PRODUCTION OF ZEOLITE-BASED COMPOSITE MATERIALS WITH HIERARCHICHAL POROSITY

Abstract

A method is provided for generating a composite material with a support structure and a coating on the surface of the support structure, the coating comprising, as active component, crystals of a zeolite material or of a zeolite-like material, with intercrystalline mesopores and/or macropores being formed in the coating, characterized in that the method comprises the following steps: a) providing a suspension which comprises nanoscale starting crystals of a zeolite material or of a zeolite-like material, and also 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 that forms the liquid phase of the suspension, to yield a coating which comprises 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 precursor compounds present are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating which comprises crystals of a zeolite material or of a zeolite-like material.

Claims

1. A method for generating a composite material with a support structure and a coating on the surface of the support structure, the coating comprising, as active component crystals of a zeolite material or of a zeolite-like material, with intercrystalline mesopores and/or macropores being formed in the coating, characterized in that the method comprises the following steps: a) providing a suspension which comprises nanoscale starting crystals of a zeolite material or of a zeolite-like material, and also 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 that forms the liquid phase of the suspension, to yield a coating which comprises 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 precursor compounds present are converted into a zeolite material or a zeolite-like material and, together with the starting crystals, form the coating which comprises crystals of a zeolite material or of a zeolite-like material.

2. The method as claimed in claim 1, wherein the providing of the suspension in step a) takes place by synthesis of the starting crystals by partial reaction of a reaction mixture which comprises (i) a solvent, (ii) the precursor compounds of the zeolite material or zeolite-like material, and also preferably (iii) a template species, and wherein the suspension thus provided, with the starting crystals and unreacted precursor compounds present therein, is applied in step b) to the surface of the support structure, without prior isolation of the synthesized starting crystals.

3. The method as claimed in one of claims 1 and 2, wherein the nanoscale starting crystals have a size of from 20 to 200 nm.

4. The method as claimed in one of claims 1 to 3, wherein the coating formed in step d) is a coating which is free from binder material.

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

7. The method as claimed in 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 a silicon compound which is selected from silicic acid, salts of silicic acid and silicic acid esters.

8. The method as claimed in as claimed in 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 an aluminum compound which is selected from aluminates, aluminum salts, hydrated aluminum and aluminum alkoxides.

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

10. The method as claimed in 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 is removed, based on the total weight of the solvent in the suspension to be applied.

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

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

Description

EXAMPLE

[0140] FIG. 1 to FIG. 3 show working examples of the method of the invention, using planar support systems as an example. The starting points for this example were planar metal plaques (1212 mm) as a model substrate for the supported compaction and conversion of an aqueous suspension consisting of (i) nanoscale zeolite silicalite-1 (purely SiO.sub.2-based zeolite of MFI topology) and (ii) noncrystallized network formers (amorphous SiO.sub.2 species and/or dissolved SiO.sub.2 species), and also (iii) unreacted template molecules.

[0141] According to step a), a suspension comprising the nanoscale zeolite material, the precursor compound of the zeolite material, and a template species was produced as follows:

[0142] First, the template (tetrapropylammonium hydroxide, TPAOH, 40 wt % in water) and deionized water were mixed in a 500 mL conical flask, the amounts being established in accordance with a TPAOH:H.sub.2O molar ratio of 1:53.33. This solution was stirred using a stirring bar at 400 rpm for a few minutes 10 minutes). Added dropwise to this solution at around 1 drop per second, with further stirring, was tetraethyl orthosilicate (TEOS, Alfa Aesar, 98%). The amount of TEOS here was established such that the final solution had the following molar composition of network former (silicon via TEOS), template and water: Si:TPAOH:H.sub.2O=1:0.36:19.2. This solution was stirred for a further 48 hours at room temperature at unchanged stirring speed in the conical flask, which was now closed. Taking account of the hydrolysis of TEOS, therefore, in the customary oxide notation, the mixture present after the aforesaid time was a so-called synthesis mixture with the following molar ratios: 1 SiO.sub.2:0.18 TPA.sub.2O:19.2 H.sub.2O:4 ethanol, and had a pH of 12.6. This synthesis mixture was transferred to a stainless steel autoclave with PTFE insert (45 mL, Parr Instrument). The hydrothermal crystallization of the crystalline zeolite took place accordingly at 90 C. in an oven (90 C.) with air circulation function for 49 hours. After the 49-hour synthesis time, 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 residues of template was utilized directly for spray coating (step b).

[0143] Spray coating took place by means of a commercial spray gun. Serving as model substrates were two stainless steel plaques (1212 mm), and drying (step c): compaction) took place under identical ambient conditions (room temperature, atmospheric pressure), to give in each case a macroscopically dry layer (cf. FIG. 1).

[0144] Subsequently, the precursor compounds present in the compacted layer were converted (step d)), in a separate closed system in each case. For this purpose, after the above-described compaction step, the coated model substrates were kept in a water vapor atmosphere in a closed system (again 45 ml autoclave with PFTFE insert from Parr) at 155 C. for 66 hours. In practice, keeping was put into practice by means of a PTFE spacer with PTFE support plate, onto which the respective coated model substrate was placed with the coating pointing upward.

[0145] The water for establishing a vapor atmosphere for the conversion was provided via the addition of pure water (experiment V1) and also by the addition of silica gel (experiment V2, mixture of 50 wt % loaded silica gel and 50 wt % activated silica gel, based on the mass in the anhydrous state) on the base of the PTFE insert, so that the PTFE spacer undertook spatial separation of the model substrate and the water from one another (V1) and of the model substrate and the silica gel mixture (V2) from one another, resepcetively, and no direct contact was possible.

[0146] In both cases, V1 and V2, a sufficient amount of H.sub.2O was present at 155 C. in the closed system to establish a relative humidity of 100%; in experiment V2, however, owing to the water sorption characteristics of the silica gel, a lower level of the water vapor partial pressure in the closed system is anticipated, particularly during the heating and cooling phase, but also during the isothermal phase at 155 C.; the silica gel mixture serves here to control the water vapor partial pressure.

[0147] After the stated 66 hours of maintenance in a vapor atmosphere, the autoclaves were cooled to room temperature, and the composite materials were removed, rinsed with deionized water and dried overnight at 75 C.

[0148] Comparison of the two resultant composite materials shows clearly that in both experiments there was sufficient water available to permit complete reaction of the initially amorphous network formers (precursor compound of the zeolite material) (see X-ray diffractrograms in FIG. 2: the success of the conversion is evident for both samples (V1 and V2) from a marked decrease in the amorphous phase in comparison to the compacted suspension, while the intensity of the characteristic MFI reflexes rises significantly).

[0149] As is clearly apparent in FIG. 3, these experiments also show that at a high water vapor partial pressure (V1) during the conversion there is evidently condensation of water on the coated model substrate, leading to the melting away of the originally locally clearly defined layer. This effect is not observed when using the silica gel (V2).

[0150] FIG. 1: Photographs of the planar model substrate in uncoated state, fixed by adhesive strip on the test stand (top, left), immediately after coating by spray application of the suspension (top, center) and after compaction of the suspension (right, drying under atmospheric conditions, adhesive strip already removed here). Bottom: scanning electron micrographs of the compacted suspension on the model substrate (bottom left: left-hand half of image clearly shows the uncoated region (where the adhesive strip was during spray coating)). Letters indicate in each case the region of enlargement.

[0151] FIG. 2: X-ray diffractograms of the compacted suspension on the model substrate (compacted) and also of the vapor-treated compacted suspension in accordance with experiment 1 (V1) and experiment 2 (V2) layer on the metal plaques.

[0152] FIG. 3: Photographic pictures (top) and scanning electron micrographs (bottom) of the metal plaques with the converted compacted suspension according to experiment 1 (left) and according to experiment 1 (right). Letters indicate in each case the region of enlargement.