Gasoline particle filter

Abstract

The present invention relates to a particulate filter comprising: a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end wherein a number of channels are inlet channels open at the inlet end and closed at the outlet end, a certain number of channels are outlet channels which are closed at the inlet ends and open at the outlet ends; and a layer of inorganic particles supported on the surface of the porous wall in the inlet channel and / or the outlet channel, in which the inorganic particles comprise or consist of boehmite particles. The invention also relates to a method for producing a particulate filter comprising applying inorganic particles comprising or consisting of boehmite particles in the inlet channel and / or the outlet channel of the substrate.

Description

Technical Field

[0001] The present invention relates to a particulate filter for treating an exhaust gas flow from a gasoline engine, the particulate filter comprising a coating of inorganic powder particles. The present invention also relates to a gasoline engine emission treatment system comprising a particulate filter and a method for treating an exhaust gas flow from a gasoline engine. Background Art

[0002] Engine exhaust mainly consists of gaseous pollutants such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) and particulate matter (PM). For gasoline engines, three-way conversion catalysts (hereinafter interchangeably referred to as TWC catalysts or TWCs) for gaseous pollutants and filters for particulate matter (PM) are well-known exhaust post-treatment means to ensure that exhaust emissions comply with emission regulations.

[0003] In contrast to the particles generated by diesel lean-burn engines, the particles generated by gasoline engines (such as direct injection engines) tend to be finer and fewer in number. This is because the combustion conditions of gasoline engines are different from those of diesel engines. In addition, the hydrocarbon composition in gasoline engine emissions is different compared to diesel engines. Particulate filters specifically for gasoline engines have been developed for decades in order to effectively treat the engine exhaust from gasoline engines.

[0004] For example, WO 2018 / 024547A1 describes a catalytic particle filter including a TWC catalytic material that penetrates the particle filter wall. Coating the TWC catalytic material on or in the filter may result in back pressure effects. In this patent application, a special coating scheme is proposed to avoid excessive increase in back pressure while providing full three-way conversion function. It is required that the coated porosity of the catalytic particle filter is less than the uncoated porosity of the particle filter.

[0005] WO2018 / 115900A1 describes a particle filter for use in an emission treatment system for a gasoline engine, the particle filter having an inlet side and an outlet side, wherein at least the inlet side is loaded with synthetic ash, the synthetic ash comprising one or more of aluminum oxide, zinc oxide, zinc carbonate, calcium oxide, calcium carbonate, cerium zirconium (mixed) oxide, zirconium oxide, cerium oxide, and hydrated aluminum oxide. It is described that the particle distribution can help prevent a significant amount of synthetic ash from entering the pores of the porous substrate.

[0006] It is well known that the filtration performance of a gasoline particulate filter will improve with increasing filter life, primarily due to the accumulation of ash and soot on the walls of the filter inlet side. In addition, it has been identified that the number of emission particles generated during the cold start phase of the test cycle represents a major portion of the total particles emitted during the test. Therefore, the particle filtration performance during the initial filtration phase, also known as fresh filtration efficiency, is a major focus in the development of gasoline particulate filters.

[0007] As particulate emissions from gasoline engines are regulated by stricter regulations, such as Euro 6 and National 6, vehicle manufacturers, ie, original equipment manufacturers (OEMs), require gasoline particulate filters to have high fresh filtration efficiency and desirably low back pressure.

[0008] There is a need to provide an improved particulate filter for treating an exhaust gas flow from a gasoline engine that can provide ultra-high fresh filter efficiency, such as greater than 90%, at relatively low back pressures. Summary of the invention

[0009] It is an object of the present invention to provide a particle filter for treating an exhaust gas flow from a gasoline engine which particle filter provides a higher fresh filter efficiency without suffering from an unacceptable increase in back pressure.

[0010] It has surprisingly been found that the object of the present invention is achieved by a particle filter comprising a layer of inorganic powder particles in the inlet channel and / or outlet channel of the filter.

[0011] Therefore, in a first aspect, the present invention provides a particle filter comprising

[0012] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0013] - a layer of inorganic particles supported on the surface of the porous wall in the inlet channel and / or the outlet channel,

[0014] The inorganic particles include boehmite particles or consist of boehmite particles.

[0015] In a second aspect, the present invention provides a method of producing a particle filter, the method comprising - providing a substrate, the substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end, and

[0016] - Inorganic particles comprising or consisting of boehmite particles are applied to the surface of the porous walls in the inlet channel and / or the outlet channel.

[0017] In a third aspect, the present invention provides an exhaust gas treatment system comprising a particle filter as described in the first aspect or a particle filter obtainable or obtained by the method as described in the second aspect, the particle filter being located downstream of a gasoline engine.

[0018] In a fourth aspect, the present invention provides a method for treating an exhaust flow from a gasoline engine, the method comprising contacting the exhaust flow with a particulate filter as described in the first aspect, a particulate filter obtainable or obtained by the method as described in the second aspect, or an exhaust treatment system as described in the third aspect.

[0019] It has been found that a particulate filter for treating exhaust gases from a gasoline engine (also referred to herein as a gasoline particulate filter) can provide improved fresh filtration efficiency compared to corresponding filters of the prior art, while no significant backpressure increase is observed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 An external view of a wall flow substrate having an inlet end and an outlet end is illustrated.

[0021] Figure 2 A longitudinal cross-sectional view of an exemplary wall flow substrate having a plurality of porous walls extending longitudinally from an inlet end to an outlet end of the substrate is illustrated.

[0022] Figure 3A , Figure 3B , Figure 3C and Figure 3D XRD patterns of alumina A, boehmite B, boehmite C, and boehmite D used in comparative examples and examples of the present invention are shown, respectively. DETAILED DESCRIPTION

[0023] The present invention is described in detail below. It should be understood that the present invention can be embodied in many different ways and should not be construed as being limited to the embodiments set forth herein.

[0024] The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The terms "comprising", "including", and the like are used interchangeably with "containing", and are to be interpreted in a non-limiting, open-ended manner. That is, for example, additional components or elements may be present. The expression "consisting of" or cognates may be encompassed by "comprising" or cognates.

[0025] In this document, the term "layer", for example in the context of an inorganic particle layer, is intended to mean a thin coating of a gas permeable material carried on a blank or pre-coated wall of a substrate. The layer may be in the form of packed particles on the walls of the substrate with gaps therebetween to allow gas to permeate through.

[0026] The term "D 10 ”, “D 50 ” and “D 90 " have their usual meanings, namely, refer to the points at which the cumulative volume from the small particle diameter side reaches 10%, 50% and 90% in the cumulative particle size distribution. The particle size distribution is measured using a laser diffraction particle size distribution analyzer.

[0027] Terms such as "palladium component," "platinum component," and "rhodium component" are intended to describe the various platinum group metals present in any possible valence state, which may be, for example, the metal or metal oxide in a catalytically active form, or may be, for example, a metal compound, complex, etc., which decomposes or is otherwise converted to a catalytically active form upon calcination or use of the catalyst.

[0028] The term "support" refers to a material in particulate form used to receive and support one or more platinum group metal (PGM) components, and optionally one or more other components, such as stabilizers, promoters and binders.

[0029] In this article, any reference to "g / ft 3 ” or “g / in 3 References to loadings in units of "are intended to mean the weight of a particular component, coating or layer per unit volume of the substrate or substrate portion on which it is supported.

[0030] According to a first aspect of the present invention, there is provided a particle filter, the particle filter comprising:

[0031] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0032] - a layer of inorganic particles supported on the surface of the porous wall in the inlet channel and / or the outlet channel,

[0033] The inorganic particles include boehmite particles or consist of boehmite particles.

[0034] As used herein, substrate refers to a structure suitable for withstanding the conditions encountered in the exhaust stream of an internal combustion engine, which can itself serve as a particulate filter, and can also carry functional materials, such as a filtration improvement layer, such as the inorganic particle layer described herein, and optionally any other layers.

[0035] The substrate includes a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels that are open at the inlet end and closed at the outlet end, and a certain number of the channels other than the inlet channels are outlet channels that are closed at the inlet end and open at the outlet end. The configuration of the substrate is also referred to as a wall-flow substrate, requiring that the engine exhaust gas in the inlet channel flows through the porous walls into the outlet channel to reach the outlet end of the substrate.

[0036] Generally speaking, the substrate may exhibit a honeycomb structure having alternating channels plugged with plugs at opposite ends.

[0037] The porous wall of the substrate is generally made of ceramic material or metal material.

[0038] Suitable ceramic materials that can be used to construct the substrate can include any suitable refractory material, such as cordierite, mullite, cordierite-alumina, silicon carbide, silicon nitride, zirconium oxide, mullite, spodumene, alumina-silicon dioxide-magnesia, zirconium silicate, magnesium silicate, sillimanite, petalite, alumina, aluminum titanate and aluminosilicate. Typically, the porous wall of the substrate is made of cordierite or silicon carbide.

[0039] Suitable metal materials that can be used to construct substrates can include heat-resistant metals and metal alloys, such as titanium and stainless steel and other alloys with iron as the basic or main component. Such alloys can contain one or more of nickel, chromium and / or aluminum, and the total amount of these metals can advantageously account for at least 15% by weight of the alloy, such as 10% to 25% by weight of chromium, 3% to 8% by weight of aluminum and up to 20% by weight of nickel. The alloy may also contain a small amount or trace of one or more metals, such as manganese, copper, vanadium, titanium, etc. The surface of the metal substrate can be oxidized at high temperatures (e.g., 1000° C. or higher) to form an oxide layer on the surface of the substrate, thereby improving the corrosion resistance of the alloy and promoting the adhesion of any coating to the metal surface.

[0040] The passage at the closed end is plugged with a plunger made of a sealing material. Any suitable sealing material may be used without limitation.

[0041] The channels of the substrate can have any suitable cross-sectional shape and size, such as circular, oval, triangular, rectangular, square, hexagonal, trapezoidal or other polygons. The substrate can have up to 700 channels (i.e., holes) per square inch of cross section. For example, the substrate can have 100 holes / square inch to 500 holes / square inch ("cpsi"), typically with 200cpsi to 400cpsi. The walls of the substrate can have different thicknesses, with a typical range of 2 mils to 0.1 inches. Preferably, the substrate has a number of inlet channels equal to the number of outlet channels, and the channels are evenly distributed throughout the substrate.

[0042] Figure 1 and Figure 2 A typical wall-flow substrate comprising a plurality of inlet channels and outlet channels is illustrated.

[0043] Figure 1 Depicted is an external view of a wall flow substrate having an inlet end (01) from which an exhaust gas stream (13) enters the substrate and an outlet end (02) from which the treated exhaust gas exits. Alternating channels are plugged with plungers to form a checkerboard pattern at the inlet end (01) shown and an opposing checkerboard pattern at the outlet end (02) not shown.

[0044] Figure 2 A longitudinal cross-sectional view of a wall-flow substrate is schematically depicted, the wall-flow substrate comprising a first plurality of channels (11) opening at an inlet end (01) and closed at an outlet end (02) and a second plurality of channels (12) opening at the outlet end (02) and closed at the inlet end (01). The channels are preferably parallel to each other to form a constant wall thickness between the channels. An exhaust gas flow entering the first plurality of channels from the inlet end cannot leave the substrate without diffusing through the porous wall (10) into the second plurality of channels.

[0045] The particle filter according to the present invention may include an inorganic particle layer on the surface of the porous wall in the inlet channel and / or the outlet channel. In other words, the inorganic particle layer can be loaded on the porous wall in the inlet channel alone, loaded on the porous wall in the outlet channel alone, or loaded on the porous wall in both the inlet channel and the outlet channel. In particular, the inorganic particle layer can be loaded on the porous wall in the inlet channel alone, or loaded on the porous wall in both the inlet channel and the outlet channel, more preferably loaded on the porous wall in the inlet channel alone.

[0046] It is understood that the inorganic particle layer is intended to be supported on the surface of the porous walls in the inlet and / or outlet channels, also referred to as an "on-wall" coating, while small amounts of inorganic particles may penetrate into the pores within the porous walls.

[0047] According to the present invention, the inorganic particles comprise boehmite particles. For example, the inorganic particles may comprise boehmite particles and optional additional inorganic particles. The additional inorganic particles may be non-PGM components such as aluminum oxide, zirconium oxide, ceria, silicon dioxide, titanium dioxide, magnesium oxide, zinc oxide, zinc carbonate, calcium oxide, calcium carbonate, silicate zeolite, aluminosilicate zeolite or a combination or composite thereof.

[0048] The additional inorganic particles may also include PGM components, such as palladium components and / or platinum components. In this article, the inorganic particle layer supported on the porous wall in the inlet channel and / or outlet channel of the substrate particularly refers to a layer that exhibits less or no, preferably no TWC activity, but if one or more PGM components are included in the inorganic particles, it may exhibit certain catalytic activity. The PGM component, if present, may be supported on particles of non-PGM components as described above, or may be separated from particles of non-PGM components. In some embodiments, the inorganic particles do not include PGM components.

[0049] For purposes of the present invention, the boehmite particles comprise the majority amount of the inorganic particles, i.e., greater than 50% by weight, which can be, for example, 75% by volume or more, 85% by volume or more, 90% by volume or more, or even 95% by volume or more based on the total volume of the inorganic particles.

[0050] Preferably, the inorganic particles may consist essentially of boehmite particles. That is, the inorganic particles include an unintentionally added amount of inorganic particles other than boehmite particles. In this context, the term "unintentionally added amount" is intended to mean no more than 1 volume %, no more than 0.5 volume %, no more than 0.1 volume % or no more than 0.05 volume %.

[0051] The BET surface area determined by nitrogen adsorption is not more than 150 m 2 / g, preferably not more than 100m 2 / g or not more than 80m 2 Boehmite particles of 1.1 g / cm2 are particularly suitable for the present invention.

[0052] Additionally or alternatively, the boehmite particles useful in the present invention may have a particle diameter no greater than 0.6 cm-1 as determined by nitrogen adsorption. 3 / g, no more than 0.4cm 3 / g or not more than 0.3cm 3 / g of BET pore volume.

[0053] The boehmite particles useful in the present invention may have a D of no greater than 50 micrometers (μm), no greater than 30 μm, or no greater than 20 μm. 90 The boehmite particles useful in the present invention may have a D of no greater than 20 μm, no greater than 15 μm, or no greater than 10 μm.50 The boehmite particles useful in the present invention may have a D of no greater than 8 μm, no greater than 5 μm, or no greater than 2 μm. 10 .

[0054] For the purposes of the present invention, there is no limitation on the source of the boehmite particles, which may be commercially available or synthesized by any known method.

[0055] The particle filter according to the present invention may include a particle loading of 0.005 g / in 3 Up to 0.83g / in 3 (i.e. about 0.3g / L to 50g / L), 0.01g / in 3 Up to 0.33g / in 3 (i.e. about 0.6 g / L to 20 g / L) or 0.015 g / in 3 Up to 0.1g / in 3 (ie, about 0.9 g / L to 6 g / L) of inorganic particle layer.

[0056] The inorganic particle layer may be applied to the surface of the porous wall of the substrate by any known process such as a dry coating process and a wash coating process.

[0057] The dry coating process is well known and is generally carried out by blowing inorganic particles in particle form or a suitable precursor thereof from an open end into the channel of the substrate by a carrier gas stream, and optionally drying and optionally calcining the coated substrate. In particular, for the purposes of the present invention, drying and calcining may not be performed after blowing in the inorganic particles in the dry coating process. By this process, no liquid carrier will be used. The inorganic particles are usually distributed on the surface of the porous wall of the channel in the form of a particle bed.

[0058] In some embodiments, boehmite particles and optional additional inorganic particles (or suitable precursors thereof) can be blown into the inlet channel from the open end of the channel toward the closed end. The particle bed formed in the inlet channel can be located on the porous wall of the inlet channel and is also opposite to the plunger that blocks the channel. The particle bed, i.e., the inorganic particle layer, is breathable, which may help to capture particulate matter (PM) in the exhaust gas stream and allow gaseous pollutants in the exhaust gas stream to penetrate through.

[0059] The layer of inorganic particles in the form of a particle bed may extend along the porous wall of the channel supporting the inorganic particles. It will be appreciated that the particle bed may extend along the entire length of the porous wall of the channel, or only along a portion of the length of the porous wall of the channel.

[0060] Washcoating processes are also well known and are generally carried out by applying a slurry in a liquid solvent (e.g., water) containing inorganic particles or a suitable precursor thereof and an optional auxiliary agent into the channel of the substrate from the open end, drying and optionally calcining the coated substrate. The inorganic particle layer applied by washcoating can be in the form of a porous coating that can extend along the porous walls of the channel that loads the inorganic particles. In addition, the porous coating can extend along the entire length of the porous wall of the channel, or only extend along a portion of the length of the porous wall of the channel.

[0061] The particle filter according to the present invention may also include a TWC coating in at least a portion of the inlet channel and / or outlet channel of the substrate. In particular, the TWC coating is present in both the inlet channel and the outlet channel of the substrate.

[0062] The TWC coating is typically in the form of a washcoat, also known as an "in-wall" coating, comprising the TWC composition.

[0063] It is to be understood that the TWC coating is intended to be supported in the pores of the porous walls of the channels, while appreciable amounts of the TWC composition may also be found on the surfaces of the porous walls in the coated channels.

[0064] There is no particular limitation on the TWC composition that can be used for the TWC coating included in the particulate filter. Generally, the TWC composition contains a platinum group metal component as a catalytically active substance, such as a rhodium component and one or both of a platinum component and a palladium component supported on carrier particles. Available materials used as a carrier may be refractory metal oxides, oxygen storage components, and any combination thereof.

[0065] Examples of refractory metal oxides may include, but are not limited to, alumina, lanthanum oxide doped alumina, barium oxide doped alumina, ceria doped alumina, zirconia doped alumina, ceria-zirconia doped alumina, lanthanum oxide-zirconia doped alumina, barium oxide-lanthanum oxide doped alumina, barium oxide-ceria doped alumina, barium oxide-zirconia doped alumina, barium oxide-lanthanum oxide-neodymia doped alumina, lanthanum oxide-ceria doped alumina, and any combination thereof.

[0066] Examples of oxygen storage components (OSC) may include, but are not limited to, reducible rare earth metal oxides such as ceria. The oxygen storage component may also include one or more of lanthanum oxide, praseodymium oxide, neodymium oxide, europium oxide, samarium oxide, ytterbium oxide, yttrium oxide, zirconium oxide, and hafnium oxide to form a composite oxide with ceria. In particular, the oxygen storage component is selected from ceria-zirconia composite oxides and stable ceria-zirconia composite oxides.

[0067] The particle filter according to the present invention may include a particle loading of 0.1 g / in 3 Up to 5.0g / in 3 (i.e. about 6.1 g / L to 305.1 g / L) or 0.5 g / in 3 Up to 3.0g / in 3 (i.e. about 30.5 g / L to 183.1 g / L) or 0.8 g / in 3 Up to 2g / in 3 (ie, about 49 g / L to 122 g / L) of TWC coating.

[0068] TWC coatings can contain a total loading of 1.0 g / ft 3 Up to 50.0g / ft 3 (i.e. about 0.04 g / L to 1.8 g / L) or 5.0 g / ft 3 Up to 20.0g / ft 3 (i.e., about 0.18 g / L to 0.71 g / L) of PGM components, calculated as the corresponding PGM elements.

[0069] The TWC coating can be applied to the substrate by any known process, typically by a washcoating process. The washcoating process is generally performed by coating a slurry of TWC catalyst particles containing the supported PGM component and optional promoters in a solvent (e.g., water), drying and calcining the coated substrate.

[0070] When present, the TWC coating will be applied to the substrate prior to supporting the inorganic particle layer as described above. When present, the TWC coating may also be referred to as an undercoating, ie, located below the inorganic particle layer.

[0071] In some exemplary embodiments, the particle filter according to the present invention comprises,

[0072] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0073] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0074] - an optional TWC coating, preferably a washcoat comprising a TWC composition,

[0075] The inorganic particles include boehmite particles or consist of boehmite particles.

[0076] In a further exemplary embodiment, the particle filter according to the present invention comprises,

[0077] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0078] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0079] - an optional washcoat layer comprising a TWC composition,

[0080] Wherein the inorganic particles include boehmite particles in an amount of 75 wt % or more, 85 wt % or more, 90 wt % or more, or even 95 wt % or more, based on the total weight of the inorganic particles.

[0081] In some other exemplary embodiments, the particle filter according to the present invention comprises,

[0082] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0083] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0084] - an optional washcoat layer comprising a TWC composition,

[0085] The inorganic particles are basically composed of boehmite particles.

[0086] In some specific embodiments, the particle filter according to the present invention comprises,

[0087] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0088] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0089] - an optional washcoat layer comprising a TWC composition,

[0090] The inorganic particles have a BET surface area determined by nitrogen adsorption of not more than 100 m 2 / g or not more than 80m 2 / g boehmite particle composition.

[0091] In some other specific embodiments, the particle filter according to the present invention comprises,

[0092] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0093] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0094] - an optional washcoat layer comprising a TWC composition,

[0095] The inorganic particles are essentially composed of a BET pore volume determined by nitrogen adsorption of not more than 0.4 cm 3 / g or not more than 0.3cm 3 / g boehmite particle composition.

[0096] In some preferred specific embodiments, the particle filter according to the present invention comprises,

[0097] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0098] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0099] - an optional washcoat layer comprising a TWC composition,

[0100] The inorganic particles have a BET surface area determined by nitrogen adsorption of not more than 100 m 2 / g and the BET pore volume is not greater than 0.4 cm 3 / g boehmite particle composition.

[0101] In some more preferred specific embodiments, the particle filter according to the present invention comprises,

[0102] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0103] - a layer of inorganic particles supported on the surface of the porous wall in at least the inlet channel, and

[0104] - an optional washcoat layer comprising a TWC composition,

[0105] The inorganic particles have a BET surface area determined by nitrogen adsorption of not more than 80 m 2 / g and the BET pore volume is not greater than 0.3 cm 3 / g boehmite particle composition.

[0106] In each of those exemplary and specific embodiments described above, it is preferred that the inorganic particles consist essentially of boehmite particles having at least one, preferably all, of the following particle size characteristics:

[0107] -D not more than 30μm 90 ,

[0108] -D not more than 15μm 50 ,as well as

[0109] -D not more than 5μm 10 .

[0110] More preferably, the inorganic particles consist essentially of boehmite particles having at least one, preferably all, of the following particle size characteristics:

[0111] -D not more than 20μm 90 ,

[0112] -D not more than 10μm 50 ,as well as

[0113] -D not more than 2μm 10 .

[0114] In the above-mentioned exemplary and specific embodiments, it is preferred that the inorganic particle layer does not contain a PGM component.

[0115] In those exemplary and specific embodiments described above, it is preferred that the particulate filter includes a washcoat layer comprising a TWC composition.

[0116] The particulate filter may be housed within a housing having an inlet and an outlet for exhaust flow, which housing may be operatively associated with and in fluid communication with the rest of the engine's exhaust system.

[0117] According to a second aspect of the present invention, there is provided a method for producing a particle filter, the method comprising:

[0118] - providing a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end, and

[0119] - applying inorganic particles comprising or consisting of boehmite particles on the surface of the porous walls in the inlet channel and / or outlet channel.

[0120] The inorganic particles may be applied onto the surface of the porous wall by a dry coating or wash coating process (preferably a dry coating process) as described above in the first aspect.

[0121] In some embodiments, the inorganic particles are applied by a dry coating process, which includes blowing inorganic particles in particle form or a suitable precursor thereof from an open end into a channel of a substrate by a carrier gas stream, without calcining after blowing the inorganic particles. In some other embodiments, the inorganic particles are applied by a dry coating process, which includes blowing inorganic particles in particle form or a suitable precursor thereof from an open end into a channel of a substrate by a carrier gas stream, without drying or calcining after blowing the inorganic particles. By such a process, the applied boehmite particles are not converted into an alumina form, and therefore the particle filter described in the first aspect of the present invention can be provided. More particularly, boehmite particles and optional additional inorganic particles (or a suitable precursor thereof) can be blown into the channel from the open end of the channel toward the closed end.

[0122] In some embodiments, the method for producing a particle filter further comprises applying a TWC coating in the porous walls in at least a portion of the inlet channel and / or outlet channel of the substrate before applying the inorganic particles to the surface of the porous walls. The TWC coating can be applied by a washcoating process as described above.

[0123] Any general description and described preferred requirements of the inorganic particles and TWC coating in the first aspect above may be applied herein by reference.

[0124] According to a third aspect, an exhaust gas treatment system is provided, comprising a particle filter as described in the first aspect or a particle filter obtainable or obtained by the method as described in the second aspect, the particle filter being located downstream of a gasoline engine.

[0125] According to a fourth aspect, there is provided a method for treating an exhaust gas flow from a gasoline engine, the method comprising contacting the exhaust gas flow with a particle filter as described in the first aspect, a particle filter obtainable or obtained from the method as described in the second aspect, or an exhaust gas treatment system as described in the third aspect.

[0126] Implementation

[0127] Various embodiments are listed below. It should be understood that the embodiments listed below can be combined with all aspects of the scope of the present invention and other embodiments.

[0128] Embodiment 1. A particle filter, comprising

[0129] - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and

[0130] - a layer of inorganic particles supported in the inlet channel and / or outlet channel, preferably on the surface of the porous wall in at least the inlet channel,

[0131] The inorganic particles include boehmite particles or consist of the boehmite particles.

[0132] Embodiment 2. A particulate filter according to Embodiment 1, wherein the inorganic particles contain the boehmite particles in an amount of 50 volume % or more, 75 volume % or more, 85 volume % or more, 90 volume % or more, or even 95 volume % or more, based on the total weight of the inorganic particles.

[0133] Embodiment 3. The particulate filter of Embodiment 2, wherein the inorganic particles consist essentially of the boehmite particles.

[0134] Embodiment 4. The particulate filter according to any one of the preceding embodiments, wherein the inorganic particle layer exhibits no three-way conversion catalytic activity.

[0135] Embodiment 5. The particulate filter according to any of the preceding embodiments, wherein the inorganic particle layer does not contain a PGM component.

[0136] Embodiment 6. A particulate filter according to any one of the preceding embodiments, wherein the boehmite particles have a particle size of no greater than 150 m 2 / g, not more than 100m 2 / g or not more than 80m 2 / g of BET surface area.

[0137] Embodiment 7. A particulate filter according to any one of the preceding embodiments, wherein the boehmite particles have a particle diameter no greater than 0.6 cm as determined by nitrogen adsorption. 3 / g, no more than 0.4cm 3 / g or not more than 0.3cm 3 / g of BET pore volume.

[0138] Embodiment 8. A particle filter according to any one of the preceding embodiments, wherein the inorganic particles have at least one of the following particle size characteristics, preferably all of the particle size characteristics,

[0139] - D not greater than 50 μm, not greater than 30 μm or not greater than 20 μm 90 ,

[0140] - D not greater than 20 μm, not greater than 15 μm or not greater than 10 μm 50 ,as well as

[0141] - D not larger than 8 μm, not larger than 5 μm or not larger than 2 μm 10 .

[0142] Embodiment 9. The particulate filter according to any of the preceding embodiments, further comprising a three-way conversion catalyst (TWC) coating, preferably a washcoat layer comprising a TWC composition.

[0143] Embodiment 10. The particulate filter according to Embodiment 9, wherein the three-way conversion catalyst coating is located in at least a portion of the inlet channel and / or outlet channel of the substrate.

[0144] Embodiment 11. The particulate filter according to any one of the preceding embodiments, comprising the inorganic particle layer having a loading amount of 0.3 g / L to 50 g / L, 0.6 g / L to 20 g / L, or 0.9 g / L to 6 g / L.

[0145] Embodiment 12. The particulate filter according to any one of the preceding embodiments, wherein the particulate filter is a gasoline particulate filter.

[0146] Embodiment 13. A method for producing a particle filter, the method comprising

[0147] - providing a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end, and

[0148] - applying inorganic particles comprising or consisting of boehmite particles on the surface of the porous walls in the inlet channel and / or outlet channel.

[0149] Embodiment 14. The method according to embodiment 13, wherein the inorganic particles are applied by a dry coating or wash coating process, preferably by a dry coating process.

[0150] Embodiment 15. A method according to Embodiment 13, wherein the inorganic particles are applied by a dry coating process, the dry coating process comprising blowing the inorganic particles or their precursors in particle form from the open end into the channels of the substrate by a carrier gas flow without drying and / or calcining after the blowing.

[0151] Embodiment 16. The method according to embodiment 15, wherein the inorganic particles consist of the boehmite particles and optionally additional inorganic particles or suitable precursors thereof.

[0152] Embodiment 17. The method of any one of Embodiments 13 to 16, wherein the inorganic particles comprise the boehmite particles in an amount of 50% by volume or more, 75% by volume or more, 85% by volume or more, 90% by volume or more, or even 95% by volume or more.

[0153] Embodiment 18. The method of Embodiment 16, wherein the inorganic particles consist essentially of the boehmite particles.

[0154] Embodiment 19. The method of any one of Embodiments 13 to 18, wherein the boehmite particles have a particle diameter no greater than 150 m / s as determined by nitrogen adsorption. 2 / g, not more than 100m 2 / g or not more than 80m 2 / g of BET surface area.

[0155] Embodiment 20. The method of any one of Embodiments 13 to 19, wherein the boehmite particles have a particle diameter no greater than 0.6 cm as determined by nitrogen adsorption. 3 / g, no more than 0.4cm 3 / g or not more than 0.3cm 3 / g of BET pore volume.

[0156] Embodiment 21. The method according to any one of embodiments 13 to 20, wherein the inorganic particles have at least one, preferably all, of the following particle size characteristics:

[0157] - D not greater than 50 μm, not greater than 30 μm or not greater than 20 μm 90 ,

[0158] - D not greater than 20 μm, not greater than 15 μm or not greater than 10 μm 50 ,as well as

[0159] - D not larger than 8 μm, not larger than 5 μm or not larger than 2 μm 10 .

[0160] Embodiment 22. The method of any one of Embodiments 13 to 21, wherein the inorganic particle layer is applied at a loading of 0.3 g / L to 50 g / L, 0.6 g / L to 20 g / L, or 0.9 g / L to 6 g / L.

[0161] Embodiment 23. An exhaust treatment system comprising a particulate filter according to any one of Embodiments 1 to 12 or a particulate filter obtainable or obtained from a method according to any one of Embodiments 13 to 22, and located downstream of a gasoline engine.

[0162] Embodiment 24. A method for treating an exhaust gas flow from a gasoline engine, the method comprising contacting the exhaust gas flow with a particulate filter according to any one of Embodiments 1 to 12, a particulate filter obtainable or obtained from a method according to any one of Embodiments 13 to 22, or an exhaust treatment system according to Embodiment 23.

[0163] Example

[0164] Various aspects of the present invention are more fully illustrated by the following examples, which are set forth for the purpose of illustrating certain aspects of the present invention and should not be construed as limiting the present invention.

[0165] I. Preparation of particle filters

[0166] Materials and characterization

[0167] The materials used as inorganic particles for preparing the particle filter in the examples are summarized in Table 1 below. The particle size was measured by a Sympatec HELOS laser diffraction particle size analyzer. The surface area and pore volume were measured by a Micromeritics ASAP2420 surface area and porosity analyzer using the BET model at 77K nitrogen adsorption. X-ray diffraction (XRD) scanning was measured by a Bruker D8 Advance, and the XRD pattern is shown in FIG. 3A to FIG. 3D middle.

[0168] Table 1

[0169]

[0170] Reference Example 1 (R1)

[0171] A gasoline particulate filter cordierite substrate S1 was used as a reference filter (blank filter), which had a size of 118.4 mm (D) × 127 mm (L) and a volume of 1.4 L (about 85.4 in 3 ), a pore density of 300 cells per square inch (cpsi), a wall thickness of 8 mils, and a porosity of 65% as determined by mercury intrusion measurement.

[0172] Reference Example 2 (R2)

[0173] A particulate filter with a TWC coating was prepared from the same filter substrate as the blank filter of Reference Example 1 (substrate S1) by applying the TWC washcoat layer to both the inlet and outlet channels of the blank filter.

[0174] In a planetary mixer (P-mixer), 24.21 g of a 9.68 wt% aqueous solution of rhodium nitrate was impregnated onto 255 g of high surface area gamma alumina powder to form a wet powder while achieving initial wetness. In a planetary mixer (P-mixer), 14.37 g of a 16.31 wt% aqueous solution of diethanolamine hexahydroxyplatinate was impregnated onto 712 g of a ceria / zirconia (40% ceria) composite powder to form a wet powder while achieving initial wetness. An aqueous slurry was formed by mixing the above two wet powders with 1124 g of deionized water, to which 78 g of barium nitrate and 68 g of a 21.3 wt% aqueous solution of zirconium nitrate were added. The pH of the slurry was adjusted to 3.6 with nitric acid. The slurry was ground to a particle size D 90 The washcoat layer was 4.5 μm and then coated into the inlet channel of the blank filter at 50% of the washcoat layer loading, and coated into the outlet channel of the blank filter at the remaining 50% of the washcoat layer loading. The coated substrate was then dried at 150° C. for 1 hour and then calcined at 550° C. for 1 hour.

[0175] The obtained inlet TWC coating has a viscosity of about 1.23 g / in 3 (75 g / L) washcoat loading and about 10.0 g / ft 3 (0.35 g / L) total PGM loading, with a Pt / Rh ratio of 5 / 5.

[0176] The TWC coating prepared by the same process is referred to herein as TWC-1.

[0177] Reference Example 3 (R3)

[0178] A gasoline particulate filter cordierite substrate S2 was used as a reference filter (blank filter), which had a size of 132.1 mm (D) × 127 mm (L) and a volume of 1.74 L (about 106.1 in). 3 ), a pore density of 300 cells per square inch (cpsi), a wall thickness of 8 mils, and a porosity of 65% as determined by mercury intrusion measurement.

[0179] Reference Example 4 (R4)

[0180] A particulate filter with a TWC coating was prepared from the same filter substrate as the blank filter of Reference Example 3 (Substrate S2) by applying the TWC washcoat layer to both the inlet and outlet channels of the blank filter.

[0181] In a planetary mixer (P-mixer), 20.08 g of a 9.79 wt % aqueous solution of rhodium nitrate was impregnated onto 257 g of high surface area gamma alumina powder to form a wet powder while achieving initial wetness. In a planetary mixer (P-mixer), 12.05 g of a 16.31 wt % aqueous solution of diethanolamine hexahydroxyplatinate was impregnated onto 698 g of a ceria / zirconia (40% ceria) composite powder to form a wet powder while achieving initial wetness. An aqueous slurry was formed by mixing the above two wet powders with 894 g of deionized water, to which 78 g of barium nitrate and 67 g of a 21.0 wt % aqueous solution of zirconium nitrate were added. The pH of the slurry was adjusted to 3.6 with nitric acid. The slurry was ground to a particle size D 90 The washcoat layer was 4.5 μm and then coated into the inlet channel of the blank filter at 50% of the washcoat layer loading, and coated into the outlet channel of the blank filter at the remaining 50% of the washcoat layer loading. The coated substrate was then dried at 150° C. for 1 hour and then calcined at 550° C. for 1 hour.

[0182] The obtained inlet TWC coating has a thermal conductivity of about 1.47 g / in 3 (90 g / L) washcoat loading and about 10.0 g / ft 3(0.35 g / L) total PGM loading, with a Pt / Rh ratio of 5 / 5.

[0183] The TWC coating prepared by the same process is referred to herein as TWC-2.

[0184] Comparative Example 1 (C1)

[0185] A particulate filter having a TWC coating and an alumina particle layer was prepared.

[0186] A particle filter with a TWC coating (TWC-1) was first prepared by applying the same process as described in Reference Example 2 on a blank filter (substrate S1) identical to that described in Reference Example 1. Then, alumina A powder was mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the inlet channel of the filter. After coating, the filter with the inorganic particle layer in the inlet channel was calcined at a temperature of 550°C for 1 hour. The loading amount of aluminum oxide A powder was 4 g / L (0.066 g / in 3 ).

[0187] Comparative Example 2 (C2)

[0188] A particulate filter having a TWC coating and an alumina particle layer was prepared.

[0189] First, a particle filter with a TWC coating (TWC-1) was prepared by applying the same process as described in Reference Example 2 on a cordierite substrate S3 as a blank filter, which had a size of 143.8 mm (D) × 152.4 mm (L) and a volume of 2.48 L (about 151.3 in 3 ), a pore density of 300 pores per square inch (cpsi), a wall thickness of 8 mils, and a porosity of 65% as determined by mercury intrusion measurement. Alumina A powder was then mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the inlet channel of the filter. After coating, the filter with the inorganic particle layer in the inlet channel was calcined at a temperature of 550°C for 1 hour. The loading amount of aluminum oxide A powder was 2g / L (0.033g / in 3 ).

[0190] Comparative Example 3 (C3)

[0191] A particulate filter having a TWC coating and an alumina particle layer was prepared.

[0192] A particle filter with a TWC coating (TWC-2) was first prepared by applying the same process as described in Reference Example 4 on a blank filter (substrate S2) identical to that described in Reference Example 3. Then, alumina A powder was mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the inlet channel of the filter. After coating, the filter with the inorganic particle layer in the inlet channel was calcined at a temperature of 550°C for 1 hour. The loading amount of aluminum oxide A powder was 3g / L (0.05g / in 3 ).

[0193] Comparative Example 4 (C4)

[0194] A particulate filter having a TWC coating and an alumina particle layer was prepared.

[0195] The preparation of the particle filter was the same as that of Comparative Example 3, except that the loading amount of aluminum oxide A powder was 5 g / L (0.082 g / in 3 ).

[0196] Comparative Example 5 (C5)

[0197] A particulate filter having a TWC coating and an alumina particle layer was prepared.

[0198] The preparation of the particle filter was the same as that of Comparative Example 3, except that the loading amount of aluminum oxide A powder was 7 g / L (0.115 g / in 3 ).

[0199] Embodiment 1 (E1) of the present invention

[0200] A particulate filter having a TWC coating and a boehmite B particle layer was prepared.

[0201] A particle filter with a TWC coating (TWC-1) was first prepared by applying the same process as described in Reference Example 2 on a blank filter (substrate S1) identical to that described in Reference Example 1. Then, boehmite B powder was mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the inlet channel of the filter. The loading amount of boehmite B powder is 3.6g / L (0.06g / in 3 ).

[0202] Embodiment 2 of the present invention (E2)

[0203] A particulate filter having a TWC coating and a boehmite C particle layer was prepared.

[0204] A particle filter with a TWC coating (TWC-1) was first prepared by applying the same process as described in Reference Example 2 on a blank filter (substrate S3) identical to that described in Comparative Example 2. Then, boehmite C powder was mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the inlet channel of the filter. The loading amount of boehmite C powder is 1.12g / L (0.018g / in 3 ).

[0205] Embodiment 3 of the present invention (E3)

[0206] A particulate filter having a TWC coating and a boehmite D particle layer was prepared.

[0207] A particle filter with a TWC coating (TWC-2) was first prepared by applying the same process as described in Reference Example 4 on a blank filter (substrate S2) identical to that described in Reference Example 3. Then, boehmite D powder was mixed with a carrier gas and heated at 600 m / s at room temperature. 3 / h flow rate into the filter inlet channel. The loading of boehmite D powder is 2.4g / L (0.04g / in 3 ).

[0208] Embodiment 4 of the present invention (E4)

[0209] A particulate filter having a TWC coating and a boehmite D particle layer was prepared.

[0210] The preparation of the particle filter was the same as in Example 3 of the present invention, except that the loading amount of boehmite D powder was 3.6 g / L (0.06 g / in 3 ).

[0211] II. Filtration performance

[0212] II.1 Backpressure

[0213] Through SuperFlow SF-1020Flowbench at 600m 3 The back pressure (BP) of the particle filter in all examples was investigated, measured under a cold air flow of 1.25 V / h.

[0214] II.2 Fresh filtration efficiency

[0215] According to the standard procedure defined in “BS EN ISO 29463-5:2018–Part 5:Test method for filter elements”, the 3The filtration efficiency of the particle filter in the above embodiment in a fresh state (0 km or out-of-box state) was measured on a fixed air filter performance test bench with a cold air flow of 1.5 / h, using aerosol di-(2-ethyl-hexyl) sebacate as the particle. The particle number (PN) of particles ranging between 0.10 μm and 0.15 μm was recorded by a PN counter both upstream and downstream of the test filter. The fresh filtration efficiency (FFE) was calculated according to the following equation:

[0216]

[0217] The test results of each particulate filter in the above examples are summarized in Table 2 below.

[0218] Table 2

[0219]

[0220] From the comparison of Reference Example 1 (R1) with Reference Example 2 (R2) and Reference Example 3 (R3) with Reference Example 4 (R4), it can be seen that the particle filter with TWC coating has higher back pressure (BP) and lower fresh filtration efficiency (FFE) than the blank filter, which may be because the TWC component penetrates into the porous wall of the substrate of the particle filter. In addition, by applying a layer of aluminum oxide A particles as shown in Comparative Example 1 (C1), the fresh filtration efficiency (FFE) can be improved, and the increase in back pressure is also acceptable. Surprisingly, by applying a layer of boehmite B particles as shown in Example 1 (E1) of the present invention, the fresh filtration efficiency (FFE) can be improved to a greater extent, and the increase in back pressure is also acceptable. The fresh filtration efficiency of the particle filter of Example 1 (E1) of the present invention can reach 96%, which is much higher than 88% of Comparative Example 1 (C1), and the back pressure of the two particle filters is 63mbar to 64mbar, which is very close.

[0221] Furthermore, under the same back pressure, the particle filter of Inventive Example 2 (E2) exhibited significantly higher fresh filtration efficiency (FFE) than that of Comparative Example 2 (C2).

[0222] The surprising improvements provided by the use of boehmite as the inorganic particles can also be observed by comparing Inventive Examples 3 and 4 with Comparative Examples 3 to 5. It is noteworthy that the particle filter of Inventive Example 3 (E3) exhibits comparable back pressure, but its fresh filtration efficiency is significantly higher than that of Comparative Example 3 (C3). In addition, compared to Comparative Example 5 (C5), the particle filter of Inventive Example 3 (E3) exhibits similar fresh filtration efficiency at significantly lower back pressure. The particle filter of Inventive Example 4 (E4) can exhibit a fresh filtration efficiency of 98%, which is higher than that of Comparative Example 5 (C5), and the particle filter of Inventive Example 4 (E4) even exhibits a lower back pressure than that of Comparative Example 5 (C5).

[0223] It has been demonstrated that a particulate filter comprising a layer of boehmite particles outperforms a comparative filter made from alumina particles in terms of the balance of backpressure and fresh filtration efficiency. It is expected that a particulate filter comprising a layer of boehmite particles will perform better after calcination, since it is known that calcination generally results in lower backpressure than a corresponding filter prepared without calcination.

[0224] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations may be made to the methods and apparatus of the present invention without departing from the spirit and scope of the present invention. Therefore, the present invention is intended to include modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A particle filter, comprising: - a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end; and - an inorganic particle layer supported in the inlet channel and / or outlet channel, preferably on the surface of the porous wall in at least the inlet channel, wherein the inorganic particles comprise or consist of boehmite particles.

2. The particulate filter according to claim 1, wherein the inorganic particles comprise the boehmite particles in an amount of 50% by volume or more, 75% by volume or more, 85% by volume or more, 90% by volume or more, or even 95% by volume or more, based on the total weight of the inorganic particles.

3. The particulate filter of claim 2, wherein the inorganic particles consist essentially of the boehmite particles. 4 . The particulate filter according to claim 1 , wherein the inorganic particle layer exhibits no three-way conversion catalytic activity.

5. The particulate filter according to any one of the preceding claims, wherein the inorganic particle layer does not contain a PGM component.

6. A particulate filter according to any one of the preceding claims, wherein the boehmite particles have a particle size of no greater than 150 m / s as determined by nitrogen adsorption. 2 / g, not more than 100m 2 / g or not more than 80m 2 / g of BET surface area.

7. A particulate filter according to any one of the preceding claims, wherein the boehmite particles have a relative humidity of no greater than 0.6 cm 2 as determined by nitrogen adsorption. 3 / g, no more than 0.4cm 3 / g or not more than 0.3cm 3 / g of BET pore volume.

8. The particle filter according to any one of the preceding claims, wherein the inorganic particles have at least one, preferably all, of the following particle size characteristics: - D not greater than 50 μm, not greater than 30 μm or not greater than 20 μm 90 , - D not greater than 20 μm, not greater than 15 μm or not greater than 10 μm 50 ,as well as - D not larger than 8 μm, not larger than 5 μm or not larger than 2 μm 10 .

9. A particle filter according to any one of the preceding claims, further comprising a three-way conversion catalyst (TWC) coating, preferably a washcoat comprising a TWC composition. 10 . The particulate filter according to claim 9 , wherein the three-way conversion catalyst coating is located in at least a portion of the inlet channel and / or the outlet channel of the substrate.

11. The particle filter according to any one of the preceding claims, comprising a layer of inorganic particles having a loading of 0.3 to 50 g / L, 0.6 to 20 g / L, or 0.9 to 6 g / L.

12. A particle filter according to any one of the preceding claims, the particle filter being a gasoline particle filter.

13. A method for producing a particle filter, the method comprising - providing a substrate comprising a plurality of longitudinally extending porous walls to form a plurality of parallel channels extending from an inlet end to an outlet end, wherein a certain number of the channels are inlet channels open at the inlet end and closed at the outlet end, and a certain number of the channels are outlet channels closed at the inlet end and open at the outlet end, and - applying inorganic particles comprising or consisting of boehmite particles on the surface of the porous walls in the inlet channel and / or the outlet channel.

14. The method according to claim 13, wherein the inorganic particles are applied by a dry coating or wash coating process, preferably by a dry coating process.

15. The method according to claim 13, wherein the inorganic particles are applied by a dry coating process, the dry coating process comprising blowing the inorganic particles or their precursors in particle form from the open end into the channels of the substrate by a carrier gas flow without drying and / or calcining after the blowing.

16. The method according to claim 15, wherein the inorganic particles consist of the boehmite particles and optionally additional inorganic particles or suitable precursors thereof.

17. The method of any one of claims 13 to 16, wherein the inorganic particles comprise the boehmite particles in an amount of 50% by volume or more, 75% by volume or more, 85% by volume or more, 90% by volume or more, or even 95% by volume or more.

18. The method of claim 16, wherein the inorganic particles consist essentially of the boehmite particles.

19. The method of any one of claims 13 to 18, wherein the boehmite particles have a particle size of no greater than 150 m / s as determined by nitrogen adsorption. 2 / g, not more than 100m 2 / g or not more than 80m 2 / g of BET surface area.

20. The method of any one of claims 13 to 19, wherein the boehmite particles have a particle diameter no greater than 0.6 cm as determined by nitrogen adsorption. 3 / g, no more than 0.4cm 3 / g or not more than 0.3cm 3 / g of BET pore volume.

21. The method according to any one of claims 13 to 20, wherein the inorganic particles have at least one, preferably all, of the following particle size characteristics: - D not greater than 50 μm, not greater than 30 μm or not greater than 20 μm 90 , - D not greater than 20 μm, not greater than 15 μm or not greater than 10 μm 50 ,as well as - D not larger than 8 μm, not larger than 5 μm or not larger than 2 μm 10 .

22. The method of any one of claims 13 to 21, wherein the inorganic particle layer is applied at a loading of 0.3 g / L to 50 g / L, 0.6 g / L to 20 g / L, or 0.9 g / L to 6 g / L.

23. An exhaust gas treatment system comprising a particle filter according to any one of claims 1 to 12 or a particle filter obtainable or obtained from a method according to any one of claims 13 to 22 and located downstream of a gasoline engine.

24. A method for treating an exhaust gas flow from a gasoline engine, the method comprising contacting the exhaust gas flow with a particle filter according to any one of claims 1 to 12, a particle filter obtainable or obtained from a method according to any one of claims 13 to 22, or an exhaust gas treatment system according to claim 23.

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