Supported methanol steam reforming hydrogen production catalyst and preparation method and application thereof

Abstract

The invention discloses a supported catalyst for hydrogen production by methanol steam reforming and a preparation method and application thereof, the catalyst is composed of active components and a carrier, the active components are CuO and ZnO, and the carrier is g-C3N4-NS; according to the method, the carbon nitride nanosheet (g-C3N4-NS) is used as a carrier for the first time, the CuO-ZnO / g-C3N4-NS methanol steam reforming hydrogen production Cu-based catalyst is prepared through a reverse coprecipitation method, and the catalyst has relatively high activity, the methanol conversion rate is greater than 92%, the CO selectivity is low, and the catalyst has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen production catalysts, and in particular relates to a supported methanol steam reforming hydrogen production catalyst and a preparation method and application thereof. Background Art

[0002] Due to the continuous exploitation and consumption of fossil energy, environmental problems are becoming increasingly serious. To address this problem, people have begun to pay attention to the research and application of clean, green and alternative energy. Hydrogen energy, as a recognized clean secondary energy source, has been widely studied and has broad development prospects.

[0003] The research on hydrogen production technology is of great significance to the application of hydrogen energy. Among various hydrogen production processes, methanol steam reforming (MSR) hydrogen production process has gradually become a key development process in the field of hydrogen production due to its advantages such as easy storage and transportation of raw materials, mild reaction conditions, low energy consumption, high hydrogen production efficiency, low CO content and easy separation. The core technology of hydrogen production technology is the catalyst. At present, Cu-based catalysts are widely used in methanol steam reforming hydrogen production process due to their high reactivity, H2 selectivity, mature preparation process and low cost. However, the reactivity and stability of Cu-based catalysts need to be improved.

[0004] The g-C3N4 material has a two-dimensional layered structure similar to graphene, with a distance of about 3.3nm between layers, and the layers are connected by weak van der Waals forces. Compared with some traditional semiconductor catalysts, the advantages of non-metallic polymer g-C3N4 are very prominent: 1. Easy to prepare; 2. Excellent physical and chemical stability; 3. Easy to control the surface. Nanosheets (g-C3N4-NS) with a thickness of about 2nm can be prepared by thermal oxidation exfoliation, which can reach 306nm. 2 / g specific surface area, which is suitable as a support material for Cu-based catalysts.

[0005] Therefore, the present application aims to develop a Cu-based catalyst with g-C3N4-NS as a carrier to further improve the reaction activity, stability and other properties of the Cu-based catalyst and achieve better catalytic effect. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a supported methanol steam reforming hydrogen production catalyst and a preparation method and application thereof.

[0007] The present invention prepares a methanol steam reforming hydrogen production catalyst containing active components CuO and ZnO loaded on g-C3N4-NS by a reverse coprecipitation method. The catalyst prepared by the method has high methanol steam reforming hydrogen production activity at low temperatures and low CO selectivity, thereby achieving a better catalytic effect.

[0008] The technical solution of the present invention is as follows:

[0009] A supported methanol steam reforming hydrogen production catalyst, consisting of an active component and a carrier;

[0010] The active components are CuO and ZnO, and the support is g-C3N4-NS (g-C3N4 nanosheets);

[0011] Based on the total mass of the catalyst, the mass proportion of CuO is 55-75%, the mass proportion of ZnO is 15-35%, and the mass proportion of g-C3N4-NS is 10%.

[0012] In the present invention, the preparation method of the carrier g-C3N4-NS is as follows:

[0013] (1) adding urea into a crucible, placing it in a muffle furnace, heating it to 550°C at a rate of 2.3°C / min, calcining it for 4 hours, and then cooling it to room temperature at a rate of 1°C / min to obtain g-C3N4 (yellow solid, ground into powder for later use);

[0014] In step (1), the crucible is covered with a lid and wrapped with tin foil for calcination;

[0015] (2) adding g-C3N4 into a crucible, placing it in a muffle furnace, heating it to 500°C at a rate of 5°C / min, calcining it for 2h, and then naturally cooling it to room temperature to obtain g-C3N4-NS;

[0016] In step (2), the crucible is opened for calcination.

[0017] The preparation method of the supported methanol steam reforming hydrogen production catalyst of the present invention is as follows:

[0018] S1: Dissolve copper nitrate and zinc nitrate in deionized water to obtain solution A, and disperse ammonium carbonate and g-C3N4-NS in deionized water to obtain suspension B;

[0019] Specifically, ammonium carbonate and g-C3N4-NS were added to deionized water and stirred, and after the ammonium carbonate was dissolved, ultrasonic treatment was performed for 30 minutes to obtain suspension B;

[0020] "Solution A" and "suspension B" have no special meanings. They are marked as "A" and "B" only to distinguish different mixed systems.

[0021] S2: Suspension B was placed in a water bath, and solution A was added dropwise to suspension B at 65°C and stirring (speed 400 rpm) for co-precipitation. After the precipitation was completed, constant temperature stirring was continued for 4 h, followed by ultrasonic treatment for 30 min, and then the mixture was aged at room temperature for 18 h;

[0022] The drop rate of solution A is preferably 1 to 2 drops / s;

[0023] S3: The aged mixture is filtered, washed, and dried to obtain a precursor, and the obtained precursor is placed in a tube furnace, and the temperature is set to 350-450° C., the time is 3-4 hours, and the heating rate is 2-3° C. / min, and calcined in an Ar atmosphere. After the calcination is completed, it is naturally cooled to room temperature to obtain the supported methanol steam reforming hydrogen production catalyst;

[0024] Specifically, the aged mixture is poured into a Buchner funnel for suction filtration, then washed with deionized water, and dried in an oven at 60-70° C.; the dried precursor is ground and placed in a porcelain boat, which is then calcined in a tubular furnace.

[0025] The application method of the supported methanol steam reforming hydrogen production catalyst of the present invention is as follows:

[0026] The supported methanol steam reforming hydrogen production catalyst and quartz sand are uniformly mixed, loaded into a quartz tube, placed in a fixed bed reactor, and H2 / Ar mixed gas is introduced, and the temperature is raised from room temperature to 300°C and kept for 90 minutes for reduction activation; after the activation is completed, the H2 / Ar mixed gas is cut off, and the reaction gas is introduced, and the temperature is set at 200-300°C to carry out methanol steam reforming hydrogen production reaction, and the gas chromatograph is used for detection;

[0027] The reaction gas composition is as follows: 10% methanol vapor, 10.5% water vapor, and 79.5% nitrogen by volume.

[0028] The technical principles of the present invention include:

[0029] The Cu-based catalyst for hydrogen production by methanol steam reforming of the present invention uses carbon nitride nanosheets (g-C3N4-NS) as a carrier. During the preparation process, a thinner carbon nitride nanosheet (g-C3N4-NS) is first prepared by a thermal oxidation peeling method. Its excellent physical and chemical properties make the prepared CuO-ZnO / g-C3N4-NS catalyst have higher stability. The carbon nitride nanosheets peeled by thermal oxidation have a thinner sheet structure and can provide a larger specific surface area, so that the g-C3N4-NS can be better composited with active metals for hydrogen production by methanol steam reforming, further improving the reaction activity.

[0030] Furthermore, the present invention uses a reverse coprecipitation method to carry out Cu 2+ 、Zn 2+ Precipitation, the precipitation process is carried out in an alkaline solution, the pH value changes from high to low, which can make Cu 2+ 、Zn 2+At the same time, they are uniformly precipitated to form a co-precipitate in which the Cu and Zn components are uniformly dispersed with each other, so that the prepared catalyst is active in a lower temperature range and maintains good activity, stability and low CO selectivity in long-term test reactions.

[0031] The beneficial effects of the present invention are:

[0032] The present invention uses carbon nitride nanosheets (g-C3N4-NS) as a carrier for the first time, and prepares a CuO-ZnO / g-C3N4-NS methanol steam reforming hydrogen production Cu-based catalyst by a reverse coprecipitation method. The g-C3N4-NS material is easy to prepare, and has advantages such as excellent physical and chemical stability and a large specific surface area, which helps the Cu-based catalyst to exert its activity in the application of methanol steam reforming hydrogen production (gas phase, continuous reaction). The Cu-based catalyst prepared by the reverse coprecipitation method with CuO-ZnO nanoclusters loaded on the active carrier g-C3N4-NS has high activity in the methanol steam reforming process, a methanol conversion rate of more than 92%, and low CO selectivity, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 : XRD diagram of the catalyst in the unreduced state in Examples 1-3 of the present invention.

[0034] Figure 2 : Catalyst activity test diagram of Examples 1-6 of the present invention and the comparative example.

[0035] Figure 3 : Test diagram of CO and CO2 selectivity of catalysts in Examples 1-3 of the present invention and the comparative example.

[0036] Figure 4 : TEM image of the catalyst in Example 2 of the present invention in the state without reduction activation.

[0037] Figure 5 : Catalyst stability test diagram in Example 2 of the present invention. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively by way of examples below, and preferred embodiments of the present invention are given below. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently replacing the technical scheme of the present invention without creative results are within the protection scope of the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0040] The numerical values ​​disclosed in the embodiments of the present invention are approximate values, not definite values. When the error or experimental conditions permit, all values ​​within the error range may be included without being limited to the specific numerical values ​​disclosed in the embodiments of the present invention.

[0041] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0042] In the following examples, the Cu source is copper nitrate, the Zn source is zinc nitrate, g-C3N4-NS is prepared from urea, ammonium carbonate is the precipitant, and the solvent is deionized water.

[0043] In the following examples and comparative examples, a fixed bed reactor was used to test the catalyst performance, and the gas phase product was analyzed using a GC2060 gas chromatograph produced by Shanghai Minrui Instrument Co., Ltd. to obtain the conversion rate and selectivity.

[0044] Example 1 (CuO-ZnO / g-C3N4-NS=55:35:10)

[0045] This embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, comprising the following steps:

[0046] S1: Add urea into a crucible, place it in a muffle furnace, raise the temperature to 550°C at a heating rate of 2.3°C / min, calcine for 4 hours, and then cool to room temperature at a rate of 1°C / min. Grind the obtained yellow solid into powder to obtain g-C3N4.

[0047] S2: The obtained g-C3N4 was added into a crucible and heated to 500°C at a heating rate of 5°C / min, calcined for 2h, and then naturally cooled to room temperature to obtain g-C3N4-NS.

[0048] S3: Weigh 3.322 g of copper nitrate and 2.571 g of zinc nitrate, add them to 100 ml of deionized water, stir thoroughly to dissolve to obtain solution A, weigh 2.162 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir thoroughly to dissolve, and ultrasonically treat for 30 minutes to obtain suspension B.

[0049] S4: Suspension B is placed in a water bath, and solution A is added dropwise to suspension B at a temperature of 65°C and a rotation speed of 400 rpm for co-precipitation. After the precipitation is completed, constant temperature stirring is continued for 4 hours. After the constant temperature stirring is completed, ultrasonic treatment is performed for 30 minutes, and then the mixed solution is placed at room temperature for aging for 18 hours;

[0050] S5: Pour the aged mixture into a Buchner funnel for suction filtration, washing, and then drying to obtain a precursor. The precursor is properly ground and placed in a tube furnace, and calcined under an Ar atmosphere at a temperature of 350°C for 4 hours at a heating rate of 2°C / min. After calcination, it is naturally cooled to room temperature to obtain methanol steam reforming hydrogen production catalyst 1.

[0051] Example 2 (CuO-ZnO / g-C3N4-NS=65:25:10)

[0052] The present embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, which differs from Embodiment 1 in that, step S3: weigh 3.926 g of copper nitrate and 1.837 g of zinc nitrate, add them to 100 ml of deionized water, stir and dissolve them thoroughly to obtain solution A, weigh 2.170 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir and dissolve them thoroughly, and ultrasonically treat them for 30 minutes to obtain suspension B.

[0053] The catalyst 2 prepared in this embodiment is a methanol steam reforming hydrogen production catalyst.

[0054] Example 3 (CuO-ZnO / g-C3N4-NS=75:15:10)

[0055] The present embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, which differs from Embodiment 1 in that, step S3: weigh 4.530 g of copper nitrate and 1.102 g of zinc nitrate, add them to 100 ml of deionized water, stir and dissolve them thoroughly to obtain solution A, weigh 2.170 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir and dissolve them thoroughly, and ultrasonically treat them for 30 minutes to obtain suspension B.

[0056] The catalyst prepared in this embodiment is a methanol steam reforming hydrogen production catalyst 3.

[0057] Example 4 (CuO-ZnO / g-C3N4-NS=55:35:10)

[0058] The present embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, which differs from Embodiment 1 in that, step S3: weigh 3.322 g of copper nitrate and 2.571 g of zinc nitrate, add them to 100 ml of deionized water, stir and dissolve them thoroughly to obtain solution A, weigh 2.162 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir and dissolve them thoroughly, and ultrasonically treat them for 30 minutes to obtain suspension B; step S5: under Ar atmosphere, the temperature is set to 450°C, continued for 3 hours, and calcination is carried out at a heating rate of 2°C / min.

[0059] The catalyst 4 prepared in this embodiment is a methanol steam reforming hydrogen production catalyst.

[0060] Example 5 (CuO-ZnO / g-C3N4-NS=65:25:10)

[0061] The present embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, which differs from Embodiment 1 in that, step S3: weigh 3.926 g of copper nitrate and 1.837 g of zinc nitrate, add them to 100 ml of deionized water, stir and dissolve them thoroughly to obtain solution A, weigh 2.170 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir and dissolve them thoroughly, and ultrasonically treat them for 30 minutes to obtain suspension B; step S5: under Ar atmosphere, the temperature is set to 450°C, continued for 3 hours, and calcination is carried out at a heating rate of 2°C / min.

[0062] The catalyst 5 for producing hydrogen through methanol steam reforming is prepared in this embodiment.

[0063] Example 6 (CuO-ZnO / g-C3N4-NS=75:15:10)

[0064] The present embodiment provides a method for preparing a supported methanol steam reforming hydrogen production catalyst, which differs from Embodiment 1 in that, step S3: weigh 4.530 g of copper nitrate and 1.102 g of zinc nitrate, add them to 100 ml of deionized water, stir and dissolve them thoroughly to obtain solution A, weigh 2.170 g of ammonium carbonate and 0.2 g of g-C3N4-NS, add them to 100 ml of deionized water, stir and dissolve them thoroughly, and ultrasonically treat them for 30 minutes to obtain suspension B; step S5: under Ar atmosphere, the temperature is set to 450°C, continued for 3 hours, and calcination is carried out at a heating rate of 2°C / min.

[0065] The catalyst 6 prepared in this embodiment is a methanol steam reforming hydrogen production catalyst.

[0066] Comparative Example (Commercial Catalyst DL118)

[0067] This comparative example uses the commercial catalyst DL118 (CuO-ZnO-Al2O3, wherein the mass percentage of CuO is 65%) as a comparative catalyst.

[0068] Experiment on hydrogen production by methanol steam reforming

[0069] The catalysts of Examples 1-6 and the comparative catalyst were used to carry out a methanol steam reforming hydrogen production experiment. The specific experimental scheme is as follows:

[0070] Weigh 200 mg of the catalyst of the above-mentioned embodiment 1-6 and the comparative catalyst and 800 mg of quartz sand and mix them uniformly, load them into a quartz tube with an inner diameter of 10 mm, an outer diameter of 20 mm, and a length of 50 cm, and perform reduction activation in a fixed bed reactor, introduce a H2 / Ar (H2 volume fraction 9.74%) mixed gas with a flow rate of 40 ml / min, raise the temperature from room temperature to 300°C and keep it at this temperature for 90 min for reduction activation. After activation, cut off the H2 / Ar (H2: 9.74%) mixed gas, introduce a reaction gas (volume fraction: 10% methanol vapor, 10.5% water vapor, 79.5% nitrogen), set the temperature to a specified temperature, and start the methanol steam reforming hydrogen production reaction performance test. The collected data is obtained by FID1 and TCD detection of the product by a GC2060 gas chromatograph of Shanghai Kerui Instrument Co., Ltd.

[0071] from Figure 1 It can be seen from the XRD diagram that the intensity of the characteristic diffraction peak of CuO in Examples 1-3 increases successively, and the intensity of the characteristic diffraction peak of ZnO decreases successively, which is consistent with the gradient of the component content of CuO and ZnO in Examples 1-3.

[0072] from Figure 2 It can be seen from the catalyst activity test graph that the methanol conversion rate of Example 1 is higher than that of Example 4, the methanol conversion rate of Example 2 is higher than that of Example 5, and the methanol conversion rate of Example 3 is higher than that of Example 6. Taking Example 1 and Example 4 as examples, the two examples only have different calcination conditions during the preparation process. The calcination conditions of Example 1 are 350°C and 4h, and the calcination conditions of Example 4 are 450°C and 3h. The conditions of the other two groups of examples are the same. It can be concluded that the calcination conditions of 350°C and 4h are more suitable for the preparation of CuO-ZnO / g-C3N4-NS catalyst.

[0073] from Figure 3It can be seen that the CO selectivity of Examples 1-3 is lower than that of the comparative example, indicating that the CuO-ZnO / g-C3N4-NS catalyst prepared with g-C3N4-NS as a carrier has a lower CO selectivity. CO is a by-product of the MSR reaction. The lower its content in the product, the higher the purity of the target product, which can improve the problem of CO poisoning at the anode in the fuel cell and has good application prospects.

[0074] from Figure 4 From the TEM image of the catalyst of Example 2 which was not reduced, it can be seen that the CuO-ZnO nanoclusters are uniformly dispersed on the g-C3N4-NS. It can be seen that the thinner layer structure of g-C3N4-NS provides a larger specific surface area, which is conducive to the dispersion of active metal nanoparticles, thereby improving the low-temperature activity of the active components and the stability of the catalyst.

[0075] Combined with Figure 2 , 3 5 It can be concluded that the catalyst of Example 2 has the best activity in methanol steam reforming hydrogen production, indicating that the catalyst ratio (CuO-ZnO / g-C3N4-NS=65:25:10) is the best, and the calcination conditions (350°C, 4h, N2) are the best. The methanol conversion rate of the catalyst reaches the highest (92.3%) at a reaction temperature of 300°C.

[0076] In summary, the present invention prepares a Cu-based catalyst for methanol steam reforming hydrogen production with carbon nitride nanosheets (g-C3N4-NS) as a carrier. In the preparation process, a thinner carbon nitride nanosheet (g-C3N4-NS) is first prepared by thermal oxidation exfoliation. The excellent physical and chemical stability of the carbon nitride nanosheet makes the prepared CuO-ZnO / g-C3N4-NS catalyst more stable. The carbon nitride nanosheets exfoliated by thermal oxidation have a thinner layer structure and can provide a larger specific surface area, so that g-C3N4-NS can better composite with active metals for methanol steam reforming hydrogen production, further improving the reaction activity. Furthermore, the reverse coprecipitation method is used to prepare CuO-ZnO / g-C3N4-NS. 2+ 、Zn 2+ Precipitation, the precipitation process is carried out in an alkaline solution, the pH value changes from high to low, which can make Cu 2+ 、Zn 2+ At the same time, they are uniformly precipitated to form a co-precipitate in which the Cu and Zn components are uniformly dispersed with each other, so that the prepared catalyst is active in a lower temperature range and maintains good activity, stability, and low CO selectivity in long-term test reactions, and has good application prospects.

[0077] The above-described embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A supported methanol steam reforming catalyst for hydrogen production, characterized in that: It is composed of active ingredients and carriers; The active components are CuO and ZnO, and the carrier is g-C3N4-NS.

2. The supported methanol steam reforming catalyst for hydrogen production according to claim 1, characterized in that: Based on the total mass of the catalyst, the mass proportion of CuO is 55-75%, the mass proportion of ZnO is 15-35%, and the mass proportion of g-C3N4-NS is 10%.

3. The supported methanol steam reforming catalyst for hydrogen production according to claim 1, characterized in that: The carrier g-C3N4-NS was prepared as follows: (1) adding urea into a crucible, placing it in a muffle furnace, heating it to 550°C at a rate of 2.3°C / min, calcining it for 4 hours, and then cooling it to room temperature at a rate of 1°C / min to obtain g-C3N4; In step (1), the crucible is covered with a lid and wrapped with tin foil for calcination; (2) adding g-C3N4 into a crucible, placing it in a muffle furnace, heating it to 500°C at a rate of 5°C / min, calcining it for 2h, and then naturally cooling it to room temperature to obtain g-C3N4-NS; In step (2), the crucible is opened for calcination.

4. The method for preparing a supported methanol steam reforming hydrogen production catalyst according to claim 1, characterized in that: The preparation method is as follows: S1: Dissolve copper nitrate and zinc nitrate in deionized water to obtain solution A, and disperse ammonium carbonate and g-C3N4-NS in deionized water to obtain suspension B; S2: Suspension B is placed in a water bath, and solution A is added dropwise to suspension B at 65°C with stirring for co-precipitation. After the precipitation is completed, constant temperature stirring is continued for 4 hours, followed by ultrasonic treatment for 30 minutes, and then the mixture is aged at room temperature for 18 hours; S3: The aged mixture is filtered, washed, and dried to obtain a precursor, and the obtained precursor is placed in a tubular furnace, and the temperature is set to 350-450°C, the time is 3-4h, and the heating rate is 2-3°C / min. It is calcined in an Ar atmosphere, and naturally cooled to room temperature after calcination to obtain the supported methanol steam reforming hydrogen production catalyst.

5. Use of the catalyst as claimed in claim 1 in the methanol steam reforming hydrogen production reaction.

6. The use according to claim 5, characterized in that Here’s how: The supported methanol steam reforming hydrogen production catalyst and quartz sand were uniformly mixed, loaded into a quartz tube, placed in a fixed bed reactor, introduced with H2 / Ar mixed gas, and heated from room temperature to 300°C and kept for 90 minutes for reduction activation; After activation, the H2 / Ar mixed gas was cut off, the reaction gas was introduced, the temperature was set at 200-300°C, and the methanol steam reforming hydrogen production reaction was carried out, and the detection was carried out by gas chromatograph; The reaction gas composition is as follows: 10% methanol vapor, 10.5% water vapor, and 79.5% nitrogen by volume.

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