Preparation method of s-modified znal2o4 nanosheet catalyst for catalytic decomposition of cf4 in aluminum electrolysis flue gas

Abstract

A preparation method of an S modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in electrolytic aluminum flue gas, comprising the following steps: step 1, adding sulfuric acid solution to ZnAl2O4 nanosheet, after fully stirring, transferring to an oven, after the sample is completely dried, obtaining an S modified ZnAl2O4 precursor sample; step 2, transferring the S modified ZnAl2O4 precursor sample to a muffle furnace, after high-temperature calcination and cooling, obtaining the S modified ZnAl2O4 nanosheet catalyst. The ratio of the amount of ZnAl2O4 nanosheet to the sulfuric acid solution in step 1 is 0.09-0.11 g / ml, and step 2 is calcined at 640-660 DEG C for 22-26 h. The prepared S modified ZnAl2O4 nanosheet catalyst can reach 100% efficiency in catalytic decomposition of CF4 on a fixed bed reaction chamber at 600 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental catalysis, and relates to a preparation method of an S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in electrolytic aluminum flue gas. BACKGROUND

[0002] In recent years, the electrolytic aluminum industry in China has developed rapidly. In 2022, the electrolytic aluminum industry in China produced about 550 million tons of carbon dioxide (CO2), accounting for 5% of the global net CO2 emissions. 8.0 million tons of CF4 were produced, which has a global warming potential (GWP) of 7390 times that of carbon dioxide (CO2), equivalent to emitting 590 million tons of CO2. CF4 is very stable and has a lifetime of 50,000 years in the atmosphere, and its impact on the atmospheric environment is almost permanent. At present, CF4 has been included in the list of important greenhouse gas emission reduction, therefore, it is particularly important to treat the CF4 gas emitted by the electrolytic aluminum industry.

[0003] CF4 has a highly symmetrical single-carbon structure, and its bond energy reaches 543 kJ mol -1 Therefore, it is necessary to have harsh conditions to break the structure of the CF4 molecule. At present, a variety of CF4 treatment methods have been developed, but there are generally problems such as high energy consumption, harsh reaction conditions, and toxic by-product loading. The catalytic hydrolysis method is the most effective method for treating CF4

[0004] molecules at present because it is simple to operate, has a relatively low treatment temperature, and does not produce harmful end products. However, the efficiency of catalytic hydrolysis of CF4 is low, and it is necessary to develop a high-efficiency catalyst for improving the efficiency of catalytic hydrolysis of CF4 to solve this problem. SUMMARY

[0005] The purpose of the embodiment of the application is to provide a preparation method of an S-modified ZnAl2O4 nanosheet for catalytic decomposition of CF4 in electrolytic aluminum flue gas, so as to solve the problem that the efficiency of treating CF4 gas by the catalytic hydrolysis method is low at present.

[0006] The technical scheme adopted by the embodiment of the application is: a preparation method of an S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in electrolytic aluminum flue gas, comprising the following steps:

[0007] Step 1, sulfuric acid solution is added to ZnAl2O4 nanosheets, and after being fully stirred, the sample is transferred to an oven. After the sample is completely dried, an S-modified ZnAl2O4 precursor sample is obtained. The ratio of the amount of ZnAl2O4 nanosheets to the amount of sulfuric acid solution is 0.09-0.11 g / ml.

[0008] Sulfuric acid etching of ZnAl2O4 nanosheets exposes more active sites, thereby enabling catalytic hydrolysis of CF4;

[0009] The specific preparation process of ZnAl2O4 nanosheets in step 1 is as follows:

[0010] Step S1: Add aluminum nitrate nonahydrate and zinc nitrate hexahydrate to deionized water and stir thoroughly until the solution is completely clear to obtain a mixed reaction solution;

[0011] Step S2: Transfer the mixed reaction solution to an oil bath, add ammonia water dropwise, and then transfer it to a centrifuge tube. After centrifugation and washing with water multiple times, place it in an oven to dry and obtain a white precursor powder.

[0012] Step S3: The obtained white precursor powder is transferred to a muffle furnace, calcined at high temperature and cooled to obtain ZnAl2O4;

[0013] In step S3, the obtained white precursor powder is transferred to a muffle furnace and reacted at 580~620℃ for 4~6h. After cooling to room temperature, ZnAl2O4 nanosheets are obtained.

[0014] Step 2: Transfer the S-modified ZnAl2O4 precursor sample to a muffle furnace, calcine at 640~660℃ for 22~26h, and then cool to obtain the S-modified ZnAl2O4 nanosheet catalyst.

[0015] Furthermore, in step S1, the molar ratio of Al:Zn ranges from 1.9 to 2.1:1.

[0016] Furthermore, in step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 75~85℃ and heated, while ammonia water is added dropwise during stirring.

[0017] Furthermore, in step S2, ammonia is added dropwise until the pH reaches 8.5-9.5.

[0018] Furthermore, in step S2, the stirring speed during the addition of ammonia is 550~650 rpm, and the ammonia is added at a rate of 2~4 ml / min.

[0019] Furthermore, in step S3, the heating rate of the muffle furnace is 1.5~2.5℃ / min.

[0020] The beneficial effects of this invention are as follows: First, a ZnAl2O4 nanosheet catalyst is prepared, and then the ZnAl2O4 nanosheet catalyst is modified with sulfuric acid solution to obtain the S-modified ZnAl2O4 nanosheet catalyst S-ZnAl2O4. This method has low raw material cost, simple preparation method, and short reaction time. The prepared S-modified ZnAl2O4 nanosheet catalyst can achieve 100% efficiency in catalytic decomposition of CF4 in a fixed bed reaction chamber at 600℃ and maintains its inactivation for 20 hours, exhibiting good catalytic efficiency and stability. This solves the problem of low efficiency in treating CF4 gas by the current catalytic hydrolysis method. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Fig. 1 This is an X-ray diffraction pattern of ZnAl2O4 and S-ZnAl2O4 nanosheets. In the figure, the horizontal axis 2θ represents the diffraction angle (degree), and the vertical axis Intensity represents the intensity (au).

[0023] Fig. 2 These are transmission electron microscopy (TEM) images of ZnAl2O4 and S-ZnAl2O4 nanosheets, where (a) is a TEM image of ZnAl2O4 nanosheets and (b) is a TEM image of S-ZnAl2O4 nanosheets.

[0024] Fig. 3 These are high-resolution transmission electron microscopy (TEM) images of ZnAl2O4 and S-ZnAl2O4 nanosheets. (a) is a high-resolution TEM image of ZnAl2O4 nanosheets, and (b) is a high-resolution TEM image of S-ZnAl2O4 nanosheets.

[0025] Fig. 4 This is a stability graph of CF4 hydrolysis catalyzed by ZnAl2O4 nanosheets, where the horizontal axis h represents time (hours) and the vertical axis CF4decomposition represents the decomposition rate of CF4 (%).

[0026] Fig. 5 This is a stability graph of CF4 hydrolysis catalyzed by S-ZnAl2O4 nanosheets, where the horizontal axis h represents time (hours) and the vertical axis CF4decomposition represents the decomposition rate of CF4 (%). Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing a ZnAl2O4 nanosheet catalyst for the catalytic decomposition of CF4 in aluminum electrolysis flue gas, comprising the following steps:

[0030] Step S1: Add 7.503g of aluminum nitrate nonahydrate and 2.972g of zinc nitrate hexahydrate to 500ml of deionized water. At this time, the molar ratio of Al:Zn is 2:1. Stir thoroughly until the solution is completely clear. Specifically, stir at a stirring rate of 550~650 rpm for 1.5~2.5h to obtain a mixed reaction solution.

[0031] Step S2: Transfer the obtained mixed reaction solution to an oil bath at 80°C and heat it. Add ammonia water dropwise while stirring and react for 2 hours. Then transfer it to a centrifuge tube, centrifuge and wash it with water multiple times, and dry it in an oven to obtain a white precursor powder. The stirring speed when adding ammonia water is 600 rpm. Add ammonia water dropwise until pH=9.0, and the dropwise rate of ammonia water is 3 ml / min.

[0032] Step S3: The obtained white precursor powder is transferred to a muffle furnace and reacted at 600℃ for 4 hours. After cooling to room temperature, ZnAl2O4 nanosheets are obtained. The heating rate of the muffle furnace is 2℃ / min. The high-temperature treatment in the muffle furnace is used to further oxidize the white precursor powder obtained in step S2 to obtain ZnAl2O4 nanosheets.

[0033] Example 2

[0034] The difference between this embodiment and Embodiment 1 is that the molar ratio of Al:Zn in step S1 is 1.5:1.

[0035] Example 3

[0036] The difference between this embodiment and Embodiment 1 is that the molar ratio of Al:Zn in step S1 is 1.9:1.

[0037] Example 4

[0038] The difference between this embodiment and Embodiment 1 is that the molar ratio of Al:Zn in step S1 is 2.1:1.

[0039] Example 5

[0040] The difference between this embodiment and Embodiment 1 is that the molar ratio of Al:Zn in step S1 is 2.5:1.

[0041] Example 6

[0042] The difference between this embodiment and embodiment 1 is that in step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 60°C for heating, and ammonia water is added dropwise during the stirring process. After reacting for 3 hours, the solution is transferred to a centrifuge tube.

[0043] Example 7

[0044] The difference between this embodiment and Embodiment 1 is that in step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 75°C for heating, and ammonia water is added dropwise during stirring. After reacting for 1.5 hours, the mixture is transferred to a centrifuge tube.

[0045] Example 8

[0046] The difference between this embodiment and Embodiment 1 is that in step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 85°C for heating, and ammonia water is added dropwise during the stirring process. After reacting for 2.5 hours, the solution is transferred to a centrifuge tube.

[0047] Example 9

[0048] The difference between this embodiment and Embodiment 1 is that in step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 90°C for heating, and ammonia water is added dropwise during stirring. After reacting for 1 hour, the solution is transferred to a centrifuge tube.

[0049] Example 10

[0050] The difference between this embodiment and Embodiment 1 is that in step S2, ammonia water is added dropwise until pH=8, and the dropwise rate of ammonia water is 2ml / min.

[0051] Example 11

[0052] The difference between this embodiment and Embodiment 1 is that in step S2, ammonia water is added dropwise until pH=8.5, and the dropwise addition rate of ammonia water is 2ml / min.

[0053] Example 12

[0054] The difference between this embodiment and Embodiment 1 is that in step S2, ammonia water is added dropwise until pH=9.5, and the dropwise addition rate of ammonia water is 4ml / min.

[0055] Example 13

[0056] The difference between this embodiment and Embodiment 1 is that in step S2, ammonia water is added dropwise until pH=10, and the dropwise rate of ammonia water is 4ml / min.

[0057] Example 14

[0058] This embodiment provides a method for preparing an S-modified ZnAl2O4 nanosheet catalyst for the catalytic decomposition of CF4 in aluminum electrolysis flue gas, comprising the following steps:

[0059] Step 1: Slowly add 20 ml of sulfuric acid solution to 2.00 g of ZnAl2O4 nanosheets prepared in Example 1, i.e., the ratio of ZnAl2O4 nanosheets to sulfuric acid solution is 0.1 g / ml. After stirring thoroughly, transfer to an oven and dry the sample completely. Specifically, the stirring speed is 550~650 rpm and the stirring time is 22~26 h. Dry at 75~85℃ for 22~26 h and cool to room temperature to obtain the S-modified ZnAl2O4 precursor sample.

[0060] Step 2: The S-modified ZnAl2O4 precursor sample was transferred to a muffle furnace and calcined at 650℃ for 24h. After cooling, the S-modified ZnAl2O4 nanosheet catalyst was obtained. The heating rate of the muffle furnace was 2℃ / min.

[0061] The characterization results of the samples synthesized in Examples 1 and 14 are as follows: Figs. 1-3 As shown, the XRD phase of ZnAl2O4 after S modification is still ZnAl2O4 as the main phase. The ZnAl2O4 nanosheets changed from about 50 nm to about 10 nm before and after sulfuric acid modification, and the lattice fringe spacing was 2.89 Å.

[0062] Example 15

[0063] The difference between this embodiment and Example 14 is that the ratio of the amount of ZnAl2O4 nanosheets to sulfuric acid solution used in step 1 is 0.05 g / ml.

[0064] Example 16

[0065] The difference between this embodiment and Embodiment 14 is that the ratio of the amount of ZnAl2O4 nanosheets to sulfuric acid solution used in step 1 is 0.09 g / ml.

[0066] Example 17

[0067] The difference between this embodiment and Embodiment 14 is that the ratio of the amount of ZnAl2O4 nanosheets to sulfuric acid solution used in step 1 is 0.11 g / ml.

[0068] Example 18

[0069] The difference between this embodiment and Embodiment 14 is that the ratio of ZnAl2O4 nanosheets to sulfuric acid solution in step 1 is 0.15 g / ml.

[0070] Example 19

[0071] The difference between this embodiment and embodiment 14 is that in step 2, the furnace is calcined at 640°C for 26 hours, and the heating rate of the muffle furnace is 1.5°C / min.

[0072] Example 20

[0073] The difference between this embodiment and embodiment 14 is that in step 2, the furnace is calcined at 660°C for 22 hours, and the heating rate of the muffle furnace is 2.5°C / min.

[0074] Example 21

[0075] The difference between this embodiment and embodiment 14 is that in step 2, the furnace is calcined at 600°C for 30 hours, and the heating rate of the muffle furnace is 1°C / min.

[0076] Example 22

[0077] The difference between this embodiment and embodiment 14 is that in step 2, the furnace is calcined at 700°C for 18 hours, and the heating rate of the muffle furnace is 3°C / min.

[0078] Example 23

[0079] The difference between this embodiment and Example 14 is that step 1 uses ZnAl2O4 nanosheets prepared in Examples 2-13.

[0080] Example 24

[0081] This embodiment provides a method for catalytic hydrolysis of CF4 in aluminum electrolysis flue gas, including the following steps:

[0082] (1) The ZnAl2O4 nanosheets prepared in Example 1 and the S-modified ZnAl2O4 nanosheet catalyst prepared in Example 14 were respectively loaded into quartz tubes and the quartz tubes were loaded into the reaction chamber of the fixed bed.

[0083] (2) A mixture of CF4 and air is pre-introduced into the gas path system. The volume concentration of CF4 in the mixture is 0.25%, the volume concentration of air is 99.75%, and the flow rate of the mixture is 33.3 ml / min. After the gas path stabilizes, the fixed bed reaction chamber is heated to 580-620℃ at a rate of 8-12℃ / min. Water is introduced into the vaporization chamber through an injection pump at a rate of 0.6-0.8 ml / h to heat the vaporization chamber at a temperature of 200℃. Water vapor is then introduced into the reaction chamber.

[0084] (3) The tail gas obtained from the catalytic hydrolysis of CF4 is first passed through a deionized water bottle, then dried through a drying tube. The dried gas is then analyzed by a gas chromatograph to determine its components and content. Figs. 4-5As shown, the ZnAl2O4 nanosheets prepared in Example 1 exhibited very low catalytic activity, while the S-modified ZnAl2O4 nanosheet catalyst prepared in Example 14 achieved a 100% decomposition efficiency for the hydrolysis of CF4 at a reaction temperature of 600℃, which could be maintained for 20 hours, demonstrating good catalytic decomposition efficiency and stability. The specific decomposition efficiencies of the S-modified ZnAl2O4 nanosheet catalysts from Examples 15-26 at a reaction temperature of 600℃ are shown in Table 1.

[0085] Table 1. Performance data of S-modified ZnAl2O4 nanosheet catalysts for catalytic hydrolysis of CF4 in Examples 15-26.

[0086]

[0087] The catalytic hydrolysis activity of ZnAl2O4 nanosheets prepared in Examples 2-13 was basically the same as that in Example 1, with almost no activity (the decomposition efficiency of catalytic hydrolysis of CF4 was less than 8% at 600℃). In Example 23, the ZnAl2O4 nanosheets prepared in Examples 2-13 were used to prepare S-modified ZnAl2O4 nanosheet catalysts. The decomposition efficiency of the S-modified ZnAl2O4 nanosheet catalysts at a reaction temperature of 600℃ is shown in Table 2, which reflects the influence of different preparation process parameters of ZnAl2O4 nanosheets on the catalytic performance of S-modified ZnAl2O4 nanosheet catalysts.

[0088] Table 2 Performance data of ZnAl2O4 nanosheet catalysts with different S-modification for catalytic hydrolysis of CF4

[0089]

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing an S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas, characterized in that, Includes the following steps: Step 1: Add sulfuric acid solution to ZnAl2O4 nanosheets, stir thoroughly, and transfer to an oven. After the sample is completely dried, the S-modified ZnAl2O4 precursor sample is obtained; wherein, the ratio of ZnAl2O4 nanosheets to sulfuric acid solution is 0.09-0.11 g / ml. Sulfuric acid etching of ZnAl2O4 nanosheets exposes more active sites, thereby enabling catalytic hydrolysis of CF4; The specific preparation process of ZnAl2O4 nanosheets in step 1 is as follows: Step S1: Add aluminum nitrate nonahydrate and zinc nitrate hexahydrate to deionized water and stir thoroughly until the solution is completely clear to obtain a mixed reaction solution; Step S2: Transfer the mixed reaction solution to an oil bath, add ammonia water dropwise, and then transfer it to a centrifuge tube. After centrifugation and washing with water multiple times, place it in an oven to dry and obtain a white precursor powder. Step S3: The obtained white precursor powder is transferred to a muffle furnace, calcined at high temperature and cooled to obtain ZnAl2O4; In step S3, the obtained white precursor powder is transferred to a muffle furnace and reacted at 580~620℃ for 4~6h. After cooling to room temperature, ZnAl2O4 nanosheets are obtained. Step 2: Transfer the S-modified ZnAl2O4 precursor sample to a muffle furnace, calcine at 640~660℃ for 22~26h, and then cool to obtain the S-modified ZnAl2O4 nanosheet catalyst.

2. The method for preparing the S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas according to claim 1, characterized in that, In step S1, the molar ratio of Al:Zn ranges from 1.9 to 2.1:

1.

3. The method for preparing the S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas according to claim 1, characterized in that, In step S2, the obtained mixed reaction solution is transferred to an oil bath at a temperature of 75~85℃ and heated, while ammonia water is added dropwise during stirring.

4. The method for preparing the S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas according to claim 3, characterized in that, In step S2, ammonia is added dropwise until the pH reaches 8.5-9.

5.

5. The method for preparing the S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas according to claim 3, characterized in that, In step S2, the stirring speed during the addition of ammonia is 550-650 rpm, and the ammonia dripping rate is 2-4 ml / min.

6. The method for preparing the S-modified ZnAl2O4 nanosheet catalyst for catalytic decomposition of CF4 in aluminum electrolysis flue gas according to claim 1, characterized in that, In step S3, the heating rate of the muffle furnace is 1.5~2.5℃ / min.

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