A method for preparing an AB2O4 type oxide ammonia decomposition catalyst

Abstract

The application discloses a preparation method of an AB2O4 type oxide ammonia decomposition catalyst, and comprises the following steps: uniformly loading active metals on a silicon carbide carrier by a hydrothermal method to prepare the high-efficiency ammonia decomposition catalyst; wherein the hydrothermal reaction temperature is 180 DEG C, and the reaction time is 12 hours. The application loads transition metals on the silicon carbide by the hydrothermal method to prepare a high-efficiency low-temperature ammonia decomposition catalyst, the catalyst synthesis process is simple, and the catalyst is easy to repeat; the prepared catalyst particles are easy to control and not prone to agglomeration, the ammonia decomposition performance of the catalyst is improved, and the reaction temperature of the complete ammonia decomposition is reduced.

Description

Technical Field

[0001] This invention belongs to the field of ammonia decomposition technology, specifically relating to a method for preparing an AB2O4 type oxide ammonia decomposition catalyst. Background Technology

[0002] The rapid development of the global economy and the overexploitation of traditional fossil fuels such as oil and coal have made energy shortages inevitable, leading to several unavoidable problems: oil is a crucial pillar of current energy supply, and finding alternatives is essential; providing the most convenient and efficient storage and transportation methods for energy fuels is also a major issue in the current energy structure; due to their high energy density and ease of transport, liquefied hydrocarbons and partially vaporized hydrocarbons such as liquefied petroleum gas (LPG) are currently the only viable fuels for automobiles. The excessive consumption of fossil fuels and the resulting environmental pollution have spurred the development of clean and renewable energy sources. There is an urgent need to find alternatives to fossil fuels like oil, and among many new energy sources, hydrogen energy has attracted significant attention and is considered one of the most promising alternatives.

[0003] Currently, almost all hydrogen is produced from catalytic steam reforming of natural gas, which is the mature and commercially viable technology for large-scale hydrogen production. While water electrolysis is a well-known and mature technology for producing clean and high-purity hydrogen, it involves significant energy loss. Another challenge currently facing hydrogen technology is its storage and transportation. Hydrogen has a very high gravimetric energy density (119.7 MJ / kg at 25°C, its lower calorific value). -1 And 1 Bar), but the volumetric energy density is very low (8.96 GJ m). -3 Hydrogen is difficult to compress. Furthermore, hydrogen tends to diffuse within materials, leading to embrittlement or weakening of storage materials. Therefore, chemical hydrogen storage is particularly important. Ammonia is a hydrogen-rich fuel; the volumetric hydrogen density of liquid ammonia is more than 1.5 times that of liquid hydrogen, giving it the highest volumetric hydrogen density compared to other hydrogen storage materials. Ammonia is easily compressed and liquefied (pressurized to 1 MPa at room temperature or cooled to -33°C at room pressure), which can solve the problem of difficult hydrogen storage. It has a high octane number and good anti-knock properties. Complete combustion of ammonia produces only water and nitrogen, with no greenhouse gases produced, making it clean and pollution-free. Therefore, the production of hydrogen through ammonia decomposition shows great promise.

[0004] The decomposition of ammonia is an endothermic reaction (2NH3(g) → N2(g) + 3H2(g); ΔH = 92 kJ / mol) -1 According to thermodynamic principles, the conversion rate of ammonia can reach 99.99% under conditions of 400℃ and 1 atm. However, ammonia can only decompose at temperatures above 800℃ under normal pressure. In order to reduce energy consumption, research is being conducted on highly efficient ammonia decomposition catalysts to reduce the activation energy of the reaction.

[0005] Therefore, there is an urgent need in this field for a novel catalyst with high catalytic activity and high-temperature stability. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an AB2O4 type oxide ammonia decomposition catalyst.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an AB2O4 type oxide ammonia decomposition catalyst, comprising,

[0010] Dissolve nitrates A and B completely in deionized water, then add a precipitant to allow the solution to precipitate completely.

[0011] The reaction was then carried out using a hydrothermal method, and the AB2O4 type oxide precursor was obtained by drying after the reaction was completed.

[0012] The AB2O4 type oxide precursor was calcined in a muffle furnace after being heated at a uniform rate to achieve internal thermal diffusion of metal ions in the material, thus obtaining the AB2O4 type oxide.

[0013] Where A is Cu, Co or Ni, B is Fe, Cr or Al, the hydrothermal reaction temperature is 180℃, and the reaction time is 12h.

[0014] In a preferred embodiment of the preparation method described in this invention, the precipitant includes ammonia.

[0015] In a preferred embodiment of the preparation method described in this invention, the calcination is carried out at a temperature of 600–900°C for a time of 4–5 hours.

[0016] In a preferred embodiment of the preparation method described in this invention, the ammonia decomposition catalyst comprises AFe2O4, ACr2O4 and AAl2O4, wherein A is Cu, Co or Ni.

[0017] As a preferred embodiment of the preparation method described in this invention, the synthesis method of AFe2O4 includes:

[0018] Weigh Fe(NO3)3·9H2O and A(NO3)2·xH2O according to the stoichiometric coefficient of AFe2O4, place them in a beaker, add deionized water and stir evenly, then add ammonia water to completely precipitate the solution, transfer it to a reaction vessel for hydrothermal reaction, and react at 180℃ for 12h.

[0019] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0020] The precursor was calcined in a muffle furnace at 700°C for 5 hours and then naturally cooled to obtain the AFe2O4-700 catalyst.

[0021] In a preferred embodiment of the preparation method described in this invention, the A(NO3)2·xH2O are Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O, respectively.

[0022] As a preferred embodiment of the preparation method described in this invention, the synthesis method of ACr2O4 includes:

[0023] Weigh Cr(NO3)3·9H2O and A(NO3)2·xH2O according to the stoichiometric coefficient of ACr2O4, place them in a beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it into a reaction vessel for hydrothermal reaction, and react at 180℃ for 12h.

[0024] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0025] The precursor was calcined in a muffle furnace at 700°C for 5 hours and then naturally cooled to obtain the ACr2O4-700 catalyst.

[0026] Among them, A(NO3)2·xH2O are Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O, respectively.

[0027] As a preferred embodiment of the preparation method described in this invention, the synthesis method of Al2O4 includes:

[0028] Weigh Al(NO3)3·9H2O and A(NO3)2·xH2O according to the stoichiometric coefficient of AAl2O4, place them in a beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it into a reaction vessel for hydrothermal reaction, and react at 180℃ for 12h.

[0029] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0030] The precursor was placed in a muffle furnace for calcination at 700℃ for 5 hours and then naturally cooled to obtain the AAl2O4-700 catalyst.

[0031] Among them, A(NO3)2·xH2O are Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O, respectively.

[0032] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing AB2O4 type oxide ammonia decomposition catalysts to obtain AB2O4 type oxide catalysts.

[0033] Another objective of this invention is to overcome the shortcomings of the prior art and provide the application of AB2O4 type oxide catalysts in efficient ammonia decomposition.

[0034] Beneficial effects of this invention:

[0035] This invention provides a method for preparing an AB2O4 type oxide ammonia decomposition catalyst. The synthesis process is simple and easy to repeat. The prepared catalyst particles are easy to control and do not easily agglomerate, which improves the ammonia decomposition performance of the catalyst and reduces the reaction temperature for complete ammonia decomposition. The AB2O4 type oxide has good stability, which improves the stability of the ammonia decomposition catalyst. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0037] Figure 1 The image shows the XRD pattern of NiFe2O4 synthesized in Example 1 of this invention.

[0038] Figure 2 The image shows the XRD pattern of NiCr2O4 synthesized in Example 2 of this invention.

[0039] Figure 3 The image shows the XRD pattern of NiAl2O4 synthesized in Example 3 of this invention. Detailed Implementation

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0042] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0043] The ammonia decomposition reaction performance evaluation method in this invention:

[0044] The test was conducted using a fixed-bed reactor (quartz tube with an inner diameter of 4 mm) and an ammonia space velocity of 18000 ml gcat. -1 h -1 The reaction temperature is 300℃~800℃, and the step size is 50℃.

[0045] 0.1g of catalyst was placed in a quartz tube. The flow rate of NH3 was 30ml / min, and the gas flow rate was controlled by a mass flow meter. The reaction heating rate was 10℃ / min. Each reaction temperature was stabilized for 30min before measurement. The tail gas after the reaction was analyzed by gas chromatography using a thermal conductivity detector at 150℃. H2 was used as the carrier gas, and the chromatographic column was a dedicated amine analysis column from Shanghai Oni, with a column temperature of 110℃ and a carrier gas flow rate of 40ml / min.

[0046] The ammonia decomposition conversion rate of this invention is calculated according to the following formula:

[0047]

[0048] Among them, X NH3 For NH3 conversion rate, A NH3,in A represents the total amount of ammonia in the feed gas. NH3,out This represents the amount of unconverted ammonia.

[0049] Example 1

[0050] (1) Preparation of AFe2O4 series catalysts for high-temperature thermocatalytic ammonia decomposition:

[0051] Weigh a certain amount of Fe(NO3)3·9H2O and A(NO3)2·xH2O (where A(NO3)2·xH2O is Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O respectively) according to the stoichiometric coefficient of AFe2O4, place them in a 300ml beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it to a 500ml reaction vessel for hydrothermal reaction at 180℃ for 12h;

[0052] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0053] The precursor was placed in a muffle furnace for calcination at 700℃ for 5 hours, and then naturally cooled to obtain different iron-based spinel oxide catalysts.

[0054] Catalysts with a mesh size of 40–60 were used to evaluate the performance of ammonia decomposition reaction.

[0055] (2) Determination of ammonia decomposition conversion rate

[0056] The ammonia decomposition performance of this series of catalysts was evaluated by testing (Table 1). The results showed that when NiFe2O4 was used to catalyze ammonia decomposition, the NH3 conversion rate reached 65.66% at 600℃.

[0057] After XRD analysis of NiFe2O4 (see...) Figure 1 The diffraction peaks of NiFe2O4 (86-2267) in the figure are obvious, indicating that the crystallinity is very high.

[0058] Table 1

[0059]

[0060] Example 2

[0061] (1) Preparation of ACr2O4 series catalysts for high-temperature thermocatalytic ammonia decomposition:

[0062] Weigh a certain amount of Cr(NO3)3·9H2O and A(NO3)2·xH2O (where A(NO3)2·xH2O is Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O respectively) according to the stoichiometric coefficient of ACr2O4, place them in a 300ml beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it to a 500ml reaction vessel for hydrothermal reaction, and react at 180℃ for 12h;

[0063] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0064] The precursor was placed in a muffle furnace for calcination at 700°C for 5 hours, and then naturally cooled to obtain different chromium-based spinel oxide catalysts.

[0065] Screening for 40-60 mesh is used to evaluate the performance of ammonia decomposition reaction.

[0066] (2) Determination of ammonia decomposition conversion rate

[0067] The ammonia decomposition performance of this series of catalysts was evaluated by testing (Table 2). The results showed that when NiCr2O4 was used to catalyze ammonia decomposition, the NH3 conversion rate reached 48.58% at 600℃.

[0068] After XRD analysis of NiCr2O4 (see...) Figure 2 The NiCr2O4 (75-0198) diffraction peaks in the figure are obvious, indicating that its crystallinity is very high.

[0069] Table 2

[0070]

[0071] Example 3

[0072] (1) Preparation of Al2O4 series catalysts for high-temperature thermocatalytic ammonia decomposition:

[0073] Weigh a certain amount of Al(NO3)3·9H2O and A(NO3)2·xH2O (where A(NO3)2·xH2O are Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Ni(NO3)2·9H2O, respectively) according to the stoichiometric coefficient of AAl2O4, place them in a 300ml beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it to a 500ml reaction vessel for hydrothermal reaction, and react at 180℃ for 12h;

[0074] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0075] The precursor was calcined in a muffle furnace at 700°C for 5 hours and then naturally cooled to obtain the ACr2O4 catalyst.

[0076] Different aluminum-based spinel oxide catalysts were obtained after natural cooling, and those with a mesh size of 40-60 were screened out for evaluation of ammonia decomposition reaction performance.

[0077] (2) Determination of ammonia decomposition conversion rate

[0078] The ammonia decomposition performance of this series of catalysts was evaluated by testing (Table 3). The results showed that when NiAl2O4 was used to catalyze ammonia decomposition, the NH3 conversion rate reached 87.04% at 600℃. After XRD analysis of NiAl2O4 (see Table 3), the conversion rate was further improved. Figure 3 The figure shows obvious diffraction peaks of NiAl2O4 (10-0339), but there are also relatively obvious diffraction peaks of NiO (78-0643).

[0079] Table 3

[0080]

[0081] Example 4

[0082] (1) Preparation of NiAl2O4-T series catalysts for high-temperature thermocatalytic ammonia decomposition:

[0083] Weigh a certain amount of Al(NO3)3·9H2O and Ni(NO3)2·xH2O according to the stoichiometric coefficient of NiAl2O4, place them in a 300ml beaker, add deionized water and stir evenly, then add ammonia water to make the solution completely precipitate, transfer it to a 500ml reaction vessel for hydrothermal reaction, and react at 180℃ for 12h.

[0084] The suspension in the reactor was transferred into a beaker and dried in an oven at 80°C to obtain the catalyst precursor.

[0085] The precursors were placed in a muffle furnace and calcined at different calcination temperatures T for 5 h (calcination temperatures were 600℃, 700℃, 800℃, and 900℃, respectively). After natural cooling, NiAl2O4-T catalysts were obtained and named NiAl2O4-600, NiAl2O4-700, NiAl2O4-800, and NiAl2O4-900, respectively.

[0086] Screening for 40-60 mesh is used to evaluate the performance of ammonia decomposition reaction.

[0087] (2) Determination of ammonia decomposition conversion rate

[0088] The ammonia decomposition performance of this series of catalysts was evaluated by testing (Table 4). The results showed that the catalytic activity of the catalyst first increased and then decreased with the increase of calcination temperature. When the calcination temperature was 700℃, that is, when NiAl2O4-700 had the best catalytic ammonia decomposition activity, the NH3 conversion rate reached 87.04% at 600℃.

[0089] Table 4

[0090]

[0091] Further research by the inventors revealed that spinel-type oxides synthesized by hydrothermal methods for iron-based spinel, chromium-based spinel, and aluminum-based spinel all exhibit high thermal stability and high crystallinity.

[0092] The present invention provides a highly efficient ammonia decomposition catalyst with high catalytic activity. The conversion rate at 600℃ reaches 87.04% (NiAl2O4), which is much higher than that of other spinels. The reason is that NiAl2O4 spinel oxide has a high specific surface area, high porosity, and oxygen vacancies, which provide key active sites for the formation of NiO with NiAl2O4, thereby improving the conversion rate of ammonia decomposition.

[0093] This invention prepares a high-efficiency, low-temperature ammonia decomposition catalyst via a hydrothermal method. The catalyst synthesis process is simple and reproducible. The prepared catalyst particles are easy to control and do not easily agglomerate, thereby improving the ammonia decomposition performance of the catalyst and reducing the reaction temperature for complete ammonia decomposition.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. Use of an AB2O4-type oxide catalyst in the decomposition of ammonia, characterized in that: The preparation method of the catalyst comprises the following steps: According to the stoichiometric number of NiAl2O4, Al(NO3)3·9H2O and Ni(NO3)2·6H2O are weighed, deionized water is added and stirred uniformly, ammonia water is added to make the solution fully precipitate, and then the solution is moved into a reaction kettle to perform hydrothermal reaction at 180℃ for 12h; The suspension in the reaction kettle is moved into a beaker and dried in a constant temperature oven at 80℃ to obtain a catalyst precursor; The precursor is placed in a muffle furnace to perform calcination at 700℃ for 5h, and the NiAl2O4-700 catalyst is obtained after natural cooling. The NiAl2O4 spinel oxide has high specific surface area, high porosity, and oxygen vacancies, which provides key active sites for the generation of NiO along with NiAl2O4, thereby improving the conversion rate of ammonia decomposition.

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