EP1171236A1 - Compositions used as nox trap, based on manganese and an alkaline or alkaline-earth and use for treating exhaust gases - Google Patents

Compositions used as nox trap, based on manganese and an alkaline or alkaline-earth and use for treating exhaust gases

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Publication number
EP1171236A1
EP1171236A1 EP00917174A EP00917174A EP1171236A1 EP 1171236 A1 EP1171236 A1 EP 1171236A1 EP 00917174 A EP00917174 A EP 00917174A EP 00917174 A EP00917174 A EP 00917174A EP 1171236 A1 EP1171236 A1 EP 1171236A1
Authority
EP
European Patent Office
Prior art keywords
manganese
support
oxide
compositions
alkaline
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Withdrawn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
EP00917174A
Other languages
German (de)
French (fr)
Inventor
Thierry Birchem
Catherine Hedouin
Thierry Seguelong
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.)
Rhodia Chimie SAS
Original Assignee
Rhodia Chimie SAS
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Filing date
Publication date
Application filed by Rhodia Chimie SAS filed Critical Rhodia Chimie SAS
Publication of EP1171236A1 publication Critical patent/EP1171236A1/en
Withdrawn legal-status Critical Current

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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
    • B01D53/9404—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
    • B01J23/02—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the alkali- or alkaline earth metals or beryllium
    • 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
    • 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
    • B01D2255/202—Alkali metals
    • B01D2255/2027—Sodium
    • 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
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/2073—Manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines

Definitions

  • the present invention relates to compositions which can be used as NOx traps, based on manganese and an alkali or an alkaline earth, and their use in the treatment of exhaust gases.
  • NOx nitrogen oxides
  • the present invention relates to compositions which can be used as NOx traps, based on manganese and an alkali or an alkaline earth, and their use in the treatment of exhaust gases.
  • NOx nitrogen oxides
  • the reduction of emissions of nitrogen oxides (NOx) from the exhaust gases of automobile engines in particular is carried out using “three-way” catalysts which use the reducing gases present in the mixture stoichiometrically. Any excess oxygen results in a sudden deterioration in the performance of the catalyst.
  • certain engines such as diesel engines or gasoline engines operating in lean burn are fuel efficient but emit exhaust gases which permanently contain a large excess of oxygen of at least 5% for example.
  • a standard three-way catalyst therefore has no effect on NOx emissions in this case.
  • the limitation of NOx emissions is made imperative by the tight
  • NOx traps which are capable of oxidizing NO to NO2 and then adsorbing the NO2 thus formed. Under certain conditions, the NO2 is released and then reduced in 2 by reducing species contained in the exhaust gases.
  • These NOx traps still have certain drawbacks, however. Thus, their optimal operating range is located in a relatively low temperature zone, generally between 200 ° C and 270 ° C and they are little or not effective at higher temperatures. It would therefore be interesting to have a system that can operate at temperatures higher than those of current systems. In addition, they may have low thermal stability in a hydrothermal medium or in an oxidizing medium at high temperature. Improving this stability would therefore be an advantage. In addition, they are generally based on precious metals. However, these metals are expensive and their availability can be problematic. It would also be interesting to have catalysts free of precious metals to reduce costs.
  • the object of the invention is therefore the development of a composition which can be used as a NOx trap at high temperatures and, possibly, in the absence of precious metal.
  • Another object of the invention is to provide a NOx trap with good thermal stability.
  • rare earth is understood for the whole of the description the elements of the group constituted by yttrium and the elements of the periodic classification with atomic number included inclusively between 57 and 71.
  • the oxygen storage capacity to which reference is made in this description is determined by a test which evaluates the capacity of the support or of the product to successively oxidize injected quantities of oxygen carbon monoxide and to consume injected quantities oxygen to reoxidize the product.
  • the method used is said to be alternate.
  • the carrier gas is pure helium at a flow rate of 101 / h.
  • the injections are made via a loop containing 16ml of gas.
  • the injected quantities of CO are carried out using a gas mixture containing 5% of CO diluted in helium while the injected quantities of O2 are made from a gaseous mixture containing 2.5% of ⁇ 2 diluted in l 'helium.
  • the gas analysis is carried out by chromatography using a thermal conductivity detector.
  • the quantity of oxygen consumed makes it possible to determine the oxygen storage capacity.
  • the characteristic value of the oxygen storage capacity is expressed in ml of oxygen (under normal conditions of temperature and pressure) per gram of product introduced and it is measured at 400 ° C.
  • the oxygen storage capacity measurements given in the description are made on products pretreated at 900 ° C. in air for 6 hours in a muffle furnace.
  • the compositions of the invention comprise a support and an active phase.
  • the term support must be taken in a broad sense to designate, in the composition, the majority element (s) and / or either without catalytic activity or own trapping activity, or having a catalytic activity or trapping not equivalent to that of the phase active; and on which or on which the other elements are deposited.
  • the active phase is based on manganese and at least one other element A chosen from alkali metals and alkaline earth metals.
  • alkaline element mention may be made more particularly of sodium and potassium.
  • alkaline earth element there may be mentioned in particular barium.
  • the composition may include one or more elements A, any reference in the following description to element A must therefore be understood as being able to also apply in the case where there are several elements A.
  • the manganese and A elements are present in the composition of the invention in a chemically bound form.
  • a chemically bound form By this 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.
  • This compound or this phase may in particular be represented by the formula A x Mn y 2 ⁇ ⁇ ⁇ 0) of years which 0.5 ⁇ y / x ⁇ 6, the value of ⁇ depends on the nature of the element A and the oxidation state of manganese.
  • phase or compound of formula (1) there may be mentioned by way of example those of the vernadite, hollandite, romanechite or psilomelane, bimessite, todorokite, buserite or lithiophonte type.
  • the compound can optionally be hydrated.
  • the compound can moreover have a lamellar structure of the Cdl type.
  • the formula (1) is given here by way of illustration, it would not be departing from the scope of the present invention if the compound had a different formula insofar as of course the manganese and the element A are well chemically linked.
  • the degree of oxidation of manganese can vary between 2 and 7 and, more particularly between 3 and 7.
  • this element and manganese can be present in the form of a compound of type K 2 Mn 4 O 8
  • barium it can be a compound of type BaMnO
  • the invention covers the case where the active phase consists essentially of manganese and one or more other elements A chosen from alkali and alkaline earth metals, manganese and element A being chemically linked.
  • consists essentially is meant that the composition of the invention may have a NOx trap activity in the absence in the active phase of any element other than manganese and the element (s) A, such as for example an element of the precious metal or other metal type used usually in catalysis
  • compositions of the invention also comprise a support.
  • a support any porous support which can be used in the field of catalysis can be used. It is preferable that this support has chemical inertness with respect to the manganese and A elements sufficient to avoid a substantial reaction of one or of these elements with the support which would be likely to hinder the creation of a chemical bond between the manganese and the element A However, in the case of a reaction between the support and these elements, it it is possible to use larger quantities of manganese and of element A to obtain the desired chemical bond between these elements
  • This support can be based on alumina Any type of alumina capable of having a specific surface can be used HERE sufficient for application in catalysis.
  • aluminas resulting from the rapid dehydration of at least one aluminum hydroxide, such as baye ⁇ te, hydrargillite or gibbsite, nordstrandite, and / or from at least one aluminum oxyhydroxide such as boehmite , pseudoboehmite and diaspore
  • stabilizing element mention may be made of rare earths, barium, silicon, titanium and zirconium.
  • rare earth mention may be made very particularly of cerium, lanthanum or the lanthanum-neodymium mixture.
  • the preparation of the stabilized alumina is carried out in a manner known per se, in particular by impregnating the alumina with solutions of salts, such as nitrates, of the abovementioned stabilizing elements or else by co-drying of an alumina precursor and salts of these elements then calcination
  • the support can also be based on an oxide chosen from cerium oxide, zirconium oxide or their mixtures
  • this phase corresponds in fact to that of a cenic oxide Ce ⁇ 2 cubic crystallized and whose mesh parameters are more or less offset with respect to a pure ceric oxide, thus reflecting the incorporation of zirconium in the crystal lattice of cerium oxide, and therefore obtaining a true solid solution. Mention may also be made for mixtures of cerium oxide and zirconium oxide based on these two oxides and in addition of scandium oxide or of a rare earth other than cerium, and in particular those described in the application. WO patent
  • compositions have a specific surface after calcination for 6 hours at
  • the support is based on cerium oxide and it further comprises silica. Supports of this type are described in patent applications EP-A-207857 and EP-A-547924, the teaching of which is incorporated here.
  • the total content of manganese, alkaline, and alkaline earth can vary within wide limits. The minimum content is that below which NOx adsorption activity is no longer observed. This content can be in particular between 2 and 50%, more particularly between 5 and 30%, this content being expressed in atomic% by ratio to the sum of the moles of oxide (s) of the support and of the elements concerned in the active phase.
  • the respective contents of manganese, alkaline, and alkaline earth can also vary within wide proportions, the manganese content can be in particular equal to, or close to that of alkaline or alkaline earth
  • the alkali is potassium in a content (as expressed above) which can be between 10 and 50% and more particularly between 30 and 50%
  • compositions of the invention can be prepared by a process in which the support is brought into contact with manganese and at least one other element A or with precursors of manganese and at least one other element A and in which calcination is carried out the whole at a temperature sufficient to create a chemical bond between the manganese and the element A.
  • salts one can choose the salts of inorganic acids such as nitrates, sulfates or chlorides.
  • the salts of organic acids and in particular the salts of saturated aliphatic carboxylic acids or the salts of hydroxycarboxylic acids.
  • the support is then impregnated with the solution or the slip. More particularly, dry impregnation is used. Dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the element which is equal to the pore volume of the solid to be impregnated. It may be advantageous to deposit the elements of the active phase in two stages. Thus, it is advantageous to deposit the manganese in a first step then the element A in a second.
  • the support After impregnation, the support is optionally dried and then it is calcined. It should be noted that it is possible to use a support which has not yet been calcined prior to impregnation.
  • the deposition of the active phase can also be done by atomization of a suspension based on salts or compounds of the elements of the active phase and of the support.
  • the atomized product thus obtained is then calcined.
  • compositions for which the support is made of cerium oxide, element A is potassium are excluded from the present invention, in the proportions of Mn and K indicated and where the potassium and manganese precursor used in the preparation process, which has just been described, is potassium permanganate.
  • the calcination is carried out, as indicated above, at a temperature sufficient to create a chemical bond between the manganese and the element A.
  • This temperature varies according to the nature of the element A but, in the case of a calcination in air , it is generally at least 600 ° C, more particularly at least 700 ° C, it can in particular be between 800 ° C and 850 ° C. Higher temperatures are generally not necessary since the chemical bond between the manganese and the element A is already formed but on the other hand they can cause a reduction in the specific surface of the support likely to decrease the catalytic properties of the composition.
  • the duration of the calcination depends in particular on the temperature and it is also fixed so as to be sufficient to create a chemical bond of the elements.
  • compositions of the invention as described above are in the form of powders but they can optionally be shaped to be in the form of granules, beads, cylinders or honeycombs of variable dimensions.
  • the invention also relates to a gas treatment process for the reduction of nitrogen oxide emissions using the compositions of the invention.
  • gases capable of being treated by the present invention are, for example, those from gas turbines, boilers of thermal power stations or even internal combustion engines. In the latter case, they may in particular be diesel engines or of engines operating in lean mixture
  • compositions of the invention function as NOx traps when they are brought into contact with gases which have a high oxygen content.
  • the value ⁇ is correlated with the air / fuel ratio in a manner known per se, in particular in the field of internal combustion engines.
  • Such gases can be those of an engine operating in a lean burn mixture and which have an oxygen content ( expressed in volume) for example at least 2% as well as those which have an even higher oxygen content, for example gases from engines of the diesel type, i.e. e of at least 5% or more than 5%, more particularly of at least 10%, this content being, for example, between 5% and 20%
  • the invention also applies to gases of the above type which may further contain water in an amount of the order of 10% for example.
  • the invention also relates to a system for the treatment of gases with a view to reducing the emissions of nitrogen oxides, gases which may be of the type of those mentioned above and very particularly those having an excess of oxygen relative to the value stoichiometric
  • This system is characterized in that it comprises a composition as described above.
  • it can comprise a coating (wash coat) with catalytic properties and based on these compositions, on a substrate of the type, for example metallic monolith or in ceramic
  • the invention also relates to the use of the compositions in the manufacture of such a system. Examples will now be given.
  • NOx trap evaluation test is carried out as follows:
  • 0J5 g of the powdered NOx trap are loaded into a quartz reactor.
  • the powder used was previously compacted, then ground and sieved so as to isolate the particle size range between 0J25 and 0.250 mm.
  • the reaction mixture at the inlet of the reactor has the following composition (by volume):
  • the overall flow rate is 30 Nl / h.
  • the WH is around 150,000 h "1 .
  • NOx NO + NO2
  • NO and NOx signals are given by an ECOPHYSICS NOx analyzer, based on the principle of chemiluminescence.
  • NOx traps are evaluated by determining the total amount of NOx adsorbed (expressed in mgNO / g of trap or active phase) until the trap phase is saturated. The experiment is repeated at different temperatures between 250 ° C and 500 ° C. It is thus possible to determine the optimal temperature zone for the operation of the NOx traps.
  • Manganese nitrate Mn (N03) 2.4H 2 O, potassium nitrate KNO3 99.5%, barium nitrate Ba (N03) 2 99.5% and sodium nitrate NaNO 3 99.5% are used. .
  • the supports used are HSA5 ® of Rhodia cerium oxide, a cerium oxide HSA1 ® of Rhodia, zirconium oxide comprising cerium oxide
  • the active phase is based on manganese with another element A which is K, Ba or Na
  • the elements are impregnated on the support one after the other.
  • the operating protocol is as follows: - Dry impregnation of the first element
  • HSA5 ® support for Examples 9 and 10 the HSA514® carrier, for Example 11 the carrier ZrO 2 / CeO 2 and for Example 12 the HSA1® support.
  • SBET stands for the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical 'The Journal of the American Chemical Society, 60, 309 (1938) ".
  • the RX analysis only shows the CeO 2 phase.
  • the RX analysis reveals the CeO 2 phase and a K 2 Mn 4 O 8 type phase referenced in the JCPDS files 16-0205. Analysis by microscopy shows the presence of large crystals formed by Mn and K from 200nm to 300nm approximately. Manganese is in oxidation states III and IV.
  • the RX analysis reveals the CeO 2 phase and a BaMnO 3 type phase.
  • the RX analysis reveals the CeO 2 phase and a Na 07 MnO 2- ⁇ type phase.
  • compositions of the invention there is a significant shift in Tmax towards high temperatures compared to compositions in which the manganese and the other element are not chemically linked. Furthermore, these compositions are effective in storing NOx even in the absence of platinum or another precious metal.
  • EXAMPLE 13 This example illustrates the thermal stability of the compositions according to the invention.
  • Example 4 The same composition is used as for Example 4, but calcined for 6 hours at 750 ° C. in a nitrogen atmosphere containing 10% by volume of hydrogen.
  • the results in catalysis of the composition are given in the table below in which the results of Example 4 have also been reported for comparison: Table 3
  • a support based on cerium oxide, zirconium oxide and lanthanum oxide is used in the respective proportions by weight CeO 2 / Zr ⁇ 2 / La 2 O 3 of 67/23/10 calcined 2 hours at 800 ° C.
  • the amount of NOx stored is given in table 4 below.
  • a support based on alumina calcined for 2 hours at 500 ° C. is used.
  • a dry impregnation is carried out with manganese and potassium under the conditions described above and in the following molar proportions:
  • the product After impregnation, the product is calcined for 6 hours at 750 ° C. It has an SBET surface of 129m 2 / g.
  • the amount of NOx stored is given in table 5 below.

Abstract

The invention concerns compositions used as NOx trap, based on manganese and an alkaline or an alkaline-earth and their use for treating exhaust gases. Said compositions comprise a carrier and an active phase; and they are characterised in that the active phase is based on manganese and at least another element A selected among alkalines or alkaline-earths, the manganese and element A being chemically bound. Said compositions can be used in a process for treating gases to reduce nitrogen oxide emissions, as NOx traps, said gases being derived from internal combustion engines and in particular diesel engines or lean-burn engines.

Description

COMPOSITIONS UTILISABLES COMME PIEGE A NOx. A BASE DE MANGANESECOMPOSITIONS FOR USE AS A NOx TRAP. MANGANESE BASED
ET D'UN ALCALIN OU D'UN ALCALINO-TERREUX ET UTILISATION DANS LEAND AN ALKALINE OR AN ALKALINE EARTH AND USE THEREOF
TRAITEMENT DES GAZ D'ECHAPPEMENTEXHAUST GAS TREATMENT
RHODIA CHIMIERHODIA CHEMISTRY
La présente invention concerne des compositions utilisables comme piège à NOx, à base de manganèse et d'un alcalin ou d'un alcalino-terreux et leur utilisation dans le traitement des gaz d'échappement. On sait que la réduction des émissions des oxydes d'azote (NOx) des gaz d'échappement des moteurs d'automobiles notamment, est effectuée à l'aide de catalyseurs "trois voies" qui utilisent stoechiométriquement les gaz réducteurs présents dans le mélange. Tout excès d'oxygène se traduit par une détérioration brutale des performances du catalyseur. Or, certains moteurs comme les moteurs diesel ou les moteurs essence fonctionnant en mélange pauvre (lean burn) sont économes en carburant mais émettent des gaz d'échappement qui contiennent en permanence un large excès d'oxygène d'au moins 5% par exemple. Un catalyseur trois voies standard est donc sans effet sur les émissions en NOx dans ce cas. Par ailleurs, la limitation des émissions en NOx est rendue impérative par le durcissement des normes en post combustion automobile qui s'étendent maintenant à ces moteurs.The present invention relates to compositions which can be used as NOx traps, based on manganese and an alkali or an alkaline earth, and their use in the treatment of exhaust gases. It is known that the reduction of emissions of nitrogen oxides (NOx) from the exhaust gases of automobile engines in particular is carried out using “three-way” catalysts which use the reducing gases present in the mixture stoichiometrically. Any excess oxygen results in a sudden deterioration in the performance of the catalyst. However, certain engines such as diesel engines or gasoline engines operating in lean burn are fuel efficient but emit exhaust gases which permanently contain a large excess of oxygen of at least 5% for example. A standard three-way catalyst therefore has no effect on NOx emissions in this case. Furthermore, the limitation of NOx emissions is made imperative by the tightening of standards in automotive post combustion which now extend to these engines.
Pour résoudre ce problème, on a proposé notamment des systèmes appelés pièges à NOx, qui sont capables d'oxyder NO en NO2 puis d'adsorber le NO2 ainsi formé. Dans certaines conditions, le NO2 est relargué puis réduit en 2 par des espèces réductrices contenues dans les gaz d'échappement. Ces pièges à NOx ont encore toutefois certains inconvénients. Ainsi, leur domaine de fonctionnement optimal est situé dans une zone de température relativement basse, généralement entre 200°C et 270°C et ils sont peu ou pas efficaces à des températures plus élevées. Il serait donc intéressant de pouvoir disposer d'un système pouvant fonctionner à des températures plus hautes que celles des systèmes actuels. En outre, ils peuvent présenter une stabilité thermique faible en milieu hydrothermal ou en milieu oxydant à haute température. L'amélioration de cette stabilité constituerait donc un avantage. Par ailleurs, ils sont généralement à base de métaux précieux. Or, ces métaux sont chers et leur disponibilité peut être problématique. Il serait aussi intéressant de pouvoir disposer de catalyseurs sans métaux précieux pour en réduire les coûts.To solve this problem, systems called NOx traps have been proposed, which are capable of oxidizing NO to NO2 and then adsorbing the NO2 thus formed. Under certain conditions, the NO2 is released and then reduced in 2 by reducing species contained in the exhaust gases. These NOx traps still have certain drawbacks, however. Thus, their optimal operating range is located in a relatively low temperature zone, generally between 200 ° C and 270 ° C and they are little or not effective at higher temperatures. It would therefore be interesting to have a system that can operate at temperatures higher than those of current systems. In addition, they may have low thermal stability in a hydrothermal medium or in an oxidizing medium at high temperature. Improving this stability would therefore be an advantage. In addition, they are generally based on precious metals. However, these metals are expensive and their availability can be problematic. It would also be interesting to have catalysts free of precious metals to reduce costs.
L'objet de l'invention est donc la mise au point d'une composition qui peut être utilisée comme piège à NOx à des températures hautes et, éventuellement, en l'absence de métal précieux. Un autre objet de l'invention est de procurer un piège à NOx à bonne stabilité thermique.The object of the invention is therefore the development of a composition which can be used as a NOx trap at high temperatures and, possibly, in the absence of precious metal. Another object of the invention is to provide a NOx trap with good thermal stability.
Dans ce but, les compositions utilisables comme piège à NOx, selon l'invention, comprennent un support et une phase active, et elles sont caractérisées en ce que la phase active est à base de manganèse et d'au moins un autre élément A choisi parmi les alcalins et les alcalino-terreux, le manganèse et l'élément A étant chimiquement liés; étant exclues, d'une part, les compositions dans lesquelles A est le potassium, où le support est l'oxyde de cérium et où les deux éléments manganèse et potassium sont apportés par le permanganate de potassium dans des proportions atomiques [K]/([K]+[CeO2])=0J6 et [Mn]/([Mn]+[CeO2])=0J6, et étant exclue, d'autre part, la composition dans laquelle A est le potassium et où le support est à base d'un oxyde de cérium, d'un oxyde de zirconium et d'un oxyde de lanthane dans les proportions respectives en poids par rapport aux oxydes de 72/24/2, et où le support présente en outre une capacité de stockage de l'oxygène de 2,8ml d'O2/g. D'autres caractéristiques, détails et avantages de l'invention apparaîtront encore plus complètement à la lecture de la description qui va suivre, ainsi que des divers exemples concrets mais non limitatifs destinés à l'illustrer.For this purpose, the compositions which can be used as NOx trap, according to the invention, comprise a support and an active phase, and they are characterized in that the active phase is based on manganese and at least one other element A chosen among alkali and alkaline earth, manganese and element A being chemically linked; being excluded, on the one hand, the compositions in which A is potassium, where the support is cerium oxide and where the two elements manganese and potassium are provided by potassium permanganate in atomic proportions [K] / ( [K] + [CeO2]) = 0J6 and [Mn] / ([Mn] + [CeO 2 ]) = 0J6, and being excluded, on the other hand, the composition in which A is potassium and where the support is based on a cerium oxide, a zirconium oxide and a lanthanum oxide in the respective proportions by weight relative to the oxides of 72/24/2, and where the support also has a storage capacity 2.8 ml of oxygen O 2 / g. Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows, as well as various concrete but nonlimiting examples intended to illustrate it.
Par terre rare on entend pour l'ensemble de la description les éléments du groupe constitué par l'yttrium et les éléments de la classification périodique de numéro atomique compris inclusivement entre 57 et 71.By rare earth is understood for the whole of the description the elements of the group constituted by yttrium and the elements of the periodic classification with atomic number included inclusively between 57 and 71.
La capacité de stockage de l'oxygène à laquelle il est fait référence dans cette description est déterminée par un test qui évalue la capacité du support ou du produit à successivement oxyder des quantités injectées de monoxyde de carbone d'oxygène et à consommer des quantités injectées d'oxygène pour réoxyder le produit. La méthode employée est dite alternée.The oxygen storage capacity to which reference is made in this description is determined by a test which evaluates the capacity of the support or of the product to successively oxidize injected quantities of oxygen carbon monoxide and to consume injected quantities oxygen to reoxidize the product. The method used is said to be alternate.
Le gaz porteur est de l'hélium pur à un débit de 101/h. Les injections se font par l'intermédiaire d'une boucle contenant 16ml de gaz. Les quantités injectées de CO sont effectués en utilisant un mélange gazeux contenant 5% de CO dilué dans l'hélium tandis que les quantités injectées d'02 se font à partir d'un mélange gazeux contenant 2,5% d'θ2 dilué dans l'hélium. L'analyse des gaz est effectuée par chromatographie à l'aide d'un détecteur de conductivité thermique.The carrier gas is pure helium at a flow rate of 101 / h. The injections are made via a loop containing 16ml of gas. The injected quantities of CO are carried out using a gas mixture containing 5% of CO diluted in helium while the injected quantities of O2 are made from a gaseous mixture containing 2.5% of θ2 diluted in l 'helium. The gas analysis is carried out by chromatography using a thermal conductivity detector.
La quantité d'oxygène consommée permet de déterminer la capacité de stockage d'oxygène. La valeur caractéristique du pouvoir de stockage d'oxygène est exprimée en ml d'oxygène (dans les conditions normales de température et de pression) par gramme de produit introduit et elle est mesurée à 400°C. Les mesures de capacité de stockage d'oxygène données dans la description sont faites sur des produits prétraités à 900°C sous air pendant 6 heures dans un four à moufle. Les compositions de l'invention comprennent un support et une phase active. Le terme support doit être pris dans un sens large pour désigner, dans la composition, le ou les éléments majoritaires et/ou soit sans activité catalytique ni activité de piégeage propre, soit présentant une activité catalytique ou de piégeage non équivalente à celle de la phase active; et sur lequel ou sur lesquels sont déposés les autres éléments. Pour simplifier, on parlera dans la suite de la description de support et de phase active ou supportée mais on comprendra que l'on ne sortirait pas du cadre de la présente invention dans le cas où un élément décrit comme appartenant à la phase active ou supportée était présent dans le support, par exemple en y ayant été introduit lors de la préparation même du support.The quantity of oxygen consumed makes it possible to determine the oxygen storage capacity. The characteristic value of the oxygen storage capacity is expressed in ml of oxygen (under normal conditions of temperature and pressure) per gram of product introduced and it is measured at 400 ° C. The oxygen storage capacity measurements given in the description are made on products pretreated at 900 ° C. in air for 6 hours in a muffle furnace. The compositions of the invention comprise a support and an active phase. The term support must be taken in a broad sense to designate, in the composition, the majority element (s) and / or either without catalytic activity or own trapping activity, or having a catalytic activity or trapping not equivalent to that of the phase active; and on which or on which the other elements are deposited. To simplify, we will speak in the following description of support and active or supported phase but it will be understood that it would not go beyond the scope of the present invention in the case where an element described as belonging to the active or supported phase was present in the support, for example by having been introduced into it during the preparation of the support itself.
Selon une caractéristique de l'invention, la phase active est à base de manganèse et d'au moins un autre élément A choisi parmi les alcalins et les alcalino-terreux Comme élément alcalin, on peut citer plus particulièrement le sodium et le potassium. Comme élément alcalino-terreux, on peut mentionner notamment le baryum. Comme la composition peut comprendre un ou plusieurs éléments A, toute référence dans la suite de la description à l'élément A devra donc être comprise comme pouvant s'appliquer aussi au cas où il y aurait plusieurs éléments A.According to a characteristic of the invention, the active phase is based on manganese and at least one other element A chosen from alkali metals and alkaline earth metals. As alkaline element, mention may be made more particularly of sodium and potassium. As alkaline earth element, there may be mentioned in particular barium. As the composition may include one or more elements A, any reference in the following description to element A must therefore be understood as being able to also apply in the case where there are several elements A.
Par ailleurs, les éléments manganèse et A sont présents dans la composition de l'invention sous une forme chimiquement liée. On entend par là qu'il y a des liaisons chimiques entre le manganèse et l'élément A résultant d'une réaction entre eux, ces deux éléments n'étant pas simplement juxtaposés comme dans un simple mélange.Furthermore, the manganese and A elements are present in the composition of the invention in a chemically bound form. By this 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.
Ainsi, les éléments manganèse et A peuvent être présents sous la forme d'un composé ou d'une phase de type oxyde mixte. Ce composé ou cette phase peuvent notamment être représentés par la formule AxMnyθ2±δ 0) dans laquelle 0,5<y/x<6, la valeur de δ dépendant de la nature de l'élément A et de l'état d'oxydation du manganèse. Comme phase ou composé de formule (1) on peut citer à titre d'exemple ceux du type vernadite, hollandite, romanéchite ou psilomélane, bimessite, todorokite, buserite ou lithiophonteThus, the elements manganese and A can be present in the form of a compound or of a phase of mixed oxide type. This compound or this phase may in particular be represented by the formula A x Mn y 2 θ ± δ 0) of years which 0.5 <y / x <6, the value of δ depends on the nature of the element A and the oxidation state of manganese. As phase or compound of formula (1) there may be mentioned by way of example those of the vernadite, hollandite, romanechite or psilomelane, bimessite, todorokite, buserite or lithiophonte type.
Le composé peut être éventuellement hydraté. Le composé peut par ailleurs avoir une structure lamellaire de type Cdl . La formule (1) est donnée ici à titre illustratif, on ne sortirait pas du cadre de la présente invention si le composé présentait une formule différente dans la mesure bien entendu où le manganèse et l'élément A seraient bien chimiquement liés.The compound can optionally be hydrated. The compound can moreover have a lamellar structure of the Cdl type. The formula (1) is given here by way of illustration, it would not be departing from the scope of the present invention if the compound had a different formula insofar as of course the manganese and the element A are well chemically linked.
L'analyse par RX ou par microscopie électronique permet de mettre en évidence la présence d'un tel composé. Le degré d'oxydation du manganèse peut varier entre 2 et 7 et, plus particulièrement entre 3 et 7. Dans le cas du potassium, cet élément et le manganèse peuvent être présents sous la forme d'un composé de type K2Mn4O8 Dans le cas du baryum, il peut s'agir d'un composé de type BaMnOAnalysis by X-ray or by electron microscopy makes it possible to demonstrate the presence of such a compound. The degree of oxidation of manganese can vary between 2 and 7 and, more particularly between 3 and 7. In the case of potassium, this element and manganese can be present in the form of a compound of type K 2 Mn 4 O 8 In the case of barium, it can be a compound of type BaMnO
L'invention couvre le cas où la phase active consiste essentiellement en du manganèse et en un ou plusieurs autres éléments A choisi parmi les alcalins et les alcalino-terreux, le manganèse et l'élément A étant chimiquement liés Par "consiste essentiellement" on entend que la composition de l'invention peut avoir une activité de piège à NOx en l'absence dans la phase active de tout élément autre que le manganèse et le ou les éléments A, comme par exemple un élément du type métal précieux ou autre métal utilisé habituellement en catalyseThe invention covers the case where the active phase consists essentially of manganese and one or more other elements A chosen from alkali and alkaline earth metals, manganese and element A being chemically linked. By "consists essentially" is meant that the composition of the invention may have a NOx trap activity in the absence in the active phase of any element other than manganese and the element (s) A, such as for example an element of the precious metal or other metal type used usually in catalysis
Les compositions de l'invention comprennent en outre un support Comme support, on peut mettre en œuvre tout support poreux utilisable dans le domaine de la catalyse II est préférable que ce support présente une inertie chimique vis à vis des éléments manganèse et A suffisante pour éviter une reaction substantielle d'un ou de ces éléments avec le support qui serait susceptible de gêner la création d'une liaison chimique entre le manganèse et l'élément A Toutefois, dans le cas d'une réaction entre le support et ces éléments, il est possible de mettre en œuvre des quantités plus importantes de manganèse et d'élément A pour obtenir la liaison chimique recherchée entre ces éléments Ce support peut être à base d'alumine On peut utiliser ICI tout type d'alumine susceptible de présenter une surface spécifique suffisante pour une application en catalyse. On peut mentionner les alumines issues de la déshydratation rapide d'au moins un hydroxyde d'aluminium, tel que la bayeπte, l'hydrargillite ou gibbsite, la nordstrandite, et/ou d'au moins un oxyhydroxyde d'aluminium tel que la boehmite, la pseudoboehmite et le diasporeThe compositions of the invention also comprise a support. As a support, any porous support which can be used in the field of catalysis can be used. It is preferable that this support has chemical inertness with respect to the manganese and A elements sufficient to avoid a substantial reaction of one or of these elements with the support which would be likely to hinder the creation of a chemical bond between the manganese and the element A However, in the case of a reaction between the support and these elements, it it is possible to use larger quantities of manganese and of element A to obtain the desired chemical bond between these elements This support can be based on alumina Any type of alumina capable of having a specific surface can be used HERE sufficient for application in catalysis. Mention may be made of aluminas resulting from the rapid dehydration of at least one aluminum hydroxide, such as bayeπte, hydrargillite or gibbsite, nordstrandite, and / or from at least one aluminum oxyhydroxide such as boehmite , pseudoboehmite and diaspore
On peut aussi utiliser une alumine stabilisée Comme élément stabilisant on peut citer les terres rares, le baryum, le silicium, le titane et le zirconium Comme terre rare on peut mentionner tout particulièrement le cérium, le lanthane ou le mélange lanthane- néodyme. La préparation de l'alumine stabilisée se fait d'une manière connue en soi, notamment par imprégnation de l'alumine par des solutions de sels, comme les nitrates, des éléments stabilisants précités ou encore par coséchage d'un précurseur d'alumine et de sels de ces éléments puis calcinationOne can also use a stabilized alumina. As stabilizing element, mention may be made of rare earths, barium, silicon, titanium and zirconium. As rare earth, mention may be made very particularly of cerium, lanthanum or the lanthanum-neodymium mixture. The preparation of the stabilized alumina is carried out in a manner known per se, in particular by impregnating the alumina with solutions of salts, such as nitrates, of the abovementioned stabilizing elements or else by co-drying of an alumina precursor and salts of these elements then calcination
Le support peut aussi être à base d'un oxyde choisi parmi l'oxyde de cérium, l'oxyde de zirconium ou leurs mélangesThe support can also be based on an oxide chosen from cerium oxide, zirconium oxide or their mixtures
On peut mentionner notamment pour les mélanges d'oxyde de cérium et d'oxyde de zirconium ceux décrits dans les demandes de brevets EP-A- 605274 et EP-A- 735984 dont l'enseignement est incorpore ICI On peut plus particulièrement utiliser les supports à base d'oxyde de cérium et de zirconium dans lesquels ces oxydes sont présents dans une proportion atomique céπum/zirconium d'au moins 1 Pour ces mêmes supports, on peut aussi utiliser ceux qui se présentent sous forme d'une solution solide. Dans ce cas, les spectres en diffraction X du support révèlent au sein de ce dernier l'existence d'une seule phase homogène Pour les supports les plus riches en cérium, cette phase correspond en fait à celle d'un oxyde cénque Ceθ2 cubique cristallisé et dont les paramètres de mailles sont plus ou moins décalés par rapport à un oxyde cérique pur, traduisant ainsi l'incorporation du zirconium dans le réseau cristallin de l'oxyde de cérium, et donc l'obtention d'une solution solide vraie. On peut encore mentionner pour les mélanges d'oxyde de cérium et d'oxyde de zirconium à base de ces deux oxydes et en outre d'oxyde de scandium ou d'une terre rare autre que le cérium, et notamment ceux décrits dans la demande de brevet WOMention may in particular be made, for mixtures of cerium oxide and zirconium oxide, of those described in patent applications EP-A-605,274 and EP-A-735,984, the teaching of which is incorporated HERE. supports based on cerium and zirconium oxide in which these oxides are present in a céπum / zirconium atomic proportion of at least 1 For these same supports, it is also possible to use those which are in the form of a solid solution. In this case, the X-ray diffraction spectra of the support reveal within the latter the existence of a single homogeneous phase. For the supports richest in cerium, this phase corresponds in fact to that of a cenic oxide Ceθ2 cubic crystallized and whose mesh parameters are more or less offset with respect to a pure ceric oxide, thus reflecting the incorporation of zirconium in the crystal lattice of cerium oxide, and therefore obtaining a true solid solution. Mention may also be made for mixtures of cerium oxide and zirconium oxide based on these two oxides and in addition of scandium oxide or of a rare earth other than cerium, and in particular those described in the application. WO patent
97/43214 dont l'enseignement est incorporé ici Cette demande décrit en particulier des compositions à base d'un oxyde de cérium, d'un oxyde de zirconium et d'un oxyde d'yttnum, ou encore, outre l'oxyde de cérium et l'oxyde de zirconium à base d'au moins un autre oxyde choisi parmi l'oxyde de scandium et les oxydes de terres rares à l'exception du cérium, dans une proportion atomique céπum/zirconium d'au moins 197/43214, the teaching of which is incorporated here This application describes in particular compositions based on a cerium oxide, a zirconium oxide and a yttnum oxide, or also, in addition to cerium oxide and zirconium oxide based on at least one other oxide chosen from scandium oxide and rare earth oxides with the exception of cerium, in a cerum / zirconium atomic proportion of at least 1
Ces compositions présentent une surface spécifique après calcination 6 heures àThese compositions have a specific surface after calcination for 6 hours at
900°C d'au moins 35nrι2/g et une capacité de stockage de l'oxygène à 400°C d'au moins 1 ,5ml d'02 g900 ° C of at least 35nrι2 / g and an oxygen storage capacity at 400 ° C of at least 1.5ml of 02 g
Selon un mode de réalisation particulier de l'invention, le support est à base d'oxyde de cérium et il comprend en outre de la silice. Des supports de ce type sont décrits dans les demandes de brevets EP-A-207857 et EP-A-547924 dont l'enseignement est incorporé ici. La teneur totale en manganèse, alcalin, et alcalino-terreux peut varier dans de larges proportions. La teneur minimale est celle en deçà de laquelle on n'observe plus d'activité d'adsorption des NOx Cette teneur peut être comprise notamment entre 2 et 50%, plus particulièrement entre 5 et 30%, cette teneur étant exprimée en % atomique par rapport à la somme des moles d'oxyde(s) du support et des éléments concernés de la phase active. Les teneurs respectives en manganèse, alcalin, et alcalino-terreux peuvent aussi varier dans de larges proportions, la teneur en manganèse peut être notamment égale à, ou proche de celle en alcalin ou alcalino-terreuxAccording to a particular embodiment of the invention, the support is based on cerium oxide and it further comprises silica. Supports of this type are described in patent applications EP-A-207857 and EP-A-547924, the teaching of which is incorporated here. The total content of manganese, alkaline, and alkaline earth can vary within wide limits. The minimum content is that below which NOx adsorption activity is no longer observed. This content can be in particular between 2 and 50%, more particularly between 5 and 30%, this content being expressed in atomic% by ratio to the sum of the moles of oxide (s) of the support and of the elements concerned in the active phase. The respective contents of manganese, alkaline, and alkaline earth can also vary within wide proportions, the manganese content can be in particular equal to, or close to that of alkaline or alkaline earth
Selon une variante intéressante de l'invention, l'alcalin est le potassium dans une teneur (comme exprimée ci-dessus) qui peut être comprise entre 10 et 50% et plus particulièrement entre 30 et 50%According to an interesting variant of the invention, the alkali is potassium in a content (as expressed above) which can be between 10 and 50% and more particularly between 30 and 50%
On peut préparer les compositions de l'invention par un procédé dans lequel on met en contact le support avec le manganèse et au moins un autre élément A ou avec des précurseurs du manganèse et d'au moins un autre élément A et où on calcine l'ensemble à une température suffisante pour créer une liaison chimique entre le manganèse et l'élément A.The compositions of the invention can be prepared by a process in which the support is brought into contact with manganese and at least one other element A or with precursors of manganese and at least one other element A and in which calcination is carried out the whole at a temperature sufficient to create a chemical bond between the manganese and the element A.
Une méthode utilisable pour la mise en contact précitée est l'imprégnation. On forme ainsi tout d'abord une solution ou une barbotine de sels ou de composés des éléments de la phase supportée.One method which can be used for the aforementioned contacting is impregnation. This first forms a solution or slip of salts or compounds of the elements of the supported phase.
A titre de sels, on peut choisir les sels d'acides inorganiques comme les nitrates, les sulfates ou les chlorures.As salts, one can choose the salts of inorganic acids such as nitrates, sulfates or chlorides.
On peut aussi utiliser les sels d'acides organiques et notamment les sels d'acides carboxyliques aliphatiques saturés ou les sels d'acides hydroxycarboxyliques. A titre d'exemples, on peut citer les formiates, acétates, propionates, oxalates ou les citrates. On imprègne ensuite le support avec la solution ou la barbotine. On utilise plus particulièrement l'imprégnation à sec. L'imprégnation à sec consiste à ajouter au produit à imprégner un volume d'une solution aqueuse de l'élément qui est égal au volume poreux du solide à imprégner. II peut être avantageux d'effectuer le dépôt des éléments de la phase active en deux étapes. Ainsi, on peut avantageusement déposer le manganèse dans un premier temps puis l'élément A dans un deuxième.It is also possible to use the salts of organic acids and in particular the salts of saturated aliphatic carboxylic acids or the salts of hydroxycarboxylic acids. By way of examples, mention may be made of formates, acetates, propionates, oxalates or citrates. The support is then impregnated with the solution or the slip. More particularly, dry impregnation is used. Dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the element which is equal to the pore volume of the solid to be impregnated. It may be advantageous to deposit the elements of the active phase in two stages. Thus, it is advantageous to deposit the manganese in a first step then the element A in a second.
Après imprégnation, le support est éventuellement séché puis il est calciné. Il est à noter qu'il est possible d'utiliser un support qui n'a pas encore été calciné préalablement à l'imprégnation.After impregnation, the support is optionally dried and then it is calcined. It should be noted that it is possible to use a support which has not yet been calcined prior to impregnation.
Le dépôt de la phase active peut aussi se faire par atomisation d'une suspension à base de sels ou de composés des éléments de la phase active et du support. On calcine ensuite le produit atomisé ainsi obtenu.The deposition of the active phase can also be done by atomization of a suspension based on salts or compounds of the elements of the active phase and of the support. The atomized product thus obtained is then calcined.
Comme indiqué plus haut, sont exclues de la présente invention les compositions pour lesquelles le support est en oxyde de cérium, l'élément A est le potassium, dans les proportions de Mn et K indiquées et où le précurseur du potassium et du manganèse utilisé dans le procédé de préparation, qui vient d'être décrit, est le permanganate de potassium.As indicated above, the compositions for which the support is made of cerium oxide, element A is potassium, are excluded from the present invention, in the proportions of Mn and K indicated and where the potassium and manganese precursor used in the preparation process, which has just been described, is potassium permanganate.
La calcination se fait, comme indiqué plus haut, à une température suffisante pour créer une liaison chimique entre le manganèse et l'élément A. Cette température varie suivant la nature de l'élément A mais, dans le cas d'une calcination sous air, elle est généralement d'au moins 600°C plus particulièrement d'au moins 700°C, elle peut être notamment comprise entre 800°C et 850°C. Des températures supérieures ne sont généralement pas nécessaires dans la mesure où la liaison chimique entre le manganèse et l'élément A est déjà formée mais par contre elles peuvent entraîner une diminution de la surface spécifique du support susceptible de diminuer les propriétés catalytiques de la composition. La durée de la calcination dépend notamment de la température et elle est fixée aussi de manière à être suffisante pour créer une liaison chimique des éléments.The calcination is carried out, as indicated above, at a temperature sufficient to create a chemical bond between the manganese and the element A. This temperature varies according to the nature of the element A but, in the case of a calcination in air , it is generally at least 600 ° C, more particularly at least 700 ° C, it can in particular be between 800 ° C and 850 ° C. Higher temperatures are generally not necessary since the chemical bond between the manganese and the element A is already formed but on the other hand they can cause a reduction in the specific surface of the support likely to decrease the catalytic properties of the composition. The duration of the calcination depends in particular on the temperature and it is also fixed so as to be sufficient to create a chemical bond of the elements.
Les compositions de l'invention telles que décrites plus haut se présentent sous forme de poudres mais elles peuvent éventuellement être mises en forme pour se présenter sous forme de granulés, billes, cylindres ou nids d'abeille de dimensions variables.The compositions of the invention as described above are in the form of powders but they can optionally be shaped to be in the form of granules, beads, cylinders or honeycombs of variable dimensions.
L'invention concerne aussi un procédé de traitement de gaz en vue de la réduction des émissions des oxydes d'azote mettant en œuvre les compositions de l'invention. Les gaz susceptibles d'être traités par la présente invention sont, par exemple, ceux issus de turbines à gaz, de chaudières de centrales thermiques ou encore de moteurs à combustion interne Dans ce dernier cas, il peut s'agir notamment de moteurs diesel ou de moteurs fonctionnant en mélange pauvreThe invention also relates to a gas treatment process for the reduction of nitrogen oxide emissions using the compositions of the invention. The gases capable of being treated by the present invention are, for example, those from gas turbines, boilers of thermal power stations or even internal combustion engines. In the latter case, they may in particular be diesel engines or of engines operating in lean mixture
Les compositions de l'invention fonctionnent comme pièges à NOx lorsqu'elles sont mises en contact avec des gaz qui présentent une teneur élevée en oxygène Par gaz présentant une teneur élevée en oxygène, on entend des gaz présentant un excès d'oxygène par rapport à la quantité nécessaire pour la combustion stœchiométnque des carburants et, plus précisément, des gaz présentant un excès d'oxygène par rapport à la valeur stœchiométrique λ = 1 , c'est à dire les gaz pour lesquels la valeur de λ est supérieure à 1. La valeur λ est corrélée au rapport air/carburant d'une manière connue en soi notamment dans le domaine des moteurs à combustion interne De tels gaz peuvent être ceux de moteur fonctionnant en mélange pauvre (lean burn) et qui présentent une teneur en oxygène (exprimée en volume) par exemple d'au moins 2% ainsi que ceux qui présentent une teneur en oxygène encore plus élevée, par exemple des gaz de moteurs du type diesel, c'est à dire d'au moins 5% ou de plus de 5%, plus particulièrement d'au moins 10%, cette teneur pouvant par exemple se situer entre 5% et 20%The compositions of the invention function as NOx traps when they are brought into contact with gases which have a high oxygen content. By gases having a high oxygen content, we mean gases having an excess of oxygen relative to the quantity necessary for the stoichiometric combustion of fuels and, more precisely, of the gases having an excess of oxygen compared to the stoichiometric value λ = 1, that is to say the gases for which the value of λ is greater than 1. The value λ is correlated with the air / fuel ratio in a manner known per se, in particular in the field of internal combustion engines. Such gases can be those of an engine operating in a lean burn mixture and which have an oxygen content ( expressed in volume) for example at least 2% as well as those which have an even higher oxygen content, for example gases from engines of the diesel type, i.e. e of at least 5% or more than 5%, more particularly of at least 10%, this content being, for example, between 5% and 20%
L'invention s'applique aussi aux gaz du type ci-dessus qui peuvent contenir en outre de l'eau dans une quantité de l'ordre de 10% par exemple. L'invention concerne aussi un système pour le traitement de gaz en vue de la réduction des émissions des oxydes d'azote, gaz qui peuvent être du type de ceux mentionnés précédemment et tout particulièrement ceux présentant un excès d'oxygène par rapport à la valeur stœchiométnque Ce système est caractérisé en ce qu'il comprend une composition telle que décrite plus haut Ainsi, il peut comprendre un revêtement (wash coat) à propriétés catalytiques et à base de ces compositions, sur un substrat du type par exemple monolithe métallique ou en céramiqueThe invention also applies to gases of the above type which may further contain water in an amount of the order of 10% for example. The invention also relates to a system for the treatment of gases with a view to reducing the emissions of nitrogen oxides, gases which may be of the type of those mentioned above and very particularly those having an excess of oxygen relative to the value stoichiometric This system is characterized in that it comprises a composition as described above. Thus, it can comprise a coating (wash coat) with catalytic properties and based on these compositions, on a substrate of the type, for example metallic monolith or in ceramic
Enfin, l'invention concerne aussi l'utilisation des compositions dans la fabrication d'un tel système. Des exemples vont maintenant être donnés.Finally, the invention also relates to the use of the compositions in the manufacture of such a system. Examples will now be given.
Dans ces exemples, le test d'évaluation des pièges à NOx est réalisé de la manière suivante :In these examples, the NOx trap evaluation test is carried out as follows:
On charge 0J5 g du piège à NOx en poudre dans un réacteur en quartz. La poudre utilisée a préalablement été compactée puis broyée et tamisée de manière à isoler la tranche granulométrique comprise entre 0J25 et 0,250 mm.0J5 g of the powdered NOx trap are loaded into a quartz reactor. The powder used was previously compacted, then ground and sieved so as to isolate the particle size range between 0J25 and 0.250 mm.
Le mélange réactionnel à l'entrée du réacteur a la composition suivante (en volume):The reaction mixture at the inlet of the reactor has the following composition (by volume):
- NO : 300 vpm - 02 : 10 %- NO: 300 vpm - 02: 10%
- CO2 : 10 %- CO2: 10%
- H2O : 10 % - N2 : qsp 100 %- H2O: 10% - N2: qs 100%
Le débit global est de 30 Nl/h. La WH est de l'ordre de 150.000 h"1.The overall flow rate is 30 Nl / h. The WH is around 150,000 h "1 .
Les signaux de NO et NOx (NOx = NO + NO2) sont enregistrés en permanence, ainsi que la température dans le réacteur.The NO and NOx signals (NOx = NO + NO2) are permanently recorded, as well as the temperature in the reactor.
Les signaux de NO et NOx sont donnés par un analyseur de NOx ECOPHYSICS, basé sur le principe de la chimiluminescence. L'évaluation des pièges à NOx s'effectue en déterminant la quantité totale de NOx adsorbés (exprimée en mgNO/g de phase piège ou active) jusqu'à saturation de la phase piège. L'expérience est répétée à différentes températures entre 250°C et 500°C. Il est ainsi possible de déterminer la zone de température optimale pour le fonctionnement des pièges à NOx.The NO and NOx signals are given by an ECOPHYSICS NOx analyzer, based on the principle of chemiluminescence. NOx traps are evaluated by determining the total amount of NOx adsorbed (expressed in mgNO / g of trap or active phase) until the trap phase is saturated. The experiment is repeated at different temperatures between 250 ° C and 500 ° C. It is thus possible to determine the optimal temperature zone for the operation of the NOx traps.
EXEMPLES 1 à 12EXAMPLES 1 to 12
Matières premières:Raw materials:
On utilise du nitrate de manganèse Mn(N03)2,4H2O, du nitrate de potassium KNO3 99,5%, du nitrate de baryum Ba(N03)2 99,5% et du nitrate de sodium NaNO3 99,5%.Manganese nitrate Mn (N03) 2.4H 2 O, potassium nitrate KNO3 99.5%, barium nitrate Ba (N03) 2 99.5% and sodium nitrate NaNO 3 99.5% are used. .
Les supports utilisés sont un oxyde de cérium HSA5® de Rhodia, un oxyde de cérium HSA1® de Rhodia, un oxyde de zirconium comprenant de l'oxyde de cériumThe supports used are HSA5 ® of Rhodia cerium oxide, a cerium oxide HSA1 ® of Rhodia, zirconium oxide comprising cerium oxide
(proportions respectives en poids ZrO2/CeO2 de 80/20), un oxyde de cérium comprenant de la silice (99,15% CeO2, 0,85% SiO2) HSA514® de Rhodia, tous ces supports ont été calcinés 2 heures à 500°C. Préparation de la composition :(respective proportions by weight ZrO 2 / CeO 2 of 80/20), a cerium oxide comprising silica (99.15% CeO 2 , 0.85% SiO 2 ) HSA514 ® from Rhodia, all these supports have been calcined 2 hours at 500 ° C. Preparation of the composition:
La phase active est à base de manganèse avec un autre élément A qui est K, Ba ou NaThe active phase is based on manganese with another element A which is K, Ba or Na
On procède de la manière suivante :We proceed as follows:
1ère étape: Dépôt du 1er élément supporté1st stage: Deposit of the 1st supported element
Cette étape consiste à déposer l'élément Mn dans une proportion de 10% atomique par rapport au nombre de moles de l'élément et de moles d'oxyde(s) du support à savoir: [Mn]/([Mn] + [Oxyde(s) du support] )=0J soit [Mn]=0J et [Oxyde(s) du support]=0,9.This step consists in depositing the element Mn in a proportion of 10 atomic% relative to the number of moles of the element and of moles of oxide (s) of the support, namely: [Mn] / ([Mn] + [ Support oxide (s)]) = 0J or [Mn] = 0J and [Support oxide (s)] = 0.9.
2ième étape: Dépôt du 2i®me élément supporté2nd stage: Deposit of the 2nd supported element
Elle consiste à déposer le deuxième élément supporté à savoir 10% atomique de A par rapport à la somme des nombres de moles d'oxyde soit :It consists of depositing the second supported element, namely 10 atomic% of A relative to the sum of the numbers of moles of oxide, ie:
[A]/( [Mn] + [A] +[Oxyde(s) du support] )=0,1 avec A= K, Ba ou Na On utilise l'imprégnation à sec qui consiste à imprégner le support considéré avec l'élément supporté dissout dans une solution de volume égal au volume poreux du support (déterminé à l'eau : O.δcm^/g) et de concentration permettant d'atteindre le dopage recherché.[A] / ([Mn] + [A] + [Oxide (s) of the support]) = 0.1 with A = K, Ba or Na We use dry impregnation which consists in impregnating the support considered with l 'supported element dissolved in a solution of volume equal to the pore volume of the support (determined with water: O.δcm ^ / g) and concentration allowing to reach the desired doping.
Dans le cas présent les éléments sont imprégnés sur le support l'un à la suite de l'autre.In the present case, the elements are impregnated on the support one after the other.
Le protocole opératoire est le suivant: - Imprégnation à sec du premier élémentThe operating protocol is as follows: - Dry impregnation of the first element
- Séchage à l'étuve (110βC, 2H)- Drying in the oven (110 β C, 2H)
- Calcination 2h 500°C (5°C/min)- Calcination 2h 500 ° C (5 ° C / min)
- Imprégnation à sec du deuxième élément- Dry impregnation of the second element
- Séchage à l'étuve (110°C, 2H) Après l'imprégnation, les produits sont calcinés à 500°C. 600°C, 700°C, 800°C ou- Drying in an oven (110 ° C, 2H) After impregnation, the products are calcined at 500 ° C. 600 ° C, 700 ° C, 800 ° C or
850°C, 6 heures sous air.850 ° C, 6 hours in air.
Les compositions suivantes ont ainsi été préparées :The following compositions were thus prepared:
Pour les exemples 1 à 8 on a utilisé le support HSA5® , pour les exemples 9 et 10 le support HSA514®, pour l'exemple 11 le support ZrO2/CeO2 et pour l'exemple 12 le support HSA1®.For Examples 1 to 8 was used HSA5 ® support, for Examples 9 and 10 the HSA514® carrier, for Example 11 the carrier ZrO 2 / CeO 2 and for Example 12 the HSA1® support.
Exemple 1 comparatif : [Mn]=10% atomique, [K]=10% atomique, calciné 2h à 500°C SBET= 115m2/g. Exemple 2 : [Mn]=10% atomique, [K]=10% atomique, calciné 2h à 600°C SBET= 106m2/g.Comparative Example 1: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 2 hours at 500 ° C SBET = 115m 2 / g. Example 2: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 2 hours at 600 ° C SBET = 106m 2 / g.
Exemple 3 : [Mn]=10% atomique, [K]=10% atomique, calciné 2h à 700°C SBET= 15m2/g. Exemple 4 : [Mn]=10% atomique, [K]=10% atomique, calciné 6h à 850°C, SBET≈Example 3: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 2 hours at 700 ° C SBET = 15m 2 / g. Example 4: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 6 hours at 850 ° C, SBET≈
12m2/g.12m 2 / g.
Exemple 5 comparatif : [Mn]=10% atomique, [Ba] =10% atomique, calciné 2h à 500°C SBET= 112m2/g.Comparative example 5: [Mn] = 10 atomic%, [Ba] = 10 atomic%, calcined for 2 hours at 500 ° C SBET = 112m 2 / g.
Exemple 6 : [Mn]=10% atomique, [Ba]=10% atomique, calciné 6h à 850°C SBET= 23m2/g.Example 6: [Mn] = 10 atomic%, [Ba] = 10 atomic%, calcined for 6 hours at 850 ° C SBET = 23m 2 / g.
Exemple 7 comparatif : [Mn]=10% atomique, [Na]=10% atomique, calciné 2h à 500°C SBET= 112m2/g.Comparative Example 7: [Mn] = 10 atomic%, [Na] = 10 atomic%, calcined for 2 hours at 500 ° C SBET = 112m 2 / g.
Exemple 8 : [Mn]=10% atomique, [Na]=10% atomique, calciné 6h à 850°C SBET= 6m2/g. Exemple 9 : [Mn]=10% atomique, [K]=10% atomique, calciné 2h à 800°C SBET=Example 8: [Mn] = 10 atomic%, [Na] = 10 atomic%, calcined for 6 hours at 850 ° C SBET = 6m 2 / g. Example 9: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 2 hours at 800 ° C SBET =
6m2/g.6m 2 / g.
Exemple comparatif 10 : on utilise la même composition que dans l'exemple 9 mais calcinée 2h à 500°C SBET= 111m2/g.Comparative Example 10: the same composition is used as in Example 9 but calcined for 2 h at 500 ° C. SBET = 111 m 2 / g.
Exemple 11 : [Mn]=10% atomique, [K]=10% atomique, calciné 6h à 850°C SBET= 11m2/g.Example 11: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 6 hours at 850 ° C SBET = 11m 2 / g.
Exemple 12 : [Mn]=10% atomique, [K]=10% atomique, calciné 6h à 850°C SBET= 5m2/g.Example 12: [Mn] = 10 atomic%, [K] = 10 atomic%, calcined for 6 hours at 850 ° C SBET = 5m 2 / g.
SBET signifie la surface spécifique B.E.T. déterminée par adsorption d'azote conformément à la norme ASTM D 3663-78 établie à partir de la méthode BRUNAUER - EMMETT- TELLER décrite dans le périodique 'The Journal of the American Chemical Society, 60, 309 (1938)".SBET stands for the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical 'The Journal of the American Chemical Society, 60, 309 (1938) ".
Dans le cas des exemples comparatifs, l'analyse RX ne fait apparaître que la phase CeO2. Dans le cas des exemples 2, 3, 4, 9 et 11 , l'analyse RX fait apparaître la phase CeO2 et une phase de type K2Mn4O8 référencée dans les fiches JCPDS 16- 0205. L'analyse par microscopie montre la présence de gros cristaux constitués par Mn et K de 200nm à 300nm environ. Le manganèse est dans des états d'oxydation III et IV. Pour l'exemple 6, l'analyse RX fait apparaître la phase CeO2 et une phase de type BaMnO3. Pour l'exemple 8, l'analyse RX fait apparaître la phase CeO2 et une phase de type Na07MnO2-δ. Les résultats pour le piégeage des NOx des produits des exemples sont donnés dans les tableaux ci-dessous, les valeurs indiquées dans les tableaux correspondent à la quantité de NOx stockée, exprimée en mg de NO/g de phase active : Tableau 1In the case of the comparative examples, the RX analysis only shows the CeO 2 phase. In the case of Examples 2, 3, 4, 9 and 11, the RX analysis reveals the CeO 2 phase and a K 2 Mn 4 O 8 type phase referenced in the JCPDS files 16-0205. Analysis by microscopy shows the presence of large crystals formed by Mn and K from 200nm to 300nm approximately. Manganese is in oxidation states III and IV. For example 6, the RX analysis reveals the CeO 2 phase and a BaMnO 3 type phase. For example 8, the RX analysis reveals the CeO 2 phase and a Na 07 MnO 2-δ type phase. The results for the NOx trapping of the products of the examples are given in the tables below, the values indicated in the tables correspond to the quantity of NOx stored, expressed in mg of NO / g of active phase: Table 1
Tableau 2Table 2
On observe pour les compositions de l'invention un déplacement de la Tmax important vers les hautes températures par rapport à des compositions dans lesquelles le manganèse et l'autre élément ne sont pas chimiquement liés. Par ailleurs, ces compositions sont efficaces pour stocker les NOx même en l'absence de platine ou d'un autre métal précieux.For the compositions of the invention, there is a significant shift in Tmax towards high temperatures compared to compositions in which the manganese and the other element are not chemically linked. Furthermore, these compositions are effective in storing NOx even in the absence of platinum or another precious metal.
EXEMPLE 13 Cet exemple illustre la stabilité thermique des compositions selon l'invention.EXAMPLE 13 This example illustrates the thermal stability of the compositions according to the invention.
On utilise la même composition que pour l'exemple 4 mais on calcine 6h à 750°C dans une atmosphère d'azote contenant 10% en volume d'hydrogène. Les résultats en catalyse de la composition sont donnés dans le tableau ci-dessous dans lequel on a aussi reporté pour comparaison les résultats de l'exemple 4 : Tableau 3The same composition is used as for Example 4, but calcined for 6 hours at 750 ° C. in a nitrogen atmosphere containing 10% by volume of hydrogen. The results in catalysis of the composition are given in the table below in which the results of Example 4 have also been reported for comparison: Table 3
On n'observe pas de différences sensibles entre les résultats du produit vieilli de l'exemple 13 et celui de l'exemple 4.No appreciable differences are observed between the results of the aged product of Example 13 and that of Example 4.
EXEMPLE 14EXAMPLE 14
On utilise dans cet exemple un support à base d'oxyde de cérium, d'oxyde de zirconium et d'oxyde de lanthane dans les proportions respectives en poids CeO2/Zrθ2/La2O3 de 67/23/10 calciné 2 heures à 800°C.In this example, a support based on cerium oxide, zirconium oxide and lanthanum oxide is used in the respective proportions by weight CeO 2 / Zrθ 2 / La 2 O 3 of 67/23/10 calcined 2 hours at 800 ° C.
On effectue une imprégnation à sec par du manganèse et du potassium dans les conditions décrites précédemment et dans les proportions en mole suivantes : [Mn] /( [Mn] + [oxydes du support] ) = 0J [K] /( [K] +[Mn] + [oxydes du support] ) = 0,4 Après imprégnation, le produit est calciné 2h à 850°C. Il présente une surfaceA dry impregnation is carried out with manganese and potassium under the conditions described above and in the following molar proportions: [Mn] / ([Mn] + [oxides of the support]) = 0J [K] / ([K] + [Mn] + [oxides of the support]) = 0.4 After impregnation, the product is calcined for 2 hours at 850 ° C. It has a surface
SBET de 2m2/g.SBET of 2m 2 / g.
On donne dans le tableau 4 ci-dessous, la quantité de NOx stockée, exprimée comme précédemment.The amount of NOx stored, expressed as above, is given in table 4 below.
Tableau 4Table 4
On observe dans le cas de cet exemple des quantités de NOx stockées particulièrement élevées. EXEMPLE 15In the case of this example, there are particularly high quantities of NOx stored. EXAMPLE 15
On utilise dans cet exemple un support à base d'alumine calciné 2 heures à 500°C. On effectue une imprégnation à sec par du manganèse et du potassium dans les conditions décrites précédemment et dans les proportions en mole suivantes :In this example, a support based on alumina calcined for 2 hours at 500 ° C. is used. A dry impregnation is carried out with manganese and potassium under the conditions described above and in the following molar proportions:
[Mn] /( [Mn] + [AI2O3]) = 0,1 [K] /( [K] +[Mn] + [AI2O3] ) = 0,2[Mn] / ([Mn] + [AI 2 O 3 ]) = 0.1 [K] / ([K] + [Mn] + [AI 2 O 3 ]) = 0.2
Après imprégnation, le produit est calciné 6h à 750°C. Il présente une surface SBET de 129m2/g.After impregnation, the product is calcined for 6 hours at 750 ° C. It has an SBET surface of 129m 2 / g.
On donne dans le tableau 5 ci-dessous, la quantité de NOx stockée, exprimée comme précédemment.The amount of NOx stored, expressed as above, is given in table 5 below.
Tableau 5Table 5

Claims

REVENDICATIONS
1- Compositions utilisables comme piège à NOx, comprenant un support et une phase active, caractérisées en ce que la phase active est à base de manganèse et d'au moins un autre élément A choisi parmi les alcalins et les alcalino-terreux, le manganèse et l'élément A étant chimiquement liés; étant exclues, d'une part, les compositions dans lesquelles A est le potassium, où le support est l'oxyde de cérium et où les deux éléments manganèse et potassium sont apportés par le permanganate de potassium dans des proportions atomiques [K]/([K]+[CeO2])=0J6 et [Mn]/([Mn]+[CeO2])=0J6, et étant exclue, d'autre part, la composition dans laquelle A est le potassium et où le support est à base d'un oxyde de cérium, d'un oxyde de zirconium et d'un oxyde de lanthane dans les proportions respectives en poids par rapport aux oxydes de 72/24/2, et où le support présente en outre une capacité de stockage de l'oxygène de 2,8ml d'O2/g.1- Compositions usable as NOx trap, comprising a support and an active phase, characterized in that the active phase is based on manganese and at least one other element A chosen from alkali and alkaline-earth, manganese and element A being chemically linked; being excluded, on the one hand, the compositions in which A is potassium, where the support is cerium oxide and where the two elements manganese and potassium are provided by potassium permanganate in atomic proportions [K] / ( [K] + [CeO2]) = 0J6 and [Mn] / ([Mn] + [CeO 2 ]) = 0J6, and being excluded, on the other hand, the composition in which A is potassium and where the support is based on a cerium oxide, a zirconium oxide and a lanthanum oxide in the respective proportions by weight relative to the oxides of 72/24/2, and where the support also has a storage capacity 2.8 ml of oxygen O 2 / g.
2- Compositions selon la revendication 1 , caractérisées en ce que l'élément A est le potassium, le sodium ou le baryum.2- Compositions according to claim 1, characterized in that the element A is potassium, sodium or barium.
3- Compositions selon la revendication 1 ou 2, caractérisées en ce que le support est à base d'un oxyde choisi parmi l'alumine, l'oxyde de cérium, l'oxyde de zirconium ou les mélanges d'oxyde de cérium et d'oxyde de zirconium.3- Compositions according to claim 1 or 2, characterized in that the support is based on an oxide chosen from alumina, cerium oxide, zirconium oxide or mixtures of cerium oxide and d 'zirconium oxide.
4- Compositions selon la revendication 3, caractérisées en ce que le support est à base d'oxyde de cérium et il comprend en outre de la silice.4- Compositions according to claim 3, characterized in that the support is based on cerium oxide and it further comprises silica.
5- Procédé de préparation d'une composition selon l'une des revendications précédentes, caractérisé en ce qu'on met en contact le support avec le manganèse et au moins un autre élément A ou avec des précurseurs du manganèse et d'au moins un autre élément A et en ce qu'on calcine l'ensemble à une température suffisante pour créer une liaison chimique entre le manganèse et l'élément A5- Method for preparing a composition according to one of the preceding claims, characterized in that the support is brought into contact with the manganese and at least one other element A or with manganese precursors and at least one other element A and in that the whole is calcined at a temperature sufficient to create a chemical bond between the manganese and the element A
6- Procédé de traitement de gaz en vue de la réduction des émissions des oxydes d'azote, caractérisé en ce qu'on utilise une composition selon l'une des revendications 1 à 4. 7- Procédé selon la revendication 6, caractérisé en ce qu'on traite un gaz d'échappement de moteur à combustion interne.6- A gas treatment process for the reduction of emissions of nitrogen oxides, characterized in that a composition according to one of claims 1 to 4 is used. 7- A method according to claim 6, characterized in that an exhaust gas from an internal combustion engine is treated.
8- Procédé selon la revendication 6, caractérisé en ce qu'on traite un gaz présentant un excès d'oxygène par rapport à la valeur stœchiométrique.8- A method according to claim 6, characterized in that one treats a gas having an excess of oxygen compared to the stoichiometric value.
9- Procédé selon l'une des revendications 7 ou 8, caractérisé en ce que la teneur en oxygène des gaz est d'au moins 2% en volume.9- Method according to one of claims 7 or 8, characterized in that the oxygen content of the gases is at least 2% by volume.
10- Système pour le traitement d'un gaz d'échappement de moteur à combustion interne, caractérisé en ce qu'il comprend une composition selon l'une des revendications 1 à 4.10- System for the treatment of an exhaust gas from an internal combustion engine, characterized in that it comprises a composition according to one of claims 1 to 4.
11- Utilisation d'une composition selon l'une des revendications 1 à 4 pour la fabrication d'un système pour le traitement d'un gaz d'échappement de moteur à combustion interne. 11- Use of a composition according to one of claims 1 to 4 for the manufacture of a system for the treatment of an exhaust gas from an internal combustion engine.
EP00917174A 1999-04-12 2000-04-10 Compositions used as nox trap, based on manganese and an alkaline or alkaline-earth and use for treating exhaust gases Withdrawn EP1171236A1 (en)

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FR9904524 1999-04-12
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FR2841438A1 (en) * 2002-06-26 2004-01-02 Rhodia Elect & Catalysis CIGARETTE COMPRISING A CATALYST FOR THE TREATMENT OF SMOKE

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FR2791907B1 (en) 2002-06-21
FR2791907A1 (en) 2000-10-13
JP2002540933A (en) 2002-12-03
WO2000061289A1 (en) 2000-10-19
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BR0009752A (en) 2002-01-08
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