Patent Description:
Selective catalytic reduction (SCR) of nitrogen oxides can be carried out using a zeolite promoter with a reductant such as ammonia, urea, and/or hydrocarbon in the presence of oxygen. While a variety of zeolite forms are known, certain forms, such as zeolite beta and chabazite have been particularly utilized for forming metal-promoted catalysts, particularly for SCR applications.

The catalysts employed in the SCR process ideally should be able to retain good catalytic activity over the wide range of temperature conditions of use, for example, about <NUM> to about <NUM> or higher, under hydrothermal conditions, which are often encountered such as during the regeneration of a soot filter, a component of the exhaust gas treatment system used for the removal of particles.

Metal-promoted zeolite catalysts useful in SCR have included, among others, iron-promoted zeolite catalysts and copper-promoted zeolite catalysts. For example, Iron-promoted zeolite beta has been described in <CIT>. The process of preparation of metal containing Chabazite particularly can include exchange of the desired metal species with accompanying removal of alkali metals, such as sodium, which can be detrimental to the hydrothermal stability of the final catalyst. The typical Na<NUM>O level of Na-Chabazite is between <NUM>,<NUM> and <NUM>,<NUM> ppm. Sodium is known to degrade the zeolite structure under hydrothermal aging conditions via formation of Na<NUM>SiO<NUM> and Na<NUM>Al<NUM>O4 and concomitant dealumination of the zeolite.

Previous attempts to form Iron-exchanged zeolite using the chabazite form, have proven difficult. For example, <CIT> proposes a method of preparing Iron-zeolite chabazite without ion exchange since the publication points out that it has been difficult to incorporate iron into chabazite zeolites such as SSZ-<NUM> using traditional ion-exchange methods due to the small pore openings of the chabazite structure (e.g., in the <NUM>-<NUM> Angstrom range). The publication posits that its direct incorporation of iron during synthesis of the chabazite is preferred because incorporating iron into chabazite with ion exchange is not feasible due to the small pore size of chabazite. Nevertheless, because of the prevalence of utilization of ion-exchange in forming promoted zeolite catalysts, it would be useful to provide further methods for formation of Iron-exchanged zeolites particularly Iron-exchanged chabazites.

The invention is defined in appended claim <NUM>. Preferred embodiments are defined in the appended dependent claims <NUM> to <NUM>. The present invention provides processes for forming Iron-exchanged zeolites, <NPL> relates to a process for preparing Fe/Cu-SSZ-<NUM> as a catalyst for the ammonia selective catalytic reduction of NO. The process comprises first preparing a Cu-exchanged SSZ-<NUM> and adding the Cu-SSZ-<NUM> slowly to a Fe(NO<NUM>)<NUM>·<NUM><NUM>O solution for ion-exchange at <NUM> in water for <NUM> hours under stirring, followed by drying and calcining. <NPL> relates to the ion-exchange of a NaY zeolite using <NUM> aqueous solution of Fe(III) sulfate at ambient temperature for <NUM>. <NPL> relates to a process for preparing ferric exchanged Y zeolites comprising treating NaY zeolites with aqueous solution of ferric acetate-acetic acid at a pH of about <NUM> at <NUM>, followed by washing with hot distilled water and drying at <NUM> overnight. <CIT> relates to the preparation of a SCR-active molecular sieve basedcatalyst which comprises combining a molecular sieve with at least one ionic iron species and at least one organic compound to form a mixture and calcining. <NPL> relates to a process for preparing an iron-exchanged zeolite comprising combining zeolites H-USYY with an aqueous solution of ferric chloride at <NUM> for <NUM>. After ion exchange, the sample was filtered, thoroughly washed, dried and then calcined. <NPL> relates to a process for preparing an iron-exchanged zeolite comprising combining zeolite clinoptilolite with an aqueous solution of ferric chloride in an acetate buffer at pH <NUM> for one hour at room temperature.

The presently described invention arises at least in part from the surprising finding that the ability to form Iron-exchanged zeolites, particularly small pore zeolites, can be significantly improved through specific use of Iron(III) salts instead of Iron(II) salts.

The present invention relates to a process for preparing an Iron-exchanged According to the present invention, the process comprises zeolite. According to the present invention, the process comprises combining a zeolite with Iron(III) cations in an aqueous medium such that the Iron(III) cations are exchanged into or onto the zeolite and an Iron(III)-exchanged zeolite is thus formed. The exchange of Iron(III) into or onto the zeolite is carried out at a temperature of <NUM> to <NUM> for a time of <NUM> to <NUM> minutes. The zeolite has a chabazite (CHA) structure and the aqueous medium further comprises a buffering agent which comprises ammonium acetate. The process is defined according to any one of claims <NUM> to <NUM>. Preferably, about <NUM>% by weight or greater of the Iron(III) cations (or other amounts as further described herein) are exchanged into the zeolite. In one or more further embodiments, the process for preparing an Iron-exchanged zeolite can be further defined in relation to one or more of the following statements, which can singly relate to the process or can be combined in any number and/or order.

The zeolite can be a sodium-containing zeolite.

The zeolite can be an NH<NUM>-containing zeolite.

The zeolite can be an H-containing zeolite.

The Iron(III) cations can be provided directly from an Iron (III) salt.

The Iron(III) salt can be selected from the group consisting of Iron(III) halides, Iron(III) citrates, Iron(III) nitrates, Iron(III) sulfates, Iron(III) acetate, and combinations thereof.

The Iron(III) salt can be selected from the group consisting of Iron(III) nitrates, Iron(III) sulfates, and combinations thereof.

The Iron(III) cations can provided in situ via oxidation of an Iron(II) salt.

The Iron(II) salt can be oxidized in the aqueous medium by addition of an oxidizing agent to the aqueous medium.

The oxidizing agent can be one or more of air, substantially pure oxygen (e.g., having an O<NUM> purity of about <NUM>% or greater, about <NUM>% or greater, or about <NUM>% or greater), and peroxo compounds.

About <NUM>% by weight or greater of the Iron(III) cations can be exchanged into the zeolite. The Iron(III)-exchanged zeolite can comprise Iron(III) in an amount of about <NUM>% by weight or greater.

The Iron(III)-exchanged zeolite can comprise Iron(III) in an amount of about <NUM>% by weight to about <NUM>% by weight.

The Iron(III)-exchanged zeolite can comprise sodium, NH<NUM>, or H cations.

One or more cations can be present in the Iron(III)-exchanged zeolite in an amount of about <NUM>,<NUM> ppm or less.

The zeolite and the Iron(III) cations can be combined in an aqueous medium at a pH of less than <NUM>.

The zeolite and the Iron(III) cations can be combined at a pH of about <NUM> to about <NUM>.

The zeolite and the Iron (III) cations can be combined at a pH of about <NUM> to about <NUM>.

The process can result in substantially no ammonium nitrate formation.

The process can further comprise washing and filtering the Iron(III)-exchanged zeolite to a solution conductivity of about <NUM> micromhos or less.

These and other features, aspects, and advantages of the invention will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below.

The present invention will now be described more fully hereinafter with reference to exemplary embodiments thereof.

As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise. The present invention is directed to a process for preparing an Iron-exchanged zeolite, the process comprising combining a zeolite with Iron(III) cations in an aqueous medium such that the Iron(III) cations are exchanged into or onto the zeolite to thus form an Iron(III)-exchanged zeolite, wherein the exchange of Iron(III) into or onto the zeolite is carried out at a temperature of <NUM>ºC to <NUM>ºC for a time of <NUM> to <NUM> minutes, wherein the zeolite has a chabazite (CHA) structure and wherein the aqueous medium further comprises a buffering agent which comprises ammonium acetate. Zeolites are understood to be aluminosilicate crystalline materials having substantially uniform pore sizes which, depending upon the type of zeolite and the type and amount of cations included in the zeolite lattice, can range from about <NUM> Angstroms to about <NUM> Angstroms in diameter. The present processes are useful to overcome difficulties in previously forming Iron-exchanged zeolites that are suitable for use, for example, in an SCR catalyst.

In particular, the inventors have discovered that the ability to successfully form an Iron-exchanged zeolite using zeolites of the chabazite form can be significantly improved utilizing Iron(III) salts as the Iron source instead of Iron(II) salts. It was surprising to find that both Iron uptake and cation (e.g., sodium) removal can approach <NUM>%.

The process of the invention is directed to Iron exchange in a zeolite of the chabazite form. Chabazite has a framework structure consisting of a stacked sequence of <NUM>-rings in the order AABBCC. , forming double <NUM>-rings at each apex of the rhombic unit cell. Chabazite may thus be characterized as being of the type of zeolite having a double <NUM>-ring (D6R) building unit. Such structure typically provides a cage that can be referred to as the chabazite cage. Thus, the International Zeolite Association has defined the chabazite structure as being a small pore zeolite with <NUM> member-ring pore openings (approximately <NUM> Angstroms) accessible through its <NUM>-dimensional porosity. The cage-like structure results from the connection of the D6R building units by <NUM> rings. According to the present invention, the process comprises one or more embodiments, the zeolite can be an aluminosilicate zeolite, a borosilicate, a gallosilicate, a SAPO, an ALPO, a MeAPSO, or a MeAPO. More particularly, the zeolite can be one or more of SSZ-<NUM>. SSZ-<NUM>, natural chabazite, zeolite K-G, Linde D, Linde R, LZ-<NUM>, LZ-<NUM>, LZ-<NUM>, ZK-<NUM>, SAPO-<NUM>, SAP <NUM>-<NUM>, SAP0. <NUM>, and ZYT-<NUM>. In some embodiments, the zeolite can have a silica to alumina molar ratio in the range of about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to <NUM>.

The zeolite can be in the H-form in one or more embodiments. In other embodiments, the zeolite can be in an exchanged form, including cation-exchanged forms.

The zeolite particularly is a sodium-containing zeolite that typically can have greater than <NUM>,<NUM> ppm sodium present in the framework thereof. According to the present invention, the process comprises particular, a sodium-containing zeolite useful in Ironexchange can have greater than <NUM>,<NUM> ppm, greater than <NUM>,<NUM> ppm, or greater than <NUM>,<NUM> ppm sodium ions present, for example about <NUM>,<NUM> ppm to about <NUM>,<NUM> ppm, about <NUM>,<NUM> ppm to about <NUM>,<NUM> ppm, or about <NUM>,<NUM> ppm to about <NUM>,<NUM> ppm sodium ions based on the total weight of the zeolite. In some embodiments, the zeolite can be exchanged with other cations, such as ammonium cations or hydrogen cations, in ranges such as noted above. It is understood that the use of "ppm" above and throughout the present application is intended to mean ppm by weight.

The process for preparing an Iron-exchanged zeolite according to the invention comprises combining a zeolite with Iron(III) cations in an aqueous medium such that the Iron(III) cations are exchanged into the zeolite. The aqueous medium includes a buffering agent. Preferably, the Iron(III) cations uniformly exchange with a different cation, such as H*, NH<NUM>+, Na+, or the like. Use of Iron(III) cations beneficially can improve the process such that about <NUM>% by weight or greater of the Iron(III) cations are exchanged into or onto the zeolite. In some embodiments, about <NUM>% by weight or greater, about <NUM>% by weight or greater, about <NUM>% by weight or greater, about <NUM>% by weight or greater, about <NUM>% by weight or greater, or about <NUM>% by weight or greater of the Iron(III) cations can be exchanged into or onto the zeolite. In particular, about <NUM>% by weight to about <NUM>% by weight, about <NUM>% by weight to about <NUM>% by weight, or about <NUM>% by weight to about <NUM>% by weight of the Iron(III) cations can be exchanged into or onto the zeolite. The Iron(III) cations can be provided directly or indirectly.

Any Iron(III) salt can be used in the present ion exchange process to directly provide the Iron(III) cations in the aqueous medium. In some embodiments, organic lron(III) salts can be used - e.g., Iron(III) citrate, Iron(III) acetate, and Iron(III) oxalate. In some embodiments, inorganic Iron(III) salts can be used - e.g., Iron(III) halides, Iron(III) nitrates, and Iron(III) sulfates. If desired, combinations of two or more different Iron(III) salts can be used. In particular embodiments, the Iron(III) salt can be Iron(III) nitrate and/or Iron(III) sulfate. Various forms of the salts can be used, such as hydrates thereof. Iron(III) complexes with organic ligands can be used, as well as Iron(III) combinations with organic or inorganic anions.

In some embodiments, Iron(III) cations can be provided indirectly by in situ formation using an Iron(II) salt. More particularly, the Iron(II) can be oxidized so as to generate the Iron(III) cations in situ. For example, air or substantially pure oxygen may be pumped through the solution. Other oxidizing agents may also be utilized for in situ Iron(III) formation including, but not limited to, peroxo compounds (e.g., H<NUM>O<NUM>, peroxodisulfate), or even strong oxidizers, such as permanganates and perchlorates, or the like wherein the aqueous medium further comprises a buffering agent which comprises ammonium acetate.

The zeolite and the Iron(III) salt (or Iron(II) salt and oxidizer) are combined in an aqueous medium In some embodiments, the aqueous medium can include one or more further components. The buffering agent is useful to maintain the ion exchange solution within a desired pH range. For example, it can be beneficial for the ion exchange solution (which is intended to include the aqueous medium) to be at a pH of less than <NUM>. More particularly, pH can be in a range of about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. Other materials that may be utilized, particularly to maintain a pH in a range as described above, include but are not limited to: ammonium sulfate; ammonium carbonate; ammonium bicarbonate; and ammonium formate. In some embodiments, it can be beneficial to alter the order of addition of components in carrying out the exchange. For example, the order of addition can be based upon the nature of the zeolite. According to the present invention, the process comprises embodiments utilizing a sodium-containing zeolite, the buffer (e.g., ammonium acetate) can be added to the aqueous medium before addition of the Iron(III) cations. In embodiments utilizing zeolite in the H-form or NH<NUM>-form, the buffer can be added to the aqueous medium after addition of the Iron(III) cations.

Following the ion exchange, the Iron-exchanged zeolite can be subject to one or more steps of filtering alone or in combination with washing. For example, the Iron-exchanged zeolite can be filtered from the aqueous medium to provide the finished product. In some embodiments, washing and filtering can be carried out utilizing a filter press. In such methods, the Iron-exchanged zeolite solution is pumped into a filter press unit wherein the Iron-exchanged zeolite solids collect on the filter webs. The increasing pressure on the filter webs as the solids are collected is beneficial to force non-solids through the web and into the filtrate. If desired, air may be forced through the filter cakes to further remove the non-solids. In one or more embodiments, filtering can be carried out with a funnel filter (e.g., a Buechner filter) and appropriate filter paper, and filtering may be augmented by application of a vacuum.

The filter cakes with the Iron-exchanged zeolite can be washed by pumping of an aqueous solvent through the filter cakes on the webs. The aqueous solvent, in some embodiments, can be demineralized water. In some embodiments, washing can be carried out until the filtrate has a desired conductivity. Any recognized method for measuring filtrate conductivity can be utilized according to the present disclosure such as, for example, the methods described in ASTM D1125-<NUM>, Standard Test Methods for Electrical Conductivity and Resistivity of Water. Standard conductivity measurement devices, such as a VWR® symphony™ Handheld Meter with a conductivity probe, can be used, preferably calibrating the device with a conductivity standard. Washing preferably can be carried out until the filtrate has a measured conductivity of about <NUM> microsiemens (micromhos) or less, about <NUM> microsiemens (micromhos) or less, about <NUM> microsiemens (micromhos) or less, or about <NUM> microsiemens (micromhos) or less, more particularly about <NUM> microsiemens (micromhos) to about <NUM> microsiemens (micromhos), about <NUM> microsiemens (micromhos) to about <NUM> microsiemens (micromhos), or about <NUM> microsiemens (micromhos) to about <NUM> microsiemens (micromhos). In some embodiments, washing can be particularly used to remove a variety of ions from the solution, such as sodium, iron, ammonium, nitrates, acetate, and the like.

The Iron-exchanged zeolite prepared according to the process of the present invention can exhibit particular properties. The zeolite is characterized in that cations in the zeolite have been exchanged with Iron(III) ions. The cation content will be within a range as otherwise described herein. The zeolite prepared according to the process of the present invention can include Iron(III) in an amount of about <NUM>% by weight or greater, about <NUM>% by weight or greater, about <NUM>% by weight or greater, or about <NUM>% by weight or greater - e.g., about <NUM>% by weight to about <NUM>% by weight, about <NUM>% by weight to about <NUM>% by weight, or about <NUM>% by weight to about <NUM>% by weight. The Iron particularly can be substantially in the form of Iron(III) oxide - Fe<NUM>O<NUM>.

In one or more embodiments, the Iron-exchanged zeolite prepared according to the process of the present invention can be characterized in relation to the positional arrangement of the Iron(III) cations relative to the zeolite. In particular, the Iron(III) cations are preferably substantially uniformly dispersed onto the zeolite. For example, the Iron(III) cations can be adsorbed onto the zeolite with little or substantially none of the Iron(III) cations being present as extraframework cations. Beneficially, however, the Iron(III) cations adsorbed onto the zeolite prepared according to the process of the present invention can move into extra-framework cationic positions during use of the material (e.g., as a catalyst) or during steaming of the material.

The Iron-exchanged zeolite can be in a substantially powdered form. In some embodiments, the Iron-exchanged zeolite prepared according to the process of the present invention can have a surface area of about <NUM><NUM>/g or greater, about <NUM><NUM>/g or greater, about <NUM><NUM>/g or greater, or about <NUM><NUM>/g or greater, such as about <NUM><NUM>/g to about <NUM><NUM>/g, about <NUM><NUM>/g to about <NUM><NUM>/g, or about <NUM><NUM>/g to about <NUM><NUM>/g. Surface area can be BET surface area, such as can be determined according to DIN <NUM> or ASTM D3663-<NUM>(<NUM>), Standard Test Method for Surface Area of Catalysts and Catalyst Carriers, ASTM International, West Conshohocken, PA, <NUM>.

In some embodiments, the zeolite prepared according to the process of the present invention can be characterized in relation to the presence of sulfur therein. For example, the Iron-exchanged zeolite can comprise sulfate in an amount of about <NUM> ppm or greater, about <NUM> ppm or greater, about <NUM> ppm or greater, or about <NUM>,<NUM> ppm or greater, such as about <NUM> ppm to about <NUM>,<NUM> ppm, about <NUM> ppm to about <NUM>,<NUM> ppm, or about <NUM> ppm to about <NUM>,<NUM> ppm, based upon the total weight of the Iron-exchanged zeolite.

The process of the present invention can be particularly beneficial in relation to the ability to avoid formation of certain by-products. For example, some processes for forming an Iron(II) exchanged zeolite can result in formation of ammonium nitrate, and removal of the by-product can be troublesome - e.g., requiring detonation to explosively decompose the material. In some embodiments, the processes, however, can be particularly beneficial in that the process results in substantially no ammonium nitrate formation.

The Iron-exchanged zeolite prepared according to the process of the present invention can be utilized, for example, as a catalyst, particularly in the selective catalytic reduction of NOx. In some embodiments, the Iron-exchanged zeolite can be used as a molecular sieve, adsorbent, catalyst, catalyst support, or binder. The Iron-exchanged zeolite prepared according to the process of the present invention can be used in the form of self-supporting catalytic particles; however, in various embodiments, it can be dispersed, coated, or otherwise combined with a carrier substrate. In some embodiments, the Iron-exchanged zeolite can be formed into a slurry and applied, for example, as a washcoat to a substrate. If desired, a binder, such as titania, zirconia, or alumina may be used.

According to one or more embodiments, the substrate for the Iron-exchanged zeolite prepared according to the process of the present invention may be constructed of any material typically used for preparing automotive catalysts and will typically comprise a metal or ceramic honeycomb structure. The substrate typically provides a plurality of wall surfaces upon which the Iron-exchanged zeolite, for example as a washcoat, is applied and adhered, thereby acting as a carrier for the catalyst composition.

Exemplary metallic substrates 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 advantageously comprise at least <NUM>% by weight of the alloy, e.g., about <NUM> to about25% by weight of chromium, about <NUM> to about <NUM>% by weight of aluminum, and up to <NUM>% by weight of nickel. The alloys may also contain small or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium and the like. The surface or the metal carriers may be oxidized at high temperatures, e.g., <NUM>,<NUM> and higher, to form an oxide layer on the surface of the substrate, improving the corrosion resistance of the alloy and facilitating adhesion of the washcoat layer to the metal surface.

Ceramic materials used to construct the substrate may include any suitable refractory material, e.g., cordierite, cordierite-α alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicates, zircon, petalite, α alumina, aluminosilicates and the like. The substrates may be employed in various shapes such as corrugated sheet or monolithic form.

Any suitable substrate may be employed, such as a monolithic flow-through substrate having a plurality of fine, parallel gas flow passages extending from an inlet to an outlet face of the substrate such that passages are open to fluid flow. The passages, which are essentially straight paths from the inlet to the outlet, are defined by walls on which the catalytic material is coated as a washcoat so that the gases flowing through the passages contact the catalytic material. The flow passages of the monolithic substrate are thinwalled channels which can be of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. Such structures may contain from about <NUM> to about <NUM> or more gas inlet openings (i.e. "cells") per square centimeter of cross section (cpsc) (<NUM> to about <NUM> or more gas inlet openings (i.e. "cells") per square inch of cross section (cpsi)), more usually from about <NUM> to <NUM> cpsc (<NUM> to <NUM> cpsi). The wall thickness of flow-through substrates can vary, with a typical range being between <NUM> and <NUM> (<NUM> and <NUM> inches). A representative commercially-available flow-through substrate is the Corning <NUM>/<NUM> cordierite material, which is constructed from cordierite and has <NUM> cpsc (<NUM> cpsi) and a wall thickness of <NUM> (<NUM> mil). However, it will be understood that the invention is not limited to a particular substrate type, material, or geometry.

In alternative embodiments, the substrate may be a wall-flow substrate, wherein each passage is blocked at one end of the substrate body with a non-porous plug, with alternate passages blocked at opposite end-faces. This requires that gas flow through the porous walls of the wall-flow substrate to reach the exit. Such monolithic substrates may contain up to about <NUM> or more cpsc (<NUM> or more cpsi), such as about <NUM> to <NUM> cpsc (<NUM> to <NUM> cpsi). The cross-sectional shape of the cells can vary as described above. Wall-flow substrates typically have a wall thickness between <NUM> and <NUM> (<NUM> and <NUM> inches). A representative commercially available wall-flow substrate is the Corning CO substrate, which is constructed from a porous cordierite. However, it will be understood that the invention is not limited to a particular substrate type, material, or geometry.

The Iron-exchanged zeolites and catalysts formed using the Iron-exchanged zeolites can be utilized in a wide variety of systems and methods. As non-limiting examples, the Iron-exchanged zeolites prepared according to the present invention can be used: as a catalyst in selective catalytic reduction (SCR) or nitrogen oxides, or NOx; as a catalyst for oxidation of NH<NUM>, such as the oxidation of NH<NUM> slip in diesel systems; as a catalyst for the decomposition of N<NUM>O; as a catalyst for soot oxidation; as a catalyst for emission control in Advanced Emission Systems, such as Homogeneous Charge Compression Ignition (HCCI) engines, as an additive in fluid catalytic cracking (FCC) processes; as a catalyst in organic conversion reactions; or as a catalyst in stationary source processes. If desired, one or more precious metals (e.g., Pd or Pt) can be added to the Iron-exchanged zeolite.

In some aspects, the present disclosure also relates to an emission (or exhaust) treatment system that incorporates the Iron-exchanged zeolite prepared as according to the process of the present invention. The zeolite particularly can be used in an integrated emissions treatment system comprising one or more additional components for the treatment of exhaust gas emissions, particularly diesel exhaust. For example, the emission treatment system may comprise a diesel oxidation catalyst (DOC) component, a catalyzed soot filter (CSF) component, and/or a selective catalytic reduction (SCR) catalytic article. The treatment system can include further components, such as ammonia oxidation materials, additional particulate filtration components, NOx storage and/or trapping components, and reductant injectors.

An exemplary catalyst comprising an Iron-exchanged zeolite prepared according to the process of the present invention is illustrated in <FIG>, shows a refractory substrate member <NUM>, in accordance with one or more embodiments. Referring to <FIG>, the refractory substrate member <NUM> is a cylindrical shape having a cylindrical outer surface <NUM>, an upstream end face <NUM> and a downstream end face <NUM>, which is substantially identical to end face <NUM>. Substrate member <NUM> has a plurality of fine, parallel gas flow passages <NUM> formed therein. As see in <FIG>, flow passages <NUM> are formed by walls <NUM> and extend through substrate <NUM> from upstream end face <NUM> to downstream end face <NUM>, the passages <NUM> being unobstructed so as to permit the flow of a fluid, e.g., a gas stream, longitudinally through substrate <NUM> via gas flow passages <NUM> thereof. As is more easily seen in <FIG>, walls <NUM> are so dimensioned and configured that gas flow passages <NUM> have a substantially regular polygonal shape, substantially square in the illustrated embodiment, but with rounded corners as described in <CIT>. A catalytic coating layer <NUM> is adhered to or coated onto the walls <NUM> of the substrate member. As shown in <FIG>, an additional catalytic coating layer <NUM> is coated over the catalytic coating layer <NUM>. In one or more embodiments, a third catalytic coating layer (not shown) can be applied to the substrate beneath. As will be appreciated by one of skill in the art, a catalyst comprising an Iron-exchanged zeolite prepared according to the process of the present invention can thus include one catalytic coating layer or a plurality of catalytic coating layers. The iron(III)-exchanged zeolite prepared according to the process of the present invention may be present in catalytic coating layer <NUM> and/or in the additional catalytic coating layer <NUM>.

Exemplary emission treatment systems may be more readily appreciated by reference to <FIG>, which depict a schematic representation of an emission treatment system comprising an Iron-exchanged zeolite prepared according to the process of the present invention, in accordance with one or more embodiments of the present invention. <FIG> shows an exemplary embodiment of an emission treatment system <NUM> comprising an engine <NUM>, a diesel oxidation catalyst (DOC) <NUM>, a selective catalytic reduction (SCR) component <NUM>, and a catalyzed soot filter (CSF) <NUM>. An exhaust conduit <NUM> is in fluid communication with the engine <NUM> via an exhaust manifold and the DOC <NUM>. Exhaust from the DOC <NUM> is next conveyed via exhaust conduit line <NUM> to the downstream SCR component <NUM>. An ammonia precursor (e.g. aqueous urea) is injected via line <NUM> into the exhaust line <NUM>. The exhaust gas stream with added ammonia is conveyed via line <NUM> to the SCR component <NUM> for the treatment and/or conversion of NOx. The CSF <NUM> is downstream of the SCR catalyst <NUM>, and the exhaust gas stream may be conveyed to the CSF <NUM> via exhaust conduit <NUM>. It is understood that one or both of the DOC <NUM> and the CSF <NUM> can be optional and thus may be absent from the emission treatment system. As such, the emission treatment system may include the engine <NUM>, the SCR catalyst <NUM>, and a connecting exhaust line. The ammonia injection line <NUM> can also be present in such embodiments. In particular, an SCR system including the Iron-exchanged zeolite prepared according to the process of the present invention that is integrated in the exhaust gas treatment system of a vehicle can include the following components: an SCR catalyst comprising an Iron-exchanged zeolite prepared according to the process of the present invention; a urea storage tank; a urea pump; a urea dosing system; a urea injector/nozzle; and a respective control unit. Such elements, and further elements useful in an emission treatment system according to the present disclosure, are described in <CIT>.

In some aspects, the present invention also can relate to a method for selectively reducing nitrogen oxides (NOx) from a stream, such as an exhaust gas. In particular, the stream can be contacted with a catalyst including an Iron-exchanged zeolite prepared according to the process of the present invention. The term nitrogen oxides, or NOx, as used herein encompasses any and all oxides of nitrogen, including but not limited to N<NUM>O, NO, N<NUM>O<NUM>, NO<NUM>, N<NUM>O<NUM>, N<NUM>O<NUM>, and NO<NUM>. The Iron-exchanged zeolites prepared according to the process of the present invention invention particularly can be used as a catalytically active material in a method for removing nitrogen oxides from exhaust gases of internal combustion engines, in particular diesel engines, which operate at combustion conditions with air in excess of that required for stoichiometric combustion, i.e., at lean conditions.

In some embodiments, an Iron-exchanged zeolite prepared according to the process of the present invention used as an SCR catalyst can be effective so as to provide a NOx conversion of at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>% over a temperature range of about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

The present invention is more fully illustrated by the following examples, which are set forth to illustrate certain aspects of the present invention and are not to be construed as limiting thereof. Relative concentrations (percent by weight and ppm) are understood to relate to the total weight of the Iron exchanged zeolite.

The starting material for the testing was Na-SSZ13 (<NUM>) [<NUM>]. Initially, SSZ-<NUM> was crystallized as described in <CIT>, using trimethyladamantyl ammonium hydroxide as the template and sodium hydroxide as a further source of OH. The pH was adjusted to <NUM>, and the material was recovered by filtration and dried before calcining at <NUM> to produce the Na-form of SSZ-<NUM>. Chemical analysis showed the material to have <NUM>% by weight SiO2:Al2O3, and <NUM>% by weight of Na<NUM>O on a volatile-free basis. XRD indicated that pure SSZ-<NUM> had been obtained. The BET surface of the calcined material, determined according to DIN <NUM>, was <NUM><NUM>/g. The resulting powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The mixture was heated to approximately <NUM>. Ammonium Iron(II) sulfate (<NUM>) was added followed by ammonium sulfate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(II) exchanged zeolite had an Iron concentration of <NUM>% (<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

The starting material for the testing was Na-SSZ13 (I) [<NUM>]. Initially, SSZ-<NUM> was crystallized as described in <CIT>, trimethyladamantyl ammonium hydroxide as the template and sodium hydroxide as a further source of OH. The pH was adjusted to <NUM>, and the material was recovered by filtration and dried before calcining at <NUM> to produce the Na-form of SSZ-<NUM>. Chemical analysis showed the material to have <NUM>% by weight SiO2:A12O3, and <NUM>% by weight of Na<NUM>O on a volatile-free basis. XRD indicated that pure SSZ-<NUM> had been obtained. The BET surface of the calcined material, determined according to DIN <NUM>, was <NUM><NUM>/g. The resulting powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The mixture was heated to approximately <NUM>. Ammonium Iron(II) sulfate (<NUM>) was added followed by ammonium sulfate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(II) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM>,<NUM> ppm) by weight.

The starting material for the testing was Na-SSZ13 (<NUM>) [<NUM>]. Initially, SSZ-<NUM> was crystallized as described in <CIT>, using trimethyladamantyl ammonium hydroxide as the template and sodium hydroxide as a further source of OH. The pH was adjusted to <NUM>, and the material was recovered by filtration and dried before calcining at <NUM> to produce the Na-form of SSZ-<NUM>. Chemical analysis showed the material to have <NUM>% by weight SiO2:Al2O3, and <NUM>% by weight of Na<NUM>O on a volatile-free basis. XRD indicated that pure SSZ-<NUM> had been obtained. The BET surface of the calcined material, determined according to DIN <NUM>, was <NUM><NUM>/g. The resulting powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The mixture was heated to approximately <NUM>. Iron(II) sulfate hexahydrate (<NUM>) was added followed by ammonium sulfate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(II) exchanged zeolite had an Iron concentration of <NUM>% (<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

The starting material for the testing was Na-SSZ13 (<NUM>) [<NUM>]. Initially, SSZ-<NUM> was crystallized as described in <CIT>, using trimethyladamantyl ammonium hydroxide as the template and sodium hydroxide as a further source of OH. The pH was adjusted to <NUM>, and the material was recovered by filtration and dried before calcining at <NUM> to produce the Na-form of SSZ-<NUM>. Chemical analysis showed the material to have <NUM>% by weight SiO2:A12O3, and <NUM>% by weight of Na<NUM>O) on a volatile-free basis. XRD indicated that pure SSZ-<NUM> had been obtained. The BET surface of the calcined material, determined according to DIN <NUM>, was <NUM><NUM>/g. The resulting powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The mixture was heated to approximately <NUM>. Iron(II) sulfate hexahydrate (<NUM>) was added. Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(II) exchanged zeolite had an Iron concentration of <NUM>% (<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(II) sulfate hexahydrate (<NUM>) was added. Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(II) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM>,<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(III) ammonium citrate (<NUM>) was added. Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM>,<NUM> ppm) by weight. Although not wishing to be bound by theory, it is believed that Iron(III) ammonium citrate did not exchange significantly because of the pH of the solution.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(II) sulfate hexahydrate (<NUM>) was added followed by ammonium acetate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(III) nitrate (<NUM>) was added followed by ammonium acetate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(III) sulfate (<NUM>) was added. Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM> % (<NUM>,<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>) was added to <NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. The mixture was heated to approximately <NUM>. Iron(III) sulfate (<NUM>) was added followed by ammonium acetate (<NUM>). Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

Powdered, sodium-containing zeolite (<NUM>,<NUM>) was added to <NUM>,<NUM> deionized water. The zeolite was SSZ-<NUM> CHA-type aluminosilicate with pore sizes of approximately <NUM> x <NUM>. Ammonium acetate (<NUM>,<NUM>) was added with <NUM> deionized water as rinse water. The mixture was heated to approximately <NUM>. Iron(III) sulfate (<NUM>) was added with <NUM> deionized water as rinse water. Solution pH was <NUM>. The mixture was held at temperature for approximately <NUM> minutes. The mixture was then washed and filtered in a Buechner filter, and the filtrate was dried. Dry weight of recovered Iron(III) exchanged zeolite was <NUM>,<NUM>. The resulting Iron(III) exchanged zeolite had an Iron concentration of <NUM>% (<NUM>,<NUM> ppm) by weight (calculated as Fe<NUM>O<NUM>) and a sodium concentration of <NUM>% (<NUM> ppm) by weight.

As can be seen above, inventive Examples <NUM> and <NUM>-<NUM> resulted in Iron(III) exchange such that the resulting zeolite included greater than <NUM>% by weight Iron(III) and less than <NUM> ppm sodium. The average Iron(III) concentration in the inventive ion-exchanged zeolites was <NUM>% by weight. On the contrary, the comparative examples using Iron(II) salts resulted in zeolites including <NUM>% Iron(II) on average (with two comparative examples achieving <NUM>% and <NUM>% Iron(II) by weight but the remaining comparative examples achieving less than <NUM>% Iron(II). It was surprising to find that the use of Iron(III) cations instead of Iron(II) cations could provide such a significant increase in the amount of Iron exchange in the zeolites tested, the average iron concentration in the Iron(III) tests being approximately four times greater than the average iron concentration in the Iron(II) tests.

Further Iron(III) exchanged zeolites were prepared in the manner as described above. The materials used and the nature of the resultant exchanged zeolites are shown in TABLE <NUM>.

Claim 1:
A process for preparing an Iron-exchanged zeolite, the process comprising combining a zeolite with Iron(III) cations in an aqueous medium such that the Iron(III) cations are exchanged into or onto the zeolite to thus form an lron(lll)-exchanged zeolite, wherein the exchange of Iron(III) into or onto the zeolite is carried out at a temperature of <NUM> to <NUM> for a time of <NUM> to <NUM> minutes, wherein the zeolite has a chabazite (CHA) structure and wherein the aqueous medium further comprises a buffering agent which comprises ammonium acetate.