Ruthenium-based catalyst for hydrogen production through medium and low temperature ammonia decomposition as well as preparation method and application of ruthenium-based catalyst

Abstract

The invention belongs to the technical field of hydrogen production catalysis, and particularly relates to a ruthenium-based catalyst for hydrogen production through medium and low temperature ammonia decomposition as well as a preparation method and application of the ruthenium-based catalyst. The ruthenium-based catalyst for hydrogen production through ammonia decomposition at medium and low temperature comprises a metal active component, a carrier and an accelerant, the metal active component is active metal ruthenium, and the carrier is composite aluminum oxide containing metal oxide; the metal active component accounts for 1wt%-5wt% of the catalyst; the metal oxide contained in the composite aluminum oxide is magnesium oxide and / or cerium oxide, and the metal oxide accounts for 0wt%-30wt% of the composite aluminum oxide; the molar ratio of the metal active component to the accelerant is 0.5-2.0. The ruthenium-based catalyst prepared by the invention has the advantages of high conversion efficiency of catalyzing ammonia decomposition to produce hydrogen, simple preparation process, convenience in process expansion, controllable input amount of ruthenium metal and high utilization rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production catalysis, and specifically relates to a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, and a preparation method and application thereof. Background Art

[0002] Hydrogen energy has the advantages of being green, zero-carbon, renewable, high in energy density, high in calorific value, high in energy utilization efficiency, and a wide range of raw material sources. In addition, its combustion product is water, which does not cause environmental pollution. It is regarded as a clean energy with great application prospects. Therefore, hydrogen storage technology is very important. Large-scale economic, efficient production, storage and safe transportation technologies will directly affect the large-scale use of hydrogen energy technology.

[0003] In recent years, ammonia has received more and more attention as a hydrogen storage medium, but its storage and transportation have very high requirements. Ammonia has many advantages. Ammonia is easy to liquefy, has a pungent odor, is non-flammable and non-toxic at low concentrations, has a high hydrogen storage density, has mature production, storage and transportation technologies, and has no carbon emissions during the hydrogen production process. It is an efficient, clean and safe hydrogen storage carrier. Therefore, in the future hydrogen economy, NH3 may play an important role as a H2 carrier.

[0004] At present, most industrial ammonia decomposition hydrogen production uses iron or nickel catalysts, the reaction temperature is above 800℃, the energy consumption is high, and the equipment is severely corroded. Therefore, the research and development of high-activity catalysts suitable for medium and low temperature (reaction temperature does not exceed 500℃) ammonia decomposition has received widespread attention. Studies have shown that ruthenium (Ru) metal nanoparticles exhibit excellent medium and low temperature activity for ammonia decomposition reactions and are one of the best active components reported so far. Its supported catalysts mainly include Ru / carbon nanotubes, Ru / activated carbon, Ru / Al2O3, Ru / MgO, etc. Among them, Ru / carbon nanotube catalysts exhibit high low temperature activity, but carbon nanotubes are relatively expensive, have low packing density, increase molding costs, and are prone to methanation under hydrogen reaction conditions, which limits their large-scale practical application; the preparation methods of Ru / MgO catalysts reported in the literature currently include impregnation method, deposition precipitation method, polyol reduction method, colloidal deposition method, chemical vapor deposition method, etc. At present, the preparation route of magnesium oxide supported ruthenium-based catalyst is to first synthesize a magnesium compound carrier, and then the loaded ruthenium precursor is calcined and reduced to prepare Ru / MgO, and then impregnated with alkali metal solutions such as potassium, and calcined and reduced to obtain K / Ru / MgO. The preparation process involves multiple liquid phase syntheses and calcination reduction treatments, which is cumbersome and time-consuming, increases the catalyst production cost, and the activity of the prepared catalyst is limited. Summary of the invention

[0005] The present invention aims to solve the problems of high cost and complicated process in the preparation process of ruthenium-based catalysts, and provides a ruthenium-based catalyst for hydrogen production by decomposing ammonia at a medium or low temperature, and a preparation method and application thereof. The ruthenium-based catalyst for hydrogen production by decomposing ammonia provided by the present invention can improve the stability of the carrier by using alumina containing a specific proportion of magnesium oxide and cerium oxide as a carrier, and can also promote hydrogen production by decomposing ammonia and improve the catalytic activity.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the embodiment of the present invention is:

[0007] In a first aspect, an embodiment of the present invention provides a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at a medium or low temperature, comprising a metal active component, a carrier and a promoter, wherein the metal active component is active metal ruthenium, and the carrier is a composite alumina containing a metal oxide;

[0008] The metal active component accounts for 1wt%-5wt% of the catalyst;

[0009] The metal oxide contained in the composite alumina is magnesium oxide and / or cerium oxide, and the metal oxide accounts for 0wt%-30wt% of the composite alumina;

[0010] The molar ratio of the metal active component to the promoter is 0.5-2.0.

[0011] In a second aspect, an embodiment of the present invention provides a method for preparing the ruthenium-based catalyst for hydrogen production by decomposing ammonia at medium and low temperatures as described in the first aspect, comprising the following steps:

[0012] Step S1, selecting a composite alumina containing metal oxides as a carrier, and testing the amount of deionized water required for initial wetness impregnation thereof;

[0013] Step S2, adding deionized water to the ruthenium precursor solution to dilute the ruthenium precursor solution to a desired concentration;

[0014] Step S3, adding the diluted ruthenium precursor solution obtained in step S2 dropwise into the continuously stirred carrier, and aging overnight after the dropwise addition is completed;

[0015] Step S4, drying the powder obtained in step S3, reducing it, and calcining it to obtain a precursor of a ruthenium-based catalyst;

[0016] Step S5, adding a promoter solution to the precursor of the ruthenium-based catalyst obtained in step S4 and stirring, leaving it for 2-4 hours, and drying;

[0017] Step S6, reducing and calcining the ruthenium-based catalyst precursor obtained in step S5 to obtain a ruthenium-based catalyst.

[0018] Furthermore, in step S2, the solute in the ruthenium precursor solution is ruthenium nitrosyl nitrate, and the mass of the solvent in the ruthenium precursor solution after dilution is the same as the mass of deionized water required for initial wetness impregnation of the carrier.

[0019] Furthermore, in step S4, the obtained powder is first dried in an oven at 100-150° C. for 2-4 h, and then reduced in a reducing atmosphere at 300-500° C. for 2-4 h.

[0020] Furthermore, in step S5, the promoter solution is an alkali metal salt solution including potassium carbonate, potassium nitrate or cesium nitrate, the mass of the solvent in the solution is the same as the mass of deionized water required for the initial wet impregnation of the carrier, and after being placed for 2-4 hours, it is dried in an oven at 100-150° C. for 2-4 hours.

[0021] Further, in step S6, the powder obtained in step S5 is reduced in a reducing atmosphere at 300-500° C. for 2-4 hours.

[0022] Further, the reducing atmosphere in step S4 and step S6 is: a hydrogen-argon mixed gas or a hydrogen-nitrogen mixed gas;

[0023] The volume percentage of hydrogen in the hydrogen-argon mixed gas is 3%-10%, and the air velocity is controlled at 5000-6000h -1 .

[0024] In a third aspect, an embodiment of the present invention provides an application of the ruthenium-based catalyst described in the first aspect, wherein the catalyst is used to catalyze the decomposition of ammonia at medium and low temperatures to produce hydrogen, and the reaction temperature during the decomposition to produce hydrogen does not exceed 500°C.

[0025] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0026] 1. The ruthenium-based ammonia decomposition hydrogen production catalyst provided by the present invention can improve the stability of the carrier by using alumina containing a specific ratio of magnesium oxide and cerium oxide as a carrier, and can also promote the decomposition of ammonia to produce hydrogen and improve the catalytic activity.

[0027] 2. The present invention optimizes the selection of carriers, the molar ratio of raw materials and the preparation of solutions to make the reaction more complete and efficient, reduce the waste of raw materials and energy consumption, make the catalyst synthesis process more stable, further reduce energy consumption, obtain the final catalyst through heat treatment, avoid the energy consumption of multiple roasting and grinding, and achieve the effect of reducing the energy consumption of catalyst preparation.

[0028] 3. The 3% ruthenium-based ammonia decomposition hydrogen production catalyst provided by the present invention has a hydrogen production capacity of 15000 h. -1 At a space velocity of 1.50 ℃ and a reaction temperature of 350℃, the ammonia conversion efficiency can reach 97.5%

[0029] 4. The Ru-based catalyst provided by the present invention has a simple preparation process, good repeatability, can be scaled up for production, and is easy to apply to industrial applications. DETAILED DESCRIPTION

[0030] The following specific embodiments are provided for a better understanding of the present invention, but are not limited to the best implementation mode described, and do not constitute limitations on the content of the invention and the scope of protection. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the present invention with the features of other prior arts shall fall within the scope of protection of the present invention.

[0031] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0032] Example 1

[0033] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0034] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3 and CeO2 are 85% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, the drying time is 4h, and the test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 70.7g;

[0035] Step S2, taking 24.88 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 45.86 g of deionized water, and stirring evenly by magnetic force;

[0036] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 3%;

[0037] Step S4, drying the 3% Ru-CeAl powder in step S3 at 120°C in an oven for 4 hours, and then reducing the catalyst precursor prepared above in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.0%, controlling the reduction temperature to 500°C, the time to 3 hours, and the space velocity to 5000h -1 ;

[0038] Step S5, adding 70.7 g of deionized water to 1.96 g of potassium nitrate powder, stirring until completely dissolved, and then dropwise adding to the ruthenium-based catalyst precursor cooled in step S4, leaving for 2 hours, and drying in an oven at 120° C. for 4 hours;

[0039] Step S6: The ruthenium-based catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 500° C., the time is 3 h, and the space velocity is 5000 h -1 , and obtained 3% Ru-CeAl-K catalyst.

[0040] Example 2

[0041] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0042] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3, CeO2 and MgO are 65%, 20% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, and drying for 4 hours. The test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 52.9g;

[0043] Step S2, taking 24.88 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 28.02 g of deionized water, and stirring evenly by magnetic force;

[0044] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 3%;

[0045] Step S4, drying the catalyst precursor with 3% ruthenium by mass in step S3 in an oven at 120°C for 4 hours, and then reducing the catalyst precursor in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5%, controlling the reduction temperature to 500°C, the time to 3 hours, and the space velocity to 6000h -1 ;

[0046] Step S5, add 52.9 g of deionized water to 0.67 g of potassium carbonate powder, stir until completely dissolved, then dropwise add the catalyst precursor cooled in step S4, leave for 2 hours, and dry in an oven at 120° C. for 4 hours;

[0047] Step S6: The catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 500°C, the time is 3h, and the space velocity is 6000h-1. -1 , and obtained 3%Ru-CeMgAl-K catalyst.

[0048] Example 3

[0049] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0050] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3, CeO2 and MgO are 65%, 20% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, and drying for 4 hours. The test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 52.9g;

[0051] Step S2, taking 24.88 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 28.02 g of deionized water, and stirring evenly by magnetic force;

[0052] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 3%;

[0053] Step S4, drying the catalyst precursor with a ruthenium mass percentage of 3% in step S3 in an oven at 120°C for 4 hours, and then reducing the catalyst precursor in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5%, controlling the reduction temperature to 300°C, the time to 3 hours, and the space velocity to 6000h -1 ;

[0054] Step S5, add 52.9 g of deionized water to 0.67 g of potassium carbonate powder, stir until completely dissolved, and then dropwise add to the catalyst precursor cooled in step S4, leave for 2 hours, and dry in an oven at 120° C. for 4 hours;

[0055] Step S6: The catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 300°C, the time is 3h, and the space velocity is 6000h -1 , and obtained 3%Ru-CeMgAl-K catalyst.

[0056] Example 4

[0057] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0058] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3, CeO2 and MgO are 65%, 20% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, and drying for 4 hours. The test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 52.9g;

[0059] Step S2, taking 8.05 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 44.85 g of deionized water, and stirring evenly by magnetic force;

[0060] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 1%;

[0061] Step S4, drying the catalyst precursor with 1% ruthenium by mass in step S3 in an oven at 120°C for 4 hours, and then reducing the dried catalyst precursor in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5%, controlling the reduction temperature to 400°C, the time to 3 hours, and the space velocity to 5000 h -1 ;

[0062] Step S5, adding 52.9 g of deionized water to 0.3 g of cesium nitrate powder, stirring until completely dissolved, and then dropwise adding to the catalyst precursor cooled in step S4, leaving for 2 hours, and drying in an oven at 120° C. for 4 hours;

[0063] Step S6: The catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 400°C, the time is 3h, and the space velocity is 5000h-1. -1 , and obtained 1% Ru-CeMgAl-Cs catalyst.

[0064] Example 5

[0065] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0066] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3 and CeO2 are 85% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, drying for 4 hours, and the test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 70.7g;

[0067] Step S2, taking 40.22 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 30.48 g of deionized water, and stirring evenly by magnetic force;

[0068] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 5%;

[0069] Step S4: drying the catalyst precursor Ru-CeAl powder with a ruthenium mass percentage of 5% in step S3 in an oven at 120°C for 4 hours, and then reducing the catalyst precursor in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 10%, controlling the reduction temperature to 400°C, the time to 3 hours, and the space velocity to 6000h -1 ;

[0070] Step S5, add 70.7 g of deionized water to 1.09 g of potassium carbonate powder, stir until completely dissolved, and then dropwise add to the catalyst precursor cooled in step S4, leave for 2 hours, and dry in an oven at 120° C. for 4 hours;

[0071] Step S6: reducing the catalyst precursor obtained in step S5 in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5%, controlling the reduction temperature to 400°C, the time to 3h, and the space velocity to 6000h -1 , and obtained 5% Ru-CeAl-K catalyst.

[0072] Comparative Example 1

[0073] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0074] Step S1, selecting a composite alumina powder material, in which the mass proportions of Al2O3 and CeO2 are 85% and 15% respectively, taking the above powder material for pretreatment, the pretreatment temperature is 120°C, drying for 4 hours, and the test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 70.7g;

[0075] Step S2, taking 24.88 g of ruthenium nitrosyl nitrate solution, wherein the mass fraction of metallic ruthenium in the ruthenium nitrosyl nitrate solution is 12.43%, adding 45.86 g of deionized water, and stirring the mixture evenly with magnetic force;

[0076] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of the composite alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 3%;

[0077] Step S4, drying the catalyst precursor Ru-CeAl powder with a ruthenium mass percentage of 3% in step S3 in an oven at 120° C. for 4 hours, and then calcining the dried catalyst precursor in an air atmosphere at a calcination temperature of 400° C. for 3 hours;

[0078] Step S5, add 70.7 g of deionized water to 0.67 g of potassium carbonate powder, stir until completely dissolved, then dropwise add the catalyst precursor cooled in step S4, leave for 2 hours, and dry in an oven at 120° C. for 4 hours;

[0079] Step S6: The catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 400°C, the time is 3h, and the space velocity is 5000h-1. -1 , and obtained 3% Ru-CeAl-K catalyst.

[0080] Comparative Example 2

[0081] BASF's commercial ruthenium-based catalyst was found to contain 3% precious metal ruthenium, and the main supporting material was pure Al2O3 material.

[0082] Comparative Example 3

[0083] A method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, comprising the following steps:

[0084] Step S1, selecting an alumina powder material, wherein the mass proportion of Al2O3 in the powder material is 99.5%, and the remainder is inevitable impurities; taking the above powder material for pretreatment, the pretreatment temperature is 120°C, the drying time is 4h, and the test shows that the amount of deionized water required for initial wet impregnation of 100g of the above powder material is 95.8g;

[0085] Step S2, taking 24.88 g of ruthenium nitrate solution, in which the mass fraction of metallic ruthenium in the ruthenium nitrate solution is 12.43%, adding 70.92 g of deionized water, and stirring evenly by magnetic force;

[0086] Step S3, adding the diluted ruthenium nitrosyl nitrate aqueous solution dropwise to 100 g of alumina powder material which is constantly stirred, stopping stirring after the dropwise addition is completed, and aging overnight to obtain a catalyst precursor with a ruthenium mass percentage of 3%;

[0087] Step S4, drying the 3% Ru-Al powder in step S3 at 120°C in an oven for 4 hours, and then reducing the catalyst precursor prepared above in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.0%, controlling the reduction temperature to 500°C, the time to 3 hours, and the space velocity to 5000h -1 ;

[0088] Step S5, adding 95.8 g of deionized water to 1.96 g of potassium nitrate powder, stirring until completely dissolved, and then dropwise adding to the ruthenium-based catalyst precursor cooled in step S4, leaving for 2 hours, and drying in an oven at 120° C. for 4 hours;

[0089] Step S6: The ruthenium-based catalyst precursor obtained in step S5 is placed in a hydrogen-nitrogen atmosphere with a hydrogen volume percentage of 3.5% for reduction, and the reduction temperature is controlled to be 500° C., the time is 3 h, and the space velocity is 5000 h -1 , and obtained a 3% Ru-Al-K catalyst.

[0090] The ruthenium-based catalysts prepared in the above Examples 1-5 and Comparative Examples 1-3 were tested for their catalytic activity in hydrogen production by decomposition of ammonia. The test process was as follows: the above ruthenium-based catalyst was pressed into tablets, and after being sieved through a combination of 20-mesh and 40-mesh sieves, 5 g of the catalyst particles retained in the sieves were respectively taken and loaded into a fixed bed. The reaction gas was a mixture of ammonia and argon, in which the ammonia gas volume fraction was 10%, and the space velocity was 15000 h -1 , the working pressure is normal pressure, the reaction temperature is 300-400°C, and the gas components at the fixed bed outlet are tested. The corresponding test results are shown in Table 1.

[0091] Table 1 Evaluation results of ammonia decomposition activity of examples and comparative examples

[0092]

[0093] It can be seen from the data in Table 1 that the preparation process and support material of the ruthenium-based catalyst have a very important influence on the catalytic activity of the catalyst. Comparing Example 1 with Comparative Example 1, the activity of the catalyst for hydrogen production from ammonia decomposition after secondary reduction is significantly improved. The results show that the calcination of the ruthenium precursor in air causes the size of the ruthenium particles to increase, which affects the activity of the ruthenium-based catalyst for hydrogen production from ammonia decomposition. Compared with Comparative Example 3, Example 1 and Example 2 illustrate that under the same ruthenium content and preparation process, by using alumina containing a specific proportion of magnesium oxide and cerium oxide as a carrier, ammonia decomposition and hydrogen production can be promoted and the catalytic activity can be improved. Compared with Example 3, Example 2 has the highest conversion efficiency at 350°C, indicating that the choice of reduction temperature and the choice of promoter will affect the activity of the catalyst. Although Example 5 has the highest conversion efficiency, the use of precious metal ruthenium is large, which will increase the production cost. Compared with Comparative Example 2, Examples 1-3 have obvious performance advantages at 300-400°C, especially 300°C-350°C.

[0094] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. After reading the above teachings of the present invention, it is possible for ordinary technicians in the relevant field to make other different forms of changes or modifications based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures, characterized in that: It comprises a metal active component, a carrier and a promoter, wherein the metal active component is active metal ruthenium, and the carrier is a composite alumina containing metal oxide; The metal active component accounts for 1wt%-5wt% of the ruthenium-based catalyst; The metal oxide contained in the composite alumina is magnesium oxide and / or cerium oxide, and the metal oxide accounts for 0wt%-30wt% of the composite alumina; The molar ratio of the metal active component to the promoter is 0.5-2.

0.

2. The method for preparing the ruthenium-based catalyst for hydrogen production by decomposing ammonia at medium and low temperatures according to claim 1, characterized in that: The following steps are involved: Step S1, selecting a composite alumina containing metal oxides as a carrier, and testing the amount of deionized water required for initial wetness impregnation thereof; Step S2, adding deionized water to the ruthenium precursor solution to dilute the ruthenium precursor solution to a desired concentration; Step S3, adding the diluted ruthenium precursor solution obtained in step S2 dropwise to the continuously stirred carrier, and aging overnight after the dropwise addition is completed; Step S4, drying the powder obtained in step S3, reducing it, and calcining it to obtain a precursor of a ruthenium-based catalyst; Step S5, adding the promoter solution to the precursor of the ruthenium-based catalyst obtained in step S4 and stirring, leaving it for 2-4 hours, and drying; Step S6: reducing and calcining the ruthenium-based catalyst precursor obtained in step S5 to obtain a ruthenium-based catalyst.

3. The method for preparing the ruthenium-based catalyst for hydrogen production by decomposition of ammonia at medium and low temperatures according to claim 2, characterized in that: In step S2, the solute in the ruthenium precursor solution is ruthenium nitrosyl nitrate, and the mass of the solvent in the ruthenium precursor solution after dilution is the same as the mass of deionized water required for initial wetness impregnation of the carrier.

4. The method for preparing the ruthenium-based catalyst for hydrogen production by decomposition of ammonia at medium and low temperatures according to claim 2, characterized in that: In step S4, the obtained powder is first dried in an oven at 100-150° C. for 2-4 h, and then reduced in a reducing atmosphere at 300-500° C. for 2-4 h.

5. The method for preparing the ruthenium-based catalyst for hydrogen production by decomposition of ammonia at medium and low temperatures according to claim 2, characterized in that: In step S5, the accelerator solution is an alkali metal salt solution including potassium carbonate, potassium nitrate or cesium nitrate. The mass of the solvent in the solution is the same as the mass of deionized water required for the initial wet impregnation of the carrier. After being placed for 2-4 hours, it is dried in an oven at 100-150° C. for 2-4 hours.

6. The method for preparing a ruthenium-based catalyst for hydrogen production by decomposing ammonia at medium and low temperatures according to claim 2, characterized in that: In step S6, the powder obtained in step S5 is reduced in a reducing atmosphere at 300-500°C for 2-4h.

7. The method for preparing a ruthenium-based catalyst for producing hydrogen by decomposing ammonia at medium and low temperatures according to claim 4 or 6, characterized in that: The reducing atmosphere in step S4 and step S6 is: a hydrogen-argon mixed gas or a hydrogen-nitrogen mixed gas; The volume percentage of hydrogen in the hydrogen-argon mixed gas is 3%-10%, and the air velocity is controlled at 5000-6000h -1 .

8. The use of the ruthenium-based catalyst according to claim 1, characterized in that: The catalyst is used for catalyzing the decomposition of ammonia at medium and low temperatures to produce hydrogen, and the reaction temperature during the decomposition to produce hydrogen does not exceed 500°C.

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