Core-shell structure cobalt-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to a cobalt-based catalyst with a core-shell structure as well as a preparation method and application of the cobalt-based catalyst. The core-shell structure cobalt-based catalyst contains an original core material, cobalt and an auxiliary agent, the specific surface area of the original core material is 50-400 m < 2 > / g, the pore volume is 0.1-1.5 cm < 3 > / g, the content of cobalt is 2-15% by mass in terms of metal elements based on the total mass of the cobalt-based catalyst, 70-95% by mass of the cobalt element is dispersed in a shell layer of the catalyst, the thickness of the shell layer is 0.02-0.5 mm, and the particle size of the shell layer is 1-10 microns. And the content of the auxiliary agent is 1-13% by mass in terms of auxiliary agent elements. The preparation method has the advantages that the preparation method is simple, the cost is low, 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 invention relates to a core-shell cobalt-based catalyst. More specifically, the present invention relates to a core-shell cobalt-based catalytic material and a method for preparing the same. The present invention also relates to the use of the core-shell cobalt-based catalytic material in the catalytic oxidation treatment of volatile organic compounds under trace oxygen conditions. Background Art

[0002] In recent years, with the increasing requirements of the country for environmental protection, recovery technologies such as adsorption, catalytic oxidation, high temperature incineration, absorption, condensation and membrane separation have been widely used in the recovery / treatment of various waste gases containing volatile organic compounds (VOCs). 3 Exhaust gases are typically treated using catalytic oxidation. For example, the VOC-containing tail gas generated during the production of purified terephthalic acid is treated using an HPCCU (high-pressure catalytic combustion unit). Generally speaking, the catalytic oxidation reaction of VOC-containing exhaust gases is controlled by external diffusion. The goal of academia and industry is to develop catalysts with fully exposed active components or catalysts with active components fully dispersed in the shell.

[0003] Core-shell catalysts have been reported in many literatures. For example, patent CN119158598B discloses a core-shell catalyst comprising a core and an outer shell, wherein the core comprises a carrier and non-precious metals, co-metals, and additives loaded on the carrier, and the outer shell comprises an alumina coating layer and a precious metal active component loaded on the alumina coating layer, wherein the additives are S and / or P. The catalyst preparation process is relatively complicated, and the additives S and / or P are not conducive to the catalytic oxidation reaction of VOCs. CN119549163A designs a catalyst in which Pt is deposited on the surface of a carbon carrier by atomic layer deposition, and then deposits the metal oxide CuOx onto the metal Pt surface. Although the catalyst can control the size of Pt particles at the atomic scale, its preparation process involves chemical deposition technology, which is cumbersome and costly. CN119608149A first prepared a competitive adsorption sol by a competitive adsorption method, and then prepared a high-efficiency anti-poisoning PTA exhaust gas oxidation catalyst by ball milling with an insoluble manganese precursor and an inert carrier. In general, the preparation process of the catalyst is relatively cumbersome, and whether the active components of the catalyst of the core-shell structure are fully exposed or distributed in the core-shell is not involved, and the stability of the catalyst is not reflected in the embodiments. In the WO2022127911A1 patent, a catalytic material with a core of spherical porous Mn2O3 and a shell of undoped or Cu-doped flaky MnO2 is prepared. The catalyst is nanoscale, and the application of 400-1500nm powder materials in the catalytic oxidation of VOCs is challenging. In the CN119771489A patent, a Cu-SSZ-13 molecular sieve with a low core silicon-aluminum ratio, a high copper loading, a high shell silicon-aluminum ratio, and a low copper loading is prepared, and the active component copper is not fully enriched on the outer surface.

[0004] In summary, there is an urgent need in the art for a catalyst in which the active components are highly dispersed and fully exposed 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 of VOCs in the presence of trace oxygen to maintain long-term performance. Summary of the Invention

[0005] In view of the above objectives, the inventors conducted diligent research and found that by using a core material as the original matrix and combining it with appropriate cobalt components and auxiliary components, a core-shell structured cobalt-based catalyst can be prepared. This 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 structure cobalt-based catalyst comprising an original core material, cobalt and an additive, wherein the specific surface area of ​​the 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 cobalt-based catalyst, the content of cobalt is 2 to 15 mass% in terms of metal element, wherein 76 to 95 mass% of the cobalt element is dispersed in the shell layer of the catalyst, the thickness of the shell layer is 0.02 to 0.5 mm, and the content of the auxiliary agent is 1 to 13 mass% in terms of auxiliary agent element.

[0007] According to the present invention, the additive is at least one of titanium, vanadium, chromium, gallium, antimony, manganese, tungsten, rhenium, bismuth, tin, lanthanum, and cerium. More preferably, it is at least one of titanium, vanadium, chromium, antimony, bismuth, cerium, manganese, and tin, and even more preferably, it is at least one of antimony, bismuth, cerium, manganese, and tin.

[0008] According to the present invention, the valence state of cobalt is basically divalent cobalt and trivalent cobalt, Co 3+ / Co 2+ The ratio is 0.2 to 0.8.

[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 sieve: specifically including at least one 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 core material has a certain macroscopic shape, the length of its edges or diameters in a certain direction is greater than 2 mm, and the shape is spherical, Raschig ring, strip, clover, four-leaf clover or irregular particles.

[0014] The present invention also provides a method for preparing a core-shell structured cobalt-based catalyst, comprising the following steps:

[0015] (1) contacting an original core material, an auxiliary element precursor, an appropriate additive, and a solvent to form a mixed contact body; wherein, relative to the original core material, the amount of the additive is 0 to 30% by mass of the original core material, the amount of the solvent is 0.5 to 170% by mass of the original core material, and the composition of the auxiliary element precursor and the original core material after calcination conforms to the aforementioned provisions of the present invention;

[0016] (2) contacting the mixed contact body with a cobalt precursor in a predetermined ratio in the presence of a dispersion medium to obtain a composite system;

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

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

[0019] According to the present invention, the auxiliary element precursor in step (1) 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, cerium chloride, cerium nitrate, manganese nitrate, bismuth nitrate, zinc nitrate, lanthanum nitrate, antimony acetate, etc. can be cited.

[0020] According to the present invention, the cobalt precursor in step (2) refers to a substance that can generate the cobalt mentioned above in this article after being calcined in step (3), preferably a soluble salt of cobalt, more preferably a water-soluble salt of cobalt, and even more preferably, at least one selected from the group consisting of nitrates, sulfates, sulfites, phosphates, halides, hydrogen phosphates, and hydrogen carbonates of cobalt.

[0021] 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 auxiliary element precursor, 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 between 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.

[0022] According to the present invention, in the contacting step (2), the mixed contact body and the cobalt precursor are contacted in a predetermined ratio. There is no particular limitation on the manner in which the contacting step is carried out, as long as sufficient contact between the raw material components is achieved and a uniform composite system is formed. For example, mixing (with auxiliary stirring if necessary) until uniformity is achieved can be performed in any manner known in the art.

[0023] 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.

[0024] The contacting step of step (1) and step (2) can be carried out at any temperature from 0°C to 150°C, for example, at room temperature. When the temperature is higher than the boiling point of the solvent, it can be carried out in a pressure vessel so that the corresponding boiling point under pressure is higher than the temperature. From the point of view of convenience, normal temperature is preferred, but sometimes it is not limited thereto. The contacting time is adjusted to obtain a uniform contact product, and is generally 0.5 to 5 hours, but sometimes it is not limited thereto.

[0025] According to the present application, in the contacting step (2), the mixture product after preparation, especially when the mixture product is with slurry, can sometimes be dried by any means known in the art, for example, drying (such as at 60 to 150°C, preferably at 70 to 120°C), air drying, and air drying, to remove any dispersion medium (such as water) that can be introduced during its preparation. According to the present application, the dried mixture product is also simply referred to as the mixture product.

[0026] According to the present application, the additive used in step (1) is at least one of protein, urea, chitosan, cellulose, cyanamide, dicyandiamide, melamine, methyl guanamine, and polydopamine.

[0027] According to the present application, in step (1), cellulose can be used those known in the art, such as methyl cellulose, hydroxymethyl cellulose, and the like can be mentioned.

[0028] According to the present application, the solvent used in step (1) includes at least one of water, alcohol, acid, ether, and ester. The acid includes inorganic acid, organic acid. As the inorganic acid, at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, perchloric acid can be selected. As the organic acid, a polycarboxylic acid can be selected, such as C 2-20 alkane, such as oxalic acid, succinic acid, adipic acid, and the like can be mentioned. As the polycarboxylic acid, C 2-20 alkane, such as malic acid, tartaric acid, citric acid, and the like can be mentioned.

[0029] According to the present application, in step (1), alcohol, ether, ester, further refers to alcohol, ether, ester with the number of carbon atoms greater than 2, such as ethanol, propanol, butanol, butyl ether, ethyl acetate, ethylene glycol, glycerol, polymethyl methacrylate, and the like can be mentioned, also includes the molecular formula of fatty alcohol polyoxyethylene ether is RO(CH2CH2O)5H, R is C7-C9; the molecular formula of alkyl phenol polyoxyethylene ether is RC6H4O(CH2CH2O)nH, R is C9-C12, n is 9-12; the molecular formula of secondary octanol polyoxyethylene ether is C8H 17 (CH2CH2O)nH, n is 1-6.

[0030] 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.

[0031] 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.

[0032] 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-oxygen mixture, air-nitrogen mixture, air-oxygen mixture, air-carbon dioxide mixture, and oxygen-carbon dioxide mixture.

[0033] The present invention also provides an application of a core-shell structured cobalt-based catalyst for catalytic oxidation treatment of volatile organic compounds in the presence of trace amounts of oxygen.

[0034] In the application of the present invention, a core-shell structure cobalt-based catalyst is loaded into a reactor, and a gas containing trace oxygen (300-3000ppm oxygen) and volatile organic compounds (non-methane total hydrocarbons at 400-1800mg / 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℃.

[0035] 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.

[0036] The beneficial effects of the present invention are: the preparation method of the core-shell structure cobalt-based catalyst provided by the present invention is simple and feasible, and the cobalt component is dispersed in the shell layer in a large proportion. Compared with the existing core-shell structure cobalt-based catalyst, the cobalt in the catalyst provided by the present invention mainly exists in the form of metal oxides. 3+ / Co 2+ The ratio of 0.2 to 0.8 is high, and the cobalt component is highly dispersed in the shell layer. Strong interactions exist between cobalt, the carrier, and the additives, preventing active components from falling off and slowing crystallization. The catalyst exhibits excellent resistance to carbon deposition when used to catalyze the oxidation of VOCs pollutant molecules in trace oxygen conditions, thereby extending the catalyst's lifespan. Furthermore, the core-shell cobalt-based catalyst obtained using the preparation method of the present invention exhibits improved water resistance and maintains good stability in the presence of water vapor. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the SEM image of Example 1. DETAILED DESCRIPTION

[0038] 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.

[0039] 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.

[0040] The present invention is further described in detail below with reference to examples, but the present invention is not limited to these examples.

[0041] 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.

[0042] In the present invention, the cobalt and promoter element contents of the core-shell structure catalyst are determined by X-ray fluorescence spectrometer according to ASTM D7085-2004.

[0043] In the present invention, the thickness of the cobalt metal on the catalyst surface is measured using SEM with mapping.

[0044] 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.

[0045] The cobalt valence in the cobalt-based catalyst was determined by XPS (X-ray photoelectron spectroscopy). 3+ / Co 2+ The valence state ratio was calculated by XPS peak fitting.

[0046] Example 1

[0047] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), manganese nitrate, hydroxymethyl cellulose and water are contacted in a mass ratio of 1:0.35:0.3:2 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% cobalt nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide to cobalt element in the composite system is 50:3.5, and the composite system is calcined in air at 500°C for 5 hours to obtain a core-shell structured cobalt-based catalyst A, wherein the mass percentage of cobalt is 5.8%, the mass percentage of manganese is 9.1%, the cobalt content within 0.2 mm of the shell layer of the spherical alumina reaches 91% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.67.

[0048] SEM images of core-shell cobalt-based catalyst A Figure 1 ,from Figure 1 It can be seen that cobalt is highly dispersed in the catalyst shell.

[0049] Example 2

[0050] Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), cerium nitrate, hydroxymethyl propyl cellulose and water are contacted in a mass ratio of 1:0.15:0.3:1.2 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% cobalt chloride to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of aluminum oxide to cobalt element in the composite system is 50:4.2, and the composite system is calcined in air at 520°C for 3 hours to obtain a core-shell structure cobalt-based catalyst B, wherein the mass percentage of cobalt is 6.8%, the mass percentage of cerium is 12.1%, the cobalt content within 0.2 mm of the shell layer of the spherical alumina reaches 95% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.73.

[0051] Example 3

[0052] Spherical silicon oxide (diameter 3.2-3.6 mm, specific surface area 327 m 2 / g, pore volume is 0.49cm 3 / g), antimony acetate, polyethylene glycol-1000 and ethanol are contacted in a mass ratio of 1:0.1:0.3:0.9 to prepare a mixed contact body at 50°C, and the mixed contact body is contacted again with an aqueous solution with a cobalt acetate mass concentration of 15% and a nitric acid aqueous solution (pH=2) with a mass concentration of 0.05 times that of the cobalt acetate to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of aluminum oxide to cobalt in the composite system is 50:4.5, and the composite system is calcined in air at 450°C for 4 hours to obtain a core-shell structured cobalt-based catalyst C, wherein the mass percentage of cobalt is 7.8%, the mass percentage of antimony is 3.6%, the cobalt content within 0.3mm of the shell layer of the spherical alumina reaches 90% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.66.

[0053] Example 4

[0054] Spherical silicon oxide (diameter 3.2-3.6 mm, specific surface area 327 m 2 / g, pore volume is 0.49cm 3 / g), bismuth nitrate, polyethylene glycol-1000 and ethanol are contacted in a mass ratio of 1:0.11:0.3:0.9 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% cobalt acetate and an aqueous nitric acid solution (pH=2) with a mass of 0.05 times that of cobalt acetate to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of aluminum oxide to cobalt in the composite system is 50:5, and the composite system is calcined in air at 450°C for 4 hours to obtain a core-shell structure cobalt-based catalyst D, wherein the mass percentage of cobalt is 8.6%, the mass percentage of bismuth is 5.0%, the cobalt content within 0.3mm of the shell layer of the spherical alumina reaches 91% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.71.

[0055] Example 5

[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), vanadyl oxalate pentahydrate, melamine and ethanol are contacted in a mass ratio of 1:0.35:0.3:0.9 to prepare a mixed contact body at 50° C., and the mixed contact body is contacted again with a cobalt nitrate aqueous solution with a mass concentration of 15% to obtain a composite system, the contact temperature is 50° C., wherein the mass ratio of spherical molecular sieve to cobalt element in the composite system is 50:5.5, and the composite system is calcined under an oxygen-air mixture (wherein the volume fraction of oxygen is 25%) at 500° C. for 3 hours to obtain a core-shell structured cobalt-based catalyst E, wherein the mass percentage of cobalt is 9.2%, the mass percentage of vanadium is 6.0%, the cobalt content within 0.3 mm of the shell of the spherical molecular sieve reaches 80% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.50.

[0057] Example 6

[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 m2 / g, pore volume is 0.41cm 3 / g), the cylinder, titanium sulfate, protein powder and isopropanol were contacted in a mass ratio of 1:0.18:0.3:1 to prepare a mixed contact body at 50°C, and the mixed contact body was contacted again with an acetic acid solution (pH 4) with a mass concentration of 10% cobalt nitrate to obtain a composite system, the contact temperature was 60°C, wherein the mass ratio of MgAl2O4:cobalt element in the composite system was 50:7, and the composite system was calcined in air at 480°C for 5 hours to obtain a core-shell structure cobalt-based catalyst F, wherein the mass percentage of cobalt was 11.9%, the mass percentage of titanium was 3.0%, the cobalt content within 0.3 mm of the shell layer of MgAl2O4 reached 79% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.51.

[0059] Example 7

[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), the cylinder, antimony acetate, cerium nitrate, protein powder and isopropanol are contacted in a mass ratio of 1:0.13:0.1:0.2:1 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 10% cobalt nitrate to obtain a composite system, the contact temperature is 60°C, wherein the mass ratio of TiO2 nanotubes: cobalt elements in the composite system is 50:7, and the composite system is calcined in air at 450°C for 4 hours to obtain a core-shell structure cobalt-based catalyst G, wherein the mass percentage of cobalt is 9.8%, the mass percentage of antimony is 4.3%, and the mass percentage of cerium is 3.5%. The cobalt content within 0.3 mm of the shell layer of the TiO2 nanotube cylinder reaches 87% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.81.

[0061] Example 8

[0062] The cylindrical magnesium oxide (diameter 3mm, height 8mm, specific surface area 79m 2 / g, pore volume is 0.09cm3 / g), tin dichloride, hydroxymethyl cellulose and water in a mass ratio of 1:0.11:0.5:1.4, to prepare a mixed contact body at 40°C, and the mixed contact body was contacted again with an aqueous solution with a mass concentration of 20% cobalt nitrate and 1 / 10 of the mass fraction of cobalt nitrate in n-butanol to obtain a composite system, the contact temperature was 50°C, wherein the mass ratio of magnesium oxide to cobalt element in the composite system was 50:4.2, and the composite system was calcined in air at 480°C for 4 hours to obtain a core-shell structured cobalt-based catalyst H, wherein the mass percentage of cobalt was 7.2%, the mass percentage of tin was 5.8%, the cobalt content within 0.3mm of the shell layer of the cylindrical magnesium oxide reached 85% of the total cobalt content, Co 3+ / Co 2+ The ratio is 0.70.

[0063] Example 9

[0064] 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), gallium nitrate nonahydrate, hydroxymethyl propyl cellulose and ethylene glycol were contacted in a mass ratio of 1:0.23:0:1.1 to prepare a mixed contact body at 45°C, and the mixed contact body was contacted again with an aqueous solution with a mass concentration of 20% cobalt nitrate to obtain a composite system, the contact temperature was 50°C, wherein the mass ratio of silicon oxide-alumina: cobalt in the composite system was 50:4.2, and the composite system was calcined in air at 480°C for 4 hours to obtain a core-shell structured cobalt-based catalyst I, wherein the mass percentage of cobalt was 7.3%, the mass percentage of gallium was 5.4%, the cobalt content within 0.3mm of the shell layer of the cylindrical silicon oxide-alumina reached 75% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.41.

[0065] Example 10

[0066] The cylindrical zinc oxide (diameter 3mm, height 8mm, specific surface area 59m 2 / g, pore volume is 0.08cm 3 / g), chromium nitrate, hydroxymethyl cellulose and water are contacted in a mass ratio of 1:0.43:0.5:1.3 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% cobalt nitrate and 1 / 20 of the mass fraction of cobalt nitrate in n-butanol to obtain a composite system, and the contact temperature is 50°C, wherein the mass ratio of cylindrical zinc oxide: cobalt element in the composite system is 50:7.8, and the composite system is calcined in air at 550°C for 3 hours to obtain a core-shell structured cobalt-based catalyst J, wherein the mass percentage of cobalt is 12.4%, the mass percentage of chromium is 7.5%, the cobalt content within 0.4mm of the shell of the cylindrical zinc oxide reaches 70% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.47.

[0067] Example 11

[0068] 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), ammonium metatungstate, protein powder and ethylene glycol are contacted in a mass ratio of 1:0.13:0.33:1.1 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% cobalt nitrate to obtain a composite system, and the contact temperature is 60°C, wherein the mass ratio of chromium oxide-alumina: cobalt element in the composite system is 50:7.6, and the composite system is calcined in air at 500°C for 4 hours to obtain a core-shell structured cobalt-based catalyst K, wherein the mass percentage of cobalt is 11.5%, the mass percentage of tungsten is 7.7%, the cobalt content within 0.3mm of the shell layer of the cylindrical chromium oxide-alumina reaches 72% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.47.

[0069] Comparative Example 1

[0070] Based on Example 1, the cobalt content was increased. Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), manganese nitrate, hydroxymethyl cellulose and water in a mass ratio of 1:0.45:0.3:2, 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 20% cobalt nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide to cobalt element in the composite system is 50:11, and the composite system is calcined in air at 500°C for 5 hours to obtain a cobalt-based catalyst A-1, wherein the mass percentage of cobalt is 16.0%, the mass percentage of manganese is 10.0%, the cobalt content within 0.2mm of the shell layer of the spherical alumina reaches 56% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.38.

[0071] Comparative Example 2

[0072] Based on Example 1, the mass percentage of the auxiliary element was increased. Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), manganese nitrate, hydroxymethyl cellulose and water in a mass ratio of 1:0.68:0.3:2, 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 20% cobalt nitrate to obtain a composite system, the contact temperature is 50°C, wherein the mass ratio of aluminum oxide to cobalt element in the composite system is 50:3.5, and the composite system is calcined in air at 500°C for 5 hours to obtain a cobalt-based catalyst A-2, wherein the mass percentage of cobalt is 5.4%, the mass percentage of manganese is 16.3%, the cobalt content within 0.2mm of the shell layer of the spherical alumina reaches 87% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.51.

[0073] Comparative Example 3

[0074] Based on Example 1, the preparation method was changed. Spherical alumina (diameter 3.2-3.6 mm, specific surface area 261 m 2 / g, pore volume is 0.41cm 3 / g), manganese nitrate, cobalt nitrate, hydroxymethyl cellulose and water in a mass ratio of 1:0.68:0.22:0.3:2 were contacted at 40° C. to prepare a mixed contact body, and the composite system was calcined in air at 500° C. for 5 hours to obtain a core-shell structure cobalt-based catalyst A-3, wherein the mass percentage of cobalt is 5.8%, the mass percentage of manganese is 9.1%, the cobalt content within 0.2 mm of the shell layer of the spherical alumina reaches 23% of the total cobalt content, and Co 3+ / Co 2+ The ratio is 0.36.

[0075] Application Examples 1-14

[0076] The core-shell structure cobalt-based catalyst in Example 1-11 and the cobalt-based catalyst in Comparative Example 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, 1800 ppm of oxygen, the balance being nitrogen, at a space velocity of 2000 h -1 and a reaction temperature of 320℃. The performance of the catalyst was investigated for 1000 hours. The non-methane total hydrocarbon conversion rate is shown in Table 1.

[0077] Table 1 Evaluation results of catalysts for catalyzing oxidation of VOCs

[0078]

[0079] As can be seen from Table 1, the cobalt-based catalyst with core-shell structure obtained by the preparation method of the present application has the characteristics of strong carbon deposition resistance and stable activity in the presence of trace oxygen.

[0080] The cobalt-based catalyst with core-shell structure obtained in Comparative Example 1 and Comparative Example 3 has a lower content of cobalt element dispersed in the shell layer of the catalyst, and has poorer carbon deposition resistance and activity than the present application.

[0081] The cobalt-based catalyst with core-shell structure obtained in Comparative Example 2 has a higher content of additives. Since the content of additives is outside the protection range, it also has poorer carbon deposition resistance and activity than the present application.

[0082] Application Example 15

[0083] The core-shell structure cobalt-based catalyst A in Example 1 was 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, 1800 ppm of oxygen, the balance being nitrogen, the water vapor concentration was controlled to be 5% (volume fraction), at a space velocity of 2000 h -1 and a reaction temperature of 320℃. The performance of the catalyst was investigated. The initial conversion rate was 98%, the conversion rate remained 98% after 200 hours of reaction, and the conversion rate was 98% after 500 hours. It can be seen that the core-shell structure cobalt-based catalyst obtained by the preparation method of the present application has better water resistance and still has good stability in the presence of water vapor.

[0084] 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 cobalt-based catalyst, characterized in that: Contains original core material, cobalt and additives, wherein the specific surface area of ​​the 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 cobalt-based catalyst, the content of cobalt is 2 to 15 mass% in terms of metal element, wherein 70 to 95 mass% of the cobalt element is dispersed in the shell layer of the catalyst, the thickness of the shell layer is 0.02 to 0.5 mm, and the content of the auxiliary agent is 1 to 13 mass% in terms of auxiliary agent element.

2. A core-shell structure cobalt-based catalyst according to claim 1, characterized in that: The auxiliary agent is at least one of titanium, vanadium, chromium, gallium, antimony, manganese, tungsten, rhenium, bismuth, tin, lanthanum and cerium.

3. A core-shell structure cobalt-based catalyst according to claim 1, characterized in that: The valence state of cobalt is basically divalent cobalt and trivalent cobalt, Co 3+ / Co 2+ The ratio is 0.2 to 0.

8.

4. The core-shell cobalt-based catalyst according to claim 1, characterized in that: The 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 sieve: 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. The core-shell cobalt-based catalyst according to claim 1, characterized in that: The core material has a certain macroscopic shape, and the length of its edges or diameters in a certain direction is greater than 2 mm. The shape is spherical, Raschig ring, strip, clover, four-leaf clover or irregular particles.

6. A method for preparing a core-shell structured cobalt-based catalyst, characterized in that: The following steps are involved: (1) contacting an original core material, an auxiliary element precursor, an additive, and a solvent to form a mixed contact body; wherein, relative to the original core material, the amount of the additive is 0 to 30% by mass of the original core material, the amount of the solvent is 0.5 to 170% by mass of the original core material, and the composition of the auxiliary element precursor and the original core material after calcination conforms to the provisions of claim 1; (2) contacting the mixed contact body with a cobalt precursor in a predetermined ratio in the presence of a dispersion medium to obtain a composite system; (3) calcining the composite system to obtain the core-shell structured cobalt-based catalyst.

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

8. The preparation method according to claim 6, characterized in that The solvent used in step (1) is at least one of water, alcohol, acid, ether and ester.

9. The preparation method according to claim 6, characterized in that In step (2), the dispersion medium is at least one of water, alcohol, acid and ester.

10. The preparation method according to claim 6, characterized in that In step (3), the calcination temperature is 400-650° C., the calcination time is 1-10 hours, and the calcination atmosphere is air, nitrogen-oxygen mixture, air-nitrogen mixture, air-oxygen mixture, air-carbon dioxide mixture or oxygen-carbon dioxide mixture.

11. Use of the core-shell cobalt-based catalyst according to any one of claims 1 to 5 or the core-shell cobalt-based catalyst prepared according to the preparation method according to any one of claims 6 to 10 in catalytic oxidation treatment of volatile organic compounds in the presence of trace oxygen.

12. The use according to claim 11, characterized in that The reaction conditions are as follows: a core-shell cobalt-based catalyst is loaded into the reactor, and a VOC 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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