Production of zeolite-based composite materials with hierarchical porosity

Description

[0001] The present invention relates to a method for providing a composite material in which a support structure is provided with a coating which has a zeolitic or zeolite-like component with a controlled intra- and intercrystalline porosity.

[0002] The most widely used technical method for producing a composite material comprising at least one active zeolitic or zeolite-like component and a substrate is coating the substrate with a suitable binder. Conventionally, such active (catalytic or sorption) composite materials are produced by coating a substrate, usually ceramic, with a suspension—the so-called "washcoat"—which contains a binder in addition to the active component (e.g., zeolite). The coating step is followed by a suitable post-treatment (temperature treatment), which then allows the binder to exert its bonding effect (e.g., B. Mitra and D. Kunzru: Washcoating of Different Zeolites on Cordierite Monoliths. In: Journal of the American Ceramic Society, 2008 (91) 64-70).As an industrially relevant example of the use of such a composite material, zeolite-coated ceramic honeycomb structures, used, among other things, in the denitrification of exhaust gas streams, can be mentioned. Besides the aforementioned coating of support structures, the shaping of granules or extrudates for, for example, catalytic or sorptive fixed-bed applications can be understood as a special case of supported composite materials, in which the supporting effect is exerted by the interaction of the binder and the active component itself ("self-supporting system").

[0003] Regardless of whether a self-supporting or a supported system is considered, such materials suffer from the disadvantage of reducing the activity of the resulting material due to the dilution of the active component (zeolite) with the binder material (binder).

[0004] One method that attempts to circumvent this disadvantage, but has not yet achieved large-scale industrial application, is the recrystallization or reactive recrystallization of the zeolitic active component onto an inert or reactive support structure. However, this method is inherently limited to active materials that, from a chemical and structural perspective, offer the possibility of recrystallization – typical examples of which are therefore aluminum- and silicon-containing support materials. Even though binder-free composite materials can be produced in this way (e.g., J. Bauer, R. Herrmann, W. Mittelbach and W. Schwieger: Zeolite / aluminum composite adsorbents for application in adsorption refrigeration. In: International Journal of Energy Research, 2009 (33) 1233-1249; S. Ivanova, B. Louis, B. Madani, JP Tessonnier, MJ Ledoux and C. Pham-Huu: ZSM-5 coatings on β-SiC monoliths: Possible new structured catalyst for the methanol-to-olefins process.In: Journal of Physical Chemistry C, 2007 (111) 4368-4374), this method is subject to significant limitations regarding the choice of support and the combination of support and active component. Furthermore, particularly in the case of crystallization on an inert support material, a considerable amount of excess powder is generated, which does not contribute to the actual production of the composite material (e.g., A. Zampieri, A. Dubbe, W. Schwieger, A. Avhale and R. Moos: ZSM-5 zeolite films on Si substrates grown by in situ seeding and secondary crystal growth and application in an electrochemical hydrocarbon gas sensor. In: Microporous and Mesoporous Materials, 2008 (111) 530-535).

[0005] Furthermore, conventional methods are subject to limitations insofar as the synthesis of nanoscale zeolites, in particular, can only be carried out to a maximum conversion of significantly less than 100% with respect to the network-forming atoms. For example, conversion rates of up to 65% are reported in the literature for the zeolite ZSM-5 (crystal size approx. 100 nm) (CS Tsay and AST Chiang: The synthesis of colloidal zeolite TPA-silicalite-1. In: Microporous and Mesoporous Materials, 1998 (26) 89-99; AE Persson, BJ Schoeman, J. Sterte and JE Otterstedt: The synthesis of discrete colloidal particles of TPA-silicalite-1. In: Zeolites, 1994 (14) 557-567), which necessitates separation processes. One way to circumvent this limitation is the "top-down" approach, in which the nanoscale is achieved by grinding large zeolite crystals.In this case, however, the crystallinity of the resulting nanocrystals decreases significantly, necessitating post-crystallization (T. Wakihara, A. Ihara, S. Inagaki, J. Tatami, K. Sato, K. Komeya, T. Meguro, Y. Kubota and A. Nakahira: Top-Down Tuning of Nanosized ZSM-5 Zeolite Catalyst by Bead Milling and Recrystallization. In: Crystal Growth & Design, 2011 (11) 5153-5158). The latter, however, is disadvantageous for both economic and environmental reasons.

[0006] WO 92 / 19574 A1 discloses a method for producing zeolite layers on a support.

[0007] The object of the present invention was therefore to provide a method by which zeolite materials or zeolite-like materials can be efficiently applied to support structures without the need for an added binder. Furthermore, the method should allow the creation of desired porosity properties.

[0008] As a solution to this problem, the present invention provides a method for producing a composite material with a support structure and a coating on the surface of the support structure, wherein the coating comprises crystals of a zeolite material or a zeolite-like material as an active component, and wherein intercrystalline meso- and / or macropores are formed in the coating. The method according to the invention comprises the following steps: a) Providing a suspension containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material; b) Applying the suspension provided in step a) to the surface of the support structure; c) Condensing the suspension applied in step b) by at least partially removing the solvent that forms the liquid phase of the suspension to obtain a coating containing the starting crystals and the precursor compounds; d) Maintaining the coating obtained in step c) on the surface of the support structure in a vapor-containing atmosphere at an elevated temperature, so that the contained precursor compounds are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating.comprising the crystals of a zeolite material or a zeolite-like material, , wherein the provision of the suspension in step a) is carried out by synthesizing the starting crystals by partially reacting a reaction mixture containing (i) a solvent, and (ii) the precursor compounds of the zeolite material or zeolite-like material, and wherein the suspension thus provided in step b) containing the starting crystals and unreacted precursor compounds is applied to the surface of the support structure without prior isolation of the synthesized starting crystals.

[0009] According to a preferred embodiment, the reaction mixture contains, in addition to the solvent and the precursor compounds of the zeolite material or zeolite-like material (iii), a template species.

[0010] The suspension thus prepared is then applied to the surface of the support structure in step b) together with the starting crystals and unreacted precursor compounds contained in the suspension, without prior isolation of the synthesized starting crystals. Accordingly, the process of this preferred embodiment comprises the following steps: a) Providing a suspension containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material, by synthesizing the starting crystals through partial reaction of a reaction mixture containing (i) a solvent, (ii) the precursor compounds of the zeolite material or zeolite-like material, and (iii) a template species; b) Applying the suspension provided in step a), containing the starting crystals and unreacted precursor compounds, without prior isolation of the synthesized starting crystals, to the surface of the support structure; c) Condensing the suspension applied in step b) by at least partially removing the solvent forming the liquid phase of the suspension to obtain a coating containing the starting crystals and the precursor compounds.d) Holding the coating obtained in step c) on the surface of the support structure in a vaporous atmosphere at an elevated temperature, so that the contained precursor compounds are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating comprising crystals of a zeolite material or a zeolite-like material.

[0011] This method allows for the efficient application of zeolite or zeolite-like materials to support structures without the need for an added binder. The method according to the invention makes it possible to specifically optimize the porosity and activity properties (e.g., catalytic and / or sorptive) of the applied material for a potential application. The porosity of the composite material is determined, on the one hand, by the porosity of the active material itself (e.g., microporous zeolite), on the other hand, by the porosity of the resulting layer, and by any potential porosity of the support material (e.g., a three-dimensional, open cellular structure). Ultimately, a hierarchy of pore size can be established by adjusting process and material parameters.Furthermore, the inventive method opens up the possibility of producing a multifunctionality of the applied material by combining different active components or their precursors already in the suspension, which thereby replaces complex and costly processes such as ion exchange or impregnation.

[0012] Furthermore, particularly with the aid of the embodiment of the invention described above, in which a suspension of nanocrystals and precursor material is generated and subsequently applied as a coating to the surface of the support structure without isolating the nanocrystals, the process achieves extremely high efficiency with regard to the material utilization of the starting materials for the synthesis of nanoscale zeolite materials or zeolite-like materials. Surprisingly, conversion rates of up to 100% with respect to the network-forming atoms are achievable. Complete conversion of the network-forming components thus eliminates the need for processes to separate the nanoscale product from the unreacted components in the product suspension, resulting in drastic savings with respect to both time-consuming and costly separation processes as well as material input.

[0013] Finally, the application of a coating in step a) can be carried out using conventional methods, and without the applied coating undergoing macroscopic changes during the further course of the process (for example, local spreading of the layer due to "running" of the coating, etc.). This opens up the possibility of applying material with the aforementioned benefit to a support structure, even in a locally limited area. The inventive method for producing a composite material with a support structure and a coating on the surface of the support structure, wherein the coating comprises crystals of a zeolite material or a zeolite-like material as an active component and wherein intergranular meso- and / or macropores are formed in the coating, is characterized in that the method comprises the following steps: a) Providing a suspension containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material; b) Applying the suspension provided in step a) to the surface of the support structure; c) Condensing the suspension applied in step b) by at least partially removing the solvent that forms the liquid phase of the suspension to obtain a coating containing the starting crystals and the precursor compounds; d) Maintaining the coating obtained in step c) on the surface of the support structure in a vapor-containing atmosphere at an elevated temperature, so that the contained precursor compounds are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating.comprising the crystals of a zeolite material or a zeolite-like material, , wherein the provision of the suspension in step a) is carried out by synthesizing the starting crystals by partially reacting a reaction mixture containing (i) a solvent, and (ii) the precursor compounds of the zeolite material or zeolite-like material, and wherein the suspension thus provided in step b) containing the starting crystals and unreacted precursor compounds is applied to the surface of the support structure without prior isolation of the synthesized starting crystals.

[0014] The method according to the invention is suitable for use with a variety of support structures in a variety of shapes. For example, two-dimensionally extended structures such as plates, sheets, or films can be used as support structures. These can be planar or shaped. Further examples of suitable geometric shapes for the support structure are granules, tubes, honeycomb structures, or open-cell, foam-like structures. A certain roughness of the surfaces is also advantageous, as it promotes, for example, the stable bonding of the coating in the composite material. Preferably, the support structure is a porous structure, for example, a structure made of a material that has macropores.

[0015] Examples of suitable materials that can form or be contained in the support structure are preferably silicate materials, ceramic materials, metallic materials, or combinations thereof.

[0016] The coating in the composite material formed according to the invention can completely or partially cover the surface of the support structure. As mentioned above, the method according to the invention is suitable, among other things, for applying a coating with crystals made of a zeolite material or zeolite-like material locally to parts of the surface of a support material, for example, in order to selectively structure surfaces.

[0017] The coating of the composite material formed according to the invention comprises crystals of a zeolite material or a zeolite-like material as an active component, preferably crystals of a zeolite material. The activities that can be provided at the surface of the composite material with the aid of such an active component are well known to those skilled in the art. Zeolite materials or zeolite-like materials are characterized, for example, by desired sorption properties and / or by catalytic properties. Catalytic properties can be achieved or enhanced, for example, by the incorporation of suitable catalytically active guest molecules into the zeolite framework structure of the zeolite material or zeolite-like material.

[0018] In addition to the crystals of a zeolite material or a zeolite-like material, the coating of the composite material formed according to the invention can comprise one or more further active components and / or one or more inert materials. The coating can also consist of the crystals of a zeolite material or a zeolite-like material, preferably the crystals of a zeolite material. As will be evident from the advantages of the invention explained above, it is particularly preferred that the coating of the composite material formed according to the invention, as well as the precursors or intermediates formed for its production in steps a), b), and c) of the process according to the invention, are free of binder material. The zeolite material or the zeolitic material, or their precursor compounds, are naturally not included in the term "binder material."

[0019] The following describes the composition of a zeolite material or zeolite-like material for use in the present invention. Unless otherwise specified, this information applies both to the crystals of a zeolite material or zeolite-like material in the coating of the composite material produced as the final product of the process according to the invention, and to the starting crystals of a zeolite material or a zeolite-like material used in step a) of the process.

[0020] The zeolite material and the zeolite-like material exhibit a zeolitic framework structure. Such framework structures are known to those skilled in the art. They have channels and / or cages connected by openings (pores) and are suitable, for example, for the incorporation of guest molecules.

[0021] Zeolite material is typically defined as a material with a zeolitic framework structure composed of silicon (Si), oxygen (O), and possibly aluminum (Al). Silicon atoms (Si), oxygen atoms (O), and possibly aluminum atoms (Al) are typically the only elements that make up the zeolitic framework structure in the zeolite material. In the zeolitic framework of a zeolite material, silicon oxide tetrahedra and, if applicable, aluminum oxide tetrahedra are linked via shared oxygen atoms. While the composition of the individual tetrahedra can be represented by SiO₄ or AlO₄, the stoichiometry of the oxide components in the zeolite material is usually given by the formula SiO₂ or SiO₄ / 2 or AlO₂ or AlO₄ / 2, respectively, due to the oxygen atoms being shared by several tetrahedra.

[0022] A zeolite-like material is one that also exhibits a zeolitic framework structure, but this framework is not solely composed of silicon (Si), oxygen (O), and possibly aluminum (Al). Instead, elements other than Si, O, and Al can contribute to or form the framework. These are typically elements that can exist in tetrahedral coordination and are capable of forming an oxide network (referred to here as a "network-forming element"). Typical network-forming elements suitable for providing a zeolitic framework material, in addition to Si and Al, are other elements from groups 3, 4, and 5 of the periodic table (groups 13, 14, and 15 according to the current IUPAC classification). Examples include one or more elements selected from phosphorus (P), boron (B), titanium (Ti), and gallium (Ga).The term "zeolite-like" is also used by those skilled in the art to describe materials that, in extreme cases, may not contain any silicon but instead form tetrahedral networks, for example, of aluminum and phosphorus, such as the so-called aluminum phosphates (AIPO-n materials), and can form identical or similar structures to those of classical zeolites. Preferably, the zeolitic framework structure of a zeolite-like material is formed from silicon, oxygen, possibly aluminum, and one or more elements selected from phosphorus, boron, titanium, and gallium.

[0023] In connection with the composite material provided according to the invention and the starting crystals used according to the invention, zeolite materials and zeolite-like materials are also referred to by the common generic term "zeolitic materials".

[0024] As is known to those skilled in the art, the zeolitic framework structure of zeolite materials and zeolite-like materials is formed by tetrahedral basic units linked via shared oxygen atoms. In these tetrahedral basic units, one atom T is surrounded by four oxygen atoms, which are, however, shared with neighboring tetrahedra, so that the basic units are also described by the formula TO₂ or TO₄ / 2. Here, T denotes an element capable of forming an oxide network and which can exist in tetrahedral coordination (also referred to here as a "network-forming element"). Typical network-forming elements whose oxides are suitable for providing zeolite materials and zeolite-like materials are elements of groups 3, 4, and 5 of the periodic table (groups 13, 14, and 15 according to the current IUPAC classification). Examples include one or more elements selected from Si, Al, P, B, Ti, or Ga.If trivalent atoms T occur in the framework structure in the form of linked tetrahedra TO 2, such as Al, B or Ti, they carry a negative formal charge. This charge is usually balanced by the presence of cations, whereby cations of one type or cations of different types can be used.

[0025] Preferably, the zeolitic framework structure in the crystals of the zeolite material or the zeolite-like material in the coating of the composite material provided according to the invention and in the starting crystals is composed of tetrahedral SiO₂ units, wherein silicon atoms in the framework structure may be replaced by one or more other network-forming elements selected from elements of main groups 3, 4, and 5 of the periodic table (groups 13, 14, and 15 according to the current IUPAC classification). Preferably, the other network-forming elements are one or more elements selected from boron, aluminum, phosphorus, and titanium. More preferably, the zeolitic framework structure is composed of tetrahedral SiO₂ units, wherein silicon atoms in the framework structure may be replaced by aluminum, or it is composed exclusively of SiO₂ units.Typically, no more than 30%, preferably no more than 20%, and more preferably no more than 10% of all silicon atoms in the zeolitic framework structure are replaced by other elements. This percentage refers to the number of all network-forming atoms, and thus all tetrahedrally coordinated positions in the zeolitic framework structure, as 100%.

[0026] The cations used to balance any formal charges potentially present in the framework structure are preferably selected from alkali, alkaline earth, or ammonium cations. A characteristic feature of zeolites or zeolitic materials is the mobility or exchangeability of the cations.

[0027] As mentioned above, the zeolitic framework structure of the crystals of the zeolite material or zeolitic material in the coating and the starting crystals is preferably formed by linked SiO₂ tetrahedra (also referred to as SiO₄ / 2) or by linked SiO₂ and AlO₂ (also referred to as SiO₄ / 2 and AlO₄ / 2) tetrahedra. Although a certain amount of the Si atoms may be replaced by other tetravalent atoms, and / or a certain amount of the Al atoms may be replaced by other trivalent atoms, it is more preferred that the framework structure consists of the SiO₂ and AlO₂ tetrahedra, or only of SiO₂ tetrahedra, such that the crystals are of a zeolite material. The structure of a zeolite material with such a zeolite framework can be represented by the formula Mx / n [(AlO2)x (SiO2)y] or Mx / n [(AlO2)x (SiO2)y] · z H2O. In this formula, M represents one or more types of cations with valence or charge n (e.g.,Alkali and / or alkaline earth cations, so that n is typically 1 or 2, and can also take values ​​between 1 and 2 in the presence of both alkali and alkaline earth cations), and z H₂O represents water molecules that may be adsorbed in the pores of the zeolite framework. The variables x and y represent the proportion of neutral SiO₂ tetrahedra and negatively charged AlO₂ tetrahedra, respectively.

[0028] According to the invention, suitable zeolite materials comprise pure silicate variants that do not contain Al or in which x in the formula above is equal to 0. Suitable zeolite materials containing Si and Al typically have a molar ratio Si / Al (and in particular the ratio y / x in the formula above) of at least 1; for example, the molar ratio of a high-silicate zeolite material is preferably at least 3.5, more preferably at least 10, and in particular at least 15.

[0029] Materials used as zeolite-like materials are preferably those in which the molar ratio of tetrahedrally coordinated silicon atoms to the sum of any other tetrahedrally coordinated network-forming atoms present, such as boron, aluminum, phosphorus, or titanium, in the zeolite framework structure is at least 1. High-silicate materials can also be cited as examples here. In general, high-silicate zeolite materials or zeolite materials are characterized by the fact that the molar ratio of tetrahedrally coordinated silicon atoms to the sum of any other tetrahedrally coordinated network-forming atoms present, such as boron, aluminum, phosphorus, or titanium, in the zeolite framework structure is preferably at least 3.5, more preferably at least 10, and particularly at least 15.

[0030] As is known to those skilled in the art, zeolite materials form characteristic framework structures depending on the choice of framework constituents and the synthesis conditions, for which specific type designations have been established. Examples of high-silicate zeolite materials that may be included in the coating are those of the MFI, BEA, MOR, FER, MWW, MTW, DDR, CHA, AEI, or MEL structure types. Zeolite materials of the MFI and BEA types are particularly preferred as high-silicate zeolite materials. Examples of aluminum-rich zeolite materials that may be included in the coating are zeolite A, X, or Y, which are also abbreviated as LTA and FAU, respectively.

[0031] The coating in the composite material produced according to the invention can contain more than one zeolite material or zeolite-like material; for example, two different zeolite materials, two different zeolite-like materials, or a zeolite material and a zeolite-like material can be combined. Preferably, exactly one zeolite material or exactly one zeolite-like material, and in particular exactly one zeolite material, is included.

[0032] As mentioned above, the coating in the composite material produced according to the invention can comprise, in addition to the crystals of a zeolite material or a zeolite-like material, one or more further active components. Examples of further active components include metals, in particular metals or transition metals such as Fe, Co, Ni, Mo, Zn, Ti, Cu, Ru, Rh, Pd, or Pt. These can be present, for example, in the form of metal particles. Such particles, if present, are preferably nanoparticles with a size, determined, for example, by means of electron microscopy, of less than 1 µm, particularly preferably 200 nm or less, and especially preferably 100 nm or less. Typically, the size is 20 nm or larger, preferably 30 nm or larger. Other examples of further active components are metal compounds, for example, compounds of the metals or transition metals mentioned above as examples, such as oxides or sulfides.Metal or transition metal compounds can also be incorporated into the coating, for example in the form of metal particles such as the nanoparticles mentioned above.

[0033] As mentioned above, the coating in the composite material produced according to the invention can comprise one or more inert materials in addition to the crystals of a zeolite material. Such materials can be selected by a person skilled in the art depending on the intended application of the composite material. As is known to those skilled in the art, the term "inert" here refers to materials that behave inertly in this application. Preferably, however, the provided coating is free of such inert materials. Such an incorporation of inert materials can be advantageous, for example, when the activity of the active species is high and local dilution is required to control, for example, heat input or output. Nevertheless, when using the method according to the invention, the local intensive mixing and spatial proximity of the active species of a bi- or multifunctional combination of the active components can be maintained.

[0034] The crystals of the zeolite material or the zeolite-like material preferably form the main component of the coating in the composite material produced according to the invention, i.e., they are present in a proportion of 50 wt.% or more, more preferably 80 wt.% or more, particularly preferably 90 wt.% or more, and most preferably 100 wt.%, based on the total weight of the coating. The weight fraction of the zeolite material or the zeolite-like material also includes any guest molecules and / or cations necessary for charge neutrality that may be contained therein.

[0035] The crystals of the zeolite material or the zeolite-like material of the coating in the composite material produced according to the invention are typically, as with the starting crystals, nanoscale crystals. The crystal size, e.g., determined by means of electron microscopy, is not exclusively but preferably smaller than 1 µm, particularly preferably 200 nm or smaller, and especially preferably 100 nm or smaller. Typically, the size is 20 nm or larger, preferably 30 nm or larger.

[0036] Crystal size can be determined, for example, by analyzing scanning electron microscope images. The concept of the equivalent diameter of a sphere with the same projection area can be applied for this purpose.

[0037] For this purpose, the projection surfaces A proj of N crystals on the SEM images are determined using suitable image analysis software (for example, "ImageJ"; see Rasband, WS, ImageJ, US National Institutes of Health, Bethesda, Maryland, USA, http: / / imagej.nih.gov / ij / , 1997-2015) (here: crystal projections approximated as ellipses) and the equivalent sphere diameter is calculated according to the following equation: d eq = A proj π

[0038] From the N equivalent diameters thus obtained, the sum of sizes Q or size density distribution q can also be determined, and the corresponding average diameter deq,mean can be calculated and specified. Unless otherwise stated, the crystal size is the mean equivalent diameter of the crystals. Preferably, the equivalent diameter of all crystals lies within the size ranges or preferred size ranges specified above.

[0039] It should be noted that the particles visible as individual crystals in the SEM images may, from a crystallographic perspective, consist of several crystallites. The size of these identically structured, coherent crystal regions—crystallites—can be estimated, for example, from the X-ray diffractogram based on the half-widths of the X-ray reflections.

[0040] The crystals of the zeolite material or zeolite-like material in the coating of the composite material provided according to the invention typically exhibit a microporous framework structure. As is characteristic of zeolitic structures, the micropores of the framework structure form a pore system of interconnected micropores. Unless otherwise specified in individual cases, reference to micropores is made according to the IUPAC convention, whereby micropores are defined as pores with a pore diameter dP of less than 2 nm, mesopores as pores with a diameter dP of 2 to 50 nm, and macropores as pores with a diameter greater than 50 nm [Haber et al. IUPAC, Pure and Appl. Chem., 63 (1991) 1227]. The pore diameters can be determined, for example, by means of sorption methods using gases.

[0041] As a result of the manufacturing process according to the invention, the crystals of the zeolite material or zeolite-like material in the coating of the provided composite material are arranged such that the spaces between the crystals form the intergranular meso- and / or macropores of the coating. As explained above, the designation follows the IUPAC convention, i.e., pores with a pore diameter dP of 2 to 50 nm are designated as mesopores, and pores with a diameter greater than 50 nm are designated as macropores. Typically, the crystals of the zeolite material or zeolite-like material in the coating of the provided composite material are arranged in such a way that, for example, they are still recognizable as individual crystals in electron micrographs of the coating, which, however, preferably touch or, more preferably, are intergrown.

[0042] The inventive method thus makes it possible to provide a composite material with controlled hierarchical porosity. Existing micropores are defined by the type of zeolite or zeolite-like material used, while meso- and / or macropores are defined, for example, by the quantity and size of the crystals of the zeolite or zeolite-like material and their resulting arrangement during coating.

[0043] The coating thickness can be adjusted as needed over a wide range, if necessary by applying multiple coats. Typically, the coating thickness ranges from 20 nm to 200 µm. The thickness can be determined, for example, by cross-sectional image analysis, typically using SEM imaging.

[0044] To produce the composite material, a suspension is first provided in step a) containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material. As is understandable to a person skilled in the art, the precursor compounds in the suspension are typically selected such that they can be used to form a zeolite material or zeolite-like material whose composition corresponds to that of the material contained in the suspension.

[0045] The crystal size of the nanoscale starting crystals, e.g., determined from electron micrographs as described above for the coating crystals, is preferably less than 1 µm, more preferably 200 nm or less, and more preferably 100 nm or less. Typically, the size is 20 nm or larger, more preferably 30 nm or larger. The values ​​are preferably given as mean equivalent diameters. More preferably, the equivalent diameter of all crystals lies within the size ranges or preferred size ranges specified above.

[0046] Regarding the composition of the starting crystals from a zeolite material or a zeolite-like material, preferably from a zeolite material, the explanations given above concerning the composition of both the starting crystals and the crystals of the zeolite material or zeolite-like material in the provided coating apply. Typically, the composition of the starting crystals corresponds to that of the crystals of the zeolite material or zeolite-like material in the provided coating.

[0047] Precursor compounds of zeolite materials or zeolite-like materials, such as those contained in the suspension provided in step a), are also familiar to those skilled in the art. These are typically compounds of network-forming elements that are dissolved in the solvent forming the liquid phase of the suspension or suspended in colloidal form or as an amorphous solid. Typical network-forming elements whose oxides are suitable for providing zeolite materials and zeolite-like materials are elements of groups 3, 4, and 5 of the periodic table (groups 13, 14, and 15 according to the current IUPAC classification). Preferred examples are one or more elements selected from Si, Al, P, B, Ti, or Ga; more preferred examples are Si and Al.

[0048] Examples of suitable compounds of these network-forming elements are salts, including metallates, hydroxides, and alkoxides. Specific exemplary silicon compounds suitable as precursor compounds are silicic acids, salts of silicic acid, and silicic acid esters (such as tetraethyl orthosilicate). The term silicic acid encompasses both orthosilicic acid and oligomeric and / or solid polycondensation products thereof, such as silica gels, precipitated silicas, and Aerosil. Exemplary aluminum compounds suitable as precursor compounds are aluminum salts such as aluminum nitrate, aluminates such as alkali aluminates, aluminum alkoxides such as aluminum triisopropylate, and aluminum hydrates such as aluminum trihydrate. Exemplary titanium compounds are titanium salts, titanates, titanium tetraethanolate, and titanium alkoxy compounds such as titanium isopropoxide. Exemplary phosphorus compounds are phosphates and phosphoric acid esters.Examples of boron compounds are boric acid, borates or boric acid esters, such as triethyl borate or trimethyl borate.

[0049] In addition to the starting crystals and precursor compounds, the suspension provided in step a) preferably contains a template species, i.e., a substance that can act as a template for the synthesis of a zeolitic framework structure. Preferably, this is an organic compound.

[0050] Suitable organic compounds, also known as organic templates or structure-directing substances, are known to those skilled in the art. These are generally alcohols, phosphorus compounds, amines, or ammonium compounds, preferably tetraorganoammonium cations or tetraorganophosphonium cations, which are typically used in the form of their salts, such as halides or hydroxides.

[0051] More preferably, these are tetraorganoammonium cations or tetraorganophosphonium cations bearing four hydrocarbon residues, in particular hydrocarbon residues that are independently selected from alkyl, aryl, and alkaryl residues. Preferably, the alkyl residues are C1-C4 alkyl residues. Phenyl is preferred as the aryl residue, and benzyl as the alkaryl residue. Tetraalkylammonium cations are particularly preferred, such as the tetramethylammonium cation (e.g., in the form of tetramethylammonium hydroxide), the tetraethylammonium cation (e.g., in the form of tetraethylammonium hydroxide), the tetrapropylammonium cation (e.g., in the form of tetrapropylammonium hydroxide), the tetrabutylammonium cation, or the triethylmethylammonium cation. Further preferred examples are the tetrabutylphosphium cation, the triphenylbenzylphosphonium cation, or the trimethylbenzylammonium cation. In addition, for example,Primary, secondary or cyclic amines (such as piperidine), imines (such as hexamethyleneimine) or alcohols can also be used as organic templates.

[0052] The following table provides a non-restrictive overview of common organic compounds used as template species and the zeolitic framework structures obtainable through their use: Organic molecules Zeolites (network type) TMA - (Tetramethylammonium) X (FAU), Sodalite (SOD), ZSM-10 (MOZ), ZSM-3 (EMT-FAU), ZSM-5 (MFI), ZSM-11 (MEL), ZSM-39 (MTN) TEA - (Tetraethylammonium) +< ZSM-5 (MFI), ZSM-11(MEL), SAPO-34 (CHA), UZM-5 (UFI), ZSM-20 (EMT-FAU), ZSM-12 (MTW), Beta (BEA) TBP - (Tetrabutylphosphonium) +< ZSM-5 (MFI), ZSM-11 (MEL) TPA - (Tetrapropylammonium) +< ZSM-5 (MFI), AlPO 4 -5 (AFI), ZETA-1, ZETA-3 TPBP - (Triphenylbenzylphosphonium) +< ZSM-11 (MEL) TMBA - (Trimethylbenzylammonium) +< ZSM-11 (MEL) TBA - (Tetrabutylammonium) +< ZSM-5 (MFI), ZSM-11 (MEL) TEMA - (Triethylmethylammonium) +< ZSM-12 (MTW) Primary and secondary amines ZSM-5 (MFI), ZSM-22 (TON), ZSM-35 (FER) Piperidine Ferrierite (FER) HMI - (Hexamethyleneimine) PSH-3 (MWW), ZSM-5 (MFI), SAPO-35 (LEV) alcohols ZSM-5 (MFI)

[0053] If the presence of another active component in the coating of the composite material is desired, it can also be included directly or in the form of a precursor compound in the suspension provided in step a). As mentioned above, examples of suitable additional active components are metals, in particular metals or transition metals such as Fe, Co, Ni, Mo, Ti, Zn, Cu, Ru, Rh, Pd, or Pt. They can be included in the suspension, for example, in the form of metallic nanoparticles or in the form of a metal compound. Metal compounds can be introduced, for example, as an oxide or sulfide, as a salt of a corresponding metal cation, or as a complex compound of a corresponding metal.

[0054] If desired, the suspension can also contain other materials, e.g., inert materials, which are to be included in the coating of the composite material provided according to the invention. Preferably, however, the suspension, and also the provided coating, are free of such inert materials.

[0055] Additives that facilitate the processing of the suspension, such as a dispersant, can also be used. However, as mentioned above, the suspension is typically free of a binder or binding agent.

[0056] The solvent that forms the liquid phase of the suspension can be a single solvent or a mixture of two or more solvents. For reasons of cost-effectiveness and environmental compatibility, water is particularly suitable as a solvent.

[0057] To provide the suspension in step a) (not according to the invention), the nanoscale starting crystals, the precursor compound, preferably additionally the template species, and other optional components can be added to the solvent in any order. According to the embodiment of the process discussed above, the suspension is provided by synthesizing the starting crystals in step a) by partially reacting a reaction mixture containing (i) a solvent, (ii) the precursor compounds of the zeolite material or zeolite-like material, and preferably further (iii) a template species. The result is the suspension containing the nanoscale starting crystals of a zeolite material or a zeolite-like material, precursor compounds of the zeolite material or zeolite-like material, and preferably further a template species.In step b), the suspension thus provided is applied to the surface of the support structure with the starting crystals and unreacted precursor compounds contained therein, without prior isolation of the synthesized starting crystals.

[0058] Typically, the solids concentration in suspensions is preferably not greater than 30% wt / wt, and more preferably not greater than 20%. For example, the solids concentration can be in the range of 10 to 30% wt / wt. The term "solids concentration" refers to the total concentration of all materials (in particular, the nanoscale starting crystals and precursor compounds of the zeolite or zeolite-like material, but also other optional active components that are later present as solids in the coating of the composite material). The concentrations of other components (e.g., auxiliary components such as template species) can be adjusted according to the desired structure in the coating.

[0059] A preferred embodiment of the invention is a method for producing a composite material with a support structure and a coating on the surface of the support structure, wherein the coating comprises crystals of a zeolite material or a zeolite-like material as an active component and wherein intercrystalline meso- and / or macropores are formed in the coating, characterized in that the method comprises the following steps: a) Providing a suspension containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material, by synthesizing the starting crystals through partial reaction of a reaction mixture containing (i) a solvent, (ii) the precursor compounds of the zeolite material or zeolite-like material, and (iii) a template species; b) Applying the suspension provided in step a), containing the starting crystals and unreacted precursor compounds, without prior isolation of the synthesized starting crystals, to the surface of the support structure; c) Condensing the suspension applied in step b) by at least partially removing the solvent forming the liquid phase of the suspension to obtain a coating containing the starting crystals and the precursor compounds.d) Holding the coating obtained in step c) on the surface of the support structure in a vaporous atmosphere at an elevated temperature, so that the contained precursor compounds are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating comprising crystals of a zeolite material or a zeolite-like material.

[0060] The synthesis of nanoscale starting crystals by partial reaction of a reaction mixture containing (i) a solvent, (ii) the precursor compounds of the zeolite or zeolite-like material, and preferably (iii) a template species, is typically carried out under hydrothermal conditions, for example, by crystallizing the starting crystals at a temperature generally between 70°C and 220°C for a few hours to 5 days. Importantly, the precursor compounds are not completely converted, so that the resulting suspension contains unreacted precursor compounds in addition to the starting crystals. Preferably, a conversion rate of 60–80 mol% should be achieved, based on the total number of moles of network-forming elements in the original reaction mixture as 100 mol%.Preferably, a suspension is provided in which 60 - 80 mol% of the network-forming elements in the precursor compounds of the original reaction mixture have been converted to nanoscale starting crystals.

[0061] In step b) of the inventive method, the suspension provided in step a) is applied to the surface of the support structure. A number of conventional methods are available for application, such as spin coating, dip coating, doctor blade application, or spraying. As explained above, the suspension can be applied in such a way that the entire surface of the support structure is covered with the suspension, or that the surface is only partially covered. Localized application is also possible using the methods mentioned above as examples, optionally supported by masking parts of the surface where no coating is to be applied.

[0062] In step c), the suspension applied in step b) is compacted by at least partial removal of the solvent that forms the liquid phase of the suspension to obtain a coating containing the starting crystals and the precursor compounds. Furthermore, the coating contains other optional components, which were previously mentioned as optional components of the suspension, in particular, as a preferred additional component, template species that allow the control of structure formation for different zeolite types or zeolitic framework structures.

[0063] The solvent can be at least partially removed using known methods, such as increasing the temperature, reducing the partial pressure of the solvent in the vicinity of the applied suspension, or combinations thereof. In addition to heat and / or pressure reduction or vacuum, methods such as freeze-drying can also be employed.

[0064] Typically, to compact the suspension in step c), at least 40 wt.% of the solvent, preferably at least 50 wt.%, more preferably at least 75 wt.%, and particularly preferably at least 85 wt.% of the solvent, based on the total weight of the solvent in the suspension to be applied, is removed. However, the proportion of solvent removed is typically less than 100 wt.%, so that a residual solvent content remains in the coating obtained in step c).

[0065] If necessary, e.g. to adjust the thickness of the coating, steps b) and c), and possibly also steps a), b) and c), of the inventive method can be repeated several times, e.g. twice or three times, before step d) is carried out.

[0066] In step d) of the process according to the invention, the coating obtained in step c) on the surface of the support structure is held in a vapor-containing atmosphere at an elevated temperature in order to convert the precursor compounds of the zeolite material or zeolite-like material contained in the coating into a corresponding zeolite material or a zeolite-like material. Thus, the converted precursor compounds, together with the starting crystals, form the coating, which comprises crystals of a zeolite material or a zeolite-like material.

[0067] Typically, the zeolite material or zeolite-like material formed from the precursor compounds during the conversion in step d) grows onto the initial crystals in the coating. Preferably, this growth occurs such that the additional zeolite material or zeolite-like material formed from the precursor compounds connects the initial crystals in the coating, and as a result, the crystals of the zeolite material or zeolite-like material in the coating according to the invention are in contact and, particularly preferably, intergrown.

[0068] The vapor-containing atmosphere used in step d) is typically a water vapor-containing atmosphere. However, contact between the coating obtained in step c) and a liquid solvent, e.g., liquid water, should be avoided in step d). The water vapor content of the atmosphere is preferably at a relative humidity of 60 to 100%, more preferably 80 to 95%.

[0069] The increased temperature in step d) is preferably in the range of 70 to 200 °C, more preferably 100 to 170 °C, and particularly preferably 100 to 160 °C.

[0070] According to a preferred embodiment, in step d) the coating obtained in step c) on the surface of the support structure is therefore held in a water vapor-containing atmosphere at a temperature of 100 to 170 °C, wherein the relative humidity of the atmosphere is between 60 and 100 %.

[0071] The duration of holding the coating obtained in step c) in the vapor-containing atmosphere at elevated temperature in step d) can be suitably selected by a person skilled in the art depending on the type of zeolite or zeolite-like material and the temperature. It is generally between 0.5 and 192 hours, preferably, for example for a zeolite material of type ZSM-5 (MFI type), typically between 2 and 96 hours, more preferably between 10 and 72 hours.

[0072] Holding the coating obtained in step c) in the vapor-containing atmosphere at elevated temperature in step d) can take place in an open system under atmospheric pressure, so that the partial pressures of the vaporous substances are determined by their content in the ambient air.

[0073] Preferably, the holding of the coating obtained in step c) in the vapor-containing atmosphere at elevated temperature in step d) takes place in a closed system, e.g., in an autoclave, in order to be able to control the composition of the vapor-containing atmosphere well. The pressure in the closed system can, in principle, be below, above, or at atmospheric pressure. When step d) is carried out in a water vapor-containing atmosphere at temperatures at or above 100 °C, the pressure is typically above atmospheric pressure.

[0074] The pressure, and consequently the partial pressures of the vaporous components in the atmosphere, when the coating obtained in step c) is held on the surface of the support structure at an elevated temperature, can be precisely controlled, for example, autogenously via the phase equilibrium(s) of the existing species at the selected temperature, or by one or more internal or external control devices or mechanisms. For example, a control device or mechanism of an instrumental, physical, or chemical nature, or a combination thereof, can be used. If a water vapor-containing atmosphere is used in step d), the coated support material can, for example, be held in a closed system at an elevated temperature to which liquid water has been added. Possible methods for precisely controlling the water vapor partial pressure include, for example...These are substances that are able to reversibly bind water, such as salts or their hydrates, or silica gel.

[0075] Following step d), additional follow-up treatment steps can be carried out if necessary.

[0076] Particularly when using an organic compound as a template species in the suspension provided in step a), it may be desirable, for example, to remove any remaining template species from the composite material obtained after step d) by means of a post-treatment, preferably a thermal post-treatment.

[0077] Other post-treatment steps known to those skilled in the art for a composite material containing a zeolite material or zeolite-like material as an active component include, for example, one or more steps selected from calcination, extraction, thermal treatment, leaching, steam treatment, acid treatment, ion exchange and mechanical shaping. Example

[0078] Figures 1 to 3 Exemplary embodiments of the inventive process are shown using planar support systems as an example. For this purpose, planar metal platelets (12 x 12 mm) were used as a model substrate for the supported compaction and transformation of an aqueous suspension consisting of (i) nanoscale zeolite Silikalith-1 (pure SiO2-based zeolite of the MFI topology) and (ii) non-crystallized network formers (amorphous SiO2 species and / or dissolved SiO2 species) as well as (iii) unreacted template molecules.

[0079] According to step a), a suspension containing the nanoscale zeolite material, the precursor compound of the zeolite material, and a template species was prepared as follows: First, the template (tetrapropylammonium hydroxide, "TPAOH", 40 wt.% in water) and deionized water were mixed in a 500 mL Erlenmeyer flask, the amounts adjusted according to a molar ratio of TPAOH : H₂O = 1 : 53.33. This solution was stirred at 400 rpm using a magnetic stir bar for a few minutes (≤ 10 minutes). Tetraethyl orthosilicate ("TEOS", Alfa Aesar, 98%) was then added dropwise to this solution at approximately 1 drop per second while continuing to stir. The amount of TEOS was adjusted so that the final solution had the following molar composition of network former (silicon via TEOS), template and water: Si : TPAOH : H 2 O = 1 : 0.36 : 19.2.This solution was stirred for a further 48 hours at room temperature in the now sealed Erlenmayer flask at an unchanged stirring speed. Taking into account the hydrolysis of TEOS, a synthesis mixture with the following molar ratios was obtained after the aforementioned time, using the usual oxide notation: 1 SiO₂ : 0.18 TPA₂O : 19.2 H₂O : 4 ethanol, exhibiting a pH of 12.6. This synthesis mixture was transferred to a stainless steel autoclave with a PTFE insert (45 mL, Parr instrument). Hydrothermal crystallization of the crystalline zeolite was carried out in a convection oven (90 °C) for 49 hours at 90 °C. After the 49-hour synthesis period, the autoclaves were removed from the oven and cooled to room temperature. The milky suspension consisting of the zeolitic nanocrystals, the unreacted silica species and the template residues was used directly for a spray coating (step b).

[0080] The spray coating was applied using a standard spray gun. Two stainless steel plates (12 x 12 mm) served as model substrates and were dried under identical ambient conditions (room temperature, atmospheric pressure) (step c): "compaction") resulting in a macroscopically dry layer in each case (see figure). Figure 1 ).

[0081] The precursor compounds contained in the compacted layer were then converted (step d)) in separate closed systems. For this purpose, the coated model substrates, after the compaction step described above, were held in a water vapor atmosphere in a closed system (also 45 ml autoclaves with a Parr PTFE insert) at 155°C for 66 hours. In practice, this holding was achieved using a PTFE spacer with a PTFE support plate, onto which the respective coated model substrate was placed with the coating facing upwards.

[0082] The water for setting a vapor atmosphere for the conversion was provided by adding pure water (experiment V1) and by adding silica gel (experiment V2, mixture of 50 wt% loaded and 50 wt% activated silica gel based on the mass in the anhydrous state) at the bottom of the PTFE insert, so that the PTFE spacer spatially separated the model substrate and the water (V1) or the model substrate and the silica gel mixture (V2) from each other and no direct contact was possible.

[0083] In both cases V1 and V2, there was a sufficient amount of H2O to maintain a relative humidity of 100% at 155°C in the closed system. However, in experiment V2, due to the water sorption characteristics of the silica gel, a lower level of water vapor partial pressure is to be expected in the closed system, especially during the heating and cooling phases, but also during the isothermal phase at 155°C. The silica gel mixture serves here to control the water vapor partial pressure.

[0084] After the aforementioned 66 hours of holding in a steam atmosphere, the autoclaves were cooled to room temperature, the composite materials were removed, rinsed with deionized water and dried overnight at 75 °C.

[0085] The comparison of the two composite materials obtained in this way clearly shows that in both experiments sufficient water was available to allow complete conversion of the initially amorphous network formers (precursor compound of the zeolite material) (see X-ray diffractograms in Figure 2 The success of the conversion is evident for both samples (V1 and V2) by a significant decrease in the amorphous phase compared to the condensed suspension, while the intensity of the characteristic MFI reflections increases significantly.

[0086] As in Figure 3 As can be clearly seen, these experiments also show that at high water vapor partial pressure (V1) during the conversion, condensation of water apparently occurs on the coated model substrate, leading to the "dispersion" of the originally locally well-defined layer. This effect is not observed when using the silica gel (V2).

[0087] Figure 1 :Photographs of the planar model substrate in its uncoated state, fixed to the test rig with adhesive tape (top, left), immediately after coating by spraying on the suspension (top, center), and after compaction of the suspension (right, drying under atmospheric conditions, adhesive tape already removed). Below: Scanning electron micrographs of the compacted suspension on the model substrate (bottom left: left half of the image clearly shows the uncoated area (adhesive tape present during spray coating)). Letters indicate the magnification range.

[0088] Figure 2 : X-ray diffractograms of the compacted suspension on the model substrate ("compacted") and of the steam-treated compacted suspension according to experiment 1 ("V1") and experiment 2 ("V2") layer on the metal plates.

[0089] Figure 3 :Photographic images (top) and scanning electron microscope images (bottom) of the metal plates with the transformed, condensed suspension after experiment 1 (left) and after experiment 1 (right). Letters indicate the magnification range.

Claims

1. A process for producing a composite material having a support structure and a coating on the surface of said support structure, the coating comprising, as an active component, crystals of a zeolite material or a zeolite-like material, with intercrystalline mesopores and / or macropores being formed within the coating, characterized in that the process comprises the following steps: a) providing a suspension containing nanoscale starting crystals of a zeolite material or a zeolite-like material, as well as precursor compounds of the zeolite material or zeolite-like material, b) applying the suspension provided in step a) to the surface of the support structure, c) compacting the suspension applied in step b) by at least partially removing the solvent forming the liquid phase of the suspension in order to obtain a coating containing the starting crystals and the precursor compounds, d) keeping the coating obtained in step c) on the surface of the support structure in a vapor-containing atmosphere at an elevated temperature so that the contained precursor compounds are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating comprising crystals of a zeolite material or a zeolite-like material, wherein the suspension is provided in step a) by synthesizing the starting crystals by partially reacting a reaction mixture which contains (i) a solvent, and (ii) the precursor compounds of the zeolite material or zeolite-like material, and wherein the suspension thus provided, with the starting crystals and unreacted precursor compounds contained therein, is applied in step b) to the surface of the support structure without prior isolation of the synthesized starting crystals.

2. The process as claimed in claim 1, wherein the reaction mixture contains, in addition to the solvent and the precursor compounds of the zeolite material or zeolite-like material, (iii) a template species.

3. The process as claimed in any one of claims 1 or 2, wherein the nanoscale starting crystals have a size, determined as the average equivalent diameter as illustrated in the description, of 20 to 200 nm.

4. The process as claimed in any one of claims 1 to 3, wherein the coating formed in step d) is a coating that is free of binding material.

5. The process as claimed in any one of claims 1 to 4, wherein the zeolite material or zeolite-like material formed during the conversion in step d) connects starting crystals in the coating.

6. The process as claimed in any one of claims 1 to 5, wherein the support structure is formed from a metallic or ceramic material.

7. The process as claimed in any one of claims 1 to 6, wherein the precursor compounds of the zeolite material or zeolite-like material in the suspension provided in step a) comprise at least one type of silicon compound selected from silicic acid, salts of silicic acid, and silicic acid esters.

8. The process as claimed in any one of claims 1 to 7, wherein the precursor compounds of the zeolite material or zeolite-like material in the suspension provided in step a) comprise at least one type of aluminum compound selected from aluminates, aluminum salts, hydrated aluminum, and aluminum alcoholates.

9. The process as claimed in any one of claims 2 to 8, wherein the template species is a tetraorganoammonium cation or a tetraorganophosphonium cation.

10. The process as claimed in any one of claims 1 to 9, wherein during the step of compacting the suspension in step c), at least 40% by weight of the solvent, based on the total weight of the solvent in the suspension to be applied, is removed.

11. The process as claimed in any one of claims 1 to 10, wherein in step d) keeping the coating obtained in step c) on the surface of the support structure in a water vapor-containing atmosphere is performed at an elevated temperature in the range of 100 to 170°C.

12. The process as claimed in any one of claims 1 to 11, wherein steps b) and c) are carried out a plurality of times.