Method for obtaining metal oxides supported on mesoporous silica particles

Abstract

A method for obtaining metal oxides supported on mesoporous silica particles includes a) providing a solution of at least one metal salt, b) providing a solution of at least one template forming agent of the general formula (I) Y.sub.3Si(CH.sub.2).sub.nX (I), wherein X is a complexing functional group; Y is OH or a hydrolysable moiety selected from the group containing halogen, alkoxy, aryloxy, acyloxy, c) mixing the metal salt solution and the complex forming agent solution to obtain a metal precursor; d) adding at least one solution containing at least one pore structure directing agent to the metal precursor to obtain a metal precursor template mixture; e) adding at least one alkali silicate solution to the metal precursor template mixture at room temperature to obtain a silica-supported metal complex; and f) calcination of the silica-supported metal complex under air to obtain the supported metal oxide mesoporous silica particles.

Claims

1. A method for preparing metal oxides supported on mesoporous silica particles comprising the steps of: a) providing a solution of at least one metal salt, wherein the metal is selected from a group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Ir, Pt and Au; b) providing a solution of at least one complex forming agent, wherein the at least one complex forming agent is of the general formulae (I)
Y.sub.3Si(CH.sub.2).sub.nX(I) wherein: X is a complexing functional group, Y is OH or a hydrolysable moiety selected from the group consisting of halogen, alkoxy, aryloxy, and acyloxy, and n is 1; c) mixing the metal salt solution of step a) and the complex forming agent solution of step b) to obtain a metal precursor solution with a pH value between 6-12, which functional group/metal ratio is 1; d) adding a buffered solution containing at least one pore structure directing agent (SDA) (or template) adjusted to a pH range between 2 and 8; e) mixing the metal precursor solution of step c) and the buffered template solution of step d) to obtain a buffered metal precursor-template-mixture; f) adding at least one alkali silicate solution to the metal precursor-template mixture of step d) at room temperature to obtain a silica-supported metal complex, at a pH adjusted to a range between 4 and 8; and g) calcining of the silica-supported metal complex of step f) under air to obtain the supported metal oxide mesoporous silica particles.

2. The method according to claim 1, wherein Y is OH, C.sub.1-6-Alkoxy, C.sub.6-10-Aryloxy, or C.sub.2-7-Acyloxy.

3. The method according to claim 1, wherein X is hydroxy (OH), amine (NR.sup.2.sub.2, where R.sup.2 is H or an alkyl chain), imino, urea (NH)CO(NH.sub.2)), amide (CONH.sub.2)), carboxylic acid (CO.sub.2H), carboxylic acid anion (CO.sub.2), sulfonic acid (SO.sub.3H), sulfonic acid anion (SO.sub.3), methanethionic acid (CS.sub.2H), phosphonate (PO.sub.3R.sup.3.sub.2 with R.sup.3 is an alkyl chain), phosphonic acid (PO.sub.3H.sub.2), sulfide (S), phosphine (PR.sup.4.sub.2, where R.sup.4 is H or an alkyl chain), pyridine, or pyrazine.

4. The method according to claim 1, wherein the at least one complex forming agent of general formulae (i) is selected from a group comprising Carboxyethylsilanetriol sodium salt, (3-Aminopropyl)trimethoxysilane, N1-(3-Trimethoxysilylpropyl)diethylenetriamine, N-(2-Aminoethyl)-3-aminopropylsilanetriol, 3-Aminopropylsilanetriol, (N,N-Dimethylaminopropyl)trimethoxysilane, 1-[3-(Trimethoxysilyl)propyl]urea, N-[3-(Trimethoxysilyl)propyl]ethylenediamine, 3-[Bis(2-hydroxyethyl) amino]propyl-triethoxysilane, N-(Trimethoxysilylpropyl)-ethylenediaminetriacetate, tripotassium salt, N-(Trimethoxysilylpropyl) ethylene-diaminetriacetate, tripotassium salt, 3-(Trihydroxysilyl)-1-propanesulfonic acid, (2-diethylphosphatoethyl) triethoxysilane, 3-(trihydroxysilyl)propyl methylphosphonate, Bis[3-(triethoxysilyl) propyl]tetrasulfide, Bis[3-(triethoxysilyl)propyl]disulphide, (2-Dicyclohexylphosphinoethyl) triethoxysilane, 2-(Diphenylphosphino)ethyl-triethoxysilane, 2-(4-pyridylethyl) triethoxysilane, 3-(4-pyridylethyl)thiopropyltrimethoxysilane and (3-Bromopropyl)trimethoxysilane.

5. The method according to claim 1, wherein the metal salt and the complex forming agent are mixed in a ratio 1.

6. The method according to claim 1, wherein the at least one pore structure directing agent (SDA) or template is a non-ionic polymeric pore structure directing agent.

7. The method according to claim 1, wherein the SDA or template is dissolved in a buffered solution adjusted to a pH range between 2 and 8.

8. The method according to claim 1, wherein the metal precursor-template-mixture obtained in step d) is stirred at room temperature for 12-36 h.

9. The method according to claim 1, wherein the at least one alkali silica solution comprises an aqueous sodium silicate solution.

10. The method according to claim 1, wherein the at least one alkali silica solution comprises the alkali silicate in an amount between 20 and 40 wt % based on the total solution.

11. The method according to claim 1, wherein in step f) the pH of the mixture is adjusted to a range between 4 and 8 in a buffered system.

12. The method according to claim 1, wherein the buffer system is composed of acetic acid/sodium acetate, sodium citrate/citric acid, Na.sub.2HPO.sub.4/citric acid, HCl/sodium citrate or Na.sub.2HPO/NaH.sub.2PO.sub.4.

13. The method according to claim 1, wherein the silica-supported metal complex obtained in step f) is allowed to age for 12 to 48 h at a temperature between 20 C. and 100 C.

14. The method according to claim 1, wherein the calcination of the supported metal silica complex in step g) is carried out at a temperature between 40 and 800 C. for 2-12 h.

15. The method according to claim 1, wherein the metal oxide is used as affinity material for enzyme purification, enzyme immobilization, or catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following the proposed solution is explained in more detail by means of the example with reference to the Figures.

(2) FIG. 1 shows a scheme of a general route for the preparation of nickel oxide supported ordered mesoporous silica as one embodiment of the present method.

(3) FIG. 2 shows a schematic representation of the steps involved in the synthesis of nickel oxide supported ordered mesoporous silica as one embodiment of the present method.

(4) FIG. 3 shows a process flow diagram for the continuous production of silica-supported nickel complex.

(5) FIG. 4 shows Adsorption-desorption isotherm of the nickel oxide supported on ordered mesoporous silica obtained by the present method.

(6) FIG. 5 shows pore size distribution of the nickel oxide supported on ordered mesoporous silica obtained by the present method.

(7) FIG. 6 shows transmission electron microscopy images of the nickel oxide supported on ordered mesoporous silica obtained by the present method.

DETAILED DESCRIPTION

(8) In the following the process steps of the present method are described in more detail for the synthesis of nickel oxide supported mesoporous silica. FIGS. 1 and 2 depict the general route for the preparation of NiO@OMS.

(9) The supported nickel complex is formed via a one-pot synthesis that takes place immediately at room temperature. The synthesis is based on the condensation of the inexpensive sodium silicate precursor and a nickel precursor using a triblock copolymer as a structure directing agent (hereby referred to as the template) under quasi-neutral conditions.

(10) The formation of the nickel precursor takes place using a silanetriol-functionalised ligand of the general formulae (I) able to form a nickel(II) carboxylate complex. The formed supported nickel complex is calcined at 500 C. under air to remove all the organics (template and functional groups), leading to the deposition of well-distributed nickel(II) oxide species on the surface of the mesoporous silica support.

(11) The one-pot synthesis of the supported nickel complex takes place in water under adequate pH conditions. The precursor solutions require an optimal pH to achieve (1) a maximal loading of nickel, and (2) fast condensation of the silica and nickel precursors. The nickel precursor, which is prepared by reaction of nickel(II) sulfate hexahydrate (NiSO.sub.4.Math.6H.sub.2O) and disodium salt of carboxyethylsilanetriol (herein CES) according to formulae (I) in water, has a pH in the range of 8-12, which ensures a complete stoichiometric reaction between the reactants in a CES:Ni molar ratio of 2:1.

(12) On the other hand, the fast condensation of the silica precursor, sodium silicate, and the nickel precursor takes place at a pH5, for which an acetic acid/acetate buffer is used.

(13) The condensation of the precursors in such a short time leads to a material with well-dispersed nickel species, which upon calcination leads to a final material with desirable physical properties (high surface area, large pore size, high pore volume, well-dispersed nickel oxide species).

(14) The scheme of FIG. 3 provides a conceptual process flow diagram for a continuous production of supported metal silica complex. The set up comprise a synthesis section (left side) and a downstream section (right side).

(15) The synthesis section comprises one feed tank F-1 for the silica precursor solution, and a second feed tank F-2 for the mixed solution containing the metal salt, the complex forming agent and the at least one pore structure directing agent (SDA).

(16) The synthesis section comprises furthermore the static mixers SM-1 for mixing both of the solutions.

(17) The downstream section comprises the devices and apparatus required for aging, separating, drying and calcination. Specifically, the downstream section comprises aging tank A-1, a filter unit for separating the silica-supported metal complex, a washing unit, a drying unit and a calcination unit for calcination of the silica-supported metal complex to obtain the metal oxide supported on mesoporous silica particles.

(18) Pumps P-1, P-2 are used for transporting the feeds and suspensions in the synthesis section and downstream section.

EXPERIMENTAL SECTION

Example 1

(19) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.77 g (2.9 mmol Ni) of nickel(II) sulfate hexahydrate were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(20) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO.sub.2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the nickel-carboxyethylsilanetriol-template mixture, leading to the instant formation of a green precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(21) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

(22) The calcined material was characterized by nitrogen physisorption to obtain information about the pore structure and properties of the material. The adsorption-desorption isotherm, shown in FIG. 4, can be classified as type IV, according to the IUPAC classification, and has a type-I hysteresis loop, typical of mesoporous materials with uniform pore structure.

(23) The pore size distribution was calculated using the DFT model using the adsorption branch of the isotherm. A narrow pore size distribution is observed in FIG. 5, with a maxima at 6.5 nm.

(24) From the adsorption-desorption isotherm, the total surface area was calculated using the BET model, and the pore size distribution using the DFT model using the adsorption branch. The data is presented in Table 1.

(25) TABLE-US-00001 TABLE 1 Physical properties of the NiO@OMS material. Total Pore Pore surface area diameter volume (m2/g) (nm) (ml/g) NiO@OMS 485.7 6.5 0.65

(26) The NiO@OMS was also characterized by powder X-ray diffraction. The small-angle X-ray diffraction pattern shows the presence of the (100) diffraction peak at 0.98 typical of 2D hexagonal mesostructures, such as SBA-15 or COK-12.

(27) The wide-angle X-ray diffraction analysis reveals the broad pattern typical of the amorphous silica matrix. There is no presence of diffraction peaks associated to large nanoparticles of NiO or any other species, which indicates the well-distributed nature of the NiO species as a 2D sub-monolayer.

(28) The NiO@OMS material was also characterized by transmission electron microscopy. From the recorded TEM images, shown in FIG. 6, a cylindrical pore structure can be observed, typical for hexagonal mesostructures of the type of SBA-15 or COK-12. A pore diameter of 6.5 nm was measured from a recorded image in the perpendicular direction to the pore axis, which is consistent with data obtained by N2 physisorption analysis. The deposition of nickel oxide on the surface of the silica support did not lead to a collapse of the ordered structured, which was also revealed by SAXRD and N2 physisorption analysis. The presence of large nanoparticles encapsulated inside the pores is not observed even at the largest magnification, which confirms that nickel oxide exists as a well-dispersed layer on the surface of the silica matrix.

(29) Point EDX analysis was carried out during the TEM measurement, and the presence of Ni, O and Si was confirmed.

(30) The material was also characterized by diffuse reflectance UV-vis spectroscopy. Compared to bulk NiO, the spectrum of the NiO@OMS material do not show the presence of absorption bands in the visible region (Liu, D.; Quek, X. Y.; Cheo, W. N. E.; Lau, R.; Borgna, A.; Yang, Y. J. Catal. 2009, 266 (2), 380), which indicates the absence of large 3D nanoparticles, further supporting the observations clone by wide-angle X-ray diffraction. Instead, the presence of NiO as well-dispersed species is expected. The presence of absorption bands in the UV region suggests that all the nickel centers exist in a distorted tetrahedral environment, possibly by forming ONiOSiO bonds, as previously suggested (Lu, B.; Kawamoto, K. Catal. Sci. Technol. 2014, 4 (12), 4313).

Example 2

(31) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.73 g (1.93 mmol Al) of aluminum nitrate nonahydrate (Al(NO3)3.Math.9H2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(32) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the aluminium-carboxyethylsilanetriol-template mixture, leading to the instant formation of a white precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h

(33) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

Example 3

(34) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.54 g (2.9 mmol Cu) of copper(II) nitrate hemi(pentahydrate) (Cu(NO3)2.Math.xH2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(35) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the copper-carboxyethylsilanetriol-template mixture, leading to the instant formation of a blue-green precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(36) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

Example 4

(37) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.84 g (2.9 mmol Co) of cobalt(II) nitrate hexahydrate (Co(NO3)2.Math.6H2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(38) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the cobalt-carboxyethylsilanetriol-template mixture, leading to the instant formation of a pink precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(39) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

Example 5

(40) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 1.17 g (2.9 mmol Fe) of iron(III) nitrate nonahydrate (Fe(NO3)3.9H2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(41) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the iron-carboxyethylsilanetriol-template mixture, leading to the instant formation of a brown precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(42) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

Example 6

(43) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.52 g (1.45 mmol Zr) of zirconium(IV) sulfate tetrahydrate (Zr(SO4)2.Math.4H2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(44) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the zirconium-carboxyethylsilanetriol-template mixture, leading to the instant formation of a light yellow precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(45) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.

Example 7

(46) 2 g of P123 were dissolved in 54 g of deionized water (DIW). To this solution, 2.26 g of acetic acid and 5.67 g of anhydrous sodium acetate were added and the solution was stirred. 0.77 g (2.9 mmol Pd) of palladium(II) nitrate dihydrate (Pd(NO3)2.Math.2H2O) were dissolved in 20 g of DIW, and 4.58 g (5.8 mmol Si) of a solution of the disodium salt of carboxyethylsilanetriol (25 wt % in water) were added and the mixture was stirred. After one hour of stirring, both solutions were mixed and the resulting solution was stirred for 24 h at room temperature.

(47) After this time, 5.20 g (23.4 mmol Si) of a solution of sodium silicate (27% SiO2, 10% NaOH) were added to 15 g of DIW, and the resulting solution was added to the palladium-carboxyethylsilanetriol-template mixture, leading to the instant formation of a brown precipitate. The reaction mixture was stirred for 5 minutes, and then aged under static conditions for 24 h.

(48) The solid material was filtered under vacuum and washed with 500 g of DIW. The material was then dried at 80 C. for 12 hours. Finally, the material was calcined at 500 C. for 6 h using a temperature ramp of 5 C./min.