Cobalt-cerium catalyst for low-temperature catalytic conversion of light alkanes, preparation method and application thereof

Abstract

The invention discloses a preparation method of a cobalt-cerium catalyst for catalytic low-temperature conversion of light alkanes, and the steps are as follows: Dissolve a cobalt salt precursor and a cerium salt precursor in ultrapure water to obtain solution A; Dissolve NaOH and Na2CO3 in ultrapure water to obtain solution B; Under vigorous stirring at 40 °C, simultaneously drop solution A and solution B into ultrapure water at a suitable dropping rate; After the titration is completed, stir and crystallize the mixture for 10-15 h; Filter the precipitate obtained by cooling the product to room temperature, wash it until clean and dry; Calcinate the powder in a muffle furnace under an air atmosphere for 4-6 h to obtain the cobalt-cerium catalyst. This cobalt-cerium catalyst has significant low-temperature activity advantages compared with other transition metal catalysts, can reduce the operating cost during the use of the catalyst, and also has good cycle stability and water resistance, showing good industrial application potential and prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and specifically relates to a cobalt-cerium catalyst for low-temperature catalytic degradation of low-carbon alkanes, its preparation method and application. Background Art

[0002] Low-carbon alkanes refer to saturated alkanes with carbon atoms less than or equal to 4, namely methane, ethane, propane and butane, which are typical greenhouse gases. The low-carbon alkanes emitted into the atmosphere will react with nitrogen oxides in the air to produce photochemical smog and ozone, causing problems such as global climate deterioration and directly endangering human health. Therefore, it is urgent to effectively remove the low-carbon chain alkanes directly emitted into the atmosphere to avoid the environmental problems brought by them.

[0003] Due to the high bond energy of the C-H bond and the stable chemical properties of low-carbon alkanes, their low-temperature efficient activation and catalytic degradation are currently the focus and challenge of research. Noble metal catalysts have good oxidation performance, but they are limited by cost and service life, and it is urgent to develop replaceable high-quality catalysts with good economy. Among them, transition metal oxides have good catalytic activity comparable to noble metal catalysts for the catalytic combustion of VOCs, and have good economy, which is the mainstream direction for future catalyst research and development. However, most of the existing transition catalysts still have the disadvantages of low stability and catalytic activity, which limit their practical industrial production. In view of this, it is of great significance to develop a transition metal cobalt-cerium catalyst for low-carbon alkane degradation to solve the problems existing in the existing transition metal catalysts. Summary of the Invention

[0004] To solve one of the above problems, the present invention provides a cobalt-cerium catalyst for low-temperature catalytic degradation of low-carbon alkanes, its preparation method and application. The cobalt-cerium catalyst has good low-temperature conversion activity and cycle stability for the catalytic degradation of short-chain alkanes, and has good water resistance, good economy and industrial application value.

[0005] To achieve the above object, the present invention adopts the following technical means:

[0006] The first aspect of the present invention provides a preparation method of a cobalt-cerium catalyst for low-temperature catalytic degradation of low-carbon alkanes, comprising the following steps:

[0007] (1) Dissolve a cobalt salt precursor and a cerium salt precursor in ultrapure water to obtain solution A;

[0008] (2) Dissolve NaOH and Na2CO3 in ultrapure water to obtain solution B;

[0009] (3) Under vigorous stirring at 40 °C, simultaneously drop the solution A obtained in (1) and the solution B obtained in (2) into ultrapure water at an appropriate dropping rate;

[0010] After the titration is completed, the mixture formed in (3) is stirred and crystallized for 10 - 15 h;

[0011] (5) Filter the precipitate obtained when the product in (4) is cooled to room temperature, wash it until clean and dry it;

[0012] (6) Calcinate the powder obtained in (5) in a muffle furnace under an air atmosphere for 4 - 6 h to obtain the cobalt - cerium catalyst.

[0013] In the embodiments of the present invention, in the cobalt salt precursor and the cerium salt precursor in step (1), the molar ratio of Co / Ce is (0.3 - 5):1. In some preferred embodiments of the present invention, the molar ratio of Co / Ce is (3 - 5):1; more preferably, the molar ratio of Co / Ce is 3:1.

[0014] In the embodiments of the present invention, in step (2), the amount of substance of Na2CO3 is twice that of the cerium salt precursor; the amount of substance of NaOH is twice that of the cobalt salt precursor and the cerium salt precursor, and the volumes of solution A and solution B are the same.

[0015] In the embodiments of the present invention, in step (3), a suitable dropping rate is to keep the pH value of the solution after dropping at 10 ± 0.2.

[0016] In the embodiments of the present invention, in step (4), the stirring time is 30 - 60 min and the crystallization temperature is 60 - 80 °C.

[0017] In the embodiments of the present invention, in step (5), the cleaning method is: centrifugally clean with deionized water until the filtrate is neutral, and the drying temperature is 60 - 80 °C.

[0018] In the embodiments of the present invention, in step (6), the air flow rate is 50 - 100 mL / min and the calcination temperature is 300 - 450 °C.

[0019] The second aspect of the present invention provides the cobalt - cerium catalyst prepared by the method described in the first aspect.

[0020] The third aspect of the present invention provides the application of the cobalt - cerium catalyst described in the second aspect in the degradation of low - carbon alkane pollutants in the atmosphere.

[0021] In some embodiments of the present invention, the low - carbon alkanes include propane, ethane, and methane.

[0022] In some embodiments of the present invention, the present invention also provides the application of the cobalt - cerium catalyst described in the second aspect in the catalytic degradation of propane at low temperature. The catalytic degradation temperature of propane is lower than 200 °C, and during the catalytic degradation, the mass space velocity is 30000 - 120000 mL·g -1 ·h-1 The application also includes the application of catalytic degradation of propane under humid conditions.

[0023] Advantages of the present invention

[0024] Compared with the prior art, the present invention has the following advantages: The present invention uses transition metals cobalt and cerium as raw materials, which greatly saves costs compared with noble metal catalysts and has good economic efficiency. The cobalt-cerium metal catalyst prepared by the invention has significant low-temperature activity advantages compared with other transition metal catalysts, which can reduce the operation cost during the use of the catalyst. At the same time, it also has good cycle stability and water resistance, has good industrial application potential and prospects, and can be widely applied to the field of efficient degradation of lower alkanes in the atmosphere. Description of the drawings

[0025] Figure 1 Shows the SEM images of the catalysts prepared in Examples 1-4;

[0026] Figure 2 Shows the XRD characterization images of the catalysts prepared in Examples 1-4;

[0027] Figure 3 Shows the comparison results of the propane degradation performance of the catalysts prepared in Examples 1-4 under dry conditions;

[0028] Figure 4 Shows the comparison results of the propane degradation performance of the catalysts prepared in Examples 1-4 under humid conditions;

[0029] Figure 5 Shows the graph of the change of propane conversion rate with temperature of the catalyst prepared in Example 3 at different weight hourly space velocities;

[0030] Figure 6 Shows the test result graph of the cycle performance of the catalyst prepared in Example 3;

[0031] Figure 7 Shows the catalytic degradation comparison graph of methane, ethane, and propane of the catalyst prepared in Example 3;

[0032] Figure 8 Shows the comparison graph of the propane degradation of the catalysts prepared in Example 3, Comparative Example 1, and Comparative Example 2 under dry conditions; wherein, Comparative Example 1 is the hydrothermal method, Comparative Example 2 is the single titration method, and Example 3 is the double titration method;

[0033] Figure 9 Shows the comparison graph of the propane degradation of the catalysts prepared in Example 3, Comparative Example 1, and Comparative Example 2 under humid conditions; wherein, Comparative Example 1 is the hydrothermal method, Comparative Example 2 is the single titration method, and Example 3 is the double titration method;

[0034] Figure 10 It shows the comparison chart of the long-term stable catalytic performance of the catalysts prepared in Example 2 and Example 3 under humid conditions. Detailed implementation mode

[0035] The following examples are used here to demonstrate the preferred embodiments of the present invention. Those skilled in the art will understand that the technologies disclosed in the following examples represent the technologies discovered by the inventors that can be used to implement the present invention, and therefore can be regarded as the preferred solutions for implementing the present invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed here, and still obtain the same or similar results, without departing from the spirit or scope of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The materials cited herein and their citations will be incorporated by reference. Those skilled in the art will recognize or can learn through routine experimentation many equivalent technologies of many specific embodiments of the invention described herein. These equivalents will be included in the claims.

[0037] The technical solutions of this patent will be further described in detail below in combination with the specific implementation mode.

[0038] A preparation method of a cobalt-cerium catalyst includes the following steps:

[0039] (1) Dissolve a cobalt salt precursor and a cerium salt precursor in ultrapure water to obtain solution A; wherein, in the cobalt salt precursor and the cerium salt precursor, the molar ratio of Co / Ce is (0.3-5):1;

[0040] (2) Dissolve NaOH and Na2CO3 in ultrapure water to obtain solution B; wherein, the amount of substance of Na2CO3 is twice that of the cerium salt precursor; the amount of substance of NaOH is twice that of the cobalt salt precursor and the cerium salt precursor, and the volumes of solution A and solution B are the same;

[0041] (3) Under vigorous stirring at 40 °C, simultaneously drop solution A obtained in (1) and solution B obtained in (2) into ultrapure water at a suitable dropping rate to keep the pH value of the solution after dropping at 10±0.2;

[0042] (4) After the titration is completed, stir and crystallize the mixture formed in (3) for 10-15 h; the stirring time is 30-60 min, and the crystallization temperature is 60-80 °C;

[0043] (5) Filter the precipitate obtained after the product in (4) is cooled to room temperature, wash it by centrifugation with deionized water until the filtrate is neutral, and dry at a temperature of 60 - 80 °C;

[0044] (6) Calcinate the powder obtained in (5) in a muffle furnace under an air flow rate of 50 - 100 mL / min at a temperature of 300 - 450 °C for 4 - 6 h to obtain the cobalt-cerium catalyst.

[0045] Example 1

[0046] Dissolve 0.003 mol of cobalt nitrate hexahydrate and 0.009 mol of cerium nitrate hexahydrate in 25 mL of ultrapure water to obtain solution A. Dissolve 0.024 mol of NaOH and 0.018 mol of Na2CO3 in 25 mL of ultrapure water to obtain solution B. Under vigorous stirring at 40 °C, simultaneously add solution A and solution B dropwise to 25 mL of ultrapure water, and ensure that the solution pH = 10 by controlling the dropping rate. After the titration is completed, continue to stir the formed mixture for 35 min, then stop stirring, and crystallize at 70 °C for 12 h. Cool to room temperature, filter the obtained precipitate, wash it until pH = 7, dry at 70 °C for 12 h, and calcinate the obtained powder in a muffle furnace at 300 °C in an air atmosphere for 5 h to prepare the cobalt-cerium catalyst: Co1Ce3 catalyst.

[0047] Example 2

[0048] Dissolve 0.006 mol of cobalt nitrate hexahydrate and 0.006 mol of cerium nitrate hexahydrate in 25 mL of ultrapure water to obtain solution A. Dissolve 0.024 mol of NaOH and 0.012 mol of Na2CO3 in 25 mL of ultrapure water to obtain solution B. Under vigorous stirring at 40 °C, simultaneously add solution A and solution B dropwise to 25 mL of ultrapure water, and ensure that the solution pH = 10 by controlling the dropping rate. After the titration is completed, continue to stir the formed mixture for 35 min, then stop stirring, and crystallize at 70 °C for 12 h. Cool to room temperature, filter the obtained precipitate, wash it until pH = 7, dry at 70 °C for 12 h, and calcinate the obtained powder in a muffle furnace at 300 °C in an air atmosphere for 5 h to prepare the cobalt-cerium catalyst: Co1Ce1 catalyst.

[0049] Example 3

[0050] Dissolve 0.009 mol of cobalt nitrate hexahydrate and 0.003 mol of cerium nitrate hexahydrate in 25 mL of ultrapure water to obtain solution A. Dissolve 0.024 mol of NaOH and 0.006 mol of Na2CO3 in 25 mL of ultrapure water to obtain solution B. Under vigorous stirring at 40 °C, solution A and solution B are simultaneously added dropwise to 25 mL of ultrapure water, and the dropping rate is controlled to ensure that the solution pH = 10 ± 0.2. After the titration is completed, the formed mixture is continuously stirred for 35 min, then the stirring is stopped, and crystallization is carried out at 70 °C for 12 h. Cool to room temperature, filter the obtained precipitate, wash it until the pH = 7, dry it at 70 °C for 12 h, and then calcine the obtained powder in a muffle furnace at 300 °C in an air atmosphere for 5 h to prepare the cobalt-cerium catalyst: Co3Ce1 catalyst.

[0051] Example 4

[0052] Dissolve 0.010 mol of cobalt nitrate hexahydrate and 0.002 mol of cerium nitrate hexahydrate in 25 mL of ultrapure water to obtain solution A. Dissolve 0.024 mol of NaOH and 0.004 mol of Na2CO3 in 25 mL of ultrapure water to obtain solution B. Under vigorous stirring at 40 °C, solution A and solution B are simultaneously added dropwise to 25 mL of ultrapure water, and the dropping rate is controlled to ensure that the solution pH = 10. After the titration is completed, the formed mixture is continuously stirred for 35 min, then the stirring is stopped, and crystallization is carried out at 70 °C for 12 h. Cool to room temperature, filter the obtained precipitate, wash it until the pH = 7, dry it at 70 °C for 12 h, and then calcine the obtained powder in a muffle furnace at 300 °C in an air atmosphere for 5 h to prepare the cobalt-cerium catalyst: Co5Ce1 catalyst.

[0053] Comparative Example 1

[0054] Prepare the Co3Ce1 catalyst by the hydrothermal method as follows:

[0055] Take 0.03 mol of Co(NO3)3·6H2O and 0.01 mol of Ce(NO3)3·6H2O and dissolve them in 100 mL of ultrapure water; dissolve 0.1 mol of CO(NH2)2 in 100 mL of ultrapure water. Mix the two solutions together and transfer them to a reaction kettle, react at 110 °C for 24 h, wash with ultrapure water and absolute ethanol, dry the obtained product in a vacuum at 60 °C for 12 h, and calcine the obtained powder in air at 300 °C for 5 h to finally prepare the Co3Ce1 hydrothermal catalyst.

[0056] Comparative Example 2

[0057] Prepare the Co3Ce1 catalyst by the single titration method as follows:

[0058] Take 25 mL each of 0.3 mol / L Co(NO3)3·6H2O and 0.1 mol / L Ce(NO3)3·6H2O salt solutions and place them in a 250 mL flask. Separately, prepare 100 mL of an alkali solution by mixing a certain amount of NaOH and Na2CO3. While vigorously stirring the above mixed salt solution, add the alkali solution to the salt solution at a certain rate. Dropwise add for about 45 minutes. After the solution pH reaches 10 ± 0.1, stir for 10 minutes until the solution pH remains constant. Crystallize in a water bath at 90 °C for 6 h to form a flocculent blue suspension. After cooling, filter off the supernatant, wash the precipitate with deionized water, and centrifuge 4 - 5 times (until the pH is 7.0 ± 0.5). Dry the precipitate at 60 °C for 12 h, and calcine the obtained powder in air at 300 °C for 5 h to finally prepare the Co3Ce1 single-titration catalyst.

[0059] Performance Testing and Characterization

[0060] (1)Physicochemical performance tests were carried out on the catalysts prepared in Examples 1 - 4 under the same conditions, and the results are shown in Table 1.

[0061] Table 1 Physicochemical Properties of the Catalysts Prepared in Examples 1 - 4

[0062]

[0063] The results in the above table show that Co3Ce1 has the highest specific surface area and, compared with other catalysts, has better low-temperature catalytic activity.

[0064] (2)SEM and XRD characterization tests were carried out on the catalysts prepared in Examples 1 - 4, and the results are as Figure 1 and Figure 2 shown.

[0065] It can be seen from Figure 1 that as the Co / Ce ratio increases, the shape of the catalyst changes from strip-shaped to block-shaped, and Co3Ce1 presents uniform hexagonal flakes with a high aspect ratio; the obtained crystal planes of CeO2 (111), Co3O4 (220), and Co3O4 (311) have lattice spacings of 0.31 nm, 0.29 nm, and 0.24 nm respectively.

[0066] (3)Propane degradation performance tests were carried out on the catalysts prepared in Examples 1 - 4 under dry and humid conditions, and the results are as Figure 3 and Figure 4 shown.

[0067] The results show that it can be seen from Figure 3 that Co3Ce1 and Co5Ce1 have the best catalytic conversion efficiency for propane. It can be seen from Figure 4It can be seen that under humid conditions, the catalytic performance of Co1Ce3 and Co1Ce1 for propane decreases significantly, while that of Co3Ce1 and Co5Ce1 for propane is more stable.

[0068] (4)The graph of the propane conversion rate varying with the velocity of the catalyst prepared in Example 3 at different weight hourly space velocities is as Figure 5 shown.

[0069] The results show that: at three different weight hourly space velocities of 30000 mL·g -1 ·h -1 , 60000 mL·g -1 ·h -1 , and 120000 mL·g -1 ·h -1 , the T90 temperatures of the catalyst are 193 °C, 210 °C, and 221 °C respectively. At 30000 mL·g -1 ·h -1 , Co3Ce1 has a lower catalytic temperature for propane conversion.

[0070] (5)The recycling experiment was carried out on the catalyst prepared in Example 3, and the results are as Figure 6 shown.

[0071] The results show that: after the Co3Ce1 catalyst is recycled 5 times, the difference in catalytic performance changes is small, showing excellent recycling performance.

[0072] (6)The catalytic experiments of methane, ethane, and propane were carried out using the catalyst prepared in Example 3 respectively, and the catalytic conversion rate results are as Figure 7 shown.

[0073] The results show that: the Co3Ce1 catalyst has a lower catalytic conversion temperature for propane, and the T90 temperature is below 200 °C.

[0074] (7)The propane degradation experiments were carried out on the catalysts prepared in Example 3, Comparative Example 1, and Comparative Example 2 respectively under dry conditions and humid conditions. The performance curves of different catalysts for propane degradation are as Figure 8 and Figure 9 shown.

[0075] The results show that: for the catalysts prepared by the double titration method in Example 3, the hydrothermal method in Comparative Example 1, and the single titration method in Comparative Example 2, the differences in propane conversion rates at different temperatures under dry conditions are not significant, as Figure 8As shown, the T90 temperature is below 200 °C. However, under humid conditions, the performance of the catalyst prepared by the double titration method in Example 3 is stable, and the T90 temperature is still below 200 °C. However, for the catalyst prepared by the hydrothermal method in Comparative Example 1 and the single titration method in Comparative Example 2, the performance stability is poor, and the T90 temperature rises above 200 °C. This shows that the Co3Ce1 catalyst prepared by the double titration method has better water resistance.

[0076] (8) The catalysts prepared in Examples 2 and 3 were tested for stability by adding 5 vol% H2O under the conditions of a propane concentration of 2000 ppm, a mass space velocity of 30000 mL·g -1 ·h -1 , and a reaction temperature of 225 °C. The results are as Figure 10 shown.

[0077] The results show that compared with Co1Ce1, the catalytic performance of Co3Ce1 shows almost no change under humid conditions, demonstrating excellent stability and better water resistance.

[0078] All documents mentioned in the present invention are incorporated herein by reference as if each document was individually incorporated by reference. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. Preparation method of cobalt-cerium catalyst for low-temperature catalysis of low-carbon alkanes, characterized in that, It includes the following steps: (1) Dissolve the cobalt salt precursor and cerium salt precursor in ultrapure water to obtain solution A; (2) Dissolve NaOH and Na2CO3 in ultrapure water to obtain solution B; (3) Under vigorous stirring at 40 °C, simultaneously add solution A obtained in (1) and solution B obtained in (2) to ultrapure water at an appropriate dropping rate; (4) After the titration is completed, stir and crystallize the mixture formed in (3) for 10 - 15 h; (5) Filter the precipitate obtained after the product in (4) is cooled to room temperature, wash it until clean and dry; (6) Calcinate the powder obtained in (5) in a muffle furnace under an air atmosphere for 4 - 6 h to obtain the cobalt-cerium catalyst; In the cobalt salt precursor and cerium salt precursor in step (1), the molar ratio of Co / Ce is (3 - 5):1; In step (3), the appropriate dropping rate is to keep the pH value of the solution after dropping at 10 ± 0.2; In step (2), the amount of substance of Na2CO3 is twice that of the cerium salt precursor; the amount of substance of NaOH is twice that of the cobalt salt precursor and the cerium salt precursor, and the volumes of solution A and solution B are the same; In step (6), the air flow rate is 50 - 100 mL / min, and the calcination temperature is 300 - 450 °C.

2. The preparation method of the cobalt-cerium catalyst for low-temperature catalytic dehydrogenation of lower alkanes according to claim 1, characterized in that, In step (4), the stirring time is 30 - 60 min, and the crystallization temperature is 60 - 80 °C.

3. The preparation method of the cobalt-cerium catalyst for low-temperature catalytic dehydrogenation of light alkanes according to claim 1, characterized in that, In step (5), the cleaning method is: centrifuge and wash with deionized water until the filtrate is neutral, and the drying temperature is 60 - 80 °C.

4. The cobalt-cerium catalyst prepared by the method according to any one of claims 1 - 3.

5. The application of the cobalt-cerium catalyst according to claim 4 in the degradation of low-carbon alkane pollutants in the atmosphere.

6. The application according to claim 5, characterized in that: The low-carbon alkane is propane.

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