A cobalt-based composite catalyst and its preparation method and application
By preparing a cobalt-based composite catalyst and utilizing the ion exchange of magnesium hydroxide nanosheets with cobalt salts and cerium salts to form a cobalt-cerium mixed hydroxide, the problems of high cost and poor stability of precious metal catalysts were solved, and efficient propane removal and conversion were achieved.
Patent Information
- Application Number
- CN202310978104.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-04
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2043-08-04
AI Technical Summary
In the prior art, precious metal catalysts have the problems of high cost, low dispersion, and poor stability when treating volatile organic compounds (VOCs), and the preparation process is complicated, which is not conducive to industrial large-scale production.
A cobalt-based composite catalyst is used. Magnesium hydroxide nanosheets are mixed with a cobalt salt precursor in the presence of water to form cobalt hydroxide nanosheets. The nanosheets are then ion-exchanged with a cerium salt precursor and calcined to construct defect sites on the catalyst surface, thereby promoting the adsorption and activation of propane.
It achieves efficient and low-cost propane removal with high propane conversion rate and good stability. It is suitable for low-concentration propane removal system and has excellent catalytic performance.
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Figure CN119455959B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a cobalt-based composite catalyst and a preparation method and application thereof. Background Art
[0002] Volatile organic compounds (VOCs) participate in atmospheric photochemical reactions, forming secondary organic aerosols. These may be a major source of smog and are a key focus of environmental protection efforts both domestically and internationally. Incomplete reactions often occur during the directional oxidation process in coal chemical production, leading to the accumulation of VOCs in exhaust gases or circulating carrier gases. This not only poses a risk of explosion during chemical production but also creates photochemical phenomena, polluting the surrounding environment.
[0003] Catalytic oxidation is a common technology for VOCs treatment. Propane, a typical VOC tail gas, is widely present in liquefied natural gas, compressed natural gas, and liquefied petroleum gas. One effective treatment method is catalytic oxidation. Currently, supported precious metal catalysts are widely used. However, precious metals are inherently expensive and require complex extraction and purification techniques, resulting in high usage, high cost, low dispersion, and poor stability. The development of efficient and stable non-precious metal catalysts is crucial to the advancement of this technology, especially in terms of cost control.
[0004] CN107876060A discloses a cerium-cobalt catalyst for the complete oxidation of propane, its preparation method, and application. Cobalt salt and cerium salt are added to a tert-butanol solution containing an inorganic acid, a polyether surfactant, and sodium lauryl sulfate, stirred until completely dissolved, and then placed at 20-70°C for 1-3 hours. The reaction is then freeze-dried and calcined to obtain a cerium-cobalt catalyst for the complete oxidation of propane. The catalyst prepared by this prior art has the advantages of high activity, low cost, and high stability. However, it requires the additional addition of a surfactant and requires extreme conditions such as liquid nitrogen and refrigerator freezing, which requires strict control and high energy consumption.
[0005] CN113856690A discloses a cobalt-based catalyst for the catalytic combustion of low-concentration methane, its preparation method, and its application. A Ni-Co-based spinel doped with the rare earth element Ce is produced using a single-mode microwave combined with self-propagating combustion. The catalyst achieves a methane conversion rate exceeding 90% at 440°C and exhibits high catalytic stability in the presence of 5 vol% H₂O and 5 vol% CO₂. The catalyst features low cost, a simple preparation process, a large specific surface area, and excellent activity and stability. However, the complex instrumentation required for this prior art preparation makes it unsuitable for large-scale industrial production. Summary of the Invention
[0006] The purpose of the present invention is to provide a non-noble metal cobalt-based composite catalyst with high propane removal rate and high conversion rate and suitable for low-concentration propane removal system.
[0007] In order to achieve the above object, the first aspect of the present invention provides a cobalt-based composite catalyst, which contains 25-50wt% of cobalt, 5-10wt% of cerium, and 0.5-2wt% of magnesium, calculated as elements; the cobalt-based composite catalyst has an oxygen vacancy content of 20-60% and a specific surface area of 20-200m 2 / g.
[0008] The second aspect of the present invention provides a method for preparing the cobalt-based composite catalyst described in the first aspect, comprising the following steps:
[0009] (1) In the presence of water, magnesium hydroxide nanosheets are mixed with a cobalt salt precursor to obtain a mixture I containing cobalt hydroxide nanosheets; the second mixing time is 2-30 hours; the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:0.5-3, calculated as metal elements; the average thickness of the magnesium hydroxide nanosheets is 1-20 nm, and the specific surface area is 100-500 m 2 / g;
[0010] (2) drying the mixture I to obtain the cobalt hydroxide nanosheets; the drying temperature is not higher than 40° C.;
[0011] (3) crystallizing the cobalt hydroxide nanosheets and the cerium salt precursor in the presence of water to obtain a mixture II; the molar ratio of the cobalt element in the cobalt hydroxide nanosheets to the cerium element in the cerium salt precursor is 1:0.01-1, calculated as the metal element;
[0012] (4) subjecting the mixture II to a second calcination treatment to obtain the cobalt-based composite catalyst; the conditions of the second calcination treatment include: a temperature of 200-800° C., a heating rate of 2-20° C. / min, and a time of 2-4 h.
[0013] The third aspect of the present invention provides a cobalt-based composite catalyst prepared by the method described in the second aspect.
[0014] The fourth aspect of the present invention provides use of the cobalt-based composite catalyst described in the first or third aspect in the treatment of propane-containing gas.
[0015] This invention provides a simple and controllable non-precious metal catalyst for efficient propane tail gas removal in petrochemical production processes. Using an ion exchange method, an ultrathin magnesium hydroxide precursor serves as a template. Cobalt hydroxide nanosheets are formed in situ by solubility product differences. In the presence of water, the cobalt hydroxide nanosheets are then further ion-exchanged with a cerium salt precursor to produce a cobalt-cerium mixed hydroxide precursor. This is then calcined to yield a cobalt-based composite catalyst. By regulating the cobalt-cerium mixing ratio, salt solution concentration, and calcination temperature, surface defects are efficiently created on the catalyst surface, controlling the catalyst particle size, promoting substrate adsorption and activation, and ultimately improving overall catalytic performance.
[0016] In the cobalt-based composite catalyst provided by the present invention, new catalytic sites are constructed at the interface between the active material Co3O4 and the carrier CeO2. The method provided by the present invention can enable the active metal precursor and the carrier to fully fuse and change each other, constructing more doped oxygen vacancies to adsorb and activate propane, thereby enhancing the overall catalytic performance of the catalyst.
[0017] The cobalt-based composite catalyst provided by the present invention is a non-noble metal catalyst, which is low in cost and highly efficient and stable. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is a transmission electron microscope image of magnesium hydroxide nanosheets in Example 1;
[0019] Figure 2 This is a transmission electron microscope image of magnesium hydroxide nanosheets in Example 1;
[0020] Figure 3 This is a transmission electron microscope image of cobalt hydroxide nanosheets in Example 1;
[0021] Figure 4 This is a transmission electron microscope image of the cobalt-based composite catalyst of Example 1;
[0022] Figure 5 is the X-ray diffraction (XRD) pattern of the cobalt-based composite catalyst of Example 1;
[0023] Figure 6 1 is an element distribution diagram of the cobalt-based composite catalyst of Example 1;
[0024] Figure 7 is a distribution diagram of Co element in the cobalt-based composite catalyst of Example 1;
[0025] Figure 8 is a distribution diagram of Ce element in the cobalt-based composite catalyst of Example 1;
[0026] Figure 9 This is the distribution diagram of the O element in the cobalt-based composite catalyst of Example 1. DETAILED DESCRIPTION
[0027] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.
[0028] As mentioned above, the first aspect of the present invention provides a cobalt-based composite catalyst, which contains 25-50wt% cobalt, 5-10wt% cerium, and 0.5-2wt% magnesium, calculated as the elements; the cobalt-based composite catalyst has an oxygen vacancy content of 20-60% and a specific surface area of 20-200m 2 / g.
[0029] Preferably, calculated on an element basis, the cobalt-based composite catalyst contains 40-50 wt% of cobalt, 7-10 wt% of cerium, and 0.5-2 wt% of magnesium.
[0030] Preferably, the oxygen vacancy content of the cobalt-based composite catalyst is 30-40%, and the specific surface area is 50-100m 2 / g.
[0031] In the present invention, the cobalt element, cerium element and magnesium element are all present in the cobalt-based composite catalyst in the form of oxides.
[0032] Preferably, the average particle diameter of the cobalt-based composite catalyst is 1-20 nm, more preferably 1-10 nm.
[0033] The cobalt-based composite catalyst provided by the present invention has a high catalytic effect on raw gas with a propane concentration of ≤5v%, a reaction mass space velocity of 60,000mL / g / h, a propane conversion rate of ≥1% at above 100°C, a propane conversion rate of ≥99% at above 350°C, stability of ≥300h, and can ensure that the residual propane volume concentration in the raw gas after the reaction is ≤50ppm.
[0034] As mentioned above, the second aspect of the present invention provides a method for preparing the cobalt-based composite catalyst described in the first aspect, comprising the following steps:
[0035] (1) In the presence of water, magnesium hydroxide nanosheets are mixed with a cobalt salt precursor to obtain a mixture I containing cobalt hydroxide nanosheets; the second mixing time is 2-30 hours; the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:0.5-3, calculated as metal elements; the average thickness of the magnesium hydroxide nanosheets is 1-20 nm, and the specific surface area is 100-500 m2 / g;
[0036] (2) drying the mixture I to obtain the cobalt hydroxide nanosheets; the drying temperature is not higher than 40° C.;
[0037] (3) crystallizing the cobalt hydroxide nanosheets and the cerium salt precursor in the presence of water to obtain a mixture II; the molar ratio of the cobalt element in the cobalt hydroxide nanosheets to the cerium element in the cerium salt precursor is 1:0.01-1, calculated as the metal element;
[0038] (4) subjecting the mixture II to a second calcination treatment to obtain the cobalt-based composite catalyst; the conditions of the second calcination treatment include: a temperature of 200-800° C., a heating rate of 2-20° C. / min, and a time of 2-4 h.
[0039] pass Figure 1 and Figure 2 The transmission electron micrograph of the magnesium hydroxide nanosheets shown shows that the magnesium hydroxide nanosheets described herein exhibit irregular flakes. The inventors discovered that using magnesium hydroxide nanosheets of this size as a template, combined with the other technical features of the present invention, yields a cobalt-based composite catalyst with superior catalytic performance.
[0040] Preferably, in step (1), the average thickness of the magnesium hydroxide nanosheets is 1-10 nm.
[0041] According to a preferred embodiment, the method further comprises: first mixing the magnesium oxide particles with water to obtain the magnesium hydroxide nanosheets; the conditions for the first mixing include: a stirring rate of 70-150 rpm, a temperature of 18-40° C., and a time of 10 min to 24 h.
[0042] Preferably, the amount of the magnesium oxide particles used is such that the initial concentration of magnesium in the reaction system formed by the first mixing is 1.0-1.5 mol / L.
[0043] Preferably, the magnesium oxide particles are obtained by subjecting a magnesium precursor to a first calcination treatment; and the average particle diameter of the magnesium oxide particles is 5-30 nm.
[0044] Preferably, the conditions of the first calcination treatment include: temperature of 600-1000° C., heating rate of 2-20° C. / min, time of 2-4 h, and air flow rate of 10-100 mL / min.
[0045] Preferably, the magnesium precursor is selected from at least one of light magnesium oxide, basic magnesium carbonate, and magnesium chloride hexahydrate.
[0046] According to a preferred embodiment, the magnesium precursor is basic magnesium carbonate and / or magnesium chloride hexahydrate, and the second mixing time in step (1) is 2-5 hours. The inventors of the present invention have found in research that using basic magnesium carbonate and / or magnesium chloride hexahydrate as the magnesium precursor can significantly shorten the reaction time of the second mixing and improve the production efficiency of the cobalt-based composite catalyst.
[0047] According to another preferred embodiment, the magnesium precursor is light magnesium oxide, and the second mixing time in step (1) is 20-30 hours. The inventors of the present invention have found in their research that the cobalt-based composite catalyst prepared using light magnesium oxide as a magnesium precursor has better catalytic performance.
[0048] In the present invention, after the solid-liquid mixture containing magnesium hydroxide nanosheets is obtained through the first mixing, the cobalt salt precursor can be directly introduced into the mixture for the second mixing. Alternatively, the solid-liquid mixture containing magnesium hydroxide nanosheets can be sequentially washed, filtered, and dried to obtain the magnesium hydroxide nanosheets, which are then used to participate in the second mixing. The present invention will not be further described herein, and those skilled in the art should not be construed as limiting the present invention.
[0049] The magnesium hydroxide nanosheets obtained in the present invention may also contain unreacted magnesium oxide particles. When participating in the second mixing in step (1), the unreacted magnesium oxide particles in the magnesium hydroxide nanosheets can continue to react to obtain magnesium hydroxide nanosheets. At the same time, the magnesium hydroxide nanosheets are used as templates and the difference in solubility product is utilized to in-situ form the cobalt hydroxide nanosheets through an ion exchange method.
[0050] pass Figure 3 It can be seen from the transmission electron microscope image of the cobalt hydroxide nanosheet shown in that the cobalt hydroxide nanosheet of the present invention is irregular in shape and very thin.
[0051] Preferably, in step (1), the amount of the cobalt salt precursor used is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.1-2 mol / L, more preferably 0.4-0.8 mol / L. The inventors have found that under this more preferred condition, the propane removal rate and catalyst conversion rate of the cobalt-based composite catalyst obtained by the present invention are higher.
[0052] Preferably, in step (1), the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:1-2, calculated as metal elements.
[0053] Preferably, in step (1), the cobalt salt precursor is selected from at least one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate.
[0054] More preferably, in step (1), the cobalt salt precursor is cobalt nitrate hexahydrate. The inventors of the present invention have found in their research that, compared with other water-soluble cobalt salts, the cobalt-based composite catalyst prepared by selecting cobalt nitrate hexahydrate as the cobalt salt precursor has better catalytic activity and higher propane conversion rate.
[0055] Preferably, in step (1), the second mixing conditions include: a stirring rate of 70-150 rpm, a temperature of 18-40° C., and a time of 2-30 h.
[0056] Preferably, in step (2), the drying temperature is 20-40°C, preferably 20-30°C, and the drying time is 20-26 hours. The inventors of the present invention have found that when the drying conditions are controlled within this preferred range, the ion exchange effect between the cobalt hydroxide nanosheets and the cerium salt precursor is better, thereby preparing a cobalt-based composite catalyst with higher catalytic activity.
[0057] In step (2) of the present invention, before the drying treatment, a pre-treatment method of washing and filtering is also included, which will not be described in detail herein and should not be construed as limiting the present invention by those skilled in the art.
[0058] Preferably, in step (3), the molar ratio of the cobalt element in the cobalt hydroxide nanosheets to the cerium element in the cerium salt precursor is 1:0.025-1, calculated as metal element.
[0059] Preferably, in step (3), the amount of the cerium salt precursor used is such that the initial concentration of cerium element in the reaction system formed by the crystallization treatment is 0.01-2.5 mol / L.
[0060] Preferably, in step (3), the cerium salt precursor is selected from at least one of cerous nitrate hexahydrate, cerous chloride heptahydrate, and cerous sulfate tetrahydrate.
[0061] Preferably, in step (3), the conditions of the crystallization treatment include: temperature of 100-120° C. and time of 4-12 h.
[0062] The present invention has no particular limitation on the equipment for performing the crystallization treatment, as long as it can meet the conditions required by the present invention. For example, the crystallization treatment is performed in an oven. The present invention will not go into details here, and those skilled in the art should not understand it as a limitation of the present invention.
[0063] During the crystallization process of the present invention, the cobalt hydroxide nanosheets and the cerium salt precursor are further ion-exchanged to obtain the mixture II containing the cobalt-cerium mixed hydroxide precursor. At the same time, the water in the crystallization reaction system gradually evaporates to finally obtain the dry mixture II.
[0064] Preferably, in step (4), the conditions for the second calcination treatment include: a temperature of 200-400°C, a heating rate of 3-15°C / min, a time of 2-3 hours, and an air flow rate of 10-100 mL / min. The inventors of the present invention have found that under these preferred second calcination treatment conditions, the cobalt-based composite catalyst provided by the present invention has a higher propane removal rate and catalyst conversion rate, and has more excellent catalytic performance.
[0065] As mentioned above, the third aspect of the present invention provides a cobalt-based composite catalyst prepared by the method described in the second aspect.
[0066] from Figure 4 It can be seen from the transmission electron microscope image of the cobalt-based composite catalyst that the cobalt-based composite catalyst particles provided by the present invention have small and uniform particle sizes and a higher specific surface area.
[0067] Figure 5 The XRD pattern of the cobalt-based composite catalyst, wherein 2-theta is the angle of 2θ at which the X-ray diffractometer scans the entire diffraction area, which exists as the angle change and the horizontal coordinate of the X-ray diffraction spectrum; Co3O4@CeO2 indicates that the cobalt-based composite catalyst is a CeO2-supported catalyst. Figure 5 It can be seen that Co3O4 and CeO2 show obvious diffraction peaks respectively.
[0068] Since the magnesium content in the cobalt-based composite catalyst of the present invention does not reach the detection limit of XRD, the present invention uses inductively coupled plasma technology (ICP) to detect the magnesium content in the cobalt-based composite catalyst.
[0069] Figure 6 Co3O4@CeO2 indicates that the cobalt-based composite catalyst is a CeO2-supported catalyst. Figures 6 to 9 It can be seen from the element distribution diagram that Co, Ce and O elements are evenly distributed, so that CeO2 can penetrate into Co3O4 well and enhance the synergistic interaction of Co-O-Ce.
[0070] In the cobalt-based composite catalyst provided by the present invention, there are Co-Ov-Ce defects (oxygen vacancies) on the surface between the cobalt element, cerium element and oxygen element. Such doped oxygen vacancies can construct new catalytic sites, thereby achieving the beneficial effects of enhancing the catalyst adsorption and activation of propane.
[0071] The "Ov" mentioned in the present invention refers to the oxygen vacancies on the catalyst surface.
[0072] As mentioned above, the fourth aspect of the present invention provides use of the cobalt-based composite catalyst described in the first or third aspect in the treatment of propane-containing gas.
[0073] Preferably, the concentration of propane in the propane-containing gas is ≤5v%.
[0074] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are all commercially available.
[0075] In the following examples, the specific surface areas of magnesium hydroxide nanosheets and cobalt-based composite catalysts were determined using nitrogen adsorption-desorption method.
[0076] In the following examples, an XPS ray photoelectron spectrometer (manufacturer: Thermo Fisher Scientific, model: Thermo Kalpha) was used to measure the oxygen vacancy content of the cobalt-based composite catalyst.
[0077] Example 1
[0078] S1: The magnesium precursor was first calcined at 750°C for 2 h at an air flow rate of 30 mL / min and a heating rate of 5°C / min to obtain magnesium oxide particles (with an average particle diameter of 20 nm). The magnesium oxide particles were first mixed with water at 75 rpm and 25°C for 24 h, and then washed, filtered, and dried to obtain magnesium hydroxide nanosheets (with an average thickness of 3 nm and a specific surface area of 250 m 2 / g);
[0079] The magnesium precursor is basic magnesium carbonate; the amount of magnesium oxide particles used is 0.0125 mol, and the amount of magnesium oxide particles used is such that the initial concentration of magnesium in the first mixed system is 1.25 mol / L;
[0080] S2: In the presence of water, all the magnesium hydroxide nanosheets obtained in step S1 were mixed with the cobalt salt precursor at 100 rpm and 25° C. for a second time for 3 hours to obtain a mixture I containing cobalt hydroxide nanosheets;
[0081] The cobalt salt precursor is cobalt nitrate hexahydrate, and the amount used is 0.0125 mol. The amount of the cobalt salt precursor is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.5 mol / L (the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:1, calculated as the metal element);
[0082] S3: washing the mixture I with water, filtering it, and then drying it at 25°C for 24 hours to obtain cobalt hydroxide nanosheets;
[0083] S4: In the presence of water, the cobalt hydroxide nanosheets and the cerium salt precursor were mixed uniformly and then placed in an oven at 120° C. for crystallization for 12 h to obtain a mixture II;
[0084] The cerium salt precursor is cerous nitrate hexahydrate, and the amount used is 0.0005 mol. The amount of the cerium salt precursor is such that the initial concentration of cerium in the reaction system formed by the crystallization treatment is 0.0125 mol / L, and the molar ratio of cobalt in the cobalt hydroxide nanosheets to cerium in the cerium salt precursor is 1:0.025, calculated as the metal element.
[0085] S5: subjecting the mixture II to a second calcination treatment at 300° C. for 2 h at an air flow rate of 50 mL / min and a heating rate of 3° C. / min to obtain a cobalt-based composite catalyst.
[0086] Example 2
[0087] S1: The magnesium precursor was first calcined at 750°C for 2 h at an air flow rate of 40 mL / min and a heating rate of 3°C / min to obtain magnesium oxide particles (with an average particle diameter of 25 nm). The magnesium oxide particles were first mixed with water at 120 rpm and 25°C for 24 h, and then washed, filtered, and dried to obtain magnesium hydroxide nanosheets (with an average thickness of 2 nm and a specific surface area of 170 m 2 / g);
[0088] The magnesium precursor is light magnesium oxide; the amount of magnesium oxide particles used is 0.0125 mol, and the amount of magnesium oxide particles used is such that the initial concentration of magnesium in the first mixed system is 1.25 mol / L;
[0089] S2: In the presence of water, all the magnesium hydroxide nanosheets obtained in step S1 are mixed with the cobalt salt precursor at 80 rpm and 25° C. for a second time for 24 hours to obtain a mixture I containing cobalt hydroxide nanosheets;
[0090] The cobalt salt precursor is cobalt nitrate hexahydrate, and the amount used is 0.0125 mol. The amount of the cobalt salt precursor is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.5 mol / L (the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:1, calculated as the metal element);
[0091] S3: washing the mixture I with water, filtering it, and then drying it at 25°C for 24 hours to obtain cobalt hydroxide nanosheets;
[0092] S4: In the presence of water, the cobalt hydroxide nanosheets and the cerium salt precursor were mixed uniformly and then placed in an oven at 100° C. for crystallization treatment for 4 hours to obtain a mixture II;
[0093] The cerium salt precursor is cerous chloride heptahydrate, and the amount used is 0.0005 mol. The amount of the cerium salt precursor is such that the initial concentration of cerium in the reaction system formed by the crystallization treatment is 0.0125 mol / L, and the molar ratio of cobalt in the cobalt hydroxide nanosheets to cerium in the cerium salt precursor is 1:0.025, calculated as the metal element.
[0094] S5: subjecting the mixture II to a second calcination treatment at 400° C. for 3 h at an air flow rate of 30 mL / min and a heating rate of 7° C. / min to obtain a cobalt-based composite catalyst.
[0095] Example 3
[0096] This embodiment is carried out using a process similar to that of Example 1, except that in step S2, the cobalt salt precursor is cobalt chloride hexahydrate; the amount of the cobalt salt precursor used is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.2 mol / L, and the type and amount of the cobalt salt precursor remain unchanged;
[0097] A cobalt-based composite catalyst is prepared.
[0098] Example 4
[0099] This embodiment adopts a process similar to that of Example 1, except that in step S4, the molar ratio of the cobalt element in the cobalt hydroxide nanosheets to the cerium element in the cerium salt precursor is 1:0.015, calculated as the metal element; the type and amount of the cerium salt precursor remain unchanged;
[0100] A cobalt-based composite catalyst is prepared.
[0101] Example 5
[0102] This embodiment adopts a process similar to that of embodiment 1, except that in step S5, the temperature of the second calcination treatment is adjusted from 300°C to 500°C, and the other conditions remain unchanged;
[0103] A cobalt-based composite catalyst is prepared.
[0104] Example 6
[0105] This embodiment adopts a process similar to that of embodiment 2, except that this embodiment does not perform the first roasting treatment, and directly uses light magnesium oxide to participate in the first mixing. Specifically:
[0106] S1: Light magnesium oxide and water were first mixed at 75 rpm and 25 ° C for 24 hours, and then washed, filtered, dried, and other steps to obtain magnesium hydroxide nanosheets (average thickness of 2 nm, specific surface area of 180 m 2 / g);
[0107] The amount of light magnesium oxide used is 0.0125 mol, and the initial concentration of light magnesium oxide in the first mixed system is 1.25 mol / L;
[0108] S2: In the presence of water, all the magnesium hydroxide nanosheets obtained in step S1 are mixed with the cobalt salt precursor at 90 rpm and 25° C. for a second time for 24 hours to obtain a mixture I containing cobalt hydroxide nanosheets;
[0109] The cobalt salt precursor is cobalt nitrate hexahydrate, and the amount used is 0.0125 mol. The amount of the cobalt salt precursor is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.5 mol / L (the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:1, calculated as the metal element);
[0110] S3: washing the mixture I with water, filtering it, and then drying it at 25°C for 24 hours to obtain cobalt hydroxide nanosheets;
[0111] S4: In the presence of water, the cobalt hydroxide nanosheets and the cerium salt precursor were mixed uniformly and then placed in an oven at 100° C. for crystallization treatment for 4 hours to obtain a mixture II;
[0112] The cerium salt precursor is cerous chloride heptahydrate, and the amount used is 0.0005 mol. The amount of the cerium salt precursor is such that the initial concentration of cerium in the reaction system formed by the crystallization treatment is 0.0125 mol / L, and the molar ratio of cobalt in the cobalt hydroxide nanosheets to cerium in the cerium salt precursor is 1:0.025, calculated as the metal element.
[0113] S5: subjecting the mixture II to a second calcination treatment at 400° C. for 3 h at an air flow rate of 30 mL / min and a heating rate of 7° C. / min to obtain a cobalt-based composite catalyst.
[0114] Example 7
[0115] This embodiment adopts a process similar to that of embodiment 1, except that in step S3, the drying temperature is adjusted from 25°C to 40°C, and the other conditions remain unchanged;
[0116] A cobalt-based composite catalyst is prepared.
[0117] Example 8
[0118] This example is carried out using a process similar to that of Example 1, except that in step S2, the cobalt salt precursor cobalt nitrate hexahydrate is replaced with an equimolar amount of cobalt sulfate heptahydrate, and the rest remain unchanged;
[0119] A cobalt-based composite catalyst is prepared.
[0120] Example 9
[0121] This embodiment adopts a process similar to that of Example 1, except that in step S2, the cobalt salt precursor cobalt nitrate hexahydrate is replaced with cobalt acetate tetrahydrate; specifically:
[0122] Step S2: In the presence of water, all the magnesium hydroxide nanosheets obtained in step S1 are mixed with the cobalt salt precursor at 100 rpm and 25° C. for a second time for 3 hours to obtain a mixture I containing cobalt hydroxide nanosheets;
[0123] The cobalt salt precursor is cobalt acetate tetrahydrate, and the amount used is 0.0125 mol. The amount of the cobalt salt precursor is such that in the reaction system formed by the second mixture, the initial concentration of the cobalt element is 0.1 mol / L (in terms of metal elements, the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:1).
[0124] The rest remained unchanged to prepare a cobalt-based composite catalyst.
[0125] Comparative Example 1
[0126] This comparative example was carried out using a process similar to that of Example 1, except that in step S2, the amount of cobalt nitrate hexahydrate, a cobalt salt precursor, used was 0.00357 mol (calculated as metal elements, the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets was 1:3.5), and the rest remained unchanged;
[0127] A cobalt-based composite catalyst is prepared.
[0128] Comparative Example 2
[0129] Preparation of Cobalt-based Composite Catalyst by Impregnation Method
[0130] 5.82 g of cobalt nitrate hexahydrate was added to 5 mL of deionized water, followed by 0.09 g of CeO2. The slurry was stirred and evaporated at 110°C until completely dry. It was then calcined at 300°C to obtain a cobalt-based composite catalyst.
[0131] Comparative Example 3
[0132] This comparative example was carried out using a process similar to that of Example 1, except that in step S3, the drying temperature was adjusted from 25°C to 60°C, and the other conditions remained unchanged;
[0133] A cobalt-based composite catalyst is prepared.
[0134] Comparative Example 4
[0135] This comparative example was carried out using a process similar to that of Example 1, except that in step S5, the temperature of the second calcination treatment was adjusted from 300°C to 900°C, and the other conditions remained unchanged;
[0136] A cobalt-based composite catalyst is prepared.
[0137] The composition and parameter characteristics of the cobalt-based composite catalysts prepared in each example are shown in Table 1.
[0138] Table 1
[0139]
[0140] Test Example 1
[0141] The catalytic propane reaction was tested on a fixed bed. The specific test process is as follows:
[0142] 0.70g of the cobalt-based composite catalyst of the present invention is taken to carry out propane catalytic oxidation reaction, which is carried out on a micro-fixed bed evaluation device gas chromatography online analysis integrated system device. Catalyst pressed tablets are sieved, and catalyst particles (0.4-0.85mm) are selected and loaded into a stainless steel reaction tube covered with a quartz liner, switched to the required reaction temperature, and propane and air mixed raw gas are respectively introduced to react, wherein the propane volume concentration in the raw gas is 2500ppm, and the air velocity is 60000mL / g / h, and the reaction temperature is controlled by heating. During the reaction process, after each temperature point is stabilized for 30min, chromatographic sampling is carried out on-line analysis.
[0143] The cobalt-based composite catalyst provided by the present invention has a high catalytic effect on propane in the feed gas, with a reaction mass space velocity of 60,000 mL / g / h, a propane conversion rate of ≥1% at temperatures above 100°C, and a propane conversion rate of ≥99% at temperatures above 350°C. The present invention provides exemplary data, as shown in Table 2, to illustrate the catalytic effect of the cobalt-based composite catalyst prepared in Example 1.
[0144] Propane conversion rate (%) = (volume flow rate of propane in raw gas - volume flow rate of propane in tail gas after reaction) / volume flow rate of propane in raw gas × 100%
[0145] Table 2
[0146] Temperature (℃) Propane conversion rate (%) 100 1.17 125 1.30 150 3.46 175 6.84 200 20.65 225 61.30 250 83.22 275 92.62 300 96.56 325 98.38 350 99.33
[0147] From the data in Table 2, it can be seen that the propane conversion rate is 1.17% at 100°C, and 99.33% at temperatures above 350°C, and the propane conversion is more complete as the temperature increases.
[0148] Test Example 2
[0149] The cobalt-based composite catalysts prepared in the examples and comparative examples were used to carry out propane catalytic oxidation reaction. The specific test process is as follows:
[0150] Take 0.35g of the cobalt-based composite catalyst prepared in each example to carry out propane catalytic oxidation reaction, and carry out on a micro-fixed bed evaluation device gas chromatography online analysis integrated system device. The catalyst tablet is sieved, and catalyst particles (0.4-0.85mm) are selected and loaded into a stainless steel reaction tube with a quartz liner. Switch to the required reaction temperature, and pass into propane and air mixed raw gas to react, wherein the propane volume concentration in the raw gas is 2500ppm, and the air velocity is 60000mL / g / h, and the reaction temperature is controlled by heating. During the reaction process, after each temperature point is stable for 30min, chromatographic sampling is carried out online analysis.
[0151] Propane conversion rate (%) = (volume flow rate of propane in raw gas - volume flow rate of propane in tail gas after reaction) / volume flow rate of propane in raw gas × 100%
[0152] The cobalt-based composite catalysts prepared in each embodiment and comparative example were used to carry out propane catalytic oxidation reaction, and the T 50 and T 90 Value, T 50 、T 90 They represent the reaction temperatures at which propane conversion is 50% and 90%, respectively.
[0153] The results are shown in Table 3.
[0154] Table 3
[0155] <![CDATA[T 50 (℃)]]> <![CDATA[T 90 (℃)]]> Example 1 217 268 Example 2 212 263 Example 3 220 273 Example 4 230 336 Example 5 225 300 Example 6 230 310 Example 7 251 335 Example 8 250 338 Example 9 253 292 Comparative Example 1 265 370 Comparative Example 2 235 348 Comparative Example 3 290 380 Comparative Example 4 269 365
[0156] It can be seen from the data in Table 3 that when the cobalt-based composite catalyst obtained by the technical solution provided by the present invention is used for catalytic oxidation of propane, T 50 and T 90 The lower the value, the higher the activity of the catalyst and the better the catalytic performance.
[0157] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.
Claims
1. A method for preparing a cobalt-based composite catalyst, characterized in that: The following steps are involved: (1) In the presence of water, magnesium hydroxide nanosheets are mixed with a cobalt salt precursor to obtain a mixture I containing cobalt hydroxide nanosheets; the second mixing time is 2-30 hours; the molar ratio of the cobalt element in the cobalt salt precursor to the magnesium element in the magnesium hydroxide nanosheets is 1:0.5-3, calculated as metal elements; the average thickness of the magnesium hydroxide nanosheets is 1-20 nm, and the specific surface area is 100-500 m 2 / g; (2) drying the mixture I to obtain the cobalt hydroxide nanosheets; the drying temperature is not higher than 40° C.; (3) crystallizing the cobalt hydroxide nanosheets and the cerium salt precursor in the presence of water to obtain a mixture II; the molar ratio of the cobalt element in the cobalt hydroxide nanosheets to the cerium element in the cerium salt precursor is 1:0.01-1, calculated as the metal element; (4) subjecting the mixture II to a second calcination treatment to obtain the cobalt-based composite catalyst; The conditions of the second calcination treatment include: temperature of 200-800°C, heating rate of 2-20°C / min, and time of 2-4h; Calculated by elements, the cobalt-based composite catalyst contains 25-50 wt% of cobalt, 5-10 wt% of cerium, and 0.5-2 wt% of magnesium; The cobalt-based composite catalyst has an oxygen vacancy content of 20-60% and a specific surface area of 20-200 m 2 / g.
2. The method according to claim 1, wherein The average particle diameter of the cobalt-based composite catalyst is 1-20 nm.
3. The method according to claim 1 or 2, wherein The method further includes: first mixing magnesium oxide particles with water to obtain the magnesium hydroxide nanosheets; the conditions for the first mixing include: a stirring rate of 70-150 rpm, a temperature of 18-40° C., and a time of 10 min to 24 h.
4. The method according to claim 3, wherein: The magnesium oxide particles are obtained by subjecting a magnesium precursor to a first calcination treatment; the average particle diameter of the magnesium oxide particles is 5-30 nm.
5. The method according to claim 4, wherein The conditions of the first calcination treatment include: temperature of 600-1000° C., heating rate of 2-20° C. / min, time of 2-4 hours, and air flow rate of 10-100 mL / min.
6. The method according to claim 4 or 5, wherein: The magnesium precursor is selected from at least one of light magnesium oxide, basic magnesium carbonate, and magnesium chloride hexahydrate.
7. The method according to claim 1 or 2, wherein: In step (1), the amount of the cobalt salt precursor used is such that the initial concentration of the cobalt element in the reaction system formed by the second mixing is 0.1-2 mol / L; and / or, In step (1), the cobalt salt precursor is selected from at least one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate.
8. The method according to claim 1 or 2, wherein: In step (1), the second mixing conditions include: a stirring rate of 70-150 rpm, a temperature of 18-40° C., and a time of 2-30 h.
9. The method according to claim 1 or 2, wherein: In step (2), the drying temperature is 20-40°C and the drying time is 20-26 hours.
10. The method according to claim 1 or 2, wherein: In step (3), the amount of the cerium salt precursor used is such that the initial concentration of cerium in the reaction system formed by the crystallization treatment is 0.01-2.5 mol / L; and / or, In step (3), the cerium salt precursor is selected from at least one of cerous nitrate hexahydrate, cerous chloride heptahydrate, and cerous sulfate tetrahydrate.
11. The method according to claim 1 or 2, wherein: In step (3), the crystallization treatment conditions include: temperature of 100-120°C and time of 4-12 hours.
12. The method according to claim 1 or 2, wherein: In step (4), the conditions of the second calcination treatment include: temperature of 200-400°C, heating rate of 3-15°C / min, time of 2-3h, and air flow rate of 10-100mL / min.
13. A cobalt-based composite catalyst prepared by the method according to any one of claims 1 to 12.
14. Use of the cobalt-based composite catalyst according to claim 13 in the treatment of propane-containing gas.
15. The use according to claim 14, wherein: The concentration of propane in the propane-containing gas is ≤5v%.