A catalyst for hydrogen production by microwave-driven methanol-water reforming

Abstract

The application discloses a kind of catalysts for microwave-driven methanol-water reforming hydrogen production.The catalyst is composite catalyst obtained by CuO / ZnO composite oxide active component being supported on the surface of microwave absorption component, and the microwave absorption component is carbon nanotube or mixture of carbon nanotube and graphite;The mass of microwave absorption component accounts for 10-40wt.% of the mass of the entire catalyst;It is prepared by impregnation loading method.The application uses carbon with appropriate graphitization degree and specific surface area as carrier and as microwave absorption material at the same time, and loading copper-zinc oxide shows excellent wave-absorbing performance and methanol / water reforming reaction performance, and the preparation process is simple, when applied to microwave-driven methanol / water reforming hydrogen production, methanol can be converted to nearly 100% under the condition of using lower molar ratio of methanol / water raw material, and the H2 content in reforming gas product is about 70mol.%, and the CO content is less than 1mol.%.

Description

Technical Field

[0001] This invention relates to a methanol steam reforming hydrogen production catalyst, specifically to the application of this methanol reforming hydrogen production catalyst in a microwave-driven hydrogen production process, belonging to the field of hydrogen energy. Background Technology

[0002] Methanol is a basic raw material for chemical production, abundant in supply, with a high hydrogen-to-carbon ratio, stable properties, and convenient storage and transportation, making it an ideal feedstock for hydrogen production. The main methods for producing hydrogen from methanol include methanol cracking, partial oxidation of methanol, and methanol steam reforming. Among these, methanol steam reforming is simple and easy to implement, with mild reaction conditions, and can produce a high volume ratio of hydrogen and a low content of carbon monoxide. The subsequent purification process is also simple. This has led to the widespread application of methanol steam reforming technology in small-scale industrial hydrogen production and its significant potential in the fuel cell field.

[0003] Traditional methanol steam reforming technology employs conventional externally heated fixed-bed reactors. While fixed-bed reactors offer uniform heat transfer and high operational flexibility, they are limited by the heating mode and require substantial amounts of insulation material. Furthermore, heat transfer within the bed leads to a significant radial temperature gradient in the catalyst bed, affecting the reaction rate at the reactor center and resulting in substantial energy loss due to low heat transfer efficiency. Conventional heating processes typically involve large-scale equipment, making miniaturization difficult and unsuitable for applications requiring rapid start-up and shutdown, such as supplying hydrogen to hydrogen fuel cell vehicles. Unlike the heat conduction heating method of traditional fixed-bed reactors, microwave reactors can instantly transfer energy to the catalyst particles in the form of electromagnetic waves, utilizing the catalyst itself for heating. This achieves efficient energy utilization while enabling rapid start-up or shutdown of the reforming reaction. Microwave heating provides a uniform temperature distribution within the catalyst bed, effectively utilizing the catalyst surface. This significantly reduces the amount of catalyst required, allowing for a more compact and miniaturized system, thus reducing costs. Using catalysts adapted to microwave conditions, methanol reforming catalytic reactions can efficiently produce hydrogen at a reaction temperature of only 200-300℃.

[0004] Traditional thermocatalytic methanol / water reforming for hydrogen production primarily uses copper-zinc active components supported on alumina, zirconium oxide, or similar materials as catalysts. However, alumina and zirconium oxide supports do not exhibit significant microwave responsiveness. Therefore, the methanol / water reforming catalysts described above, suitable for conventional thermal processes, are not applicable to microwave processes. Summary of the Invention

[0005] One of the objectives of this invention is to provide a microwave-driven methanol-water reforming catalyst for hydrogen production, which has high catalytic efficiency and fast reaction rate.

[0006] The second objective of this invention is to provide the application of the above-mentioned catalyst in microwave-driven methanol-water reforming hydrogen production reaction.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a microwave-driven methanol-water reforming catalyst for hydrogen production. The catalyst is a composite catalyst obtained by supporting a CuO / ZnO composite oxide active component on the surface of a microwave-absorbing component. The microwave-absorbing component is carbon nanotubes or a mixture of carbon nanotubes and graphite. The carbon nanotubes are moderately graphitized multi-walled carbon nanotubes with a carbon content ≥98 wt.%, a diameter of 5–15 nm, an aspect ratio of 600–10000, and the Raman spectrum intensity ratio of the D peak to the G peak is used to measure the degree of graphitization. D / I G Its specific surface area is 50–300 m², ranging from 0.01 to 1.0. 2 / g, resistivity 0.001~0.015Ω·m (four-probe method, probe contact area 1cm²) 2 (Sample test amount 0.1g, measured under 30MPa compaction pressure); the graphite particle size range is 2000-5000 mesh, and the carbon content is ≥99wt.%; the mass of the microwave absorbing component accounts for 10-40wt.% of the total catalyst mass.

[0009] As a further preferred embodiment of the present invention, the microwave absorbing component accounts for 20 to 40 wt.% of the total catalyst mass.

[0010] As a further preferred embodiment of the present invention, the molar ratio of Cu to Zn in the active component of the CuO / ZnO composite oxide is 1.

[0011] As a further preferred embodiment of the present invention, the catalyst is also doped with a modifying element, which is one or more of cerium, zirconium, palladium, and platinum, and the modified component accounts for 5 to 40 wt.% of the total mass of the catalyst. More preferably, the proportion is 10 to 20 wt.%.

[0012] As a further preferred embodiment of the present invention, the catalyst is prepared by the following steps:

[0013] A Cu / Zn composite oxide precursor mixture is prepared by mixing copper and zinc precursors with corresponding Cu / Zn molar ratios, followed by adding 2–5 times the mass of distilled water to form a CuO / ZnO composite oxide precursor solution. A microwave-absorbing component is then added to the solution, followed by ultrasonic treatment for 30–60 minutes, stirring at room temperature for 2–5 hours, drying the solution, and finally calcining it in an inert gas atmosphere at 400–500°C. Strict control of these calcination conditions prevents the oxidizing properties of the nitrate precursor from affecting the graphitization degree of the carbon nanotube support, thus ensuring the consistency of catalyst performance.

[0014] As a further preferred embodiment of the present invention, it further includes: adding a nitrate, acetate, or hydroxide containing the modified element to the CuO / ZnO composite oxide precursor mixed solution.

[0015] As a further preferred embodiment of the present invention, the copper precursor is one or more of copper nitrate and its hydrate, copper acetate and its hydrate; the zinc precursor is one or more of zinc nitrate and its hydrate, zinc acetate and its hydrate, zinc chloride and its hydrate, and zinc hydroxide.

[0016] As a further preferred embodiment of the present invention, the drying temperature is 100–160°C.

[0017] Secondly, the present invention provides the application of the above-mentioned catalyst in a microwave-driven methanol-water reforming hydrogen production reaction.

[0018] The suitable water-to-ethanol molar ratio for the methanol-water aqueous solution feedstock is 1.0–1.3, preferably within the range of 1.0. During the reaction, the microwave radiation power density is controlled between 20 and 400 kW / m². 3 Preferred power is 50-200 kW / m³. 3 .

[0019] The catalyst can be activated directly by introducing methanol / water feedstock under microwave conditions, without the need for additional H2 pre-reduction. Under methanol / water feedstock conditions, once the preset reaction temperature of 200–270°C is reached, a stable H2 / CO2 mixed gas flow with a CO content of less than 1 mol% can be rapidly achieved.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The catalyst provided by this invention uses carbon nanotubes, graphite, or other carbon materials with suitable graphitization degree and specific surface area as supports and simultaneously as microwave absorbing materials. The supported copper-zinc oxide exhibits excellent microwave absorption performance and methanol / water reforming reaction performance. The reactivity and selectivity of the copper-zinc catalyst with carbon nanotubes as supports can be further improved after elemental modification, which is beneficial for significantly reducing the CO content in the reforming product gas stream of methanol / water feedstock under low water-to-methanol ratio conditions.

[0022] 2. This invention selects a carbon support with suitable graphitization degree and specific surface area, which can significantly improve the ability of copper-zinc catalysts to absorb microwaves and convert them into energy forms such as heat. Simultaneously, the larger specific surface area of ​​the carbon material primarily improves the dispersion of the copper-zinc active components. Therefore, compared to copper-zinc catalysts supported on traditional Al2O3, ZrO2, etc., the activity of copper-zinc catalysts in methanol / water reforming for hydrogen production can be improved. Combining the two major functions of microwave absorption and dispersion of active components, the carbon material support for copper-zinc catalysts involved in this invention can greatly improve the heating of the catalyst at the microscale, facilitating the direct transfer of energy to the active sites of the catalytic reaction and driving the reforming reaction, thereby improving the energy efficiency of the catalytic reforming hydrogen production process and reducing the energy consumption of the reforming hydrogen production process.

[0023] 3. Based on the beneficial effects 1 and 2, the copper-zinc catalyst provided by this invention can not only be efficiently applied to the microwave-driven methanol / water reforming hydrogen production process, but also achieve near 100% methanol conversion under the condition of using a low water-to-methanol molar ratio (1.0-1.3:1) methanol / water feedstock, and the H2 content in the reformed gas product is ~70 mol.% and the CO content is less than 1 mol.%.

[0024] 4. This invention controls the calcination conditions for catalyst preparation at 400–500℃, effectively achieving complete decomposition of copper and zinc precursors. This calcination temperature range also ensures that the CuO and ZnO nanoparticles generated from precursor decomposition do not sinter together, thus promoting high dispersion of the active components. Furthermore, the calcination process must be carried out under an inert atmosphere. An inert atmosphere avoids significant ablation of the carbon nanotube support by oxygen in the air and the highly oxidizing copper and zinc nitrate precursors used within the 400–500℃ range, ensuring the stability and controllability of the carbon nanotube support and the overall catalyst performance. In practice, under air-atmosphere calcination conditions, the ablation rate of the carbon nanotube support is typically as high as 20–30%, significantly affecting important indicators such as the carbon support content and graphitization degree of the final catalyst, making it difficult to ensure controllable catalyst performance. In contrast, calcination under inert atmospheres such as N2 and Ar allows the ablation rate of the carbon nanotube support in the catalyst to be stably controlled below 2%, resulting in highly consistent catalyst performance across different batches. Attached Figure Description

[0025] Figure 1 The composition of microwave methanol-water reformed products at different temperatures in Comparative Example 1 is shown.

[0026] Figure 2 The composition of microwave methanol-water reformed products at different temperatures in Comparative Example 2;

[0027] Figure 3 The composition of microwave methanol-water reformed products at different temperatures in Comparative Example 3;

[0028] Figure 4 The composition of microwave methanol-water reformed products at different temperatures in Comparative Example 4;

[0029] Figure 5 The composition of the microwave methanol-water reforming products at different temperatures in Example 1;

[0030] Figure 6 The change in conversion rate of methanol-water reforming with temperature for different catalysts in microwave chemiluminescence;

[0031] Figure 7 The composition of the microwave methanol-water reforming products at different temperatures in Example 4;

[0032] Figure 8 The composition of the microwave methanol-water reforming products at different temperatures in Example 5;

[0033] Figure 9 The change in microwave methanol-water reforming conversion rate with temperature for catalysts with different carbon nanotube contents;

[0034] Figure 10 Scanning electron microscope (SEM) images of the catalyst and its corresponding carbon nanotube support in Example 1: (a) Scanning electron microscope image of the catalyst in Example 1; (b) Scanning electron microscope image of the corresponding carbon nanotube support.

[0035] Figure 11 The X-ray diffraction patterns of Comparative Examples 1, 3-4 and Example 1 are shown.

[0036] Figure 12 The composition of the microwave methanol-water reformed products at different temperatures in Example 6;

[0037] Figure 13 The effect of cerium-modified catalysts on the CO content in the product at different temperatures;

[0038] Figure 14 A comparison of the heating curves of catalysts supported by single carbon nanotubes and catalysts supported by carbon nanotubes / graphite (with the same total carbon content) under microwave conditions.

[0039] Figure 15For comparison of the performance, physicochemical properties, and heating characteristics of the microwave methanol / water reforming hydrogen production catalysts in the comparative examples and embodiments: (a) is a graph showing the methanol conversion rate of each catalyst as a function of reaction temperature; (b) is a graph showing the CO content in the reforming tail gas of each catalyst as a function of reaction temperature; (c) is a graph showing the dielectric constant of each catalyst; (d) is a graph showing the dielectric loss factor of each catalyst; (e) is a graph showing the heating curve of each catalyst at the same power (300W); and (f) is a graph showing the resistivity of each catalyst bed. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0041] Comparative Example 1

[0042] Catalyst preparation:

[0043] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0044] (2) The obtained mixed solution was thoroughly dried in an oven at 150°C. The dried product was placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product was then calcined at 500°C for 1 hour to obtain catalyst 1#.

[0045] Experimental procedure:

[0046] (1) Take 3g of catalyst 1# and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0047] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0048] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 1000 W, corresponding to a microwave radiation power density of 500 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 270°C.

[0049] Under the above conditions, methanol showed almost no reaction at 190℃, and the conversion rate was 66.11% at 270℃, indicating incomplete conversion. Within the temperature range of 190–270℃, the CO content in the product gas increased with increasing temperature. The results of Comparative Example 1 are shown in Table 1 and [Table data missing]. Figure 1 .

[0050] Table 1. Composition of microwave methanol-water reforming products and methanol conversion rate at different temperatures in Comparative Example 1

[0051]

[0052] Comparative Example 2

[0053] Catalyst preparation:

[0054] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0055] (2) Add 0.5g of silicon carbide (α phase, purity ≥99wt.%, particle size 150 mesh) to the precursor mixture solution obtained in step (1), sonicate for 30min, stir at room temperature for 3 hours, and then put the resulting mixture into an oven at 150℃ to dry thoroughly.

[0056] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 2# (the mass ratio of silicon carbide support in the final catalyst is 10%).

[0057] Experimental procedure:

[0058] (1) Take 3g of catalyst 2# and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0059] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0060] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 1000 W, corresponding to a microwave radiation power density of 500 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 270°C.

[0061] Under the above conditions, the conversion rate of methanol at 270℃ was 87.89%, indicating incomplete conversion. Within the temperature range of 190–270℃, the CO content in the product gas increased with increasing temperature. The results of Comparative Example 2 are shown in Table 2 and... Figure 2 .

[0062] Table 2. Composition of microwave methanol-water reforming products and methanol conversion rate at different temperatures in Comparative Example 2

[0063]

[0064] Comparative Example 3

[0065] Catalyst preparation:

[0066] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0067] (2) Add 0.5g of graphite powder (particle size of 5000 mesh, carbon content ≥99wt.%) to the precursor mixture solution obtained in step (1), sonicate for 30min, stir at room temperature for 3 hours, and then put the resulting mixture into an oven at 150℃ to dry thoroughly.

[0068] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 3# (the mass ratio of the support graphite powder in the final catalyst is 10%).

[0069] Experimental procedure:

[0070] (1) Take 3g of catalyst #3 and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0071] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0072] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 1000 W, corresponding to a microwave radiation power density of 500 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 270°C.

[0073] Under the above conditions, the conversion rate of methanol at 270℃ was 77.47%, indicating incomplete conversion. Within the temperature range of 190–270℃, the CO content in the product gas increased with increasing temperature. The results for Comparative Example 3 are shown in Table 3. Figure 3 .

[0074] Table 3. Composition of microwave methanol-water reforming products and methanol conversion rate at different temperatures in Comparative Example 3

[0075]

[0076] Comparative Example 4

[0077] Catalyst preparation:

[0078] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0079] (2) Add 0.5g of conductive carbon black powder (carbon content ≥ 99.5wt.%, BET specific surface area 61m²). 2 / g, four-probe method, probe contact area 1cm² 2 The sample test amount is 0.1g, and the resistivity under 30MPa compaction pressure is 1~1.2Ω·m) to the precursor mixture solution obtained in step (1), sonicated for 30min, stirred at room temperature for 3 hours, and then the mixture is placed in an oven at 150℃ to dry thoroughly.

[0080] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst #4 (the mass ratio of conductive carbon black in the final catalyst is 10%).

[0081] Experimental procedure:

[0082] (1) Take 3g of catalyst #4 and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0083] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0084] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 270°C.

[0085] Under the above conditions, methanol reacts completely at 270℃. Within the temperature range of 190–270℃, the CO content in the product gas increases with increasing temperature. The results of Comparative Example 4 are shown in Table 4. Figure 4 .

[0086] Table 4. Composition of microwave methanol-water reforming products and methanol conversion rate at different temperatures in Comparative Example 4

[0087]

[0088] Example 1

[0089] Catalyst preparation:

[0090] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0091] (2) Add 0.5g of carbon nanotubes (moderately graphitized multi-walled carbon nanotubes, carbon content ≥99wt.%, tube diameter 8-15nm, aspect ratio 1000-2000, Raman spectrum D peak to G peak intensity ratio I D / I G The specific surface area is 246 m², with a value of 0.867. 2 / g, four-probe method, probe contact area 1cm² 2 The sample test amount was 0.1g, and the resistivity was measured to be 0.005Ω·m under a compaction pressure of 30MPa. The sample was added to the precursor mixture obtained in step (1), ultrasonically treated for 30min, stirred at room temperature for 3 hours, and then the mixture was thoroughly dried in an oven at 150℃.

[0092] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 5# (the mass ratio of the carrier carbon nanotubes in the final catalyst is 10%).

[0093] Figure 10 The image shown is a scanning electron microscope (SEM) image of the catalyst from Example 1. The SEM image reveals that copper-zinc active nanoparticles are uniformly dispersed on the surface of the carbon nanotube support, and the carbon nanotubes form a linear network between the copper-zinc active nanoparticles. Combined with the excellent conductivity of carbon nanotubes, this network structure will improve the overall conductivity of the catalyst, and theoretically, it could be beneficial for promoting microwave-driven redox reactions such as methanol / water reforming.

[0094] Figure 11The X-ray diffraction patterns are shown for Comparative Examples 1, 3-4, and Example 1. These patterns reveal that the CuO and ZnO diffraction peak intensities of the catalysts supported by graphite, carbon black, and carbon nanotubes all decreased while the full width at half maximum (FWHM) increased, exhibiting a diffraction trend. This indicates that the support enhanced the dispersion of the copper and zinc active components. Compared to graphite as the support, the carbon nanotube-supported catalyst showed the disappearance of the carbon diffraction peak at 2θ = 26.3°, indirectly indicating that the graphitization degree of carbon nanotubes was weaker than that of graphite. Furthermore, the CuO and ZnO diffraction peak intensities of the carbon nanotube-supported catalyst decreased while the FWHM further increased, suggesting that carbon nanotubes promoted better dispersion of the copper and zinc components. The enhanced dispersion of the active components theoretically benefits the catalyst's activity.

[0095] Experimental procedure:

[0096] (1) Take 3g of catalyst 5# and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0097] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0098] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 250°C.

[0099] Under the above conditions, methanol can react completely at 250℃. Within the temperature range of 190~250℃, the CO content in the product gas increases with increasing temperature. The results of Example 1 are shown in Table 5 and... Figure 5 .

[0100] Table 5. Composition of microwave methanol-water reforming products and methanol conversion rate at different temperatures in Example 1

[0101]

[0102] Example 2

[0103] Catalyst preparation:

[0104] (1) Take 6.83g of copper nitrate trihydrate and 8.22g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0105] (2) Add 1g of carbon nanotubes (the same as in Example 1) to the precursor mixture solution obtained in step (1), sonicate for 30min, stir at room temperature for 3 hours, and then put the mixture into an oven at 150℃ to dry thoroughly.

[0106] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 6# (the mass ratio of the carrier carbon nanotubes in the final catalyst is 20%).

[0107] Experimental procedure:

[0108] (1) Take 3g of catalyst 6# and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. Quartz wool is placed on the top and bottom of the quartz tube. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0109] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0110] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 250°C.

[0111] Under the above conditions, methanol reacts completely at 250°C. Within the temperature range of 190–250°C, the CO content in the product gas increases with increasing temperature. The results of Example 2 are shown in Table 6. Figure 7 .

[0112] Table 6. Composition and methanol conversion rate of microwave methanol-water reforming products at different temperatures in Example 2

[0113]

[0114] Example 3

[0115] Catalyst preparation:

[0116] (1) Take 4.67g of copper nitrate trihydrate and 5.62g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0117] (2) Add 2g of carbon nanotubes (the same as in Example 1) to the precursor mixture solution obtained in step (1), sonicate for 30min, stir at room temperature for 3 hours, and then put the mixture into an oven at 150℃ to dry thoroughly.

[0118] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 7# (the mass ratio of the carrier carbon nanotubes in the final catalyst is 40%).

[0119] Experimental procedure:

[0120] (1) Take 3g of catalyst #7 and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0121] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0122] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 250°C.

[0123] Under the above conditions, methanol can react completely at 230℃. Within the temperature range of 170~230℃, the CO content in the product gas increases with increasing temperature. The results of Example 3 are shown in Table 7 and... Figure 8 As shown.

[0124] Table 7. Composition and methanol conversion rate of microwave methanol-water reforming products at different temperatures in Example 3

[0125]

[0126] Example 4

[0127] Catalyst preparation:

[0128] (1) Take 4.67g of copper nitrate trihydrate, 5.62g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and 0.63g of cerium nitrate hexahydrate and add them to 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0129] (2) Add 0.5g of carbon nanotubes (the same as in Example 1) to the precursor mixture solution obtained in step (1), sonicate for 30min, stir at room temperature for 3 hours, and then put the mixture into an oven at 150℃ to dry thoroughly.

[0130] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst #8 (the mass ratio of the carrier carbon nanotubes in the final catalyst is 10%).

[0131] Experimental procedure:

[0132] (1) Take 3g of catalyst #8 and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0133] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0134] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 250°C.

[0135] Under the above conditions, the methanol conversion rate reached 98.21% at 270℃. Within the temperature range of 190–270℃, the CO content in the product gas increased with increasing temperature, but significantly decreased compared to the CO content of the unmodified catalyst. The results of Example 4 are shown in Table 8. Figure 12 As shown.

[0136] Table 8. Composition and methanol conversion rate of microwave methanol-water reforming products at different temperatures in Example 4

[0137]

[0138] Example 5

[0139] Catalyst preparation:

[0140] (1) Take 4.67g of copper nitrate trihydrate and 5.62g of zinc nitrate hexahydrate (copper-zinc molar ratio of 1:1) and add 50mL of deionized water and stir thoroughly to form a precursor mixed solution;

[0141] (2) Add 0.5g of carbon nanotubes (same as in Example 1) and 0.5g of graphite (3000 mesh particle size, carbon content ≥99wt.%) to the precursor mixture solution obtained in step (1), sonicate for 30 min, stir at room temperature for 3 hours, and then put the mixture into an oven at 150℃ to dry thoroughly.

[0142] (3) The dried product in step (2) is placed in a tube furnace and heated to 500°C at a rate of 10°C / min in a nitrogen atmosphere. The product is then calcined at 500°C for 1 hour to obtain catalyst 9# (the mass ratio of the support in the final catalyst is 20%).

[0143] Experimental procedure:

[0144] (1) Take 3g of catalyst 9# and put it into a quartz reaction tube with a length of 60cm and an inner diameter of 12mm. The quartz tube is filled with quartz wool at the top and bottom. The catalyst filling height is 8cm. Put the quartz tube containing the catalyst into the center of the microwave reactor.

[0145] (2) Before the experiment, purge with 99.999% high-purity argon gas at a flow rate of 400 mL / min for 10 min;

[0146] (3) The reaction was carried out using a methanol-water solution (water / ethanol molar ratio of 1:1) introduced into the quartz reaction tube at a flow rate of 0.06 mL / min via a medium-pressure constant flow pump with an accuracy of ±0.5%. Simultaneously, the microwave reactor was activated with a power of 220 W, corresponding to a microwave radiation power density of 110 kW / m². 3 The product was obtained by reacting at different temperatures ranging from 190 to 250°C.

[0147] Under the above conditions, the methanol conversion rate reached 98% at 250℃, which was comparable to that of a carbon nanotube-supported catalyst with the same content. However, it exhibited better microwave response under microwave conditions, and the heating rate of the catalyst bed under microwave radiation of the same power (300W) was greatly enhanced, demonstrating stronger energy-saving potential. The methanol-water reforming reaction results and reaction bed heating curves of Example 5 are shown in Tables 9 and 9, respectively. Figure 14 .

[0148] Table 9. Comparison of composition and methanol conversion rate of microwave methanol-water reforming products at different temperatures in Examples 2 and 5

[0149]

[0150] Comparing Comparative Examples 1-4 and Example 1, the effects of different supports on the reforming performance of the catalyst are as follows: Figure 6As shown in the figure. The results indicate that carbon nanotubes, conductive carbon black, and graphite, as carbon supports, all significantly enhanced the activity of copper-zinc catalysts in methanol / water reforming for hydrogen production under microwave conditions. However, under the same carbon support content, carbon nanotubes showed the strongest ability to improve the microwave reforming hydrogen production performance of copper-zinc catalysts.

[0151] Comparing Examples 1-3, the effect of different carbon nanotube contents on the reforming performance of the catalyst is as follows: Figure 9 As shown, within the range of 10–40 wt.%, the microwave reforming hydrogen production activity of the copper-zinc catalyst significantly increases with increasing carbon nanotube support content. When the carbon nanotube content exceeds 40%, the dispersion of the copper-zinc active components and the overall conductivity of the catalyst no longer significantly improve; on the contrary, the overall catalyst activity may decrease due to the reduced content of the copper-zinc active components. With a carbon nanotube content of 40 wt.%, 100% methanol conversion can be achieved at 230℃. Compared to the implementation cases with 10 wt.% and 20 wt.% carbon nanotubes, the 100% methanol conversion temperature is reduced by 20℃ or more. This reduction in reforming temperature is beneficial for further significantly reducing the energy consumption of the methanol / water reforming hydrogen production process.

[0152] Comparing Examples 1 and 4, the effect of cerium-modified catalyst on CO content in reformed gas is as follows: Figure 13 As shown, cerium modification can significantly suppress CO generation in carbon nanotube-supported copper-zinc catalysts at methanol conversion rates close to 100%. Under the same reaction conditions, 5 wt.% cerium modification can reduce the CO content in the reformed gas stream by 50 wt.% or more, fully demonstrating the effectiveness of cerium modification.

[0153] Comparative results of Examples 2 and 5 (Table 9 and 5) Figure 14 This indicates that, compared with catalysts using carbon nanotubes as a single support, catalysts using a mixture of carbon nanotubes and graphite as a support further enhance or improve microwave heating of the catalyst bed while maintaining the same level of catalytic activity, which is beneficial for improving the energy efficiency of the reforming hydrogen production process.

[0154] The significant differences in hydrogen production results between the comparative examples and embodiments above demonstrate the crucial influence of the support on the performance of microwave-catalyzed reforming for hydrogen production. Therefore, determining a suitable support to ensure a high degree of compatibility between the copper-zinc active components and the support, thereby achieving overall high catalyst performance, is the technical problem this invention aims to solve. The strength of the support's ability to absorb microwaves and convert them into heat is positively correlated with the endothermic reaction of methanol / water reforming for hydrogen production. From the perspective of microwave thermal effects alone, superior dielectric properties (representing stronger microwave absorption capabilities, specifically the dielectric constant) and a faster heating rate under microwave radiation are more beneficial to the methanol / water reforming for hydrogen production. For the catalysts in each comparative example and embodiment, physical properties such as dielectric properties and conductivity were tested, and the results are as follows: Figure 15As shown. For convenience, the catalysts in the comparative examples and embodiments are named in the format "CuZnXX-YY", where XX represents the support used (SiC for silicon carbide, CNTs for carbon nanotubes, and G for graphite), and YY represents the mass fraction of the support in the entire catalyst. Following this naming convention, the catalyst for Comparative Example 1 is CuZn; the catalyst for Comparative Example 2 is CuZnSiC-10; the catalyst for Comparative Example 3 is CuZnG-10; the catalyst for Example 1 is CuZnCNTs-10; and the catalyst for Example 3 is CuZnCNTs-40. However, the hydrogen production results of the above comparative examples and embodiments are not consistent with the dielectric properties of their respective supports and microwave radiation heating rates. This indicates that considering only the thermal effect of microwaves does not necessarily guarantee a highly efficient methanol / water microwave reforming hydrogen production catalyst.

[0155] Depend on Figure 15 It can be seen that CuZnG-10 exhibits significantly better dielectric properties and heating rate than CuZnCNTs-10. Based on this, if only the thermal effect of microwaves is utilized, graphite as the microwave absorbing component is more advantageous than carbon nanotubes. However, besides the thermal effect of microwaves, some microwaves absorbed by the catalyst material will induce the formation of an internal electric field in the catalyst, generating polarization and storing energy in the catalyst material in the form of potential energy. The electron migration process under this internal electric field is also the energy transfer process. The conductivity of the catalyst material determines the strength of electron migration, thus affecting the overall electron migration in the methanol / water reforming redox reaction process. This application uses carbon nanotubes as the microwave absorbing component, whose one-dimensional linear structure is more conducive to forming a rich conductive network structure than the two-dimensional layered graphite. Figure 10 a and Figure 15 (f) shows that the bed resistivity of CuZnCNTs-10 at a compaction pressure of 2 MPa is ~85 Ω·m, while the bed resistivity of CuZnG-10 is ~135 Ω·m, which corroborates this result. The bed conductivity of CuZnCNTs-10 is much better than that of CuZnG-10, thus demonstrating that while CuZnCNTs-10 is inferior in dielectric properties and microwave heating performance, its reformability is far superior to that of CuZnG-10 (as shown in Tables 3 and 5). Figure 15 (As shown in a and 15b). Furthermore, carbon nanotubes, compared to supports such as graphite and SiC, provide a larger specific surface area, promoting the dispersion of the CuZn active component and thus benefiting the catalyst's hydrogen production performance during reforming. Therefore, for microwave-driven methanol / water reforming hydrogen production catalysts, it is necessary to comprehensively consider and balance factors beneficial to methanol / water reforming hydrogen production performance, such as the support's microwave absorption response, the dispersion of the active component, and conductivity. This will allow for the determination of suitable supports and the synthesis of structurally sound catalysts, creatively leveraging the synergistic enhancement effect of microwave thermal and non-thermal effects to achieve highly efficient methanol / water reforming hydrogen production.

[0156] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A microwave-driven catalyst for methanol-water reforming to produce hydrogen, characterized in that, The catalyst is a composite catalyst obtained by supporting a CuO / ZnO composite oxide active component on the surface of a microwave absorbing component. The microwave absorbing component is carbon nanotubes or a mixture of carbon nanotubes and graphite. The carbon nanotubes are moderately graphitized multi-walled carbon nanotubes with a carbon content ≥98 wt.%, a diameter of 5~15 nm, and an aspect ratio of 600~10000. The degree of graphitization is measured by the ratio of the D peak to the G peak intensity in the Raman spectrum. D / I G Its specific surface area is 50~300 m², ranging from 0.01 to 1.

0. 2 / g, resistivity 0.001~0.015Ω·m; the graphite particles have a particle size range of 2000~5000 mesh, carbon content ≥99wt.%; the microwave absorbing component accounts for 10~40 wt.% of the total catalyst mass. The catalyst is prepared by the following steps: a copper precursor and a zinc precursor with a Cu / Zn molar ratio are mixed, and then 2 to 5 times the mass of distilled water is added to the mixture to prepare a CuO / ZnO composite oxide precursor mixed solution. Microwave absorbing components are then added to the mixed solution, and the mixture is ultrasonically treated for 30 to 60 minutes. After stirring at room temperature for 2 to 5 hours, the moisture is dried, and finally the catalyst is calcined in an inert gas at 400 to 500°C.

2. The microwave-driven methanol-water reforming hydrogen production catalyst according to claim 1, characterized in that, The microwave absorbing component accounts for 20-40 wt.% of the total catalyst mass.

3. The microwave-driven methanol-water reforming hydrogen production catalyst according to claim 1, characterized in that, The molar ratio of Cu to Zn in the active component of the CuO / ZnO composite oxide is 1.

4. A microwave-driven methanol-water reforming hydrogen production catalyst according to any one of claims 1 to 3, characterized in that, The catalyst is also doped with a modifying element, which is one or more of cerium, zirconium, palladium and platinum, and the modified component accounts for 5 to 40 wt.% of the total catalyst mass.

5. The microwave-driven methanol-water reforming hydrogen production catalyst according to claim 1, characterized in that, Also includes: Nitrates, acetates, or hydroxides containing modified elements are added to the CuO / ZnO composite oxide precursor mixed solution.

6. The microwave-driven methanol-water reforming hydrogen production catalyst according to claim 1, characterized in that, The copper precursor is one or more of copper nitrate and its hydrate, copper acetate and its hydrate; the zinc precursor is one or more of zinc nitrate and its hydrate, zinc acetate and its hydrate, zinc chloride and its hydrate, and zinc hydroxide.

7. The microwave-driven methanol-water reforming hydrogen production catalyst according to claim 1, characterized in that, The drying temperature is 100~160℃.

8. The application of the catalyst according to claim 1 in a microwave-driven methanol-water reforming hydrogen production reaction, wherein the water:methanol molar ratio of the methanol / water mixed feedstock is 1.

0.

9. The application according to claim 8, characterized in that, During the reaction, the microwave radiation power density was controlled between 20 and 400 kW / m². 3 .

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