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
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/8621—Removing nitrogen compounds
  • B01D53/8625—Nitrogen oxides
  • B01D53/8628—Processes characterised by a specific catalyst
• • 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
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
  • B01J29/20—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type containing iron group metals, noble metals or copper
• • 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
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
  • B01J29/20—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type containing iron group metals, noble metals or copper
  • B01J29/22—Noble metals
• • 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
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
  • B01J29/20—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type containing iron group metals, noble metals or copper
  • B01J29/24—Iron group metals or copper

Definitions

• Catalyst in particular for reducing NO x , and method for reducing N0 y
• the invention relates to a catalyst, in particular for reducing NO X , as well as a method for reducing NO X.
• US Pat. No. 5,149,512 describes a process for the reduction of NO x by methane, in the presence of oxygen, in which a catalyst consisting of a zeolite in particular of mordenite structure with a pore size between 5 and 15 ⁇ , exchanged with cobalt, is used.
• European patent application No. EP-A- 0 286 507 describes the use of a zeolite with a mordenite structure in ammonium or acid form called "large pores", that is to say with a size of pores greater than 6.6 ⁇ , for the reduction of NO x in the presence of oxygen.
• This document also describes the use of a zeolite of mordenite structure called "small pores”, that is to say with a pore size less than 4.4 ⁇ , exchanged with copper for the reduction of NO x in presence of oxygen.
• ammonia is used as the NO x reducing agent.
• the use and storage of ammonia are very delicate.
• the invention aims to overcome the drawbacks associated with the use of ammonia and at the same time to obtain better NO x conversion rates.
• the invention provides a catalyst characterized in that it consists of a zeolite with a "small pore” mordenite structure exchanged with Pd and / or Co.
• the zeolite is exchanged with Pd, only, at a content of Pd 2+ cations of between approximately 0.4% and approximately 0.6% by weight relative to the weight total catalyst.
• the zeolite is exchanged with Co only, at a content of Co 2+ cations of between approximately 1.2% and approximately 3.2% by weight relative to the total weight of the catalyst.
• the zeolite is exchanged with between approximately 0.4% and approximately 0.6% by weight of Pd 2+ cations and between approximately 1.2% and approximately 3.2 % by weight of Co 2+ cations, relative to the total weight of the catalyst.
• the zeolite is in sodium form or in ammonium form with an Si / Ai ratio equal to 5.5.
• the invention also provides a process for the reduction of NO X by methane or any mixture mainly containing methane, characterized in that it comprises bringing a reaction medium comprising NO x and methane into contact with the catalyst according to the invention. 'invention.
• the NO X reduction process according to the invention is further characterized in that the reaction medium additionally contains oxygen.
• the reaction medium can also contain sulfur compounds.
• the invention also relates to a catalyst for the reduction of NO x by methane or any mixture mainly containing methane, consisting of a zeolite with a mordenite structure "with small pores" exchanged with Pd and / or Co.
• this NO x reduction catalyst according to the invention is a zeolite with a "small pore" mordenite structure exchanged with between approximately 0.4% and approximately 0.6% by weight of Pd and / or between approximately 1, 6% and approximately 3.2% by weight of Co relative to the weight of the catalyst.
• the zeolite constituting the NO x reduction catalyst of the invention has a Si / Al molar ratio equal to 5.5.
• FIG. 1 illustrates the percentages of conversion of NO X and CH 4 obtained with a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores" exchanged with 0.5% by weight of Pd relative to the total weight of the catalyst, in the presence of 10% oxygen, depending on the reduction temperature.
• FIG. 2 illustrates the percentages of conversion of NO x and CH4 using a catalyst according to the invention consisting of a zeolite of mordenite type with "small pores” exchanged with 1.9% by weight of Co relative to the total weight catalyst in the presence of 10% oxygen, depending on the reduction temperature.
• FIG. 3 illustrates the percentages of conversion of NO x and of CH 4 using a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores” exchanged with 1.9% by weight Co and 0.6% by weight weight of Pd, in the presence of 10% oxygen, as a function of the reduction temperature.
• the catalyst in particular for selective reduction of NO x , according to the invention is a zeoli ⁇ : he of mordenite structure of the so-called “small pore” variety, that is to say that this zeolite does not adsorb molecules of benzene which have a kinetic diameter of about 6.6 ⁇ .
• a zeolite with a mordenite structure will be called “small pores” when the diameter of these pores is less than 5 ⁇ and will be said to be “large pores” when the diameter of these pores will be larger than 5 ⁇ .
• the zeolite with mordenite structure has a Si / Al molar ratio of 5.5. It is a powdered mordenite in sodium form (NaM) or preferably in ammonium form (NH4M).
• the catalysts of the invention are prepared by exchange from a solution of cobalt, palladium or palladium / cobalt salts, in a manner known per se.
• the salts used for the exchanges in aqueous solution are palladium tetramine and cobalt acetate.
• the zeolites are then shaped into granules by pelleting with about 10% by weight relative to the total weight of the catalyst of a silica-based binder, then granulation and sieving to 0.5 - 1 mm.
• the catalysts are then activated in air at 500 ° C for two hours and then evaluated in catalytic reduction by methane in a tubular stainless steel reactor surrounded by heating shells.
• the temperature is controlled by regulators and the concentration of the various gases at the inlet of the reactor is ensured by flowmeters mass.
• the NO and NO2 concentrations in the gas mixtures were measured by chemiluminescence, and the N2O concentrations by infrared.
• a zeolite with a mordenite structure with "small pores” has already been used for the reduction of nitrogen oxides in the presence of oxygen.
• this reduction is carried out using ammonia as the reducing agent and the zeolite was exchanged with copper.
• Two catalysts were then prepared, one consisting of a zeolite with a mordenite structure with "small pores” exchanged with 2.5% by weight of Cu and the other consisting of a zeolite with a mordenite structure with "large pores "exchanged with 2.25% Cu, as described above. These two catalysts were tested for their NO x to nitrogen conversion activities using ammonia as a reducing agent in the presence of 5% oxygen.
• a catalyst consisting of a "small pore” mordenite it has been discovered that, surprisingly, a catalyst consisting of a structural zeolite "small pore” mordenite exchanged with Co and / or Pd made it possible to obtain conversion percentages of NO X to N 2 much higher than those obtained using the same catalyst, but consisting of a "large pore” zeolite , even in the presence of water, oxygen and even sulfur compounds such as SO2 as will be discussed below.
• Example 1 To better understand the object and the advantages of the invention, several modes of implementation will now be described by way of purely illustrative and non-limiting examples.
• Example 1
• a catalyst consisting of a “small pore” mordenite structure zeolite exchanged with 0.5% by weight of Pd relative to the total weight of the catalyst was prepared, as described previously.
• the basic mordenite was a mordenite in its ammonium form. This catalyst was then tested under the following conditions:
• the catalyst according to the invention consisting of a zeolite with mordenic structure with "small pores" exchanged with 0.5% by weight of palladium by compared to total weight of the catalyst has good NO x reduction activity at relatively low temperatures between 300 and 250 ° C.
• the maximum conversion obtained is approximately 53% at 400 ° C and this in the presence of 10% by volume relative to the total volume of gas, of oxygen.
• Example 2 NO x reduction activity of a catalyst according to the invention containing 1.6% by weight of Co
• a catalyst consisting of a zeolite with a mordenite structure with "small pores”, exchanged with 1.6% by weight of cobalt relative to the total weight of the catalyst, was prepared as described previously from a mordenite in ammonium form.
• a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores” exchanged with 1.6% by weight of palladium relative to the total weight of the catalyst, has a NO x conversion activity much higher than those of the prior art at the same reduction temperature, that is to say 450 ° C.
• patent US 149 512 reported a percentage of conversion of NO X of 27% at 450 ° C with a mordenite with "large pores” whereas with the catalyst of the invention a percentage of conversion of NO x included is obtained. between 60 and 65% between 400 and 450 ° C and this in the presence of 10% oxygen.
• a catalyst consisting of a zeolite with a mordenite structure with "small pores” exchanged with 1.6% by weight of cobalt and 0.47% by weight of palladium relative to the total weight of the catalyst was prepared under the same conditions as above from an ammonium-shaped ordenite.
• the bimetallic Pd / Co catalyst has strong activity over a wide range of temperatures. It is also noted that the NO x transformation rate is exalted at 400 ° C. In fact, it is of the order of 70% with total conversion of methane and this in the presence of 10% of oxygen.
• Two catalysts were prepared from, respectively, a zeolite of mordenite structure with "small pores” of ammonium form exchanged with 0.5% by weight relative to the total weight of the catalyst, of Pd and a zeolite of structure "Large pore” ammonium mordenite exchanged with 0.5% by weight relative to the total weight of the catalyst, of Pd, under the same conditions as above.
• the catalyst consisting of a "small pore” mordenite structure zeolite exhibits a higher activity than the catalyst consisting of a "large pore” mordenite.
• a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores” in the ammonium form exchanged with 1.9% by weight of Co relative to the total weight of the catalyst, a catalyst consisting of a zeolite with a mordenite structure with "small pores” in ammonium form exchanged with 0.6% by weight of Pd relative to the total weight of the catalyst, and a catalyst constituted by a zeolite with mordenite structure with "small pores” in ammonium form exchanged with 1.2 % by weight of Co and 0.6% by weight of Pd relative to the total weight of the catalyst, were prepared under the same conditions as above.
• test conditions were as follows:
• a catalyst according to the invention consisting of a zeolite with a mordenite structure, in ammonium form with "small pores”, exchanged with 3.2% by weight of cobalt relative to the total weight of the catalyst and a catalyst according to the invention consisting of a zeolite with a mordenite structure in ammonium form with "small pores” exchanged with 2.8% by weight of Co and 0.4% by weight of palladium relative to the total weight of the catalyst were synthesized as above. These two catalysts were tested under the same conditions as above.
• a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores", in ammonium form, exchanged with 0.59% by weight of Pd and 1.18% by weight of Co relative to the total weight of the catalyst was prepared as before.
• This catalyst was tested with a reaction mixture containing increasing amounts, up to 10% by volume relative to the total volume of the reaction mixture of oxygen.
• test conditions were as follows
• a catalyst according to the invention consisting of a zeolite with a mordenite structure with "small pores", in ammonium form, exchanged with 0.50% by weight of Pd ez 2.56% by weight of Co relative to the total weight of the catalyst was prepared as before.
• This catalyst corresponds substantially to the catalyst of Example 3.
• This catalyst was tested with a reaction mixture containing between 0% and 10% of water.
• test conditions were as follows:
• Catalysts are generally very sensitive to the presence of water.
• Catalysts are known to have a very high sensitivity to "sulfur poisons".
• Example 6 The catalyst of Example 6 was then tested in the presence of 3% by volume, relative to the total gas volume, of water and of 0.50 ppm and 500 ppm of SO2, respectively.
• test conditions were as follows Test conditions NO 200 ppm CH 4 300 ppm
• the bimetallic catalyst according to the invention therefore has many advantages and is a particularly preferred embodiment thereof.
• test conditions were as follows:
• test conditions were as follows

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• 1996
  • 1996-10-10 FR FR9612386A patent/FR2754468B1/fr not_active Expired - Fee Related
• 1997
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