WO2004035203A1 - Catalytic composition based on alumina, manganese, potassium, rubidium or cesium and platinum and use thereof as nox trap in gas treatment - Google Patents

Catalytic composition based on alumina, manganese, potassium, rubidium or cesium and platinum and use thereof as nox trap in gas treatment Download PDF

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Publication number
WO2004035203A1
WO2004035203A1 PCT/FR2003/003040 FR0303040W WO2004035203A1 WO 2004035203 A1 WO2004035203 A1 WO 2004035203A1 FR 0303040 W FR0303040 W FR 0303040W WO 2004035203 A1 WO2004035203 A1 WO 2004035203A1
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platinum
alumina
composition
manganese
composition according
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PCT/FR2003/003040
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French (fr)
Inventor
Marco Daturi
Catherine Hedouin
Thierry Lesage
Jacques Saussey
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Centre National De La Recherche Scientifique
Rhodia Electronics And Catalysis
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Priority to AU2003301285A priority Critical patent/AU2003301285A1/en
Publication of WO2004035203A1 publication Critical patent/WO2004035203A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • 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
    • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/656—Manganese, technetium or rhenium
    • B01J23/6562—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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • 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
    • 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
    • B01D2255/206—Rare 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
    • B01D2255/207—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 a catalytic composition based on alumina, manganese, potassium, rubidium or cesium and platinum and its use as a NOx trap in the treatment of gases with a view to reducing the emissions of oxides of nitrogen.
  • NOx traps which are capable of oxidizing NO to NO2 and then adsorbing the NO2 thus formed. Under certain conditions, NO2 is released and then reduced to N2 by reducing species contained in the exhaust gases. These NOx traps, however, need to be further improved with regard to their adsorption capacity, their selectivity and also the range of temperatures in which they are effective.
  • the object of the invention is therefore to provide products exhibiting such an improvement.
  • the composition of the invention is a catalytic composition which is characterized in that it comprises: - an alumina doped with at least one rare earth chosen from yttrium, cerium, lanthanum, praseodymium, neodymium and the samarium; - manganese and at least one other element E chosen from potassium, rubidium and cesium; the atomic ratio E / Mn being between 1, 5 and 5; - platinum.
  • the invention relates to a gas treatment process with a view to reducing the emissions of nitrogen oxides, characterized in that a composition of the type described above is used as the NOx trap.
  • a composition of the type described above is used as the NOx trap.
  • the composition of the invention comprises first of all alumina. Any type of alumina capable of having a specific surface sufficient for application in catalysis can be used in the context of the present invention.
  • aluminas resulting from the rapid dehydration of at least one aluminum hydroxide, such as bayerite, hydrargillite or gibbsite, nordstrandite, and / or from at least one aluminum oxyhydroxide such as boehmite, pseudoboehmite and diaspore.
  • at least one aluminum hydroxide such as bayerite, hydrargillite or gibbsite, nordstrandite
  • at least one aluminum oxyhydroxide such as boehmite, pseudoboehmite and diaspore.
  • Alumina is however a doped alumina. It indeed includes one or more doping elements which are chosen from ryttrium, cerium, lanthanum, praseodymium, neodymium and samarium. Cerium can be more particularly used. The amount of doping rare earth is at most 50% and it is more particularly between 5% and 30%. These quantities are expressed in mass of rare earth oxide relative to the total mass of alumina and rare earth oxide.
  • doped alumina can be carried out in a manner known per se, in particular by impregnating the alumina with solutions of salts, such as nitrates, of the abovementioned doping elements or else by co-drying of an alumina precursor and salts of these elements then calcination.
  • salts such as nitrates
  • Ripening can be carried out by suspending the alumina in water and then heating to a temperature of, for example, between 70 and 110 ° C. After curing, the alumina is subjected to a heat treatment.
  • the composition of the invention also comprises manganese and at least one other element E which is chosen from potassium, rubidium and cesium. Element E can be very particularly potassium.
  • the atomic ratio E / Mn is between 1, 5 and 5 and it can more particularly be between 1, 5 and 3 and even more particularly between 1, 5 and 2.
  • the amount of manganese, in the composition is between 5% and 20% and that in element E between 5% and 30%, more particularly between 10% and 25%, these quantities being expressed in molar% relative to the average molar mass of doped alumina .
  • the composition of the invention comprises platinum. According to a variant, it can also comprise rhodium, in combination with platinum, in a Rh / Pt mass ratio which, generally, is between 1/16 and 1/1, more particularly between 1/7 and 1/3 . The proportion of platinum or platinum and rhodium is generally at most 1%.
  • the maximum content of platinum or of platinum and rhodium is not critical insofar as one of the characteristics of the composition of the invention is that it can be effective with a low content of precious metal and therefore , a higher content is not of interest. This content can more particularly be at most 0.5%.
  • the minimum proportion of platinum or platinum and rhodium is that from which a NOx trap effect of the composition can be observed.
  • the doped alumina generally constitutes a support and the manganese, the element E and the platinum with, if appropriate, rhodium, constitute the supported phase.
  • 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.
  • support and active or supported phase 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.
  • composition of the invention can be prepared by a process in which the support is brought into contact with manganese, platinum with optionally rhodium and at least one other element E or with precursors of manganese, platinum, rhodium and at least one other element E and in which the whole is calcined at a temperature sufficient to transform the precursors or the elements into oxides.
  • this temperature is at least 500 ° C., more particularly at least 600 ° C.
  • salts the salts of inorganic acids such as nitrates, sulfates or chlorides can be chosen.
  • 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.
  • Dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the element of the active phase 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 several stages. Thus, it is advantageous to deposit the manganese at first and then the element E in a second and the precious metal (Pt, Rh) last. Between the stages of depositing each of the elements of the active phase, it is possible to include an intermediate stage of calcination.
  • 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.
  • composition of the invention as described above is in the form of a powder but it can optionally be shaped to be in the form of granules, beads, cylinders or honeycombs of variable dimensions.
  • the compositions can also be used in catalytic systems comprising a coating (wash coat) with catalytic properties and based on these compositions, on a substrate of the type, for example metallic or ceramic monolith.
  • the invention also relates to a gas treatment process with a view to reducing the emissions of nitrogen oxides using the composition of the invention.
  • gases capable of being treated by the present invention are, for example, those originating from gas turbines, boilers of thermal power stations or even internal combustion engines. In the latter case, it may in particular be diesel engines or engines operating in a lean mixture.
  • compositions of the invention function as NOx traps but also as a promoter for the reduction of nitrogen oxides, in particular when they are brought into contact with gases which have a high oxygen content.
  • gas having a high oxygen content gases having an excess of oxygen relative to the quantity necessary for the stoichiometric combustion of fuels and, more specifically, gases having an excess of oxygen relative to the stoichiometric value.
  • ⁇ 1. 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 are those of an engine operating in a lean burn mixture and which have an oxygen content (expressed by volume) of at least 2%, as well as those which have an even higher oxygen content, for example gases of diesel type engines, that is to say at least 5% or more than 5%, more particularly at least 10%, this content can for example be between 5 and 20%.
  • compositions of the invention can be combined with complementary depollution systems, such as three-way catalysts, which are effective when the value of ⁇ is less than or equal to 1 in the gases, or alternatively with hydrocarbon injection systems. or exhaust gas recycling (EGR system) for diesels. They can also be combined with NOx removal catalysts for diesels.
  • complementary depollution systems such as three-way catalysts, which are effective when the value of ⁇ is less than or equal to 1 in the gases, or alternatively with hydrocarbon injection systems. or exhaust gas recycling (EGR system) for diesels.
  • EGR system exhaust gas recycling
  • the invention also relates to a catalytic 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 compared to the stoichiometric value.
  • This system is characterized in that it comprises a composition as described above. Examples will now be given.
  • a platinum solution of dinitrodiamine type (18.7% by mass of Pt), manganese nitrate Mn (N ⁇ 3) 2.4H2 ⁇ and potassium nitrate KNO3 99.5% are used.
  • the support used is an SB3 Condea alumina calcined for 2 hours at
  • This step consists in depositing the active element Mn in an amount equal to 10 mol% relative to the average molar mass of the support (AI 2 O 3 -10% CeO 2 ).
  • 2nd step Deposition of the second active element: This step consists of depositing the second active element K in an amount of 20 mol% relative to the average molar mass of the support.
  • This step consists in depositing the third active element Pt in a proportion of 0.5% by mass relative to the whole of the composition.
  • the elements are impregnated on the support successively by the dry impregnation method.
  • This method consists in impregnating the support considered with the element of the active phase dissolved in a solution of volume equal to the pore volume of the support (determined with water: 0.5 cm 3 / g) and of concentration making it possible to reach the concentration sought.
  • the operating protocol is as follows:
  • a gas flow of the following composition (by volume) is passed over the two compositions, at a total flow rate of 12.5 ml / min:
  • the amount of NO adsorbed in ⁇ mol per gram of catalyst is given in table 1 below after 1 hour of exposure to the gas flow.
  • the composition according to the invention adsorbs a greater amount of NO. It is effective over a wider range of temperatures because the value of 250 to 200 ° C. for the comparative composition is very low and therefore implies that part of the NOx is not trapped and therefore that the composition is not not effective at this temperature unlike the case of the composition of the invention. It may also be noted that the amount of NO adsorbed at 200 ° C is of the same order of magnitude as that adsorbed by the comparative composition at 300 ° C-400 ° C.
  • composition according to the invention transforms all of the NO unlike the case of the comparative composition.
  • composition of the invention gives a better result in nitrogen selectivity, over a shorter time, in rich regime, which implies a fuel economy in the operation of the engine.
  • the results are not modified in the case of the comparative composition.

Abstract

The invention concerns a catalytic composition characterized in that it comprises an alumina doped with at least a rare earth selected among, yttrium, cerium, lanthanum, praseodymium, neodymium and samarium; manganese and at least one other element selected among potassium, rubidium and cesium, the atomic ratio E/Mn ranging between 1.5 and 5; and platinum. The inventive composition can be used for trapping NOx in gas treatment, in particular exhaust gases, for reducing nitrogen oxide emissions.

Description

COMPOSITION CATALYTIQUE A BASE D'ALUMINE, DE MANGANESE, DE POTASSIUM, DE RUBIDIUM OU DE CESIUM ET DE PLATINE ET SON UTILISATION COMME PIEGE A NOX DANS LE CATALYTIC COMPOSITION BASED ON ALUMINA, MANGANESE, POTASSIUM, RUBIDIUM OR CESIUM AND PLATINUM AND ITS USE AS A NOX TRAP IN THE
TRAITEMENT DE GAZGAS TREATMENT
La présente invention concerne une composition catalytique à base d'alumine, de manganèse, de potassium, de rubidium ou de césium et de platine et son utilisation comme piège à NOx dans le traitement de gaz en vue de la réduction des émissions des oxydes d'azote.The present invention relates to a catalytic composition based on alumina, manganese, potassium, rubidium or cesium and platinum and its use as a NOx trap in the treatment of gases with a view to reducing the emissions of oxides of nitrogen.
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 stcechiométriquement les gaz réducteurs présents dans le mélange. Tout excès d'oxygène se traduit par une détérioration brutale des performances du catalyseur.It is known that the reduction of emissions of nitrogen oxides (NOx) from exhaust gases from 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.
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.However, some 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 N2 par des espèces réductrices contenues dans les gaz d'échappement. Ces pièges à NOx ont toutefois besoin d'être encore améliorés en ce qui concerne leur capacité d'adsorption, leur sélectivité et aussi la gamme de températures dans laquelle ils sont efficaces.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, NO2 is released and then reduced to N2 by reducing species contained in the exhaust gases. These NOx traps, however, need to be further improved with regard to their adsorption capacity, their selectivity and also the range of temperatures in which they are effective.
L'objet de l'invention est donc de fournir des produits présentant une telle amélioration.The object of the invention is therefore to provide products exhibiting such an improvement.
Dans ce but, la composition de l'invention est une composition catalytique qui est caractérisée en ce qu'elle comprend : - une alumine dopée par au moins une terre rare choisie parmi l'yttrium, le cérium, le lanthane, le praséodyme, le néodyme et le samarium; - du manganèse et au moins un autre élément E choisi parmi le potassium, le rubidium et le césium; le rapport atomique E/Mn étant compris entre 1 ,5 et 5; - du platine.For this purpose, the composition of the invention is a catalytic composition which is characterized in that it comprises: - an alumina doped with at least one rare earth chosen from yttrium, cerium, lanthanum, praseodymium, neodymium and the samarium; - manganese and at least one other element E chosen from potassium, rubidium and cesium; the atomic ratio E / Mn being between 1, 5 and 5; - platinum.
Par ailleurs, l'invention concerne un procédé de traitement de gaz en vue de la réduction des émissions des oxydes d'azote, caractérisé en ce qu'on utilise comme piège à NOx une composition du type décrit ci-dessus. 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. La composition de l'invention comporte tout d'abord de l'alumine. On peut utiliser dans le cadre de la présente invention 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 bayérite, Phydrargillite ou gibbsite, la nordstrandite, et/ou d'au moins un oxyhydroxyde d'aluminium tel que la boehmite, la pseudoboehmite et le diaspore.Furthermore, the invention relates to a gas treatment process with a view to reducing the emissions of nitrogen oxides, characterized in that a composition of the type described above is used as the NOx trap. 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. The composition of the invention comprises first of all alumina. Any type of alumina capable of having a specific surface sufficient for application in catalysis can be used in the context of the present invention. Mention may be made of aluminas resulting from the rapid dehydration of at least one aluminum hydroxide, such as bayerite, hydrargillite or gibbsite, nordstrandite, and / or from at least one aluminum oxyhydroxide such as boehmite, pseudoboehmite and diaspore.
L'alumine est toutefois une alumine dopée. Elle comprend en effet un ou plusieurs éléments dopants qui sont choisis parmi ryttrium, le cérium, le lanthane, le praséodyme, le néodyme et le samarium. Le cérium peut être plus particulièrement utilisé. La quantité en terre rare dopante est d'au plus 50% et elle est plus particulièrement comprise entre 5% et 30%. Ces quantités sont exprimées en masse d'oxyde de terre rare par rapport à la masse totale d'alumine et d'oxyde de terre rare.Alumina is however a doped alumina. It indeed includes one or more doping elements which are chosen from ryttrium, cerium, lanthanum, praseodymium, neodymium and samarium. Cerium can be more particularly used. The amount of doping rare earth is at most 50% and it is more particularly between 5% and 30%. These quantities are expressed in mass of rare earth oxide relative to the total mass of alumina and rare earth oxide.
La préparation de l'alumine dopée peut se faire d'une manière connue en soi, notamment par imprégnation de l'alumine par des solutions de sels, comme les nitrates, des éléments dopants précités ou encore par coséchage d'un précurseur d'alumine et de sels de ces éléments puis calcination.The preparation of doped alumina can be carried out in a manner known per se, in particular by impregnating the alumina with solutions of salts, such as nitrates, of the abovementioned doping elements or else by co-drying of an alumina precursor and salts of these elements then calcination.
On peut citer par ailleurs une autre préparation de l'alumine dopée dans laquelle la poudre d'alumine issue de la déshydratation rapide d'un hydroxyde ou d'un oxyhydroxyde d'aluminium est soumise à une opération de mûrissement en présence d'un agent dopant qui peut être plus particulièrement constitué par un composé du lanthane, ce composé pouvant être encore plus particulièrement un sel. Le mûrissement peut se faire par mise en suspension de l'alumine dans l'eau puis chauffage à une température comprise par exemple entre 70 et 110°C. Après le mûrissement, l'alumine est soumise à un traitement thermique. La composition de l'invention comprend en outre du manganèse ainsi qu'au moins un autre élément E qui est choisi parmi le potassium, le rubidium et le césium. L'élément E peut être tout particulièrement le potassium.Mention may also be made of another preparation of doped alumina in which the alumina powder resulting from the rapid dehydration of an aluminum hydroxide or oxyhydroxide is subjected to a ripening operation in the presence of an agent dopant which can be more particularly constituted by a lanthanum compound, this compound possibly being even more particularly a salt. Ripening can be carried out by suspending the alumina in water and then heating to a temperature of, for example, between 70 and 110 ° C. After curing, the alumina is subjected to a heat treatment. The composition of the invention also comprises manganese and at least one other element E which is chosen from potassium, rubidium and cesium. Element E can be very particularly potassium.
Le rapport atomique E/Mn est compris entre 1 ,5 et 5 et il peut être plus particulièrement compris entre 1 ,5 et 3 et encore plus particulièrement entre 1 ,5 et 2. En outre, généralement, la quantité en manganèse, dans la composition, est comprise entre 5% et 20% et celle en élément E entre 5% et 30%, plus particulièrement entre 10% et 25%, ces quantités étant exprimées en % molaire par rapport à la masse molaire moyenne de l'alumine dopée. Enfin, la composition de l'invention comprend du platine. Selon une variante, elle peut comprendre aussi du rhodium, en combinaison avec le platine, dans un rapport en masse Rh/Pt qui, généralement, est compris entre 1/16 et 1/1, plus particulièrement entre 1/7 et 1/3. La proportion de platine ou de platine et de rhodium est généralement d'au plus 1%. Il s'agit d'une proportion massique par rapport à l'ensemble de la composition. Il est à noter que la teneur maximale en platine ou en platine et rhodium n'est pas critique dans la mesure où une des caractéristiques de la composition de l'invention est de pouvoir être efficace avec une teneur faible en métal précieux et de ce fait, une teneur plus élevée ne présente pas d'intérêt. Cette teneur peut être plus particulièrement d'au plus 0,5%. La proportion minimale en platine ou en platine et rhodium est celle à partir de laquelle on peut observer un effet piège à NOx de la composition.The atomic ratio E / Mn is between 1, 5 and 5 and it can more particularly be between 1, 5 and 3 and even more particularly between 1, 5 and 2. In addition, generally, the amount of manganese, in the composition, is between 5% and 20% and that in element E between 5% and 30%, more particularly between 10% and 25%, these quantities being expressed in molar% relative to the average molar mass of doped alumina . Finally, the composition of the invention comprises platinum. According to a variant, it can also comprise rhodium, in combination with platinum, in a Rh / Pt mass ratio which, generally, is between 1/16 and 1/1, more particularly between 1/7 and 1/3 . The proportion of platinum or platinum and rhodium is generally at most 1%. It is a mass proportion in relation to the entire composition. It should be noted that the maximum content of platinum or of platinum and rhodium is not critical insofar as one of the characteristics of the composition of the invention is that it can be effective with a low content of precious metal and therefore , a higher content is not of interest. This content can more particularly be at most 0.5%. The minimum proportion of platinum or platinum and rhodium is that from which a NOx trap effect of the composition can be observed.
Pour la composition de l'invention, l'alumine dopée constitue généralement un support et le manganèse, l'élément E et le platine avec, le cas échéant, le rhodium, constituent la phase supportée.For the composition of the invention, the doped alumina generally constitutes a support and the manganese, the element E and the platinum with, if appropriate, rhodium, constitute the supported phase.
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 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.
On peut préparer la composition de l'invention par un procédé dans lequel on met en contact le support avec le manganèse, le platine avec éventuellement le rhodium et au moins un autre élément E ou avec des précurseurs du manganèse, du platine, du rhodium et d'au moins un autre élément E et dans lequel on calcine l'ensemble à une température suffisante pour transformer les précurseurs ou les éléments en oxydes. Généralement, cette température est d'au moins 500°C, plus particulièrement d'au moins 600°C.The composition of the invention can be prepared by a process in which the support is brought into contact with manganese, platinum with optionally rhodium and at least one other element E or with precursors of manganese, platinum, rhodium and at least one other element E and in which the whole is calcined at a temperature sufficient to transform the precursors or the elements into oxides. Generally, this temperature is at least 500 ° C., more particularly at least 600 ° C.
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 abovementioned contact is impregnation. This first forms a solution or a 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, the salts of inorganic acids such as nitrates, sulfates or chlorides can be chosen.
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.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.
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 de la phase active 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 plusieurs étapes. Ainsi, on peut avantageusement déposer le manganèse dans un premier temps puis l'élément E dans un deuxième et le métal précieux (Pt, Rh) en dernier lieu. Entre les étapes de dépôt de chacun des éléments de la phase active, il est possible d'inclure une étape intermédiaire de calcination.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 of the active phase 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 several stages. Thus, it is advantageous to deposit the manganese at first and then the element E in a second and the precious metal (Pt, Rh) last. Between the stages of depositing each of the elements of the active phase, it is possible to include an intermediate stage of calcination.
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.
La composition de l'invention telle que décrite plus haut se présente sous forme d'une poudre mais elle peut éventuellement être mise en forme pour se présenter sous forme de granulés, billes, cylindres ou nids d'abeille de dimensions variables. Les compositions peuvent aussi être utilisées dans des systèmes catalytiques comprenant un revêtement (wash coat) à propriétés catalytiques et à base de ces compositions, sur un substrat du type par exemple monolithe métallique ou en céramique. L'invention concerne aussi un procédé de traitement de gaz en vue de la réduction des émissions des oxydes d'azote mettant en œuvre la composition de l'invention.The composition of the invention as described above is in the form of a powder but it can optionally be shaped to be in the form of granules, beads, cylinders or honeycombs of variable dimensions. The compositions can also be used in catalytic systems comprising a coating (wash coat) with catalytic properties and based on these compositions, on a substrate of the type, for example metallic or ceramic monolith. The invention also relates to a gas treatment process with a view to reducing the emissions of nitrogen oxides using the composition of the 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 pauvre.The gases capable of being treated by the present invention are, for example, those originating from gas turbines, boilers of thermal power stations or even internal combustion engines. In the latter case, it may in particular be diesel engines or engines operating in a lean mixture.
Les compositions de l'invention fonctionnent comme pièges à NOx mais aussi comme promoteur de réduction des oxydes d'azote, notamment 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 stœchiométrique des carburants et, plus précisément, des gaz présentant un excès d'oxygène par rapport à la valeur stœchiométrique λ = 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 sont ceux de moteur fonctionnant en mélange pauvre (lean burn) et qui présentent une teneur en oxygène (exprimée en volume) 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 but also as a promoter for the reduction of nitrogen oxides, in particular when they are brought into contact with gases which have a high oxygen content. By gas having a high oxygen content is meant gases having an excess of oxygen relative to the quantity necessary for the stoichiometric combustion of fuels and, more specifically, gases having an excess of oxygen relative to the stoichiometric value. λ = 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 are those of an engine operating in a lean burn mixture and which have an oxygen content (expressed by volume) of at least 2%, as well as those which have an even higher oxygen content, for example gases of diesel type engines, that is to say at least 5% or more than 5%, more particularly at least 10%, this content can for example be between 5 and 20%.
Les compositions de l'invention peuvent être associées à des systèmes complémentaires de dépollution, comme des catalyseurs trois voies, qui sont efficaces lorsque la valeur de λ est inférieure ou égale à 1 dans les gaz, ou encore à des systèmes à injection d'hydrocarbures ou à recyclage des gaz d'échappement (système EGR) pour les diesels. Elles peuvent être aussi associées à des catalyseurs d'élimination des NOx pour les diesels.The compositions of the invention can be combined with complementary depollution systems, such as three-way catalysts, which are effective when the value of λ is less than or equal to 1 in the gases, or alternatively with hydrocarbon injection systems. or exhaust gas recycling (EGR system) for diesels. They can also be combined with NOx removal catalysts for diesels.
L'invention concerne aussi un système catalytique 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 stœchiométrique. Ce système est caractérisé en ce qu'il comprend une composition telle que décrite plus haut. Des exemples vont maintenant être donnés.The invention also relates to a catalytic 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 compared to the stoichiometric value. This system is characterized in that it comprises a composition as described above. Examples will now be given.
On prépare dans les conditions qui sont données ci-dessous deux compositions, l'une selon l'invention, l'autre comparative. Matières premièresTwo compositions are prepared under the conditions which are given below, one according to the invention, the other comparative. Raw materials
On utilise une solution de platine de type dinitrodiamine (18,7% en masse de Pt), du nitrate de manganèse Mn(Nθ3)2,4H2θ et du nitrate de potassium KNO3 99,5%. Le support utilisé est une alumine SB3 Condea calcinée 2 heures àA platinum solution of dinitrodiamine type (18.7% by mass of Pt), manganese nitrate Mn (Nθ3) 2.4H2θ and potassium nitrate KNO3 99.5% are used. The support used is an SB3 Condea alumina calcined for 2 hours at
500°C puis imprégnée à 10% en masse d'oxyde de cérium et enfin calcinée 2 heures à 500°C.500 ° C then impregnated with 10% by mass of cerium oxide and finally calcined for 2 hours at 500 ° C.
Préparation de la composition selon l'inventionPreparation of the composition according to the invention
On procède en trois étapes pour le dépôt. 1 ère étape : Dépôt du premier élément actif :There are three steps to filing. 1st step: Deposit of the first active element:
Cette étape consiste à déposer l'élément actif Mn dans une quantité égale à 10% molaire par rapport à la masse molaire moyenne du support (AI2O3-10% CeO2).This step consists in depositing the active element Mn in an amount equal to 10 mol% relative to the average molar mass of the support (AI 2 O 3 -10% CeO 2 ).
2ième étape : Dépôt du second élément actif : Cette étape consiste à déposer le deuxième élément actif K dans une quantité de 20% molaire par rapport à la masse molaire moyenne du support.2nd step: Deposition of the second active element: This step consists of depositing the second active element K in an amount of 20 mol% relative to the average molar mass of the support.
3ième étape : Dépôt du troisième élément actif :3rd step: Deposit of the third active element:
Cette étape consiste à déposer le troisième élément actif Pt dans une proportion de 0,5% en masse par rapport à l'ensemble de la composition. Les éléments sont imprégnés sur le support successivement par la méthode d'imprégnation à sec. Cette méthode consiste à imprégner le support considéré avec l'élément de la phase active dissout dans une solution de volume égal au volume poreux du support (déterminé à l'eau : 0,5 cm3/g) et de concentration permettant d'atteindre la concentration recherchée. Le protocole opératoire est le suivant :This step consists in depositing the third active element Pt in a proportion of 0.5% by mass relative to the whole of the composition. The elements are impregnated on the support successively by the dry impregnation method. This method consists in impregnating the support considered with the element of the active phase dissolved in a solution of volume equal to the pore volume of the support (determined with water: 0.5 cm 3 / g) and of concentration making it possible to reach the concentration sought. The operating protocol is as follows:
- Imprégnation à sec du premier élément- Dry impregnation of the first element
- Séchage à l'étuve (110°C, 2H)- Drying in the oven (110 ° C, 2H)
- Calcination 2h 500°C- Calcination 2h 500 ° C
- Imprégnation à sec du deuxième élément - Séchage à l'étuve (110°C, 2H)- Dry impregnation of the second element - Drying in the oven (110 ° C, 2H)
- Calcination 6h 750°C- Calcination 6h 750 ° C
- Imprégnation à sec du troisième élément- Dry impregnation of the third element
- Séchage à l'étuve (110°C, 2H)- Drying in the oven (110 ° C, 2H)
- Calcination 6h 750°C Préparation d'une composition comparative- Calcination 6h 750 ° C Preparation of a comparative composition
On procède comme dans le cas de la composition précédente mais avec une teneur en potassium de 10% molaire. EXEMPLE 1The procedure is as in the case of the preceding composition but with a potassium content of 10 mol%. EXAMPLE 1
On fait passer sur les deux compositions, à un débit total de 12,5 mL/min, un flux gazeux de composition suivante (en volume) :A gas flow of the following composition (by volume) is passed over the two compositions, at a total flow rate of 12.5 ml / min:
NO : 1000 ppm, O2 :10% dans de l'argon. On donne dans le tableau 1 ci-dessous la quantité de NO adsorbée en μmole par gramme de catalyseur après 1 heure d'exposition au flux gazeux.NO: 1000 ppm, O 2 : 10% in argon. The amount of NO adsorbed in μmol per gram of catalyst is given in table 1 below after 1 hour of exposure to the gas flow.
Tableau 1Table 1
Figure imgf000008_0001
On voit que la composition selon l'invention adsorbe une plus grande quantité de NO. Elle est efficace sur une plus large gamme de températures car la valeur de 250 à 200°C pour la composition comparative est très basse et implique de ce fait qu'une partie des NOx n'est pas piégée et donc que la composition n'est pas efficace à cette température contrairement au cas de la composition de l'invention. On peut noter par ailleurs que la quantité de NO adsorbée à 200°C est du même ordre de grandeur que celle adsorbée par la composition comparative à 300°C-400°C.
Figure imgf000008_0001
It can be seen that the composition according to the invention adsorbs a greater amount of NO. It is effective over a wider range of temperatures because the value of 250 to 200 ° C. for the comparative composition is very low and therefore implies that part of the NOx is not trapped and therefore that the composition is not not effective at this temperature unlike the case of the composition of the invention. It may also be noted that the amount of NO adsorbed at 200 ° C is of the same order of magnitude as that adsorbed by the comparative composition at 300 ° C-400 ° C.
EXEMPLE 2 On fait passer sur les deux compositions, à un débit total de 40 mL/min et à 400°C, deux flux gazeux selon un régime alterné et dans les conditions suivantes :EXAMPLE 2 Two gas streams are passed over the two compositions, at a total flow rate of 40 ml / min and at 400 ° C., according to an alternating regime and under the following conditions:
- pendant 2 minutes un flux « pauvre » qui correspond à la composition suivante (en volume) : NO : 1000 ppm, O2 :10% dans de l'argon ; - pendant 1 minute, un flux « riche » qui correspond soit à la composition- for 2 minutes a "poor" flow which corresponds to the following composition (by volume): NO: 1000 ppm, O 2 : 10% in argon; - for 1 minute, a “rich” flow which corresponds either to the composition
(en volume): CO : 2%, H2 : 0,7%, O2 : 0,55%, H2O : 1,5% soit à la composition (en volume): CO : 2%, H2 : 0,7%, O2 : 0,55%, dans l'argon dans les deux cas.(by volume): CO: 2%, H 2 : 0.7%, O 2 : 0.55%, H 2 O: 1.5% or by composition (by volume): CO: 2%, H 2 : 0.7%, O 2 : 0.55%, in argon in both cases.
On donne dans le tableau 2 ci-dessous le pourcentage des différents constituants de l'effluent gazeux après passage sur la composition selon l'invention et sur la composition comparative. Tableau 2The percentage of the various constituents of the gaseous effluent after passing over the composition according to the invention and over the comparative composition is given in table 2 below. Table 2
Figure imgf000009_0001
Figure imgf000009_0001
On voit que la composition selon l'invention transforme la totalité des NO contrairement au cas de la composition comparative.We see that the composition according to the invention transforms all of the NO unlike the case of the comparative composition.
EXEMPLE 3EXAMPLE 3
On procède comme dans l'exemple 2 avec comme seule différence un flux riche de 30 secondes au lieu d'1 minute. On obtient les résultats suivants :The procedure is as in Example 2 with the only difference being a rich flow of 30 seconds instead of 1 minute. The following results are obtained:
Tableau 3Table 3
Figure imgf000009_0002
Figure imgf000009_0002
On obtient avec la composition de l'invention un meilleur résultat en sélectivité en azote, sur un temps plus court, en régime riche, ce qui implique une économie en carburant dans le fonctionnement du moteur. Les résultats ne sont pas modifiés dans le cas de la composition comparative. The composition of the invention gives a better result in nitrogen selectivity, over a shorter time, in rich regime, which implies a fuel economy in the operation of the engine. The results are not modified in the case of the comparative composition.

Claims

REVENDICATIONS
1 - Composition catalytique, caractérisée en ce qu'elle comprend :1 - Catalytic composition, characterized in that it comprises:
- une alumine dopée par au moins une terre rare choisie parmi ryttrium, le cérium, le lanthane, le praséodyme, le néodyme et le samarium;- an alumina doped with at least one rare earth chosen from ryttrium, cerium, lanthanum, praseodymium, neodymium and samarium;
- du manganèse et au moins un autre élément E choisi parmi le potassium, le rubidium et le césium; le rapport atomique E/Mn étant compris entre 1 ,5 et 5;- manganese and at least one other element E chosen from potassium, rubidium and cesium; the atomic ratio E / Mn being between 1, 5 and 5;
- du platine.- platinum.
2- Composition selon la revendication 1 , caractérisée en ce qu'elle comprend une quantité en terre rare précitée d'au plus 50%, plus particulièrement comprise entre 5% et 30%, en masse d'oxyde de terre rare par rapport à la masse d'alumine et d'oxyde de terre rare.2- Composition according to claim 1, characterized in that it comprises a quantity of the aforementioned rare earth of at most 50%, more particularly between 5% and 30%, by mass of rare earth oxide relative to the mass of alumina and rare earth oxide.
3- Composition selon la revendication 1 ou 2, caractérisée en ce qu'elle comprend une quantité en manganèse comprise entre 5% et 20% et une teneur en élément E comprise entre 5% et 30%, ces quantités étant exprimées en % molaire par rapport à la masse molaire moyenne de l'alumine dopée.3- Composition according to claim 1 or 2, characterized in that it comprises a quantity of manganese of between 5% and 20% and a content of element E of between 5% and 30%, these quantities being expressed in molar% by compared to the average molar mass of doped alumina.
4- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend en outre du rhodium.4- Composition according to one of the preceding claims, characterized in that it further comprises rhodium.
5- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend du platine, éventuellement avec du rhodium, en une proportion massique de platine ou de platine et de rhodium d'au plus 1%.5- Composition according to one of the preceding claims, characterized in that it comprises platinum, optionally with rhodium, in a mass proportion of platinum or platinum and rhodium of at most 1%.
6- Procédé de traitement de gaz en vue de la réduction des émissions des oxydes d'azote, caractérisé en ce qu'on utilise comme piège à NOx une composition selon l'une des revendications précédentes.6- A gas treatment process for the reduction of nitrogen oxide emissions, characterized in that a composition according to one of the preceding claims is used as the NOx trap.
7- Procédé selon la revendication 6, caractérisé en ce qu'on traite un gaz d'échappement de moteurs à combustion interne.7- A method according to claim 6, characterized in that one treats an exhaust gas from internal combustion engines.
8- Procédé selon la revendication 7, caractérisé en ce qu'on traite un gaz présentant un excès d'oxygène par rapport à la valeur stœchiométrique. 9- Procédé selon l'une des revendications 7 ou 8, caractérisé en ce que la teneur en oxygène des gaz est d'au moins 5% en volume.8- A method according to claim 7, characterized in that one treats a gas having an excess of oxygen compared to the stoichiometric value. 9- Method according to one of claims 7 or 8, characterized in that the oxygen content of the gases is at least 5% by volume.
10- Système catalytique pour le traitement d'un gaz, notamment d'un gaz d'échappement de moteurs à combustion interne, caractérisé en ce qu'il comprend une composition selon l'une des revendications 1 à 5. 10- Catalytic system for the treatment of a gas, in particular an exhaust gas from internal combustion engines, characterized in that it comprises a composition according to one of claims 1 to 5.
PCT/FR2003/003040 2002-10-17 2003-10-15 Catalytic composition based on alumina, manganese, potassium, rubidium or cesium and platinum and use thereof as nox trap in gas treatment WO2004035203A1 (en)

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GB2561628B (en) * 2016-10-04 2021-02-17 Johnson Matthey Plc NOx adsorber catalyst

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FR2845932A1 (en) 2004-04-23
AU2003301285A1 (en) 2004-05-04

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