Preparation method and application of a core-shell catalyst with high activity and high stability

Abstract

This invention patent relates to the field of energy materials and hydrogen production, specifically to a preparation method and application of a core-shell catalyst with high activity and high stability. The invention is prepared by the sol-gel method. According to the molar ratio of n La :n A :n B = 1:1:m, metal nitrates are weighed, where m = 0.1, 0.2, 0.3 or 0.4. Water is added and stirred to prepare a nitrate mixed solution; a complexing agent is added, and the amount of the complexing agent is 1 to 2 times the total molar amount of the metal salts; water is added and stirred until completely dissolved; it is evaporated to dryness by water bath or oil bath, and the water bath or oil bath temperature is 343K to 363K until the solution is stirred into a gel state and dried; after drying, the gel is ground into a powder and calcined at a temperature of 973K to 1173K, cooled to room temperature, and ground to obtain the core-shell catalyst LaAO3@BO x . The preparation method of the invention has simple and convenient process, cheap raw materials, does not involve the use of dangerous instruments, has simple steps and shortens the preparation time.

Description

Technical Field

[0001] The present invention relates to the field of energy materials and hydrogen production, and more specifically to a simple preparation method of a core-shell catalyst with high activity and high stability and its application in the methanol steam reforming hydrogen production reaction. Background Art

[0002] As an efficient and pollution-free energy carrier, hydrogen energy has significant advantages in addressing climate change, environmental pollution, and energy security. Currently, the main methods for hydrogen production include: electrolysis of water for hydrogen production, biomass for hydrogen production, and hydrogen production from other hydrocarbons, etc. Among various hydrogen production methods, methanol reforming for hydrogen production technology is gradually becoming one of the rapidly developing technologies in the hydrogen production field due to the characteristics that the raw material is liquid at room temperature and atmospheric pressure, easy to transport and store, inexpensive and readily available, high energy density, containing only one carbon atom, no stable C-C bonds, and high hydrogen production content. The conversion methods mainly include methanol decomposition for hydrogen production, partial oxidation of methanol for hydrogen production, and methanol steam reforming for hydrogen production. Among them, methanol steam reforming for hydrogen production has advantages such as low cost, mild reaction conditions, easy separation, and few by-products compared with the other two hydrogen production methods. The core of the methanol steam reforming for hydrogen production technology is the catalyst, and the most commonly used one is the copper-based catalyst. However, the copper-based catalyst has problems such as poor thermal stability and easy sintering and deactivation, resulting in a short catalyst life. The core-shell structured catalyst is an effective way to reduce the sintering of metal particles in the catalyst, and the core-shell structure can also promote the interaction between the shell layer and the core layer, thus affecting the stability and activity of the catalyst. However, the existing core-shell structured catalysts have defects such as complicated preparation methods, high preparation costs, and long time consumption.

[0003] Currently, the preparation methods of core-shell structured catalysts generally include direct chemical precipitation method, self-assembly method, electroless plating method, template method, and radiation synthesis, etc. Among them, the direct chemical precipitation method and the self-assembly method are relatively common synthesis methods. However, the preparation processes of the above synthesis methods are relatively complicated, requiring too much time. The synthesis processes often include steps such as centrifugation and washing, and some even require separate preparation of the shell layer and the core layer, which increases the complexity of the preparation and takes a long time. For example, the literature Yunlong Tian, Xiaoqian Ma, et al. Journal of Analytical and Applied Pyrolysis, 2022, 164, 105539 used an improved method (direct chemical precipitation method) to prepare the Ni-Co@SiO2 catalyst. First, the metal oxide core was prepared by calcining the polymer, and then through the improved Prepare a core-shell structured catalyst. Add the prepared oxide nanoparticles and cetyltrimethylammonium bromide (CTAB) into 100 ml of ethanol solution and stir for 1 h, then add 25% concentrated NH₃·H₂O and ultrasonically treat for 30 min, then add a certain amount of ethanol solution and tetraethyl orthosilicate (TEOS) and ultrasonically treat for 1 h, and then stir at room temperature for 6 h. After the stirring ends, collect the solid, then centrifuge for 20 min, wash repeatedly with distilled water and ethanol for 3 times, dry in an oven, calcine in a muffle furnace, and grind to obtain the core-shell catalyst. For another example, the Ni-Nd@Al core-shell catalyst was prepared in the literature Jianglong Pu, Eika W Qian, et al. International Journal of Hydrogen Energy, 2021, 46(79): 39108-39121. First, prepare Nd-doped Ni nanoparticles, disperse them into absolute ethanol, add aluminum isopropoxide and CTAB, and then add distilled water and stir for 24 h. After centrifugation, wash with deionized water for 3 times, and then wash with ammonium nitrate methanol solution twice, dry and calcine, and grind to obtain the core-shell catalyst. Since the time required for centrifugation and washing is relatively long, and the core metal nanoparticles also need to be prepared separately, this greatly increases the time of the catalyst preparation process and also increases the preparation cost. In addition, the above preparation process uses an autoclave, which also increases the difficulty and danger of the preparation process. Therefore, it is of great application significance to research and develop a methanol reforming hydrogen production catalyst with a simple preparation process, low cost, green environmental protection. Summary of the Invention

[0004] The present invention proposes a simple sol-gel method for synthesizing a core-shell catalyst LaAO₃@BO x , the preparation process of this method is simple, the raw materials are widely sourced, low in price, green and environmentally friendly, without dangerous instruments such as autoclaves, and has a short preparation time, low energy consumption, and is suitable for large-scale preparation. At the same time, the core-shell catalyst prepared by this method has good activity and stability, showing excellent catalytic activity and no deactivation phenomenon in the long-term stability test.

[0005] To achieve the above invention purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a preparation method for preparing a core-shell catalyst LaAO₃@BO x The method is prepared by the sol-gel method, and the core-shell catalyst is LaAO₃@BO x , where A is one or more of Ni, Fe, Co, Al, Cr, and B is one or more of Cu, Zn, Mg, Y, Ce; the method includes the following steps:

[0007] (1) According to n La: n A : n B Weigh metal nitrates in a molar ratio of 1:1:m and put them into a beaker, where m = 0.1, 0.2, 0.3 or 0.4. Then add a small amount of deionized water and stir to prepare a nitrate mixed solution;

[0008] (2) Add a complexing agent. The amount of the complexing agent is 1 - 2 times the total molar amount of the metal salts in step (1); add deionized water and stir evenly until completely dissolved;

[0009] (3) Evaporate the mixed solution obtained in step (2) in a water bath or oil bath. The temperature of the water bath or oil bath is 343K - 363K, and the rotation speed is 100 - 300r / min until the solution is stirred into a gel state and dried;

[0010] (4) After drying, grind the gel into a powder, calcine it at a temperature of 973K - 1173K for 4h - 6h, with a heating rate of 10K / min - 20K / min, cool it to room temperature, and grind it to obtain the core - shell catalyst LaAO3@BO x .

[0011] In the above - mentioned technical solution, further, A is Co and B is Cu; the molar ratio of La ions, Co ions and Cu ions is 1:1:0.2.

[0012] In the above - mentioned technical solution, further, the complexing agent is one or a combination of citric acid, urea, oxalic acid, EDTA, glycine, etc.

[0013] In the above - mentioned technical solution, further, the complexing agent is a combination of citric acid and EDTA, and the molar ratio of the total metal ions, citric acid and EDTA is: 1:1.5:1.

[0014] In the above - mentioned technical solution, further, the ratio of the amount of water added in step (2) to the total molar amount of metal ions is 550ml - 650ml:1.

[0015] In the above - mentioned technical solution, further, the temperature of the water bath or oil bath in step (3) is 353K, and the rotation speed is 200r / min; the drying temperature is 353K - 383K, and the drying time is 12h - 24h. Preferably, the drying temperature is 373K and the drying time is 12h.

[0016] In the above - mentioned technical solution, further, in step (4), the calcination temperature is 973K and the calcination time is 5h.

[0017] The present invention also provides a core - shell catalyst LaAO3@BO x , and the catalyst is prepared by the aforementioned preparation method.

[0018] The present invention also provides the application of the catalyst in methanol reforming for hydrogen production.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The preparation method of the present invention is simple and convenient, the raw materials are inexpensive, it does not involve the use of dangerous instruments, it will not pose a threat to personal safety, the steps of the preparation method are simple, the preparation time is shortened, the cumbersome preparation process is reduced, and it is suitable for large-scale preparation.

[0021] The catalyst prepared by the present invention can be directly applied to the catalytic process without a reduction process, which greatly saves time and energy consumption in engineering applications and has good market application value.

[0022] The core-shell catalyst prepared by the present invention can enhance the interaction between the shell layer and the core layer, thereby enhancing the catalytic performance, and this kind of catalyst still has high activity under long-term reaction conditions and has good durability.

[0023] The catalyst of the present invention shows excellent catalyst performance in the application of methanol steam reforming. When the catalytic temperature is 873K, the methanol conversion rate can reach 100%, and the hydrogen production amount is also very considerable. In the long-term stability test, no deactivation phenomenon occurred, and the catalytic performance of the catalyst showed good catalytic activity. The methanol conversion rate was always around 100%, and the selectivity of the gas products was almost a straight line without obvious fluctuations, which benefited from the high stability of the core-shell catalyst prepared by this preparation method.

[0024] The catalyst prepared by the present invention is expected to become one of the very promising catalysts for methanol steam reforming to produce hydrogen. Description of the Drawings

[0025] Figure 1 It is a curve graph of the methanol conversion rate and hydrogen production amount of LaCoO3@CuO-0.2 at different temperatures.

[0026] Figure 2 It is a gas product selectivity graph of LaCoO3@CuO-0.2 at different temperatures.

[0027] Figure 3 It is an XRD pattern of the prepared LaCoO3@CuO-x.

[0028] Figure 4 It is a TEM image of the prepared LaCoO3@CuO-0.2.

[0029] Figure 5 It is a data graph of the long-term stability test of the prepared LaCoO3@CuO-0.2 for 50h. Detailed Embodiments

[0030] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0031] Example 1: Preparation of core-shell catalyst LaCoO3@CuO-0.2

[0032] The specific preparation process is as follows:

[0033] Taking the preparation of 0.02 mol of LaCoO3@CuO-0.2 catalyst as an example. First, weigh 0.02 mol of La(NO3)3·6H2O, 0.02 mol of Co(NO3)3·6H2O, and 0.004 mol of Cu(NO3)2·3H2O, put them into a beaker, then add 30 ml of deionized water, stir evenly to prepare a metal precursor solution. Then, according to the molar ratio of the total metal ions to citric acid being 1:1.25, weigh the corresponding mass of citric acid and put it into the precursor solution, add 30 ml of deionized water, stir evenly, and then put it into an instant-heating constant-temperature heating magnetic stirrer. The temperature of the stirrer is always maintained at 343 K until it is stirred into a gel state;

[0034] Put the wet gel obtained in the above process into a constant-temperature drying oven with a temperature always maintained at 373 K, and the drying time is 12 h to obtain a dry gel;

[0035] After grinding the obtained dry gel into powder, put it into a crucible, and then place the crucible in a muffle furnace at a temperature of 973 K and calcine for 5 h;

[0036] Then cool and grind the catalyst powder obtained in the above process to obtain the core-shell catalyst LaCoO3@CuO-0.2; Figure 4 It can be clearly seen that the catalyst prepared in this application has a core-shell structure. The bright area is the shell layer, and the dark area is the core layer structure. Combining with Figure 3 the XRD pattern, it can be determined that a core-shell catalyst has been synthesized.

[0037] Put the prepared core-shell catalyst into a fixed-bed reactor for methanol steam reforming experiments. First, adjust the feed water-alcohol ratio, and then adjust the feed rate to 4 ml / h. Weigh 0.3 g of the catalyst and put it into a tubular furnace. When the temperature is raised to 873 K, introduce methanol steam to start the reaction, and use a gas analyzer to record the data, as shown in Figure 1 and Figure 2 , and a long-term stability test was carried out, and the data results are shown in Figure 5 .

[0038] Figure 1It is a graph of the methanol conversion rate and hydrogen production of LaCoO3@CuO-0.2 at different temperatures. It can be clearly observed that when the temperature is 873K, it shows the best level among the six groups of temperatures, with a methanol conversion rate of 100% and the hydrogen production reaching the maximum value of 7.62 mmol / min / g cat When the temperature is 823K, the methanol conversion rate decreases slightly.

[0039] Figure 2 It is a graph of the gas product selectivity of LaCoO3@CuO-0.2 at different temperatures. It can be seen from the graph that when the temperature is 873K, the selectivities of hydrogen, CO, and CO2 are 90%, 7%, and 20% respectively. When the temperature is 823K, the selectivities of hydrogen, CO, and CO2 are 93%, 6%, and 20% respectively, and the difference between the two is not very large.

[0040] Figure 5 It is a data graph of the long-term stability test of LaCoO3@CuO-0.2 for 50h. It can be observed from the graph that the conversion rate of methanol fluctuates slightly but always remains at about 100% without obvious changes. The average hydrogen production reaches 7.7 mmol / min / g cat The selectivity of hydrogen is mainly distributed in the range of 85-92%. The selectivities of CO and CO2 can almost be regarded as a straight line with almost no obvious fluctuations. The selectivity of CO always remains between 7%-8%, and the average selectivity of CO2 is close to 20%. Obviously, the catalyst shows excellent catalytic stability during the test and no deactivation occurs.

[0041] Example 2

[0042] The difference from Example 1 is only the different molar ratios of La(NO3)3·6H2O, Co(NO3)3·6H2O, and Cu(NO3)2·3H2O, which are as follows:

[0043] To prepare LaCoO3@CuO-0.1, the molar ratio of La(NO3)3·6H2O, Co(NO3)3·6H2O, and Cu(NO3)2·3H2O is 0.02:0.02:0.002.

[0044] To prepare LaCoO3@CuO-0.3, the molar ratio of La(NO3)3·6H2O, Co(NO3)3·6H2O, and Cu(NO3)2·3H2O is 0.02:0.02:0.006.

[0045] To prepare LaCoO3@CuO-0.4, the molar ratio of La(NO3)3·6H2O, Co(NO3)3·6H2O, and Cu(NO3)2·3H2O is 0.02:0.02:0.008.

[0046] From Figure 3 It can be seen that by comparing with the standard PDF card, the catalyst prepared in this invention is a mixture of LaCoO3 and CuO.

[0047] Example 3: Preparation of core-shell catalyst LaNiO3@ZnO-0.1

[0048] The specific preparation process is as follows:

[0049] Taking the preparation of 0.02 mol of LaNiO3@ZnO-0.1 catalyst as an example. First, weigh 0.02 mol of La(NO3)3·6H2O, 0.02 mol of Ni(NO3)3·6H2O, and 0.002 mol of Zn(NO3)2·6H2O, put them into a beaker, then add 30 ml of deionized water, stir evenly to prepare a metal precursor solution. Then, according to the molar ratio of the total metal ions, citric acid, and EDTA being 1:1.5:1, weigh the corresponding mass of citric acid and put it into the precursor solution, add 50 ml of deionized water, stir evenly, and then put it into an instant-heating constant-temperature heating magnetic stirrer. The temperature of the stirrer is always maintained at 353 K until it is stirred into a gel state;

[0050] Put the wet gel obtained above into a constant-temperature drying oven with a temperature always maintained at 383 K, and the drying time is 12 h to obtain a dry gel;

[0051] After grinding the obtained dry gel into powder, put it into a crucible, and then place the crucible in a muffle furnace at a temperature of 1073 K and calcine for 5 h;

[0052] Then cool and grind the catalyst powder obtained above to obtain the core-shell catalyst LaNiO3@ZnO-0.1;

[0053] Put the prepared core-shell catalyst into a fixed-bed reactor for methanol steam reforming experiment. First, adjust the feed water-alcohol ratio, and then adjust the feed rate to 5 ml / h. Weigh 0.4 g of the catalyst and put it into a tubular furnace. When the temperature rises to 823 K, introduce methanol steam to start the reaction.

[0054] Example 4: Preparation of core-shell catalyst LaNi 0.5 Al 0.5 O3@CuO-0.1

[0055] The specific preparation process is as follows:

[0056] To prepare 0.02 mol of LaNi 0.5 Al 0.5 O3@CuO-0.1 catalyst as an example. First, weigh 0.02 mol of La(NO3)3·6H2O, 0.01 mol of Ni(NO3)3·6H2O, 0.01 mol of Al(NO3)3·9H2O and 0.002 mol of Cu(NO3)2·3H2O, put them into a beaker, then add 25 ml of deionized water, stir evenly to prepare a metal precursor solution. Then, according to the molar ratio of the total metal ions, glycine and EDTA being 1:1.25:1, weigh the corresponding mass of citric acid and put it into the precursor solution, add 30 ml of deionized water, stir evenly, and then put it into an instant heating constant temperature magnetic stirrer. The temperature of the stirrer is always maintained at 363 K until it is stirred into a gel state;

[0057] Put the wet gel obtained from the above process into a constant temperature drying oven with a temperature always maintained at 383 K, and the drying time is 24 h to obtain a dry gel;

[0058] After grinding the obtained dry gel into powder, put it into a crucible, and then put the crucible into a muffle furnace at a temperature of 1173 K and calcine for 6 h;

[0059] Then cool and grind the catalyst powder obtained from the above process to obtain the core-shell catalyst LaNi 0.5 A l0.5 O3@CuO-0.1;

[0060] Put the prepared core-shell catalyst into a fixed-bed reactor for methanol steam reforming experiment. First, adjust the feed water-alcohol ratio, and then adjust the feed rate to 3 ml / h. Weigh 0.3 g of the catalyst and put it into a tubular furnace. When the temperature rises to 773 K, introduce methanol steam to start the reaction.

[0061] Example 5:

[0062] Compared with Example 1, the difference is that 0.02 mol of La(NO3)3·6H2O, 0.16 mol of Co(NO3)3·6H2O and 0.04 mol of Cu(NO3)2·3H2O are weighed, and other preparation conditions are the same. It is judged by XRD that no copper oxide is produced, and it can be seen from the TEM image that no core-shell structure is formed. The prepared catalyst is the perovskite catalyst LaCo 0.8 Cu 0.2 O3. It can be seen from this that when preparing the core-shell catalyst of the present invention, the molar ratio of the raw materials has a great influence.

[0063] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible variations and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, all content that does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a core-shell catalyst LaAO3@BO x , characterized in that The method is prepared by the sol-gel method, and the core-shell catalyst is LaAO3@BO x , where A is one or more of Ni, Fe, Co, and Al, and B is one or more of Cu and Zn; the method includes the following steps: (1) According to n La : n A : n B = 1:1:m in molar ratio, where m = 0.1, 0.2, 0.3 or 0.4, weigh metal nitrates, add deionized water and stir to prepare a mixed nitrate solution; (2) Add a complexing agent, and the amount of the complexing agent is 1 to 2 times the total molar amount of the metal salt in step (1); add deionized water and stir evenly until completely dissolved; (3) Evaporate the mixed solution obtained in step (2) in a water bath or an oil bath. The temperature of the water bath or the oil bath is 343K - 363K, and the rotation speed is 100 - 300 r / min until the solution is stirred into a gel state, and then dry it; (4)After drying, grind the gel into powder, calcine it at a temperature of 973K - 1173K for 4h - 6h, with a heating rate of 10K / min - 20K / min, cool it to room temperature, and then obtain the core-shell catalyst LaAO3@BO after grinding x .

2. The preparation method of the core-shell catalyst LaAO3@BO as claimed in claim 1 x , characterized in that A is Co, and B is Cu; the molar ratio of La ions, Co ions and Cu ions is 1:1:0.

2.

3. The preparation method of the core-shell catalyst LaAO3@BO according to claim 1 x , characterized in that The complexing agent is one or a combination of citric acid, oxalic acid, EDTA, glycine, etc.

4. The preparation method of the core-shell catalyst LaAO3@BO according to claim 3 x , characterized in that The complexing agent is a combination of citric acid and EDTA, and the molar ratio of the total metal ions, citric acid and EDTA is: 1:1.5:

1.

5. The preparation method of the core-shell catalyst LaAO3@BO according to claim 1 x , characterized in that In step (2), the ratio of the amount of water added to the total molar amount of metal ions is 550 mL - 650 mL:

1.

6. The preparation method of the core-shell catalyst LaAO3@BO according to claim 1 x , characterized in that In step (3), the temperature of the water bath or the oil bath is 353K, and the rotation speed is 200 r / min; the drying temperature is 353K - 383K, and the drying time is 12h - 24h.

7. The preparation method of the core-shell catalyst LaAO3@BO as claimed in claim 6 x , characterized in that The drying temperature is 373K, and the drying time is 12h.

8. The preparation method of the core-shell catalyst LaAO3@BO according to claim 1 x , characterized in that In step (4), the calcination temperature is 973K, and the calcination time is 5h.

9. A core-shell catalyst LaAO3@BO x , characterized in that The catalyst is prepared by the preparation method described in any one of claims 1 - 8.

10. The core-shell catalyst LaAO3@BO as claimed in claim 9 x for use in methanol reforming for hydrogen production.

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