Lithium-promoted ruthenium-based ammonia decomposition catalyst and preparation method thereof

Abstract

The invention provides a lithium-promoted ruthenium-based ammonia decomposition catalyst and a preparation method thereof, and belongs to the technical field of thermocatalysis. The preparation method comprises the following steps: mixing LiNO3 and Al (NO3) 3.9 H2O to obtain a first mixed solution, dropwise adding the first mixed solution and a NaOH solution into a Na2CO3 solution to generate a precipitate, keeping the pH value of the precipitate stable to obtain a lithium-aluminum composite hydroxide precursor, and roasting the precursor to obtain a lithium-aluminum composite oxide; and dispersing the lithium-aluminum composite oxide in ethanol, dropwise adding a ruthenium precursor solution to obtain a second mixed solution, carrying out vacuum evaporation treatment on the second mixed solution, and finally carrying out reduction treatment to obtain the lithium-promoted ruthenium-based ammonia decomposition catalyst. The catalyst provided by the invention shows good activity and stability in an ammonia decomposition reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal catalysis, and in particular to a lithium-promoted ruthenium-based ammonia decomposition catalyst and a preparation method thereof. Background Art

[0002] Hydrogen energy offers advantages such as being green, efficient, carbon-free, and having a wide range of applications. However, its development is constrained by its poor safety and difficulty in storage and transportation. Ammonia is an excellent hydrogen storage medium, offering advantages such as cleanliness, low carbon emissions, high energy density, excellent safety, easy liquefaction, storage and transportation, and low cost. The development of ammonia as a hydrogen storage medium is expected to not only resolve the challenges of traditional high-pressure hydrogen storage and transportation but also connect the traditional synthetic ammonia industry with hydrogen energy and renewable energy industries, developing a "hydrogen-ammonia" green circular economy route that aligns with my country's energy structure. This is of great significance for safeguarding national energy and environmental security and sustainable socioeconomic development.

[0003] Ammonia decomposition to produce hydrogen is a key technology in the ammonia-hydrogen energy sector. Theoretically, the equilibrium conversion rate of the ammonia decomposition reaction can reach 99% at a temperature of 400°C. However, in practice, this reaction requires temperatures above 1000°C, necessitating the use of catalysts to lower the ammonia decomposition temperature. Currently, ammonia decomposition catalysts primarily consist of non-precious metals and precious metals. Non-precious metal catalysts, such as nickel, cobalt, and iron, are inexpensive but exhibit poor low-temperature activity, requiring higher temperatures to achieve high ammonia conversion rates. High-temperature operation, however, places high demands on engineering and equipment, requires external energy input, and reduces ammonia energy conversion efficiency. Precious metal catalysts, such as ruthenium (Ru), exhibit excellent low-temperature activity. Despite their high cost and limited resources, the development of high-performance Ru-based catalysts has attracted considerable attention. Numerous studies have shown that the support is a key factor influencing the activity of Ru catalysts. Literature reports suggest that carbon nanotube (CNT)-supported Ru catalysts exhibit excellent low-temperature activity for ammonia decomposition. However, CNTs can undergo methanation side reactions under reaction conditions, impacting catalyst activity and lifetime. Furthermore, their high cost increases catalyst costs. Therefore, replacing carbon supports with metal oxide supports has become the current research focus.

[0004] Alumina (Al2O3) is the most widely used catalyst support in industry. It has the advantages of high specific surface area and good thermal stability. However, the alkalinity of alumina support is weak, which is not conducive to the construction of electron-rich ruthenium metal active sites. Therefore, the activity of Ru / Al2O3 catalyst for ammonia decomposition reaction is often low. In order to improve the activity of Ru / Al2O3 catalyst, adding alkali metal promoters for modification is an effective method. Alkali metal promoters can provide electrons to ruthenium metal, weaken the interaction between surface adsorbed nitrogen species and ruthenium metal, promote the recombination and desorption of nitrogen species, and thus improve the ammonia decomposition activity. Ju et al. used the impregnation method to impregnate potassium carbonate solution into γ-Al2O3, dried it, and calcined it at 600℃ to obtain K-Al2O3 modified support, and then impregnated it with ruthenium chloride acetone solution, and prepared Ru / K-Al2O3 catalyst after ammonia reduction treatment at 550℃. Among them, 5wt% Ru / 0.23K-Al2O3 catalyst was prepared at 30000mL·g -1 ·h -1 , the ammonia conversion rate at 450℃ reached 82.4%. It should be pointed out that potassium carbonate crystal phase appeared on the 0.23K-Al2O3 modified support. Wang et al. impregnated ruthenium chloride, lanthanum nitrate and cesium acetate solution into γ-Al2O3 support, and prepared Ru / Al2O3, RuLa / Al2O3, RuCs / Al2O3 and RuLaCs / Al2O3 catalysts after drying at 120℃, calcining at 550℃ and reducing at 450℃ with 20% H2 / N2. Among them, RuLaCs / Al2O3 showed the highest catalytic activity and stability. -1 ·h -1 , and ammonia conversion at 450°C is >99%. However, the activity of RuCs / Al2O3 is only 5% higher than that of Ru / Al2O3. Bajus et al. impregnated LiOH, KOH, and CsOH solutions into commercial Ru / γ-Al2O3 catalysts to obtain alkali metal-modified ruthenium catalysts. The results showed that LiOH had a better promoting effect than KOH and CsOH. It should be noted that LiOH and CsOH react with γ-Al2O3 in the solid phase to form lithium aluminate (LiAlO2) and cesium aluminate (CsAlO2).

[0005] Although the addition of alkali metal promoters can enhance the ammonia decomposition activity of Ru / Al2O3 catalysts to a certain extent, the dispersion and promotion effect of alkali metal promoters are significantly affected by the preparation method and require further improvement. Currently, the impregnation method is commonly used to modify Ru / Al2O3 catalysts by adding alkali metal promoters. However, this method has many drawbacks, such as uneven dispersion of the alkali metal promoter, solid-phase reaction with the Al2O3 support to form aluminates, and partial coverage of ruthenium metal active sites, resulting in poor promotion effect.

[0006] Therefore, it is of great practical significance to provide a simple and effective alkali metal additive doping method to improve the dispersion state of the alkali metal additive and its interaction with ruthenium metal, thereby obtaining a lithium-promoted ruthenium-based ammonia decomposition catalyst with excellent catalytic performance. Summary of the Invention

[0007] The purpose of the present invention is to provide a lithium-promoted ruthenium-based ammonia decomposition catalyst and a preparation method thereof, aiming to solve technical problems such as unstable dispersion state, uneven dispersion, reaction with the carrier and covering of some active sites of the alkali metal additive in the catalyst preparation process of the prior art.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst, comprising the following steps:

[0010] Mixing LiNO3 and Al(NO3)3·9H2O to obtain a first mixed solution;

[0011] Adding the first mixed solution and NaOH solution dropwise to a Na2CO3 solution to generate a precipitate, maintaining the pH of the precipitate stable, and obtaining a lithium aluminum composite hydroxide precursor;

[0012] calcining the lithium aluminum composite hydroxide precursor to obtain a lithium aluminum composite oxide;

[0013] Dispersing the lithium aluminum composite oxide in ethanol, and then adding a ruthenium precursor solution dropwise to obtain a second mixed solution;

[0014] The second mixed solution is subjected to vacuum evaporation treatment to remove ethanol therein, and finally subjected to reduction treatment to obtain the lithium-promoted ruthenium-based ammonia decomposition catalyst.

[0015] Furthermore, the molar ratio of LiNO3 to Al(NO3)3·9H2O is 0.125-0.5:1, the concentration of the Na2CO3 solution is 0-0.15 mol / L, and the concentration of the NaOH solution is 2 mol / L.

[0016] Furthermore, the pH value is 10.

[0017] Furthermore, the calcination temperature is 500° C. and the calcination time is 5 hours.

[0018] Furthermore, the ruthenium precursor solution is ruthenium acetate, and the concentration of the ruthenium precursor solution is 1.1-5.6 mmol / L.

[0019] Furthermore, the usage ratio of the lithium aluminum composite oxide, ethanol and ruthenium precursor solution is 1 g:15 mL:0.0249-0.1245 g.

[0020] Furthermore, the vacuum evaporation temperature is 55°C.

[0021] Furthermore, the reducing atmosphere of the reduction treatment is H2, the reducing temperature is 700°C, and the reducing time is 30 minutes.

[0022] The present invention also provides a lithium-promoted ruthenium-based ammonia decomposition catalyst obtained by the preparation method of the lithium-promoted ruthenium-based ammonia decomposition catalyst described in the above technical solution.

[0023] The present invention also provides the use of the lithium-promoted ruthenium-based ammonia decomposition catalyst described in the above technical solution in ammonia decomposition.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0025] (1) The present invention uses lithium aluminum composite hydroxide as a carrier-auxiliary agent precursor to achieve a one-step synthesis of the carrier and the auxiliary agent. Compared with the currently commonly used impregnation method, the process has fewer operating procedures, a shorter preparation cycle, and is simpler and easier to operate.

[0026] (2) The lithium aluminum composite hydroxide of the present invention is thermally decomposed to form a lithium aluminum composite oxide. The lithium ions enter the alumina lattice and are highly dispersed. This not only increases the surface alkalinity of the catalyst, but also forms a strong interaction with the ruthenium metal, thereby increasing the dispersion and electron density of the ruthenium metal and significantly promoting the catalyst activity.

[0027] (3) The ruthenium catalyst of the present invention is reduced by hydrogen at 700°C to obtain highly dispersed ruthenium metal nanoparticles with an average particle size of 1.8 nm and excellent anti-sintering performance;

[0028] (4) The ruthenium catalyst of the present invention exhibits good activity and stability for the ammonia decomposition reaction. The ammonia decomposition conversion rate of the 3% Ru / Li2O-Al2O3 catalyst in pure ammonia, 30,000 mL / (gcat·h), and 500°C is 94%, and the activity remains stable during the 100-h reaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the X-ray powder diffraction spectrum of the carrier-auxiliary agent precursor of Example 1 of the present invention;

[0030] Figure 2 is the X-ray powder diffraction spectrum of the catalyst of Example 1 of the present invention;

[0031] Figure 3This is a high-angle annular dark-field scanning transmission electron microscopy image of the catalyst of Example 1 of the present invention;

[0032] Figure 4 This is the temperature-programmed desorption curve of carbon dioxide of the catalyst of Example 1 of the present invention;

[0033] Figure 5 This is the X-ray photoelectron spectrum of the catalyst of Example 1 of the present invention;

[0034] Figure 6 This is the X-ray powder diffraction spectrum of the carrier-auxiliary agent precursor of Example 2 of the present invention;

[0035] Figure 7 is the X-ray powder diffraction spectrum of the catalyst of Example 2 of the present invention;

[0036] Figure 8 This is the X-ray powder diffraction spectrum of the carrier-auxiliary agent precursor of Example 3 of the present invention;

[0037] Figure 9 is the X-ray powder diffraction spectrum of the catalyst of Example 3 of the present invention;

[0038] Figure 10 This is the X-ray powder diffraction spectrum of the carrier-auxiliary agent precursor of Example 4 of the present invention;

[0039] Figure 11 is the X-ray powder diffraction spectrum of the catalyst of Example 4 of the present invention;

[0040] Figure 12 is the X-ray powder diffraction spectrum of the catalyst of Example 5 of the present invention;

[0041] Figure 13 is the X-ray powder diffraction spectrum of the catalyst of Example 6 of the present invention;

[0042] Figure 14 This is the X-ray powder diffraction spectrum of the carrier-auxiliary agent precursor of Comparative Example 1 of the present invention;

[0043] Figure 15 This is the X-ray powder diffraction spectrum of the catalyst of Comparative Example 1 of the present invention;

[0044] Figure 16 This is a high-angle annular dark-field scanning transmission electron microscope image of the catalyst of Comparative Example 1 of the present invention;

[0045] Figure 17 This is the X-ray powder diffraction spectrum of the catalyst of Comparative Example 2 of the present invention;

[0046] Figure 18 This is a high-angle annular dark-field scanning transmission electron microscopy image of the catalyst of Comparative Example 2 of the present invention;

[0047] Figure 19The ammonia decomposition activity test results of the catalyst of Example 1 of the present invention are as follows;

[0048] Figure 20 The long-term stability test results of ammonia decomposition of the catalyst of Example 1 of the present invention are as follows;

[0049] Figure 21 This is the X-ray powder diffraction spectrum of the catalyst of Example 1 of the present invention after long-term stability testing of ammonia decomposition;

[0050] Figure 22 This is a high-angle annular dark-field scanning transmission electron microscopy image of the catalyst of Example 1 of the present invention after long-term stability testing of ammonia decomposition. DETAILED DESCRIPTION

[0051] The present invention provides a method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst, comprising the following steps:

[0052] Mixing LiNO3 and Al(NO3)3·9H2O to obtain a first mixed solution;

[0053] Adding the first mixed solution and NaOH solution dropwise to a Na2CO3 solution to generate a precipitate, maintaining the pH of the precipitate stable, and obtaining a lithium aluminum composite hydroxide precursor;

[0054] calcining the lithium aluminum composite hydroxide precursor to obtain a lithium aluminum composite oxide;

[0055] Dispersing the lithium aluminum composite oxide in ethanol, and then adding a ruthenium precursor solution dropwise to obtain a second mixed solution;

[0056] The second mixed solution is subjected to vacuum evaporation treatment to remove ethanol therein, and finally subjected to reduction treatment to obtain the lithium-promoted ruthenium-based ammonia decomposition catalyst.

[0057] Mixing LiNO3 and Al(NO3)3·9H2O to obtain a first mixed solution;

[0058] wherein the mixing is carried out under magnetic stirring;

[0059] In the present invention, the molar ratio of LiNO3 to Al(NO3)3·9H2O is preferably 0.125-0.5:1, the concentration of the Na2CO3 solution is preferably 0-0.15 mol / L, and the concentration of the NaOH solution is preferably 2 mol / L.

[0060] Adding the first mixed solution and NaOH solution dropwise to a Na2CO3 solution to generate a precipitate, maintaining the pH of the precipitate stable, and obtaining a lithium aluminum composite hydroxide precursor;

[0061] The first mixed solution was added dropwise to the Na2CO3 solution, while simultaneously adding NaOH solution to maintain a constant pH value of the precipitation. After precipitation, the suspension was filtered, washed with deionized water, dried, and finally ground into a powder to obtain a lithium aluminum composite hydroxide precursor.

[0062] In the present invention, the pH value is preferably 10.

[0063] calcining the lithium aluminum composite hydroxide precursor to obtain a lithium aluminum composite oxide;

[0064] In the present invention, the calcination temperature is preferably 500° C., and the calcination time is preferably 5 hours.

[0065] In the present invention, the lithium aluminum composite oxide is a Li2O-Al2O3 composite oxide, and lithium ions enter the aluminum oxide lattice in a highly dispersed state.

[0066] Dispersing the lithium aluminum composite oxide in ethanol, and then adding a ruthenium precursor solution dropwise to obtain a second mixed solution;

[0067] In the present invention, the ruthenium precursor solution is preferably ruthenium acetate, and the concentration of the ruthenium precursor solution is preferably 1.1-5.6 mmol / L.

[0068] In the present invention, the usage ratio of the lithium aluminum composite oxide, ethanol and ruthenium precursor solution is preferably 1 g:15 mL:0.0249-0.1245 g.

[0069] The second mixed solution is subjected to vacuum evaporation treatment to remove ethanol therein, and finally subjected to reduction treatment to obtain the lithium-promoted ruthenium-based ammonia decomposition catalyst.

[0070] In the present invention, the temperature of the vacuum evaporation is preferably 55°C.

[0071] In the present invention, the reducing atmosphere of the reduction treatment is preferably H2, the reducing temperature is preferably 700°C, and the reducing time is preferably 30 minutes.

[0072] The present invention also provides a lithium-promoted ruthenium-based ammonia decomposition catalyst obtained by the preparation method of the lithium-promoted ruthenium-based ammonia decomposition catalyst described in the above technical solution.

[0073] The catalyst of the present invention has a ruthenium content of 1-5wt%, a small ruthenium metal particle size, a high dispersion, and exhibits good catalytic activity and stability in ammonia decomposition reaction.

[0074] The present invention also provides the use of the lithium-promoted ruthenium-based ammonia decomposition catalyst described in the above technical solution in ammonia decomposition.

[0075] In the present invention, unless otherwise specified, the raw materials required for preparation are all commercially available products well known to those skilled in the art.

[0076] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0077] Example 1

[0078] (1) Under magnetic stirring, an aqueous solution containing 3.5384 g of LiNO3 and 38.5075 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.5) was added dropwise to 2.7200 g of Na2CO3 solution, and NaOH solution (2 mol L -1 ), maintaining the solution pH at 10±0.5. The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder;

[0079] (2) 1 g of oxide powder was weighed and dispersed in 15 mL of ethanol, and 0.0747 g of ruthenium acetate was weighed and dissolved in 15 mL of deionized water. The ruthenium acetate solution was then added dropwise to the ethanol dispersion and stirred for 30 min. The resulting suspension was subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product was tableted, crushed, and sieved. A 30-60 mesh sample was taken and reduced with H2 at 700°C for 30 min to obtain a catalyst, which was labeled as 3% Ru / Li(0.5)-Al2O3.

[0080] The crystal structure of the synthesized carrier-aid precursor was characterized by X-ray powder diffraction. Figure 1 As shown, based on Figure 1 It can be seen that the diffraction peaks at 2θ = 13.6°, 23.5°, 27.5°, 42.2°, 47.5°, 56.4°, 74.9°, and 76.7° correspond to Li2Al4(OH) 12 The (002), (101), (004), (112), (202), (008), (303) and (10,10) crystal planes of CO3·xH2O indicate the formation of lithium aluminum complex hydroxide.

[0081] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 2 As shown, based on Figure 2It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; no obvious ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°, indicating that the ruthenium metal particle size was small.

[0082] The particle size of ruthenium metal was analyzed by high-angle annular dark field scanning transmission electron microscopy. Figure 3 As shown, based on Figure 3 It can be seen that the ruthenium metal particles are mainly concentrated in the range of 1-3 nm, with an average particle size of 1.8 nm.

[0083] The basic sites of the catalyst were analyzed by temperature-programmed desorption of carbon dioxide. Figure 4 As shown, based on Figure 4 It can be seen that a strong desorption peak appears at 50-500 °C, indicating that there are a large number of basic sites on the catalyst surface.

[0084] X-ray photoelectron spectroscopy was used to analyze the electronic state of Ru metal in the catalyst. Figure 5 As shown, based on Figure 5 It can be seen that the peaks with binding energies of 461.5eV and 466.5eV correspond to Ru 0 Ru x+ , Ru x+ The existence of species indicates that there is a strong interaction between ruthenium metal and lithium additive.

[0085] Example 2

[0086] (1) Under magnetic stirring, an aqueous solution containing 1.3707 g of LiNO3 and 19.8892 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.375) was added dropwise to 1.0537 g of Na2CO3 solution, and NaOH solution (2 molL) was added by a peristaltic pump. -1 ), maintaining the solution pH at 10±0.5. The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder;

[0087] (2) Weigh 1 g of the oxide powder and disperse it in 15 mL of ethanol. Weigh 0.0747 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 3%Ru / Li(0.375)-Al2O3.

[0088] The crystal structure of the synthesized carrier precursor was characterized by X-ray powder diffraction. Figure 6 As shown, based on Figure 6 It can be seen that the diffraction peaks at 2θ = 13.6°, 23.5°, 27.5°, 42.2°, 47.5°, 56.4°, 74.9°, and 76.7° correspond to Li2Al4(OH) 12 The (002), (101), (004), (112), (202), (008), (303) and (10,10) crystal planes of CO3·xH2O; the diffraction peaks located near 2θ=21.8°, 23.6°, 32.3°, 47.5° and 62.6° correspond to the (100), (01-1), (11-1), (11-1) and (13-1) crystal planes of Al(OH)3, respectively, indicating the formation of lithium aluminum composite hydroxide.

[0089] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 7 As shown, based on Figure 7 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; no obvious ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°, indicating that the ruthenium metal particle size was small.

[0090] Example 3

[0091] (1) Under magnetic stirring, an aqueous solution containing 0.9450 g of LiNO3 and 20.5681 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.25) was added dropwise to 0.7264 g of Na2CO3 solution, and NaOH solution (2 mol L -1The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder.

[0092] (2) Weigh 1 g of the oxide powder and disperse it in 15 mL of ethanol. Weigh 0.0747 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 3%Ru / Li(0.25)-Al2O3.

[0093] The crystal structure of the synthesized carrier precursor was characterized by X-ray powder diffraction. Figure 8 As shown, based on Figure 8 It can be seen that the diffraction peaks at 2θ = 13.6°, 23.5°, 27.5°, 42.2°, 47.5°, 56.4°, 74.9°, and 76.7° correspond to Li2Al4(OH) 12 The (002), (101), (004), (112), (202), (008), (303) and (10,10) crystal planes of CO3·xH2O; the diffraction peaks located near 2θ=21.8°, 23.6°, 32.3°, 47.5° and 62.6° correspond to the (100), (01-1), (11-1), (11-1) and (13-1) crystal planes of Al(OH)3, respectively, indicating the formation of lithium aluminum composite hydroxide.

[0094] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 9 As shown, based on Figure 9 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; no obvious ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°, indicating that the ruthenium metal particle size was small.

[0095] Example 4

[0096] (1) Under magnetic stirring, an aqueous solution containing 0.4892 g of LiNO3 and 21.2950 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.125) was added dropwise to 0.3761 g of Na2CO3 solution, and NaOH solution (2 molL) was added by a peristaltic pump. -1 The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder.

[0097] (2) Weigh 1 g of the oxide powder and disperse it in 15 mL of ethanol. Weigh 0.0747 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 3%Ru / Li(0.125)-Al2O3.

[0098] The crystal structure of the synthesized carrier precursor was characterized by X-ray powder diffraction. Figure 10 As shown, based on Figure 10 It can be seen that the diffraction peaks at 2θ = 13.6°, 23.5°, 27.5°, 42.2°, 47.5°, 56.4°, 74.9°, and 76.7° correspond to Li2Al4(OH) 12 The (002), (101), (004), (112), (202), (008), (303) and (10,10) crystal planes of CO3·xH2O; the diffraction peaks located near 2θ=21.8°, 23.6°, 32.3°, 47.5° and 62.6° correspond to the (100), (01-1), (11-1), (11-1) and (13-1) crystal planes of Al(OH)3, respectively, indicating the formation of lithium aluminum composite hydroxide.

[0099] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 11 As shown, based on Figure 11 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; weaker ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°.

[0100] Example 5

[0101] (1) Under magnetic stirring, an aqueous solution containing 3.5384 g of LiNO3 and 38.5075 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.5) was added dropwise to 2.7200 g of Na2CO3 solution, and NaOH solution (2 mol L -1 The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder.

[0102] (2) Weigh 1 g of the oxide powder and disperse it in 15 mL of ethanol. Weigh 0.0249 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 1%Ru / Li(0.5)-Al2O3.

[0103] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 12 As shown, based on Figure 12 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; no obvious ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°, indicating that the ruthenium metal particle size was small.

[0104] Example 6

[0105] (1) Under magnetic stirring, an aqueous solution containing 3.5384 g of LiNO3 and 38.5075 g of Al(NO3)3·9H2O (Li / Al molar ratio = 0.5) was added dropwise to 2.7200 g of Na2CO3 solution, and NaOH solution (2 mol L -1 The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain a lithium aluminum composite hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain a lithium aluminum composite oxide, which was then ground into powder.

[0106] (2) Weigh 1 g of the oxide powder and disperse it in 15 mL of ethanol. Weigh 0.1245 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 5%Ru / Li(0.5)-Al2O3.

[0107] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 13 As shown, based on Figure 13 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3; no diffraction peaks of lithium compounds were observed, indicating that lithium ions entered the alumina lattice and were highly dispersed; no obvious ruthenium metal diffraction peaks were seen at 2θ=44.9° and 51.6°, indicating that the ruthenium metal particle size was small.

[0108] Comparative Example 1

[0109] (1) Under magnetic stirring, an aqueous solution containing 22.0751 g of Al(NO3)3·9H2O was added dropwise to a 1.3600 g Na2CO3 solution. At the same time, a NaOH solution (2 mol L -1 The resulting precipitate was filtered, washed with deionized water, and dried at 100°C overnight to obtain an aluminum hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain aluminum oxide, which was then ground into powder.

[0110] (2) Weigh 1 g of aluminum oxide powder and disperse it in 15 mL of ethanol. Weigh 0.0747 g of ruthenium acetate and dissolve it in 15 mL of deionized water. Then, add the ruthenium acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The resulting product is tableted, crushed, and sieved. A 30-60 mesh sample is reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled 3% Ru / Al2O3.

[0111] The crystal structure of the synthesized carrier precursor was characterized by X-ray powder diffraction. Figure 14 As shown, based on Figure 14It can be seen that the diffraction peaks located near 2θ=21.8°, 23.6°, 32.3°, 47.5°, and 62.6° correspond to the (100), (01-1), (11-1), (11-1), and (13-1) crystal planes of Al(OH)3, respectively.

[0112] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 15 As shown, based on Figure 15 It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3, and obvious ruthenium metal diffraction peaks are seen at 2θ=44.9° and 51.6°.

[0113] The particle size of ruthenium metal was analyzed by high-angle annular dark field scanning transmission electron microscopy. Figure 16 As shown, based on Figure 16 It can be seen that the distribution of ruthenium metal particles is uneven, some ruthenium metal particles are larger than 5nm, and the average particle size of ruthenium metal is 3.8nm.

[0114] Comparative Example 2

[0115] (1) Under magnetic stirring, an aqueous solution containing 22.0751 g of Al(NO3)3·9H2O was added dropwise to a 1.3600 g Na2CO3 solution. At the same time, a NaOH solution (2 mol L -1 The resulting precipitate was filtered, washed with deionized water, and dried overnight at 100°C to obtain an aluminum hydroxide precursor, which was then calcined at 500°C for 5 hours to obtain aluminum oxide, which was then ground into powder.

[0116] (2) Weigh 0.8722 g of aluminum oxide powder and disperse it in 15 mL of ethanol. Weigh 0.5895 g of lithium nitrate (Li / Al molar ratio = 0.5) and 0.0747 g of ruthenium acetate and dissolve them in 15 mL of deionized water. Then add the acetate solution dropwise to the ethanol dispersion and stir for 30 minutes. The resulting suspension is subjected to vacuum rotary evaporation of the solvent at 55°C. The obtained product is tableted, crushed, and sieved. A 30-60 mesh sample is taken and reduced with H2 at 700°C for 30 minutes to obtain a catalyst. The catalyst is labeled as 3% Ru-Li 0.5 / Al2O3.

[0117] The crystal structure of the prepared catalyst was characterized by X-ray powder diffraction. Figure 17 As shown, based on Figure 17It can be seen that the diffraction peaks at 2θ=22.6°, 37.3°, 43.9°, 46.2°, 53.8°, 72.1°, and 79.8° correspond to the (111), (220), (311), (222), (400), (511), and (440) crystal planes of γ-Al2O3, and the diffraction peaks at 2θ=25.9°, 38.9°, 40.5°, 57.4°, and 72.6° correspond to the (101), (102), (200), (212), and (302) crystal planes of lithium aluminate LiAlO2, respectively, indicating that the lithium additive and the alumina carrier underwent a solid-phase reaction; weaker ruthenium metal diffraction peaks were observed at 2θ=44.9° and 51.6°.

[0118] The particle size of ruthenium metal was analyzed by high-angle annular dark field scanning transmission electron microscopy. Figure 18 As shown, based on Figure 18 It can be seen that the ruthenium metal particles are mainly concentrated in the range of 1-5nm, some particles are larger than 5nm, and the average particle size is 3.1nm.

[0119] X-ray powder diffraction spectra and high-angle annular dark-field scanning transmission electron microscopy spectra of the catalysts in Examples 1-4 and Comparative Example 1 show that the ruthenium metal particle size decreases after the addition of lithium, demonstrating that the addition of the lithium additive effectively inhibits ruthenium metal sintering. Comparison of the catalysts in Example 1 and Comparative Example 2 reveals that the ruthenium metal particle size supported by the lithium-aluminum composite oxide is smaller than that of the catalyst prepared using the traditional impregnation method, indicating that the incorporation of lithium ions into the alumina lattice more effectively inhibits ruthenium metal sintering.

[0120] Table 1 lists the specific surface area, pore volume, and average pore diameter of the catalysts in Examples 1-4 of the present invention and those in Comparative Examples 1 and 2. Comparing Comparative Examples 1 and 2 reveals that lithium doping using the traditional impregnation method results in a significant decrease in specific surface area, likely due to the formation of lithium aluminate (LiAlO2). In comparison, the specific surface area of ​​the catalysts in Examples 1-4 decreases less significantly, remaining relatively high.

[0121] Table 1 Specific surface area and pore structure data of ruthenium catalysts of Examples 1 to 4 and Comparative Examples 1 to 2

[0122]

[0123]

[0124] The activity of the catalyst for the ammonia decomposition reaction was evaluated in a fixed-bed reactor at atmospheric pressure. The reaction conditions were: catalyst dosage 50 mg, pure ammonia feed gas at a flow rate of 25 mL / min, a space velocity of 30,000 mL / (gcat·h), atmospheric pressure, and a reaction temperature of 300-600°C.

[0125] Figure 19 The graph of the ammonia decomposition conversion rate of the catalyst in Example 1 as a function of reaction temperature is shown. Figure 19 It can be seen that as the reaction temperature increases, the ammonia decomposition conversion rate gradually increases. The conversion rate at 550°C is 98.8%, which is close to complete conversion.

[0126] Table 2 shows the ammonia decomposition conversion rates of the catalysts of Examples 1-6 and Comparative Examples 1-2 at 400-600°C. Table 2 shows that the ammonia conversion rates of the catalysts of Examples 1, 5, and 6 increase with increasing ruthenium content. When the ruthenium content is 5%, the ammonia conversion rate at 500°C reaches 98.4%. Comparing the ammonia conversion rates of the catalysts of Examples 1-4 and Comparative Example 1 shows that the addition of a lithium promoter significantly improves the ammonia decomposition activity of the catalysts. At a reaction temperature of 500°C, the ammonia conversion rate of the 3% Ru / Al2O3 catalyst is only 40.0%. As the lithium promoter content increases, the ammonia decomposition activity of the catalyst increases. When the Li / Al molar ratio is 0.5, the ammonia conversion rate at 500°C reaches 94.8%. Comparing the ammonia conversion rates of Example 1 and Comparative Example 2 shows that, given the same ruthenium and lithium contents, the catalyst of Example 1 is significantly more active than the catalyst of Comparative Example 2, demonstrating that the lithium-aluminum composite oxide significantly enhances activity. This can be attributed to the strong interaction between Ru metal and the lithium promoter, which improves the Ru metal dispersion and electron density, thereby promoting the catalytic activity.

[0127] Table 2 Ammonia decomposition conversion rate of catalysts of Examples 1-6 and Comparative Examples 1-2 at 400-600°C

[0128]

[0129]

[0130] Figure 20 This is the long-term stability test result of the catalyst in Example 1 at 500°C and 30,000 mL / (gcat·h) for ammonia decomposition reaction. Figure 20 It can be seen that the initial ammonia conversion rate is 94%, and the ammonia conversion rate remains basically unchanged after 100 hours of reaction, showing excellent long-term stability.

[0131] Figure 21 This is the X-ray powder diffraction spectrum of the catalyst after stability test, based on Figure 21 It can be seen that no obvious ruthenium metal diffraction peaks can be seen at around 2θ=44.9° and 51.6°.

[0132] Figure 22 This is a high-angle annular dark field scanning transmission electron microscopy image of the catalyst after stability test, based on Figure 22It can be seen that the ruthenium metal particles are mainly concentrated in the range of 1-3 nm, with an average particle size of 1.6 nm, which is comparable to the ruthenium metal particle size of the reduction catalyst, indicating that the catalyst of the present invention has excellent anti-sintering ability.

[0133] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst, characterized in that: The following steps are involved: Mixing LiNO3 and Al(NO3)3·9H2O to obtain a first mixed solution; Adding the first mixed solution and NaOH solution dropwise to a Na2CO3 solution to generate a precipitate, while maintaining the pH of the precipitate unchanged, to obtain a lithium aluminum composite hydroxide precursor; calcining the lithium aluminum composite hydroxide precursor to obtain a lithium aluminum composite oxide; Dispersing the lithium aluminum composite oxide in ethanol, and then adding a ruthenium precursor solution dropwise to obtain a second mixed solution; The second mixed solution is subjected to vacuum evaporation treatment to remove ethanol therein, and finally subjected to reduction treatment to obtain the lithium-promoted ruthenium-based ammonia decomposition catalyst.

2. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The molar ratio of the LiNO3 and Al(NO3)3·9H2O is 0.125-0.5:1, the concentration of the Na2CO3 solution is 0-0.15 mol / L, and the concentration of the NaOH solution is 2 mol / L.

3. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The pH value is 10.

4. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The calcination temperature is 500° C. and the calcination time is 5 hours.

5. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The ruthenium precursor solution is ruthenium acetate, and the concentration of the ruthenium precursor solution is 1.1-5.6 mmol / L.

6. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The usage ratio of the lithium aluminum composite oxide, ethanol and ruthenium precursor solution is 1g:15mL:0.0249-0.1245g.

7. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The temperature of the vacuum evaporation was 55°C.

8. The method for preparing a lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 1, wherein: The reducing atmosphere of the reduction treatment is H2, the reducing temperature is 700°C, and the reducing time is 30 minutes.

9. A lithium-promoted ruthenium-based ammonia decomposition catalyst obtained by the preparation method of the lithium-promoted ruthenium-based ammonia decomposition catalyst according to any one of claims 1 to 8.

10. Use of the lithium-promoted ruthenium-based ammonia decomposition catalyst according to claim 9 in ammonia decomposition.

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