Classifications

• • 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
  • B01D53/9481—Catalyst preceded by an adsorption device without catalytic function for temporary storage of contaminants, e.g. during cold start
• • 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)
• • 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
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
• • 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
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
  • F01N13/0093—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are of the same type
• • 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
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
• • 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
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• • 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
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
  • F01N3/0842—Nitrogen oxides
• • 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
  • B01D2255/1021—Platinum
• • 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
  • B01D2255/1025—Rhodium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
  • B01D2255/2042—Barium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/908—O2-storage component incorporated in the catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
  • B01D2258/012—Diesel engines and lean burn gasoline engines
• • 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
  • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the present invention relates to an exhaust system for a diesel engine, which system comprising a first nitrogen oxide (NO x )- trap comprising at least one first NO x absorbent and platinum.
• a first nitrogen oxide (NO x )- trap comprising at least one first NO x absorbent and platinum.
• Exhaust gases from compression ignition engines comprise a mixture of pollutants including carbon monoxide (CO), unbumed hydrocarbons (HC), nitrogen oxides (NO x ) and particulate matter (PM) including volatile and soluble organic fractions (NOF and SOF respectively).
• the ⁇ O x component can comprise nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ).
• the level of these pollutants in exhaust gases from internal combustion engines it is permissible to exhaust to atmosphere is regulated by legislation. Such legislation can be met by engine design, engine management and/or exhaust gas after treatment, and typically a combination of all three measures.
• DOC platinum-based diesel oxidation catalyst
• Diesel nitrogen oxides (NO x ) emissions are presently controlled by engine management, such as exhaust gas recirculation (EGR).
• EGR exhaust gas recirculation
• PM emissions including NOF and SOF are increased.
• the DOC is used to treat NOF and SOF in order to meet presently legislated limits for PM.
• Another prior art exhaust system primarily for treating diesel exhaust comprises an oxidation catalyst for oxidising NO in the exhaust gas to NO 2 and a downstream filter for trapping PM.
• a process for treating diesel PM that uses this arrangement is described in EP 0341382 or US patent no. 4,902,487, both of which are incorporated herein by reference.
• the process comprises passing diesel exhaust gas including PM and NO unfil tered over an oxidation catalyst to convert the NO to NO 2 , collecting soot on the filter and combusting the collected soot by reaction with the NO 2 .
• This technology is commercially available as Johnson Matthey's Continuously Regenerating Trap or CRT .
• NO 2 is toxic and can cause headaches, dizziness and nausea in low doses. It also has an objectionable smell.
• NO 2 can slip past the filter and be undesirably exhausted to atmosphere.
• a modern diesel engine produces a relatively high amount of NO x in the form of NO .
• the exhaust gas is first passed over a platinum oxidation catalyst, the NO 2 can be removed by facile low temperature oxidation of hydrocarbons present in the exhaust gas. This process is known as lean NO x catalysis.
• the NO x absorbent material can poison the lean NO x activity of the platinum, thereby reducing the conversion efficiency of the process.
• the oxidation of NO to NO 2 becomes sufficiently rapid for significant quantities of NO 2 to be formed and a conventional platinum containing NO x -trap then starts to become effective.
• a NO x -trap is purposely designed for absorbing and storing NO x in lean exhaust gases (lambda > 1 conditions), and releasing and eat alytically reducing the stored NO x in rich exhaust gases (1 > lambda conditions).
• the engine is controlled so that periodically it is run rich during normal lean-running operation.
• a NO x -trap typically includes active materials for three functions: an oxidation catalyst, such as platinum; a NO x absorbent, for example a compound of an alkali metal e.g.
• an alkaline earth compound typified by barium oxide or a compound of a rare earth metal, such as lanthanum; and a reduction catalyst, such as rhodium.
• the or each alkali metal and alkaline earth metal compound is present as an oxide, although it may also be present in use as a hydroxide or a carbonate.
• NO x -trap a composition comprising a NO x absorbent and at least one catalytic material, such as a platinum group metal.
• NO x absorbent refers to a material, e.g. alkaline earth metal compound, alkali metal compound or rare earth metal compound, capable of absorbing NO 2 in lean exhaust gas.
• An oxidation catalyst is purposely designed to provide for the reaction of gaseous components with oxygen, typically in as wide a temperature range as possible, especially at lower temperatures.
• the catalyst oxidises whenever oxygen is available for reaction in the gas stream.
• Active components of an oxidation catalyst can include platinum, palladium or a base metal active for oxidation such as manganese, copper, molybdenum, cobalt or any other transition element that is active for oxidation.
• An oxygen storage component is purposely designed to absorb oxygen from lean exhaust gases and to release oxygen in rich exhaust gas conditions.
• suitable OSC include ceria doped with transition metals, e.g. zirconium, or other rare earth metals and manganese-based materials.
• Our WO 02/18753 (incorporated herein by reference) describes an exhaust system for a lean-burn internal combustion engine, including a diesel engine, comprising an oxidation catalyst upstream of a NO x -trap for oxidising relatively large amounts of unbumed hydrocarbons present in exhaust gas in normal lean-running conditions and for oxidising NO in the exhaust gas to NO 2 in lean-running conditions.
• a clean-up catalyst comprising an oxygen storage component such as ceria, an oxidation component, such as platinum, a NO x reducing component, for example rhodium, and a component for suppressing H 2 S, for example NiO, Fe 2 O 3 , MnO 2j CoO and CrO 2 , is disposed downstream of the NO x -trap.
• an oxygen storage component such as ceria
• an oxidation component such as platinum
• a NO x reducing component for example rhodium
• a component for suppressing H 2 S for example NiO, Fe 2 O 3 , MnO 2j CoO and CrO 2
• WO 01/94760 we disclose an exhaust system for a diesel engine comprising a solid NO x absorbent for absorbing NO x from relatively cool exhaust gas and desorbing adsorbed NO x and passing it to atmosphere by intermittently increasing the temperature of the exhaust gas.
• the invention provides an exhaust system for a diesel engine, which system comprising a first NO x -trap comprising at least one first NO x absorbent and platinum, characterised in that at least one second NO x absorbent is disposed upstream of the first NO x - trap, which at least one second NO x absorbent is not associated with platinum.
• a further advantage of this system over the above-mentioned prior art system is that the system of the invention generates less N 2 O by lean NO x catalysis over the platinum component of the first NO x -trap.
• An aspect of the present invention is the concept of absorbing NO 2 on the second
• NO x absorbent at relatively low temperature when the downstream first NO x trap is too cool to catalyse the reduction of NO x to N 2 , and thermally releasing the NO x when the first NO x -trap is up to temperature, e.g. >200°C, such as >225°C, >250°C, >275°C or
• the engine can include an engine control unit (ECU) programmed, in use, intermittently to adjust to the exhaust gas composition to the rich side for regenerating the at least one first NO ⁇ absorbent.
• ECU engine control unit
• the at least one second NO x -absorbent can be associated with a base metal catalyst, e.g. a manganese compound, a cobalt compound or a copper compound, for oxidising nitrogen monoxide (NO) to nitrogen dioxide (NO 2 ) in lean exhaust gas or a non-platinum platinum group metal, such as rhodium or iridium for reducing NO x to N 2 in rich exhaust gas, or other non-platinum PGMs such as palladium, osmium and ruthenium, preferably the at least one second NO x -absorbent is free from components other than the NO x -absorbent and optional support.
• a base metal catalyst e.g. a manganese compound, a cobalt compound or a copper compound
• a non-platinum platinum group metal such as rhodium or iridium for reducing NO x to N 2 in rich exhaust gas, or other non-platinum PGMs such as pal
• Each first and second NO x absorbent can be selected from alkaline earth metal compounds, alkali metal compounds or rare-earth metal compounds.
• Suitable alkaline earth metals include calcium, magnesium, strontium and barium.
• Alkali metals can be potassium and/or caesium and rare earth metals can be cerium, yttrium or praseodymium.
• the first and second NO x absorbent can be supported on a suitable support, such as particulate alumina, silica, zirconia, titania, ceria or a mixture or composite oxide according to any two or more thereof, such as ceria-zirconia or alumina-silica
• Composite oxide as defined herein means a largely amorphous oxide material comprising oxides of at least two elements which are not true mixed oxides consisting of the at least two elements.
• the NO x -absorbent can comprise the support e.g. ceria per se or alumina per se.
• compounds according to the invention can be oxides, although they may be present as nitrates, hydroxides or carbonates in exhaust gas containing NO x , CO and H 2 O.
• the first NO x -trap can be coated on a flow-through monolith, but in one embodiment, it is coated on a particulate filter.
• the particulate filter can include a DOC, optionally comprising supported platinum and/or palladium.
• the first NO x trap can be disposed downstream of the filter, which arrangement adopting the process of EP 0341832 and disclosed in EP 0758713.
• a catalyst for oxidising NO to NO 2 such as platinum on an alumina support, disposed between the at least one second NO x absorbent and the first NO x -tra ⁇ as described in our WO 02/18753.
• pulses of rich exhaust gas can be produced by the engine to convert stored NO x to nitrogen.
• hydrocarbon or carbon monoxide could pass through the system to atmosphere.
• the gas downstream of the first NO x -trap can be passed over an oxidation catalyst comprising an oxygen storage component, so even if the gas is overall reducing, reductants can still be oxidised, and prevented from entering the atmosphere.
• the oxidation catalyst comprises platinum or palladium supported on a bulk ceria-zirconia composite oxide oxygen storage component.
• the invention provides a diesel engine, optionally a light-duty diesel engine (as defined by the relevant legislation) comprising an exhaust system according to the invention.
• the invention provides a flow-through substrate comprising a NO x -trap comprising a first zone coated with a composition comprising at least one first NO x absorbent and platinum and a second zone coated with a composition comprising at least one second NO x -absorbent, which at least one second NO x absorbent is not associated with platinum.
• the invention provides a method of treating NO x in the exhaust gas of a diesel engine, which method comprising (i) absorbing NO 2 from lean exhaust gas in at least one second NO x absorbent when a downstream first NO x -trap comprising at least one first NO x absorbent and platinum is inactive for reducing NO x using a suitable reductant; (ii) thermally desorbing stored NO x ; and (iii) reducing thermally desorbed NO x on the first NO x -trap using a suitable reductant.
• the method comprises the step between steps (i) and (ii) of adsorbing thermally desorbed NO x on the at least one first NO x absorbent.
• Figure 1 is a schematic diagram of a diesel engine comprising an exhaust system according to the invention
• Figure 2 is a trace of time against NO 2 concentration (ppm) and temperature showing the experimental conditions used in the Examples;
• Figure 3 is a trace showing NO 2 adsorption and desorption for a conventional NO x trap comprising 5:1 Pt:Pd at a total loading of 120gft "3 (4.25g litre "1 );
• Figure 3 A is a trace showing HC detected downstream of the NO x absorbent in the experiment shown in Figure 3;
• Figure 4 is a trace showing NO 2 adsorption and desorption for a washcoat component containing Pt at a loading of 80gft "3 ;
• Figure 4A is a trace showing HC detected downstream of the NO x absorbent in the experiment shown in Figure 4;
• Figure 5 is a trace showing NO 2 adsorption and desorption for the washcoat component of the Figure 4 material without platinum;
• Figure 5 A is a trace showing HC detected downstream of the NO x absorbent in the experiment shown in Figure 5.
• 12 is a diesel engine
• 14 is a Pt-free NO ⁇ -trap comprising a second NO x -absorbent, e.g. alumina, barium supported on alumina or ceria
• 16 is a NO x -trap comprising a first NO x -absorbent, such as barium supported on alumina, platinum and rhodium
• 18 is the exhaust tailpipe.
• Optional components include an oxidation catalyst 20, such as platinum on alumina, and/or an oxidation catalyst 22 comprising an OSC, such as ceria-zirconium composite oxide.
• a ceramic flow through monolith 1.5 inch (38mm) diameter and 3 inches (76mm) long was coated with a conventional NO x -trap formulation containing platinum and rhodium at a ratio of 5:1 and total loading of 120gft "3 (4.25g litre "1 ) and a barium on alumina NO x -absorbent.
• the catalyst was fitted into a standard gas flow rig and a synthetic gas mixture passed over it at a space velocity of SO ⁇ OOhr "1 .
• the gas mixture composition is shown in Table 1 and remained lean for all the tests.
• the gas mixture (without NO 2 ) flowing through the catalyst was heated to 500°C and held at this temperature for 5 minutes in order to purge the catalyst.
• the gas was allowed to cool to 120°C and held at this temperature while the NO 2 was added for a period of 5 minutes.
• the NO was switched off and the gas temperature increased to 500°C for 5 minutes to purge the catalyst (Fig 2).
• the NO and NO x /NO 2 at the outlet to the catalyst was continuously measured so that adsorption (storage) and desorption could be monitored (Fig 3).
• the results show that NO 2 was not stored at 120°C, but was all converted to NO by reaction with HC (Fig 4A).
• Example 3 Similar results to those shown in Example 3 were obtained from a barium on alumina NO x absorbent material.

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• 2003
  • 2003-10-01 EP EP03751012A patent/EP1549419A1/de not_active Withdrawn
  • 2003-10-01 WO PCT/GB2003/004290 patent/WO2004030798A1/en not_active Application Discontinuation
  • 2003-10-01 US US10/530,166 patent/US20060117736A1/en not_active Abandoned
  • 2003-10-01 JP JP2005500062A patent/JP2006512534A/ja active Pending

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