A method of synthesizing a titanated zeolite and the zeolite obtained thereby

Abstract

A method for the preparation of a titanated zeolite, such as a titanated chabazite (CHA) zeolite or a titanated AEI zeolite. The method comprises (i) forming a reaction gel comprising a precursor zeolite, a structure directing agent (SDA), NaOH and / or KOH, and a SiO2 source; and (ii) heating the reaction gel. The precursor zeolite comprises a titanium loaded precursor zeolite and heating the reaction gel comprises heating to a temperature and for a duration suitable to convert the titanium loaded precursor zeolite into a titanated zeolite. The titanium loaded precursor zeolite may be prepared via an organotitanium compound, such as a titanium alkoxide.

Description

[0001] A METHOD OF SYNTHESIZING A TITANATED ZEOLITE AND THE ZEOLITE OBTAINED THEREBY

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a method for the preparation of a titanated zeolite, such as a titanated chabazite (CHA) zeolite or a titanated AEI zeolite. More particularly, the present invention relates to a method for the preparation of a titanated zeolite having a silica-alumina ratio (SAR) of from 10 to 30 and a titanium content of 0.5 to 3wt%. The invention further relates to a catalyst article comprising the titanated zeolite and a method for the treatment of an exhaust gas which comprises contacting an exhaust gas with a catalyst article comprising the titanated zeolite.

[0004] BACKGROUND OF THE INVENTION

[0005] Zeolites are crystalline or quasi-crystalline aluminosilicates constructed of repeating TO4 tetrahedral units with T being most commonly Si, Al or P (or combinations of tetrahedral units). These units are linked together to form frameworks having regular cavities and / or channels of molecular dimensions within the crystal. Numerous types of synthetic zeolites have been synthesized and each has a unique framework based on the specific arrangement its tetrahedral units. By convention, each topological type is assigned a unique three-letter code (e.g., “CHA” or “AEI”) by the International Zeolite Association (IZA).

[0006] NH3-SCR is the most effective technique for NOx abatement in lean-burning engine exhaust after-treatment. In this regard, Cu-SSZ-13 has been commercialized as an NH3-SCR catalyst for its significant advantages of excellent catalytic performance and hydrothermal stability. SSZ-13 (framework type code CHA) is a high-silica aluminosilicate zeolite and Cu- SSZ-13 refers to the copper loaded zeolite, commonly prepared by incipient wetness or ionexchange.

[0007] Wang et al. (Ind. Eng. Chem. Res. 2022, 61, 15066-15075) describe the doping effect of transition metals (Fe, Ti, Mn and Ce) on the structure and catalytic performance of Cu-SSZ- 13 zeolite catalysts for the NH3-SCR reaction. Transition metal doping was found to lead to substitution of the Cui species at ion-exchange sites, zeolite framework structure collapse, and migration of active Cu species into more stable sites during hydrothermal aging, as well as agglomeration of Cu / Fe species during SO2 pre-treatment. US9,889,437 describes an SCR catalyst comprising a zeolite with a framework material of silicon and aluminum atoms, wherein a fraction of the silicon atoms are isomorphously substituted with Ti.

[0008] Kunitake et al. (Microporous and Mesoporous Materials 215 (2015) 58-66) describe a synthesis of titanated chabazite by hydrothermal conversion of titanated faujasite. A peak assigned to isolated tetrahedrally coordinated Ti species was clearly observed in the UV-vis spectra and in the FT-IR spectra of the Ti-CHA, confirming that Ti was incorporated in the zeolite framework. Funase et al. (Advanced Porous Materials Vol. 4, 62-72, 2016) describe hydrothermal conversion of titanated FAU ([Al, Ti]-FAU) to AEI zeolite ([Al, Ti]-AEI).

[0009] Zhang et al. (Microporous and Mesoporous Materials 255 (2018) 61-68) describe enhanced photocatalytic activity of a TiCb / zeolite composite for abatement of pollutants. The characterization results are said to illustrate that anatase TiCb nanoparticles were stabilized on the surface of the zeolite support.

[0010] There remains a need in the art of for alternative methods for the synthesis of zeolites, especially those which exhibit hydrothermal stability and / or improved NOx conversion (e.g., at low temperature, either fresh or aged) for use in NOx abatement catalysts in the selective catalytic reduction of NOx.

[0011] SUMMARY OF THE INVENTION

[0012] One aspect of the invention is directed to a method for the manufacture of a titanated zeolite, the method comprising:

[0013] (i) forming a reaction gel comprising a precursor zeolite, a structure directing agent (SDA), NaOH and / or KOH, and a SiO2 source; and

[0014] (ii) heating the reaction gel; wherein, the precursor zeolite comprises a titanium loaded precursor zeolite and heating the reaction gel comprises heating to a temperature and for a duration suitable to convert the titanium loaded precursor zeolite into a titanated zeolite.

[0015] A second aspect of the invention is directed to a method for the manufacture of a titanium loaded precursor zeolite for use in the method of the first aspect, the method comprising (i) providing a composition comprising a precursor zeolite, a titanium source and optionally water, the precursor zeolite having an aluminosilicate framework that defines pores therein; and

[0016] (ii) heating the composition to load titanium into the pores and thereby provide a titanium loaded precursor zeolite; wherein the titanium source comprises an organotitanium compound.

[0017] Another aspect of the invention is directed to a titanated zeolite having an SAR of from 10 to 30. The titanated zeolite is producible by the method of the first aspect of the invention.

[0018] Another aspect of the invention is directed to a titanium loaded zeolite. The titanium loaded zeolite is producible by the method of the second aspect of the invention.

[0019] Another aspect of the invention is directed to intermediates produced during the methods of the first and second aspects of invention.

[0020] Another aspect of the invention is a catalyst article for the treatment of an exhaust gas, the catalyst article comprising the titanated zeolite as described herein.

[0021] Another aspect of the invention is directed to a method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the catalyst article described herein.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Fig- 1 shows XRD pattern of a bare USY (lower line), a titanium loaded USY (middle line) and Example 1 (Ti-USY after activation at 550°C, upper line).

[0024] Fig- 2 shows SEM images of Ti-AEI Example 2.

[0025] Fig. 3 shows SEM images of Ti-CHA Example 3.

[0026] Fig- 4 shows SEM images of Ti-CHA Example 4.

[0027] Fig. 5 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2, Example 4 and Example 6 in fresh condition.

[0028] Fig. 6 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2, Example 4 and Example 6 after 750°C aging for 80hrs.

[0029] Fig. 7 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2 after 900°C aging for 5hrs and Example 4 and Example 6 after 800°C aging for 16hrs. Fig- 8 shows UV-Vis of activated Example 4 and a comparative Titanium-free CHA.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] A first aspect of the present invention is directed to a method for the manufacture of a titanated zeolite, the method comprising:(i) forming a reaction gel comprising a precursor zeolite, a structure directing agent (SDA), NaOH and / or KOH, and a SiO2 source; and

[0032] (ii) heating the reaction gel; wherein, the precursor zeolite comprises a titanium loaded precursor zeolite and heating the reaction gel comprises heating to a temperature and for a duration suitable to convert the titanium loaded precursor zeolite into a titanated zeolite.

[0033] The present disclosure will now be described further. In the following passages, different aspects / embodiments of the disclosure are defined in more detail. Each aspect / embodiment so defined may be combined with any other aspect / embodiment or aspects / embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0034] The invention is concerned with the manufacture of titanated zeolites, also known as zeolites having framework titanium, i.e. where the Ti is part of the zeolite framework structure. The titanated zeolite has repeating TO4 tetrahedral units with T being Si, Al and Ti.

[0035] The titanated zeolite (a zeolite having framework titanium) is prepared by means of a titanium loaded precursor zeolite (a zeolite having extra-framework titanium). The precursor zeolite has an aluminosilicate framework, i.e. repeating TO4 tetrahedral units with T being Si and Al. The titanium may be loaded within the pores of the aluminosilicate framework rather than being part of the framework. The inventors propose that the titanium is incorporated into the zeolite framework during interzeolite conversion (IZC, also known as interzeolite transformation) in the presence of a structure directing agent (SDA). A titanium loaded precursor zeolite, such as a titanium loaded FAU, is converted to a titanated small pore zeolite (a.k.a. small-pore zeolite with framework titanium) such as a titanated CHA or titanated AEI. The precursor zeolite and the titanated zeolite have different frameworks. Typically, the precursor zeolite will have a larger pore size than the titanated zeolite. In contrast, prior art methods teach the incorporation of Ti into the framework of a precursor zeolite, i.e. a titanated precursor zeolite rather than the titanium loaded precursor zeolite employed in the present invention. For example, Funase etal. describes the preparation of a titanated AEI via hydrothermal conversion of a titanated FAU (Ti in the FAU framework). The Ti was incorporated into dealuminated FAU using a post-synthetic method under acidic conditions. Dealuminated FAU (Si / Al = 2.8, Tosoh CO., Japan) was added to (NHFhTiFe (Aldrich, USA) solution. Sulfuric acid solution was added to the suspension in order to maintain the Ph value of the suspension (Ph= 1) during titanation. Funase et al. attempted a more conventional preparation using only amorphous hydrogel prepared from fumed silica, aluminium hydroxide, titanium isopropoxide, NaOH, and 1,1 -diethyl-2, 6- dimethylpiperidinium hydroxide (DEDMPOH). However, AEI zeolite could not be produced and the authors concluded that this indicates that the use of titanated FAU zeolite as the starting material is a crucial parameter for the synthesis of titanated AEI.

[0036] CN116282067 describes the preparation of a SSZ-39 (AEI) molecular sieve from raw materials that contain heteroatoms. Example 3 describes hydrothermal conversion of TiUSY in the presence of 3,5-dimethyl-N,N-dimethylhydroxypiperidine (as organic template ) to yield titanated SSZ-39.

[0037] US9,889,437B2 describes the preparation of the sodium form of an isomorphously substituted zeolitic material from a reaction gel through autoclave hydrothermal synthesis. Based on silica equivalents, the reaction gel comprises: 0.03 AI2O3: SiCh: 0.07 TiCh: 0.06 Na2O: 0.08 ATMAOH: 2.33 H2O gel. Based on alumina equivalents, the reaction gel comprises: AI2O3: 33.33 SiO2: 2.33 TiO2: 2.00 Na2O: 2.67 ATMAOH: 77.67 H2O gel.

[0038] The method of the invention involves forming a reaction gel which may be referred to as a reaction mixture. Such reaction gels are well known in the art of zeolite synthesis. The reaction gel comprises a structure directing agent (SDA), sodium and / or potassium hydroxide, a silica source and a precursor zeolite.

[0039] Synthesis of zeolite crystals involves reacting the precursor zeolite (an alumina source) and silica in the presence of an SDA (a structure directing agent also referred to as a template or SDA; SDA cations can be referred to as SDA+) at elevated temperatures for several days. During crystallization, the alumina and silica co-join to form a crystalline structure around the SDA. The reactants, reaction conditions, and the species of SDA all impact which type or types of frameworks that are synthesized. When sufficient crystallization has occurred, the crystals are removed from the mother liquor and dried. After the crystals are separated from the mother liquor, the organic SDA is thermally degraded and removed from the crystalline structure, thus leaving a porous molecular sieve.

[0040] The SDA for use in the invention is typically an organic SDA (OSD A) and typically a hydroxide or salt. In an embodiment, the SDA may be selected from a list comprising (e.g. consisting of):

[0041] N,N,N-trimethyl- 1 -adamantylammonium

[0042] N,N,N-dimethylethylcyclohexylammonium trimethyl(cyclohexylmethyl) ammonium tetraethylammonium

[0043] N-Ethyl-N,N-dimethylcyclohexylammonium benzyltrimethyl ammonium

[0044] N,N,N -tri ethyl cy cl ohexy 1 ammonium

[0045] N,N,N-trimethylcyclohexyl ammonium

[0046] N,N,N-di ethylmethylcyclohexyl ammonium trimethyl phenyl ammonium triethylmethyl ammonium

[0047] N,N-dimethyl-3,5-dimethylpiperidinium

[0048] 1 , 1 -diethyl-2,6-dimethyl piperidinium.

[0049] In one embodiment the desired titanated zeolite is a titanated chabazite and the SDA is selected from a list comprising (e.g. consisting of):

[0050] N,N,N-trimethyl- 1 -adamantylammonium

[0051] N,N,N-dimethylethylcyclohexylammonium, benzyltrimethylammonium, and tetraethyl ammonium .

[0052] In one embodiment the desired titanated zeolite is a titanated AEI and the SDA is selected from a list comprising (e.g. consisting of):

[0053] N,N-dimethyl-3,5-dimethylpiperidinium

[0054] 1 , 1 -diethyl-2,6-dimethyl piperidinium. The SDA may be selected from one or more of:

[0055] N,N,N-trialkyl cyclohexylammonium derivates such as N, Nodimethyl ethyl cy cl ohexy 1 ammonium ;

[0056] N,N,N- trialkyl benzylammonium derivates such as benzyltrimethylammonium; trialkyl (cyclohexylmethyl) ammonium derivates such as trimethyl(cyclohexylmethyl) ammonium;

[0057] [NR1R2R3R4] +, wherein Ri, R2; R3 and R4 are independently an alkyl group having one to four carbon atoms, wherein the alkyl group can be optionally substituted by one or more hydroxyl groups, such as tetraethylammonium.

[0058] The SDA cation for use in the method may be A,A,A-trimethyladamantylammonium (TMAd+), which is also known as an organic SDA cation. The SDA cation of the present invention is typically associated with anions which can be any anion that is not detrimental to the formation of the zeolite. Representative anions include elements from Group 17 of the Periodic Table (e.g., fluoride, chloride, bromide and iodide), hydroxide, acetate, sulfate, tetrafluoroborate, carboxylate, and the like.

[0059] The reaction gel is formed by the addition of one or both of sodium hydroxide and potassium hydroxide. Where only one of sodium and potassium hydroxide are used to form a reaction gel, sodium hydroxide is preferred.

[0060] The reaction gel comprises a precursor zeolite (which serves as an alumina source and a silica source) and a separate silica source. The precursor zeolite is typically an aluminosilicate zeolite, having a framework that consists essentially of aluminium, silicon and oxygen. The precursor zeolite may have a molar silica to alumina ratio (SAR) of 4 or more, 8 or more or 10 or more and / or the precursor zeolite may have a molar silica to alumina ratio (SAR) of 40 or less, 30 or less, or 15 or less. The precursor zeolite may have a SAR of 10 to 14, such as 11, 12 or 13.

[0061] Preferably, the source of silica is one or more of sodium silicate, potassium silicate, silica gel, silica sol, fumed silica, silicon alkoxides, and precipitated silica, preferably silica sol. Silica sol is a colloidal suspension of silica in water. The reaction gel may comprise a further source of alumina (in addition to the precursor zeolite) which may be one or more of sodium aluminate, aluminum salts such as aluminum sulfate, aluminium nitrate, aluminum chloride, aluminum hydroxide, aluminum alkoxides, and alumina, preferably one or more of aluminum hydroxide and aluminum sulfate.

[0062] The titanium loaded precursor zeolite may be selected from titanium loaded FAU, a titanium loaded BEA, a titanium loaded MFI and / or a titanium loaded FER. The titanium loaded precursor zeolite is preferably a titanium loaded FAU (e.g., titanium loaded USY) or a titanium loaded BEA.

[0063] As is known in the art, the reaction composition may be described in terms of the equivalent amount of SiCh, AI2O3, M2O (where M is Na and / or K), SDA, and H2O present in the reaction gel. The reaction gel for the present method can also be described by the equivalent amount of TiCh. In other words, the reaction gel composition may be described by the ratio: AI2O3 : aSiCh : bSDA : CM2O : dEEO : eTiCh wherein the reaction composition is normalised to a molar amount (1 mole) of AI2O3 equivalent. As will be appreciated, the scale of the reaction and the absolute number of moles may vary. Examples of suitable reaction gels are described below.

[0064] The method of the present invention comprises forming a reaction gel whereby, relative to the molar amount of AI2O3 equivalent (i.e. 1 mole of AI2O3, which is provided by the titanium loaded precursor zeolite), the gel may comprise from 0.001 to 5 moles of TiCh equivalent. It is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises at least 0.05 moles of the TiCh equivalent, preferably at least 0.1 moles, more preferably at least 0.2 moles of the TiCh equivalent or at least 0.3 moles of TiCh equivalent. Similarly, it is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises 2 moles or less of the TiCh equivalent, more preferably 1 moles or less of the TiCh equivalent or 0.5 moles or less of the TiCh equivalent. In one embodiment, relative to the molar amount of AI2O3 equivalent, the gel comprises from 0.1 to 1 moles of the TiCh equivalent, more preferably from 0.2 to 0.5 moles of the TiCh equivalent.

[0065] The method of the present invention comprises forming a reaction gel whereby, relative to the molar amount of AI2O3 equivalent (i.e. 1 mole of AI2O3, which is provided by the titanium loaded precursor zeolite), the gel may comprise from 0.1 to 20 moles of the SDA.

[0066] Accordingly, it is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises at least 0.1 moles of the SDA, preferably at least 0.2 moles, more preferably at least 0.5 moles of the SDA or at least 1.0 moles of SDA. Similarly, it is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises 20 moles or less of the SDA, more preferably 15 moles or less of the SDA or 10 moles or less of the SDA. In one embodiment, relative to the molar amount of AI2O3 equivalent, the gel comprises from 0.2 to 10 moles of the SDA, more preferably from 0.5 to 5 moles of the SDA. This range is particularly useful where the SDA comprises N,N,N-trimethyladamantylammonium to yield a titanated CHA. In another embodiment, relative to the molar amount of AI2O3 equivalent, the gel comprises from 1 to 15 moles of the SDA, more preferably from 2 to 12 moles of the SDA. This range is particularly helpful where the SDA comprises N,N-dimethyl-3,5-dimethylpiperidinium to yield a titanated AEI.

[0067] In some preferred embodiments, relative to the molar amount of AI2O3 equivalent, the gel comprises from 0.5 to 1.5 moles of SDA, preferably from 0.8 to 1.2 moles, even more preferably 0.9 to 1.1 moles, for example, about 1 moles of SDA. Generally, lower amounts of SDA may be preferred in embodiments wherein one or more of the amount of SiCh equivalent, the total amount of Na2O and K2O equivalent (i.e. M2O equivalent wherein M is Na and K insofar as either or both of Na and / or K are present), and the amount of water present in the reaction gel is within the generally higher amounts described herein.

[0068] It is particularly preferred that at least one of the amounts of SiCh equivalent, M2O equivalent, and water are as described herein. The inventors have found that the combination of the amounts of each of these reaction gel components with the relatively low amount of SDA (i.e. from 0.1 to 2 moles relative to AI2O3) allows for an improvement in the synthesis of a low SAR titanated zeolite, particularly one having a low mesoporosity and / or a high crystallinity as described herein. More preferably, at least two of these parameters are used in combination with the amount of SDA, such as the amount of water which is preferably greater when the amount of SiCh equivalent is greater, and in a preferred embodiment, all of the amounts of SiCh equivalent, M2O equivalent, and water fall within the ranges described herein.

[0069] It is particularly preferred that the M2O equivalent, that is the total amount of Na2O and K2O equivalent (one or both may be present), relative to the molar amount of AI2O3 equivalent, is at least 3 or 4 moles, preferably from 3 to 15 moles, more preferably from 4 to 14 moles, more preferably from 4 to 13 moles. Equally, it may be said that “c” in the gel composition may be any of these ranges or values. For example, in some embodiments, higher amounts of M2O equivalent are preferred such as at least 3 moles, more preferably at least 4 or 5 moles. In some particularly preferred embodiments, the amount of M2O equivalent, relative to the molar amount of AI2O3 equivalent in the reaction gel is from 9 to 14 moles. Where lower amounts of M2O equivalent are preferred, the amount of M2O equivalent is preferably from 3 to 8 moles, preferably from 4 to 8 moles.

[0070] In some embodiments, it is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises an amount of SiCh equivalent of at least 10 moles, preferably 20 to 90 moles, 20 to 40 moles, or 20 to 35 moles. Equally, it may be said that “a” in the gel composition may be any of these ranges or values. For example, in some embodiments, higher amounts of SiCh equivalent are preferred such as from 40 to 90 moles, preferably from 50 to 70 moles, e.g. when a titanated AEI is desired. In some preferred embodiments, about 30 moles of SiCh equivalent are preferred, e.g. when a titanated CHA is desired.

[0071] In some embodiments, it is preferred that, relative to the molar amount of AI2O3 equivalent, the gel comprises water and the water is present in an amount of at least 700 moles, preferably at least 1000 moles such as from 1000 to 2000 moles. Equally, it may be said that “d” in the gel composition may be any of these ranges or values. For example, in some embodiments, higher amounts of water are preferred (in particular where higher amounts of SiCh equivalent or M2O equivalent are added) such as from 800 to 1500 moles, preferably from 900 to 1400 moles, such as about 1100 moles. A particular advantage of the present method is that the inventors have found that the method does not require the use of seed crystals so as to form the desirable titanated zeolite. Accordingly, it is preferred that the reaction gel does not comprise seed crystals (i.e. CHA seed crystals).

[0072] Thus, in one particular preferred embodiment on the present invention, the gel consists of the precursor zeolite, the structure directing agent (SDA), sodium and / or potassium hydroxide, the silica source, and water, and, optionally, a further sodium and / or potassium salt.

[0073] The method of the present invention further comprises a step of heating the gel to a temperature and for a duration suitable for the formation of the titanated zeolite, i.e. interzeolite conversion. Preferably, the temperature to which the heated is heated for such a suitable duration is from 100 °C to 200 °C; more preferably from 110°C to 190°C, 120°C to 180°C, 130°C to 170°C, or even 145°C to 165°C, such as around 155°C. The duration for which the gel is heated to a suitable temperature, is preferably at least 10 hours, more preferably, 20 to 40 hours. The duration for which the gel is heated to a suitable temperature, is preferably 100 hours or less, more preferably, 80 hours or less or 50 hours or less. It is particularly preferred that the gel is heated to these temperatures and held at these temperatures for these durations, e.g. for at least 10 hours at a temperature of from 100 °C to 200 °C.

[0074] Preferably, the titanated zeolite product resulting from heating the reaction gel for such a temperature and duration is recovered by typical vacuum filtration. Preferably, the filtered product is washed with demineralized (also known as deionized) water is used to remove residual mother liquor. Preferably, the titanated zeolite product is washed until the filtrate conductivity is below 0.1 mS. Preferably, the filtered and washed product is then dried at temperatures of greater than 100°C, preferably about 120°C.

[0075] In some preferred embodiments, the method further adding iron and / or copper to the titanated zeolite by ion exchange. As described herein, iron and / or copper exchanged zeolites are particularly preferred as NH3-SCR catalysts and the product obtained after growth of the titanated zeolite during the heating step may be ion exchanged with iron and / or copper to provide such an ion exchanged zeolite.

[0076] The titanated zeolite of the invention may have a SAR of at least 9 or at least 10. The titanated zeolite of the present invention may have a SAR of at most 30, such as at most 25, such as at most 20 or at most 15. In some embodiments, the titanated zeolite is a titanated CHA having a SAR of from 10 to 20, 11 to 13, or 16 to 18. In other embodiments described herein, the titanated zeolite is a titanated AEI having a SAR of from 15 to 25, such as from 18 to 23 or from 19 to 21.

[0077] In combination with the desired SAR, the present invention provides a titanated zeolite having a mesoporous surface area of less than 35 m2 / g, preferably no greater 30 m2 / g, more preferably no greater than 25 m2 / g. In some embodiments, the titanated zeolite can have a mesoporous surface area of no greater than 12 m2 / g. In certain embodiments, the titanated zeolite can a mesoporous surface area of 1-30 m2 / g, 2-25 m2 / g, 20-30 m2 / g, or 5-15 m2 / g. The inventors have identified specific gel formulations which enable the production of titanated zeolites with the desired SAR as described herein together with a mesoporous surface area of less than 35 m2 / g.

[0078] Mesoporous surface area may be measured using any conventional technique in the art. For example, by measuring the Ar or N2 adsorption isotherms on the activated samples at 87 or 77 K, respectively, according to the Brunauer-Emmett-Teller (BET) method. Prior to measurement the samples are heated under vacuum to remove physiosorbed water. The pore size distributions are measured by the nonlocal density functional theory (NLDFT). The mesopore surface area is calculated by the difference between the apparent BET and the micropore surface areas.

[0079] In combination with any of the desired features as described above, the present invention may provide a titanated zeolite having a BET surface area of 500-800 m2 / g; preferably, 600-800 m2 / g; or more preferably, 650-800 m2 / g.

[0080] Preferably, the titanated zeolite has a crystallinity of greater than 95%. The presence of uniform crystals supports the presence of Ti in the framework.

[0081] Preferably, the titanated zeolite has a granular particle. That is, it is preferred that the titanated zeolite has a particulate morphology whereby the zeolite crystals have a three dimensional shape in contrast to rod like particles having a substantially one dimensional shape or disk or plate like particles having a two dimensional shape. It is preferred that the zeolite has a granular particle comprising or consisting of cubic crystals.

[0082] Preferably, the titanated zeolite has a mean longest edge crystal size of no greater than 5 microns (pm), preferably, no greater than 3 microns. In some embodiments, the zeolite can have a mean longest edge crystal size of 0.1- 5 microns, preferably, 0.3-3 microns, or 0.5-1.5 microns. Such an average crystal size may be determined using standard microscopic techniques such as scanning electron microscopy (SEM). The measurement is taken over a statistically meaningful portion of the zeolites produced. The inventors observed uniform, cubic crystals 0.5-1.5 pm of Ti-CHA and Ti-AEI, which are very similar to CHA and AEI made without titanium.

[0083] In one particularly preferred embodiment, the titanated zeolite is an iron and / or copper exchanged titanated zeolite. Transition metal exchanged zeolites are particularly effective as catalysts for the abatement of NOx in NH3-SCR catalysts.

[0084] In a further aspect of the present invention, there is provided a catalyst article for the treatment of an exhaust gas, the catalyst article comprising the titanated zeolite as described herein.

[0085] In yet a further aspect, there is provided a method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the catalyst article described herein.

[0086] The titanated zeolite of the invention is obtained by interzeolite conversion of a titanium loaded precursor zeolite. The invention also resides in the titanium loaded precursor zeolite and its method of preparation. The method comprises providing a composition comprising a precursor zeolite, a titanium source and optionally water, the precursor zeolite having an aluminosilicate framework that defines pores therein; and heating the composition to load titanium into the pores and thereby provide a titanium loaded precursor zeolite; wherein the titanium source comprises an organotitanium compound.

[0087] The organotitanium compound may comprise a titanium alkoxide. The titanium alkoxide may be described with reference to a general formula Ti(OR)4 wherein each R is independently selected from an alkyl or aryl group having from 1-12 carbon atoms, e.g., from 1 to 6 carbon atoms, such as from 2 to 4 carbon atoms. In one embodiment each R is selected from methyl, ethyl, propyl or butyl.

[0088] The organotitanium compound may comprise titanium methoxide, titanium ethoxide, titanium isopropoxide and / or titanium butoxide, and is preferably titanium butoxide. The composition may be described with reference to a ratio between the precursor zeolite and the organotitanium compound (e.g. by mass). The ratio by mass of precursor zeolite (e.g. USY) to organotitanium compound (e.g. titanium butoxide) may be at least 3: 1, at least 5: 1 or at least 10: 1. The ratio by mass of precursor zeolite (e.g. USY) to organotitanium compound (e.g. titanium butoxide) may be no more than 30: 1, 20:1 or 10: 1. Preferably, the ratio by mass of precursor zeolite (e.g. USY) to organotitanium compound is from 5 to 15: 1

[0089] The composition (comprising precursor zeolite, organotitanium and water) may have a pH at SATP (standard ambient temperature and pressure) of from 2 to 9, such as from 2.5 to 4.

[0090] The method may further comprise isolating, drying and calcining the titanium loaded precursor zeolite prior to use in the preparation of the titanated zeolite.

[0091] EXAMPLES

[0092] General procedure:

[0093] Synthesis gel mixture is prepared by blending the selected raw materials at room temperature according to the synthesis gel composition. The resulting fluid mixture is then transferred into and sealed in an agitated reactor. In crystallization step, the synthesis gel is crystallized via hydrothermal treatment. The crystallization temperature is 100°C to 200°C depending on the gel composition. Crystallization is carried out with continuously mixing the synthesis gel by agitation. The amount of time for crystallization is from 5 hours to 10 days.

[0094] After crystallization, the resulting zeolite product is recovered by typical vacuum filtration. In the washing step, demineralized water is used to remove residual mother liquor from solid product until the filtrate conductivity is below 0.1 mS.

[0095] In the drying step, the moisture water of the filtered solid product (filter cake) is removed by drying overnight in a 120°C oven to obtain a dry powder.

[0096] Calcination of the dry product (powder) then bums off the OSDA, followed by ammonium ion exchange to remove the alkali cations, and the final calcination to convert the product from ammonium form to activated form. Example 1: Loading titanium onto FAU (Ti-USY)

[0097] USY (H-form SAR 12, precursor zeolite) is loaded with titanium butoxide (TBOT, organotitanium compound) at a ratio by mass 10: 1 zeolite : TBOT ratio in demineralized water and heated to 100°C under strong agitation for 2 hours. The titanium loaded FAU is filtered, dried then calcined at 550°C for 1 hour.

[0098] The titanium loaded FAU content was measured by XRF (X-ray fluorescence) and LOI (loss on ignition, to determine water content) (70.2% SiO2, 8.8% AI2O3, 18.4% H2O, 2.4% TiCh) and is the sole source of titanium and alumina in the subsequent interzeolite conversion.

[0099] Example 2: Synthesis of H-Ti-AEI (titanated zeolite)

[0100] 10.7g of the titanium loaded USY (Example 1) is added to 131.5g of demineralized water. 55.6g ofN,N-dimethyl-3, 5-dimethylpiperidinium hydroxide (32.0%) , 92.8g of sodium silicate (28.8% SiCh, 9.0% Na2O, 62.2% H2O) and 9.45g of silica solution (40.0% SiCh) are added subsequently to the synthesis gel and agitated until homogenous.

[0101] The molar recipe for the synthesis is 68 SiCh - 1 AI2O3 - 14.5 Na2O - 1400 H2O - 12.0 OSDA - 0.35 TiCh.

[0102] The synthesis gel is transferred to a 600mL stainless steel agitated autoclave where it is heated to 155°C under agitation for 24 hours. The reaction vessel is cooled, and the product was filtered and washed multiple times with demineralized water. The wet cake zeolite is dried at 120°C for 12 hours. The dry crystallized material is analyzed on XRD.

[0103] Titanium AEI is calcined at 550°C for 6 hours with l°C / min ramp rate. The calcined zeolite is ion exchanged twice in a 10% ammonium sulfate solution for 1.5 hours at 100°C then filtered, washed and dried at 120°C for 12 hours. The dried NFE-form zeolite was calcined at 550°C for 6 hours with l°C / min ramp rate. The final product is a H-form Ti-AEI.

[0104] Example 3: Synthesis of H-Ti-CHA (titanated zeolite)

[0105] 16.7g of the titanium loaded USY (Example 1) is added to 215.5g of demineralized water. 11.0g of N,N,N-trimethyladamantylammonium hydroxide solution (25.5%) , 45.3g of sodium silicate (28.8% SiCh, 9.0% Na2O, 62.2% H2O) and 11 ,5g of sodium hydroxide solution (50%) are added subsequently to the synthesis gel and agitated until homogenous.

[0106] The molar recipe for the synthesis is 30 SiCh - 1 AI2O3 - 10.4 Na2O - 1100 H2O - 1.0 OSDA - O.47 TiCh.

[0107] The synthesis gel is transferred to a 600mL stainless steel agitated autoclave where it is heated to 155°C under agitation for 24 hours. The reaction vessel is cooled, and the product was filtered and washed multiple times with demineralized water. The wet cake zeolite is dried at 120°C for 12 hours. The dry crystallized material is analyzed on XRD.

[0108] Titanium CHA is calcined at 550°C for 6 hours with l°C / min ramp rate. The calcined zeolite is ion exchanged twice in a 10% ammonium sulfate solution for 1.5 hours at 100°C then filtered, washed and dried at 120°C for 12 hours. The dried NH3-form zeolite was calcined at 550°C for 6 hours with l°C / min ramp rate. The final product is a H-form Ti-CHA.

[0109] Example 4-6

[0110] The procedure of Example 3 was repeated but with the amounts of starting raw materials and the molar gel recipe varied to produce Ti-CHA with different SAR, Si / Ti ratio and Ti / Al ratio. Crystallization and post synthesis methods for producing activated form zeolite is the same as in Example 3.

[0111] CHARACTERIZATION

[0112] N.d.: not detected

[0113] Referring to Fig. 1 there is shown an XRD pattern of USY (the bare precursor zeolite, lowest line), a titanium loaded USY before calcination (middle line) and a calcined titanium loaded USY (Example 1, upper line). The peaks are the same in each case and are representative of the FAU framework.

[0114] XRD patterns for example 2 (fresh and activated) were representative of an AEI zeolite demonstrating that interzeolite conversion has taken place. Fig. 2 shows SEM images of Ti- AEI Example 2. The uniform, cubic crystals 0.5- 1.5 pm seen of Ti-AEI are very similar to AEI made without titanium. Only zeolite crystals are seen and no debris from TiO2 is seen.

[0115] XRD patterns for examples 3 to 6 (fresh and activated) were representative of a CHA zeolite demonstrating that interzeolite conversion has taken place. Fig. 3 shows SEM images of Ti- CHA Example 3. Fig. 4 shows SEM images of Ti-CHA Example 4. The uniform, cubic crystals 0.5-1.5 pm seen of Ti-CHA are very similar to CHA made without titanium. Only zeolite crystals are seen; no debris from TiO2 is seen.

[0116] Fig. 8 shows UV-Vis of activated Example 4 and a comparative Titanium-free CHA. The UV- Vis demonstrates that Ti is in the framework.

[0117] CATALYSTS PERFORMANCE TESTING

[0118] The titanated zeolites were copper loaded and assessed in terms of NOx conversion and N2O make. The activated products were loaded with Cu on anhydrous mass base of H-form CHA / AEI by incipient wetness impregnation using the required amount of copper (II) acetate dissolved in the pre-determined amount of demineralized water. The metal impregnated titanated zeolite was dried overnight at 80 °C and then calcined in air at 550 °C for 4 hours. The Cu-titanated zeolites were pelletized, crushed, and screened to collect the particles with size between 35 40 to 60 mesh. The thus prepared particle-form Cu-titanated zeolites was referred as fresh sample. Aging treatments were also applied in air flow with 10% H2O by volume.

[0119] Fig. 5 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2, Example 4 and Example 6 in fresh condition. All three titanated zeolites are useful as catalysts.

[0120] Fig. 6 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2, Example 4 and Example 6 after 750°C aging for 80hrs. As expected, catalytic activity reduces after aging.

[0121] Fig. 7 shows NOx Conversion (left) and N2O make (right) of Cu-loaded Example 2 after 900°C aging for 5hrs and Example 4 and Example 6 after 800°C aging for 16hrs. Example 2 (AEI) breaks down under these conditions but Examples 4 and 6 are still effective.

[0122] As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features and is also intended to include the option of the features necessarily being limited to those described. In other words, the term also includes the limitations of “consisting essentially of’ (intended to mean that specific further components can be present provided they do not materially affect the essential characteristic of the described feature) and “consisting of’ (intended to mean that no other feature may be included such that if the components were expressed as percentages by their proportions, these would add up to 100%, whilst accounting for any unavoidable impurities), unless the context clearly dictates otherwise.

[0123] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

Claims

Claims:

1. A method for the manufacture of a titanated zeolite, the method comprising:(i) forming a reaction gel comprising a precursor zeolite, a structure directing agent (SDA), NaOH and / or KOH, and a SiO2 source; and(ii) heating the reaction gel; wherein, the precursor zeolite comprises a titanium loaded precursor zeolite and heating the reaction gel comprises heating to a temperature and for a duration suitable to convert the titanium loaded precursor zeolite into a titanated zeolite.

2. The method of claim 1, wherein the titanium loaded precursor zeolite is a large pore zeolite or a medium pore zeolite and the titanated zeolite is a small pore zeolite.

3. The method of claim 1, wherein the reaction gel has a TiCh / AI2O3 ratio of from 0.1- 1.0, such as 0.2-0.5.

4. The method of any one of claims 1 to 3, wherein the reaction gel has(i) a SiCh / AhCh ratio of from 10-100, such as from 30-70;(ii) a Na2O / SiCh ratio of from 0.1-0.5, such as from 0.15-0.35;(iii) a SDA / SiCh ratio of from 0.01 to 0.3, such as from 0.01 to 0.2; and / or(iv) a H2O / SiO2 ratio of from 15-50, such as from 20-40.

5. The method of any one of claims 1 to 4, wherein the titanium loaded precursor zeolite comprises a titanium loaded FAU, a titanium loaded BEA, a titanium loaded MFI and / or a titanium loaded FER.

6. The method of claim 5, wherein the titanium loaded precursor zeolite comprises a titanium loaded FAU, such as a titanium loaded USY.

7. The method of any one of the preceding claims, wherein the SDA is selected from N,N,N-trimethyl- 1 -adamantylammonium, N,N,N-dimethylethylcyclohexylammonium, N,N- dimethyl-3,5-dimethylpiperidinium and benzyltrimethylammonium, and tetraethylammonium.

8. The method of any one of the preceding claims, wherein the SiCh source comprises one or more of sodium silicate, potassium silicate, silica gel, silica solution, fumed silica, silicon alkoxides, and precipitated silica, such as silica sol.

9. The method of any one of the preceding claims, wherein heating the reaction gel comprises heating to a temperature of from 100°C to 200°C, preferably from 120°C to 180°C, for a duration of from 10 to 100 hours.

10. The method of any one of the preceding claims, further comprising an initial step of preparing the titanium loaded precursor zeolite from an organotitanium compound, such as a titanium alkoxide.

11. The method according to any one of the preceding claims, wherein the method further comprises adding iron and / or copper to the titanated zeolite by ion-exchange.

12. A titanated zeolite producible by the method of any one of the preceding claims.

13. A titanated zeolite having a SAR of from 10 to 30 and optionally one or more of the following features: (a) a mesoporous surface area of less than 35 m2 / g; (b) a BET surface area of 600-800 m2 / g; and / or (c) a micropore volume of 0.2-0.3 cm2 / g.

14. The titanated zeolite of claim 12 or 13, having a CHA or AEI framework, optionally, comprising 0.5 -3.0% titanium by mass.

15. A method for the preparation of a titanium loaded precursor zeolite, the method comprising providing a composition comprising a precursor zeolite, a titanium source and optionally water, the precursor zeolite having an aluminosilicate framework that defines pores therein; and heating the composition to load titanium into the pores and thereby provide a titanium loaded precursor zeolite; wherein the titanium source comprises an organotitanium compound.

16. The method of claim 15, wherein the organotitanium compound comprises a titanium alkoxide.

17. The method of claim 16, wherein the titanium alkoxide comprises Ti(OR)4 wherein each Ris independently selected from an alkyl or aryl group having from 1-12 carbon atoms.

18. The method of claim 17, wherein the organotitanium compound comprises titanium methoxide, titanium ethoxide, titanium isopropoxide and / or titanium butoxide.

19. The method of any one of claims 15 to 18, wherein the composition has a pH at standard ambient temperature and pressure of from 2 to 9.

20. The method of any one of claims 15 to 19, further comprising isolating, drying and calcining the titanium loaded precursor zeolite.

21. A titanium loaded precursor zeolite produced by the method of any one of claims 15 to 20.

22. A composition for use in the method of claim 15 comprising a precursor zeolite, a titanium source and optionally water, wherein the titanium source comprises an organotitanium compound.

23. The method of claim 15 or the composition of claim 21, wherein the ratio by mass of the precursor zeolite to the organotitanium compound is from 8 to 12: 1.

24. A catalyst article for the treatment of an exhaust gas, the catalyst article comprising the titanated zeolite of to any one of claims 11 to 14.

25. A method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the catalyst article according to claim 24.

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