Methods of treating a porous ceramic body with inorganic particles

Abstract

Methods for providing inorganic deposits, such as refractory oxide nanoparticles, on a porous surface which include atomization a sol-gel suspension; aerosolizing at least a portion of the suspension into droplets; evaporating organic solvent from the droplets to form agglomerates of the particles; depositing the agglomerates onto the substrate; and curing the silane binder in the agglomerates on the substrate to form a network of inorganic particles bound to the substrate as inorganic deposits.

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 / 602917, 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 two-pot sol-gel process is advantageously utilized.

[0005] 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 asubstrate, such as a porous substrate having interconnected pores that permit gas flow therethrough.

[0006] In an aspect, a method of treating a porous substrate, such as a porous ceramic body, is disclosed herein, the method comprising: atomizing a suspension comprised of silanized inorganic particles, a sol-gel binder, 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; removing one or more liquid component from the droplets to form agglomerates; and depositing the agglomerates into or onto the porous substrate, such as a porous ceramic body. The deposited agglomerates can be comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker. The method preferably also comprises directing the agglomerates toward the porous ceramic body, which would occur before the agglomerates are deposited on the porous substrate. The one or more liquid component can be the organic solvent, or water, or both the organic solvent and water.

[0007] In another aspect, a method of treating a porous substrate, such as a porous ceramic body, is disclosed herein, the method comprising: forming a first suspension by mixing a slurry of silanized inorganic particles with a sol-gel binder; mixing the first suspension with an organic solvent to form a second suspension; atomizing the second suspension to form an aerosol of droplets; removing liquid from the droplets to form agglomerates; and depositing the agglomerates into or onto the porous substrate, such as a porous ceramic body. The deposited agglomerates can be comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker. The method preferably also comprises directing the agglomerates toward the porous ceramic body, which would occur before the agglomerates are deposited on the porous substrate. The one or more liquid component can be the organic solvent, or water, or both the organic solvent and water.

[0008] The first suspension can be referred to as an intermediate suspension. The intermediate suspension can comprise a MTMS, an organosilane binder, or a silane crosslinker, or a combination thereof. The organic solvent can dilute the intermediate suspension.

[0009] The second suspension can be referred to as a binder-inorganic particle suspension. The second suspension may include an added solvent such as water or organic solvent.

[0010] The liquid removed from the droplets can be the organic solvent, water, or a combination thereof.

[0011] In an aspect disclosed herein, contact between the sol-gel binder and the silane crosslinker is maintained while on or in the porous ceramic body for a time sufficient to cause crosslinking between the sol-gel binder and the particles, preferably to form a cross-linked network of the binder and the particles and the porous substrate body to provide a network of inorganic particles bound to the substrate as inorganic deposits.

[0012] In an aspect disclosed herein, the method further comprises curing the agglomerates to affix the agglomerates to the porous ceramic body.

[0013] In an aspect disclosed herein, the silanized inorganic particle slurry is preferably formed by acidifying inorganic particles with an acid, and optionally water, to create a slurry of acidified inorganic particles by mixing inorganic particles with water and an acid, and adding a silane binder precursor to the acidified particles, that is the slurry of acidified particles, and hydrolyzing the silane and grafting the hydrolyzed silane to the acidified inorganic particles. The grafting may occur by allowing the hydrolyzing and grafting to occur for an adequate period of time at temperatures around room temperature sufficient to cause the silane binder precursor to hydrolyze the binder precursor and to become grafted to the acidified inorganic particles. Thus, in aspects, the method can comprise mixing a silanized inorganic particle slurry with a sol-gel binder to form a binder-inorganic particle suspension.

[0014] In an aspect disclosed herein, the binder precursor preferably is a silane.

[0015] 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 agglomerates toward the porous ceramic body, wherein the directing comprises carrying the agglomerates by a carrier gas which passes through at least some of the walls to deposit at least some of the agglomerates by filtration, that is a filtration deposition process.

[0016] 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.

[0017] 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.

[0018] 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

[0019] FIG. 1 schematically illustrates an embodiment of a process of depositing inorganic particles onto a surface as disclosed herein.

[0020] FIG. 2 schematically illustrates an apparatus for depositing inorganic particles onto honeycomb filter bodies as disclosed herein.

[0021] FIG. 3 schematically illustrates processing steps as disclosed herein of priming / silanization of alumina particles.

[0022] FIG. 4 schematically illustrates processing steps as disclosed herein for forming a silane binder.

[0023] FIG. 5 schematically illustrates processing steps as disclosed herein for a two-step sol-gel method for formulating an alumina suspension.

[0024] FIG. 6 lists an exemplary composition of an alumina aerosol suspension as disclosed herein.

[0025] FIG. 7 lists process deposition conditions used for treating comparative samples with agglomerates which contain a siloxane binder.

[0026] FIG. 8 lists experimental data including various fdtration efficiencies from a comparative sample that was deposited with agglomerates containing a siloxane binder.

[0027] FIG. 9 lists experimental data including various filtration efficiencies for Example 1 as disclosed herein.

[0028] FIG. 10 lists experimental data including various filtration efficiencies for Example 2 as disclosed herein.

[0029] FIG. 11 graphically illustrates filtration efficiency experimental data for as-cured FE of samples of the particulate filter bodies treated with sol-gel as disclosed herein in Example 1, and compared to that of the comparative particulate filter bodies treated with agglomerates and siloxane binder.

[0030] FIG. 12 graphically illustrates loss in filtration efficiency experimental data for samples of the particulate filter bodies treated with sol-gel as disclosed herein in Example 1, and compared to that of the comparative particulate filter bodies treated with agglomerates and siloxane binder, after each was exposed to a water durability test.DETAILED DESCRIPTION

[0031] 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

[0032] 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.

[0033] 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".

[0034] 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.

[0035] 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.

[0036] As used herein, "green" or "green ceramic" are used interchangeably and refer to an unsintered or unfired material, unless otherwise specified.

[0037] 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.

[0038] In an aspect, methods are disclosed herein of treating a porous substrate, such as a porous ceramic body, via a sol-gel process, the method comprising: atomizing a suspension comprised of silanized inorganic particles, a sol-gel binder, 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; removing one or more liquid components, such as the organic solvent, water, or a combination of water and organic solvent, from the droplets to form agglomerates, such as comprised of comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker; and depositing the agglomerates into or onto the porous substrate (such as a porous ceramic body). The method may further comprise directing the agglomerates toward the porous ceramic body] backspace.

[0039] Thus, one of the liquid components is water; water is preferably removed from the droplets to form agglomerates. Another of the liquid components is organic solvent, which is preferably removed from the droplets to form agglomerates. More preferably, both water and organic solvent are removed from the droplets to form agglomerates

[0040] In another aspect disclosed herein are methods of treating a porous substrate (such as a porous ceramic body) via sol-gel, the method comprising: forming a first (or “intermediate”) suspension by mixing a slurry of silanized inorganic particles with a sol-gel binder (which may comprise MTMS, and or organosilane binder, and / or a silane cross-linker); mixing the first suspension (or “intermediate suspension”) with an organic solvent to form a second suspension (or “binder-inorganic particle”); atomizing the second suspension to form an aerosol of droplets; removing liquid (such as the organic solvent, water, or both water and an organic solvent) from the droplets to form agglomerates (such as agglomerates comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker); and depositing the agglomerates into or onto the porous substrate. The methods may further comprise directing the agglomerates toward the porous substrate or porous ceramic body. In an aspect, contact between the sol -gel binder and the silane cross-linker is maintained on or in the porous ceramic body for a time sufficient to cause cross-linking between the sol-gel binder and the particles, preferably to form a cross-linked network for securing the particles with respect to the porous ceramic body. In an aspect, the method further comprises curing the agglomerates to affix the agglomerates to the porous ceramic body. Organic solvent may be provided in an amount thatthat dilutes the intermediate suspension. In an aspect, the silamzed inorganic particle slurry is formed by acidifying inorganic particles with an acid (or acid and water, i.e. creating a slurry of acidified inorganic particles by mixing inorganic particles with water and an acid), adding a silane-to the acidified particles (such as the slurry of acidified particles) and hydrolyzing the silane and grafting the hydrolyzed silane to the acidified inorganic particles. In various aspects, the grafting may be conducted at or near room temperature for a period of time for the silane binder precursor to hydrolyze the binder precursor and to become grafted to the acidified inorganic particles. In an aspect, the method further comprises mixing a silanized inorganic particle slurry with a sol-gel binder to form a binder-inorganic particle suspension.

[0041] In another aspect methods are disclosed herein for providing inorganic oxide deposits on a surface of a substrate, the method comprising: aerosolizing at least a portion of a sol-gel suspension into droplets, the sol-gel suspension comprised of inorganic particles, an organic solvent, and a silane binder; evaporating the organic solvent from the droplets to form agglomerates comprising the inorganic particles and the silane binder; and depositing the agglomerates onto the substrate. The methods further preferably comprise curing the silane binder on the substrate to form a network of inorganic particles bound to the substrate.

[0042] In various aspects, the inorganic particles may comprise silicon-containing particles or aluminum-containing particles or both. In various aspects, the inorganic particles consist essentially of silica particles and alumina particles.

[0043] In various aspects, the inorganic particles comprise nanoparticles, or microparticles, or both. The inorganic particles can comprise oxide particles, or carbide particles, or both. For example, the inorganic particles are metal oxide particles.

[0044] In various aspects, the curing step comprises hydrolyzing the silane binder and grafting the hydrolyzed silane binder to the inorganic particles. In various aspects, the curing is performed in the presence of a curing catalyst. For example, the curing catalyst may be an organic acid, such as citric acid. The curing catalyst can be present in the suspension, or the curing catalyst can be present in the droplets, or can be present in the agglomerates, or combinations thereof.

[0045] In various aspects, the curing step comprises cross-linking the silane binder.

[0046] In various aspects, the curing comprises heating the agglomerates deposited on the substrate. In various aspects, the curing comprises hydrolyzing and grafting the silane binder to the inorganic particles, such as oxide nanoparticles.

[0047] In various aspects, the organic solvent is an alcohol. The organic solvent may be selected from the group consisting of ethanol, methanol, isopropanol, and combinations thereof. In a particular aspects, the organic solvent comprises ethanol.

[0048] In various aspects, the silane binder comprises at least one alkoxysilane, at least one alkyl alkoxysilane, or combinations thereof. Thus, the silane binder may comprise at least one alkoxysilane. For example, the silane binder may comprise at least one methoxysilane, at least one ethoxysilane, or combinations thereof; the silane binder may comprise methyltriethoxysilane (MTES), methyltrimethoxysilane (MTMS), or a combination thereof.

[0049] In various aspects, the droplets are conveyed toward the substrate by a carrier gas. The carrier gas can comprise an inert gas. For example, the carrier gas may comprise, or even consist essentially of, nitrogen.

[0050] Thus, in various aspects, the porous substrate comprises a porous ceramic body. The porous ceramic body may advantageously comprise a honeycomb structure. The honeycomb structure can comprise 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; preferably, at least some of the channels are plugged with a sealing material. Thus, for example, the previously noted directing comprises carrying the agglomerates by a carrier gas which passes through at least some of the walls to deposit at least some of the agglomerates by filtration.

[0051] Deposition by filtration may be accomplished by a process such as that schematically illustrated in FIG. 1 which 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; evaporating liquid vehicle to form agglomerates 420; depositing of material, e.g., agglomerates, on the walls of a wall-flow filter 425, and posttreatment 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. Filtration deposition methods ofagglomerates 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 of agglomerates 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.

[0052] 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.

[0053] 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 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 evaporation chamber 523 is defined by an evaporation section 553 of the duct 551, which may comprise a first section of non-uniform diameter 527 and a second section of substantially uniform diameter 529. The evaporation 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.

[0054] 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 are separately 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.

[0055] A heated carrier gas 505 can flow over the nozzle 520. The atomizing gas 515 can be heated to form a heated atomizing gas. Temperature of the nozzle may be regulated as desired.

[0056] 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.

[0057] The outlet flow from the nozzle intermixes with the heated carrier gas 505, thereby forming a gas-liquid-particulate-binder mixture, which flows through the chamber of the duct 551. For example, the gas-liquid-particulate-binder mixture flows through the evaporation chamber 523 of the evaporation section 553 and into the deposition zone 531 at the outlet end 525 of the evaporation section 553. At the intermixing, the gas-liquid-particulate-binder mixture may be heated inside the chamber by the heated carrier gas.

[0058] The outlet flow of the nozzle and the heated carrier gas can enter the evaporation chamber 523 of the evaporation section 553 from substantially the same direction. In the evaporation chamber 523, 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.

[0059] The deposition zone 531 in fluid communication with the duct 551 houses a plugged ceramic honeycomb body 530, for example, a wall-flow particulate filter. The deposition zone 531 has an inner diameter that is larger than the outer diameter of the ceramic honeycomb body 530. To avoid leakage of the 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.

[0060] The mixture flows into the ceramic honeycomb body 530 thereby depositing the inorganic material of the suspension on the ceramic honeycomb body. Specifically, the agglomerates and the gaseous carrier stream pass into the honeycomb body such that the gaseous carrier stream passes through the porous walls of the honeycomb body, and the walls of the honeycomb body trap the agglomerates, wherein the agglomerates and / or aggregatesthereof are deposited on or in the walls of the honeycomb body. Upon post-treatment curing the inorganic material binds to the ceramic honeycomb body.

[0061] 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. The aerosolized suspension is dried and deposited on one or more walls of the particulate filter as agglomerates of filtration material, which is present as discrete regions of filtration material, or in some portions or some embodiments as a layer, or both, wherein the agglomerates are comprised of primary particles of inorganic material.

[0062] 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.

[0063] 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.

[0064] For example, in various aspects, a two-step 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. In various aspects, the alumina suspension can comprise a mixture of (i) silanized, or “primed”, aluminaslurry, (ii) sol -gel binder (which is preferably a silane based binder) and (iii) an organic solvent, such as ethanol, methanol, and / or isopropanol. The suspension can be advantageously prepared via a two-step sol-gel method using organic acid, or inorganic acid, as catalyst. A controlled amount of the particles can then be applied to the internal walls of a porous ceramic honeycomb filter body, such as a bare GPF honeycomb body, via filtration 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.

[0065] COMPARATIVE PARTICULATE FILTER BODIES TREATED WITH AGGLOMERATES

[0066] 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 spray 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.

[0067] In contrast to such approach, the methods disclosed herein comprise silanes being used in the sol-gel process for priming / silanizing the inorganic particles such as alumina particles. 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. Also, the priming / silanization of the inorganic (alumina) particles disclosed herein can advantageously produce agglomerates with well-dispersed alumina particles within each agglomerate, and among the various agglomerates, without the use of such dispersants, which results in the formation of fine (small size) agglomerates, or “snowballs”, thus providing higher clean filtration efficiency for a wall flow filter such as a gasoline particular filter with a plugged honeycomb structure, for example and FE of 93%), to be achieved at lower loading of the inorganic deposits on the honeycomb body, for example < 5 g / L that is grams of inorganic deposits per overall volume of the honeycomb filter body.

[0068] We have also found that the methods disclosed herein provide enhanced durability of the filtration 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.

[0069] Thus, the methods disclosed herein can comprise sol-gel type processing for formulating an alumina suspension.

[0070] 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; evaporating the organic solvent from the droplets to form agglomerates of the particles such as oxide nanoparticles, the organic solvent, the silane binder, and the citric acid from the droplets; depositing the agglomerates onto the substrate; and curing the silane binder on the substrate to form a network of inorganic particles, such as a network of nanoparticles, bound to the substrate.

[0071] SILANE BINDER

[0072] 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).

[0073] 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.

[0074] In embodiments, the inorganic particles comprise silicon-containing particles, or aluminum-containing particles, or both.

[0075] In embodiments, the inorganic particles comprise nanoparticles. In embodiments, all of the inorganic particles are nanoparticles.

[0076] CURING HYDROLYZING CROS S-LINK NETWORK

[0077] 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.

[0078] 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.

[0079] 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 agglomerates. In embodiments, the curing step comprises cross-linking the silane binder.

[0080] 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.

[0081] In embodiments, the curing comprises heating the agglomerates deposited on the substrate. In embodiments, the curing comprises hydrolyzing and grafting the silane binder to the oxide nanoparticles.

[0082] ALCOHOL

[0083] In embodiments, the organic solvent is an alcohol. In embodiments, the organic solvent is selected from the group consisting of ethanol, methanol, isopropanol, andcombinations thereof. In embodiments, the organic solvent comprises ethanol. In embodiments, the organic solvent is ethanol.

[0084] DROPLETS CONVEYED BY CARRIER GAS

[0085] 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.

[0086] SUBSTRATE / FILTER BODY

[0087] In embodiments, the substrate is a filter body. In embodiments, the agglomerates are deposited on a surface of the filter body by filter deposition. In embodiments, at least some of the agglomerates 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.

[0088] In embodiments, the depositing step further comprises filter depositing the agglomerates on, in, or both on and in, a wall of the substrate.

[0089] 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 filter depositing the agglomerates on, in, or both on and in, a plurality of the walls of the honeycomb body.

[0090] In an aspect, filter bodies are disclosed herein comprising a honeycomb body containing agglomerates of inorganic particles grafted to each other and to the honeycomb body with products of hydrolysis.

[0091] 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 porous walls 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.

[0092] 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.

[0093] In embodiments, the deposited amount of the first particles per volume of the honeycomb structure is less than 7.0 grams / liter.

[0094] In embodiments, the deposited amount of the first particles per volume of the honeycomb structure is less than 5.0 grams / liter.

[0095] In embodiments, the inorganic particles are comprised of a primary particle size in the range of 0. 1 to 1 pm.

[0096] 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.

[0097] MEMBRANE

[0098] In embodiments, the network of inorganic particles forms a membrane on the substrate.

[0099] Accordingly, in various aspects disclosed herein the internal walls of a filter body comprising a honeycomb structure of porous ceramic walls can be treated with agglomerates made from a liquid suspension comprising a mixture of silanized (or primed) inorganic particles (preferably refractory inorganic particles), organic or inorganic acid, a silane binder such as methyltrialkoxy silane, for example MTMS or MTES or a combination thereof, and ethanol formulated in a two-step sol-gel process.

[0100] 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 a spray deposition process, removing the alcohol, forming and depositing agglomerates, and curing at moderate temperature to affix the membrane onto the internal walls of the honeycomb body.

[0101] 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 containing primed / silanized alumina slurry and silane binder for depositing high filtration efficiency deposits or layers or membrane onto particulate filter bodies, wherein in various aspects the alumina suspension is formulated in a two-step solgel method by preparing a silane binder and adding the binder to a primed alumina slurry.

[0102] FIG. 3 is a schematic representation of a two-step sol -gel process for formulating an alumina suspension as disclosed herein and as utilized in the following Examples.

[0103] 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, iii) a silane (for example MTMS or MTES) is added and stirred for 20 hours to graft the hydrolyzed silane molecules on the alumina particles.

[0104] FIGS. 4-5 schematically represent the formulation of the primed / silanized alumina slurry and of the binder, respectively, as disclosed herein and as utilized in the following Examples.

[0105] FIG. 4 shows processing steps for formulating the sol-gel binder: i) ethanol and DI water are measured into a glass container, ii) HCI is added to adjust the pH to 4 and iii) MTMS is added and stirred for 1 hour.

[0106] FIG. 5 shows processing steps for formulating the alumina suspension: i) a silanized (primed) alumina slurry is measured into a glass container, ii) a sol-gel binder is added and stirred for 3 hours, iii) ethanol is added to dilute the suspension to the target alumina loading (l lwt.%) for the suspension, and iv) the suspension is stirred until ready to spray through a nozzle.

[0107] In preparing the Examples, the alumina suspension was spray dried into agglomerates which were directed to a gasoline particulate fdter honeycomb body deposited on the internal walls of gasoline particulate fdters 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 agglomerates were produced by atomizing the suspension via high pressure nozzles into a heated deposition chamber. After spraying into the chamber, the ethanol evaporated, and an agglomerate of silanized alumina particles remained in the form of a “snowball” shape which was then sucked into the inlet channels of the gasoline particulate filter body using a blower at the exit of the deposition chamber. The filtration efficiency of the filter body at various processing stages was measured.

[0108] EXAMPLE I

[0109] The alumina suspension for spray deposition was formulated by separately preparing and then mixing together a primed, i.e. silanized, alumina slurry and a sol-gel binder. The primed alumina slurry was prepared as shown schematically in FIG. 3 using sol-gel process. The primed alumina slurry was prepared by mixing 233.33 parts alumina slurry (Alunol 30,30wt% milled Almatis A1000 alumina in ethanol), 1.51 parts DI water, 0.45 trifluoroacetic acid and 3.74 parts MTES and stirred for 20 hours. The modified binder was prepared as shown schematically in FIG. 4. The binder was prepared by mixing 27.52 parts ethanol, 15.87 parts DI water, 0.81 parts HCI and 30 parts MTMS and stirred for 1 hour. The final alumina suspension was formulated as shown schematically in FIG. 5. The composition of the suspension is shown in Table 1 in FIG. 6. The suspension was prepared by mixing 200 parts primed alumina slurry, 46.39 parts binder and 288.59 parts and ethanol and stirred at room temperature for 12 hours. The suspension was applied to gasoline particular filter honeycomb bodies of cordierite with average porosity of 55% (by mercury porosimetry), 300 cells per square inch, and 8 mil average thickness cell walls, with a diameter of 4.25” and 4.724” length with the deposition conditions provided in Table 2 in FIG. 7.

[0110] 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 is provided in FIG. 8 for comparison.

[0111] The particulate filtration performance of the gasoline particulate filter body prepared from the suspension disclosed herein in Example 1 is provided in FIG. 9.

[0112] To verify the results, deposition was repeated with a freshly prepared alumina suspension. The FE data for the repeat run is provided in FIG. 10

[0113] The plots of as-cured FE and water durability of the sol-gel based gasoline particulate filter bodies compared to those of the known filter bodies are provided in FIGS. 11 and 12, respectively.

[0114] 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).

[0115] EXAMPLE 2

[0116] 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. The modified binder was prepared as shown schematically in FIG. 2. The binder was prepared by mixing27.52 parts ethanol, 15.87 parts DI water, 0.76 parts citric acid and 30 parts MTMS and stirred for 1 hour.

[0117] EXAMPLE S

[0118] In Example 3, the alumina aerosol suspension was formulated in the same manner as in Example 2 except that the trifluoroacetic acid and MTES used in the formulation of the primed alumina slurry were respectively replaced with HCI and MTMS. The primed alumina slurry was prepared by mixing 233.33 parts alumina slurry (Alunol 30, 30wt% milled Almatis A1000 alumina in ethanol), 1.98 parts DI water, 0.21parts HCI and 3.74 parts MTMS and stirred for 20 hours.

[0119] 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 are disposed below the surface of the filter body; 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.

[0120] 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 silanized inorganic particles, a sol-gel binder, 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; removing one or more liquid components from the droplets to form agglomerates, depositing the agglomerates into or onto the porous substrate.

2. The method of claim 1 wherein the agglomerates are comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker when deposited into or onto the porous substrate.

3. The method of claims 1 -2 wherein the method further comprises directing the agglomerates toward the porous ceramic body.

4. The method of claims 1-3 wherein one of the liquid components is water.

5. The method of claim 4 wherein water is removed from the droplets in the formation of the agglomerates.

6. The method of claims 1-3 wherein one of the liquid components is an organic solvent.

7. The method of claim 6 wherein the organic solvent is removed from the droplets in the formation of the agglomerates.

8. The method of claims 1-7 wherein the porous substrate is a porous ceramic body.

9. A method of treating a porous substrate, the method comprising:forming a first suspension by mixing a slurry of silanized inorganic particles with a solgel binder; mixing the first [intermediate] suspension with an organic solvent to form a second suspension; atomizing the second suspension to form an aerosol of droplets; removing liquid from the droplets to form agglomerates, depositing the agglomerates into or onto the porous substrate.

10. The method of claim 9 wherein contact between the sol-gel binder and the silane crosslinker is maintained on or in the porous ceramic body for a time sufficient to cause cross-linking between the sol-gel binder and the particles [forms a cross-linked network] .

11. The method of claim 9 further comprising curing the agglomerates to affix the agglomerates to the porous ceramic body.

12. The method of claim 9 wherein the silanized inorganic particle slurry is formed by acidifying inorganic particles with an acid,13. The method of claim 9 wherein the method further comprises adding a silane to the that acidified particles and hydrolyzing the silane and grafting the hydrolyzed silane to the acidified inorganic particles.

14. The method of claim 9 wherein the method further comprises mixing a silanized inorganic particle slurry with a sol-gel binder to form a binder-inorganic particle suspension.

15. The method of claim 9 wherein the sol-gel binder comprises MTMS.

16. The method of claim 9 wherein the sol-gel binder comprises an organosilane binder.

17. The method of claim 9 wherein the sol-gel binder comprises a silane cross-linker.

18. The method of claim 1 wherein the agglomerates are comprised of the silanized inorganic particles, the sol-gel binder, and the silane cross-linker when deposited into or onto the porous substrate.

19. The method of claims 1-2 wherein the method further comprises directing the agglomerates toward the porous ceramic body.

20. The method of claim 9 wherein one of the liquid components is water.

21. The method of claim 20 wherein water is removed from the droplets in the formation of the agglomerates.

22. The method of claim 9 wherein one of the liquid components is an organic solvent.

23. The method of claim 22 wherein the organic solvent is removed from the droplets in the formation of the agglomerates.

24. The method of claim 9 wherein the porous substrate is a porous ceramic body.

25. The method of claim 1 wherein the porous substrate comprises a porous ceramic body.

26. The method of claim 25 wherein the porous ceramic body comprises a honeycomb structure.

27. The method of claim 26 wherein 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.

28. The method of claim 27 wherein at least some of the channels are plugged with a sealing material.

29. The method of claim 28 wherein the directing comprises carrying the agglomerates by a carrier gas which passes through at least some of the walls to deposit at least some of the agglomerates by filtration.

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