Molecular modification method and application of supported metal catalyst

Abstract

The invention discloses a molecular modification method and application of a supported metal catalyst. Comprising the following steps: contacting a supported metal catalyst with a gas molecule modifier; the gas molecule modifier is selected from at least one of CO, NO, NO2 and N2O; the supported metal catalyst comprises an active metal component and a carrier. According to the molecular modification method, in-situ regulation and control of the electron state of an active site is realized through adsorption of the molecular modifier on the active center of the supported metal catalyst, and the reaction activity and selectivity of the supported metal catalyst such as rhodium, palladium, ruthenium and platinum can be remarkably improved. The method is simple to operate and strong in universality, can effectively adjust the reaction activity of the catalyst, and has a very strong application prospect.

Description

Technical Field

[0001] The present application relates to a molecular modification method of a supported metal catalyst and its application, belonging to the field of supported metal catalyst modulation. Background Art

[0002] Supported metal catalysts are a commonly used type of catalyst, characterized by loading metal species (single atoms or nanoparticles) on a carrier with a high specific surface area to improve the catalytic activity and selectivity of the reaction. The carrier plays a supporting role and provides a place for the active metal to attach. The metal acts as an active site to achieve adsorption of reactants, catalytic reactions, and product desorption. The catalytic process is essentially a process of reconstructing the chemical bonds of reactant molecules through electron transfer between the active metal center and the reactant molecules. Therefore, the electronic properties of the active metal often determine the performance of the catalyst (NanoLett., 2021, 21, 9835-9837).

[0003] Traditional methods for regulating the reaction activity of supported metal catalysts mainly focus on changing the type of active metal or support (Mol. Catal., 2021, 511, 111731), doping additives (Chem Catal., 2022, 2: 2253-2261), changing the coordinating atoms or types around the metal (Angew. Chem. Int. Ed. Engl., 2022, 61, e202205077; J. Am. Chem. Soc., 2021, 143, 18854-18858) and other methods to adjust the electron density of the active metal center and improve the reaction performance. However, in different reaction systems, the performance requirements for supported metal catalysts are often different. For example, in the direct conversion of methane, a strongly electrophilic metal-oxygen active center needs to be formed to promote the activation of the CH bond, but it cannot cause excessive dissociation to generate CO2; in the decomposition reaction of hydroxylamine nitrate (HAN) propellant, since the propellant is composed of an oxidant, fuel, solvent water and a small amount of additives, it has high thermodynamic stability and is not easily catalytically decomposed. The addition of fuel and solvent makes it more difficult to decompose, so it is necessary to increase the effect of the catalyst metal center and the oxidant HAN to enhance the catalytic activity and completely decompose it to produce a large amount of gas. The common point of the above two reactions is that they both use metal catalysts to first catalyze the decomposition of the oxidant to produce highly active metal-oxygen intermediates as active centers, further catalyze the selective breakage of methane or fuel molecules CH, and finally achieve methane selective oxidation or low-temperature rapid decomposition of the propellant. Therefore, by increasing the electron density of the active center to promote the reaction between the metal and the oxidant, it is expected to significantly improve the activity of the catalyst.

[0004] Although the current methods for regulating the electronic properties of supported catalysts can be used to design the catalytic site structure, they are poorly adaptable to the catalytic system and are highly dependent on specific carriers and metals. Once the carrier or active metal type is changed, the corresponding electronic state regulation method must be re-explored, which cannot be widely adapted to more types of supported metal catalysts. Therefore, developing widely applicable electronic state regulation methods is of great significance for improving the performance of supported metal catalysts. Summary of the invention

[0005] The purpose of the present invention is to provide a method for molecularly modifying a supported metal catalyst and its application, which can effectively adjust the electronic state of the active metal center, thereby improving the catalytic reaction efficiency and regulating the product selectivity. The method has the characteristics of simple operation and strong universality, and is easy to promote and apply.

[0006] To achieve the above object, according to one aspect of the present invention, a method for molecularly modifying a supported metal catalyst to regulate the electronic state of an active metal center is provided. The specific process includes dynamically regulating the electronic state of the active site by adsorbing a gas molecule modifier on the active metal center;

[0007] The following steps are involved:

[0008] contacting a supported metal catalyst with a gas molecule modifier;

[0009] The gas molecule modifier is selected from at least one of CO, NO, NO2, and N2O.

[0010] The supported metal catalyst comprises a highly dispersed active metal and a carrier;

[0011] The active metal is selected from at least one of rhodium, palladium, ruthenium and platinum;

[0012] The carrier is selected from at least one of alumina, cerium oxide, zinc oxide, β-type molecular sieve, ZSM-5 type molecular sieve, and MOR type molecular sieve;

[0013] The silicon-aluminum ratio of the β-type molecular sieve, ZSM-5 type molecular sieve, and MOR type molecular sieve is independently 8 to 120;

[0014] The active metal exists in the form of nanoparticles on the supported metal catalyst;

[0015] The mass content of the active metal in the form of nanoparticles on the supported metal catalyst is 10 to 20 wt%;

[0016] Optionally, the active metal exists in the form of a single atom on the supported metal catalyst;

[0017] On the supported metal catalyst, the mass content of the active metal in the form of single atoms is 0.02 to 0.5 wt %.

[0018] The supported metal catalyst is obtained by the following steps:

[0019] The carrier is immersed in a solution containing an active metal precursor, dried and calcined to obtain the supported metal catalyst.

[0020] The active metal precursor is selected from at least one of rhodium chloride, palladium chloride, ruthenium chloride and chloroplatinic acid.

[0021] In the solution containing the active metal precursor, the concentration of the active metal precursor is 0.005-2 mol / L.

[0022] Specifically, the steps include:

[0023] The metal precursor is firstly introduced into the carrier pores or defect sites by the equal volume impregnation method, or adsorbed on the Bronsted acid sites of the molecular sieve pores by electrostatic action, and then dried and calcined to form a supported metal catalyst.

[0024] Optionally, the drying temperature is 60 to 120° C.; the drying time is 10 to 12 hours;

[0025] Optionally, the calcination conditions are: calcination in air or hydrogen atmosphere, calcination temperature is 350-550° C.; calcination time is 2-5 h; and the flow rate of the atmosphere is 20-30 mL / min.

[0026] Optionally, the volume composition of the hydrogen atmosphere during calcination is: 20-100%. The balance atmosphere is nitrogen;

[0027] Optionally, the upper limit of the drying temperature can be independently selected from 100°C and 120°C; the lower limit can be independently selected from 60°C and 100°C;

[0028] Optionally, the upper limit of the drying time can be independently selected from 11h and 12h; the lower limit can be independently selected from 10h and 11h;

[0029] Optionally, the upper limit of the calcination temperature can be independently selected from 450°C and 550°C; the lower limit can be independently selected from 350°C and 450°C;

[0030] Optionally, the upper limit of the calcination time can be independently selected from 4h and 5h; the lower limit can be independently selected from 2h and 3h;

[0031] Optionally, the upper limit of the atmosphere flow rate can be independently selected from 25 mL / min and 30 mL / min; the lower limit can be independently selected from 20 mL / min and 25 mL / min;

[0032] According to another aspect of the present application, there is provided an application of the above-mentioned molecular modification method of a supported metal catalyst for direct methane conversion reaction;

[0033] The process includes:

[0034] The raw material gas containing methane and a gas molecule modifier is contacted with a raw material liquid containing water, a supported metal catalyst and an oxidant to react and obtain an oxygen-containing compound.

[0035] In the raw gas, the volume fraction of the gas molecule modifier is 10 to 60%;

[0036] In the raw material solution, the oxidant is selected from H2O2 and / or K2S2O8;

[0037] The concentration of the oxidant is 0.2-0.5 mol / L;

[0038] Optionally, the upper limit of the concentration of the oxidant can be independently selected from 0.3 mol / L, 0.4 mol / L, 0.5 mol / L; the lower limit can be independently selected from 0.2 mol / L, 0.3 mol / L, 0.4 mol / L;

[0039] The concentration of the supported metal catalyst is 0.2 to 2 g / L;

[0040] Optionally, the concentration of the supported metal catalyst is any value among 0.2 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, or a range between any two values.

[0041] The reaction pressure is 1-5 MPa;

[0042] Optionally, the upper limit of the reaction pressure can be independently selected from 4MPa and 5MPa; the lower limit can be independently selected from 1MPa and 2MPa.

[0043] The reaction temperature is 20 to 90°C;

[0044] Optionally, the upper limit of the reaction temperature can be independently selected from 50°C, 60°C, 70°C, 80°C, 90°C; the lower limit can be independently selected from 20°C, 30°C, 40°C, 50°C, 60°C.

[0045] The reaction time is 0.5 to 10 hours;

[0046] The reaction is carried out in a batch reactor.

[0047] According to another aspect of the present application, there is provided an application of the above-mentioned molecular modification method of a supported metal catalyst for catalytic decomposition reaction of hydroxylamine nitrate-based green liquid propellant;

[0048] The following steps are involved:

[0049] At room temperature, a gas molecule modifier is introduced to contact with a supported metal catalyst for pretreatment, and then a hydroxylamine nitrate-based green liquid propellant is introduced to cause a catalytic decomposition reaction.

[0050] Specifically,

[0051] The supported metal catalyst is added to a 0.2-0.5 mol / L aqueous oxidant solution and ultrasonicated, and then placed in a high-pressure reactor. A mixed gas consisting of CH4 and a molecular modifier is introduced into the reactor. The total pressure is 1-5 MPa, the reaction temperature is 20-90°C, and the reaction is carried out for 0.5-10 hours.

[0052] For the HAN propellant catalytic decomposition reaction, firstly, at room temperature, a gas molecular modifier is introduced into a HAN engine catalytic bed containing a catalyst at a flow rate of 5 to 15 mL / s, and pre-treated for 0.5 to 1 h. Then, the HAN-based liquid propellant is supplied by using nitrogen and the raw gas of the molecular modifier and a solenoid valve control method. After the catalyst and the HAN-based liquid propellant come into contact, a catalytic decomposition reaction occurs, and the HAN-based liquid propellant and the catalyst are quickly started at room temperature.

[0053] The mass percentage of each component of the HAN-based liquid propellant is: 15% to 30% of triazolamine nitrate, 20% to 40% of hydroxylamine nitrate, 10% to 20% of hydrazine nitrate, 12% to 25% of methanol, and 8% to 20% of water.

[0054] Optionally, the triazine nitrate content is 25% to 30%;

[0055] Optionally, the hydroxylamine nitrate content is 20% to 25%;

[0056] Optionally, the content of hydrazine nitrate is 10% to 15%;

[0057] Optionally, the methanol content is 20% to 25%.

[0058] The beneficial effects that the present invention can produce include:

[0059] 1) The present invention utilizes other molecular modifiers to dynamically regulate the coordination environment of the active sites of the supported metal catalyst, change the electronic state of the active sites during the reaction, and accelerate the reaction rate.

[0060] 2) The present invention can significantly change the selectivity of the product by regulating the active metal center using different types of molecular modifiers, and can directionally generate different types of oxygen-containing compounds. Taking the direct conversion of methane as an example, when CO is used as a molecular modifier, CO can participate in the reaction to generate acetic acid, and its selectivity can reach 99%; when NO is used as a molecular modifier, NO does not participate in the reaction, and the product is mainly methanol, and the selectivity can reach 99%.

[0061] 3) The molecular modification method provided by the present invention can be applied to the coordination and electronic state regulation of various carriers and various metals, and can be applied to various reaction systems. It is not limited to specific active components, carriers and catalytic reactions, has strong universality, and greatly reduces research costs.

[0062] 4) The molecular modification method provided by the present invention can be applied to catalysts to achieve rapid reaction of methane at room temperature, or rapid start-up of HAN liquid propellant at room temperature, and has good low-temperature activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is a thermal test performance test diagram of the catalyst used in the catalytic decomposition reaction of hydroxylamine nitrate-based green liquid propellant in Example 10 of the present application.

[0064] Figure 2 This is a thermal test performance test diagram of the catalyst used in the catalytic decomposition reaction of hydroxylamine nitrate-based green liquid propellant in Example 11 of the present application.

[0065] Figure 3 This is a thermal test performance test diagram of the catalyst used in the catalytic decomposition reaction of hydroxylamine nitrate-based green liquid propellant in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0066] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0067] Unless otherwise specified, the raw materials and catalysts in the examples of this application were purchased through commercial channels.

[0068] The selectivity calculation method of the liquid phase oxygen-containing compound in the methane conversion example of the present application is as follows:

[0069] Product selectivity = {product amount / (total methane amount-remaining methane amount)}×100%

[0070] The turnover frequency (TOF) value of the catalyst is calculated as follows:

[0071] TOF = amount of substance of oxygen-containing compound produced by reaction / amount of substance of active metal in supported metal catalyst / reaction time.

[0072] Preparation Example 1:

[0073] Preparation of Pd / β, Pd / ZSM-5, and Pd / MOR supported metal catalysts with a loading of 0.1 wt.%

[0074] Place 1g of H-β zeolite molecular sieve carrier with Si / Al of 12.5 in a beaker, take 1mL of palladium chloride solution with a concentration of 0.01mol / L, add it dropwise to the zeolite molecular sieve, stir evenly until the sample becomes viscous, and stop stirring. After standing for 6 hours, put it in a vacuum drying oven and dry it at 60℃ under vacuum conditions for 12 hours. After drying, the catalyst was calcined at 500℃ in an air atmosphere for 3 hours to obtain a Pd / β single atom catalyst. The air flow rate is 25mL / min. The heating rate is 2℃ / min. The palladium loading in the catalyst is determined by ICP-OES characterization.

[0075] The carriers were replaced with H-ZSM-5 type with Si / Al of 12.5 and H-MOR type zeolite molecular sieves with Si / Al of 12.5, respectively, and prepared according to the above conditions to obtain catalysts with a loading of 0.1wt.% Pd / ZSM-5 and 0.1wt.% Pd / MOR.

[0076] Preparation Example 2:

[0077] Preparation of Rh / β, Rh / ZSM-5, and Rh / MOR supported metal catalysts with a loading of 0.1 wt.%

[0078] According to the operation of Preparation Example 1, the precursor solution was replaced with a 0.01 mol / L rhodium chloride solution. The prepared catalysts were recorded as 0.1 wt. % Rh / β, 0.1 wt. % Rh / ZSM-5, and 0.1 wt. % Rh / MOR.

[0079] Preparation Example 3:

[0080] Preparation of Ru / β, Ru / ZSM-5, and Ru / MOR supported metal catalysts with a loading of 0.1 wt.%

[0081] According to the operation of Preparation Example 1, the precursor solution was replaced with a 0.01 mol / L ruthenium chloride solution. The prepared catalysts were recorded as 0.1 wt.% Ru / β, 0.1 wt.% Ru / ZSM-5, and 0.1 wt.% Ru / MOR.

[0082] Preparation Example 4:

[0083] Preparation of Pt / β, Pt / ZSM-5, and Pt / MOR supported metal catalysts with a loading of 0.1 wt.%

[0084] According to the operation of Preparation Example 1, the precursor solution was replaced with a 0.005 mol / L chloroplatinic acid solution. The prepared catalysts were recorded as 0.1 wt.% Pt / β, 0.1 wt.% Pt / ZSM-5, and 0.1 wt.% Pt / MOR.

[0085] Preparation Example 5:

[0086] Preparation of Rh / ZSM-5 supported metal catalyst with a loading of 0.5 wt.%

[0087] According to the operation of Preparation Example 2, the precursor solution was replaced with a 0.05 mol / L rhodium chloride solution. The prepared catalyst was recorded as 0.5 wt.% Rh / ZSM-5.

[0088] Preparation Example 6:

[0089] Preparation of Rh / ZSM-5-H supported metal catalyst with a loading of 0.5 wt.%

[0090] The specific operation is the same as that of Preparation Example 5, except that the calcination conditions are changed. After drying, the catalyst is calcined at 450° C. for 3 h in a hydrogen atmosphere with a volume fraction of 100%, and then naturally cooled to obtain a 0.5 wt.% Rh / ZSM-5-H catalyst.

[0091] Preparation Example 7:

[0092] Preparation of Pd / Al2O3, Pd / CeO2, and Pd / ZnO supported metal catalysts with a loading of 0.1 wt.%

[0093] The specific operation is the same as that of Preparation Example 1, except that the carrier is replaced by Al2O3, CeO2, and ZnO respectively.

[0094] Preparation Example 9:

[0095] Preparation of Ru / β, Ru / ZSM-5, and Ru / MOR supported metal catalysts with a loading of 10 wt.%

[0096] According to the operation of Preparation Example 1, the precursor solution was replaced with a 1 mol / L ruthenium trichloride solution. The prepared catalysts were recorded as 10 wt.% Ru / β, 10 wt.% Ru / ZSM-5, and 10 wt.% Ru / MOR.

[0097] Preparation Example 10:

[0098] Preparation of Pt / β, Pt / ZSM-5, and Pt / MOR supported metal catalysts with a loading of 20 wt.%

[0099] According to the operation of Preparation Example 1, the precursor solution was replaced with a 2 mol / L chloroplatinic acid solution. The prepared catalysts were recorded as 20 wt.% Pt / β, 20 wt.% Pt / ZSM-5, and 20 wt.% Pt / MOR.

[0100] Embodiment 1:

[0101] Take the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1 for example to catalyze the conversion of CH4 to oxygen-containing compounds under molecular modification (CO):

[0102] The catalyst's direct methane conversion to oxygen-containing compounds reaction performance was evaluated using an intermittent high-pressure reactor. 25 mg of 0.1 wt.% Pd / ZSM-5 catalyst was added to 15 mL of 0.5 mol / L aqueous hydrogen peroxide solution, followed by ultrasonic treatment for 5 min. 20 bar CH4 and 20 bar CO were added to the reaction vessel. The reactor was placed in a heating furnace, the room temperature was maintained at 25 ° C, and the reaction was continued for 1 hour. The solution was continuously stirred with a magnetic cross rotor during the reaction. After the reaction was completed, the reactor was cooled with ice water. When the solution temperature was below 10 ° C, the gas composition was analyzed using a gas chromatograph. The reaction liquid after filtering the catalyst was collected and the amount of oxygen-containing compounds in the liquid was quantified by nuclear magnetic resonance (NMR) measurement. The selectivity of liquid-phase oxygen-containing compounds and the TOF value of the catalyst were calculated.

[0103] Table 1 Reaction performance of catalyst 0.1wt.%Pd / ZSM-5 in H2O2 aqueous solution

[0104]

[0105] Embodiment 2:

[0106] Study on the reaction performance of different oxidants for methane conversion to produce reaction compounds:

[0107] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1 was used, and the aqueous hydrogen peroxide solution was replaced with a 0.5mol / L K2S2O8 aqueous solution to compare the changes in reaction performance:

[0108] Table 2 Reaction performance of catalyst 0.1wt.%Pd / ZSM-5 in K2S2O8 aqueous solution

[0109]

[0110] As shown in the table, the selectivity of acetic acid reached 40% and the TOF reached 50h -1 The conversion efficiency is not as good as that of the system with H2O2 as the oxidant.

[0111] Embodiment 3:

[0112] Study on the reaction performance of different molecular modifiers for methane conversion to produce oxygen-containing compounds:

[0113] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1 was used, and the molecular modifier CO was replaced by NO, NO2, and N2O, respectively, and the reaction performance changes were compared:

[0114] Table 3 Reaction performance of catalyst 0.1wt.% Pd / ZSM-5 in different molecular modifiers DD230300I-DL

[0115]

[0116] As shown in the table, the molecular modification effects of CO and NO are the most obvious, and under a CO atmosphere, the product is mainly acetic acid, while under a NO atmosphere, the product is mainly methanol, indicating that molecular modifiers can not only improve the reaction activity, but also directionally change the product selectivity.

[0117] Embodiment 4:

[0118] Comparison of reaction performance of single atom catalysts loaded on different carriers:

[0119] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5, 0.1wt.% Pd / β, 0.1wt.% Pd / MOR obtained in Preparation Example 1 and the 0.1wt.% Pd / Al2O3, 0.1wt.% Pd / CeO2, 0.1wt.% Pd / ZnO catalysts obtained in Preparation Example 7 were used to carry out methane conversion reaction and compare the catalytic performance:

[0120] Table 4 Performance comparison of Pd catalysts loaded on different carriers

[0121]

[0122]

[0123] As shown in the table, the molecular sieve carrier, especially the ZSM-5 molecular sieve, has a significant promoting effect on the production of acetic acid.

[0124] Embodiment 5:

[0125] Study on the reaction performance of methane conversion to oxygen-containing compounds on Pd catalysts with different supports without molecular modifiers:

[0126] According to the method shown in Example 1, using 0.1wt.% Pd / ZSM-5, 0.1wt.% Pd / β, 0.1wt.% Pd / MOR obtained in Preparation Example 1 and 0.1wt.% Pd / Al2O3, 0.1wt.% Pd / CeO2, 0.1wt.% Pd / ZnO catalysts obtained in Preparation Example 7, the reaction gas was changed to 40bar 50vol.% CH4 / N2, and the reaction performance changes were compared:

[0127] Table 5 Comparison of reaction performance of Pd catalysts on different supports without molecular modification

[0128]

[0129]

[0130] As shown in the table, compared with the results of Example 2, it is found that in the absence of a molecular modifier, the TOF of the oxygen-containing compound decreases significantly.

[0131] Embodiment 6:

[0132] Study on the reaction performance of supported catalysts with different active metals for methane conversion to produce oxygen-containing compounds:

[0133] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1, the 0.1wt.% Rh / ZSM-5 catalyst obtained in Preparation Example 2, the 0.1wt.% Ru / ZSM-5 catalyst obtained in Preparation Example 3 and the 0.1wt.% Ir / ZSM-5 catalyst obtained in Preparation Example 4 were used to carry out methane conversion reaction, and the catalytic performance was compared:

[0134] Table 6 Comparison of reaction performance of different metal supported catalysts

[0135]

[0136] As shown in the table, considering the conversion frequency and acetic acid selectivity, the Pd single atom catalyst has the best reaction performance.

[0137] Embodiment 7:

[0138] Effect of molecular modifiers on the performance of methane conversion to oxygenates over different active metal supported catalysts:

[0139] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1, the 0.1wt.% Rh / ZSM-5 catalyst obtained in Preparation Example 2, the 0.1wt.% Ru / ZSM-5 catalyst obtained in Preparation Example 3 and the 0.1wt.% Pt / ZSM-5 catalyst obtained in Preparation Example 4 were used to carry out methane conversion reaction, and the reaction gas was changed to 40bar 50vol.% CH4 / N2, and the reaction performance changes were compared:

[0140] Table 7 Comparison of reaction performance of different metal-supported catalysts without molecular modification

[0141]

[0142] As shown in the table, compared with the results of Example 4, it is found that the TOF of oxygen-containing compounds of supported catalysts of different metals in the corresponding reactions without molecular modifiers decreases significantly. Combined with the results of Examples 2 and 3, this shows the universality of this molecular modification method for the regulation of supported catalysts.

[0143] Embodiment 8:

[0144] Comparison of reaction performance of supported metal catalysts at different temperatures:

[0145] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1 was used to carry out methane conversion reaction at 50°C, 70°C, and 90°C, respectively, and the catalytic performance was compared:

[0146] Table 8 Comparison of reaction performance of 0.1wt.% Pd / ZSM-5 at different reaction temperatures

[0147]

[0148] As shown in the table, when the reaction temperature increases, the activation rate of the catalyst for methane increases, but the selectivity of acetic acid also gradually decreases.

[0149] Embodiment 9:

[0150] Effects of different volume fractions of molecular modifiers on the reaction performance of supported metal catalysts:

[0151] According to the method shown in Example 1, the 0.1wt.% Pd / ZSM-5 catalyst obtained in Preparation Example 1 was used, and 20bar CH4 was kept unchanged. Methane conversion reactions were carried out at 5bar, 10bar, 20bar, and 30bar CO, respectively, and their reaction performances were compared:

[0152] Table 9 Comparison of reaction performance of 0.1wt.% Pd / ZSM-5 under different volume fractions of CO

[0153]

[0154]

[0155] As shown in the table, with the increase of CO volume fraction, the rate of methane activation and the selectivity of acetic acid first increased and then decreased. This may be due to the excessive adsorption of CO, which will poison the Pd metal center.

[0156] Embodiment 10:

[0157] First, the 10wt.% Ru / β catalyst prepared in Preparation Example 9 is loaded into the HAN engine catalyst bed. Then, at room temperature, CO gas molecules are introduced into the HAN engine catalyst bed at a flow rate of 5mL / s. After pretreatment for 1h, HAN-based liquid propellant (containing 30% triazolamine nitrate, 20% hydroxylamine nitrate, 10% hydrazine nitrate, 25% methanol and 15% water) is supplied by nitrogen and CO squeezing and solenoid valve control. The propellant and catalyst are ignited in a steady state at room temperature, and catalytic decomposition is carried out to produce high-temperature and high-pressure combustion gas. The catalyst thermal test performance test is evaluated by measuring the engine catalyst bed temperature and the combustion chamber pressure. The test results are shown in Figure 1 The curve marked with T in the figure is the temperature of the engine catalyst bed, and the curve marked with Pc is the pressure of the engine combustion chamber. It can be seen from the figure that the HAN-based liquid propellant undergoes catalytic decomposition at room temperature. After completing the 10s steady-state test, the catalyst bed temperature rises, the chamber pressure is stable, and the catalyst performance is good.

[0158] Embodiment 11:

[0159] The difference from Example 10 is that first, 20 wt.% of the Pt / ZSM-5 catalyst prepared in Preparation Example 10 is loaded into the HAN engine catalyst bed, and then at room temperature, NO gas molecules are introduced into the HAN engine catalyst bed containing the catalyst at a flow rate of 10 mL / s, pretreated for 0.5 h, and HAN-based liquid propellant (15% triazaneamine nitrate, 40% hydroxylamine nitrate, 20% hydrazine nitrate, 15% methanol, 10% water) is supplied by nitrogen and NO pushing and solenoid valve control. The other material amounts and operating conditions are the same as those in Example 10. The test results are shown in FIG. Figure 2 ,From the figure, it can be seen that the HAN based liquid propellant undergoes catalytic ,decomposition at room temperature, completing the 10 s steady-state test, the catalytic bed ,temperature rises, the chamber pressure is stable, and the catalyst performance is good.

[0160] Comparative Example 1:

[0161] The difference from Example 10 is that the 10 wt.% Ru / β catalyst prepared in Preparation Example 9 is loaded into the HAN engine catalyst bed, without CO gas molecule pretreatment, and only nitrogen extrusion and solenoid valve control are used to supply HAN-based liquid propellant at room temperature. The other material amounts and operating conditions are the same as those in Example 10. The test results are shown in FIG. Figure 3 ,From the figure, it can be seen that the HAN-based liquid propellant builds pressure very slowly at room temperature, and the pressure is low, basically no catalytic decomposition occurs, and the catalyst bed temperature hardly rises, indicating that the catalyst activity is poor.

[0162] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for molecular modification of a supported metal catalyst, characterized in that: The following steps are involved: contacting a supported metal catalyst with a gas molecule modifier; The gas molecule modifier is selected from at least one of CO, NO, NO2, and N2O.

2. The molecular modification method according to claim 1, characterized in that The supported metal catalyst comprises an active metal and a carrier; The active metal is selected from at least one of rhodium, palladium, ruthenium and platinum; The carrier is selected from at least one of alumina, cerium oxide, zinc oxide, β-type molecular sieve, ZSM-5 type molecular sieve, and MOR type molecular sieve; Preferably, the silicon-aluminum ratio of the β-type molecular sieve, ZSM-5 type molecular sieve, and MOR type molecular sieve is independently 8 to 120; The active metal exists in the form of nanoparticles on the supported metal catalyst; The mass content of the active metal in the form of nanoparticles on the supported metal catalyst is 10 to 20 wt%; Preferably, the active metal exists in the form of a single atom on the supported metal catalyst; On the supported metal catalyst, the mass content of the active metal in the form of single atoms is 0.02 to 0.5 wt %.

3. The molecular modification method according to claim 2, characterized in that: The supported metal catalyst is obtained by the following steps: The carrier is immersed in a solution containing an active metal precursor, dried and calcined to obtain the supported metal catalyst.

4. The molecular modification method according to claim 3, characterized in that: The active metal precursor is selected from at least one of rhodium chloride, palladium chloride, ruthenium chloride and chloroplatinic acid; In the solution containing the active metal precursor, the concentration of the active metal precursor is 0.005-2 mol / L.

5. An application of the molecular modification method of a supported metal catalyst according to any one of claims 1 to 4, characterized in that: Used for direct methane conversion reaction; The process includes: The raw material gas containing methane and a gas molecule modifier is contacted with a raw material liquid containing water, a supported metal catalyst and an oxidant to react and obtain an oxygen-containing compound.

6. The use according to claim 5, characterized in that: In the raw gas, the volume fraction of the gas molecule modifier is 10 to 60%; In the raw material solution, the oxidant is selected from H2O2 and / or K2S2O8; The concentration of the oxidant is 0.2-0.5 mol / L; The concentration of the supported metal catalyst is 0.2 to 2 g / L; The reaction pressure is 1-5 MPa; The reaction temperature is 20 to 90°C; The reaction time is 0.5 to 10 hours; The reaction is carried out in a batch reactor.

7. An application of the molecular modification method of a supported metal catalyst according to any one of claims 1 to 4, characterized in that: Used for catalytic decomposition reaction of hydroxylamine nitrate-based green liquid propellant; The following steps are involved: At room temperature, a gas molecule modifier is introduced to contact with a supported metal catalyst for pretreatment, and then a hydroxylamine nitrate-based green liquid propellant is introduced to cause a catalytic decomposition reaction.

8. The use according to claim 7, The flow rate of the gas molecule modifier is 5 to 15 ml / s.

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