Highly dispersed noble metal catalyst, method for preparing the same, and use thereof

Abstract

The application provides a high-dispersion noble metal catalyst and a preparation method thereof. The application adopts the method of ionizing radiation to irradiate noble metal precursors and variable-valence metal precursors or oxides thereof to obtain a catalyst with noble metal components and variable-valence metal components loaded on a carrier. The variable-valence metal with mixed valence can adjust the electronic properties of the noble metal and the carrier, and further improve the performance of the catalyst. In addition, the method does not need to use a surfactant, and does not have a traditional high-temperature calcination (reduction) process, has wide applicability and can be prepared on a large scale. The catalyst has good application effect in carbon two selective hydrogenation reaction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a highly dispersed noble metal catalyst and a preparation method and application thereof. BACKGROUND

[0002] Noble metal catalysts are a very important class of catalytic materials in catalytic technology, which are widely used in petrochemical industry, energy utilization and environmental protection. For noble metal catalysts, more and more research results show that in addition to the properties of noble metals, the reaction performance of the catalysts depends largely on the chemical environment and the size of the noble metal particles. The reduction of the size of noble metal particles not only provides more active centers to promote the occurrence of the reaction, but also greatly improves the utilization rate of noble metal atoms, reduces the cost of catalysts and promotes the large-scale application in industry. Therefore, it is of great significance and application prospect to prepare noble metal catalysts with high dispersion. At present, the common preparation methods of highly dispersed supported noble metal catalysts mainly include liquid solution immersion method, precipitation deposition method, sol immobilization method, atomic layer deposition method and high temperature pyrolysis method. In the paper "Preparation of High Dispersion Noble Metal Catalysts with Modified Cellulose and Their Hydrogenation Performance", under the action of stabilizer sodium carboxymethyl cellulose, hydrogen was introduced into the solution containing Pd precursor, and highly dispersed Pd nanoparticles with controllable size were synthesized by liquid phase synthesis, which were then loaded on Al2O3 carrier to obtain PdNPs / Al2O3 catalyst with excellent catalytic performance. CN109420515A uses NaBH4 or KBH4 as reducing agent, and slowly hydrolyzes to produce active metal precursors adsorbed on the surface of the carrier, and then reduces the metal precursors to prepare highly dispersed supported metal catalysts. CN106582620A adds a noble metal precursor solution to an alkaline suspension containing a powdered carrier, and then performs atomization, stirring, aging and other steps to precipitate, deposit and anchor the noble metal on the surface of the powdered carrier. After reduction, filtration and washing, a highly dispersed supported noble metal powder catalyst is obtained. CN110756219A obtains a Pt particle suspension by oil-bathing Pt precursor solution and polyvinylpyrrolidone, and then drops it into TiO2 / ZSM-5 molecular sieve. After stirring, centrifugation and drying, Al2O3 or TiO2 film is deposited by atomic layer deposition method, and high dispersion and high stability Pt-based catalyst is obtained after calcination. However, the above methods generally need to use a large amount of surfactants or reducing agents, which are easy to cause sintering and agglomeration of noble metal nanoparticles during the high-temperature calcination removal process. At the same time, these methods are complex, harsh and polluting, and the scale is limited to the laboratory, which is difficult to scale up.

[0003] Therefore, it has become one of the research hotspots to develop new green and environmentally friendly, widely applicable and scalable production of highly dispersed noble metal catalysts and preparation methods. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a highly dispersed noble metal catalyst and a preparation method thereof. The present application uses ionizing radiation to irradiate a noble metal precursor and a variable valence metal precursor or its oxide to obtain a catalyst with a noble metal component and a variable valence metal component supported on a carrier. The ionizing radiation changes the valence of the variable valence metal and promotes the generation of oxygen defects in the structure of the oxide species, which not only makes the variable valence metal play a role in diluting the noble metal particles, but also enhances the interaction between the noble metal particles and the carrier, thereby limiting the tendency of the noble metal particles to migrate, nucleate and aggregate during the reduction process of ionizing radiation, significantly improving the dispersion and atomic utilization rate of the noble metal particles. At the same time, the variable valence metal with mixed valence can also adjust the electronic properties of the noble metal and the carrier, thereby improving the performance of the catalyst. In addition, this method does not require the use of surfactants or traditional high-temperature calcination (reduction) processes, has wide applicability and can be prepared on a large scale. The catalyst has good application effect in carbon dioxide selective hydrogenation reaction.

[0005] One of the objects of the present application is to provide a highly dispersed noble metal catalyst, which comprises a noble metal component, a variable valence metal component and an oxide carrier, and optionally a variable valence metal oxide; or, which comprises a noble metal component, a variable valence metal oxide, and optionally a variable valence metal component, and optionally an oxide carrier.

[0006] Specifically,

[0007] The noble metal component is selected from at least one of platinum, palladium, ruthenium, rhodium;

[0008] The variable valence metal component is selected from at least one of iron, copper, tungsten, tin, indium, gallium, cerium, lanthanum, molybdenum, titanium, vanadium, rhenium;

[0009] The variable valence metal oxide is selected from at least one of iron oxide, diiron trioxide, copper oxide, cuprous oxide, tungsten oxide, tin oxide, indium oxide, gallium oxide, cerium oxide, lanthanum oxide, molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, preferably at least one of iron oxide, indium oxide, gallium oxide, cerium oxide, tungsten oxide, titanium oxide;

[0010] The oxide carrier is selected from at least one of silicon oxide, aluminum oxide, calcium oxide, magnesium oxide, zinc oxide, barium oxide, preferably at least one of aluminum oxide, calcium oxide, magnesium oxide, barium oxide;

[0011] The content of the noble metal component in the noble metal catalyst is 0.005-10% by mass, the total content of the variable valence metal component and the variable valence metal in the variable valence metal oxide is 0.005-99.9% by mass, and the content of the oxide carrier is 0-99.9%; preferably, the content of the noble metal component is 0.01-3% by mass, the total content of the variable valence metal component and the variable valence metal in the variable valence metal oxide is 0.01-99.5% by mass, and the content of the oxide carrier is 1-99%.

[0012] The variable valence metal component and the variable valence metal oxide have high oxidation states and low oxidation states, and the content of the low oxidation state variable valence metal in the variable valence metal component and / or the variable valence metal oxide in the noble metal catalyst is 12-70% by mass, preferably 20-50% by mass.

[0013] The second object of the present application is to provide a preparation method of the above-mentioned high-dispersion noble metal catalyst, which comprises subjecting a catalyst system comprising the noble metal component, the variable valence metal component and / or the variable valence metal oxide, and optionally the carrier component to ionizing radiation treatment to obtain the high-dispersion noble metal catalyst.

[0014] In the preparation method of the above-mentioned catalyst:

[0015] The ionizing radiation can be carried out on a radiation device commonly used in the art, and preferably, the radiation source of the ionizing radiation is selected from at least one of gamma rays, X-rays, and electron beams, preferably at least one of 60 Co rays, 137 Cs rays, X-rays, and electron beams; the irradiation time of the ionizing radiation is 0.1-48 h, preferably 0.5-36 h; and the irradiation dose rate of the ionizing radiation is 0.01-20 kGy / min, preferably 0.5-10 kGy / min.

[0016] When the radiation source is gamma rays, the catalyst system is added with a free radical scavenger solution before ionizing radiation. The free radical scavenger is selected from at least one of alcohol compounds, preferably at least one of methanol, ethanol, ethylene glycol, and isopropyl alcohol, and more preferably at least one of methanol and ethanol; the volume percentage concentration of the free radical scavenger solution is 1-99%, preferably 5-55%; and the amount of the free radical scavenger solution added is not limited, which can only be enough to soak the catalyst system comprising the above-mentioned components.

[0017] The preparation method of the catalyst system comprises:

[0018] The noble metal salt compound and the variable valence metal salt compound are loaded on the component comprising the variable valence metal oxide and the optional oxide carrier, preferably the component comprising the variable valence metal oxide and the optional oxide carrier is impregnated in the solution of the noble metal salt compound and the optional variable valence metal salt compound, and the catalyst system is obtained by taking out and drying.

[0019] The noble metal salt compound and the variable valence metal salt compound are loaded on the component comprising the variable valence metal oxide and the optional oxide carrier, preferably the component comprising the variable valence metal oxide and the optional oxide carrier is impregnated in the solution of the noble metal salt compound and the optional variable valence metal salt compound, and the catalyst system is obtained by taking out and drying.

[0020] Specifically, the noble metal salt compound is selected from at least one of chloride, nitrate, acetate, sulfate and metal organic compound of the noble metal, and is preferably selected from at least one of chloride, nitrate and acetate of the noble metal;

[0021] The variable valence metal salt compound is selected from at least one of chloride, nitrate, acetate, sulfate and metal organic compound of the variable valence metal, and is preferably selected from at least one of nitrate and acetate;

[0022] The molar concentration of the solution of the noble metal salt compound is 0.1-100 mg / mL, and is preferably 1-80 mg / mL; the molar concentration of the solution of the variable valence metal salt compound is 0.2-200 mg / mL, and is preferably 0.5-150 mg / mL; and the molar concentration of the solution of the metal salt comprising the noble metal salt compound and the variable valence metal salt compound is 0.8-300 mg / mL, and is preferably 1-280 mg / mL.

[0023] The drying method can be completed by using the drying process and equipment commonly used in the art, for example, ordinary heating drying or vacuum freeze drying, and is preferably selected from vacuum freeze drying, which can prevent the noble metal that has been reduced and the variable valence metal in low valence state from being oxidized and aggregated. Specifically, the drying temperature is -100-150 ℃, and the drying time is 2-48 h; and preferably, the drying temperature is -60--10 ℃, and the drying time is 6-24 h.

[0024] The loading can be achieved by using the loading methods and process conditions commonly used in the art, preferably by using an impregnation process, in particular, one of the following methods can be selected: isochoric impregnation, unsaturated impregnation, excess impregnation, surface spray impregnation, and vacuum impregnation. When the loaded noble metal salt compound and / or the variable valence metal salt compound contains two or more metals, a one-step impregnation method can be used, i.e., several noble metal salt compounds and / or variable valence metal salt compounds are dissolved to form a mixed solution for impregnation. A step-by-step impregnation method can also be used, i.e., different noble metal salt compounds and / or variable valence metal salt compounds are independently configured into solutions, and then step-by-step impregnation is performed; when the step-by-step impregnation method is used, the carrier needs to be dried between two impregnations, and ionizing radiation treatment can be performed after each step of impregnation as needed, or ionizing radiation treatment can be performed after all metal components are loaded.

[0025] The third object of the present application is to use the high-dispersion noble metal catalyst or the high-dispersion noble metal catalyst obtained by the above preparation method as a hydrogenation reaction catalyst.

[0026] The present application uses ionizing radiation to irradiate noble metal precursors and variable valence metal precursors or oxides thereof to obtain a catalyst loaded with noble metal components and variable valence metal components on the carrier. The ionizing radiation reduces part of the high-oxidation-state variable valence metal components in the variable valence metal oxide carrier to low-oxidation-state variable valence metals, changes the valence state of the variable valence metal and promotes the generation of oxygen defects in the oxide structure, which not only makes the variable valence metal play a role in diluting the noble metal particles, but also enhances the interaction between the noble metal particles and the carrier, thereby limiting the migration, nucleation and aggregation tendency of the noble metal particles during the ionizing radiation reduction process, and significantly improving the dispersion and atomic utilization rate. At the same time, the variable valence metal with mixed valence can also adjust the electronic properties of the noble metal and the carrier, thereby improving the catalyst performance. In addition, this method does not require the use of surfactants or traditional high-temperature calcination (reduction) processes, has wide applicability and can be prepared on a large scale. The catalyst has good application effect in carbon two selective hydrogenation reaction.

[0027] Compared with the prior art, the catalyst and the preparation method thereof have the following advantages:

[0028] a. The present application uses the characteristics of ionizing radiation method and the characteristics of variable valence metal to limit the migration, nucleation and aggregation tendency of noble metal atoms on the carrier, and compared with conventional methods, a catalyst with more uniform particle size, higher noble metal dispersion, and better catalytic activity and selectivity can be obtained;

[0029] b.The present application can control the particle size and distribution of the active component of the catalyst by changing the type and content of noble metal and variable valence metal, the type of carrier, the impregnation method, the irradiation time and dose rate, etc., so that the catalyst suitable for the reaction characteristics can be prepared according to the needs of different selected hydrogenation reactions.

[0030] c.The present application does not need to use a surfactant, and also eliminates the high-temperature calcination and reduction process in the conventional method, so that the method is simple, energy-saving and environment-friendly, and can be used for large-scale production of catalysts.

[0031] d.The catalyst of the present application does not need to use hydrogen or other reducing agents for activation, and can be directly used. DETAILED DESCRIPTION

[0032] It is necessary to point out here that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments of the present application made by those skilled in the art according to the content of the present application still fall within the protection scope of the present application.

[0033] The raw materials used in the examples are all commercially available.

[0034] Example 1

[0035] Take 3 ml of PdCl2 solution with a concentration of 5 mg / mL, load on the surface of 30 g of TiO2 carrier by unsaturated impregnation, then add an appropriate amount of 45% methanol solution to wet the surface of the carrier, and then use a Co γ radiation source to irradiate in a vacuum at room temperature for 10 h at a dose rate of 60 Gy / min. Wash the sample with deionized water for 3 times, and then vacuum dry at-50℃ for 8 h to obtain catalyst A1, wherein the Pd content is 0.05 wt%. 60 Co γ radiation source at a dose rate of 60 Gy / min for 12 h. Wash the sample with deionized water for 3 times, and then vacuum dry at-50℃ for 8 h to obtain catalyst A2, wherein the Pd content is 0.25 wt%.

[0036] Example 2

[0037] Take 10 ml of Pd(NO3)2 solution with a concentration of 10 mg / L, load on the surface of 40 g of TiO2-WO3 mixed carrier (TiO2 content accounts for 40% of the total weight of the carrier, which is prepared by kneading TiO2 and WO3) by surface spraying impregnation, then add an appropriate amount of 45% methanol solution to wet the surface of the carrier, and then use a Co γ radiation source to irradiate in a vacuum at room temperature for 10 h at a dose rate of 60 Gy / min. Wash the sample with deionized water for 3 times, and then vacuum dry at-50℃ for 8 h to obtain catalyst A1, wherein the Pd content is 0.05 wt%. 60 Co γ radiation source at a dose rate of 60 Gy / min for 12 h. Wash the sample with deionized water for 3 times, and then vacuum dry at-50℃ for 8 h to obtain catalyst A2, wherein the Pd content is 0.25 wt%.

[0038] Example 3

[0039] Take the concentration of 2 mg / L Pd(OAc)2(acetate palladium) solution 10 ml, by saturated immersion loaded on the surface of 80 g TiO2-Al2O3 mixed carrier (TiO2 content of 1% of the total weight of the carrier, prepared by kneading TiO2 and Al2O3), then add the appropriate amount of 45% ethanol solution to wet the surface of the carrier, in a vacuum at room temperature environment using 60 Co gamma radiation source at a dose rate of 80 Gy / min for 8 h. Then washed with deionized water sample 3 times, after -50 °C vacuum drying 8 h, to obtain the catalyst A3, wherein the Pd content of 0.025 wt%.

[0040] Example 4

[0041] Take the concentration of 1 mg / ml Pd(NO3)2 and 50 mg / ml K2TiO(C2O4)2 mixed solution 50 ml, by surface immersion loaded on the surface of 100 g TiO2-Al2O3 mixed carrier (TiO2 content of 70% of the total weight of the carrier, prepared by kneading TiO2 and Al2O3), then add the appropriate amount of 45% ethanol solution to wet the surface of the carrier, in a vacuum at room temperature environment using 60 Co gamma radiation source at a dose rate of 80 Gy / min for 16 h. Then washed with deionized water sample 3 times, after -50 °C vacuum drying 8 h, to obtain the catalyst A4, wherein the Pd content of 0.05 wt%.

[0042] Example 5

[0043] Take the concentration of 2 mg / ml Pd(NO3)2 solution 50 ml, by surface immersion loaded on the surface of 100 g Al2O3 carrier, -50 °C vacuum drying 8 h. Then take the concentration of 50 mg / ml K2TiO(C2O4)2 solution 50 ml surface immersion loaded on the above obtained Pd loaded Al2O3 carrier sample, add the appropriate amount of 45% ethanol solution to wet the surface of the carrier, in a vacuum at room temperature environment using 60 Co gamma radiation source at a dose rate of 80 Gy / min for 16 h. Then washed with deionized water sample 3 times, after -50 °C vacuum drying 8 h, to obtain the catalyst A5, wherein the Pd content of 0.1 wt%.

[0044] Example 6

[0045] Take the concentration of 50 mg / ml K2TiO(C2O4)2 solution 50 ml, by surface immersion loaded on the surface of 100 g Al2O3 carrier, add the appropriate amount of 45% ethanol solution to wet the surface of the carrier, in a vacuum at room temperature environment using 60The Co γ radiation source was irradiated at a dose rate of 80 Gy / min for 6 h. A 20 ml solution of Pd(NO3)2 with a concentration of 2 mg / ml was used to load the Ti-loaded Al2O3 carrier sample obtained above by surface spraying, and after the carrier surface was wetted with an appropriate amount of 45% ethanol solution, the sample was used in a vacuum chamber at room temperature 60 The Co γ radiation source was irradiated at a dose rate of 80 Gy / min for 12 h. The irradiated sample was washed with deionized water three times, and then dried in a vacuum at -50°C for 8 h to obtain catalyst A6, which had a Pd content of 0.1 wt%.

[0046] Example 7

[0047] A 20 ml mixed solution of Pd(NO3)2 with a concentration of 2.1 mg / ml and K2TiO(C2O4)2 with a concentration of 30 mg / ml was used to load the surface of 60 g of a WO3-Al2O3 mixed carrier (WO3 content 20% of the total weight of the carrier, prepared by kneading WO3 and Al2O3) by surface spraying, and after the carrier surface was wetted with an appropriate amount of 45% ethanol solution, the sample was used in a vacuum chamber at room temperature 60 The Co γ radiation source was irradiated at a dose rate of 80 Gy / min for 16 h. The irradiated sample was washed with deionized water three times, and then dried in a vacuum at -50°C for 8 h to obtain catalyst A7, which had a Pd content of 0.07 wt%.

[0048] Example 8

[0049] A 50 ml solution of Pd(NO3)2 with a concentration of 2 mg / ml was used to load the surface of 100 g of a WO3-Al2O3 mixed carrier (WO3 content 10% of the total weight of the carrier) by surface spraying, and then dried in a vacuum at -50°C for 8 h. A 50 ml solution of K2TiO(C2O4)2 with a concentration of 50 mg / ml was used to load the surface of the Pd-loaded WO3-Al2O3 carrier sample obtained above by surface spraying, and after the carrier surface was wetted with an appropriate amount of 45% ethanol solution, the sample was used in a vacuum chamber at room temperature 60 The Co γ radiation source was irradiated at a dose rate of 80 Gy / min for 16 h. The irradiated sample was washed with deionized water three times, and then dried in a vacuum at -50°C for 8 h to obtain catalyst A8, which had a Pd content of 0.1 wt%.

[0050] Example 9

[0051] A 30 ml mixed solution of PdCl2 with a concentration of 2.1 mg / ml and PtCl4 with a concentration of 2.1 mg / ml was used to load the surface of 60 g of a TiO2-Al2O3 mixed carrier (TiO2 content 50% of the total weight of the carrier, prepared by kneading TiO2 and Al2O3) by equal-volume impregnation, and after the carrier surface was wetted with an appropriate amount of 45% ethanol solution, the sample was used in a vacuum chamber at room temperature60 The Co γ radiation source was used to irradiate for 18 h at a dose rate of 50 Gy / min. The irradiated sample was washed with deionized water three times and then dried in a vacuum at -50 °C for 8 h to obtain catalyst A9, which contained 0.07 wt% Pd and 0.07 wt% Pt.

[0052] Example 10

[0053] A mixed solution of Pd(NO3)2 at a concentration of 1.05 mg / ml and K2TiO(C2O4)2 at a concentration of 30 mg / ml was taken in an amount of 20 ml and was loaded onto the surface of 60 g of a WO3-Al2O3 mixed carrier (the WO3 content was 30% of the total weight of the carrier, which was prepared by kneading WO3 and Al2O3) by equal-volume impregnation. After the carrier surface was moistened with an appropriate amount of 45% isopropanol solution, the carrier was dried in a vacuum at room temperature. 60 The Co γ radiation source was used to irradiate for 9 h at a dose rate of 80 Gy / min. The irradiated sample was washed with deionized water three times and then dried in a vacuum at -50 °C for 8 h. A PtCl4 solution at a concentration of 2.1 mg / ml was taken in an amount of 20 ml and was loaded onto the surface of the above-mentioned sample by equal-volume impregnation. After the carrier surface was moistened with an appropriate amount of 45% isopropanol solution, the carrier was dried in a vacuum at room temperature. 60 The Co γ radiation source was used to irradiate for 9 h at a dose rate of 80 Gy / min. The irradiated sample was washed with deionized water three times and then dried in a vacuum at -50 °C for 8 h. A PtCl4 solution at a concentration of 2.1 mg / ml was taken in an amount of 20 ml and was loaded onto the surface of the above-mentioned sample by equal-volume impregnation. After the carrier surface was moistened with an appropriate amount of 45% isopropanol solution, the carrier was dried in a vacuum at room temperature.

[0054] Comparative Example 1

[0055] A PdCl2 solution at a concentration of 5 mg / ml was taken in an amount of 3 ml and was loaded onto the surface of 30 g of an Al2O3 carrier by unsaturated impregnation. After the carrier surface was moistened with an appropriate amount of 45% methanol solution, the carrier was dried in a vacuum at room temperature. 60 The Co γ radiation source was used to irradiate for 10 h at a dose rate of 60 Gy / min. The sample was washed with deionized water three times and then dried in a vacuum at -50 °C for 8 h to obtain catalyst D1, which contained 0.05 wt% Pd.

[0056] Comparative Example 2

[0057] A PdCl2 solution at a concentration of 5 mg / ml was taken in an amount of 3 ml and was loaded onto the surface of 30 g of an Al2O3 carrier by unsaturated impregnation. After the carrier surface was moistened with an appropriate amount of 45% methanol solution, the carrier was dried in a vacuum at room temperature and then calcined at 500 °C for 8 h and reduced with hydrogen at 180 °C for 3 h to obtain catalyst D2, which contained 0.05 wt% Pd.

[0058] Comparative Example 3

[0059] A solution of PdCl2with a concentration of 5 mg / mL was taken in 3 mL, which was loaded on the surface of 30 g of TiO2carrier by unsaturated impregnation, dried, calcined at 500°C for 8 h, and then reduced by hydrogen at 180°C for 3 h to obtain catalyst D3, wherein the Pd content was 0.05 wt%.

[0060] Comparative Example 4

[0061] A solution of Pd(NO3)2with a concentration of 10 mg / L was taken in 10 mL, which was loaded on the surface of 40 g of TiO2-WO3mixed carrier (TiO2content accounted for 40% of the total weight of the carrier, which was prepared by kneading TiO2and WO3) by surface spraying impregnation, dried, calcined at 400°C for 10 h, and then reduced by hydrogen at 200°C for 4 h to obtain catalyst D4, wherein the Pd content was 0.25 wt%.

[0062] Comparative Example 5

[0063] A solution of Pd(OAc)2with a concentration of 2 mg / L was taken in 10 mL, which was loaded on the surface of 80 g of TiO2-Al2O3mixed carrier (TiO2content accounted for 1% of the total weight of the carrier, which was prepared by kneading TiO2and Al2O3) by saturated impregnation, dried, calcined at 400°C for 10 h, and then reduced by hydrogen at 220°C for 4 h to obtain catalyst D5, wherein the Pd content was 0.025 wt%.

[0064] Comparative Example 6

[0065] A mixed solution of Pd(NO3)2with a concentration of 1 mg / ml and K2TiO(C2O4)2with a concentration of 50 mg / ml was taken in 50 mL, which was loaded on the surface of 100 g of TiO2-Al2O3mixed carrier (TiO2content accounted for 70% of the total weight of the carrier, which was prepared by kneading TiO2and Al2O3) by surface spraying impregnation, dried, calcined at 400°C for 8 h, and then reduced by hydrogen at 200°C for 4 h to obtain the catalyst D6, wherein the Pd content was 0.05 wt%.

[0066] Comparative Example 7

[0067] A solution of K2TiO(C2O4)2with a concentration of 50 mg / ml was taken in 60 mL, which was loaded on the surface of 100 g of Al2O3carrier by surface spraying impregnation, dried, calcined at 350°C for 8 h, and then reduced by hydrogen at 180°C for 2 h. A solution of Pd(NO3)2with a concentration of 2 mg / ml was taken in 50 mL, which was loaded on the sample by surface spraying impregnation, dried, calcined at 350°C for 8 h, and then reduced by hydrogen at 180°C for 2 h to obtain the catalyst D7, wherein the Pd content was 0.1 wt%.

[0068] Comparative Example 8

[0069] A mixed solution of Pd(N03)2with a concentration of 2.1 mg / ml and K2TiO(C204)2with a concentration of 30 mg / ml was taken in an amount of 20 ml and was supported on the surface of 60 g of a WO3-Al203mixed carrier (WO3content 20% by weight of the total carrier, prepared by kneading WO3and Al203) by surface impregnation, dried and calcined at 450°C for 8 h and reduced with hydrogen at 180°C for 2 h to obtain the catalyst D8, which has a Pd content of 0.07% by weight.

[0070] Comparative Example 9

[0071] A mixed solution of PdCl2with a concentration of 2.1 mg / ml and PtCl4with a concentration of 2.1 mg / ml was taken in an amount of 30 ml and was supported on the surface of 60 g of a Ti02-Al203mixed carrier (Ti02content 50% by weight of the total carrier, prepared by kneading Ti02and Al203) by equal volume impregnation, dried and calcined at 450°C for 8 h and reduced with hydrogen at 180°C for 2 h to obtain the catalyst D9, which has a Pd content of 0.07% by weight and a Pt content of 0.07% by weight.

[0072] Comparative Example 10

[0073] A mixed solution of Pd(N03)2with a concentration of 1.05 mg / ml and K2TiO(C204)2with a concentration of 30 mg / ml was taken in an amount of 20 ml and was supported on the surface of 60 g of a WO3-Al203mixed carrier (WO3content 30% by weight of the total carrier, prepared by kneading WO3and Al203) by equal volume impregnation, dried and calcined at 450°C for 8 h and reduced with hydrogen at 180°C for 2 h. A solution of PtCl4with a concentration of 2.1 mg / ml was taken in an amount of 20 ml and was supported on the surface of the above sample by equal volume impregnation, dried and calcined at 450°C for 8 h and reduced with hydrogen at 180°C for 2 h to obtain the catalyst D10, which has a Pd content of 0.035% by weight and a Pt content of 0.07% by weight.

[0074] Testing of noble metal dispersion in the catalysts of Example 11

[0075] The catalysts prepared in the above examples and comparative examples were tested for noble metal dispersion using a Micromeritics Chemisorb 2920 chemisorption instrument. After pretreatment of 0.100 g of sample, pulse adsorption was carried out at 110°C to adsorption saturation, with a volume of 50 μL per pulse. The results of the testing of noble metal dispersion are shown in Table 1.

[0076] Testing of content of variable valence metal elements in low valence state in Example 12

[0077] The variable valence metal elements on the surface of the catalysts of Examples (A1-A10) and Comparative Examples (D1-D10) were tested and analyzed using a Thermofisher ESCALAB250 X-ray spectrometer (X-ray source: Al Ka, 15 kV, 150 W), background subtraction was performed using ThermoAvantage software, peak fitting was performed on the characteristic peaks of the variable valence metal elements, and the proportion of the corresponding low valence state variable valence metal elements was calculated using the built-in sensitivity factor method of the software. The Ti element was selected for Ti2p peak, and the W element was selected for W4f peak. The test results are shown in Table 1.

[0078] Example 13 Carbon Dioxide Selective Hydrogenation Catalytic Reaction

[0079] The catalysts prepared in the above examples and comparative examples were subjected to carbon dioxide selective hydrogenation catalytic reaction experiments, and the method was as follows:

[0080] 10 ml of catalyst was loaded into a stainless steel reactor with an inner diameter of 2 cm, and nitrogen was used for purging and replacement. In order to prevent oxidation of the sample in air and to ensure the repeatability of the evaluation results, all samples were reduced by hydrogen at 180°C for 2h.

[0081] Hydrogenated carbon dioxide raw material gas was introduced into the reactor. The composition (mole fraction) of the raw material gas was ethane 6%, ethylene 93.5%, acetylene 0.5%, and the hydrogen / acetylene ratio was 1.7; the experimental space velocity was 10000h -1 The carbon dioxide selective hydrogenation catalytic performance of the above catalysts was evaluated at intervals of 5°C in the range of 60-100°C, the composition of the material at the outlet of the reactor was determined using gas chromatography, and the acetylene conversion rate and ethylene selectivity at different temperatures were calculated. The calculation methods of the conversion rate and selectivity of ethylene are as follows:

[0082] C2H2 conversion rate

[0083]

[0084] C2H4 selectivity

[0085]

[0086] The activity of the test sample was expressed as the acetylene conversion rate at 75°C, and the selectivity was expressed as the ethylene selectivity when the acetylene was completely converted. The test results are shown in Table 1.

[0087] Table 1. Test results of catalysts obtained from examples and comparative examples

[0088]

[0089] As can be seen from the results in Table 1, the noble metal dispersion of the catalysts (A1-A10) prepared by irradiating the support containing both noble metal and variable valence metal components with ionizing radiation in Examples (1-10) is significantly higher than that of the catalyst (D1) containing only noble metal component and the support of non-variable valence metal oxide and the catalysts (D2-D10) prepared by conventional calcination-reduction method. The results of elemental valence state analysis also show that the proportion of low oxidation state variable valence metal of the catalysts of Examples is significantly higher than that of the catalysts of Comparative Examples. The presence of a large amount of low oxidation state variable valence metal can promote the generation of oxygen defects on the surface of the support, thereby limiting the agglomeration of noble metal atoms and improving the dispersion thereof. At the same time, the low oxidation state variable valence metal can also transfer electrons with the noble metal component. Both of the above two effects caused by the variable valence metal can significantly affect the adsorption of reactants and products on the noble metal as active center, the reaction energy barrier and desorption, thereby improving the performance of the catalyst. Therefore, it can be seen that in the selective hydrogenation of acetylene, the catalysts of Examples are higher than the catalysts of Comparative Examples in both activity and selectivity.

Claims

1. A highly dispersed noble metal catalyst comprising a noble metal component, a variable valence metal component, and an oxide carrier, wherein the low oxidation state variable valence metal in the variable valence metal component accounts for 12-70% of the total variable valence metal element in the variable valence metal component in terms of mass percentage; or a variable valence metal oxide, and a variable valence metal component, and optionally an oxide carrier, wherein the low oxidation state variable valence metal in the variable valence metal component and the variable valence metal oxide accounts for 12-70% of the total variable valence metal element in the variable valence metal component and the variable valence metal oxide in terms of mass percentage. The content of the noble metal component in the noble metal catalyst is 0.01-3% in terms of mass percentage; the noble metal component is selected from at least one of platinum, palladium, ruthenium, and rhodium; the variable valence metal component is selected from at least one of tungsten and titanium; and the variable valence metal oxide is selected from at least one of tungsten oxide and titanium oxide. The preparation method of the highly dispersed noble metal catalyst comprises loading a noble metal salt compound and a variable valence metal salt compound on a component comprising an oxide carrier and / or a variable valence metal oxide, and then performing ionizing radiation treatment to obtain the highly dispersed noble metal catalyst.

2. The noble metal catalyst according to claim 1, wherein the oxide carrier is selected from at least one of silicon oxide, aluminum oxide, calcium oxide, magnesium oxide, zinc oxide, and barium oxide.

3. The noble metal catalyst according to claim 2, wherein the oxide carrier is selected from at least one of aluminum oxide, calcium oxide, magnesium oxide, and barium oxide.

4. The noble metal catalyst according to claim 1, wherein the low oxidation state variable valence metal in the variable valence metal component accounts for 20-50% of the total variable valence metal element in the variable valence metal component in terms of mass percentage; or the low oxidation state variable valence metal in the variable valence metal component and the variable valence metal oxide accounts for 20-50% of the total variable valence metal element in the variable valence metal component and / or the variable valence metal oxide in terms of mass percentage.

5. The noble metal catalyst according to claim 4, wherein the total content of the variable valence metal in the variable valence metal component and the variable valence metal oxide is 0.01-99.5% in terms of mass percentage, and the content of the oxide carrier is 1-99%.

6. The preparation method according to claim 5, wherein the noble metal salt compound and the variable valence metal salt compound are loaded on a component comprising a variable valence metal oxide and / or an oxide carrier.

7. The preparation method according to claim 6, wherein the ionizing radiation source is selected from at least one of gamma rays, X-rays, and electron beams; the ionizing radiation time is 0.1-48 h; and / or the ionizing radiation dose rate is 0.01-20 kGy / min.

8. The preparation method according to claim 7, wherein ​ 6. A process for the preparation of a highly dispersed noble metal catalyst as defined in any one of claims 1 to 5, which comprises subjecting a catalyst system comprising the noble metal component, the variable valence metal component, the variable valence metal oxide and / or the oxide support component to ionizing radiation, to obtain the highly dispersed noble metal catalyst; the catalyst system being prepared by a process comprising: ​ ​ ​ ​ ​ ​ The irradiation source of the ionizing irradiation is selected from 60 Co-rays, 137 Cs-rays, X-rays, electron beams; and / or, The irradiation time of the ionizing radiation is 0.5-36h; and / or, The irradiation dose rate of the ionizing radiation is 0.5-10kGy / min.

9. The preparation method according to claim 7, wherein, When the irradiation source is gamma ray, the catalyst system is ionizing irradiated after adding the radical scavenger solution.

10. The preparation method according to claim 9, wherein, The radical scavenger is selected from alcohol compounds; and / or, The volume percentage concentration of the radical scavenger solution is 1-99%.

11. The preparation method according to claim 10, wherein, The radical scavenger is selected from at least one of methanol, ethanol, ethylene glycol, and isopropyl alcohol; and / or, The volume percentage concentration of the radical scavenger solution is 5-55%.

12. The preparation method according to claim 11, wherein, The radical scavenger is selected from at least one of methanol and ethanol.

13. The preparation method according to claim 6, characterized in that, The preparation method of the catalyst system comprises: The oxide carrier and / or the variable valence metal oxide are immersed in a metal salt solution containing a noble metal salt compound and a variable valence metal salt compound, and the catalyst system is obtained by taking out and drying.

14. The preparation method according to claim 13, wherein, The noble metal salt compound is selected from at least one of chloride, nitrate, acetate, sulfate, and metal organic compound of noble metal; and / or, The variable valence metal salt compound is selected from at least one of chloride, nitrate, acetate, sulfate, and metal organic compound of variable valence metal; and / or, The molar concentration of the noble metal salt compound solution is 0.1-100mg / mL; and / or, The molar concentration of the variable valence metal salt compound solution is 0.2-200mg / mL; and / or, The molar concentration of the metal salt solution containing the noble metal salt compound and the variable valence metal salt compound is 0.8-300mg / mL; and / or, The drying temperature is -100-150℃, and the drying time is 2-48h.

15. The preparation method according to claim 14, wherein, The noble metal salt compound is selected from at least one of chloride, nitrate, and acetate of noble metal; and / or, The variable valence metal salt compound is selected from at least one of nitrate and acetate; and / or, The molar concentration of the noble metal salt compound solution is 1-80mg / mL; and / or, The molar concentration of the variable valence metal salt compound solution is 0.5-150mg / mL; and / or, The molar concentration of the metal salt solution containing the noble metal salt compound and the variable valence metal salt compound is 1-280mg / mL; and / or, The drying temperature is -60--10℃, and the drying time is 6-24h.

16. The use of the high-dispersion noble metal catalyst according to any one of claims 1-5 or the high-dispersion noble metal catalyst obtained by the preparation method according to any one of claims 6-15 in a hydrogenation reaction.

17. Use according to claim 16, characterized in that, Used as carbon two selective hydrogenation reaction.

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