Classifications

• • 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
  • B01J37/082—Decomposition and pyrolysis
  • B01J37/088—Decomposition of a metal salt
• • 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
• • 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
  • B01J29/049—Pillared clays
• • 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/701—Integrated with dissimilar structures on a common substrate
  • Y10S977/712—Integrated with dissimilar structures on a common substrate formed from plural layers of nanosized material, e.g. stacked structures

Definitions

• the invention relates to a process for the production of catalytically active sheet silicates with one or more intermediate layers, in particular Al and / or tipped coated clays.
• Catalysts in particular denox catalysts, that is to say those for removing nitrogen oxides (NO x ) in exhaust gases, are used on a large scale in exhaust gas aftertreatment in motor vehicles.
• the catalysts consist of a carrier material with an active coating and shake-proof, temperature-insulated storage in a housing. Granulate and monolite sintered from AI2O 3 are used as carrier materials.
• the active catalyst layer consists of small amounts of precious metals (Pt, Rh, Pd) and is known to be sensitive to lead.
• Such automotive or three-way or selective catalysts have proven themselves and are used to reduce NO in a first step while generating NH 3 . After adding secondary air, the almost complete oxidation of CO and HC can then take place in a second step. NH 3 also burns back to NO.
• the charge cations in the intermediate layers of the respective layered silicates can be replaced by larger inorganic hydroxymetal cations. This happens in a mostly aqueous solution.
• the resulting substance is then dried and calcined (cf. the article by RQ Long and RT Yang "The promoting role of rare earth oxides on Fe-exchanged TiO2-pillared clay for selective catalytic reduction on nitric oxide by ammonia"; Applied Catalysis B: Environmental 27. (2000) 87-95). This is complex from the course of the process. The invention seeks to remedy this overall.
• the invention is based on the technical problem of specifying a process for producing catalytically active sheet silicates, with the aid of which a largely emission-free catalyst base material can be produced in a simple manner.
• the subject of the invention is a process for the production of catalytically active layered silicates, in particular nano-positive layered silicates, with one or more intermediate layers, in particular Al- and / or Ti-pillared clays, after which the layered silicate is given a metal solution, preferably polycationic Metal solution, added and then the mixture is dried to produce metal atom pillars supporting the respective interlayer, after which a metal salt, in particular transition metal salt, is further added to the dry substance thus formed to produce a dry mixture, and then the dry mixture is heated so that yourself the metal atoms or. Store transition metal atoms under gas in the intermediate layer. As a result, a cation exchange takes place in the intermediate layers through dry mixing and heating.
• a metal solution preferably polycationic Metal solution
• the catalytically active layered silicates are usually so-called nanocomposite layered silicates, that is to say those layered silicates in which the described solid ion exchange or. the incorporation of the metal atoms or transition metal atoms takes place in the nanometer range.
• nanocomposite layered silicates that is to say those layered silicates in which the described solid ion exchange or. the incorporation of the metal atoms or transition metal atoms takes place in the nanometer range.
• This mainly includes metal oxides or.
• Metal polyoxides basically metal compounds (with oxygen), which provide the supportive effect through the formation of pillars in the respective intermediate layer.
• the layer metal silicate is the metal solution or.
• polycationic metal solution or metal ion complex solution is added and then the mixture is dried to form pillars or pillars supporting the respective intermediate layer, calcined and, if necessary, added in ammonium form. This usually takes place in an alkaline environment, with sodium hydroxide solution mostly being used to prepare the metal solution.
• Layered silicate the sodium hydroxide or aluminum hydroxide previously in solution is excreted and the metal ions or. Metal complex ions are stored in the Intermediate layers from or on the surfaces of the layered silicates. After drying, they form pillars in the nanometer range in the intermediate layer. As a result, the intermediate layers or spaces between the silicate layers are not only widened, but also defined in terms of the layer spacing.
• an aluminum and / or titanium and / or iron solution as the metal solution.
• copper and / or chromium solutions or a polyoxide mixture of these metals can be used.
• any transition metals in pure form or as mixtures are particularly suitable for this.
• the use 'of titanium chloride can be used in combination with sodium hydroxide.
• iron chloride with sodium hydroxide ' This creates aluminum hydroxide (AI (OH) 3 ), for example, by adding solutions of the aluminum salts (here: aluminum chloride) with sodium hydroxide solution or sodium hydroxide (NAOH) in water. Overall, the otherwise poorly soluble aluminum hydroxide is excreted from the solution.
• the wet-chemical modification of the layered silicate described leads to the metal atoms previously in solution (for example Al, Fe, Ti atoms, etc.) being deposited in the intermediate layer or layers of the layered silicates and here metal atom pillars supporting the intermediate layer form after drying. In this way, the gaps between the silicate layers not only widened, but also defined in terms of the layer spacing.
• the catalytic effect can consequently be optimally adjusted over a wide temperature range by mixing the layered silicates which are subjected to different pillaring processes to the dry substance.
• the dry substance produced from the two layer silicates, which were initially pretreated differently, is then subjected, as described, to a solid / solid reaction in conjunction with the metal salt or transition metal salt. If a copper salt is used here, the coating described or the incorporation of the copper atoms into the intermediate layer occurs.
• metal atoms or transition metal atoms which are usually copper atoms, are primarily in connection with the previously created metal atom pillars - made responsible for the catalytic effect.
• a transition metal salt or transition metal atoms it is not only possible to keep the costs of the catalytically active sheet silicate produced in this way low. But especially with copper there is no longer a risk that it will evaporate at the high temperatures prevailing in a catalytic converter and be released into the environment. This is a clear difference to the precious metals such as platinum used up to now.
• the invention recommends washing the mixture of layered silicate and the first polyhydroxide cation complex solution after adding the metal solution, then filtering it and only then heating it slowly, for example to 100 ° C., the reaction forming the hydrated nano -Pillars or metal atom pillar itself takes place at room temperature.
• the subsequent drying process is carried out with a rapid or shock-like temperature increase, starting at approximately 100 ° C. (for example 100 ° C. in approximately 10 minutes or more) up to approximately 500 ° C. (or also above), so that the metal atom pillars described settle in the respective intermediate layer.
• There is a homogeneous distribution of the dehydrated metal atom pillars in the intermediate layers which may be freed of water and (sodium) hydroxide.
• thermal dehydration and the subsequent recombination of the metal atom pillars This recombination is largely irreversible.
• the layered silicate modified in this way is several 100 ° C has the necessary temperature stability to be used as a catalyst.
• the catalytically active cations in the form of mostly transition metal ions made of, for example, titanium, iron, cobalt, nickel, copper, zinc etc. must be embedded in the intermediate layer prepared with the aid of the metal atom pillars.
• transition metal ions made of, for example, titanium, iron, cobalt, nickel, copper, zinc etc.
• non-transition metal atoms i.e. those of the main groups, at this point, such as. B. sodium, potassium, rubidium etc.
• noble metal ions for example gold or silver, which can be added to the transition metal salts in mostly low concentrations as salts. These (noble) metal ions may ensure, as it were, doping of the mostly incorporated transition metal ions.
• NO x nitrogen oxides
• N2 nitrogen
• O2 oxygen
• a reducing agent during operation such as. B. Methane.
• the main goal is in any case the selective catalytic chemical reduction of the NO x gases with the help of different .Reductions, such as. B. HC and / or CO and / or NH3.
• the metal as a metal salt is dry-mixed with the previously prepared dry substance from the layered silicates with embedded metal atom pillars. Copper nitrate in particular has been found as metal salts
• Copper salt with release of nitrogen oxides nitrogen dioxide (NO 2 ) or sulfur dioxide (SO 2 ) in the example.
• nitrogen oxides nitrogen dioxide (NO 2 ) or sulfur dioxide (SO 2 )
• SO 2 sulfur dioxide
• an exchange of solids can take place and / or the intermediate layers and / or inner / outer surfaces can also be covered the desired metal atoms or metal atom clusters.
• the bottom line is that metal or copper atoms or ions and / or metal atom clusters remain. or copper atom clusters, which are predominantly embedded in the intermediate layer.
• the remaining metal atoms or metal ions or metal atom clusters occupy the outer surfaces. consequently there is at least partially a thermal exchange of the charge-compensating cations in the intermediate layers of the layered silicates by the aforementioned metal atoms or metal ions, which essentially contribute to the catalytic effect of the layered silicate produced in this way.
• the intermediate layers predominantly result in a uniform distribution of the metal atoms.
• the resulting substance or the end product can be slightly moistened in order to take any shape, optionally with the addition of a binder and optionally a plasticizer.
• This binder may just be water, aluminum oxide or a ceramic material.
• the end product can be easily shaped and processed, for example as part of an extrusion process. In this way, simple monolithic Structures or so-called pellets, ie small moldings, are produced that are directly suitable for use as automotive exhaust gas catalysts. Before that, however, it is still necessary to heat and dry the extrudate or the pellets produced in this way.
• the monolithic structures and the pellets offer the advantage that they are catalytically active over their entire volume. This is different if the catalytically active layered silicate produced by the process described as a coating in conjunction with an (inert) carrier material, such as. B. Coatin is used.
• a coating can be produced, for example, by dropping a solution of the layered silicate according to the invention onto the carrier material. Since the metal atoms in the intermediate layers are arranged in a wide-meshed manner, there is no risk that, when using such a coated support material as a catalyst, undesired sintering processes occur in operation, which reduce the catalytic effect. This advantage is of course even more pronounced when using monolithic catalysts made from the layered silicate according to the invention or pellets, that is to say a more or less coarse-grained granulate.
• two-layer minerals such as kaolinite or aluminum silicates can be used as layered silicate.
• the invention is preferably used for three-layer minerals or even four-layer minerals. Montmorillonite or ben- proven tonit. Further advantageous measures are described in the claims 15.
• starting material is bentonite, in particular calcium bentonite with the main ingredient montmorillonite used, which is composed of about 57 wt .-% SiO 2, about 23 wt .-% Al2O3, about 3 wt .-% Fe2 ⁇ 3 and about 10 weight .-% H2O is composed.
• This starting material is finely ground to increase the specific inner crystalline surface. Fine grinding can increase the effectiveness of the catalyst base material made from it.
• pillaring i. H. the wet chemical incorporation of pillars (etall) atoms into the two intermediate layers of the three-layer mineral used.
• the finely ground mineral powder is previously dispersed in water, but this is not mandatory because an aluminum hydroxide solution (A10H) is added to the powder or the dispersion anyway.
• A10H aluminum hydroxide solution
• the ratio of the mass of bentonite compared to the volume of the total suspension can be determined and set using the aluminum hydroxide solution in the dispersion. This ratio is a measure of the concentration of the pillaring system, ie a measure of how many pillar atoms are ultimately required in the intermediate layers.
• the aluminum content is of particular importance compared to bentonite. Because if there is too much aluminum in the solution based on the bentonite content, this leads to a decrease in the specific inner surface as a result of the increased formation of aluminum pillars. Likewise, an aluminum content that is too low compared to the bentonite concentration in the solution after the dispersion has the effect that the intermediate layer does not have the required stability, which can be particularly noticeable when the temperature rises.
• the bentonite modified with aluminum pillars in the intermediate layer is dried, as described above. Copper nitrate or copper sulfate is added dry to this dry substance as the metal salt. This dry mixture is then heated to 450 ° C to 550 ° C so that nitrogen dioxide or sulfur dioxide escape and the remaining copper atoms or copper ions are embedded in the previously formed intermediate layer with the aluminum atom pillars.
• layer silicates known per se which have a catalytic effect on an exhaust gas flow and for this purpose use metal atoms made of copper, for example, embedded in the intermediate layer. These copper atoms in the electrical field of the intermediate layer are able to split nitrogen oxides in particular. All of this is achieved through relatively simple wet and dry chemical treatment methods and grinding processes.
• the layered silicate used is equipped with a large specific surface.
• the built-in catalytic in the electrical field formed by the surrounding intermediate layer Cations are firmly integrated into the crystal structure, negative effects that the prior art cannot prevent can practically be ruled out.
• the catalytically active layered silicates produced within the scope of the invention do not tend to have any emissions which are harmful to the environment or to health - not even at elevated temperatures, as are generally observed in motor vehicle exhaust gas catalysts.
• the resulting substance can be shaped directly or by adding a binder, if necessary, for example with the aid of an extrusion process. Complicated shaping processes are therefore no longer necessary. As a result, a practically emission-free catalyst base material is provided, which can also be shaped inexpensively and practically as desired.
• the modified layered silicate produced in the process according to the invention can not only be used as a catalyst base material, but is also suitable for soot filtering in diesel vehicles.
• the intermediate layers absorb the individual soot particles, with the nitrogen oxides (N0 X) in the exhaust ensure that the thus realized soot filter does not become clogged.
• the nitrogen oxides oxidize the carbon of the soot particles to carbon dioxide (CO 2 ) which leaves the soot filter in question in gaseous form. So not only does nitrogen oxides break down, but soot particles are filtered and chemically converted at the same time.
• the individual process steps are shown again in the context of the flow chart shown in FIG. 1.
• the layer material or the starting material is optionally sieved and dried in step 1.1.
• a grinding process is also conceivable as part of process measure 1.1.
• This starting material is then dispersed, for example, in water, as indicated in step 1.2.
• a bentonite dispersion is created.
• the metal solution under 2.1 is prepared by dissolving a metal salt (aluminum salt) with the addition of sodium hydroxide solution and shaping the desired metal solution (aluminum hydroxide solution) according to 2.2.
• the starting dispersion or bentonite dispersion 1.2 and the metal salt solution or aluminum hydroxide solution 2.2 are mixed with one another for the "pillaring" process.
• This can take place with or without ultrasound support to improve the mixture, in the course of process step 3.1.
• the solution or mixture prepared in this way is then washed and filtered in step 3.2 and then dried or calcined as part of measure 4.1. This usually happens at temperatures between 400 ° C and 600 ° C within a period of one to twelve hours.
• This is followed by a sieving process which discharges a dry substance in step 4.2, which contains grain sizes of less than 500 ⁇ m.
• This dry mixture is now intensively dry mixed with the metal salt, for example copper salt, or other metal salts in step 5.1.
• the catalytically active metal atoms or transition metal atoms are embedded in the intermediate layer in the course of procedure 6.1, where this dry mixture is heated or calcined, for a period of one to twelve hours.
• a shaping process as part of measure 6.2 with or without the additional use of binder materials or plasticizers.
• the finished product is available monolithically, as pellets or as a solution for coating a carrier material.
• the end product is particularly resistant to water vapor, which predestines it for use in the exhaust system of a motor vehicle for catalytic exhaust gas purification.

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• 2002
  • 2002-09-30 DE DE10245963A patent/DE10245963A1/de not_active Withdrawn
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