Composite metal-organic framework catalyst, preparation method and application thereof

Abstract

The application provides a composite metal organic framework catalyst and a preparation method and application thereof, the composite metal organic framework catalyst is a core-shell structure, the inner core is a hollow metal organic framework material, and the shell is a metal organic framework material; a sandwich layer is arranged between the inner core and the shell, and the sandwich layer is composed of uniformly distributed platinum group metal nanoparticles. The platinum group metal nanoparticles are arranged between the inner core hollow metal organic framework material and the shell metal organic framework material, accurate distribution of the platinum group metal nanoparticles is realized, the interaction between the platinum group metal nanoparticles and the inner core and the shell is effectively enhanced, a high-efficiency synergistic catalytic effect is generated, the stability of the catalyst is improved, and the selectivity and catalytic efficiency of the catalyst are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal organic framework materials, and particularly relates to a composite metal organic framework catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] Metal organic framework (MOF), also known as porous coordination polymer, is assembled by organic ligand and inorganic metal ion or cluster, and has the characteristics of high specific surface area, adjustable pore size, controllable chemical composition and surface function, and definite metal node, which has attracted great attention in heterogeneous catalysis. However, there are some shortcomings in the application of solid MOF in catalysis, such as slow mass transfer and difficulty in entering the internal space.

[0003] Hollow MOF (HoMOF) as a new framework structure has great potential for heterogeneous catalysis due to its short channel length, large cavity structure and more exposed active sites. In addition, HoMOF can produce synergistic catalytic effect after being combined with metal nanoparticles, and show significantly enhanced catalytic performance compared with single-component materials. So far, typical yolk-shell structures have been constructed, for example, CN112642482B discloses a preparation method of metal ion-anchored hollow covalent organic framework material and its photocatalytic application. A MOF / COF material with yolk-shell structure is obtained by selective etching method, using ZIF-67, p-phenylenediamine and tri-aldehyde-based phloroglucinol in an o-dichlorobenzene / n-butanol / pyrrolidine solution system. The internal metal organic framework is etched away by acid washing, and the metal ion is anchored on the covalent organic framework. However, the nanoparticles are usually larger than 10 nanometers, and the interaction with the MOF shell is usually weak, resulting in relatively low catalytic performance. Another structure is to disperse metal nanoparticles in the entire HoMOF shell by traditional impregnation and reduction method, however, the size and distribution of metal nanoparticles are difficult to control accurately.

[0004] Therefore, it is urgent to develop a new synthesis strategy to realize efficient collocation of metal nanoparticles and HoMOF, so as to obtain high stability and high catalytic efficiency. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a composite metal organic framework catalyst as well as a preparation method and application thereof. In the present application, platinum group metal nanoparticles are arranged between the inner core hollow metal organic framework material and the outer shell metal organic framework material, realizing accurate distribution of platinum group metal nanoparticles, effectively enhancing the interaction between platinum group metal nanoparticles and the inner core and the outer shell, and producing high-efficiency synergistic catalytic effect, which not only improves the stability of the catalyst, but also significantly improves the selectivity and catalytic efficiency of the catalyst.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite metal-organic framework catalyst, wherein the composite metal-organic framework catalyst has a core-shell structure, the core being a hollow metal-organic framework material and the outer shell being a metal-organic framework material;

[0008] A sandwich layer is provided between the core and the outer shell, the sandwich layer being composed of uniformly distributed platinum group metal nanoparticles.

[0009] This invention places platinum group metal nanoparticles between a hollow metal-organic framework (MOF) core and an MOF shell, achieving precise distribution of the platinum group metal nanoparticles. This effectively enhances the interaction between the platinum group metal nanoparticles and the core and shell, resulting in a highly efficient synergistic catalytic effect that not only improves the stability of the catalyst but also significantly enhances its selectivity and catalytic efficiency.

[0010] The catalyst provided by this invention maintains essentially unchanged conversion rate and selectivity after being recycled 20 times, indicating that the catalyst has excellent stability.

[0011] As a preferred embodiment of the present invention, the particle size D50 of the composite metal-organic framework catalyst is 150-200 nm, for example, it can be 150 nm, 180 nm or 200 nm.

[0012] Preferably, the particle size D50 of the platinum group metal nanoparticles is 2-5 nm, for example, it can be 2 nm, 4 nm or 5 nm.

[0013] Preferably, based on the mass of the hollow metal-organic framework material, the content of the platinum group metal nanoparticles is 0.5-2 wt.%, for example, it can be 0.5 wt.%, 1 wt.%, or 2 wt.%.

[0014] In this invention, if the content of platinum group metal nanoparticles is too low, the catalytic performance will be low; if the content of platinum group metal nanoparticles is too high, they will easily aggregate and fall off during the coating process.

[0015] As a preferred technical solution of the present invention, the thickness of the outer shell is 10-20nm, for example, it can be 10nm, 15nm or 20nm.

[0016] In this invention, if the thickness of the outer shell is too small, the nanoparticles are easily exposed, reducing the interaction with the MOF and lowering the catalytic performance; if the thickness of the outer shell is too large, the steric hindrance effect becomes greater, making it difficult for reactant molecules to contact the nanoparticles, thus reducing the catalytic performance.

[0017] As a preferred technical solution of the present application, the hollow metal organic framework material comprises a hollow MIL material.

[0018] It should be noted that the MIL material is a series of materials of the MIL-53 framework, which is characterized in that the material structure will change between the large pore and the narrow pore under the influence of external factors. Common MIL-53 framework series materials include MIL-53Cr, MIL-100Cr, MIL-101Cr, MIL-100Fe, MIL-177-LT, MIL-177-HT, MIL-45Co, MIL-45Fe, MIL-53AI, MIL-53Sc, MIL-88Sc, MIL-8, MIL-9, MIL-47, MIL-51, MIL-59, MIL-69, MIL-88, MIL-91, MIL-96, MIL-101, MIL-103, MIL-102, MIL-110 or MIL-125, etc.

[0019] Preferably, the metal organic framework material comprises a MIL material.

[0020] Preferably, the platinum group metal nanoparticles comprise any one or a combination of at least two of Ru nanoparticles, Pt nanoparticles, Rh nanoparticles or Ir nanoparticles, preferably a combination of Ru nanoparticles and Pt nanoparticles.

[0021] In a second aspect, the present application provides a preparation method of the composite metal organic framework catalyst according to the first aspect, which comprises the following steps:

[0022] (1) mixing a solution containing a hollow metal organic framework material and a solution of platinum group metal nanoparticles to obtain a hollow metal organic framework material with platinum group metal nanoparticles distributed on the surface, denoted as hollow MOF@platinum group metal nanoparticles;

[0023] (2) mixing a solution containing the hollow MOF@platinum group metal nanoparticles and a solution of metal organic framework material precursors, performing a hydrothermal reaction, and then etching the product of the hydrothermal reaction to obtain a composite metal organic framework catalyst.

[0024] The preparation method provided by the present application has the advantages of easy operation, simple equipment, easy implementation, high generation efficiency, etc., and does not cause an increase in the production cost of the catalyst, and has a high level of industrial application.

[0025] It should be noted that during the hydrothermal reaction after mixing the solution containing the hollow MOF@platinum group metal nanoparticles and the solution of metal organic framework material precursors, the hollow MOF becomes solid, and in the subsequent etching process, the solid becomes hollow again, ensuring the existence of the hollow MOF in the core.

[0026] As a preferred technical solution of the present application, the volume ratio of the solution containing hollow metal organic framework material and the solution of platinum group metal nanoparticles in step (1) is (8-12):(1-3), wherein the volume selection range "8-12" of the solution containing hollow metal organic framework material may be, for example, 8, 9, 10, 11 or 12, etc., and the volume selection range "1-3" of the solution of platinum group metal nanoparticles may be, for example, 1, 1.5, 2, 2.5 or 3, etc.

[0027] In the present application, if the volume ratio of the solution containing hollow metal organic framework material and the solution of platinum group metal nanoparticles is too small, i.e. the volume of the solution of platinum group metal nanoparticles is too large, it will lead to excessive adsorption, and the nanoparticles are easy to aggregate and fall off in the subsequent coating process; if the volume ratio of the solution containing hollow metal organic framework material and the solution of platinum group metal nanoparticles is too large, i.e. the volume of the solution of platinum group metal nanoparticles is too small, it will lead to too little adsorption, reducing the catalytic performance.

[0028] Preferably, the solute concentration of the solution containing hollow metal organic framework material in step (1) is 10-30 mg / mL, which may be, for example, 10 mg / mL, 20 mg / mL or 30 mg / mL, etc.

[0029] Preferably, the mixing process in step (1) is accompanied by stirring.

[0030] Preferably, the temperature of the mixing in step (1) is room temperature.

[0031] It should be noted that room temperature refers to 25±5℃, which may be, for example, 20℃, 25℃ or 30℃, etc.

[0032] Preferably, the mixing time in step (1) is 1-3h, which may be, for example, 1h, 1.5h, 2h, 2.5h or 3h, etc.

[0033] Preferably, after the mixing in step (1), the steps of centrifugation and washing are further carried out.

[0034] As a preferred technical solution of the present application, the preparation method of the hollow metal organic framework material in step (1) comprises the following steps:

[0035] Mixing the metal salt, the organic ligand and the solvent, carrying out hydrothermal reaction to obtain the metal organic framework material, and then acid etching the metal organic framework material to obtain the hollow metal organic framework material.

[0036] Preferably, in the process of acid etching, the etchant added includes acid and water, and the acid includes glacial acetic acid.

[0037] Preferably, the metal salt includes chromium salt.

[0038] It should be noted that the present application does not limit the specific type of chromium salt, for example, it can be chromium nitrate nonahydrate and the like.

[0039] Preferably, the organic ligand comprises terephthalic acid.

[0040] Preferably, the molar ratio of the organic ligand and the metal salt is 1:(1-2.2), for example, it can be 1:1, 1:1.5, 1:2 or 1:2.2 and the like.

[0041] Preferably, the temperature of the hydrothermal reaction is 160-200℃, for example, it can be 160℃, 170℃, 180℃, 190℃ or 200℃ and the like, and the time is 4-6h, for example, it can be 4h, 5h or 6h and the like.

[0042] Preferably, during the acid etching process, the temperature is 160-200℃, for example, it can be 160℃, 170℃, 180℃, 190℃ or 200℃ and the like, and the time is 2-5h, for example, it can be 2h, 3h, 4h or 5h and the like.

[0043] Preferably, after the acid etching is completed, the steps of standing, centrifuging and washing are further carried out.

[0044] As a preferred technical solution of the present application, the volume ratio of the solution containing the MOF@ platinum group metal nanoparticles and the metal organic framework material precursor solution in step (2) is (0.8-1.2):(0.8-1.2), wherein the volume selection range "0.8-1.2" of the solution containing the MOF@ platinum group metal nanoparticles can be 0.8, 0.9, 1, 1.1 or 1.2 and the like, and the volume selection range "0.8-1.2" of the metal organic framework material precursor solution can be 0.8, 0.9, 1, 1.1 or 1.2 and the like.

[0045] In the present application, if the volume ratio of the solution containing the MOF@ platinum group metal nanoparticles and the metal organic framework material precursor solution is too small, i.e. the volume of the metal organic framework material precursor solution is too large, the thickness of the shell layer is too large, which affects the mass transfer process; if the volume ratio of the solution containing the MOF@ platinum group metal nanoparticles and the metal organic framework material precursor solution is too large, i.e. the volume of the metal organic framework material precursor solution is too small, the thickness of the shell layer is too small, and the nanoparticles are easily exposed.

[0046] Preferably, the solute concentration of the metal organic framework material precursor solution in step (2) is 40-60mg / mL, for example, it can be 40mg / mL, 50mg / mL or 60mg / mL and the like.

[0047] Preferably, the mixing in step (2) is accompanied by stirring.

[0048] Preferably, the mixing in step (2) is performed for 20-40 min, for example, 20 min, 25 min, 30 min, 35 min, or 40 min, etc.

[0049] Preferably, the hydrothermal reaction in step (2) is performed at a temperature of 130-170℃, for example, 130℃, 140℃, 150℃, 160℃, or 170℃, etc.

[0050] Preferably, the hydrothermal reaction in step (2) is performed for 3-5 h, for example, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc.

[0051] Preferably, the etching in step (2) comprises:

[0052] The product of the hydrothermal reaction is dispersed in a mixed solvent composed of water and acid to obtain a suspension, and the suspension is subjected to an etching reaction.

[0053] It should be noted that the acid in the mixed solvent includes glacial acetic acid.

[0054] Preferably, the etching reaction is performed at a temperature of 130-170℃, for example, 130℃, 140℃, 150℃, 160℃, or 170℃, etc.

[0055] Preferably, the etching reaction is performed for 3-7 h, for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 6 h, 6.5 h, or 7 h, etc.

[0056] Preferably, after the etching in step (2), the process further comprises the steps of standing, centrifuging, and washing.

[0057] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0058] (I) stirring and dispersing terephthalic acid and a chromium salt in water at a molar ratio of 1:(1-2.2), and then performing a hydrothermal reaction at 160-200℃ for 4-8 h, standing, centrifuging to obtain a MIL-101 product, washing, and then re-dispersing the MIL-101 product in an aqueous solvent to obtain an aqueous solution containing MIL-101;

[0059] (II) stirring and dispersing the aqueous solution containing MIL-101 in a mixed solvent composed of water and acid at a volume ratio of (8-12):1 for 3-7 min to obtain a suspension, and then performing an etching reaction on the suspension at 160-200℃ for 2-6 h, standing, centrifuging, and washing to obtain a hollow MIL-101, denoted as HoMIL-101.

[0060] (III) re-dispersing the HoMIL-101 in an organic solvent to obtain a HoMIL-101-containing solution with a solute concentration of 10-30 mg / mL, stirring and mixing the HoMIL-101-containing solution and a platinum group metal nanoparticle solution at a volume ratio of (8-12):(1-3) at room temperature for 1-3 h, and then centrifuging and washing to obtain HoMIL-101 with platinum group metal nanoparticles distributed on the surface, denoted as HoMIL-101@platinum group metal nanoparticle;

[0061] (IV) re-dispersing the HoMIL-101@platinum group metal nanoparticle in an aqueous solvent to obtain a HoMIL-101@platinum group metal nanoparticle-containing solution, stirring and mixing the HoMIL-101@platinum group metal nanoparticle-containing solution and a MIL-101 precursor solution with a solute concentration of 40-60 mg / mL at a volume ratio of (0.8-1.2):(0.8-1.2) for 20-40 min, and then performing a hydrothermal reaction at 130-170 ℃ for 3-5 h, and after the reaction, standing, centrifuging and washing to obtain an intermediate product;

[0062] (V) re-dispersing the intermediate product in an aqueous solvent to obtain an intermediate product-containing solution, stirring and dispersing the intermediate product-containing solution in a mixed solvent composed of water and acid at a volume ratio of (8-12):1 for 3-7 min to obtain a suspension, and then performing an etching reaction at 130-170 ℃ for 3-7 h, and after the reaction, standing, centrifuging and washing to obtain a composite metal organic framework catalyst, denoted as HoMIL-101@platinum group metal nanoparticle@MIL-101.

[0063] It should be noted that the present application does not specifically limit the selection of the organic solvent in step (III), and examples thereof include N,N-dimethylformamide and the like.

[0064] In a third aspect, the present application provides an application of the composite metal organic framework catalyst as described in the first aspect, and the composite metal organic framework catalyst is applied to catalyze cascade conversion of oxygen-containing compounds.

[0065] It should be noted that the oxygen-containing compounds are derived from biomass, and the specific types are not limited, and examples thereof include levulinic acid, vanillin and derivatives thereof, and the like.

[0066] The numerical range described in the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and the present application does not list the specific point values included in the range for the sake of brevity and simplicity.

[0067] Compared with the prior art, the present application has the following beneficial effects:

[0068] (1) The present application sets platinum group metal nanoparticles between the inner core hollow metal organic framework material and the outer shell metal organic framework material, realizes the accurate distribution of platinum group metal nanoparticles, effectively enhances the interaction of platinum group metal nanoparticles with the inner core and the outer shell, and produces a high-efficiency synergistic catalytic effect, which significantly improves the catalytic efficiency of the catalyst. In addition, the conversion rate and selectivity of the catalyst remain basically unchanged after 20 cycles, indicating that the catalyst has excellent stability.

[0069] (2) The conversion rate of the catalyst provided by the present application for preparing r-valerolactone from levulinic acid is as high as 100%, the selectivity is as high as 100%, the turnover frequency (TOF value) is 1885h -1 , and the catalytic efficiency is high.

[0070] (3) The preparation method provided by the present application has the advantages of easy operation, simple equipment, easy implementation, high generation efficiency, etc., and does not cause an increase in the production cost of the catalyst, and has a high industrial application level. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 The process flow chart for preparing the composite metal organic framework catalyst in Example 1 in the present application is shown in the figure.

[0072] Figure 2 The SEM image of the composite metal organic framework catalyst prepared in Example 1 in the present application is shown in the figure. DETAILED DESCRIPTION

[0073] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations on the present application.

[0074] Example 1

[0075] The present embodiment provides a composite metal organic framework catalyst, which is a core-shell structure, the inner core is HoMIL-101, and the outer shell is MIL-101;

[0076] A sandwich layer is arranged between the inner core and the outer shell, and the sandwich layer is composed of uniformly distributed Ru nanoparticles;

[0077] The particle size D50 of the composite metal organic framework catalyst is 178.4 nm, the particle size D50 of the Ru nanoparticles is 2.4 nm, the content of the Ru gold nanoparticles is 1 wt.% based on the mass of the hollow metal organic framework material, and the thickness of the outer shell is 14.2 nm.

[0078] The embodiment also provides a preparation method of the composite metal organic framework catalyst, and the preparation method comprises the following steps:

[0079] (1) stirring and dispersing chromium nitrate nine water (0.4 g) and terephthalic acid (0.11 g) in a molar ratio of 1.5:1 in 10 mL of deionized water, mixing uniformly to obtain a mixed solution, and then transferring the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave, and performing a hydrothermal reaction at 180°C for 6 h in an oven, after the reaction is completed, transferring the reaction product to a conical tube for standing, and then centrifuging the upper suspension to obtain a MIL-101 product, and then washing with deionized water, and after washing, redispersing the washed product in 4 mL of deionized water to obtain a MIL-101-containing aqueous solution;

[0080] (2) diluting 1 mL of the MIL-101-containing aqueous solution to 5 mL with deionized water, and then stirring and dispersing in a mixed solvent composed of water (5 mL) and glacial acetic acid (0.5 mL) in a volume ratio of 10:1 for 5 min to obtain a suspension, and then transferring the suspension to a polytetrafluoroethylene-lined autoclave, and performing an etching reaction on the suspension at a temperature of 180°C for 4 h to obtain a reaction product, standing the reaction product and removing the crystalline precipitate at the bottom, and then centrifuging to collect the remaining product and washing with deionized water and DMF for 3 times to obtain a hollow MIL-101, denoted as HoMIL-101;

[0081] (3) redispersing the HoMIL-101 in 10 mL of DMF to obtain a HoMIL-101-containing solution with a solute concentration of 20 mg / mL, and then adding 2 mL of a Ru nanoparticle solution dropwise to 10 mL of the HoMIL-101-containing solution (the volume ratio of the HoMIL-101-containing solution to the Ru nanoparticle solution is 10:2) under stirring, and then stirring and mixing the mixed solution at room temperature 25°C for 2 h, and then performing centrifugation and washing with DMF and deionized water for 3 times to obtain HoMIL-101 with Ru nanoparticle interlayers distributed on the surface, denoted as HoMIL-101@Ru;

[0082] (4) 200 mg of chromium nitrate nine hydrate and 55 mg of terephthalic acid were dissolved in 5 mL of deionized water to obtain a MIL-101 precursor solution, and the HoMIL-101@Ru was re-dispersed in 5 mL of deionized water to obtain a HoMIL-101@Ru-containing solution; the HoMIL-101@Ru-containing solution (5 mL) and the MIL-101 precursor solution (5 mL) with a solute concentration of 51 mg / mL were mixed by stirring at a volume ratio of 1:1 for 30 min, and then transferred to a polytetrafluoroethylene-lined autoclave for a hydrothermal reaction at 150°C for 4 h. After the reaction, the product was transferred to a conical tube for standing, and the upper suspension was centrifuged. Subsequently, the product was washed with deionized water three times to obtain an intermediate product, denoted as MIL-101@Ru@MIL-101;

[0083] (5) The MIL-101@Ru@MIL-101 was re-dispersed in 5 mL of deionized water to obtain a MIL-101@Ru@MIL-101-containing aqueous solution, and 5 mL of the MIL-101@Ru@MIL-101-containing aqueous solution was dispersed by stirring in a mixed solvent composed of deionized water (5 mL) and glacial acetic acid (0.5 mL) at a volume ratio of 10:1 for 5 min to obtain a suspension, and the suspension was transferred to a polytetrafluoroethylene-lined autoclave for an etching reaction at 150°C for 5 h. After the reaction, the product was allowed to stand, and the bottom crystalline precipitate was removed. Then, the product was centrifuged and washed with distilled water three times to obtain the composite metal organic framework catalyst, denoted as HoMIL-101@Ru@MIL-101.

[0084] Figure 1 A process flow diagram for preparing the composite metal organic framework catalyst of the present embodiment is shown. As can be seen from the diagram, MIL-101 is first prepared, then etched to obtain hollow MIL-101, then HoMIL-101@Ru is prepared, and then MIL-101 is coated on the surface again to obtain MIL-101@Ru@MIL-101, and after etching, the composite metal organic framework catalyst with a structure of HoMIL-101@Ru@MIL-101 is obtained.

[0085] Figure 2 A SEM image of the composite metal organic framework catalyst prepared in the present embodiment is shown. As can be seen from the image, Fig. (a) is a morphology image of several catalysts. As can be seen from the image, the inner core is a hollow metal organic framework material, the outer shell is a metal organic framework material, and a dot-shaped interlayer is arranged between the inner core and the outer shell. As can be seen from Figs. (b)-(d), the particle size D50 of the composite metal organic framework catalyst is 178.4 nm, the particle size D50 of the inner core is 150 nm, and the thickness of the outer shell is 14.2 nm.

[0086] Example 2

[0087] The embodiment provides a composite metal organic framework catalyst, the composite metal organic framework catalyst is a core-shell structure, the inner core is HoMIL-101, and the shell is MIL-101;

[0088] A sandwich layer is arranged between the inner core and the shell, and the sandwich layer is composed of uniformly distributed Rh nanoparticles;

[0089] The particle size D50 of the composite metal organic framework catalyst is 182.7 nm, the particle size D50 of the Rh nanoparticles is 3.4 nm, the content of the Rh nanoparticles is 0.5 wt.%, based on the mass of the hollow metal organic framework material, and the thickness of the shell is 10 nm.

[0090] The embodiment further provides a preparation method of the composite metal organic framework catalyst, and the preparation method comprises the following steps:

[0091] (1) stirring and dispersing chromium nitrate nine hydrates (0.4 g) and terephthalic acid (0.11 g) in a molar ratio of 1.5:1 in 10 mL of deionized water, uniformly mixing to obtain a mixed solution, then transferring the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave, and performing a hydrothermal reaction at 160 DEG C in an oven for 8 h, after the reaction is completed, transferring the reaction product to a conical tube for standing, then centrifuging the upper suspension to obtain a MIL-101 product, then washing with deionized water, and after washing, dispersing the washed product in 4 mL of deionized water to obtain a MIL-101-containing aqueous solution;

[0092] (2) diluting 1 mL of the MIL-101-containing aqueous solution to 5 mL with deionized water, then stirring and dispersing in a mixed solvent composed of water (4 mL) and glacial acetic acid (0.5 mL) in a volume ratio of 8:1 for 3 min to obtain a suspension, then transferring the suspension to a polytetrafluoroethylene-lined autoclave, and performing an etching reaction on the suspension at a temperature of 160 DEG C for 6 h to obtain a reaction product, standing the reaction product and removing the crystalline precipitate at the bottom, then centrifugally collecting the remaining product and washing with deionized water and DMF for 3 times to obtain a hollow MIL-101, denoted as HoMIL-101;

[0093] (3) the HoMIL-101 is re-dispersed in 10 mL of DMF to obtain a HoMIL-101-containing solution with a solute concentration of 20 mg / mL, 3 mL of the Rh nanoparticle solution is added dropwise into 8 mL of the HoMIL-101-containing solution (the volume ratio of the HoMIL-101-containing solution to the Rh nanoparticle solution is 8:3) under stirring, and then the mixed solution is stirred and mixed at room temperature 25℃ for 3 h, followed by centrifugation and washing with DMF and deionized water for 3 times to obtain HoMIL-101 with an interlayer of Rh nanoparticles distributed on the surface, denoted as HoMIL-101@Rh;

[0094] (4) 200 mg of chromium nitrate nine hydrate and 55 mg of terephthalic acid are dissolved in 5 mL of deionized water to obtain a MIL-101 precursor solution, and the HoMIL-101@Rh is re-dispersed in 5 mL of deionized water to obtain a HoMIL-101@Rh-containing solution; the HoMIL-101@Rh-containing solution (4 mL) and the MIL-101 precursor solution (6 mL) with a solute concentration of 51 mg / mL are stirred and mixed at a volume ratio of 0.8:1.2 for 20 min, and then transferred to a polytetrafluoroethylene-lined autoclave for hydrothermal reaction at 130℃ for 5 h, after the reaction is completed, the product is transferred to a conical tube for standing, the upper suspension is centrifuged, and then the product is washed with deionized water for 3 times to obtain an intermediate product, denoted as MIL-101@Rh@MIL-101;

[0095] (5) the MIL-101@Rh@MIL-101 is re-dispersed in 5 mL of deionized water to obtain a MIL-101@Rh@MIL-101-containing aqueous solution, and 5 mL of the MIL-101@Rh@MIL-101-containing aqueous solution is dispersed in a mixed solvent composed of deionized water (4 mL) and glacial acetic acid (0.5 mL) at a volume ratio of 8:1 for 7 min to obtain a suspension, and the suspension is transferred to a polytetrafluoroethylene-lined autoclave for etching reaction at 130℃ for 7 h, after the reaction is completed, the product is allowed to stand and the bottom crystalline precipitate is removed, and then the product is centrifuged and washed with distilled water for 3 times to obtain the composite metal organic framework catalyst, denoted as HoMIL-101@Rh@MIL-101.

[0096] Example 3

[0097] The present embodiment provides a composite metal organic framework catalyst, which has a core-shell structure, the inner core is HoMIL-101, and the outer shell is MIL-101;

[0098] The interlayer is composed of uniformly distributed Ir nanoparticles.

[0099] The composite metal organic framework catalyst has a particle size D50 of 177.6 nm, the Ir nanoparticles have a particle size D50 of 3.9 nm, the content of the Ir nanoparticles is 2 wt.% based on the mass of the hollow metal organic framework material, and the thickness of the shell is 20 nm.

[0100] The embodiment also provides a preparation method of the composite metal organic framework catalyst, and the preparation method comprises the following steps:

[0101] (1) stirring and dispersing chromium nitrate nine-water (0.4 g) and terephthalic acid (0.11 g) in a molar ratio of 1.5:1 in 10 mL of deionized water, uniformly mixing to obtain a mixed solution, and then transferring the mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave, and performing a hydrothermal reaction at 200 °C for 4 h in an oven, after the reaction is completed, transferring the reaction product to a conical tube for standing, and then centrifuging the upper suspension to obtain a MIL-101 product, and then washing with deionized water, and after washing, redispersing the washed product in 4 mL of deionized water to obtain a MIL-101-containing aqueous solution;

[0102] (2) diluting 1 mL of the MIL-101-containing aqueous solution to 5 mL with deionized water, and then stirring and dispersing in a mixed solvent composed of water (6 mL) and glacial acetic acid (0.5 mL) in a volume ratio of 12:1 for 7 min to obtain a suspension, and then transferring the suspension to a polytetrafluoroethylene-lined autoclave, and performing an etching reaction on the suspension at a temperature of 200 °C for 2 h to obtain a reaction product, standing the reaction product and removing the bottom crystalline precipitate, and then centrifuging to collect the remaining product and washing with deionized water and DMF for 3 times to obtain a hollow MIL-101, denoted as HoMIL-101;

[0103] (3) redispersing the HoMIL-101 in 10 mL of DMF to obtain a HoMIL-101-containing solution with a solute concentration of 20 mg / mL, and then adding 0.85 mL of an Ir nanoparticle solution dropwise to 10 mL of the HoMIL-101-containing solution (the volume ratio of the HoMIL-101-containing solution to the Ir nanoparticle solution is 12:1) under stirring, and then stirring and mixing the mixed solution at room temperature 25 °C for 1 h, and then centrifuging and washing with DMF and deionized water for 3 times to obtain HoMIL-101 with an Ir nanoparticle interlayer distributed on the surface, denoted as HoMIL-101@Ir;

[0104] (4) 200 mg of chromium nitrate nine hydrate and 55 mg of terephthalic acid were dissolved in 5 mL of deionized water to obtain a MIL-101 precursor solution, and the HoMIL-101@Ir was re-dispersed in 5 mL of deionized water to obtain a HoMIL-101@Ir-containing solution; the HoMIL-101@Ir-containing solution (6 mL) and the MIL-101 precursor solution (4 mL) with a solute concentration of 51 mg / mL were stirred and mixed in a volume ratio of 1.2:0.8 for 40 min, and then transferred to a polytetrafluoroethylene-lined autoclave for a hydrothermal reaction at 170°C for 3 h; after the reaction, the product was transferred to a conical tube for standing, the upper suspension was centrifuged, and then the product was washed with deionized water for 3 times to obtain an intermediate product, denoted as MIL-101@Ir@MIL-101;

[0105] (5) The MIL-101@Ir@MIL-101 was re-dispersed in 5 mL of deionized water to obtain a MIL-101@Ir@MIL-101-containing aqueous solution, and 5 mL of the MIL-101@Ir@MIL-101-containing aqueous solution was dispersed in a mixed solvent composed of deionized water (6 mL) and glacial acetic acid (0.5 mL) in a volume ratio of 12:1 for 3 min to obtain a suspension, and the suspension was transferred to a polytetrafluoroethylene-lined autoclave for an etching reaction at 170°C for 3 h; after the reaction, the product was allowed to stand and the bottom crystalline precipitate was removed, and then the product was centrifuged and washed with distilled water for 3 times to obtain the composite metal organic framework catalyst, denoted as HoMIL-101@Ir@MIL-101.

[0106] Example 4

[0107] The difference between this example and Example 1 is that the content of Ru nanoparticles in the prepared composite metal organic framework catalyst is 0.3 wt.% by adjusting the amount of Ru nanoparticle solution added in step (3).

[0108] The rest of the preparation method and parameters remain the same as those of Example 1.

[0109] Example 5

[0110] The difference between this example and Example 1 is that the content of Ru nanoparticles in the prepared composite metal organic framework catalyst is 2.5 wt.% by adjusting the amount of Ru nanoparticle solution added in step (3).

[0111] The rest of the preparation method and parameters remain the same as those of Example 1.

[0112] Example 6

[0113] The difference between this example and Example 1 is that the thickness of the shell of the composite metal organic framework catalyst prepared is 5 nm by adjusting the amount of the MIL-101 precursor solution added in step (4).

[0114] The rest of the preparation method and parameters remain the same as in Example 1.

[0115] Example 7

[0116] The difference between this example and Example 1 is that the thickness of the shell of the composite metal organic framework catalyst prepared is 25 nm by adjusting the amount of the MIL-101 precursor solution added in step (4).

[0117] The rest of the preparation method and parameters remain the same as in Example 1.

[0118] Comparative Example 1

[0119] The difference between this comparative example and Example 1 is that no Ru nanoparticle solution is added in step (3), i.e. the composite metal organic framework catalyst does not contain the interlayer composed of Ru nanoparticles.

[0120] The rest of the preparation method and parameters remain the same as in Example 1.

[0121] Comparative Example 2

[0122] The difference between this comparative example and Example 1 is that steps (4) and (5) are not performed, i.e. the catalyst obtained is HoMIL-101@Ru.

[0123] The rest of the preparation method and parameters remain the same as in Example 1.

[0124] Comparative Example 3

[0125] The difference between this comparative example and Example 1 is that steps (3) and (4) are replaced in sequence, i.e. the coating of the shell is performed first, and then the loading of Ru, and the composite metal organic framework catalyst obtained is HoMIL-101@MIL-101@Ru.

[0126] The rest of the preparation method and parameters remain the same as in Example 1.

[0127] Performance test

[0128] The composite metal organic framework catalysts prepared in the above examples and comparative examples are used to catalyze the preparation of r-valerolactone from levulinic acid, and the specific steps include:

[0129] Each sample containing the same amount was dispersed in 5 mL of water, and then 0.5 mmol of levulinic acid (LA) was added to the above solution. Subsequently, the solution was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave, and the H2 pressure of the autoclave was set to 1 MPa. During the catalytic process, the reaction solution was magnetically stirred at 50℃ at a speed of 300 rpm for the required time. The obtained reaction solution was filtered through a filter membrane (0.22 nm), and then analyzed by gas chromatography (GC, Shimadzu).

[0130] The conversion rate of levulinic acid, the selectivity, and the TOF value of the above catalytic process were tested, and the test results are shown in Table 1.

[0131] Table 1

[0132]

[0133] Analysis:

[0134] As can be seen from the above table, the platinum group metal nanoparticles are arranged between the inner core hollow metal organic framework material and the outer shell metal organic framework material, the accurate distribution of the platinum group metal nanoparticles is realized, the interaction between the platinum group metal nanoparticles and the inner core and the outer shell is effectively enhanced, the high-efficiency synergistic catalytic effect produced makes the catalytic efficiency of the catalyst significantly improved, and in particular, the conversion rate of the catalyst provided by the application for catalyzing levulinic acid to produce r-valerolactone is as high as 100%, the selectivity is as high as 100%, and the TOF value is 1885 h -1 , and the catalytic efficiency is high.

[0135] As can be seen from the data results of Examples 1-3, under this specific reaction condition, Rh and Ir have lower hydrogen activation ability than Ru, so under the same reaction time, the conversion rate and the TOF value when Rh and Ir are used as the interlayer are low.

[0136] As can be seen from the data results of Example 1 and Examples 4-5, if the content of the platinum group metal nanoparticles is too low, the catalytic performance will decrease; if the content of the platinum group metal nanoparticles is too high, with the increase of the Ru active sites, the hydrogen activation ability of the catalyst will gradually increase, so the conversion rate will be higher and higher, but in the coating process, the platinum group metal nanoparticles are easy to aggregate and fall off, which will result in a low TOF value.

[0137] As can be seen from the data results of Example 1 and Examples 6-7, if the thickness of the outer shell is too small, the steric hindrance effect will decrease, the activity will increase, the conversion rate and the TOF value will be high, but the stability of the too thin outer shell is poor and it is easy to fall off; if the thickness of the outer shell is too large, the steric hindrance effect will increase, which will result in a decrease of the activity and a decrease of the catalytic performance.

[0138] From the data results of Example 1 and Comparative Example 1, if the composite metal organic framework catalyst does not contain the interlayer composed of Ru nanoparticles, the hydrogen cannot be activated, and there is no catalytic effect.

[0139] From the data results of Example 1 and Comparative Example 2, if the obtained catalyst is HoMIL-101@Ru, the Ru is easy to aggregate and fall off during the reaction process, which can cause the catalytic performance to decrease.

[0140] From the data results of Example 1 and Comparative Example 3, if the obtained composite metal organic framework catalyst is HoMIL-101@MIL-101@Ru, that is, the coating of the outer shell is first performed, and then the Ru is loaded, the Ru is easy to aggregate and fall off during the reaction process, which can cause the catalytic performance to decrease.

[0141] The applicant declares that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of the selected materials, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.

Claims

1. The application of a composite metal-organic framework catalyst, characterized in that, The composite metal-organic framework catalyst is used to catalyze the production of γ-valerol from levulinic acid. The composite metal-organic framework catalyst has a core-shell structure, with the core being a hollow metal-organic framework material and the outer shell being a metal-organic framework material; A sandwich layer is provided between the core and the outer shell, and the sandwich layer is composed of uniformly distributed platinum group metal nanoparticles; The particle size D50 of the composite metal-organic framework catalyst is 150-200 nm; Based on the mass of the hollow metal-organic framework material, the content of the platinum group metal nanoparticles is 0.5-2 wt.%. The hollow metal-organic framework material includes hollow MIL material; the metal-organic framework material includes MIL material.

2. The application according to claim 1, characterized in that, The particle size D50 of the platinum group metal nanoparticles is 2-5 nm.

3. The application according to claim 1, characterized in that, The thickness of the outer shell is 10-20 nm.

4. The application according to claim 1, characterized in that, The platinum group metal nanoparticles include any one or a combination of at least two of Ru nanoparticles, Pt nanoparticles, Rh nanoparticles, or Ir nanoparticles.

5. The application according to claim 1, characterized in that, The preparation method of the composite metal-organic framework catalyst includes the following steps: (1) Mix the solution containing hollow metal-organic framework material with the solution of platinum group metal nanoparticles to obtain a hollow metal-organic framework material with platinum group metal nanoparticles distributed on the surface, denoted as hollow MOF@platinum group metal nanoparticles; (2) The solution containing the hollow MOF@platinum group metal nanoparticles and the metal-organic framework material precursor solution are mixed and subjected to hydrothermal reaction. Then the product of the hydrothermal reaction is etched to obtain the composite metal-organic framework catalyst.

6. The application according to claim 5, characterized in that, The volume ratio of the solution containing hollow metal-organic framework material and the solution of platinum group metal nanoparticles in step (1) is (8-12):(1-3).

7. The application according to claim 5, characterized in that, The solute concentration of the solution containing the hollow metal-organic framework material in step (1) is 10-30 mg / mL.

8. The application according to claim 5, characterized in that, The mixing process described in step (1) is accompanied by stirring.

9. The application according to claim 5, characterized in that, The mixing temperature in step (1) is room temperature.

10. The application according to claim 5, characterized in that, The mixing time in step (1) is 1-3 hours.

11. The application according to claim 5, characterized in that, After mixing as described in step (1), centrifugation and washing are also performed.

12. The application according to claim 5, characterized in that, The preparation method of the hollow metal-organic framework material in step (1) includes the following steps: Metal salt, organic ligand and solvent are mixed and subjected to hydrothermal reaction to obtain metal-organic framework material. Then, the metal-organic framework material is acid etched to obtain hollow metal-organic framework material.

13. The application according to claim 12, characterized in that, The metal salts include chromium salts.

14. The application according to claim 12, characterized in that, The organic ligands include terephthalic acid.

15. The application according to claim 12, characterized in that, The molar ratio of the organic ligand to the metal salt is 1:(1-2.2).

16. The application according to claim 12, characterized in that, The hydrothermal reaction is carried out at a temperature of 160-200℃ for 4-6 hours.

17. The application according to claim 12, characterized in that, During the acid etching process, the temperature is 160-200℃ and the time is 2-5 hours.

18. The application according to claim 12, characterized in that, After the acid etching is completed, the steps of settling, centrifugation and washing are also performed.

19. The application according to claim 5, characterized in that, In step (2), the volume ratio of the solution containing the hollow MOF@platinum group metal nanoparticles to the metal-organic framework precursor solution is (0.8-1.2):(0.8-1.2).

20. The application according to claim 5, characterized in that, The solute concentration of the metal-organic framework precursor solution in step (2) is 40-60 mg / mL.

21. The application according to claim 5, characterized in that, The mixing process described in step (2) involves stirring.

22. The application according to claim 5, characterized in that, The mixing time in step (2) is 20-40 minutes.

23. The application according to claim 5, characterized in that, The temperature of the hydrothermal reaction in step (2) is 130-170℃.

24. The application according to claim 5, characterized in that, The hydrothermal reaction time in step (2) is 3-5 hours.

25. The application according to claim 5, characterized in that, The etching step in step (2) includes: The products of the hydrothermal reaction are dispersed in a mixed solvent of water and acid to obtain a suspension, which is then subjected to an etching reaction.

26. The application according to claim 25, characterized in that, The etching reaction is carried out at a temperature of 130-170℃.

27. The application according to claim 25, characterized in that, The etching reaction takes 3-7 hours.

28. The application according to claim 5, characterized in that, After the etching described in step (2) is completed, the steps of settling, centrifugation and washing are also performed.

29. The application according to claim 5, characterized in that, The preparation method includes the following steps: (I) Terephthalic acid and chromium salt in a molar ratio of 1:(1-2.2) are stirred and dispersed in water, and then subjected to a hydrothermal reaction at 160-200℃ for 4-6 hours. After standing and centrifugation, the MIL-101 product is obtained. After washing, the MIL-101 product is redispersed in an aqueous solvent to obtain an aqueous solution containing MIL-101. (II) The aqueous solution containing MIL-101 is stirred and dispersed in a mixed solvent of water and acid with a volume ratio of (8-12):1 for 3-7 minutes to obtain a suspension. Then, the suspension is subjected to an etching reaction at 160-200℃ for 2-5 hours. After standing, centrifugation and washing, hollow MIL-101 is obtained, which is denoted as HoMIL-101. (III) The HoMIL-101 is redispersed in an organic solvent to obtain a HoMIL-101-containing solution with a solute concentration of 10-30 mg / mL. The HoMIL-101-containing solution and the platinum group metal nanoparticle solution are stirred and mixed at room temperature at a volume ratio of (8-12):(1-3) for 1-3 h. Then, the mixture is centrifuged and washed to obtain HoMIL-101 with a platinum group metal nanoparticle interlayer on the surface, denoted as HoMIL-101@platinum group metal nanoparticles. (IV) The HoMIL-101@platinum group metal nanoparticles are redispersed in an aqueous solvent to obtain a solution containing HoMIL-101@platinum group metal nanoparticles. The solution containing HoMIL-101@platinum group metal nanoparticles and a MIL-101 precursor solution with a solute concentration of 40-60 mg / mL are stirred and mixed at a volume ratio of (0.8-1.2):(0.8-1.2) for 20-40 min. Then, a hydrothermal reaction is carried out at 130-170℃ for 3-5 h. After the reaction is completed, the mixture is allowed to stand, centrifuged and washed to obtain an intermediate product. (V) The intermediate product is redispersed in an aqueous solvent to obtain a solution containing the intermediate product. The solution containing the intermediate product is stirred and dispersed in a mixed solvent of water and acid with a volume ratio of (8-12):1 for 3-7 min to obtain a suspension. Then, an etching reaction is carried out at 130-170℃ for 3-7 h. After the reaction is completed, the mixture is allowed to stand, centrifuged and washed to obtain a composite metal-organic framework catalyst, denoted as HoMIL-101@platinum group metal nanoparticles@MIL-101.

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