Vanadium-containing SCR catalyst and method for its preparation

Abstract

According to the present invention there is provided a method for producing a catalyst for the selective catalytic reduction of NOX in a gas mixture. The method comprises the steps of: (a) preparing a slurry comprising vanadium (V), antimony (Sb) and a reactive media to form a colloidal sol of VSbO4; (b) combining the colloidal sol of VSbO4 with a catalyst support material, which comprises depositing the colloidal sol of VSbO4 on the catalyst support material, to form a mixture; and (c) optionally drying and calcining the resulting mixture. The invention also relates to catalyst produced by the method, associated uses thereof.

Description

[0001] P102443

[0002] A method of making an SCR catalyst

[0003] FIELD OF THE INVENTION

[0004] This invention relates to a method for making a selective catalytic reduction catalyst, a catalyst article made according to the method and the use of the catalyst article in the selective catalytic reduction of NOx.

[0005] BACKGROUND

[0006] Hydrocarbon combustion in diesel engines, stationary gas turbines, and other systems generates exhaust gas that must be treated to remove nitrogen oxides (NOX), which comprises NO (nitric oxide) and NO2 (nitrogen dioxide), with NO being the majority of the NOXformed. NOXis known to cause several health issues in people as well as causing several detrimental environmental effects including the formation of smog and acid rain. To mitigate both the human and environmental impact from NOXin exhaust gas, it is desirable to eliminate these undesirable components, preferably by a process that does not generate other noxious or toxic substances.

[0007] Exhaust gas generated in lean-burn and diesel engines is generally oxidative. NOXneeds to be reduced selectively with a catalyst and a reductant in a process known as selective catalytic reduction (SCR) that converts NOXinto elemental nitrogen (N2) and water.

[0008] In an SCR process, a gaseous reductant, typically anhydrous ammonia, aqueous ammonia, or urea, is added to an exhaust gas stream prior to the exhaust gas contacting the catalyst. The reductant is absorbed onto the catalyst and the NOXis reduced as the gases pass through or over the catalyzed substrate.

[0009] The reduction reaction may be described as follows:

[0010] 4NH3+4NO+O2^4N2+6H2O

[0011] In order to maximize the conversion of NOX, it is often necessary to add more than a stoichiometric amount of ammonia (NH3) to the gas stream. It will be appreciated that the more efficient the conversion of NOX, the less ammonia (NH3) remains unreacted (i.e. ammonia slippage is reduced). The release of unreacted ammonia into the atmosphere is detrimental to the health of people and to the environment. In addition, ammonia is caustic, especially in its aqueous form. Condensation of ammonia and water in regions of the exhaust line downstream of the exhaust catalysts can result in a corrosive mixture that can damage the exhaust system. Therefore, the release of ammonia in exhaust gas should be minimised as far as possible. P102443

[0012] It is known that promoted vanadium antimony oxide (VSbOx) catalysts may be used for the ammoxidation of hydrocarbons to produce nitriles. US 4 784 979 (US '979) discloses a method of making a catalyst precursor by reacting the ion VO(C>2)+in aqueous solution with an antimony compound that contains Sb having a valence of 3. In one embodiment, the VO(C>2)+ion is made by reacting H2O2 with a vanadium compound. US '979 further discloses the making of such a catalyst by drying and calcining the precursor of the invention. The catalyst is stated to be useful for ammoxidation of propane.

[0013] Supported promoted VSbOxcatalysts are also known as is their use as selective reduction catalysts for NOX. However, these are often made by mixing the vanadium source, antimony source and support together (e.g., US2023 / 0077366), or by adding soluble V and Sb salts to the support, drying and calcining (e.g., US 1172074). W02017101449 discloses a catalyst composition prepared by slurrying V2O5 and SbOa in water, spray drying and reslurrying in water, to which TiCh and a Si binder are added. VSbCU is only formed after the combined mixture of V2O5, SbOa and TiCh is calcined.

[0014] The present inventors have surprisingly found that preforming VSbCU and then depositing it on a support produces a catalyst with improved SCR performance at equivalent V loading or similar performance with thrifted V loadings, as well as improving activity, selectivity and / or durability.

[0015] OBJECT OF THE INVENTION

[0016] The object of the invention is to provide an alternate and novel method for making a catalyst comprising a selective catalytic reduction VSbOxcatalyst and a support, for the reduction of NOXin a gas mixture which at least partially results in increased activity, selectivity and / or durability. The object of the invention further extends to a catalyst prepared by the method and to the use of the catalyst for the selective reduction of NOX.

[0017] BRIEF DESCRIPTION OF FIGURES

[0018] Figure 1 shows rutile VSbO4 as the only crystalline phase present after preparing a slurry comprising vanadium (V), antimony (Sb) and a reactive media to form a colloidal sol of VSbO4 ("X" in the Figure). Figure 1 also shows an amorphous form of VSbO4 supported on a titania support ("+" in the Figure).

[0019] DETAILED DESCRIPTION

[0020] According to the present invention there is provided a method for producing a catalyst for the selective catalytic reduction of NOXin a gas mixture, the method comprising the steps of:

[0021] (a) preparing a slurry comprising vanadium (V), antimony (Sb) and a reactive media to form a colloidal sol of VSbO4; P102443

[0022] (b) combining the colloidal sol of VSbCU with a catalyst support material into a mixture; and

[0023] (c) optionally drying and calcining the resulting mixture.

[0024] The catalyst comprises a metal oxide material (i.e. VSbCU), optionally doped with a dopant, supported on a catalyst support material (preferably titania). The metal oxide material can be undoped or doped with a dopant.

[0025] The reactive media used in the method of the invention may be selected from the list comprising hydrogen peroxide, inorganic peroxides, metal chlorates, chlorites, perchlorates, hypochlorites, metal bromates, hypobromates, perbromates, bromites, ozone, peroxydisulfuric acid, metal salts of peroxydisulfate, nitric acid or metal nitrates.

[0026] In a preferred form of the invention the reactive media is hydrogen peroxide.

[0027] In an embodiment of the invention the molar ratio of the reactive media to V is between 1-10, preferably from 2-6, e.g. 4, 4.5 or 5. In a particularly preferred embodiment, the reactive media is hydrogen peroxide and the molar ratio of hydrogen peroxide to V is between 1-10, preferably from 2- 6, e.g., 4, 4.5 or 5.

[0028] It will be appreciated by those skilled in the art that precursors of V and Sb may be used to form an oxide thereof under oxidation or otherwise. Accordingly, and in a preferred form of the invention, the step of preparing a slurry comprises mixing a source of V, preferably an oxide of V, more preferably V2O5 with the reactive material and thereafter adding and a source of Sb, preferably an oxide of Sb, more preferably SbjOa, to form the colloidal sol. Suitably, the source of V and the source of Sb can undergo a redox reaction in the reactive media to form the colloidal sol.

[0029] The precursor of vanadium may be selected from the group comprising (e.g. consisting essentially of or consisting of) ammonium vanadate, vanadyl oxalate, vanadium pentoxide, vanadium monoethanolamine, vanadium chloride, vanadium trichloride oxide, vanadyl sulfate and vanadium antimonate.

[0030] The precursor of antimony may be selected from the group comprising (e.g. consisting essentially of or consisting of) antimony acetate, ethylene glycol antimony, antimony sulfate, antimony nitrate, antimony chloride, antimony sulfide, antimony oxide and antimony vanadate.

[0031] In one embodiment, the slurry can be prepared by mixing V2O5 and the reactive media to form a first slurry; and subsequently adding Sb20a to the first slurry. In a particularly preferred embodiment, the P102443 slurry can be prepared by mixing V2O5 and H2O2 to form a first slurry; and subsequently adding Sb20a to the first slurry.

[0032] In an alternative embodiment, the slurry can be prepared by mixing V2O5, Sb20a and the reactive media in a single step, e.g., the slurry can be prepared by V2O5, Sb20a and H2O2 in a single step.

[0033] In an embodiment of the invention, the molar ratio of H2O2:V in the slurry is about 1 to 10, preferably from about 2-6. In a preferred form of the invention the molar ratio is about 4.5.

[0034] The molar ratio of V:Sb in the slurry can be from about 1:1 to 1:10, preferably from 1:1 to 1:4, e.g. from 1:1 to 1:2. In some preferred embodiments, the molar ratio of V:Sb comprises Sb in a molar excess (i.e. V:Sb of <1.0). For example, the molar ratio of Sb:V can be at least 1.1 (e.g. 1.1 to 10, suitably 1.1 to 4), preferably at least 1.2 (e.g. 1.2 to 10, suitably 1.2 to 4). The molar ratio of V:Sb (or Sb:V, as the case may be) can be in a range comprising any combination of the aforementioned limits.

[0035] For purposes of this specification, the term "about" means approximately and refers to a range that is optionally ± 25%, preferably ± 10%, more preferably, ± 5%, or most preferably ± 1% of the value with which the term is associated.

[0036] In an embodiment of the invention, the colloidal sol of VSbCU is optionally filtered prior to being combined with the catalyst support material to form a mixture.

[0037] In an alternative embodiment of the invention, the colloidal sol of VSbCU is not filtered prior to being combined with the catalyst support material to form a mixture. In one embodiment the colloidal sol of VSbCU is used directly and combined with the catalyst support material to form a mixture. In an alternative embodiment, the colloidal sol of VSbCU is diluted (e.g., diluted with water) and combined with the catalyst support material to form a mixture.

[0038] The step of combining the colloidal sol of VSbCU entails depositing the colloidal sol of VSbCU on the catalyst support material. That is, the method can comprise a step of depositing the colloidal sol of VSbCU on the catalyst support material such that VSbCU is supported on the catalyst support material. In some embodiments, the VSbCU can comprise nanoparticles or molecular clusters dispersed or otherwise supported on the catalyst support material. Suitably, the nanoparticles or molecular clusters have a largest cross-sectional dimension of less than 10 nm, suitably less than 5 nm, less than 2 nm, and suitably less than 1 nm. Such dimensions can be determined using TEM. In preferred embodiments, VSbCU is supported on the catalyst support material as a nanoscale layer having a thickness of less than 10 nm, preferably less than 5 nm, and suitably less than 2 nm; or as a sub- nanoscale layer having a thickness of less than 1 nm. Suitably, the sub-nanometre layer comprises an atomic monolayer or few atomic layers (e.g. up to about 5 atomic layers). The nanoscale or sub- P102443 nanoscale layer can provide partial or full coverage of the catalyst support material. In some embodiments, the sub-nanoscale layer can comprise an epitaxial layer or sub-epitaxial layer. This thickness of the nanoscale and sub-nanoscale layers can be determined using transmission electron microscopy (TEM). The colloidal sol of VSbCU may be added to the catalyst support material as a washcoat or as an extrusion paste containing the catalyst support material. The method can further comprise a step of applying the washcoat to a honeycomb substrate, such as a flow-through monolith substrate or a filter monolith substrate (e.g. a wall filter monolith substrate). Accordingly, there is also provided a catalytic article comprising a honeycomb substrate coated with a catalyst, wherein the catalyst comprises a metal oxide material supported on a catalyst support material (preferably TiCh), wherein the metal oxide material comprises a VSbCU catalyst, optionally doped with a dopant.

[0039] Typically, the catalyst support material has a larger mean average particle size (diameter) than the metal oxide material. Suitably, the mean average particle size of the catalyst support material is an order magnitude (e.g. at least 10 times, suitably at least 100 times) larger than a mean average largest cross-sectional dimension of the (VSbCU) metal oxide material. The catalyst support material can have a D5O particle size in a range of 1 to 100 pm, suitably 1 pm to 50 pm. The D5o (and Dgo) particle size of the catalyst support material can be determined by laser diffraction (e.g. using a Malvern Mastersizer laser diffraction particle size analyser) using a diluted dispersion of the catalyst support material.

[0040] The catalyst support material is typically a metal oxide, preferably titanium dioxide (TiCh). The metal oxide can be doped or undoped. Suitable dopants can include one or more of silica, tungsten (W), and antimony (Sb). In a preferred form of the invention, the catalyst support material is (undoped) titanium dioxide (TiCh).

[0041] In one form of the method of the invention, the steps of drying and calcining the mixture are performed at a temperature of about 400°C to about 600°C, preferably between 450°C and 550°C, more preferably at about 500°C.

[0042] In an alternate embodiment of the invention, the slurry comprising V, Sb and the reactive media may additionally comprise one or more dopants. The dopant may preferably be selected from the group comprising (e.g. consisting essentially of or consisting of) Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Fe, Sn and P. In a preferred embodiment, the dopant is selected from the group comprising (e.g. consisting essentially of or consisting of) Ti, Zr, Mo, Fe, W, Nb, Ta and Sn. The dopant dopes the metal oxide material (i.e. the VSbCU material).

[0043] According to the method of the invention, a catalyst is produced thereby, wherein the catalyst comprises V in an amount of 0.5-5 wt% based on the total weight of the catalyst (and including the P102443 catalyst support material). In some embodiments, preferably the catalyst comprises V in an amount of 0.5-4 wt.%, more preferably 1.0 wt.% to 3.0 wt.%, suitably 1.5 wt.% to 2.5 wt.%. In some embodiments, the catalyst comprises V in an amount of 0.5-1.5wt%, suitably from 1 to 1.2 wt%, e.g. about 0.87 wt% based on the total weight of the catalyst (and including the catalyst support material). The catalyst can comprise V in an amount in a range comprising any combination of the aforementioned limits. The composition of the catalyst, including the amount of V, can be determined using elemental analysis as is known in the art.

[0044] According to the method of the invention, a catalyst is produced thereby, wherein the catalyst comprises Sb in an amount of 1.2-20 wt%, 1.5 wt.% to 15 wt.%, preferably 2 wt.% to 11 wt.%, 2- 10wt%, from 3 to 8 wt% or from 4 to 6 wt%, e.g. about 5.55 wt% based on the total weight of the catalyst (and including the catalyst support material). The catalyst can comprise Sb in an amount in a range comprising any combination of the aforementioned limits. The composition of the catalyst, including the amount of Sb, can be determined using elemental analysis as is known in the art.

[0045] According to the method of the invention, a catalyst is produced thereby, wherein the catalyst comprises doped or undoped VSbCU in an amount in a range of about 3 wt.% to about 42 wt.%, 4 wt.% to about 38 wt.%, 5 wt.% to 30 wt.%, preferably 6 wt.% to 25 wt.%, more preferably about 7 wt.% to about 20 wt.%, e.g. about 10 wt.% to 15 wt.%. Suitably, the balance (wt.%) consists essentially of, or consists of, the catalyst support material. The catalyst can comprise VSbCU in an amount in a range comprising any combination of the aforementioned limits. The composition of the catalyst can be determined using elemental analysis as is known in the art.

[0046] According to the method of the invention, a catalyst is produced thereby, wherein the catalyst comprises the catalyst support material in an amount of at least 58 wt.%, at least 62 wt.%, at least 70 wt.%, at least 75 wt.% at least 80 wt.%, at least 90 wt.%, at least 93 wt.%, at least 94wt.%, at least 95 wt.% at least 96 wt.%, based on the total weight of the catalyst. The catalyst comprises the catalyst support material in an amount of less than 97 wt.%, less than 96 wt.%, less than 95 wt.%, less than 94 wt.%, less than 93 wt.% and suitably less than 90 wt.%, based on the total weight of the catalyst. The catalyst can comprise the catalyst support material in an amount in a range comprising any combination of the aforementioned limits. For example, the catalyst can comprise the catalyst support material in an amount in a range of 58-97 wt.%, 62-96 wt.%, 70- 95 wt.%, 75-94 wt.%, 80-93 wt.%, 85-90 wt.%, based on the total weight of the catalyst. In preferred embodiments, the balance (wt%) consists essentially of (or consists of) the metal oxide (i.e. doped or undoped VSbCU). The amount of the catalyst support material can be determined using ICP as is known in the art. P102443

[0047] According to a second aspect of the invention, there is provided a catalyst for the selective catalytic reduction of NOXin a gas mixture, wherein the catalyst is produced according to the method as hereinbefore described.

[0048] The catalyst produced according to the method of the invention comprises a metal oxide material (i.e. a VSbCU-based catalyst), optionally doped with a dopant, which is supported on a catalyst support material. In some preferred embodiments, the catalyst comprises VSbCU, optionally doped with a dopant, supported on a titania support. The catalyst made by the present method can provide comparable activity for NOXconversion at lower loadings.

[0049] The metal oxide material can comprise vanadium in a 4+ oxidation state (V4+) in amount higher than an amount of vanadium in a 4+ oxidation state (V4+) present in a reference VSbCU catalyst prepared by an incipient wetness impregnation method, as determined by electron paramagnetic resonance (EPR) spectroscopy, e.g. using the measurement conditions described below. For example, the catalyst of the present disclosure can exhibit a higher EPR integration value associated with vanadium in a 4+ oxidation state compared with the reference VSbCU catalyst prepared by incipient wetness impregnation, as measured by EPR spectroscopy, e.g. using the measurement conditions described below. The catalyst of the invention and the reference VSbCU catalyst have the same elemental composition and the same molar ratio of V:Sb.

[0050] In a third aspect of the invention there is provided a catalyst article produced according to the method as hereinbefore described to selectively reduce NOXin a gas mixture.

[0051] The catalyst article produced according to the method of the invention comprises a metal oxide material (i.e. a VSbCU-based catalyst), optionally doped with a dopant, which is supported on a catalyst support material, and which is coated on a honeycomb substrate, such as a flow-through monolith substrate or a filter monolith substrate (e.g. a wall filter monolith substrate).. In some preferred embodiments, the catalyst comprises VSbCU, optionally doped with a dopant, supported on a titania support.

[0052] In accordance with a fourth aspect of the invention there is provided a catalyst comprising a catalyst supported on a titania support, wherein said catalyst is VSbCU in an amorphous form. By "amorphous form", it is meant that when X-ray diffraction is performed on the sample, no crystalline structure is observed (i.e., amorphous materials are substantially devoid of peaks associated with crystalline structure), as demonstrated in Figure 1. According to H. P. Klug and L. E. Alexander ("X-ray Diffraction Procedures - For Polycrystalline and Amorphous Materials", 2ndEdition, 1974, John Wiley & Sons, page 791), crystalline materials are characterized by three-dimensional periodicity of the order of six P102443 unit translations. Accordingly, amorphous materials lack order on this scale. The pattern shown by the VSbCU colloidal sol ("X" in Figure 1) shows a clear crystal pattern demonstrating a rutile structure. When the VSbCU is supported on TiCU ("+" in Figure 1), the rutile crystal pattern is not observed, indicating that the VSbCU is present in an amorphous form. Without being bound by theory, it is thought that some Sb could be being dissolved into the TiCU, which decomposes the VSbCU particles but retains enough Sb to promote V activity. Again without wishing to be bound by any theory, it is believed that such migration of antimony (Sb) from the VSbCU (mixed) metal oxide into the catalyst support material (e.g. TiCU) can dope the catalyst support material. For example, in some embodiments of the present method, it is believed that Sb, which is initially present in the VSbCU, can dope the TiCU catalyst support material. As such, the catalyst obtained from the present method can comprise VSbCU supported on a Sb-doped catalyst support material, e.g. Sb-doped TiCU.

[0053] In a fifth aspect there is provided a catalyst for the selective catalytic reduction of NOXin a gas mixture, the catalyst comprising a metal oxide material (i.e. a VSbCU-based catalyst), optionally doped with a dopant, supported on a catalyst support material (preferably TiCU). In some preferred embodiments, the catalyst comprises VSbCU, optionally doped with a dopant, supported on a titania support. The catalyst (and preferably the metal oxide material) comprises vanadium in a 4+ oxidation state in amount that is higher than an amount of vanadium in a 4+ oxidation state comprised in a comparable reference VSbCU catalyst prepared by an incipient wetness impregnation method, as determined by electron paramagnetic resonance (EPR) spectroscopy. The catalyst of the present disclosure and the reference VSbCU catalyst made using an incipient wetness impregnation method are comparable in the sense that they suitably have the same elemental composition, have the same molar ratio of V:Sb (in the metal oxide material), suitably the same loading of the metal oxide material on the catalyst support material, and suitably comprise the same catalyst support material (which is preferably TiCU). The metal oxide material can be in an amorphous form.

[0054] In a further aspect there is provided use of a catalyst produced according to the method of the first aspect to selectively reduce NOXin a gas mixture.

[0055] In a further aspect there is provided a method of selectively reducing NOXin a gas mixture, such as an exhaust gas, the method comprising contacting a gas mixture comprising nitrogen oxides and a nitrogen-containing reducing agent with a catalyst produced according to the method of the first aspect, or a catalyst according to the second, third, fourth or fifth aspects. The catalyst comprises a VSbCU-based catalyst supported on a catalyst support material (preferably TiCU). Optionally, the VSbO4-based catalyst can be doped with a dopant. The catalyst can be coated on a honeycomb substrate. P102443

[0056] EXAMPLES

[0057] Example 1 - Preparation of Catalyst A

[0058] Colloidal VSbCU was prepared as described in US4784979 and J. Catal., 230, 317 (2005) by Standard Oil (later BP). 1.01 g V2O5 was reacted with 5.0 ml 30 vol% H2O2 diluted to 50 ml with H2O, to form a V peroxy solution. To this was added 2.21 g solid Sb20a and the mixture heated to reflux for 1.5 hrs to form a black colloidal VSbO4 dispersion / slurry (V / Sb = 0.73).

[0059] The slurry was filtered, re-slurried and filtered again to form a supernatant. The supernatant was added to TiO2 and stirred at room temperature for 1 hour, followed by heating to 55°C for 2 hours to form a second slurry. The resulting second slurry was allowed to settle and formed a supernatant and precipitate. This was filtered, dried and calcined at 500°C for 2 hours to form a VSbCU / TiCU sample (Catalyst A). Elemental analysis found 0.87 wt% V (V / Sb molar ratio = 0.37).

[0060] In addition, a portion of the colloidal VSbCU slurry was also directly calcined at 500°C in 2 hrs. XRD of this showed rutile VSbCU as the only crystalline phase present (see Figure 1).

[0061] Example 2 - Preparation of Catalyst B (comparative)

[0062] VSb / TiCU was prepared by mixing V oxalate and Sb acetate (dissolved in tartaric acid) and added to TiCU through incipient wet impregnation. This formed a catalyst comprising 2wt% V and 2wt%Sb.

[0063] Example 3 - Preparation of Catalyst C (comparative)

[0064] VSb / TiCU was prepared by mixing V oxalate and Sb acetate (dissolved in tartaric acid) and added to TiCU through incipient wet impregnation. This formed a catalyst comprising 2wt% V and 4wt%Sb.

[0065] Example 4 - SCR data

[0066] Catalyst A and Catalyst B were submitted to SCR testing:

[0067] Catalyst A was 0.87 wt% VSbCU / TiCU (i.e. 0.87 wt.% V)

[0068] Catalyst B was 2 wt% VSb / TiCU (2wt% Sb)

[0069] Catalyst C was 2 wt% VSb / TiCU (4wt% Sb) P102443

[0070] The powder catalysts were pelletised and tested fresh or aged using transient testing protocol (SV=60K / h) the samples were heated to 150°C and exposed to 500 ppm NOx, 550 ppm NH3, 10 %Ch, 5 % H2O, 300 ppm CO, 8% CO2, balance N2. The temperature was ramped at 10°C / min to 550°C.

[0071] Table 1:

[0072] The initial (fresh) testing of Catalyst A (~lwt% VSbOx / TiO2) under SCR conditions showed slightly lower activity than Catalyst B and C. On ageing (580°C, 100 hrs) the activity of Catalyst A was improved such that it matched that of Catalyst B and C. This shows that Catalyst A has comparable activity to the catalysts with half the V loading.

[0073] Example 5 - Preparation of Catalyst D

[0074] Colloidal VSbO4 was prepared as in Example 1 using 1.00g of V2O5, 2.2 g of Sb20a and 5 ml of 30 vol% H2O2 diluted to 50 ml. The colloidal dispersion was centrifuged, washed with H2O and recentrifuged with the resulting supernatants combined to give 140 ml of colloid.

[0075] 17.5 ml of the colloid was added to 5.1 g of TiCh powder and stirred for 1 hr. To this was added 2 drops of 0.88 NH3 solution and then 3 drops of concentrated HNO3 solution. The slurry was then filtered, washed, dried at 105 °C and calcined at 500 °C for 2 hrs in air. Elemental analysis found 0.74 wt% V and 3.03 wt% Sb (V / Sb molar ratio = 0.58).

[0076] Example 6 - Preparation of Catalyst E

[0077] Colloidal VSbCU was prepared as in Example 1 using 1.00g of V2O5, 2.2g of Sb2C>3 and 5 ml of 30 vol% H2O2 diluted to 50 ml. The colloidal dispersion was centrifuged, washed with H2O and recentrifuged with the resulting supernatants combined to give 170 ml of colloid. P102443

[0078] 50 ml of the colloid was added to 10.0 g of TiCU powder slurried in 50 ml of H2O. The combined slurry was stirred for 4 hrs and then filtered, dried at 105 °C and calcined at 500 °C for 2 hrs in air.

[0079] Elemental analysis found 0.81 wt% V and 2.18 wt% V (V / Sb molar ratio = 0.89)

[0080] Example 7 - Preparation of Catalyst F

[0081] Colloidal VSbCU was prepared as in Example 1 using 1.00 g of V2O5, 1.9 g of Sb20a and 5 ml of 30 vol% H2O2 diluted to 50 ml. The resulting colloidal dispersion was diluted to give 150 ml of colloid.

[0082] 30 ml of the colloid was added to 10.0 g of TiCU powder slurried in 70 ml of H2O. The combined slurry was stirred for 4 hrs and then filtered, dried at 105 °C and calcined at 500 °C for 2 hrs in air. Elemental analysis found 1.04 wt% V and 2.89 wt% V (V / Sb molar ratio = 0.86).

[0083] Example 8 - Preparation of Catalyst G

[0084] Colloidal VSbCU was prepared as in Example 1 using 1.00 g of V2O5, 1.9 g of Sb20a and 5 ml of 30 vol% H2O2 diluted to 50 ml. The resulting colloidal dispersion was diluted to give 150 ml of colloid.

[0085] 30 ml of the colloid was added to 10.0 g of TiO2 powder slurried in 65 ml of H2O. The combined slurry was stirred for 4 hrs and then filtered, dried at 105 °C and calcined at 500 °C for 2 hrs in air. Elemental analysis found 0.94 wt% V and 2.40 wt% V (V / Sb molar ratio = 0.94).

[0086] Example 9 - Preparation of Comparative Catalysts H and I

[0087] VSb / TiCU was prepared by mixing V oxalate and Sb acetate (dissolved in tartaric acid) and added to TiCU through incipient wet impregnation. This formed a catalyst comprising 1 wt% V and 2.4wt%Sb (Example H) or 1 wt% V and 4.2 wt% Sb (Example I).

[0088] Example 10 - EPR data

[0089] Electron Paramagnetic Resonance (EPR) spectra were measured using a Bruker Magnettech ESR 5000 benchtop spectrometer (X-band). Spectra were collected with a magnetic field range of 250 to 450 mT, a microwave power of 20 mW and an amplitude frequency of 0.2 mT at room temperature. Spectra were double integrated and resulting values corrected for sample weight and V content.

[0090] EPR spectra under these conditions measured the V4+content of the samples. This is an indication of V-Sb interaction as it is known that the formation of VSbCU contains vanadium in both +3 and +4 oxidation states (T. Birchall & A.W.SIeight, Inorganic Chemistry, 15 (4), 868 (1976)). Therefore, the higher V4+content the greater the V-Sb interaction (as VSbCU), which corresponds to a higher EPR integration value. P102443

[0091] Catalysts A, D to I were measured using EPR and the results are shown in Figure 2. In general, it was found that a lower V / Sb atomic ratio correlated with a higher EPR integration value, and therefore an expected increase in V-Sb interaction.

[0092] The EPR integration values of the invention (Catalysts A, D to G) were higher than those of the comparative examples (Catalysts H & I) at comparable V / Sb atomic ratios. Therefore, without wishing to be bound by any theory, it is believed that the catalysts of the invention show higher V-Sb interaction, which may result in higher catalytic activity for the selective catalytic reduction of NOX.

Claims

P102443Claims:

1. A method for producing a catalyst for the selective catalytic reduction of NOXin a gas mixture, the method comprising the steps of:(a) preparing a slurry comprising vanadium (V), antimony (Sb) and a reactive media to form a colloidal sol of VSbCU;(b) combining the colloidal sol of VSbCU with a catalyst support material, which comprises depositing the colloidal sol of VSbCU on the catalyst support material, to form a mixture; and(c) optionally drying and calcining the resulting mixture.

2. The method of claim 1, wherein the reactive media is hydrogen peroxide.

3. The method of claim 1 or claim 2, wherein the step of preparing a slurry comprises mixing an oxide of V, preferably V2O5 and an oxide of Sb, preferably SbjOa.

4. The method of any preceding claim, wherein the slurry is prepared by mixing V2O5 and H2O2 to form a first slurry; and subsequently adding Sb20a to the first slurry.

5. The method of claim 4, wherein the molar ratio of H2O2:V in the slurry is about 1 to 10, preferably from about 2-6, e.g., about 4.5.

6. The method of claim 4 or claim 5, wherein the molar ratio of V:Sb in the slurry is from about 1:1 to 1:10, preferably from 1:1 to 1:4, e.g. from 1:1 to 1:2.

7. The method of any preceding claim, wherein said colloidal sol of VSbCU is filtered prior to being combined with the catalyst support material.

8. The method of any one of claims 1 to 7, wherein the step of combining the colloidal sol of VSbCU is prepared by adding the colloidal sol of VSbCU to a washcoat or extrusion paste containing the catalyst support material.P1024439. The method of claim 8 further comprising a step of applying the washcoat to a honeycomb substrate, such as a flow-through monolith substrate or a filter monolith substrate.

10. The method of any preceding claim, wherein the catalyst support material is present in an amount in a range of from 58 wt.% to 97 wt.%, based on the total weight of the catalyst.

11. The method of any preceding claim, wherein the catalyst support material is titanium dioxide (TiO2).

12. The method of any preceding claim, wherein the slurry comprising V, Sb and the reactive media additionally comprises a dopant, preferably wherein said dopant is selected from the group comprising Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Fe, Sn and P.

13. The method of any preceding claim, wherein the catalyst comprises V in an amount of 0.5-1.5wt%, preferably about 0.87 wt% and Sb in an amount of 2-10wt%, preferably about 5.55 wt%.

14. A catalyst for the selective catalytic reduction of NOXin a gas mixture, wherein the catalyst is produced according to the method of any preceding claim.

15. A catalyst according to claim 14, wherein the catalyst comprises vanadium in a 4+ oxidation state in amount that is higher than an amount of vanadium in a 4+ oxidation state comprised in a reference VSbCU catalyst prepared by an incipient wetness impregnation method, as determined by electron paramagnetic resonance (EPR) spectroscopy, wherein the catalyst and the reference VSbCU catalyst have the same molar ratio of V:Sb.

16. Use of a catalyst produced according to the method of any one of claims 1 to 13 to selectively reduce NOXin a gas mixture.

17. A catalyst comprising a catalyst supported on a titania support, wherein said catalyst is VSbCU in an amorphous form.

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