EP0994749A1 - Method for treating gases to reduce nitrogen oxide emissions using a catalytic composition based on silica and titanium oxide - Google Patents

Method for treating gases to reduce nitrogen oxide emissions using a catalytic composition based on silica and titanium oxide

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Publication number
EP0994749A1
EP0994749A1 EP98935077A EP98935077A EP0994749A1 EP 0994749 A1 EP0994749 A1 EP 0994749A1 EP 98935077 A EP98935077 A EP 98935077A EP 98935077 A EP98935077 A EP 98935077A EP 0994749 A1 EP0994749 A1 EP 0994749A1
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EP
European Patent Office
Prior art keywords
catalytic
catalytic composition
support
silica
platinum
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.)
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Application number
EP98935077A
Other languages
German (de)
French (fr)
Inventor
Catherine Hedouin
Pierre Macaudiere
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Rhodia Chimie SAS
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Rhodia Chimie SAS
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Publication date
Application filed by Rhodia Chimie SAS filed Critical Rhodia Chimie SAS
Publication of EP0994749A1 publication Critical patent/EP0994749A1/en
Withdrawn legal-status Critical Current

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    • 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
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/08—Silica
    • 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
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9427—Processes characterised by a specific catalyst for removing nitrous oxide
    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
    • B01J35/61—
    • 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
    • B01J37/0211—Impregnation using a colloidal suspension
    • 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
    • B01J37/08—Heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/21—Organic compounds not provided for in groups B01D2251/206 or B01D2251/208
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1021—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B01D2255/2063—Lanthanum
    • 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
    • B01D2255/20707—Titanium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/30—Silica
    • B01J35/23—
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to a gas treatment process for the reduction of emissions of nitrogen oxides using a catalytic composition with a support based on silica and titanium oxide.
  • 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 the NOx emissions of these engines.
  • the limitation of NOx emissions is made imperative by the tightening of standards in automotive post combustion which now extend to this type of engine.
  • the process of the invention for the treatment of gases for the reduction of emissions of nitrogen oxides, is of the type in which a catalytic composition is used comprising a catalytic phase on a support and it is characterized in that that the support is based on silica and titanium oxide in an atomic proportion Ti / Ti + Si of between 0.1 and 15%.
  • the main characteristic of the catalytic composition used in the process of the invention resides in the support of this composition.
  • This support is based on silica and titanium oxide in the specific proportion which has been given above.
  • this proportion can be between 1 and
  • supports having a high specific surface area and thermally stable are advantageously use.
  • the term “specific surface” is understood here to mean the BET specific surface area determined by nitrogen adsorption in accordance with standard AST D 3663-78 established on the basis of the BRUNAUER - E METT-TELLER method described in the periodical "The Journal of the American Society, ⁇ , 309 (1938) ".
  • the supports with these surface values are generally of the mesoporous type, that is to say that they have the characteristic of having a significant pore volume provided by mesopores (pores with a diameter between 2 and 10 nm).
  • the support based on silica and titanium oxide can be prepared by any process capable of leading to a support of sufficient specific surface.
  • organic silicon compounds are generally used in the form of solutions in alcohols, in particular in aliphatic alcohols.
  • titanium compound there may be used organic titanium compounds such as the alkyl- or alkoxy-titanates which are generally employed in the form of alcoholic solutions as for the silicon compound.
  • the surfactant it is possible to use more particularly those of the active cation type such as amides and quaternary ammonium salts.
  • the reaction can be carried out by mixing the organic silicon compound and the titanium compound and then heating.
  • the surfactant is then added to the mixture thus heated.
  • the precipitate obtained after the reaction is separated from the reaction medium.
  • This precipitate is then calcined, generally in air, to obtain the support which can then be shaped.
  • Calcination can be done in two parts. In the first part, calcination is carried out at a temperature sufficient to remove the surfactant. This temperature can be around 650 ° C. In the second part, calcination is carried out at a temperature at least equal to that at which the catalyst will be used. This temperature can be . about 750 ° C.
  • the support can be in various forms such as granules, balls, cylinders or honeycomb of variable dimensions.
  • the support can comprise, as additives, one or more rare earth oxides.
  • rare earth is meant the elements of the group constituted by yttrium and the elements of the periodic classification of atomic number included inclusively between 57 and 71. Mention may be made, as rare earth, of lanthanum more particularly.
  • the additive content expressed in atomic% additive / Ti + Si + additive may be at most 20%, more particularly at most 10%.
  • the catalytic composition of the invention can also comprise a catalytic phase.
  • This phase can be based on at least one metal chosen from the elements included in groups IIIA to IIB of the periodic table.
  • the catalytic phase is based on at least one metal chosen from the metals of group VIII of the periodic table.
  • metals which can be used in the catalytic phase include platinum, palladium, rhodium, ruthenium, iridium. Mention may also be made of iron, copper, chromium as well as vanadium, niobium, tantalum, molybdenum and tungsten.
  • the metal content of the catalytic phase and, in particular of platinum, of the composition can vary within wide proportions. Usually, this proportion, expressed by weight of metal relative to the weight of the support is between 500 and 40,000 ppm, preferably between 2,500 and 20,000 ppm and even more particularly between 5,000 and 15,000 ppm.
  • the catalytic phase can be deposited on the support, preferably the calcined support, by any known technique.
  • the platinum is provided in the form of a sol.
  • the platinum sol will preferably be chosen to have a size of colloids between 2 nm and 10 nm and more particularly between 3 nm and 8 nm.
  • the size of colloids is determined by electron transmission microscopy (TEM).
  • the impregnation is carried out "dry", that is to say that the total volume of solution or soil used is approximately equal to the total pore volume developed by the support to be impregnated. Concerning the determination of this pore volume, it can be carried out according to the method known with a mercury porosimeter or by measuring the amount of water absorbed by a sample.
  • the support is optionally dried and then it is calcined.
  • the drying is most often carried out in air, at a temperature which can vary between 80 and 300 ° C. and preferably chosen between 100 and 150 ° C. Drying continues until obtaining a constant weight. Generally, the drying time is between 1 and 24 hours.
  • the calcination of the support with the catalytic or active phase deposited is generally carried out at a temperature of at most 750 ° C and more particularly at most 550 ° C in the case where platinum is used in the catalytic phase.
  • the duration of the calcination can, for its part, vary within wide limits, for example between 1 and 24 hours, preferably between 2 and 10 hours. Calcination is generally carried out in air, but calcination carried out for example under inert gas is obviously not excluded.
  • the size of the platinum particles in the composition after calcination is substantially identical to that of the colloids mentioned above.
  • the deposition of the catalytic phase can also be done by atomization.
  • the support is introduced, for example in the form of a suspension, into a solution or a sol of the element or elements constituting the catalytic phase and the mixture thus formed is spray-dried.
  • One can operate with a gas outlet temperature between 100 and 150 ° C. Then calcined under the conditions described above.
  • gases which may comprise nitrogen oxides in combination optionally with carbon oxides and / or hydrocarbons, with a view to reducing the emissions of nitrogen oxides in particular.
  • 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.
  • the value ⁇ is correlated with the air / fuel ratio in a manner known per se, in particular in the field of internal combustion engines.
  • the invention applies to the treatment of gases from systems of the type described in the previous paragraph and operating continuously under conditions such that ⁇ is always strictly greater than 1.
  • the invention thus applies, on the one hand, to the treatment of engine gases operating in a lean burn mixture and which have an oxygen content (expressed by volume) generally between 2.5 and 5% and, on the other hand, to the treatment of gases which have an even higher oxygen content, for example gases from engines of the diesel type, 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%.
  • the gases can contain hydrocarbons and, in such a case, one of the reactions which one seeks to catalyze is the reaction HC (hydrocarbons) + NO x .
  • the hydrocarbons which can be used as a reducing agent for the elimination of NOx are in particular the gases or the liquids of the families of saturated carbides, ethylenic carbides, acetylenic carbides, aromatic carbides and hydrocarbons from petroleum fractions such as for example methane , ethane, propane, butane, pentane, hexane, ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, kerosene and gas oil.
  • the gases can also contain, as reducing agent, organic compounds containing oxygen.
  • organic compounds containing oxygen may especially be alcohols of the type, for example saturated alcohols such as methanol, ethanol or propanol; ethers such as methyl ether or ethyl ether; esters such as methyl acetate and ketones.
  • the invention also applies to the treatment of gases containing no hydrocarbons or organic compounds as a reducing agent.
  • 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 mentioned above.
  • This system is characterized in that it comprises a catalytic composition such as that described above.
  • the catalytic composition can be in various forms such as granules, beads, cylinders or honeycomb of variable dimensions.
  • compositions can also be used in catalytic systems comprising a coating (wash coat) incorporating these compositions, the coating being arranged on a substrate of the type, for example metallic or ceramic monolith.
  • a coating wash coat
  • the systems are mounted in a known manner in the exhaust pipes of vehicles in the case of application to the treatment of exhaust gases.
  • the invention also relates to the process for manufacturing the above-mentioned catalytic systems using a catalytic composition of the type described above.
  • the support used has an Ti / Ti + Si atomic proportion of 9% and it is prepared as follows:
  • TEOS tetraethyte orthosilicates
  • the titanium alkoxide solution is rapidly added with vigorous stirring to the TEOS solution.
  • a clear solution is then obtained which is heated to 72 ° C. with stirring for 3 hours.
  • a solution containing 0.27 mole of dodecylamine is prepared.
  • the solution containing the TEOS mixture and is then added to the solution containing the surfactant DDA.
  • the whole is kept under vigorous stirring for 18 hours at room temperature.
  • the surfactant is removed by calcining the precipitate thus obtained in air at a temperature of 650 ° C. for 4 hours.
  • the precipitate is calcined for 4 hours at 750 ° C in air (temperature rise rate 1 ° C / min).
  • the support thus prepared is dry impregnated with platinum in Droportions of 1 or 2% by weight.
  • the impregnated support is dried in an oven at 110 ° C. for 2 hours, then calcined under the conditions given in the table below. - Products obtained
  • the powdered catalyst 50 mg are loaded into a quartz reactor.
  • the powder used was previously granulated at 0.125 and 0.250 mm.
  • the reaction mixture at the inlet of the reactor has the following composition (by volume):
  • the overall flow is 30 Nl h.
  • the WH is around 500,000 h * 1 .
  • the HC signal is given by a BECKMAN detector of the total hydrocarbon type, based on the principle of detection by flame ionization.
  • the NO x signal is given by a NO x ECOPHYSICS analyzer, based on the principle of chemistry-luminescence.
  • the CO and N 2 O signal is given by a ROSEMOUNT infrared analyzer.
  • the catalytic activity is measured from the HC (C3H6), CO and NO x signals as a function of the temperature during a programmed temperature rise from 150 to 700 ° C at a rate of 15 ° C / min and from the following relationships:
  • TCO CO conversion rate
  • the catalysts can activate under the conditions of the tests, the catalytic activity is given during the second consecutive passage in the test under the same conditions.
  • Product 1 is used (catalyst used for NOx reduction). The results are given in Table 1 below.
  • Product 1 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 2 below.
  • Product 2 (catalyst used for NOx reduction) is used. The results are given in Table 3 below.
  • Product 2 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 4 below.
  • Product 4 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 6 below.
  • Product 5 is used but with a gas mixture which no longer contains CO or C3H5 (catalyst used in direct decomposition). The results are given in Table 7 below.
  • a catalytic composition based on platinum is used on a titanium support comprising lanthanum.
  • the impregnation is followed by drying in an oven (110 ° C, 2 h), calcination at 500 ° C for 2 h with a rise in temperature to 1 ° C / min.
  • the platinum content is 1%.
  • the catalyst thus prepared is used under the abovementioned conditions in reduction. The results are given in Table 8 below. Table 8
  • composition according to the invention makes it possible to obtain a catalytic activity in a temperature window of 250 to 400 ° C. Furthermore, the compositions obtained from a platinum sol and used in the presence of a reducing agent can exhibit an increased and maximum catalytic activity from 250 ° C. and which manifests itself from the first pass.

Abstract

The invention concerns a method for treating gases to reduce nitrogen oxide emissions wherein a catalytic composition containing a catalytic phase on a support is used, characterised in that the support is based on silica and titanium oxide in an atomic proportion Ti/Ti+Si ranging between 0.1 and 15 %. The method is particularly useful for treating exhaust gases of diesel engines or of engines using a weak mixture.

Description

PROCEDE DE TRAITEMENT DE GAZ POUR LA REDUCTION DES EMISSIONS DESGAS TREATMENT PROCESS FOR REDUCING EMISSIONS OF
OXYDES D'AZOTE UTILISANT UNE COMPOSITION CATALYTIQUE AVEC UNNITROGEN OXIDES USING A CATALYTIC COMPOSITION WITH A
SUPPORT A BASE DE SILICE ET D'OXYDE DE TITANESUPPORT BASED ON SILICA AND TITANIUM OXIDE
La présente invention concerne un procédé de traitement de gaz pour la réduction des émissions des oxydes d'azote utilisant une composition catalytique avec un support à base de silice et d'oxyde de titane. 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 de ces moteurs. 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 ce type de moteurs.The present invention relates to a gas treatment process for the reduction of emissions of nitrogen oxides using a catalytic composition with a support based on silica and titanium oxide. 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 the NOx emissions of these engines. Furthermore, the limitation of NOx emissions is made imperative by the tightening of standards in automotive post combustion which now extend to this type of engine.
Il existe donc un besoin réel d'un catalyseur efficace pour la réduction des émissions des NOx pour ce type de moteurs et, plus généralement, pour le traitement de gaz contenant des NOx. En outre, on cherche à obtenir des catalyseurs qui présentent une activité à température moyenne.There is therefore a real need for an effective catalyst for reducing NOx emissions for this type of engine and, more generally, for the treatment of gases containing NOx. In addition, it is sought to obtain catalysts which exhibit activity at medium temperature.
Dans ce but, le procédé de l'invention, pour le traitement de gaz pour la réduction des émissions des oxydes d'azote, est du type dans lequel on utilise une composition catalytique comprenant une phase catalytique sur un support et il est caractérisé en ce que le support, est à base de silice et d'oxyde de titane dans une proportion atomique Ti/Ti+Si comprise entre 0,1 et 15%.For this purpose, the process of the invention, for the treatment of gases for the reduction of emissions of nitrogen oxides, is of the type in which a catalytic composition is used comprising a catalytic phase on a support and it is characterized in that that the support is based on silica and titanium oxide in an atomic proportion Ti / Ti + Si of between 0.1 and 15%.
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.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.
La caractéristique principale de la composition catalytique utilisée dans le procédé de l'invention réside dans le support de cette composition. Ce support est à base de silice et d'oxyde de titane dans la proportion spécifique qui a été donnée plus haut.The main characteristic of the catalytic composition used in the process of the invention resides in the support of this composition. This support is based on silica and titanium oxide in the specific proportion which has been given above.
Selon un mode de réalisation particulier, cette proportion peut être comprise entre 1 etAccording to a particular embodiment, this proportion can be between 1 and
10%. Il est avantageux d'utiliser des supports ayant une surface spécifique élevée et stable thermiquement. On peut ainsi avantageusement utiliser des supports présentant une surface spécifique d'au moins 350 m2/g et plus particulièrement d'au moins 600 m2/g après calcination 6 heures à 750°C. On entend ici par surface spécifique, la surface spécifique B.E.T. déterminée par adsorption d'azote conformément à la norme AST D 3663-78 établie à partir de la méthode BRUNAUER - E METT- TELLER décrite dans le périodique "The Journal of the American Society, δϋ, 309 (1938)".10%. It is advantageous to use supports having a high specific surface area and thermally stable. One can thus advantageously use supports having a specific surface of at least 350 m2 / g and more particularly of at least 600 m2 / g after calcination 6 hours at 750 ° C. The term “specific surface” is understood here to mean the BET specific surface area determined by nitrogen adsorption in accordance with standard AST D 3663-78 established on the basis of the BRUNAUER - E METT-TELLER method described in the periodical "The Journal of the American Society, δϋ, 309 (1938) ".
Les supports avec ces valeurs de surface sont généralement du type mésoporeux, c'est à dire qu'ils présentent la caractéristique d'avoir un volume poreux significatif apporté par des mésopores (pores de diamètre compris entre 2 et 10nm).The supports with these surface values are generally of the mesoporous type, that is to say that they have the characteristic of having a significant pore volume provided by mesopores (pores with a diameter between 2 and 10 nm).
Le support à base de silice et d'oxyde de titane peut être préparé par tout procédé susceptible de conduire à un support de surface spécifique suffisante.The support based on silica and titanium oxide can be prepared by any process capable of leading to a support of sufficient specific surface.
On peut ainsi mentionner plus particulièrement un procédé par texturation micellaire utilisant comme source de silice, des composés organiques du silicium, notamment des al yl-silicates comme l'orthosilicate de tétraéthyle et en faisant réagir cette source de silice avec un composé ou une source de titane, en présence d'un tensio-actif. Ces composés organiques du silicium sont généralement mis en oeuvre sous forme de solutions dans des alcools, en particulier dans des alcools aliphatiques. Comme composé du titane, on peut utiliser des composés organiques du titane comme les alkyl- ou alcoxy-titanates qui sont généralement employés sous forme de solutions alcooliques comme pour le composé du silicium. En ce qui concerne le tensio-actif on peut utiliser plus particulièrement ceux du type à cation actif comme les amides et les sels d'ammonium quaternaires. On peut conduire la réaction en mélangeant le composé organique du silicium et le composé de titane puis en chauffant. On ajoute ensuite le tensioactif au mélange ainsi chauffé. Le précipité obtenu après la réaction est séparé du milieu réactionnel. Ce précipité est ensuite calciné, généralement sous air, pour obtenir le support qui pourra ensuite être mis en forme. La calcination peut se faire en deux parties. Dans la première partie, on calcine à une température suffisante pour éliminer le tensio-actif. Cette température peut être d'environ 650°C. Dans la deuxième partie, on calcine à une température au moins égale à celle à laquelle le catalyseur sera utilisé. Cette température peut être.d'enyiron 750°Ç.One can thus more particularly mention a process by micellar texturing using as source of silica, organic silicon compounds, in particular al-yl-silicates like tetraethyl orthosilicate and by reacting this source of silica with a compound or a source of titanium, in the presence of a surfactant. These organic silicon compounds are generally used in the form of solutions in alcohols, in particular in aliphatic alcohols. As the titanium compound, there may be used organic titanium compounds such as the alkyl- or alkoxy-titanates which are generally employed in the form of alcoholic solutions as for the silicon compound. As regards the surfactant, it is possible to use more particularly those of the active cation type such as amides and quaternary ammonium salts. The reaction can be carried out by mixing the organic silicon compound and the titanium compound and then heating. The surfactant is then added to the mixture thus heated. The precipitate obtained after the reaction is separated from the reaction medium. This precipitate is then calcined, generally in air, to obtain the support which can then be shaped. Calcination can be done in two parts. In the first part, calcination is carried out at a temperature sufficient to remove the surfactant. This temperature can be around 650 ° C. In the second part, calcination is carried out at a temperature at least equal to that at which the catalyst will be used. This temperature can be . about 750 ° C.
Le support peut se présenter sous diverses formes telles que granulés, billes, cylindres ou nid d'abeille de dimensions variables.The support can be in various forms such as granules, balls, cylinders or honeycomb of variable dimensions.
Le support peut comprendre à titre d'additifs un ou plusieurs oxydes de terres rares. Par terre rare on entend les éléments du groupe constitué par l'yttrium et les éléments de la classification périodique de numéro atomique compris inclusivement entre 57 et 71. On peut citer comme terre rare le lanthane plus particulièrement. La teneur en additif exprimée en % atomique additif/Ti+Si+additif peut être d'au plus 20%, plus particulièrement d'au plus 10%.The support can comprise, as additives, one or more rare earth oxides. By rare earth is meant the elements of the group constituted by yttrium and the elements of the periodic classification of atomic number included inclusively between 57 and 71. Mention may be made, as rare earth, of lanthanum more particularly. The additive content expressed in atomic% additive / Ti + Si + additive may be at most 20%, more particularly at most 10%.
La composition catalytique de l'invention peut comporter en outre une phase catalytique. Cette phase peut être à base d'au moins un métal choisi parmi les éléments compris dans les groupes IIIA à IIB de la classification périodique.The catalytic composition of the invention can also comprise a catalytic phase. This phase can be based on at least one metal chosen from the elements included in groups IIIA to IIB of the periodic table.
Plus particulièrement, la phase catalytique est à base d'au moins un métal choisi parmi les métaux du groupe VIII de la classification périodique.More particularly, the catalytic phase is based on at least one metal chosen from the metals of group VIII of the periodic table.
La classification périodique des éléments à laquelle il est fait référence est celle publiée dans le Supplément au Bulletin de la Société Chimique de France n° 1 (janvier 1966).The periodic classification of the elements to which reference is made is that published in the Supplement to the Bulletin of the Société Chimique de France No. 1 (January 1966).
A titre d'exemple de métaux utilisables dans la phase catalytique, on peut citer le platine, le palladium, le rhodium, le ruthénium, l'iridium. On peut aussi citer le fer, le cuivre, le chrome ainsi que le vanadium, le niobium, le tantale, le molybdène et le tungstène. La teneur en métal de la phase catalytique et, notamment en platine, de la composition peut varier dans de larges proportions. Habituellement, cette proportion, exprimée en poids de métal par rapport au poids de support est comprise entre 500 et 40000ppm, de préférence entre entre 2500 et 20000ppm et encore plus particulièrement entre 5000 et 15000ppm. La phase catalytique peut être déposée sur le support, de préférence le support calciné, par toute technique connue.Examples of metals which can be used in the catalytic phase include platinum, palladium, rhodium, ruthenium, iridium. Mention may also be made of iron, copper, chromium as well as vanadium, niobium, tantalum, molybdenum and tungsten. The metal content of the catalytic phase and, in particular of platinum, of the composition can vary within wide proportions. Usually, this proportion, expressed by weight of metal relative to the weight of the support is between 500 and 40,000 ppm, preferably between 2,500 and 20,000 ppm and even more particularly between 5,000 and 15,000 ppm. The catalytic phase can be deposited on the support, preferably the calcined support, by any known technique.
On peut ainsi utiliser la technique d'imprégnation par trempage du support dans une solution ou un sol du ou des éléments constituant la phase catalytique puis élimination de l'excès de solution ou de sol par égouttage ou par passage dans un évaporateur rotatif.It is thus possible to use the impregnation technique by soaking the support in a solution or a soil of the element or elements constituting the catalytic phase and then removing the excess solution or soil by draining or by passing through a rotary evaporator.
Dans le cas particulier d'une phase catalytique à base de platine et selon une variante de l'invention, le platine est apporté sous forme d'un sol. Le sol de platine sera de préférence choisi pour présenter une taiHe de colloïdes comprise entre 2nm et 10nm et plus particulièrement entre 3nm et 8nm. La taille de colloïdes est déterminée par microscopie â transmission électronique (MET).In the particular case of a catalytic phase based on platinum and according to a variant of the invention, the platinum is provided in the form of a sol. The platinum sol will preferably be chosen to have a size of colloids between 2 nm and 10 nm and more particularly between 3 nm and 8 nm. The size of colloids is determined by electron transmission microscopy (TEM).
Selon une variante particulière, l'imprégnation est réalisée "à sec", c'est à dire que le volume total de solution ou de sol utilisé est approximativement égal au volume poreux total développé par le support à imprégner. Concernant la détermination de ce volume poreux, elle peut être réalisée selon la méthode connue au porosimètre à mercure ou bien par mesure de la quantité d'eau absorbée par un échantillon.According to a particular variant, the impregnation is carried out "dry", that is to say that the total volume of solution or soil used is approximately equal to the total pore volume developed by the support to be impregnated. Concerning the determination of this pore volume, it can be carried out according to the method known with a mercury porosimeter or by measuring the amount of water absorbed by a sample.
Après imprégnation, le support est éventuellement séché puis il est calciné. Le séchage est le plus souvent effectué à l'air, à une température qui peut varier entre 80 et 300°C et choisie de préférence entre 100 et 150°C. Le séchage est poursuivi jusqu'à l'obtention d'un poids constant. Généralement, la durée du séchage est comprise entre 1 et 24 heures. La calcination du support avec la phase catalytique ou active déposée s'effectue généralement à une température d'au plus 750°C et plus particulièrement d'au plus 550°C dans le cas où le platine est utilisé dans la phase catalytique. La durée de la calcination peut, quant à elle, varier dans de larges limites, par exemple entre 1 et 24 heures, de préférence entre 2 et 10 heures. La calcination est généralement opérée sous air, mais une calcination menée par exemple sous gaz inerte n'est bien évidemment pas exclue.After impregnation, the support is optionally dried and then it is calcined. The drying is most often carried out in air, at a temperature which can vary between 80 and 300 ° C. and preferably chosen between 100 and 150 ° C. Drying continues until obtaining a constant weight. Generally, the drying time is between 1 and 24 hours. The calcination of the support with the catalytic or active phase deposited is generally carried out at a temperature of at most 750 ° C and more particularly at most 550 ° C in the case where platinum is used in the catalytic phase. The duration of the calcination can, for its part, vary within wide limits, for example between 1 and 24 hours, preferably between 2 and 10 hours. Calcination is generally carried out in air, but calcination carried out for example under inert gas is obviously not excluded.
Il est possible aussi de réaliser la calcination dans un mélange eau-azote (10% en volume d'eau dans l'azote par exemple). Dans ce cas, on calcine à une température d'au plus 850°C, de préférence aux environs de 750°C. Ce traitement permet d'activer la composition et il est particulièrement intéressant dans le cas d'une composition pour laquelle la phase catalytique comprend du platine.It is also possible to carry out the calcination in a water-nitrogen mixture (10% by volume of water in nitrogen for example). In this case, it is calcined at a temperature of at most 850 ° C., preferably around 750 ° C. This treatment makes it possible to activate the composition and it is particularly advantageous in the case of a composition for which the catalytic phase comprises platinum.
Dans le cas particulier d'une composition dont la phase catalytique est à base de platine apporté par un sol et avec un support de type mésoporeux et avec les valeurs de surface spécifique données plus haut, la taille des particules de platine dans la composition après calcination est sensiblement identique à celle des colloïdes mentionnée plus haut.In the particular case of a composition whose catalytic phase is based on platinum provided by a soil and with a support of the mesoporous type and with the specific surface values given above, the size of the platinum particles in the composition after calcination is substantially identical to that of the colloids mentioned above.
Le dépôt de la phase catalytique peut aussi se faire par atomisation. Dans ce cas, on introduit le support, par exemple sous forme d'une suspension, dans une solution ou un sol de l'élément ou des éléments constituant la phase catalytique et on sèche par atomisation le mélange ainsi formé. On peut opérer avec une température de sortie des gaz comprise entre 100 et 150°C. On calcine ensuite dans les conditions décrites plus haut. Les compositions telles que décrites ci-dessus s'appliquent au traitement de gaz pouvant comprendre des oxydes d'azote en combinaison éventuellement avec des oxydes de carbone et/ou des hydrocarbures, en vue de la réduction des émissions des oxydes d'azote notamment.The deposition of the catalytic phase can also be done by atomization. In this case, the support is introduced, for example in the form of a suspension, into a solution or a sol of the element or elements constituting the catalytic phase and the mixture thus formed is spray-dried. One can operate with a gas outlet temperature between 100 and 150 ° C. Then calcined under the conditions described above. The compositions as described above apply to the treatment of gases which may comprise nitrogen oxides in combination optionally with carbon oxides and / or hydrocarbons, with a view to reducing the emissions of nitrogen oxides in particular.
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.
L'invention s'applique ainsi au traitement des gaz qui présentent une teneur élevée en oxygène et qui contiennent des oxydes d'azote, en vue de réduire les émissions de ces oxydes. 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 stoechiométrique des carburants et, plus précisément, des gaz présentant en permanence un excès d'oxygène par rapport à la valeur stoechiométrique 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. En d'autres termes, l'invention s'applique au traitement des gaz issus de systèmes du type décrit au paragraphe précédent et fonctionnant en permanence dans des conditions telles que λ soit toujours strictement supérieur à 1. Dans le cas des gaz présentant une teneur élevée en oxygène, l'invention s'applique ainsi, d'une part, au traitement des gaz de moteur fonctionnant en mélange pauvre (lean burn) et qui présentent une teneur en oxygène (exprimée en volume) généralement comprise entre 2,5 et 5% et, d'autre part, au traitement des gaz 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 invention thus applies to the treatment of gases which have a high oxygen content and which contain nitrogen oxides, with a view to reducing the emissions of these oxides. 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 permanently 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. In other words, the invention applies to the treatment of gases from systems of the type described in the previous paragraph and operating continuously under conditions such that λ is always strictly greater than 1. In the case of gases having a content high in oxygen, the invention thus applies, on the one hand, to the treatment of engine gases operating in a lean burn mixture and which have an oxygen content (expressed by volume) generally between 2.5 and 5% and, on the other hand, to the treatment of gases which have an even higher oxygen content, for example gases from engines of the diesel type, 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 gaz peuvent contenir des hydrocarbures et, dans un tel cas, une des réactions que l'on cherche à catalyser est la réaction HC (hydrocarbures) + NOx. Les hydrocarbures qui peuvent être utilisés comme agent réducteur pour l'élimination des NOx sont notamment les gaz ou les liquides des familles des carbures saturés, des carbures éthyléniques, des carbures acétyléniques, des carbures aromatiques et les hydrocarbures des coupes pétrolières comme par exemple le méthane, l'éthane, le propane, le butane, le pentane, l'hexane, l'éthylène, le propylène, l'acétylène, le butadiène, le benzène, le toluène, le xylène, le kérosène et le gaz oil.The gases can contain hydrocarbons and, in such a case, one of the reactions which one seeks to catalyze is the reaction HC (hydrocarbons) + NO x . The hydrocarbons which can be used as a reducing agent for the elimination of NOx are in particular the gases or the liquids of the families of saturated carbides, ethylenic carbides, acetylenic carbides, aromatic carbides and hydrocarbons from petroleum fractions such as for example methane , ethane, propane, butane, pentane, hexane, ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, kerosene and gas oil.
Les gaz peuvent contenir aussi comme agent réducteur, des composés organiques contenant de l'oxygène. Ces composés peuvent être notamment les alcools du type par exemple alcools saturés comme le méthanol, l'éthanol ou le propanol; les éthers comme l'éther méthylique ou l'éther éthylique; les esters comme l'acétate de méthyle et les cétones.The gases can also contain, as reducing agent, organic compounds containing oxygen. These compounds may especially be alcohols of the type, for example saturated alcohols such as methanol, ethanol or propanol; ethers such as methyl ether or ethyl ether; esters such as methyl acetate and ketones.
L'invention s'applique aussi au traitement de gaz ne contenant pas d'hydrocarbures ni de composés organiques comme agent réducteur.The invention also applies to the treatment of gases containing no hydrocarbons or organic compounds as a reducing agent.
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. Ce système est caractérisé en ce qu'il comprend une composition catalytique4elle que décrites plus haut. -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 mentioned above. This system is characterized in that it comprises a catalytic composition such as that described above. -
Dans ce système, la composition catalytique peut se présenter sous diverses formes telles que granulés, billes, cylindres ou nid d'abeille de dimensions variables.In this system, the catalytic composition can be in various forms such as granules, beads, cylinders or honeycomb of variable dimensions.
Les compositions peuvent aussi être utilisées dans des systèmes catalytiques comprenant un revêtement (wash coat) incorporant ces compositions, le revêtement étant disposé sur un substrat du type par exemple monolithe métallique ou en céramique. Les systèmes sont montés d'une manière connue dans les pots d'échappement des véhicules dans le cas de l'application au traitement des gaz d'échappement.The compositions can also be used in catalytic systems comprising a coating (wash coat) incorporating these compositions, the coating being arranged on a substrate of the type, for example metallic or ceramic monolith. The systems are mounted in a known manner in the exhaust pipes of vehicles in the case of application to the treatment of exhaust gases.
L'invention concerne aussi enfin le procédé de fabrication des systèmes catalytiques précités mettant en oeuvre une composition catalytique du type décrit précédemment.Finally, the invention also relates to the process for manufacturing the above-mentioned catalytic systems using a catalytic composition of the type described above.
Des exemples vont maintenant être donnés.Examples will now be given.
ExemplesExamples
I - Synthèse des catalyseursI - Synthesis of the catalysts
- Matières premières :- Raw materials :
On utilise une solution de platine de type (24,88% en Pt) et un sol de platine de taille de colloïdes de 5-7nm et de concentration de 10g/l. Le sol est obtenu en portant sous reflux une solution comprenant un mélange de polyvinylpyrrolidone, de h^PtClβ et de méthanol.We use a platinum type solution (24.88% in Pt) and a platinum sol of colloid size of 5-7nm and concentration of 10g / l. The sol is obtained by carrying under reflux a solution comprising a mixture of polyvinylpyrrolidone, h ^ PtClβ and methanol.
Le support utilisé présente une proportion atomique Ti/Ti+Si de 9% et il est préparé de la manière suivante :The support used has an Ti / Ti + Si atomic proportion of 9% and it is prepared as follows:
On dilue préalablement 1 mole d'orthosilicates de tétraéthyte (TEOS) dans 6,54 moles d'éthanol et 0,1 mole d'alcoxyde de titane Ti(i-C3HyO)4 dans 1 ,99 moles d'alcool isopropylique.1 mole of tetraethyte orthosilicates (TEOS) is diluted beforehand in 6.54 moles of ethanol and 0.1 mole of titanium alkoxide Ti (i-C3HyO) 4 in 1.99 moles of isopropyl alcohol.
Dans un réacteur muni d'un agitateur, on ajoute rapidement sous agitation vigoureuse la solution d'alcoxyde de titane à la solution de TEOS. On obtient alors une solution limpide qui est chauffée à 72°C sous agitation pendant 3 heures. Parallèlement, on prépare une solution contenant 0,27 mole de dodécylamineIn a reactor fitted with an agitator, the titanium alkoxide solution is rapidly added with vigorous stirring to the TEOS solution. A clear solution is then obtained which is heated to 72 ° C. with stirring for 3 hours. At the same time, a solution containing 0.27 mole of dodecylamine is prepared.
(DDA) dans 21,2 moles d'eau.(DDA) in 21.2 moles of water.
La solution contenant le mélange TEOS et est alors ajoutée à la solution contenant le tensioactif DDA. L'ensemDle est maintenu sous agitation vigoureuse pendant 18 heures à température ambiante. L'élimination du tensioactif est réalisée en calcinant sous air le précipité ainsi obtenu à une température de 650°C pendant 4 heures. Ensuite, le précipité est calciné 4 heures à 750°C sous air (vitesse de montée en température 1°C/mn).The solution containing the TEOS mixture and is then added to the solution containing the surfactant DDA. The whole is kept under vigorous stirring for 18 hours at room temperature. The surfactant is removed by calcining the precipitate thus obtained in air at a temperature of 650 ° C. for 4 hours. Then, the precipitate is calcined for 4 hours at 750 ° C in air (temperature rise rate 1 ° C / min).
Le support ainsi préparé est imprégné à sec par du platine dans des Droportions de 1 ou 2% en poids. On sèche à l'étuve le support imprégné à 110°C pendant 2 heures, puis on calcine dans les conditions données dans le tableau qui suit. - Produits obtenusThe support thus prepared is dry impregnated with platinum in Droportions of 1 or 2% by weight. The impregnated support is dried in an oven at 110 ° C. for 2 hours, then calcined under the conditions given in the table below. - Products obtained
* le % de Pt est exprimé en poids de métal par rapport au poids de support. **La surface spécifique est déterminée par la mesure BET un point.* the% of Pt is expressed in weight of metal relative to the weight of support. ** The specific surface is determined by the BET measurement at one point.
Il - Tests catalytiquesIl - Catalytic tests
On charge 50mg du catalyseur en poudre dans un réacteur en quartz. La poudre utilisée a préalablement été granulée à 0,125 et 0,250mm. Le mélange réactionnel à l'entrée du réacteur a la composition suivante (en volume) :50 mg of the powdered catalyst are loaded into a quartz reactor. The powder used was previously granulated at 0.125 and 0.250 mm. The reaction mixture at the inlet of the reactor has the following composition (by volume):
- NO = 300 vpm- NO = 300 vpm
- C3H6 = 300 vpm- C3H6 = 300 vpm
- CO = 350 vpm - O2 = 10%- CO = 350 vpm - O 2 = 10%
- CO2 = 10%- CO 2 = 10%
- H2O = 10%- H 2 O = 10%
- N2 = qsp 100%- N 2 = qs 100%
Le débit global est de 30 Nl h. La WH est d'environ 500000 h*1.The overall flow is 30 Nl h. The WH is around 500,000 h * 1 .
Pour les essais réalisé en l'absence de réducteur, les débits de CO et de C3H6 sont supprimés et remplacés par un débit équivalent d'azote de manière à conserver la même VVH. .For the tests carried out in the absence of a reducing agent, the CO and C3H6 flow rates are eliminated and replaced by an equivalent nitrogen flow rate so as to keep the same VVH. .
Les signaux de HC {C^H , CO et NOx (NOx = NO + NO ) sont enregistrés en permanence ainsi que la température dans le réacteurThe signals of HC {C ^ H, CO and NO x (NO x = NO + NO) are permanently recorded as well as the temperature in the reactor
Le signal de HC est donné par un détecteur BECKMAN du type hydrocarbures totaux, basé sur le principe de la détection par ionisation de flamme.The HC signal is given by a BECKMAN detector of the total hydrocarbon type, based on the principle of detection by flame ionization.
Le signal de NOx est donné par un analyseur de NOx ECOPHYSICS, basé sur le principe de la chimie-luminescence. Le signal de CO et N2O est donné par un analyseur à infrarouge ROSEMOUNT. L'activité catalytique est mesurée à partir des signaux HC (C3H6), CO et NOx en fonction de la température lors d'une montée en température programmée de 150 à 700°C à raison de 15°C/mn et à partir des relations suivantes :The NO x signal is given by a NO x ECOPHYSICS analyzer, based on the principle of chemistry-luminescence. The CO and N 2 O signal is given by a ROSEMOUNT infrared analyzer. The catalytic activity is measured from the HC (C3H6), CO and NO x signals as a function of the temperature during a programmed temperature rise from 150 to 700 ° C at a rate of 15 ° C / min and from the following relationships:
- Le taux de conversion de HC (THC) en % qui est donné par :- The conversion rate of HC (THC) in% which is given by:
T (HC) = 100(HC°-HC)/HC° avec HC° signal de HC à l'instant t = 0 qui correspond au signal de HC obtenu avec le mélange réactionnel lors du by-pass du réacteur catalytique et HC est le signal de HC à l'instant t.T (HC) = 100 (HC ° -HC) / HC ° with HC ° signal of HC at time t = 0 which corresponds to the signal of HC obtained with the reaction mixture during the by-pass of the catalytic reactor and HC is the HC signal at time t.
- Le taux de conversion des CO (TCO) en % qui est donné par :- The CO conversion rate (TCO) in% which is given by:
T(CO) = 100(CO°-CO)/CO° avec CO° signal de CO à l'instant t = 0 qui correspond au signal de CO obtenu avec le mélange réactionnel lors du by-pass du réacteur catalytique et CO est le signal de CO à l'instant t.T (CO) = 100 (CO ° -CO) / CO ° with CO ° CO signal at time t = 0 which corresponds to the CO signal obtained with the reaction mixture during the bypass of the catalytic reactor and CO is the CO signal at time t.
- Le taux de conversion des NOx (TNOx) en % qui est donné par :- The conversion rate of NO x (TNO x ) into% which is given by:
T(NOx) = 100(NOx°-NOx)/NOx° avec NOx° signal de NOx à l'instant t = 0 qui correspond au signal de NOx obtenu avec le mélange réactionnel lors du by-pass du réacteur catalytique et NOx est le signal de NOx à l'instant t.T (NO x ) = 100 (NO x ° -NO x ) / NO x ° with NO x ° signal of NO x at time t = 0 which corresponds to the signal of NO x obtained with the reaction mixture during the by- pass of the catalytic reactor and NO x is the signal of NO x at time t.
Du fait que les catalyseurs peuvent s'activer dans les conditions du tests, l'activité catalytique est donnée lors du second passage consécutif en test dans les mêmes conditions.Because the catalysts can activate under the conditions of the tests, the catalytic activity is given during the second consecutive passage in the test under the same conditions.
EXEMPLE 1EXAMPLE 1
On utilise le produit 1 (catalyseur utilisé en réduction des NOx). Les résultats sont donnés dans le tableau 1 ci-dessous.Product 1 is used (catalyst used for NOx reduction). The results are given in Table 1 below.
Tableau 1Table 1
EXEMPLE 2 EXAMPLE 2
On utilise le produit 1 mais avec un mélange gazeux qui ne comporte plus de CO ni de C3H6 (catalyseur utilisé en décomposition directe). Les résultats sont donnés dans le tableau 2 ci-dessous.Product 1 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 2 below.
Tableau 2Table 2
EXEMPLE 3EXAMPLE 3
On utilise le produit 2 (catalyseur utilisé en réduction des NOx). Les résultats sont donnés dans le tableau 3 ci-dessous.Product 2 (catalyst used for NOx reduction) is used. The results are given in Table 3 below.
Tableau 3Table 3
EXEMPLE 4EXAMPLE 4
On utilise le produit 2 mais avec un mélange gazeux qui ne comporte plus de CO ni de C3H6 (catalyseur utilisé en décomposition directe). Les résultats sont donnés dans le tableau 4 ci-dessous.Product 2 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 4 below.
Tableau 4Table 4
EXEMPLE 5EXAMPLE 5
On utilise le produit 3 (catalyseur utilisé en réduction des NOx). Les résultats sont donnés dans te tableau 5 ci-dessous. Tableau 5Product 3 is used (catalyst used for NOx reduction). The results are given in Table 5 below. Table 5
EXEMPLE 6EXAMPLE 6
On utilise le produit 4 mais avec un mélange gazeux qui ne comporte plus de CO ni de C3H6 (catalyseur utilisé en décomposition directe). Les résultats sont donnés dans le tableau 6 ci-dessous.Product 4 is used but with a gas mixture which no longer contains CO or C3H6 (catalyst used in direct decomposition). The results are given in Table 6 below.
Tableau 6Table 6
EXEMPLE 7 EXAMPLE 7
On utilise le produit 5 mais avec un mélange gazeux qui ne comporte plus de CO ni de C3H5 (catalyseur utilisé en décomposition directe). Les résultats sont donnés dans le tableau 7 ci-dessous.Product 5 is used but with a gas mixture which no longer contains CO or C3H5 (catalyst used in direct decomposition). The results are given in Table 7 below.
Tableau 7Table 7
EXEMPLE 8 COMPARATIFCOMPARATIVE EXAMPLE 8
On utilise une composition catalytique à base de platine sur un support en titane comprenant du lanthane. La composition est obtenue par imprégnation à sec par le sol de platine mentionné plus haut d'un oxyde de titane comprenant 10% en poids d'oxyde de lanthane (SBE=80m2/g) et qui a été précalciné 2h à 750°C. L'imprégnation est suivie d'un séchage à l'étuve (110°C, 2 h), d'une calcination à 500°C pendant 2 h avec une montée en température à 1°C/min. La teneur en platine est de1%. Le catalyseur ainsi préparé est utilisé dans les conditions précitées en réduction. Les résultats sont donnés dans le tableau 8 ci-dessous. Tableau 8A catalytic composition based on platinum is used on a titanium support comprising lanthanum. The composition is obtained by dry impregnation with the above-mentioned platinum sol of a titanium oxide comprising 10% by weight of lanthanum oxide (SBE = 80 m 2 / g) and which has been precalcined for 2 h at 750 ° C. . The impregnation is followed by drying in an oven (110 ° C, 2 h), calcination at 500 ° C for 2 h with a rise in temperature to 1 ° C / min. The platinum content is 1%. The catalyst thus prepared is used under the abovementioned conditions in reduction. The results are given in Table 8 below. Table 8
On obtient un T^QX maximum d'au plus 41 ,6% à 300°C.A maximum T ^ QX of at most 41.6% is obtained at 300 ° C.
Les exemples ci-dessus montrent que la composition selon l'invention permet d'obtenir une activité catalytique dans une fenêtre de température de 250 à 400°C. Par ailleurs, les compositions obtenues à partir d'un sol de platine et utilisées en présence d'un réducteur peuvent présenter une activité catalytique augmentée et maximale dès 250°C et qui se manifeste dès le premier passage. The above examples show that the composition according to the invention makes it possible to obtain a catalytic activity in a temperature window of 250 to 400 ° C. Furthermore, the compositions obtained from a platinum sol and used in the presence of a reducing agent can exhibit an increased and maximum catalytic activity from 250 ° C. and which manifests itself from the first pass.

Claims

REVENDICATIONS
1- Procédé de traitement de gaz pour la réduction des émissions des oxydes d'azote dans lequel on utilise une composition catalytique comprenant une phase catalytique sur un support, caractérisé en ce que le support est à base de silice et d'oxyde de titane dans une proportion atomique Ti/Ti+Si comprise entre 0,1 et 15%.1- Gas treatment process for the reduction of nitrogen oxide emissions in which a catalytic composition is used comprising a catalytic phase on a support, characterized in that the support is based on silica and titanium oxide in an atomic proportion Ti / Ti + Si of between 0.1 and 15%.
2- Procédé selon la revendication 1 , caractérisé en ce qu'on utilise une composition catalytique dont le support est à base de silice et d'oxyde de titane dans une proportion comprise entre 1 et 10%.2- A method according to claim 1, characterized in that one uses a catalytic composition whose support is based on silica and titanium oxide in a proportion between 1 and 10%.
3- Procédé selon la revendication 1 ou 2, caractérisé en ce qu'on utilise une composition catalytique dont la phase catalytique est à base d'au moins un métal choisi parmi les éléments compris dans les groupes IIIA à IIB de la classification périodique, plus particulièrement parmi les métaux du groupe VIII de la classification périodique.3- A method according to claim 1 or 2, characterized in that a catalytic composition is used whose catalytic phase is based on at least one metal chosen from the elements included in groups IIIA to IIB of the periodic table, more particularly among the metals of group VIII of the periodic table.
4- Procédé selon la revendications, caractérisé en ce qu'on utilise une composition catalytique dont la phase catalytique est à base de platine.4- A method according to claims, characterized in that a catalytic composition is used whose catalytic phase is based on platinum.
5- Procédé selon la revendication 4, caractérisé en ce qu'on utilise une composition catalytique dans laquelle le platine a été apporté sous forme d'un sol.5- Method according to claim 4, characterized in that a catalytic composition is used in which the platinum has been provided in the form of a sol.
6- Procédé selon la revendication 5, caractérisé en ce qu'on utilise une composition catalytique dans laquelle le platine a été apporté sous forme d'un sol dont la taille de colloïdes est comprise entre 2nm et 10nm et plus particulièrement entre 3nm et 8nm.6- A method according to claim 5, characterized in that a catalytic composition is used in which the platinum has been provided in the form of a sol whose colloid size is between 2 nm and 10 nm and more particularly between 3 nm and 8 nm.
7- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on utilise une composition catalytique dont le support présente une surface spécifique d'au moins 350 m /g. et plus particulièrement d'au moins 600 m2/g après calcination 6 heures à 750°C.7- Method according to one of the preceding claims, characterized in that a catalytic composition is used whose support has a specific surface of at least 350 m / g. and more particularly at least 600 m 2 / g after calcination for 6 hours at 750 ° C.
8- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on utilise une composition catalytique dont le support comprend un ou plusieurs oxydes de terres rares.8- Method according to one of the preceding claims, characterized in that a catalytic composition is used whose support comprises one or more rare earth oxides.
9- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on traite un gaz d'échappement de moteurs diesel ou de moteurs fonctionnant en mélange pauvre. 10- Procédé selon l'une des revendications précédentes, caractérisé en ce que la teneur en oxygène des gaz est d'au moins 5% en volume.9- Method according to one of the preceding claims, characterized in that one treats an exhaust gas from diesel engines or engines operating in lean mixture. 10- Method according to one of the preceding claims, characterized in that the oxygen content of the gases is at least 5% by volume.
11 - Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on traite un gaz en présence d'un hydrocarbure ou d'un composé organique contenant de l'oxygène.11 - Method according to one of the preceding claims, characterized in that a gas is treated in the presence of a hydrocarbon or an organic compound containing oxygen.
12- Système catalytique pour la mise en oeuvre du procédé selon l'une des revendications 1 à 11 , caractérisé en ce qu'il comprend une composition catalytique telle que définie dans l'une des revendications 1 à 8.12- Catalytic system for implementing the method according to one of claims 1 to 11, characterized in that it comprises a catalytic composition as defined in one of claims 1 to 8.
13- Procédé de fabrication d'un système catalytique selon la revendication 12, caractérisé en ce qu'on met en oeuvre une composition catalytique telle que définie dans l'une des revendications 1 à 8. 13- Process for manufacturing a catalytic system according to claim 12, characterized in that a catalytic composition is used as defined in one of claims 1 to 8.
EP98935077A 1997-07-03 1998-07-01 Method for treating gases to reduce nitrogen oxide emissions using a catalytic composition based on silica and titanium oxide Withdrawn EP0994749A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9708422A FR2765492B1 (en) 1997-07-03 1997-07-03 GAS TREATMENT PROCESS FOR THE REDUCTION OF NITROGEN OXIDE EMISSIONS USING A CATALYTIC COMPOSITION WITH A SUPPORT BASED ON SILICA AND TITANIUM OXIDE
FR9708422 1997-07-03
PCT/FR1998/001410 WO1999001216A1 (en) 1997-07-03 1998-07-01 Method for treating gases to reduce nitrogen oxide emissions using a catalytic composition based on silica and titanium oxide

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