A MOF-confined platinum-molybdenum-based polyacid cluster catalyst, its precise preparation method and application

Abstract

This invention discloses a MOF-confined platinum-molybdenum-based polyacid cluster catalyst, its precise preparation method, and its applications. The catalyst comprises zirconium-based MOFs, within which Pt-containing or Pt-free molybdenum-based polyacid clusters are dispersed. Pt is deposited on the Pt-free molybdenum-based polyacid clusters. This catalyst exhibits high atom utilization, mild reaction conditions, high carbon dioxide conversion, excellent stability, and high methanol selectivity, demonstrating superior performance compared to commercial CuZnAl2O3 under the same conditions, and possesses broad industrial application prospects.

Description

Technical Field

[0001] This invention relates to a MOF-confined platinum-molybdenum-based polyacid cluster catalyst, its precise preparation method, and its application, belonging to the field of heterogeneous catalytic materials technology. Background Technology

[0002] With the acceleration of global industrialization and the excessive consumption of fossil fuels, the concentration of carbon dioxide (CO2) in the atmosphere continues to rise, exacerbating the greenhouse effect and climate change. Developing efficient and economical technologies for the resource utilization of CO2 has become a global focus. Among these, the hydrogenation of carbon dioxide to methanol (CO2 + 3H2 → CH3OH + H2O) has attracted considerable attention due to its technological feasibility and economic potential. Methanol is not only an important chemical raw material but can also serve as a clean fuel or hydrogen storage carrier, showing broad application prospects.

[0003] Currently, research on carbon dioxide hydrogenation to methanol technology mainly focuses on catalyst development, reaction process optimization, and system integration. Traditional catalyst systems are primarily copper-based catalysts (such as Cu / ZnO / Al2O3), with their active centers (Cu...)... 0 Copper-based catalysts have limited adsorption and activation capabilities for CO2, necessitating reactions to be carried out at relatively high temperatures (250-300℃) and pressures (5-10 MPa). These high-temperature, high-pressure conditions not only increase energy consumption but also easily trigger side reactions (such as the reverse water-gas shift reaction, generating CO) and reduce methanol selectivity. Furthermore, copper-based catalysts suffer from problems such as easy sintering and sulfur poisoning, resulting in insufficient long-term stability and hindering their industrial application.

[0004] In recent years, novel catalytic systems such as precious metal (e.g., Pd, Pt) catalysts and transition metal oxides (e.g., In₂O₃, ZrO₂) catalysts have been proposed. However, precious metal catalysts tend to aggregate under prolonged reducing atmosphere conditions, exhibiting poor stability and hindering large-scale application. While metal oxide catalysts are lower in cost, their low-temperature (mild) activity is insufficient, and active sites are easily covered by reaction intermediates, leading to rapid deactivation. Furthermore, in existing processes, hydrogen (H₂) is mostly derived from fossil fuel reforming, failing to achieve "green hydrogen" coupling, resulting in high carbon emissions throughout the entire life cycle and diminishing the environmental value of the technology. Summary of the Invention

[0005] The purpose of this invention is to provide a MOF-confined platinum-molybdenum-based polyacid cluster catalyst, its precise preparation method, and its applications. The confinement effect of the MOF channels effectively inhibits the migration and aggregation of active components, improves stability, and exhibits excellent catalytic performance under mild conditions. Under the same conditions, it shows superior performance compared to commercial CuZnAl2O3.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A MOF-confined platinum-molybdenum polyacid cluster catalyst includes zirconium-based MOFs, wherein Pt-containing or Pt-free molybdenum-based polyacid clusters are dispersed within the channels of the zirconium-based MOFs, and Pt is deposited on the Pt-free molybdenum-based polyacid clusters.

[0008] Preferably, the molybdenum-based polyacid clusters are Dawson-type and / or Keggin-type and / or Anderson-type and / or wheel-shape-type molybdenum-based polyacid clusters.

[0009] The precise preparation method of any of the above-mentioned MOFs-confined platinum-molybdenum-based polyacid cluster catalysts involves adding zirconium-based MOFs into a Pt-containing molybdenum-based polyacid solution, followed by shaking treatment, washing, soaking, centrifugation, and drying.

[0010] Alternatively, zirconium-based MOFs can be added to a Pt-free molybdenum-based polyacid solution, shaken, washed, soaked, centrifuged, and dried to obtain a MOF-confined molybdenum-based polyacid cluster precursor; then, Pt can be loaded onto the molybdenum-based polyacid clusters of the MOF-confined molybdenum-based polyacid cluster precursor by liquid phase impregnation or atomic layer deposition.

[0011] Preferably, the zirconium-based MOFs are any one of NU1000, UiO-66, NU1008, MOF-808 and NU-1200.

[0012] Preferably, the mass ratio of zirconium-based MOFs to Pt-containing molybdenum polyacid in a Pt-containing molybdenum polyacid solution and Pt-free molybdenum polyacid in a Pt-free molybdenum polyacid solution is (1-2):(2-6).

[0013] Application of any of the above-mentioned MOFs-confined platinum-molybdenum-based polyacid cluster catalysts in the hydrogenation of carbon dioxide to methanol.

[0014] Preferably, before using the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst to catalyze the hydrogenation of carbon dioxide to methanol, a reduction treatment step is performed on the catalyst. Specifically, the catalyst is placed in a nitrogen or inert atmosphere containing 5-15% H2 at 200-300°C for 0.5-2 hours.

[0015] Preferably, the conditions for catalytic hydrogenation of carbon dioxide to methanol using MOF-confined platinum-molybdenum-based polyacid cluster catalysts are: 160-240℃, 3-5MPa, and reaction space velocity of 1500-24000mL / g / h.

[0016] The beneficial effects of this invention are as follows:

[0017] This catalyst enables the hydrogenation of carbon dioxide to methanol under low-temperature (mild) conditions by generating a methoxy intermediate at room temperature. Simultaneously, the platinum-molybdenum polyacid clusters confined within the MOF channels remain stable under prolonged reaction conditions, preventing sintering and ensuring high catalytic activity and methanol selectivity; under the same conditions, it exhibits superior performance compared to commercial CuZnAl2O3.

[0018] This catalyst has the following advantages: high dispersion of active sites and high atom utilization, enabling the hydrogenation of carbon dioxide to methanol to proceed under low-temperature (mild) conditions. It also exhibits good stability, as the active sites are confined within the pores of MOFs, preventing aggregation and deactivation under carbon dioxide hydrogenation conditions, and demonstrating excellent performance in a 4000-hour stability test.

[0019] This catalyst possesses characteristics such as high atom utilization, mild reaction conditions, high carbon dioxide conversion rate, excellent stability, and high methanol selectivity, which makes it exhibit superior performance compared to commercial CuZnAl2O3 under the same conditions, and it has broad prospects for industrial application. Attached Figure Description

[0020] Figure 1 1cPt@P2Mo 18 Stability test data for @NU1000 catalyst;

[0021] Figure 2 For P2Mo 18 @NU1000 catalyst aberration electron microscope image, (a) 20 nm scale bar, (b) 5 nm scale bar;

[0022] Figure 3 For NU1000, PtMo6@NU1000, PMo 12 @NU1000 and P2Mo 18 XRD data for @NU1000;

[0023] Figure 4 For NU1000, PtMo6@NU1000, PMo 12 @NU1000 and P2Mo 18 Nitrogen adsorption-desorption data (a) and pore size distribution data (b) for @NU1000;

[0024] Figure 5 For P2Mo 18 @NU1000 and 1cPt@P2Mo 18 @NU1000 catalyst NMR 32 P-spectrum;

[0025] Figure 6 1cPt@P2Mo 18@NU1000 catalyst Mo(a) and Pt(b) photoelectron spectra as a function of temperature under 1 atm reaction gas;

[0026] Figure 7 1cPt@P2Mo 18 The infrared spectrum of the @NU1000 catalyst over time under room temperature reaction gas shows that as the reaction proceeds, intermediate species such as (a) methoxy CH3O*, (b) carbon monoxide CO*, and (c) carbonate CO3H gradually increase. Detailed Implementation

[0027] The catalyst provided in this application is derived from Dawson-type polyacid P2Mo. 18 O 62 and / or Kegging-type polyacids PMo 12 O 40 and / or wheel-shaped polyacid Mo 36 O 112 Pt was selectively deposited within the confined Dawson-type polyacid P2Mo pores of zirconium-based MOFs NU1000 using liquid phase impregnation or atomic layer deposition (ALD) techniques. 18 O 62 and / or Kegging-type polyacids PMo 12 O 40 and / or wheel-shaped polyacid Mo 36 O 112 On the cluster, a spatially isolated dual-active-site synergistic system is formed, or Anderson-type polyacid PtMo6O 24 It can be confined within the pores of zirconium-based MOFs NU1000.

[0028] Among them, 1cPt@P2Mo 18 The @NU1000 catalyst exhibits excellent catalytic performance under mild conditions (160-240℃, 3-5MPa): CO2 single-pass conversion reaches 18-25%, methanol selectivity is ≥70%, and no significant degradation was observed after 4000 hours of continuous operation. Infrared spectroscopy shows that the catalyst can generate methoxy intermediates at room temperature, and the confinement effect of MOF channels effectively inhibits the migration and aggregation of active components.

[0029] The catalyst provided in this application effectively solves the problems of low catalytic activity, poor stability, and low selectivity of methanol in traditional catalysts made of precious metals at low temperatures, and provides a highly efficient and stable catalytic material for the resource utilization of carbon dioxide.

[0030] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst provided by the present invention and its application in the hydrogenation of carbon dioxide to methanol.

[0031] Example 1: 1cPt@P2Mo 18 @NU1000, 1cPt@PMo 12 @NU1000 and 1cPt@Mo 36 O 116 Preparation of @NU1000:

[0032] a) Add 150mg H6P2Mo 18 O 62 Prepare a solution with 10 ml of water and add 50 mg of NU1000. Shake on a shaker for three days, wash three times with water and three times with acetone, then soak in acetone overnight, centrifuge and dry to obtain P2Mo. 18 @NU1000;

[0033] 150mg H3PMo 12 O 40 Prepare a solution with 10 ml of water and add 50 mg of NU1000. Shake on a shaker for three days, wash three times with water and three times with acetone, then soak in acetone overnight, centrifuge and dry to obtain PMo. 12 @NU1000;

[0034] 300mg wheel-shaped polyacid Mo 36 O 116 Prepare a solution with 10 ml of water and add 50 mg of NU1000. Shake on a shaker for three days, wash three times with water and three times with acetone, then soak in acetone overnight, centrifuge and dry to obtain Mo. 36 O 116 @NU1000;

[0035] b) In an atomic layer deposition reactor (CAS Aikomi), at a chamber temperature of 120°C, using (trimethyl)methylcyclopentadiene platinum (MeCpPtMe3) as a precursor (65°C), P2Mo 18 @NU1000, PMo 12 @NU1000 and Mo 36 O 116 A Pt ALD cycle was performed on the @NU1000 support. The precursor MeCpPtMe3 pulse duration and N2 purge duration were 100 seconds and 300 seconds, respectively. The resulting samples were denoted as 1cPt@P2Mo. 18 @NU1000, 1cPt@PMo 12 @NU1000, 1cPt@Mo 36 O 116 @NU1000.

[0036] Example 2: PtMo6O24 Preparation of @NU1000:

[0037] 137mg PtMo6O 24 Prepare a solution with 10 ml of water and add 50 mg of NU1000. Shake on a shaker for three days, wash three times with water and three times with acetone, then soak in acetone overnight, centrifuge and dry. The obtained sample is recorded as PtMo6@NU1000.

[0038] Comparative Example 1: Preparation of 1cPt@NU1000:

[0039] In an atomic layer deposition reactor (CAS Aikomi), at a chamber temperature of 120℃, a single cycle of Pt ALD was performed on a NU1000 support using (trimethyl)methylcyclopentadiene platinum (MeCpPtMe3) as the precursor (65℃). The MeCpPtMe3 precursor pulse time and N2 purge time were 100 seconds and 300 seconds, respectively. The resulting sample was denoted as 1cPt@NU1000.

[0040] The Pt content of the catalysts obtained in Examples 1, 2 and Comparative Example 1 was determined, and the results are shown in Table 1.

[0041] Table 1. Pt content of the catalysts obtained in Examples 1, 2 and Comparative Example 1

[0042]

[0043] As can be seen from Table 1, under the same deposition conditions, MOF support NU1000 hardly deposits Pt; however, with the increase of protons in polyacid clusters, more MeCpPtMe3 reacts with them, resulting in a higher Pt content in the deposition load.

[0044] The highest Pt loading is 1cPt@P2Mo 18 @NU1000 conducted stability tests in the hydrogenation of carbon dioxide to methanol (using a hydrogen (10%, volume content) argon mixture for reduction at 250°C for 1 h, followed by the introduction of a reaction gas of 24% (volume content) CO2, 72% (volume content) H2 and residual argon, under conditions of 5 MPa, 200°C, and a reaction space velocity of 5000 mL / g / h, using 100 g of 1cPt@P2Mo). 18 @NU1000 was used for the carbon dioxide hydrogenation to methanol reaction, and the results are shown below. Figure 1 .Depend on Figure 1 It can be seen that the material operates stably under the reaction conditions, with methanol selectivity remaining above 70%, and no significant degradation was observed after 4000 hours.

[0045] Figure 2 For the preparation of P2Mo 18The spherical aberration electron microscope image from @NU1000 shows that polyacid clusters are uniformly dispersed within the pores of MOFs, with no obvious aggregation observed.

[0046] Figure 3 For NU1000 and the prepared P2Mo 18 @NU1000、PMo 12 XRD data of @NU1000 and PtMo6@NU1000 show that various polyacid clusters are confined within the pores of NU1000, and the structure of NU1000 remains unchanged.

[0047] Figure 4 P2Mo prepared for NU1000 18 @NU1000、PMo 12 The nitrogen adsorption-desorption and pore size distribution data of @NU1000 and PtMo6@NU1000 show that various polyacid clusters are confined within the pores of NU1000.

[0048] Figure 5 For P2Mo 18 @NU1000 and 1cPt@P2Mo 18 @NU1000 catalyst NMR 32 P spectrum, P2Mo 18 After confinement to NU1000 and deposition of Pt, the structure is somewhat distorted.

[0049] Figure 6 1cPt@P2Mo 18 The photoelectron spectra of Mo and Pt under 1 atm reaction gas for the @NU1000 catalyst as a function of temperature show that the oxidation states of Pt and Mo decrease with increasing temperature.

[0050] Figure 7 1cPt@P2Mo 18 The infrared spectrum of the @NU1000 catalyst over time under room temperature reaction gas clearly shows the reaction intermediates CO* and CH3O*.

[0051] After reduction at 250°C for 1 hour using a hydrogen (10% by volume) argon mixture, a reaction gas of 24% (by volume) CO2, 72% (by volume) H2 and residual argon was introduced. The reaction was carried out at 5 MPa, 180°C, and a reaction space velocity of 9000 mL / g / h using 100 g of the catalysts obtained in Examples 1, 2, and Comparative Example 1, as well as a commercial CuZnAl2O3 catalyst and a 5 wt% Pt / C catalyst. The performance of the reaction is shown in Table 2.

[0052] Table 2. Performance of the catalysts obtained in Examples 1, 2, and Comparative Example 1, as well as the commercial CuZnAl2O3 catalyst and the 5wt%Pt / C catalyst, in catalyzing the hydrogenation of CO2 to methanol.

[0053]

[0054] As shown in Table 2, the 5wt% Pt / C and 1cPt@NU1000 catalysts exhibited almost no CO2 hydrogenation activity. However, with increasing Pt / Mo loading, the Pt / Mo dual-site and interfacial coordination effects were enhanced, leading to improved CO2 activity and methanol selectivity of the catalysts prepared in the examples.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The application of a MOF-confined platinum-molybdenum-based polyacid cluster catalyst in the hydrogenation of carbon dioxide to methanol, characterized in that, MOFs confined platinum-molybdenum polyacid cluster catalysts include zirconium-based MOFs, in which molybdenum-based polyacid clusters containing Pt or without Pt are dispersed in the channels of zirconium-based MOFs, and Pt is deposited on the molybdenum-based polyacid clusters without Pt. The conditions for catalytic hydrogenation of carbon dioxide to methanol are: 160-240℃, 3-5MPa, and reaction space velocity of 1500-24000mL / g / h. Among them, the precise preparation method of MOFs-confined platinum-molybdenum-based polyacid cluster catalyst is to add zirconium-based MOFs into a Pt-containing molybdenum-based polyacid solution, shake, wash, soak, centrifuge, and dry. Alternatively, zirconium-based MOFs can be added to a Pt-free molybdenum-based polyacid solution, shaken, washed, soaked, centrifuged, and dried to obtain a MOF-confined molybdenum-based polyacid cluster precursor; then, Pt can be loaded onto the molybdenum-based polyacid clusters of the MOF-confined molybdenum-based polyacid cluster precursor by liquid phase impregnation or atomic layer deposition.

2. The application of the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst according to claim 1 in the hydrogenation of carbon dioxide to methanol, characterized in that, The molybdenum-based polyacid clusters are Dawson-type and / or Keggin-type and / or Anderson-type and / or wheel-shape-type molybdenum-based polyacid clusters.

3. The application of the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst according to claim 1 in the hydrogenation of carbon dioxide to methanol, characterized in that, The zirconium-based MOFs are any one of NU1000, UiO-66, NU1008, MOF-808 and NU-1200.

4. The application of the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst according to claim 1 in the hydrogenation of carbon dioxide to methanol, characterized in that, The mass ratio of zirconium-based MOFs to Pt-containing molybdenum polyacid in Pt-containing molybdenum polyacid solution and Pt-free molybdenum polyacid in Pt-free molybdenum polyacid solution is (1-2):(2-6).

5. The application of the MOFs-confined platinum-molybdenum-based polyacid cluster catalyst according to claim 1 in the hydrogenation of carbon dioxide to methanol, characterized in that, Before using MOFs-confined platinum-molybdenum-based polyacid cluster catalysts to catalyze the hydrogenation of carbon dioxide to methanol, a reduction treatment step was performed on the catalyst. Specifically, the catalyst was placed in a nitrogen or inert atmosphere containing 5-15% H2 at 200-300℃ for 0.5-2 hours.

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