Metal silicide, preparation method and hydrogenation reaction method

Abstract

The invention discloses a metal silicide, the metal silicide is prepared by pyrolysis of a precursor, the precursor comprises polyhedral oligomeric silsesquioxane and a metal salt, and the structural formula of the polyhedral oligomeric silsesquioxane is (RsiO3 / 2) n, wherein n is an even number in the range of 6-20. According to the metal silicide, polyhedral oligomeric silsesquioxane is selected as a silicon source, the metal silicide can be prepared through a one-step heating silicification method at a low temperature, and the metal silicide shows good catalytic performance when being applied to a selective hydrogenation reaction of carbon-carbon triple bonds.

Description

Technical Field

[0001] The present invention relates to the field of metal silicide materials, and in particular to a metal silicide, a preparation method and a hydrogenation reaction method. Background Art

[0002] Metal silicides are now widely used in thermoelectric materials, solar energy conversion, lithium-ion batteries, catalysis and other fields due to their unique physical and chemical properties. Compared with other metal-based compound catalysts, metal silicide catalysts are a new type of catalytic material, and their main application areas are not limited to traditional reactions such as hydrogenation / dehydrogenation and oxidation, but can also be used in photocatalysis and electrocatalysis reactions.

[0003] At present, the common methods for preparing silicides include: molten salt reaction method, chemical vapor deposition method and one-step temperature silicide method. The molten salt reaction method uses silicon powder / SiCl4 / sodium fluorosilicate and metal chloride as precursors to generate metal silicides under the combined action of high temperature and high pressure, molten salt and alkali metal / alkaline earth metal reducing agents. However, the preparation process of this method is relatively harsh. The reducing agents used in the reaction are mostly active single metals such as K and Na, which are dangerous. Moreover, the silicides prepared by this method, such as NbSi2, CrSi2, MoSi2, etc., are mostly not suitable for catalytic reactions. Chemical vapor deposition is an effective method for preparing highly dispersible catalysts by regulating the type of precursor, deposition time, and deposition temperature. It is also a common means of preparing metal silicide catalysts. However, this method also faces some disadvantages: since CVD has certain requirements for the saturated vapor pressure of the precursor, there are currently few types of silicon sources that meet this requirement and most of them are toxic and harmful, which is not conducive to the development concept of green chemistry today.

[0004] Polyhedral oligomeric silsesquioxane (POSS) is a polyhedral oligomeric silsesquioxane with the structural formula (RSiO 1.5 ) n The new organic-inorganic hybrid materials with n=6, 8, 10, 12, etc. are often used in semiconductor materials, insulator materials, liquid crystals and other materials because of their advantages such as no pollution, good heat resistance and insulation. The R group in POSS determines its material properties. The type of R group in POSS can be changed according to needs to design functional materials that meet different application fields. Summary of the invention

[0005] In order to improve the problems faced by the existing metal silicide preparation method, the present invention provides a metal silicide, which uses polyhedral oligomeric silsesquioxane as a silicon source to avoid using a polluting silicon source, and can prepare the metal silicide by a one-step temperature-raising silicidation method at a relatively low temperature, and is applied to the selective hydrogenation reaction of a carbon-carbon triple bond, which exhibits good catalytic performance. The present invention also provides a preparation method of the metal silicide, and a method for a hydrogenation reaction.

[0006] A first aspect of the present invention provides a metal silicide, which is prepared by pyrolysis of a precursor, wherein the precursor includes a polyhedral oligomeric silsesquioxane and a metal salt;

[0007] The structural formula of the polyhedral oligomeric silsesquioxane is: (RsiO 3 / 2 ) n ; Where n is an even number between 6 and 20.

[0008] According to some embodiments of the invention, R is phenyl, vinyl or halogen.

[0009] According to some embodiments of the present invention, the metal salt is nitrate, acetate or acetylacetonate.

[0010] According to some embodiments of the present invention, the metal salt contains a metal element, and the metal element is Pt, Pd, Ni, Ru, Cu, Co or Mn.

[0011] The second aspect of the present invention provides a method for preparing the above-mentioned metal silicide, comprising the steps of mixing polyhedral oligomeric silsesquioxane and a metal salt in an organic solvent and pyrolyzing them to generate the metal silicide.

[0012] According to some embodiments of the present invention, the organic solvent may be any organic solvent that can dissolve the inorganic metal precursor.

[0013] According to some embodiments of the present invention, the mass ratio of the polyhedral oligomeric silsesquioxane to the metal salt is 50 to 400:1, preferably 80 to 120:1, and more preferably 100:1.

[0014] According to some embodiments of the present invention, the pyrolysis conditions include: the pyrolysis temperature is 800°C to 1000°C, preferably 900°C to 1000°C, and more preferably 1000°C.

[0015] According to some embodiments of the present invention, the heating rate of the pyrolysis is 5 to 20°C / min, preferably 18 to 20°C / min.

[0016] According to some embodiments of the present invention, the pyrolysis is performed under a hydrogen or nitrogen atmosphere.

[0017] According to some embodiments of the present invention, after the mixing and before the pyrolysis, a step of removing the organic solvent is also included.

[0018] According to some specific embodiments of the present invention, the method for removing the organic solvent is rotary evaporation.

[0019] According to some specific embodiments of the present invention, after removing the organic solvent by rotary evaporation, the mixture is dried for 8 to 12 hours and then transferred to a tube furnace for pyrolysis.

[0020] According to some embodiments of the present invention, the preparation method further comprises a post-treatment process after pyrolysis, and the post-treatment process comprises: contacting the sample obtained by pyrolysis with an alkali solution, and roasting the contacted sample to obtain a product.

[0021] According to some embodiments of the present invention, the concentration of the alkali solution is 1.5 to 2.5 mol / L.

[0022] According to some embodiments of the present invention, the contacting time with the alkali solution is 10 to 14 hours.

[0023] According to some specific embodiments of the present invention, after the sample is contacted with the alkaline solution, it is filtered, dried, and then transferred to a muffle furnace for calcination.

[0024] In the present invention, the alkali treatment of the pyrolyzed sample is performed to remove the excess SiO2 and carbon layer generated during the preparation of the Pd2Si / SiO2 catalyst under high temperature conditions to expose more active sites.

[0025] According to some embodiments of the present invention, the calcination temperature is 500°C to 800°C, preferably 600°C.

[0026] According to some embodiments of the present invention, the calcination time is 1 to 3 hours, preferably 2 hours.

[0027] According to some embodiments of the present invention, the heating rate of the calcination is 5 to 10° C. / min.

[0028] The third aspect of the present invention provides a method for hydrogenation reaction, wherein a raw material containing compound I is contacted with a catalyst to prepare a product containing compound II, wherein compound I has a carbon-carbon triple bond, and compound II has a carbon-carbon double bond, and the catalyst is the metal silicide described in the first aspect or the metal silicide prepared by the preparation method described in the second aspect.

[0029] According to some embodiments of the present invention, the compound I is selected from acetylene, phenylacetylene, p-aminophenylacetylene or p-chlorophenylacetylene;

[0030] The compound II is selected from ethylene, styrene, p-aminostyrene or p-chlorostyrene.

[0031] According to some embodiments of the present invention, the reaction conditions of the hydrogenation reaction include: 25-35° C., 0.1 MPaH 2 , 800-1200 rpm / min.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The metal silicide of the present invention uses polyhedral oligomeric silsesquioxane as a silicon source, thereby avoiding the use of polluting silicon sources in the traditional preparation process of metal silicide;

[0034] (2) The preparation method of the metal silicide of the present invention reduces the calcination temperature required for the silicide from 2000°C to 3000°C to 800°C to 1000°C by optimizing the silicon source, thereby reducing the process difficulty and providing a feasible idea for mass production of metal silicide materials in industry;

[0035] (3) The metal silicide prepared by the present invention has a low metal content and better catalytic performance;

[0036] (4) The metal silicide of the present invention can be used as a catalyst in the selective hydrogenation reaction of carbon-carbon triple bonds. When the conversion rate is 90%, the selectivity of the carbon-carbon double bond intermediate product can still reach more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The XRD spectra of Pd-POSS of the metal silicide of the present invention are as follows: (a) different calcination temperatures, (b) different feed ratios, (c) different calcination atmospheres, and (d) different heating rates. DETAILED DESCRIPTION

[0038] In order to make the present invention more easily understood, the present invention will be described in detail below in conjunction with embodiments. These embodiments are only for illustration and are not intended to limit the application scope of the present invention.

[0039] In the present invention, dimethoxymethylsilane was purchased from MacLean Company with CAS No. 1112-39-6;

[0040] Phenyltriethoxysilane was purchased from MacLean Company, CAS No. 780-69-8;

[0041] Vinyl POSS was purchased from McLean Company, CAS No. 69655-76-1;

[0042] Chloropropyl POSS was purchased from Maclean Company with CAS No. 161678-38-2.

[0043] Example 1

[0044] Preparation of phenyl-POSS: First, add 600 mL of distilled water to a 1000 mL three-necked flask, heat to 50°C in a water bath, and keep the temperature constant. Then, add 12 g of dimethoxymethylsilane and 100 g of phenyltriethoxysilane to the distilled water at a drop rate of 2 g / min, and stir mechanically for 45 minutes after the addition is complete to fully hydrolyze. Then, slowly add 20 g of a 10% NaOH aqueous solution at one time, continue stirring for 60 minutes, add 30 g of a 10% CH3COOH aqueous solution to neutralize the alkali in the reaction system, then filter and wash, place the obtained wet powder in an oven, dry at 80°C for 6 hours, and grind the dried product to obtain a white powder.

[0045] Preparation of Pd2Si / SiO2 catalyst: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 5°C / min in a hydrogen atmosphere, and then pyrolyzed for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for later use.

[0046] Preparation of Pd2Si / SiO2-HT: In order to remove the excess SiO2 and carbon layer generated during the preparation of Pd2Si / SiO2 catalyst under high temperature conditions to expose more active sites, the Pd2Si / SiO2 catalyst was first placed in a 2 mol / L NaOH solution for washing for 12 hours. The obtained solid powder was washed to neutrality and then placed in a muffle furnace and heated to 600°C at a heating rate of 10°C / min and maintained for 2 hours. After the muffle furnace was cooled to room temperature, the sample was taken out to obtain metal silicide 1.

[0047] Example 2

[0048] The implementation method is the same as that of Example 1, the only difference being the preparation of the Pd2Si / SiO2 catalyst.

[0049] Preparation of Pd2Si / SiO2 catalyst: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 5°C / min in an air atmosphere, and then pyrolyzed for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for later use.

[0050] A metal silicide 2 is obtained.

[0051] Example 3

[0052] The implementation method is the same as that of Example 1, the only difference being the preparation of the Pd2Si / SiO2 catalyst.

[0053] Preparation of Pd2Si / SiO2 catalyst: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere, and then pyrolyzed for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for later use.

[0054] A metal silicide 3 is obtained.

[0055] Example 4

[0056] The implementation method is the same as that of Example 1, the only difference being the preparation of the Pd2Si / SiO2 catalyst.

[0057] Preparation of Pd2Si / SiO2 catalyst: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 10°C / min in a hydrogen atmosphere, and then pyrolyzed for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for later use.

[0058] A metal silicide 4 is obtained.

[0059] Example 5

[0060] The implementation method is the same as that of Example 1, the only difference being the preparation of the Pd2Si / SiO2 catalyst.

[0061] Preparation of Pd2Si / SiO2 catalyst: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 20°C / min in a hydrogen atmosphere, and then pyrolyzed for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for later use.

[0062] A metal silicide 5 is obtained.

[0063] Example 6

[0064] The same method as in Example 1 was used to prepare phenyl-POSS.

[0065] Ru x Preparation of Si / SiO2 catalyst: Take 20 mg of anhydrous RuCl3 and dissolve it in 20 mL of ethanol. After stirring for 20 minutes, add 1 g of phenyl-POSS and continue stirring for 1 hour. Remove ethanol by rotary evaporation at 40°C and dry at 70°C for 10 hours. Grind the dried sample thoroughly and transfer it to a tubular furnace. In a hydrogen atmosphere, heat the temperature at a rate of 20°C / min to 1000°C and keep the temperature constant for 2 hours. Then, after the tubular furnace is cooled to room temperature, take out the sample and grind it to obtain metal silicide 6.

[0066] Example 7

[0067] The same method as in Example 1 was used to prepare phenyl-POSS.

[0068] Pt x Preparation of Si / SiO2 catalyst: 20 mg PtCl4 was dissolved in 20 mL ethanol, stirred for 20 minutes, and then 1 g phenyl-POSS was added. Stirring was continued for 1 hour, and the ethanol was removed by rotary evaporation at 40°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace. The temperature was increased at a rate of 20°C / min to 1000°C under a hydrogen atmosphere and kept constant for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground to obtain metal silicide 7.

[0069] Example 8

[0070] The same method as in Example 1 was used to prepare phenyl-POSS.

[0071] Preparation of Ni2Si / SiO2 catalyst: 20 mg of nickel acetylacetonate was dissolved in 20 mL of tetrahydrofuran, stirred for 20 minutes, and then 1 g of phenyl-POSS was added. Stirring was continued for 1 hour, and tetrahydrofuran was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace. The temperature was increased to 1000°C at a rate of 20°C / min under a hydrogen atmosphere, and then kept constant for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground to obtain metal silicide 8.

[0072] Example 9

[0073] Preparation method of catalyst using vinyl POSS as silicon source: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 1 g of vinyl-POSS was added, and stirring was continued for 1 hour. Toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 900°C at a heating rate of 5°C / min, 10°C / min, and 20°C / min in air, hydrogen, and nitrogen atmospheres, respectively, and then calcined for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for use.

[0074] Preparation of vinyl Pd2Si / SiO2-HT: In order to remove the excess SiO2 and carbon layer generated in the process of preparing the vinyl Pd2Si / SiO2 catalyst under high temperature conditions to expose more active sites, we first placed the vinyl Pd2Si / SiO2 catalyst in a 2 mol / L NaOH solution for washing for 12 hours, washed the obtained solid powder until neutral, and then placed it in a muffle furnace and heated to 600°C at a heating rate of 10°C / min and maintained for 2 hours. After the muffle furnace cooled to room temperature, the sample was taken out to obtain metal silicide 9.

[0075] Example 10

[0076] Preparation method of catalyst using chloropropyl POSS as silicon source: 20 mg of palladium acetate was dissolved in 20 mL of toluene, stirred for 20 minutes, and then 2.6 g of chloropropyl-POSS was added, and stirring was continued for 1 hour. Toluene was removed by rotary evaporation at 35°C, and dried at 70°C for 10 hours. The dried sample was fully ground and transferred to a tube furnace, and heated to 800-1000°C at a heating rate of 5°C / min in a hydrogen atmosphere, and then calcined for 2 hours. After the tube furnace was cooled to room temperature, the sample was taken out and ground for use.

[0077] Preparation of chloropropyl Pd2Si / SiO2-HT: In order to remove the excess SiO2 and carbon layer generated in the process of preparing the chloropropyl Pd2Si / SiO2 catalyst under high temperature conditions to expose more active sites, we first placed the chloropropyl Pd2Si / SiO2 catalyst in a 2 mol / L NaOH solution for washing for 12 hours, washed the obtained solid powder until neutral, and then placed it in a muffle furnace and heated to 600°C at a heating rate of 10°C / min and maintained for 2 hours. After the muffle furnace cooled to room temperature, the sample was taken out to obtain metal silicide 10.

[0078] Application Example 1

[0079] By changing the calcination temperature (600°C, 800°C, 1000°C) of Example 1, the feed ratio (the mass ratio of polyhedral oligomeric silsesquioxane: metal salt is 1:10, 1:30, 1:50, respectively), the calcination atmosphere (H2, N2, air) and the heating rate (5°C / min, 10°C / min, 20°C / min), different metal silicides were obtained, and XRD tests were performed on these metal silicides to obtain Figure 1 .

[0080] according to Figure 1 It can be seen that in the silicide prepared in the present application, palladium exists in the form of palladium silicide, and the content of elemental palladium is small, which can inhibit excessive hydrogenation in the hydrogenation reaction and improve the selectivity of the target product.

[0081] Application Example 2

[0082] The metal silicides 1 and 6-10 prepared in Examples 1 and 6-10 were used in the selective hydrogenation reaction of carbon-carbon triple bonds, and the hydrogenation products were quantitatively analyzed by gas chromatography. The reactant conversion rate and the selectivity of the carbon-carbon double bond of the product are shown in Table 1.

[0083] Table 1

[0084] catalyst Reactants Reactant conversion rate (%) Intermediate product selectivity (%) Metal silicide 1 Phenylacetylene 99.3 95.6 Metal silicide 1 Acetylene 96.8 96.8 Metal silicide 1 p-Aminophenylacetylene 91.9 98.0 Metal silicide 1 p-Chlorophenylacetylene 98.3 96.2 Metal silicide 6 Phenylacetylene 99.6 95.5 Metal silicide 7 Phenylacetylene 98.4 96.5 Metal silicide 8 Phenylacetylene 99.0 95.3 Metal silicide 9 Phenylacetylene 98.5 96.7 Metal silicide 10 Phenylacetylene 94.7 93.5

[0085] Reaction conditions: 30°C, 0.1MPa H2, 1000rpm / min

[0086] In summary, the metal silicide provided by the present invention uses polyhedral oligomeric silsesquioxane as a silicon source, reduces the calcination temperature, and is applied to the selective hydrogenation reaction of carbon-carbon triple bonds. It can still have a high selectivity for carbon-carbon double bond intermediates under the condition of high reaction conversion rate.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, under the technical enlightenment provided by the present invention, as common knowledge in the field, other equivalent variations and improvements can also be made, which should also be regarded as the protection scope of the present invention.

Claims

1. A metal silicide, characterized in that: The metal silicide is prepared by pyrolysis of a precursor, wherein the precursor includes a polyhedral oligomeric silsesquioxane and a metal salt; The structural formula of the polyhedral oligomeric silsesquioxane is: (RSiO 1.5 ) n ; Where n is an even number between 6 and 20.

2. The metal silicide according to claim 1, characterized in that: R is phenyl, vinyl or halogen.

3. The metal silicide according to claim 1 or 2, characterized in that: The metal salt is nitrate, acetate or acetylacetonate.

4. The metal silicide according to any one of claims 1 to 3, characterized in that: The metal salt contains a metal element, and the metal element is Pt, Pd, Ni, Ru, Cu, Co or Mn.

5. The method for preparing a metal silicide according to any one of claims 1 to 4, characterized in that: The method comprises the steps of mixing polyhedral oligomeric silsesquioxane and metal salt in an organic solvent and thermally decomposing the mixture to generate metal silicide.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the polyhedral oligomeric silsesquioxane to the metal salt is 50 to 400:1, preferably 80 to 120:

1.

7. The preparation method according to claim 5 or 6, characterized in that: The pyrolysis conditions include: the pyrolysis temperature is 800°C to 1000°C, preferably 900°C to 1000°C; and / or, the heating rate of the pyrolysis is 5 to 20°C / min, preferably 18 to 20°C / min; and / or, the pyrolysis is carried out under a hydrogen or nitrogen atmosphere; And / or, after the mixing and before the pyrolysis, a step of removing the organic solvent is also included.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The preparation method further comprises a post-treatment process after pyrolysis, wherein the post-treatment process comprises: contacting the sample obtained by pyrolysis with an alkali solution, and roasting the contacted sample to obtain a product; Preferably, the concentration of the alkali solution is 1.5 to 2.5 mol / L; and / or, the contact time with the alkali solution is 10 to 14 hours; And / or, the calcination temperature is 500°C to 800°C, preferably 600°C; And / or, the calcination time is 1 to 3 hours, preferably 2 hours; And / or, the heating rate of the calcination is 5-10°C / min.

9. A method for hydrogenation reaction, characterized in that: The method comprises contacting a raw material containing a compound I with a catalyst to prepare a product containing a compound II, wherein the compound I has a carbon-carbon triple bond, and the compound II has a carbon-carbon double bond, and the catalyst is a metal silicide according to any one of claims 1 to 5 or a metal silicide prepared by the preparation method according to any one of claims 6 to 9.

10. The method according to claim 9, characterized in that The compound I is selected from acetylene, phenylacetylene, p-aminophenylacetylene or p-chlorophenylacetylene; The compound II is selected from ethylene, styrene, p-aminostyrene or p-chlorostyrene.

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