Preparation process of high-activity supported cobalt-based catalyst

Abstract

The invention discloses a preparation process of a high-activity supported cobalt-based catalyst in the technical field of thermocatalysis, which comprises the following steps: 1) precipitation reaction: in a hydrothermal precipitation reactor, adding a cetyl trimethyl ammonium bromide aqueous solution and urea into a 0-0.08 mol / L cobalt nitrate aqueous solution and a 0-0.008 mol / L manganese nitrate aqueous solution, and precipitating the urea and cobalt cations to generate cobalt hydroxide; 2) solid-liquid separation: carrying out solid-liquid separation on the material obtained in the previous step in solid-liquid separation equipment to obtain a solid-phase material which is a cobalt hydroxide crude product, and carrying out further impurity removal treatment to obtain a cobalt carbonate product; and 3) heat treatment: in heat treatment reaction equipment, carrying out heat treatment on the cobalt carbonate product obtained in the previous step to obtain a product with manganese oxide loaded on cobaltosic oxide, and realizing complete catalytic oxidation of carbon monoxide at room temperature, thereby reducing emission of carbon monoxide and realizing energy conservation and emission reduction.

Description

Technical Field

[0001] The invention relates to the technical field of thermal catalysis, and in particular to a preparation process of a cobalt-based catalyst. Background Art

[0002] With the progress and development of society and the improvement of residents' living standards, people are facing new crises and challenges while obtaining abundant material resources. The popularity of a large number of motor vehicles has made people's daily travel more convenient, but it has also directly led to a surge in the number of motor vehicles, so the problem of motor vehicle exhaust emissions and purification treatment needs to be solved urgently. The pollutants in automobile exhaust are mainly carbon monoxide (CO), hydrocarbons, sulfur oxides, nitrogen oxides, suspended solid particles, etc. About 40~80% of automobile exhaust emissions are released during the cold start process, and during the cold start process of the automobile engine, CO and hydrocarbons are discharged into the atmosphere without treatment. At present, the problem of air pollution has received more and more attention from people. As one of the three major gas pollutants in the world, CO is colorless and odorless and kills people invisibly. CO is highly toxic. CO has a strong binding force with hemoglobin in human blood, making it difficult for oxygen and hemoglobin to bind, which eventually leads to hypoxia in the human brain and causes poisoning. When the volume content of CO in the air reaches 0.01~0.12%, the human body will experience symptoms such as headache, nausea, and coma. When the content reaches 0.16~0.60%, the higher the concentration of CO, the greater the possibility of death in a short period of time. In order to solve the problem of CO gas emissions, the most widely used technology at present is thermal catalysis, which uses a catalyst to convert toxic CO gas into non-toxic carbon dioxide (CO2) at a certain temperature and then emit it. The addition of a catalyst reduces the activation energy of the catalytic oxidation reaction, thereby increasing the reaction rate and reducing the reaction conversion temperature, saving unnecessary energy consumption.

[0003] Among cobalt-based catalysts, compared with rock salt structure CoO and hexagonal structure Co2O3, cobalt tetroxide with spinel structure is widely used in the field of environmental catalysis. This is because cobalt tetroxide contains both Co (II) and Co (III), of which Co (II) is located at the spinel tetrahedral site and Co (III) is located at the spinel octahedral site, which makes it subject to the interaction between the two valence ions when participating in some redox reactions, thus showing excellent catalytic oxidation activity. However, in the presence of water in the reaction, the activity of cobalt tetroxide will be greatly affected, and the active sites of the reaction will be blocked, resulting in the inactivation of the catalyst. In addition, the doping of supported metals will affect the electronic structure, redox ability and defects of cobalt oxide to a certain extent, which will change the activity of the catalyst. It is worth mentioning that low-temperature catalytic CO oxidation technology is not only of great significance in human health and environmental protection such as automobile exhaust treatment, but also has extensive and important practical application value in the fields of gas purification in the petrochemical industry, catalyst reforming process in hydrocarbon processing, development of proton fuel cells, CO gas sensor purifiers, etc. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a process for preparing a highly active supported cobalt-based catalyst, which can achieve complete catalytic oxidation of carbon monoxide at room temperature, thereby reducing carbon monoxide emissions and achieving energy conservation and emission reduction.

[0005] The object of the present invention is achieved by: a process for preparing a highly active supported cobalt-based catalyst, comprising the following steps: Step 1) precipitation reaction: in a hydrothermal precipitation reactor, adding a hexadecyltrimethylammonium bromide aqueous solution and urea to a 0-0.08 mol / L cobalt nitrate and a 0-0.008 mol / L manganese nitrate aqueous solution, and urea and cobalt cations precipitate to form cobalt hydroxide; Step 2) solid-liquid separation: In a solid-liquid separation device, the material obtained in the previous step is subjected to solid-liquid separation. The solid phase material obtained by the solid-liquid separation is a crude cobalt hydroxide product, which is further subjected to impurity removal treatment to obtain a cobalt carbonate product; Step 3) Heat treatment: In a heat treatment reaction device, the cobalt carbonate product obtained in the previous step is heat treated to obtain a product in which manganese oxide is loaded on cobalt tetroxide.

[0006] Furthermore, in the precipitation reaction of step 1), the molar ratio of urea added to cobalt cation is (0-0.017):(0-0.08), and the operating temperature is 25°C.

[0007] Furthermore, the concentration of the urea aqueous solution in step 1) is 0-0.28 mol / L, and the operating temperature is 25°C.

[0008] Furthermore, in step 1), the concentration of the hexadecyltrimethylammonium bromide aqueous solution is 0-0.13 mol / L, and the operating temperature is 25°C.

[0009] Furthermore, in the hydrothermal precipitation reaction in step 1), the hydrothermal temperature is 160° C. to 180° C., and the hydrothermal time is 2 h to 5 h.

[0010] Furthermore, in step 2), the separation method is suction filtration, the drying temperature is 80° C., and the drying time is 12 h.

[0011] Furthermore, in the solid-liquid separation process of step 2), the solid-liquid separation device is any one of a filter press, a centrifugal filter, a blade filter, a pipeline device and a vacuum filtration device.

[0012] Furthermore, in step 3), the heat treatment temperature is 150° C. to 550° C., and the heat treatment time is 3 hours.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a hydrothermal precipitation method to obtain metal manganese-doped nanowire-stacked spherical cobalt tetroxide, thereby achieving low-temperature complete conversion of carbon monoxide; the present invention increases the adsorption of oxygen on the surface of the cobalt-based catalyst by the addition of metal manganese, promotes the adsorption of carbon monoxide, improves the activity of the cobalt-based catalyst, achieves complete conversion of carbon monoxide at room temperature, and reduces direct emissions of carbon monoxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0015] Figure 1 These are three different morphologies of stacked balls according to the present invention: (a) nanowire stacked balls; (b) nanosheet stacked balls; and (c) cube stacked balls.

[0016] Figure 2 The XPS spectra of the catalyst samples of the present invention are shown in Figure 2; (a) is the Co 2p XPS spectrum, and (b) is the O 1s XPS spectrum. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The test materials used in the examples of the present invention, unless otherwise specified, were purchased from commercial channels. In the examples of the present application, the catalyst evaluation, conversion rate and selectivity calculation methods are as follows: In the experiment, the CO probe reaction was carried out in a CO catalytic oxidation micro-fixed bed evaluation device. In the constant temperature zone of the reaction tube, quartz wool was used as the reaction bed support, and 50 mg of sample and 50 mg of quartz sand were accurately weighed, mixed evenly and loaded into the reaction tube. Before the reaction started, the catalyst was first pretreated and purged at 180 ° C for 120 min in a high-purity N2 atmosphere to remove impurities on the sample surface and promote the generation of oxygen vacancies on the catalyst surface. After the pretreatment, the reactor temperature dropped to room temperature and the test began. The test reaction gas was a CO mixed gas (V CO :V O2 :V N2 =1.6:21.4:77.0), the inlet gas flow rate is 30 mL / min, the reactor is controlled to stabilize at the reaction temperature for 30 min before sampling, each temperature point is sampled 5 times and the average value is finally taken, and the gas after the reaction enters the HF-900 gas chromatography (GC) for online analysis and processing. The gas chromatography filling column is a 5A molecular sieve filling column (Φ4mm×2 mm stainless steel column), and the chromatographic analysis conditions are: column temperature 45 ℃, vaporization temperature 100 ℃, TCD thermal conductivity detector temperature 100 ℃, bridge flow 100 mA. The conversion rate of CO is calculated according to the formula: Among them, X CO(%) —CO conversion rate; (CO) in —Initial CO concentration; (CO) out —CO concentration after reaction.

[0019] Example 1 In a 100mL beaker, add 1.46g Co(NO3)2·6H2O and 0.1g Mn(NO3)2·xH2O and dissolve them in 60mL deionized water, and stir thoroughly for 30min; add 0.0175g CTAB and 1g CO(NH2)2 to the above solution, and continue stirring for 30min; put it into a high-pressure reactor, heat it at 160℃ for 2h, and after the hydrothermal treatment, let it stand until the temperature drops to room temperature to obtain a deep red precursor; the generated deep red precursor is washed with 400mL deionized water, filtered, and dried at 80℃ for 12h; after drying, the solid is placed in a crucible furnace, heated to 250℃ at 2℃ / min in an air atmosphere and calcined for 3h to obtain a supported cobalt-based catalyst.

[0020] Example 2 In a 100mL beaker, add (CH3COO)2Co·4H2O 1.25g, Mn(NO3)2·xH2O 0.1g and dissolve in 60mL ethylene glycol, and stir thoroughly for 30min. Add CTAB 2.916g and CH3COONa 2.45g to the above solution, and continue stirring for 30min. Put it in a high-pressure reactor, heat it at 180℃ for 12h, and after the hydrothermal is completed, let it stand until the temperature drops to room temperature to obtain a precursor; the generated precursor is washed with 400mL of deionized water, filtered, and dried at 80℃ for 12h; after drying, the solid is placed in a crucible furnace, heated to 250℃ at 2℃ / min in an air atmosphere and calcined for 3h to obtain a supported cobalt-based catalyst.

[0021] Example 3 In a 100mL beaker, add 1.25g (CH3COO)2Co·4H2O and 0.1g Mn(NO3)2·xH2O to 60mL ethylene glycol and stir thoroughly for 30min. Add 1g CO(NH2)2 to the above solution and continue stirring for 30min. Put it in a high-pressure reactor and heat it at 180℃ for 12h. After the hydrothermal treatment, let it stand until the temperature drops to room temperature to obtain a precursor; the generated precursor is washed with 400mL of deionized water, filtered, and dried at 80℃ for 12h; after drying, place the solid in a crucible furnace, heat it to 250℃ at 2℃ / min in an air atmosphere and calcine it for 3h to obtain a supported cobalt-based catalyst.

[0022] Embodiments 4 to 10 Table 1 Effect of different preparation processes on the catalytic oxidation performance of carbon monoxide

[0023] According to Table 1, Example 1 is a nanowire stacking sphere, Example 2 is a nanosheet stacking sphere, and Example 3 is a cube stacking sphere. Figure 1As shown, three cobalt-based catalysts prepared with similar morphologies and the same metal addition amount are compared. The nanowire stacked spheres with 10% manganese metal addition have the best performance and can be completely converted at room temperature. The specific surface area of ​​the nanowire stacked sphere catalyst is larger than that of the other two morphologies, thereby exposing more defects, which is conducive to the participation of highly active oxygen in the carbon monoxide oxidation reaction. It can be seen from the comparison of Examples 1 and 4-7 in Table 1 that different amounts of manganese addition will result in different catalyst performance. Too low manganese content will lead to incomplete electron transfer between Mn-Co species; when the manganese content is too high, the manganese species will accumulate and aggregate on the surface of the nanowire stacked spheres, thereby blocking the pores and reducing performance.

[0024] Figure 2 -a, it can be found that the addition of Mn species causes the Co 2p orbital of the series of catalysts to shift toward the direction of high binding energy, indicating that the electron density of the surface Co species decreases, which indicates that there is a strong interaction between the Mn-Co species. It can be found from Table 2 that the introduction of Mn species makes Co 3+ This further illustrates that the doping of manganese species will reduce the electron density of surface cobalt species.

[0025] Table 2 Sample XPS fitting data results Sample name <![CDATA[Co 3+ / (What 2+ +What 3+ ) a (%)]]> <![CDATA[O ads / (O latt +O ads ) a (%)]]> <![CDATA[Co3O4-C]]> 53.77 21.61 10MnCo 55.23 26.68 Figure 2 -b, it can be found that the introduction of Mn species causes the O 1s of the catalyst to shift toward the low binding energy direction, which may be due to the ads The mobility of the catalyst is enhanced and the electron density is increased. From the XPS fitting results in Table 2, the 10MnCo catalyst has more surface active oxygen content and Co 3+ The presence of a large amount of O ads and Co 3+ It plays an important role in the catalytic CO oxidation process.

[0026] Comparison between Example 1 and 8-11 shows that appropriate calcination temperature is conducive to the formation of more surface adsorbed oxygen vacancies, which is conducive to the participation of highly active oxygen in the reaction.

[0027] The present invention is not limited to the above embodiments, and any technical solution formed by equivalent replacement or equivalent replacement belongs to the scope of protection claimed by the invention. In addition to the above embodiments, there are many implementation schemes of the present invention, and any technical solution formed by equivalent replacement or equivalent replacement belongs to the scope of protection claimed by the present invention.

[0028] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A process for preparing a highly active supported cobalt-based catalyst, characterized in that: The following steps are involved: Step 1) precipitation reaction: in a hydrothermal precipitation reactor, adding a hexadecyltrimethylammonium bromide aqueous solution and urea to a 0-0.08 mol / L cobalt nitrate and a 0-0.008 mol / L manganese nitrate aqueous solution, and urea and cobalt cations precipitate to form cobalt hydroxide; Step 2) solid-liquid separation: In a solid-liquid separation device, the material obtained in the previous step is subjected to solid-liquid separation. The solid phase material obtained by the solid-liquid separation is a crude cobalt hydroxide product, which is further subjected to impurity removal treatment to obtain a cobalt carbonate product; Step 3) Heat treatment: In a heat treatment reaction device, the cobalt carbonate product obtained in the previous step is heat treated to obtain a product in which manganese oxide is loaded on cobalt tetroxide.

2. The process for preparing a highly active supported cobalt-based catalyst according to claim 1, characterized in that: In step 1), in the precipitation reaction, the molar ratio of urea to cobalt cation is (0-0.017):(0-0.08), and the operating temperature is 25°C.

3. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: The concentration of the urea aqueous solution in step 1) is 0-0.28 mol / L, and the operating temperature is 25°C.

4. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: The concentration of the hexadecyltrimethylammonium bromide aqueous solution in step 1) is 0-0.13 mol / L, and the operating temperature is 25°C.

5. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: In the hydrothermal precipitation reaction in step 1), the hydrothermal temperature is 160° C. to 180° C., and the hydrothermal time is 2 h to 5 h.

6. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: Step 2) The separation method is suction filtration, the drying temperature is 80°C, and the drying time is 12h.

7. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: In step 2), during the solid-liquid separation process, the solid-liquid separation device is any one of a filter press, a centrifugal filter, a blade filter, a pipeline device and a vacuum filter.

8. A process for preparing a highly active supported cobalt-based catalyst according to claim 1 or 2, characterized in that: Step 3) During the heat treatment process, the heat treatment temperature is 150°C to 550°C, and the heat treatment time is 3 hours.

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