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
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
• • 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
  • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
• • 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
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/32—Manganese, technetium or rhenium
  • B01J23/34—Manganese
• • 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
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/19—Catalysts containing parts with different compositions
• • 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
  • B01D2255/202—Alkali metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/202—Alkali metals
  • B01D2255/2022—Potassium
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/206—Rare earth metals
  • B01D2255/2065—Cerium
• • 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
  • B01D2255/2073—Manganese
• • 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
  • B01J2523/00—Constitutive chemical elements of heterogeneous 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
  • 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 a device comprising a catalytic composition based on two, and possibly three, catalysts which can be used in the treatment of exhaust gases from engines operating in lean mixture in particular.
• the device is particularly suitable for exhaust gases from motor vehicle engines.
• NOx traps which are capable of oxidizing NO to N0 2 and then adsorbing the N0 2 thus formed. Under certain conditions, N0 2 is released and then reduced to N 2 by reducing species contained in the exhaust gases. These NOx traps give interesting results. However, there is a need for even more efficient catalytic systems.
• the device according to the invention comprises at least one substrate on which a catalytic composition is deposited, said catalytic composition comprising:
• a first catalyst which comprises at least one precious metal on a support based on cerium oxide, titanium oxide or a mixture of zirconium oxide and titanium oxide; - a second catalyst of the NOx trap type.
• the composition is deposited in the form of a coating on a substrate or monolith of the metallic or ceramic type.
• a ceramic substrate is given in EP 036052; an example of a metallic substrate is given in WO 9817431.
• the characteristic of the device of the invention is the fact that it comprises a catalytic composition consisting of a combination of two or three types of catalysts which will be described below.
• the device comprises a composition which comprises a combination of two catalysts.
• the first catalyst comprises at least one precious metal on a specific support.
• the support of the first catalyst can firstly be based on cerium oxide.
• cerium oxides or ceric oxides which can be used in the invention are known products.
• ceric hydroxide or certain oxygenated salts such as nitrates, sulfates, carbonates, oxalates or acetates (cf. Paul PASCAL, "Nouveau Traite de Chimie Minérale", Vol. VII, p. 777, (1959)), the ceric hydroxide being able to be in the form of precipitates or colloidal suspensions. It is thus possible to use cerium oxides as described in patent applications EP-A-153227, EP-A-388567 or EP-A-300852.
• the support based on cerium oxide can also comprise at least one oxide of another rare earth.
• the quantity of rare earth expressed as oxide can be in particular between 20% and 40% by mass of the cerium oxide / rare earth oxide combination.
• the rare earth may more particularly be lanthanum, neodymium, praseodymium and terbium.
• the support can also be based on a cerium oxide further comprising an alkali or an alkaline earth.
• the alkaline earth can more particularly be barium, calcium and the alkaline cesium.
• the content of alkali or alkaline earth can be in particular between 0.1% and 20%, more particularly between 2% and 10% content expressed by weight of alkali metal oxide or alkaline earth metal relative to the weight of the whole composition.
• the support can also be based on a ternary composition, that is to say a cerium oxide, an oxide of another rare earth and a zirconium oxide.
• the composition can also include several oxides of another rare earth.
• compositions of this type mention may be made of those described in patent application WO-97/43214. They can thus be prepared by a process in which a mixture is prepared in a liquid medium containing a compound of cerium, a compound of yttrium, scandium or another rare earth and a compound of zirconia, the said mixture is heated ; the precipitate obtained is recovered and this precipitate is calcined.
• the above mixture is prepared using a zirconium solution which is such that the amount of base necessary to reach dre the equivalent point during an acid-base assay of this solution checks the condition OH " / Zr molar ratio ⁇ 1.65.
• compositions can advantageously be in the form of a solid solution.
• the X-ray diffraction spectra of these compositions indeed reveal, within the latter, the existence of a single homogeneous phase.
• this phase corresponds in fact to that of a ceric oxide Ce ⁇ 2 crystallized and whose mesh parameters are more or less offset compared to a pure ceric oxide, thus translating the incorporation of zirconium and of the other element in the crystal lattice of cerium oxide, and therefore obtaining a true solid solution.
• the rare earth may more particularly be lanthanum, neodymium, praseodymium and terbium.
• the support can also be based on a quaternary composition, that is to say a cerium oxide, an oxide of another rare earth, a zirconium oxide and a fourth element which can be an alkali or an alkaline earth.
• the alkaline earth can more particularly be barium, calcium and the alkaline cesium.
• the content of alkali or alkaline earth can be in particular between 0.1% and 20%, more particularly between 2% and 10%, content expressed by weight of alkali metal oxide or of alkaline-earth relative to the weight of the entire composition.
• the contents of the other elements can have the respective values given above for the remaining part of the composition.
• the support can also be based on cerium oxide and silica.
• cerium oxide and silica As a support of this type, it is possible to use the compositions based on cerium oxide and on silica described in patent application EP-A-207 857. Mention may also be made of the compositions described in EP-A-547924 which differ from the previous ones by a lower silica content, that is to say a silica content of less than 2% by weight of ceric oxide and which can in particular be between 0.1% and 1% by weight of ceric oxide.
• the support for the first catalyst can be based on titanium oxide.
• the support may more particularly be based on titanium oxide and a rare earth oxide.
• This rare earth can be in particular lanthanum.
• the support can also be based on titanium oxide and tungsten oxide.
• the proportion by weight of rare earth or tungsten expressed as a percentage of rare earth oxide or tungsten oxide relative to the whole of the composition can be in particular between 0.1% and 20%, more particularly between 2% and 10%.
• the support can also be based on titanium oxide and silica.
• titanium oxide and silica For compositions based on titanium oxide and silica, reference may be made to patent application WO-99/01216. In these compositions the atomic proportion Ti / Ti + Si is between 0.1 and 15%, more particularly between 1 and 10%. They can in particular be prepared by a process by micellar texturing using surfactants and, as source of silica, alkyl-silicates such as tetraethyl orthosilicate. These alkyl silicates are generally used in the form of solutions in alcohols, in particular in aliphatic alcohols. Likewise, alkyl or alkoxy titanates can be used as a source of titanium which are also used in the form of alcoholic solutions.
• the alkyl silicates and the alkyl or alkoxy titanates are mixed and then heated.
• the surfactant is then added to the mixture thus heated.
• the precipitate obtained is separated from the reaction medium.
• This precipitate is then calcined, generally in air, to obtain the support which can then be shaped. Calcination can be done in two parts. In the first part, calcination is carried out at a temperature sufficient to remove the surfactant. This temperature can be around 650 ° C. In the second part, calcination is carried out at a temperature at least equal to that at which the catalyst will be used. This temperature can be around 750 ° C.
• the support for the first catalyst can be based on a mixture of zirconium oxide and titanium oxide.
• a support can be obtained by coprecipitation of the titanium and zirconium salts or else by impregnation of an oxide of one of these elements with a salt of the other.
• the second catalyst which forms part of the composition of the device according to the first embodiment of the invention is a catalyst of the NOx trap type.
• Catalysts of this type are also well known.
• Catalysts which include an alkaline or alkaline earth element such as potassium or strontium with platinum can be given as an example.
• platinum-free catalysts which comprise manganese and potassium on a support which may, for example, be alumina or else zirconia, cerium oxide or a zeolite.
• a support which may, for example, be alumina or else zirconia, cerium oxide or a zeolite.
• Such a catalyst is of the type described in EP-A-764460.
• EP-A-1034026 may consist of manganese and cerium oxide only or, according to another variant, they may include manganese, cerium oxide and at least one other element chosen from terbium, gadolinium, europium, sammarium, neodymium and praseodymium. It should be noted that in the case of this alternatively, the cerium oxide can be mixed with zirconium oxide.
• catalysts of the NOx trap type of those described in WO-00/61289 and which comprise a support and an active phase based on manganese and at least one other element A chosen from alkali and alkaline- earthy, manganese and element A being chemically linked.
• chemically bound is meant that there are chemical bonds between the manganese and the element A, resulting from a reaction between them, these two elements not being simply juxtaposed as in a simple mixture.
• the elements manganese and A can be present in the form of a compound or of a phase of mixed oxide type.
• the element A can more particularly be potassium, sodium or barium and the support can be based on an oxide chosen from cerium oxide, zirconium oxide or their mixtures. It is also possible to use a catalyst of this type, the support of which is made of alumina, optionally stabilized for example with cerium oxide.
• Element A can be in particular barium and the support can be based on alumina or alumina stabilized by silicon, zirconium, barium or a rare earth which can be in particular cerium.
• the support can also be based on silica.
• catalysts which comprise a combination of a first compound comprising a support and an active phase, the active phase being based on manganese and at least one other element Chose from alkali and alkaline earth, manganese and element A being chemically linked; and of a second compound comprising a support and an active phase based on manganese and at least one other element B chosen from alkali metals, alkaline earth metals and rare earths.
• the ele- elements A and B can be chosen from potassium, sodium or barium and the support can be based on alumina or alumina stabilized by silicon, zirconium, barium or a rare earth which can in particular be cerium .
• the support can also be based on silica.
• the second catalyst when it is of the type described in WO-
• 00/61289, WO-00/64580 or in WO-00/67904 may additionally contain platinum.
• the invention also presents a second embodiment which also makes it possible to improve the treatment of exhaust gases.
• the device of the invention comprises a third catalyst.
• This third catalyst is a catalyst which exhibits at least one NOx reduction function.
• It can in particular be a catalyst of the three-way type.
• the catalysts which are capable of effecting in a gas the conversion of carbon monoxide and of hydrocarbons into carbon dioxide and that of NOx into nitrogen.
• these catalysts mention may be made of those based on at least one precious metal with at least one oxide chosen from alumina, cerium oxide, mixed oxides of cerium and zirconium or mixed oxides of cerium and of zirconium further comprising a rare earth.
• cerium oxides or mixed oxides of cerium and zirconium which are particularly suitable for such catalysts, mention may be made of those described in EP-A-300852, EP-A-605274, WO-97/02213 and WO-97/43214 especially.
• the support for the active phase can be a refractory oxide and can comprise, for example, silica, alumina, silico-aluminates or else mixed oxides such as alumina in combination with silica, a zirconium oxide , a cerium oxide and / or a titanium oxide.
• Such catalysts are described in patent application EP-A-60740.
• the relative proportions of the catalysts which have been described above can be any. More particularly, the second catalyst can represent between 25% and 75%, more particularly between 40% and 60%, by mass of the total composition, the one or two other catalyst constituting from 75% to 25%, more particularly from 60% to 40% of this mass in variable proportions, in particular equal proportions.
• the first catalyst must represent at least 25% of the mass of the second catalyst.
• the catalysts are preferably arranged in such a way that the first catalyst described above is located first in the direction of flow of the treated gas. In this case, the one or two other catalysts can be either separated and then arranged in any order, or mixed.
• these different catalysts, mixed or not, can be placed on a single substrate or on separate substrates.
• the first and second catalysts can for example be placed on a first substrate and the third catalyst on a second substrate.
• gases capable of being treated in the context of the present invention are those from internal combustion engines. These may in particular be diesel engines or petrol engines operating in a lean mixture.
• the device of the invention is particularly applicable to the treatment of gases which have a high oxygen content, produced by engines normally operating in a lean mixture.
• the value ⁇ is correlated to the air / fuel ratio in a manner known per se, in particular in the field of internal combustion engines.
• Such gases may be those of an engine operating in a lean burn mixture and which have an oxygen content (expressed by volume) for example of at least 2%, as well as those which have an even higher oxygen content, for example.
• oxygen content expressed by volume
• diesel engine gases that is to say at least 5% or more than 5%, more particularly at least 8%, this content may for example be between 5% and 20%.
• the NOx produced are retained on the NOx trap. After a certain operating time when the engine is supplied with lean mixture, the NOx trap must be regenerated.
• the engine can for example be temporarily supplied with a rich mixture.
• the device of the invention further comprises means for temporarily supplying the engine with a rich mixture.
• These means can for example take the form of air / fuel mixture injectors controlled by a computer.
• the computer is adapted to establish the air-fuel ratio supplied to the engine so that the engine operates normally while being supplied with a lean mixture, that is to say with an excess of air relative to the fuel.
• the computer is also adapted so that the engine runs temporarily in a rich mixture, that is to say with an excess of fuel compared to the air.
• the invention also relates to a process for treating gases with a view to reducing emissions of nitrogen oxides using the device of the invention as described above.
• the process of the invention comprises in particular : - storage phases, where the engine is supplied with a lean mixture, and during which the nitrogen oxides produced by the engine are retained in a catalyst of the NOx trap type;
• the invention applies to the manufacture of an exhaust line for the treatment of an exhaust gas from an internal combustion engine; the exhaust line can then comprise, in addition to the device of the invention, any other member useful for the mechanical and / or chemical and / or electrical and / or acoustic treatment of the exhaust gas or of the liquid or solid elements present therein. ; among these bodies, mention may be made in particular of particle filters and in particular the type of filter described in FR-2,787,137. It is also conceivable to use a substrate of the common metallic or ceramic type for the device of the invention and at least one other member useful for the treatment of gases, in particular in the case of the particle filter.
• the first catalyst A is prepared according to the teaching of patent application WO-97/43214.
• a mixed oxide of composition Ceo, 66Zro, o4Pro, 3 ⁇ 2 is used as support.
• 200g of this support are impregnated with 19g of an aqueous solution of rhodium nitrate, the concentration of which is 9% by mass of Rh.
• a slurry is produced from this catalyst by incorporating 400g of AI 2 0 3 and 400ml demineralized water in an acetic medium so that the pH drops to 4. Then a grinding of the slurry is carried out so as to obtain a particle size such that d 5 o ⁇ 10 microns.
• This slurry is then used to coat a cordierite substrate of the honeycomb type with a cell density of 400 / 6.5 and a volume equal to 500 cm 3 .
• the substrate thus coated is then dried and then calcined by passage through the oven.
• a substrate is thus obtained on which a coating or washcoat is deposited comprising catalyst A at a rate of 300 g / l with a load of Rhodium of 24 g / ft 3 . 2) Catalyst B
• the second catalyst B is a catalyst of the NOx trap type which is prepared by successively depositing on a cordierite substrate of the honeycomb type a support based on alumina and cerine then 3 gels based respectively on Mn (N0 3 ) 2 , KN0 3 and Pt (N0 3 ) 2 .
• the support used which comprises 10% by weight of Ce0 2 relative to Al 2 0 3 , is obtained from an alumina of the CONDEA SB3 type according to the teaching of WO00 / 61289.
• a gel obtained is injected as follows: 265g of Mn (N0 3 ) 2 , 4H 2 0 are dissolved in demineralized water added with nitric acid to adjust the pH to 4 and obtain a final volume of 2800cm 3 . 1.2% GUAR® powder is then introduced in order to obtain a viscosity of approximately 1000 centipoise.
• the gel-coated substrate is then dried and then calcined by passage through the oven.
• a gel obtained is injected as follows: 110 g of KN0 3 are dissolved in demineralized water added with nitric acid to adjust the pH to 4 and obtain a final volume of 2800cm 3 . 1.2% GUAR® powder is then introduced in order to obtain a viscosity of approximately 1000 centipoise.
• the gel-coated substrate is then dried and then calcined by passage through the oven.
• a gel obtained is injected as follows: 9.4 g of a stock solution of Pt (N0 3 ) 2 at 30% are dissolved in 1000 ml. The pH is adjusted to 4 using nitric acid. 1.2% GUAR® powder is then introduced in order to obtain a viscosity of 1000 centipoise.
• the gel-coated substrate is then dried and then calcined by passage through the oven.
• the successive deposition of the support and the 3 gels makes it possible to obtain a substrate on which is deposited a coating or washcoat comprising catalyst B of the NOx trap type at the rate of 300 g / 1 with a platinum charge equal to 60 g / ft 3 .
• COMPARATIVE EXAMPLE 2 For the comparative example, the activity of a compound device is evaluated in the direction of flow of the gases to be treated:
• NOx are eliminated in two phases.
• a first phase where NOx is adsorbed, the engine operating in a lean mixture.
• a second phase where the NOX are desorbed and converted when the engine operates in a rich mixture.
• the devices described above are installed on the exhaust line of a "lean burn" engine.
• the engine is operated in lean mixture (duration 30 sec.) With richness peaks (duration 2sec).
• the concentrations of the various gas constituents are measured upstream and downstream of the device via a HORIBA® rack (in particular measurement of NOx by chemiluminescence). The percentage of NOx eliminated is deduced for different temperature points.
• the duration of the evaluation test is 1000 seconds, ie 32 oxidant / reducer cycles. During the test period, the NOx concentration in the outlet gases is measured. The results obtained at 300 ° C and 450 ° C are given in the table below.

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• Exhaust Gas After Treatment (AREA)

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