Medium temperature water gas shift catalyst and method of making

Abstract

The present application relates to a kind of medium-temperature water vapor shift catalyst and its preparation method.The catalyst is high defect site cerium oxide nanorod coated sub-nano Pt catalyst, and there is a thin cerium oxide coating on the Pt sub-nano cluster.The catalyst is applied to water vapor shift reaction, and shows very high water vapor shift activity in the temperature range of 250~450 ℃, and the CO conversion rate is close to the thermodynamic equilibrium conversion rate at ultra-high space velocity (300000 h ‑1 ).In addition, the catalyst has high structural strength and stability.

Description

Technical Field

[0001] This invention relates to a mid-temperature water vapor shift catalyst and its preparation method, and more specifically to a sub-nanometer Pt catalyst coated with cerium oxide nanorods with high defect sites, exhibiting high water vapor shift activity in the temperature range of 250–450 °C and at ultra-high space velocities (100,000–800,000 h⁻¹). -1 The CO conversion rate is close to the thermodynamic equilibrium conversion rate. Background Technology

[0002] The clean and sustainable utilization of fossil fuels is currently a hot topic in energy research. Fuel cells, which generate electricity through an electrochemical reaction between hydrogen and oxygen, can continuously convert chemical energy into electrical energy. They offer advantages such as high efficiency and environmental friendliness, attracting widespread attention from energy researchers worldwide. However, fuel cells suffer from the drawback of the inability to safely store the feedstock hydrogen, making hydrogen source technology one of the technological bottlenecks limiting the large-scale commercialization of fuel cell vehicles. Hydrogen production through hydrocarbon reforming offers significant advantages in terms of economy and safety, making it a hot research topic for on-site hydrogen production technology in fuel cells. However, this process inevitably generates large amounts of CO. CO can cause irreversible poisoning of the platinum electrode in the fuel cell, and its concentration must be reduced to below tolerable limits before entering the battery system. Furthermore, CO can be converted into hydrogen through a water-gas shift reaction, further improving energy utilization efficiency.

[0003] Currently, the most widely used water-gas shift catalysts in industry are CuZn and Fe-based catalysts. CuZn catalysts have an operating temperature window of 190-250℃. Due to the low tammam and hutting temperatures of copper, the catalyst is prone to sintering and deactivation as the reaction temperature increases. CuZn catalysts require a pre-activation process before use, making them unsuitable for the rapid and frequent start-up environments of fuel cells. Fe-based catalysts contain the highly toxic species Cr, which can easily cause pollution and toxicity to personnel and the environment during production, use, and disposal. Fe-based catalysts also have low activity, making them unsuitable for compact fuel cell systems. Therefore, there is an urgent need to develop novel water-gas shift catalysts that can adapt to the high-temperature operating conditions of fuel cell hydrogen production systems. Summary of the Invention

[0004] This invention aims to provide a highly active intermediate-temperature water-gas shift reaction catalyst (e.g., 250–450 °C). This catalyst is a sub-nanometer Pt catalyst coated with cerium oxide nanorods with high defect sites, exhibiting excellent water-gas shift reaction performance under ultra-high space velocities and in an intermediate-temperature reaction range. Furthermore, the catalyst prepared by this invention has a simple preparation method and good reaction stability.

[0005] Based on the above objectives, the technical solution adopted by the present invention is as follows:

[0006] 1. A catalyst for a medium-temperature water-gas shift reaction, comprising a Pt@CeO2 compound, wherein the CeO2 is a high-defect-site nanorod, the Pt is a sub-nano cluster, and the Pt cluster has a thin CeO2 coating layer.

[0007] 2. The mass percentage of Pt in the catalyst is 0.1%-5%, the diameter of the CeO2 nanorods is 5-30 nm, the length is 50-100 nm, and the defect sites (based on Ce) are... 3+ XPS peak area and Ce 3+ and Ce 4+ The percentage content (calculated by the sum of XPS peak areas) is 20%-30%; the size of Pt sub-nanometer clusters is 0.4-2nm; the CeO2 coating layer on Pt clusters is about 0.1-0.6nm.

[0008] 3. The preparation steps of the Pt@CeO2 catalyst are as follows:

[0009] (1) Dissolve Ce salt in ultrapure water to prepare a solution;

[0010] (2) Dissolve the strong base in ultrapure water to prepare an alkaline solution;

[0011] (3) At room temperature, mix the two solutions from step (1) and step (2) thoroughly and stir vigorously for 30 minutes;

[0012] (4) Transfer the solution obtained in step (3) into a flask and perform hydrothermal treatment for 12 to 48 hours;

[0013] (5) Filter out the solid material obtained in step (4), wash it three times with water and ethanol respectively, and then dry it;

[0014] (6) Mix and disperse the solid obtained in step (5) and Pt salt in ultrapure water, stir for 30 min and then sonicate for 30 min;

[0015] (7) Transfer the mixture obtained in step (6) to a hydrothermal reactor and hydrothermally treat it for 8 to 24 hours;

[0016] (8) Separate the solid from step (7), wash it three times with water and ethanol respectively, dry it, and calcine it.

[0017] 4. In the catalyst preparation step (1), the Ce salt is one or a mixture of two of cerium nitrate, cerium sulfate, and cerium trichloride; in step (2), the strong base is one or a mixture of two of NaOH and KOH; in step (3), the molar ratio of Ce salt to base is 1:100 to 1:150; and in step (5), the Pt salt is one or a mixture of two of chloroplatinic acid, tetraammonium chloride platinum, and tetraammonium nitrate platinum.

[0018] 5. The hydrothermal treatment temperature in step (4) of catalyst preparation is 80-120℃; the hydrothermal treatment temperature in step (6) is 140-240℃; the calcination temperature in step (8) is 300-500℃, the calcination time is 3-8 hours, the heating rate is 2-10℃ / min, and the calcination atmosphere is an inert atmosphere.

[0019] 6. CeO2 nanorods with high defect sites coated with Pt sub-nano catalysts were applied to water-gas shift reactions at reaction temperatures of 250–450 °C and gas hourly space velocities of 100,000–800,000 h⁻¹. -1 .

[0020] Compared with traditional water-gas shift reaction catalysts, the sub-nanometer Pt catalyst coated with cerium oxide nanorods with high defect sites prepared in this invention can achieve CO conversion at extremely high space velocities and has good catalyst stability. Attached Figure Description

[0021] Figure 1 HR-TEM image of a sub-nanometer Pt catalyst coated with cerium oxide nanorods with high defect sites. Detailed Implementation

[0022] To further illustrate the invention, the following embodiments are provided, but they do not limit the scope of the invention as defined by the appended claims.

[0023] Example 1

[0024] a. Weigh 1.736g Ce(NO3)3·6H2O and 19.2g NaOH and dissolve them in 10ml and 70ml of ultrapure water, respectively.

[0025] b. Mix the two solutions from a, stir at room temperature for 30 minutes, then transfer to a flask and seal for hydrothermal treatment at 100°C for 24 hours.

[0026] c. Separate the solid from b, wash it three times with ultrapure water and ethanol respectively, and then dry it at 60°C overnight.

[0027] d. Mix the dried solid from c with Pt(NH)4Cl2, with a Pt loading of 1wt% in the catalyst, disperse in 70ml of ultrapure water, sonicate for 30min, then transfer to a hydrothermal reactor and hydrothermally treat at 170℃ for 12h.

[0028] e. Separate the solid from d, wash it three times with ultrapure water and ethanol respectively, and then dry it at 60°C overnight.

[0029] f. The solid from step e is calcined at a heating rate of 5 °C / min under an inert atmosphere (nitrogen) from room temperature to 400 °C for 4 h to obtain a sub-nanometer Pt@CeO2 catalyst coated with cerium oxide nanorods with high defect sites.

[0030] The obtained Pt@CeO2 catalyst was subjected to structural characterization tests. Figure 1 This is an HR-TEM image of the Pt@CeO2 catalyst. The image shows that the CeO2 nanorods have a diameter of approximately 8-12 nm and a length of approximately 50-80 nm. The nanorods contain a large number of defect sites, with a defect site percentage of 26% (based on CeO2 content). 3+ XPS peak area and Ce 3+ and Ce 4+ (Calculated by the ratio of the sum of XPS peak areas); Pt clusters are approximately 0.6-1 nm in size, with a CeO2 coating layer outside the clusters, which is approximately 0.5-0.8 nm thick.

[0031] Comparative Example 1

[0032] Using the same Pt ​​loading and commercial CeO2 as a support, Pt particles were loaded onto commercial CeO2 via colloidal deposition, and then calcined using the same method as described in Example 1 to obtain a Pt / CeO2 catalyst. The Pt particle size of this catalyst is approximately 1 nm.

[0033] Example 2

[0034] Except for the use of Pt(NH)4Cl2 with a Pt loading of 0.1 wt% in step d, the Pt@CeO2 catalyst was prepared using the same method as described in Example 1, with a Pt loading of 0.1 wt%. The CeO2 nanorods had a diameter of approximately 8-12 nm and a length of approximately 50-80 nm, and the nanorods had a large number of defect sites, with a defect site percentage of 28% (based on CeO2 content). 3+ XPS peak area and Ce 3+ and Ce 4 + (Calculated by the ratio of the sum of XPS peak areas); Pt clusters are approximately 0.4-0.6 nm in size, with a CeO2 coating layer outside the clusters, which is approximately 0.5-0.8 nm thick.

[0035] Example 3

[0036] Except for the use of Pt(NH)4Cl2 with a Pt loading of 0.5 wt% in step d, the Pt@CeO2 catalyst was prepared using the same method as described in Example 1, with a Pt loading of 0.5 wt%. The CeO2 nanorods had a diameter of approximately 8-12 nm and a length of approximately 50-80 nm, and the nanorods had a large number of defect sites, with a defect site percentage of 26% (based on CeO2 content). 3+ XPS peak area and Ce3+ and Ce 4 + (Calculated by the ratio of the sum of XPS peak areas); Pt clusters are approximately 0.5-0.8 nm in size, with a CeO2 coating layer outside the clusters, which is approximately 0.5-0.8 nm thick.

[0037] Example 4

[0038] Except for the use of Pt(NH)4Cl2 with a Pt loading of 1.5 wt% in step d, the Pt@CeO2 catalyst was prepared using the same method as described in Example 1, with a Pt loading of 1.5 wt%. The CeO2 nanorods had a diameter of approximately 8-12 nm and a length of approximately 50-80 nm, and the nanorods had a large number of defect sites, with a defect site percentage of 26% (based on CeO2 content). 3+ XPS peak area and Ce 3+ and Ce 4 + (Calculated by the ratio of the sum of XPS peak areas); Pt clusters are approximately 0.8-1.2 nm in size, with a CeO2 coating layer outside the clusters, which is approximately 0.5-0.8 nm thick.

[0039] Example 5

[0040] Except for the use of Pt(NH)4Cl2 with a Pt loading of 2 wt% in step d, the Pt@CeO2 catalyst was prepared using the same method as described in Example 1, with a Pt loading of 2 wt%. The CeO2 nanorods had a diameter of approximately 8-12 nm and a length of approximately 50-80 nm, and the nanorods had a large number of defect sites, with a defect site percentage of 26% (based on CeO2 content). 3+ XPS peak area and Ce 3+ and Ce 4+ (Calculated by the ratio of the sum of XPS peak areas); Pt clusters are approximately 1-1.5 nm in size, with a CeO2 coating layer outside the clusters, which is approximately 0.5-0.8 nm thick.

[0041] Example 6

[0042] The 1 wt% Pt@CeO2 catalyst obtained in Example 1 was sieved to 20-40 mesh, loaded into a reaction tube, and a CO / H2O / N2 mixed gas (8% CO volume content and 20% H2O volume content) was introduced at a space velocity of 150,000 h⁻¹. -1 The reaction temperature was 350℃, and the CO conversion rate was 95%.

[0043] Comparative Example 2

[0044] Same as Example 6, except that the catalyst was changed to the 1 wt% Pt / CeO2 catalyst obtained in Comparative Example 1, and the CO conversion rate was 12%.

[0045] Example 7

[0046] Same as Example 6, except the reaction temperature is 250°C and the CO conversion rate is 78%.

[0047] Example 8

[0048] Same as Example 6, except the reaction temperature is 300°C and the CO conversion rate is 86%.

[0049] Example 9

[0050] Same as Example 6, except the reaction temperature is 325°C and the CO conversion rate is 92%.

[0051] Example 10

[0052] Same as Example 6, except the reaction temperature is 375°C and the CO conversion rate is 94%.

[0053] Example 11

[0054] Same as Example 6, except the reaction temperature is 400°C and the CO conversion rate is 91%.

[0055] Example 12

[0056] Same as Example 6, except the reaction temperature is 450°C and the CO conversion rate is 88%.

[0057] Example 13

[0058] Same as Example 6, except the airspeed is 100,000 h. -1 The CO conversion rate was 93%.

[0059] Example 14

[0060] Same as Example 6, except the airspeed is 300,000 h. -1 The CO conversion rate is 90%.

[0061] Example 15

[0062] Same as Example 6, except the airspeed is 500,000 h. -1 The CO conversion rate was 88%.

[0063] Example 16

[0064] Same as Example 6, except the airspeed is 800,000 h. -1 The CO conversion rate is 85%.

[0065] Example 17

[0066] Same as Example 6, except that the catalyst was changed to the 0.1 wt% Pt@CeO2 catalyst obtained in Example 2, and the CO conversion rate was 85%.

[0067] Example 18

[0068] Same as Example 6, except that the catalyst was changed to the 0.5 wt% Pt@CeO2 catalyst obtained in Example 3, and the CO conversion rate was 94%.

[0069] Example 19

[0070] Same as Example 6, except that the catalyst was changed to the 1.5 wt% Pt@CeO2 catalyst obtained in Example 4, and the CO conversion rate was 95%.

[0071] Example 20

[0072] Same as Example 6, except that the catalyst was changed to the 2wt% Pt@CeO2 catalyst obtained in Example 5, and the CO conversion rate was 95%.

[0073] Example 21

[0074] Similar to Example 6, after the reaction continued for 300 hours, the CO conversion rate stabilized at 94.5%.

[0075] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. All equivalent changes made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a catalyst for a medium-temperature water-steam shift reaction, characterized in that: The catalyst is Pt@CeO2, where CeO2 is a nanorod with high defect sites, Pt is a sub-nano cluster, and the Pt cluster has a thin CeO2 coating layer. The catalyst contains 1%-2% Pt by mass, CeO2 nanorods with a diameter of 8-12 nm, a length of 50-100 nm, and a defect site content of 26%; Pt sub-nano clusters with a size of 0.6-1.5 nm; and CeO2 coating on Pt clusters with a thickness of 0.5-0.8 nm. The preparation method of the catalyst for the intermediate-temperature water-steam shift reaction includes the following steps: (1) Dissolve Ce salt in water to prepare a solution; (2) Dissolve the strong base in water to prepare an alkaline solution; (3) At room temperature, mix the two solutions from step (1) and step (2) thoroughly and stir vigorously for 30 minutes; (4) The solution obtained in step (3) is subjected to hydrothermal treatment for 24 hours; (5) Filter out the solid material obtained in step (4), wash it with water and ethanol respectively, and then dry it; (6) Disperse the solid and Pt salt obtained in step (5) in water, stir for 10-40 min and then sonicate for 10-40 min; (7) The mixed system obtained in step (6) is hydrothermally treated for 12 hours; (8) Separate the solid from step (7), wash it with water and ethanol respectively, dry it and calcine it; The hydrothermal treatment temperature in step (4) is 80~120℃. o C; The hydrothermal treatment temperature in step (6) is 140~240℃. o C; The roasting temperature in step (8) is 300-500℃. o C, Calcination time is 3-8 hours, and the heating rate from room temperature to calcination temperature is 4-10. o C / min, the roasting atmosphere is an inert atmosphere.

2. The preparation method according to claim 1, characterized in that: In step (1), the Ce salt is one or more of cerium nitrate, cerium sulfate, and cerium trichloride; In step (2), the strong base is one or both of NaOH and KOH; The molar ratio of Ce salt to strong base in the solution obtained in step (3) is 1:80~1:150; In step (6), the Pt salt is one or more of chloroplatinic acid, tetraammonium chloride platinum, and tetraammonium nitrate platinum.

3. The preparation method according to claim 1, characterized in that: The molar ratio of Ce salt to strong base in the solution obtained in step (3) is 1:100 to 1:

130.

4. The application of the catalyst prepared by the preparation method according to any one of claims 1 to 3 as a catalyst for a medium-temperature water-gas shift reaction.

5. The application according to claim 4, characterized in that: The reaction temperature is 250~450℃ o C, air space velocity is 100,000~800,000 h⁻¹ -1 .

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