An iron oxide-supported ruthenium-based catalyst and its preparation and application

Abstract

The present invention belongs to the field of preparation and application of novel catalysts, and relates to a ruthenium-based catalyst supported on iron oxide, its preparation method and application. It consists of two active components, namely iron oxide and noble metal Ru, and Ru is dispersed on iron oxide in the form of single atoms, with the Ru content being 0.01 - 5 wt% of the total mass of the catalyst. The catalyst of the present invention is suitable for obtaining a highly dispersed Ru catalyst, can achieve low-temperature startup of HAN-based propellants and the catalyst at -3 °C, and is expected to replace iridium catalysts. At the same time, it is also applicable to the highly efficient and highly selective water-gas shift reaction, with the CO reaction rate reaching 1.84 mol CO ·g Ru ‑1 ·h ‑1 at 250 °C, and there is no methanation side reaction, and the hydrogen production rate is increased by 4.9 times compared with that of nanoparticles.

Description

Technical Field

[0001] The present invention belongs to the field of preparation and application of novel catalysts, and relates to a ruthenium-based catalyst supported on iron oxide, a preparation method and an application thereof, specifically, a dual-component catalyst of iron oxide and single-atom dispersed ruthenium for low-temperature decomposition of HAN-based green propellants and for highly efficient and highly selective water-gas shift reactions, and its preparation and application. Background Art

[0002] At present, the attitude and orbit control power systems of satellites and other spacecraft generally adopt liquid monopropellant hydrazine-based propellant technology. However, hydrazine is a highly toxic propellant, and there are great risks in aspects such as ground storage, filling operation, use and maintenance, etc., and strict protection measures and ground support must be taken. With the development needs of space power technology, the adoption of green and non-toxic liquid monopropellant technology has become an inevitable trend of development. Countries around the world are competing to develop green liquid non-toxic propellant technology, and among them, green non-toxic propellants represented by hydroxylammonium nitrate (HAN) have become typical representatives of future green propellants. It has the advantages of being green, non-toxic, pollution-free, high specific impulse, good stability, etc. At present, it has completed flight verification and is entering the stage of technology application and promotion. However, its main problem lies in the relatively high catalytic ignition temperature, and the reactor and storage tank need to be equipped with a heating system, resulting in an increase in system load and being not conducive to its popularization and application. Therefore, it is urgent to develop a catalyst with high and low temperature decomposition activities. At the same time, the core active component in the current catalyst is iridium. Iridium is a rare precious metal and a high-level strategic material. There are few deposits in the world, and there is basically no iridium resource in China. It completely depends on imports. At the same time, the iridium on the space catalyst cannot be recycled. With the turmoil of the international situation, iridium is actually controlled by countries such as Europe and the United States. In the past year, its price has soared (from more than 200,000 yuan per kilogram to nearly 1.5 million yuan per kilogram), and it is at risk of import blockade at any time. It is necessary to carry out research on novel catalysts and replace iridium with an active metal material with controllable sources. Ruthenium is the metal material with the closest microstructure and properties to iridium, which means that the route of replacing iridium with ruthenium is the most feasible. However, ruthenium is not easy to be evenly dispersed, resulting in low activity. Single-atom catalysts are a new strategy for catalyst preparation that can effectively improve the metal utilization rate, increase the reaction activity, and improve the reaction selectivity. The present invention prepares a single-atom dispersed Ru supported on iron oxide to obtain a highly dispersed Ru catalyst, which can effectively improve its low-temperature activity for HAN-based propellants, can achieve low-temperature startup of HAN-based propellants and catalysts at -3 °C, and can be applied to the low-temperature catalytic decomposition of HAN-based propellants and realize the replacement of iridium catalysts.

[0003] Meanwhile, in our research, we found that this catalyst can be applied to the water-gas shift reaction for hydrogen production. Under the requirements of the carbon peak and carbon neutrality strategic background, the production and utilization of hydrogen energy have attracted more and more extensive attention. At present, there are few reports on the application of Ru in the water-gas shift reaction. On the one hand, it is because the Ru-based catalyst has low activity in the water-gas shift reaction. On the other hand, the Ru-based catalyst is prone to the side reaction of methanation, resulting in the loss of hydrogen energy (J. Am. Chem. Soc., 2017, 139, 9739-9754). By means of strong coordination between single-atom metals and supports, not only can single atoms be effectively stabilized, making the utilization rate of metal atoms reach 100% (Acc. Chem. Res., 2013, 46, 1740; Nat. Rev. Chem., 2018, 2, 65-81), but also the reaction can be promoted through the dual-component synergistic effect between the metal and the support, effectively improving the reaction activity (J. Am. Chem. Soc., 2013, 135, 15314; J. Phys. Chem. C., 2014, 118, 21945). In addition, the size effect caused by single-atom dispersion will affect the reaction selectivity by influencing the adsorption behavior or adsorption strength of reactants or products (J. Am. Chem. Soc., 2018, 140, 13736-13745). Iron oxide is a catalyst with a long history used in the industrial water-gas shift reaction and can also be used as a redox support to load noble metals, thereby achieving better WGS reaction activity (Catal. Rev.-Sci. Eng., 2009, 51, 325-440). At the same time, theoretical calculations show that a strong interaction is formed between iron oxide and Ru with a relatively high binding energy (ACS Catal. 2015, 5, 544-552). This strong interaction will be beneficial to the formation of single-atom Ru and the generation of the dual-site synergistic effect between the metal and the support. Therefore, the strategy of preparing single-atom dispersed Ru supported on iron oxide is expected to achieve a highly active and highly selective water-gas shift reaction for Ru-based catalysts. Summary of the Invention

[0004] The purpose of the present invention is to provide a single-atom Ru catalyst supported on iron oxide for the low-temperature decomposition of HAN-based green propellants and the highly efficient and highly selective water-gas shift reaction, and its preparation.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A ruthenium-based catalyst supported on iron oxide, which is composed of two components, iron oxide and ruthenium single atoms. The support is iron oxide, and ruthenium is dispersed in the form of single atoms. The ruthenium content is 0.01-5 wt% of the total mass of the catalyst.

[0007] A preparation method of a ruthenium catalyst supported on iron oxide is as follows:

[0008] The Ru precursor and soluble iron salt are formulated into a homogeneous solution by a coprecipitation method, and the solution is added to an equal volume of alkali solution at a rate of 1-5 mL·min -1 . The pH value is adjusted by adding the alkali solution, followed by stirring reaction, static aging, suction filtration, washing, drying, calcination, and reduction to obtain the target catalyst.

[0009] The Ru precursor is one or more of ruthenium chloride, ruthenium acetylacetonate, ruthenium nitrosyl nitrate, and ruthenium iodide with a ruthenium mass fraction of 0.05-5 wt% in the solution.

[0010] The iron salt is iron nitrate (Fe(NO3)3·9H2O) or iron chloride (FeCl3).

[0011] The alkali solution is one or more of 0.1-0.5 M sodium hydroxide, potassium hydroxide, sodium carbonate, or ammonia water solution, and the adjusted pH value is 7.0-11.0.

[0012] The required reaction and aging temperatures are 20-80 °C, the reaction time is 1-5 h, and the aging time is 1-3 h.

[0013] The required washing and drying temperatures are 20-80 °C; the washing water volume is 0.5-2 L, and the drying time is 6-24 h.

[0014] The required calcination atmosphere is air, the calcination temperature is 200-600 °C, and the calcination time is 2-6 h.

[0015] Before the catalyst is applied, it needs to be reduced. The reduction treatment conditions are: reduction at 200-400 °C for 0.5-2 h in a 5-30 vol% H2 atmosphere, and the other gases in the atmosphere are one or more of He, Ar, and N2.

[0016] The catalyst is used in the catalytic decomposition of HAN-based propellants. The prepared single-atom ruthenium-based catalyst is loaded into the catalytic bed of the propellant engine, and the propellant is supplied by a gas extrusion and solenoid valve control method. Both the propellant and the catalyst are at -3 °C, and the catalytic decomposition generates high-temperature and high-pressure gas. By measuring the engine catalytic bed temperature T, the combustion chamber pressure Pc, and the time t experienced from the solenoid valve being energized to the thrust (or combustion chamber pressure) rising to 80% of the full-course average value 80 , the assessment of the catalyst's hot test performance is achieved.

[0017] The ruthenium catalyst supported on iron oxide is applied to the highly efficient and highly selective water-gas shift reaction. A raw material gas with a composition of 1-5 vol% CO, 3-20 vol% H2O, and the rest being He is used at a space velocity of 1×10 4 -1×10 5 mL·gcat -1 ·h -1 It is introduced into a fixed-bed reactor filled with the ruthenium catalyst supported on iron oxide, and the water-gas shift reaction is carried out at 50-600 °C under atmospheric pressure.

[0018] The catalyst of the present invention is suitable for obtaining a highly dispersed Ru catalyst, can realize the low-temperature start-up of HAN-based propellant and the catalyst at -3 °C, and is expected to replace the iridium catalyst. At the same time, it is also applicable to the highly efficient and highly selective water-gas shift reaction. When the temperature is 250 °C, the CO reaction rate reaches 1.84 mol CO ·g Ru -1 ·h -1 , and there is no methanation side reaction, and the hydrogen production rate is increased by 4.9 times compared with that of nanoparticles.

[0019] Compared with the prior art, the substantial features of the present invention are:

[0020] 1. The catalyst prepared by the method of the present invention has the characteristics of dual-component synergistic catalysis and the active component is dispersed in a single-atom form. The obtained catalyst is composed of iron oxide and ruthenium as dual active components. The synergistic effect is beneficial to improving the catalyst activity. Ruthenium is dispersed on the iron oxide support in a single-atom form, increasing the active sites and reducing the catalyst cost.

[0021] 2. The catalyst of the present invention can disperse the active component Ru at the single-atom level, effectively improve the catalyst activity, can realize the application of Ru in the catalytic field of HAN-based propellants, and is expected to replace the iridium catalyst.

[0022] 3. When the catalyst of the present invention is applied to the water-gas shift reaction, it can realize a highly efficient and highly selective reaction. Among them, the CO reaction rate of the single-atom catalyst reaches 1.84 mol CO ·g Ru -1 ·h -1 , and there is no methanation side reaction (see Figure 3 the data results). Description of the Drawings

[0023] Figure 1 This is the XRD pattern after the reduction treatment of the Ru / FeO catalysts with different loadings and different dispersion degrees prepared in Example 2, Example 7 and Comparative Example 4 of the present invention. It can be seen that the main component of the catalyst is Fe3O4, and there is no diffraction peak of Ru or RuO2, indicating that Ru exists in a highly dispersed form. x This is the single-atom dispersed 0.18 wt% Ru / FeO prepared in Example 2 of the present invention

[0024] Figure 2 ​x Aberration-corrected electron microscopy image of the catalyst after reduction treatment. It can be seen that Ru on the catalyst exists in the form of single atoms.

[0025] Figure 3 For the Ru / FeO with different loadings prepared in Examples 2, 3, 4, 5, 6, and 7 of the present invention x Comparison chart of CO conversion rate and CH4 selectivity for temperature-programmed water-gas shift of the catalyst after reduction treatment.

[0026] Figure 4 Comparison chart of CO conversion rate and CH4 selectivity for temperature-programmed water-gas shift of different supported Ru-based catalysts prepared in Examples 2 and 7 and Comparative Examples 1, 2, and 3 of the present invention after reduction treatment.

[0027] Figure 5 For the Ru / FeO with different dispersions prepared in Example 2 and Comparative Example 4 of the present invention x Comparison chart of CO conversion rate and CH4 selectivity for temperature-programmed water-gas shift of the catalyst after reduction treatment.

[0028] Figure 6 For the Ru / FeO with different dispersions prepared in Examples 2 and 7 and Comparative Example 4 of the present invention x Comparison chart of CO reaction rate (250 °C) and CH4 selectivity (350 °C) for water-gas shift of the catalyst after reduction treatment.

[0029] Figure 7 For the Ru / FeO with different dispersions prepared in Example 2 and Comparative Example 4 of the present invention x Comparison chart of stability of CO conversion rate and CH4 selectivity for water-gas shift at 300 °C of the catalyst after reduction treatment.

[0030] Figure 8 For the single-atom Ru / FeO prepared in Example 20 and Comparative Example 5 of the present invention x Catalyst and the Ru / FeO prepared by deposition-precipitation method x Ignition test data of HAN-based propellant engine under double -3 °C conditions for the catalyst after reduction treatment. Figure 8 (a) shows the hot-spot ignition test data of the single-atom Ru / FeO x catalyst, Figure 8 (b) shows the hot-spot ignition test data of the Ir / FeO x catalyst prepared by deposition-precipitation method. Detailed implementation manners

[0031] The following examples are used to illustrate the present invention in more detail and do not limit the content of the present invention.

[0032] Example 1:

[0033] 3.78 g of iron nitrate (Fe(NO3)3·9H2O) was added to 100 mL of ultrapure water and stirred evenly. The above solution was added dropwise to 100 mL of 0.3 mol / L NaOH solution at a rate of 3 mL / min under strong stirring, and the pH was adjusted to 8 to form a precipitate. The reaction was continued to stir at 80 °C for 3 h, aged statically for 1 h, filtered, and washed with hot water. It was placed at 80 °C for 12 h to dry, and calcined in air at 400 °C for 4 h to obtain FeO x Support.

[0034] Example 2:

[0035] 3.78 g of iron nitrate (Fe(NO3)3·9H2O) and 1.8 g of 0.1 wt% ruthenium chloride solution were added to 100 mL of ultrapure water and stirred evenly. The above solution was added dropwise to 100 mL of 0.3 mol / L NaOH solution at a rate of 3 mL / min under strong stirring, and the pH was adjusted to 8 to form a coprecipitate. The reaction was continued to stir at 80 °C for 3 h, aged statically for 1 h, filtered, and washed with hot water. It was placed at 80 °C for 12 h to dry the catalyst, and calcined in air at 400 °C for 4 h to obtain 0.18 wt% Ru / FeO x Catalyst.

[0036] Examples 3 - 7:

[0037] Different from Example 2, different masses of ruthenium chloride solution were used to obtain Ru / FeO catalysts with different loadings. The preparation method was the same as that in Example 2, and the specific conditions are shown in the following table: x For the water-gas shift reaction activity and selectivity of Ru / FeO catalysts with different loadings after reduction treatment. 100 mg of the catalyst was added to a fixed-bed reactor, reduced at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere, cooled to 150 °C under He purge, and a feed gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest He was introduced, with a space velocity of 1.8×10

[0038]

[0039] From Figure 3 Comparing the water-gas shift reaction activity and selectivity of Ru / FeO x catalysts with different loadings after reduction treatment. 100 mg of the catalyst was added to a fixed-bed reactor, reduced at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere, cooled to 150 °C under He purge, and a feed gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest He was introduced, with a space velocity of 1.8×10 4 mL·g cat -1 ·h -1, under atmospheric pressure, the temperature was programmed from 150 °C to 400 °C at a rate of 5 °C / min for the water-gas shift reaction, and detection was carried out at intervals of 25 °C or 50 °C. After stabilizing for 20 min at each detection temperature, the tail gas was detected by chromatography. It was found that when the Ru loading increased, the activity of the water-gas shift reaction was improved; however, when the Ru loading increased to 0.4 wt% and above, the methanation side reaction began to occur, and the degree of methanation increased with the increase of the Ru loading. This indicates that the Ru loaded on the Ru / FeO x catalyst promotes the reaction, and the Ru loading can be preferably 0.18 wt%, and after the loading increases, Ru still mainly exists in the form of single atoms and is highly dispersed.

[0040] Examples 8-11:

[0041] Different from Example 2, different ruthenium precursors or alkali solutions were used, and different solution dropping rates were adopted, and the others were the same as Example 2. 100 mg of the catalyst was added to a fixed-bed reactor and reduced at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere. The temperature was lowered to 150 °C with He, and a raw material gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest being He was introduced, and the space velocity was 1.8×10 4 mL·g cat -1 ·h -1 , and the water-gas shift reaction was carried out at 300 °C under atmospheric pressure, and the tail gas was detected by chromatography. The specific catalyst preparation conditions and the activity of the catalyst after reduction treatment for the water-gas shift reaction (the conversion rate of CO at 300 °C) are shown in the following table:

[0042]

[0043] From the results of the above Examples 8-11, it can be seen that the reaction activity of the 0.18% Ru / FeO x catalyst is not greatly affected by the type of ruthenium precursor, the type of alkali solution, and the solution dropping rate.

[0044] Comparative Examples 1-3:

[0045] Ru catalysts supported on different carriers were prepared by the deposition-precipitation method. The Ru content was 0.18 wt% or 2.5 wt%.

[0046] Add 1g of TiO2 carrier or Al2O3 carrier to 100mL ultrapure water and stir to form a suspension; take 1.8g or 25g of 0.1wt% ruthenium chloride solution, add 100mL ultrapure water, stir and dilute, and add dropwise to the carrier suspension under strong stirring at a rate of 3mL / min, adjust the pH to 8 with 0.2M sodium hydroxide solution, stir and react at 80℃ for 3h, let stand for aging for 1h, filter, wash with hot water, place at 80℃ for 12h to dry the catalyst, and roast in air at 400℃ for 4h to obtain the target catalyst. The specific conditions are shown in the following table:

[0047]

[0048]

[0049] Depend on Figure 4 The activity and selectivity of water-gas shift reaction after reduction treatment of Ru-based catalysts with different supports were compared. 100 mg of catalyst was added to a fixed bed reactor and reduced at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere. The temperature was dropped to 150 °C after He purge, and a raw gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest He was introduced at a space velocity of 1.8 × 10 4 mL·g cat -1 ·h -1 , the water-gas shift reaction was carried out by heating the temperature from 150℃ to 600℃ at a rate of 5℃ / min under normal pressure, and the detection was carried out at intervals of 50℃. After stabilizing at each detection temperature for 20 minutes, the tail gas was detected by chromatography. It was found that for Al2O3, TiO2, FeO2 and 2.5wt% ruthenium loaded with a higher loading of 2.5wt% x , the reaction activity increases successively, but they are all accompanied by different degrees of methanogenic side reactions. When the Ru loading is reduced to 0.18wt%, 0.18%Ru / FeO x The reaction activity of Ru / FeO2 is much higher than that of 0.18%Ru / TiO2, and no methanogenic side reaction occurs. x Catalyst carrier FeO x The effect on the reaction, and the Ru loading amount may be preferably 0.18 wt%.

[0050] Comparative Example 4:

[0051] Nanoparticle-dispersed RuNP / FeO was prepared by nanosol deposition precipitation method. x The catalyst has a Ru content of 2.0 wt%.

[0052] Add 1 g of the iron oxide support prepared in Example 1 to 100 mL of ethylene glycol and stir to form a suspension; take 10 g of the ruthenium nano-sol precursor ethylene glycol solution (ruthenium concentration is 0.2 wt%, ruthenium nano-particle size is 1 - 2 nm), add it to 100 mL of ethylene glycol and stir to dilute, and dropwise add it to the strongly stirred support suspension at a rate of 3 mL / min, and adjust the pH value to 8 with 0.2 M sodium hydroxide solution. Then stir and react at 80 °C for 3 h, stand and age for 1 h, filter, wash with hot water, place at 80 °C for 12 h to dry the catalyst, and calcine in air at 400 °C for 4 h to obtain the target catalyst.

[0053] From Figure 5 Compare the water-gas shift reaction activity and selectivity of single-atom (Example 2) and nano-sized (Comparative Example 4) Ru / FeO with different loadings. Take 100 mg of the catalyst and add it to a fixed-bed reactor, reduce it at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere, lower the temperature to 150 °C under He purge, introduce a feed gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest being He, and the space velocity is 1.8×10 x mL·g 4 mL·g cat -1 ·h -1 -1, and carry out the water-gas shift reaction at atmospheric pressure by programming the temperature from 150 °C to 400 °C at a rate of 5 °C / min, and detect at intervals of 50 °C. After stabilizing for 20 min at each detection temperature, use chromatography to detect the tail gas. It is found that 0.18 wt% Ru with single-atom dispersion has comparable WGS reaction activity and higher reaction selectivity (methanation side reaction is 0%) compared with 2.0 wt% RuNP with high-loading nano-particle dispersion. This shows the superiority of single-atom Ru on the Ru / FeO x catalyst of the present invention.

[0054] From Figure 6 Compare the water-gas shift reaction activity of Ru / FeO catalysts with different Ru dispersion degrees, which are 0.18 wt% Ru / FeO with single-atom dispersion x (Example 2), 2.5 wt% Ru / FeO with single-atom and nano-cluster mixed existence x (Example 7), and 2.0 wt% RuNP / FeO with nano-particle dispersion x (Comparative Example 4). Take 100 mg of the catalyst and add it to a fixed-bed reactor, reduce it at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere, lower the temperature to 150 °C under He purge, introduce a feed gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest being He, and the space velocity is 1.8×10 x (Comparative Example 4). Take 100 mg of the catalyst and add it to a fixed-bed reactor, reduce it at 300 °C for 0.5 h in a 10 vol% H2 / He atmosphere, lower the temperature to 150 °C under He purge, introduce a feed gas with a composition of 2 vol% CO, 10 vol% H2O, and the rest being He, and the space velocity is 1.8×10 4 mL·gcat -1 ·h -1 At normal pressure, the water-gas shift reaction was carried out at 250 °C and 350 °C respectively, and the tail gas was detected by chromatography to obtain the CO reaction rate (250 °C) and the CH4 selectivity (350 °C). It was found that when the Ru dispersion degree changed from nanoparticles, to the coexistence of single atoms and nanoclusters, and then to single-atom dispersion, the CO reaction rate per unit Ru gradually increased, and the reaction rate on Ru single atoms was 4.9 times that of Ru nanoparticles. And the Ru single-atom catalyst had the highest selectivity (the methanation side reaction was 0%). This shows the superiority of single-atom Ru on the Ru / FeO x catalyst of the present invention.

[0055] A fixed-bed microreactor evaluation device was used to test the water-gas shift reaction of the catalyst. The catalyst dosage was 100 mg, the reaction gas volume composition was 2 vol% CO + 10 vol% H2O + He, the total gas flow rate was 30 mL / min (STP), and the mass space velocity was 1.8×10 4 mL·g cat -1 ·h -1 ; Before the test, the catalyst was pre-reduced by heating in a 10 vol% H2 atmosphere (the other gas was He), and after cooling to room temperature, a temperature-programmed activity test was carried out. The test temperature range was 150 - 600 °C, and samples were taken after maintaining a constant temperature for 20 min at each temperature point to be measured. The composition of the reaction gas at the outlet was detected by chromatography, and the CO conversion rate and CH4 selectivity were calculated.

[0056] The calculation method of the CO conversion rate is as follows:

[0057] CO Conversion(%) = {([CO] in - [CO] out ) / [CO] in} × 100%

[0058] Where: [CO] in , [CO] out are the CO chromatographic peak areas at the inlet and the reactor outlet respectively.

[0059] The calculation method of the CH4 selectivity is as follows:

[0060] CH4 Selectivity(%) = (correction factor * [CH4] out / [CO] in ) × 100%

[0061] Where: [CO] in is the CO chromatographic peak area at the inlet, [CH4] outIt is the CH4 chromatographic peak area at the reactor outlet.

[0062] Examples 12 - 18: Investigate the influence of reduction treatment conditions and water - gas shift test conditions

[0063] Take 100 mg of the 0.18 wt% Ru / FeO catalyst prepared in Example 2 x and place it in a fixed - bed reactor. Reduce it at 200 - 400 °C for 0.5 - 2 h in a 5 - 30 vol% H2 atmosphere; then test the activity of the catalyst for the water - gas shift reaction at 300 °C. The test conditions are a feed gas of 1 - 5 vol% CO, 3 - 20 vol% H2O, and the rest is He, and the space velocity is 1×10 4 ~1×10 5 mL·g cat -1 ·h -1 . The test results of Examples 2, 12 - 18 are shown in the following table:

[0064]

[0065]

[0066] From the results of the above Examples 2, 12 - 18, it can be seen that for the 0.18 wt% Ru / FeO x catalyst, the reaction activity first increases and then decreases with the increase of the reduction temperature. The reduction temperature can be preferably 300 °C; the reaction activity of the catalyst is not greatly affected by the reduction atmosphere, test atmosphere, and mass space velocity.

[0067] Example 19: Investigate the stability of the water - gas shift reaction of Ru / FeOx catalysts with different dispersion degrees

[0068] Take 100 mg of the 0.18 wt% Ru / FeO catalyst prepared in Example 2 x and 100 mg of the 2.0 wt% RuNP / FeO catalyst prepared in Comparative Example 4 x and place them in a fixed - bed reactor. Reduce them at 300 °C for 0.5 h in a 10 vol% H2 atmosphere; then test the stability and selectivity of the catalysts for the water - gas shift reaction at 300 °C. The test conditions are a feed gas of 2 vol% CO, 10 vol% H2O, and the rest is He, and the space velocity is 1.8×10 4 mL·g cat -1 ·h -1 .

[0069] From Figure 7 comparing the single - atom (Example 2) and nano - sized (Comparative Example 4) Ru / FeO xThe stability and selectivity of the catalysts in the water-gas shift reaction were investigated, and it was found that both catalysts exhibited relatively stable water-gas shift reaction activity. Meanwhile, the single-atom catalyst demonstrated higher selectivity (the side reaction of methanation was 0%). This indicates the superiority of single-atom Ru on the Ru / FeO catalyst of the present invention. x of the single-atom Ru on the catalyst.

[0070] Example 20:

[0071] 3.78 g of iron nitrate (Fe(NO3)3·9H2O) and 50 g of a 0.1 wt% ruthenium chloride solution were added to 100 mL of ultrapure water and stirred evenly. The above solution was then added dropwise to 100 mL of a 0.3 mol / L NaOH solution at a rate of 3 mL / min under strong stirring to adjust the pH to 8, forming a coprecipitate. The reaction was continued by stirring at 80 °C for 3 h, aged by standing for 1 h, filtered, and washed with hot water. The catalyst was dried by placing it at 80 °C for 12 h, calcined in air at 400 °C for 4 h, and reduced in a 10 vol% H2 atmosphere at 300 °C for 0.5 h to obtain the 5 wt% Ru / FeO x catalyst.

[0072] Comparative Example 5:

[0073] 1 g of the iron oxide support prepared in Example 1 was added to an aqueous solution of iridium chloride and stirred into a suspension to make the mass loading of Ir 5%. The pH value was adjusted to 8 with a 0.2 M sodium hydroxide solution. Subsequently, the reaction was stirred at 80 °C for 3 h, aged by standing for 1 h, filtered, washed with hot water, dried by placing it at 80 °C for 12 h, calcined in air at 400 °C for 4 h, and reduced in a 10 vol% H2 atmosphere at 300 °C for 0.5 h to obtain the target comparative catalyst.

[0074] The prepared catalyst was loaded into the catalytic bed of a propellant engine. The temperatures of both the propellant and the catalyst were -3 °C. The propellant was supplied by means of high-pressure gas extrusion and solenoid valve control. After the -3 °C propellant came into contact with the -3 °C catalyst, it was rapidly catalytically decomposed to produce high-temperature and high-pressure gas. By measuring the temperature of the engine catalytic bed and the combustion chamber pressure (combustion pressure), the thermal test performance of the catalyst was evaluated. If rapid decomposition does not occur, it is impossible to increase the temperature and generate a stable combustion pressure.

[0075] From Figure 8 comparing the thermal ignition test data of the single-atom Ru / FeO x catalyst and the thermal ignition test data of the Ir / FeO x catalyst prepared by the deposition precipitation method, it can be seen that the single-atom Ru / FeO x can be rapidly ignited and started under the double -3 °C condition, showing good low-temperature activity. While the Ir / FeO xThe catalyst activity is poor and it fails to start ignition successfully. It shows that highly dispersed Ru can effectively improve the catalyst activity and is expected to replace the iridium catalyst.

Claims

1. Application of an iron oxide-supported ruthenium-based catalyst, characterized in that: The described ruthenium catalyst supported on iron oxide consists of a two-component system of iron oxide and ruthenium single atoms. The carrier is iron oxide, and ruthenium is dispersed in the form of single atoms on the iron oxide. The ruthenium content is 0.01 - 5 wt% of the total mass of the catalyst. The catalyst is used for the low-temperature catalytic decomposition of HAN-based propellants at 0 °C to -10 °C. Alternatively, the ruthenium catalyst supported on iron oxide is applied to the water-gas shift reaction. The preparation method of the catalyst is as follows: By using the co-precipitation method, a Ru precursor and a soluble iron salt are formulated into a homogeneous solution, and the solution is added to an equal volume of an alkali solution at a rate of 1-5 mL·min -1 to adjust the pH value by adding the alkali solution, followed by stirring reaction, static aging, suction filtration, washing, drying, calcination, and reduction to obtain the target catalyst; The required calcination atmosphere is air, the calcination temperature is 200 - 600 °C, and the calcination time is 2 - 6 h. The required reduction conditions are: reduction at 200 - 400 °C for 0.5 - 2 h in a 5 - 30 vol% H2 atmosphere, and the other gases in the atmosphere are one or more of He, Ar, and N2.

2. The application of the ruthenium catalyst supported on iron oxide according to claim 1, wherein The catalyst is used for the low-temperature catalytic decomposition of HAN-based propellants at 0 °C to -3 °C.

3. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that, The Ru precursor is one or more of ruthenium chloride, ruthenium acetylacetonate, ruthenium nitrosyl nitrate, and ruthenium iodide with a ruthenium mass fraction of 0.05 - 5 wt% in the solution.

4. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that, The iron salt is one or both of iron nitrate and iron chloride.

5. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that: The alkali solution is one or more of 0.1 - 0.5 M sodium hydroxide, potassium hydroxide, sodium carbonate, or ammonia water solution, and the adjusted pH value is 7.0 - 11.

0.

6. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that, The required reaction and aging temperature is 20 - 80 °C, the reaction time is 1 - 5 h, and the aging time is 1 - 3 h.

7. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that: The required washing and drying temperature is 20 - 80 °C; the washing water volume is 0.5 - 2 L, and the drying time is 6 - 24 h.

8. Use of the ruthenium catalyst supported on iron oxide according to claim 1, characterized in that: When the ruthenium catalyst supported on iron oxide is applied to the water-gas shift reaction, a feed gas composed of 1-5 vol% CO, 3-20 vol% H2O, and the rest being He is fed into a fixed-bed reactor containing the ruthenium catalyst supported on iron oxide at a space velocity of 1×10 4 ~1×10 5 mL·g cat -1 ·h -1 and the water-gas shift reaction is carried out at 50-600 °C under atmospheric pressure.

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