Nano-catalyst, preparation method thereof and application of nano-catalyst in reverse water-gas shift reaction

Abstract

The invention relates to the technical field of catalysts, in particular to a nano-catalyst, a preparation method of the nano-catalyst and application of the nano-catalyst in a reverse water-gas shift reaction. According to the nano-catalyst provided by the invention, Pt is successfully packaged in a pore channel of the S-1 molecular sieve with the meso-micro hierarchical pore structure through hydro-thermal treatment, and due to the fact that meso pores are introduced into the S-1 molecular sieve with the meso-micro hierarchical pore structure, mass transfer hindrance is effectively reduced, and then the activity of the catalyst is greatly improved; meanwhile, Pt sintering is hindered due to the confinement effect of molecular sieve pore channels, so that the stability of the catalyst is maintained; therefore, the nano-catalyst provided by the invention has better stability in the reverse water-gas shift reaction. Tests show that the nano-catalyst provided by the invention still has higher activity, carbon monoxide selectivity and carbon dioxide conversion rate after the reaction is performed for 50 hours in the process of catalyzing the reverse water-gas shift reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, in particular to a nano catalyst and a preparation method thereof and application in a reverse water-gas shift reaction. Background Art

[0002] The utilization of fossil resources has greatly promoted the development of human society, but excessive exploitation has led to the increasing depletion of this non-renewable energy source and the emission of large amounts of carbon dioxide, exacerbating global warming and placing tremendous pressure on the ecological environment. Converting carbon dioxide into high-value-added chemicals or fuels is one of the most attractive ways to alleviate the severe depletion of fossil resources and the pressure of climate change. In recent years, due to the development of renewable energy power generation and green hydrogen production through electrocatalytic water splitting, the hydrogenation of greenhouse gas carbon dioxide to produce basic chemicals or fuels has become one of the hottest research areas in C1 chemistry. The reverse water gas shift reaction uses renewable hydrogen to directly hydrogenate carbon dioxide into carbon monoxide, which can be used in Fischer-Tropsch synthesis or other syngas processes to produce various value-added chemicals.

[0003] In the reverse water-gas shift reaction, high temperature conditions and reducing atmospheres (CO, H2) will promote metal migration and agglomeration, leading to catalyst deactivation. Zeolites are known for their ordered microporous structure, excellent thermal stability and chemical stability, and are considered to be ideal carriers for anchoring metal nanoparticles. In recent years, in situ hydrothermal synthesis has become an important method for preparing molecular sieve-coated small metal nanoparticles / clusters, providing high catalytic activity, selectivity and stability for a variety of catalytic reactions. However, there is no clear guidance on the specific design of molecular sieve-coated small metal nanoparticles / clusters that can achieve high catalytic activity, selectivity and stability, and the performance of molecular sieve-coated small metal nanoparticles / clusters catalysts prepared by existing technologies is uneven. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a nanocatalyst and a preparation method thereof and an application in the reverse water-gas shift reaction. The nanocatalyst provided by the present invention has high catalytic activity, selectivity and stability in the reverse water-gas shift reaction.

[0005] The present invention provides a nanocatalyst, comprising:

[0006] S-1 molecular sieve with meso-micro hierarchical pore structure;

[0007] Pt is encapsulated in the pores of the S-1 molecular sieve with the meso-micro multi-level pore structure.

[0008] The nanocatalyst of the present invention includes an S-1 molecular sieve with a meso-micro multi-level pore structure. The S-1 molecular sieve is an MFI type molecular sieve, that is, a microporous molecular sieve. The inventors of the present application creatively discovered that by introducing a mesoporous structure into the S-1 molecular sieve, the S-1 molecular sieve is transformed into a meso-micro multi-level pore structure having both mesopores and micropores. Due to the introduction of the mesopores, the mass transfer barrier is reduced, thereby greatly improving the catalyst activity. In addition, the confining effect of the molecular sieve pores can limit the sintering of Pt under harsh reaction conditions. Therefore, Pt is uniformly encapsulated in the pores of the S-1 molecular sieve with the meso-micro multi-level pore structure. The resulting nanocatalyst has high catalytic activity and stability in the reverse water vapor shift reaction, and at the same time has high carbon monoxide selectivity.

[0009] The Pt loading in the S-1 molecular sieve with a meso-micro hierarchical pore structure of the present invention is 0.5 wt% to 1.0 wt%. Preferably, the Pt loading in the S-1 molecular sieve with a meso-micro hierarchical pore structure is 0.6 wt% to 0.8 wt%. In certain embodiments of the present invention, the Pt loading in the S-1 molecular sieve with a meso-micro hierarchical pore structure is 0.7 wt%.

[0010] The present invention also provides a method for preparing the nanocatalyst described in any of the above technical solutions, comprising the following steps:

[0011] S1) evaporating a mixture of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, water and a Pt source to obtain a xerogel;

[0012] S2) hydrothermally treating the dry gel obtained in step S1) to obtain a nanocatalyst.

[0013] The present invention first evaporates water from a mixture of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, water, and a Pt source to obtain a xerogel. Specifically, the present invention first uniformly mixes SiO2, a tetrapropylammonium hydroxide solution, polyvinylpyrrolidone, water, and a Pt source solution to obtain a mixture of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, water, and a Pt source. The mixture is then evaporated to obtain a xerogel under heating. The evaporation is performed at a temperature of 60°C to 90°C.

[0014] The Pt source of the present invention is selected from one or more of Pt(NH2CH2CH2NH2)4Cl2, H2PtCl6, and Pt(NH3)4(NO3)2. The tetrapropylammonium hydroxide solution of the present invention is preferably an aqueous solution of tetrapropylammonium hydroxide. The water of the present invention is preferably deionized water. The molar concentration of Pt in the Pt source of the present invention in the mixed solution is 0.001 mmol / mL to 0.004 mmol / mL; the mass ratio of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, and water is (1-4):(3-4):(0.2-0.6):(30-50).

[0015] In certain embodiments of the present invention, SiO2, a 25wt% aqueous solution of tetrapropylammonium hydroxide, polyvinylpyrrolidone, water, and 1 mL of a 0.09mol / L aqueous solution of a Pt source are uniformly mixed to obtain a mixture of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, water, and a Pt source, and the mixture is then heated to evaporate the water to obtain a dry gel; wherein the amount of the SiO2 is 1g to 4g; the amount of the 25wt% aqueous solution of tetrapropylammonium hydroxide is 8g to 12g, the amount of the polyvinylpyrrolidone is 200mg to 600mg, and the volume of the water is 30mL to 50mL.

[0016] After obtaining the dry gel in the present invention, the obtained dry gel is subjected to hydrothermal treatment to obtain a nanocatalyst. Specifically, the obtained dry gel is subjected to hydrothermal treatment in the presence of a small amount of water to obtain the nanocatalyst described in the present invention. In certain embodiments of the present invention, the obtained dry gel is transferred to the lining of a 100mL hydrothermal kettle, a small amount of water is added to the kettle, the kettle is sealed, and the dry gel is hydrothermally treated in an oven to obtain the nanocatalyst described in the present invention. The temperature of the hydrothermal treatment in the present invention is 100°C to 150°C, and the time of the hydrothermal treatment is 36h to 72h. The mass ratio of water used in the hydrothermal treatment of the present invention to the dry gel is (1 to 5):6.

[0017] After the obtained dry gel is subjected to hydrothermal treatment, the present invention further includes washing the hydrothermally treated product and then drying it to obtain the nanocatalyst described in the present invention. The specific operation of the washing described in the present invention is as follows: the hydrothermally treated product is centrifuged, the product obtained by centrifugation is ultrasonically washed with a polar solvent, and then the centrifugation and ultrasonic washing are repeated. The centrifugation described in the present invention is carried out at a speed of 10,000 rpm / min to 15,000 rpm / min, preferably at a speed of 13,000 rpm / min. The centrifugation time of the present invention is preferably 10 minutes to 15 minutes. The ultrasonic washing time of the present invention is preferably 1 minute to 2 minutes. The polar solvent described in the present invention is preferably deionized water.

[0018] The present invention also provides the use of the nanocatalyst described in any of the above technical solutions, or the nanocatalyst obtained by the preparation method described in any of the above technical solutions, in a reverse water-gas shift reaction. Specifically, the nanocatalyst described in the present invention and quartz sand are used as a fixed-bed catalyst. The fixed-bed catalyst is thermally reduced under an H2 atmosphere. The reduced fixed-bed catalyst is then subjected to a reverse water-gas shift reaction in a mixed reaction gas containing CO2 and H2 to produce CO.

[0019] The present invention uses the nanocatalyst and quartz sand as a fixed bed catalyst in a mass ratio of (1-3):(97-99). The present invention first performs thermal reduction on the fixed bed catalyst under a H2 atmosphere. The flow rate of the H2 atmosphere is 30 mL / min to 50 mL / min. The thermal reduction temperature is 550°C to 650°C, and the thermal reduction time is 0.8 h to 1.2 h. The thermal reduction heating rate is 8°C / min to 12°C / min.

[0020] After thermal reduction, the fixed-bed catalyst undergoes a reverse water-gas shift reaction in a mixed reaction gas containing CO2 and H2 to produce CO. Specifically, the mixed reaction gas containing CO2 and H2 is charged into the fixed-bed catalyst after thermal reduction at a flow rate of 150 to 200 mL / min to perform a reverse water-gas shift reaction to produce CO. The mixed reaction gas containing CO2 and H2 is preferably a 24% CO2 / 72% H2 / Ar reaction gas. The temperature of the reverse water-gas shift reaction is 550°C to 650°C, preferably 600°C.

[0021] The present invention provides a nanocatalyst, a preparation method thereof, and an application thereof in the reverse water-gas shift reaction. The nanocatalyst provided by the present invention successfully encapsulates Pt in the pores of the S-1 molecular sieve with a meso-micro multi-level pore structure through hydrothermal treatment. Since the S-1 molecular sieve with a meso-micro multi-level pore structure introduces mesopores, the mass transfer barrier is limitedly reduced, thereby greatly improving the activity of the catalyst. At the same time, the confinement effect of the molecular sieve pores hinders Pt sintering and thus maintains the stability of the catalyst. Therefore, the nanocatalyst of the present invention has good stability in the reverse water-gas shift reaction. Experiments have shown that the nanocatalyst provided by the present invention still has high activity, carbon monoxide selectivity, and carbon dioxide conversion rate after 50 hours of catalytic reverse water-gas shift reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD patterns of Pt@meso-S-1, Pt@S-1, and S-1 materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0023] Figure 2 This is a graph of carbon dioxide conversion rate versus time in the reverse water-gas shift reaction of Pt@meso-S-1, Pt@S-1, and Pt / SiO2 materials prepared in Example 1, Comparative Example 2, and Comparative Example 3 of the present invention;

[0024] Figure 3 A line graph showing the carbon monoxide / methane selectivity versus time in the reverse water gas shift reaction of Pt@meso-S-1, Pt@S-1, and Pt / SiO2 materials prepared in Example 1, Comparative Example 2, and Comparative Example 3 of the present invention;

[0025] Figure 4 This is a transmission electron micrograph of the Pt@meso-S-1 material prepared in Example 1 of the present invention after catalyzing the reverse water-gas shift reaction for 50 hours;

[0026] Figure 5 This is a transmission electron micrograph of the Pt@S-1 material prepared in Comparative Example 2 of the present invention after catalyzing the reverse water-gas shift reaction for 35 hours;

[0027] Figure 6 This is a transmission electron micrograph of the Pt / SiO2 material prepared in Comparative Example 3 of the present invention after catalyzing the reverse water-gas shift reaction for 30 hours;

[0028] Figure 7 This is a N2 adsorption-desorption isotherm of the Pt@meso-S-1 material prepared in Example 1 of the present invention;

[0029] Figure 8 This is a N2 adsorption-desorption isotherm curve of the Pt@S-1 material prepared in Comparative Example 2 of the present invention;

[0030] Figure 9 The pore size distribution diagrams of the Pt@meso-S-1 material prepared in Example 1 of the present invention and the Pt@S-1 material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0031] The present invention discloses a nanocatalyst, a preparation method thereof, and an application in a reverse water-gas shift reaction. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0032] The present invention will be further described below with reference to the embodiments:

[0033] Example 1

[0034] The present invention provides a Pt@meso-S-1 nanomaterial, the synthesis method of which is as follows:

[0035] 2.4 g of SiO2 powder, 9.6 g of a 25 wt% aqueous solution of tetrapropylammonium hydroxide, 330 mg of polyvinylpyrrolidone, 50 mL of deionized water, and 1 mL of a 0.09 M Pt(NH2CH2CH2NH2)4Cl2 aqueous solution were mixed thoroughly. The mixture was evaporated to dryness at 70°C to obtain a xerogel. The xerogel was transferred to the inner lining of a 100 mL hydrothermal autoclave, 2 mL of water was added, the autoclave was sealed, and the autoclave was hydrothermaled at 130°C for 48 h. The solid was then ultrasonically cleaned with deionized water and centrifuged to obtain a solid. This step was repeated three times, and the solid was then dried at 60°C overnight to obtain the Pt@meso–S–1 nanocatalyst.

[0036] Comparative Example 1

[0037] The present invention provides an S-1 nanomaterial, the synthesis method of which is as follows:

[0038] A 25wt% aqueous solution of tetrapropylammonium hydroxide (13.00g) and 15mL of deionized water were mixed and stirred for 10 minutes. 8.32g of tetraethyl orthosilicate was added to the solution and stirred for 9 hours to form a homogeneous phase. The reaction mixture was then transferred to a 100mL hydrothermal autoclave, sealed, and hydrothermaled at 180°C for 96 hours. The solid was then ultrasonically cleaned with deionized water and centrifuged to obtain a solid. This step was repeated three times, followed by drying at 60°C overnight to obtain the S-1 nanomaterial.

[0039] Comparative Example 2

[0040] The present invention provides a Pt@S-1 nanomaterial, the synthesis method of which is as follows:

[0041] 1 mL of 0.09 M Pt(NH₂CH₂CH₂NH₂)₄Cl₂ aqueous solution was added to a mixture of 13.00 g of 25 wt% tetrapropylammonium hydroxide aqueous solution and 15 mL of deionized water, and stirred for 10 minutes. 8.32 g of tetraethyl orthosilicate was added to the above solution and stirred for 9 hours to form a homogeneous phase. Finally, the reaction mixture was transferred to a 100 mL hydrothermal autoclave, sealed, and hydrothermaled at 180°C for 96 hours. The solid was then ultrasonically cleaned with deionized water and centrifuged to obtain a solid. This step was repeated three times, and then dried at 60°C overnight to obtain the Pt@S–1 nanomaterial.

[0042] Comparative Example 3

[0043] The present invention provides a Pt / SiO2 nanomaterial, the synthesis method of which is as follows:

[0044] Weigh 500 mg of silica powder into a 50 mL beaker, add 20 mL of deionized water, and sonicate for 10 minutes. Then, add 350 μL of a 10 mg Pt / mL H₂PtCl₆ aqueous solution while stirring. Stir for 30 minutes, then evaporate the water to dryness. Scrape off the solid to obtain Pt / SiO₂.

[0045] The catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 were subjected to XRD testing. The results are as follows: Figure 1 As shown, Figure 1 These are the XRD patterns of Pt@meso-S-1, S-1, and Pt@S-1 materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0046] The catalysts prepared in Example 1, Comparative Example 2, and Comparative Example 3 were tested for their reverse water-gas shift reaction performance. 10 mg of catalyst was evenly mixed with 990 mg of quartz sand, filled into a quartz tube, and then loaded into a fixed bed. The catalyst was first pretreated, heated to 600°C at 10°C / min under a 40 mL / min H2 atmosphere, and reduced at 600°C for 1 hour. 24% CO2 / 72% H2 / 4% N2 reaction gas (volume ratio) was then introduced at a flow rate of 166.67 mL / min to perform a reverse water-gas shift reaction test at 600°C. The tail gas entered the gas chromatograph to monitor the gas components and their proportions. The data was processed to obtain the carbon dioxide conversion rate and CO selectivity, as shown in FIG. Figure 2 As shown, Figure 2 The carbon dioxide conversion rate vs. time diagram of the Pt@meso-S-1, Pt@S-1, and Pt / SiO2 materials prepared in Example 1, Comparative Example 2, and Comparative Example 3 of the present invention in the reverse water-gas shift reaction. Figure 3 As shown, Figure 3 This is a line graph of carbon monoxide / methane selectivity versus time in the reverse water-gas shift reaction of Pt@meso-S-1, Pt@S-1, and Pt / SiO2 materials prepared in Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0047] In addition, the morphology of the Pt@meso-S-1 catalyzed reverse water-gas shift reaction prepared in Example 1 of the present invention was observed after 50 hours. Figure 4 As shown, Figure 4 This is a transmission electron micrograph of the Pt@meso-S-1 material prepared in Example 1 of the present invention after catalyzing the reverse water-gas shift reaction for 50 hours.

[0048] The morphology of the Pt@S-1 catalyzed reverse water-gas shift reaction prepared in Comparative Example 2 of the present invention was observed after 35 hours. Figure 5 As shown, Figure 5 This is a transmission electron micrograph of the Pt@S-1 material prepared in Comparative Example 2 of the present invention after catalyzing the reverse water-gas shift reaction for 35 hours.

[0049] The morphology of the Pt / SiO2 catalyzed reverse water-gas shift reaction prepared in Comparative Example 3 of the present invention was observed after 20 hours. Figure 6 As shown, Figure 6 This is a transmission electron micrograph of the Pt / SiO2 material prepared in Comparative Example 3 of the present invention after 30 hours of catalytic reverse water-gas shift reaction.

[0050] Depend on Figures 2 to 6 It can be seen that the Pt@meso-S-1 nanocatalyst obtained in the present invention has excellent catalytic effect in the reverse water gas shift reaction, with high apparent carbon dioxide conversion rate and carbon monoxide selectivity, and the catalyst is still not deactivated after 50 hours of reaction, indicating that the structure of the catalyst is very stable and can survive harsh reaction conditions without deactivation.

[0051] The Pt@meso-S-1 material prepared in Example 1 of the present invention and the Pt@S-1 material prepared in Comparative Example 2 were subjected to N2 adsorption-desorption isotherm test and pore size distribution characterization. The results are shown in FIG. Figures 7 to 9 As shown, Figure 7 This is a N2 adsorption-desorption isotherm of the Pt@meso-S-1 material prepared in Example 1 of the present invention; Figure 8 This is a N2 adsorption-desorption isotherm curve of the Pt@S-1 material prepared in Comparative Example 2 of the present invention; Figure 9 The pore size distribution diagrams of the Pt@meso-S-1 material prepared in Example 1 of the present invention and the Pt@S-1 material prepared in Comparative Example 2.

[0052] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A nanocatalyst, characterized in that: include: S-1 molecular sieve with meso-micro hierarchical pore structure; Pt is encapsulated in the pores of the S-1 molecular sieve with the meso-micro multi-level pore structure.

2. The nanocatalyst according to claim 1, characterized in that The Pt loading amount in the S-1 molecular sieve with the meso-micro hierarchical pore structure is 0.5 wt % to 1.0 wt %.

3. The nanocatalyst according to claim 2, characterized in that The Pt loading amount in the S-1 molecular sieve with the meso-micro hierarchical pore structure is 0.6 wt % to 0.8 wt %.

4. A method for preparing a nanocatalyst, characterized in that: The following steps are involved: S1) evaporating a mixture of SiO2, tetrapropylammonium hydroxide, polyvinylpyrrolidone, water and a Pt source to obtain a xerogel; S2) hydrothermally treating the dry gel obtained in step S1) to obtain a nanocatalyst.

5. The preparation method according to claim 4, characterized in that In step S1), the Pt source is selected from one or more of Pt(NH2CH2CH2NH2)4Cl2, H2PtCl6, and Pt(NH3)4(NO3)2.

6. The preparation method according to claim 4, characterized in that In step S1), the molar concentration of Pt in the Pt source in the mixed solution is 0.001 mmol / mL to 0.004 mmol / mL; The mass ratio of SiO2, tetrapropylammonium hydroxide, polyvinyl pyrrolidone and water is (1-4): (3-4): (0.2-0.6): (30-50).

7. The preparation method according to claim 4, characterized in that In step S1), the water is evaporated at a temperature of 60°C to 90°C.

8. The preparation method according to claim 4, characterized in that In step S2), the temperature of the hydrothermal treatment is 100° C. to 150° C., and the time of the hydrothermal treatment is 36 h to 72 h.

9. The preparation method according to claim 4, characterized in that In step S2), the mass ratio of water used in the hydrothermal treatment to the dry gel is (1-5):

6.

10. Use of the nanocatalyst according to any one of claims 1 to 3 or the nanocatalyst obtained by the preparation method according to any one of claims 4 to 9 in the reverse water-gas shift reaction.

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