Patent Application
20210316288
The present invention relates to a hybrid material, a method for the preparation thereof and its use as a catalyst support and/or for the decontamination of liquid or gaseous media.
The hybrid material according to the invention forms part of materials having a high specific surface area and an organized structure, namely a cellular structure having several types of porosity.
A “hybrid” material is understood to mean a material carrying inorganic functional groups and organic functional groups.
Such materials may find applications in many fields such as heterogeneous catalysis, solid phase extraction, filtration, electronics, optics or acoustics.
A material with an organized structure is known from FR-2 852 947, which is in the form of a monolith made of an inorganic material. A monolith is understood to mean a solid subject having an average size of at least 1 mm. The inorganic material consists of a polymer of an inorganic oxide, for example a polymer obtained from tetraethoxysilane Si(OEt)4. This material is obtained by a high internal phase inverse emulsion polymerization method and possesses three degrees of porosity: microporosity, mesoporosity and macroporosity. The presence of surface silanol groups, which have a certain degree of acidity, makes it possible to use this material in heterogeneous catalysis, but only in acid catalysis.
Materials are also known from the publication by A: Desforges et al., Adv. Func. Mater., 2005, 15, 1689-1695, having a porous organic Matrix based on styrene and divinylbenzene, functionalized by organic groups. These materials are obtained in the form of a monolith by a high internal phase inverse emulsion polymerization method. The monolith has both a macroporous character and a mesoporous character. Such materials are used satisfactorily as catalyst supports, for example a palladium catalyst in the form of nanoparticles. However, catalytic reactions carried out with such materials can be performed at a maximum temperature of 80° C., a temperature above which the organic matrix deteriorates and loses its monolithic character. Such a disadvantage thus limits the use of these materials to a considerable extent.
A continual need therefore exists for finding novel materials having improved properties prepared with known materials, and that are capable of acting as catalyst supports, notably in the rapidly expanding field of heterogeneous catalysis based on supported noble metals.
The inventors have been able to develop a material in the form of a monolith consisting of an inorganic polymer that is functionalized by special organic groups. They have discovered that such a material surprisingly exhibits high performance as a catalyst support, in the field of heterogeneous catalysis. Indeed, notably when it is associated under certain conditions with palladium nanoparticles, this material reveals itself to be more effective than known catalysts based on palladium on active carbon, and this at temperatures that may extend up to approximately 200° C. Moreover, this material is also efficient in other applications, notably the decontamination of liquid or gaseous media.
A material according to the present invention is a solid cellular monolith consisting of a polymer of an inorganic oxide, characterized in that:
A monolith is understood to mean an object of which the smallest of its dimensions is greater than one millimeter.
The inorganic oxide is an oxide of one or more elements, at least one of these elements being of the type capable of forming an alkoxide. As examples of elements capable of forming an alkoxide, mention may be made of Si, and metals such as Ti, Zr, Th, Nb, Ta, V, W and Al.
The inorganic oxide may be a simple oxide, and it then consists of an oxide of one of the above elements. The inorganic oxide may also be a mixed oxide of at least two elements, and at least one of the elements is chosen from the above elements, it being possible for the other elements to be notably B or Sn.
An inorganic polymer consisting of a polymer of silicon oxide or of a mixed oxide of silicon is particularly preferred.
In one embodiment, the inorganic oxide polymer carries a single type of R group. In another embodiment, the inorganic oxide polymer carries at least two different types of R group.
In particular, the organic group R may be:
A material according to the invention may be obtained by a method in which an emulsion is prepared by adding an oily phase to an aqueous solution of surfactant, at least one tetra-alkoxide (noted herein after by TAM) precursor of the inorganic oxide polymer is added to the aqueous surfactant solution, before or after preparing the emulsion, the reaction mixture is allowed to stand until the precursor condenses, and then the mixture is dried so as to obtain a monolith, said method being characterized in that at least one precursor alkoxide carrying an organic R group is added (noted hereinafter by the compound AMR).
In one embodiment, AMR is introduced into the aqueous surfactant solution before the oily phase is added.
In another embodiment, AMR is introduced into the oil phase that is then added to the aqueous TAM solution to form the emulsion.
In a 3rd embodiment, the inorganic monolith obtained from the aqueous surfactant solution and TAM after drying is impregnated with a solution of AMR.
In the 1st and 2nd embodiments, the hybrid monolith obtained at the end of the drying step may advantageously be subjected to a heat treatment, preferably carried out at a temperature of between 140° C. and 180° C. (for example for a period of 6 hours with a temperature rise of 2° C. per minute) with the aim of consolidating the monolith.
The mass ratio AMR/TAM is preferably less than 20/80. If the proportion of AMR is greater than 20%, the mechanical strength of the monolith is weakened.
Implementation of the first embodiment makes it possible to obtain a hybrid material in which the R groups are distributed statistically on the surface as well as in the core of the material.
Implementation of the second embodiment makes it possible to obtain a hybrid material having R groups distributed substantially on the surface of the material.
Implementation of the third embodiment makes it possible to obtain a hybrid material on which the R groups are present exclusively on the surface.
TAM is a tetra-alkoxide of a tetravalent element, possibly in a hydrolyzed and/or partially condensed form. Silicon tetra-alkoxides are particularly preferred, in particular tetramethoxysilane and tetraethoxysilane (TEOS). A silicate or any other substituted oligomer may also be used.
The compound AMR is advantageously chosen from trialkoxysilanes bearing an R group as defined above.
As an example, mention may be made of
The oily phase may consist of dodecane, or a silicone oil.
The surfactant compound may be a cationic surfactant chosen notably from tetradecyltrimethylammonium bromide (TTAB), dodecyltrimethylammonium bromide or cetyl-trimethylammonium bromide. When the surfactant compound is cationic, the reaction medium is brought to a pH below 3, preferably below 1. Cetyl-trimethylammonium bromide is particularly preferred.
The surfactant composition may also be an anionic surfactant chosen from sodium dodecylsulfate, sodium dodecylsulfonate and sodium dioctylsulfosuccinate (AOT). When the surfactant composition is anionic, the reaction medium is brought to a pH above 10.
The surfactant compound may finally be a non-ionic surfactant chosen from surfactants with an ethoxylated head, and nonylphenols. When the surfactant composition is non-ionic, the reaction medium is brought to a pH above 10 or below 3, preferably below 1.
For the preparation of a hybrid material carrying more than one type of R group, the various precursors of the various R groups may be introduced simultaneously into the reaction medium, or introduced during two successive steps.
When the precursors of the various R groups are introduced into the reaction medium during two successive steps, the first step may consist of the addition of an AMR′ compound according to the previously mentioned first or second variants, and the second step may consist of the subsequent grafting of an AMR″ compound (according to the previously mentioned third variant). In this case, it is understood that R′ and R″ each corresponds to the definition of R given above, R′ being different from R″.
A material according to the invention is particularly useful as a support for a metal catalyst, such as Pd, Au or Pt.
A supported catalyst is prepared by a method consisting of impregnating a monolith according to the invention with a solution of a catalyst metal precursor, and then of reducing the precursor.
The catalyst metal precursor is preferably an acetate or a chloride, for example Pd(CH3COO)2, PdCl2, PtCl4 or AuCl4.
The precursor is used in the form of a solution in a solvent, for example THF, THF/water, acetone/water or ethanol/water, according to the hydrophilic/lipophilic balance of the polymer forming the foam.
When the supported catalyst is intended to be used for a reaction in an oxidizing medium, a supported catalyst is preferably used prepared in the presence of a phosphine, for example triphenylphosphine.
A supported catalyst according to the present invention is of use notably for a Suzuki-Myaura reaction. The Suzuki-Myaura reaction is a carbon-carbon coupling reaction that makes it possible to form a biphenyl compound from an aryl iodide and an aryl hydrobromide.
A supported catalyst according to the present invention is also of use for the reaction of a Z—Ar—BH(NiPr2) compound with an Ar—Z′ compound in the presence of a Pd(O) catalyst, a base and water so as to obtain an Ar—Ar compound, according to the following equation of the reaction:
According to the reaction medium in which the catalyst has to be used, its hydrophilic or hydrophobic character may be adjusted by the choice of the Z or Z′ groups. For example, a Z or Z′ group of the alkyl or phenyl type increases the hydrophobic character of the hybrid material. A material carrying SH groups and/or NH2 groups is particularly useful as a metal catalyst support, since the presence of a non-binding doublet on sulfur and nitrogen permits electron stabilization of the metal nanoparticles formed.
A monolith consisting of an inorganic polymer of the prior art, described for example in the aforementioned Fr-2,852,947, could not be used as a metal catalyst support, on account of the fact that the inorganic polymer constituting said monolith of the prior art possesses only silanol groups on the surface that do not enable heterogeneous nucleation of the metal nanoparticles to be induced.
A material according to the present invention may also be useful for a Mitzoroki-Heck reaction, which is a carbon-carbon coupling reaction that makes it possible to form a biphenyl compound from an aryl halide (1) and styrene (2). Said reaction gives a mixture of E and Z isomers of stilbene. The halogen is chosen from Cl, Br and I. The equation for the reaction is given below for an iodide.
When the R substituent of a hybrid material according to the present invention is a lower alkyl group (1 to 3 carbon atoms) or a phenyl group, the hybrid material has a large capacity to adsorb aromatic compounds such as benzene, toluene or xylene (called hereinafter “BXT compounds”). It is therefore particularly useful for the decontamination of liquid or gaseous media that contain these compounds.
When the medium to be contaminated is a liquid medium, decontamination is carried out by immersion of the hybrid material in the liquid to be decontaminated.
When the medium to be decontaminated is a gaseous medium, the hybrid material is placed in a chamber, for example a column, and the gas to be decontaminated is led through the chamber.
A monolith of the prior art that possesses silanol groups on the surface, has a hydrophilic character to a high degree, which notably limits the impregnation of the the monolith by hydrophobic liquids such as benzene, xylene or toluene.
ka to 3kb are SAXS diffusion profiles produced on the g-amino-SiO and g-mercapto-SiO monoliths.
The present invention is illustrated by the concrete examples described hereinafter, to which it is however not limited.
Examples A1 to A 3 concern the preparation of hybrid materials according to the invention, example A4 describes the characterization of the materials obtained, examples B1 to B2 describe the preparation of supported catalysts from materials according to the invention, example C1 and C2 describe catalytic tests, and examples D1 and D2 described decontamination treatment tests.
Preparation of an SiO2 Monolith Carrying R Groups, with R=Benzyl
This example illustrates the first variant of the method.
4.05 g of tetraethoxysilane (TEOS) and 1 g of benzyltriethoxysilane were added to 16.01 g of a 35% by weight aqueous solution of tetradecyltrimethylammonium bromide (TTAB). 5.87 g of 37% HCl were then added. In order to permit hydrolysis of the compounds before the oily phase was added, the solution prepared in this way was left with stirring for 5 minutes. The oily phase, consisting of 40.06 g of dodecane, was then added dropwise, and the system was then emulsified by hand with a mortar. The emulsion prepared in this way was placed in a closed plastic container in order to allow the precursors to condense. The condensation step proceeded over a period of one week. The oily phase was then extracted by immersing the compound in a THF/acetone solvent (80/20 by volume) for 24 hours. This washing step was repeated three times, before the immersed compound was left for one hour in an acetone solution. The compound was then dried by leaving it in air in a beaker with a non-airtight lid on top, in order to prevent too violent or rapid evaporation of the washing solvent that would bring about the formation of crack zones in the monolith prepared in this way. Finally, the compound was treated for 6 hours at 180° C. (temperature rise rate of 2° C. per minute), so as to sinter it slightly and in this way to improve its mechanical strength.
Other trialkoxysilanes could also be used for the preparation of SiO2 hybrid monoliths, by following the same operating mode as described above according to the first variant of the method according to the invention. They consisted of the following AMR compounds: methyltriethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-aminopropyl) triethoxysilane, 3-(2,4-dinitrophenylamino)propyltriethoxysilane, N-(2-aminoethyl)-3 aminopropyltrimethoxysilane and N-(3-trimethoxysilylpropyl) pyrrole.
Table 1 gives, for each preparation, the weights (in grams) of tetraethoxysilane (TEOS), of the AMR compound, of TTAB, of dodecane and of the HCl used.
Preparation of an SiO2 Monolith Carrying R Groups with R=3-Mercaptopropyl
This example illustrates the second variant of the method.
4.02 g of TEOS were added to 16.01 g of a 35% by weight aqueous solution of tetradecyltrimethylammonium bromide (TTAB). 5.87 g of 37% hydrochloric acid were then added. In order to permit hydrolysis of the TEOS before the oily phase was added, the solution prepared in this way was left with stirring for 3 minutes. The oily phase, consisting of 40.06 g of dodecane containing 1.02 g of (3-mercaptopropyl)trimethoxysilane) was added dropwise, and the system was then emulsified by hand with a mortar. The emulsion prepared in this way was placed in a closed plastic container in order to allow the precursors to condense. The condensation step proceeded over a period of one week. The oily phase was then extracted by immersing the compound in a THF/acetone solvent (80/20 by volume) for 24 hours. This washing step was repeated three times, before the immersed compound was left for one hour in an acetone solution. The compound was then dried by leaving it in air in a beaker with a non-airtight lid on top. The compound was then treated for 6 hours at 180° C. (temperature rise rate of 2° C. per minute), so as to sinter it slightly and in this way to improve its mechanical strength.
Other trialkoxysilanes were also used for the preparation of SiO2 hybrid monoliths, following the same operating mode as described above according to the second variant of the method according to the invention. They consisted of the following AMR compounds: methyltriethoxysilane, benzyltriethoxysilane, (3-aminopropyl)triethoxysilane, 3-(2,4-dinitrophenylamino)propyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-(3-trimethoxysilylpropyl)pyrrole.
Table 2 gives, for each preparation, the weights (in grams) of tetraethoxysilane (TEOS), of the AMR compound, of TTAB, of dodecane and of the HCl used.
Preparation of an SiO2 Monolith Carrying R Groups with =3-Pyrrolylpropyl. This Example Illustrates the Third Variant of the Invention.
The SiO2 monolith was first prepared. To this end, 6.1 g of hydrochloric acid were introduced into 16.07 g of a 35% by weight TTAB solution. 5.01 g of TEOS were then added dropwise as well as 40.02 g of decane, while emulsifying by hand by means of a mortar. The condensation step for the precursor proceeded for a period of one week and the oily phase was then extracted by immersing the monolith obtained in THF for hours, this step being repeated three times. The monolith was then carefully dried, so as to avoid too violent evaporation of THF. The monolith was then calcined at 600° C. in air for 6 hours, so as to sinter it slightly and to release the mesoporosity (induced by TTAB micelles). The material constituting the monolith thus obtained is called hereinafter “native silica”.
In a second step, 3-pyrrolylpropyl groups were grafted onto the SiO2 monolith synthesized in the first step, by proceeding in the following way: 3.1 g. of N-(3-trimethoxysilylpropyl)pyrrole were introduced into 150.40 g of chloroform. 1.2 g of the SiO2 monolith were then immersed in this solution. In order to increase the diffusion kinetics, the beaker containing the solution and the monolith was placed in a chamber under vacuum until the monolith fell to the bottom of the beaker. It could be ensured in this way that the monolith was completely impregnated by the reaction medium. This step lasted between 5 and 10 minutes. The beaker was then taken out of the vacuum chamber and then closed and allowed to stand for 24 hours. The compound obtained was then placed for one hour in a beaker containing acetone. The monolith was then dried in air in a beaker having a non-airtight lid on top.
Other trialkoxysilanes were also used to prepare hybrid SiO2 monoliths, by following the same operating mode as that described above, according to the third variant of the method according to the invention. They consisted of the following compounds: methyltriethoxysilane,
Table 3 gives, for each preparation, the weights (in grams) of the SiO2 monolith, trialkoxysilane (AMR) and chloroform used.
The monoliths obtained according to examples A1, A2 and A3 (namely according to the three variants of the method according to the invention) were characterized by various analytical methods so as to reveal their macroporous, mesoporous and microporous character. The monoliths obtained according to the first variant of the method exhibited the same properties as those obtained according to the second variant. Consequently, the data presented below for monoliths synthesized according to example A1 were acceptable for monoliths synthesized according to example A2 carrying the same R groups.
The monoliths subjected to characterization were as follows: pyrrole-SiO-1a, methyl-SiO-1a, DNP-amino-SiO-1a, mercapto-1a, benzyl-SiO-2a, mercapto-SiO-1a, g-amino-SiO and g-mercapto-SiO.
The general appearance of a monolith according to the invention is presented in the photograph of
The photographic plates of figures 1b to 1f were obtained by transmission electron microscopy (TEM). These plates were produced on pyrrole-SiO-1a, methyl-SiO-1a, DNP-amino-SiO-1a, benzyl-SiO-2a, mercapto-SiO-1a monoliths, containing respectively 3-pyrrolylpropyl groups (plate 1b), methyl groups (plate 1c), 3-(2,4-dinitrophenylamino)propyl groups (plate 1d), benzyl groups (plate 1e) and 3-mercaptopropyl groups (plate 1f).
The plate of
These plates show that the macroscopic cells were polydispersed with a size varying between 5 μm and 30 μm. The macroscopic structure of the monoliths resembled an aggregation of hollow spheres (similar to that of the native silica monolith of example A3), with the exception of the monolith having (dinitrophenylamino)propyl groups (plate 1d), of which the intercellular walls were completely mineralized.
Mercury intrusion macroporosimetry measurements were performed at ambient temperature for various samples.
The sample was weighed and degassed under a vacuum of 6×10−6 MPa, before being placed in a measuring cell. The measuring cell was then filled with mercury at a pressure of 3.4×10−3 MPa and then successive pressures were generated between 3.4×10−3 MPa and 120 MPa (which corresponded to the theoretical pore diameters). At each pressure, the electrical capacity was measured by the rod of a penetrometer and a deduction was made of the volume of mercury that had penetrated into the sample. The results are given in the table 4 below.
The results of mercury intrusion porosimetry measurements have been given in
It follows from these measurements that the windows connecting two adjacent macropores have a bimodal character. These windows and the associated macropores correspond to the characteristic sizes that permit impregnation with and rapid flow of solvent within the material (Darcy's law). These interconnected macropores (by inter-pore windows) will make it possible to irrigate all the mesopores and in this way to optimize all the surface area of the materials, which constitutes an important property for impregnation by BXT compounds.
The mesoporous character was studied by transmission electron microscopy associated with small angle X-ray diffraction measurements (SAXS).
ka to 3 kb are SAXS diffusion profiles performed on other samples.
The correspondence between the monoliths and curves of
It follows that all the materials exhibited a mesoporous character. The figures also show that
Specific surface area measurements were also performed by nitrogen adsorption-desorption techniques (B.E.T. and B.J.H. methods). The results are given in table 5 below.
From the results of table 5, it may be concluded that the monoliths had a super-microporous character (pore size between 10 and 20 Å) as well as a mesoporous character (pore size greater than 35 Å). These results confirm that the grafting of organic groups onto the surface of the pores reduces the specific surface area and the pore volume compared with native silica.
The BJH method essentially gave mesopores having a size greater than 35 Å. The microporosity was obtained by difference with the BET data. The pore size distribution, obtained by the theory of differential functions, gave a bimodality of the pore sizes centered on 15 Å (super-micropores) and 25 Å (mesopores).
The pore size distribution was also determined by the DFT (differential functional theory) method. The results are given in
The correspondence between the monoliths and the figures is given in the table below.
The results that follow from these figures are in good agreement with the results obtained by the BET and BJH methods since, for all the samples, the curves exhibited a bimodal character with a peak around 10 Å (presence of micropores) and a peak around 22 Å (presence of mesopores).
The microporous character of the monoliths was also studied by NMR 29Si measurements, of which the results are given in
The spectra correspond, from top to bottom, to the methyl-SiO-1a, mercapto-SiO-1a, benzyl-SiO-1a, pyrrole-SiO-1a, and DNP-amino-1a monoliths.
The T and Q peaks of the spectra are attributed as indicated in table 6.
This method made it possible to identify and quantify the various siloxane groups present in the monoliths. Table 7 gives a comparison of the results obtained from NMR 29Si measurements with the expected results from the molar ratios of the precursors of the reaction (TEOS and alkoxysilane groups).
The experimental results (two right hand columns) were in agreement with the theoretical calculations (two left hand columns) which show that the synthetic method used made it possible to control well the final composition of the material.
Moreover, infrared spectroscopy measurements were taken so as to verify that the final treatment of the monoliths at 180° C. for 6 hours had not damaged the R groups.
The spectra obtained are shown in
These spectra show the signals corresponding respectively to the 3-pyrrolylpropyl group (1360 cm−1 and 1650 cm−1,
The R groups present in the monoliths were thus not damaged by the effect of heat treatment.
The supported catalysts were prepared from materials obtained according to the method of example A3, and carrying respectively N-(2-aminoethyl)-3-aminopropyl, 3-aminopropyl, 3-mercaptopropyl, 3-(2,4-dinitrophenylamino)propyl and N-(3-propyl)pyrrole groups and a material carrying 3-mercaptopropyl groups prepared according to the method of example 1.
A hybrid monolith obtained according to the method of example A3 was impregnated with a 5×10−2 M solution of Pd(CH3COO)2 in THF for a period of two days, while employing three degassing cycles of 15 minutes each, and a 0.5 M NaBH4 solution was then added in a water/THF mixture (50/50). This mixture was allowed to stand for one day using the same degassing cycles as previously, and the materials were then recovered by filtration, washed with an ethanol/acetone mixture (80/20 by volume) for 24 hours with stirring, and dried in the open air.
The following table indicates the catalytic systems prepared and the modified monolith from which each one was derived.
The catalytic systems obtained were characterized by transmission electron microscopy.
The monoliths used were obtained by the method of example 3, except for the PD@Mercapto-SiO2 monolith of
These plates gave important information on the degree of aggregation of the supported catalysts, knowing that an increase in the degree of aggregation corresponds to a reduction in the active surface area and consequently the catalytic efficiency.
Supported catalysts were prepared from the same hybrid monoliths as those indicated in example B1, in the presence of triphenylphospine.
Pd(CH3COO)2 (0.33 g, 1.5 mmol) was dissolved in 30 ml of THF in order to obtain a concentration of 5×10−2 mol·1−1. Triphenylphosphine was then added (two equivalents, 3 mmol, 0.78 g). The mixture was stirred until completely dissolved. A change of color was then observed, the solution passing from a brown color to a bright red color. A 0.8 g quantity of hybrid material was added and three degassing cycles of 15 minutes each were carried out for three days so as completely to impregnate the hybrid material.
A freshly prepared solution of NaBH4 (10 equivalents, 0.56 g, 15 mmol) in 30 ml of a water/THF mixture (50/50 v/v), was added to the solution containing the hybrid material with gentle stirring. The solution became black.
The blocks of hybrid material were recovered by filtration, washed for two days with ethanol with stirring and then dried in the open air.
The TEM plates obtained were similar to those for materials prepared according to example B1.
The palladium content was determined by elementary analysis for the sample of material carrying mercapto groups. It was 3.9% by weight.
Supported catalysts were prepared from the hybrid monoliths prepared according to example 3.
1 g of the monolith obtained according to example A3 was added to a solution containing Pd(CH3COO)2 (0.33 g, 1.5 mmol) and triphenylphosphine PPh3 (4 equivalents, 6 mmol, 1.57 g) in 30 ml of THF to obtain a concentration of 5×10−2 mol·l−1 of acetate, and was left in the dark for 2 days.
A freshly prepared solution of NaBH4 (10 equivalents, 0.56 g, 15 mmol) in 30 ml of a water/THF mixture 50/50 v/v), was added to the solution containing the hybrid material with gentle stirring. The color of the reaction medium changed from yellow to black in one hour.
The monolith of hybrid material was then recovered by filtration, washed for two days with ethanol until it became colorless and then dried in the open air.
A supported catalyst was prepared in this way, on the one hand with a g-amino-SiO monolith and on the other with a g-mercapto-SiO monolith.
Characterization with TEM
The TEM plates obtained were similar to those of materials prepared according to example B1.
A Pd@g-mercapto-SiO monolith carrying mercaptopropyl groups and Pd particles generated by heterogeneous nucleation were obtained according to the same method, and its XPS diagram was similar to that of the Pd@g-amino-SiO monolith.
The Pd content of the supported catalyst was determined by elementary analysis. It was 3.9% by weight for the sample carrying Pd@g-amino-SiO groups and 4.1% by weight for the sample carrying Pd@g-mercapto-SiO groups.
The catalytic activity of the various catalytic systems obtained according to examples B1 and B2 was tested on the Suzuki-Myaura reaction, employing the following operating procedure.
A 50 ml three-necked flask was used provided with a condenser at −20° C.
1 equivalent (0.097 g) of the catalytic system was introduced into the flask as well as 200 equivalents (0.576 g) of K2CO3, an internal standard and 5 mL of dioxane.
A mixture was prepared of 100 equivalents (0.3905 g) of iodobenzene, 150 equivalents (0.3584 g) of phenylboronic acid and 5 mL of dioxane, and this mixture was introduced into the three-necked flask with the aid of a syringe. The three-necked flask was then left in an oil bath at 115° C. under reflux with dioxane for 3 days and a follow-up was carried out by taking samples at regular intervals.
Assessments of the state of the reaction were established by liquid phase chromatography, bringing the temperature from 50° to 180° C. at a rate of 6° C. a minute on a Varian 3300, using an injector at 220° C., a detector at 200° C. at a pressure of 10 psi, a DB5 column that had a length of 30 m, an internal diameter of 0.25 mm and a film that had a thickness of 0.1 μm.
The degree of conversion obtained with each of the catalytic systems is shown as a function of time on
The catalysts according to the invention that were tested are indicated in the following table with the corresponding figures:
It appears that the catalytic systems according to the invention obtained by the method of, example B1 (without phosphine) possessed an activity close to that obtained by palladium nanoparticles on active carbon. They had however the advantage of being in a monolithic form and therefore not requiring a separation step with the catalyzed material by filtration or centrifugation for example. The materials tested thus possessed satisfactory performance and were more easily employed than a conventional catalyst such as the palladium/active carbon system.
It moreover appears that the material according to the invention obtained by the method of B2, that is to say in the presence of triphenylphosphine, possessed superior activity to that obtained by palladium nanoparticles on active carbon.
The catalytic activity of the various materials obtained according to examples B2 and B3 were tested on the Mitzoroki-Heck reaction, that may be shown schematically in the following manner
E and Z denoting isomers of stilbene.
A solution containing 10 mmol, (2.04 g) of iodobenzene 1, 15 mmol (1.56 g) of styrene 2, 11 mmol (1.11 g) of triethylamine, 5 mmol (0.85 g) of dodecane (as a reference standard for gas chromatography) and 10 mL of DMF and the supported catalyst were placed in a glass flask provided with a tap with sintered glass. The reaction medium was purged with argon for 10 min, and then the reactor was placed in an oil bath at 155° C., without stirring. Samples were extracted periodically and diluted with THF at 0° C., so as to follow the degree of conversion.
After the reaction had finished, the liquid phase was extracted from the reactor, under argon, through the sinter, a new mixture of reagents was introduced into the reactor and a new reaction was carried out. This operation was reproduced several times in order to test the stability of the catalyst with time.
The operations above were carried out on the one hand with a monolith bearing mercaptopropyl groups and on the other hand with a monolith carrying aminopropyl groups.
For the preparation of this catalyst, 0.055 g of support were used instead of 0.11 g. This was the same catalyst, but half the amount was used.
An SiO2 monolith containing methyl groups, obtained by the method described in example A3 was used for the decontamination of a gas flow containing toluene.
0.1021 g of said monolith was used for treating a gas flow containing 241.8 mg of toluene in 1 g hexane. These proportions corresponded to a toluene level close to that generally encountered in the atmosphere, namely 10 μg/m3. Hexane was used as a carrier for toluene by reason of its quite high saturated vapor pressure, preventing it from condensing on the walls and on account of the fact that it is transparent in UV-visible.
The percentage impregnation of the monolith by toluene was estimated by UV-visible spectroscopy. The absorption band for toluene in the UV-visible is situated at 268.2 nm.
It appeared that 80% of toluene contained in the gas flow was absorbed by the monolith and that this phenomenon was stable with time, since it proceeded in the same way for more than an hour.
It should be noted that this result, although convincing, is not optimal on account of the fact that the measuring chamber was not totally filled with the monolith, but contained pieces of monolith separated by empty spaces.
Similar results were obtained with hybrid monoliths containing methyl or phenyl groups, synthesized according to the methods of examples A1 and A2.
An SiO2 monolith containing phenyl groups, obtained by the method described in the example A3, was used for the decontamination of a liquid phase consisting of toluene.
The hybrid monolith became opalescent after one hour's immersion in the liquid phase containing toluene. The monolith was therefore not dissolved, but took the refractive index of the surrounding medium, which showed that it had been impregnated by toluene. This phenomenon came from the special porous character of the monolith (triple porosity), of its hydrophobic character induced by phenyl groups, and the inorganic Si—O—Si connectivity that insured cohesion of the porous edifice.
Similar results were obtained with hybrid monoliths containing methyl or phenyl groups, synthesized according to the methods of examples A1 and A2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0701077 | Feb 2007 | FR | national |
| PCT/FR2008/000193 | Feb 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR08/00193 | 2/14/2008 | WO | 00 | 2/7/2013 |
