Noble metal catalyst with core-shell structure as well as preparation method and application of noble metal catalyst

Abstract

The invention relates to a core-shell structure noble metal catalyst as well as a preparation method and application thereof. The core-shell structure noble metal catalyst contains an original core material, a noble metal agent and an auxiliary agent, the specific surface area of the original core material is 50-400m < 2 > / g, the pore volume is 0.1-1.5 cm < 3 > / g, based on the total mass of the noble metal catalyst, the noble metal content is 0.1-0.8% by mass, 97-100% by mass of the noble metal is dispersed in the shell layer of the catalyst, the thickness of the shell layer is 0.02-0.2 mm, and the pore volume of the noble metal agent is 0.1-1.5 cm < 3 > / g. And the content of the auxiliary agent is 0.5-2.6 mass% in terms of auxiliary agent elements. The core-shell structure noble metal catalyst has the advantages that the preparation method is simple, batch production is easy, and VOCs components can be removed through efficient catalytic oxidation under the condition of trace oxygen.

Description

TECHNICAL FIELD

[0001] The present application relates to a core-shell structure noble metal catalyst. More particularly, the present application relates to a core-shell structure noble metal catalytic material and a preparation method thereof. The present application also relates to the application of the core-shell structure noble metal catalytic material in the catalytic oxidation treatment of volatile organic compounds under trace oxygen conditions. BACKGROUND

[0002] In recent years, with the increasing requirements of the state for environmental protection, recovery technologies such as adsorption method, catalytic oxidation method, high-temperature incineration method, absorption method, condensation method and membrane separation method are widely used in the recovery / treatment of various waste gas containing volatile organic compounds (VOCs). Among them, catalytic oxidation method is usually used to treat waste gas with stable flow and pollutant concentration of 500-9000 mg / m 3 . For example, the tail gas containing VOCs generated in the production process of purified terephthalic acid is treated by HPCCU (high pressure catalytic combustion unit). Generally speaking, the catalytic oxidation reaction of waste gas containing VOCs is controlled by external diffusion, and how to construct a catalyst with fully exposed active components or a catalyst with active components fully in the shell is the goal pursued by the academic and industrial circles.

[0003] Catalysts with core-shell structure have been reported in many literatures. For example, CN119158598A discloses a core-shell structure catalyst, which comprises an inner core and an outer shell, the inner core comprises a carrier and non-noble metal, auxiliary metal and auxiliary agent supported on the carrier, the outer shell comprises an alumina coating layer and noble metal active component supported on the alumina coating layer; the non-noble metal comprises Ni; the auxiliary metal is selected from at least one of Group VIB metal and Group VIIB metal; the auxiliary agent is S and / or P. The preparation process of this catalyst is relatively complex, and the auxiliary agent S and / or P is not conducive to the oxidation reaction of VOCs. CN202411722892.6 discloses a catalyst with a carrier as the core and at least one of Pt, Ir, Rh, Ru and Pd as the active component. This catalyst can reduce hexavalent uranium to tetravalent uranium, but the stability of this catalyst in the reduction process is not introduced. CN201610785058.0 provides a catalyst with a core part containing tricobalt tetroxide and a noble metal, and a shell part containing silicon dioxide. This catalyst is used for methane combustion and still has good catalytic combustion stability at a reaction temperature of 900°C. This catalyst places the active component in the inner core of the catalyst, and methane and other media need to penetrate the shell SiO2 to contact with the active component.

[0004] In summary, there is an urgent need in this field for a catalyst in which the active components are highly dispersed on the outer surface of the catalyst, and the carrier, auxiliary agent and active components have strong interactions. The catalyst can be manufactured at low cost and can be used for catalytic oxidation and purification of VOCs in the presence of trace oxygen, maintaining long-term performance. Summary of the Invention

[0005] In view of the technical problems in the prior art, the inventors have conducted diligent research based on the existing technology and found that by using a core material as the original matrix and further combining it with appropriate precious metal active components and auxiliary components, a core-shell structured precious metal catalyst can be prepared. The catalyst can complete the catalytic oxidation conversion of VOCs in the presence of trace amounts of oxygen, thus completing the present invention.

[0006] Specifically, the present invention provides a core-shell structured noble metal catalyst comprising an original core material, a noble metal and an additive, wherein the specific surface area of ​​the original core material is 50 to 400 m 2 / g, pore volume is 0.1~1.5cm 3 / g, based on the total mass of the precious metal catalyst, the content of the precious metal is 0.1-0.8 mass%, preferably 0.4-0.8 mass%, more preferably 0.4-0.7 mass%, 97-100 mass% of the precious metal is dispersed in the catalyst shell, the thickness of the shell is 0.02-0.5 mm, and the content of the auxiliary agent is 0.5-2.6 mass% in terms of auxiliary agent elements.

[0007] According to the present invention, the precious metal is at least one of ruthenium, palladium, iridium and platinum, and the auxiliary agent is at least one of titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, gallium, molybdenum, antimony, manganese, tungsten, rhenium, bismuth, lanthanum, cerium, indium and praseodymium, preferably one or a combination of two or more of cobalt, copper, zinc, antimony, bismuth, lanthanum, cerium and manganese, and further preferably one or a combination of two or more of cobalt, zinc, antimony, cerium and manganese.

[0008] According to the present invention, the dispersion degree of the noble metal in the catalyst shell is 30 to 78%, preferably 43 to 78%.

[0009] According to the present invention, the core material is selected from at least one of (a), (b) and (c):

[0010] (a) Alumina, titania, zirconia, silica, cerium oxide, zinc oxide, magnesium oxide, silica-alumina, silica-magnesia, chromia-alumina, and silica-zirconia;

[0011] (b) Molecular sieves: specifically including one or a combination of two or more of ZSM, X, Y, β, and mordenite;

[0012] (c) Spinels with the general formula MO-Al2O3, where M is a divalent metal, form compounds such as MgAl2O4, FeAl2O4, ZnAl2O4, CaAl2O4 and others.

[0013] According to the present invention, the original core material has a certain macroscopic shape, which can be spherical, Raschig ring, strip, clover, four-leaf clover or irregular particles.

[0014] The present invention also provides a method for preparing any one of the above core-shell structured noble metal catalysts, comprising the following steps:

[0015] (1) contacting an original core material with an additive and a solvent to form a mixed contact body; wherein the amount of the additive is 0 to 50% by mass of the original core material, and the amount of the solvent is 0.5 to 170% by mass of the original core material;

[0016] (2) contacting the mixed contact body with an auxiliary element precursor and a noble metal component precursor in a predetermined ratio to obtain a composite system;

[0017] (3) calcining the composite system to obtain the core-shell structured noble metal catalyst.

[0018] According to the present invention, the predetermined ratio is such that the composition of the core-shell structured precious metal catalyst finally obtained after the calcination step complies with the aforementioned provisions of the present invention.

[0019] According to the present invention, the precious metal component precursor refers to a substance that can generate the precious metal mentioned above in this article after calcination in the step (3), preferably a soluble salt and a soluble acid of a precious metal, further preferably a water-soluble salt and a water-soluble acid of a precious metal, further preferably, at least one selected from the acetates, nitrates, halides and halides of precious metals, and even more preferably, at least one selected from the acetates, chlorides and chlorinated acids of precious metals.

[0020] According to the present invention, the precious metal substance is a substance containing one or more of ruthenium, palladium, iridium, and platinum. For example, substances containing ruthenium can be exemplified by ruthenium trichloride, ruthenium tetrachloride, ruthenium chloride containing phenyl, tetrapropylammonium perruthenate, and tetrapropylammonium perruthenate. For example, substances containing ruthenium can be exemplified by iridium trichloride, chloroiridic acid, and tris(2-phenylpyridine)iridium. For example, substances containing platinum can be exemplified by chloroplatinic acid, ammonium chloroplatinate, platinum nitrate, platinum dichloride, methylchloroplatinum hydrate, dichlorocarbonyldichloroplatinum, and dinitrodiaminoplatinum. For another example, substances containing palladium can be exemplified by palladium chloride dihydrate and palladium nitrate.

[0021] According to the present invention, the auxiliary element precursor refers to a substance that can generate the auxiliary element described above after calcination in step (3), such as a soluble salt of the auxiliary element, more preferably at least one selected from the group consisting of acetate, ammonium salt, sulfate, phosphate, nitrate, and halide salt of the auxiliary element, and even more preferably at least one selected from the group consisting of acetate, nitrate, and chloride salt of the auxiliary element. For example, cobalt nitrate, cerium nitrate, copper chloride, zinc nitrate, lanthanum nitrate, antimony acetate, etc. can be cited.

[0022] According to the present invention, in the contacting step (1), there is no particular limitation on the order in which the components (i.e., the original core material, the additive, and the solvent) are contacted. Furthermore, according to the present invention, there is no particular limitation on the manner in which the contacting step is performed, as long as sufficient contact of the components is achieved and a uniform mixed contact body is formed. For example, the components may be mixed (with auxiliary stirring, if necessary) until uniformity is achieved in any manner known in the art.

[0023] According to the present invention, in the contacting step (2), there is no particular restriction on the order in which the raw material components (i.e., the contact body, the auxiliary element precursor, and the precious metal component precursor) are contacted. Furthermore, according to the present invention, there is no particular restriction on the manner in which the contacting step is performed, as long as sufficient contact between the raw material components is achieved and a uniform composite system is formed. For example, the raw material components may be mixed (with auxiliary stirring, if necessary) until uniformity is achieved in any manner known in the art.

[0024] If necessary, in order to make the contact more uniform and sufficient, or to facilitate the contact, the contact step can also be carried out in the presence of a dispersion medium (such as water). The contact product obtained at this time may be in the form of a mixture with an impregnation liquid, a slurry or a paste liquid.

[0025] The contacting steps of step (1) and step (2) can be carried out at any temperature between 0°C and 150°C, for example, at room temperature. When the temperature is higher than the boiling point of the solvent, the reaction can be carried out in a pressure vessel so that the boiling point corresponding to the pressure is higher than the temperature. From the perspective of convenience, room temperature is preferred, but this is not always limited to this. The contact time is based on obtaining a uniform contact product and is generally 0.5 to 5 hours, but this is not always limited to this.

[0026] According to the present invention, in the contacting step (2), after the mixed product is prepared, especially when the mixed product is a slurry, it can sometimes be dried by any means known in the art, such as oven drying (e.g., at 60-150° C., preferably 70-120° C.), air drying, or air drying, to remove any dispersion medium (e.g., water) that may have been introduced during its preparation. According to the present invention, the dried mixed product is also simply referred to as a mixed product.

[0027] According to the present invention, the additive used in step (1) is selected from at least one of protein, urea, chitosan, cellulose, cyanamide, dicyandiamide, melamine, methylguanamine and dopamine.

[0028] According to the present invention, in step (1), the cellulose used may be those known in the art, such as methyl cellulose, hydroxymethyl cellulose, etc.

[0029] According to the present invention, the solvent used in step (1) is selected from at least one of water, alcohol, acid, ether and ester. The acid includes inorganic acid and organic acid. As the inorganic acid, at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and perchloric acid can be selected. As the organic acid, polycarboxylic acid can be selected, for example, C with 2 to 10 (preferably 3 to 6) carboxyl groups can be selected. 2-20 Examples of alkanes include oxalic acid, succinic acid, adipic acid, and the like. Examples of polycarboxylic acids include C 2-10 (preferably 3-6) carboxyl groups and one or more hydroxyl groups. 2-20 Examples of alkanes include malic acid, tartaric acid, and citric acid.

[0030] According to the present invention, in step (1), alcohol, ether, ester further refers to alcohol, ether, ester having more than 2 carbon atoms, such as ethanol, propanol, butanol, butyl ether, ethyl acetate, ethylene glycol, glycerol, polymethyl methacrylate, etc., and also includes fatty alcohol polyoxyethylene ether with a molecular formula of RO(CH2CH2O)5H, R is C7-C9; alkylphenol polyoxyethylene ether with a molecular formula of RC6H4O(CH2CH2O)nH, R is C9-C12, n is 9-12; octanol polyoxyethylene ether with a molecular formula of C8H 17 (CH2CH2O)nH, n is 1 to 6.

[0031] According to the present invention, the dispersion medium in step (2) includes at least one of water, alcohol, acid, and ester. The acid includes an inorganic acid and an organic acid. As the inorganic acid, at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and perchloric acid can be selected. As the organic acid, a polycarboxylic acid can be selected, for example, C-10 with 2 to 10 (preferably 3 to 6) carboxyl groups can be selected. 2-20 Examples of alkanes include oxalic acid, succinic acid, adipic acid, and the like. Examples of polycarboxylic acids include C 2-10 (preferably 3-6) carboxyl groups and one or more hydroxyl groups. 2-20 Examples of alkanes include malic acid, tartaric acid, and citric acid.

[0032] According to the present invention, the alcohol, ether and ester in the dispersion medium in step (2) further refers to alcohols, ethers and esters having a carbon number greater than 2, such as ethanol, propanol, butanol, butyl ether, ethyl acetate, ethylene glycol, glycerol, polymethyl methacrylate, etc., and also includes fatty alcohol polyoxyethylene ethers having a molecular formula of RO(CH2CH2O)5H, R is C7-C9; alkylphenol polyoxyethylene ethers having a molecular formula of RC6H4O(CH2CH2O)nH, R is C9-C12, and n is 9-12; and octanol polyoxyethylene ethers having a molecular formula of C8H 17 (CH2CH2O)nH, n is 1 to 6.

[0033] According to the present invention, the calcination temperature of the calcined composite system in step (3) is 400-650° C., the calcination time is 1-10 hours, and the calcination atmosphere conditions are any one of air, nitrogen, hydrogen, nitrogen-hydrogen mixture, nitrogen-carbon monoxide mixture, air-carbon monoxide mixture, helium, argon, helium-hydrogen mixture, helium-carbon monoxide mixture, argon-hydrogen mixture, and helium-carbon monoxide mixture.

[0034] The present invention also provides a use of any one of the above core-shell structured noble metal catalysts for catalytic oxidation treatment of volatile organic compounds in the presence of trace amounts of oxygen.

[0035] According to the application of the present invention, a core-shell structured noble metal catalyst is loaded into a reactor, and a stream containing trace oxygen (300-3000 ppm oxygen) and volatile organic compounds (non-methane total hydrocarbons at 400-1800 mg / m 3 ) gas (the remaining balance gas is mainly nitrogen) VOCs gas, the gas space velocity is 1000~10000h -1 , the reaction temperature is 220-400℃.

[0036] In the application of the present invention, a gas containing trace oxygen (300-3000ppm oxygen) and volatile organic compounds (non-methane total hydrocarbons at 400-1800mg / m 3 ) gas, wherein the volatile organic matter is one or a combination of two or more of formaldehyde, methanol, dimethyl ether, ethanol, acetaldehyde, acetic acid, ethylene glycol, glycerol, aromatic hydrocarbons, substituted aromatic hydrocarbons, substituted methane, C2-C10 alkanes, C6-C16 aromatic hydrocarbons, and C4-C16 cycloalkanes.

[0037] Beneficial effects of the present invention:

[0038] The preparation method of the core-shell precious metal catalyst provided by the present invention is simple and feasible, and a large proportion of the precious metal components are dispersed in the shell layer. Compared with existing core-shell precious metal catalysts, the precious metal in the catalyst provided by the present invention is highly dispersed, and there is a strong interaction between the precious metal and the carrier and the auxiliary agent, so that the precious metal is better anchored in the shell layer, the active components of the catalyst are not easy to fall off, and the precious metal grains are not easy to grow and agglomerate during the reaction process, thereby improving the life of the catalyst. The core-shell precious metal catalyst provided by the present invention can treat VOCs pollutant molecules in the presence of trace oxygen without carbon accumulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the SEM image of Example 1. DETAILED DESCRIPTION

[0040] The embodiments of the present invention will be described in more detail below with reference to specific embodiments. However, those skilled in the art will understand that the specific embodiments described below are only for illustrating the present invention and should not be regarded as limiting the scope of protection of the present invention. On the contrary, the present invention is intended to cover all alternatives, modifications and equivalents that may be included within the scope of the present invention as defined by the claims.

[0041] Unless otherwise specified, the various embodiments of the present invention may be combined in any manner, and the conversion, deformation, and change of the technical solutions obtained thereby are also included in the scope of the present invention and do not exceed the scope of the present invention.

[0042] The present invention is further described in detail below with reference to examples, but the present invention is not limited to these examples.

[0043] In the present invention, the surface area is measured by the BET specific surface area method, and the pore volume is measured by the BJH (Barrett-Joyner-Halenda) method.

[0044] In the present invention, the precious metal content in the core-shell catalyst is determined by spectrophotometry according to GB / T 23277-2009. The additive element content is determined by X-ray fluorescence spectrometry according to ASTM D7085-2004.

[0045] In the present invention, the dispersion of the noble metal in the catalyst is measured by chemical adsorption of carbon monoxide gas on a Micromeritics 2920 chemical adsorption instrument, as described in the literature (A simple method for CO chemisorption studies under continuous flow: Adsorption and desorption behavior of Pt / Al2O3 catalysts, Applied Catalysis A: General, 2012, 446-446: 221-230) and Modern Catalysis Research Methods (Edited by Xin Qin, Luo Mengfei, and Xu Jie, Science Press).

[0046] In the present invention, the thickness of the noble metal on the catalyst surface is measured using SEM with mapping.

[0047] In the present invention, the carbon deposition of the catalyst is tested by thermogravimetric analysis under air conditions at a heating rate of 10° C. / min.

[0048] Example 1

[0049] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.5:1.3, to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a zinc nitrate mass concentration of 20% and an aqueous solution with a chloroplatinic acid mass concentration of 5% to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: zinc element: platinum element in the composite system is 50:0.3:0.3, and the composite system is calcined in air at 500°C for 5 hours to obtain a core-shell structured precious metal catalyst A, wherein the mass percentage of platinum is 0.59%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reaches 99% of the total platinum content, the platinum dispersion is 62%, and the mass percentage of zinc is 0.59%.

[0050] SEM images of core-shell noble metal catalyst A Figure 1 .from Figure 1 It can be seen that the precious metal platinum is highly dispersed in the catalyst shell.

[0051] Example 2

[0052] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), hydroxymethylpropyl cellulose and water in a mass ratio of 1:0.3:1.2 to prepare a mixed contact body at 50°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 15% cobalt nitrate and an aqueous solution with a mass concentration of 5% chloroplatinic acid to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of aluminum oxide: cobalt element: platinum element in the composite system is 50:0.4:0.2, and the composite system is calcined under nitrogen conditions at 520°C for 3 hours to obtain a core-shell structured precious metal catalyst B, wherein the mass percentage of platinum is 0.40%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reaches 98% of the total platinum content, the platinum dispersion is 65%, and the mass percentage of cobalt is 0.79%.

[0053] Example 3

[0054] Spherical silicon oxide (diameter 3.2-3.6 mm, specific surface area 327 m 2 / g, pore volume is 0.49cm 3 / g), polyethylene glycol-1000 and ethanol in a mass ratio of 1:0.3:0.9, a mixed contact body is prepared at 50°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 15% lanthanum nitrate and an aqueous solution with a mass concentration of 5% palladium chloride to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of aluminum oxide: lanthanum element: palladium element in the composite system is 50:0.6:0.4, and the composite system is calcined in air at 520°C for 4 hours to obtain a core-shell structured precious metal catalyst C, wherein the mass percentage of palladium is 0.67%, the palladium content within 0.3 mm of the shell layer of the spherical alumina reaches 98% of the total palladium content, the dispersion of palladium is 58%, and the mass percentage of lanthanum is 1.0%.

[0055] Example 4

[0056] Spherical molecular sieve (ZSM-5, diameter 2.2-2.8 mm, specific surface area 351 m 2 / g, pore volume is 0.47cm 3 / g), melamine and ethanol are contacted in a mass ratio of 1:0.3:0.9 to prepare a mixed contact body at 50°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 15% of vanadyl oxalate and an aqueous solution with a mass concentration of 5% of ruthenium chloride to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of spherical molecular sieve: vanadium element: ruthenium element in the composite system is 50:0.7:0.35, and the composite system is calcined at 520°C in a carbon monoxide-nitrogen mixture (wherein the volume fraction of carbon monoxide is 30%) for 3 hours to obtain a core-shell structured precious metal catalyst D, wherein the mass percentage of ruthenium is 0.68%, the ruthenium content within 0.2 mm of the shell layer of the spherical alumina reaches 98% of the total ruthenium content, the dispersion of ruthenium is 49%, and the mass percentage of vanadium is 1.3%.

[0057] Example 5

[0058] MgAl2O4 with a spinel structure was synthesized according to the literature (Low-temperature synthesis of mesoporous nanocrystalline magnesium aluminate (MgAl2O4) spinel with high surface area using a novel modified sol-gel method, Advanced Powder Technology, 2017, 28 (4): 1249-1257) and MgAl2O4 was formed into cylinders (diameter 4 mm, height 8 mm, specific surface area 263 m 2 / g, pore volume is 0.41cm 3 / g), contacting the cylinder, protein powder and isopropanol in a mass ratio of 1:0.2:1 to prepare a mixed contact body at 50°C, and again contacting the mixed contact body with an aqueous solution having a mass concentration of 10% titanium sulfate and an aqueous solution having a mass concentration of 5% iridium trichloride to obtain a composite system, the contact temperature being 60°C, wherein the mass ratio of MgAl2O4:titanium element:iridium element in the composite system is 50:0.2:0.35, and calcining the composite system under hydrogen conditions at 500°C for 5 hours to obtain a core-shell structured precious metal catalyst E, wherein the mass percentage of iridium is 0.69%, the iridium content within 0.2 mm of the shell of the cylinder reaches 97% of the total iridium content, the iridium dispersion is 43%, and the mass percentage of titanium is 0.4%.

[0059] Example 6

[0060] TiO2 nanotubes were synthesized according to the literature (TiO2 nanotubes supported V2O5 for the selective oxidation of methanol to dimethoxymethane, Microporous and Mesoporous Materials, 2008, 116(1-3): 614-621) and were formed into cylinders (with a diameter of 4 mm, a height of 8 mm, and a specific surface area of ​​257 m 2 / g, pore volume is 0.79cm 3 / g), contacting the cylinder, protein powder and isopropanol in a mass ratio of 1:0.2:1 to prepare a mixed contact body at 50°C, and again contacting the mixed contact body with an aqueous solution having a mass concentration of 5% ammonium tungstate and an aqueous solution having a mass concentration of 5% iridium trichloride to obtain a composite system, the contact temperature being 60°C, wherein the mass ratio of TiO2 nanotubes: tungsten element: iridium element in the composite system is 50:1:0.33, and calcining the composite system under hydrogen conditions at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst F, wherein the mass percentage of iridium is 0.64%, the iridium content within 0.1 mm of the shell of the cylinder reaches 97% of the total iridium content, the iridium dispersion is 43%, and the mass percentage of tungsten is 1.9%.

[0061] Example 7

[0062] The cylindrical magnesium oxide (diameter 3mm, height 8mm, specific surface area 79m 2 / g, pore volume is 0.09cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.45:1.3, to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a zinc nitrate mass concentration of 20% and an aqueous solution with a chloroplatinic acid mass concentration of 5% to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: zinc element: platinum element in the composite system is 50:0.3:0.3, and the composite system is calcined under hydrogen conditions at 500°C for 4 hours to obtain a core-shell structured precious metal catalyst G, wherein the mass percentage of platinum is 0.59%, the platinum content within 0.1 mm of the shell of the cylinder reaches 97% of the total platinum content, the platinum dispersion is 61%, and the mass percentage of zinc is 0.59%.

[0063] Example 8

[0064] The cylindrical zinc oxide (diameter 3mm, height 8mm, specific surface area 59m 2 / g, pore volume is 0.08cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.45:1.3, to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a zinc nitrate mass concentration of 20% and an aqueous solution with a chloroplatinic acid mass concentration of 5% to obtain a composite system, the contact temperature being 50°C, wherein the mass ratio of aluminum oxide: zinc element: platinum element in the composite system is 50:0.45:0.3, and the composite system is calcined under hydrogen conditions at 500°C for 3 hours to obtain a core-shell structured precious metal catalyst H, wherein the mass percentage of platinum is 0.59%, the platinum content within 0.2 mm of the shell of the cylinder reaches 97% of the total platinum content, the platinum dispersion is 67%, and the mass percentage of zinc is 0.88%.

[0065] Example 9

[0066] The cylindrical silica-alumina composite carrier (3 mm in diameter, 6 mm in height, and a specific surface area of ​​211 m 2 / g, pore volume is 0.32cm 3 / g), hydroxymethylpropyl cellulose and ethylene glycol in a mass ratio of 1:0.45:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is contacted again with an aqueous solution with a copper nitrate mass concentration of 20%, an aqueous solution with a chloroplatinic acid mass concentration of 5%, and ethyl acetate with a mass ratio of 0.1 times the mass of the copper nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of silicon oxide-alumina: copper element: platinum element in the composite system is 50:0.38:0.5, and the composite system is calcined in air at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst I, wherein the mass percentage of platinum is 0.98%, the platinum content within 0.2 mm of the shell of the cylinder reaches 97% of the total platinum content, the platinum dispersion is 37%, and the mass percentage of copper is 0.74%.

[0067] Example 10

[0068] The cylindrical silica-alumina composite carrier (3 mm in diameter, 6 mm in height, and a specific surface area of ​​211 m 2 / g, pore volume is 0.32cm 3 / g), hydroxymethylpropyl cellulose and ethylene glycol in a mass ratio of 1:0.43:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an ethylene glycol solution with a mass concentration of 20% antimony acetate and an aqueous solution with a mass concentration of 5% chloroplatinic acid to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of silicon oxide-alumina: antimony element: platinum element in the composite system is 50:0.38:0.28, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst J, wherein the mass percentage of platinum is 0.55%, the platinum content within 0.2 mm of the shell of the cylinder reaches 97% of the total platinum content, the platinum dispersion is 69%, and the mass percentage of antimony is 0.74%.

[0069] Example 11

[0070] The cylindrical silica-alumina composite carrier (3 mm in diameter, 6 mm in height, and a specific surface area of ​​211 m 2 / g, pore volume is 0.32cm 3 / g) and ethylene glycol in a mass ratio of 1:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 20% ammonium molybdate and an aqueous solution with a mass concentration of 5% chloroplatinic acid to obtain a composite system at a contact temperature of 50°C, wherein the mass ratio of silicon oxide-alumina:molybdenum element:platinum element in the composite system is 50:0.45:0.33. The composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction of 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst K, wherein the mass percentage of platinum is 0.64%, the platinum content within 0.2 mm of the cylinder shell reaches 97% of the total platinum content, the platinum dispersion is 62%, and the mass percentage of molybdenum is 0.88%.

[0071] Example 12

[0072] The cylindrical chromium oxide-aluminum oxide composite support (3 mm in diameter, 6 mm in height, and a specific surface area of ​​189 m 2 / g, pore volume is 0.23cm 3 / g), hydroxymethylpropyl cellulose and ethylene glycol in a mass ratio of 1:0.33:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 20% gallium nitrate and an aqueous solution with a mass concentration of 5% chloroplatinic acid to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of chromium oxide-aluminum oxide: gallium element: platinum element in the composite system is 50:0.35:0.40, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst L, wherein the mass percentage of platinum is 0.78%, the platinum content within 0.2 mm of the shell of the cylinder reaches 97% of the total platinum content, the platinum dispersion is 54%, and the mass percentage of gallium is 0.68%.

[0073] Example 13

[0074] A cylindrical chromium oxide-aluminum oxide composite support (3 mm in diameter, 6 mm in height, and a specific surface area of ​​189 m 2 / g, pore volume is 0.23cm 3 / g), hydroxymethylpropyl cellulose and ethylene glycol in a mass ratio of 1:0.33:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 20% ammonium rhenate and an aqueous solution with a mass concentration of 5% palladium chloride to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of chromium oxide-aluminum oxide: rhenium element: palladium element in the composite system is 50:0.56:0.41, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst M, wherein the mass percentage of palladium is 0.79%, the palladium content within 0.2 mm of the shell of the cylinder reaches 99% of the total palladium content, the dispersion of palladium is 39%, and the mass percentage of rhenium is 1.1%.

[0075] Example 14

[0076] A cylindrical chromium oxide-aluminum oxide composite support (3 mm in diameter, 6 mm in height, and a specific surface area of ​​189 m 2 / g, pore volume is 0.23cm 3 / g), hydroxymethylpropyl cellulose and ethanol in a mass ratio of 1:0.33:1.1 to prepare a mixed contact body at 40°C, and the mixed contact body is contacted again with an ethanol solution with a mass concentration of 20% bismuth nitrate and an aqueous solution with a mass concentration of 5% palladium chloride to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of silicon oxide-alumina: bismuth element: palladium element in the composite system is 50:0.45:0.32, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst N, wherein the mass percentage of palladium is 0.63%, the palladium content within 0.2 mm of the shell of the cylinder reaches 99% of the total palladium content, the palladium dispersion is 45%, and the mass percentage of bismuth is 0.89%.

[0077] Example 15

[0078] A cylindrical chromium oxide-aluminum oxide composite support (3 mm in diameter, 6 mm in height, and a specific surface area of ​​189 m 2 / g, pore volume is 0.23cm 3 / g), urea and water in a mass ratio of 1:0.35:0.3, a mixed contact body is prepared at 40°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 10% indium nitrate and an aqueous solution with a mass concentration of 5% palladium chloride to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of silicon oxide-aluminum oxide: indium element: palladium element in the composite system is 50:0.5:0.32, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst O, wherein the mass percentage of palladium is 0.63%, the palladium content within 0.2 mm of the shell of the cylinder reaches 99% of the total palladium content, the palladium dispersion is 43%, and the mass percentage of indium is 0.97%.

[0079] Example 16

[0080] The clover alumina carrier (specific surface area 198m 2 / g, pore volume is 0.26cm 3 / g), urea and water in a mass ratio of 1:0.35:1.2, to prepare a mixed contact body at 40°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 25% manganese nitrate and an aqueous solution with a mass concentration of 10% platinum nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: manganese element: platinum element in the composite system is 50:1:0.31, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst P, wherein the mass percentage of platinum is 0.63%, the platinum content within 0.2 mm of the clover shell reaches 99% of the total platinum content, the platinum dispersion is 43%, and the mass percentage of manganese is 0.97%.

[0081] Example 17

[0082] A cylindrical chromium oxide-aluminum oxide composite support (3 mm in diameter, 6 mm in height, and a specific surface area of ​​189 m 2 / g, pore volume is 0.23cm 3 / g), urea and water in a mass ratio of 1:0.35:1, a mixed contact body is prepared at 40°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 20% indium nitrate and an aqueous solution with a mass concentration of 5% palladium chloride to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of chromium oxide-aluminum oxide: indium element: palladium element in the composite system is 50:0.5:0.32, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a core-shell structured precious metal catalyst Q, wherein the mass percentage of palladium is 0.62%, the palladium content within 0.2 mm of the clover shell reaches 99% of the total palladium content, the palladium dispersion is 41%, and the mass percentage of indium is 0.97%.

[0083] Example 18

[0084] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.5:1.3, a mixed contact body is prepared at 40°C, and the mixed contact body is again contacted with an aqueous solution with a mass concentration of 20% cerium nitrate and an aqueous solution with a mass concentration of 5% chloroplatinic acid to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: cerium element: platinum element in the composite system is 50:0.33:0.33, and the composite system is calcined in air at 500°C for 5 hours to obtain a core-shell structured precious metal catalyst R, wherein the mass percentage of platinum is 0.63%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reaches 99% of the total platinum content, the platinum dispersion is 61%, and the mass percentage of cerium is 0.65%.

[0085] Example 19

[0086] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.5:1.3 to prepare a mixed contact body at 40°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 20% cerium nitrate and an aqueous solution with a mass concentration of 5% chloroplatinic acid at a contact temperature of 50°C, and then contacted again with an ethylene glycol solution with a mass concentration of 10% antimony acetate at a contact temperature of 60°C, wherein the mass ratio of aluminum oxide: cerium element: antimony element: platinum element in the composite system is 50:0.22:0.11:0.33, and the composite system is calcined in air at 500°C for 5 hours to obtain a core-shell structured precious metal catalyst S, wherein the mass percentage of platinum is 0.64%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reaches 99% of the total platinum content, the platinum dispersion is 61%, the mass percentage of cerium is 0.43%, and the mass percentage of antimony is 0.22%.

[0087] Comparative Example 1

[0088] Based on Example 16, manganese nitrate was replaced with tin nitrate. Clover alumina carrier (Jiangsu F company, specific surface area of ​​198m 2 / g, pore volume is 0.26cm 3 / g), urea and water in a mass ratio of 1:0.35:1.2, a mixed contact body is prepared at 40°C, and the mixed contact body is contacted again with an aqueous solution with a mass concentration of 25% tin nitrate and an aqueous solution with a mass concentration of 10% platinum nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: tin element: platinum element in the composite system is 50:1:0.31, and the composite system is calcined under hydrogen-nitrogen conditions (hydrogen gas volume fraction is 15%) at 550°C for 4 hours to obtain a precious metal catalyst P-1, wherein the mass percentage of platinum is 0.63%, the platinum content within 0.2 mm of the clover shell reaches 99% of the total platinum content, the platinum dispersion is 36%, and the mass percentage of tin is 0.97%.

[0089] Comparative Example 2

[0090] Based on Example 1, the Pt content was increased. Spherical alumina (Anhui A company, diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), hydroxymethyl cellulose and water in a mass ratio of 1:0.5:1.3, a mixed contact body is prepared at 40°C, and the mixed contact body is again contacted with an aqueous solution with a zinc nitrate mass concentration of 20% and an aqueous solution with a chloroplatinic acid mass concentration of 5% to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide: zinc element: platinum element in the composite system is 50:0.3:0.5, and the composite system is calcined in air at 500°C for 5 hours to obtain a precious metal catalyst A-1, wherein the mass percentage of platinum is 0.98%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reaches 99% of the total platinum content, the dispersion of platinum is 39%, and the mass percentage of zinc is 0.59%.

[0091] Comparative Example 3

[0092] Based on Example 1, the preparation method was changed. Spherical alumina (Anhui A company, diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g) was contacted again with an aqueous solution having a 20% by mass concentration of zinc nitrate and an aqueous solution having a 5% by mass concentration of chloroplatinic acid to obtain a composite system, the contact temperature being 50°C, wherein the mass ratio of aluminum oxide:zinc element:platinum element in the composite system was 50:0.3:0.5, and the composite system was calcined in air at 500°C for 5 hours to obtain a precious metal catalyst A-2, wherein the mass percentage of platinum was 0.98%, the platinum content within 0.2 mm of the shell layer of the spherical alumina reached 75% of the total platinum content, the platinum dispersion was 33%, and the mass percentage of zinc was 0.59%.

[0093] Application Examples

[0094] The core-shell noble metal catalysts in Examples 1-19 and the noble metal catalysts in Comparative Examples 1-3 were respectively loaded into a fixed bed, and 500 mg / m 3 Acetaldehyde, 100 mg / m 3 Toluene, 50 mg / m 3 Ethanol and 50 mg / m 3 Ethylene glycol, 1800ppm oxygen, balance nitrogen, at a space velocity of 2000h -1 The performance of the catalyst was investigated for 1000 hours at a reaction temperature of 320°C. The conversion of total non-methane hydrocarbons is shown in Table 1.

[0095] Table 1 Evaluation results of catalyst catalytic oxidation of VOCs

[0096]

[0097] As can be seen from Table 1, the precious metal with a core-shell structure obtained by the preparation method of the present invention has the characteristics of strong resistance to carbon deposition and stable activity in the presence of trace oxygen.

[0098] Compared to the present invention;

[0099] In Comparative Example 1, the auxiliary element is tin, and the anti-carbon deposition ability and activity of the core-shell structure cobalt-based catalyst obtained therefrom are inferior to those of the present invention.

[0100] The core-shell cobalt-based catalyst obtained in Comparative Example 2 has a high content of additives, and its anti-carbon deposition ability and activity are inferior to those of the present invention.

[0101] In the core-shell cobalt-based catalyst obtained in Comparative Example 3, the precious metal platinum has a low dispersion in the shell layer, and its anti-carbon deposition ability and activity are inferior to those of the present invention.

[0102] Although the present invention has been described in detail herein with reference to exemplary embodiments, it should be understood that the invention is not limited to the embodiments described. Those having ordinary skill in the art and having access to the teachings herein will recognize other variations, modifications, and embodiments within the scope of the invention. Therefore, the present invention should be broadly construed in accordance with the claims set forth below.

Claims

1. A core-shell structured noble metal catalyst, characterized in that: Contains original core material, precious metal agent and additives. The specific surface area of ​​the original core material is 50-400m 2 / g, pore volume is 0.1~1.5cm 3 / g, based on the total mass of the precious metal catalyst, the content of the precious metal is 0.1-0.8 mass%, 97-100 mass% of the precious metal is dispersed in the catalyst shell, the shell thickness is 0.02-0.2 mm, and the content of the auxiliary agent is 0.5-2.6 mass% in terms of auxiliary agent elements.

2. A core-shell structured noble metal catalyst according to claim 1, characterized in that: The precious metal is at least one of ruthenium, palladium, iridium and platinum, and the auxiliary agent is at least one of titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, gallium, molybdenum, antimony, manganese, tungsten, rhenium, bismuth, lanthanum, cerium, indium and praseodymium, preferably at least one of cobalt, copper, zinc, antimony, bismuth, lanthanum, cerium and manganese or a combination of two or more, more preferably at least one of cobalt, zinc, antimony, cerium and manganese.

3. The core-shell noble metal catalyst according to claim 1, characterized in that: The dispersion degree of the noble metal in the catalyst shell is 30 to 78%, preferably 43 to 78%.

4. A core-shell structured noble metal catalyst according to claim 1, characterized in that The original core material is selected from at least one of (a), (b) and (c): (a) alumina, titania, zirconia, silica, cerium oxide, zinc oxide, magnesium oxide, silica-alumina, silica-magnesia, chromia-alumina, and silica-zirconia; (b) Molecular sieves: specifically including at least one of ZSM, X, Y, β, and mordenite; (c) Spinels with the general formula MO-Al2O3, where M is a divalent metal, form compounds such as MgAl2O4, FeAl2O4, ZnAl2O4, CaAl2O4 and others.

5. A method for preparing a core-shell structured noble metal catalyst, characterized in that: The following steps are involved: (1) contacting an original core material with an additive and a solvent to form a mixed contact body; wherein the amount of the additive is 0 to 50% by mass of the original core material, and the amount of the solvent is 0.5 to 170% by mass of the original core material; (2) contacting the mixed contact body with an auxiliary element precursor and a noble metal component precursor in a predetermined ratio to obtain a composite system; (3) calcining the composite system to obtain the core-shell structured noble metal catalyst.

6. The preparation method according to claim 5, characterized in that The additive used in step (1) is selected from at least one of protein, urea, chitosan, cellulose, cyanamide, dicyandiamide, melamine, methylguanamine and polydopamine.

7. The preparation method according to claim 5, characterized in that The solvent used in step (1) is selected from at least one of water, alcohol, acid, ether and ester.

8. The preparation method according to claim 5, characterized in that In step (2), the mixed contact body is contacted with the auxiliary element precursor and the noble metal component precursor in the presence of a dispersion medium, and the dispersion medium is selected from at least one of water, alcohol, acid and ester.

9. The preparation method according to claim 5, characterized in that The calcination temperature of the composite system in step (3) is 400-650° C., the calcination time is 1-10 hours, and the calcination atmosphere conditions are air, nitrogen, hydrogen, nitrogen-hydrogen mixture, nitrogen-carbon monoxide mixture, air-carbon monoxide mixture, helium, argon, helium-hydrogen mixture, helium-carbon monoxide mixture, argon-hydrogen mixture or helium-carbon monoxide mixture.

10. Use of the core-shell structured noble metal catalyst according to any one of claims 1 to 4 or the core-shell structured noble metal catalyst prepared according to the preparation method according to any one of claims 5 to 9 in the catalytic oxidation treatment of volatile organic compounds in the presence of trace oxygen.

11. The use according to claim 10, characterized in that The reaction conditions are as follows: a core-shell noble metal catalyst is loaded into the reactor, and a VOCs gas containing 300-3000 ppm oxygen is introduced at a gas space velocity of 1000-10000 h -1 , the reaction temperature is 220-400℃.

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