CN113845398A

CN113845398A - Composite catalyst capable of replacing iridium catalyst and preparation method and application thereof

Info

Publication number: CN113845398A
Application number: CN202111123819.3A
Authority: CN
Inventors: 王晓东; 丛伟民; 尹颖华; 王智刚; 张万生; 杨天卓; 张涛
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2021-09-24
Filing date: 2021-09-24
Publication date: 2021-12-28
Anticipated expiration: 2041-09-24
Also published as: CN113845398B

Abstract

A composite catalyst capable of replacing iridium catalyst is prepared by composite catalyst composed of active metal ruthenium, mullite fiber, binding material, spodumene and talc, and has a certain macroscopic shape; the composite catalyst comprises the following components: the total mass of the mullite fiber and the bonding material is 100 percent, wherein the mass percent of the mullite fiber is 50 to 80 percent. The spodumene accounts for 0.5-5 wt%, the talcum accounts for 1-5 wt%, and the active metal ruthenium accounts for 25-40 wt%. The mass percent of spodumene is spodumene mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent, the mass percent of talc is spodumene mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent, and the mass percent of active metal ruthenium is ruthenium mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent. Compared with the prior art, the composite catalyst has excellent decomposition activity of hydrazine propellant and green propellant, can replace iridium catalyst, and solves the problem of dependence on tactical supplies of iridium.

Description

Composite catalyst capable of replacing iridium catalyst and preparation method and application thereof

Technical Field

The method relates to a preparation method and application of a composite catalyst capable of replacing an iridium catalyst, and the composite catalyst can replace the iridium-based catalyst, is used for catalytic decomposition of hydrazine propellants and ADN-based/HAN-based green propellants, and can effectively reduce the cost.

Background

The monopropellant liquid propulsion technology adopts a catalyst to realize the rapid decomposition of a propellant, and generates high-temperature fuel gas to provide required force or moment for the attitude/orbit control of the aerospace vehicle. Hydrazine propellants are mainly adopted in China, green propellants are developed in recent years, and iridium catalysts are used in the green propellants. The active metal iridium is a core component of the catalyst, directly determines the catalytic performance of the catalyst, is a rare noble metal and a high-grade strategic material, has few mineral deposits in the world, basically has no iridium resource in China, completely depends on import, and can not be recycled on the aerospace catalyst. With the fluctuation of international situation, iridium is practically controlled by countries such as europe and the united states, the price of iridium rises dramatically in recent years (from 20 ten thousand yuan/kg to 150 ten thousand yuan/kg), and risks of import blocking are faced at any time. Therefore, there is an urgent need to develop a new catalyst research for substituting iridium for an active metal material with a controllable source.

Ruthenium and iridium belong to the same platinum group, ruthenium has the electronegativity of 2.20, is the same as iridium, and has an atomic radius higher than that of iridium

And the number of the d orbital electrons is 15, and the iridium alloy is a metal material with the microstructure and the properties most similar to those of iridium. This means that a route using ruthenium instead of iridium is most feasible. Iridium catalyst for use in propulsion of aerospace vehicle, iridium-supported catalystThe loading is more than or equal to 30 percent, and the ruthenium can reach the catalytic performance similar to that of the iridium catalyst only by the same loading. However, the traditional multiple impregnation method is difficult to increase the ruthenium loading to more than 20%. At present, ruthenium-based catalysts are mainly applied to hydrogenation and ammonia synthesis and decomposition reactions, the metal loading capacity is not higher than 10%, the ruthenium content of the existing after-bed catalyst for decomposing the DT-3 propellant catalyst is 5%, and corresponding reports of high-loading (mass fraction is more than or equal to 20%) ruthenium-based catalysts are not available. Soluble ruthenium salt is prepared into a liquid forming agent containing active metal, and the liquid forming agent is directly kneaded into a carrier to prepare the high-loading (25-35%) ruthenium composite catalyst. The catalyst is applied to the decomposition of the catalyst of hydrazine propellant and green propellant for the first time, realizes the stable ignition of the propellant and the engine, and can realize the in-situ substitution of the iridium-based catalyst.

Disclosure of Invention

The invention develops a preparation method and application of a composite catalyst capable of replacing an iridium catalyst, and the composite catalyst can replace a common iridium-based catalyst.

In order to achieve the purpose, the invention adopts the technical scheme that:

a composite catalyst capable of replacing iridium catalyst is a composite catalyst composed of active metal ruthenium, mullite fiber, a binding material, spodumene and talc, and has a certain macroscopic shape; the composite catalyst comprises the following components: the mullite fiber is taken as 100 percent of the total mass of the mullite fiber and the bonding material, wherein the mass percent of the mullite fiber is 50 to 80 percent, and the balance is the bonding material. The spodumene accounts for 0.5-5 wt%, the talcum accounts for 1-5 wt%, and the active metal ruthenium accounts for 25-40 wt%. The mass percent of spodumene is spodumene mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent, the mass percent of talc is spodumene mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent, and the mass percent of active metal ruthenium is ruthenium mass/total mass of the mullite fiber and the bonding material multiplied by 100 percent.

The binding material is selected from one or more of kaolin, clay, silica sol and pseudo-boehmite.

Further, in the technical scheme, the mullite fiber is a commercially available polycrystalline mullite fiber, the average fiber diameter is 1-5 μm, and the fiber length is less than 50 μm.

Further, in the above technical solution, the macroscopic shape of the composite catalyst is any one of the following: irregular particle type, hollow column type, sheet type, spoke type, ellipsoid type, spherical type, cylindrical type, Raschig ring type, clover type and honeycomb ceramic type.

A preparation method of a composite catalyst capable of replacing an iridium catalyst is characterized by comprising the following steps:

step 1, ball milling and mixing of solid-state molding powder

Weighing four solid powders of mullite fiber, bonding material, spodumene and talc according to the content proportion of the raw materials, ball-milling and mixing:

step 2, preparing liquid forming agent containing active metal

Dissolving ruthenium soluble salt of active metal ruthenium in a peptizing agent solution according to a proportion to form a mixed solution; adding a proper amount of surfactant into the mixed solution and then adding a pore-forming agent;

step 3, preparing blank, kneading, mulling and staling

Mixing the solid forming powder obtained in the step 1 with the liquid forming agent containing active metal prepared in the step 2, kneading the mixture into a plastic clay dough, and ageing the plastic clay dough under the conditions of heat preservation and moisture preservation;

step 4, forming, drying, granulating and pre-roasting the aged plastic mud dough;

step 5, hydrothermal reaming and crystallization

Placing the pre-roasted molded composite catalyst in a hydrothermal reaction kettle for hydrothermal crystallization reaction;

step 6, high-temperature reduction

The high temperature reduction is carried out under a hydrogen atmosphere.

Further, in the above technical solution, preferably, step 1, ball milling and mixing of the solid molding powder:

weighing four solid powders of mullite fiber, binding material, spodumene and talc according to the proportion: with mullite fibresAnd the total mass of the bonding material is 100 percent, wherein the mass percent of the mullite fiber is 50 to 80 percent, and the balance is the bonding material. The spodumene accounts for 0.5-5 wt% of the total weight of the composition, and the talc accounts for 1-5 wt%. Putting the four kinds of powder into a ball mill, and dispersing, crushing and fully mixing the four kinds of powder through ball milling; sampling and detecting the particle size distribution of the mixed powder in the ball milling process, and determining the particle size D of the mixed powder₅₀Finishing ball milling when the particle size reaches 15-35 mu m, and detecting the particle size distribution of the mixed powder by a laser particle size method;

further, in the above technical solution, preferably, step 2, preparing a liquid forming agent containing an active metal:

firstly, preparing a peptizing agent solution with the concentration of 1-1.5 mol/L by using deionized water, wherein the peptizing agent is selected from one or more of phosphoric acid, nitric acid, acetic acid, formic acid and citric acid; then dissolving ruthenium soluble salt with the active metal ruthenium mass percent of 25-40% of the total mass of the mullite fiber and the bonding material in a peptizing agent solution to form a mixed solution; adding a proper amount of surfactant into the mixed solution, and dissolving the pore-forming agent into the mixed solution to form a liquid forming agent containing active metal, wherein the soluble ruthenium salt is ruthenium trichloride, and the surfactant is one of sulfonate, sulfate, long-chain ammonium salt, polyoxyethylene ether, diethanolamine and triethanolamine. The pore-forming agent is one or more than two of polyethylene, polyethylene glycol, polyethylene oxide, cellulose methyl ether, polyvinyl alcohol, polyacrylamide, urea, thiourea, cellulose, starch and sesbania powder.

Further, in the above technical solution, preferably, step 3, billet preparation, kneading and aging:

mixing the solid forming powder obtained in the step 1 and the liquid forming agent containing active metal prepared in the step 2, kneading the mixture in a kneading machine to form a plastic mud dough, repeatedly kneading the plastic mud dough in a vacuum pug mill for 3-5 times, and ageing the mixture for more than 6 hours under the conditions of heat preservation and moisture preservation;

further, in the above technical solution, preferably, step 4, forming, drying, granulating and pre-baking

Forming the aged plastic mud dough in a forming machine, adjusting the feeding speed, controlling the forming pressure to be more than 10MPa, slowly drying the formed primary blank under the conditions of heat preservation and moisture preservation, and pre-roasting the dried primary blank after the dried primary blank is early stood by a cutting machine, wherein the roasting atmosphere is inert atmosphere, and the roasting temperature is 550-850 ℃;

further, in the above technical solution, preferably, step 5, hydrothermal reaming and crystallization:

placing the pre-roasted molded composite catalyst in a hydrothermal reaction kettle, adding deionized water without carrier, adjusting the pH value to 6-9 by ammonia water or acetic acid, heating to 180 ℃ under a sealed condition, standing for 3-7 days at the temperature, quenching with water, cooling, and taking out;

further, in the above technical solution, preferably, step 6, high temperature reduction:

the high-temperature reduction is carried out in a hydrogen atmosphere, the concentration of hydrogen is 10-100%, the heating rate is 3-4 ℃, the constant temperature is 550-850 ℃, and the constant temperature is 1-6 hours.

The invention provides application of the catalyst in catalytic decomposition of hydrazine propellants and ADN-based and HAN-based green propellants.

The invention has the following advantages:

the invention adopts soluble ruthenium salt as a liquid forming agent for preparing the active metal, directly kneads the soluble ruthenium salt into the carrier, avoids the problem that the traditional multiple dipping method is difficult to improve the ruthenium carrying capacity to more than 20 percent, and prepares the ruthenium composite catalyst with high carrying capacity (25 to 35 percent). The mullite fiber is used as a base material to prepare the composite catalyst with a macroscopic shape, the fibrous mullite microcrystal does not need to be accumulated in the formed catalyst to form a three-position net-shaped framework, mutually communicated channels are generated in the catalyst, and the active ruthenium metal can be uniformly dispersed on the inner wall of the pore channel. The spodumene component improves the thermal shock resistance of the composite catalyst, and the talc is a structural stabilizer. For the explosive type rapid reaction process of catalytic decomposition of the propellant, the pore channel with good penetrability is beneficial to rapid mass transfer, so that the activity of the catalyst is effectively improved, the catalytic performance of the catalyst is similar to that of an iridium catalyst, and the internal explosion can be effectively avoided by improving the thermal shock resistance and the structural stability. Compared with the prior art, the composite catalyst developed by the invention has excellent decomposition activity of hydrazine propellant and green propellant, can replace iridium catalyst, and solves the dependence on tactical materials iridium.

Drawings

FIG. 1 shows Ru/Al prepared in example 1 of the present invention₂O₃Catalyst and comparative Ru/Al₂O₃Catalyst and Ir/Al₂O₃Electron microscopy particle statistics and active site test data for DT-3 propellant of catalyst.

FIG. 2 shows Ru/Al prepared in example 1 of the present invention₂O₃Catalyst and comparative Ir/Al₂O₃DT-3 propellant Engine light-off test data for the catalyst. FIG. 2(a) is Ir/Al₂O₃DT-3 propellant engine light-off test data for the catalyst; FIG. 2(b) shows Ru/Al₂O₃DT-3 propellant Engine light-off test data for the catalyst.

FIG. 3 shows Ru/Al prepared in example 1 of the present invention₂O₃Catalyst and comparative Ir/Al₂O₃ADN-based propellant engine light-off test data for the catalyst. FIG. 3(a) is Ir/Al₂O₃ADN-based propellant engine light-off test data for the catalyst; FIG. 3(b) shows Ru/Al₂O₃ADN-based propellant engine light-off test data for the catalyst.

FIG. 4 shows Ru/Al prepared in example 1 of the present invention₂O₃Catalyst and comparative Ir/Al₂O₃HAN-based propellant engine light-off test data for the catalyst. FIG. 4(a) is Ir/Al₂O₃HAN-based propellant engine ignition test data for the catalyst; FIG. 4(b) shows Ru/Al₂O₃HAN-based propellant engine light-off test data for the catalyst.

FIG. 5 is DT-3 propellant engine light-off test data for the Ru composite catalyst prepared in example 2 of the present invention.

FIG. 6 is DT-3 propellant engine light-off test data for the Ru composite catalyst prepared in example 3 of the invention.

Detailed Description

The prepared high-load ruthenium-based catalyst is filled in a catalyst bed of a propellant engine, the propellant is supplied by adopting a gas extrusion and solenoid valve control mode, the propellant is catalytically decomposed at room temperature to generate high-temperature and high-pressure fuel gas, and the test of the thermal test performance of the catalyst is examined by measuring the temperature T of the catalyst bed of the engine, the pressure Pc of a combustion chamber and the time T80 from the electrification of the solenoid valve to the rise of the thrust (or the pressure of the combustion chamber) to 80 percent of the average value in the whole process.

And counting the sizes of the metal particles on the catalyst by a JSM-7800F ultrahigh-resolution thermal field emission scanning electron microscope.

And detecting the number of active sites on the catalyst by a chemical adsorption instrument.

The electron microscope particle statistical method comprises the following steps: selecting 200 metal particles from 3-5 electron microscope pictures of different positions of a catalyst, measuring the particle size of the metal particles, and counting the particle size distribution; the active site test method comprises the following steps: and testing the saturated adsorption capacity of the catalyst on CO by adopting a CO pulse adsorption method, wherein the default is that one active site can adsorb one CO molecule, and the quantity of substances for adsorbing CO of the catalyst per unit mass is calculated, namely the quantity of the active sites of the catalyst.

30 wt% Ir/Al prepared by isovolumetric immersion method₂O₃Catalyst and 20% Ru/Al₂O₃For comparison. 30 wt% Ir/Al₂O₃The preparation method of the catalyst comprises the following steps: preparing a chloroiridic acid solution with the iridium content of 35 wt%, soaking the chloroiridic acid solution on alumina forming particles in the same volume, drying the particles at 120 ℃ for 2 hours, roasting the particles at 500 ℃ in an air atmosphere for 2 hours, and reducing the particles at 500 ℃ in a hydrogen atmosphere for 4 hours; 20% Ru/Al₂O₃The preparation method comprises the following steps: preparing a ruthenium trichloride solution with the ruthenium content of 35 wt%, soaking the solution on the alumina forming particles in the same volume, drying the particles in vacuum for 2 hours at the temperature of 80 ℃, roasting the particles for 2 hours at the temperature of 400 ℃ in a nitrogen atmosphere, and reducing the particles for 2 hours at the temperature of 400 ℃ in a hydrogen atmosphere.

Example 1

Weighing 60g of mullite fiber, 40g of kaolin, 2g of spodumene and 3g of talcum, putting the materials into a planetary ball mill for ball milling, setting the rotating speed to be 100rpm,sampling every 2 hours, detecting the particle size distribution of the mixture by using a laser particle sizer, and after 10 hours, detecting the particle size D of the mixture₅₀The ball milling was finished at 25 μm, and the powder was taken out. Preparing 1mol/L phosphoric acid solution by deionized water, placing 150mL of the solution in a triangular flask, adding 61.49g of ruthenium trichloride, stirring at room temperature to completely dissolve the ruthenium trichloride, then adding 0.5g of hexadecyl sodium sulfonate, 5g of sesbania powder, and heating to 40 ℃ under stirring to obtain the uniform and viscous liquid forming agent containing the active metal. Mixing the ball-milled solid forming powder with the prepared liquid forming agent containing the active metal, uniformly stirring, kneading into a plastic mud mass in a kneading machine, then putting into a vacuum pug mill for repeated pugging for 4 times, covering the pug mass with semi-dry semi-wet gauze, and ageing in a humidity preserving box for 8 hours. Extruding the aged plastic mud mass into strips by a strip extruding machine, selecting a die with the diameter of 1.8mm, adjusting the feeding speed, controlling the strip extruding pressure to be 15MPa, slowly drying the extruded strips in a constant-temperature constant-humidity room, controlling the room temperature to be 20 ℃ and the humidity to be 45 Rh% by a constant-temperature constant-humidity air conditioner, drying the extruded strips to be constant weight, granulating in a cutting machine, pre-roasting the granulated formed product by adopting a temperature programming method, wherein the pre-roasting is divided into three stages, the temperature rising rate of the first stage is 0.5 ℃/min, the constant temperature is 150 ℃, the constant temperature time is 1 hour, the temperature rising rate of the second stage is 1 ℃/min, the constant temperature is 380 ℃, the constant temperature time is 2 hours, the temperature rising rate of the third stage is 2 ℃/min, the constant temperature is 750 ℃, the constant temperature time is 4 hours, the roasting atmosphere is argon, and naturally cooling is adopted after the roasting is finished. And placing the carrier particles obtained after pre-roasting in a hydrothermal reaction kettle, adding excessive volume of deionized water, adjusting the pH to about 8.5 by using ammonia water, adding the mixture to 180 ℃ under a sealed condition, standing the mixture for 5 days at the temperature, quenching the mixture by using water, cooling and taking out the mixture. And (3) carrying out high-temperature reduction on the catalyst particles after the hydrothermal treatment, wherein the reducing gas is pure hydrogen, the heating rate is 3 ℃/min, the constant temperature is 850 ℃, and the constant temperature is kept for 2 hours. And naturally cooling after reduction to prepare the 30 wt% Ru composite catalyst. The size of metal particles on the catalyst is detected by an ultrahigh resolution thermal field emission scanning electron microscope, the number of active sites on the catalyst is detected by a chemical adsorption instrument, and the analytical and statistical data are shown in figure 1.The DT-3 propellant engine ignition test data is shown in fig. 2(b), the ADN-based propellant engine ignition test data is shown in fig. 3(b), and the HAN-based propellant engine ignition test data is shown in fig. 4 (b).

With 30 wt% Ir/Al₂O₃The catalyst is used as a comparison, the metal particle size and the activity bit data are shown in figure 1, the DT-3 propellant engine ignition test data is shown in figure 2(a), the ADN-based propellant engine ignition test data is shown in figure 3(a), and the HAN-based propellant engine ignition test data is shown in figure 4 (a).

As can be seen from FIG. 1, the high-loading ruthenium-based catalyst prepared by the method has the advantages of small metal particles, uniform distribution and active site number similar to that of Ir.

As can be seen from a comparison of fig. 2, 3 and 4, the high-loading ruthenium-based catalyst has a catalytic activity similar to that of the iridium-based catalyst, and can effectively replace the iridium catalyst.

Example 2

The same procedure as in example 1 was followed, except that: 60g of medium mullite fiber is changed into 70g, 40g of kaolin is changed into 30g, 2g of spodumene is changed into 0.5g, 3g of talc is changed into 5g, and the granularity D of the mixture is changed₅₀The thickness is changed from 25 μm to 15 μm. 1mol/L phosphoric acid solution is changed into 1mol/L nitric acid solution, 61.49g of ruthenium trichloride is changed into 47.05g, and 5g of sesbania powder is changed into 5g of polyethylene glycol. The aging time is changed from 8 hours to 16 hours, the extrusion pressure is changed from 15MPa to 20MPa, the pH value is adjusted to 8.5 by ammonia water and is adjusted to 6 by acetic acid, and the standing time is changed from 5 days to 3 days. The reduction heating rate is changed from 3 ℃/min to 4 ℃/min, and the constant temperature is changed from 850 ℃ to 550 ℃. Prepare 25 wt% Ru composite catalyst. The DT-3 propellant engine ignition test data is shown in FIG. 5.

Example 3

The same procedure as in example 1 was followed, except that: changing 60g of medium mullite fiber into 80g, 40g of kaolin into 20g of pseudoboehmite, 2g of spodumene into 3g, 3g of talc into 4g, and the granularity D of the mixture₅₀The thickness is changed from 25 μm to 30 μm. 1mol/L phosphoric acid solution is changed into 1.5mol/L formic acid solution, 61.49g of ruthenium trichloride is changed into 71.73g, and 5g of sesbania powder is changed into 5g of cellulose methyl ether. Changing aging for 8 hours to 24 hours, changing extrusion pressure of 15MPa to 30MPa, and adjusting with ammonia waterThe pH value was changed from 8.5 to 7.5, and the standing for 5 days was changed to 7 days. The reduction heating rate is changed from 3 ℃/min to 3.5 ℃/min, and the constant temperature is changed from 850 ℃ to 650 ℃. The 35 wt% Ru composite catalyst is prepared. The DT-3 propellant engine ignition test data is shown in FIG. 6.

Claims

1. A composite catalyst capable of replacing an iridium catalyst is characterized in that: the composite catalyst comprises active metal ruthenium, mullite fiber, a binding material, spodumene and talc;

wherein, the contents of spodumene, talcum, active metal ruthenium and mullite fiber are respectively 0.5-5%, 1-5%, 25-40% and 50-80% of the total weight of the mullite fiber and the bonding material in sequence;

2. The method for preparing the composite catalyst according to claim 1, comprising the steps of:

step 1, ball milling and mixing of solid-state molding powder

step 2, preparing liquid forming agent containing active metal

step 3, preparing blank, kneading, mulling and staling

step 5, hydrothermal reaming and crystallization

step 6, high-temperature reduction

The high temperature reduction is carried out under a hydrogen atmosphere.

3. The method for preparing the composite catalyst according to claim 2, comprising the steps of:

step 1, ball milling and mixing of solid-state molding powder

Weighing four solid powder bodies of mullite fiber, bonding material, spodumene and talcum according to the content proportion of the raw materials, and ball-milling: the total mass of the mullite fiber and the bonding material is 100 percent, wherein the mass percent of the mullite fiber is 50 to 80 percent, and the balance is the bonding material; the spodumene accounts for 0.5-5 wt% of the total weight of the composition, and the talc accounts for 1-5 wt%. Putting the four kinds of powder into a ball mill, and dispersing, crushing and fully mixing the four kinds of powder through ball milling; sampling and detecting the particle size distribution of the mixed powder in the ball milling process, and determining the particle size D of the mixed powder₅₀Finishing ball milling when the particle size reaches 15-35 mu m, and detecting the particle size distribution of the mixed powder by a laser particle size method;

step 2, preparing liquid forming agent containing active metal

Firstly, preparing a peptizing agent solution with the concentration of 1-1.5 mol/L by using deionized water, wherein the peptizing agent is selected from one or more of phosphoric acid, nitric acid, acetic acid, formic acid and citric acid; then dissolving ruthenium soluble salt with the mass percent of active metal ruthenium of 25-40% in a peptizing agent solution to form a mixed solution; after a proper amount of surfactant is added into the mixed solution, the pore-forming agent is dissolved in the mixed solution to form a liquid forming agent containing active metal, wherein the soluble ruthenium salt is ruthenium trichloride.

Step 3, preparing blank, kneading, mulling and staling

step 4, forming, drying, granulating and pre-roasting

step 5, hydrothermal reaming and crystallization

step 6, high-temperature reduction

4. The method for preparing the composite catalyst capable of replacing the iridium catalyst according to claim 2, wherein the mullite fiber used in the step 1 is a commercially available polycrystalline mullite fiber, the average diameter of the fiber is 1-5 μm, and the fiber length is less than 50 μm.

5. The method for preparing the composite catalyst capable of replacing the iridium catalyst according to claim 2, wherein the surfactant used in the step 2 is one of sulfonate type, sulfate type, long-chain ammonium salt type, polyoxyethylene ether type, diethanolamine and triethanolamine.

6. The method for preparing a composite catalyst capable of replacing an iridium catalyst according to claim 2, wherein the pore-forming agent in the step 2 is one or more of polyethylene, polyethylene glycol, polyethylene oxide, cellulose methyl ether, polyvinyl alcohol, polyacrylamide, urea, thiourea, cellulose, starch, and sesbania powder.

7. The method for preparing a composite catalyst capable of replacing an iridium catalyst according to claim 2, wherein the hydrothermal pore expansion and crystallization processes of the step 5 are performed before the high-temperature reduction.

8. The method for preparing the composite catalyst capable of replacing the iridium catalyst in claim 2, wherein the macroscopic shape of the composite catalyst is any one of the following shapes: irregular particle type, hollow column type, sheet type, spoke type, ellipsoid type, spherical type, cylindrical type, Raschig ring type, clover type and honeycomb ceramic type.

9. The catalyst according to claim 1 or the catalyst obtained by the preparation method according to any one of claims 1 to 8 is used for catalytic decomposition of hydrazine propellants, ADN-based and HAN-based green propellants.