A synthetic method for highly active PdFe@Fe5C2 / Fe3O4 catalyst and its application

Abstract

This invention belongs to the field of noble metal catalyst design and synthesis, specifically relating to a highly active PdFe@Fe5C2 / Fe3O4 catalyst, its preparation method, and its application. In the catalyst, the support is Fe3O4, and the active component is PdFe@Fe5C2; the PdFe@Fe5C2 has a core-shell structure, wherein the core structure is a PdFe alloy with a Pd to Fe molar ratio of 3:1, and the shell structure is Fe5C2. The catalyst is prepared by carbonizing a PdFe / Fe2O3 catalyst at 300–500℃ for 2–5 hours under normal pressure to obtain the PdFe@Fe5C2 / Fe3O4 catalyst. This invention provides mild preparation conditions; the introduction of PdFe alloy nanoparticles under low temperature and normal pressure conditions rapidly promotes the formation of the Fe5C2 coating layer, shortens the carbonization time, and significantly improves the catalyst activity.

Description

Technical Field

[0001] This invention belongs to the field of noble metal catalyst design and synthesis, specifically relating to a highly active PdFe@Fe5C2 / Fe3O4 catalyst, its preparation method, and its application. Background Technology

[0002] Converting CO2 into high-value-added chemicals can not only reduce CO2 emissions and mitigate the greenhouse effect, but also address the energy crisis and promote sustainable energy development. Among these processes, the catalytic conversion of CO2 to CO (reverse water-gas shift) is fundamental to many important industrial processes, such as syngas conversion. However, due to the chemical inertness of CO2 and the complexity of its molecules and products during hydrogenation, the actual activation and conversion efficiency of CO2 still needs improvement, necessitating highly efficient catalysts with high activity and selectivity.

[0003] Recent research indicates that the formation of iron carbide during the ambient pressure rWGS reaction can promote increased reactivity. For example, Fe3C is produced at high temperatures (>500℃), while Fe5C2 is produced at low temperatures (<500℃). However, this iron carbide formation is often bulk carbonization, which requires a relatively long carbonization time. Summary of the Invention

[0004] Based on the above background technology, the present invention provides a highly active PdFe@Fe5C2 / Fe3O4 catalyst, its preparation method and application. By introducing PdFe alloy nanoparticles, the highly active Fe5C2 coating layer is rapidly generated under relatively mild conditions (normal pressure, low temperature), which shortens the carbonization time and improves the catalytic reaction activity.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a Fe3O4-supported PdFe alloy catalyst, wherein the support is Fe3O4 and the active component is PdFe@Fe5C2; the PdFe@Fe5C2 has a core-shell structure, wherein the core structure is a PdFe alloy, the molar ratio of Pd to Fe is 3:1, and the shell structure is Fe5C2.

[0007] Based on the above technical solution, preferably, the loading of the PdFe alloy is 0.5 to 5 wt%.

[0008] Another aspect of the present invention provides a method for preparing the Fe3O4-supported PdFe alloy catalyst described above, the method comprising the following steps: under normal pressure, carbonizing the PdFe / Fe2O3 catalyst at 300-500°C for 2-5 hours to obtain the PdFe@Fe5C2 / Fe3O4 catalyst.

[0009] Based on the above technical solution, preferably, the carbonization atmosphere is a mixture of H2 and CO2, with a volume ratio of H2 to CO2 of 3:1, and the space velocity of the reaction is 30,000–40,000 mLg. -1 h -1 .

[0010] Based on the above technical solutions, preferably, the carbonization treatment temperature is 350-450℃.

[0011] Based on the above technical solution, preferably, the preparation method of the PdFe / Fe2O3 catalyst includes the following steps:

[0012] (1) Dissolve palladium acetylacetonate, iron acetylacetonate and polyvinylpyrrolidone in 1,2-propanediol to obtain metal precursor solution A;

[0013] (2) Take the metal precursor solution A obtained in step (1) and mix it with 1,2-propanediol and Fe2O3, heat it in an oil bath to 100-150°C, and stir it for 1 hour under N2 atmosphere to obtain solution B;

[0014] (3) Add NaHB4 powder to solution B obtained in step (2), heat to 150-180℃, keep warm for 2-3 hours, and obtain solution C;

[0015] (4) Cool solution C to room temperature, wash and dry it, and then heat it at 200-500℃ for 0.5-5 hours in an oxidizing atmosphere to obtain PdFe / Fe2O3 catalyst.

[0016] Based on the above technical solution, preferably, in step (1), the mass ratio of palladium acetylacetone, iron acetylacetone and polyvinylpyrrolidone is 3.6:1:12.2.

[0017] The present invention also provides an application of the above-mentioned PdFe@Fe5C2 / Fe3O4 catalyst in the reaction of carbon dioxide hydrogenation to carbon monoxide.

[0018] Based on the above technical solution, preferably, the reaction gas for the production of carbon monoxide by hydrogenation of carbon dioxide is a mixture of hydrogen and carbon dioxide, with a volume ratio of hydrogen to carbon dioxide of 3:1, a flow rate of 24 mL / min, and a reaction pressure of atmospheric pressure.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. The preparation conditions of this invention are mild. PdFe alloy nanoparticles are introduced under low temperature and normal pressure conditions, which can rapidly promote the formation of Fe5C2 coating layer. On the one hand, it can shorten the carbonization time, save raw material gas, and has greater industrial potential and value. On the other hand, it can greatly improve the catalyst activity.

[0021] 2. The method provided by this invention is simpler and easier to implement for preparing special PdFe@Fe5C2 core-shell structures, thereby significantly reducing labor costs;

[0022] 3. The preparation method of the present invention does not use substances containing chlorine, nitrogen, phosphorus and potassium elements, so there is no residue of these active elements, which is beneficial to improving the activity of the catalyst. Attached Figure Description

[0023] Figure 1 The images show AC-STEM images of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention, where a is Example 1, b is Comparative Example 1, and c is Comparative Example 2.

[0024] Figure 2 These are XRD patterns of Example 1, Comparative Example 1, and Comparative Example 2 in this invention;

[0025] Figure 3 This is a comparison of the activity generated in situ in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] The preparation method for 0.5% PdFe@Fe5C2 / Fe3O4 includes the following steps:

[0029] (1) Dissolve 18 mg palladium acetylacetonate, 5 mg iron acetylacetonate (molar ratio of Pd to Fe is 3:1) and 61 mg polyvinylpyrrolidone (PVP) in 1,2-propanediol (6.2 mL) to obtain metal precursor solution A with a Pd concentration of 1 mg / mL.

[0030] (2) Add 2 mL of the above metal precursor solution A to a container containing 50 mL of 1,2-propanediol and 400 mg of Fe2O3 support (PdFe alloy loading: ~0.5%). wt In a flask, the mixture was ultrasonically stirred, heated to 100°C in an oil bath, and stirred for 1 hour under N2 atmosphere to obtain solution B.

[0031] (3) Add 7 mg of NaHB4 powder to the above solution B and heat to 160℃. After keeping warm for 2 hours, solution C is obtained.

[0032] (4) Wait for solution C to cool to room temperature, then wash it several times by centrifugation with acetone to obtain a dry solid powder, and heat-treat it at 200-500℃ for 0.5-5 hours under an oxidizing atmosphere to obtain a 0.5% PdFe / Fe2O3 catalyst;

[0033] (5) The above 0.5% PdFe / Fe2O3 catalyst was treated with a reaction gas for 5 hours (the reaction gas consisted of 72% hydrogen and 24% carbon dioxide by volume, and the flow rate was 24 mL / min) to obtain a 0.5% PdFe@Fe5C2 / Fe3O4 catalyst.

[0034] Comparative Example 1

[0035] The preparation method for 0.05% Pd-Fe5C2 includes the following steps:

[0036] (1) Mix 0.94 mg palladium nitrate with 4.2125 g ferric nitrate nonahydrate, and sonicate to obtain solution 1;

[0037] (2) Add solution 1 to an aqueous solution containing 1.2514 g sodium hydroxide (150 mL), adjust its pH to 10, stir for 3 hours in an 80°C water bath, and let stand for 3 hours to obtain solution 2;

[0038] (3) The solution 2 above was filtered five times with hot water at about 50°C to remove the ions in the solution 2. After drying in an oven at 80°C for 24 hours, it was taken out and heat-treated in a muffle furnace at 300°C for 2 hours to obtain 0.05% Pd-Fe2O3 single-atom catalyst.

[0039] (4) The above 0.05% Pd-Fe2O3 single-atom catalyst was treated with a reaction gas for 20 hours (the reaction gas consisted of 72% hydrogen and 24% carbon dioxide by volume, and the flow rate was 24 mL / min) to obtain a 0.05% Pd-Fe5C2 catalyst.

[0040] Comparative Example 2

[0041] Preparation of 0.5% Pd@FeO x / Fe3O4, the preparation method includes the following steps:

[0042] (1) Mix 0.4g of iron oxide and 0.0056g of palladium acetylacetone in a flask, add 60ml of deionized water to the flask and mix. After ultrasonic treatment to dissolve evenly, obtain solution 3.

[0043] (2) Seal the solution 3 obtained in the above steps with a glass stopper and stir at room temperature for 3 hours (speed: 500 r / min);

[0044] (3) The solvent was separated by rotary distillation in the reactor. After being taken out, it was heat-treated in a muffle furnace at 300°C for 2 hours to obtain 0.5% Pd / Fe2O3 catalyst.

[0045] (4) The above 0.5% Pd / Fe2O3 catalyst was treated with a reaction gas for 30 hours (the reaction gas consisted of 72% hydrogen and 24% carbon dioxide by volume, with a flow rate of 24 mL / min) to obtain 0.5% Pd@FeO X / Fe3O4 catalyst.

[0046] Example 2

[0047] The catalysts prepared in Example 1 and Comparative Examples 1-2 were used in reverse water-gas shift reaction (rWGS) (the reaction gas composition was 72% hydrogen and 24% carbon dioxide, the flow rate was 24 mL / min, and the catalyst weight was 40 mg). Their catalytic activity at 400 °C was tested. The catalytic performance of Comparative Examples 1-2 and Example 1 at 400 °C is shown in Table 1.

[0048] Table 1

[0049]

[0050] As can be seen from Table 1, the catalyst of Example 1 of the present invention is comparable to that of 0.05% Pd-Fe5C2 (Comparative Example 1), and is superior to that of 0.5% Pd@FeO. x The Fe3O4 catalyst (Comparative Example 2) demonstrates that the formation of Fe5C2 further promotes the conversion of CO2, resulting in more of the target product.

[0051] from Figure 1 It can be seen that for 0.5% PdFe@Fe5C2 / Fe3O4, there are PdFe alloy nanoparticles and an Fe5C2 coating layer; for 0.05% Pd-Fe5C2 catalyst, there are obvious Fe5C2 lattice striations, indicating bulk carbonization of the support; however, for 0.5% Pd@FeO X Regarding the Fe3O4 catalyst, Pd particles are affected by FeO. x No Fe5C2 was observed after coating.

[0052] from Figure 2As can be seen, the Fe5C2 diffraction peak of 0.5% PdFe@Fe5C2 / Fe3O4 is weak, further verifying the TEM results. Fe5C2 is only generated on the alloy surface, and the catalyst support is still the Fe3O4 phase. The Fe5C2 diffraction peak of 0.05% Pd-Fe5C2 is significantly stronger, indicating that the introduction of single atoms can generate more Fe5C2 under these conditions. 0.5% Pd@FeO X The Fe3O4 catalyst still exhibits obvious Fe5C2 diffraction peaks because the presence of a small number of single atoms in the catalyst promotes the bulk carbonization of the support.

[0053] Figure 3 This invention provides a comparison of the in-situ generated activity of Examples 1, 1, and 2 of the present invention. Figure 3 It can be seen that it only takes 5 hours to convert 0.5% PdFe / Fe2O3 to 0.5% PdFe@Fe5C2 / Fe3O4, but it takes 20 hours to carbonize 0.05% Pd-Fe2O3 to 0.05% Pd-Fe5C2, and for 0.5% Pd@FeO X The Fe3O4 catalyst showed only a slight increase in activity after 20 hours, indicating that the carbonization time was at least 20 hours. Therefore, the catalyst of this invention, due to the presence of PdFe alloy nanoparticles, significantly shortens the Fe5C2 formation time and promotes the formation of a highly active PdFe@Fe5C2 / Fe3O4 structure.

[0054] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A PdFe alloy catalyst supported on Fe3O4, characterized in that, In the catalyst, the support is Fe3O4, and the active component is PdFe@Fe5C2; the PdFe@Fe5C2 has a core-shell structure, wherein: the core structure is a PdFe alloy, the molar ratio of Pd to Fe is 3:1, and the shell structure is Fe5C2; The preparation method of the Fe3O4 supported PdFe alloy catalyst includes the following steps: under normal pressure, the PdFe / Fe2O3 catalyst is carbonized at 300~500℃ for 2~5 h to obtain the PdFe@Fe5C2 / Fe3O4 catalyst; The preparation method of the PdFe / Fe2O3 catalyst includes the following steps: (1) Dissolve palladium acetylacetonate, iron acetylacetonate and polyvinylpyrrolidone in 1,2-propanediol to obtain metal precursor solution A; (2) Take the metal precursor solution A obtained in step (1) and mix it with 1,2-propanediol and Fe2O3, heat it in an oil bath to 100~150℃, and stir it for 1 hour under N2 atmosphere to obtain solution B; (3) Add NaBH4 powder to solution B obtained in step (2), heat to 150~180℃, keep warm for 2~3h, and obtain solution C; (4) Cool solution C to room temperature, wash and dry it, and then heat it at 200~500℃ for 0.5~5 hours under an oxidizing atmosphere to obtain PdFe / Fe2O3 catalyst.

2. The catalyst according to claim 1, characterized in that, The catalyst contains PdFe alloy with a loading of 0.5-5 wt%.

3. A method for preparing the Fe3O4-supported PdFe alloy catalyst according to any one of claims 1-2, characterized in that, The method includes the following steps: under normal pressure, the PdFe / Fe2O3 catalyst is carbonized at 300~500℃ for 2~5 h to obtain the PdFe@Fe5C2 / Fe3O4 catalyst; The preparation method of the PdFe / Fe2O3 catalyst includes the following steps: (1) Dissolve palladium acetylacetonate, iron acetylacetonate and polyvinylpyrrolidone in 1,2-propanediol to obtain metal precursor solution A; (2) Take the metal precursor solution A obtained in step (1) and mix it with 1,2-propanediol and Fe2O3, heat it in an oil bath to 100~150℃, and stir it for 1 hour under N2 atmosphere to obtain solution B; (3) Add NaBH4 powder to solution B obtained in step (2), heat to 150~180℃, keep warm for 2~3h, and obtain solution C; (4) Cool solution C to room temperature, wash and dry it, and then heat it at 200~500℃ for 0.5~5 hours under an oxidizing atmosphere to obtain PdFe / Fe2O3 catalyst.

4. The preparation method according to claim 3, characterized in that, In step (1), the mass ratio of palladium acetylacetone, iron acetylacetone and polyvinylpyrrolidone is 3.6:1:12.

2.

5. The preparation method according to claim 3, characterized in that, The carbonization atmosphere is a mixed gas of H2 and CO2, the volume ratio of H2 and CO2 in the mixed gas is 3:1, and the space velocity of the carbonization atmosphere is 30000-40000 mL / g -1 h -1 .

6. The preparation method according to claim 3, characterized in that, The carbonization treatment temperature is 350~450 ℃.

7. The use of a catalyst according to any one of claims 1-2 or a catalyst prepared by any one of claims 3-6 in the reaction of carbon dioxide hydrogenation to carbon monoxide.

8. The application according to claim 7, characterized in that, The reaction gas for the hydrogenation of carbon dioxide to produce carbon monoxide is a mixture of hydrogen and carbon dioxide, with a volume ratio of hydrogen to carbon dioxide of 3:1, a flow rate of 20~30 mL / min, and a reaction pressure of atmospheric pressure.

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