An alloy catalyst, a method for preparing the same, and an application thereof

Abstract

The application provides an alloy catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a palladium source, a copper source and a solvent to obtain a precursor salt solution, mixing and grinding the precursor salt solution with zinc oxide, and then performing a calcination treatment to obtain a calcined material; (2) performing a high-temperature reduction treatment on the calcined material to obtain the alloy catalyst. According to the application, a second active metal Cu is added to a traditional Pd / ZnO catalyst, and a PdCu / ZnO alloy catalyst is formed after reduction, so that the low-temperature and normal-pressure performance of a methanol reforming hydrogen reaction is greatly improved while the cost is reduced, and the selectivity of a byproduct CO is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and relates to an alloy catalyst and a preparation method and application thereof. BACKGROUND

[0002] Most of the existing technologies for hydrogen production by methanol steam reforming (CH3OH+H2O→3H2+CO2) adopt copper-based catalysts. The copper-based catalysts have the advantages of good low-temperature activity and low selectivity of byproduct CO, but are prone to high-temperature sintering. There are also noble metal palladium directly supported on ZnO for methanol steam reforming reaction, which not only has good high-temperature activity, but also is resistant to sintering. However, the high price of noble metals limits their application in practice, and the low-temperature catalytic performance is limited.

[0003] CN115414931A discloses a preparation method of a Pd / ZnO catalyst for hydrogen production by methanol steam reforming. The method comprises the following steps: dispersing zinc oxide into diethylene to form a suspension, then adding a sodium tetrachloropalladate precursor, dipping for a period of time, centrifuging, washing and drying to obtain the Pd / ZnO catalyst, and then reducing the Pd / ZnO catalyst by hydrogen to form a part of PdZn alloy, and finally using the Pd / ZnO catalyst for hydrogen production reaction. The Pd loading amount is 1.0-4.0wt.%. The methanol conversion rate of the Pd / ZnO catalyst is only 94% (3.0wt.% Pd) at a reaction temperature of 400℃, which still cannot make the methanol completely converted, indicating that the catalytic performance of the Pd / ZnO catalyst is poor. Moreover, the Pd content is high, the cost is high, and the catalyst is not conducive to industrial production.

[0004] CN101632929A discloses a high-temperature methanol steam reforming catalyst for hydrogen production and a preparation method thereof. The catalyst comprises an active component of group VIII metal, an additive ZnO and a carrier modified Al2O3 pellet, wherein the group VIII metal is one or more of Pd, Pt, Rh and Ir, and the content of the active component accounts for 2.6-10wt.% of the carrier. The preparation method adopts the methods of parallel flow impregnation and ultrasonic dispersion, and the carrier Al2O3 pellet needs to be modified by rare earth metals La, Ce or Y. The synthesis steps are complex, the noble metal loading amount is high, and the catalyst is not conducive to industrialization. The catalyst has good performance only at a temperature of greater than 250℃, and the application scene is limited.

[0005] CN108855065A discloses a method for using a Pd / ZnAl2O4 catalyst in methanol steam reforming to produce hydrogen. The catalyst uses Pd as the active component and zinc-aluminum spinel as the support, and is synthesized by an impregnation method. The Pd content is 0.1–5%, and it needs to be reduced with hydrogen to form a PdZn alloy before use. However, this preparation method uses nitric acid as the precursor solution for the precious metal Pd, which poses an environmental hazard to its preparation and widespread application. Furthermore, the reaction pressure is 0.1–5 MPa, making it difficult to rule out the positive impact of condition control on the reaction, thus affecting the assessment of the catalyst's performance. Therefore, this method is not suitable for methanol reforming to produce hydrogen under normal pressure.

[0006] CN114260016A discloses a method for using Pd / ZnFe x Al 2-x A method for using O4 catalyst in methanol reforming to produce hydrogen includes the following steps: adding zinc salt, doped metal ion salt, and aluminum salt to isopropanol for a hydrothermal reaction to obtain ZnM. x Al 2-x O4 spinel carrier; loading noble metal Pd salts onto ZnMn using methods such as impregnation or sol-gel methods. x Al 2-x The catalyst is supported on an O4 carrier and treated with hydrogen before use, with a Pd content of 0.1–0.5%. This method involves first synthesizing the carrier via a hydrothermal process, and then loading the precious metal. The process is complex, the synthesis cost is high, and it is not conducive to the industrial production of the catalyst.

[0007] The catalyst described in the above scheme has good catalytic performance under high temperature and high pressure, but the preparation process is complicated and has the problems of large loading of precious metals and high cost. Summary of the Invention

[0008] The purpose of this invention is to provide an alloy catalyst, its preparation method, and its application. This invention adds a second active metal, Cu, to a traditional Pd / ZnO catalyst, and after reduction, forms a PdCu / ZnO alloy catalyst. This reduces costs while significantly improving the low-temperature and atmospheric-pressure performance of methanol reforming for hydrogen production and reducing the selectivity of the byproduct CO.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing an alloy catalyst, the method comprising the following steps:

[0011] (1) A precursor salt solution is obtained by mixing a palladium source, a copper source and a solvent. The precursor salt solution is then mixed and ground with zinc oxide and calcined to obtain a calcined material.

[0012] (2) The calcined material is subjected to high-temperature reduction treatment to obtain the alloy catalyst.

[0013] This invention employs a simple one-step impregnation method to obtain PdO-CuO / ZnO, which is then subjected to hydrogen treatment to obtain a PdCu / ZnO alloy catalyst. This invention modifies the active component of the catalyst by adding a second active metal, Cu, to form a PdCu alloy. This improves the low-temperature activity of the methanol reforming hydrogen production reaction and significantly reduces CO selectivity. CO selectivity refers to the proportion of CO byproduct generated by the catalyst in all products during the reaction. Lower CO selectivity indicates a lower concentration of byproducts in the catalyst, and thus better catalyst performance.

[0014] Preferably, the palladium source in step (1) includes palladium nitrate.

[0015] Preferably, the copper source includes copper nitrate.

[0016] Preferably, the solvent includes deionized water.

[0017] Preferably, the mass ratio of palladium in the palladium source to copper in the copper source in step (1) is 1:(0.5~2), for example: 1:0.5, 1:0.8, 1:1, 1:1.5 or 1:2, etc.

[0018] Preferably, the total mass concentration of palladium and copper sources in the precursor salt solution is 15–30 kg / m³. 3 For example: 15kg / m 3 18kg / m 3 20kg / m 3 25kg / m 3 Or 30kg / m 3 wait.

[0019] Preferably, the total mass ratio of palladium in the palladium source and copper in the copper source to zinc oxide is (1.5-3):100, for example: 1.5:100, 1.8:100, 2:100, 2.5:100 or 3:100, etc.

[0020] Preferably, the mixing and grinding method in step (1) includes placing zinc oxide in a mortar and grinding while adding a precursor salt solution dropwise.

[0021] Preferably, the mixing and grinding time is 3 to 8 minutes, for example: 3 minutes, 4 minutes, 5 minutes, 6 minutes or 8 minutes.

[0022] Preferably, the mixture is subjected to a settling and drying process after grinding.

[0023] Preferably, the settling time is 4 to 8 hours, for example: 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0024] Preferably, the drying temperature is 105-120°C, for example: 105°C, 110°C, 112°C, 115°C or 120°C.

[0025] Preferably, the drying time is 10 to 15 hours, for example: 10 hours, 11 hours, 12 hours, 14 hours or 15 hours.

[0026] Preferably, the heating rate of the calcination process in step (1) is 1.5 to 2.5 °C / min, for example: 1.5 °C / min, 1.8 °C / min, 2 °C / min, 2.2 °C / min or 2.5 °C / min, etc.

[0027] Preferably, the calcination temperature is 320-380℃, for example: 320℃, 340℃, 350℃, 360℃ or 380℃.

[0028] Preferably, the roasting time is 3 to 5 hours, for example: 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0029] Preferably, grinding and sieving are performed before the high-temperature reduction treatment in step (2).

[0030] Preferably, the mesh size of the sieve is 40 to 60 mesh, for example: 40 mesh, 45 mesh, 50 mesh, 55 mesh or 60 mesh, etc.

[0031] Preferably, the atmosphere for the high-temperature reduction treatment in step (2) includes a mixture of hydrogen and nitrogen.

[0032] Preferably, the hydrogen gas accounts for 8% to 15% of the volume of the mixed gas, for example: 8%, 9%, 10%, 12% or 15%.

[0033] Preferably, the flow rate of the mixed gas is 80-120 mL / min, for example: 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min or 120 mL / min, etc.

[0034] Preferably, the heating rate of the high-temperature reduction treatment in step (2) is 8 to 12°C / min, for example: 8°C / min, 9°C / min, 10°C / min, 11°C / min or 12°C / min, etc.

[0035] Preferably, the temperature of the high-temperature reduction treatment is 280 to 320°C, for example: 280°C, 290°C, 300°C, 310°C or 320°C.

[0036] Preferably, the high-temperature reduction treatment time is 1.5 to 3 hours, for example: 1.5 hours, 1.8 hours, 2 hours, 2.5 hours or 3 hours.

[0037] In a second aspect, the present invention provides an alloy catalyst, which is prepared by the method described in the first aspect.

[0038] Preferably, the alloy catalyst comprises a zinc oxide support and palladium and copper active components supported on the surface of the zinc oxide support.

[0039] Preferably, the mass fraction of the palladium active component is 0.8% to 1.2% based on 100% of the mass of the alloy catalyst, for example: 0.8%, 0.9%, 1%, 1.1% or 1.2%, etc.

[0040] Preferably, the mass fraction of the copper active component is 0.5% to 2%, for example: 0.5%, 0.8%, 1%, 1.5% or 2%.

[0041] The catalyst described in this invention has a low loading of active components, with Pd content of only about 1 wt.% and Cu content of 0.5-2 wt.%. The addition of copper not only improves the catalytic activity of the alloy catalyst, but also reduces the CO selectivity of the catalyst.

[0042] Thirdly, the present invention provides an application of the alloy catalyst as described in the second aspect, wherein the alloy catalyst is used for methanol reforming to produce hydrogen.

[0043] The alloy catalyst described in this invention has favorable catalytic reaction conditions (atmospheric pressure, low temperature less than 250°C), which greatly improves the low-temperature performance of methanol reforming to hydrogen production reaction, namely, it improves low-temperature activity, reduces the selectivity of by-product CO, achieves good catalyst performance, is low in cost, is easy to industrialize, and has broad application prospects.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The catalyst described in this invention solves the problems of poor low-temperature activity and high CO selectivity of traditional Pd / ZnO catalysts. It has excellent low-temperature activity and low CO selectivity, and is suitable for methanol reforming to produce hydrogen. The preparation method is simple and easy to produce on a large scale in industry.

[0046] (2) The catalyst of the present invention can achieve a methanol conversion rate of more than 3.9% and a CO selectivity of less than 17% at 175°C, a methanol conversion rate of more than 14% and a CO selectivity of less than 17.6% at 225°C, a methanol conversion rate of more than 32.1% and a CO selectivity of less than 13.8% at 200°C, and a methanol conversion rate of more than 65.9% and a CO selectivity of less than 9.9% at 250°C. Attached Figure Description

[0047] Figure 1 This is the XRD pattern of the alloy catalyst described in Example 1.

[0048] Figure 2 This is a comparison chart of the catalytic methanol conversion rates of the catalysts described in Example 1 and Comparative Example 1.

[0049] Figure 3 This is a comparison graph of the CO selectivity of the catalysts described in Example 1 and Comparative Example 1. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0051] Example 1

[0052] This embodiment provides an alloy catalyst, and the preparation method of the alloy catalyst is as follows:

[0053] (1) Weigh 0.0750g Pd(NO3)2·2H2O and 0.1133g Cu(NO3)2·3H2O and dissolve them in 3mL of deionized water to prepare a precursor salt solution; weigh 3g ZnO support and place it in a mortar, and grind while adding the precursor salt solution dropwise; after grinding for 5min, seal the sample and let it stand at room temperature for 6h; then place the sample in an oven at 110℃ for 12h to dry; finally, place the sample in a muffle furnace and calcine it at 350℃ for 4h at a heating rate of 2℃ / min to obtain the calcined material;

[0054] (2) The calcined material was pressed into tablets and ground through a 40-mesh sieve. Under a 10% H2 / N2 atmosphere at a heating rate of 10℃ / min, the temperature was increased to 300℃ for 2 hours to obtain the alloy catalyst. The loading of copper in the alloy catalyst was 1 wt.% and the loading of palladium was 1 wt.%.

[0055] The XRD pattern of the alloy catalyst is as follows: Figure 1 As shown.

[0056] Example 2

[0057] This embodiment provides an alloy catalyst, and the preparation method of the alloy catalyst is as follows:

[0058] (1) Weigh 0.0601g Pd(NO3)2·2H2O and 0.2265g Cu(NO3)2·3H2O and dissolve them in 3mL of deionized water to prepare a precursor salt solution; weigh 3g ZnO support and place it in a mortar, and grind while adding the precursor salt solution dropwise; after grinding for 5min, seal the sample and let it stand at room temperature for 6h; then place the sample in an oven at 105℃ for 12h to dry; finally, place the sample in a muffle furnace and calcine it at 320℃ for 5h at a heating rate of 2℃ / min to obtain the calcined material;

[0059] (2) The calcined material was pressed into tablets and ground through a 40-mesh sieve. It was then reduced to 280°C for 3 hours at a heating rate of 10°C / min under a 10% H2 / N2 atmosphere at a rate of 100 mL / min to obtain the alloy catalyst. The copper loading in the alloy catalyst was 2 wt.% and the palladium loading was 0.8 wt.%.

[0060] Example 3

[0061] This embodiment provides an alloy catalyst, and the preparation method of the alloy catalyst is as follows:

[0062] (1) Weigh 0.0750g Pd(NO3)2·2H2O and 0.1133g Cu(NO3)2·3H2O and dissolve them in 3mL of deionized water to prepare a precursor salt solution; weigh 3g ZnO support and place it in a mortar, and grind while adding the precursor salt solution dropwise; after grinding for 5min, seal the sample and let it stand at room temperature for 6h; then place the sample in an oven at 120℃ for 10h to dry; finally, place the sample in a muffle furnace and calcine it at 380℃ for 3h at a heating rate of 2℃ / min to obtain the calcined material;

[0063] (2) The calcined material was pressed into tablets and ground through a 40-mesh sieve. Under a 10% H2 / N2 atmosphere at a heating rate of 10℃ / min, the temperature was increased to 320℃ for 1.5h to obtain the alloy catalyst. The loading of copper in the alloy catalyst was 1wt.% and the loading of palladium was 1wt.%.

[0064] Example 4

[0065] The only difference between this embodiment and Embodiment 1 is that the copper loading is 0.5 wt.%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0066] Example 5

[0067] The only difference between this embodiment and Embodiment 1 is that the copper loading is 2.0 wt.%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0068] Example 6

[0069] The only difference between this embodiment and Embodiment 1 is that the calcination temperature in step (1) is 300°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0070] Example 7

[0071] The only difference between this embodiment and Embodiment 1 is that the calcination temperature in step (1) is 400°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0072] Example 8

[0073] The only difference between this embodiment and embodiment 1 is that the temperature of the high-temperature reduction treatment in step (2) is 250°C, while the other conditions and parameters are exactly the same as in embodiment 1.

[0074] Example 9

[0075] The only difference between this embodiment and embodiment 1 is that the temperature of the high-temperature reduction treatment in step (2) is 350°C, while the other conditions and parameters are exactly the same as in embodiment 1.

[0076] Comparative Example 1

[0077] The only difference between this comparative example and Example 1 is that no copper source is added; all other conditions and parameters are exactly the same as in Example 1.

[0078] Performance testing:

[0079] The performance of the catalysts obtained in Examples 1-9 and Comparative Example 1 in methanol reforming for hydrogen production was tested under the following reaction conditions: 100 mg catalyst, a molar ratio of water to methanol of 1.5, and a methanol mass hourly space velocity (MHSV) of 2.3 h⁻¹. -1 At normal pressure, the test results are shown in Table 1:

[0080] Table 1

[0081]

[0082] As shown in Table 1, and based on Examples 1-3, the catalyst of the present invention can achieve a methanol conversion rate of over 3.9% and a CO selectivity of less than 17% at 175°C; a methanol conversion rate of over 14% and a CO selectivity of less than 17.6% at 225°C; a methanol conversion rate of over 32.1% and a CO selectivity of less than 13.8% at 200°C; and a methanol conversion rate of over 65.9% and a CO selectivity of less than 9.9% at 250°C.

[0083] A comparison of Examples 1 and 4-5 shows that the mass ratio of palladium to copper in the alloy catalyst of the present invention affects its performance. The alloy catalyst with better performance is obtained when the mass ratio of palladium to copper is controlled at 1:(0.5-2). If the copper loading is too high, the methanol conversion rate will decrease. If the copper loading is too low, the selectivity of the by-product CO will increase.

[0084] A comparison of Examples 1 and 6-7 shows that the calcination temperature affects the performance of the alloy catalyst during its preparation. Controlling the calcination temperature between 320 and 380°C yields a better-performing alloy catalyst. Excessively high or low calcination temperatures will reduce methanol conversion and increase the selectivity of the byproduct CO.

[0085] A comparison of Examples 1 and 8-9 shows that the temperature of the high-temperature reduction treatment affects the performance of the alloy catalyst during its preparation. Controlling the high-temperature reduction treatment temperature between 280 and 320°C results in a better performance alloy catalyst. If the high-temperature reduction treatment temperature is too high or too low, the methanol conversion rate will decrease and the selectivity of the by-product CO will increase.

[0086] The comparison graph of the catalytic methanol conversion rates of the catalysts described in Example 1 and Comparative Example 1 is shown below. Figure 2 As shown in the figure, the comparison graph of CO selectivity of the catalysts described in Example 1 and Comparative Example 1 is as follows. Figure 3 As shown, by comparing Example 1 and Comparative Example 1, it can be seen that the present invention modifies the active component of the catalyst by adding a second active metal Cu to form a PdCu alloy, thereby improving the low-temperature activity of the methanol reforming hydrogen production reaction and significantly reducing the CO selectivity.

[0087] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an alloy catalyst, characterized in that, The preparation method includes the following steps: (1) A precursor salt solution is obtained by mixing a palladium source, a copper source and a solvent. The precursor salt solution is then mixed with zinc oxide, ground and calcined to obtain a calcined material. (2) The calcined material is subjected to high-temperature reduction treatment to obtain the alloy catalyst; In step (1), the mass ratio of palladium in the palladium source to copper in the copper source is 1:(0.5~2); Based on the mass of the alloy catalyst (100%), the mass fraction of the palladium active component is 0.8-1.2%, and the mass fraction of the copper active component is 0.5-2%. The alloy catalyst is used for methanol reforming to produce hydrogen.

2. The preparation method according to claim 1, characterized in that, The palladium source in step (1) includes palladium nitrate.

3. The preparation method according to claim 1, characterized in that, The copper source in step (1) includes copper nitrate.

4. The preparation method according to claim 1, characterized in that, The solvent in step (1) includes deionized water.

5. The preparation method according to claim 1, characterized in that, The total mass concentration of palladium and copper sources in the precursor salt solution is 15~30 kg / m³. 3 .

6. The preparation method according to claim 1, characterized in that, The total mass ratio of palladium in the palladium source and copper in the copper source to zinc oxide is (1.5~3):

100.

7. The preparation method according to claim 1, characterized in that, The mixing and grinding method described in step (1) includes placing zinc oxide in a mortar and grinding while adding a precursor salt solution dropwise.

8. The preparation method according to claim 1, characterized in that, The mixing and grinding time in step (1) is 3 to 8 minutes.

9. The preparation method according to claim 1, characterized in that, After mixing and grinding in step (1), the mixture is allowed to stand and then dried.

10. The preparation method according to claim 9, characterized in that, The settling time is 4 to 8 hours.

11. The preparation method according to claim 9, characterized in that, The drying temperature is 105~120℃.

12. The preparation method according to claim 9, characterized in that, The drying process takes 10-15 hours.

13. The preparation method according to claim 1, characterized in that, The heating rate of the calcination process in step (1) is 1.5~2.5℃ / min.

14. The preparation method according to claim 1, characterized in that, The roasting temperature in step (1) is 320~380℃.

15. The preparation method according to claim 1, characterized in that, The roasting process in step (1) takes 3 to 5 hours.

16. The preparation method according to claim 1, characterized in that, Before the high-temperature reduction treatment in step (2), the material is ground and sieved.

17. The preparation method according to claim 16, characterized in that, The sieve mesh size is 40-60 mesh.

18. The preparation method according to claim 1, characterized in that, The atmosphere for the high-temperature reduction treatment in step (2) includes a mixture of hydrogen and nitrogen.

19. The preparation method according to claim 18, characterized in that, The hydrogen gas accounts for 8-15% of the volume of the mixed gas.

20. The preparation method according to claim 18, characterized in that, The flow rate of the mixed gas is 80~120 mL / min.

21. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature reduction treatment in step (2) is 8~12℃ / min.

22. The preparation method according to claim 1, characterized in that, The temperature of the high-temperature reduction treatment in step (2) is 280~320℃.

23. The preparation method according to claim 1, characterized in that, The high-temperature reduction treatment in step (2) takes 1.5 to 3 hours.

24. An alloy catalyst, characterized in that, The alloy catalyst is prepared by the method according to any one of claims 1-23; The alloy catalyst comprises a zinc oxide support and palladium and copper active components supported on the surface of the zinc oxide support; Based on the mass of the alloy catalyst as 100%, the mass fraction of the palladium active component is 0.8~1.2%; and the mass fraction of the copper active component is 0.5~2%.

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