DE102011121971A1 - Process for modifying the pore size of zeolites - Google Patents

Abstract

The present invention relates to a process for modifying the adsorption capacity of zeolites, comprising the steps of a) providing a metal-exchanged, silicon-rich zeolite, b) treating the zeolite with an aqueous solution of an alkali metal silicate, c) filtering, drying and calcining the treated zeolite d) Reacting the calcined zeolite with an ammonium compound and then calcining. Furthermore, the present invention comprises a modified zeolite obtainable by means of the process according to the invention and its use as a catalyst for the selective reduction of hydrocarbons.

Description

The present invention relates to a process for the modification of the pore size of zeolites as well as to zeolites obtainable by the process which are suitable inter alia as a catalyst for the selective catalytic reduction (SCR) of hydrocarbons.

Metal-doped zeolites are known from the prior art and are used, for example, as catalysts in stationary and mobile exhaust gas purification. In particular, they are often used in catalytic converters for the purification of diesel exhaust gases in internal combustion engines.

Due to the harmful impact of nitrogen oxide emissions on the environment, it is important to further reduce these emissions. Significantly lower NO _x emission limits for stationary and automotive exhaust gases than currently available are foreseen in the United States in the near future and are also under discussion in the European Union.

In order to achieve these limits, in the case of mobile combustion engines (diesel engines), this can no longer be met by internal engine measures alone, but only by exhaust aftertreatment, for example with suitable catalysts.

The denitrification of combustion exhaust gases is also referred to as DeNO. In automotive engineering, selective catalytic reduction (SCR) is one of the most important DeNO _x techniques. As the reducing agent commonly used hydrocarbons (HC-SCR) or ammonia (NH ₃ -SCR) and NH ₃ precursors such as urea (Ad-Blue ^®). Metal-exchanged zeolites (also called "metal-doped zeolites") have proven to be very active SCR catalysts that can be used in a wide temperature range. They are mostly non-toxic and produce less N ₂ O and SO ₃ than the usual V ₂ O ₅ based catalysts. In particular, iron-doped zeolites, by virtue of their high activity and resistance to sulfur under hydrothermal conditions, are good alternatives to the conventionally employed vanadium catalysts. Conventional methods of doping zeolites with metals include, for example, methods such as liquid ion exchange, solid phase ion exchange, vapor phase ion exchange, mechanochemical processes, impregnation processes and the so-called ex-scaffolding procedures.

In the case of the SCR process, it is important to cope with two different tasks, since on the one hand hydrocarbons are to be separated from the exhaust gas stream and, on the other hand, a catalytic denitration using iron- or copper-doped zeolites is required. Used as a hydrocarbon trap (so-called cold start trap) is often zeolite material in the H-form.

Zeolites used as hydrocarbon trap have certain characteristic properties. Thus, the hydrocarbon uptake capacity should be as high as possible and the zeolites should simultaneously have a high hydrocarbon desorption temperature. A high desorption temperature is particularly advantageous since the desorption step thus simultaneously serves for the oxidation of the hydrocarbons and the latter proceeds more completely at higher temperatures.

In contrast, when zeolites are used in SCR catalysis, a high hydrocarbon adsorption capacity is disadvantageous. However, to ensure the catalytic activity for the SCR reaction, the amount of metal-containing zeolite used is fixed ( DE 10 2007 024 125.0 )

The SCR reaction is temperature dependent. Since these catalysts are preferably used in internal combustion engines in cars or trucks for denitrification of the exhaust stream, a high proportion of hydrocarbons in the SCR zeolite adsorbed because the SCR reaction usually takes place at below 300 ° C, depending on the driving style of the motor vehicle driver. With the strong adsorption of hydrocarbons in the zeolite increases the risk of sudden inflammation when short-term temperature peaks occur. This leads to the destruction of the zeolite material, damage to the catalyst and in the worst case to ignition and explosion of the vehicle.

This problem can be avoided when using narrow pore zeolites as catalysts, for example SAPO-34 with a CHA topology. A disadvantage of the narrow-pored zeolites is that iron loading is almost impossible, in particular by liquid exchange processes. It is known z. Example, the use of copper-exchanged SAPO-34, which leads in the SCR reaction, however, at elevated temperatures to increased nitrous oxide formation and lower stability to water vapor and water. In addition, it is possible that copper-exchanged zeolites may be prone to dioxin formation in the SCR reaction.

The object of the present invention was therefore to provide a process with which zeolites can be obtained which have a high SCR activity and at the same time a low adsorption capacity for hydrocarbons, in particular for aromatic hydrocarbons.

• a) Bereitstellens eines metallausgetauschten, siliziumreichen Zeolithen,
• b) Behandelns des Zeolithen mit einer wässrigen, Lösung eines Alkalisilikats,
• c) Filtrierens, Trocknens und Kalzinierens des behandelten Zeolithen
• d) Umsetzens des kalzinierten Zeolithen mit einer Ammoniumverbindung und anschließendem erneuten Kalzinieren

This object is achieved by a method for modifying the adsorption capacity of zeolites, comprising the steps of

• a) providing a metal-exchanged, silicon-rich zeolite,
• b) treating the zeolite with an aqueous solution of an alkali silicate,
• c) filtering, drying and calcining the treated zeolite
• d) reacting the calcined zeolite with an ammonium compound and then re-calcining

Surprisingly, the process of the present invention allows the size of the input spores of zeolites to be reduced, i. H. However, that no or less hydrocarbons, especially aromatic hydrocarbons can diffuse or penetrate into the interior of the zeolite, but leaves the internal structure of the zeolite, in particular the diameter of its inner channels unchanged.

The term "zeolite" is used in the context of the present invention as defined by the International Mineralogical Association ( DS Coombs et al., Can. Mineralogist, 35, 1997, 1571 ) a crystalline substance from the group of aluminum silicates with spatial network structure of the general formula M ^{n +} _n [(AlO ₂ ) _x (SiO ₂ ) _y ] i ^t H ₂ O understood that consist of SiO ₄ / AlO ₄ tetrahedra, which are linked by common oxygen atoms to a regular three-dimensional network. The ratio of Si / Al = y / x is always ≥ 1 according to the so-called "Loewenstein rule", the occurrence of the neighboring two adjacent negatively charged AlO ₄ ^- tetrahedra forbids. Although there are more exchange sites for metals available at a low Si / Al ratio, the zeolite is becoming increasingly thermally unstable.

The zeolite structure contains voids and channels characteristic of each zeolite. The zeolites are classified according to their topology into different structures (see above). The zeolite framework contains open cavities in the form of channels and cages that are normally occupied by water molecules and extra framework cations that can be exchanged. An aluminum atom has an excess negative charge which is compensated by these cations. The interior of the pore system represents the catalytically active surface. The more aluminum and the less silicon a zeolite contains, the denser the negative charge in its lattice and the more polar its internal surface. The pore size and structure are determined by the Si / Al ratio, which affects most of the catalytic character of a zeolite, in addition to the parameters of preparation (use or type of template, pH, pressure, temperature, presence of seed crystals). In the present case, it is particularly preferred if the Si / Al ratio of a zeolite according to the invention is in the range from 10 to 500 (corresponds to a ratio (modulus) of SiO ₂ / Al ₂ O ₃ of 20-1,000), preferably from 10 to 300 ,

In liquid exchange processes for the preparation of metal-exchanged (doped) zeolites, there is a strong affinity for the exchange of polyvalent and heavy metal cations for lighter cations, and in particular against hydrogen and / or NH ₄ ⁺ .

In the case of the hydrated zeolites, the dehydration is usually carried out at temperatures below about 400 ° C and is for the most part reversible.

The presence of 2- or 3-valent cations as a tetrahedral center in the zeolite framework, the zeolite receives a negative charge in the form of so-called anion sites, in the vicinity of which are the corresponding cation positions. The negative charge is compensated by the incorporation of cations in the pores of the zeolite material. The zeolites are mainly distinguished by the geometry of the cavities formed by the rigid network of SiO ₄ / AlO ₄ tetrahedra. The entrances to the cavities are formed by 8, 10 or 12 "rings" (narrow, medium and large pore zeolites). Certain zeolites show a uniform structure structure (eg ZSM-5 with MFI topology) with linear or zigzag-shaped channels, in others close larger cavities behind the pore openings on, for. B. in the Y and A zeolites, with the topologies FAU and LTA. In general, 10 and 12 "ring" zeolites are preferred according to the invention.

In principle, any zeolite, in particular any 10 and 12 "ring" zeolite, can be used in the context of the present invention. Zeolites having the topologies AEL, BEA, CHA, EUO, FAO, FER, KFI, LTA, LTL, MAZ, MOR, MEL, MTW, LEV, OFF, TON and MFI are preferred according to the invention. Very particular preference is given to zeolites of the topological structures BEA, MFI, FER, MOR, MTW and TUN. According to the invention zeolite-like materials can also be used, as for example in the US 5,250,282 are described, the disclosure of which is fully incorporated herein by reference. Further inventively preferred zeolite materials are mesoporous zeolite materials of silicates or aluminosilicates, which are known under the name M41S and described in detail in the US 5,098,684 and the US 5,102,643 are described, the disclosure of which is also fully incorporated by reference.

Furthermore, so-called silicoaluminum phosphates (SAPOs) can be used according to the invention, which can be prepared from isomorphously exchanged aluminum phosphates.

Important for all of the aforementioned materials is only that you have a maximum of a "10-ring topology".

Typically, the metal content or degree of exchange of a zeolite is significantly determined by the metal species present in the zeolite. In this case, the zeolite can be doped with only a single metal or with different metals.

There are usually three different centers in zeolites, referred to as α, β and γ positions, which define the position of exchange sites (also referred to as "interchangeable locations"). All of these three positions are accessible to reactants during the NH ₃ -SCR reaction, particularly when using MFI, BEA, FER, MOR, MTW, and TRI zeolites.

The so-called α-type cations show the weakest binding to the zeolite framework and are last filled in a liquid ion exchange. The occupancy rate is strongly increasing with increasing metal content from an exchange rate of about 10% and amounts to a total of about 10 to 50% at a degree of exchange to M / Al = 0.5. Cations at this point represent very active redox catalysts.

The β-type cations, on the other hand, show an average binding strength to the zeolite framework, which in the liquid ion exchange, especially at low exchange rates, represent the most occupied position and most effectively catalyze the HC-SCR reaction. This position is filled up immediately after the γ-position and its occupancy rate decreases from an exchange rate of about 10% with increasing metal content and is about 50 to 90% for a degree of exchange to M / Al = 0.5. It is known in the prior art that, starting from a degree of exchange of M / Al> 0.56, typically only polynuclear metal oxides are deposited or deposited.

The γ-type cations are those cations with the strongest binding to the zeolite framework and thermally most stable. They are the least occupied position in liquid ion exchange, but are filled up first. Cations, especially iron and cobalt, at these positions are highly active and are the most catalytically active cations.

The preferred metals for exchange and doping are catalytically active metals such as Fe, Co, Ni, Cu, Ag, Co, V, Rh, Pd, Pt, Ir, most preferably Fe, Co, Ni and Cu, in particular preferred embodiments Fe or Cu, which can also form bridged dimeric species, as they are mainly present at high exchange degrees.

Overall, the amount of metal calculated as the corresponding metal oxide 1 to 5 wt .-% based on the weight of the metal-doped zeolite. It is especially preferred that more than 50% of the exchangeable sites (ie α, β and γ sites) are replaced. Most preferably, more than 70% of interchangeable sites are replaced. However, vacancies should still remain, which are preferably Brønsted acid sites. This is because NO is strongly absorbed at both the exchanged metal centers and also at ion exchange sites or at Brønstedt centers of the zeolite framework. In addition, NH ₃ preferentially reacts with the strongly acidic Brønstedt centers, the presence of which is therefore very important for a successful NH ₃ -SCR reaction. The simultaneous presence of free residual exchange sites and / or Brønstedt acidic centers and the metal-exchanged lattice sites is thus according to the invention very particularly preferred. Therefore, a degree of exchange of 70-90% is most preferred. At more than 90% degree of exchange, activity reduction was observed in the reduction of NO to N ₂ and the SCR-NH ₃ reaction.

Due to the risk of hydrothermal deactivation of metal-exchanged zeolites, which precedes dealumination and migration of metal from the ion exchange centers of the zeolite, it is preferred that the doping metals do not form a stable compound with aluminum, as this promotes dealumination.

The treatment with an alkali silicate under the conditions according to the invention surprisingly leads to a reduction in the pore size of the input pores, which in turn leads to a significantly lower hydrocarbon loading due to the reduced accessibility of the inner zeolite surface for larger organic molecules.

According to the invention, the term "alkali metal silicate" is understood to mean aqueous basic solutions of SiO ₂ which can be represented by the general formula M ₂ O.SiO ₂ , where M is one or more alkali metals, ie Li, Na or K. Such compounds are often referred to as water glass or as alkali metal salts of silica.

It is preferred that the average pore sizes (determined according to DIN 66135 according to the method of Horvath-Kawazoe) of the zeolites used in the invention in the range of 0.4 to 1.5 nm.

In one embodiment of the method according to the invention, a zeolite is used which has a mean pore size of 0.5 to 0.6 nm.

In developments of the present invention, the zeolite is selected from the group consisting of ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BPH, BRE, BSV, CAN, CAS, CDO, CFI, CGF, CGS, CHA, CHI, -CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA , GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, IMF, ISV, ITE, ITH, ITR, ITW, IWR, IWS, IWV, IWW, JBW, JRY, KFI, LAU, LEV, LIO, LIT , LOT, LOV, LTA, LTF, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MRE, MSE, MSO, MTF, MTN, MTT, MTW, MVY , MWW, NAB, NAT, NES, NON, NPO, NSI, OBW, OFF, OSI, OSO, OWE, PAR, PAU, PHI, PON, PUN, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR , RWY, SAF, SAO, SAS, SAT, SAV, SBE, SBN, SBS, SBT, SFE, SFF, SFG, SFH, SFN, SFO, SFS, SGT, SIV, SOD, SOF, SOS, SSF, SSY, STF , STI, STO, STT, STW, SVR, SZR, TER, THO, TOL, TONE, TSC, TUN, UEI, UFI, UOS, UOZ, USI, UTL, VET, VFI, VNI, VSV, WEI, WEN, YUG and ZON.
their crystal structures according to IZA under http://www.izaonline.org/ are described.

In certain embodiments of the invention zeolites are used which have a maximum of a "10-ring topology", such as. MFI, MEL and DO. In one embodiment of the present invention, MFI is used. Similarly, a zeolite with MOR topology can be used.

The zeolites can be used both in their H or NH ₄ form, usually the H form is preferred.

The metal-exchanged zeolite can in this case be prepared and reused directly in situ by means of customary methods known to the person skilled in the art, or a commercially available metal-exchanged zeolite can also be used in the process according to the invention.

The silicon-rich zeolite is selected according to the invention so that it has an Si-Al ₂ (SiO ₂ / Al ₂ O ₃ ) ratio (modulus) of between 20 and 1000, in developments of the invention from 20 to 200.

The preferred application for zeolites obtained according to the invention is exhaust gas catalysis. The zeolites must therefore be hydrothermally stable. Under a SiO ₂ / Al ₂ O ₃ ratio of 20, the hydrothermal stability is too low. If the modulus is too high, the ion exchange capacity, ie the amount of exchangeable metal, is too low and the metal exchanged zeolite is therefore less active in the SCR reaction.

The metal of the metal-exchanged zeolite is selected in embodiments of the method according to the invention from the group consisting of Fe, Cu, Co, Mn, Au, Ag, Ru, Ce, Rh, Pt, Pd, Zr, Ag, W, La, as well as mixtures thereof, most preferably Fe, Cu, Co, Ni. In specific embodiments of the present invention, as already mentioned above, the metal is iron or copper.

In preferred embodiments of the process, the calcination in step d) and f) is carried out at a temperature of 450 ° C to 750 ° C. At higher temperatures, the zeolite structure is damaged.

The ammonium compound used in step e) is preferably ammonium nitrate or ammonium sulfate, in particular for reasons of cost. However, it is possible to use other ammonium compounds as well.

The object of the present invention is further achieved by providing a zeolite with a modified, preferably reduced pore size of the entrance pores obtainable by the process according to the invention described in detail above. In this context, it is important to point out again that the inner channels remain unchanged in their structure or their diameter.

The zeolite is preferably metal-containing and the metal is selected from the group consisting of Fe, Cu, Mn, Au, Ag, Ru, Ce, Rh, Pt, Pd, Zr, Ag, W, La and mixtures thereof. In preferred embodiments, the metal is selected from Fe, Cu and Mn, or mixtures thereof.

Typically, the zeolite is in the H-form or ammonium form, so that, if necessary, a further exchange can take place.

The zeolite obtainable according to the invention is used as catalyst or adsorber. In preferred embodiments of the present invention, the zeolite obtainable according to the invention finds use in the selective reduction of nitrogen oxides (SCR) in the presence of hydrocarbons, especially in motor vehicles.

The invention is explained in more detail below with reference to figures and exemplary embodiments, without these being to be understood as limiting.

Figure 4 shows a diffraction pattern of a prior art Fe-MFI zeolite and a reduced pore size zeolite of the present invention

shows a toluene TPD diagram of Fe-MFI of the prior art

shows a toluene TPD diagram of inventive Fe-MFI

Figure 10 shows a benzene TPD diagram of Fe-MFI of the prior art

shows a benzene TPD diagram of inventive Fe-MFI

Methods section:

The methods and devices used are listed below, but should not be construed as limiting.

Determination of the BET surface area:

The BET surface area was determined according to DIN 66131 (Multipoint determination), as well as after the DIN ISO 9277 , according to the European standard 2003-05 issued determination of the specific surface area of solids by gas adsorption by the BET method (according to Brunauer, S .; Emett, P .; Plate, EJ Am. Chem. Soc. 1938, 60, 309. ) with a gem of the Fe. Micromeritics: 0.100 g of powdered sample was left for 30 min. baked at 350 ° C, then connected to the vacuum and while heated at 350 ° C in vacuo until a pressure of <0.1 mbar was reached. After cooling under vacuum and N ₂ addition, the sample was reweighed in the baked state. Measurement: 5 point BET measurement with N ₂ at the temperature of liquid nitrogen in the p / p 0 range 0.004-0.14.

Determination of the pore size distribution

The determination of the pore size distribution was carried out according to the DIN 66135 according to the method of Horvath-Kawazoe.

TPD measurement

The TPD measurement was carried out by means of an Autochem II instrument from Micromeritics benzene / toluene-TPD and was carried out as follows: Pretreatment: He-flow, 5 ° C / min. from room temperature to 350 ° C, hold for 2 h, cool to 40 ° C loading: Pass He-pulses enriched with benzene / toluene (vapor pressure at 40 ° C) through the sample until constant peak areas are obtained (maximum 20 pulses); Desorption: He-flow, 10 ° C / min. from 40 ° C to 500 ° C, hold for 2 h Detection: with mass spectrometer (benzene: amu = 78, toluene: amu = 91)

XRD measurement

The XRD measurements were carried out by means of a D4 Endeavor device from Bruker; Measurement parameters: Scan type: locked coupled Scan mode: continuous 2 theta range: 5-50 Step size: 0.030 deg 2 theta Time / step: 3.0 sec. Divergence slit: V12 mm Sample rotation: 30 rpm XRay tube: Cu 40 kV, 40 mA.

embodiments

Example 1: Preparation of a reduced-pure-size (RPS) -MFI zeolite

100 g of a Fe-MFI zeolite (commercially available as Fe-TZP-302 from Süd-Chemie Zeolites GmbH Bitterfeld) are dispersed in 400 g of distilled water. Then 140 g of a Na silicate solution (SiO ₂ content 26.7 wt .-%) are added. The mixture is heated to 55 ° C and stirred for about 30 min. Subsequently, the zeolite is filtered off and calcined at 600 ° C for 3 h.

Example 2: XRD / BET measurement

shows a comparison of a diffraction pattern of the original Fe-MFI and the RPS-Fe-MFI. It can be clearly seen that the framework structure of the RPS-Fe MFI is still intact and shows the typical diffraction pattern of a zeolite with MFI structure. Table 1 shows the measured BET surface areas for Fe-MFI and RPS-Fe-MFI. There is a slight decrease in the BET surface area. However, the remaining surface area of almost 300 m ² / g is still sufficient for using this material as a catalyst. Table 1: Comparison of BET Surfaces zeolite BET [m ² / g] Fe-MFI 364 RPS-Fe-MFI 297

Example 3: Toluene TPD and benzene TPD

The narrowing of the pores of the zeolite according to the invention can be easily detected on the basis of adsorption experiments. With a significant pore narrowing, the adsorption of larger (eg cyclic or branched) hydrocarbons will decrease significantly. Therefore, toluene and benzene TPD measurements were performed. The sample to be measured is baked for 2 hours at 350 ° C in a helium stream. Then loaded at 40 ° C with toluene or benzene and then heated at a heating rate of 10 K / min to 500 ° C. Subsequently, the toluene or benzene desorption was measured as a function of temperature by means of a mass spectrometer.

and The toluene TPD measurements show Fe-MFI and RPS-Fe-MFI. Table 2 shows the desorbed total amounts of toluene. Table 2: Comparison of desorbed amount of toluene zeolite Toluene desorption [μmol / g sample] Fe-MFI 491 RPS-Fe-MFI 147

It can be seen on the one hand that with RPS-Fe-MFI the desorbed amount of toluene is lower by a factor of 3.3 than in the case of Fe-MFI. On the other hand, the maximum desorption curve for RPS-Fe-MFI is shifted by about 40 ° C to a higher temperature. Both results show that the treatment method according to the invention has led to a reduction of the pores.

The adsorption of the smaller benzene molecule also shows differences between RPS-Fe-MFI and Fe-MFI. This is in the and and Table 3. Table 3: Comparison of desorbed amount of benzene zeolite Benzene desorption [μmol / g sample] Fe-MFI 471 RPS-Fe-MFI 254

For RPS Fe MFI, the desorbed amount of toluene is lower by a factor of 1.85 than in Fe MFI. Although the difference is smaller than in toluene adsorption, it is still significant.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007024125 [0008]
• US 5250282 [0019]
• US 5098684 [0019]
• US 5102643 [0019]

Cited non-patent literature

• DS Coombs et al., Can. Mineralogist, 35, 1997, 1571 [0014]
• DIN 66135 [0032]
• http://www.izaonline.org/ [0034]
• DIN 66131 [0054]
• DIN ISO 9277 [0054]
• European standard 2003-05 [0054]
• Brunauer, S .; Emett, P .; Plate, EJ Am. Chem. Soc. 1938, 60, 309. [0054]
• DIN 66135 [0055]

Claims (11)

A process for modifying the adsorption capacity of zeolites, comprising the steps of a) providing a metal-exchanged, silicon-rich zeolite, b) treating the zeolite with an aqueous solution of an alkali silicate, c) filtering, drying and calcining the treated zeolite d) reacting the calcined zeolite with an ammonium compound and then calcining. The method of claim 1, wherein a zeolite is used which has a pore size of 0.4 to 0.8 nm. The method of claim 2, wherein the zeolite is selected from the group consisting of ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC , APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BPH, BRE, BSV, CAN, CAS, CDO, CFI, CGF, CGS , CHA, CHI, CLO, CON, CZP, DAC, GDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA , GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, IMF, ISV, ITE, ITH, ITR, ITW, IWR, INS, IWV, IWW, JBW, JRY, KFI, LAU, LEV, LIO, - LIT, LOT, LOV, LTA, LTF, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MRE, MSE, MSO, MTF, MTN, MTT, MTW, MVY, MWW, NAB, NAT, NES, NON, NPO, NSI, OBW, OFF, OSI, OSO, OWE, -PAR, PAU, PHI, PON, PUN, RHO, RON, RRO, RSN, RTE, RTH, RUT , RWR, RWY, SAF, SAO, SAS, SAT, SAV, SBE, SBN, SBS, SBT, SFE, SFF, SFG, SFH, SFN, SFO, SFS, SGT, SIV, SOD, SOF, SOS, SSF, SSY , STF, STI, STO, STT, STW, SVR, SZR, TER, THO, TOL, TONE, TSC, TUN, UEI, UF I, UOS, UOZ, USI, UTL, VET, VFI, VNI, VSV, WEI, WEN, YUG and ZON. The method of claim 3, wherein the silicon-rich zeolite is selected to have a Si-Al ratio between 20 to 1000. The method of claim 4, wherein the metal of the metal-exchanged zeolite is selected from the group consisting of Fe, Cu, Mn, Au, Ag, Ru, Ce, Rh, Pt, Pd, Zr, Ag, W, La, and mixtures thereof. A process according to claim 5, wherein the calcination in step c) and d) is carried out at a temperature of 450 ° C to 750 ° C. The method of claim 6, wherein ammonium nitrate or ammonium sulfate is used as the ammonium compound in step d). Zeolite with reduced pore size of the entrance pores obtainable by the process according to one of claims 1 to 7. The zeolite of claim 8, wherein the zeolite is metal-containing and the metal is selected from the group consisting of Fe, Cu, Mn, Au, Ag, Ru, Ce, Rh, Pt, Pd, Zr, Ag, W, La, and mixtures thereof , Use of the zeolite according to claim 8 or 9 as catalyst or adsorber. Use according to claim 10 for the selective reduction of nitrogen oxides in the presence of hydrocarbons.

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