EP2731718A1 - Method for coating a catalysed particulate filter and a particulate filter - Google Patents

Method for coating a catalysed particulate filter and a particulate filter

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Publication number
EP2731718A1
EP2731718A1 EP12728482.6A EP12728482A EP2731718A1 EP 2731718 A1 EP2731718 A1 EP 2731718A1 EP 12728482 A EP12728482 A EP 12728482A EP 2731718 A1 EP2731718 A1 EP 2731718A1
Authority
EP
European Patent Office
Prior art keywords
catalyst
ammonia
filter
active
washcoat
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP12728482.6A
Other languages
German (de)
French (fr)
Inventor
Pär L. GABRIELSSON
Keld Johansen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Topsoe AS
Original Assignee
Haldor Topsoe AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Haldor Topsoe AS filed Critical Haldor Topsoe AS
Priority claimed from PCT/EP2012/061328 external-priority patent/WO2013007466A1/en
Publication of EP2731718A1 publication Critical patent/EP2731718A1/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
    • B01D53/9463—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on one brick
    • B01D53/9468—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on one brick in different layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0244—Coatings comprising several layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0246—Coatings comprising a zeolite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1023—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20738—Iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20761—Copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/915—Catalyst supported on particulate filters
    • B01D2255/9155—Wall flow filters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/82—Phosphates
    • B01J29/84—Aluminophosphates containing other elements, e.g. metals, boron
    • B01J29/85—Silicoaluminophosphates [SAPO compounds]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B01J37/0027—Powdering
    • B01J37/0036—Grinding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating
    • B01J37/0219—Coating the coating containing organic compounds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
    • F01N2510/0684—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having more than one coating layer, e.g. multi-layered coatings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/2073—Selective catalytic reduction [SCR] with means for generating a reducing substance from the exhaust gases

Definitions

  • the present invention relates to a multifunctional
  • the invention is a method for the preparation of a
  • TWC three way catalyst
  • SCR selective catalytic reduction
  • the multifunctional catalysed filter is in particular useful for the cleaning of exhaust gas from lean burn gasoline engines, such as the gasoline direct injection (GDI) engine.
  • GDI gasoline direct injection
  • GDI engines generate more carbonaceous soot than gasoline premixed injection engines.
  • Euro 5+ Diesel legislation is expected to be used for GDI in the future with a particulate mass limit at 4.5mg/km, which requires filtration of the engine exhaust in order to reach the above limit.
  • filters for use in automotive applications are the wall flow type filter consisting of honeycombed
  • Gas inlet channels are open at their gas inlet side and blocked at the opposite outlet end and the gas outlet channels are open at the outlet end and blocked the inlet end, so that a gas stream entering the wall flow filter is forced through the partition walls before into the outlet channels.
  • exhaust gas from gasoline engines contains nitrogen oxides (NOx) , carbon monoxide and unburnt hydrocarbons, which are chemical compounds
  • Catalysts being active in the removal or reduction of NOx, carbon monoxide and hydrocarbons to harmless compounds are per se known in the art.
  • the patent literature discloses numerous cleaning systems comprising separate catalyst units for the removal of harmful compounds from engine exhaust gas. Also known in the art are exhaust gas particulate filters coated with catalysts catalysing oxidation of hydrocarbons and particulate matter together with selective catalytic reduction (SCR) of NOx by reaction with ammonia being added as such or as precursor thereof into the exhaust gas.
  • SCR selective catalytic reduction
  • catalysts are segmentarily or zone coated in different zones of the filter. Segmentary or zone coating of different catalysts on the filter is an expensive and difficult preparation process.
  • the present invention suggests an easier method for the preparation of particulate filers catalysed with different catalysts for the selective reduction of nitrogen oxides with ammonia and removal of hydrocarbons, carbon monoxide and excess ammonia.
  • the invention provides a method of preparation a catalysed wall flow filter, comprising the steps of a) providing a wall flow filter body with a plurality longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls; b) providing a catalyst washcoat comprising a first
  • catalyst composition being active in reaction of nitrogen oxides with carbon monoxide and hydrogen to ammonia
  • the first catalyst composition has a particle size being smaller than average pore diameter of the porous partition walls and the second catalyst
  • composition has a particle size with is larger than the average pore diameter of the porous partition walls; c) coating the filter body with the catalyst washcoat by introduction of the washcoat into outlet end of the outlet channels; and d) drying and heat treating the coated filter body to obtain the catalysed particulate filter.
  • NOx +H 2 /CO NH 3 +C0 2 +H 2 0 are palladium, platinum, a mixture of palladium and rhodium and a mixture of palladium, platinum and rhodium.
  • These catalysts catalyse the ammonia formation under rich burn operating conditions of the gasoline engine, i.e.
  • Palladium is the preferred catalyst with the highest ammonia formation.
  • Ammonia being thus formed within the inlet channels by the above reaction permeates through the partition walls of the filter into the outlet channels and is during the rich operating conditions adsorbed in the SCR catalyst in the outlet flow channels.
  • Both the ammonia forming catalyst and the SCR catalyst are preferably deposited on the partition walls on the sides facing the inlet channel and the outlet channel,
  • NOx being present in the exhaust gas reacts with the ammonia stored in the SCR catalyst by the following
  • SCR catalyst are per se known in the art.
  • the preferred catalyst being active in the selective reduction of nitrogen oxides comprises at least one of a zeolite, a silica aluminum phosphate, an ion exchanged zeolite, silica aluminum phosphate promoted with iron and/or copper, one or more base metal oxides.
  • a further preferred SCR catalyst for use in the invention is a silica aluminium phosphate with chabazite structure, such as SAPO 34, promoted with copper and/or iron.
  • the wall flow filter comprises in an embodiment of the invention additionally an ammonia oxidation catalyst arranged in each outlet flow channel at least in the region of the outlet end of the filter.
  • a preferred ammonia oxidation catalyst comprises palladium, platinum or a mixture thereof.
  • ammonia By contact with the ammonia oxidation catalyst, ammonia is oxidised to nitrogen and water.
  • the ammonia oxidation catalyst may be deposited directly on the partition wall in the outlet channels of the filter in the outlet region or provided as surface layer on surface of the SCR catalyst layer.
  • the invention provides additionally a method of preparation of a catalysed wall flow filter.
  • the invention provides a of
  • preparation a catalysed wall flow filter comprising the steps of a) providing a wall flow filter body with a plurality longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls; b) providing a catalyst washcoat comprising a first
  • the first catalyst composition being active in reaction of nitrogen oxides with carbon monoxide and hydrogen to ammonia and a second catalyst composition being active in selective reduction of nitrogen oxides by reaction with ammonia to nitrogen, the first catalyst composition has a mode
  • composition has a mode particle size being larger than the average pore diameter of the porous partition walls; c) coating the filter body with the catalyst washcoat by introduction of the washcoat into outlet end of the outlet channels; and d) drying and heat treating the coated filter body to obtain the catalysed particulate filter.
  • the filter is additionally coated with a so called ammonia slip catalyst, which is a catalyst being active in the oxidation of excess of ammonia to nitrogen and water.
  • composition being active in the selective oxidation of ammonia; and coating at least a part of the outlet channels with the washcoat subsequently to the coating with the catalyst washcoat .
  • the catalysts being usually in particle form are milled or agglomerated to the required particle size and suspended in water or organic solvents, optionally with addition of binders, viscosity improvers, foaming agents or other processing aids.
  • the filter is then washcoated according to common practice, including applying vacuum in the filter, pressurizing the washcoat or by dip coating.
  • the amount of the first catalyst coated on the filter is typically 10 to 140 g/1, and the amount of the second catalyst on the filter is typically 10 to lOOg /l.
  • the total catalyst loading on the filter is typically in the range of 40 to 200 g/1.
  • filter materials for use in the invention are silicon carbide, aluminium titanate,
  • Example A suspension of the first catalyst composition is in a first step prepared from a powder mixture of palladium rhodium deposited on cerium oxide and alumina particles of a particle size smaller than the filter wall mean pore size .
  • a suspension of the mixture first catalyst is prepared by mixing 20 g of these powders in 40 ml demineralised water pr liter filter.
  • a dispersing agent Zephrym PD-7000 and an antifoam agent are added. The suspension is milled in a bead mill. The particle sizes of the final suspension must be smaller than the mean pore diameter of the pores in the wall of the wall flow filter
  • a suspension of a second catalyst is made by mixing and dispersing 100 g of silica aluminium phosphate SAPO-34 promoted with 2% copper in 200 ml demineralised water pr liter filter.
  • a dispersing agent Zephrym PD-7000 and an antifoam agent are added. The particle sizes must be larger than the mean pore diameter of the pores in the wall of the wall flow filter
  • the suspensions of the first catalyst and the second catalyst are then mixed to one suspension.
  • a high porosity (approximately 60% and wall mean pore size approx 18 ⁇ ) conventionally plugged SiC wall flow filter is used.
  • the mixed suspensions of first and the second catalyst is washcoated from the filters outlet end of the filters permeate side by standard washcoat methods permeate side, dried and calcined at 750°C

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Biomedical Technology (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Catalysts (AREA)

Abstract

Method for the preparation of a wall flow particulate filter catalysed at its inlet side with a first catalyst having activity in the removal of residual hydrocarbons and carbon monoxide and catalysing at rich burn engine operation conditions the reaction of nitrogen oxides with hydrogen and/or carbon monoxide to ammonia and catalysed at its outlet side with a second catalyst having activity in the selective reduction of NOx by reaction with ammonia being formed in the inlet side. The method involves the provision of a first catalyst having a particle size smaller than the filter wall mean pore size, and a second catalyst having a particle size larger than the filter wall mean pore size, and mixing the first and second catalyst into one suspension, which is used for washcoating from the outlet end. The first catalyst thereby diffuses into the partition wall.

Description

METHOD FOR COATING A CATALYSED PARTICULATE FILTER AND A PARTICULATE FILTER
The present invention relates to a multifunctional
catalysed engine exhaust particulate filter. In particular, the invention is a method for the preparation of a
multifunctional catalysed particulate filter being
catalysed with a three way catalyst (TWC) and a catalyst being active in removing nitrogen oxides by the known NH3 - selective catalytic reduction (SCR) process, and optionally with a catalyst having activity in the oxidation of excess ammonia to nitrogen.
The multifunctional catalysed filter is in particular useful for the cleaning of exhaust gas from lean burn gasoline engines, such as the gasoline direct injection (GDI) engine.
GDI engines generate more carbonaceous soot than gasoline premixed injection engines. In Europe the Euro 5+ Diesel legislation is expected to be used for GDI in the future with a particulate mass limit at 4.5mg/km, which requires filtration of the engine exhaust in order to reach the above limit.
Typically, filters for use in automotive applications are the wall flow type filter consisting of honeycombed
structured body, wherein particulate matter is captured on or in partition walls of the honeycomb structure. These filters have a plurality longitudinal flow channels
separated by gas permeable partition walls. Gas inlet channels are open at their gas inlet side and blocked at the opposite outlet end and the gas outlet channels are open at the outlet end and blocked the inlet end, so that a gas stream entering the wall flow filter is forced through the partition walls before into the outlet channels.
In addition to soot particles, exhaust gas from gasoline engines contains nitrogen oxides (NOx) , carbon monoxide and unburnt hydrocarbons, which are chemical compounds
representing a health and environmental risk and must be reduced or removed from the exhaust gas.
Catalysts being active in the removal or reduction of NOx, carbon monoxide and hydrocarbons to harmless compounds are per se known in the art.
The patent literature discloses numerous cleaning systems comprising separate catalyst units for the removal of harmful compounds from engine exhaust gas. Also known in the art are exhaust gas particulate filters coated with catalysts catalysing oxidation of hydrocarbons and particulate matter together with selective catalytic reduction (SCR) of NOx by reaction with ammonia being added as such or as precursor thereof into the exhaust gas.
Multifunctional diesel particulate filters coated with different catalysts catalysing the above mentioned
reactions are also known in the art. In the known multifunctional filters, the different
catalysts are segmentarily or zone coated in different zones of the filter. Segmentary or zone coating of different catalysts on the filter is an expensive and difficult preparation process. Compared to known technique, the present invention suggests an easier method for the preparation of particulate filers catalysed with different catalysts for the selective reduction of nitrogen oxides with ammonia and removal of hydrocarbons, carbon monoxide and excess ammonia.
Thus, the invention provides a method of preparation a catalysed wall flow filter, comprising the steps of a) providing a wall flow filter body with a plurality longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls; b) providing a catalyst washcoat comprising a first
catalyst composition being active in reaction of nitrogen oxides with carbon monoxide and hydrogen to ammonia
together with a second catalyst composition being active in selective reduction of nitrogen oxides by reaction with ammonia to nitrogen, the first catalyst composition has a particle size being smaller than average pore diameter of the porous partition walls and the second catalyst
composition has a particle size with is larger than the average pore diameter of the porous partition walls; c) coating the filter body with the catalyst washcoat by introduction of the washcoat into outlet end of the outlet channels; and d) drying and heat treating the coated filter body to obtain the catalysed particulate filter.
The advantage of either the first catalyst has a smaller particle size than the mean pore diameter of the partition walls and the second catalyst particles have a larger particle size than the mean pore diameter of the walls is to allow the first catalyst particles to diffuse
effectively into the partition walls and to prevent the second catalyst from diffusing into the channels where the specific catalytic activity is nor desired.
It is then possible to coat the filter body with different catalysts inlet and outlet flow channels with a single washcoat .
Useful catalyst for the reaction of Nox to ammonia by the following reaction:
NOx +H2/CO = NH3 +C02 +H20 are palladium, platinum, a mixture of palladium and rhodium and a mixture of palladium, platinum and rhodium.
These catalysts catalyse the ammonia formation under rich burn operating conditions of the gasoline engine, i.e.
λ<1. Palladium is the preferred catalyst with the highest ammonia formation.
Ammonia being thus formed within the inlet channels by the above reaction permeates through the partition walls of the filter into the outlet channels and is during the rich operating conditions adsorbed in the SCR catalyst in the outlet flow channels.
Both the ammonia forming catalyst and the SCR catalyst are preferably deposited on the partition walls on the sides facing the inlet channel and the outlet channel,
respectively .
In a subsequent lean burn operation cycle of the engine, NOx being present in the exhaust gas reacts with the ammonia stored in the SCR catalyst by the following
reaction :
NOx + NH3 = N2 + H20 As already mentioned above, SCR catalyst are per se known in the art. For use in the invention, the preferred catalyst being active in the selective reduction of nitrogen oxides comprises at least one of a zeolite, a silica aluminum phosphate, an ion exchanged zeolite, silica aluminum phosphate promoted with iron and/or copper, one or more base metal oxides.
A further preferred SCR catalyst for use in the invention is a silica aluminium phosphate with chabazite structure, such as SAPO 34, promoted with copper and/or iron.
In order to remove the excess ammonia having not reacted with NOx, the wall flow filter comprises in an embodiment of the invention additionally an ammonia oxidation catalyst arranged in each outlet flow channel at least in the region of the outlet end of the filter. A preferred ammonia oxidation catalyst comprises palladium, platinum or a mixture thereof.
By contact with the ammonia oxidation catalyst, ammonia is oxidised to nitrogen and water.
The ammonia oxidation catalyst may be deposited directly on the partition wall in the outlet channels of the filter in the outlet region or provided as surface layer on surface of the SCR catalyst layer.
The invention provides additionally a method of preparation of a catalysed wall flow filter. In its broad embodiment the invention provides a of
preparation a catalysed wall flow filter, comprising the steps of a) providing a wall flow filter body with a plurality longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls; b) providing a catalyst washcoat comprising a first
catalyst composition being active in reaction of nitrogen oxides with carbon monoxide and hydrogen to ammonia and a second catalyst composition being active in selective reduction of nitrogen oxides by reaction with ammonia to nitrogen, the first catalyst composition has a mode
particle size being smaller than average pore diameter of the porous partition walls and the second catalyst
composition has a mode particle size being larger than the average pore diameter of the porous partition walls; c) coating the filter body with the catalyst washcoat by introduction of the washcoat into outlet end of the outlet channels; and d) drying and heat treating the coated filter body to obtain the catalysed particulate filter.
Specific catalyst compositions for use in the invention are mentioned hereinbefore and further disclosed in claims 2 to 4.
In further an embodiment of the invention, the filter is additionally coated with a so called ammonia slip catalyst, which is a catalyst being active in the oxidation of excess of ammonia to nitrogen and water.
Thus in this embodiment the inventive method comprises the steps of providing a second washcoat containing a catalyst
composition being active in the selective oxidation of ammonia; and coating at least a part of the outlet channels with the washcoat subsequently to the coating with the catalyst washcoat .
When preparing the washcoats for use in the invention, the catalysts being usually in particle form are milled or agglomerated to the required particle size and suspended in water or organic solvents, optionally with addition of binders, viscosity improvers, foaming agents or other processing aids.
The filter is then washcoated according to common practice, including applying vacuum in the filter, pressurizing the washcoat or by dip coating.
The amount of the first catalyst coated on the filter is typically 10 to 140 g/1, and the amount of the second catalyst on the filter is typically 10 to lOOg /l. The total catalyst loading on the filter is typically in the range of 40 to 200 g/1.
Examples of suitable filter materials for use in the invention are silicon carbide, aluminium titanate,
cordierite, alumina, mullite or combinations thereof.
Example A suspension of the first catalyst composition is in a first step prepared from a powder mixture of palladium rhodium deposited on cerium oxide and alumina particles of a particle size smaller than the filter wall mean pore size .
A suspension of the mixture first catalyst is prepared by mixing 20 g of these powders in 40 ml demineralised water pr liter filter. A dispersing agent Zephrym PD-7000 and an antifoam agent are added. The suspension is milled in a bead mill. The particle sizes of the final suspension must be smaller than the mean pore diameter of the pores in the wall of the wall flow filter A suspension of a second catalyst is made by mixing and dispersing 100 g of silica aluminium phosphate SAPO-34 promoted with 2% copper in 200 ml demineralised water pr liter filter. A dispersing agent Zephrym PD-7000 and an antifoam agent are added. The particle sizes must be larger than the mean pore diameter of the pores in the wall of the wall flow filter The suspensions of the first catalyst and the second catalyst are then mixed to one suspension.
A high porosity (approximately 60% and wall mean pore size approx 18 μιη) conventionally plugged SiC wall flow filter is used.
The mixed suspensions of first and the second catalyst is washcoated from the filters outlet end of the filters permeate side by standard washcoat methods permeate side, dried and calcined at 750°C

Claims

Claims
1. Method of preparation a catalysed wall flow filter, comprising the steps of a) providing a wall flow filter body with a plurality longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls; b) providing a catalyst washcoat comprising a first
catalyst composition being active in reaction of nitrogen oxides with carbon monoxide and hydrogen to ammonia and a second catalyst composition being active in selective reduction of nitrogen oxides by reaction with ammonia to nitrogen, the first catalyst composition has a mode
particle size being smaller than average pore diameter of the porous partition walls and the second catalyst
composition has a mode particle size being larger than the average pore diameter of the porous partition walls; c) coating the filter body with the catalyst washcoat by introduction of the washcoat into outlet end of the outlet channels; and d) drying and heat treating the coated filter body to obtain the catalysed particulate filter.
2. The method of claim 1, wherein the catalyst being active in conversion of nitrogen oxides to ammonia includes palladium, platinum, a mixture of palladium and rhodium and a mixture of palladium, platinum and rhodium.
3. The method of claim 1, wherein the catalyst being active in conversion of nitrogen oxides to ammonia consists of palladium.
4. The method according to anyone of claims 1 to 3, wherein the catalyst being active in the selective
reduction of nitrogen oxides comprises at least one of a zeolite, a silica aluminum phosphate, an ion exchanged zeolite, silica aluminum phosphate promoted with iron and/or copper, one or more base metal oxides.
5. The method according to anyone of the preceding claims, further comprising the steps of providing a second washcoat containing a catalyst
composition being active in the oxidation of ammonia; and coating a part of outlet channels at region at the outlet end with the second washcoat.
6. A catalysed wall flow filter being prepared in accordance with anyone of the preceding claims.
EP12728482.6A 2011-07-13 2012-06-14 Method for coating a catalysed particulate filter and a particulate filter Withdrawn EP2731718A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DKBA201100537 2011-07-13
PCT/EP2012/061328 WO2013007466A1 (en) 2011-07-13 2012-06-14 Method for coating a catalysed particulate filter and a particulate filter

Publications (1)

Publication Number Publication Date
EP2731718A1 true EP2731718A1 (en) 2014-05-21

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Application Number Title Priority Date Filing Date
EP12728482.6A Withdrawn EP2731718A1 (en) 2011-07-13 2012-06-14 Method for coating a catalysed particulate filter and a particulate filter

Country Status (1)

Country Link
EP (1) EP2731718A1 (en)

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2013007466A1 *

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