A method for efficiently photo-driven ammonia decomposition to produce hydrogen using γ-alumina modified with metal nanoclusters

Abstract

The present invention relates to a method for efficiently photocatalytically decomposing ammonia to produce hydrogen by using γ-alumina modified with metal nanoclusters, belonging to the technical field of chemical engineering. The method of the present invention is specifically as follows: The method is carried out under a closed environment, light irradiation conditions, and in the presence of a γ-alumina catalyst modified with metal nanoclusters; the process of the method is as follows: In a closed reaction device, dry ammonia gas is filled, and the entire reaction device is maintained at atmospheric pressure to carry out the photocatalytic decomposition of ammonia to produce hydrogen reaction. The method of the present invention realizes the efficient decomposition of ammonia to produce hydrogen under a xenon lamp light source, and the reaction environment is mild and simple. The alumina catalyst modified with metal nanoclusters prepared by the present invention by using the characteristics of the metal nanocluster catalyst such as increased surface free energy, quantum size effect, unsaturated coordination environment, and metal-support interaction has high catalytic activity for the decomposition of ammonia.

Description

Technical Field

[0001] The present invention relates to a method for efficiently photocatalytically decomposing ammonia to produce hydrogen by using metal nanocluster-modified γ-aluminum oxide, belonging to the field of chemical engineering technology. Background Art

[0002] The massive consumption of fossil energy has continuously attracted worldwide attention, and the transformation of the energy structure is imminent. Hydrogen energy has advantages such as being green, efficient, carbon-free in emissions, and having a wide range of applications, and is the key to realizing the transformation of the energy structure and carbon dioxide emission reduction. In March 2022, it was clarified in China that hydrogen energy is an integral part of the future national energy system, and the clean and low-carbon characteristics of hydrogen energy should be fully utilized to promote the green and low-carbon transformation of energy-consuming terminals such as transportation and industry, as well as high-energy-consuming and high-emission industries; at the same time, it was clarified that hydrogen energy is a key direction of strategic emerging industries and a new growth point for building a green and low-carbon industrial system and creating industrial transformation and upgrading.

[0003] Since hydrogen is prone to leakage, has high requirements for storage containers, and is very reactive, it is very easy to burn and explode when mixed with air, so the storage and transportation cost is very high and the safety is poor. Ammonia (NH3) consists of one nitrogen atom and three hydrogen atoms and is one of the ideal hydrogen storage media; at normal pressure, when the temperature drops to -33°C, it can be liquefied, which is convenient for safe transportation. And liquid ammonia has a complete trade and transportation system, which can greatly reduce the cost and safety problems of hydrogen energy storage and transportation.

[0004] However, using ammonia as an energy source alone will also cause a series of problems. For example, although an ammonia internal combustion engine does not need to reduce hydrogen from ammonia, in addition to generating NO x (NO x This is one of the main substances of photochemical smog) emissions, it may also cause other problems such as difficult ignition, low flame speed, and higher compression ratio. Therefore, decomposing ammonia into hydrogen and applying it in hydrogen energy vehicles can perfectly achieve a closed-loop nitrogen cycle.

[0005] Currently, the decomposition of NH3 reported in the literature mainly relies on thermal catalysis. Thermal catalysis provides energy through high temperatures to reach the activation energy required for the reaction. This method requires high energy consumption to meet the high-temperature reaction conditions (WO0187770A1, WO0208117A1, CN1456491A, CN1528657A, CN1712132A), which is contrary to sustainable development. Photocatalytic technology uses sunlight as the direct energy to drive the reaction, enabling deep reactions without heating and having the natural advantages of being green and energy-saving. Currently, it has been widely applied in CO2 reduction (CN111939987A, CN111701586A, CN111450826A). Studies by Halas (Science, 2018, 362, 69 - 72; Science, 2022, 378, 889 - 893) and others have found that the hot carriers generated in nanoparticles can stimulate the adsorbed molecules on the catalyst surface through electrons or vibrations, thereby reducing the activation energy barrier of chemical reactions and triggering reactions that are not supported by traditional thermodynamics or kinetics (such as ammonia decomposition), but the conversion rate is lower than 2%. γ-aluminum oxide (γ-Al2O3) has a high specific surface area, strong surface adsorption capacity, and good surface acidity and alkalinity, so it constitutes most of the catalyst carriers. Metal nanoclusters have characteristics such as increased surface free energy, quantum size effect, unsaturated coordination environment, and metal-support interaction, and are widely used in catalytic reactions. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for efficiently photocatalytically decomposing ammonia to produce hydrogen using γ-aluminum oxide modified with metal nanoclusters.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for efficiently photocatalytically decomposing ammonia to produce hydrogen using γ-aluminum oxide modified with metal nanoclusters, the method is carried out under a closed environment, light conditions, and in the presence of a γ-aluminum oxide catalyst modified with metal nanoclusters; the process of the method is as follows: in a closed reaction device, dry ammonia gas is filled, and the entire reaction device is maintained at atmospheric pressure to carry out the photocatalytic decomposition of ammonia to produce hydrogen reaction;

[0009] The catalyst consists of an active component and a carrier, wherein the active component is one or more of Ni, Ru, and Au; the carrier is γ-Al2O3; the active component is dispersed in a single nanocluster state on the carrier, that is, the catalyst is γ-Al2O3 modified with one or more metal nanoclusters of Ni, Ru, and Au; the dosage of the catalyst is 10 mg of catalyst per 100 ml of ammonia gas.

[0010] Further, the catalyst is γ-Al2O3 modified with Ru metal nanoclusters, γ-Al2O3 modified with Ni metal nanoclusters, or γ-Al2O3 modified with Au metal nanoclusters.

[0011] Further, the mass ratio of the active component to γ-Al2O3 in the catalyst is 1-7:100. Preferably, the mass ratio of the active component to γ-Al2O3 in the catalyst is 5:100.

[0012] Further, the light source of the illumination is a xenon lamp. Preferably, the illumination is a 300W xenon lamp; the light irradiation intensity is 0.7W / cm 2 -1.3W / cm 2 .

[0013] In a preferred embodiment of the present invention, the catalyst is γ-Al2O3 modified with Ru metal nanoclusters, the mass ratio of Ru to γ-Al2O3 in the catalyst is 5:100, the light source of the illumination is a xenon lamp, and the light irradiation intensity is 1.3W / cm 2 , and the reaction time for photocatalytic decomposition of ammonia to produce hydrogen is 15 min.

[0014] Further, the metal nanocluster-modified alumina nanoparticle catalyst is prepared by a precipitation method, an impregnation method, and a two-step synthesis and control method, including the following steps:

[0015] 1) Weigh aluminum nitrate and ammonia water in an equimolar ratio, dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution, and then obtain aluminum hydroxide solid powder through centrifugation, washing, and drying;

[0016] 2) Calcinate the aluminum hydroxide powder obtained in step 1), and naturally cool it to room temperature to obtain γ-alumina nanoparticles;

[0017] 3) Disperse the γ-alumina powder obtained in step 2) in water, drop the salt solution of the metal to be modified into the alumina suspension according to a certain mass ratio, keep stirring in a dark environment for 120 min, then centrifuge, wash, and dry to remove impurities;

[0018] 4) Place the dry powder obtained in step 3) in a tubular furnace, and perform low-temperature treatment in a hydrogen atmosphere to obtain the target product.

[0019] Further, in step 2), during the calcination treatment, the temperature is raised at a rate of 5°C / min and calcined at 700±25°C for 5 h.

[0020] Further, in the step 3), the salt solution for modifying the metal is a metal chloride solution of Ni, Ru or Au, and the mass ratio of the modifying metal to γ-aluminum oxide is 1-7:100. Preferably, the salt solution for modifying the metal is a metal chloride solution of Ru, and the mass ratio of the modifying metal Ru to γ-aluminum oxide is 5:100.

[0021] Further, in the step 4), during the low-temperature treatment, the temperature is increased at a heating rate of 5 °C / min and treated at 300 °C - 500 °C for 480 minutes. Preferably, it is treated at 400 °C for 480 minutes.

[0022] In the present invention, the anchoring of metal nanoclusters on the surface of γ-Al2O3 requires treatment in a hydrogen atmosphere. The finally obtained product is used as a catalyst in the photocatalytic decomposition of ammonia.

[0023] In the present invention, the modification of γ-aluminum oxide with metal nanoclusters of the present invention realizes different photocatalytic decomposition activation performances by selecting different metal nanoclusters and metal contents, and has the advantages of simple preparation method, high decomposition activity and stable performance.

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

[0025] 1) The present invention first applies metal nanocluster materials to the field of gas-solid phase photocatalytic decomposition of ammonia to produce hydrogen. The metal nanocluster catalyst prepared by the present invention using the characteristics of increased surface free energy, quantum size effect, unsaturated coordination environment and metal-support interaction of metal nanoclusters has high catalytic activity for the decomposition of ammonia. A series of metal nanocluster-modified γ-aluminum oxide catalysts prepared by the present invention, where the metal nanoclusters are dispersed active center sites, γ-aluminum oxide effectively adsorbs ammonia small molecules, and the nanocluster active sites can effectively convert light energy into the energy for activating ammonia small molecules, effectively reducing the energy barrier for ammonia activation; the required amount of catalyst is small, the reaction conditions are mild, no pressurization or heating is required, and the catalyst performance is stable for a long time.

[0026] 2) The method of the present invention can achieve efficient decomposition of ammonia under the reaction condition of light source irradiation. The reaction conditions are simple and can be carried out under normal temperature and pressure conditions without high temperature and high pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 X-ray diffraction patterns of Ru, Ni and Au metal nanocluster-modified γ-Al2O3 and pure γ-Al2O3 photocatalytic ammonia decomposition materials prepared in Example 1, Example 5 and Example 6. From Figure 1 It can be seen that the introduction of metal nanoclusters has no obvious effect on the lattice structure of γ-aluminum oxide. Figure 1Among them, Ru 5wt% means the mass ratio of Ru / γ-Al2O3 is 5:100, Au 5wt% means the mass ratio of Au / γ-Al2O3 is 5:100, and Ni 5wt% means the mass ratio of Ni / γ-Al2O3 is 5:100.

[0028] Figure 2 It is the scanning electron microscope photo of the γ-Al2O3 photo-driven ammonia decomposition material modified by Ru metal nanoclusters prepared in Example 1.

[0029] Figure 3 It is the transmission electron microscope photo of the γ-Al2O3 photo-driven ammonia decomposition material modified by Ru metal nanoclusters prepared in Example 1. From Figure 3 It can be seen that Ru exists in γ-aluminum oxide in the form of metal nanoclusters.

[0030] Figure 4 It is the high-resolution transmission electron microscope photo of the γ-Al2O3 photo-driven ammonia decomposition material modified by Ru metal nanoclusters prepared in Example 1. From Figure 4 It can be seen that high-resolution STEM shows clear characteristic lattice fringes of Ru elemental substance.

[0031] Figure 5 It is the performance test of hydrogen production by photo-driven decomposition of ammonia gas with γ-Al2O3 modified by Ru metal nanoclusters prepared in Examples 1-4. Figure 5 Among them, Ru wt% successively represents the mass ratios of Ru / γ-Al2O3 as 1:100, 3:100, 5:100, and 7:100.

[0032] Figure 6 It is the performance test of hydrogen production by photo-driven decomposition of ammonia gas with γ-Al2O3 modified by Ru metal nanoclusters prepared in Example 1.

[0033] Figure 7 It is the test to explore the influencing factors of photo-driven decomposition of ammonia gas to produce hydrogen with γ-Al2O3 modified by Ru metal nanoclusters prepared in Example 1.

[0034] Figure 8 It is the performance test of hydrogen production by photo-driven decomposition of ammonia gas with γ-Al2O3 modified by Ru metal nanoclusters prepared in Example 1.

[0035] Figure 9 It is the performance test of hydrogen production by photo-driven decomposition of ammonia gas with γ-Al2O3 modified by Ru metal nanoclusters prepared in Example 1.

[0036] Figure 10 It is the performance test of hydrogen production by photo-driven decomposition of ammonia gas with γ-Al2O3 modified by Ru metal nanoclusters prepared in Example 1. Figure 10Among them, Ru 5wt% represents a mass ratio of Ru / γ-Al2O3 of 5:100. Detailed implementation manners

[0037] The following further describes the present invention in detail in conjunction with the accompanying drawings and specific embodiments. The following examples are only used to help those skilled in the relevant art further understand the present invention, rather than limiting the present invention in any form. Those skilled in the relevant art, on the premise of the concept of the present invention, make reasonable improvements and adjustments, which all fall within the protection scope of the present invention.

[0038] Example 1

[0039] The steps for preparing the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material agent are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution, and then obtain aluminum hydroxide solid powder through centrifugation, washing, and drying. Place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min in an air atmosphere for 5 h, and naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and add ruthenium chloride solution to the suspension according to the mass ratio of Ru / γ-Al2O3 of 5:100. Keep stirring in a dark environment for 120 min, and then wash, filter, and dry. Place the dried powder in a tube furnace and treat it at 5 °C / min under a hydrogen atmosphere at 300, 400, and 500 °C for 480 minutes to obtain three target products, and naturally cool to obtain the Ru metal nanocluster-modified γ-aluminum oxide catalyst.

[0040] During the preparation process of Example 1, with the mass ratio of Ru / γ-Al2O3 being 5:100, the target product obtained by treating at 400 °C under a hydrogen atmosphere was used as the detection object for identification. The results are shown in Figure 1-4 .

[0041] Figure 1 XRD patterns of the γ-Al2O3 and pure γ-Al2O3 photo-driven ammonia decomposition materials modified with Ru, Ni, and Au metal nanoclusters prepared in Example 1, Example 5, and Example 6. From Figure 1 it can be seen that the introduction of metal nanoclusters has no obvious effect on the lattice structure of γ-aluminum oxide.

[0042] Figure 2 SEM photograph of the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material prepared in Example 1. Figure 3 TEM photograph of the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material prepared in Example 1. From Figure 2 and 3 it can be seen that Ru exists in the form of metal nanoclusters in γ-aluminum oxide.

[0043] Figure 4 High-resolution transmission electron microscopy image of the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material prepared in Example 1. It can be seen from Figure 4 that high-resolution STEM shows clear characteristic lattice fringes of elemental Ru.

[0044] Using the three catalysts prepared in Example 1, the photo-driven ammonia decomposition to hydrogen reaction was carried out respectively, and the process is as follows:

[0045] Experiment under a 300W Xe lamp in the laboratory: In a closed reaction device, 10 mg of the catalyst prepared in Example 1 was placed, and 100 mL of dry ammonia gas was filled. The whole reaction device was kept at atmospheric pressure, and the photo-driven ammonia decomposition to hydrogen reaction was carried out. The light irradiation intensity was adjusted, and samples were taken at fixed intervals to detect the remaining amount of the reaction gas and the amount of product generated by gas chromatography.

[0046] The test results of the photo-driven ammonia decomposition to hydrogen reaction performance are shown in Figure 5-10 .

[0047] Figure 5 Performance test of the Ru metal nanocluster-modified γ-Al2O3 for photo-driven ammonia decomposition to hydrogen prepared in Examples 1-4. It can be seen from Figure 5 that the catalysts prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, and the preparation temperatures are 300, 400, and 500 °C) all showed the activity of catalytic decomposition of ammonia gas under the irradiation of a 300W xenon lamp in the laboratory. When the light irradiation intensity is 0.7 W / cm 2 , the sample with a Ru / γ-Al2O3 mass ratio of 5:100 and a preparation temperature of 400 °C prepared in Example 1 has the best catalytic activity.

[0048] It can be seen from Figure 6 that under the irradiation of a 300W xenon lamp in the laboratory, the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, preparation temperature is 400 °C) shows high catalytic decomposition activity, and the ammonia conversion rate is affected by different light intensities. When the light irradiation intensity is 1.3 W / cm 2 , the conversion rate of ammonia to hydrogen reaches 100%.

[0049] To explore the role of light in ammonia decomposition for hydrogen production, the Ru metal nanocluster-modified γ-Al2O3 ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, and the preparation temperature is 400 °C) was used as the experimental material, and the following comparative experiments were conducted: First, using the method of the present invention, in a closed environment, only light irradiation was carried out, and by adjusting the light intensity, the surface temperature of the catalyst reached 360 °C, 380 °C, 390 °C, 400 °C, and 420 °C respectively. This method only adds light irradiation without additional heating; second, using the existing method, without additional light irradiation, in a closed environment, only heating was carried out, so that the surface temperature of the catalyst reached 360 °C, 380 °C, 390 °C, 400 °C, and 420 °C respectively. From Figure 7 It can be seen that the Ru metal nanocluster-modified γ-Al2O3 ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, and the preparation temperature is 400 °C) shows high catalytic decomposition activity mainly due to the photocatalytic decomposition reaction driven by light rather than the thermal catalytic reaction simply affected by temperature.

[0050] From Figure 8 It can be seen that for the Ru metal nanocluster-modified γ-Al2O3 light-driven ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, preparation temperature is 400 °C), under the irradiation of a 300W xenon lamp in the laboratory, when the light irradiation intensity is 1.3 W / cm 2 ², at 15 minutes, ammonia has been completely converted into hydrogen.

[0051] From Figure 9 It can be seen that for the Ru metal nanocluster-modified γ-Al2O3 light-driven ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, preparation temperature is 400 °C), under the irradiation of a 300W xenon lamp in the laboratory, when the space-time flow rate (GHSV) is 12000, the conversion rate of ammonia decomposition into hydrogen reaches 82.6% and remains stable for 120 hours.

[0052] From Figure 10 It can be seen that for the Ru metal nanocluster-modified γ-Al2O3 light-driven ammonia decomposition material prepared in Example 1 (Ru / γ-Al2O3 mass ratio is 5:100, preparation temperature is 400 °C), under the irradiation of a 300W xenon lamp in the laboratory, the conversion rate of ammonia decomposition into hydrogen corresponding to different GHSVs is different, and the larger the GHSV, the lower the conversion rate.

[0053] Example 2

[0054] The steps for preparing the Ru metal nanocluster-modified γ-Al2O3 photocatalytic ammonia decomposition material are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution. After centrifugation, washing, and drying, obtain the aluminum hydroxide solid powder. Place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min in an air atmosphere for 5 h of calcination treatment. Naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and add ruthenium chloride solution dropwise to the suspension according to a mass ratio (Ru / γ-Al2O3) of 1:100. Keep stirring in a dark environment for 120 min, then wash, filter, and dry. Place the dried powder in a tube furnace and treat it at 5 °C / min in a hydrogen atmosphere at 300, 400, and 500 °C for 480 minutes to obtain three target products. Naturally cool to obtain the Ru metal nanocluster-modified γ-aluminum oxide catalyst.

[0055] Using the three catalysts prepared in Example 2, perform the photocatalytic ammonia decomposition for hydrogen production reaction respectively, and the process is the same as that in Example 1. The test conditions for the photocatalytic ammonia decomposition for hydrogen production reaction are as in Example 1.

[0056] Figure 5 For the performance test of the Ru metal nanocluster-modified γ-Al2O3 photocatalytic ammonia decomposition for hydrogen production prepared in Examples 1-4. From Figure 5 It can be seen that: The catalyst prepared in Example 2 (Ru / γ-Al2O3 mass ratio is 1:100, and the preparation temperature is 400 °C) shows the activity of catalytic ammonia decomposition under the irradiation of a 300 W xenon lamp in the laboratory.

[0057] Example 3

[0058] The steps for preparing the Ru metal nanocluster-modified γ-Al2O3 photocatalytic ammonia decomposition material agent are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution. After centrifugation, washing, and drying, obtain the aluminum hydroxide solid powder. Place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min in an air atmosphere for 5 h of calcination treatment. Naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and add ruthenium chloride solution dropwise to the suspension according to a mass ratio (Ru / γ-Al2O3) of 3:100. Keep stirring in a dark environment for 120 min, then wash, filter, and dry. Place the dried powder in a tube furnace and treat it at 5 °C / min in a hydrogen atmosphere at 300, 400, and 500 °C for 480 minutes to obtain three target products. Naturally cool to obtain the Ru metal nanocluster-modified γ-aluminum oxide catalyst.

[0059] Using the three catalysts prepared in Example 3, the photo-driven ammonia decomposition for hydrogen production reaction was carried out respectively, and the process was the same as that in Example 1. The test conditions for the photo-driven ammonia decomposition for hydrogen production reaction were the same as those in Example 1.

[0060] Figure 5 For the performance test of the Ru metal nanocluster-modified γ-Al2O3 for photo-driven ammonia decomposition to hydrogen prepared in Examples 1-4. From Figure 5 It can be seen that: the catalysts prepared in Example 3 (Ru / γ-Al2O3 mass ratio is 3:100, and the preparation temperatures are 300, 400 and 500 °C) all showed the activity of catalytic ammonia decomposition under the irradiation of a 300W xenon lamp in the laboratory.

[0061] Example 4

[0062] The steps for preparing the Ru metal nanocluster-modified γ-Al2O3 photo-driven ammonia decomposition material are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution, and then obtain aluminum hydroxide solid powder through centrifugation, washing and drying. Place it in a muffle furnace and calcine it at a heating rate of 5 °C / min to 700 °C for 5 h in an air atmosphere, and naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and add ruthenium chloride solution to the suspension according to the mass ratio (Ru / γ-Al2O3) of 7:100. Keep stirring in the dark environment for 120 min, and then wash, filter and dry. Place the dried powder in a tube furnace and treat it at 5 °C / min in a hydrogen atmosphere at 300, 400 and 500 °C for 480 minutes to obtain three target products, and naturally cool to obtain the Ru metal nanocluster-modified γ-aluminum oxide catalyst.

[0063] Using the three catalysts prepared in Example 4, the photo-driven ammonia decomposition for hydrogen production reaction was carried out respectively, and the process was the same as that in Example 1. The test conditions for the photo-driven ammonia decomposition for hydrogen production reaction were the same as those in Example 1.

[0064] Figure 5 For the performance test of the Ru metal nanocluster-modified γ-Al2O3 for photo-driven ammonia decomposition to hydrogen prepared in Examples 1-4. From Figure 5 It can be seen that: the catalysts prepared in Example 3 (Ru / γ-Al2O3 mass ratio is 7:100, and the preparation temperatures are 300, 400 and 500 °C) all showed the activity of catalytic ammonia decomposition under the irradiation of a 300W xenon lamp in the laboratory.

[0065] Example 5

[0066] The steps for preparing the Ni metal nanocluster modified γ-Al2O3 photo-driven ammonia decomposition material are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution. After centrifugation, washing, and drying, obtain the aluminum hydroxide solid powder. Place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min in an air atmosphere for 5 h of calcination treatment. Naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and dropwise add nickel chloride solution to the suspension according to the mass ratio (Ni / γ-Al2O3) of 5:100. Keep stirring in a dark environment for 120 min, then wash, filter, and dry. Place the dried powder in a tubular furnace and treat it at 500 °C for 480 minutes at a heating rate of 5 °C / min in a hydrogen atmosphere to obtain the target product. Naturally cool it to obtain the Ni metal nanocluster modified γ-aluminum oxide catalyst.

[0067] Using the catalyst prepared in Example 5, carry out the photo-driven ammonia decomposition to produce hydrogen reaction, and the process is the same as that in Example 1. The test conditions for the photo-driven ammonia decomposition to produce hydrogen reaction are as in Example 1.

[0068] Example 6

[0069] The steps for preparing the Au metal nanocluster modified γ-Al2O3 photo-driven ammonia decomposition material are as follows: Weigh equimolar amounts of aluminum nitrate and ammonia water. Dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution. After centrifugation, washing, and drying, obtain the aluminum hydroxide solid powder. Place it in a muffle furnace and heat it to 700 °C at a heating rate of 5 °C / min in an air atmosphere for 5 h of calcination treatment. Naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles. Disperse the γ-aluminum oxide in pure water, and dropwise add chloroauric acid solution to the suspension according to the mass ratio (Au / γ-Al2O3) of 5:100. Keep stirring in a dark environment for 120 min, then wash, filter, and dry. Place the dried powder in a tubular furnace and treat it at 500 °C for 480 minutes at a heating rate of 5 °C / min in a hydrogen atmosphere to obtain the target product. Naturally cool it to obtain the Au metal nanocluster modified γ-aluminum oxide catalyst.

[0070] Using the catalyst prepared in Example 6, carry out the photo-driven ammonia decomposition to produce hydrogen reaction, and the process is the same as that in Example 1. The test conditions for the photo-driven ammonia decomposition to produce hydrogen reaction are as in Example 1.

[0071] The test methods are the same, and the catalyst dosages are equal. However, for the mass ratios of Ru / γ-Al2O3 being 5:100, Ru / γ-Al2O3 being 1:100, Ru / γ-Al2O3 being 3:100, Ru / γ-Al2O3 being 7:100, Au / γ-Al2O3 being 5:100, and Ni / γ-Al2O3 being 5:100, the order of the photocatalytic decomposition performance efficiency of ammonia from high to low is: Ru / γ-Al2O3 mass ratio of 5:100 > Ru / γ-Al2O3 mass ratio of 7:100 > Ru / γ-Al2O3 mass ratio of 3:100 > Ni / γ-Al2O3 mass ratio of 5:100 > Ru / γ-Al2O3 mass ratio of 1:100 > Au / γ-Al2O3 mass ratio of 5:100.

[0072] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent transformation made by using the content of the specification of the present invention, directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for efficiently photocatalytically decomposing ammonia to produce hydrogen by using γ-aluminum oxide modified with metal nanoclusters, characterized in that, The method is carried out under the conditions of a closed environment, light conditions, and the presence of a γ-aluminum oxide catalyst modified with metal nanoclusters; the process of the method is as follows: In a closed reaction device, dry ammonia gas is filled, and the entire reaction device is maintained at atmospheric pressure to carry out a photo-driven ammonia decomposition hydrogen production reaction; The catalyst is composed of an active component and a carrier, where the active component is one or more of Ni, Ru, and Au; the carrier is γ-Al2O3; the active component is dispersed in a single nanocluster state on the carrier, that is, the catalyst is γ-Al2O3 modified with one or more of Ni, Ru, and Au metal nanoclusters; the dosage of the catalyst is 10 mg of catalyst per 100 ml of ammonia.

2. The method according to claim 1, characterized in that, The catalyst is γ-Al2O3 modified with Ru metal nanoclusters, γ-Al2O3 modified with Ni metal nanoclusters, or γ-Al2O3 modified with Au metal nanoclusters.

3. The method according to claim 1, characterized in that, The mass ratio of the active component to γ-Al2O3 in the catalyst is 1-7:

100.

4. The method according to claim 1, characterized in that, The light source of the light irradiation is a xenon lamp, and the light irradiation intensity is 0.7 W / cm 2 -1.3 W / cm 2 .

5. The method according to claim 1, wherein The catalyst described is γ-Al2O3 modified with Ru metal nanoclusters. The mass ratio of Ru to γ-Al2O3 in the catalyst is 5:

100. The light source for the light irradiation is a xenon lamp, and the light irradiation intensity is 1.3 W / cm 2 , and the reaction time for the photocatalytic decomposition of ammonia to produce hydrogen is 15 min.

6. The method according to claim 1, wherein The γ-aluminum oxide catalyst modified with metal nanoclusters is prepared by precipitation method, impregnation method, and two-step synthesis control, including the following steps: 1) Weigh aluminum nitrate and ammonia water in an equimolar ratio, dissolve aluminum nitrate in deionized water, then mix it with the ammonia water solution, and then obtain aluminum hydroxide solid powder through centrifugation, washing, and drying; 2) Calcinate the aluminum hydroxide powder obtained in step 1), and naturally cool it to room temperature to obtain γ-aluminum oxide nanoparticles; 3) Disperse the γ-aluminum oxide powder obtained in step 2) in water, drop the salt solution of the metal to be modified into the alumina suspension according to a certain mass ratio, keep stirring in the dark environment for 120 min, then centrifuge, wash, and dry to remove impurities; 4) Place the dry powder obtained in step 3) in a tube furnace, and carry out low-temperature treatment in a hydrogen atmosphere to obtain the target product; In step 2), during the calcination treatment, the temperature is raised at a rate of 5 °C / min, and calcination treatment is carried out at 700 ± 25 °C for 5 h.

7. The method according to claim 6, characterized in that, In step 3), the salt solution of the metal to be modified is a metal chloride solution of Ni, Ru, or Au, and the mass ratio of the metal to be modified to γ-aluminum oxide is 1-7:

100.

8. The method according to claim 6, wherein In step 4), during the low-temperature treatment, the temperature is raised at a rate of 5 °C / min, and treatment is carried out at 300 °C - 500 °C for 480 minutes.

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