Application of a molybdenum carbide catalyst with exposed specific crystal faces instead of noble metals

Abstract

The application discloses application of an exposed specific crystal face MoC catalyst which can replace noble metal. The catalyst is prepared by directly nitriding and carbonizing commercial MoO3 nanorods, can regulate and control exposure of a large number of (200) crystal faces on the surface, and can realize catalytic decomposition of a propellant at room temperature, under the working condition that a catalytic bed is preheated to 200 DEG C or above, the activity and stability of the catalyst are equivalent to those of a noble metal catalyst, the noble metal catalyst can be effectively replaced to be used for catalytic decomposition of the HAN-based liquid propellant, and problems such as low noble metal reserves, high price, and dependence on import of some strategic noble metals are solved.

Description

Technical Field

[0001] This invention relates to the application of a MoC catalyst with exposed specific crystal facets that can replace precious metals, and more specifically to a MoC catalyst with exposed specific crystal facets that can replace precious metals for the catalytic decomposition of hydroxylamine nitrate (HAN)-based liquid propellants. Background Technology

[0002] Propulsion technology is the core guarantee for spacecraft in aerospace and other fields to perform high-efficiency missions, ensuring that spacecraft complete tasks such as orbit and attitude control with low mass consumption. Monocomponent liquid propulsion technology uses catalysts to achieve rapid decomposition of propellants, generating high-temperature combustion gases to provide the necessary force or torque for aerospace vehicle attitude / orbit control. Currently, hydrazine-based propellants dominate the application of monocomponent liquid propulsion technology in spacecraft, satellites, and rockets. However, hydrazine-based propellants are toxic, flammable, explosive, and highly polluting, requiring cumbersome ground support and maintenance systems, severely impacting the rapid response and maneuverability of equipment. Green, non-toxic monocomponent propellant technology can solve these technical problems. Current research hotspots are ammonium dinitramide (ADN) and hydroxylamine nitrate (HAN)-based liquid propellants, which, as high-performance, green, non-toxic, and storable new liquid propellants, represent a new research direction and development trend in space chemical propulsion technology.

[0003] HAN-based liquid propellants offer advantages such as being non-toxic, pollution-free, and highly safe. They pose no harm to operators, are environmentally friendly, significantly simplify personnel protection and ground support facilities, have short maintenance cycles, can be pre-packaged, and improve equipment operational mobility. Catalyst technology is one of the core components of HAN-based liquid propulsion technology. It plays a crucial role in converting the chemical energy of HAN liquid propellants into kinetic energy. The performance of the catalyst is critical to the complete decomposition of HAN liquid propellants and the magnitude of kinetic energy output. HAN liquid propellants themselves are characterized by high safety, high performance, and high stability, placing extremely high demands on the catalytic activity of the catalyst.

[0004] Currently, HAN-based liquid propellants commonly use precious metal catalysts. The core components of these catalysts include platinum group metals, primarily platinum and iridium. However, the low reserves and high prices of these precious metals result in high catalyst costs. Furthermore, iridium is a rare precious metal and a high-level strategic material; its reserves are scarce globally, and my country has virtually no iridium resources, relying entirely on imports. Therefore, research into novel precious metal alternatives for catalysts is of paramount importance.

[0005] Transition metal carbides refer to a class of compounds formed by carbonizing transition non-noble metals. For example, molybdenum carbide is a filled metal compound formed by carbon atoms filling the crystal lattice of the transition metal molybdenum. The electronic effect between molybdenum and carbon causes a change in the density of electronic states near the Fermi level of the transition metal, resulting in noble metal-like properties, and is one of the options for noble metal substitution (Chem.Rev.1996,96,1477-1498).

[0006] MoC is currently an important research subject for noble metal-like catalysts due to its large specific surface area; however, it is rapidly deactivated because its surface is easily oxidized to MoO3. Researchers have used MoC as a support to load other metals to obtain catalysts with high catalytic activity. However, these efforts often improve catalyst stability by adding large amounts of noble metals to quickly eliminate oxygen species on the catalyst surface, but they do not fundamentally solve the problem of noble metal substitution. Existing technologies have not shown the application of MoC and other noble metal-like catalysts in the catalytic decomposition of HAN-based liquid propellants. Summary of the Invention

[0007] The purpose of this invention is to provide an application of a MoC catalyst with exposed specific crystal faces that can replace noble metals for the catalytic decomposition of HAN-based liquid propellants.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An application of a MoC catalyst with exposed specific crystal faces that can replace precious metals is proposed. By nitriding and carbonizing MoO3 with nanorod morphology, an α-phase MoC nanorod catalyst with 50%-80% of the surface exposed (200) crystal faces is obtained for the catalytic decomposition of hydroxylamine nitrate-based liquid propellants.

[0010] Furthermore, in the above technical solution, the (020) and its parallel crystal planes in the MoO3 crystal with the nanorod morphology account for 70%-100% of the total crystal plane content, with a length of 1-500μm and a diameter of 1-300nm.

[0011] Furthermore, in the above technical solution, the reaction conditions for the catalytic decomposition of the hydroxylamine nitrate propellant are as follows: the catalytic bed is preheated to 200°C or above, and the ignition of the hydroxylamine nitrate liquid propellant is achieved under pulsed or steady-state conditions.

[0012] Furthermore, in the above technical solution, the MoC catalyst needs to be activated before application. The conditions are 500-700℃, treatment for 1-3 hours, and heating rate of 2-20℃ / min. The treatment atmosphere is 1-100% CH4 / H2, 1-100% H2 / He, or 1-100% H2 / Ar.

[0013] Furthermore, in the above technical solution, the MoC catalyst is ultimately obtained by nitriding and carbonizing MoO3 with a nanorod morphology; the specific preparation steps are as follows:

[0014] 1) MoO3 with nanorod morphology was placed in a reaction apparatus and subjected to nitriding treatment at 600-900℃ under a nitrogen atmosphere to obtain MoN. x ;

[0015] 2) Nitrided MoN x The mixture was placed in the reaction apparatus and carbonized at 600-900°C under a 1-100% CH4 / H4 mixed gas to obtain MoC. x catalyst;

[0016] 3) Introduce 0.1-10% O2 / Ar or air into MoC x The catalyst is passivated at 10-50℃ to obtain the MoC catalyst.

[0017] Furthermore, in the above technical solution, the heating rate of the nitriding treatment in step 1) is 2-20℃ / min, the holding time is 60-240min, and the nitrogen-containing atmosphere is NH3, N2, 1-100% NH3 / He, 1-100% N2 / He, 1-100% NH3 / Ar, or 1-100% N2 / Ar.

[0018] Furthermore, in the above technical solution, the heating rate of carbonization in step 2) is 2-20℃ / min, and the holding time is 60-240min.

[0019] Furthermore, in the above technical solution, the passivation time in step 3) is 10-20 hours.

[0020] A MoCNR catalyst for the catalytic decomposition of HAN-based liquid propellants is disclosed. The catalyst is prepared by calcination, specifically by nitriding and carbonizing commercially available MoO3 nanorods to obtain the final MoCNR catalyst. The process involves placing a certain amount of nanorod-shaped MoO3 in a tube furnace and treating it under a nitrogen atmosphere to obtain MoNNR. x Sample MoN x The material was then placed in a tube furnace and carbonized in a CH4 / H4 mixed atmosphere to obtain MoC. x Then, O2 / Ar is continuously introduced for passivation to obtain the desired catalyst.

[0021] The prepared MoC NR catalyst was loaded into the catalytic bed of a propellant engine, and the propellant was supplied by gas extrusion. The propellant catalytically decomposed to produce high-temperature and high-pressure combustion gas. The thermal performance of the catalyst was evaluated by measuring the temperature T of the engine catalytic bed and the pressure Pc of the combustion chamber. The reaction conditions for the catalytic decomposition of HAN-based propellant were as follows: the catalytic bed was preheated to 200°C or above (for catalyst thermal testing, the better the catalyst performance, the lower the temperature requirement for catalytic bed preheating). Ignition of HAN-based liquid propellant was achieved under pulsed or steady-state conditions.

[0022] Compared with existing technologies, the essential features of this invention are:

[0023] 1. The noble metal-like MoC catalyst with specific exposed crystal faces prepared by this invention has been successfully used for the catalytic decomposition of HAN-based liquid propellants, realizing the application of highly efficient and stable non-noble metal carbide catalysts in the field of catalytic decomposition reaction of HAN-based liquid propellants;

[0024] 2. Compared with conventional MoC catalysts in the prior art, the MoC NR catalyst prepared by this invention has better stability, solving the problem of poor catalyst stability caused by MoC oxidation and deactivation;

[0025] 3. It is expected to replace precious metal catalysts in the catalytic decomposition reaction of HAN-based liquid propellants, thereby solving the problems of low reserves and high prices of precious metals, and the dependence on imports for some strategic precious metals.

[0026] 4. This invention can obtain a highly efficient and stable non-precious metal catalyst with noble metal-like properties by nitriding and carbonizing commercial MoO3 nanorods. The process is simple, the cost is controllable, and it has broad prospects for industrial application. Attached Figure Description

[0027] Figure 1 The results of a 100s steady-state ignition test of a liquid HAN engine with the MoC NR catalyst obtained in Example 1 are shown.

[0028] Figure 2 The results of the pulse ignition test of the MoC NR catalyst obtained in Example 1 on a liquid HAN engine are shown.

[0029] Figure 3 The XRD characterization results are for MoO3, MoO3NR, MoC, and MoCNR.

[0030] Figure 4 This is a TEM image of MoC.

[0031] Figure 5 This is a TEM image of MoC NR.

[0032] Figure 6 SEM images of MoC NR and MoC.

[0033] Figure 7 Results of 100s steady-state ignition test of a liquid HAN engine with a 2wt% Pt / α-MoC catalyst.

[0034] Figure 8 Results of a 100s steady-state ignition test of a liquid HAN engine with a 2wt% Ir / Al2O3 catalyst.

[0035] Figure 9 The results of a 5s steady-state ignition test of a liquid HAN engine with a common MoC catalyst. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] The prepared MoC NR catalyst was loaded into the catalytic bed of a propellant engine. The propellant was supplied by gas extrusion and electromagnetic valve control. The propellant catalytically decomposed to produce high-temperature and high-pressure combustion gas. The thermal performance of the catalyst was evaluated by measuring the temperature T of the engine catalytic bed and the pressure Pc of the combustion chamber.

[0038] A 2wt% Pt / α-MoC catalyst, a 2wt% Ir / Al2O3 catalyst, and a conventional MoC catalyst were used as comparisons.

[0039] Example 1:

[0040] 1 g of nanorod-shaped MoO3NR was placed in a tube furnace, NH3 was introduced, and the temperature was increased to 700℃ at 10℃ / min and held for 2 h. After cooling to room temperature, 20% CH4 / H2 was introduced, and the mixture was calcined at 700℃ for 2 h. After cooling, 1% O2 / Ar was introduced for passivation for 12 h to prepare a MoC NR catalyst with (200) crystal planes accounting for 70%-80% (MoO3 NR refers to MoO3 crystals with a nanorod morphology, where the (020) crystal plane and its parallel crystal planes account for 70%-100% of the total crystal plane content, with a length of 1-500 μm and a diameter of 1-300 nm). The XRD characterization results of the MoC NR catalyst are shown below. Figure 3 TEM images can be found Figure 5 SEM images can be found here. Figure 6 The results of the 100s steady-state ignition test are shown in [the table below]. Figure 1 The results of the pulse ignition test are shown in Figure 2 .from Figure 2 and Figure 7 The experimental results show that the catalyst with a specific crystal facet prepared in this invention has similar catalytic activity to noble metal catalysts and can effectively replace noble metal catalysts.

[0041] Example 2:

[0042] 1 g of MoO3 NR nanorods were placed in a tube furnace, and 50% NH3 / Ar was introduced. The temperature was increased to 700℃ at 10℃ / min and held for 2 h. After cooling to room temperature, 20% CH4 / H2 was introduced, and the mixture was calcined at 700℃ for 2 h. After cooling, 1% O2 / Ar was introduced for passivation for 12 h to prepare a MoC NR catalyst with approximately 60% (200) crystal plane content.

[0043] Example 3:

[0044] 1 g of MoO3 NR nanorods were placed in a tube furnace, NH3 was introduced, and the temperature was increased to 700℃ at 10℃ / min and held for 2 h. After cooling to room temperature, 50% CH4 / H2 was introduced, and the mixture was calcined at 700℃ for 2 h. After cooling, 1% O2 / Ar was introduced for passivation for 12 h to prepare a MoC NR catalyst with approximately 70% (200) crystal plane content.

[0045] Example 4:

[0046] 1g of MoO3NR nanorods were placed in a tube furnace, NH3 was introduced, and the temperature was increased to 700℃ at 10℃ / min and held for 2h. After cooling to room temperature, 20% CH4 / H2 was introduced, and the mixture was calcined at 500℃ for 2h. After cooling, 1% O2 / Ar was introduced for passivation for 12h to obtain a MoC NR catalyst with approximately 50% N species on the surface and (200) crystal planes.

[0047] Example 5:

[0048] 1g of MoO3NR nanorods were placed in a tube furnace, NH3 was introduced, and the temperature was increased to 700℃ at 10℃ / min and held for 2h. After cooling to room temperature, 20% CH4 / H2 was introduced, and the mixture was calcined at 900℃ for 2h. After cooling, 1% O2 / Ar was introduced for passivation for 12h to prepare a MoC NR catalyst with a small portion of over-carbonized surface and approximately 70% (200) crystal plane content.

[0049] Comparative Example 1:

[0050] A 2 wt% Pt / α-MoC catalyst was prepared, and the preparation method is described in Nature 589, 396–401 (2021). The prepared 2 wt% Pt / α-MoC catalyst was loaded into a propellant engine catalyst bed. Propellant was supplied using a gas extrusion and solenoid valve control method. The thermal performance of the catalyst was evaluated by measuring the engine catalyst bed temperature T and the combustion chamber pressure Pc. The ignition results are as follows: Figure 7 As shown.

[0051] Comparative Example 2:

[0052] A 2wt% Ir / Al2O3 catalyst was prepared, following a method described in "Catalytic Decomposition of Hydroxylamine Nitrate at Room Temperature" 28(01), 1-2 (2007). The prepared 2wt% Ir / Al2O3 catalyst was loaded into the catalyst bed of a propellant engine. Propellant was supplied using a gas extrusion and solenoid valve control method. The catalyst's thermal performance was assessed by measuring the engine catalyst bed temperature T and combustion chamber pressure Pc. Ignition results are as follows: Figure 8 As shown.

[0053] Comparative Example 3:

[0054] 1 g of ordinary MoO3 was placed in a tube furnace, NH3 was introduced, and the temperature was increased to 700℃ at 10℃ / min and maintained for 2 h. After cooling to room temperature, 20% CH4 / H2 was introduced, and the mixture was calcined at 700℃ for 2 h. After cooling, 1% O2 / Ar was introduced for passivation for 12 h to prepare MoC. The XRD characterization results of the MoC catalyst are shown below. Figure 3 TEM images can be found Figure 4 SEM images can be found here. Figure 6 The prepared MoC catalyst was loaded into the catalytic converter bed of a propellant engine. Propellant was supplied using a gas extrusion and solenoid valve control method. The thermal performance of the catalyst was evaluated by measuring the engine catalytic converter bed temperature T and the combustion chamber pressure Pc. The test results are as follows: Figure 9 As shown, this indicates that ordinary MoC catalysts cannot achieve ignition under the same experimental conditions.

[0055] Results analysis:

[0056] from Figure 1 As can be seen, when the solenoid valve is opened, the HAN-based liquid propellant decomposes immediately upon contact with the MoC NR catalyst. The instantaneously generated high-temperature and high-pressure mixed gas causes the combustion pressure to rise rapidly and quickly reach a stable value, maintained at 1.1 MPa. At the same time, the catalyst bed temperature Tc also gradually rises from the initial ignition temperature of 200℃ to a maximum bed temperature of 800℃, indicating that the catalyst has excellent decomposition performance of the HAN-based liquid propellant engine.

[0057] from Figure 2It can be seen that the MoC NR catalyst prepared in this invention has good stability under pulsed injection of HAN-based liquid propellant. The combustion pressure generated by each pulse injection of HAN-based liquid propellant is basically stable at around 1.1 MPa, indicating that the catalyst has good pulsed decomposition performance of HAN-based liquid propellant.

[0058] from Figure 3 As can be seen from the XRD pattern, the precursor nanorod-shaped MoO3NR has stronger (020), (040), and (060) crystal planes compared to granular MoO3. The nanorod-shaped MoC NR obtained after nitriding and carbonization treatment has stronger (200) crystal planes and higher content.

[0059] from Figure 4 As can be seen from the TEM results, MoC exhibits a granular morphology, and its surface is mainly composed of (111) crystal planes.

[0060] from Figure 5 As can be seen from the TEM results, MoC NR exhibits a nanorod morphology, and its surface is mainly composed of (200) crystal planes.

[0061] from Figure 6 As can be seen from the SEM results, MoC exhibits a granular morphology, while MoC NR exhibits a nanorod morphology.

[0062] from Figure 7 It can be seen that the MoC catalyst loaded with precious metals in Comparative Example 1 requires the catalyst bed to be preheated to 300°C in order to achieve the same effect as the MoC catalyst without precious metals in this invention in catalytically decomposing HAN-based liquid propellants. On the other hand, it proves that the MoC of this invention can replace precious metals to achieve efficient and stable catalytic decomposition of HAN-based liquid propellants at a lower ignition temperature (200°C).

[0063] from Figure 8 It can be seen that the catalyst of the present invention has comparable engine hot test performance to the conventional catalyst of strategic precious metal Ir in Comparative Example 2, further proving that the catalyst of the present invention can replace conventional precious metal catalysts.

[0064] from Figure 9 It can be seen that the catalyst bed needs to be preheated to 500℃ for the ordinary MoC catalyst in Comparative Example 3 to achieve initial decomposition of HAN-based liquid propellant. From the thermal test data, the combustion pressure Pc curve has a large roughness, the combustion pressure oscillates violently, the steady state lasts only 5s, and the combustion pressure decreases. This indicates that the ordinary MoC catalyst cannot achieve ignition of HAN-based liquid propellant under the same test conditions and does not meet the basic conditions for engineering application.

Claims

1. An application of a MoC catalyst with exposed specific crystal planes that can replace noble metals, characterized in that: By nitriding and carbonizing MoO3 nanorods, α-phase MoC nanorod catalysts with 50%-80% of the surface exposed (200) crystal planes were obtained and used for the catalytic decomposition of hydroxylamine nitrate liquid propellants. The MoC catalyst is obtained by nitriding and carbonizing MoO3 with a nanorod morphology; the specific preparation steps are as follows: 1) MoO3 with nanorod morphology was placed in a reaction apparatus and subjected to nitriding treatment at 600-900 °C under a nitrogen atmosphere to obtain MoN. x ; 2) Nitrided MoN x The mixture was placed in the reaction apparatus and carbonized at 600-900 °C under a 1-100% CH4 / H4 mixed gas to obtain MoC. x catalyst; 3) Introduce 0.1-10% O2 / Ar or air into MoC x The catalyst is passivated at 10-50 °C to obtain the MoC catalyst.

2. The application according to claim 1, characterized in that: In the MoO3 crystals with the nanorod morphology, (020) and its parallel crystal planes account for 70%-100% of the total crystal plane content, with a length of 1-500 μm and a diameter of 1-300 nm.

3. The application according to claim 1, characterized in that: The reaction conditions for the catalytic decomposition of the hydroxylamine nitrate liquid propellant are as follows: the catalytic bed is preheated to 200°C or above, and the ignition of the hydroxylamine nitrate liquid propellant is achieved under pulsed or steady-state conditions.

4. The application according to claim 1, characterized in that: The MoC catalyst needs to be activated before application. The conditions are 500-700 °C for 1-3 h, with a heating rate of 2-20 °C / min. The treatment atmosphere is 1-100% CH4 / H2, 1-100% H2 / He, or 1-100% H2 / Ar.

5. The application of the catalyst according to claim 1, characterized in that, In step 1), the heating rate of the nitriding treatment is 2-20 °C / min, and the holding time is 60-240 min. The nitrogen-containing atmosphere is NH3, N2, 1-100% NH3 / He, 1-100% N2 / He, 1-100% NH3 / Ar, or 1-100% N2 / Ar.

6. The application of the catalyst according to claim 1, characterized in that, In step 2), the heating rate for carbonization is 2-20℃ / min, and the holding time is 60-240 min.

7. The application of the catalyst according to claim 1, characterized in that, The passivation time in step 3) is 10-20 h.

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