Preparation method of catalyst for catalytic oxidation of VOCs and application of catalyst

Abstract

The invention discloses a preparation method of a catalyst for catalytic oxidation of VOCs (volatile organic compounds), which comprises the following steps: a, mixing a Pd salt solution, Zr-MOF powder and a solvent to obtain a mixed solution; b, the mixed solution obtained in the step a is filtered and washed, N, N-dimethylformamide is adopted as a washing agent for the last time of washing, then drying treatment is conducted in a drying oven, and precursor powder is obtained; and c, roasting the precursor powder obtained in the step b to prepare the catalyst for catalytic oxidation of VOCs. The preparation method is simple, the raw material cost is low, the prepared catalyst has high activity and stability, the reaction activation temperature of VOCs combustion is reduced, and the catalyst is suitable for catalytic combustion of benzene VOCs.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and specifically relates to a method for preparing a catalyst for catalytically oxidizing VOCs. Furthermore, it also relates to the application of the catalyst for catalytically oxidizing VOCs. Background Art

[0002] VOCs waste gas is highly polluting, and its large-scale emission will cause serious damage to the ecological environment, thus affecting human normal life and production. Catalytic combustion is one of the most promising VOCs pollution control technologies. One of the main challenges in the catalytic degradation of VOCs is the development of combustion catalysts with excellent performance. Precious metals have attracted widespread attention from researchers due to their excellent low-temperature catalytic activity and stability. Precious metals are expensive and scarce. In order to improve their utilization efficiency, precious metals are usually loaded onto carriers to obtain loaded catalysts. The MOF framework structure has a confinement effect, which can effectively control the uniform growth of precious metal nanoparticles on the MOF surface without agglomeration. However, the current use of MOF as a catalyst carrier still has the problem of insufficient stability. Therefore, in-depth research on the preparation method of precious metal catalysts is needed. Summary of the Invention

[0003] The present invention is based on the inventors' discovery and understanding of the following facts and problems: Although there are many types of MOFs materials, most MOFs have poor stability. Metal zirconium-based MOFs have excellent physical and chemical stability. High-temperature calcination to prepare supported zirconium-based catalysts can achieve high dispersion and strong interaction of the various elements, effectively improving catalytic performance. However, during the preparation process, zirconium-based MOFs undergo hydrolysis, resulting in structural destruction and affecting catalytic activity. Therefore, there is an urgent need to study and improve zirconium-based MOFs as supported catalysts.

[0004] The present invention aims to address, at least to a certain extent, one of the technical problems in the related art. To this end, embodiments of the present invention provide a method for preparing a catalyst for the catalytic oxidation of VOCs. The preparation method is simple, the raw material cost is low, and the resulting catalyst exhibits high activity and stability, lowers the reaction activation temperature for VOC combustion, and is suitable for use as a catalyst for the catalytic combustion of benzene-based VOCs.

[0005] The method for preparing a catalyst for catalytic oxidation of VOCs according to an embodiment of the present invention comprises the following steps:

[0006] a. mixing a Pd salt solution, Zr-MOF powder, and a solvent to obtain a mixed solution;

[0007] b. The mixed solution obtained in step a was filtered and washed, the last washing using a lotion of N, N-dimethylformamide, and then dried in an oven to obtain a precursor powder;

[0008] c. calcining the precursor powder obtained in step b to obtain a catalyst for catalytic oxidation of VOCs.

[0009] Advantages and technical effects of the preparation method of the catalyst for catalytic oxidation of VOCs in the embodiment of the present invention: 1. In the embodiment of the present invention, a metal zirconium-based MOFs material is used as a carrier material. By washing the MOFs material loaded with Pd element with N,N-dimethylformamide (DMF) as a detergent in the last washing treatment, the hydrolysis of MOFs in the subsequent high-temperature drying process is effectively inhibited, so that the drying treatment can be completed in an oven without the need for vacuum dynamic drying treatment. The crystal structure of the Zr-MOF material is well retained, which is conducive to the uniform dispersion of the Pd element on the surface of the Zr-MOF material and improves the dispersion of the precious metal; 2. The method of the embodiment of the present invention, the catalyst prepared has excellent activity and stability, has high catalytic activity for VOCs combustion reaction, and can reduce the reaction activation temperature of VOCs combustion, is suitable for use as a catalyst for catalytic combustion of VOCs, especially has excellent performance in catalytic oxidation of toluene, and has broad application prospects in the field of catalytic oxidation of organic waste gas; 3. The method of the embodiment of the present invention has a simple and easy preparation process, low raw material cost, mild process conditions, low energy consumption, no secondary pollution, and is conducive to industrial large-scale production.

[0010] In some embodiments, in step a, the Pd salt solution includes at least one of a palladium nitrate aqueous solution, a palladium chloride aqueous solution, a palladium sulfate aqueous solution, and a palladium acetate aqueous solution.

[0011] In some embodiments, in step a, the solvent comprises at least one of water or ethanol.

[0012] In some embodiments, in step a, the method for preparing the Zr-MOF powder comprises: dissolving 1,3,5-benzenetricarboxylic acid and ZrClO2·8H2O in a mixed solvent comprising DMF and formic acid, heating the mixture for reaction, and obtaining white powder Zr-MOF after filtering, washing, drying, and grinding.

[0013] In some embodiments, the reaction temperature is 100-130° C., and the reaction time is 12-48 h.

[0014] In some embodiments, in step b, the mass concentration of N,N-dimethylformamide in the detergent used in the final washing is not less than 99%.

[0015] In some embodiments, in step b, the drying temperature is 120-160° C., and the drying time is 3-6 hours.

[0016] In some embodiments, in step c, the calcination temperature is 500-800° C., and the calcination time is 2-6 hours.

[0017] In some embodiments, in step c, the mass percentage of Pd element in the prepared catalyst for catalytic oxidation of VOCs is 0.01-10%.

[0018] An embodiment of the present invention also provides a method for catalytically removing VOCs gas, comprising: subjecting VOCs gas to a combustion reaction in the presence of air, using a catalyst prepared by the method of an embodiment of the present invention. The catalyst employed in the catalytic removal method of VOCs gas in an embodiment of the present invention exhibits excellent stability and catalytic activity for the VOCs combustion reaction, effectively lowering the activation temperature of the combustion reaction, enabling the VOCs gas combustion reaction to occur at a relatively low temperature, thereby effectively reducing the energy consumption for removing VOCs and lowering processing costs.

[0019] In some embodiments, the temperature of the combustion reaction is controlled to be 210-225°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is the XRD pattern of the catalyst precursors prepared in Example 1 and Comparative Examples 1-3;

[0021] Figure 2 1 is the EDS graph of the catalyst precursors prepared in Example 1, Comparative Examples 1 and 2;

[0022] Figure 3 1 is a SEM image of Zr-MOF, precursor and catalyst prepared in Example 1, Comparative Examples 1 and 2;

[0023] Figure 4 1 is a graph showing the toluene catalytic combustion activity test of the catalysts prepared in Example 1 and Comparative Examples 1-3;

[0024] Figure 5 This is a test chart of the toluene catalytic combustion stability of the catalysts prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0026] The method for preparing a catalyst for catalytic oxidation of VOCs according to an embodiment of the present invention comprises the following steps:

[0027] a. mixing a Pd salt solution, Zr-MOF powder, and a solvent to obtain a mixed solution;

[0028] b. The mixed solution obtained in step a was filtered and washed, the last washing using a lotion of N, N-dimethylformamide, and then dried in an oven to obtain a precursor powder;

[0029] c. calcining the precursor powder obtained in step b to obtain a catalyst for catalytic oxidation of VOCs.

[0030] The preparation method of the catalyst for catalytic oxidation of VOCs according to the embodiment of the present invention uses a metal zirconium-based MOFs material as a carrier material. By washing the MOFs material loaded with the Pd element with N,N-dimethylformamide (DMF) as a detergent in the final washing process, the hydrolysis of the MOFs in the subsequent high-temperature drying process is effectively inhibited, so that the drying process can be completed in an oven without the need for vacuum dynamic drying treatment. The crystal structure of the Zr-MOF material is well retained, which is conducive to the uniform dispersion of the Pd element on the surface of the Zr-MOF material and improves the dispersion of the precious metal. The method of the embodiment of the present invention, the catalyst prepared has excellent activity and stability, has high catalytic activity for VOCs combustion reaction, and can reduce the reaction activation temperature of VOCs combustion. It is suitable for use as a catalyst for catalytic combustion of VOCs, especially for catalytic oxidation of toluene. It has excellent performance and has broad application prospects in the field of catalytic oxidation of organic waste gas. The method of the embodiment of the present invention has a simple and easy preparation process, low raw material cost, mild process conditions, low energy consumption, no secondary pollution, and is conducive to industrial large-scale production.

[0031] In some embodiments, in step a, the Pd salt solution comprises at least one of a palladium nitrate aqueous solution, a palladium chloride aqueous solution, a palladium sulfate aqueous solution, and a palladium acetate aqueous solution. In the embodiments of the present invention, there is no particular limitation on the Pd salt, and any soluble palladium salt commonly used in the prior art can be applied to the method of the present invention.

[0032] In some embodiments, in step a, the solvent comprises at least one of water or ethanol, preferably water. In the embodiments of the present invention, using water and / or ethanol as the solvent does not adversely affect the morphology of the Zr-MOF material. Preferably, water is used as the solvent because it helps increase the loading of the precious metal element.

[0033] In some embodiments, in step a, the Zr-MOF powder preparation method includes dissolving 1,3,5-benzenetricarboxylic acid and ZrClO2·8H2O in a mixed solvent including DMF and formic acid, heating the mixture for reaction, preferably at a temperature of 100-130°C for 12-48 hours, and filtering, washing, drying, and grinding to obtain a white powdered Zr-MOF. In the methods of the embodiments of the present invention, there are no particular limitations on the Zr-MOF preparation method; any Zr-MOF material prepared by conventional methods can be used as the support material in the embodiments of the present invention.

[0034] In some embodiments, in step b, the mass concentration of N,N-dimethylformamide in the detergent used in the final wash is not less than 99%. In the present invention, N,N-dimethylformamide with industrial grade purity or above is preferably used to better inhibit the hydrolysis of the Zr-MOF material and maintain its intact crystal structure.

[0035] In some embodiments, in step b, the drying temperature is 120-160° C., and the drying time is 3-6 hours. In the embodiments of the present invention, by using DMF as a washing agent in the final washing step, the hydrolysis of MOFs during high-temperature drying is effectively suppressed, and the material can be dried at a higher temperature, shortening the drying time and improving production efficiency.

[0036] In some embodiments, in step c, the calcination temperature is 500-800° C. and the calcination time is 2-6 hours. In the embodiments of the present invention, there is no particular limitation on the calcination temperature of the Zr-MOF catalyst precursor loaded with Pd element, and the calcination temperature commonly used in the prior art can be applied to the method of the present invention.

[0037] In some embodiments, in step c, the mass percentage of Pd in ​​the catalyst for catalytic oxidation of VOCs is 0.01-10%. The method of the embodiment of the present invention can make the Pd element uniformly dispersed on the surface of the Zr-MOF support material, and even with a low Pd loading, it has excellent catalytic activity for the VOCs combustion reaction.

[0038] An embodiment of the present invention further provides a method for catalytically removing VOCs gas, comprising: subjecting VOCs gas to a combustion reaction in the presence of air, using a catalyst prepared by the method of an embodiment of the present invention; preferably, the temperature of the combustion reaction is controlled to be 210-225°C. The catalyst used in the catalytic removal method of VOCs gas in an embodiment of the present invention has excellent stability and catalytic activity for the VOCs combustion reaction, and effectively lowers the activation temperature of the combustion reaction, allowing the combustion reaction of the VOCs gas to occur at a relatively low temperature, thereby effectively reducing the energy consumption for removing VOCs and lowering processing costs.

[0039] The present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0040] Example 1

[0041] Preparation of Zr-MOF: 2.52 g of 1,3,5-benzenetricarboxylic acid (H3BTC) and 11.64 g of ZrClO2·8H2O were added to a flask containing a mixed solvent of 300 mL of DMF and 300 mL of formic acid. The mixture was stirred for 1 hour until completely dissolved. Using a reflux condenser, the mixture was rapidly heated to 130°C and held for 48 hours. Centrifugation at 8000 rpm for 5 minutes yielded a white precipitate. The precipitate was washed with DMF and then shaken for 10-15 minutes. This process was repeated three times. The mixture was then dynamically dried at 80°C overnight under vacuum. After drying, the Zr-MOF was ground to obtain a white powder.

[0042] Preparation of catalyst precursor: Take 0.1 ml of 54 mg Pd / ml palladium nitrate aqueous solution and add it to 150 ml of deionized water, add 2 g of the Zr-MOF powder prepared above to the solution, stir at room temperature (25°C) for 1 hour, centrifuge at 8000 r / min for 5 minutes, wash twice with deionized water, and finally wash once with 99.5 wt% DMF as a lotion, dry at 130°C for 5 hours, and grind to obtain catalyst precursor powder after drying.

[0043] Preparation of catalyst: The precursor powder was heated to 700° C. at a heating rate of 2.5° C. / min and calcined at 700° C. for 3 h to obtain a catalyst material, wherein the mass percentage of Pd element in the catalyst was 0.47 wt %.

[0044] The XRD pattern of the catalyst precursor prepared in this example is shown in Figure 1 The EDS pattern of the prepared catalyst precursor is shown in Figure 2 The SEM images of the prepared Zr-MOF, catalyst precursor and catalyst are shown in Figure 3 .

[0045] Example 2

[0046] The method is the same as that in Example 1, except that the solvent used in preparing the catalyst precursor is ethanol. Specifically, 0.5 ml of a 54 mg Pd / ml palladium nitrate aqueous solution is added to 150 ml of ethanol, and then Zr-MOF powder is added to the solution.

[0047] In the catalyst prepared in this example, the mass percentage of Pd element in the catalyst is 0.36 wt %.

[0048] Example 3

[0049] The method is the same as that of Example 1, except that in the preparation of the catalyst precursor, the washing treatment is first washed twice with ethanol and finally washed once with 99.5 wt % DMF as a washing agent.

[0050] Example 4

[0051] The method is the same as that of Example 1, except that the amount of palladium salt used is different. The mass percentage of Pd element in the prepared catalyst is 0.2%.

[0052] Comparative Example 1

[0053] The method is the same as that in Example 1, except that in the preparation of the catalyst precursor, the last washing step is not performed with DMF, but with deionized water, that is, deionized water is used for three washing steps.

[0054] The XRD pattern of the catalyst precursor prepared in this comparative example is shown in Figure 1 The EDS pattern of the prepared catalyst precursor is shown in Figure 2 The SEM images of the prepared Zr-MOF, catalyst precursor and catalyst are shown in Figure 3 .

[0055] Comparative Example 2

[0056] The method is the same as that in Example 1, except that in the preparation of the catalyst precursor, ethanol with a purity of 99.9 wt% is used instead of DMF for the last washing treatment.

[0057] The XRD pattern of the catalyst precursor prepared in this comparative example is shown in Figure 1 The EDS pattern of the prepared catalyst precursor is shown in Figure 2 The SEM images of the prepared Zr-MOF, catalyst precursor and catalyst are shown in Figure 3 .

[0058] Comparative Example 3

[0059] The method is the same as that of Example 2, except that in the preparation of the catalyst precursor, ethanol with a purity of 99.9 wt % is used instead of DMF for the last washing treatment.

[0060] The XRD pattern of the catalyst precursor prepared in this comparative example is shown in Figure 1 .

[0061] The catalysts prepared in the examples and comparative examples were tested for VOCs catalytic activity.

[0062] Test method: The test gas used is air, with a toluene concentration of 1000ppm and a total gas flow rate of 300mL·min -1 , the reaction mass space velocity is 180,000 mL·h -1 ·g -1 Under the action of the catalysts prepared in each embodiment and comparative example, combustion reactions were carried out at different test temperatures to test the activity and stability of the catalysts. The test results are shown in Table 1 and Figure 4 and Figure 5 .

[0063] Table 1

[0064] Reaction temperature Toluene conversion Example 1 210℃ 98％ Example 2 219℃ 98％ Example 3 225℃ 98％ Example 4 221℃ 98％ Comparative Example 1 260℃ 94％ Comparative Example 2 230℃ 98％ Comparative Example 3 241℃ 96％

[0065] As can be seen from Table 1, the catalysts prepared in Examples 1-4 exhibited more excellent catalytic activity, and the activation temperature of the toluene combustion reaction was low. At a reaction temperature of 210-225°C, the toluene conversion rate could reach 98%. In particular, the catalyst prepared in Example 1 could reduce the activation temperature to 206°C. Figure 4 The activation temperature in the present invention refers to the minimum reaction temperature required for the catalyst to show activity, usually referring to the minimum reaction temperature T50 at which the VOCs conversion rate reaches 50%.

[0066] pass Figure 1 and Figure 3 It can be seen that in the method of Comparative Example 1, water is used as the washing agent in the last washing, and the crystal phase and morphology of the catalyst precursor obtained are significantly changed compared with the unloaded support material Zr-MOF. The crystallinity of the precursor after loading the Pd element is reduced, and the regular octahedral structure is destroyed. This is because the support material Zr-MOF is hydrolyzed during the drying process at 130°C, and the structure is destroyed. The hydrolysis process is shown in formula (1).

[0067]

[0068] In the method of Comparative Example 2, ethanol was used as the washing agent in the last washing. Similarly, the morphology of the precursor changed compared with the carrier material Zr-MOF. The carrier material Zr-MOF loaded with Pd element was hydrolyzed during the high-temperature drying process, the structure was destroyed to a certain extent, and the precious metals agglomerated. The hydrolysis process is shown in formula (2).

[0069]

[0070] Further through Figure 2 It can be seen that the Pd on the surface of the catalyst precursor of Example 1 is more evenly dispersed; the Pd on the surface of the catalyst precursor of Comparative Example 1 is severely agglomerated, mainly because the last time water is used as a wash solvent, the precursor is hydrolyzed during the high-temperature drying process, and the regular octahedral structure is destroyed; in Comparative Example 2, ethanol is used as a wash solvent for the last time, which also causes the precursor to be hydrolyzed during the high-temperature drying process, and the Pd on the surface of the catalyst precursor undergoes a certain degree of agglomeration.

[0071] In the preparation method of Example 1, DMF was used as a washing agent in the last washing. Figure 3 It can be seen that there is no obvious change in the morphology of the precursor material compared with the support material Zr-MOF, indicating that Zr-MOF did not react during the oven drying process at 130°C, and the crystal structure of Zr-MOF was well preserved, which is conducive to the uniform dispersion of the Pd element, thereby improving the activity of the catalyst, and the activation temperature of toluene combustion can be reduced to 206°C. At a reaction temperature of 210°C, the toluene conversion rate can reach 98%.

[0072] Figure 5 This is a catalyst stability test diagram. Figure 5 It can be seen that the toluene conversion rate of the catalyst prepared in Example 1 was able to be stably maintained at approximately 98% after operating at 210°C for 100 hours, demonstrating that the catalyst prepared by the method of the present invention has a stable structure and exhibits excellent catalytic stability. In contrast, in Comparative Example 1, due to the use of water as the final wash solvent, the crystal structure of the Zr-MOF support material was destroyed. As a result, the toluene conversion rate dropped from 82% to 73% after operating at 220°C for 100 hours. The stability of the catalyst in Comparative Example 1 at 220°C was significantly reduced compared to that in Example 1.

[0073] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0074] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a catalyst for catalytic oxidation of VOCs, characterized in that: The steps include: a. mixing a Pd salt solution, Zr-MOF powder, and a solvent to obtain a mixed solution; b. The mixed solution obtained in step a was filtered and washed, the last washing using a lotion of N, N-dimethylformamide, and then dried in an oven to obtain a precursor powder; c. calcining the precursor powder obtained in step b to obtain a catalyst for catalytic oxidation of VOCs.

2. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In the step a, the Pd salt solution includes at least one of a palladium nitrate aqueous solution, a palladium chloride aqueous solution, a palladium sulfate aqueous solution, and a palladium acetate aqueous solution.

3. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In the step a, the solvent includes at least one of water or ethanol.

4. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In step a, the preparation method of the Zr-MOF powder includes: dissolving 1,3,5-benzenetricarboxylic acid and ZrClO2·8H2O in a mixed solvent including DMF and formic acid, heating for reaction, and obtaining white powder Zr-MOF after filtering, washing, drying and grinding.

5. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 4, characterized in that: The reaction temperature is 100-130° C., and the reaction time is 12-48 hours.

6. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In the step b, the mass concentration of N,N-dimethylformamide in the detergent used in the final washing is not less than 99%; And / or, the drying temperature is 120-160° C., and the drying time is 3-6 hours.

7. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In the step c, the calcination temperature is 500-800° C., and the calcination time is 2-6 hours.

8. The method for preparing a catalyst for catalytic oxidation of VOCs according to claim 1, characterized in that: In the step c, the mass percentage of the Pd element in the prepared catalyst for catalytic oxidation of VOCs is 0.01-10%.

9. A method for catalytic removal of VOCs gas, characterized in that: The VOCs gas is subjected to a combustion reaction in the air, and the catalyst used is a catalyst prepared by the method according to any one of claims 1 to 8.

10. The method for catalytic removal of VOCs gas according to claim 9, characterized in that: The temperature of the combustion reaction is controlled at 210-225°C.

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