Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9413—Processes characterised by a specific catalyst
  • B01D53/9418—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
  • 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
  • B01J23/06—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of zinc, cadmium or mercury
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/206—Ammonium compounds
  • B01D2251/2062—Ammonia
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/208—Hydrocarbons
• • 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
  • B01D2255/2025—Lithium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/206—Rare earth metals
  • B01D2255/2065—Cerium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20707—Titanium
• • 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
  • B01D2255/20792—Zinc
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/209—Other metals
  • B01D2255/2092—Aluminium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/30—Silica
• • 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
• • 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
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• • 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 zinc aluminate with a high specific surface, a composition which is a precursor of this aluminate, a process for the preparation of this aluminate and of this composition and the use of the aluminate in a process for treating gases, in particular gases. automobile exhaust.
• the zinc aluminate of the invention is characterized in that after calcination at 800 ° C, 8 hours, a specific surface of at least 85m 2 / g.
• the invention also relates to a precursor composition of a zinc aluminate which is characterized in that it comprises compounds of zinc and aluminum and in that it is capable of forming, after calcination, a zinc aluminate, this aluminate having after calcination at 800 ° C, 8 hours a specific surface of at least 85m2 / g.
• Another object of the invention is a process for preparing an aluminate or a composition of the type described above, a process which is characterized in that it comprises the following stages:
• a zinc salt and an aluminum alkoxide are brought into contact in a solvent medium;
• the aluminate of the invention is a zinc aluminate. It has a spinel-type structure ZnA ⁇ O II can occur under one or more lacunar or excess phases in zinc compared to ZnA ⁇ O these phases corresponding to the formulas Zn-
• the values of x can respond more particularly to the following relationships: 0 ⁇ x ⁇ 0.85, 0 ⁇ x ⁇ 0.8 and more particularly 0 ⁇ x ⁇ 0.5. Finally, x can verify the relation 0.4 ⁇ x ⁇ 0.85.
• the aluminate can also comprise one or more additives. These additives are chosen from the elements of groups IA,
• additives can in particular be present in the aluminate in partial substitution for zinc or aluminum.
• a characteristic of the aluminate of the invention is its specific surface.
• specific surface means, the BET specific surface determined by nitrogen addition in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical 'The Journal of the American Chemical Society, 6_Q, 309 (1938) ".
• ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical 'The Journal of the American Chemical Society, 6_Q, 309 (1938) ".
• this specific surface is at least 85m2 / g. It can be at least 90 m 2 / g and more particularly at least 100 m - ⁇ / g, always after calcination at 800 ° C, 8 hours. Values of at least 120m2 / g can be reached.
• the aluminate of the invention may have, after calcination at 900 ° C, 2 hours, a specific surface of at least 70m2 / g, more particularly at least ⁇ Om ⁇ / g.
• specific surfaces of at least 50 m 2 / g can be observed, more particularly at least 70 m 2 / g. This means that the aluminate surface is stable over a wide temperature range.
• the values which have just been given above are understood for calcinations in air. It may further be noted that the aluminate of the invention has a high resistance to aging.
• the aluminate of the invention may also have a pore volume of at least 0.6 ml / g, this porosity is determined by porosimetry by mercury intrusion. The measurements were made on a Micromeretics Auto Pore 9220 device on powders put to degas overnight in an oven heated to 200 ° C. The operating parameters are as follows: Constant penetrometer: 21, 63, capillary volume: 1, 1, contact angle: 140 °.
• the porosity can more particularly be at least 2 ml / g and for example be between 2.5 and 3.5 ml / g.
• the invention also relates to a precursor composition of the aluminate as just described above.
• This composition includes compounds of zinc and aluminum and, where appropriate, compounds of the additives mentioned above.
• the main characteristic of the precursor composition is its ability to give, after calcination, a zinc aluminate.
• the calcination temperature from which the aluminate is formed is approximately 500 ° C.
• the aluminate thus obtained has the characteristics given above, that is to say that if it is calcined at a temperature of 800 ° C. for 8 hours, it retains a high specific surface of at least 85 m 2 / g , more particularly at least 90m2 / g and even more particularly at least minus 100m2 / g.
• all the surface values given above for the aluminate at temperatures of 800 ° C and 900 ° C also apply here.
• the process for preparing the aluminate and its precursor composition will now be described.
• the first step of this process consists in bringing into a solvent medium a salt, a sol or a zinc alkoxide and an aluminum alkoxide with optionally a salt, a sol or an alkoxide of at least one aforementioned additive.
• the zinc salt or alkoxide, as well as the salt or alkoxide of the additive must be soluble in the solvent medium.
• the zinc or additive salt is for example an inorganic salt such as a nitrate or a chloride or an organic salt such as a citrate, an oxalate or an acetate.
• the aluminum alkoxide may for example be an ethoxide, a butoxide or an isopropoxide.
• the solvent medium is chosen from any medium in which the salt or zinc alkoxide and aluminum alkoxide are soluble.
• an alcoholic solvent is used.
• saturated mono-alcohols and more particularly those with a short chain (for example in CQ at most) such as methanol, ethanol, propanol, butanol.
• unsaturated alcohols and polyalcohols such as for example ethylene glycol, propylene glycol, hexylene glycol, propanediol, butanediol.
• the bringing together of the reactants in the solvent medium can be done in any way.
• the zinc salt and the aluminum alkoxide are brought into contact by adding to the aluminum alkoxide, which constitutes a base stock, the zinc salt in the solvent medium, ie dissolved beforehand in this medium.
• the second step of the process of the invention consists in hydrolyzing the mixture obtained in the previous step.
• This hydrolysis is done by adding water to the mixture.
• the hydrolysis is carried out using an amount of water in excess relative to the aluminum alkoxide. This excess is determined by the mole ratio of H2 ⁇ / mole of aluminum alkoxide. Generally, this ratio can be at least 6, more particularly at least 10 and even more particularly at least 20. However, in the case of the preparation of a zinc-deficient aluminate, this ratio can be more low. More specifically, in the case of the preparation of an aluminate having a Zn / Al ratio of less than 0.4, the mole ratio of I- ⁇ O / mole of aluminum alkoxide may be at least 3, more particularly at least 4.
• the water can be provided in the form of a water-alcohol mixture, the alcohol possibly being chosen in particular from those mentioned above concerning the solvent medium. Mention may more particularly be made of ethanol.
• the hydrolysis leads to the formation of a precipitate of the elements.
• the precipitate obtained is separated from the reaction medium by any known means, in particular by centrifugation.
• the precipitate can be washed if necessary.
• the precipitate can then optionally be dried.
• the precursor composition of the invention is obtained at this stage.
• the aluminate is prepared by calcining the precipitate (precursor composition) at a temperature of at least 500 ° C.
• Another process for the preparation of an aluminate or a precursor according to the invention may be mentioned in the case where the latter comprises an additive of the type mentioned above.
• This process consists in adding the additive not during the synthesis of the aluminate but by impregnating either the precursor composition, for example the dried precipitate, or the aluminate itself, ie the calcined precipitate. The impregnation is done using a solution of a salt of the additive of the type given previously for example.
• Dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the element which is equal to the pore volume of the solid to be impregnated.
• the invention further relates to a method for treating exhaust gases from motor vehicles in which a catalytic system comprising an aluminate is used as described above.
• the invention also relates to a method in which a catalytic system comprising this same aluminate is used for the treatment of gases which may comprise nitrogen oxides with a view to reducing the emissions of these nitrogen oxides.
• the gases which can be treated in this case are, for example, those 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 aluminate of 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.
• the value ⁇ is correlated to the air / fuel ratio in a manner known per se in particular in the field of internal combustion engines.
• the aluminate of the invention applies to the treatment of gases from systems of the type described in the preceding paragraph and operating continuously under conditions such that ⁇ is always strictly greater than 1.
• the aluminate of the invention thus applies, on the one hand, to the treatment of engine gases operating in a lean mixture (lean bum) and which have an oxygen content (expressed by volume ) generally between 2.5 and 5% and, on the other hand, 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 contain a reducing agent which can be one or more hydrocarbons and one of the reactions which it is sought to catalyze in this case 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 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 gases may also contain as ammonia reducing agent.
• the aluminate can be used in catalytic compositions which can be in various forms such as granules, beads, cylinders or honeycomb of variable dimensions, these compositions possibly comprising the aluminate of l invention on any support usually used in the field of catalysis, such as, for example, Zr ⁇ 2, AI2O3, Ti ⁇ 2, Ce ⁇ 2, Si ⁇ 2 or mixtures thereof.
• the invention also relates more particularly to a catalytic system for the gas treatment processes described above.
• This system is characterized in that it comprises an aluminate on a substrate.
• Such a system generally includes a coating (wash coat) incorporating the aluminate and a support of the type described above, the coating being deposited 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.
• the invention also finally relates to the use of an aluminate or of a precursor composition as described above for the manufacture of such a catalytic system. Examples will now be given.
• This example concerns the preparation of ZnAl2 ⁇ 4.
• the following raw materials are used:
• the precipitate is dried in an oven in a thin layer at 70 ° C. for 48 hours. Finally, the product is calcined. The temperature rise takes place at 5 ° C / min. The temperature is then kept level at the value and for the durations given below.
• the specific surface of the product is 136m 2 / g.
• the specific surface of the product is 125m 2 / g.
• the specific surface of the product is 115m 2 / g.
• the specific surface of the product is 101m 2 / g. After 2 hours calcination at 1000 ° C, the specific surface of the product is
• EXAMPLE 2 The precipitate obtained in Example 1 is dried for 48 hours at 70 ° C. It is then impregnated with a solution of SnCl2.2H2 ⁇ dissolved in ethanol. The technique used is dry impregnation. The amount of Sn deposited is equal to 1.6% by weight relative to the zinc aluminate oxide. The product thus obtained is dried in an oven for 2 hours at 110 ° C. and then calcined for 8 hours at 800 ° C. (rising speed 5 ° C./min). The specific surface of the product thus obtained is equal to 115 m 2 / g.
• This example concerns the preparation of ZnA ⁇ 680,204
• This solution is added to 2.25 mole of aluminum tri-sec-butoxide previously introduced into the reactor with vigorous stirring (500 rpm). The mixture is heated to 70 ° C and maintained for 2 hours at this temperature. A water / ethanol mixture (50/50 by volume) is then added with a flow rate of 5 ml / min. The water / tri-aluminum butoxide ratio is equal to 25. The medium is allowed to cool with stirring overnight. The precipitate obtained is separated by centrifugation. The precipitate obtained is dried in a thin layer at 70 ° C for 48 hours and then calcined for 8 hours at 800 ° C (rise speed 5 ° C / min).
• the specific surface of the product thus obtained is equal to 113 m 2 / g.
• This example relates to the preparation of Zno.95Cao.05Al2 ⁇ 4
• the same raw materials are used as in Example 1 with, in addition, a solution of Ca (NO3) 2- 4H 2 0 at 98% purity.
• the specific surface of the product thus obtained is equal to 119 m 2 / g.
• This example concerns the preparation of no.95 io.osAl2 ⁇ 4.
• Example 2 The same raw materials are used as in Example 1 with, in addition, a 99% purity Li (NO 3) solution. 1.19 moles of the zinc salt are dissolved in 1 liter of hexylene glycol and then introduced
• This solution is added to 2.5 moles of aluminum tri-sec-butoxide previously introduced into the reactor with vigorous stirring (500 rpm).
• the mixture is heated to 70 ° C and maintained for 2 hours at this temperature.
• a water / ethanol mixture (50/50 by volume) is then added with a flow rate of 5 ml / min.
• the water / tri-dry aluminum butoxide ratio is equal to 28.
• the medium is allowed to cool with stirring overnight.
• the precipitate obtained is separated by centrifugation.
• the precipitate obtained is dried in a thin layer at 70 ° C for 48 hours and then calcined for 8 hours at 800 ° C (rise speed 5 ° C / min).
• the specific surface of the product thus obtained is equal to 108 m 2 / g.
• This example relates to an aluminate of formula ZnAl2O4 which comprises silver as an additive.
• the precipitate obtained in Example 1 is dried for 48 hours at 70 ° C. It is then impregnated with a solution of AgN03 (99.8%). The technique used is dry impregnation.
• the quantity of silver deposited is equal to 1.6% by weight relative to the zinc aluminate oxide.
• the product thus obtained is dried in an oven for 2 hours at 110 ° C. and then calcined for 8 hours at 800 ° C. (rising speed 5 ° C./min).
• the specific surface of the product thus obtained is equal to 90 m 2 / g.
• Example 1 The procedure is as in Example 1 for the preparation of zinc aluminates having different Zn / AI ratios. The same raw materials are used in the necessary proportions. For products 7-1 to 7-3 the mole ratio of H2 ⁇ / mole of aluminum alkoxide is 28. For products 7-4 to 7-6 this ratio is 4. We give below the characteristics of the prepared products.
• the products obtained in the previous examples are tested to assess their catalytic performance.
• 0.2 g of the powdered catalyst is loaded into a quartz reactor.
• the powder used was previously compacted, then ground and sieved so as to isolate the particle size range between 0.125 and 0.250 mm.
• the HC signal is given by a BECKMAN total HC detector, based on the principle of flame ionization detection.
• NO and NO x are given by a NO x analyzer ECOPHYSICS, based on the principle of chemistry-luminescence: it gives the values of NO, NO x and NO2, the latter being calculated by difference of the signals of NO x and No.

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• 1998
  • 1998-05-26 FR FR9806610A patent/FR2779071B1/fr not_active Expired - Fee Related
• 1999
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