Methods of treating a porous ceramic body with inorganic particles

Abstract

Methods for providing inorganic deposits on a porous surface of a substrate, including atomizing a suspension comprised of inorganic particles, a binder precursor, a silane cross-linker, and a liquid, to form an aerosol of droplets; depositing the droplets into or onto the porous substrate; and forming a silane binder in situ on the porous substrate from the binder precursor provided by the droplets, thereby binding the inorganic particles to the porous substrate.

Description

METHODS OF TREATING A POROUS CERAMIC BODY WITH INORGANIC PARTICLESCross Reference to Related ApplicationBACKGROUND

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Serial No. 63 / 602,907, filed on November 27, 2023, the content of which is relied upon and incorporated herein by reference in its entirety.Field

[0002] The present specification relates to methods of treating a porous ceramic body with inorganic particles via sol-gel.Technical Background

[0003] Wall-flow filters are employed to remove particulates from fluid exhaust streams, such as from combustion engine exhaust. Examples include diesel particulate filters used to remove particulates from diesel engine exhaust gases and gasoline particulate filters (GPF) used to remove particulates from gasoline engine exhaust gases. Exhaust gas to be filtered enters inlet cells and passes through the cell walls to exit the filter via outlet channels, with the particulates being trapped on or within the inlet cell walls as the gas traverses and then exits the filter.SUMMARY

[0004] Aspects of the disclosure pertain to methods of depositing inorganic particles into or onto a filter body such as onto a surface, such as surfaces of porous ceramic honeycomb filter bodies, as well as the porous filter bodies containing the inorganic particles. In one or more aspects the methods comprise the use of a sol-gel process, and in particular aspects a one-pot sol-gel process is advantageously utilized.

[0005] In various aspects, methods are disclosed herein which comprise a process, preferably a one pot sol-gel process, for formulating, or generating, an alumina suspension, and methods of applying the suspension to porous ceramic monoliths in the form of droplets of thesuspension which contain inorganic particles, preferably inorganic refractory particles, such as metal oxide particles. Such suspensions are useful for depositing a high filtration efficiency “membrane” of particles, preferably nanoparticles or microparticles, onto a porous ceramic honeycomb body such as a particulate filter body. Exemplary alumina suspensions disclosed herein can comprise a mixture of (i) alumina slurry, (ii) methyl trialkoxysilane such as methyltrimethoxysilane (MTMS) as a precursor or source of in-situ generated binder and (iii) an organic solvent such as ethanol, methanol, or isopropanol. The suspension composition can be prepared via one pot sol-gel process using organic or inorganic acid as catalyst. A controlled amount of the suspension can be applied to the internal walls of a porous ceramic honeycomb structured body via aerosol deposition to form an inorganic layer of the inorganic particles, or a “membrane”, which enhances the filtration capabilities of a particulate filter comprising such porous ceramic body. The methyl trialkoxy silane can serve as a binder precursor, such that the methyl trialkoxysilane can be cured to bind the particles to the porous ceramic body, or to other particles, or both, thus providing an in-situ formed binder.

[0006] In various aspects, methods are disclosed herein for providing inorganic particle deposits, such as refractory oxide nanoparticles, on a surface, such as a porous surface of a substrate, such as a porous substrate having interconnected pores that permit gas flow therethrough.

[0007] In aspects disclosed herein, the porous substrate comprises a porous ceramic body. In various aspects, the porous ceramic body comprises a honeycomb structure. In embodiments, the honeycomb structure comprises a plurality of intersecting walls forming a plurality of cells defining a plurality of channels extending from one of the honeycomb structure to an opposite end of the honeycomb structure. In embodiments, at least some of the channels are plugged with a sealing material, or plugging material. In aspects disclosed herein, the method does can further comprise directing the droplets toward the porous ceramic body, wherein the directing comprises carrying the droplets by a carrier gas which passes through at least some of the walls to deposit at least some of the inorganic particles in the droplets by filtration, that is a filtration deposition process.

[0008] As used herein, the loading of the inorganic particles is reported in g / L, which is grams per overall exterior dimension volume of the honeycomb body in liters.

[0009] Additional features and advantages will be set forth in the detailed description, which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, comprising the detailed description, which follows, the claims, as well as the appended drawings.

[0010] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 schematically illustrates a process of depositing inorganic particles onto a surface as disclosed herein.

[0012] FIG. 2 schematically illustrates an apparatus for depositing inorganic particles onto honeycomb filter bodies.

[0013] FIG. 3 schematically illustrates processing steps as disclosed herein for forming a sol-gel suspension suitable for aerosol deposition.

[0014] FIG. 4 lists an exemplary composition of an alumina aerosol suspension as disclosed herein.

[0015] FIG. 5 lists process deposition conditions used for treating comparative samples with agglomerates which contain a siloxane binder.

[0016] FIG. 6 lists filtration efficiency data for the comparative samples with agglomerates which contain a siloxane binder showing the inorganic particle loading, the filtration efficiency as-deposited, the filtration efficiency after curing, filtration efficiency at 650° C, filtration efficiency after exposure to a water test, and the decrease in filtration efficiency due to exposure to the water test.

[0017] FIG. 7 lists the various results parameters such as appearing in FIG. 6 and corresponding to Example 1 prepared as disclosed herein.

[0018] FIG. 8 lists the various results parameters such as appearing in FIG. 7 and corresponding to Example 2, an additional Example similar to Example 1 and conducted for repeatability.

[0019] FIG. 9 graphically shows plots of fdtration efficiency for two porous ceramic honeycomb filter bodies with a sol-gel process as disclosed herein as well as for a comparative filter body treated with agglomerates.

[0020] FIG. 10 graphically shows plots of loss in filtration efficiency after water exposure for two porous ceramic honeycomb filter bodies with a sol-gel process as disclosed herein as well as for a comparative filter body treated with agglomerates.DETAILED DESCRIPTION

[0021] Reference will now be made in detail to embodiments of methods for forming honeycomb bodies comprising a porous honeycomb body comprising deposits on, or in, or both on and in, the porous ceramic walls of the honeycomb body matrix, embodiments of which are illustrated in the accompanying drawings. In embodiments the honeycomb body matrix is a honeycomb structure such as a monolithic honeycomb, for example as produced via extrusion through a honeycomb die; or in other embodiments the honeycomb body matrix comprises two or more blocks or segments of honeycomb matrix which are included or bound together such as by cement. Deposits may comprise material that was deposited into the honeycomb body, as well as compounds that may be formed, for example, by heating, from one or materials that were deposited. For example, a binder material may be transformed by heating and / or which may be eventually burned off or volatilized, while an inorganic component (such as alumina and / or silica) remains contained within the honeycomb filter body. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.Definitions

[0022] As used in this specification and the appended claims, the singular forms "a", "an", and "the" encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and / or" unless the content clearly dictates otherwise.

[0023] As used herein, "have", "having", "include", "including", "comprise", "comprising" or the like are used in their open-ended sense, and generally mean "including, but not limited to".

[0024] A "honeycomb body," as referred to herein, comprises a ceramic honeycomb structure of a matrix of intersecting walls that form cells which define channels. The ceramic honeycomb structure can be formed, extruded, or molded from a plasticized ceramic or ceramic-forming batch mixture or paste. A honeycomb body may comprise an outer peripheral wall, or skin, which was either extruded along with the matrix of walls or applied after the extrusion of the matrix. For example, a honeycomb body can be a plugged ceramic honeycomb structure which forms a filter body comprised of cordierite or other suitable ceramic material. A plugged honeycomb body has one or more channels plugged at one, or both ends of the body.

[0025] A honeycomb body disclosed herein comprises a ceramic honeycomb structure comprising at least one wall supporting one or more particulate deposits for example which may be configured to filter particulate matter from a gas stream. The deposits can be in discrete regions or in some portions or some embodiments can form one or more layers of deposit material at a given location on the wall of the honeycomb body. The deposits according to some embodiments comprise inorganic material, in some embodiments organic material, and in some embodiments both inorganic material and organic material. For example, a honeycomb structure of a honeycomb body may, in one or more embodiments, be formed from cordierite or other porous ceramic material and further comprise material deposits disposed on or below wall surfaces of a cordierite honeycomb structure. The inorganic particles are preferably comprised of one or more ceramic or refractory materials.

[0026] As used herein, "green" or "green ceramic" are used interchangeably and refer to an unsintered or unfired material, unless otherwise specified.

[0027] The methods disclosed herein can be useful in applying a surface treatment to a an article, such as an article comprising porous walls, such as a filter or a particulate filter, which can provide an improved filtering effect, or filtration efficiency, of the particulate filter, such as a filter comprising a bare honeycomb body, or a filter comprising a honeycomb body with other material deposited thereon or therein, such as filtration material deposits, a layer, a membrane, and / or catalytic material.

[0028] Deposition by filtration may be accomplished by a process such as that schematically illustrated in FIG. Iwhich shows a process of depositing inorganic particles onto a surface, such as the surface of a wall flow filter, wherein the process 400 comprises the steps of suspension, or mixture, preparation 405, atomizing to form droplets 410, intermixing droplets and a gaseous carrier stream 415; depositing of material, on the walls of a wall-flow filter 425, and post-treatment curing 430 to, for example, bind the deposited inorganic material on, or in, or both on and in, the porous walls of the honeycomb body. Aerosol deposition methods and comprising a binder can provide a high mechanical integrity even without any high temperature curing steps (e.g., heating to temperatures in excess of 1000°C), and in some embodiments even higher mechanical integrity after a curing step such as a high temperature (e.g., heating to temperatures in excess of 1000°C) curing step. In the process in FIG. 1, the deposition eventually forms inorganic material deposits, which in some aspects are porous material deposits. The material deposits can be in the form of discrete regions of filtration material, or a layer, or a membrane, thereof. For example, at least some portions of the material deposits may be in the form of a porous inorganic layer or membrane.

[0029] FIG. 2 shows an apparatus 500 for depositing inorganic particles onto honeycomb filter bodies, the apparatus 500 comprising a duct 551, a deposition zone 531, an exit zone 536, an exit conduit 540, and a flow driver 545.

[0030] In the embodiment shown, the duct 551 spans from a first end 550 to a second end 555, defining a chamber of the duct comprising: a plenum space 503 at the first end 550 and an evaporation chamber (for depositions that include evaporation of a liquid so as to form agglomerates ) or spray chamber (for depositions that allow droplets and carrier gas to reach the target body) 523 downstream of the plenum space 503. The duct 551 may be essentially adiabatic. That is, the duct 551 may have no external sources of heat. The chamber 523 may comprise a first section of non-uniform diameter 527 and a second section of substantially uniform diameter 529. The section 553 comprises an inlet end 521 and an outlet end 525. The first section of non-uniform diameter 527 has a diameter that increases from the inlet end 521 toward the section of uniform diameter 529, which creates a diverging space for the flow to occupy.

[0031] A carrier gas is supplied to the duct 551 by a conduit 501, which may have a heat source to create a heated carrier gas 505. An atomizing gas 515 and a suspension 510 areseparately supplied by individual delivery conduits such as tubing or piping to a nozzle 520, which is at the inlet end 521 of the evaporation section 553 and is in fluid communication with the duct 551, such as with an apparatus with evaporation chamber 523. The suspension 510 is atomized in the nozzle 520 with the atomizing gas 515.

[0032] A heated carrier gas 505 can flow over the nozzle 520. The atomizing gas 515 may be heated to form a heated atomizing gas. Temperature of the nozzle may be regulated as desired.

[0033] Outlet flow from the nozzle 520 and flow of the heated carrier gas 505 are both in a "Z" direction as shown in FIG. 2. There may be a diffusing area 522 downstream of the nozzle where at least some intermixing occurs. For example, the diffusing area 522 can be located in the evaporation chamber 523, or the diffusing area 522 may be located in the plenum space 503 depending on the location of the nozzle.

[0034] The outlet flow from the nozzle intermixes with the carrier gas 505, thereby forming a gas -particulate -binder mixture, which flows through the chamber of the duct 551. For example, the mixture flows through the chamber 523 of the section 553 and into the deposition zone 531 at the outlet end 525 of the section 553. At the intermixing, the mixture may be heated inside the chamber by the heated carrier gas.

[0035] The outlet flow of the nozzle and the heated carrier gas can enter the chamber 523 of the section 553 from substantially the same direction. In the chamber 523, when forming agglomerates, substantially all of the liquid vehicle from the droplets can be evaporated thereby forming agglomerates of the particles and the binder material, the agglomerates being interspersed in a gaseous carrier stream, which is comprised of the carrier gas and the atomizing gas.

[0036] The deposition zone 531 in fluid communication with the duct 551 houses a plugged ceramic honeycomb body 530, for example, a wall-flow particulate fdter body. The deposition zone 531 has an inner diameter that is larger than the outer diameter of the ceramic honeycomb body 530. To avoid leakage ofthe gases carrying the ceramic powders, the ceramic honeycomb body 530 is sealed to the inner diameter of deposition zone 531, a suitable seal is, for example, an inflatable "inner tube". A pressure gauge, labelled as "PG" measures the difference in the pressure upstream and downstream from the particulate filter.

[0037] The mixture flows into the ceramic honeycomb body 530 thereby depositing the inorganic material of the suspension on the ceramic honeycomb body. The walls of the honeycomb body trap the liquid droplets, to be deposited on or in the walls of the honeycomb body. Upon post-treatment curing the inorganic material binds to the ceramic honeycomb body.

[0038] Downstream from the ceramic honeycomb body 530 is an exit zone 536 defining an exit chamber 535. The flow driver 545 is downstream from the ceramic honeycomb body 530, in fluid communication with the deposition zone 531 and the exit zone 536 by way of the exit conduit 540. Non-limiting examples of flow drivers are: fan, blower, and vacuum pump.

[0039] Flow through such apparatus 500 is considered in a downward direction, for example, substantially parallel to the direction of gravity. In other embodiments, an apparatus can be configured such that flow is directed in a substantially upward or vertical direction.

[0040] The methods disclosed herein can be useful in adding like filtration deposits, such as those comprising one or more types of inorganic particles. In embodiments, methods are disclosed herein that can help enable high filtration efficiency (FE) and / or low backpressure dP for particulate filters such as gasoline particulate filters. In embodiments, the porous honeycomb body comprises a porous ceramic honeycomb structure, such as a / or honeycomb body which has been extruded, fired, and provided with a select pattern of plugging or sealing various cells or channels of the honeycomb matrix, including for example a bare honeycomb body which has not yet received other filtration deposits. In various embodiments, such surface treated particulate filter is suitable for filtering exhaust gas from lean bum gasoline direct injection (GDI) engines contain particulate matter such as carbonaceous soot (e.g., soot), i.e. for example, gasoline particulate filters (GPF) with a honeycomb structure for collecting particulate matter in exhaust gases from vehicles equipped with GDI engines, or diesel particulate filters, or other particulate filters.

[0041] For example, in various aspects, a one-pot sol-gel method is disclosed herein for formulating alumina aerosol suspension and a method of applying the suspension to porous ceramic substrates or monoliths, and in more particular aspects, to a suspension useful for depositing high filtration efficiency “membrane” in a GPF honeycomb filter body. The suspension can be advantageously prepared via a one-pot sol-gel method using organic acid, or inorganic acid, as catalyst. A controlled amount of the suspension can then be applied to theinternal walls of a porous ceramic honeycomb filter body, such as a bare GPF honeycomb body, via aerosol deposition to form inorganic deposits, such as an inorganic layer or “membrane” on at least a portion of the honeycomb body, that enhances the filtration capabilities of a particulate filter such as a GPF or DPF.

[0042] COMPARATIVE PARTICULATE FILTER BODIES TREATED WITH AGGLOMERATES

[0043] One approach to manufacturing a suitable GPF high clean filtration efficiency is to deposit filtration deposits or a porous layer of inorganic material on the wall surfaces of the honeycomb matrix of a base (uncoated or undeposited) GPF. In various embodiments an ethanol-based aerosol deposition process can be utilized in which a flow of agglomerated alumina particles is generated by passing ethanol-based alumina suspension with a siloxane or a silicate binder, such as an alkoxysiloxane, through a nozzle or multiple nozzles. The as- deposited filtration material, or as-deposited layer, can comprise aggregates of alumina agglomerates with a size in the range of submicrons to a few microns.

[0044] In contrast to such approach, the methods disclosed herein the suspension can be formulated without addition of additives, such as TEA and Pluronic L-121, thus eliminating potential contamination issues associated with those ingredients which may result from generation of high volatiles. Thus, in various aspects, the suspension is free of siloxane, or triethanolamine, or triblock copolymer, or free of combinations thereof. Also, the acid modification of the inorganic particles, or inorganic refractory particles such as alumina particles, and the subsequent grafting of the hydrolyzed silanes, produce well-dispersed particles throughout the individual deposits, or layer, or layers, or membrane, without the use of such dispersants thus providing higher clean filtration efficiency for a wall flow filter such as a gasoline particular filter with a plugged honeycomb structure, for example a particle loading of alumina particles at a low loading (< 5g / L) can provide a clean FE of 93%), to be achieved at lower loading of the inorganic deposits on the honeycomb body, wherein g / L is grams of inorganic deposits per overall volume of the honeycomb filter body. We have also found that acid modification of the inorganic particles, or inorganic refractory particles such as alumina particles, and the subsequent grafting of the hydrolyzed silanes, produce well-dispersed alumina particles which allow the current FE (93%) to be achieved at lower loading (< 5g / L).

[0045] We have also found that the methods disclosed herein provide enhanced durability of the fdtration material on honeycomb body, such as after heat exposure and / or higher temperatures, as indicated with excellent filtration performance, and in some embodiments is attainable even at lower filtration material loading compared to other approaches. In embodiments, filter bodies thus produced exhibit high thermal stability and moisture resistance . Generally, the body with higher moisture resistance exhibits a smaller loss in filtration efficiency compared to the loss in filtration efficiency of a comparative filter body. Furthermore, the methods disclosed herein, in conjunction with the materials used, may be practiced with lower or reduced volatile effluents generated by the deposition process.

[0046] Thus, the methods disclosed herein can comprise sol-gel type processing for formulating an alumina suspension.

[0047] Methods are disclosed herein providing inorganic deposits, such as oxides, preferably particles of metal oxides, preferably nanoparticles thereof, on a surface, preferably porous surface, of a substrate, preferably porous substrate, which in various aspects are porous ceramic substrates, the method comprising: combining inorganic particles such as oxide nanoparticles, an organic solvent, a silane binder, and an organic acid such as citric acid into a suspension; aerosolizing at least a portion of the suspension into droplets which contain the inorganic particles such as oxide nanoparticles, the organic solvent, the silane binder, and the citric acid from the droplets; depositing the droplets onto the substrate; and curing the silane binder on the substrate to form a network of inorganic particles such as refractory nanoparticles bound to the substrate.

[0048] SILANE BINDER

[0049] In embodiments, the silane binder comprises silane. In embodiments, the silane binder comprises an alkoxysilane (that is, at least one alkoxysilane), an alkyl alkoxysilane (that is, at least one alkoxysilane), or combinations thereof. In embodiments, the silane binder comprises at least one alkoxysilane. In embodiments, the silane binder comprises at least one methoxysilane, at least one ethoxysilane, or combinations thereof. In embodiments, the silane binder comprises methyltriethoxysilane (MTES), methyltrimethoxysilane (MTMS), or a combination thereof. In embodiments, the silane binder comprises methyltriethoxysilane(MTES). In embodiments, the silane binder is methyltriethoxysilane (MTES). In embodiments, the silane binder comprises methyltrimethoxysilane (MTMS). In embodiments, the silane binder is methyltrimethoxysilane (MTMS).

[0050] In various aspects disclosed herein, the methods do not rely on siloxane binders, nor dispersants. Preferably embodiments of the methods disclosed herein do not rely on siloxanes, such as alkoxy siloxane, nor on triethanolamine (TEA) as a dispersant, nor on triblock copolymer such as Pluronic L- 121 as a dispersant (stabilization agent) or polymeric surfactant. Thus, in various aspects, the suspension is free of siloxane, or triethanolamine, or triblock copolymer, or free of combinations thereof.

[0051] In embodiments, the inorganic particles comprise silicon-containing particles and aluminum -containing particles.

[0052] In embodiments, the inorganic particles comprise silica-containing particles and alumina-containing particles.

[0053] In embodiments, the inorganic particles consist essentially of silica particles and alumina particles.

[0054] In embodiments, the inorganic particles comprise nanoparticles. In embodiments, all of the inorganic particles are nanoparticles.

[0055] CURING HYDROLYZING CROS S-LINK NETWORK

[0056] In embodiments, the curing step comprises hydrolyzing the silane binder and grafting the hydrolyzed silane binder to the inorganic particles. In embodiments, the curing step comprises hydrolyzing the silane binder and hydrolysis products of the silane binder are grafted to the nanoparticles. In embodiments, the grafting creates a cross-linked network of inorganic particles.

[0057] In embodiments, the curing is performed in the presence of a curing catalyst. Preferably the curing catalyst is an organic acid. In embodiments, the organic acid is citric acid.

[0058] In embodiments, the curing catalyst is present in the suspension. In embodiments, the curing catalyst is present in the droplets. In embodiments, the curing catalyst is present in the droplets. In embodiments, the curing step comprises cross-linking the silane binder.

[0059] In embodiments, the suspension comprises a catalytic amount of the organic acid. In embodiments, the suspension comprises no more than a catalytic amount of the organic acid.

[0060] In embodiments, the curing comprises heating the substrate including the droplets thereon. In embodiments, the curing comprises hydrolyzing and grafting the silane binder to the oxide nanoparticles.

[0061] ALCOHOL

[0062] In embodiments, the organic solvent is an alcohol. In embodiments, the organic solvent is selected from the group consisting of ethanol, methanol, isopropanol, and combinations thereof. In embodiments, the organic solvent comprises ethanol. In embodiments, the organic solvent is ethanol.

[0063] DROPLETS CONVEYED BY CARRIER GAS

[0064] In embodiments, the droplets are conveyed toward the substrate by a carrier gas. In embodiments, the carrier gas comprises an inert gas. In embodiments, the carrier gas comprises nitrogen. In embodiments, the carrier gas consists essentially of nitrogen.

[0065] SUBSTRATE / FILTER BODY

[0066] In embodiments, the substrate is a filter body. In embodiments, the particles are deposited on a surface of the filter body by aerosol deposition. In embodiments, at least some of the particles are disposed below the surface of the filter body. In embodiments, the filter body comprises a honeycomb body comprised of intersecting porous walls, and the surface is a surface of at least one of the porous walls.

[0067] In embodiments, the depositing step further comprises aerosol depositing the liquid droplets containing the particles such that the particles are disposed on, in, or both on and in, one or more wall of the substrate.

[0068] In embodiments, the substrate comprises a plugged honeycomb body comprising intersecting porous walls extending from an inlet end to an outlet end of the body and defining axial channels, wherein plugs seal at least some of the channels, and the depositing step further comprises aerosol depositing the particle -containing droplets, and therefore the particles on, in, or both on and in, a plurality of the walls of the honeycomb body.

[0069] In an aspect, filter bodies are disclosed herein comprising a honeycomb body containing inorganic particles grafted to each other and to the honeycomb body with products of hydrolysis.

[0070] In embodiments, the honeycomb body comprises a honeycomb structure extending axially from a first face to a second face, the structure being comprised of a plurality of porouswalls extending axially and having surfaces which define a plurality of axial channels, the walls having internal pores, wherein surfaces of the walls comprise surface openings to at least some of the internal pores.

[0071] In embodiments, the deposited amount of the first particles per volume of the honeycomb structure is in the range of 0. 1 to 10.0 grams / liter.

[0072] In embodiments, the deposited amount of the first particles per volume of the honeycomb structure is less than 7.0 grams / liter.

[0073] In embodiments, the deposited amount of the first particles per volume of the honeycomb structure is less than 5.0 grams / liter.

[0074] In embodiments, the inorganic particles are comprised of a particle size in the range of 0.1 to 1 pm.

[0075] In embodiments, the porous walls of the honeycomb body have a surface porosity of 35% to 75%. In embodiments, the porous walls have a median pore size of 5 to 50 micrometers. In embodiments, the porous walls have a median pore size of 5 to 30 micrometers. In embodiments, the porous walls have a median pore size of 10 to 30 micrometers.

[0076] MEMBRANE

[0077] In embodiments, the network of inorganic particles forms a membrane on the substrate.

[0078] In various aspects disclosed herein the internal walls of a filter body comprising a honeycomb structure of porous ceramic walls can be treated with a liquid suspension comprising a mixture of inorganic particles (preferably refractory inorganic particles), organic or inorganic acid, a silane binder such as methyltrialkoxysilane, for example MTMS or MTES or a combination thereof, and ethanol formulated in a one-pot sol-gel process.

[0079] In various aspects, methods are disclosed herein which comprise a one pot sol-gel process for formulating, or generating, an alumina suspension, and methods of applying the suspension to porous ceramic monoliths in the form of droplets of the suspension which contain inorganic particles, preferably inorganic refractory particles. Such suspensions are useful for depositing a high filtration efficiency “membrane” of particles, preferably nanoparticles or microparticles, onto a porous ceramic honeycomb body such as a particulate filter body. Exemplary alumina suspensions disclosed herein can comprise a mixture of (i) alumina slurry,(ii) methyl trialkoxysilane such as methyltrimethoxysilane (MTMS) as a precursor or source of in-situ generated binder and (iii) an organic solvent such as ethanol, methanol, or isopropanol. The suspension composition can be prepared via one pot sol-gel process using organic or inorganic acid as catalyst. A controlled amount of the suspension can be applied to the internal walls of a porous ceramic honeycomb structured body via aerosol deposition to form an inorganic layer of the inorganic particles, or a “membrane”, which enhances the filtration capabilities of a particulate filter comprising such porous ceramic body. The methyl trialkoxysilane can serve as a binder precursor, such that the methyl trialkoxysilane can be cured to bind the particles to the porous ceramic body, or to other particles, or both.

[0080] In various aspects, methods are thus disclosed herein comprising depositing a high filtration efficiency “membrane” into a bare plugged honeycomb body, applying an alumina suspension via aerosol deposition process, removing the alcohol, and curing at moderate temperature to affix the particles, which may be disposed in discrete patches, or in a layer over part or all of the internal surfaces of the walls, such as a membrane, onto the internal walls of the honeycomb body.

[0081] In various aspects, suspensions disclosed herein comprise alumina suspensions for forming inorganic deposits or layer or membrane on porous ceramic filters, and in particular aspects, relates to alumina suspension droplets containing alumina particles and silane binder for depositing high filtration efficiency the particles in deposits or layers or membrane onto particulate filter bodies, wherein in various aspects the alumina suspension is formulated in a one-pot sol-gel method by combining silane binder with alumina particles, preferably alumina nanoparticles.

[0082] EXAMPLES

[0083] FIG. 3 is a schematic representation of a one-pot sol-gel process for formulating an alumina suspension for aerosol deposition as disclosed herein and as utilized in the following Examples.

[0084] FIG. 3 shows : i) a-alumina dispersed in ethanol (“Alunol 30”) is measured into a glass container, ii) a mixture of de-ionized “DI” water and hydrochloric acid “HC1” is added to acidify the surface of the alumina particles and mixed to obtain an acidified alumina slurry, iii) a silane (here, MTMS) is added and stirred for 20 hours to graft the hydrolyzed silane molecules on the alumina particles, and iv) ethanol (ETOH) is added to dilute the suspensionto a target particle loading for the suspension (here, an alumina loading, for example 11 wt.%), and v) the suspension is stirred until ready to spray.

[0085] In preparing the Examples, the alumina suspension was atomized and droplets were directed to a gasoline particulate filter honeycomb body deposited on the internal walls of gasoline particulate filters with average porosity of 55% (by mercury porosimetry), 300 cells per square inch, and 8 mil average thickness cell walls, with an outer diameter of 4.25” and an overall length of 4.724”. Table 2 lists deposition conditions. The filtration efficiency of the filter body at various processing stages was measured.

[0086] EXAMPLE I

[0087] The alumina aerosol suspension for aerosol deposition was prepared as shown schematically in FIG. 3 using sol-gel process with the composition of the suspension as shown in Table 1 of FIG. 4. The suspension was prepared by mixing 200 parts alumina slurry (Alunol 30, 30 wt% milled Almatis A 1000 alumina in ethanol), 63.5 parts DI water, 1.1 parts HC1, 40 parts MTMS and 192.42 parts ethanol. The mixture was stirred at room temperature for 12 hours. The suspension was applied to gasoline particulate filter honeycomb bodies of porous cordierite having an average porosity of 55% as measured by mercury porosimetry. F 300 cells per square inch, and 8 mil average thickness cell walls, wherein the honeycomb bodies had a diameter of 4.25” and 4.724” length. Deposition conditions are provided in Table 2 of FIG. 5.

[0088] The particulate filtration performance of the gasoline particulate filter bodies prepared by a known comparative inorganic particle deposition method using a siloxane binder in an alumina suspension which was used to form agglomerates for deposition is provided in Table 3 of FIG. 6 for comparison.

[0089] The particulate filtration performance of the gasoline particulate filter body prepared from the suspension disclosed herein in Example 1 is provided in Table 4 of FIG. 7.

[0090] To verify the results, deposition was repeated with a freshly prepared alumina suspension. The FE data for the repeat run is provided in Table 5 of FIG. 8.

[0091] The plots of as-cured FE and water durability of the gasoline particulate filter bodies with sol-gel based treatment compared to those of the known filter bodies with agglomerates are provided in FIG. 9 and 10, respectively.

[0092] It can be seen that the filtration performance of filter bodies prepared by the method disclosed herein using the suspension disclosed herein is better than that of the known filter bodies in terms of filtration efficiency and water FE loss (a measure of water durability).

[0093] EXAMPLE 2

[0094] In Example 2, the alumina aerosol suspension was formulated in the same manner as in Example 1 except that citric acid was used instead of hydrochloric acid, that is the HCI used as acid catalyst in the formulation of the binder was replaced with citric acid.

[0095] In the various aspects disclosed herein: the agglomerates may be spherical; the network of inorganic particles may comprise alumina particles; the network of inorganic particles may form a membrane on the substrate; the substrate is a filter body; the agglomerates are deposited on a surface of the filter body by filter deposition; at least some of the agglomerates.

[0096] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED:

1. A method of treating a porous substrate, the method comprising: atomizing a suspension comprised of inorganic particles, a binder precursor, a silane cross-linker, and a liquid comprised of one or more liquid components which include an organic solvent, to form an aerosol of droplets; depositing the droplets into or onto the porous substrate; and forming a silane binder in situ from the binder precursor provided by the droplets, thereby binding the inorganic particles to the porous substrate.

2. The method of claim 1 wherein the inorganic particles comprise inorganic refractory particles.

3. The method of claim 1 wherein the inorganic particles comprise refractory metal oxide particles.

4. The method of claim 1 wherein the inorganic particles comprise inorganic naonparticles.

5. The method of claim 1 wherein the inorganic particles are comprised of alumina.

6. The method of claim 1 wherein the suspension is comprised of inorganic refractory particles, a methyl trialkoxysilane, and an organic solvent.

7. The method of claim 6 wherein the methyl trialkoxysilane comprises methyltrimethoxysilane (MTMS).

8. The method of claim 6 wherein the organic solvent comprises ethanol, methanol, isopropanol, or combinations thereof.

9. The method of claim 6 wherein the suspension further comprises a catalyst for promoting formation of a silane binder.

10. The method of claim 6 wherein the catalyst for promoting formation of a silane binder comprises an organic acid or an inorganic acid or both.

11. The method of claim 6 wherein the methyl trialkoxysilane is cured into the silane binder.

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