Ammonia decomposition catalyst, preparation method thereof and method for producing hydrogen through ammonia decomposition

Abstract

The invention relates to the field of hydrogen production through ammonia decomposition, and discloses an ammonia decomposition catalyst, a preparation method thereof and a method for producing hydrogen through ammonia decomposition. The catalyst comprises a carrier and a noble metal oxide loaded on the surface of the carrier, the carrier comprises an inert metal hydroxide and a fourth-period transition metal oxide, the carrier is of a sheet structure, and the fourth-period transition metal oxide is loaded on the edge of the sheet structure. The catalyst has excellent ammonia decomposition reaction catalytic activity, the ammonia gas conversion rate can reach 99% or above at the low temperature (500 DEG C), and the catalyst is a novel efficient ammonia decomposition hydrogen production catalyst.

Description

Technical Field

[0001] The invention relates to the field of hydrogen production by decomposing ammonia, and in particular to an ammonia decomposition catalyst and a preparation method thereof and a method for producing hydrogen by decomposing ammonia. Background Art

[0002] The development and utilization of green and carbon-free new energy is imminent. Hydrogen energy is regarded as the cleanest energy with the greatest development potential in the 21st century. Since the 1970s, many countries in the world have begun to conduct extensive research on hydrogen energy. However, the storage and transportation problems of hydrogen still greatly limit the widespread use of hydrogen energy. Ammonia is an ideal hydrogen storage material with a hydrogen storage capacity of 17.8wt%. It can be liquefied at only 8.5 atmospheres at room temperature and has a high volume energy density. In addition, the synthesis, liquefaction, storage and transportation technologies of ammonia are very mature, which can realize on-site hydrogen production without the release of CO in the process, which solves the existing problems of hydrogen.

[0003] Hydrogen production by ammonia decomposition generally refers to hydrogen production by thermal decomposition, which requires low-cost, high-efficiency, and low-energy catalysts as support. For example, precious metal Ru, Ir, and Pt-based catalysts have excellent catalytic effects, but their content is rare and expensive, which limits their large-scale industrial use. Next, some non-precious metals such as Ni, Co, Fe, and Cu are easy to obtain and cheap. The catalyst preparation methods such as impregnation with composite metal oxide carriers, coprecipitation, and structural transformation methods are used to improve the dispersion of active metals and the synergistic effect between metals and carriers, thereby improving the activity of the catalyst. However, the catalytic effect is still not ideal at low temperatures (<550°C). At the same time, the carrier of the ammonia decomposition catalyst has a great influence on its catalytic activity. Higher ammonia decomposition efficiency usually requires good dispersion and higher specific surface area of ​​the carrier to increase the metal component loading, and its mass fraction can reach 10 to 65wt%. However, high-load metals are prone to agglomeration during high-temperature sintering or reaction, which reduces the effective utilization rate and has an adverse effect on the catalytic effect and large-scale utilization of the catalyst. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of the existing ammonia decomposition catalyst in the prior art, such as unsatisfactory catalytic effect at low temperature (<550°C), easy agglomeration of active components during reaction, low effective utilization rate, etc., and to provide an ammonia decomposition catalyst and a preparation method thereof, and a method for producing hydrogen by decomposing ammonia. The catalyst has high catalytic activity for ammonia decomposition reaction, and at low temperature (500°C), the ammonia conversion rate can reach more than 99%.

[0005] According to a first aspect of the present invention, the present invention provides an ammonia decomposition catalyst, which includes a carrier and a precious metal oxide loaded on the surface of the carrier; the carrier includes an inert metal hydroxide and a fourth period transition metal oxide, wherein the carrier is a sheet structure, and the fourth period transition metal oxide is loaded on the edge of the sheet structure.

[0006] According to a second aspect of the present invention, the present invention provides a method for preparing the catalyst of the present invention, the method comprising: (1) forming an alkaline solution from an inert metal source, subjecting the alkaline solution to a high-pressure hydrothermal reaction, drying, grinding and calcining; (2) forming an alkaline slurry from the solid obtained in step (1) and a fourth period transition metal source, subjecting the alkaline slurry to a microwave hydrothermal reaction, drying, grinding and calcining; (3) contacting and impregnating the precious metal source solution with the solid obtained in step (2), washing, filtering, drying and grinding.

[0007] According to a third aspect of the present invention, the present invention provides a method for producing hydrogen by decomposing ammonia, the method comprising: contacting the catalyst of the present invention with ammonia gas for reaction.

[0008] The catalyst of the present invention has excellent catalytic performance and high catalytic activity for ammonia decomposition reaction. The ammonia conversion rate can reach more than 99% at low temperature (500° C.), and the ammonia decomposition conversion rate can reach more than 85% at 450° C. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a transmission electron microscope image of the catalyst sample prepared in Example 1;

[0010] Figure 2 This is the XRD pattern of the catalyst sample prepared in Example 1;

[0011] Figure 3 This is a transmission electron microscope image of the catalyst sample prepared in Comparative Example 1;

[0012] Figure 4 This is a transmission electron microscope image of the catalyst sample prepared in Comparative Example 2. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0014] The present invention provides an ammonia decomposition catalyst, which includes a carrier and a noble metal oxide loaded on the surface of the carrier; the carrier includes an inert metal-free hydroxide and a fourth period transition metal oxide, wherein the carrier is in a sheet structure, and the fourth period transition metal oxide is loaded on the edge of the sheet structure. The catalyst has excellent catalytic performance and high catalytic activity for ammonia decomposition reaction. At low temperature (500°C), the ammonia conversion rate can reach more than 99% and at 450°C, the ammonia decomposition conversion rate can reach more than 85%.

[0015] The inert metal hydroxide of the present invention refers to a metal hydroxide that does not show ammonia decomposition activity in the ammonia decomposition hydrogen production reaction, that is, does not participate in the ammonia decomposition reaction.

[0016] In the present invention, there is no special limitation on the flattened diameter of the sheet-like structure. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the flattened diameter of the sheet-like structure is 500-1000nm, preferably 500-600nm.

[0017] In the present invention, there is no special limitation on the thickness of the sheet structure. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the thickness of the sheet structure is 1-8nm, preferably 2-3nm.

[0018] According to a preferred embodiment of the present invention, the edge thickness of the fourth period transition metal oxide loading is 5-50 nm, preferably 5-15 nm.

[0019] In the present invention, the flattened diameter is the maximum diameter of the lamellar structure particles on a two-dimensional plane; the thickness is the average diameter perpendicular to the flattened diameter; and the edge thickness is the loaded thickness of the fourth period transition metal oxide loaded on the edge of the lamellar structure.

[0020] In the present invention, the content of the inert metal hydroxide in the catalyst can be selected in a wide range, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the content of the inert metal hydroxide is 30-90wt% based on the weight of the catalyst.

[0021] In the present invention, there is no special requirement for the content of the noble metal oxide in the catalyst. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the content of the noble metal oxide is 2-3wt% based on the weight of the catalyst.

[0022] In the present invention, in the catalyst, the optional range of the content of the fourth period transition metal oxide is relatively wide, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the content of the fourth period transition metal oxide is 12-68wt% based on the weight of the catalyst.

[0023] The catalyst of the present invention comprises a fourth period transition metal oxide and a noble metal oxide. Under the condition of satisfying the above-mentioned ratio characteristics, in the ammonia decomposition hydrogen production reaction, it is more conducive to the dissociation of NH at high temperature and the N at low temperature. 2 The desorption of ions can improve the low-temperature catalytic performance of the catalyst.

[0024] In the present invention, there is no special requirement for the specific type of the fourth period transition metal. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the fourth period transition metal is selected from one or more of Ni, Co, Fe, and Cu.

[0025] According to a preferred embodiment of the present invention, the fourth period transition metal is selected from Ni and Co, and the content of Ni and Co, calculated as oxides, is not less than 10 wt %, preferably 20-70 wt %.

[0026] In the present invention, there is no special requirement for the specific type of the precious metal. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the precious metal is selected from one or more of Ru, Pt, and Pd, preferably Ru.

[0027] In the present invention, there is no special requirement for the specific type of the inert metal. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the inert metal is selected from one or more of Mg, Ce, and Al.

[0028] The present invention provides a method for preparing the catalyst of the present invention, which comprises: (1) forming an alkaline solution from an inert metal source, subjecting the alkaline solution to a high-pressure hydrothermal reaction, drying, grinding and roasting; (2) forming an alkaline slurry from the solid obtained in step (1) and a fourth period transition metal source, subjecting the alkaline slurry to a microwave hydrothermal reaction, drying, grinding and roasting; and (3) contacting and impregnating the precious metal source solution with the solid obtained in step (2), washing, filtering, drying and grinding.

[0029] In the present invention, the microwave hydrothermal reaction refers to a hydrothermal reaction carried out under microwave heating conditions, and the high-pressure hydrothermal reaction refers to a hydrothermal reaction carried out in a high-pressure environment.

[0030] In the present invention, in step (1), there is no special requirement for the place where the high-pressure hydrothermal reaction is carried out, and the high-pressure reactor conventionally used in the technical field can achieve the purpose of the present invention. There is no special requirement for the reaction conditions of the high-pressure hydrothermal reaction. The following is an exemplary description, but it does not limit the scope of the present invention. For example, the reaction temperature of the high-pressure hydrothermal reaction can be 120-160° C., the reaction pressure can be 2-3 MPa, and the reaction time can be 3-6 h.

[0031] In the present invention, in order to form an alkaline solution or solution, the material is usually mixed with deionized water. There is no special requirement for the amount of deionized water added, and it can be added according to the actual situation.

[0032] In the present invention, in step (1), after the high-pressure hydrothermal reaction is completed, the post-reaction solution is washed to neutrality and then dried, which is well known to those skilled in the art; the drying, grinding and roasting are conventional operations in the art and will not be described in detail here.

[0033] In the present invention, in step (2), there is no particular limitation on the temperature of the microwave hydrothermal reaction. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the temperature of the microwave hydrothermal reaction is 60-100°C.

[0034] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the time of the microwave hydrothermal reaction. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the time of the microwave hydrothermal reaction is 15-60 minutes.

[0035] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the power of the microwave hydrothermal reaction. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the power of the microwave hydrothermal reaction is 60-300W.

[0036] According to a preferred embodiment of the present invention, the microwave hydrothermal reaction comprises: first heating at 60-70°C, 80-150W for 20-40min, and then heating at 80-90°C, 180-300W for 10-20min. The catalyst prepared by the above technical solution has more exposed active sites, a larger catalytic area, and better ammonia decomposition catalytic performance.

[0037] In the present invention, in step (2), after the microwave hydrothermal reaction is completed, the solution is washed to neutrality and then dried, which is well known to those skilled in the art.

[0038] In the present invention, in step (3), there is no special requirement for the temperature of the contact impregnation. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the temperature of the contact impregnation is 70-90° C. During the impregnation process, stirring is usually performed to completely convert the inert metal oxide obtained in step (2) into an inert metal hydroxide, and to oxidize the noble metal ions to exist and be loaded in the form of noble metal oxides. This is well known to those skilled in the art and is only briefly described here.

[0039] In the present invention, in step (3), there is no special requirement for the contact immersion time. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the contact immersion time is 4-6 hours.

[0040] In the present invention, in step (3), after contact and impregnation, the mixture is usually left to stand for 1-2 hours before washing, filtration, drying and grinding, which are well known to those skilled in the art.

[0041] In the present invention, in step (3), washing, filtration, drying and grinding are operations well known to those skilled in the art and will not be described in detail here.

[0042] In the present invention, the purpose of the present invention can be achieved by satisfying the above requirements. There is no special requirement for the specific type of the inert metal source. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the inert metal source is selected from one or more metal salts of Mg, Al, and Ce.

[0043] In the present invention, the purpose of the present invention can be achieved by satisfying the above requirements. The specific type of the fourth period transition metal source is not particularly limited. The following exemplary description is provided, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the fourth period transition metal source is selected from the fourth period transition metal salt, preferably one or more metal salts of Ni, Co, Fe, and Cu, and more preferably a mixture of metal salts of Ni and Co.

[0044] In the present invention, as long as the purpose of the present invention can be achieved, there is no special limitation on the specific type of the precious metal source. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the precious metal source is selected from precious metal salts, preferably one or more metal salts of Ru, Pt, and Pd, and more preferably a metal salt of Ru.

[0045] In the present invention, the purpose of the present invention can be achieved by satisfying the above requirements. There is no special requirement for the alkali source required to form the alkaline solution or alkaline slurry. The following exemplary description is not intended to limit the scope of the present invention. According to a preferred embodiment of the present invention, the alkali source is selected from one or more of ammonia water, urea, and sodium hydroxide. In the embodiment of the present invention, ammonia water is used as the alkali source required to form the alkaline solution to illustrate the advantages of the present invention. There is no special requirement for the concentration of ammonia water, for example, it can be 25-28wt%.

[0046] In the present invention, the purpose of the present invention can be achieved by satisfying the above requirements. The dosage relationship between the inert metal source and the alkali source is not particularly limited. The following exemplary description is provided, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the molar ratio of the inert metal source to the alkali source is 1:2-10.

[0047] In the present invention, the purpose of the present invention can be achieved by satisfying the above requirements. There is no special limitation on the dosage relationship between the fourth period transition metal source and the alkali source. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the molar ratio of the fourth period transition metal source to the alkali source is 1:6-12.

[0048] The present invention provides a method for producing hydrogen by decomposing ammonia, which comprises: contacting the catalyst of the present invention with ammonia gas for reaction.

[0049] In the present invention, the reaction temperature can be selected in a wide range, which is exemplified below, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the reaction temperature is 450-600° C. The catalyst of the present invention can achieve good catalytic conversion of ammonia at low temperature (<550° C.) and substantially complete conversion at high temperature.

[0050] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the reaction time. The following is an exemplary description, but the scope of the present invention is not limited thereby. For example, the reaction time is 2-4h.

[0051] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the reaction space velocity of the reaction. The following is an exemplary description, but it does not limit the scope of the present invention. For example, it is 8000-12000 mL·g cat -1 ·h -1 .

[0052] The present invention will be described in detail below through examples.

[0053] In the following embodiments,

[0054] The equipment used for microwave hydrothermal reaction was produced by Peian Co., Ltd., model number Discover 2.0;

[0055] In the present invention, since the noble metal oxide is uniformly dispersed and loaded on the carrier surface, and the loading amount is small, the size of the carrier with a sheet structure is regarded as the size of the catalyst sheet particles, and the flattened diameter and thickness of the sheet particles and the edge thickness of the loaded fourth period transition metal oxide are measured multiple times by transmission electron microscopy and averaged.

[0056] The content of each component in the catalyst is calculated based on the feed.

[0057] [Example 1]

[0058] (1) 15 mmol of magnesium chloride was mixed with 50 ml of deionized water, and then 2.5 ml of ammonia water (25 wt%) was added. After stirring at room temperature for 0.5 h, the mixture was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the mixture was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The mixture was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain MgO;

[0059] (2) 0.6 g of MgO obtained in step (1) was mixed with 20 ml of deionized water, 4 ml of ammonia water (25 wt%) was added, and then 7.5 mmol of nickel sulfate was added. After stirring for 10 min, a microwave hydrothermal reaction was carried out under the reaction conditions of 300 W power, 80 ° C., and 60 min. The solution was then washed to neutrality and dried at 80 ° C. for 12 h. The dried powder was ground and calcined in a muffle furnace at 500 ° C. for 2 h to obtain a precursor powder;

[0060] (3) Take 0.054 g of RuCl 3 ·3H 2 O was mixed with 10 ml of deionized water, and then the precursor powder obtained in step (2) was added, stirred at 80°C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80°C for 12 h, and ground to obtain a catalyst sample.

[0061] Figure 1 is the transmission electron microscope image of the catalyst sample. Figure 2 The XRD diagram of the catalyst sample shows that the morphology of the catalyst sample is flaky particles. After measurement, the flattened diameter of the flaky particles is 447nm, the thickness is 4.6nm, and the edge thickness is 12nm. In the catalyst, Mg(OH) 2 The content is 58wt%, NiO content is 40wt%, RuO 2 The content is 2wt%.

[0062] [Example 2]

[0063] (1) 11 mmol of aluminum nitrate was mixed with 50 ml of deionized water, and then 6 ml of ammonia water (25 wt%) was added. After stirring at room temperature for 0.5 h, the mixture was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the mixture was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The mixture was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain MgO;

[0064] (2) Take 1.1 g of Al obtained in step (1) 2 O 3 Mix with 20 ml of deionized water, add 4 ml of ammonia water (25 wt%), and then add 7.5 mmol of cobalt sulfate into the mixed solution. After stirring for 10 min, carry out microwave hydrothermal reaction. The reaction conditions are power 300 w, temperature 80 ° C, and time 60 min. Then, wash the solution to neutrality, dry it at 80 ° C for 12 h, grind the dried powder and put it into a muffle furnace at 500 ° C for 2 h to obtain a precursor powder.

[0065] (3) Take 0.054 g of RuCl 3 ·3H 2 O was mixed with 10 ml of deionized water, and then the precursor powder obtained in step (2) was added, stirred at 80°C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80°C for 12 h, and ground to obtain a catalyst sample.

[0066] The transmission electron microscopy image of the catalyst sample is Figure 1 Similarly, the XRD pattern is Figure 2 Similarly, the morphology of the catalyst sample is flaky particles. After measurement, the flattened diameter of the flaky particles is 756nm, the thickness is 1.7nm, and the edge thickness is 20nm. In the catalyst, Al(OH) 3 The content is 58wt%, CoO content is 40wt%, RuO 2 The content is 2wt%.

[0067] [Example 3]

[0068] (1) 15 mmol of magnesium chloride was mixed with 50 ml of deionized water, and then 2.5 ml of ammonia water (25 wt%) was added. After stirring at room temperature for 0.5 h, the mixture was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the mixture was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The mixture was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain MgO;

[0069] (2) 0.65 g of MgO obtained in step (1) was mixed with 20 ml of deionized water, 4 ml of ammonia water (25 wt%) was added, and then 5.25 mmol of copper sulfate was added. After stirring for 10 min, a microwave hydrothermal reaction was carried out under the reaction conditions of 200 W power, 100 ° C., and 45 min. The solution was then washed to neutrality, dried at 80 ° C. for 12 h, and the dried powder was ground and calcined in a muffle furnace at 500 ° C. for 2 h to obtain a precursor powder;

[0070] (3) Take 0.082 g of RuCl 3 ·3H 2 O was mixed with 10 ml of deionized water, and then the precursor powder obtained in step (2) was added, stirred at 80°C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80°C for 12 h, and ground to obtain a catalyst sample.

[0071] The transmission electron microscopy image of the catalyst sample is Figure 1 Similarly, the XRD pattern is Figure 2 Similarly, the morphology of the catalyst sample is flaky particles. After measurement, the flattened diameter of the flaky particles is 682nm, the thickness is 3.4nm, and the edge thickness is 15nm. In the catalyst, Mg(OH) 2 The content is 67wt%, CuO content is 30wt%, RuO 2 The content is 3wt%.

[0072] [Example 4]

[0073] (1) 15 mmol of magnesium chloride was mixed with 50 ml of deionized water, and then 2.5 ml of ammonia water (25 wt%) was added to the solution. After stirring at room temperature for 0.5 h, the solution was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the solution was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The solution was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain MgO;

[0074] (2) 0.6 g of MgO obtained in step (1) was mixed with 20 ml of deionized water, 4 ml of ammonia water (25 wt%) was added, and then 5 mmol of nickel sulfate and 2.5 mmol of cobalt sulfate were added according to the Ni:Co molar ratio of 2:1. After stirring for 10 min, a microwave hydrothermal reaction was carried out under the reaction conditions of 300 W power, 80 ° C, and 60 min. After completion, the solution was washed to neutrality, dried at 80 ° C for 12 h, and the dried powder was ground and calcined in a muffle furnace at 500 ° C for 2 h to obtain a precursor powder;

[0075] (3) Take 0.14 g of RuCl 3 ·3H2 O was mixed with 10 ml of deionized water, and then 1 g of precursor powder was added, stirred at 80 °C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80 °C for 12 h, and ground to obtain a catalyst sample.

[0076] The transmission electron microscopy image of the catalyst sample is Figure 1 Similarly, the XRD pattern is Figure 2 Similarly, the morphology of the catalyst sample is flaky particles. After measurement, the flattened diameter of the flaky particles is 583nm, the thickness is 2.6nm, and the edge thickness is 16nm. In the catalyst, Mg(OH) 2 The content is 58wt%, the content of NiO is 26.7wt%, the content of CoO is 13.3wt%, and the content of RuO 2 The content is 2wt%.

[0077] [Example 5]

[0078] (1) 15 mmol of magnesium chloride was mixed with 50 ml of deionized water, and then 2.5 ml of ammonia water (25 wt%) was added. After stirring at room temperature for 0.5 h, the mixture was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the mixture was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The mixture was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain a MgO carrier.

[0079] (2) 0.6 g of MgO obtained in step (1) was mixed with 20 ml of deionized water, 4 ml of ammonia water (25 wt%) was added, and then 5 mmol of nickel sulfate and 2.5 mmol of cobalt sulfate were added according to the Ni:Co molar ratio of 2:1. After stirring for 10 min, a microwave hydrothermal reaction was performed. The reaction conditions were: first reacting at 70°C and 150 W for 25 min, then reacting at 90°C and 300 W for 15 min, then washing the solution to neutrality, drying at 80°C for 12 h, grinding the dried powder and calcining it in a muffle furnace at 500°C for 2 h to obtain a precursor powder;

[0080] (3) Take 0.054 g of RuCl 3 ·3H 2 O was mixed with 10 ml of deionized water, and then the precursor powder obtained in step (2) was added, stirred at 80°C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80°C for 12 h, and ground to obtain a catalyst sample.

[0081] The transmission electron microscopy image of the catalyst sample is Figure 1 Similarly, the XRD pattern is Figure 2Similarly, the morphology of the catalyst sample is flaky particles. After measurement, the flattened diameter of the flaky particles is 550nm, the thickness is 2.9nm, and the edge thickness is 13nm. In the catalyst, Mg(OH) 2 The content is 58wt%, the content of NiO is 26.7wt%, the content of CoO is 13.3wt%, and the content of RuO 2 The content is 2wt%.

[0082] [Comparative Example 1]

[0083] (1) 15 mmol of magnesium chloride was mixed with 50 ml of deionized water, and then 2.5 ml of ammonia water (25 wt%) was added. After stirring at room temperature for 0.5 h, the mixture was poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 120° C. for 6 h. After the reactor was cooled to room temperature, the mixture was centrifuged and washed until neutral, and then dried at 80° C. for 12 h. The mixture was placed in a muffle furnace and calcined at 550° C. for 4 h to obtain MgO;

[0084] (2) 0.6 g of MgO obtained in step (1) was mixed with 20 ml of deionized water, 4 ml of ammonia water (25 wt%) was added, and then 7.5 mmol of nickel sulfate was added. After stirring for 10 min, a high-pressure hydrothermal reaction was carried out under the reaction conditions of 2 MPa, 120° C., and 6 h. After the reactor was cooled to room temperature, the solution was washed to neutrality and dried at 80° C. for 12 h. The dried powder was ground and calcined in a muffle furnace at 500° C. for 2 h to obtain a precursor powder.

[0085] (3) Take 0.054 g of RuCl 3 ·3H 2 O was mixed with 10 ml of deionized water, and then the precursor powder obtained in step (2) was added, stirred at 80°C for 5 h, and then allowed to stand for 1 h. After completion, it was washed with deionized water, filtered, dried at 80°C for 12 h, and ground to obtain a catalyst sample.

[0086] Figure 3 This is a transmission electron microscope image of the catalyst sample, which shows that the morphology of the catalyst sample is irregular flakes, and the flake structure has obvious agglomeration phenomenon.

[0087] [Comparative Example 2]

[0088] Take 0.6g MgO and mix it with 20ml deionized water, add 7.5mmol nickel sulfate and 0.054g RuCl 3 ·3H 2O, stirred at 80°C for 5 hours, poured into a high-pressure reactor and placed in a drying oven for a hydrothermal reaction at 2MPa, 120°C, and 6 hours. After the reactor was cooled to room temperature, the solution was washed to neutrality and dried at 80°C for 12 hours. The dried powder was ground and calcined in a muffle furnace at 500°C for 2 hours to obtain a catalyst sample.

[0089] Figure 4 This is a transmission electron microscope image of the catalyst sample, which shows that the morphology of the catalyst sample is amorphous flakes that are stacked and mixed layer by layer.

[0090]

Catalyst performance test

[0091] The ammonia decomposition performance of the nickel-based catalysts in Examples 1-5 and the catalyst samples prepared in Comparative Examples 1-2 was tested and evaluated in an ammonia decomposition tubular furnace reactor. The tubular furnace reactor quartz tube has an inner diameter of 6 mm and an outer diameter of 8 mm. 0.15 g of catalyst (40-100 mesh) was mixed with 0.9 g of quartz sand and heated to 400°C at 5°C / min for 2 h in a 50 ml / min hydrogen-argon (10%) mixed gas. The mixture was reduced for 2 h and then heated to 600°C at 5°C / min. Ammonia gas was passed at 25 ml / min for 2 h before the test was started. The reaction space velocity was 10000 mL·g cat -1 ·h -1 , the reaction temperatures are 350°C, 400°C, 450°C, 500°C, 550°C and 600°C, and the catalyst activity results are shown in Table 1;

[0092] Ammonia conversion % is:

[0093]

[0094] Table 1

[0095]

[0096]

[0097] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. An ammonia decomposition catalyst, characterized in that The catalyst comprises a carrier and a noble metal oxide loaded on the surface of the carrier; the carrier comprises an inert metal hydroxide and a fourth period transition metal oxide, wherein the carrier is in a sheet structure, and the fourth period transition metal oxide is loaded on the edge of the sheet structure.

2. The catalyst according to claim 1, wherein The flattened diameter of the sheet-like structure is 500-1000 nm, preferably 500-600 nm; and / or The thickness of the sheet structure is 1-8 nm, preferably 2-3 nm; and / or The edge thickness of the fourth period transition metal oxide loading is 5-50 nm, preferably 5-15 nm.

3. The catalyst according to claim 1 or 2, wherein In the catalyst, based on the weight of the catalyst, The content of the inert metal hydroxide is 30-90wt%; and / or The content of the noble metal oxide is 2-3wt%; and / or The content of the fourth period transition metal oxide is 12-68 wt %.

4. The catalyst according to any one of claims 1 to 3, wherein The fourth period transition metal is selected from one or more of Ni, Co, Fe, and Cu; and / or The noble metal is selected from one or more of Ru, Pt, and Pd, preferably Ru; and / or The inert metal is selected from one or more of Mg, Ce, and Al; Preferably, the fourth period transition metal is selected from Ni and Co, and the content of Ni and Co is not less than 10 wt % each, preferably 20-70 wt % each, based on the total weight of the fourth period transition metal oxide.

5. A method for preparing the catalyst according to claims 1-4, characterized in that: The method includes: (1) forming an alkaline solution from an inert metal source, subjecting the alkaline solution to a high-pressure hydrothermal reaction, drying, grinding, and roasting; (2) forming an alkaline slurry with the solid obtained in step (1) and the fourth period transition metal source, subjecting the alkaline slurry to a microwave hydrothermal reaction, drying, grinding, and calcining; (3) contacting and impregnating the precious metal source solution with the solid obtained in step (2), washing, filtering, drying and grinding.

6. The method according to claim 5, wherein: The conditions of the microwave hydrothermal reaction include: The temperature is 60-100°C; and / or Duration is 15-60 minutes; and / or Power is 60-300W; Preferably, The microwave hydrothermal reaction comprises: first heating at 60-70°C, 80-150W for 20-40min, and then heating at 80-90°C, 180-300W for 10-20min; and / or The contact immersion conditions include: Temperature of 70-90°C; and / or The time is 4-6 hours.

7. The method according to claim 5 or 6, wherein: The inert metal source is selected from inert metal salts, preferably one or more metal salts of Mg, Al, Ce; and / or The fourth period transition metal source is selected from the fourth period transition metal salts, preferably one or more metal salts of Ni, Co, Fe, Cu, more preferably a mixture of metal salts of Ni and Co; and / or The noble metal source is selected from noble metal salts, preferably one or more metal salts of Ru, Pt, Pd, more preferably a metal salt of Ru; and / or The alkaline source required to form the alkaline solution or alkaline slurry is selected from one or more of ammonia water, urea and sodium hydroxide.

8. The method according to any one of claims 7, wherein: The molar ratio of the inert metal source to the alkali source is 1:2-10; and / or The molar ratio of the fourth period transition metal source to the alkali source is 1:6-12.

9. A method for producing hydrogen by decomposing ammonia, characterized in that: The method comprises: contacting the catalyst described in any one of claims 1 to 4 with ammonia gas for reaction.

10. The method according to claim 9, wherein: The reaction conditions include: The reaction temperature is 450-600°C; and / or The reaction time is 2-4 hours; and / or Reaction space velocity is 8000-12000mL·g cat -1 ·h -1 .

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