Highly dispersed and high loading molybdenum nitride catalyst, its preparation method and application

Abstract

The application provides a high-dispersion high-load Mo2N catalyst and a preparation method and application thereof, and belongs to the technical field of ammonia decomposition. In one aspect, the high-load Mo2N catalyst coated with carbon is prepared by combining and coordinating ammonium molybdate with an amine carbon source and in-situ nitriding at high temperature in an inert gas. In another aspect, silicon balls with a supporting and dispersing effect are added to the Mo2N-carbon structure, which effectively inhibits the aggregation of molybdenum caused by carbon etching, improves the overall sintering resistance of the catalyst, and makes the catalyst have excellent ammonia decomposition stability, thereby making up for the shortcomings of existing non-noble metal catalysts, such as low load of active components, sintering and phase transition under high-temperature conditions, and catalyst deactivation. The high-dispersion high-load Mo2N catalyst obtained by the application has a conversion rate of about 90% at 600 DEG C and a WHSV of 90,000 mL / g / h, and remains basically unchanged within 200 h.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ammonia decomposition, in particular to a high-dispersion high-loading Mo2N catalyst and a preparation method and application thereof. BACKGROUND

[0002] The greenhouse gases and solid particulate pollutants generated by fossil energy have far exceeded the self-purification capacity of nature, so the development and utilization of clean energy is the key to solving the environmental and energy problems.

[0003] Hydrogen energy is considered as the most promising clean energy due to its cleanliness and high heat value. Hydrogen energy fuel cell is the most effective form of utilizing hydrogen energy, which can improve the utilization rate by 40% to 50% compared with other methods. However, the volumetric energy density of hydrogen is low, and it is difficult to store. With the current hydrogen storage technology, whether hydrogen is stored in the form of liquid or gas, there are problems such as too large volume, too high pressure, and low safety factor. If hydrogen is stored in the form of liquid fuel (ammonia, methanol, formic acid) through a certain catalytic reaction, and the stored hydrogen is released in situ for fuel cell use, the hydrogen storage problem of fuel cell can be effectively solved, and the hydrogen energy fuel cell can be further developed.

[0004] Ammonia is considered as a very promising long-term large-scale energy storage carrier in recent years. First, the industrial synthesis of ammonia has a long history, mature technology, and conditions for large-scale industrial synthesis of ammonia. In addition, ammonia molecules have high H / N ratio, high hydrogen storage capacity, and no carbon, which is easy to release hydrogen and zero carbon emission. Ammonia as a hydrogen storage carrier has high hydrogen content (17.6wt%), high energy density (3000Whkg -1 ), easy liquefaction (room temperature, 8atm), convenient storage and transportation, zero carbon emission, and non-flammable characteristics. Combined with ammonia decomposition reaction to produce hydrogen, it is expected to promote the development of hydrogen energy industry, and has great economic value and practical significance. Since the ammonia decomposition reaction is an endothermic reaction with an increase in the number of reaction molecules, increasing the reaction temperature is beneficial to improving the reaction conversion rate, which also leads to high energy consumption for ammonia decomposition at low temperature. Therefore, low-temperature and high-efficiency ammonia decomposition catalyst is the key to solving the problem of high energy consumption.

[0005] Currently, metal carbon / nitride and iron, cobalt, nickel, ruthenium-based catalysts are often applied to the study of ammonia decomposition reaction. Among them, the temperature of Fe, Co, Ni and other non-noble metal-based catalysts to reach the equilibrium conversion rate is generally 600 degrees and above, and the low-temperature ammonia decomposition activity is poor; the noble metal ruthenium-based catalyst shows the best catalytic activity, but its high price limits its popularization and application. In contrast, transition metal carbon / nitride has the properties of low cost, good thermal stability and noble metal-like, and has relatively active properties in activating small molecules (CH4, NH3, CH3OH, etc.) to produce hydrogen. Among them, the ammonia decomposition activity of molybdenum carbon / nitride is excellent, and has been widely concerned and studied. CN114100661A discloses a sol-gel method for preparing Mo2N, and the ammonia decomposition conversion rate of the reaction generated Mo2N-MoO2 composite structure is 94.3% under the condition of 30000h -1 , 600℃. Zheng et al. (Zheng, W., et al. (2013). Journal of the American Chemical Society, 135(9), 3458.) studied the change of β-Mo2C in the long-term ammonia decomposition reaction process, and the main reason for its deactivation is the formation of MoN phase with small surface area. Combined with the calculation results, it can be known that the defect sites on the surface of the catalyst are the active centers of ammonia decomposition. Zhai et al. (Zhai, L., et al. Applied Catalysis B: Environmental, 294.) used SBA-15 to limit the dispersion of Mo2N and added graphene to adjust the electronic structure, and obtained a Mo2N / SBA-15 / rGO catalyst with high ammonia decomposition activity. Although the inert carrier SBA-15 is beneficial to maintain the high specific surface area of the catalyst, the problem of its transformation into a molybdenum phase with lower activity has not been solved. SUMMARY

[0006] The purpose of the present application is to provide a high-dispersion high-load Mo2N catalyst and its preparation method and application. The high-dispersion high-load Mo2N catalyst has high activity and high stability, which makes up for the shortcomings of the existing non-noble metal catalysts, such as low load of active components, sintering and phase transformation under high temperature conditions, and catalyst deactivation.

[0007] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0008] The present application provides a high-dispersion high-load Mo2N catalyst, which comprises the following mass molar ratio of raw materials: silicon source: amine-based organic matter: molybdenum source = 0-20g: 10mmol: 1-20mmol.

[0009] Preferably, the silicon source comprises one of silica sol, silica ball, amorphous silica; the amine-containing organic compound comprises one of p-phenylenediamine, hexamethylenetetramine; the molybdenum source comprises one of ammonium paramolybdate, phosphomolybdate, sodium molybdate.

[0010] The application also provides a preparation method of the high-dispersion high-load Mo2N catalyst, comprising the following steps:

[0011] (1) dissolving the silicon source in deionized water, adding hydrochloric acid for pre-acidification treatment, sequentially adding the amine-containing organic compound solution and the molybdenum source solution, and mixing uniformly to obtain a mixed system;

[0012] (2) adjusting the PH value of the mixed system, stirring and aging, separating and washing the precipitate, and drying to obtain a precursor;

[0013] (3) placing the precursor in flowing argon for temperature rising nitridation to obtain the high-dispersion high-load Mo2N catalyst.

[0014] Preferably, in step (1), the concentration of the hydrochloric acid is 1 mol / L, and the mass-volume ratio of the silicon source to the hydrochloric acid is 0-10 g:0-2 mL.

[0015] Preferably, in step (2), the PH value is 1-5, and the stirring and aging time is 2-5 h.

[0016] Preferably, in step (3), the temperature rising nitridation method is as follows:

[0017] ramping at a rate of 5-20 ℃ / min to 600-800 ℃, and keeping the temperature for 1-4 h, then decreasing to room temperature and passivating in 1% O2 / Ar for 10-12 h.

[0018] The application also provides an application of the high-dispersion high-load Mo2N catalyst in an ammonia decomposition reaction.

[0019] Preferably, the high-dispersion high-load Mo2N catalyst needs to be pretreated before being used for hydrogen production by ammonia decomposition; the pretreatment temperature is 350-550 ℃; the temperature rising rate during the pretreatment is 5-15 ℃ / min; the pretreatment time is 30-60 min; and the pretreatment is carried out in a H2 / N2 atmosphere.

[0020] The application has the following beneficial effects compared with the prior art:

[0021] (1) The application utilizes the combination and coordination of the amine carbon source and ammonium molybdate to prepare a high-load carbon-coated molybdenum nitride catalyst by high-temperature inert gas in-situ nitridation, the molybdenum nitride load of which is as high as 46.6%, and the initial conversion rate of the obtained high-dispersion high-load Mo2N catalyst to NH3 is about 99% at 550 ℃.

[0022] (2) On the other hand, since the amorphous carbon formed by pyrolysis of organic matters is more easily etched and sintered in the ammonia decomposition reaction, thereby reducing the ammonia decomposition reaction activity, the present application adds the silicon balls having the supporting and dispersing effect in the molybdenum nitride-carbon structure, effectively inhibits the aggregation of molybdenum due to carbon etching, improves the overall sintering resistance of the catalyst, and makes the catalyst have excellent ammonia decomposition stability, thereby making up for the shortcomings of the existing non-noble metal catalysts, i.e., low active component loading, sintering and phase transition at high temperature conditions, and catalyst deactivation.

[0023] In the process of preparing the Mo2N catalyst, Mo is successfully coated and dispersed by the carbon source and in-situ nitrided into Mo2N, and when the catalyst is applied to the ammonia decomposition reaction for hydrogen production, the added carrier silica balls have a more obvious improvement in stability, so that the conversion rate is about 90% at 600℃ and WHSV = 90,000 mL / g / h, and remains basically unchanged within 200h. Moreover, the specific surface area of the Mo2N catalyst with the added SiO2 balls reaches 178.7m 2 / g, which is obviously improved compared with the sample without the added silicon balls (132.9m 2 / g). BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 XRD spectra of Mo2N catalysts prepared for Example 1, Example 5, Example 6, and Comparative Example 1;

[0026] Figure 2 N2 adsorption-desorption curves of Mo2N catalysts prepared for Example 1, Example 5, Example 6, and Comparative Example 1;

[0027] Figure 3 Pore size distribution graphs of Mo2N catalysts prepared for Example 1, Example 5, Example 6, and Comparative Example 1;

[0028] Figure 4 Transmission electron microscope graph and particle size statistical graph of the catalyst Mo2N@C(HM) prepared for Example 1;

[0029] Figure 5 High-magnification transmission electron microscope graph of the catalyst Mo2N@C(HM) prepared for Example 1;

[0030] Figure 6Transmission electron microscope image and particle size statistics chart of catalyst Mo2N@C(pP) prepared for Example 5;

[0031] Figure 7 High-magnification transmission electron microscope image of catalyst Mo2N@C(pP) prepared for Example 5;

[0032] Figure 8 Transmission electron microscope image and particle size statistics chart of catalyst Mo2N@C / SiO2 prepared for Example 6;

[0033] Figure 9 High-magnification transmission electron microscope image of catalyst Mo2N@C / SiO2 prepared for Example 6;

[0034] Figure 10 Transmission electron microscope image and particle size statistics chart of catalyst Mo2N@C(oP) prepared for Comparative Example 1;

[0035] Figure 11 High-magnification transmission electron microscope image of catalyst Mo2N@C(oP) prepared for Comparative Example 1;

[0036] Figure 12 Catalytic performance result chart of Mo2N catalysts prepared for Example 1, Example 5, Example 6, Comparative Example 1 in Test Example 1;

[0037] Figure 13 Catalytic performance result chart of Mo2N catalysts prepared for Example 2, Example 3, Example 4, Example 7 in Test Example 1;

[0038] Figure 14 Stability evaluation result chart of Mo2N catalysts prepared for Example 1, Example 6, Example 7 in Test Example 2. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present application will now be described in detail, which should be considered to be merely illustrative in nature and are not to be considered as limiting the scope of the present application, and are understood to be illustrative of certain aspects, features and embodiments of the present application.

[0040] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of, for example, the upper limit and lower limit of a range of values are to be understood to include each and every value and intervening value within the range. Every midpoint between the values, and every other stated value or intervening value in stated ranges is also included in the present application. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0041] Unless otherwise indicated, all technical and scientific terms have the same meaning as those one of ordinary skill in the art of the application described herein would attribute to such terms. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described therein. In case of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification prevails.

[0042] Various modifications and variations of the described methods and materials of the application will be apparent to those skilled in the art from the foregoing disclosure. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples are illustrative only.

[0043] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean inclusion, but not limited to, the listed materials and methods.

[0044] The present application provides a preparation method of high dispersion and high load Mo2N catalyst, comprising the following steps:

[0045] (1) dissolving a silicon source in deionized water, adding hydrochloric acid for pre-acidification treatment, sequentially adding an amine group-containing organic solution and a molybdenum source solution, and mixing uniformly to obtain a mixed system;

[0046] Preferably, the silicon source comprises one of silica sol, silica ball and amorphous silica, and more preferably, the silicon source is silica sol;

[0047] Preferably, the amine group-containing organic compound comprises one of p-phenylenediamine and hexamethylenetetramine, and more preferably, the amine group-containing organic compound is hexamethylenetetramine;

[0048] Preferably, the molybdenum source comprises one of ammonium dimolybdate, phosphomolybdic acid and sodium molybdate, and more preferably, the molybdenum source is ammonium dimolybdate;

[0049] Preferably, the silicon source: amine group-containing organic compound: molybdenum source = 0-20 g: 10 mmol: 1-4 mmol, and more preferably, the silicon source: amine group-containing organic compound: molybdenum source = 10 g: 10 mmol: 3-4 mmol;

[0050] The concentration of the hydrochloric acid is 1 mol / L, and the mass-volume ratio of the silicon source to the hydrochloric acid is 0-10 g: 0-2 mL.

[0051] (2) adjusting the PH value of the mixed system, stirring and aging, separating and washing the precipitate, and drying to obtain a precursor;

[0052] Preferably, the PH value is 1-5, and more preferably, the PH value is 2.3-2.8;

[0053] Preferably, the time for the stirring aging is 2-5h, more preferably 2-4h; the heating stirring temperature is 20-70℃.

[0054] (3) the precursor is placed in flowing argon for temperature rising nitridation to obtain high dispersion high load type Mo2N catalyst;

[0055] Preferably, the method for the temperature rising nitridation is:

[0056] at a temperature rising rate of 5-20℃ / min to 600-800℃, and keeping for 1-4h, then descending to room temperature and passivating for 10-12h in 1% O2 / Ar; more preferably, the temperature rising rate is 10-15℃ / min, and the keeping time is 2-3h.

[0057] Example 1

[0058] The example 1 of the present application gives a preparation method of high dispersion high load type Mo2N catalyst Mo2N@C(HM), which specifically comprises the following steps:

[0059] (1) 1.40g of hexamethylene tetramine (HM) is dissolved in 50ml of deionized water, and after complete dissolution, a hexamethylene tetramine solution is obtained; 3.69g of ammonium paramolybdate is dissolved in 50ml of deionized water, and after complete dissolution, an ammonium paramolybdate solution is obtained.

[0060] (2) in 50ml of deionized water, 1ml of 1M hydrochloric acid is added, then the hexamethylene tetramine solution is added, and after mixing uniformly, the ammonium paramolybdate solution is continuously slowly added dropwise, and the mixed system is obtained after mixing uniformly.

[0061] (3) the PH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and the stirring is aged for 2.5h, after the aging, the precipitate is centrifuged and separated, the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain the precursor.

[0062] (4) the precursor is placed in a tube furnace, and under the flowing argon atmosphere, the temperature is raised to 650℃ at a temperature rising rate of 5℃ / min, and the nitridation is carried out at 650℃ for 2h to obtain the high dispersion high load type Mo2N catalyst Mo2N@C(HM) with hexamethylene tetramine as the dispersion carbon source.

[0063] The Mo2N@C(HM) prepared in example 1 is subjected to XRD test, and the N2 adsorption and desorption effect, pore size, particle size, and transmission electron microscope observation are detected, and the results are shown in Figures 1-5 .

[0064] Example 2

[0065] Embodiment 2 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N-1@C(HM), specifically comprising the following steps:

[0066] (1) 1.40g of hexamethylenetetramine (HM) is dissolved in 50ml of deionized water to obtain a hexamethylenetetramine solution, and 1.23g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0067] (2) 1mL of 1M hydrochloric acid is added to 50ml of deionized water, then the hexamethylenetetramine solution is added, and after mixing, the ammonium paramolybdate solution is slowly added dropwise, and the mixture is uniformly mixed to obtain a mixed system.

[0068] (3) The pH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and aging is performed by stirring for 2.5h, and after aging, the precipitate is separated by centrifugation, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain a precursor.

[0069] (4) The precursor is placed in a tube furnace, heated to 650℃ at a heating rate of 5℃ / min under a flowing argon atmosphere, and nitrided at 650℃ for 2h to obtain a high-dispersion high-loading Mo2N catalyst Mo2N-1@C(HM) with hexamethylenetetramine as a dispersion carbon source.

[0070] Embodiment 3

[0071] Embodiment 3 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N-2@C(HM), specifically comprising the following steps:

[0072] (1) 1.40g of hexamethylenetetramine (HM) is dissolved in 50ml of deionized water to obtain a hexamethylenetetramine solution, and 1.23g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0073] (2) 1mL of 1M hydrochloric acid is added to 50ml of deionized water, then the hexamethylenetetramine solution is added, and after mixing, the ammonium paramolybdate solution is slowly added dropwise, and the mixture is uniformly mixed to obtain a mixed system.

[0074] (3) The pH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and aging is performed by stirring for 2.5h, and after aging, the precipitate is separated by centrifugation, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain a precursor.

[0075] (4) The precursor is placed in a tube furnace, heated to 650 DEG C at a heating rate of 5 DEG C / min under a flowing argon atmosphere, and nitrided at 650 DEG C for 2 h to obtain a high-dispersion high-loading Mo2N catalyst Mo2N-2@C(HM) with hexamethylenetetramine as a dispersion carbon source.

[0076] Example 4

[0077] The embodiment 4 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N-4@C(HM), which specifically comprises the following steps:

[0078] (1) 1.40g of hexamethylenetetramine (HM) is dissolved in 50ml of deionized water to obtain a hexamethylenetetramine solution, and 4.92g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0079] (2) 1ml of 1M hydrochloric acid is added to 50ml of deionized water, then the hexamethylenetetramine solution is added, and after uniform mixing, the ammonium paramolybdate solution is slowly added dropwise, and a mixed system is obtained.

[0080] (3) The PH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and aging is performed by stirring for 2.5h, and after aging, the precipitate is separated by centrifugation, and the precipitate is washed with water and ethanol three times, and then vacuum dried at 60 DEG C for 10h to obtain a precursor.

[0081] (4) The precursor is placed in a tube furnace, heated to 650 DEG C at a heating rate of 5 DEG C / min under a flowing argon atmosphere, and nitrided at 650 DEG C for 2 h to obtain a high-dispersion high-loading Mo2N catalyst Mo2N-4@C(HM) with hexamethylenetetramine as a dispersion carbon source.

[0082] Example 5

[0083] The embodiment 5 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N@C(pP), which specifically comprises the following steps:

[0084] (1) 1.08g of p-phenylenediamine (pP) is dissolved in 50ml of deionized water to obtain a p-phenylenediamine solution, and 3.69g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0085] (2) 1ml of 1M hydrochloric acid is added to 50ml of deionized water, then the p-phenylenediamine solution is added, and after uniform mixing, the ammonium paramolybdate solution is slowly added dropwise, and a mixed system is obtained.

[0086] (3) Adjust the pH value of the mixed system to 2.5 with 1M hydrochloric acid, stir for 2.5h for aging, centrifugal separation of the precipitate after aging, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain the precursor.

[0087] (4) The precursor is placed in a tube furnace, heated to 650℃ at a heating rate of 5℃ / min under a flowing argon atmosphere, and nitrided at 650℃ for 2h to obtain a high-dispersion high-load Mo2N catalyst Mo2N@C(pP) with p-phenylenediamine as a dispersed carbon source.

[0088] The Mo2N@C(pP) prepared in Example 5 is subjected to XRD test, and its N2 adsorption and desorption effect, pore size, particle size, and transmission electron microscope observation, and the results are shown in Figures 1-3 , 6, 7.

[0089] Example 6

[0090] The embodiment 6 of the present application provides a preparation method of a high-dispersion high-load Mo2N catalyst Mo2N@C / SiO2, which specifically comprises the following steps:

[0091] (1) Dissolve 1.40g of hexamethylenetetramine (HM) in 50ml of deionized water to obtain a hexamethylenetetramine solution, and dissolve 3.69g of ammonium paramolybdate in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0092] (2) Add 1mL of 1M hydrochloric acid to 10g of AS-40 silica sol, then add 50ml of deionized water, continue to add the hexamethylenetetramine solution, mix uniformly, and then continue to slowly add the ammonium paramolybdate solution to obtain a mixed system.

[0093] (3) Adjust the pH value of the mixed system to 2.5 with 1M hydrochloric acid, stir for 2.5h for aging, centrifugal separation of the precipitate after aging, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain the precursor.

[0094] (4) The precursor is placed in a tube furnace, heated to 650℃ at a heating rate of 5℃ / min under a flowing argon atmosphere, and nitrided at 650℃ for 2h to obtain a high-dispersion high-load Mo2N catalyst Mo2N@C / SiO2 with 22nm silica spheres as a dispersed carrier.

[0095] The Mo2N@C / SiO2 prepared in Example 6 is subjected to XRD test, and its N2 adsorption and desorption effect, pore size, particle size, and transmission electron microscope observation, and the results are shown in Figures 1-3 , 8, 9.

[0096] Example 7

[0097] Embodiment 7 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N@C / SiO2-2, which specifically comprises the following steps:

[0098] (1) 1.40g of hexamethylenetetramine (HM) is dissolved in 50ml of deionized water to obtain a hexamethylenetetramine solution. 3.69g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0099] (2) 1ml of 1M hydrochloric acid is added to 4g of AS-40 silica sol, then 50ml of deionized water is added, and the hexamethylenetetramine solution is continuously added. After mixing, the ammonium paramolybdate solution is continuously added dropwise, and the mixture is uniformly mixed to obtain a mixed system.

[0100] (3) The pH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and aging is performed by stirring for 2.5h. After aging, the precipitate is separated by centrifugation, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain a precursor.

[0101] (4) The precursor is placed in a tube furnace, and heated to 650℃ at a heating rate of 5℃ / min under a flowing argon atmosphere, and nitrided at 650℃ for 2h to obtain a carbon-coated high-dispersion high-loading Mo2N catalyst Mo2N@C / SiO2-2 with 22nm silica spheres as a dispersion carrier.

[0102] Comparative Example 1

[0103] Embodiment 6 of the present application provides a preparation method of a high-dispersion high-loading Mo2N catalyst Mo2N@C(oP), which specifically comprises the following steps:

[0104] (1) 1.08g of o-phenylenediamine (oP) is dissolved in 50ml of deionized water to obtain an o-phenylenediamine solution. 3.69g of ammonium paramolybdate is dissolved in 50ml of deionized water to obtain an ammonium paramolybdate solution.

[0105] (2) In 50ml of deionized water, 1ml of 1M hydrochloric acid is added, then the o-phenylenediamine solution is added, and after mixing, the ammonium paramolybdate solution is continuously added dropwise, and the mixture is uniformly mixed to obtain a mixed system.

[0106] (3) The pH value of the mixed system is adjusted to 2.5 with 1M hydrochloric acid, and aging is performed by stirring for 2.5h. After aging, the precipitate is separated by centrifugation, and the precipitate is washed with water and ethanol for three times, and then vacuum dried at 60℃ for 10h to obtain a precursor.

[0107] (4) The precursor was placed in a tube furnace and heated to 650°C at a heating rate of 5°C / min under a flowing argon atmosphere. It was then held at 650°C for 2 hours for nitriding to obtain a highly dispersed and highly supported Mo2N catalyst Mo2N@C(oP) with o-phenylenediamine as the dispersed carbon source.

[0108] The Mo2N@C(oP) prepared in Example 6 was subjected to XRD tests, and its N2 adsorption-desorption effect, pore size, and particle size were also detected. Transmission electron microscopy was also performed, and the results are as follows: Figures 1-3 As shown in Figures 10 and 11.

[0109] Experimental Example 1

[0110] Experimental Example 1 of this invention evaluated the catalytic activity of the highly dispersed and highly supported Mo2N catalysts prepared in Examples 1-8. The specific methods are as follows:

[0111] Ammonia decomposition for hydrogen production was conducted in a laboratory micro-fixed-bed reactor comprising three main parts: a reaction gas distribution system, a fixed-bed reaction system, and a detection system, to evaluate catalyst activity. The flow rate of the reaction gas in the distribution system was controlled by a mass flow meter; the fixed-bed reactor in the reaction system was a quartz tube with an inner diameter of 6 mm and a length of 40 cm; the detection system used gas chromatography to quantitatively analyze the gas components at the reactor outlet. The flow rates of each gas required for the experiment were controlled by mass flow meters, and the gases were mixed thoroughly before being introduced into the reactor.

[0112] 50 mg of catalysts from Examples 1-8 (50 mesh particle size) were weighed and placed in quartz tube reactors for the following experiments: H2 / N2 (60 ml / min, H2 / N2 = 3:1) was introduced to replace the air in the reaction tube. The catalysts were pretreated by heating to 500 °C at a rate of 10 °C / min for 50 min. After pretreatment, the gas was switched to pure ammonia, and the temperature was lowered to 400 °C. The temperature was then increased from 400 °C to 600 °C, with a 50 °C interval and a 50 min holding time. Performance was evaluated under conditions of a space velocity of 30000 mL / g / h. The results are as follows: Figure 12 , 13 As shown.

[0113] The catalyst Mo2N@C(HM) in Example 1 achieved an initial conversion of 99% for NH3 at 550°C.

[0114] The catalyst Mo2N-1@C(HM) in Example 2 achieved an initial conversion of 91% for NH3 at 550°C.

[0115] The catalyst Mo2N-2@C(HM) in Example 3 achieved an initial conversion of 97% for NH3 at 550°C.

[0116] The catalyst Mo2N-4@C(HM) in Example 4 achieved an initial conversion of 99% for NH3 at 550°C.

[0117] The catalyst Mo2N@C(pP) in Example 5 achieved an initial conversion of 76% for NH3 at 550°C.

[0118] The catalyst Mo2N@C / SiO2 in Example 6 achieved an initial conversion of 100% for NH3 at 550°C.

[0119] The catalyst Mo2N@C / SiO2-2 in Example 7 achieved an initial conversion rate of 99% for NH3 at 550 °C.

[0120] The catalyst Mo2N@C(oP) of Comparative Example 1 achieved an initial conversion of 57% for NH3 at 550 °C.

[0121] Experimental Example 2

[0122] Experimental Example 2 of this invention evaluated the catalytic activity of the highly dispersed and highly supported Mo2N catalysts prepared in Examples 1-8. The specific methods are as follows:

[0123] The same pretreatment method as in Example 1 was used. After pretreatment, the gas introduced was switched to Ar, and the temperature was raised to 600℃. The stability of the reaction was evaluated under the conditions of 600℃ and NH3 space velocity of 90,000 mL / g / h. The results are as follows: Figure 14 As shown.

[0124] Depend on Figure 14 It can be seen that after 200 hours of stability evaluation, no obvious deactivation was observed in the catalyst Mo2N@C / SiO2 of Example 6. After 40 hours of reaction, the catalyst Mo2N@C / SiO2-2 of Example 7 deactivated from 87% ammonia conversion rate to 76%. After 40 hours of reaction, the catalyst Mo2N@C(HM) of Example 1 deactivated from 80% ammonia conversion rate to 36%.

[0125] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. Use of a highly dispersed high loading Mo2N catalyst in an ammonia decomposition reaction, characterized in that, The preparation method of the high-dispersion high-loading Mo2N catalyst comprises the following steps: (1) dissolving a silicon source in deionized water, adding hydrochloric acid for pre-acidification treatment, sequentially adding an amine-containing organic solution and a molybdenum source solution, and uniformly mixing to obtain a mixed system; (2) adjusting the pH value of the mixed system, heating and stirring for aging, separating and washing the precipitate, and drying to obtain a precursor; (3) placing the precursor in flowing argon for temperature rising nitridation to obtain the high-dispersion high-loading Mo2N catalyst; The silicon source: amine-containing organic: molybdenum source = 0-20 g: 10 mmol: 1-20 mmol, wherein the silicon source is not 0 g; The silicon source includes one of silica sol, silica ball and amorphous silica; the amine-containing organic includes one of p-phenylenediamine and hexamethylenetetramine; and the molybdenum source includes one of ammonium paramolybdate, phosphomolybdic acid and sodium molybdate; In step (3), the method of temperature rising nitridation is as follows: Rising at a rate of 5-20 ℃ / min to 600-800 ℃, and keeping the temperature for 1-4 h, then reducing to room temperature and passivating in 1% O2 / Ar for 10-12 h.

2. The use of the highly dispersed and high loading Mo2N catalyst according to claim 1 in an ammonia decomposition reaction, characterized by, In step (1), the concentration of the hydrochloric acid is 1 mol / L, and the mass-volume ratio of the silicon source to hydrochloric acid is 0-10 g: 0-2 mL, wherein the silicon source and the hydrochloric acid are not 0.

3. The use of the highly dispersed and high loading Mo2N catalyst according to claim 1 in the ammonia decomposition reaction, characterized by, In step (2), the pH value is 1-5, and the stirring aging time is 2-5 h.

4. Application of the high-dispersion high-loading Mo2N catalyst in an ammonia decomposition reaction according to claim 1, wherein the high-dispersion high-loading Mo2N catalyst needs to be pretreated before ammonia decomposition for hydrogen production; the pretreatment temperature is 350-550 ℃; the temperature rising rate during pretreatment is 5-15 ℃ / min; the pretreatment time is 30-60 min; and the pretreatment is carried out in a H2 / N2 atmosphere.

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