A methanol catalyst using metal-organic framework as a precursor and a preparation method thereof

Abstract

The present invention relates to a methanol catalyst using a metal-organic framework as a precursor and a preparation method thereof. Using a metal-organic framework (MOF) as a precursor, a uniformly dispersed and regularly distributed single-atom metal node is pre-obtained depending on the MOF structure, and then a Cu-ZnO-Al2O3 methanol synthesis catalyst with highly dispersed metal active components can be obtained after calcination. The present invention can obtain a Cu-ZnO-Al2O3 methanol synthesis catalyst with atomically dispersed copper and zinc active components in a relatively convenient manner. The highly dispersed active components help to improve the accessibility of active sites, reduce the migration and agglomeration degree of active components under high-temperature conditions, and improve the thermal stability of the catalyst.

Description

Technical Field

[0001] The present invention relates to a methanol catalyst using a metal-organic framework as a precursor and a preparation method thereof, belonging to the technical field of catalyst preparation. Background Art

[0002] As an important chemical raw material and clean alternative fuel, methanol plays an increasingly important role in the world chemical industry and even in social life. In recent years, the demand for methanol and the methanol production capacity in China have shown a rapid upward trend, and the potential of the methanol market has also increased accordingly. The key to methanol synthesis is to prepare an efficient and stable methanol synthesis catalyst. At present, the most widely used methanol synthesis catalyst in industry is the Cu-ZnO-Al2O3 catalyst, in which Cu is the main catalytic active component, ZnO is used as a co-catalytic active component, and Al2O3 is used as a carrier to provide support for the active components of the catalyst.

[0003] As a co-active component, Cu-ZnO has a key influence on the catalytic effect of methanol synthesis. The dispersion degree of the copper-zinc active components in the catalyst structure affects the accessibility of the active sites during the catalytic process, and thus affects the catalytic activity and catalytic life of the catalyst ( Catalysts , 2015, 5 , 145-269). However, most of the syntheses of the Cu-ZnO-Al2O3 catalyst adopt the co-precipitation method, which is likely to cause the phenomenon of uneven dispersion of the active components and non-uniform particle sizes. In addition, the copper-based catalyst is prone to particle migration and agglomeration under high-temperature conditions, resulting in a further decrease in the accessibility of the active components, and ultimately affecting the service life of the catalyst.

[0004] Metal–organic frameworks (MOFs) are a class of crystalline porous materials formed by metal nodes (which can be single metal atoms or metal clusters) and organic ligands through coordination interactions. Due to their ultra-high specific surface area, abundant metal sites, and structural regularity and periodicity, MOFs play a unique role in the field of methanol synthesis catalysis. The application of MOFs in the field of methanol synthesis catalysts mainly has two aspects. One is to use MOFs as carriers, taking advantage of their ultra-high specific surface area and regular pores to load catalytically active components or adsorb reaction gases for catalysis (such as patents CN110975938A and CN111359672A); the other is to use MOFs as precursors, and after calcining MOFs, metal oxides or carbides are obtained using the uniformly dispersed metal nodes in the MOF structure for catalysis (such as patent CN106975486B). However, regarding how to utilize the advantages of MOFs as precursors to synergistically improve the dispersion degree of copper and zinc components in traditional catalytic systems such as Cu-ZnO-Al2O3 catalysts and alleviate the problems of uneven active components and easy sintering, further research is still needed at present. Summary of the Invention

[0005] The object of the present invention is to provide a methanol catalyst using metal–organic frameworks as precursors and a preparation method thereof, by which the dispersion degree of copper and zinc active components in the catalyst structure is increased, the high-temperature sintering problem of the catalyst is alleviated, and thus the thermal stability of the methanol synthesis catalyst is enhanced.

[0006] To achieve the above object of the present invention, the methanol catalyst using metal–organic frameworks as precursors provided by the present invention uses metal–organic framework MOF as a precursor, relies on the MOF structure to pre-obtain uniformly dispersed and regularly distributed single-atom metal nodes, and then obtains a Cu-ZnO-Al2O3 methanol synthesis catalyst with highly dispersed metal active components after calcining it.

[0007] The preparation method of the catalyst of the present invention includes the following steps.

[0008] (1) Prepare a Cu-Zn-BDC with a Cu-Zn-doped MOF structure.

[0009] (2) Prepare alumina sol by reacting an aluminum salt solution with a basic precipitant.

[0010] (3) Thoroughly mix Cu-Zn-BDC with the alumina sol.

[0011] (4) After the mixture undergoes filtration, washing, drying, calcining, and shaping processes, a Cu-ZnO-Al2O3 methanol synthesis catalyst with atomically dispersed copper and zinc active components is obtained.

[0012] Generally, the preparation of Cu-Zn-BDC: Dissolve copper nitrate, zinc nitrate, terephthalic acid (H2BDC), and triethylamine in N,N -dimethylformamide (DMF). Let it stand and sediment at room temperature. After discarding the supernatant, wash the precipitate three times with DMF and then three times with water, and then dry it in an oven for standby.

[0013] Preferably, the molar ratio of copper nitrate, zinc nitrate, H2BDC, DMF, and triethylamine is 3:1:4:83:2 - 1:3:4:333:8.

[0014] Preferably, the conditions for oven drying are drying at 80 - 120 °C for 6 - 12 hours.

[0015] The preparation method of the aluminogel precursor: Carry out a neutralization reaction between an aqueous solution of aluminum nitrate and a basic precipitant under specified pH and temperature conditions to obtain the aluminogel precursor.

[0016] Preferably, the basic precipitant is one or more of NaOH, NH3·H2O, NaHCO3, and Na2CO3.

[0017] Preferably, the pH of the neutralization reaction is controlled at 7 - 9, and the temperature is 30 - 80 °C.

[0018] Mixing the Cu-Zn-BDC and the aluminogel precursor: Vigorously stir the suspension of a quantitative amount of Cu-Zn-BDC and the aluminogel precursor at a specified temperature.

[0019] Preferably, the molar ratio of the total amount of metal atoms in the Cu-Zn-BDC to the molar amount of aluminum is 10:1 - 1:1, and the duration of mixing and stirring is 30 - 120 minutes.

[0020] After the mixture undergoes filtration, washing, drying, calcination, and shaping processes, a Cu-ZnO-Al2O3 methanol synthesis catalyst with atomically dispersed copper and zinc active components is obtained.

[0021] Preferably, the drying conditions for the sample are drying at 80 - 120 °C for 6 - 12 hours.

[0022] Preferably, the calcination conditions for the sample are calcination in an air atmosphere at 300 - 400 °C for 30 - 60 minutes.

[0023] Preferably, 2 - 6 wt% of graphite is added during the demolding and tablet pressing process of the sample.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a methanol catalyst with a metal organic framework as a precursor and a preparation method, and utilizes the characteristics of the metal nodes of the metal organic framework (MOF) itself being evenly dispersed and regularly distributed to pre-form copper-zinc-doped single-atom metal nodes in the MOF structure. Combined with the roasting method, the MOF precursor can be converted into copper-zinc oxide in situ. Through this strategy, we can obtain a Cu-ZnO-Al2O3 methanol synthesis catalyst with atomically dispersed copper-zinc active components in a relatively convenient way. The highly dispersed active components help to improve the accessibility of the active sites, reduce the degree of migration and agglomeration of the active components under high temperature conditions, and improve the thermal stability of the catalyst. DETAILED DESCRIPTION

[0025] The following specific examples are only used to further illustrate the technical solutions of the present invention in detail, and the effects of the methods of the present invention are not limited thereto.

[0026] Example 1

[0027] 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine were dissolved in a round-bottom flask containing 400 mL of DMF. After the mixture was fully reacted, it was allowed to settle at room temperature. After the supernatant was discarded, the precipitate was washed three times with DMF and three times with water, and then dried in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for use.

[0028] At 30 °C, 1 L aqueous solution containing 37.5 g aluminum nitrate nonahydrate and 1 mol / L NaOH aqueous solution were simultaneously added to the continuous neutralization reactor through a metering pump, and the pH of the solution in the continuous neutralization reactor was controlled to be 7.0. Subsequently, 228.2 g of dried Cu-Zn-BDC was added to the mixture and the stirring and beating operation was continued for 30 minutes. The mixture was filtered, washed, and dried in an oven at 80 °C for 6 hours before use.

[0029] The solid was calcined in a muffle furnace at 300 °C in an air atmosphere for 30 minutes. After 30 minutes, the solid was taken out and weighed, and 2 wt% of graphite was added, and then demolded and broken into 16-40 mesh.

[0030] Example 2

[0031] Dissolve 53.4 g of zinc nitrate hexahydrate, 14.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 60 mL of triethylamine in a round-bottom flask containing 1600 mL of DMF. After the mixture reacts fully, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water. After that, dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for standby.

[0032] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L of NaOH aqueous solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue the stirring and slurrying operation for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for standby.

[0033] Calcine the solid in a muffle furnace at 300 °C under an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% of graphite, then perform demolding and tablet pressing, and crush it into 16–40 mesh.

[0034] Example 3

[0035] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts fully, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water. After that, dry it in an oven at 120 °C for 12 hours to obtain Cu-Zn-BDC for standby.

[0036] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L of NaOH aqueous solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue the stirring and slurrying operation for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for standby.

[0037] Calcine the solid in a muffle furnace at 300 °C under an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% of graphite, then perform demolding and tablet pressing, and crush it into 16–40 mesh.

[0038] Example 4

[0039] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. After discarding the supernatant, wash the precipitate three times with DMF and then three times with water, and then dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for later use.

[0040] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and NH3·H2O to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue the stirring and slurrying operation for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for later use.

[0041] Calcine the solid in a muffle furnace at 300 °C in an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% graphite, then demold and slice it, and crush it into 16–40 mesh.

[0042] Example 5

[0043] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. After discarding the supernatant, wash the precipitate three times with DMF and then three times with water, and then dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for later use.

[0044] At 80 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L NaOH aqueous solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue the stirring and slurrying operation for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for later use.

[0045] Calcine the solid in a muffle furnace at 300 °C in an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% graphite, then demold and slice it, and crush it into 16–40 mesh.

[0046] Example 6

[0047] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water, and dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for later use.

[0048] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L aqueous NaOH solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 22.8 g of the dried Cu-Zn-BDC to the mixture and continue with the stirring and slurrying operation for 120 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for later use.

[0049] Calcine the solid in a muffle furnace at 300 °C under an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% graphite, then perform demolding and tablet pressing, and crush it to 16–40 mesh.

[0050] Example 7

[0051] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water, and dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for later use.

[0052] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L aqueous NaOH solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue with the stirring and slurrying operation for 30 minutes. Filter, wash the mixture, and dry it in an oven at 120 °C for 12 hours for later use.

[0053] Calcine the solid in a muffle furnace at 300 °C under an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 2 wt% graphite, then perform demolding and tablet pressing, and crush it to 16–40 mesh.

[0054] Example 8

[0055] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water. After that, dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for standby.

[0056] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L NaOH aqueous solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue stirring and slurrying for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for standby.

[0057] Calcine the solid in a muffle furnace at 400 °C under an air atmosphere for 60 minutes. After 60 minutes, take out the solid, weigh it, add 2 wt% graphite, then demold, slice, and crush it into 16–40 mesh.

[0058] Example 9

[0059] Dissolve 17.8 g of zinc nitrate hexahydrate, 43.5 g of copper nitrate trihydrate, 27.9 g of terephthalic acid, and 15 mL of triethylamine in a round-bottom flask containing 400 mL of DMF. After the mixture reacts sufficiently, let it stand and settle at room temperature. Discard the supernatant, then wash the precipitate three times with DMF and three times with water. After that, dry it in an oven at 80 °C for 6 hours to obtain Cu-Zn-BDC for standby.

[0060] At 30 °C, simultaneously add a 1 L aqueous solution containing 37.5 g of aluminum nitrate nonahydrate and 1 mol / L NaOH aqueous solution to a continuous neutralization reactor through a metering pump, and control the pH of the solution in the continuous neutralization reactor to 7.0. Subsequently, add 228.2 g of the dried Cu-Zn-BDC to the mixture and continue stirring and slurrying for 30 minutes. Filter, wash the mixture, and dry it in an oven at 80 °C for 6 hours for standby.

[0061] Calcine the solid in a muffle furnace at 300 °C under an air atmosphere for 30 minutes. After 30 minutes, take out the solid, weigh it, add 6 wt% graphite, then demold, slice, and crush it into 16–40 mesh.

[0062] Comparative Example

[0063] A 1 L aqueous solution containing 59.5 g of zinc nitrate hexahydrate, 144.9 g of copper nitrate trihydrate, and 37.5 g of aluminum nitrate nonahydrate was added to a continuous neutralization reactor simultaneously with 1 mol / L aqueous NaOH solution through a metering pump, maintaining the temperature at 30 °C and controlling the pH of the solution in the continuous neutralization reactor at 7.0. After the reaction was completed, the mixture was filtered, washed, and dried in an oven at 80 °C for 6 hours for later use.

[0064] The solid was calcined in a muffle furnace at 300 °C in an air atmosphere for 30 minutes. After 30 minutes, the solid was taken out, weighed, and 2 wt% graphite was added, followed by demolding and tablet pressing, and then crushed to 16–40 mesh.

[0065] Activity test conditions: The catalyst prepared using MOF as the precursor was applied to the synthesis of methanol from syngas, and the activity evaluation of the catalyst was carried out on a micro fixed-bed continuous flow reactor. The catalyst loading was 4 mL. Before the reaction, the sample was first reduced in a H2 / N2 mixed gas containing 5% H2 at atmospheric pressure and heated at a rate of 20 °C h -1 and programmed to rise to 230 °C for 10 hours. Subsequently, the catalyst was used for the catalytic reaction of methanol synthesis under the conditions that the syngas composition was: CO (13–15%), CO2 (3–5%), H2 (55–65%), the balance being N2, the space velocity was 10000 h -1 , the reaction pressure was 5.0 MPa, and the reaction temperature was 230 °C, and the measured result was the initial activity. After the catalyst was heat-treated in a syngas atmosphere at atmospheric pressure and 400 °C for 5 hours, and then restored to the above activity evaluation conditions, the measured activity result was the activity after heat resistance. Taking Example 1 and the comparative example as examples, the specific surface area, pore size, and strength data are shown in Table 1.

[0066] Table 1: Results of catalyst structure characterization

[0067] Catalyst <![CDATA[BET specific surface area (m 2 / g)]]> Pore diameter (nm) Strength (N / cm) Example 1 105 10.4 305 Comparative example 93 11.9 256

[0068] The activity evaluation results of Example 1 and the comparative example are shown in Table 2.

[0069] Table 2: Activity evaluation results

[0070]

[0071] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and are not the only ones. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. Application of a methanol catalyst with a metal-organic framework as a precursor in the preparation of methanol from syngas, characterized in that Using metal organic framework MOF as a precursor, the MOF structure is used to obtain uniformly dispersed and regularly distributed single atomic metal nodes in advance, and then the metal active components are highly dispersed to obtain a Cu-ZnO-Al2O3 methanol synthesis catalyst after calcination. The preparation method of the catalyst comprises the following steps: (1) Preparation of copper-zinc doped MOF structure Cu-Zn-BDC: Dissolve copper nitrate, zinc nitrate, terephthalic acid H2BDC, and triethylamine in N,N -dimethylformamide DMF, let it stand and settle at room temperature, discard the supernatant, and wash the precipitate with DMF and water, then dry; (2) Preparing an aluminum colloid precursor by reacting an aluminum salt solution with an alkaline precipitant; (3) Fully mix Cu-Zn-BDC and aluminum gel precursor; (4) The mixture is filtered, washed, dried, calcined and formed to obtain a Cu-ZnO-Al2O3 methanol synthesis catalyst having atomically dispersed copper and zinc active components.

2. The application according to claim 1, wherein The preparation method of the copper-zinc doped MOF structure Cu-Zn-BDC in step (1): Dissolve copper nitrate, zinc nitrate, terephthalic acid H2BDC, and triethylamine in N,N -dimethylformamide DMF. The molar ratio of copper nitrate, zinc nitrate, H2BDC, DMF, and triethylamine is 3:1:4:83:2–1:3:4:333:

8. Let it stand and settle at room temperature, discard the supernatant, wash the precipitate three times with DMF, then wash it three times with water, and dry it in an oven at 80–120 °C for 6–12 hours for standby.

3. The application according to claim 1, characterized in that The alkaline precipitant in step (2) is one or more of NaOH, NH3·H2O, NaHCO3, and Na2CO3.

4. The application according to claim 1, characterized in that, The preparation method of the aluminum gel precursor in step (2) is as follows: an aqueous solution of aluminum nitrate is subjected to a neutralization reaction with an aqueous solution of an alkaline precipitant, the precipitation pH is 7-9, and the precipitation temperature is 30-80 °C.

5. The application according to claim 1, characterized in that, In the step (3), Cu-Zn-BDC is mixed with an aluminum colloid precursor, the ratio of the total molar amount of metal atoms in Cu-Zn-BDC to the molar amount of aluminum is 10:1-1:1, and the suspension of Cu-Zn-BDC and the aluminum colloid precursor is vigorously stirred at room temperature for 30-120 minutes.

6. The application according to claim 1, characterized in that, In the step (4), the drying is carried out at 80-120 °C for 6-12 hours.

7. The application according to claim 1, characterized in that In the step (4), the sintering step is carried out in an air atmosphere at 300-400 °C for 30-60 minutes.

8. The application according to claim 1, characterized in that, In the step (4), 2-6 wt% of graphite is added to the calcined solid to facilitate demoulding and tableting.

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