be seen in Figure 1, the exhaust containing gaseous pollutants (including unburned hydrocarbons, carbon monoxide and AT THE_X) and particulate material is transported through the emission treatment system denoted as 110 exhaust, containing gaseous pollutants (including unburned hydrocarbons, carbon monoxide and NOx) and the particulate material is transported from engine 19 to a downstream position n exhaust current. The reducing agent is injected as a spray through a nozzle (not shown) into the exhaust stream. The aqueous urea shown in line 25 can serve as a precursor to ammonia, which can be mixed with air in another line 26 in a mixing station 24. Valve 23 can be used to dose precise amounts of aqueous urea, which are converted into the exhaust stream for ammonia.

The exhaust stream with the added ammonia is converted to the substrate of the SCR 12 catalyst (also referred to herein, including in the claims as "the first substrate" containing CuCHA according to one or more modalities. When passing through the first substrate 12, the NOx component of the exhaust current is converted, through selective catalytic reduction of NOx with NH₃ for N₂ and H₂O. In addition, NH₃ excess, which emerges from the entry zone, can be converted, through oxidation to a downstream ammonia oxidation catalyst (not shown) also containing CuCHA, in order to convert the ammonia to N₂ and H₂O. The first substrate is typically a flow through a monolith substrate. As will be appreciated, after a mixing distance, before it is introduced into the SCR catalyst, the radial ammonia concentration, perpendicular to the exhaust gas flow, may or may not be uniform. In the SCR 16 catalyst, NO_X is converted, with the help of NH₃, for N₂ and H₂O. NH₃ residual exhaust from SCR 16 catalyst to an NH Oxidation Catalyst₃ 16, downstream. In the NH Oxidation Catalyst₃, NH₃ residual is converted to N₂ and H₂O. The Substrate

According to one or more modalities, the substrate for the ammonia oxidation catalyst can be any of those materials used, in a typical way, for the preparation of automotive catalysts and which will typically comprise a metallic honeycomb structure or ceramic. Any suitable substrate can be employed, such as a monolithic through-flow substrate, having a plurality of parallel, thin gas flow passages that extend from an entrance to an exit face of the substrate, in such a way that they are open to the flow of fluid. The passages, which are, in essence, direct paths from the fluid inlet to the fluid outlet, are defined by the walls, over which the catalytic material is coated as a “wash coating”, in such a way that the gases, which flow through the passages, are placed in contact with the catalytic material. The flow passages of the monolithic substrate are thin-walled channels, which can be of any configuration in cross section, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc. Such structures can contain about 60 to about 1200 or more gas inlet openings (ie, “cells” by 6.45 cm² cross-section (cpsi). A representative commercially available through-flow substrate is Corning 400/6 cordierite material, which is constructed from cordierite and has 400 cpsi (400 by 6.45 cm² cross-section (cpsi)) and a wall thickness of 6 mil (152.4 micrometers). However, it should be understood that the invention is not limited to a particular type of substrate, material or geometry.

The ceramic substrate can be produced from any suitable refractory material, for example, cordierite, cordierite -oc-alumina, silicon nitride, zirconium mullite, spodumene, magnesia silica alumina, zirconium silicate, silimanite, magnesium silicates, zirconium , petalite, aalumina, aluminosilicates, and the like.

The substrates useful for the bifunctional catalyst composites of embodiments of the present invention can also be of a metallic nature and are composed of one or more metals or metal alloys. Exemplary metal supports include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys, in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium and / or aluminum, and the total amount of these metals may comprise at least 15% by weight of the alloy, for example, 10-25% chromium, 3-8% by weight of aluminum and up to 20% by weight of nickel. The alloys may also contain small amounts or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium, and the like. Metallic substrates can be used in various forms, such as in corrugated sheet or in monolithic form. A representative commercially available metallic substrate is manufactured by Emitec. However, it will be understood that the invention is not limited to a particular type of substrate, material or geometry. The surface of metal substrates can be oxidized at high temperatures, for example, 1000 ° C, or higher, in order to form an oxide layer on the substrate surface, improving corrosion resistance of the alloy. Such high temperature-induced oxidation can also improve the adhesion of the refractory metal oxide support and catalytically promoting metal components to the substrate.

Catalyst Supports

According to one or more modalities, the platinum is deposited on a refractory metal oxide support with a high surface area. Examples of high surface area refractory metal oxides include, but are not limited to, alumina, silica, titania, ceria, and zirconia and physical mixtures or combinations thereof, which include atomically doped combinations. Refractory metal oxide may consist of or contain a mixed oxide, such as silica-alumina, aluminosilicates which may be amorphous or crystalline, alumina-zirconia, alumina-lantana, alumina-barialantania-neodymium, alumina-chrome, alumina-barium, alumina -ceria, and the like. An exemplary refractory metal oxide comprises gamma-alumina having a specific surface area of ​​about 50 to about 300 m²/ g.

The zeolite component of some modalities comprises a porous aluminosilicate, on which a metal is deposited from one of the groups VB, VIB, VIIB, VIIIB, IB, or IIB of the Periodic Table. An example of these metals includes iron and copper. The zeolite component can have any of the frame structures listed in Database of Zeolite Structures, published by the International Zeolite Association (IZA). Frame structures include, but are not limited to, those of the CHA, FAU, BEA, MFI and MOR types.

The platinum component of some modalities can be supported on a zeolite, which can have any of the frame structures listed in Database of Zeolite Structures published by the International Zeolite Association (IZA). Frame structures include, but are not limited to, those of the CHA, FAU, BEA, MFI and MOR types.

The Wash Coating Layers

According to one or more embodiments, the catalyst is applied as a wash coating layer, which is deposited on, that is, is coated on and adhered to, the substrate. A suitable method of preparing the platinum component is to prepare a mixture or a solution of a platinum precursor in a suitable solvent, for example, water. In general, from an economic and environmental point of view, aqueous solutions of soluble platinum compounds or complexes are preferred. Typically, a platinum precursor is used in the form of a compound or a complex, so that a dispersion of the precursor on the support is achieved. For the purposes of the present invention, the term "platinum precursor" means any compound, complex, or the like that, upon calcination or the initial phase of use of it, is decomposed, or otherwise converted, to a catalytically active form . Suitable platinum complexes or compounds include, but are not limited to, platinum chlorides (for example, [PtCl salts₄] ', [PtCl₆] ', platinum hydroxides (for example, [Pt (OH) salts₆] '), platinum amines (for example, [Pt (NH₃)₄], [Pt (NH₃)₄]⁴⁺), platinum hydrates (for example, [Pt (OH2) 4] salts²⁺), platinum bis (acetyl acetonates), and mixed or complex compounds (for example [Pt (NH3)₂(Cl)₂]). A commercially representative source of platinum is 99% ammonium hexachloroplatinate from Strem Chemicals, Inc., which may contain traces of other precious metals. However, it should be understood that this invention is not restricted to platinum precursors of a particular type, composition, or purity. A mixture or solution of the platinum precursor is added to the support through various chemical means. These include the impregnation of a solution of the platinum precursor onto the support, which can be followed by a fixation stage, which incorporates the acid component (eg, acetic acid) or the basic component (eg, ammonium hydroxide ). This wet solid can be chemically reduced or calcined, or used as such. Alternatively, the support can be suspended in a suitable vehicle (for example, water) and reacted with the platinum precursor in solution. The latter method is more typical when the support is a zeolite, and it is desired to fix the platinum precursor to ion exchange sites on the zeolite frame. Additional processing stages may include fixation through an acidic component (eg, acetic acid) or a basic component (eg, ammonium hydroxide), chemical reduction, or, calcination.

In one or more embodiments, the wash coating layer contains a zeolite, over which a metal has been distributed from one of the groups VB, VIB, VIIB, VIIIB, IB, or IIB of the Periodic Table.

Exemplary zeolites include, but are not limited to, zeolites having one of the following crystal structures, CHA, BEA, FAU, MOR, MFI. An exemplary metal in this series is copper. A suitable method for distributing the metal over the zeolite is to first prepare a mixture or a solution of the metal precursor in a suitable solvent, for example, water. In general, from the point of view of economic and environmental aspects, aqueous solutions of soluble compounds or complexes are preferred. For the purposes of the present invention, the term "metallic precursor" means any compound, complex, or the like, which can be dispersed on the zeolite support, in order to provide a catalytically active metallic component. For exemplary Group IB metallic copper, suitable complexes or compounds include, but are not limited to, anhydrous and hydrated copper sulfate, copper nitrate, copper acetate, copper acetyl acetonate, copper oxide, copper hydroxide, and copper amine salts (for example, [Cu (NH₃)₄]²⁺. A representative commercially available copper source is 97% copper acetate from Strem Chemicals, Inc., which may contain traces of other metals, in particular iron and nickel. However, it can be understood that this invention is not restricted to metal precursors of a particular type, composition or purity. The zeolite can be allowed to react in such a way that the copper component is distributed over the zeolite. This can result in copper being distributed over the zeolite pore kennels, as well as over the outer surface of the zeolite. Copper can be distributed as copper ions (II), copper ions (I), or as copper oxide. After the copper has been distributed over the zeolite, the zeolite can be separated from the liquid phase of the suspension, washed, and dried. It can also be calcined in order to fix the copper.

In order to apply the catalyst layer to the substrate, finely divided particles of the catalyst, which consist of the platinum component and / or the metallic zeolite component, are suspended in an appropriate vehicle, for example, water, in order to form a suspension. Other promoters and / or stabilizers and / or surfactants can be added to the suspension as mixtures or solutions in water or in a water miscible vehicle. In one or more embodiments, the suspension is ground, so as to result in substantially all solids having particle sizes of less than about 10 microns, that is, between about 0.1 - 8 microns, in an average diameter. The crushing can be carried out in a ball mill, a continuous Eiger mill, or other similar equipment. In one or more embodiments, the suspension or paste may have a pH of about 2 to less than about 7. The pH of the suspension can be adjusted, if necessary, by adding an appropriate amount of an organic or inorganic acid to the suspension. The solids content of the suspension can be, for example, 20-60% by weight, and more particularly about 35-45% by weight. The substrate may then be immersed in the suspension, or the suspension may otherwise be coated on the substrate in such a way that a desired charge of the catalyst layer is deposited on the substrate. After that, the substrate is dried at about 100 ° C and calcined by heating, for example, at 30-650 ° C for about 1 hour to about 3 hours. Drying and calcination are carried out, typically, in air. The coating, drying and calcination processes can be repeated, if necessary, in order to achieve the desired final catalyst load on the support. In some cases, complete removal of the liquid and other volatile components may not occur until the catalyst is put into use and subjected to the high temperatures encountered during operation.

After calcination, the catalyst load can be determined by calculating the difference in coated and uncoated weights of the substrate. As will be apparent to those of skill in the art, the catalyst charge can be modified by changing the solids content of the coating suspension and the viscosity of the suspension. Alternatively, repeated immersions of the substrate in the coating suspension can be conducted, followed by removal of the excess suspension, as described above. In a specific embodiment, the load of the wash layer on the substrate is between about 0.2 to about 3.0 g / 16.40 cm³, or in a typical way of about 2.0 / 16.40 cm³.

EXAMPLES

Example 1: Preparation of a bifunctional ammonia oxidation catalyst.

A bifunctional AMOx catalyst preparation was started with an impregnation of the basic Pt (IV) precursor onto an oxide support by the incipient moisture method. The Pt (IV) was fixed to the support through the subsequent impregnation of an organic acid, in order to decrease it was superficial pH and precipitate the Pt (IV). The resulting powder was then suspended in deionized water, in order to provide a suspension of approximately 40% solids, and ground either through a continuous mill or through a conventional ball mill, in order to provide a particle distribution having 90% of the amount of particles less than 10 pm. The pH was monitored and was not allowed to exceed 5 in order to avoid resolubilization of the Pt (IV). Separately, a second component, which typically consists of a transition metal exchange zeolite, was suspended in water in order to provide a suspension of approximately 40% solids, and ground to a distribution of aggregate particle size, having 90% of the amount of particles less than 10 pm. To this suspension, approximately 3% ZrO was added₂ (solid base) as a zirconium acetate solution. This was required in order to avoid gelling in the mixture of the two suspensions. The two portions were mixed in appropriate portions to provide the required ratio of supported Pt and metallic exchange zeolite components. The resulting suspension was analyzed for the correct Pt content, and coated over a conventional cylindrical ceramic monolith, having dimensions of 1.0 “OD by 3.0” in length, a cell density of 400 cells / 6.45 cm², and a wall thickness of 6 mil (152.4 micrometers). The coating was performed by immersing the monolith in the suspension, in parallel with the channels, removing the excess suspension through air flow, and drying and calcining the resulting wet catalyst core. In some cases, repeated applications were required, in order to obtain objective loads, in particular for total loads> 1.0 g / 16.40 cm³. The catalyst cores were cured, in the usual way, at high temperature, before the evaluation of the catalyst activity. The specific curing conditions for each assessment were each as described below.

Example 2: Steady state evaluation of a Pt / Al catalyst₂THE₃ + FeBEA catalyst

Figure 2 shows a graphical representation of the conversion of NH₃ percentage and percentage selectivity for N₂ for a catalyst, consisting of 0.57% by weight of A1₂THE₃ (0.5 g / 16.40 cm³) providing a total Pt load of 5 g / 0.028 m³ (closed symbols). The catalyst was treated at 750 ° C for 5 hours in air, before evaluation. The data shows the almost complete conversion of NH₃ at 250 ° C, but this catalyst had the undesirable properties of constantly reducing the selectivity of N₂ was only 36%, which is probably not suitable for vehicle application. Low selectivity at high temperature is a result of NO production_X considerable by the Pt catalyst supported, according to Equation 1. Nitric oxide is well known as a primary oxidation product for ammonia in relation to the platinum supported at operating temperatures for vehicle exhaust.

Equation 1 4 NH₃ + 5O₂ -> 4 NO + 6 H₂

The conversion of NH is illustrated in Figure 2₃ and selectivity data for a catalyst, which consists of a mixture of 0.57%, by weight, of Pt over A1₂THE₃ (0.5 g / 16.40 cm³ (and beta zeolite with iron exchange (2.5 g / 16.40 cm²) (open symbols). The total catalyst load on the monolith was 3.0 g / 16.40 cm³. The iron content of beta zeolite with iron exchange was 1.1% by weight, measured as Fe₂THE₃. The data in the open symbols clearly show an NH conversion₃ almost equivalent as for the catalyst without the ferro-beta component. This was expected, as the total load of the Pt component supported was the same as above, and the primary oxidation process in relation to PT / A1₂THE₃, Equation 1, is largely unaffected by the presence of the ferro-beta component. However, the selectivity of N₂ has been substantially improved at high temperatures, in the presence of an iron exchange beta zeolite component. At 400 ° C, the selectivity of N₂increased to 70% in the catalyst containing iron-beta, a two-fold improvement over the Pt / Al catalyst₂THE₃. Iron-exchange zeolites are well-known catalysts for the coproportion of NH₃ and NO, in order to produce N₂ in a highly selective way, through the SCR reaction, Equation 2. This provides the means to understand the source of the increased selectivity in the presence of beta zeolite iron. The supported Pt component converts NH₃ to NO according to Equation 1. The beta zeolite iron then works in a way to convert the intermediate from NO to N₂ using an NH equivalent₃ unregulated, according to the SCR reaction in Equation 2. Based on this scheme, it is readily evident that optimal selectivity should be obtained when the rate for Equation 2 is competitive with, or faster than, the rate for Equation 1. As a result, we expect a decrease in NO production to be observed_X and an increase in N selectivity₂, as the amount of SCR component in the catalyst was increased (see Example 5). These data thus illustrate the value of the bifunctional concept in the design of catalysts for the selective ammonia oxidation.

Equation 2.4 NH₃ + 6 NO 5 N₂ + 6 H₂THE

Example 3: Pulse ramp test of ammonia oxidation catalysts

A pulse ramp evaluation was developed in order to measure the activity and selectivity of ammonia oxidation catalysts, under provisional conditions. The tests were performed on catalysts coated on 0.75 ”(1.9 cm) OD x 2.5” (6.35 cm) long cylindrical through-flow monoliths, with a cell density of 400 cells / 16.40 cm² (400 cells / 6.45 cm²) (and a wall thickness of 6 mil (152.4 micrometers). The test involved three stages. First, the catalyst was exposed for 1800 seconds to a gas stream of 150 ° C containing 500 ppm ammonia, 10% dioxane , 5% water vapor, and 5% carbon dioxide, the balance being dinitrogen.The GHVS was 100,000 / hour, based on the total catalyst volume. Then, the ammonia feed was turned off and the catalyst was balanced for an additional 1200 seconds, after which there was no NH₃ observable in the gas phase. At this point, the temperature was increased, in a linear fashion, from 150 ° C to 500 ° C over a period of 3000 seconds. During this temperature ramp, ammonia was added periodically to the current in 0.07 mmol pulses, with a pulse duration of 5 seconds, followed by a residence time of 55 seconds. No ammonia was added during the residency period. Figure 3 illustrates this experimental ammonia profile for a neutral cordierite substrate, showing ammonium concentration during the pre-equilibrium phase of ammonia adsorption and desorption and during the pulse ramp phase.

Example 4: Instantaneous emission profiles for the typical bifunctional ammonia oxidation catalyst

Figure 4 shows a typical instantaneous emission profile for a supported platinum catalyst. This catalyst consisted of 1 g / 16.40 cm of SBA-150 alumina, on which 30 g / 0.028 m were supported³, along with an additional 0.5 g / 16.40 cm of beta zeolite. In the low-temperature region, where ammonia is not consumed, the data shows a considerable enlargement of the NH pulses₃, due to NH retention₃ by the zeolite component. Such an increase was not observed in catalysts that did not have zeolite. As this temperature has been increased to above 200 ° C, the amount of NH₃ at the exit decreased as the NH₃ starts to be consumed in relation to the catalyst. This was associated with the immediate appearance of N₂O in the output current. N₂O was the non-N emission₂ observed up to 300 ° C, after which NO_X it became the most prevalent. This emission standard was typical for a supported platinum catalyst, but did not contain additional catalytic functionality. The objective of adding a second catalytic functionality to the catalyst formation was, therefore, to decrease NO production_X and / or N₂THE.

Example 5: Cumulative emission data for a bifunctional ammonia oxidation catalyst

The integration of the instantaneous emission data in Figure 4 provides the cumulative emission profile for ammonia oxidation, shown in Figure 5. The catalyst part was the same as for Example 3. The inflection of the NH profile₃ between 200 ° C and 250 ° C indicates the extinction region and the flat line for NH₃ above 250 ° C indicates that there was no ammonia emission above this temperature. The data clearly reveal the start of N production₂O at 225 ° C and the start of NO production_X at 300 ° C. Using the integrated data, the net emission of each species containing N over the duration of the test was determined, with the exception of N₂. The production of liquid dinitrogen was determined from a mass balance calculation, assuming that the only NH oxidation products₃ are N₂, NINTH₂ and N₂O. The catalytic selectivities for each species were calculated as the ratio of the total emission of that species to NH₃ converted.

Example 6: NO selectivity_X as a function of beta iron content for bifunctional ammonia catalysts based on supported platinum and beta iron zeolite

Figure 6 shows a graphical representation of the net selectivity of the NO production catalyst_X as a function of zeolite iron beta content in the catalyst composition. The catalyst compositions used to generate Figure 6 are provided in Table 1. Figure

6 shows data for Pt supported on SBA-150 alumina, on silica

-aluminium Siralox 1.5, and on a titania INE 108. For all these samples, the general tendency was to produce lower levels of the species NO_X as the beta-zeolite is increased.

Table 1:

<td rowspan="2">Catalyst ID</td><td colspan="5">Catalyst Composition</td>

<td>Pt</td><td>Oxide Metallic</td><td>Metal oxide charge</td><td>FeBEA charge</td><td>Part load</td>

<td></td><td>g / fp (ig / ft³ = g / 0.028 m³)</td><td></td><td>gin³(1 g / in³ = 1 g / 16.40 cm³)</td><td>gin³(1 g / in³= lg / 16.40 cm³)</td><td>gin³(1 g / in³ = 1 g / 16.40 cm³)</td>

<td>Al (Neutral control)</td><td> 0,00</td><td>none</td><td> 1,00</td><td> 0,00</td><td> 1,00</td>

<td>A2 (Neutral control)</td><td> 0,00</td><td>none</td><td> 1,00</td><td> 0,00</td><td> 1,00</td>

<td>A3</td><td> 5</td><td>A12O3 / CCO2</td><td> 2,44</td><td> 0</td><td> 2,44</td>

<td>A4</td><td> 30</td><td>Siraloxl, 5</td><td> 1</td><td> 0,5</td><td> 1,50</td>

<td>A5</td><td> 6,1</td><td>Siralox 1.5</td><td> 0,45</td><td> 0,45</td><td> 0,90</td>

<td>A6</td><td> 10</td><td>Siraloxl, 5</td><td> 0,83</td><td> 0,83</td><td> 1,66</td>

<td>A7</td><td> 10,00</td><td>Siraloxl, 5</td><td> 0,83</td><td> 2,25</td><td> 3,08</td>

<td>A8</td><td> 6,10</td><td>Siraloxl, 5</td><td> 0,45</td><td> 0,45</td><td> 0,90</td>

<td>A9</td><td> 6,10</td><td>Siraloxl, 5</td><td> 0,45</td><td> 0,45</td><td> 0,90</td>

<td>A10</td><td> 6,10</td><td>Siraloxl, 5</td><td> 0,45</td><td> 0,45</td><td> 0,90</td>

<td>All</td><td> 6,10</td><td>Siraloxl, 5</td><td> 0,45</td><td> 0,45</td><td> 0,90</td>

<td>A12</td><td> 90</td><td>Siraloxl, 5</td><td> 2,05</td><td> 0</td><td> 2,05</td>

<td>A13</td><td> 27,00</td><td>Siraloxl, 5</td><td> 0,38</td><td> 1,27</td><td> 1,65</td>

<td>A14</td><td> 26,00</td><td>Siraloxl, 5</td><td> 0,38</td><td> 1,63</td><td> 2,01</td>

<td>A15</td><td> 28</td><td>Siraloxl, 5</td><td> 0,98</td><td> 1,3</td><td> 2,28</td>

<td>A16</td><td> 25,00</td><td>INE108</td><td> 0,35</td><td> 1,13</td><td> 1,48</td>

<td>A17</td><td> 26,40</td><td>INE108</td><td> 0,38</td><td> 1,68</td><td> 2,06</td>

<td>A18</td><td> 25,00</td><td>INE108</td><td> 0,35</td><td> 1,12</td><td> 1,47</td>

<td>A19</td><td> 25,00</td><td>INE108</td><td> 0,35</td><td> 2,08</td><td> 2,43</td>

<td>A20</td><td> 25,00</td><td>INE 108</td><td> 0,35</td><td> 2,03</td><td> 2,38</td>

<td>A21</td><td> 28,00</td><td>INE108</td><td> 0,75</td><td> 2,13</td><td> 2,88</td>

<td>A22</td><td> 5,3</td><td>FeBEA</td><td> 0,42</td><td> 0,42</td><td> 0,84</td>

<td>A23</td><td> 10</td><td>FeBEA</td><td> 0,81</td><td> 0,81</td><td> 1,62</td>

<td>A24</td><td> 5,30</td><td>FeBEA</td><td> 0,42</td><td> 0,42</td><td> 0,84</td>

Example 7: Ammonia conversion as a function of beta iron content for bifunctional ammonia oxidation catalysts, based on supported platinum and zeolite beta beta.

It is important to demonstrate that the two functions in the bifunctional ammonia oxidation catalyst are kinetically independent, in such a way that the activity of each component is not negatively affected by the other. Beta iron zeolite is not an effective catalyst in itself for the oxidation of ammonia by Equation 1, and in such a way that the conversion of liquid ammonia is dominated by the supported platinum component. This is demonstrated, in a clear way, in Figure 7, which shows that the conversion of ammonia, and therefore the rate for ammonia oxidation, were not affected by the amount of zeolite beta beta in the sample. The beta beta component did not contribute strongly to ammonia oxidation, but it also did not inhibit the extinction of ammonia oxidation in relation to the supported platinum component. The data also demonstrated that the iron beta component did not influence the production of N₂O, which was consistent with the observation that iron-based catalysts do not react with N₂Below 400 ° C. This reinforces the kinetic independence of the supported platinum component and the beta iron component.

Example 8: Steady state evaluation of a Pt / Al catalyst₂THE₃ + Bifunctional CuCHA

The scheme illustrated in Figures 1 and 2 suggests that selectivity for N₂ it can be increased by increasing the amount of the active SCR component, or by using an intrinsically more active SCR component. The last strategy was illustrated by preparing a catalyst containing 0.57% Pt, by weight, on Al₂/THE₃(0.5 g / 0.028 m charge) and a copper exchange chabazite zeolite (CuCHA charge, 2.5 g / 0.028 m), in order to provide a total catalyst charge of 3.0 g / 16 , 40 cm³. The total load of the supported Pt component was identical to that in Example 2 (5 g / 0.028 m³ Pt). The catalyst was cured at 750 ° C for 5 hours in air. The catalyst was evaluated under NH oxidation conditions₃ in steady state. NH conversion₃ and the selectivity of N₂ were graphically represented as open symbols in Figure 8, along with the control sample of only Pt supported in closed symbols. As in Example 2, the conversion of NH₃ it was similar for the catalyst with and without the CuCHA component. However, the selectivity of N₂ it was substantially higher for the catalyst containing CUCHA, compared to the control sample, and it was also higher than the sample containing FeBEA. At 400 ° C, the catalyst converts 100% of NH₃ for N₂ and there was essentially NO formation_X, while the FeBEA-containing catalyst produces approximately 30% NO_X at 400 ° C. This is consistent with the independent observation that CuCHA is a much more active catalyst for the SCR reaction than FeBEA is.

The reference throughout this report to "a modality", "certain modalities", "one or more modalities" or "a modality" means that a particular aspect, structure, material or characteristic, described in connection with the modality, is included in at least one embodiment of the invention. In this way, the appearance of phrases, such that “in one or more modalities“, “in certain modalities“, “in a modality or in a modality“ in various places throughout this report do not necessarily refer to the same embodiment of the invention. In addition, the particular aspects, structures, materials or characteristics can be combined, in an appropriate way, in one or more modalities.

Although the invention has been described herein with reference to particular modalities, it should be understood that these modalities are merely illustrative of the principles and applications of the present invention. It will be evident to that person skilled in the art that many modifications and variations can be introduced in the method and apparatus of the present invention, without departing from the spirit and scope of the invention. Thus, it is intended that the present invention includes modifications and variations that are within the scope of the attached claims and their equivalents.