A precious metal / rare earth oxide composite catalyst, a preparation method and application thereof

Abstract

The present application relates to a kind of noble metal / rare earth oxide composite catalyst and its preparation method and application, belong to ammonia decomposition catalyst technical field, at least one of the problems such as low activity, poor thermal stability, high cost, difficult to use efficiently and stably below 500 DEG C of existing ammonia decomposition catalyst is solved.Solution of preparation method, including: S1, after soluble mineralizer solution and rare earth salt solution are stirred and mixed, aging is carried out, and first product is obtained;S2, after first product is stirred and dispersed uniformly with solvent, solvothermal reaction is carried out, and second product is obtained;S3, second product is calcined under predetermined atmosphere, and rare earth oxide carrier is obtained;S4, Ru precursor solution is mixed with the dispersion of rare earth oxide carrier, and heating reaction is carried out, and third product is obtained;S5, third product is calcined, and fourth product is obtained;S6, fourth product is calcined under reducing atmosphere, and supported noble metal / rare earth oxide composite catalyst is obtained.

Description

Technical Field

[0001] This invention relates to the field of ammonia decomposition catalyst technology, and in particular to a noble metal / rare earth oxide composite catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen, as a zero-carbon, high-energy-density fuel, shows great promise in replacing fossil fuels for power generation and in the utilization of clean energy. However, significant challenges remain in the production, transportation, and storage of hydrogen. Ammonia, as a highly promising hydrogen storage medium, possesses significant advantages such as high hydrogen content, high energy density, and zero carbon emissions during its decomposition process, which has driven in-depth research into ammonia decomposition hydrogen production technology.

[0003] At present, the main technical bottlenecks of ammonia decomposition catalysts are as follows: (1) Insufficient activity of non-precious metal catalysts (such as Ni and Co-based catalysts): Ideal conversion rate can usually be obtained at a high temperature above 650℃, which consumes a lot of energy and is prone to sintering and deactivation; (2) Precious metal Ru-based catalysts are expensive, and are prone to sulfur poisoning and have poor stability at high temperatures, making it difficult to promote on a large scale; (3) Reaction kinetic limitations: The rate-determining step of ammonia decomposition - nitrogen atom recombination and desorption (N2 formation) has a high energy barrier, and traditional catalysts are difficult to operate efficiently and stably below 500℃. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a noble metal / rare earth oxide composite catalyst, its preparation method and application, to solve at least one of the problems of existing ammonia decomposition catalysts, such as low activity, poor thermal stability, high cost, and difficulty in efficient and stable use below 500°C.

[0005] On one hand, the present invention provides a method for preparing a noble metal / rare earth oxide composite catalyst, comprising: S1, after stirring and mixing the soluble mineralizing agent solution and the rare earth salt solution, the mixture is aged to obtain the first product; wherein, the soluble mineralizing agent includes one of sodium carbonate, potassium carbonate, ammonium carbonate and ammonium bicarbonate, and the rare earth salt includes one of RECl3·nH2O, RE(ClO4)3·nH2O, RE(NO3)3·nH2O and RE2(SO4)3, where RE represents rare earth elements and n is the number of water molecules in the rare earth salt; S2, after the first product is stirred and dispersed evenly with the solvent, a solvothermal reaction is carried out to obtain the second product; wherein, the solvent used is a mixed solution of methanol and ethanol; S3, the second product is calcined under a predetermined atmosphere to obtain a rare earth oxide support. S4, the Ru precursor solution is mixed with the dispersion of the rare earth oxide support and heated to react, so that Ru precipitates on the rare earth oxide support to obtain the third product; wherein, the Ru precursor includes one of ruthenium chloride, ruthenium nitrite nitrate and ruthenium acetylacetone. S5, the third product is roasted to obtain the fourth product; S6, the fourth product is calcined under a reducing atmosphere to obtain a noble metal / rare earth oxide composite catalyst.

[0006] Furthermore, in S3, the predetermined atmosphere is one of Ar, O2, air, and He.

[0007] Furthermore, in S6, the reducing atmosphere is a mixture of one of H2, CO, and NH3 with Ar.

[0008] Furthermore, in S3, the calcination temperature is 500~1000℃, and the calcination time is 1~5h.

[0009] Furthermore, in S2, the solvothermal reaction is carried out with microwave assistance at a reaction temperature of 60-90°C, a microwave power of 100-300W, and a reaction time of 0.5-2h.

[0010] Furthermore, in S4, the ratio of the Ru precursor to the rare earth oxide support is: 0.45~2 mmol of Ru precursor is added per gram of rare earth oxide.

[0011] Furthermore, in S5, the third product is calcined under a protective atmosphere, wherein the calcination pressure is -0.10MPa to 0.05MPa and the calcination temperature is 600 to 1500℃.

[0012] Furthermore, in S2, the aging temperature is 40~80℃ and the aging time is 1~8h.

[0013] Furthermore, the molar ratio of the soluble mineralizer to the rare earth salt is 0.5:1 to 2:1.

[0014] On the other hand, the present invention provides a noble metal / rare earth oxide composite catalyst, prepared by the above-described method, wherein the surface rare earth ion content of the noble metal / rare earth oxide composite catalyst is greater than 20%, the oxygen vacancy content is greater than 35%, and Ru 0 Content greater than 70%.

[0015] On the other hand, the present invention also provides the application of the noble metal / rare earth oxide composite catalyst prepared by the above preparation method or the above noble metal / rare earth oxide composite catalyst in ammonia decomposition to produce hydrogen.

[0016] This invention can achieve at least one of the following beneficial effects: 1. The preparation method of the present invention, by calcining the rare earth oxide support under a predetermined atmosphere, can regulate the oxygen vacancies of the rare earth oxide, introduce defects into the catalyst, promote the loading of noble metal Ru on the rare earth oxide, and regulate the metal-support interaction; at the same time, the calcination after Ru is loaded on the rare earth oxide support further enhances the metal-support interaction between ruthenium and the rare earth oxide, increases the number of electron-rich Ru sites, provides more active sites for the catalytic reaction, and reduces the amount of Ru used, thus reducing costs.

[0017] 2. In the catalyst of the present invention, the presence of suitable low-valence rare earth element ions will promote the generation of oxygen vacancies, introduce defects into the catalyst, promote the subsequent loading of noble metal Ru on rare earth oxides, and regulate the metal-support interaction; the lower metallic state of Ru can increase the electron cloud density, making Ru more capable of donating electrons and more likely to donate electrons to N, helping to break NH bonds and promote the combination of nitrogen atoms into N2, reducing the nitrogen desorption energy barrier and constructing a highly stable anti-sintering structure.

[0018] 3. Compared with traditional preparation methods, the catalyst prepared by the method of this invention has a variety of noble metal ruthenium morphologies, which can provide more active sites and the catalyst performance is better.

[0019] 4. The catalyst of this invention exhibits good catalytic activity for hydrogen production from ammonia decomposition at temperatures ranging from 300 to 550°C. At approximately 360°C, the NH3 conversion rate reaches 50%, and at approximately 450°C, the NH3 conversion rate reaches 90%. At 450–550°C, the hydrogen production rate of the catalyst can reach 1100 mmol H2·g. -1 ·h -1 The catalyst exhibits excellent stability, with an NH3 conversion rate of approximately 97% during ammonia decomposition hydrogen production at 450℃ for 280 hours.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1The XRD patterns are of the catalysts prepared according to Examples 1-2 of the present invention. Figure 2 The XRD patterns are of the catalysts prepared according to Comparative Examples 1-2 of the present invention. Figure 3 TEM image of the catalyst prepared according to Example 1 of the present invention; Figure 4 This is a TEM image of another region of the catalyst prepared according to Example 1 of the present invention; Figure 5 This is a TEM image of another region of the catalyst prepared according to Example 1 of the present invention; Figure 6 This is a TEM image of another region of the catalyst prepared according to Example 1 of the present invention; Figure 7 This is a TEM image of another region of the catalyst prepared according to Example 1 of the present invention; Figure 8 TEM image of the catalyst prepared according to Example 2 of the present invention; Figure 9 TEM image of the catalyst prepared according to Comparative Example 1 of the present invention; Figure 10 TEM image of the catalyst prepared according to Comparative Example 2 of the present invention; Figure 11 HAADF-STEM image of the catalyst prepared according to Example 1 of the present invention; Figure 12 HAADF-STEM image of another region of the catalyst prepared according to Example 1 of the present invention; Figure 13 HAADF-STEM image of the catalyst prepared according to Comparative Example 1 of the present invention; Figure 14 The graph shows the NH3 conversion rate of the catalysts prepared according to Examples 1-4 of the present invention. Figure 15 The graph shows the NH3 conversion rate of the catalysts prepared according to Comparative Examples 1-4 of the present invention. Figure 16 The above diagram shows the H2 generation rate of the catalysts prepared according to Examples 1-4 of the present invention. Figure 17 The above diagram shows the H2 generation rate of the catalysts prepared according to Comparative Examples 1-4 of the present invention. Figure 18 This is a stability graph of the catalyst prepared according to Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. For clarity and brevity, not all features of actual embodiments are described in the specification.

[0024] The present invention provides a method for preparing a noble metal / rare earth oxide composite catalyst, the specific steps of which include: S1, after stirring and mixing the soluble mineralizing agent solution and the rare earth salt solution, the mixture is aged to obtain the first product; S2, after the first product is stirred and dispersed evenly with the solvent, a solvothermal reaction is carried out to obtain the second product; S3, the second product is calcined under a predetermined atmosphere to obtain a rare earth oxide support. S4, the Ru precursor solution is mixed with the dispersion of rare earth oxide support and heated to react, so that Ru precipitates on the rare earth oxide support to obtain the third product. S5, the third product is roasted to obtain the fourth product; S6. The fourth product is calcined under a reducing atmosphere to obtain a noble metal / rare earth oxide composite catalyst.

[0025] The preparation method of the present invention, by calcining the rare earth oxide support under a predetermined atmosphere, can regulate the oxygen vacancies of the rare earth oxide, introduce defects into the catalyst, promote the loading of noble metal Ru on the rare earth oxide, and regulate the metal-support interaction; at the same time, the calcination of Ru loaded on the rare earth oxide support further enhances the metal-support interaction between ruthenium and the rare earth oxide, and the calcination under a reducing atmosphere reduces the metallic state of ruthenium to obtain a supported Ru / rare earth oxide composite catalyst.

[0026] It should be noted that rare earth elements are selected as excellent supports for hydrogen production from ammonia decomposition due to their unique 4f electron orbital structure, excellent oxygen storage / release capacity, strong electron-donating ability, strong and tunable metal-support interactions, and the moderately basic sites required for NH3 activation. However, current applications of rare earth elements in ammonia decomposition catalysts are mostly limited to simple doping, lacking a systematic strategy for synergistic regulation of the electronic structure of rare earth elements and the ammonia decomposition reaction pathway. The catalyst prepared in this invention modulates the oxygen vacancies of rare earth oxides, adjusts the metal-support interaction between rare earth oxides and Ru, reduces the metallic state of Ru, increases the electron cloud density of Ru, making Ru more capable of donating electrons to N, facilitating the breaking of NH bonds and promoting the combination of nitrogen atoms into N2, lowering the nitrogen desorption energy barrier, and constructing a highly stable, sintering-resistant structure.

[0027] Compared with traditional preparation methods, the catalyst prepared by the method of this invention contains ruthenium in various forms, which can provide more active sites and result in superior catalyst performance.

[0028] Furthermore, this invention prepares a rare earth oxide support through steps S1 to S3. The mineralizing agent and rare earth salt solution are stirred and mixed to make the solution more uniform before aging, which can obtain a first product carbonate with a more complete particle structure and uniform component distribution. Then, the unstable intermediate phase is removed by solvothermal reaction to obtain a second product basic carbonate with more uniform particle size. Finally, the carbonate is removed by calcination under a certain atmosphere, and the oxygen vacancies of the rare earth oxide are controlled to obtain the rare earth oxide support.

[0029] According to some embodiments of the present invention, in S1, the soluble mineralizing agent is one of sodium carbonate, potassium carbonate, ammonium carbonate and ammonium bicarbonate.

[0030] According to some embodiments of the present invention, in S1, the rare earth salt is one of RECl3·nH2O, RE(ClO4)3·nH2O, RE(NO3)3·nH2O, and RE2(SO4)3. The rare earth element RE can be one or more of La, Ce, Pr, Nd, and Sm. n is the number of water molecules in the rare earth salt, and its value is determined by the type of rare earth salt and the type of rare earth element.

[0031] According to some embodiments of the present invention, in S1, the molar ratio of the soluble mineralizer to the rare earth salt is 0.5:1 to 2:1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, or 2:1. If the molar ratio is too small, the rare earth elements will not precipitate completely, wasting the sample; if the molar ratio is too large, impurity ions will be introduced.

[0032] The concentration of the soluble mineralizing agent solution is 0.25~1 mol / L, for example, 0.25 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1 mol / L. The concentration of the rare earth salt solution is 0.4~0.6 mol / L, for example, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L. The solvent in the soluble mineralizing agent solution is water.

[0033] According to some embodiments of the present invention, in S1, the soluble mineralizing agent solution and the rare earth salt solution are stirred and mixed uniformly at a certain reaction temperature. The reaction temperature is 30~90℃, and the reaction time is 0.5~3h. Exemplary examples include reaction temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃; and reaction times of 0.5h, 1h, 1.5h, 2h, 2.5h, and 3h. If the reaction temperature is too low, a large number of crystal nuclei will be generated instantaneously, resulting in excessively fine product particles and uneven composition. If the reaction temperature is too high, the solvent will evaporate, changing the solution concentration and increasing energy consumption. If the reaction time is too short, precipitation will be incomplete, and the reactants will not be fully converted into precipitates, leading to a reduced yield. If the reaction time is too long, small particles will dissolve and redeposit on the surface of larger particles, resulting in an increased average particle size and a decreased specific surface area.

[0034] According to some embodiments of the present invention, in S1, the soluble mineralizer solution and the rare earth salt solution are stirred and mixed evenly before aging. The aging temperature is 40~80℃, and the aging time is 1~8h. Exemplary examples include aging temperatures of 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, and 80℃; and aging times of 1h, 2h, 3h, 4h, 5h, 6h, 7h, and 8h. Too low an aging temperature will result in incomplete aging reaction, poor material uniformity, and low crystallinity. Too high an aging temperature will accelerate particle coarsening. Too short an aging time will lead to unstable precursor structure, and the precipitated components and structure will not reach equilibrium. Too long an aging time will lead to particle coarsening.

[0035] In S1, after aging, the solid product is collected by filtration and washed to obtain the first product.

[0036] According to some embodiments of the present invention, in S2, the solvent used is a mixed solution of methanol and ethanol. The ratio of the first product to the solvent is 0.5-1g of the first product to 50-80mL of solvent, for example, 0.5g:50mL, 0.5g:60mL, 0.5g:80mL, 0.8g:70mL, 0.8g:80mL, 1g:50mL, 1g:60mL, 1g:80mL, etc. If the solvent volume is too small, it is easy to cause insufficient particle dispersion; if the volume is too large, it is easy to cause product coarsening and low yield.

[0037] Specifically, the volume ratio of methanol to ethanol is (0.4~1.3):1, for example, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, and 1.3:1. The stirring and dispersion time of the first product and solvent is 30~60 min, for example, 30 min, 40 min, 50 min, and 60 min. A methanol to ethanol volume ratio that is too small may result in insufficient initial particle dispersion. A methanol to ethanol volume ratio that is too large will make the particles more prone to re-collision and aggregation; methanol is more polar and has lower surface tension, and an excessively high proportion may also increase health risks. A stirring and dispersion time that is too short will lead to uneven dispersion, while a stirring and dispersion time that is too long will unnecessarily increase process time and costs.

[0038] According to some embodiments of the present invention, in S2, microwave-assisted solvothermal reaction can result in more uniform product particle size and removal of intermediate reaction phases. The reaction temperature is 60-90°C, the microwave power is 100-300W, and the reaction time is 0.5-2h. For example, the reaction temperatures are 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C; the microwave powers are 100W, 120W, 150W, 180W, 200W, 220W, 250W, 280W, and 300W; and the reaction times are 0.5h, 1h, 1.5h, and 2h. Too low a microwave reaction temperature will lead to incomplete reaction or failure to start, resulting in ineffective morphology and size control and failure to achieve uniform particle size; too high a microwave reaction temperature will lead to particle agglomeration and coarsening. Insufficient microwave power leads to inadequate energy input, causing the system to take too long to reach the target temperature, thus failing to demonstrate the advantages of rapid and efficient microwave heating. Excessive microwave power results in instantaneous high temperatures, causing uncontrolled crystal nucleation and growth, leading to severe particle agglomeration and coarsening. Too short a microwave reaction time results in uneven size distribution; too long a reaction time leads to a significant increase in particle size, a decrease in specific surface area, and severe agglomeration, affecting performance. Unnecessarily extending the reaction time increases energy consumption and reduces process economics.

[0039] Specifically, the first product can be stirred and dispersed evenly with the solvent, then transferred to a high-pressure reactor and sealed. The reactor is then placed in a microwave workstation for reaction. During the reaction, the pressure is controlled between 1 and 3 MPa. If the pressure is too low, the solvent cannot form an effective solvothermal environment and may vaporize prematurely. If the pressure is too high, the nanoparticle size will increase and the specific surface area will decrease.

[0040] According to some embodiments of the present invention, in S2, after the solvothermal reaction is completed, a second product is obtained by solid-liquid separation and dried at a temperature of 60-90°C for 1-3 hours.

[0041] According to some embodiments of the present invention, in step S3, the second product is calcined under a predetermined atmosphere, wherein the predetermined atmosphere is one of Ar, O2, air, and He. Preferably, the predetermined atmosphere is one of air, Ar, and He.

[0042] According to some embodiments of the present invention, in S3, the calcination temperature is 500~1000℃, and the calcination time is 1~5h. Exemplary examples include calcination temperatures of 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃; and calcination times of 1h, 2h, 3h, 4h, and 5h. Furthermore, the heating rate can be 4~6℃ / min. If the calcination temperature is too low or the calcination time is too short, the product cannot decompose; if the calcination temperature is too high or the calcination time is too long, the product agglomerates, reducing the specific surface area. If the heating rate is too low, energy is wasted; if the heating rate is too high, the particles coarsen.

[0043] According to some embodiments of the present invention, in S4, the Ru precursor used includes one of ruthenium chloride, ruthenium nitrite, and ruthenium acetylacetonate. The ratio of Ru precursor to rare earth oxide support is: 0.45~2 mmol of Ru precursor is added per gram of rare earth oxide, for example, 0.45 mmol, 0.5 mmol, 0.8 mmol, 1 mmol, 1.2 mmol, 1.5 mmol, 1.8 mmol, or 2 mmol. If too little Ru precursor is added, the catalyst activity will decrease sharply; if too much Ru precursor is added, it will be wasteful.

[0044] According to some embodiments of the present invention, S4 specifically includes the following steps: S41, Add an alkaline solution to the rare earth oxide carrier dispersion and stir until homogeneous to adjust the pH; S42, add an alkaline solution to the Ru precursor solution and stir until homogeneous to adjust the pH; S43: The pH-adjusted rare earth oxide support dispersion obtained in S41 and S42 is mixed with the Ru precursor solution and heated to obtain the third product.

[0045] According to some embodiments of the present invention, in step S41, the rare earth oxide support obtained in step S3 is first dispersed in water (e.g., deionized water) and stirred for a certain period of time to obtain a rare earth oxide support dispersion. The concentration of the rare earth oxide support dispersion is 6.25~20 g / L, for example, 6.25 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 15 g / L, 16 g / L, 18 g / L, or 20 g / L.

[0046] In S42, the concentration of the ruthenium precursor solution is 0.045~0.2 mol / L, for example, 0.045 mol / L, 0.05 mol / L, 0.07 mol / L, 0.1 mol / L, 0.125 mol / L, 0.15 mol / L, 0.175 mol / L, and 0.2 mol / L. The solvent is water.

[0047] In S41 and S42, the alkaline solution used is one of sodium hydroxide, potassium hydroxide, barium hydroxide, or ammonia water. The amount of alkaline solution added is such that the alkaline concentration in the solution is 0.5~4 mol / L, and it is added until the solution is alkaline.

[0048] According to some embodiments of the present invention, in S4, the reaction temperature of the heating reaction is 50~80°C, and the reaction time is 1~4h. For example, the reaction temperature is 50°C, 60°C, 70°C, or 80°C; and the reaction time is 1h, 2h, 3h, or 4h.

[0049] In step S4, after the heating reaction is complete, the product is filtered, washed, and dried to obtain the third product. The drying temperature is 50~100℃, and the drying time is 3~9h.

[0050] According to some embodiments of the present invention, in step S5, the third product is calcined under a protective atmosphere, the protective atmosphere including Ar. The calcination pressure is -0.10 MPa to 0.05 MPa, the calcination temperature is 600 to 1500 °C, the calcination time is 1 to 10 min, and the heating rate is 50 to 300 °C / s. Exemplarily, the calcination pressures are -0.1 MPa, -0.09 MPa, -0.08 MPa, -0.07 MPa, -0.06 MPa, -0.05 MPa, -0.04 MPa, -0.03 MPa, -0.02 MPa, -0.01 MPa, 0.01 MPa, 0.02 MPa, 0.03 MPa, 0.04 MPa, and 0.05 MPa; the calcination temperatures are 600 °C, 700 MPa, and 800 MPa. The roasting temperatures are 0℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, and 1500℃; roasting times are 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min; heating rates are 50℃ / s, 100℃ / s, 150℃ / s, 200℃ / s, 250℃ / s, and 300℃ / s. Excessive roasting pressure may inhibit the release of volatiles from the material, such as carbon dioxide. Insufficient roasting pressure may make it difficult to maintain the required protective or reaction atmosphere, leading to air backflow into the furnace and causing product oxidation or contamination. Insufficient roasting time may prevent the completion of internal chemical reactions such as decomposition, synthesis, redox, or sintering, resulting in a low yield of the target product and high levels of impurities. Excessive roasting time increases energy consumption and wastes resources. Excessively high roasting temperatures may lead to abnormally coarse grains and consume a large amount of energy. If the calcination temperature is too low, the product decomposition and synthesis may not proceed to the required extent, and Ru and cerium dioxide may not bond tightly. If the heating rate is too fast, the product will be uneven, ruthenium will agglomerate, and the particle size will increase; if the heating rate is too slow, CeO2 grains will mature more fully, the specific surface area will be significantly reduced, and the dispersion of ruthenium will be decreased.

[0051] According to some embodiments of the present invention, in S6, the reducing atmosphere is a mixture of one of H2, CO and NH3 with Ar, for example, one of 5 vol% H2 / Ar, 5 vol% CO / Ar and 5 vol% NH3 / Ar.

[0052] According to some embodiments of the present invention, in step S6, the calcination temperature is 200~400℃, and the calcination time is 2~6h. For example, the calcination temperature is 200℃, 250℃, 300℃, 350℃, or 400℃; and the calcination time is 2h, 3h, 4h, 5h, or 6h.

[0053] Embodiments of the present invention also provide a noble metal / rare earth oxide composite catalyst, which can be prepared by the above-described method. The noble metal / rare earth oxide composite catalyst of the present invention has a surface rare earth low-valence ion content greater than 20%, an oxygen vacancy content greater than 35%, and Ru... 0 Content greater than 70%.

[0054] Furthermore, the Ru-O-RE content in the noble metal / rare earth oxide composite catalyst is greater than 25%. Here, there is a strong interaction between the noble metal ruthenium and the rare earth oxide, and Ru-O-RE represents the content of ruthenium species whose electronic structure is regulated by the rare earth oxide.

[0055] In the catalyst of this invention, the presence of suitable low-valence rare earth element ions promotes the generation of oxygen vacancies, introduces defects into the catalyst, promotes the loading of noble metal Ru on rare earth oxides, and regulates metal-support interactions. The lower metallic state of Ru can increase the electron cloud density, making Ru more capable of donating electrons and more likely to donate electrons to N, helping to break NH bonds and promote the combination of nitrogen atoms into N2, reducing the nitrogen desorption energy barrier, and constructing a highly stable anti-sintering structure. This allows the catalyst of this invention to still have highly efficient ammonia decomposition hydrogen production catalytic activity below 500°C.

[0056] Embodiments of the present invention also provide an application of the noble metal / rare earth oxide composite catalyst prepared by the above preparation method or the above noble metal / rare earth oxide composite catalyst in ammonia decomposition for hydrogen production.

[0057] The technical solution of the present invention will be further illustrated below with specific embodiments.

[0058] Example 1 This embodiment provides a method for preparing a Ru / rare earth oxide composite catalyst, including the following steps: S1. The carbonate solution and the cerium salt solution are stirred and mixed evenly at 60°C. Specifically, the carbonate solution is 3.45g of K2CO3 dissolved in 50mL of deionized water (0.5mol / L), and the cerium salt solution is 10.86g of Ce(NO3)3·6H2O dissolved in 50mL of deionized water (0.5mol / L). The cerium salt solution is heated to 60°C, and the carbonate solution is added using a peristaltic pump at a rate of 10r / min and stirred until evenly mixed. The above-mentioned mixed solution was stirred at 60°C for 1 hour at a stirring speed of 800 rpm, and then aged for 3 hours. After aging, the precipitate was filtered, washed three times with deionized water, and then placed in a forced-air drying oven at 70°C to dry, thus obtaining the dried first product.

[0059] S2, add the dried first product to a mixed solution of methanol and ethanol and stir to disperse evenly; specifically, each gram of the first product is dispersed in 50 mL of the mixed solution, the volume ratio of methanol to ethanol in the mixed solution is 1:1, the stirring time is 1 h, and the stirring speed is 500 r / min. The above solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in a microwave workstation for reaction to obtain the second product. Specifically, the solution volume occupied 60% of the reactor volume. The microwave workstation reaction conditions were: temperature 100℃, power 200W, reaction time 1h, and pressure maintained at 1.5MPa. The obtained second product was filtered, washed three times with deionized water, and then placed in a forced-air drying oven at 70℃ to dry, obtaining the dried second product. S3, the dried second product is placed in a tube furnace and calcined at 700℃ for 3h under an argon atmosphere at a heating rate of 5℃ / min to obtain a rare earth oxide support; wherein the argon flow rate is 50mL / min.

[0060] S4, Preparation of KOH solution: Add 1.12g of KOH to 10mL of deionized water and stir to disperse evenly to obtain an alkaline solution; Preparation of rare earth oxide carrier dispersion: The rare earth oxide carrier was ultrasonically dispersed in deionized water and stirred at room temperature for 0.5 h; wherein, each gram of rare earth oxide carrier was dispersed in 50 mL of deionized water (concentration of 20 g / L), the ultrasonic dispersion power was 100 W, and the ultrasonic time was 40 min. Preparation of Ru precursor solution: Add Ru precursor RuCl3 to deionized water (93.3 mg RuCl3, concentration 0.045 mol / L, to 10 mL of deionized water) and stir to disperse for a certain period of time; Alkali solution was added to the rare earth oxide carrier dispersion and Ru precursor solution respectively, and the mixture was stirred evenly. The pH value of the solution was measured to be 8-9 using pH test paper.

[0061] The pH-adjusted Ru precursor solution was slowly added dropwise to the rare earth oxide support dispersion. After the addition was complete, an alkaline solution was added to adjust the pH to 8-9. The mixture was then heated to 80°C and stirred for 2 hours at a stirring speed of 500 r / min. After the reaction was completed, the solution was filtered to obtain the precipitate, which was dried in a forced-air drying oven at 80°C for 6 hours to obtain the third product.

[0062] S5. The third product is placed in a Joule heat pipe furnace and rapidly heated to 800°C for 2 minutes in an Ar atmosphere (heating rate of 100°C / s) at a calcination pressure of 0.01 MPa to obtain the fourth product.

[0063] S6. The cooled fourth product was placed in a tube furnace and calcined at 300℃ for 3h at a heating rate of 5℃ / min under a 5% H2 / Ar2 atmosphere, wherein the argon flow rate was 47.5mL / min and the hydrogen flow rate was 2.5mL / min, to obtain the supported Ru / CeO2 composite catalyst.

[0064] Example 2 The only difference between this embodiment and Example 1 is that in S3, the second product is calcined in an air atmosphere with an air flow rate of 50 mL / min to obtain the Ru / CeO2 composite catalyst.

[0065] Example 3 The only difference between this embodiment and Example 1 is that, in S1, the carbonate solution used is 7.15g of Na2CO3·10H2O dissolved in 50mL of deionized water (0.5mol / L); in S4, the alkaline solution is an alkaline solution obtained by adding 0.81g of NaOH to 10mL of deionized water.

[0066] Example 4 The difference between this embodiment and Example 1 is only that in S1, the rare earth salt solution used is a samarium salt solution (0.5 mol / L) formed by dissolving 11.11 g of Sm2(NO3)3·6H2O in 50 mL of deionized water, and the carbonate solution is a solution (0.5 mol / L) formed by dissolving 7.15 g of Na2CO3·10H2O in 50 mL of deionized water. The Ru / Sm2O3 catalyst is ultimately obtained.

[0067] Comparative Example 1 This comparative example provides a method for preparing a Ru / CeO2 catalyst, which differs from Example 1 only in that: in S3, the second product is calcined under a N2 atmosphere with a N2 flow rate of 50 mL / min.

[0068] Comparative Example 2 This comparative example provides a method for preparing a Ru / CeO2 catalyst, which differs from Example 1 only in that: in S3, the second product is calcined under a 5% H2 / Ar atmosphere, with an argon flow rate of 47.5 mL / min and a hydrogen flow rate of 2.5 mL / min.

[0069] Comparative Example 3 This comparative example provides a method for preparing a Ru / CeO2 catalyst, which differs from Example 1 only in that step S2, namely, the dissolution in a methanol-ethanol mixed solvent and microwave heating treatment, is not performed.

[0070] Comparative Example 4 This comparative example provides a method for preparing a Ru / CeO2 catalyst, which differs from Example 1 only in that step S5, i.e., calcination in a Joule-free heat pipe furnace, is not performed.

[0071] The catalysts prepared in the above examples and comparative examples were characterized and their performance was tested. (1) The crystal structure of the catalyst was analyzed by X-ray powder diffraction (XRD) using a Dutch X-pertpowder diffractometer.

[0072] The XRD structures of the catalysts in Examples 1-2 and Comparative Examples 1-2 are as follows: Figure 1 and Figure 2 As shown in the XRD patterns, the catalysts of Examples 1 and 2 exhibit multiple characteristic diffraction peaks in the range of 2θ from 10° to 80°, corresponding to the CeO2 (PDF#43-1002) crystal phase structure; the catalysts of Comparative Examples 1 and 2 also exhibit multiple characteristic diffraction peaks, corresponding to the CeO2 (PDF#43-1002) crystal phase structure. Compared with the XRD patterns of the catalysts of Examples 1 and 2, Comparative Examples 1 and 2 show slight peaks at 34° and 53°, corresponding to the (101) and (211) crystal planes of RuO2, demonstrating the superior performance of the embodiments of the present invention in achieving noble metal dispersion.

[0073] (2) The catalyst structure was observed using a transmission electron microscope (JEOL JEM-F200, Japan), and ultrasonic treatment was performed for 1 hour before the test.

[0074] The TEM images of Examples 1-2 and Comparative Examples 1-2 are shown below. Figures 3-10 As shown. Figure 3 The TEM image of Example 1 shows that the surface of the CeO2 catalyst is composed of highly ordered (110) crystal planes with a recessed structure, which helps to increase the specific surface area and expose more active sites.

[0075] Figures 4-7 Also shown is a TEM image of Example 1. The Ru in the catalyst can be in the form of amorphous form, amorphous form growing into crystals, and Ru in a crystalline state. It can also exist in the form of embedded in cerium dioxide. The cerium dioxide structure provides attachment sites for it, indicating that the existence form and morphology of Ru can provide a variety of active sites.

[0076] Figure 8 The TEM image of Example 2 shows that RuO2 (210) and CeO2 (110) crystal planes form a clear heterogeneous interface, which is beneficial to the interface synergistic effect. Figure 9 As shown in the TEM image of Comparative Example 1, CeO2 exhibits both (111) and (110) crystal planes, indicating a change in crystal plane orientation. Figure 10The TEM image for Comparative Example 2 shows the coexistence of the (110) and (100) crystal planes of CeO2, with a clear boundary between them. No surface depressions were observed in any other catalysts besides Example 1, therefore Example 1 exhibits better activity.

[0077] (3) The dispersion state and existence form of noble metals in catalyst Ru were observed using a field emission aberration-corrected transmission electron microscope (JEOL ARM 200F).

[0078] Figures 11-12 The image shown is a HAADF-STEM image from Example 1. Figure 11 The precious metal Ru is uniformly distributed around CeO2 nanoparticles in the form of RuO2 particles. Figure 12 The noble metal Ru is distributed in an amorphous form around CeO2 nanoparticles, thereby significantly increasing the exposure density of effective active sites. Figure 13 The image shown is a HAADF-STEM image of Comparative Example 1. Compared with Example 1, the noble metals show different dispersion states. RuO2 particles are distributed in clusters on the surface of CeO2 nanoparticles. This aggregation morphology leads to a decrease in the density of accessible active sites.

[0079] (4) The surface properties of the catalyst were analyzed using X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB QXi, UK). Ce... 3+ Content, O V Content and Ru 0 The content was calculated by the following formulas (1), (2) and (3), and the calculation results are shown in Table 1.

[0080] (1) (2) (3) Among them, Ce 3+ This represents the fitted area of ​​the characteristic peak belonging to trivalent cerium ions in the XPS spectrum; Ce 4+ This represents the fitted area of ​​the characteristic peak belonging to tetravalent cerium ions in the XPS spectrum; O V This represents the peak area of ​​oxygen vacancies or defective oxygen in the XPS spectrum. L O represents the peak area belonging to lattice oxygen. C Indicates the peak area of ​​surface chemisorbed oxygen in the XPS spectrum; Ru 0 This represents the peak area of ​​metallic ruthenium (0 valence) in the XPS spectrum. This represents the peak area of ​​positively valence ruthenium. This indicates a valence state greater than 0, such as 3, 4, etc.

[0081] Table 1 Surface content of various elements in the catalyst

[0082] As shown in Table 1, the core feature of Example 1 is its superior overall performance, with the three key indicators (Ce) being the best. 3+ Ov, Ru 0 The highest value: where Ce 3+ With a content of 22.2%, it helps enhance oxygen storage and redox capabilities; the oxygen vacancy (Ov) content is as high as 43.3%, significantly higher than the two comparative samples (29.8% and 31.2%), providing more abundant active sites for catalytic reactions; at the same time, Ru 0 The content reached 73.8%, indicating the highest proportion of metallic ruthenium active centers. The synergistic effect of these three factors suggests that Example 1 is expected to have the best catalytic activity and performance advantages.

[0083] Ce in Example 2 3+ The content was 20.3%, the Ov content was 38.8%, and the Ru content was... 0 The content was 70.2%, and all three indicators were significantly higher than those of Comparative Example 1 (17.9%, 29.8%, 68.5%) and Comparative Example 2 (18.6%, 31.2%, 64.5%). Among them, the oxygen vacancy content was increased by about 30.2% compared with Comparative Example 1, demonstrating excellent oxygen vacancy regulation ability. Although the values ​​were slightly lower than those of Example 1, Example 2 still showed excellent catalytic activity potential and stable overall performance, making it an efficient and reliable solution.

[0084] Based on the combined data from Examples 1 and 2, the surface Ce of the catalyst of the present invention 3+ Content greater than 20%, oxygen vacancy content greater than 35%, Ru 0 Content greater than 70%.

[0085] (5) The Ru-O-Ce content in the catalyst was quantitatively tested using hydrogen programmed temperature reduction (Anton Paar Chem3000 chemisorption instrument).

[0086] The catalyst was purged with high-purity He at 300 °C for one hour, then cooled to room temperature. The H2 signal was monitored using a TCD detector from 30 °C to 650 °C in a 5 vol% H2 / Ar atmosphere. The Ru-O-Ce contents in the catalyst are shown in Table 2.

[0087] Table 2 Ru-O-Ce content in the catalyst

[0088] As can be seen from Table 2, the Ru-O-Ce content (i.e., the Ru content affected by the electrons of cerium due to the interaction between the noble metal Ru and cerium oxide) in the catalyst of Example 1 was the highest (33.3%), which was significantly higher than that in Comparative Examples 1 and 2 (21.0% and 18.7%). This indicates that the metal-support interaction increased the number of electron-rich Ru sites, which can provide more active sites for the catalytic reaction.

[0089] In Example 2, the Ru-O-Ce content (28.6%) was significantly higher than that of Comparative Example 1 (21.0%) and Comparative Example 2 (18.7%), with the content increasing by approximately 36.2% compared to Comparative Example 1. Although the values ​​were slightly lower than those of Example 1, Example 2 still demonstrated excellent catalytic activity potential and stable overall performance, making it an efficient and reliable solution.

[0090] Based on the combined data from Examples 1 and 2, it is shown that the Ru-O-Ce content on the surface of the catalyst of the present invention is greater than 25%.

[0091] (6) The catalysts in Examples 1-4 and Comparative Examples 1-4 were tested for activity.

[0092] 0.05 g of the prepared 40-60 mesh catalyst was uniformly mixed with 0.5 g of quartz sand and loaded into a fixed-bed quartz reactor with an inner diameter of 6 mm for NH3 decomposition activity testing. The activity testing temperature range was 300℃~600℃. First, the temperature was programmed to rise to 600℃ under N2 atmosphere (100 mL / min), then switched to NH3 atmosphere (50 mL / min) and kept at a constant temperature for 1 h. After the reduction was completed, the temperature was lowered to 300℃, and the ammonia decomposition activity was measured at 50℃ intervals within the range of 300~600℃. Data were collected after each temperature point was stabilized for 20 min. The concentrations of NH3 and N2 in the reactor outlet gas were quantitatively analyzed using an online gas chromatograph (GC-2014C, TCD detector), and the volume conversion rate of ammonia and the hydrogen generation rate were calculated according to formulas (4) and (5), respectively.

[0093] (4) (5) Where, r 催化剂 This indicates the hydrogen production rate per gram of catalyst, expressed in mmol / h / g.

[0094] Figure 14 and Figure 15The figures show the NH3 conversion rates of the catalysts prepared in Examples 1-4 and Comparative Examples 1-4, respectively, illustrating the activity data of each catalyst in the range of 300-550°C. The activities of Examples 1-4 are generally higher than those of Comparative Examples 1-4. At around 360°C, all examples achieved a conversion rate of 50%, while the comparative examples generally did not reach this level. At around 450°C, all examples achieved a conversion rate of 90%, while the comparative examples generally did not reach this level. This demonstrates the superior NH3 conversion rates of the embodiments of the present invention.

[0095] Figure 16 and Figure 17 The figures show the H2 generation rates of the catalysts prepared in Examples 1-4 and Comparative Examples 1-4, respectively, illustrating the hydrogen production rates of each catalyst. The hydrogen production rates of Examples 1-4 are generally higher than those of Comparative Examples 1-4, demonstrating the superior hydrogen production rates of the embodiments of the present invention.

[0096] To evaluate the lifetime and reliability of the synthesized catalyst in practical industrial applications, the catalyst synthesized in Example 1 was subjected to a stability test at 450°C for 280 hours. Figure 18 It can be seen that the conversion rate of the catalyst remained stable at around 97% without decreasing, indicating that the catalyst has excellent stability.

[0097] In summary, the supported noble metal / rare earth oxide composite catalyst synthesized in this invention achieves efficient and stable ammonia decomposition hydrogen production performance by virtue of its optimized active components and support structure, demonstrating significant advantages in the preparation of green hydrogen.

[0098] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a noble metal / rare earth oxide composite catalyst, characterized in that, include: S1, after stirring and mixing the soluble mineralizing agent solution and the rare earth salt solution, the mixture is aged to obtain the first product; wherein, the soluble mineralizing agent includes one of sodium carbonate, potassium carbonate, ammonium carbonate and ammonium bicarbonate, and the rare earth salt includes one of RECl3·nH2O, RE(ClO4)3·nH2O, RE(NO3)3·nH2O and RE2(SO4)3, RE represents rare earth elements, RE includes one or more of La, Ce, Pr, Nd and Sm, and n is the number of water molecules in the rare earth salt; S2, after the first product is stirred and dispersed evenly with the solvent, a solvothermal reaction is carried out to obtain the second product; wherein, the solvent used is a mixed solution of methanol and ethanol; S3, the second product is calcined under a predetermined atmosphere to obtain a rare earth oxide support. S4, the Ru precursor solution is mixed with the dispersion of the rare earth oxide support and heated to react, so that the noble metal Ru precipitates on the rare earth oxide support to obtain the third product; wherein, the Ru precursor includes one of ruthenium chloride, ruthenium nitrite nitrate and ruthenium acetylacetone. S5, the third product is roasted to obtain the fourth product; S6, the fourth product is calcined under a reducing atmosphere to obtain a noble metal / rare earth oxide composite catalyst. In S3, the predetermined atmosphere is one of Ar, O2, air, and He.

2. The preparation method according to claim 1, characterized in that, In S6, the reducing atmosphere is a mixture of one of H2, CO, and NH3 with Ar.

3. The preparation method according to claim 1, characterized in that, In S3, the calcination temperature is 500~1000℃ and the calcination time is 1~5h.

4. The preparation method according to claim 1, characterized in that, In S2, the solvothermal reaction is carried out with microwave assistance at a reaction temperature of 60-90°C, a microwave power of 100-300W, and a reaction time of 0.5-2h.

5. The preparation method according to claim 1, characterized in that, In S4, the ratio of Ru precursor to rare earth oxide support is: 0.45~2 mmol of Ru precursor is added per gram of rare earth oxide.

6. The preparation method according to claim 1, characterized in that, In step S5, the third product is calcined under a protective atmosphere, wherein the calcination pressure is -0.10 MPa to 0.05 MPa and the calcination temperature is 600 to 1500 °C.

7. The preparation method according to claim 1, characterized in that, In S1, the aging temperature is 40~80℃ and the aging time is 1~8h.

8. The preparation method according to claim 1, characterized in that, In S1, the molar ratio of the soluble mineralizer to the rare earth salt is 0.5:1 to 2:

1.

9. A noble metal / rare earth oxide composite catalyst, characterized in that, The noble metal / rare earth oxide composite catalyst is prepared by the preparation method according to any one of claims 1-8, wherein the noble metal is Ru, the content of surface rare earth low-valence ions in the rare earth element is greater than 20%, the oxygen vacancy content in the oxygen element is greater than 35%, and the Ru element contains Ru 0 Content greater than 70%; among which, oxygen vacancies ; ； Among them, O V This represents the peak area of ​​oxygen vacancies or defective oxygen in the XPS spectrum. L O represents the peak area belonging to lattice oxygen. C Indicates the peak area of ​​surface chemisorbed oxygen in the XPS spectrum; Ru 0 This represents the peak area of ​​metallic ruthenium in the XPS spectrum. This represents the peak area of ​​positively valence ruthenium. This indicates a valence state greater than 0.

10. The application of a noble metal / rare earth oxide composite catalyst prepared by the preparation method according to any one of claims 1 to 8 or the noble metal / rare earth oxide composite catalyst according to claim 9 in ammonia decomposition for hydrogen production.

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