MOFs confinement platinum-molybdenum-based polyacid cluster catalyst as well as precise preparation method and application thereof

Abstract

The invention discloses an MOFs confinement platinum-molybdenum-based polyacid cluster catalyst and a precise preparation method and application thereof. The catalyst comprises zirconium-based MOFs, a Pt-containing molybdenum-based polyacid cluster or a Pt-free molybdenum-based polyacid cluster is dispersed in a pore channel of the zirconium-based MOFs, and Pt is deposited on the Pt-free molybdenum-based polyacid cluster. The catalyst has the characteristics of high atom utilization rate, mild reaction conditions, high carbon dioxide conversion rate, excellent stability and high methanol selectivity, shows better performance than commercial CuZnAl2O3 under the same conditions, and has wide industrial application prospects.

Description

Technical Field

[0001] The present invention relates to a MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst, a precise preparation method thereof and an application, belonging to the technical field of heterogeneous catalytic materials. Background Art

[0002] With the acceleration of the global industrialization process 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 problems. Developing efficient and economical CO2 resource utilization technologies has become the focus of global attention. Among them, hydrogenation of carbon dioxide to methanol (CO2 + 3H2 → CH3OH + H2O) has attracted much attention due to its technical feasibility and economic potential. Methanol is not only an important chemical raw material but also can be used as a clean fuel or a hydrogen storage carrier, with broad application prospects.

[0003] Currently, the research on hydrogenation of carbon dioxide to methanol technology mainly focuses on catalyst development, reaction process optimization and system integration. Traditional catalyst systems are mainly based on copper-based catalysts (such as Cu / ZnO / Al2O3), and their active centers (Cu 0 ) have limited ability to adsorb and activate CO2, resulting in the reaction needing to be carried out at relatively high temperatures (250 - 300 °C) and pressures (5 - 10 MPa). High temperature and high pressure conditions not only increase energy consumption but also easily trigger side reactions (such as the reverse water-gas shift reaction to generate CO), reducing the selectivity of methanol. In addition, copper-based catalysts have problems such as easy sintering and sulfur poisoning, and their long-term stability is insufficient, restricting their industrial application.

[0004] In recent years, new catalytic systems such as noble metal (such as Pd, Pt) catalysts and transition metal oxides (such as In2O3, ZrO2) have been proposed. However, noble metal catalysts are prone to aggregation under long-term reducing atmosphere conditions, with poor stability and difficult to be applied on a large scale; while metal oxide catalysts have low cost, but their low-temperature (mild) activity is insufficient and the active sites are easily covered by reaction intermediates, resulting in a fast inactivation rate. In addition, in the existing process, hydrogen (H2) mostly comes from fossil fuel reforming, without realizing the coupling of "green hydrogen", resulting in a relatively high carbon emission in the whole life cycle and weakening the environmental protection value of the technology. Summary of the Invention

[0005] The purpose of the present invention is to provide a MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst, a precise preparation method thereof and an application. The confinement effect of MOFs pores effectively inhibits the migration and aggregation of active components, improves the stability, and shows excellent catalytic performance under mild conditions. Under the same conditions, it shows better performance than commercial CuZnAl2O3.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst, including zirconium-based MOFs, in which molybdenum-based polyoxometalate clusters containing Pt or molybdenum-based polyoxometalate clusters without Pt are dispersed in the pores of the zirconium-based MOFs, and Pt is deposited on the molybdenum-based polyoxometalate clusters without Pt.

[0007] Preferably, the molybdenum-based polyoxometalate clusters are Dawson-type and / or Keggin-type and / or Anderson-type and / or wheel-shape-type molybdenum-based polyoxometalate clusters.

[0008] The precise preparation method of any of the above-mentioned MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalysts is to add zirconium-based MOFs to a molybdenum-based polyoxometalate solution containing Pt, and after oscillating treatment, wash, soak, centrifuge, and dry; Or add zirconium-based MOFs to a molybdenum-based polyoxometalate solution without Pt, and after oscillating treatment, wash, soak, centrifuge, and dry to obtain a MOFs-confined molybdenum-based polyoxometalate cluster precursor; then load Pt onto the molybdenum-based polyoxometalate clusters of the MOFs-confined molybdenum-based polyoxometalate cluster precursor by liquid-phase impregnation or atomic layer deposition.

[0009] Preferably, the zirconium-based MOFs are any one of NU1000, UiO-66, NU1008, MOF-808, and NU-1200.

[0010] Preferably, the mass ratio of the zirconium-based MOFs to the molybdenum-based polyoxometalate containing Pt in the molybdenum-based polyoxometalate solution containing Pt and the molybdenum-based polyoxometalate without Pt in the molybdenum-based polyoxometalate solution without Pt is both: (1-2):(2-6).

[0011] The application of any of the above-mentioned MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalysts in the hydrogenation of carbon dioxide to methanol.

[0012] Preferably, before using the MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst to catalyze the hydrogenation of carbon dioxide to methanol, a reduction treatment step is also carried out on the catalyst. Specifically, the catalyst is placed in nitrogen or an inert atmosphere containing 5-15% H2 at 200-300 °C for 0.5-2 h.

[0013] Preferably, the conditions for using the MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst to catalyze the hydrogenation of carbon dioxide to methanol are: 160-240 °C, 3-5 MPa, and a reaction space velocity of 1500-24000 mL / g / h.

[0014] The beneficial effects of the present invention are as follows: This catalyst can generate methoxy intermediates at room temperature, thereby achieving the hydrogenation of carbon dioxide to methanol under low-temperature (mild) conditions. Meanwhile, the platinum molybdate polyoxometalate clusters confined in the pores of MOFs can remain stable under long-term reaction conditions, avoiding sintering and ensuring high catalytic activity and methanol selectivity. Under the same conditions, it shows better performance than commercial CuZnAl2O3. This catalyst has the following advantages: It has a relatively high dispersion of active sites and high atomic utilization efficiency, enabling the hydrogenation of carbon dioxide to methanol to proceed under low-temperature (mild) conditions. It has good stability. By confining the active sites through the pores of MOFs, the aggregation and inactivation of active sites under the reaction conditions of carbon dioxide hydrogenation are avoided, and it shows excellent performance in the 4000-hour stability test. This catalyst has the characteristics of high atomic utilization efficiency, mild reaction conditions, high carbon dioxide conversion rate, excellent stability, and high methanol selectivity, making it show better performance than commercial CuZnAl2O3 under the same conditions and having broad industrial application prospects. Description of the Drawings

[0015] Figure 1 For the stability test data of the 1cPt@P2Mo 18 @NU1000 catalyst; Figure 2 For the aberration-corrected electron microscopy images of the P2Mo 18 @NU1000 catalyst, (a) 20 nm scale bar, (b) 5 nm scale bar; Figure 3 For NU1000, PtMo6@NU1000, PMo 12 @NU1000 and P2Mo 18 @NU1000 XRD data; Figure 4 For NU1000, PtMo6@NU1000, PMo 12 @NU1000 and P2Mo 18 @NU1000 nitrogen adsorption / desorption data (a) and pore size distribution data (b); Figure 5 For P2Mo 18 @NU1000 and 1cPt@P2Mo 18 @NU1000 catalyst NMR 32 P spectrum; Figure 6 For 1cPt@P2Mo 18 @NU1000 catalyst Mo (a) and Pt (b) photoelectron spectra as a function of temperature under 1 atm reaction gas; Figure 7 For 1cPt@P2Mo 18Infrared spectra of the @NU1000 catalyst as a function of time under reaction gases at room temperature. As the reaction proceeds, the intermediate species such as (a) methoxy CH3O*, (b) carbon monoxide CO*, and (c) carbonate CO3H gradually increase. Detailed implementation mode

[0016] The catalyst provided by this application is obtained by confining Dawson-type polyoxometalate P2Mo 18 O 62 and / or Keggin-type polyoxometalate PMo 12 O 40 and / or wheel-shape polyoxometalate Mo 36 O 112 within the pores of zirconium-based MOFs NU1000, and selectively depositing Pt on the confined Dawson-type polyoxometalate P2Mo 18 O 62 and / or Keggin-type polyoxometalate PMo 12 O 40 and / or wheel-shape polyoxometalate Mo 36 O 112 clusters by liquid-phase impregnation or atomic layer deposition (ALD) technology to form a spatially isolated dual-active-site synergistic system, or confining Anderson-type polyoxometalate PtMo6O 24 within the pores of zirconium-based MOFs NU1000.

[0017] Among them, the 1cPt@P2Mo 18 @NU1000 catalyst exhibits excellent catalytic performance under mild conditions (160 - 240 °C, 3 - 5 MPa): the single-pass conversion rate of CO2 reaches 18 - 25%, the selectivity for methanol is ≥70%, and there is no obvious attenuation after continuous operation for 4000 hours. Infrared spectra show that this catalyst can generate methoxy intermediates at room temperature, and the confinement effect of the MOFs pores effectively inhibits the migration and aggregation of active components.

[0018] The catalyst provided by this application effectively solves the problems of low low-temperature catalytic activity, poor stability, and low methanol selectivity of traditional catalysts, and provides an efficient and stable catalytic material for the resource utilization of carbon dioxide.

[0019] To further illustrate the present invention, the MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst provided by the present invention and its application in the hydrogenation of carbon dioxide to methanol will be described in detail below with reference to examples.

[0020] Example 1: 1cPt@P2Mo 18 @NU1000, 1cPt@PMo 12 @NU1000 and 1cPt@Mo 36O 116 Preparation of @NU1000: a) Dissolve 150 mg of H6P2Mo 18 O 62 in 10 ml of water, add 50 mg of NU1000, shake in a shaker for three days, wash three times with water, wash three times with acetone, then soak overnight in acetone, centrifuge and dry to obtain P2Mo 18 @NU1000; Dissolve 150 mg of H3PMo 12 O 40 in 10 ml of water, add 50 mg of NU1000, shake in a shaker for three days, wash three times with water, wash three times with acetone, then soak overnight in acetone, centrifuge and separate to dry to obtain PMo 12 @NU1000; Dissolve 300 mg of wheel - shape polyoxometalate Mo 36 O 116 in 10 ml of water, add 50 mg of NU1000, shake in a shaker for three days, wash three times with water, wash three times with acetone, then soak overnight in acetone, centrifuge and separate to dry to obtain Mo 36 O 116 @NU1000; b) In an atomic layer deposition reactor (Zhongke Aikemi), at a chamber temperature of 120 °C, using (trimethyl)methylcyclopentadienyl platinum (MeCpPtMe3) as the precursor (65 °C), perform one cycle of Pt ALD on P2Mo 18 @NU1000, PMo 12 @NU1000 and Mo 36 O 116 @NU1000 supports respectively. The pulse time of the precursor MeCpPtMe3 and the N2 purge time are 100 seconds and 300 seconds in sequence. The obtained samples are denoted as 1cPt@P2Mo 18 @NU1000, 1cPt@PMo 12 @NU1000, 1cPt@Mo 36 O 116 @NU1000.

[0021] Example 2: Preparation of PtMo6O 24 @NU1000: Dissolve 137 mg of PtMo6O 24 in 10 ml of water, add 50 mg of NU1000, shake in a shaker for three days, wash three times with water, wash three times with acetone, then soak overnight in acetone, centrifuge and separate to dry. The obtained sample is denoted as PtMo6@NU1000.

[0022] Comparative Example 1: Preparation of 1cPt@NU1000: In an atomic layer deposition reactor (Zhongke Aike Mi), at a chamber temperature of 120 °C, using (trimethyl)methylcyclopentadienyl platinum (MeCpPtMe3) as the precursor (65 °C), one cycle of Pt ALD was performed on the NU1000 support. The pulse time of the precursor MeCpPtMe3 and the N2 purge time were 100 s and 300 s respectively, and the obtained sample was denoted as 1cPt@NU1000.

[0023] The Pt contents of the catalysts obtained in Example 1, Example 2 and Comparative Example 1 were measured, and the results are shown in Table 1.

[0024] Table 1 Pt contents of the catalysts obtained in Example 1, Example 2 and Comparative Example 1

[0025] As can be seen from Table 1, under the same deposition conditions, almost no Pt was deposited on the MOF support NU1000; and as the number of protons in the polyoxometalate cluster increased, the more MeCpPtMe3 reacted with it, and the higher the Pt content of the deposited load.

[0026] For 1cPt@P2Mo 18 @NU1000 with the highest Pt loading, a stability test was carried out in the hydrogenation of carbon dioxide to methanol (after reduction with a hydrogen (10%, volume content) - argon mixture at 250 °C for 1 h, introducing a reaction gas of 24% (volume content) CO2, 72% (volume content) H2 and the remaining argon, and using 100 g of 1cPt@P2Mo 18 @NU1000 to carry out the carbon dioxide hydrogenation to methanol reaction) under the conditions of 5 MPa, 200 °C and a reaction space velocity of 5000 mL / g / h. The results are shown in Figure 1 . As can be seen from Figure 1 , the material was stably operated under these reaction conditions, the methanol selectivity remained above 70%, and no obvious attenuation was observed after 4000 h.

[0027] Figure 2 The aberration-corrected electron microscopy image of the prepared P2Mo 18 @NU1000 shows that the polyoxometalate clusters are uniformly dispersed in the MOF pores and no obvious agglomeration is observed.

[0028] Figure 3 The XRD data of NU1000 and the prepared P2Mo 18 @NU1000, PMo 12 @NU1000, PtMo6@NU1000 prove that various polyoxometalate clusters are confined in the pores of NU1000 and the structure of NU1000 remains unchanged.

[0029] Figure 4 P2Mo Prepared for NU1000 18 @NU1000, PMo 12 @NU1000, N2 adsorption - desorption and pore size distribution data of PtMo6@NU1000. It can be seen that various polyoxometalate clusters are confined in the pores of NU1000.

[0030] Figure 5 For P2Mo 18 @NU1000 and 1cPt@P2Mo 18 @NU1000 catalyst NMR 32 P spectrum, after P2Mo 18 is confined to NU1000 and Pt is deposited, the structure is somewhat distorted.

[0031] Figure 6 For 1cPt@P2Mo 18 @NU1000 catalyst Mo and Pt photoelectron spectra at 1 atm reaction gas varying with temperature. It can be seen that the valences of Pt and Mo decrease with increasing temperature.

[0032] Figure 7 For 1cPt@P2Mo 18 @NU1000 catalyst infrared spectra at room - temperature reaction gas varying with time. Obvious reaction intermediates CO* and CH3O* can be seen.

[0033] After reduction with a hydrogen (10%, volume fraction) - argon mixed gas at 250 °C for 1 h, a reaction gas of 24% (volume fraction) CO2, 72% (volume fraction) H2 and the remaining argon is introduced. Under the conditions of 5 MPa, 180 °C, and a reaction space velocity of 9000 mL / g / h, the catalysts obtained in Example 1, Example 2, Comparative Example 1, commercial CuZnAl2O3 catalyst, and 5 wt% Pt / C catalyst are used for the carbon dioxide hydrogenation to methanol reaction, and their performances are shown in Table 2.

[0034] Table 2 Performances of the catalysts obtained in Example 1, Example 2, Comparative Example 1, commercial CuZnAl2O3 catalyst, and 5 wt% Pt / C catalyst for catalytic carbon dioxide hydrogenation to methanol

[0035] It can be seen from Table 2 that 5 wt% Pt / C and 1cPt@NU1000 have almost no carbon dioxide hydrogenation activity. However, with the increase in the Pt / Mo loading amount, the Pt / Mo double - site and interfacial coordination effect are enhanced, resulting in an increase in the carbon dioxide activity and methanol selectivity of the catalysts prepared in the examples.

[0036] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A MOFs-confined platinum-molybdenum-based polyoxometalate cluster catalyst, characterized in that, It includes zirconium-based MOFs, in the pores of which molybdenum-based polyoxometalate clusters containing Pt or molybdenum-based polyoxometalate clusters without Pt are dispersed, and Pt is deposited on the molybdenum-based polyoxometalate clusters without Pt.

2. The MOF-confined platinum molybdate polyoxometalate cluster catalyst according to claim 1, wherein The molybdenum-based polyoxometalate clusters are Dawson-type and / or Keggin-type and / or Anderson-type and / or wheel-shape type molybdenum-based polyoxometalate clusters.

3. The precise preparation method of the MOF-confined platinum-molybdenum-based polyoxometalate cluster catalyst according to any one of claims 1-2, characterized in that, It can be obtained by adding zirconium-based MOFs into a molybdenum-based polyoxometalate solution containing Pt, oscillating, washing, soaking, centrifuging and drying; or adding zirconium-based MOFs into a molybdenum-based polyoxometalate solution without Pt, oscillating, washing, soaking, centrifuging and drying to obtain a MOFs-confined molybdenum-based polyoxometalate cluster precursor; then loading Pt onto the molybdenum-based polyoxometalate clusters of the MOFs-confined molybdenum-based polyoxometalate cluster precursor by liquid-phase impregnation or atomic layer deposition.

4. The precise preparation method of the MOF-confined platinum molybdate polyoxometalate cluster catalyst according to claim 3, characterized in that, The zirconium-based MOFs are any one of NU1000, UiO-66, NU1008, MOF-808 and NU-1200.

5. The precise preparation method of the MOF-confined platinum molybdate polyoxometalate cluster catalyst according to claim 3, characterized in that, The mass ratios of the zirconium-based MOFs to the molybdenum-based polyoxometalate containing Pt in the molybdenum-based polyoxometalate solution containing Pt and to the molybdenum-based polyoxometalate without Pt in the molybdenum-based polyoxometalate solution without Pt are both: (1-2):(2-6).

6. Application of the MOFs-confined platinum molybdenum-based polyoxometalate cluster catalyst according to any one of claims 1-2 in the hydrogenation of carbon dioxide to methanol.

7. The application according to claim 6, characterized in that Before using the MOFs-confined platinum molybdenum-based polyoxometalate cluster catalyst to catalyze the hydrogenation of carbon dioxide to methanol, a reduction treatment step is also carried out on the catalyst. Specifically, the catalyst is placed in nitrogen or an inert atmosphere containing 5-15% H2 at 200-300 °C for 0.5-2 h.

8. The application according to claim 6, wherein The conditions for using the MOFs-confined platinum molybdenum-based polyoxometalate cluster catalyst to catalyze the hydrogenation of carbon dioxide to methanol are: 160-240 °C, 3-5 MPa, and a reaction space velocity of 1500-24000 mL / g / h.

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