A cobalt-nickel catalyst for catalytic degradation of VOCs at low temperature and a preparation method thereof

Abstract

The application discloses a cobalt-nickel catalyst for catalytic degradation of VOCs at low temperature and a preparation method thereof. Co(NO3)3.6H2O and Ni(NO3)3.6H2O are dissolved in ethylene glycol according to a mass ratio of more than 5:1, and hexadecyl trimethyl ammonium bromide is added under continuous stirring to form a solution; then, urea is introduced into the solution, and after stirring is completed, the mixture is transferred into a stainless steel autoclave lined with polytetrafluoroethylene, the autoclave is placed in an oven for several hours; after cooling to room temperature, the precipitate is centrifuged, washed and dried; and the cobalt-nickel catalyst is obtained by calcination under an air atmosphere. The catalyst prepared by the method has stable performance, can realize 90% degradation of propane at 195 DEG C, and can realize complete degradation of propane at 200 DEG C; and has certain stability and anti-poisoning performance in a sulfur-containing environment. The preparation method is simple and suitable for batch preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a cobalt-nickel catalyst for catalytic degradation of VOCs at low temperature and a preparation method thereof. Background Art

[0002] VOCs are important precursors to PM2.5 and ozone in the atmosphere, posing significant risks to human health and the environment. Propane, a VOC with stable CC and CH bonds, is difficult to completely oxidize at low temperatures, making its catalytic degradation a key environmental issue. To reduce VOC emissions and achieve environmentally friendly production, the development of efficient catalysts for the low-temperature catalytic degradation of propane is crucial.

[0003] Single-component transition metal oxide catalysts have limited effectiveness in catalyzing the degradation of VOCs. The synergistic effect between the different metal components in composite catalysts helps enhance electron mobility, improve the catalyst's redox capacity and the rate of reactive oxygen species generation, thereby significantly improving the low-temperature catalytic degradation efficiency of VOCs. Therefore, further exploration of composite catalysts for low-temperature VOC degradation is highly desirable. Summary of the Invention

[0004] In order to solve at least one of the above problems, the present invention provides a cobalt-nickel catalyst for catalytic degradation of VOCs at low temperature and a preparation method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical means:

[0006] The first aspect of the present invention provides a method for preparing a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs, comprising the following steps:

[0007] (1) Dissolve Co(NO3)3·6H2O and Ni(NO3)3·6H2O in ethylene glycol at a molar ratio of (1-9):1, add hexadecyltrimethylammonium bromide while stirring continuously, and stir to form a pink homogeneous solution;

[0008] (2) Introduce urea into the solution, seal it, and continue stirring for several hours;

[0009] (3) After stirring, the mixture was transferred to a PTFE-lined stainless steel autoclave and the autoclave was placed in an oven for several hours;

[0010] (4) The autoclave was cooled to room temperature, the resulting precipitate was centrifuged, and the precipitate was washed alternately with ethanol and deionized water and dried;

[0011] (5) The dried precipitate is calcined in an air atmosphere according to a heating program to obtain a cobalt-nickel catalyst.

[0012] In some embodiments of the present invention, in step (2), the molar ratio of urea / (Co+Ni) is 1.50.

[0013] In some embodiments of the present invention, in step (3), the temperature in the oven is 180-200° C. and the holding time is 10-12 h.

[0014] In some embodiments of the present invention, in step (4), the temperature of the drying step is 80-90° C., and the drying time is 10-12 h.

[0015] In some embodiments of the present invention, in step (5), the heating rate of the temperature program is (4-6) °C / min.

[0016] In some embodiments of the present invention, in step (5), the calcination temperature is 250-350° C. and the calcination time is 4-6 hours.

[0017] The second aspect of the present invention provides a cobalt-nickel catalyst prepared by the method described in the first aspect.

[0018] The third aspect of the present invention provides the use of the cobalt-nickel catalyst described in the second aspect in the low-temperature catalytic degradation of VOCs.

[0019] In some embodiments of the present invention, the VOCs are short-chain alkanes such as propane and ethane.

[0020] In some embodiments of the present invention, the temperature is between 180° C. and 230° C. In some embodiments of the present invention, the catalytic degradation temperature of propane is below 200° C.

[0021] Beneficial effects of the present invention

[0022] Compared with the existing technology, the present invention has the following advantages: the present invention provides a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs prepared by a solvent thermal method. The catalyst prepared by the solvent thermal method has stable performance and can achieve a 90% propane degradation rate at 195°C and complete propane degradation at 200°C. The preparation method is simple and suitable for batch production. At the same time, the composite catalyst is composed of Co and Ni in a certain ratio. When the Co:Ni ratio is greater than 5:1, it can meet the T requirement for propane catalytic degradation. 90 The catalytic temperatures are all below 200°C, and when the Co:Ni ratio is 9:1, the catalytic temperature is the lowest, 195°C, which is lower than that of the existing disclosed propane catalysts. In addition, the catalyst has certain sulfur resistance and has certain stability and anti-poisoning performance in a sulfur-containing environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure shows the comparison of the catalytic effects of the catalysts prepared in Examples 1-3 of the present invention on propane;

[0024] Figure 2 The figure shows the comparison of the catalytic effects of the catalysts prepared in Examples 1, 4-7 of the present invention on propane;

[0025] Figure 3 The figures show a comparison of the catalytic effects of the catalysts prepared in Examples 8-10 of the present invention and Comparative Examples 1-2 on propane;

[0026] Figure 4 The figures show the comparison of the catalytic effects of the catalysts prepared in Examples 10-12 of the present invention on propane;

[0027] Figure 5 The figure shows the comparison of propane catalytic effects of catalysts prepared by different preparation methods;

[0028] Figure 6 The SEM morphology comparison of catalysts prepared by different preparation methods is shown; among them, (a) is Co9Ni1_P, (b) is Co9Ni1_R, and (c) is Co9Ni1_S;

[0029] Figure 7 The surface elemental composition analysis diagram of the Co9Ni1_P catalyst prepared in Example 10 is shown;

[0030] Figure 8 The sulfur resistance test results of the Co9Ni1_P catalyst prepared in Example 10 at T = 250 ° C are shown;

[0031] Figure 9 The sulfur resistance test results of the Co9Ni1_P catalyst prepared in Example 10 at T = 300 ° C are shown;

[0032] Figure 10 The catalytic degradation effect of Co9Ni1 catalyst on propane at different gas hourly space velocities is shown;

[0033] Figure 11 The comparison of the catalytic effects of the catalysts repeatedly prepared by the method of the present invention on propane is shown;

[0034] Figure 12 The catalytic effect of Co9Ni1 catalyst on ethane and propane is shown. DETAILED DESCRIPTION

[0035] The following examples are provided to illustrate preferred embodiments of the present invention. Those skilled in the art will appreciate that the techniques disclosed in the following examples represent techniques discovered by the inventors that can be used to practice the present invention and, therefore, can be considered preferred embodiments of the present invention. However, those skilled in the art will appreciate from this disclosure that many modifications may be made to the specific embodiments disclosed herein while still achieving 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 one skilled in the art to which this invention belongs, and the disclosures herein and the materials they cite are hereby incorporated by reference. Those skilled in the art will recognize or be able to ascertain, through routine experimentation, many technical equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the claims.

[0037] The technical solution of the present application will be further described in detail below in conjunction with specific implementation methods.

[0038] Example 1 Preparation of Mn5Ce1 Catalyst

[0039] The preparation process is as follows:

[0040] Dissolve 12.5 mmol of Mn(NO3)2·H2O and 2.5 mmol of Ce(NO3)3·6H2O in 30 mL of deionized water; mix 20 mmol of NaOH and 5 mmol of anhydrous Na2CO3 and dissolve them in 30 mL of deionized water; then alternately introduce the two solutions into 25 mL of deionized water, controlling the solution pH = 10±0.5; after the titration is completed, centrifuge the precipitate, wash and dry it; and calcine it in an air atmosphere to obtain the Mn5Ce1 catalyst.

[0041] Example 2 Preparation of Co5Mn1 Catalyst

[0042] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 12.5 mmol of Co(NO3)3·6H2O and 2.5 mmol of Mn(NO3)2·H2O.

[0043] Example 3 Preparation of Co5Ni1 Catalyst

[0044] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 12.5 mmol of Co(NO3)3·6H2O and 2.5 mmol of Ni(NO3)3·6H2O.

[0045] The catalysts obtained by compounding different transition metals in Examples 1 to 3 were prepared at C3H8=2,000ppm and WHSV=30,000 h -1 Under the reaction conditions, the catalytic degradation effects of the three were compared, and the results were as follows Figure 1 shown.

[0046] The results showed that the Mn5Ce1 catalyst, with Mn as the primary active phase, could only achieve complete propane degradation at temperatures above 300°C, and its catalytic activity was significantly lower than that of the Co5Mn1 and Co5Ni1 catalysts, which have Co as the primary active phase. This preliminarily confirmed that the composite system with Co as the primary active phase has superior catalytic oxidation activity for propane.

[0047] Example 4 Preparation of Mn2Ce1 Catalyst

[0048] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 10 mmol of Mn(NO3)2·H2O and 5 mmol of Ce(NO3)3·6H2O.

[0049] Example 5 Preparation of Mn1Ce1 Catalyst

[0050] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 7.5 mmol of Mn(NO3)2·H2O and 7.5 mmol of Ce(NO3)3·6H2O.

[0051] Example 6 Preparation of Mn1Ce2 Catalyst

[0052] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 5 mmol of Mn(NO3)2·H2O and 10 mmol of Ce(NO3)3·6H2O.

[0053] Example 7 Preparation of Mn1Ce5 Catalyst

[0054] The preparation process is the same as that of Example 1, except that the components in the metal salt solution are 2.5 mmol of Mn(NO3)2·H2O and 12.5 mmol of Ce(NO3)3·6H2O.

[0055] The degradation effects of propane on the Mn-Ce catalysts prepared with different Mn-Ce composite ratios in Examples 1, 4 to 7 were compared. The results are as follows: Figure 2 shown.

[0056] The results show that the degradation effects of Mn-Ce catalysts with different proportions on propane are in the order of Mn1Ce1>Mn2Ce1>Mn5Ce1>Mn1Ce2>Mn1Ce5. Although regulating the composite proportion helps to improve the catalytic activity of Mn-Ce, the most superior Mn1Ce1 still needs a reaction temperature of 275°C to achieve complete degradation of propane, and the low-temperature activity is still significantly different from that of Co-based catalysts, and still has certain limitations.

[0057] Example 8 Preparation of Co1Ni1 catalyst

[0058] The preparation process is the same as that in Example 1, except that the components in the metal salt solution are 7.5 mmol of Co(NO3)3·6H2O and 7.5 mmol of Ni(NO3)3·6H2O.

[0059] Example 9 Preparation of Co5Ni1 catalyst

[0060] The preparation process is the same as that in Example 1, except that the components in the metal salt solution are 12.5 mmol of Co(NO3)3·6H2O and 2.5 mmol of Ni(NO3)3·6H2O.

[0061] Example 10 Preparation of Co9Ni1 catalyst

[0062] The preparation process is the same as that in Example 1, except that the components in the metal salt solution are 13.5 mmol of Co(NO3)3·6H2O and 1.5 mmol of Ni(NO3)3·6H2O.

[0063] Preparation of Co3O4 catalyst in Comparative Example 1

[0064] The preparation process is the same as that in Example 1, except that the components in the metal salt solution are 15 mmol of Co(NO3)3·6H2O.

[0065] Preparation of NiO2 catalyst in Comparative Example 2

[0066] The preparation process is the same as that in Example 1, except that the components in the metal salt solution are 15 mmol of Ni(NO3)3·6H2O.

[0067] The Co-Ni catalysts prepared in Examples 8 to 10 with different Co-Ni composite proportions and the catalysts prepared in Comparative Examples 1 and 2 were compared in terms of degradation effect on propane, and the results are shown in Table 1. Figure 3

[0068] ​The results showed that the composite catalyst with Co as the main active phase had excellent catalytic oxidation activity for propane. When the Co:Ni ratio was greater than 5:1, the T 90 All of them are below 200℃, and when the Co:Ni ratio is 9:1, the catalytic temperature is the lowest, which is 195℃.

[0069] In Examples 1 to 10, the co-precipitation method was used to prepare the catalyst. During the investigation, it was found that the co-precipitation method was affected by factors such as unstable solution pH and fluctuations in titration rate, which would cause the catalyst particles to agglomerate and affect the uniformity, and there was a certain fluctuation in the activity of the catalysts in different batches.

[0070] To this end, we explored different preparation methods.

[0071] Example 11 Preparation of Co9Ni1 Catalyst by Hydrothermal Method

[0072] The preparation process is as follows:

[0073] 13.5 mmol of Co(NO3)3·6H2O and 1.5 mmol of Ni(NO3)3·6H2O were dissolved in 60 mL of deionized water and stirred to form a solution. 30 mmol of urea was then introduced into the solution. After stirring, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in an oven at 180°C for 12 hours. The mixture was cooled to room temperature, the precipitate was centrifuged, washed, and dried, and then calcined in an air atmosphere to obtain the Co9Ni1 catalyst prepared by the hydrothermal method.

[0074] Example 12 Preparation of Co9Ni1 Catalyst by Solvothermal Method

[0075] The preparation process is as follows:

[0076] 13.5 mmol of Co(NO3)3·6H2O and 1.5 mmol of Ni(NO3)3·6H2O were dissolved in 60 mL of ethylene glycol, and 15 mmol of hexadecyltrimethylammonium bromide was added under constant stirring to form a solution. Subsequently, 22.5 mmol of urea was introduced into the solution. After stirring, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave, which was placed in an oven at 180°C for 12 hours. The mixture was cooled to room temperature, the precipitate was centrifuged, washed and dried, and calcined in an air atmosphere to obtain the Co9Ni1 catalyst prepared by the solvothermal method.

[0077] The catalytic degradation effects of Co9Ni1 catalysts prepared by coprecipitation, hydrothermal and solvent thermal methods in Examples 10 to 12 were compared for propane. Figure 4 shown.

[0078] The results showed that compared with the hydrothermal method and co-precipitation method, the Co9Ni1 catalyst prepared by the solvothermal method with hexadecyltrimethylammonium bromide as an additive showed better catalytic performance at low temperature: at 2,000 ppm propane and a mass space velocity of 30,000 mL g -1 h -1 Under the conditions of 195℃, a propane degradation rate of 90% can be achieved, and at 200℃, propane can be completely degraded.

[0079] Example 13 Co9Ni1 catalyst morphology control

[0080] The preparation process was the same as that of Example 12. During the preparation process, ammonia water and oleylamine were used instead of cetyltrimethylammonium bromide (CTAB) to assist in constructing a reducing solution atmosphere, and Co9Ni1_R and Co9Ni1_S catalysts were prepared. The catalyst prepared by adding cetyltrimethylammonium bromide (CTAB) in Example 12 was named Co9Ni1_P.

[0081] (1) The Co9Ni1 catalyst prepared above was used to compare the catalytic degradation effect of propane. The results are as follows: Figure 5 shown.

[0082] The results showed that among the three catalysts, the Co9Ni1_P catalyst exhibited the best performance in the catalytic degradation of propane alone. The Co9Ni1_R and Co9Ni1_S catalysts also exhibited excellent low-temperature activity, further validating the superior performance of this active component formulation in propane degradation reactions. The degradation performance of the three catalysts under single propane conditions showed little difference, and all were able to achieve complete propane conversion at approximately 200°C.

[0083] (2) The surface structure of the Co9Ni1 catalyst prepared above was observed using a field emission scanning electron microscope (SEM) of the German ZEISS Gemini SEM 360. The morphology comparison diagram is shown in FIG. Figure 6 As shown, (a) is the SEM characterization results of Co9Ni1_P, (b) is Co9Ni1_R, and (c) is Co9Ni1_S.

[0084] The results showed that the Co9Ni1_P catalyst prepared by the solvothermal method using CTAB as an additive exhibited a granular morphology with a high specific surface area, providing more active sites, which may be the reason for its relatively high catalytic activity. By adding different additives, catalysts with different morphologies can be prepared: Co9Ni1_R with a nanorod structure and Co9Ni1_S with a porous sheet structure.

[0085] (3) The elemental composition of the catalyst surface was analyzed using a field emission electron microscope (ZEISS Gemini SEM 360) from Germany. Figure 7 shown.

[0086] The results showed that the Co and Ni elements of Co9Ni1_P were evenly distributed and the O content was rich, as observed by electron scanning images, indicating that the solvothermal method can achieve good dispersion of different elements and thus optimize the synergistic effect between different components.

[0087] (4) In addition to the original reaction gas, 50 ppm of SO2 was introduced to simulate the actual industrial sulfur-containing atmosphere. The sulfur resistance of the Co9Ni1_P catalyst was evaluated at temperatures of T = 250 ° C and T = 300 ° C. The results are shown in Figure 2. Figure 8 and Figure 9 shown.

[0088] The results showed that at 250°C, the Co9Ni1_P catalyst rapidly deactivated in an atmosphere containing 50 ppm SO2. However, at 300°C, the catalyst maintained 100% propane conversion within 10 hours and >90% conversion efficiency within 16 hours. This demonstrates that the Co9Ni1_P composite catalyst exhibits considerable stability and resistance to poisoning in sulfur-containing environments.

[0089] (5) At a gas hourly space velocity of 30,000 h -1 、60,000mL h -1 、90,000mL h -1 The catalytic degradation effect of Co9Ni1_P catalyst on propane was tested under the following conditions. Figure 10 shown.

[0090] The results showed that the Co9Ni1 catalyst had a gas hourly space velocity of 30,000 h -1 Under the conditions of propane catalytic degradation, T 90 Below 195℃, at around 200℃, complete degradation can be achieved.

[0091] (6) The Co9Ni1_P catalyst was re-prepared using the method of Example 15 and tested for propane catalytic degradation. The results are as follows: Figure 11 shown.

[0092] The results showed that the performance of catalysts prepared by the solvothermal method from different batches remained basically consistent, showing good repeatability.

[0093] (7) The catalytic degradation effect of ethane was tested using Co9Ni1_P catalyst. The results are as follows: Figure 12 shown.

[0094] The results show that the Co9Ni1_P catalyst can also achieve low-temperature catalysis of ethane. 90 At around 225°C, complete degradation can be achieved at around 250°C.

[0095] All documents mentioned in this application are incorporated herein by reference, just as if each document were incorporated herein by reference individually. It should also be understood that after reading the above teachings of the present invention, those skilled in the art may make various changes or modifications to the present invention, and that such equivalents also fall within the scope of the present application.

Claims

1. A method for preparing a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs, characterized in that: The steps include: (1) Dissolve Co(NO3)3·6H2O and Ni(NO3)3·6H2O in ethylene glycol at a molar ratio greater than 5:1, add an equal amount of hexadecyltrimethylammonium bromide while stirring continuously, and stir to form a pink homogeneous solution; (2) Introduce urea into the solution, seal it, and continue stirring for several hours; (3) After stirring, the mixture was transferred to a PTFE-lined stainless steel autoclave and the autoclave was placed in an oven for several hours; (4) The autoclave was cooled to room temperature, the resulting precipitate was centrifuged, and the precipitate was washed alternately with ethanol and deionized water and dried; (5) calcining the dried precipitate in an air atmosphere according to a temperature increase program to obtain a cobalt-nickel catalyst; In the step (2), the molar ratio of urea / (Co+Ni) is 1.50; in the step (5), the heating rate of the heating program is (4-6)°C / min.

2. The method for preparing a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs according to claim 1, characterized in that: In the step (3), the temperature in the oven is 180-200°C and the maintenance time is 10-12 hours.

3. The method for preparing a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs according to claim 1, characterized in that: In the step (4), the temperature of the drying step is 80-90°C and the drying time is 10-12 hours.

4. The method for preparing a cobalt-nickel catalyst for low-temperature catalytic degradation of VOCs according to claim 1, characterized in that: In the step (5), the calcination temperature is 250-350° C. and the calcination time is 4-6 hours.

5. A cobalt-nickel catalyst prepared by the method according to any one of claims 1 to 4.

6. Use of the cobalt-nickel catalyst as claimed in claim 5 in the low-temperature catalytic degradation of VOCs.

7. The use according to claim 6, characterized in that: The VOCs are short-chain alkanes propane and ethane.

8. The use according to claim 6, characterized in that: The low temperature is between 180°C and 230°C, which is the T90 temperature for catalytic degradation of VOCs.

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