Method for producing catalytic filter

Abstract

A method for manufacturing a catalytic filter for an exhaust gas treatment system, the method comprising: i) providing a porous filter body; ii) providing a repair topcoat comprising: (a) one or more platinum group metals (PGMs); (b) a support material; and (c) a surfactant; iii) coating the filter body with a repair topcoat to form a coated filter body; and iv) calcining the coated filter body to form the catalytic filter, and wherein the surfactant is a non-ionic, silicon-free organic surfactant.

Description

[0001] The present invention relates to a method for the manufacture of catalysed filters suitable for use in exhaust gas treatment systems, such as for use in automobiles. In particular, the method addresses the problems caused by treatments that are now sometimes added to filter substrates to improve their filtration performance and operational lifetime without compromising the benefits of those treatments.

[0002] The provision of filter components in exhaust gas treatment systems is well known. These take the form of so-called wall-flow filters. A wall-flow filter consists of a porous material substrate having a plurality of longitudinally extending channels therein. Typically, half of these are plugged at the inlet end and the other half are plugged at the outlet end. Thus, exhaust gas entering the open inlet channels is forced through the porous walls into the outlet channels to exit the filter. Thus, soot and other particulate matter can accumulate on the filter walls. The simplest diesel particulate filter (DPF) is simply formed from a porous material, but more modern advances have led to the provision of catalytic coatings on the filter body. These can help to catalyse soot combustion to regenerate the filter, or can be present to have other catalytic benefits on components in the exhaust gas. Other well-known filter types include: catalysed soot filter (CSF), gasoline particulate filter (GPF) and selective catalytic reduction filter (SCRF). All of these are well known in the art and have characteristic formulations and components.

[0003] There have been some developments in recent years in the provision of coatings on filter substrates to improve their filtration performance and shelf life. At least some of these coatings are applied to the filter inlet channels to form a surface layer that enhances the filtration activity of the underlying porous channel walls. These coatings can comprise silica-based materials and can be used to reduce the interaction of the filter component with components in the exhaust gas.

[0004] WO2014137827 discloses a catalyst washcoat having improved porosity. The method comprises incorporating an oil-in-water macroemulsion into a catalyst slurry prior to washcoating a support substrate, and calcining the washcoated support substrate to remove the oil-in-water macroemulsion. The O / W emulsion is formed and stabilised with an organic surfactant which is calcined away in the final step. The removal of the oil by calcination helps to form a porous structure.

[0005] US9687786 discloses a diesel particulate filter capable of removing soot from exhaust gas when operated at low back pressure, the filter comprising (a) a wall-flow filter substrate having an average pore size, an inlet side, an outlet side, and a porous interior between the inlet side and the outlet side; and (b) a catalyst composition coated from the inlet side of the substrate. The catalyst composition has a D50 particle size distribution that is less than the average pore size divided by 4.9, and the outlet side is substantially free of catalyst coating.

[0006] DE102007002903 discloses the use of surfactants in catalytic washcoat suspensions as foaming aids for forming automotive catalytic converters. The surfactants are then associated with an aeration or deaeration step.

[0007] US2019 / 299139 discloses an exhaust gas purification filter which suppresses an increase in pressure loss associated with formation of a catalyst layer, and has good PM combustion quality.

[0008] US2004 / 176246 discloses a catalytic filter and a method for placing a catalyst onto a filter medium, which involves positioning the catalyst on the filter medium at a location where material to be catalysed will contact during the filtration process.

[0009] JP2002361099 discloses a method of manufacturing an inorganic fiber catalyst which sufficiently exhibits catalyst activity by uniformly depositing a catalyst active component on an inorganic fiber structure.

[0010] WO2012099868 discloses exhaust systems and components adapted for use in conjunction with gasoline engines to treat gaseous exhaust emissions such as hydrocarbons, nitrogen oxides and carbon monoxide.

[0011] US2022 / 258137 discloses a catalyst article comprising a substrate comprising a plurality of passages, and further comprising a first oxidation region and a second oxidation region comprising first and second subsets of the plurality of passages.

[0012] Applicant’s WO 2023 / 026022 Al discloses a method of forming an inorganic oxide coating on a monolithic article. The coated monolithic article is suitable for treating exhaust gas. The method comprises spraying an inorganic particulate and a silicone resin as a dry particulate aerosol to form the coating.

[0013] There is a need to address the problem of supplying washcoats having porous substrates which have been treated with a hydrophobic treatment, or to address problems associated with the prior art, or at least to provide a replacement form thereof.

[0014] According to a first aspect, there is provided a method for manufacturing a catalytic filter for use in an exhaust gas treatment system, the method comprising:

[0015] i) providing a porous filter body;

[0016] ii) providing a washcoat comprising:

[0017] (a) one or more platinum group metals (PGM);

[0018] (b) a carrier material; and

[0019] (c) a surfactant;

[0020] iii) coating the filter body with a washcoat to form a coated filter body; and

[0021] iv) calcining the coated filter body to form a catalytic filter, and

[0022] wherein the surfactant is a non-ionic, silicon-free organic surfactant.

[0023] The present disclosure will now be further described. In the following paragraphs, different aspects / embodiments of the present disclosure are defined in more detail. Unless explicitly stated otherwise, each aspect / embodiment thus defined can be combined with any other aspect / embodiment or multiple aspects / embodiments. In particular, any feature indicated as preferred or advantageous can be combined with any other feature or features indicated as preferred or advantageous. It is contemplated that features disclosed in relation to the method can be combined with those disclosed in relation to the use, and vice versa.

[0024] The inventors found that some of their products had the problem that the applied washcoat slurry failed to have a strong enough interaction with the substrate and this resulted in difficulties scaling up the prototype production and poor catalytic performance of the final product. For example, there was a loss of washcoat slurry control where a significant portion of the washcoat slurry dose travelled along the length of the substrate channel without entering the porous channel wall. In further investigations, it was found that these problems were related to modern pre-treatments applied to the substrates discussed above, for example pre-coating the filter inlet channel with a surface layer to enhance the filtration activity of the underlying porous channel wall. The inventors found that the pre-treatment had a corresponding increase in the hydrophobicity of the part.

[0025] The inventors envisaged various solutions to the washcoat slurry application problem. It was considered whether the water content of the washcoat could be reduced to minimise the interaction of the water with the inherent hydrophobicity of the substrate. This resulted in a thicker, stickier washcoat and a relative increase in washcoat solids. Similarly, they looked at including rheology modifiers, such as gums, to increase the washcoat viscosity without having to adjust the washcoat solids. While either approach could improve the ability to control the flow of the washcoat and thereby its position along the length of the substrate channel, it thereby reduced the ability to penetrate the washcoat solids into the wall (i.e. laterally). Higher washcoat solids on the wall resulted in higher back pressure and inhibited the desired location of the PGMs within the wall.

[0026] Other solutions envisaged include additional treatments of the substrate to reduce its apparent hydrophobicity. However, this was found to compromise the advantages associated with the application of the pre-treatment. One approach includes a pre-calcination step, but this was found to increase production costs and reduce the capacity of the production plant, as the parts require an additional process step to manufacture. Furthermore, the performance of the resulting product is reduced, as the effectiveness of the pre-treatment applied initially is compromised.

[0027] Finally, the inventors found that careful selection of a particular surfactant can be used to solve the problem without having to adjust the washcoat solids. Although the use of some surfactants is known, the addition of a surfactant to a washcoat composition is not conventional. This is because it is highly preferred not to include additives in the washcoat slurry that do not have a technical benefit. The inclusion of unnecessary additives increases the cost of the washcoat, but can also negatively affect the catalytic activity of the final calcined washcoat, for example by affecting the location of the PGM in the final product. Indeed, in the inventors’ tests, these adverse effects were observed for certain surfactants and certain surfactant concentrations. From this, the use of a surfactant is considered particularly unusual when preparing a PGM-containing washcoat for use in a filter.

[0028] The inventors have found that by careful selection of a surfactant, it is possible to solve the problem that has arisen. This means that they can obtain a catalytic filter that benefits from a pre-treatment of the substrate to improve its filtration performance, and at the same time maintains the catalytic activity of the catalyst coating applied.

[0029] The method involves the manufacture of a catalytic filter for use in an exhaust gas treatment system. The catalytic filter is a component of the exhaust gas treatment system, in which exhaust gas to be treated passes through the filter body. The filter body serves to remove particulate matter. The catalytic filter has catalytic properties due to the application of a washcoat containing PGM material.

[0030] The method includes the step (i) of providing a porous filter body. Preferably, the porous filter body is a wall-flow filter. The porous filter body can be ceramic, for example silicon carbide, cordierite, aluminium nitride, silicon nitride, aluminium titanate, alumina, mullite, celsian or a composite material comprising a portion of any two or more of these. Preferably, the porous filter body is composed of silicon carbide (SiC), cordierite or aluminium titanate. Preferably, the porous filter body has a hydrophobic coating applied to it, and preferably the method further comprises applying a hydrophobic surface coating to the porous filter body prior to step (iii). It is preferred that the hydrophobic coating is applied only to the surface of the inlet channels of the wall-flow filter.

[0031] In order to determine whether the porous filter body would particularly benefit from the present method, it is useful to assess whether it has hydrophobic properties or has been applied with a hydrophobic treatment. Preferably, the porous filter body provided in step (i) has a water contact angle of > 90° when measured with the Washburn uptake method. The method is well known in the art and a good summary is available at https: / / www.kruss-scientific.com / en / know-how / glossary / washburn-method. With respect to the testing of the porous filter body, a core is taken from the substrate and the core is fixed to a tensiometer, such as a Krüss Tensio, with special clamps and brought into contact with the test liquid, which is sucked into the substrate and the change in mass against time is determined. The first test liquid used is a liquid with the best wettability, where the contact angle is assumed to be 0° (e.g. n-heptane) to determine the Washburn constant c. Once the Washburn constant c is found, the contact angle of other test liquids with known surface tension, viscosity and density can be determined. A contact angle of 90° and above cannot be measured using this method as no wetting occurs, so the contact angle value of the water on the substrate does not indicate a contact angle > 90° and the substrate is considered to be hydrophobic. Conventional untreated filter substrates do not meet this and in fact, conventional SiC or cordierite substrates are so easily wetted that it is difficult to measure a value that will be close to zero.

[0032] Preferably, the hydrophobic surface coating is applied to the inlet channel of the porous filter body, preferably only to the inlet channel. The make-up washcoat is then applied to the inlet channel and / or the outlet channel. The length and extent of each make-up washcoat coating will depend on the desired catalyst performance. Applying a make-up washcoat coating to the outlet channel helps to reduce the initial hydrophobicity and repellency of the substrate as it encounters the make-up washcoat coating. It should be noted that although the make-up washcoat coating is applied to the inlet channel or the outlet channel, the material forming the make-up washcoat coating can diffuse to some extent into and through the pores of the porous body. Preferably, the total length of the make-up washcoat coating applied to the inlet channel and / or the outlet channel adds up to at least 100% of the longitudinal length of the porous filter body. That is, if there is only an outlet coating, then preferably it is 100% of the longitudinal length of the porous filter body.

[0033] Preferred embodiments provide an inlet washcoat coating extending from the inlet end of the porous filter body along 50% to 90% of the longitudinal length of the porous filter body and an outlet coating extending from the outlet end of the porous filter body along 50% to 10% of the longitudinal length of the porous filter body. More preferred embodiments provide an inlet coating extending from the inlet end of the porous filter body along 70% to 80% of the longitudinal length of the porous filter body and an outlet coating extending from the outlet end of the porous filter body along 30% to 20% of the longitudinal length of the porous filter body.

[0034] The method comprises a step (ii) of providing a washcoat. Methods of forming and applying washcoats are well known in the art and any suitable method can be used in the present application. Typically, the composition is an aqueous washcoat and the ingredients are added and dispersed prior to the coating step. The washcoat can contain conventional additives such as thickeners, acid regulators etc. Preferably, the surfactant is added as a final ingredient to minimise the opportunity for it to affect the PGM in the washcoat.

[0035] The washcoat comprises one or more platinum group metals (PGM). Preferably, the PGM is present in a total amount such that the final coating contains at least 1 g ft -3 -2 of PGM. The amount of PGM will vary depending on the catalyst product formed and the final application. Nonetheless, the presence of PGM is key because otherwise there would be no constraint on the addition of a surfactant as described herein. Preferably, the washcoat contains a total amount such that the final coating contains 1 g ft -3 -100 g ft -3 , more preferably 1 g ft -3 -5 g ft -3 , especially for CSF, and 25 g ft -3 -50 g ft -3 , especially for GPF. The PGM will be present in the washcoat as ions such as nitrate ions. Suitable Pt and Pd precursors include salts containing these metals, for example platinum nitrate and palladium nitrate.

[0036] The washcoat comprises a support material. Support materials are well known in the art and the specific nature of the support material is not critical, depending on the application. Suitable support materials include silica, alumina, ceria, ceria-zirconia and the like. Preferably, the support material comprises alumina. There can be one or more support materials. The support, such as alumina, can be doped with a dopant. The dopant can be selected from La, Sr, Si, Ba, Y, Pr, Nd, Ce and mixtures thereof. Preferably, the dopant is La, Ba or Ce. Most preferably, the dopant is La. The dopant content in the inorganic oxide support can be from 1 to 30 wt%, preferably from 2 to 25 wt%, more preferably from 3 to 20 wt%.

[0037] The washcoat comprises a surfactant. The surfactant is a non-ionic, silicon-free organic surfactant. The surfactant must be non-ionic because this minimises interactions with other components of the washcoat. Non-ionic means that the surfactant does not contain a charge, unlike a cationic surfactant or an anionic surfactant. Commercial surfactants are clearly identified as to whether they are non-ionic.

[0038] It must be silicon-free because the inventors have found that silicon-containing surfactants can react adversely with components of the washcoat, particularly affecting PGM distribution, affecting catalytic activity.

[0039] The surfactant must be organic so that it is completely removed by the calcination step. That is, there are no inorganic parts of the surfactant remaining as a residue or contaminant in the calcined catalyst.

[0040] Preferably, the surfactant comprises one or more acetylenic diol surfactants. Preferably, the one or more acetylenic diol surfactants is one or more alkoxylated acetylenic diol surfactants. More preferably, the one or more alkoxylated acetylenic diol surfactants is one or more ethoxylated acetylenic diol surfactants. More preferably, the one or more ethoxylated acetylenic diol surfactants is one or more ethoxylated tetramethyl dodecynediol surfactants. Most preferably, the surfactant comprises one or more ethoxylated acetylenic diol surfactants represented by the formula:

[0041]

[0042] where m and n are integers and the sum is from 1 to 15, preferably from 4 to 12.

[0043] Suitable surfactants and their structure and production are discussed in US5650543, the contents of which are incorporated herein by reference.

[0044] Of the above-discussed classes of surfactants, the preferred surfactant is Dynol-607 ™ which is a so-called superwetting surfactant. This meets the requirements outlined herein as preferred and overcomes the problems of the overcoat process without compromising the properties of the hydrophobic treated substrate. The term "superwetting" denotes a surfactant that achieves a low equilibrium surface tension (i.e. it is effective at lowering surface tension) and achieves a low dynamic surface tension (i.e. it acts quickly and penetrates through the washcoat very quickly even with limited mixing).

[0045] The inventors have also considered other surfactants such as Tego Twin 4200, but this has a silica functionality which can interact within the washcoat during calcination, for example. Another non-ionic surfactant is BYK-349 which also contains a siloxane functionality, but this causes the PGM washcoat to change colour; this is a clear indication that some PGM-surfactant interaction is occurring.

[0046] Ideally, the surfactant is non-reducing with respect to the Pt and / or Pd ions (and Rh ions if Rh is present) present in the washcoat. That is, preferably, the PGM is included in the washcoat as ions and the surfactant cannot reduce those ions, in particular to form a metal. Desirably, the surfactant has a reduction potential measured by cyclic voltammetry under standard conditions which is insufficient to reduce the Pt and / or Pd ions present in the washcoat. The method of measuring reduction potential using cyclic voltammetry is well known in the art and reference values are available for many materials. This ensures that there is no reaction between the surfactant and the PGM.

[0047] Preferably, the surfactant exhibits an equilibrium surface tension of less than 30 mN / m when measured on a force tensiometer using the Wilhelmy plate method (using a platinum plate). The platinum plate is used due to its low surface energy (contact angle of 0° with most liquids). The force tensiometer lowers the platinum plate into the liquid and measures the force. The surface tension of the liquid, s, can be calculated from the equation s = F / (L.cos0) where F = force, L = wetted length of the platinum plate and 0 = contact angle of the liquid on the plate (known to be 0). The surface tension < 30 mN / m, in comparison, water is approximately 72.8 mN / m at 20°C. This is a measure of the ability of the surfactant to improve the surface wetting ability of the washcoat.

[0048] Preferably, the surfactant exhibits a dynamic surface tension of less than 30 mN / m (when measured by a bubble pressure tensiometer, such as a Kruss BP100). A bubble is formed in the liquid under investigation by a capillary, and the maximum internal pressure of the bubble is measured. The dependence of the surface tension on surface age can be measured by varying the speed of bubble generation. A dynamic surface tension of less than 30 mN / m ensures that the surfactant quickly migrates to the surface of the repair basecoat paint / newly formed interface, improving the speed at which coating can be performed and the consistency of the product.

[0049] The amount of surfactant will vary depending on the specific surfactant used, but it is preferably between 0.01 and 0.5 wt% of the repair basecoat paint, preferably between 0.05 and 0.35 wt%, preferably between 0.1 and 0.2 wt%. The amount of surfactant can be determined by testing, and it is desirable to use as little surfactant as possible to avoid damaging the PGM. At the same time, there is usually a point at which adding more does not have additional benefits, which is usually just after the critical micelle concentration (CMC) of the surfactant is reached. The critical micelle concentration is defined as the concentration at which the surface (or air-liquid interface) is completely saturated with surfactant molecules, such that micelles form in the bulk. This can be determined by a series of surface tension measurements at increasing surfactant concentrations (using the Wilhelmy method on a force tensiometer). Above the CMC, the static surface tension becomes independent of the surfactant concentration. It is desirable for the amount of surfactant used to exceed this threshold to ensure that the surfactant effect is consistent within and between coating applications, but equally it is desirable for it not to significantly exceed this point as it risks interacting with the PGM.

[0050] Preferably, the repair basecoat paint consists of components (a)-(c) and water and additives in a total amount of less than 5 wt%, preferably additives in a total amount of less than 2 wt%. Preferably, the additives comprise one or more of a rheology modifier, ammonia and a pH adjuster. Rheology modifiers are discussed in, for example, US9144796. Suitable examples of rheology modifiers include polymers such as long chain polysaccharides, polyethylene glycol derivatives (PEG) and acrylic polymers. The repair basecoat paint slurry can comprise an organic pore former. Examples of pore formers include cellulose, polyethylene, starch, graphite, polypropylene, polyaramid, polytetrafluoroethylene, polystyrene, cellulose fibres and polymethylacryl-methacrylate, such as Arbocel, Vivapur, Mipelon PM-200, Propyltex, Orgasol and Remyrise.

[0051] The method comprises a step (iii) of coating the filter body with a washcoat to form a coated filter body. Preferably, the washcoat is coated on and in the outlet channels of the porous filter body in step (iii), preferably only to the outlet channels. As discussed above, this has synergistic benefits when a previous hydrophobic treatment has been applied to the inlet surface. The treatment on the inlet surface minimises the interaction between the filter body and the exhaust gases, especially moisture, and enhances the filtration performance and shelf life of the component. At the same time, coating the washcoat on the outlet channels provides catalytic performance and, because of the addition of the surfactant, it can still penetrate into and adhere to the porous body.

[0052] The method comprises a step (iv) of calcining the coated filter body to form a catalysed filter. This serves to dry and calcine the inorganic washcoat components. At the same time, the surfactant and any other carbon-based components are oxidised away. A drying step can be carried out at a lower temperature, such as 100 to 200 °C, before calcination. Calcination is routine in the art and can be carried out under usual conditions.

[0053] Preferably, the catalysed filter is a gasoline particulate filter (GPF) and wherein the washcoat further comprises an oxygen storage compound (OSC), preferably ceria or ceria-zirconia OSC, and wherein the one or more PGMs comprise Pd and Rh. When forming a GPF, preferably the washcoat has a solids content of 25 to 40 wt%.

[0054] Preferably, the catalysed filter is a catalysed soot filter (CSF) and wherein the one or more PGMs comprise Pt and optionally Pd. When forming a CSF, preferably the washcoat has a solids content of 1 to 10 wt%. CSFs generally have lower demand for catalytic materials than GPFs, so the washcoat comprises less solids.

[0055] Preferably, the method does not comprise forming an emulsion in the washcoat before coating in step (iii). The purpose of the surfactant is to change the surface tension of the washcoat and improve its adhesion, not to stabilise an emulsion.

[0056] Preferably, the method does not comprise foaming the washcoat before coating in step (iii). The purpose of the surfactant is to change the surface tension of the washcoat and improve its adhesion, not to stabilise a foam. There is no foaming step because this would actively hinder the application of the washcoat into the pores of the porous body.

[0057] Preferably, the method does not comprise degassing the washcoat before coating in step (iii). Degassing is an unnecessarily complex additional step in this method.

[0058] According to a further aspect, there is provided the use of a non-ionic, silicon-free organic surfactant for improving the washcoat adhesion of a PGM-containing washcoat to a porous filter body having a water contact angle of > 90° when measured with the Washburn uptake method. All aspects of the methods disclosed herein can also be applied to this use. Examples

[0059] The application will now be further described in connection with the following illustrative examples.

[0060] A series of catalyzed filters were produced and tested. The porous wall-flow filter bodies were cylindrical parts of 143.8 mm diameter x 152.4 mm length dimensions. All catalytic washcoats were microparticulate alumina and only 2 g / ft 3 Pt, i.e. not including Pd or (1 :0), total washcoat loading was 0.1 g / in 3 Wall-flow filter bodies coated with catalytic washcoats are referred to as “catalyzed soot filters” or “CSF”. The EFC coating coated at 12 g / L loading is disclosed in Applicant’s WO 2023 / 026022 Al and is derived from a 50:50 by weight mixture of microparticulate aluminosilicate CHA zeolite and highly cross-linked ethoxylated poly(dimethylsiloxane) powder. The calcined EFC coating is hydrophobic.

[0061] Table 1

[0062]

[0063] All calcinations were performed in a static oven at 500 °C in air.

[0064] Laboratory Synthetic Catalytic Activity Test (SCAT) The test was then performed on 1 inch (2.54 cm) diameter cores cut from the coated filter bodies. Tests were performed on “fresh” as manufactured product, “conditioned” fresh product, and “aged” fresh product under the following test conditions:

[0065] • “Fresh”: Light-off on ramp (LO) test, no preconditioning required. Each core was stabilized at an inlet gas temperature of 150 °C for 10 minutes in the light-off on ramp gas mixture test described below, before the light-off temperature ramp itself was initiated at a ramp rate of 1 °C per minute. The gas exiting the sample was analyzed to determine the conversion of the inlet composition;

[0066] • "Regulated": A fresh sample was conditioned on the SCAT apparatus itself by first exposing the sample to 100% N2, and then ramping the inlet gas temperature to 500°C at a rate of 30°C per minute, and then switching the inlet gas to the composition of the Ramp LO gas mixture described below at 500°C for 15 minutes. The "regulated" core was then stabilized in the ramp light-off gas mixture at 150°C for 10 minutes prior to beginning the ramp light-off temperature ramp itself, as described above for the "fresh" sample; and

[0067] • "Aged": A "fresh" sample was aged in air at 500°C for 200 hours in a static oven. The "aged" sample was then conditioned and tested according to the same protocol described above for the "regulated" sample.

[0068] • Ramp Light-Off (LO) gas mixture: Propylene 10 ppm (C3), Propane 10 ppm (C3), Toluene 4.3 ppm (C3), n-Decane 3 ppm (C3), CO 60 ppm, NO 500 ppm, H2O 5%, CO2 5%, O2 12%, balance N2

[0069] • Space Velocity = 25,000 h -1

[0070] The NO oxidation activity of each sample is reported in Table 2, which clearly shows the difference in oxidation activity between the test samples. The goal of this experiment was to achieve the oxidation activity of a CSF-coated filter body including an EFC coating that was as close as possible to the reference CSF-coated filter body sample without an EFC coating.

[0071] The catalytic performance of the hydrophobic treated components coated with 0.1 wt% and 0.4 wt% of the Dynol-containing washcoat was essentially the same as the reference component (non-EFC hydrophobic treatment). The performance of all components was significantly better than the component with the hydrophobic EFC treatment applied on top of the catalyzed clad component (reference). The activity of the sample with the catalytic washcoat including the PVP additive applied on top of the hydrophobic EFC coating was not matched by the sample including the Dynol additive. The NO oxidation activity of the PVP example was slightly better than the comparative example without surfactant under fresh and "regulated" conditions, and essentially the same when aged, but did not reach the NO oxidation activity of the reference without the EFC hydrophobic coating.

[0072] Table 2

[0073]

[0074] The findings of the testing are summarized as follows:

[0075] • The hydrophobic EFC coating applied on top of the CSF coating (reference) had a large impact on oxidation activity as shown for NO oxidation. The CSF washcoat (WC) applied on top of the EFC coating (comparative) which did not contain the surfactant additive showed lower N02 / NOx than the non-EFC coated reference.

[0076] • For the reference sample where the hydrophobic EFC coating was applied on top of the CSF WC, an adverse effect on oxidation activity was also observed for CO oxidation relative to the non-EFC coated reference. Fresh CO oxidation for the CSF WC applied on top of the hydrophobic EFC coating (no surfactant comparative) was initially slightly worse than the non-EFC coated reference, but as the two samples aged, the CO oxidation activity improved to become the same for both samples.

[0077] • For the reference sample where the hydrophobic EFC coating was applied on top of the CSF WC, an adverse effect on oxidation activity was also observed for HC oxidation relative to the non-EFC coated reference. Fresh HC oxidation for the CSF WC applied on top of the hydrophobic EFC coating (no surfactant comparative) was initially slightly worse than the non-EFC coated reference, but as the two samples aged, the HC oxidation activity improved to become the same for both samples.

[0078] • The addition of PVP to the CSF washcoat coating slightly improved the adjusted N02 / NOx x oxidation relative to the no surfactant comparative, but still showed a performance gap to the reference non-EFC coated CSF sample. From fresh to aged, CO oxidation improved with the addition of PVP. There was no particular benefit to HC oxidation activity with the addition of PVP whether fresh or aged.

[0079] • The addition of Dynol improved the N02 / NOx x oxidation to the level of the reference non-EFC coated sample. However, the 0.4 wt% Dynol showed slightly lower aged N02 / NOx x oxidation, possibly indicating that there was too much Dynol present.

[0080] • The addition of Dynol resulted in CO oxidation activity that was very similar to the non-EFC coated reference. Again, the 0.4 wt% Dynol coating showed slightly lower CO oxidation activity than the 0.1 wt% Dynol sample.

[0081] • The addition of Dynol, whether 0.1 wt% or 0.4 wt%, resulted in HC oxidation activity that was very similar to the non-EFC coated reference.

[0082] It will be appreciated that the testing of the Dynol addition showed that the catalytic oxidation performance of the component matched that of a non-EFC coated CSF reference component. This means that there was essentially no loss of oxidation activity performance and that the component according to the application benefits from the additional filtration improvement provided by the EFC coating, i.e. improved lower back pressure and better filtration performance.

[0083] Filtration efficiency test

[0084] The filtration efficiency test was carried out using the apparatus and method described in EP1850068 and which is available from Cambustion, Cambridge, UK ® available under the trade name "DPG Particulate Filter Testing System" (see https: / / www.cambustion.com / products / engine-exhaust-emissions / dpg-particulate-filter-testing-system), i.e.:

[0085] (i) An apparatus for generating and collecting particulate matter produced by combustion of a liquid carbonaceous fuel, the apparatus comprising: a fuel burner comprising a nozzle housed in a vessel, the vessel comprising a gas inlet and a gas outlet, the gas outlet being connected with a duct for conveying gas from the gas outlet to the atmosphere; means for detecting the rate of gas flow through the gas inlet, and means for forcing oxidising gas from the gas inlet to flow via the vessel, the gas outlet and the duct to the atmosphere; a station for collecting particulate matter from the gas flowing through the duct, and means for controlling the gas flow forcing means in response to the gas flow detected at the gas inlet, thereby to maintain the gas flow at the gas inlet at a desired rate to provide sub-stoichiometric combustion of the fuel within the vessel to promote particulate matter formation; and

[0086] (ii) A method of generating and collecting particulate matter produced by combustion of a liquid carbonaceous fuel in an oxidising gas, the method comprising combusting the fuel in a fuel burner with sub-stoichiometric amounts of oxidising gas, the fuel burner comprising a nozzle housed in a vessel; forcing the oxidising gas to flow into a gas inlet of the vessel and via a gas outlet of the vessel and a duct connected to the gas outlet to the atmosphere; collecting particulate matter at a station located within the duct; detecting the flow of oxidising gas at the gas inlet and controlling the flow of oxidising gas so that the desired flow of oxidising gas is maintained at the gas inlet.

[0087] A filter was inserted into the station for collecting particulate matter from the gas flowing through the duct. A fresh filter was first preconditioned using low sulphur diesel fuel (10 ppm S) in a lean burn combustion flow at 80 kg / hr air flow to raise the filter inlet temperature to 650°C, a temperature typically used to regenerate a filter on a vehicle loaded with soot. The temperature of this preconditioning step is well above the temperature for soot combustion and ensures that the filter under test is clean at the start. Pressure sensors placed upstream and downstream of the station were used to monitor the back pressure across the filter. The test was carried out by burning low sulphur diesel fuel (10 ppm S) at a filter inlet temperature of 250°C, 180 kg / hr air flow.

[0088] The following filtration efficiency test was carried out on the DPG particulate filter test system. At constant flow rate, the initial test used a PN counter to detect the second by second particulate number (PN) upstream of the filter. The upstream PN raw data was averaged over an 11 second detection period (averaged) to generate an 11 second average window moving second by second, to reduce the effect of any variability in the PN generation, where time "t" corresponds to the midpoint of the 11 second window. The sample filter was then tested by detecting the filtered PN (again using a PN counter). The instantaneous filtration efficiency at time "t" in the test was given by the following calculation:

[0089]

[0090] The results of the filtration efficiency analysis are shown in Table 3.

[0091] Table 3

[0092]

[0093] This test shows that the combination of EFC (hydrophobic treatment) and inclusion of a suitable surfactant results in a component that provides optimised performance, i.e. a component with the combination of improved filtration performance (better with Dynol than with PVP) resulting from the treatment; and improved catalytic oxidation performance (i.e. effective use of PGM) that matches the leading reference product (i.e. CSF WC without the hydrophobic EFC coating).

[0094] All percentages herein are by weight unless otherwise indicated.

[0095] The above detailed description has been given by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Numerous variations of the presently preferred embodiments illustrated herein will be apparent to one skilled in the art and are intended to be within the scope of the appended claims and their equivalents.

[0096] For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.

Claims

1. A method for manufacturing a catalysed filter for an exhaust gas treatment system, the method comprising: i) providing a porous filter body; ii) providing a washcoat comprising: (a) one or more platinum group metals (PGMs); (b) a support material; and (c) a surfactant; iii) coating the filter body with the washcoat to form a coated filter body; and iv) calcining the coated filter body to form the catalysed filter, and wherein the surfactant is a non-ionic, silicon-free organic surfactant.

2. The method of claim 1, wherein the porous filter body provided in step (i) has a water contact angle of > 90° when measured using the Washburn uptake method.

3. The method of claim 1 or claim 2, wherein the porous filter body is composed of silicon carbide, cordierite or aluminium titanate, and wherein the method further comprises applying a hydrophobic surface coating to the porous filter body prior to step (iii).

4. The method of claim 3, wherein the hydrophobic surface coating is applied to the inlet channels of the porous filter body, preferably to the inlet channels only.

5. The method of any preceding claim, wherein the washcoat is coated to the inlet channels of the porous filter body in step (iii), preferably to both the inlet and outlet channels.

6. The method of any preceding claim, wherein the support material comprises alumina.

7. The method of any preceding claim, wherein the catalysed filter is a gasoline particulate filter (GPF), and wherein the washcoat further comprises an oxygen storage compound (OSC), preferably ceria or ceria-zirconia OSC, and wherein the one or more PGMs comprise Pd and Rh.

8. The method of claim 7, wherein the washcoat has a solids content of 25 to 40 wt%.

9. The method of any preceding claim, wherein the catalysed filter is a catalysed soot filter (CSF), and wherein the one or more PGMs comprise Pt and optionally Pd.

10. The method of claim 9, wherein the washcoat has a solids content of 1 to 10 wt%.

11. The method of any preceding claim, wherein the washcoat consists of components (a)-(c) and water and less than 5 wt% of additives in total, preferably less than 2 wt% of additives in total.

12. The method of claim 11, wherein the additives comprise one or more of a rheology modifier, ammonia and a pH adjuster.

13. The method of any preceding claim, wherein the method does not comprise, prior to the coating in step (iii): (i) forming an emulsion in the washcoat; (ii) foaming the washcoat; or (iii) degassing the washcoat.

14. The method of any preceding claim, wherein the surfactant: (I) relative to Pt 2+ and Pd 2+ ions are non-reducing; and / or (II) exhibits an equilibrium surface tension of less than 30 mN / m; and / or (III) exhibits a dynamic surface tension of less than 30 mN / m; and / or (IV) forms from 0.01 wt% to 0.5 wt%, preferably from 0.05 wt% to 0.2 wt%, of the washcoat.

15. The method of any preceding claim, wherein the surfactant comprises one or more acetylenic diol surfactants, preferably one or more alkoxylated acetylenic diol surfactants.

16. The method of any preceding claim, wherein the PGM is present in a total amount sufficient to form a coating containing at least 1 gft -3 of PGM.

17. Use of a non-ionic, silicon-free organic surfactant for improving washcoat adhesion of a PGM-containing washcoat to a porous filter body having a water contact angle > 90° when measured using the Washburn uptake method.

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