Porous composite carrier loaded nickel-ruthenium bimetallic catalyst and preparation method thereof

Abstract

The invention relates to a porous composite carrier loaded nickel-ruthenium bimetallic catalyst and a preparation method thereof, and belongs to the technical field of catalysts. Aiming at the problems of high temperature and high pressure of a traditional iron-based catalyst, high cost of a ruthenium-based catalyst, poor adaptability of a single-carrier catalyst and the like, the bimetallic catalyst is prepared by the following steps: firstly, performing hydrochloric acid pickling on a diatomite carrier, performing furfuryl alcohol polymerization and performing pore-forming on a cetyltrimethylammonium bromide soft template to form a mesoporous structure with a high specific surface area; after compounding with cerous nitrate, a rigid-flexible carrier is constructed, so that the mechanical strength is improved, and high-temperature sintering is inhibited; and then loading nickel-ruthenium bimetal on the surface of the carrier through co-impregnation, and carrying out hydrogen reduction to form nano-particles. In addition, due to the adjustability of the ratio of double metals, the same catalyst system has the bidirectional catalytic functions of ammonia synthesis and ammonia decomposition, the dynamic requirements of an ammonia-hydrogen energy system are met, and the development cost and inventory pressure of the catalyst are remarkably reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts and relates to a porous composite carrier loaded nickel-ruthenium bimetallic catalyst and a preparation method thereof. BACKGROUND

[0002] Ammonia synthesis is a core unit reaction in modern chemical industry. The traditional Haber-Bosch process relies on magnetite or other iron-based catalysts, and needs to be operated at a high temperature of 400-500 DEG C and a high pressure of 15-30 MPa, and the hydrogen-nitrogen ratio is strictly limited to 3:1. The overall process energy consumption is high, and the catalyst is extremely sensitive to impurities in the raw material gas and is easy to be poisoned and deactivated. With the large-scale application of renewable energy hydrogen production technologies such as wind power and photovoltaic power, the supply of hydrogen presents intermittent and fluctuating characteristics. The traditional iron-based catalysts are difficult to meet the needs of new application scenarios such as distributed ammonia synthesis and dynamic load adjustment due to their narrow active temperature window and poor adaptability to hydrogen-nitrogen ratio.

[0003] In the prior art, the ruthenium-based catalyst has high activity for breaking N≡N bond and can achieve a high ammonia synthesis rate at 300-400 DEG C. However, the ruthenium-based catalyst has defects such as high cost and poor fluctuation resistance, which limits its large-scale industrial application.

[0004] At the same time, as the reverse process of ammonia synthesis, ammonia decomposition for hydrogen production also faces similar technical challenges in catalyst development. The traditional iron-based catalyst needs to work at 550-650 DEG C, while the ruthenium-based catalyst can reduce the reaction temperature to 400-500 DEG C, but also has problems such as high cost and easy deactivation. The existing catalyst system generally lacks bidirectional catalytic ability and cannot meet the compatibility requirements of the catalyst in the synthesis / decomposition cycle of the "ammonia-hydrogen" energy system.

[0005] Therefore, it is urgent to develop a bidirectional catalyst material with high catalytic activity, wide working condition adaptability and long-period stability. SUMMARY

[0006] The application aims to provide a porous composite carrier loaded nickel-ruthenium bimetallic catalyst and a preparation method thereof, which has good catalytic activity.

[0007] The application can be realized by the following technical solutions. A preparation method of a porous composite carrier loaded nickel-ruthenium bimetallic catalyst, and the specific steps of the preparation method are as follows, S1-1: Mix cerium nitrate with modified diatomite, ball mill for 6-8 h, dry at 100-120 DEG C for 12-24 h, and then calcine at 550-600 DEG C for 3-4 h at a heating rate of 5-10 DEG C / min to obtain powder A; S1-2: add powder A into deionized water to make the solid-liquid mass ratio 1: (10-20), then add a mixture of nickel nitrate and ruthenium nitrosyl nitrate, stir for 4-6 h, dry at 100-120 ℃ for 12 h to obtain powder B; S1-3: reduce powder B in a mixed gas of hydrogen and argon at 300-350 ℃ for 2-3 h, the temperature rising rate is 2 ℃ / min, to obtain the catalyst.

[0008] As a preferred technical scheme of the present application, the preparation method of the modified diatomite is as follows, S2-1: soak diatomite in a hydrochloric acid solution to make the solid-liquid ratio 1:10, stir at 70-80 ℃ for 3-4 h, wash with deionized water until the pH is neutral, and then dry at 60-70 ℃ for 12-24 h to obtain pretreated diatomite; S2-2: disperse the pretreated diatomite in a 10-20% mass fraction furfuryl alcohol solution, then add cetyltrimethylammonium bromide, ultrasonic for 2-4 h, dry at 90-100 ℃ for 6-8 h, and then calcine for 3-4 h to obtain the modified diatomite.

[0009] As a preferred technical scheme of the present application, the mass ratio of cerium nitrate to modified diatomite in S1-1 is (1-3):1.

[0010] As a preferred technical scheme of the present application, the ball milling rotation speed in S1-1 is 200-300 rpm.

[0011] As a preferred technical scheme of the present application, the addition amount of the mixture of nickel nitrate and ruthenium nitrosyl nitrate in S1-2 is 0.5-1.5% of the mass of powder A.

[0012] As a preferred technical scheme of the present application, the mass ratio of nickel nitrate to ruthenium nitrosyl nitrate in S1-2 is (0.5-2):1.

[0013] As a preferred technical scheme of the present application, the volume ratio of hydrogen to argon in S1-3 is 1: (3-4).

[0014] As a preferred technical scheme of the present application, the concentration of the hydrochloric acid solution in S2-1 is 4-6 mol / L.

[0015] As a preferred technical scheme of the present application, the addition amount of cetyltrimethylammonium bromide in S2-2 is 1-3% of the mass of the pretreated diatomite.

[0016] As a preferred technical scheme of the present application, the calcination temperature in S2-2 is 650-700 ℃.

[0017] In the preparation of modified diatomite, first, impurities in the diatomite are removed by soaking with hydrochloric acid to expose more pore structures; at the same time, active sites such as hydroxyl groups are generated on the surface of the diatomite after acid treatment, enhancing the binding ability with metal precursors. Furfuryl alcohol is polymerized on the surface of diatomite to form an organic skeleton, and after calcination at high temperature, a porous carbon structure is formed, significantly improving the specific surface area and pore volume of the carrier, and providing high dispersion space for active components. Cetyltrimethylammonium bromide (CTAB) as a soft template induces the directional polymerization of furfuryl alcohol on the surface of diatomite, forming a regular mesoporous structure, improving the connectivity of the pore channels, effectively reducing the molecular diffusion resistance of reactants and products, and significantly improving the mass transfer efficiency.

[0018] After calcination of cerium nitrate and modified diatomite, cerium oxide is uniformly anchored on the porous carbon skeleton of diatomite; the fluorite structure of cerium oxide and the mesoporous structure of diatomite form a rigid-flexible composite carrier, which improves the mechanical strength and effectively inhibits the sintering of Ni and Ru active metals and the collapse of the carrier pores during high-temperature reduction or reaction. CeO2 dynamically stores and releases oxygen species during the reaction, which can oxidize and adsorb impurities on the surface of the carrier, inhibiting Ni poisoning; at the same time, cerium oxide forms a strong metal-support interaction with Ni and Ru, which regulates the d-band center of Ni and the surface electron density of Ru through electron transfer, optimizes the adsorption-activation ability of N≡N bond and H-H bond, and reduces the reaction energy barrier.

[0019] Through co-impregnation and hydrogen reduction treatment, Ni and Ru are uniformly dispersed in the form of nanoparticles on the surface of the CeO2-modified diatomite composite carrier, the exposure degree of active sites is increased, and the catalytic efficiency is significantly improved compared with single-metal catalysts. Among them, Ni has high activity for the rupture of N≡N bond and is mainly responsible for the dissociation of N2; Ru has low H2 dissociation energy and is mainly responsible for the activation of H2; the two synergistically reduce the reaction energy barrier, significantly improving the ammonia synthesis rate. In addition, the introduction of Ru can inhibit the poisoning of Ni in a sulfur-containing atmosphere, while the presence of Ni reduces the oxidation deactivation of Ru at high temperature, prolonging the catalyst life. In ammonia decomposition for hydrogen production, by adjusting the mass ratio of Ni to Ru to (0.5-0.8):1, the NH3 decomposition efficiency can be optimized, Ru can efficiently dissociate NH3, and Ni can accelerate the desorption of H2. Ni and Ru have a synergistic effect, Ni modifies the Ru surface to inhibit NH x Intermediate adsorption and prevent catalyst poisoning. This proportionality makes the same catalyst system have the dual functions of ammonia synthesis and ammonia decomposition, which adapts to the dynamic needs of the "ammonia-hydrogen" energy system, significantly reducing the development cost and inventory pressure of the catalyst.

[0020] The beneficial effects of the present application are: The modified diatomite in the application exposes a porous structure after acid treatment, and a porous carbon skeleton is generated after furfuryl alcohol polymerization and calcination, and regular mesopores are formed in combination with a CTAB soft template to improve the specific surface area and mass transfer efficiency; cerium nitrate generates ceria nanoparticles after calcination, and forms a composite carrier with diatomite to enhance mechanical strength and inhibit high-temperature sintering; the ceria optimizes the d-band and sp-band electronic structures of Ni and Ru through oxygen storage / release and electron modification to reduce the reaction energy barrier; the bimetallic nanoparticles are highly dispersed on the carrier to synergistically improve the ammonia synthesis rate, and Ru inhibits Ni sulfur poisoning and stabilizes low-valence Ru to significantly extend the catalyst life and reduce reaction energy consumption. x The intermediate adsorption can achieve efficient ammonia decomposition performance. DETAILED DESCRIPTION

[0021] To further illustrate the technical means and effects adopted by the application to achieve the predetermined purposes, the specific embodiments, structures, features and effects according to the application are described in detail below in combination with examples.

[0022] In the examples and comparative examples of the application: Diatomite: purchased from Jinan Liyang Chemical Co., Ltd.; Cerium nitrate: purchased from Shandong Zhengxing New Material Co., Ltd.; Ruthenium nitrosyl nitrate: purchased from Shanghai Platinum Metal Material Co., Ltd.; Furfuryl alcohol: purchased from Shandong Chuangying Chemical Co., Ltd.; Cetyltrimethylammonium bromide: purchased from Shanghai Aishen Industry Co., Ltd.

[0023] Example 1 A preparation method of a porous composite carrier supported nickel-ruthenium bimetallic catalyst, the specific steps of the preparation method are as follows, S1-1: Mix cerium nitrate and modified diatomite at a mass ratio of 2:1, ball mill for 7 h at a ball mill speed of 250 rpm, dry at 110℃ for 18 h, and then calcine at 570℃ for 3.5 h at a heating rate of 5℃ / min to obtain powder A; S1-2: Add powder A to deionized water to obtain a solid-liquid mass ratio of 1:15, then add a mixture of 1% nickel nitrate and ruthenium nitrosyl nitrate based on the mass of powder A, and the mass ratio of nickel nitrate to ruthenium nitrosyl nitrate is 1.5:1, stir for 5 h, and dry at 110℃ for 12 h to obtain powder B; S1-3: Reduce powder B in a mixed gas of hydrogen and argon at a volume ratio of 1:3.5 at 330℃ for 2.5 h at a heating rate of 2℃ / min to obtain the catalyst.

[0024] The preparation method of the modified diatomite is as follows, S2-1: diatomite is soaked in a hydrochloric acid solution with a concentration of 5 mol / L so that the solid-liquid ratio is 1:10, stirred at 75 ℃ for 3.5 h, washed with deionized water until the pH is neutral, and then dried at 65 ℃ for 18 h to obtain pretreated diatomite; S2-2: the pretreated diatomite is dispersed in a furfuryl alcohol solution with a mass fraction of 15%, then 2% of cetyltrimethylammonium bromide of the mass of the pretreated diatomite is added, ultrasonically treated for 3 h, dried at 95 ℃ for 7 h, and then calcined for 3.5 h at a calcination temperature of 680 ℃ to obtain the modified diatomite.

[0025] Example 2 A preparation method of a porous composite carrier loaded nickel-ruthenium bimetallic catalyst, specific steps of the preparation method are as follows, S1-1: cerium nitrate and modified diatomite are mixed at a mass ratio of 1:1, ball milled for 6 h at a ball milling speed of 200 rpm, dried at 100 ℃ for 12 h, and then calcined at 550 ℃ for 3 h at a temperature rising rate of 5 ℃ / min to obtain powder A; S1-2: powder A is added to deionized water so that the solid-liquid mass ratio is 1:10, and then a mixture of 0.5% of nickel nitrate and nitrosyl nitric ruthenium of the mass of powder A is added, the mass ratio of nickel nitrate and nitrosyl nitric ruthenium being 1:1, stirred for 4 h, and then dried at 100 ℃ for 12 h to obtain powder B; S1-3: powder B is reduced in a mixed gas of hydrogen and argon at a volume ratio of 1:3 at 300 ℃ for 2 h at a temperature rising rate of 2 ℃ / min to obtain the catalyst.

[0026] The preparation method of the modified diatomite is as follows, S2-1: diatomite is soaked in a hydrochloric acid solution with a concentration of 4 mol / L so that the solid-liquid ratio is 1:10, stirred at 70 ℃ for 3 h, washed with deionized water until the pH is neutral, and then dried at 60 ℃ for 12 h to obtain pretreated diatomite; S2-2: the pretreated diatomite is dispersed in a furfuryl alcohol solution with a mass fraction of 10%, then 1% of cetyltrimethylammonium bromide of the mass of the pretreated diatomite is added, ultrasonically treated for 2 h, dried at 90 ℃ for 6 h, and then calcined for 3 h at a calcination temperature of 650 ℃ to obtain the modified diatomite.

[0027] Example 3 A preparation method of a porous composite carrier loaded nickel-ruthenium bimetallic catalyst, specific steps of the preparation method are as follows, S1-1: cerium nitrate and modified diatomite were mixed at a mass ratio of 3:1, ball-milled for 8 h at a rotation speed of 300 rpm, dried at 120 ℃ for 24 h, and calcined at 600 ℃ for 4 h at a temperature increasing rate of 10 ℃ / min to obtain powder A; S1-2: powder A was added to deionized water to obtain a solid-liquid mass ratio of 1:20, then a mixture of nickel nitrate and ruthenium nitrosyl nitrate was added, the mass ratio of nickel nitrate to ruthenium nitrosyl nitrate was 2:1, the amount of the mixture was 1.5% of the mass of powder A, and the mixture was stirred for 6 h and dried at 120 ℃ for 12 h to obtain powder B; S1-3: powder B was reduced in a mixed gas of hydrogen and argon at a volume ratio of 1:4 at 350 ℃ for 3 h at a temperature increasing rate of 2 ℃ / min to obtain the catalyst.

[0028] The modified diatomite was prepared by the following method, S2-1: diatomite was soaked in a hydrochloric acid solution with a concentration of 6 mol / L to obtain a solid-liquid ratio of 1:10, stirred at 80 ℃ for 4 h, washed with deionized water until the pH was neutral, and then dried at 70 ℃ for 24 h to obtain pretreated diatomite; S2-2: the pretreated diatomite was dispersed in a furfuryl alcohol solution with a mass fraction of 20%, and cetyltrimethylammonium bromide was added, the amount of cetyltrimethylammonium bromide was 3% of the mass of the pretreated diatomite, and the mixture was ultrasonically treated for 4 h, dried at 100 ℃ for 8 h, and then calcined at 700 ℃ for 4 h to obtain the modified diatomite.

[0029] Example 4 The mass ratio of nickel nitrate to ruthenium nitrosyl nitrate was 0.65:1, and the remaining steps were consistent with those of Example 1.

[0030] Example 5 The mass ratio of nickel nitrate to ruthenium nitrosyl nitrate was 0.5:1, and the remaining steps were consistent with those of Example 1.

[0031] Example 6 The mass ratio of nickel nitrate to ruthenium nitrosyl nitrate was 0.8:1, and the remaining steps were consistent with those of Example 1.

[0032] Comparative Example 1 No nickel nitrate was added in S1-2, and the remaining steps were consistent with those of Example 1.

[0033] Comparative Example 2 No ruthenium nitrosyl nitrate was added in S1-2, and the remaining steps were consistent with those of Example 1.

[0034] Comparative Example 3 The S2-2 does not add cetyl trimethyl ammonium bromide, and the remaining steps are consistent with example 1.

[0035] Comparative example 4 The S2-2 does not add furfuryl alcohol, and the remaining steps are consistent with example 1.

[0036] Comparative example 5 The unmodified diatomite is used instead of the modified diatomite, and the remaining steps are consistent with example 1.

[0037] Comparative example 6 The S1-1 does not add modified diatomite, and the remaining steps are consistent with example 1.

[0038] Comparative example 7 The S1-1 does not add cerium nitrate, and the remaining steps are consistent with example 1.

[0039] Ammonia synthesis activity test The catalysts obtained in examples 1-3 and comparative examples 1-7 are evaluated for ammonia synthesis catalytic activity. The reactor is a fixed bed with an inner diameter of 12 mm. During the test, 0.2 g of catalyst is mixed with quartz sand and packed in the isothermal zone of the reactor. The raw gas is H2:N2=3:1 (volume ratio), and the flow rate is 50 mL / min; the reaction conditions are: pressure 1 MPa, reaction temperature 350℃, reaction space velocity 3.6×10 4 cm 3 g -1 h -1 The specific experimental results are as follows.

[0040]

[0041] From the data of the above examples and comparative examples, it can be seen that the catalyst prepared by the preparation method of the present application has good ammonia synthesis catalytic activity.

[0042] Ammonia decomposition hydrogen production activity test The catalysts obtained in examples 4-6 and comparative examples 1-7 are tested for ammonia decomposition hydrogen production activity. 50 mg of the catalyst prepared in the above examples and comparative examples is mixed with 500 mg of quartz sand, and then packed into a quartz reaction tube with an inner diameter of 8 mm. Before the catalytic test, the catalyst is first activated at 600℃ for 1 h in a pure NH3 atmosphere, and then the ammonia decomposition conversion test is carried out. The products are analyzed by an online gas chromatograph (Fuli GC 9790). The conversion rate of NH3 is calculated by the following formula: X NH3 =(A1-A2) / A1×100%, where X NH3The conversion rate of NH3 is represented by A1, the peak area of ammonia before the reaction, and A2, the peak area of ammonia after the reaction. The specific experimental results are as follows.

[0043]

[0044] From the data of the above examples and comparative examples, it can be seen that the catalyst prepared by the preparation method of the present application has good ammonia decomposition hydrogen production activity.

[0045] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for preparing a porous composite support-supported nickel-ruthenium bimetallic catalyst, characterized by, Specific steps of the preparation method are as follows, S1-1: mixing cerium nitrate with modified diatomite, ball milling for 6-8 h, drying at 100-120 ℃ for 12-24 h, and calcining at 550-600 ℃ for 3-4 h at a temperature rising rate of 5-10 ℃ / min to obtain powder A; S1-2: adding powder A into deionized water to make the solid-liquid mass ratio be 1:(10-20), then adding a mixture of nickel nitrate and ruthenium nitrosyl nitrate, stirring for 4-6 h, and drying at 100-120 ℃ for 12 h to obtain powder B; S1-3: reducing powder B in a mixed gas of hydrogen and argon at 300-350 ℃ for 2-3 h at a temperature rising rate of 2 ℃ / min to obtain the catalyst.

2. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, The preparation method of the modified diatomite is as follows, S2-1: soaking diatomite in a hydrochloric acid solution to make the solid-liquid ratio be 1:10, stirring at 70-80 ℃ for 3-4 h, washing with deionized water until the pH is neutral, and drying at 60-70 ℃ for 12-24 h to obtain pretreated diatomite; S2-2: dispersing the pretreated diatomite in a 10-20% mass fraction furfuryl alcohol solution, adding cetyltrimethylammonium bromide, ultrasonicating for 2-4 h, drying at 90-100 ℃ for 6-8 h, and calcining for 3-4 h to obtain the modified diatomite.

3. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, In S1-1, the cerium nitrate and the modified diatomite are mixed in a mass ratio of (1-3):

1.

4. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, In S1-1, the ball milling rotation speed is 200-300 rpm.

5. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, In S1-2, the addition amount of the mixture of nickel nitrate and ruthenium nitrosyl nitrate is 0.5-1.5% of the mass of powder A.

6. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, In S1-2, the mass ratio of nickel nitrate and ruthenium nitrosyl nitrate is (0.5-2):

1.

7. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 1, characterized in that, In S1-3, the volume ratio of hydrogen and argon is 1:(3-4).

8. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 2, characterized in that, In S2-1, the concentration of the hydrochloric acid solution is 4-6 mol / L.

9. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 2, characterized in that, In S2-2, the addition amount of cetyltrimethylammonium bromide is 1-3% of the mass of the pretreated diatomite.

10. The method for preparing a porous composite support loaded nickel-ruthenium bimetallic catalyst according to claim 2, characterized in that, In S2-2, the calcination temperature is 650-700 ℃.

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