Method for forming an inorganic oxide coating on a monolithic article

Abstract

A method for forming an inorganic oxide coating on a monolith article is disclosed. The coated monolith article is suitable for exhaust gas treatment. The method includes spraying inorganic particles and a silicone resin as a dry particulate aerosol to form a coating layer. The invention also provides an unsintered porous monolith article for use in forming a monolith article for exhaust gas treatment. The unsintered monolith article includes a dry particulate composition including inorganic particles and a silicone resin.

Description

Technical Field

[0001] The present invention relates to a method for forming an inorganic oxide coating on a monolithic article. In particular, the coated monolithic article is suitable for the treatment of exhaust gases. More specifically, the method includes spraying inorganic particles and a silicone resin as a dry particle aerosol to form a coating layer. The present invention also relates to an unfired porous monolithic article for use in the formation of a monolithic article for the treatment of exhaust gases. In particular, the unfired monolithic article includes a dry particulate composition comprising inorganic particles and a silicone resin.

Background Art

[0002] There are concerns regarding the emission of particulate matter (PM), commonly referred to as soot, from internal combustion engines, particularly from diesel and gasoline engines for automotive applications. The main concerns are related to potential health effects, specifically those associated with very small particles having sizes in the nanometer range.

[0003] Diesel particulate filters (DPFs) and gasoline particulate filters (GPFs) have been manufactured using a variety of materials, including sintered metals, ceramics, or metal fibers. However, the most common type in actual mass production is of the wall-flow type made from porous ceramic materials fabricated in the form of a monolithic array of many small channels that extend along the length of the body. Since the alternating channels are blocked at one end, the exhaust gas is forced to pass through the porous ceramic channel walls, which prevent most of the particulate matter from passing through, so that only the filtered gas enters the environment. Ceramic wall-flow filters in commercial production include those made from cordierite, various forms of silicon carbide, and aluminum titanate. The actual shape and dimensions of a practical filter on a vehicle, as well as characteristics such as the thickness and porosity of the channel walls, depend on the application involved. The average size of the pores within the filter channel walls of a ceramic wall-flow filter through which the gas passes is typically in the range of 5 to 50 μm, usually about 20 μm. Notably, in contrast, the size of most diesel particulate matter from the high-speed diesel engines of the latest passenger cars is very small, for example, 10 to 200 nm.

[0004] Some PM can be retained within the pore structure in the filter walls, which in some applications can be gradually built up until the pores are bridged by a network of PM, which in turn will readily form a cake of particulate matter on the inner walls of the filter channels. The particulate cake is an excellent filter medium, and its presence results in very high filtration efficiency. In some applications, soot is continuously burned on the filter as it accumulates, thereby preventing the particulate cake from accumulating on the filter.

[0005] In some filters, such as lightweight diesel exhaust particulate filters, it is necessary to periodically remove trapped PM from the filter to prevent an increase in excessive backpressure that can be harmful to engine performance and can reduce fuel efficiency. In diesel applications, the retained PM is removed from the filter by burning it in air during a process, and during this process, the amount of available air and the amount of excess fuel used to achieve the high temperatures necessary to ignite the retained PM are very carefully controlled. Towards the end of this process, commonly referred to as regeneration, the removal of the last remaining particles in the filter can significantly reduce the filtration efficiency and can lead to a burst release of many small particles into the environment. Thus, the filters can have a low filtration efficiency when they are first used, after each subsequent regeneration event, and during the latter part of each regeneration process.

[0006] Accordingly, it is desirable to always improve and / or maintain the filtration efficiency, for example, during the initial life of the filter when it is first used, and / or during and immediately after regeneration, and / or when soot accumulates on the filter.

[0007] WO 2011 / 151711 (incorporated herein by reference in its entirety) describes a method of making a filter for filtering particulate matter from exhaust gases emitted from a lean burn internal combustion engine. The filter includes a porous substrate having an inlet surface and an outlet surface, the inlet surface being separated from the outlet surface by a porous structure including pores of a first average pore size. The inlet surface includes a cross-linked network including interconnected particles of a refractory material throughout the pores of the porous structure. The method includes contacting the inlet surface of the filter substrate with an aerosol including a refractory material in dry powder form.

[0008] International Publication No. WO 2021 / 028692 (which is hereby incorporated by reference in its entirety) discloses an exhaust filter for a vehicle, comprising a porous substrate having an inlet surface and an outlet surface, the porous substrate comprising an inlet channel extending from the inlet surface and an outlet channel extending from the outlet surface, the inlet channel and the outlet channel being separated by a plurality of filter walls having a porous structure, the exhaust filter for a vehicle being filled with a refractory powder having a tap density before filling of less than 0.10 g / cm 3 and having a mass filling amount of the refractory powder of less than 10 g / L, with more than 40% of the refractory powder being disposed within the porous structure of the plurality of filter walls and less than 60% of the refractory powder being coated on the outer surface of the plurality of filter walls. International Publication No. WO 2021 / 028692 also describes a suitable method and apparatus for spraying a dry refractory powder, such as a dry particulate aerosol, onto the channels of the porous substrate, and preferably more than 50%, optionally up to 100%, of the refractory powder can be disposed within the porous structure of the plurality of filter walls.

[0009] International Publication No. WO 2020 / 047708 discloses an article comprising a material such as a filtration material, for example, a porous body such as a porous ceramic honeycomb body comprising a porous inorganic layer disposed on at least a part of the porous body, and a method for producing such an article and the porous body. The method includes contacting an inorganic material in a suspension with a gaseous carrier fluid, and the suspension may be an aqueous or organic system, for example, an alcohol such as ethanol or methanol.

[0010] The inventors have found that a porous filter substrate treated with a refractory powder material as described in International Publication No. 2021 / 028692 has low water resistance and adhesiveness. For example, a porous filter substrate treated with fumed alumina (e.g., Aeroxide® Alu130) could not provide the desired water resistance under certain engine conditions, particularly during continuous engine cold starts. As described above, for example, in the case of a heavy duty diesel (HDD) catalytic soot filter (CSF) application, the filter needs to be able to withstand several ash cleaning cycles.

[0011] The inventors of the present application have developed the present invention in order to reduce and / or overcome the problems found in the prior art. The present invention provides an improved method for the manufacture of a more efficient coated monolithic article, which advantageously exhibits higher water resistance and improved filtration efficiency.

Summary of the Invention

[0012] According to a first aspect of the present invention, there is provided a method of forming an inorganic oxide coating on a monolithic article for the treatment of exhaust gas, the method comprising: providing a porous monolithic article comprising a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface; spraying inorganic particles and a silicone resin as a dry particle aerosol onto the gas contact surface to form a coating layer; firing the coating layer to provide a coated monolithic article.

[0013] In a further aspect, there is provided an unfired porous monolithic article for use in forming a monolithic article for the treatment of exhaust gas, the monolithic article comprising: providing a porous monolithic article comprising a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface; A method can be obtained by a method including the step of spraying inorganic particles and a silicone resin as a dry particle aerosol onto a gas contact surface to form a coating layer.

[0014] In another aspect, a coated monolithic article for the treatment of exhaust gas obtainable by the method described herein with respect to the first aspect is provided. The coated monolithic article has improved water resistance compared to known coated monolithic articles, and as described herein, the article is preferably a catalytic article and / or a wall flow filter. Such articles are particularly suitable for the treatment of exhaust gas, especially vehicle exhaust gas. The inventors have found that highly cross-linked silicon dioxide present in the coated monolithic article is very effective in binding inorganic particles to the gas contact surface of the channels of the porous monolithic article.

[0015] In a further aspect of the invention, a vehicle exhaust system including a coated monolithic article is provided.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] According to a first aspect of the present invention, a method for forming an inorganic oxide coating on a monolithic article for the treatment of exhaust gas is provided, the method comprising providing a porous monolithic article including a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface, spraying inorganic particles and a silicone resin as dry particle aerosols onto a gas contact surface to form a coating layer; firing the coating layer to provide a coated monolithic article.

[0018] Now, the present disclosure will be further described. In the following sections, different aspects / embodiments of the present disclosure are defined in more detail. Each aspect / embodiment so defined can be combined with any other aspect / embodiment or aspects / embodiments unless otherwise explicitly indicated. In particular, any feature shown as being preferred or advantageous can be combined with any other feature or features shown as being preferred or advantageous.

[0019] The method of the present invention forms an inorganic oxide coating on a monolithic article, thereby forming a coated monolithic article. Thus, a monolithic article having an inorganic oxide coating is suitable for use in the treatment of exhaust gases. The exhaust gas may preferably be a lean burn exhaust gas from a vehicle engine, and the exhaust gas is treated by passing the exhaust gas through the channels of the monolithic article, thereby bringing the exhaust gas into contact with the gas contact surfaces of the plurality of channels.

[0020] This method includes providing a porous monolithic article including a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface. Porous monolithic articles are well known in the art. Porous monolithic articles may also be referred to as substrates, preferably honeycomb substrates, preferably ceramic honeycomb substrates. Such a substrate includes a plurality of channels suitable for the passage of exhaust gas. The plurality of channels are parallel and extend from an inlet end (or first end) to an outlet end (or second end), i.e., the channels extend axially through the article. Typically, the channels have a square cross-section, but any known monolithic design can be used.

[0021] The porous monolithic article / substrate may be formed from, for example, sintered metal, ceramic, or metal fibers. For example, the article may be formed from cordierite, various forms of silicon carbide, or aluminum titanate.

[0022] In some embodiments, the monolithic article is a monolithic filter. The monolithic filter is particularly preferably a wall flow filter (which may also be known as a wall flow monolithic article). Wall flow filters are well-known and typically, adjacent channels are alternately blocked at each end of the monolithic article, and in use, the exhaust gas passes along the inlet channels (i.e., the channels that are open at the inlet end of the monolithic article to receive the exhaust gas) and through the channel walls into the adjacent outlet channels (i.e., the channels that are open at the outlet end of the monolithic article).

[0023] The channel walls have a pore distribution that provides the porosity required for the monolithic article, and the average dimension of the pores in the channel walls, e.g., the filter walls, is typically in the range of 5 - 50 μm. Each channel has a gas contact surface. That is, each channel has a surface suitable for contacting, for example, exhaust gas in use. The surface may be provided by the channel wall surface and / or the pores contained therein.

[0024] In another particularly preferred embodiment, the porous monolithic article is a catalyst article (i.e., a catalytic article). Catalytic porous monolithic articles are well-known and exhibit catalytic functions such as oxidation, NO x trapping, or selective catalytic reduction activity. The porous monolithic article may include one or more washcoats, preferably catalytic washcoats. A washcoat is a composition that coats and penetrates the porous structure of the article. Then, the article including one or more washcoats is preferably fired as described herein before spraying inorganic particles and silicone resin onto the channels. Thus, the catalytic article may be, for example, a Three-Way Catalyst (TWC), NO xAn absorbent, an oxidation catalyst, a selective reduction catalyst (SCR), a hydrocarbon trap, and lean NO x can be selected from the catalysts. The three-way catalyst (TWC) may contain one or more platinum group metals, particularly those selected from the group consisting of platinum, palladium, and rhodium.

[0025] In a particularly preferred embodiment, the porous monolithic article is a catalytic wall flow filter. As a result, the article can be, for example, a catalyzed soot filter (CSF), a selective catalytic reduction filter (SCRF), a lean NO x trap filter (LNTF), a gasoline particulate filter (GPF), an ammonia slip catalyst filter (ASCF), or a combination of two or more thereof (e.g., a filter including a selective catalytic reduction (SCR) catalyst and an ammonia slip catalyst (ASC)).

[0026] The shape and dimensions of the filter, such as the channel wall thickness and its porosity and other characteristics, may vary depending on the intended use of the filter. The filter can be configured to be used with an internal combustion engine to filter the exhaust gas emitted by the internal combustion engine. The internal combustion engine can be a gasoline spark ignition engine. However, the filter finds particular use when configured to be used with an internal combustion engine in the form of a diesel or gasoline engine.

[0027] The wall flow filter can be an asymmetric wall flow filter. The design of an asymmetric wall flow filter is known, for example, from WO 2005 / 030365, which discloses a honeycomb filter comprising an array of interconnected porous walls defining an array of a first channel and a second channel. The first channel is adjacent to the second channel on its side and has a larger hydraulic diameter than the second channel. The first channel has a square cross-section, and the corners of the first channel have a shape such that the thickness of the porous wall adjacent to the corner of the first channel is comparable to the thickness of the porous wall adjacent to the edges of the first and second channels. In use, the first channel having the larger hydraulic diameter is disposed on the upstream side. Society of Automotive Engineers SAE Technical Paper Series 2007-01-0656 states that "due to the gas contraction and expansion at the inlet and outlet of the filter channels, [in a catalyzed asymmetric cell technology (ACT) wall flow filter] there is a pressure loss penalty in the clean state of the ACT design. However, the filter is only in a completely clean (fully regenerated) state for a very short time during operation on a vehicle." International Publication No. WO 2005 / 030365 also describes that the advantages of an asymmetric filter design include an increase in the effective surface area available for collecting soot and ash particles at the inlet portion of the honeycomb filter, and thus an increase in the overall storage capacity of the honeycomb filter. The common general knowledge textbook "Catalytic Air Pollution Control - Commercial Technology", 3rd Edition, Ronald M. Heck et al, John Wiley & Sons, Inc., Hoboken, N.J., USA (2009) pp. 338 - 340 states that "such [asymmetric filter] channel designs allow for higher ash storage capacity combined with lower backpressure after ash deposition due to the larger hydraulic diameter and larger inlet open volume. The ACT design also helps to maintain the mechanical and thermal durability of the filter."

[0028] The method further includes spraying inorganic particles and a silicone resin as dry particle aerosol onto the gas contact surface to form a coating layer. Thus, the method includes spraying dry powder (i.e., dry particles) suspended in a gas (i.e., as an aerosol) onto the gas contact surfaces of a plurality of channels on a monolithic article. Spraying of dry powder onto a monolithic article is known in the art. Suitable methods and apparatuses are described, for example, in WO 2011 / 151711 and WO 2021 / 028692.

[0029] The inventors have surprisingly found that by including a silicone resin in the dry powder for forming the dry particle aerosol, the resulting article exhibits significantly improved water resistance and helps the adhesion of inorganic particles to the surface of the channel walls. The improved retention of inorganic particles has been found to improve the filtration efficiency of the article, as in a particularly preferred embodiment that takes advantage of the benefits of the monolithic filter article containing a silicone resin.

[0030] One major advantage of the present invention is that a monolithic article, for example a filter containing a catalyst within a filter wall, can be treated such that the inorganic coating does not interfere with the catalyst within and / or on the filter wall after the catalyst is supported on the filter. Furthermore, the inventors have found that the silicone resin described herein does not require high temperature treatment that can be harmful to the catalyst, enables more effective retention of inorganic particles, and allows them to adhere to the article channels.

[0031] Silicone resins are known and are branched cage-like oligosiloxanes and polysiloxanes. The branches in the silicone resin result from the presence of so-called "T" and / or "Q" units in the resin, which refer to RSiO3 and SiO4 units respectively (R is an alkyl or aryl group), with further silicon units bonded to oxygen atoms. The "M" unit, i.e., the R3SiO unit, is a terminal unit where the oxygen atom provides a bond to the resin backbone. Similarly, the "D" unit, i.e., the R2SiO2 unit, provides linear bonding across two oxygen atoms. One well-known unbranched chain and linear polysiloxane is polydimethylsiloxane (PDMS, i.e., (Me2SiO) n ).

[0032] As will be appreciated, the requirement for the inorganic particles and the silicone resin to be sprayed as a dry particulate aerosol requires that the silicone resin be in the form of solid particles. Thus, in this specification, the silicone resin may sometimes be referred to as silicone resin particles. Preferably, the silicone resin is solid at room temperature (e.g., about 25 °C). Thus, the silicone resin preferably has a melting point above 25 °C, preferably above 30 °C, more preferably above 35 °C. Preferably, the melting point of the silicone resin is less than 100 °C, preferably less than 95 °C, 90 °C, 85 °C or 80 °C. Unbranched polysiloxanes such as PDMS typically have a lower melting point than the branched silicone resins. For example, the melting point of PDMS is about -40 °C. WO 2011 / 151711 discloses binding the powder in place by treating with polydimethylsiloxane that forms silica when hydrolyzed at a sufficiently high temperature.

[0033] Similarly, the inventors have found that the silicone resin preferably has a glass transition temperature (Tg) of more than 30°C, preferably more than 35°C, and / or less than 100°C, preferably less than 80°C. Without being bound by theory, the inventors believe that a silicone resin having such a melting point and / or glass transition temperature is particularly suitable for the powder coating process, i.e., particularly suitable for effectively dispersing fine particles on a monolithic article together with inorganic particles, but is low enough to enable low-temperature firing, thereby effectively and efficiently adhering the inorganic particles to the gas contact surface of the channel wall.

[0034] Preferably, the inorganic particles are selected from the group consisting of zeolites, refractory oxides, and mixtures thereof. Examples of suitable zeolites include silicate zeolites, aluminosilicate zeolites, metal-substituted aluminosilicate zeolites, AlPO, MeAlPO, SAPO, MeAPSO, and the like. In some embodiments, the first and second zeolites are independently selected from aluminosilicates, borosilicates, gallosilicates, SAPO, AlPO, MeAPSO, and MeAPO zeolites. In some embodiments, the zeolite has a framework type selected from ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AVL, AWO, AWW, BCT, BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS, SCO, CFI, SGF, CGS, CHA, CHI, CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EEI, EMT, EON, EPI, ERI, ESV, ETR, EUO, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFR, IFY, IHW, IRN, ISV, ITE, ITH, ITW, IWR, IWW, JBW, KFI, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MSO, MTF, MTN, MTT, MTW, MWF, MWW, NAB, NAT, NES, NON, NPO, NPT, NSI, OBW, OFF, OSI, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV, SBE, SBS, SBT, SFE, SFF, SFG, SFH, SFN, SFO, SFW, SGT, SOD, SOS, SSY, STF, STI, STT, TER, THO, TON, TSC, UEI, UFI, UOZ, USI, UTL, VET, WI, VNI, VSV, WIE, WEN, YUG, ZON, or combinations thereof.In some embodiments, the zeolite has a framework type selected from AEI, AFT, AFV, AFX, AVL, BEA, CHA, DDR, EAB, EEI, ERI, FAU, FER, IFY, IRN, KFI, LEV, LTA, LTN, MER, MOR, MWF, MFI, NPT, PAU, RHO, RIE, RTH, SAS, SAT, SAV, SFW, TSC, and UFI.

[0035] In another preferred embodiment, the inorganic particles can be refractory oxide particles based on oxides selected from the group consisting of alumina, silica, zirconia, ceria, chromia, magnesia, calcia, titania, and any two or more of their mixed oxides. Preferably, the refractory oxide particles include calcium aluminate, fumed alumina, fumed silica, fumed titania, fumed zirconia, fumed ceria, alumina aerogel, silica aerogel, titania aerogel, zirconia aerogel, ceria aerogel, or mixtures thereof. One or more fumed refractory powders (refractory oxide particles) can be produced by an exothermic process, such as flame pyrolysis.

[0036] An example of the inorganic particles is silicic acid.

[0037] Preferably, the inorganic particles and / or silicone resin particles have a d by volume of greater than 0.2 μm, preferably greater than 0.5 μm, and / or less than 50 μm, preferably less than 25 μm, preferably less than 20 μm, preferably less than 15 μm, preferably less than 10 μm 50 thereof.

[0038] Preferably, the dry particle aerosol is formed from a dry particle composition having a tap density of less than 1.5 g / cm 3 The dry particulate composition can be referred to as a dry particulate powder. The dry particulate composition preferably consists of inorganic particles and / or silicone resin. In some preferred embodiments, the inorganic particles have a density of 0.1 g / cm 3Having a tap density of less than (typically for fumed refractory oxides). In other preferred embodiments, the inorganic particles are 0.1 g / cm 3 greater than, preferably greater than 0.2 g / cm 3 and have a tap density. For example, zeolite particles such as Cu-substituted zeolites can preferably have a tap density of about 0.25 g / cm 3 In other preferred embodiments, inorganic particles such as refractory oxide particles are less than 1.4 g / cm 3 preferably less than 1.3 g / cm 3 preferably less than 1.2 g / cm 3 and may have a tap density. As just one example, calcium aluminate can have a tap density of about 1 g / cm 3 Thus, the inorganic particles preferably have a tap density of 0.1 g / cm 3 to 1.4 g / cm 3 preferably 0.2 g / cm 3 to 1.2 g / cm 3 Silicone resin particles can have a tap density of 0.3 g / cm 3 to 0.9 g / cm 3 preferably 0.5 g / cm 3 to 0.7 g / cm 3 The dry particulate composition comprising a mixture of inorganic particles and silicone resin can preferably have the same tap density as individually described for either the inorganic particles or the silicone resin. In some preferred embodiments, the tap density of the dry particulate composition is 0.5 to 1.4 g / cm 3 preferably 0.7 g / cm 3 to 1.2 g / cm 3 .

[0039] In a preferred embodiment, the spraying step includes a first spraying step of spraying inorganic particles as a first dry particle aerosol onto a gas contact surface to form an inorganic particle layer, and then, in a second spraying step, a second spraying step of spraying a silicone resin as a second dry particle aerosol onto the inorganic particle layer to form a coating layer. Thus, the inorganic particles are sprayed onto the channels of the monolithic article before being separately sprayed onto the channels coated with the inorganic particles by the silicone resin.

[0040] Even more preferably, a mixture of inorganic particles and a silicone resin is sprayed as a dry particle aerosol onto the gas contact surface to form a coating layer. Thus, a tight mixture of the inorganic particles and the silicone resin is coated onto the gas contact surface of the channels, strengthening the adhesion of the inorganic particles to the channel walls during the firing of the silicone resin.

[0041] When a mixture of inorganic particles and a silicone resin is sprayed as a dry particle aerosol onto the gas contact surface to form a coating layer (preferably when the dry particle composition consists of inorganic particles and a silicone resin), the weight ratio of the inorganic particles to the silicone resin in the mixture is preferably greater than 0.5 (in other words, greater than 0.5:1), preferably greater than 0.7, preferably greater than 0.9, and / or less than 4, preferably less than 3, preferably less than 2.5. For example, this ratio may preferably be about 1 or about 2. Preferably, this ratio is 0.5 to 4, preferably 0.7 to 3, preferably 0.9 to 2.5, preferably 1 to 2.

[0042] Preferably, the silicone resin has a molecular weight greater than 1,000, preferably greater than 2,000, preferably greater than 5,000, preferably greater than 10,000, and / or less than 500,000, preferably less than 200,000.

[0043] As used herein, the molecular weight is the weight average molecular weight (M measured using any conventional means in the art. Wrefers to. In some embodiments, particularly those described herein where the silicone resin contains hydroxy functional groups, the hydrogen bonds provided by the hydroxy functional groups can provide a silicone resin with a sufficiently high melting point and / or glass transition temperature, so the molecular weight may be relatively low. Thus, in some embodiments, the molecular weight of the silicone resin can be 1,000 to 10,000, preferably 1,000 to 5,000, preferably 1,200 to 3,500, for example 1,500 to 2,000. A silicone resin having a molecular weight less than 1,000 is typically a liquid and is not very suitable for dry spraying or has fewer branches than larger molecules that are thought to enhance the binding of inorganic particles to monolithic articles, so it is less preferred.

[0044] Nevertheless, the molecular weight of the silicone resin may preferably be 15,000 to 150,000, preferably 20,000 to 120,000, preferably 60,000 to 100,000. Some preferred resins have an Mw of 8,000 to 15,000, some have an Mw of 20,000 to 60,000, and others have an Mw of 80,000 to 120,000.

[0045] It is particularly preferred that the silicone resin has the formula [R x SiX y O z n , where R is an alkyl group or an aryl group, X is a functional group bonded to silicon, and z is greater than 1 and less than 2. As understood, n is large enough to provide the oligomers or polymers necessary for the silicone resin, particularly a resin that is solid at room temperature. Depending on the molecular weights of the R groups and X groups, when n is greater than 10, an M W greater than 1,000 can be achieved, when n is greater than 100, an M W greater than 10,000 can be achieved, and when n is greater than 1,000, an M W greater than 100,000 can be achieved. Thus, n may preferably be greater than 10, greater than 100, greater than 1,000.

[0046] ​ As is understood, R is an alkyl or aryl group bonded to silicon, and X is a non-hydrocarbon functional group bonded to silicon. Similarly, since silicon is a tetravalent atom, it will be understood that x + y + 2z = 4. z is less than 2. This is by providing z = 2, x and y = 0, silica (i.e., silicon dioxide, (SiO2) n ). Similarly, z is greater than 1. This is by providing z = 1, x + y = 2, a substituted polysiloxane (e.g., (RXSiO) n ) consisting of "D" units that provide a linear resin (e.g., -O-(SiRX)-O-(SiRX)-O-). One example is polydimethylsiloxane. Thus, O refers to oxygen that bridges two silicon atoms in the polymer backbone of the silicone resin.

[0047] Preferably, 0 < x + y < 2, preferably 0 < x + y ≤ 1.5, preferably 0 < x + y ≤ 1. Preferably, x, y and / or x + y are greater than 0.1, preferably greater than 0.2. In one preferred embodiment, x + y is 1, providing a silicone resin generally known as polysilsesquioxane. Preferably, y is less than 1, and / or y is less than x. Even more preferably, 2y ≤ x, preferably 5y ≤ x, preferably 10y ≤ x. In one embodiment, y is 0. For example, when the polysilsesquioxane is a polyalkylsilsesquioxane such as polymethylsilsesquioxane (MeSiO 3 / 2 ) n y is 0.

[0048] Typically, when present, X is one or more of H, hydroxy (OH), Cl, and C1-C6 alkoxy, preferably one or more of OH and C1-C6 alkoxy, and preferably, the C1-C6 alkoxy is selected from methoxy (OCH3) and ethoxy (OCH2CH3). In particularly preferred embodiments, X is one or both of OH and ethoxy. However, X may be a functional group that is a reactive functional group such as aminyl (NH2, NR2), epoxy, acrylate, and vinyl, but these are less preferred because the presence of a hydroxy group or an alkoxy group is considered to provide more effective crosslinking during firing. As described above, any oxygen present in the terminal functional group does not contribute to the "O" in the above formula that refers to the silicon crosslinking oxygen atom. z does not contribute to

[0049] The inventors have found that the silicone resins described herein provide coated monolithic articles having the advantageous benefit of improved water resistance. The silicone resins have been found to be particularly advantageous for binding inorganic particles to the monolithic articles. Without being bound by theory, the inventors believe that due to the branched structure and physical properties of the silicone resin, it is possible for the resin to first melt during the firing step described herein and then bind to (and closely adhere to or deposit thereon) the inorganic particles on the gas contact surface of the channels and then begin to cure. As the resin cures, the resin forms additional -Si-O-Si-O-Si- crosslinks / bonds and further increases its branched structure. Further, the inventors believe that such bonds can also be formed with the inorganic particles that further join the particles in place in the article, such as by forming -Si-O-Al- bonds, with the gas contact surface (i.e., the monolithic article itself). As the temperature during firing continues to rise, the R and X groups are oxidized leaving a silica (SiO2) backbone. Thus, silicon- and / or aluminum-containing inorganic particles such as zeolite, calcium aluminate, alumina, and / or silica may be preferred.

[0050] Preferably, the silicone resin has a crosslinking degree of more than 55%, preferably more than 60%, more preferably more than 65%, and / or less than 85%, preferably less than 80%.

[0051] As described herein, the silicon atoms of silicone resins such as those described by the formula [R x SiX y O z n may be in one of four coordination environments, namely SiO(R / X)3, SiO2(R / X)2, SiO3(R / X), or SiO4, known in the art as "M", "D", "T", and "Q", respectively, considering the tetravalent nature of silicon. Thus, the above formula can be described as aMbDcTdQ where a + b + c + d = 1 and the crosslinking degree is defined by [(a + 2b + 3c + 4d) / 4]*100. The relative ratios of the number of silicon atoms in each coordination environment can be determined using standard spectroscopic techniques, such as multinuclear NMR spectroscopy, particularly 29 29Si NMR spectroscopy. Alternatively, for commercially available silicone resins, the crosslinking degree may be provided in the technical data sheet.

[0052] In other words, silicon dioxide (SiO2) is completely formed from "Q" SiO4 units where each silicon atom is bonded to four connecting oxygen atoms. Thus, when d is 1, this gives a crosslinking degree of 100% to silicon dioxide. On the other hand, as an example, PDMS is entirely formed from "D" Si(Me)2O2. Thus, when b is 1, this gives a crosslinking degree of 50% to polydimethylsiloxane. As a result, the silicone resin preferably has a crosslinking degree between these two extreme values and contains a mixture of such units. Thus, the silicone resin can preferably consist of MDT units, MTQ units, DTQ units or DT units.

[0053] ​Preferably, R is one or more of C1-C6 alkyl or phenyl groups. Due to the oligomeric or polymeric nature of the silicone resin, the number of monomer units is typically large. There can be many examples of both R groups and X groups, and as a result, a silicone resin as described by a single monomer unit can contain multiple different groups. As described above regarding the functional group X, X may preferably be both OH and ethoxy. Similarly, R may contain two or more of C1-C6 alkyl and / or phenyl. Thus, when R is described by two or more groups such as R’ and R’’, the formula of the silicone resin is, [R’ x’ R’’ x’’ SiX y O z n where x’ + x” = x. This applies equally to the functional group X.

[0054] Preferably, R is one or more of linear or branched alkyl and phenyl, one or more of linear alkyl and phenyl, more preferably one or both of methyl and phenyl. In some preferred embodiments where R is both methyl and phenyl, the phenyl to methyl ratio is less than 2, preferably less than 1.5, preferably less than 1, preferably less than 0.5. In some embodiments, R is phenyl. More preferably, R is methyl (i.e., the ratio is 0).

[0055] Smaller organic groups such as methyl, methoxy and ethoxy for the R and X groups are particularly preferred as they increase the SiO2 content of the starting silicone resin and reduce the weight loss during firing. Furthermore, the smoke emission and loss of volatile substances (such as H2O, CO2 and other volatile organic compounds) during firing are reduced.

[0056] ​Therefore, the silicon dioxide content of the silicone resin is preferably more than 50% by weight, preferably more than 60% by weight, preferably more than 70% by weight, preferably more than 80% by weight. The silicon dioxide content can also be referred to as the ash content, which is the weight of the product remaining after complete oxidation of the starting silicone resin by weight (in this case, the product is silicon dioxide). For example, the oxidation may be carried out at 1000 °C. Alternatively, the silicon dioxide content may be obtainable from the technical data sheet of a suitable commercially available silicone resin. Alternatively, the silicon dioxide content can be calculated based on the complete oxidation of silicon to silicon dioxide and the chemical formula of the resin. As a mere example, polymethylsilsesquioxane (MeSiO 3 / 2 ) n has a formula weight of 66.1 and a silicon atomic weight of 28.1, and is about 42.7% by weight of silicon based on the weight of the silicone resin. Silicon dioxide has a formula weight of 60.1, which is about 2.1 times greater than the formula weight of silicon. Therefore, the silicon dioxide content of polymethylsilsesquioxane is 2.1 * 42.7 = 89.7% by weight (i.e., based on the weight of the silicone resin).

[0057] One particularly preferred silicone resin for use in the method of the present invention is a highly cross-linked ethoxylated poly(dimethylsiloxane) having a silicon dioxide content of about 82% by weight and a melting point of 35 °C to 55 °C.

[0058] The method further includes firing the coating layer to provide a coated monolithic article. That is, the method includes firing a porous monolithic article having inorganic particles and a silicone resin sprayed on the gas contact surface of a plurality of channels.

[0059] Preferably, the firing step includes heating to a temperature of at least 200°C, preferably at least 300°C, more preferably at least 400°C, and / or a temperature of up to 600°C, preferably up to 550°C, more preferably up to 530°C. Thus, the firing preferably includes heating to a temperature of 200°C to 600°C, preferably 300°C to 550°C, preferably 400°C to 530°C, more preferably 400°C to 500°C, and even more preferably 400°C to 450°C.

[0060] Such temperatures have been found to be most suitable for forming an effective binder that imparts its advantageous water resistance to the coated monolithic article. Such temperatures are particularly advantageous when the porous monolithic article is a catalytic article such as a catalytic wall flow filter, since the silicone resin can be fired to crosslinked silicon dioxide without adversely affecting the catalytic efficiency (i.e., without degrading the catalytic article). Linear siloxanes such as PDMS not only effectively bind the inorganic particles and do not provide the branching necessary for attachment to the article, but also require temperatures above 550°C, and further above 600°C, for complete decomposition to SiO2. Ideally, the firing temperature is kept as low as possible to reduce the potential to affect the catalytic activity of any catalyst present in the monolithic article.

[0061] In a further aspect of the present invention, there is provided an unfired porous monolithic article for use in forming a monolithic article for the treatment of exhaust gases, the unfired porous monolithic article comprising a plurality of channels and a dry particle composition comprising inorganic particles and a silicone resin, the dry particle composition being located within the channels and / or pores of the aforementioned unfired porous monolith.

[0062] Therefore, the unfired porous monolith article is suitable for use in forming a monolith article that can be used for the treatment of exhaust gas. Preferably, the unfired porous monolith article is for use in forming a monolith article, and preferably, the monolith article is for use in the treatment of exhaust gas. The unfired porous monolith article includes a plurality of channels and a dry particulate composition containing inorganic particles and a silicone resin, as described herein with respect to the first aspect. The dry particulate composition is located within the channels and / or pores of the unfired porous monolith, i.e., the composition coats the gas contact surface of the channels.

[0063] The unfired porous monolith article containing the dry particulate composition may be formed into a monolith article by firing, thereby decomposing the silicone resin of the dry particulate composition into silicon dioxide, preferably by heating to the temperature described herein.

[0064] Preferably, the mass filling amount of the dry particulate composition is less than 50 g / L, preferably less than 30 g / L. Preferably, the mass filling amount of the inorganic particles is at least 5 g / L and / or less than 25 g / L. Preferably, the mass filling amount of the silicone resin is at least 5 g / L and / or less than 25 g / L. In a preferred embodiment, the mass filling amount of the inorganic particles is 5 g / L to 15 g / L, and / or the mass filling amount of the silicone resin is 5 g / L to 15 g / L. As an example, when the weight ratio of inorganic particles to silicone resin is 1:1, the filling amount of the inorganic particles may be 10 g / L, and the filling amount of the silicone resin may be 10 g / L, and the total filling amount of the dry particulate composition is 20 g / L. As an example, when the ratio is 2:1, the inorganic particle filling amount may be 10 g / L, the silicone resin filling amount may be 5 g / L, giving a total filling amount of 15 g / L.

[0065] In a further aspect, there is provided an unfired porous monolith article for use in forming a monolith article for the treatment of exhaust gas, the monolith article being Providing a porous monolithic article comprising a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface; Forming a coating layer by spraying inorganic particles and a silicone resin as a dry particle aerosol onto the gas contact surface. The method can be obtained by a method comprising:

[0066] In another aspect, a coated monolithic article for the treatment of exhaust gas obtainable by the method described herein with respect to the first aspect is provided. The coated monolithic article has improved water resistance compared to known coated monolithic articles, and as described herein, the article is preferably a catalyst article and / or a wall flow filter. Such articles are particularly suitable for the treatment of exhaust gas, especially vehicle exhaust gas. The inventors have found that highly cross-linked silicon dioxide present in the coated monolithic article is very effective in binding inorganic particles to the gas contact surface of the channels of the porous monolithic article.

[0067] In a further aspect of the invention, a vehicle exhaust system comprising a coated monolithic article is provided.

[0068] Example A Comparative Sample A-1 A GPF filter having a washcoat loading of 50 g / L was prepared from a cordierite substrate, 300 / 8, 1.3L type according to the procedure of Example 1 of U.S. Patent Application Publication No. 20200306692 (A1).

[0069] Comparative Sample A-2 A GPF filter was prepared in the same manner as Comparative Sample A-1.

[0070] Next, 0.5 g / L of fumed alumina powder (d 50 = 6 μm, d 90was filled. The diameter of the flow conduit was the same as the inlet surface of the filter. 550 m 3 / h of the primary gas flow of air was passed through the filter using a downstream eddy blower. The back pressure was monitored by a Wika (registered trademark) P30 pressure transmitter placed under the filter. The refractory powder was dispersed in the primary gas flow using a STAR Professional gravity-fed spray gun 1.4 mm, part number STA2591100C. 15 The STAR Professional gravity-fed spray gun was mounted 100 mm from the inlet surface of the filter. The back pressure was used to determine the stop point of the spraying of the refractory powder. After the filling was completed, the filter was fired at 500 °C for 1 hour.

[0071] Sample A-1 Sample A-1 was prepared in the same manner as Comparative Sample A-2, except that it was filled with a mixture of chabazite zeolite powder (d 50 = 2.4 μm, d 90 = 4.1 μm) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C to 55 °C, d 50 = 34 μm, d 90 = 115 μm) in a weight ratio of 2:1. The powder filling amount before firing was 8 g / L.

[0072] Sample A-2 A GPF filter with a washcoat filling amount of 100 g / L was prepared from a cordierite substrate, 300 / 8, 1.3 L type according to the procedure of Example 1 of US Patent Application Publication No. 20200306692 (A1).

[0073] Sample A-2 was composed of calcium aluminate powder (d 50 = 53 μm, d 90 = 118 μm) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C to 55 °C, d 50 = 34 μm, d 90A mixture with a weight ratio of 1:1 with (d = 115 μm) was prepared by filling it according to the addition procedure of Comparative Sample A-2. The powder filling amount was 13.8 g / L before firing.

[0074] Sample A-3 Sample A-3 was prepared in the same manner as Comparative Sample A-2, except that it was filled with a mixture having a weight ratio of 1:1 of beta zeolite powder (d 50 = 6.4 μm, d 90 = 41 μm) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82% by weight, melting point 35°C to 55°C, d 50 = 34 μm, d 90 = 115 μm). The powder filling amount before firing was 20.7 g / L.

[0075] Filtration test On the engine bench of the RDE cycle, the samples were tested for filtration efficiency for both fresh ones and those after one set of cold start idle tests. Here, the filter samples were subjected to 50 cold start / idle repetitions in which water accumulated on the filter. The results are shown in Table 1. The filtration efficiency in Table 1 is the soot particulate matter removed over the entire driving cycle.

[0076]

Table 1

[0077] The results show that for Samples A-1, A-2, and A-3, the decrease in filtration efficiency from the fresh state to 50× cold start is much lower compared to Comparative Sample A-2.

[0078] Example B Comparative Sample B-1 An SCRF filter with a washcoat loading of 116 g / L was prepared from a silicon carbide (SiC) substrate, NGK MSC-18 300 / 12, 3L type, according to the procedure of Example 1 of U.S. Patent No. 8,789,356. The washcoat contains copper-supported AEI zeolite, zirconium acetate, and an alumina binder manufactured by Valiant (zeolite to alumina weight ratio = 90:10, zirconium = 40 g / ft 3 ). The inlet coating length is about 20% of the substrate length. The outlet coating length is about 80% of the substrate length. The coated filter was dried at 110 °C and calcined at 500 °C for 1 hour.

[0079] Comparative sample B-2 An SCRF filter was prepared in the same manner as Comparative sample B-1. Then, using the method and apparatus of International Publication No. 2021 / 028692, fumed alumina powder (d 50 = 6 μm, d 90 = 12 μm) was filled into the prepared SCRF filter. The diameter of the flow conduit was the same as the inlet surface of the filter. A primary gas flow of air at 300 m 3 / h was passed through the filter using a downstream eddy blower. The back pressure was monitored by a Wika® P30 pressure transmitter placed under the filter. The powder was dispersed into the primary gas flow using a STAR Professional gravity feed spray gun 1.4 mm, part number STA2591100C. The 15 STAR Professional gravity feed spray gun was mounted 100 mm from the inlet surface of the filter. The back pressure parameter was used to determine the stopping point of the refractory powder spraying. The powder loading before firing was 4 g / L. After the filling was completed, the filter was calcined at 500 °C for 1 hour.

[0080] Sample B-1 Sample B-1 is spray-dried Cu-chabazite (3.3 wt% Cu, d 90 = 10 - 12 μm) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C - 55 °C, d 50 = 34 μm, d90 It was prepared in the same manner as Comparative Sample B-2, except that it was filled with a 1:1 weight ratio mixture with 90 (d = 115 μm). The powder filling amount before firing was 15 g / L.

[0081] Sample B-2 Sample B-2 was prepared in the same manner as Comparative Sample B-2. A 15 g / L mixture of spray-dried Cu-chabazite (3.3 wt% Cu, d 90 = 10 - 12 μm) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35°C to 55°C, d 50 = 34 μm, d 90 = 115 μm) in a weight ratio of 1:1 was filled, placed in an oven at 110°C for 15 minutes, and then cooled to room temperature. Then, it was filled with 5 g / L of a 1:1 weight ratio mixture of chabazite zeolite (d 90 = 4.9 μm) and the same silicone resin powder. The total powder filling amount before firing was 20 g / L.

[0082] Filtration efficiency The filter samples were tested under the following test conditions using the Cambustion® Diesel Particulate Filter Testing System available from Cambustion Ltd (Cambridge, UK). a) Stabilization - Mass flow rate of 250 kg / hour, 50°C, 5 minutes b) Warm-up - Mass flow rate of 250 kg / hour, 240°C, 5 minutes c) Weighing - Remove the filter from the rig and weigh it. d) Warm-up - Return the filter to the rig. Mass flow rate of 250 kg / hour, 240°C, 5 minutes e) Filling stage - Mass flow rate of 250 kg / hour, 240°C, Filling rate: 2 g / hour until a soot filling amount of 2 g / L is reached. f) Weighing - Remove the filter from the rig and weigh it.

[0083] The fuel used during the test was Carcal RF-06-08B5.

[0084] During the test, the particle counter continuously samples the sample downstream of the filter. Immediately before and immediately after a batch of the filter is tested, an "upstream" test is performed on the rig to enable the particle counter to sample the raw soot generation from the rig. The upstream test is 20 minutes in length and uses the same conditions as the above filling stage. The filtration efficiency is obtained by comparing the average of the two upstream tests (before and after the filter test) with the data from the filling stage of the filter test.

[0085] Filter both the fresh sample and the sample after the water immersion treatment. In the water immersion treatment, the filter was immersed in water for 30 seconds and then dried at 110 °C for 0.5 hour.

[0086] The filtration efficiency data collected 50 seconds after the start of the test are summarized in Table 2. According to the results, Samples B-1 and B-2 filled with a mixture of zeolite powder and silicone resin showed a significant improvement in water resistance compared to Comparative Sample 2.

[0087]

Table 2

[0088] Example C Comparative Sample C-1 The CSF filter was prepared from a silicon carbide filter substrate, 300 / 6, 2.44L type. The substrate was washcoated with a CSF catalyst composition having an alumina support with a PGM loading of 3 g / ft 3 , and a Pt:Pd weight ratio of 2:1, and a washcoat loading of 0.2 g / in 3 .

[0089] Sample C-1 A CSF filter was prepared in the same manner as Comparative Sample C-1.

[0090] Alumina (d 50 = 30 μm, density = 200 g / L) and highly crosslinked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C to 55 °C, d50 = 34 μm, d 90 A mixture with a weight ratio of 1:1 with ( = 115 μm) was applied to the CSF filter using the method and apparatus described in International Publication No. 2021 / 028692. The diameter of the flow conduit was the same as the inlet surface of the filter. The mixed powder was applied under a continuous vacuum creating an air flow of approximately 13 m / s. The back pressure was monitored by a Wika® P30 pressure transmitter placed under the filter. The powder was dispersed into the primary gas stream using a STAR Professional gravity feed spray gun 1.4 mm, part number STA2591100C. The 15 STAR Professional gravity feed spray gun was mounted 100 mm from the inlet surface of the filter. The back pressure was used to determine the stopping point of the spraying of the refractory powder. The filter was filled with 20 g / L of powder. The prepared filter was fired in air at 500 °C for 1 hour.

[0091] Sample C-2 Sample C-2 was prepared in the same manner as Sample C-1, except that a mixture with a weight ratio of 1:1 of boehmite (d 50 = 30 μm, density = 500 g / L) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C to 55 °C, d 50 = 34 μm, d 90 = 115 μm) was applied to the filter. The filter was filled with 20 g / L of powder. Next, the filter thus prepared was fired in air at 500 °C for 1 hour.

[0092] Sample C-3 Sample C-3 was prepared in the same manner as Sample C-1.

[0093] Sample C-4 Sample C-4 was prepared in the same manner as Sample C-2.

[0094] Sample C-5 Sample C-5 is silicic acid (80 mesh) and highly cross-linked ethoxylated poly(dimethylsiloxane) powder (silicon dioxide content 82 wt%, melting point 35 °C to 55 °C, d 50 = 34 μm, d90 Sample C-1 was prepared in the same manner except that a mixture with a weight ratio of 1:1 with ( = 115 μm) was applied to the filter. The filter was filled with 20 g / L of powder. Next, the filter thus prepared was calcined in air at 500 °C for 1 hour.

[0095] Back pressure Samples C-1 and C-2 were completely immersed in a container of about 6 L of deionized water for about 10 seconds, then taken out of the water, the parts were shaken to remove excess water, and dried in an oven at 115 °C for about 45 minutes.

[0096] Using Samples C-1 and C-2, a cold flow back pressure test was conducted before and after the water immersion treatment at a flow rate of 600 m 3 / h. The results are shown in Table 3.

[0097]

Table 3

[0098] Table 3 shows that water immersion caused only slight changes in the back pressure of Samples C1 and C-2.

[0099] Filtration efficiency The filtration test was carried out using a commercially available Cambustion diesel particulate generator (DPG) rig, with an upstream PN baseline used, and subsequently, as described in Example B, downstream CSF post-measurements were taken during the test, enabling the filtration efficiency to be calculated for each example.

[0100] Figure 1 compares the filtration efficiency data of Comparative Sample C-1, fresh Sample C-1, and Sample C-1 after water immersion treatment.

[0101] Figure 2 compares the filtration efficiency data of Comparative Sample C-1, fresh Sample C-2, and Sample C-2 after water immersion treatment.

[0102] Figures 1 and 2 show that much higher filtration efficiency was achieved by adding refractory oxide powder to the CSF filter. Only a slight decrease in filtration efficiency was observed after samples C-1 and C-2 were submerged in water.

[0103] Gas abrasion test For samples C-3, C-4, and C-5, a gas abrasion test was carried out using a high-pressure air nozzle. The high-pressure air nozzle operated at a flow rate of 425 L / min, at a distance of 0.5 inches from the filter surface, and moved across the filter surface at 6.7 mm / s in a zigzag pattern over the entire filter surface. Abrasion treatment was performed on both the inlet and outlet surfaces of the filter. After drying in an oven at 115 °C for 30 minutes before and after the abrasion treatment, the samples were weighed.

[0104] For samples C-3 and C-4, the cold flow backpressure was measured before and after water immersion treatment at a flow rate of 600 m 3 / h. The results are shown in Table 4.

[0105] [Table 4]

[0106] Figure 3 compares the filtration efficiency data of fresh sample C-5 and sample C-5 after abrasion treatment. Only a slight decrease in filtration efficiency was observed after sample C-5 was subjected to abrasion treatment.

[0107] As used herein, the term "dry powder" refers to a particulate composition that is not suspended or dissolved in a liquid. This does not necessarily mean that all water molecules are completely absent. The dry powder is preferably free-flowing.

[0108] As used herein, the term "tap density" refers to the tap density of a powder measured according to Method 1 of Section 2.9.35 of the European Pharmacopoeia 7.0 with 1250 taps.

[0109] As used herein, the term "g / L" (grams / liter) refers to the mass of the dry powder divided by the volume of the filter.

[0110] As used herein, the terms "loading" and "mass loading" when referring to the amount of powder refer to the mass of the powder added to the filter and can be measured by weighing the filter before and after adding the powder to the filter.

[0111] As used herein, the term "d 50 (by volume)" refers to the d 50 (by volume) measurement obtained by a Malvern Mastersizer® 3000 with an Aero s dispersion unit available from Malvern Panalytics Ltd, (Malvern, UK). Dispersion conditions: air pressure = 2 barg, feed rate = 65%, hopper gap = 1.2 mm. Set the refractive index and absorption parameters according to the instructions provided in the Malvern Mastersizer® 3000 User Manual.

[0112] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The use of the term "comprising" is intended to be interpreted as including such features but not excluding others, and is also intended to include options of features that are necessarily limited to what is described. In other words, this term also includes, unless the context clearly dictates otherwise, "consisting essentially of" (which is intended to mean that certain additional components may exist provided that they do not substantially affect the essential characteristics of the described features) and "consisting of" (which is intended to mean that when the components are expressed as percentages by their proportions, they total 100%, while accounting for any inevitable impurities but not allowing other features).

[0113] The foregoing detailed description is provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments shown herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method for forming an inorganic oxide coating on a monolithic article for the treatment of exhaust gas, comprising: providing a porous monolithic article comprising a plurality of channels for the passage of exhaust gas, each channel having a gas contact surface; spraying inorganic particles and a silicone resin as a dry particle aerosol onto the gas contact surface to form a coating layer; firing the coating layer to provide a coated monolithic article.

2. The method according to claim 1, wherein the monolithic article is a monolithic filter and / or a catalyst article.

3. The method according to claim 1 or 2, wherein: (i) the inorganic particles are sprayed onto the gas contact surface as a first dry particle aerosol to form an inorganic particle layer, and then the silicone resin is sprayed onto the inorganic particle layer as a second dry particle aerosol to form the coating layer, or (ii) a mixture of the inorganic particles and the silicone resin is sprayed onto the gas contact surface as a dry particle aerosol to form the coating layer.

4. The method according to claim 1, wherein the silicone resin has a molecular weight of more than 1,000 and / or less than 500,000.

5. The method according to claim 1, wherein the silicone resin has a glass transition temperature (Tg) of more than 30°C and / or less than 100°C.

6. The method according to claim 1, wherein the silicone resin has the formula [RxSiXyOz]n, wherein R is alkyl or aryl, X is a functional group bonded to silicon, and z is greater than 1 and less than 2.

7. The method according to claim 6, wherein y is less than 1 and / or y is less than x.

8. The method according to claim 6 or 7, wherein the silicone resin has a degree of crosslinking of more than 55% and / or less than 85%.

9. R is C １ -C ６ The method according to claim 6, wherein R is one or more of alkyl and phenyl.

10. X is one or more of H, OH, Cl and C １ -C ６ The method according to claim 6, wherein X is one or more of alkoxy.

11. The method according to claim 1, wherein the silicon dioxide content of the silicone resin is more than 50% by weight.

12. The method according to claim 1, wherein the inorganic particles are selected from the group consisting of zeolite, refractory oxide, and mixtures thereof.

13. The method according to claim 12, wherein the inorganic particles are refractory oxide particles including calcium aluminate, fumed alumina, fumed silica, fumed titania, fumed zirconia, fumed ceria, alumina aerogel, silica aerogel, titania aerogel, zirconia aerogel, ceria aerogel, or mixtures thereof.

14. The method according to claim 1, wherein the inorganic particles have a d by volume of more than 0.2 μm and / or less than 50 μm. ５０ The method according to claim 1, having.

15. The method according to claim 1, wherein the firing includes heating to a temperature of at least 200 °C and / or a maximum temperature of 600 °C.

16. The method according to claim 1, wherein the monolithic article contains one or more platinum group metals.

17. The dry particle aerosol is 1.5 g / cm ３The method according to claim 1, formed from a dry particle composition having a tap density of less than.

18. A mixture of the inorganic particles and the silicone resin is sprayed onto the gas contact surface as a dry particle aerosol to form the coating layer, and in the mixture, the weight ratio of the inorganic particles to the silicone resin is greater than 0.5 and / or less than 4. The method according to claim 1.

19. An unfired porous monolith article for use in forming a monolith article for the treatment of exhaust gases, the unfired porous monolith article comprising a plurality of channels and a dry particle composition comprising inorganic particles and a silicone resin, the dry particle composition being located within the channels and / or pores of the unfired porous monolith. Unfired porous monolith article.

20. The unfired porous monolith article according to claim 19, wherein the mass filling amount of the dry particle composition is less than 50 g / L.

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