A method for preparing a catalyst by impregnation and its use in the production of hydrogen from methanol

Abstract

This invention discloses a method for preparing a catalyst by impregnation and its application in methanol-to-hydrogen production, belonging to the field of hydrogen production technology. The method for preparing the catalyst by impregnation includes the following steps: (1) mixing alumina, zirconium oxide, cerium oxide, pore-forming agent, surfactant, and deionized water, followed by ball milling, molding, drying, and calcination to obtain a composite support; (2) stirring and mixing copper nitrate, zinc nitrate, and deionized water, adjusting the pH to obtain an impregnation solution; (3) impregnating the composite support in the impregnation solution using an equal-volume impregnation method, followed by drying, calcination, and reduction to obtain the catalyst. The catalyst prepared by the method of this invention exhibits high methanol conversion rate and H2 selectivity in the catalytic production of hydrogen from methanol, and also demonstrates excellent stability in use.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production technology, specifically to a method for preparing a catalyst by impregnation and its application in methanol-to-hydrogen production. Background Technology

[0002] With the expanding applications of hydrogen energy in fuel cells, distributed energy, and clean energy systems, efficient, stable, and controllable hydrogen production technologies have become a crucial direction for current research and industrialization. Among numerous hydrogen production pathways, methanol-to-hydrogen is considered a promising method due to its advantages such as relatively low reaction temperature, high hydrogen yield, fewer side reactions, and the ease of storage and transportation of liquid feedstock. In the methanol-to-hydrogen process, the performance of the catalyst is crucial to the reaction efficiency and the purity of the produced hydrogen. Currently, copper-based catalysts are widely used due to their excellent activity in the methanol decomposition reaction. However, existing copper-based catalysts still have the following shortcomings in actual use: (1) Copper species are prone to sintering and agglomeration during reaction and high-temperature treatment, resulting in a decrease in specific surface area and a reduction in active sites, which leads to catalytic activity decay and decreased stability; (2) In catalysts prepared by traditional impregnation method, the distribution uniformity of metal precursors on the support surface is poor, and high concentrations are easily formed in local areas, which affects the size control and dispersion state of metal particles; (3) Conventional support materials have limited adsorption and activation capabilities for water molecules, while the effective activation of water molecules has an important impact on hydrogen generation in methanol steam reforming reaction.

[0003] Chinese invention patent CN116037113A discloses a copper-based supported catalyst, its preparation method, and its application. This invention improves the hydrogen production rate of the copper-based supported catalyst in catalytic reactions by introducing PVP (polyvinyl chloride) with a number-average molecular weight ≤40,000 as a carbon support, while reducing CO selectivity. Furthermore, by controlling the formation of a sol after mixing PVP and copper salt, copper ion migration and aggregation are prevented, ensuring uniform dispersion of the active components. Combined with pyrolysis treatment, the copper metal particles have a smaller particle size, and the support forms a loose, porous structure during this process, providing more attachment sites for the active components. The resulting copper-based supported catalyst exhibits a high probability of contact area between the active components and the methanol solution in methanol aqueous reforming reactions, thus enhancing the catalyst's catalytic activity. The copper-based supported catalyst obtained by this invention is particularly suitable for methanol liquid-phase reforming to produce hydrogen, with a CO selectivity of less than 0.1% and a hydrogen production rate of 79.01 μmol / g. cat / s, but its stability needs to be improved.

[0004] Therefore, developing a novel catalyst with excellent catalytic activity and long-term stability is of great value for promoting the application of methanol-to-hydrogen technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing catalysts by impregnation and its application in methanol-to-hydrogen production.

[0006] A surfactant for preparing catalysts by impregnation method has the following chemical structural formula: .

[0007] The surfactant is obtained by reacting [[(2-hydroxyethyl)imino]bis(methylene)]diphosphonic acid with 2-chlorododecanoic acid, and the reaction equation is shown below:

[0008] The molar ratio of [[(2-hydroxyethyl)imino]bis(methylene)]diphosphonic acid to 2-chlorododecanoic acid is 1:1.05.

[0009] A method for preparing a catalyst by impregnation includes the following steps: (1) Alumina, zirconium oxide, cerium oxide, pore-forming agent, surfactant and deionized water are mixed and then ball-milled, shaped, dried and calcined to obtain a composite carrier; (2) Mix copper nitrate, zinc nitrate and deionized water, adjust the pH to obtain the impregnation solution; (3) The composite carrier is impregnated in the impregnation solution by the equal volume impregnation method, and the catalyst is obtained after drying, calcination and reduction;

[0010] In step (1), the mass ratio of alumina, zirconium oxide and cerium oxide is (6-6.5):(1-1.5):1.

[0011] In step (1), the pore-forming agent is a mixture of polyethylene glycol and urea in a mass ratio of 1:1; the amount of the pore-forming agent is 4-7% of the total mass of alumina, zirconium oxide and cerium oxide.

[0012] In step (1), the amount of surfactant added is 1-2% of the total mass of alumina, zirconium oxide and cerium oxide.

[0013] In step (2), the mass ratio of copper nitrate to zinc nitrate is (2-3):1.

[0014] In step (2), the pH is 6.5-7.5.

[0015] Application of a catalyst prepared by the above method in methanol-to-hydrogen production.

[0016] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include:

[0017] The catalyst prepared using the method of the present invention exhibits high methanol conversion and H2 selectivity when used for catalytic methanol-to-hydrogen production, and also demonstrates excellent stability in use. Attached Figure Description

[0018] Figure 1 The image shows a transmission electron microscope image of the catalyst prepared in Example 3. Detailed Implementation

[0019] Example 1 Preparation of Surfactants Under nitrogen protection, 200 ml of anhydrous ethanol and 0.1 mol of [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid were stirred and mixed. The pH was adjusted to 9 with 40 wt% sodium hydroxide solution. 0.105 mol of 2-chlorododecanoic acid (CAS No. 35300-93-7) and 5 mmol of sodium iodide were added. The mixture was heated to reflux and reacted for 30 h. After cooling to room temperature, the mixture was rotary evaporated at 45 °C to constant weight. It was recrystallized using 150 ml of acetone, filtered, and dried under vacuum at 60 °C for 12 h to obtain the surfactant. Its 1H NMR data are as follows: 1 H NMR (400 MHz, Chloroform-d) δ 11.62 (s, 1H), 7.61 (s, 4H), 4.33-4.30 (m, 1H), 4.11 (d, J = 1.8 Hz, 4H), 3.99 (t, J = 5.5 Hz, 1H), 3.75 (dd, J = 5.5, 1.2Hz, 2H), 3.53 – 3.41 (m, 2H), 2.21 – 2.01 (m, 2H), 1.39 – 1.24 (m, 16H), 0.90(t, J = 6.2 Hz, 3H); HRMS (m / z): 448.1865[M-Cl] + ;

[0020] Example 2 Preparation of Catalyst (1) 60g alumina, 10g zirconium oxide, 10g cerium oxide, 3.2g pore-forming agent (1.6g polyethylene glycol PEG-6000, 1.6g urea), 0.8g surfactant (prepared in Example 1) and 80ml deionized water were added to a ball mill. Grinding balls with diameters of 5mm and 10mm were used. The weight ratio of 5mm grinding balls to 10mm grinding balls was 2:1 and the ball-to-material ratio was 10:1. The mixture was ground at 250rpm for 30min, stopped for 15min, and the ball milling and stopping were repeated 10 times to obtain a slurry. Then, the slurry was formed by extrusion-spheronization granulation. The extrusion pressure was 2MPa, the die diameter was 1mm, and the extrusion rate was 5cm / min to obtain strip-shaped material. The strip-shaped material was then spheronized at 600rpm for 15min in a spheronizer to obtain granules. The obtained granules were dried at 110℃ for 8h, and then heated to 500℃ at a heating rate of 5℃ / min and calcined in air atmosphere for 4h to obtain a composite carrier. (2) Add 20g of copper nitrate and 10g of zinc nitrate to 80ml of deionized water, stir at 40℃ for 30min, and add ammonia water to adjust the pH of the solution to 6.5 under stirring to obtain the impregnation solution; (3) Place the composite support obtained in step (1) in a container, and add the impregnation solution prepared in step (2) dropwise to the composite support under stirring at 200 rpm. Use the equal volume impregnation method to let it stand at room temperature for 8 h. After impregnation, dry it at 80 ℃ for 15 h, and then put it in a tube furnace. Heat it to 400 ℃ for 3 h in air atmosphere at a heating rate of 5 ℃ / min, and cool it down to 250 ℃ at a rate of 5 ℃ / min. Introduce a mixed gas of nitrogen and hydrogen (nitrogen flow rate 0.1 L / min, hydrogen flow rate 0.02 L / min) and keep it at the temperature for 3 h to obtain the catalyst.

[0021] Example 3 Preparation of Catalyst (1) Add 62g alumina, 12g zirconium oxide, 10g cerium oxide, 5.04g pore-forming agent (2.52g polyethylene glycol PEG-6000, 2.52g urea), 1.26g surfactant (prepared in Example 1), and 85ml deionized water to a ball mill. Use grinding balls with diameters of 5mm and 10mm, with a weight ratio of 2:1 for 5mm and 10mm grinding balls and a ball-to-material ratio of 10:1. Grind at 250rpm for 30min, then stop for 15min. n. The mixture is circulated and ball-milled 10 times to obtain a slurry. Then, it is shaped by extrusion-spheronization granulation, with an extrusion pressure of 3 MPa, a die diameter of 1.5 mm, and an extrusion rate of 8 cm / min to obtain strip-shaped material. The strip-shaped material is then spheronized at 700 rpm for 12 min in a spheronizer to obtain granules. The granules are dried at 110℃ for 8 h, then heated to 500℃ at a heating rate of 5℃ / min and calcined in air for 4 h to obtain a composite carrier. (2) Add 25g of copper nitrate and 10g of zinc nitrate to 90ml of deionized water, stir at 40℃ for 30min, and add ammonia water to adjust the pH of the solution to 7 under stirring to obtain the impregnation solution; (3) Place the composite support obtained in step (1) in a container, and add the impregnation solution prepared in step (2) dropwise to the composite support under stirring at 200 rpm. Use the equal volume impregnation method to let it stand at room temperature for 8 h. After impregnation, dry it at 80 ℃ for 15 h, and then put it in a tube furnace. Heat it to 400 ℃ for 3 h in air atmosphere at a heating rate of 5 ℃ / min, and cool it down to 250 ℃ at a rate of 5 ℃ / min. Introduce a mixed gas of nitrogen and hydrogen (nitrogen flow rate 0.1 L / min, hydrogen flow rate 0.02 L / min) and keep it at the temperature for 3 h to obtain the catalyst.

[0022] Figure 1 The image shows a transmission electron microscope (TEM) image of the catalyst prepared in Example 3. As can be seen from the image, the active component in the catalyst is in the form of nanoscale particles, and no obvious large-size particle agglomeration was observed, indicating that the metal component has high dispersibility under the regulation of the surfactant.

[0023] Example 4 Preparation of Catalyst (1) 65g alumina, 15g zirconium oxide, 10g cerium oxide, 6.3g pore-forming agent (3.15g polyethylene glycol PEG-6000, 3.15g urea), 1.8g surfactant (prepared in Example 1), and 90ml deionized water were added to a ball mill. Grinding balls with diameters of 5mm and 10mm were used. The weight ratio of 5mm grinding balls to 10mm grinding balls was 2:1, and the ball-to-material ratio was 10:1. The mixture was ground at 250rpm for 30min, stopped for 15min, and the ball milling and stopping were repeated 10 times to obtain a slurry. Then, the slurry was formed by extrusion-spheronization granulation. The extrusion pressure was 4MPa, the die diameter was 2mm, and the extrusion rate was 10cm / min to obtain strip-shaped material. The strip-shaped material was then spheronized at 800rpm for 10min in a spheronizer to obtain granules. The obtained granules were dried at 110℃ for 8h, and then heated to 500℃ at a heating rate of 5℃ / min and calcined in air atmosphere for 4h to obtain a composite carrier. (2) Add 30g of copper nitrate and 10g of zinc nitrate to 100ml of deionized water, stir at 40℃ for 30min, and add ammonia water to adjust the pH of the solution to 7.5 under stirring to obtain the impregnation solution; (3) Place the composite support obtained in step (1) in a container, and add the impregnation solution prepared in step (2) dropwise to the composite support under stirring at 200 rpm. Use the equal volume impregnation method to let it stand at room temperature for 8 h. After impregnation, dry it at 80 ℃ for 15 h, and then put it in a tube furnace. Heat it to 400 ℃ for 3 h in air atmosphere at a heating rate of 5 ℃ / min, and cool it down to 250 ℃ at a rate of 5 ℃ / min. Introduce a mixed gas of nitrogen and hydrogen (nitrogen flow rate 0.1 L / min, hydrogen flow rate 0.02 L / min) and keep it at the temperature for 3 h to obtain the catalyst.

[0024] Comparative Example 1 The preparation method of the catalyst is basically the same as that in Example 3, except that the pore-forming agent used in step (1) is only an equal weight of polyethylene glycol PEG-6000.

[0025] Comparative Example 2 The preparation method of the catalyst is basically the same as that in Example 3, except that the pore-forming agent used in step (1) is only an equal weight of urea.

[0026] Comparative Example 3 The preparation method of the catalyst is basically the same as that in Example 3, except that no surfactant is added in step (1).

[0027] Comparative Example 4 The preparation method of the catalyst is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of a surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 1, except that [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid is replaced with an equimolar amount of [[(2-hydroxyethyl)methylamino]methyl]phosphonic acid (CAS No. 748736-22-3).

[0028] Comparative Example 5 The preparation method of the catalyst is basically the same as that in Example 3, except that the surfactant is replaced with an equal weight of a surfactant prepared by the following method: The preparation method of the surfactant is basically the same as that in Example 1, except that 2-chlorododecanoic acid is replaced with an equimolar amount of 2-chloropentanoic acid.

[0029] The catalysts prepared in the examples and comparative examples were tested for catalytic activity, and the test results are shown in Table 1.

[0030] Catalyst activity evaluation was conducted in a fixed-bed continuous flow reactor. The reactor used a 310S stainless steel reactor tube (Φ25mm×3mm×750mm) simulating an industrial tubular reactor. First, 3g of catalyst was loaded into the isothermal layer of the reactor tube, and quartz sand was filled at both ends to form a fixed bed. Then, nitrogen gas was introduced at a rate of 50ml / min to purge the system and perform an airtightness test. After the test, a mixture of nitrogen and hydrogen gas (hydrogen content 10% v / v) was introduced at a rate of 50ml / min, and the temperature was increased to 250℃ at 10℃ / min and held for 2 hours for reduction activation. Nitrogen gas was then introduced at a rate of 50ml / min, and the temperature was increased to 300℃ at 5℃ / min. 120ml of a methanol-water mixture (methanol to water molar ratio 1:1) was fed into the reaction system using a metering pump at a rate of 2ml / min, while the nitrogen flow rate was gradually reduced until it was shut off. After the system had been running stably for 1 hour, the pressure was increased to 0.3MPa within 30 minutes. After stabilizing the reaction under these conditions for 2 hours, the reaction product was cooled and separated into liquid phase by a condenser. The gas phase was then introduced into a gas chromatograph via a six-way valve for online analysis, with the gas flow rate measured at the terminal using a mass flow meter. The methanol conversion rate was measured again after 600 hours of continuous operation to evaluate the catalyst stability.

[0031] Methanol conversion rate is calculated using the following formula: ; H2 selectivity is calculated using the following formula: ; f is the correction factor. ; Among them, F R For reforming tail gas flow rate, F is the liquid feed rate; ρ is the mixture density; α is the methanol mass content in the mixture; C CO C CO2 T1 and P1 represent the CO and CO2 content in the exhaust gas; T1 and P1 represent the temperature and pressure during the actual reaction evaluation; T2 and P2 represent the temperature (273.15K) and pressure (101.325kPa) under standard conditions.

[0032] Table 1 Performance Test Data

[0033] As can be seen from the data in Table 1, the catalyst prepared by the method of the present invention exhibits high methanol conversion rate and H2 selectivity when used for catalytic methanol-to-hydrogen production, and also demonstrates excellent stability in use.

[0034] This invention achieves precise construction and performance enhancement of catalysts through the synergistic effect of composite support composition regulation and multifunctional surfactants. In the support preparation process, alumina provides a high specific surface area framework, zirconium oxide improves thermal stability and enhances metal-support interactions, and cerium oxide relies on Ce... 3+ / Ce 4+ Reversible oxidation provides oxygen storage and migration capabilities, thereby promoting the activation of water molecules and the oxidative transformation of intermediate species during the reaction process. Simultaneously, the decomposition of polyethylene glycol and urea during calcination forms a hierarchical porous structure, improving the uniformity of the pore volume and pore size distribution of the carrier, which is beneficial for mass transfer of reactants. During the introduction of the active components, the surfactant molecules used simultaneously contain quaternary ammonium salt cations, phosphonic acid groups, carboxyl groups, hydroxyl groups, and long-chain alkyl structures. The phosphonic acid and carboxyl groups can form multi-site coordination interactions with copper and zinc metal ions, regulating the dispersion and nucleation process of metal precursors and inhibiting the migration and aggregation of metal particles during calcination and reduction. The quaternary ammonium salt cation structure has strong electrostatic adsorption capabilities, enhancing the directional adsorption of surfactant molecules on the carrier surface and promoting the uniform distribution of metal precursors on the carrier surface through electrostatic interactions, thereby further improving metal dispersibility. The hydroxyl structure helps enhance the interaction between the molecule and the hydroxyl groups on the carrier surface, improving interfacial bonding. The long-chain alkyl groups form an ordered adsorption layer on the carrier surface, producing a spatial confinement effect on the growth of metal particles, thus significantly improving the dispersion of the active metal. During calcination and reduction, the decomposition of organic components further forms defect sites and anchoring points on the support surface, strengthening the metal-support interface structure. In the methanol steam reforming reaction, highly dispersed copper species act as the main active centers to promote methanol decomposition. Cerium oxide and zinc oxide formed by the calcination decomposition of zinc nitrate synergistically promote the adsorption and activation of water molecules and promote the conversion of the byproduct carbon monoxide through oxygen migration, thereby improving hydrogen selectivity and reducing side reactions. At the same time, the stable metal-support interaction and structural confinement effect effectively inhibit metal sintering, enabling the catalyst to maintain a high methanol conversion rate and hydrogen selectivity during long-term operation, demonstrating excellent stability in use.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A surfactant for preparing catalysts by impregnation method, characterized in that, It has the following chemical structural formula: 。 2. The surfactant according to claim 1, characterized in that, It is obtained by reacting [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid with 2-chlorododecanoic acid.

3. The surfactant according to claim 2, characterized in that, The molar ratio of [[(2-hydroxyethyl)imino]bis(methylene)]diphosphonic acid to 2-chlorododecanoic acid is 1:1.

05.

4. A method for preparing a catalyst by impregnation, characterized in that, Includes the following steps: (1) Alumina, zirconium oxide, cerium oxide, pore-forming agent, surfactant as described in claim 1, and deionized water are mixed and then ball-milled, shaped, dried, and calcined to obtain a composite carrier; (2) Mix copper nitrate, zinc nitrate and deionized water, adjust the pH to obtain the impregnation solution; (3) The composite carrier is impregnated in the impregnation liquid by the equal volume impregnation method, and the catalyst is obtained after drying, calcination and reduction.

5. The method for preparing a catalyst by impregnation according to claim 4, characterized in that, In step (1), the mass ratio of alumina, zirconium oxide and cerium oxide is (6-6.5):(1-1.5):

1.

6. The method for preparing a catalyst by impregnation according to claim 4, characterized in that, In step (1), the pore-forming agent is a mixture of polyethylene glycol and urea in a mass ratio of 1:1; the amount of the pore-forming agent is 4-7% of the total mass of alumina, zirconium oxide and cerium oxide.

7. The method for preparing a catalyst by impregnation according to claim 4, characterized in that, In step (1), the amount of surfactant added is 1-2% of the total mass of alumina, zirconium oxide and cerium oxide.

8. The method for preparing a catalyst by impregnation according to claim 4, characterized in that, In step (2), the mass ratio of copper nitrate to zinc nitrate is (2-3):

1.

9. The method for preparing a catalyst by impregnation according to claim 4, characterized in that, In step (2), the pH is 6.5-7.

5.

10. The application of a catalyst prepared by the method according to any one of claims 4-9 in methanol-to-hydrogen production.

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