A preparation method and application of Co2NiO4 / CrO x composite catalyst

Abstract

The present invention provides a preparation method and application of a Co2NiO4 / CrO x composite catalyst, including: Step 1, preparing a CoNi-MOF precursor by a solvothermal method; Step 2, in-situ growing CrO x on the CoNi-MOF precursor by a hydrothermal method. This composite catalyst is applied to the thermal catalytic oxidation and decomposition of toluene. The preparation method of the present invention is economical and green, and the prepared catalyst has the characteristics of complete grain development, small and uniform particle size, and high yield. The composite catalyst of the present invention can efficiently catalytically oxidize and decompose toluene at a lower temperature, with high catalytic efficiency, a toluene conversion rate of more than 90% and good stability. T 50 is 169 °C, and T 90 is 218 °C.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, relates to spinel catalysts, and specifically relates to a preparation method and application of a Co2NiO4 / CrO x composite catalyst. Background Art

[0002] Volatile organic compounds (VOCs) are a type of air pollutant with a boiling point range of 50 - 260 °C at room temperature and atmospheric pressure. They are toxic and carcinogenic. Most volatile organic compounds not only damage the ozone layer, but more seriously, they form photochemical smog by reacting with other air-borne pollutants (such as nitrogen oxides and sulfur oxides), and also pose a threat to human health. With the acceleration of industrialization and economic growth, driven by increasingly strict emission standards, various technologies (such as adsorption, condensation, thermal combustion, non-thermal plasma, biotechnology, photocatalysis, and thermal catalytic oxidation) have been applied to VOCs elimination. Among them, thermal catalytic oxidation (which oxidizes and decomposes VOCs by relying on a catalyst through heating to supply energy, so that the gas is purified) has been considered one of the most promising technologies due to its high efficiency, low operating temperature, and fewer secondary pollutants. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a preparation method of a Co2NiO4 / CrO x composite catalyst to solve the technical problem that the catalytic performance of the VOCs catalyst prepared by the existing preparation method needs to be further improved.

[0004] Another purpose of the present invention is to provide an application of a Co2NiO4 / CrO x composite catalyst to solve the technical problem that the lower limit of the reaction temperature is high when the existing catalyst efficiently catalytically oxidizes toluene.

[0005] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] A preparation method of a Co2NiO4 / CrO x composite catalyst, the method comprising the following steps:

[0007] Step 1, preparing a CoNi-MOF precursor by a solvothermal method:

[0008] Step 101, adding cobalt nitrate hexahydrate and nickel nitrate hexahydrate into dimethylformamide (DMF), adding ethanol and deionized water thereto, using 2,5-dihydroxyterephthalic acid as a ligand, adding it to the solution, continuously stirring at 300 - 500 rpm / min for 30 - 60 min until completely dissolved to obtain a mixed solution, denoted as A.

[0009] Step 102: Add A into a hydrothermal reactor with a polytetrafluoroethylene inner lining to obtain a suspension, denoted as B.

[0010] Step 103: Centrifuge, wash, dry, and grind B to obtain CoNi-MOF precursor powder, denoted as C.

[0011] Step 2: In-situ grow CrO on the CoNi-MOF precursor by hydrothermal method x :

[0012] Step 201: Add chromium(III) nitrate nonahydrate to C and add deionized water, then perform ultrasonic treatment for 0.5 - 1 h and stir for 30 - 60 min to obtain a mixed solution, denoted as D.

[0013] Step 202: Add D into a hydrothermal reactor with a polytetrafluoroethylene inner lining at the same temperature and reaction time to obtain a suspension, denoted as E.

[0014] Step 203: Centrifuge, wash, dry under the same conditions, grind, calcine at 450 - 650 °C for 3 - 5 h, and grind finely to obtain the finished Co2NiO4 / CrO x composite catalyst.

[0015] The present invention also has the following technical features:

[0016] Preferably, in step 101, cobalt(II) nitrate hexahydrate and nickel(II) nitrate hexahydrate are added into 100 - 160 mL of DMF, and the molar ratio of cobalt(II) nitrate hexahydrate:nickel(II) nitrate hexahydrate:2,5-dihydroxyterephthalic acid is 1:2:0.5 - 2:1:1.

[0017] Preferably, in step 101, the molar ratio of DMF:ethanol:water is 10:1:1 - 15:1:1.

[0018] Preferably, in step 102, add A into a hydrothermal reactor with a polytetrafluoroethylene inner lining, heat up to 120 - 150 °C, and react for 24 - 28 h to obtain a suspension, denoted as B.

[0019] Preferably, in step 103, centrifuge, wash, dry at 80 - 120 °C, and grind B to obtain a spindle-shaped CoNi-MOF precursor powder, denoted as C.

[0020] Preferably, in step 201, add chromium(III) nitrate nonahydrate to C, control the addition amount of chromium(III) nitrate nonahydrate to be 5.2 wt% of sample C, perform ultrasonic treatment for 0.5 - 1 h, stir for 30 - 60 min to obtain a mixed solution, denoted as D. And the ratio of C:deionized water is 1 g:100 mL.

[0021] Preferably, in step 202, D is added to a hydrothermal autoclave with a polytetrafluoroethylene inner lining, the temperature is raised to 120 - 150 °C, and the reaction is carried out for 24 - 28 h to obtain a suspension, denoted as E.

[0022] Preferably, in step 203, E is centrifuged, washed, dried under the same conditions, ground, calcined at 450 - 650 °C, held for 3 - 5 h, and then finely ground to obtain the finished Co2NiO4 / CrO x composite catalyst.

[0023] The present invention also protects the Co2NiO4 / CrO x composite catalyst prepared by the preparation method of the above-mentioned Co2NiO4 / CrO x application of the composite catalyst in the thermal catalytic oxidation decomposition of toluene.

[0024] Specifically, 0.1 g of the Co2NiO4 / CrO x composite catalyst is placed in a fixed-bed reactor. The reactant feed is toluene with a mass concentration of 1000 ppm, 20 vol% O2 and N2 balance gas. The total gas flow rate is controlled to be 60 mL / min, the space velocity is 36000 mL / (g·h), and the reaction temperature is 50 - 370 °C. Toluene is thermally catalytically oxidized and decomposed into CO2 and H2O.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (Ⅰ) The preparation method of the present invention uses the solvothermal method in the first step to prepare the CoNi-MOF precursor, and then uses the hydrothermal method in the second step to in-situ grow CrO x on the CoNi-MOF precursor. After calcination, the Co2NiO4 / CrO x composite catalyst is obtained. This preparation method is economical, green, and the prepared catalyst has the characteristics of complete grain development, small particle size and uniform distribution, and high yield.

[0027] (Ⅱ) The preparation method of the present invention uses 2,5-dihydroxyterephthalic acid as a ligand to form a spindle-shaped CoNi-MOF precursor in the previous synthesis process, which has the advantages of simple process, high yield and low cost.

[0028] (Ⅲ) The spindle-shaped CoNi-MOF precursor synthesized in the previous step of the preparation method of the present invention can form a support system for the subsequent reaction in the reaction system, allowing CrO x to grow in-situ on it to a higher degree, which well solves the problem of difficult dispersion and easy aggregation of CrO x . Moreover, the overall experimental conditions required are mild, the pollution is small, and the yield is high.

[0029] (Ⅳ) In the present invention, CrO is in-situ grown on a shuttle-shaped CoNi-MOF precursor x , and by controlling the hydrothermal time in the synthesis process and regulating the ratio, the catalytic activity problem of the catalyst is solved, so that the Co2NiO4 / CrO x composite catalyst has excellent catalytic performance.

[0030] (Ⅴ) The composite catalyst of the present invention can efficiently catalytically oxidize and decompose toluene at a relatively low temperature, with high catalytic efficiency, a toluene conversion rate of more than 90% and good stability. T 50 is 169 °C, and T 90 is 218 °C. Description of the Drawings

[0031] Figure 1 is the SEM image of the composite catalyst prepared in Example 1.

[0032] Figure 2 is the SEM image of the composite catalyst prepared in Example 2.

[0033] Figure 3 is the SEM image of the composite catalyst prepared in Example 3.

[0034] Figure 4 is the SEM image of the catalyst prepared in Comparative Example 1.

[0035] Figure 5 is the SEM image of the catalyst prepared in Comparative Example 2.

[0036] Figure 6 is the XRD pattern of the catalysts prepared in Example 1 and Comparative Examples 1-2.

[0037] The specific content of the present invention will be further explained in detail below in conjunction with examples. Detailed Embodiments

[0038] It should be noted that all raw materials in the present invention, unless otherwise specified, are all raw materials known in the prior art.

[0039] Spinel catalysts, especially cobalt-based spinels (Co2MO4, where M is a transition metal), have been widely used in the catalytic oxidation of toluene due to their economic and efficient catalytic performance. The synergistic effect between its two metal sites is an effective strategy to activate lattice oxygen and can significantly affect the catalytic oxidation activity. Metals Co and M are located in octahedral and tetrahedral positions respectively. By optimizing electron exchange and appropriately replacing Co with other elements, higher catalytic activity and thermal stability than single oxides can be obtained. However, the catalytic oxidation activity and stability of the bimetallic Co2MO4 cobalt-based spinel for toluene are not satisfactory, and the low-temperature catalytic activity of Co2MO4 still needs to be further improved. Therefore, in the present invention, a two-step method is adopted to introduce CrO x to improve the low-temperature activity and selectivity of Co2NiO4. By selecting different ligands and changing the hydrothermal time, different chromium-doped nickel-cobalt spinels Co2NiO4 / CrO x composite catalysts are prepared for the study of the performance of low-temperature catalytic oxidation of toluene, thereby proposing a preparation method and application of a chromium-doped nickel-cobalt spinel Co2NiO4 / CrO x composite catalyst.

[0040] In the present invention, the Co2NiO4 / CrO x composite catalyst is a chromium-doped nickel-cobalt spinel composite catalyst. The value range of x in CrO x is 2 to 10.

[0041] The present invention discloses a preparation method of a Co2NiO4 / CrO x composite catalyst and its application in the thermal catalytic oxidation and decomposition of toluene. In the first step of this method, a shuttle-shaped CoNi-MOF precursor is prepared by a solvothermal method, and in the second step, CrO is in-situ grown on Co2NiO4 by a hydrothermal method x to obtain a Co2NiO4 / CrO x composite catalyst. Compared with traditional methods, the operation process of the present invention is simple and environmentally friendly, and is applicable to large-scale production. The prepared grains are completely developed, have small particle size and uniform distribution, and can expose more active sites.

[0042] In the present invention, in the application of the Co2NiO4 / CrO x composite catalyst in the thermal catalytic oxidation and decomposition of toluene, during the reaction, the temperature controller is adjusted to measure the catalytic activity at different temperatures, and it is maintained for one hour at each temperature, and then detected. The tail gas is detected by a gas chromatograph, and the toluene conversion rate is obtained by the following formula:

[0043]

[0044] In the formula: X toluene represents the toluene conversion rate; [toluene] inand [toluene] out represent the inlet and outlet concentrations of toluene, respectively. Using T 50 to evaluate the low-temperature activity of the catalyst, and T 90 to evaluate the high-temperature activity of the catalyst, which are the temperatures corresponding to a toluene conversion rate of 50% and 90%, respectively.

[0045] The results show that Co2NiO4 / CrO x The thermal catalytic toluene oxidation performance of the composite catalyst for organic pollutants toluene in the atmosphere is significantly improved, and its T 50 is 169 °C, and T 90 is 218 °C.

[0046] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0047] Example 1:

[0048] This example provides a preparation method of a Co2NiO4 / CrO x composite catalyst, and this method includes the following steps:

[0049] Step 1, preparing a CoNi-MOF precursor by a solvothermal method:

[0050] Add 1.5 g of cobalt nitrate and 1.625 g of nickel nitrate to a mixture of DMF: ethanol: water with a volume ratio of 15:1:1, and add 0.5328 g of 2,5-dihydroxyterephthalic acid thereto, stir magnetically for 1 h to form a homogeneous solution. Then, transfer the solution to a 200 mL stainless steel autoclave lined with polytetrafluoroethylene, and then heat it in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min to form a CoNi-MOF precursor.

[0051] Step 2, in-situ growing CrO on the CoNi-MOF precursor by a hydrothermal method x :

[0052] Weigh the CoNi-MOF precursor sample and add deionized water (sample: deionized water = 1 g: 100 mL). Weigh 5.2 wt% of chromium nitrate nonahydrate, perform ultrasonic treatment for 0.5 h, stir for 60 min, and after mixing evenly, transfer the solution to a stainless-steel autoclave lined with polytetrafluoroethylene, and heat it in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min, and then calcine it at 550 °C for 4 h and grind it to obtain Co2NiO4 / CrO x composite catalyst.

[0053] Example 2:

[0054] This example provides a preparation method of a Co2NiO4 / CrO x composite catalyst, and this method includes the following steps:

[0055] Step 1, prepare the CoNi-MOF precursor by the solvothermal method:

[0056] Add 1.3 g of cobalt nitrate and 1.2 g of nickel nitrate to a mixture of DMF: ethanol: water with a volume ratio of 15:1:1, and add 0.5328 g of 2,5-dihydroxyterephthalic acid thereto, stir magnetically for 1 h to form a homogeneous solution. Then, transfer the solution to a 200 mL stainless-steel autoclave lined with polytetrafluoroethylene, and then heat it in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min to form the CoNi-MOF precursor.

[0057] Step 2, in-situ grow CrO on the CoNi-MOF precursor by the hydrothermal method x :

[0058] Weigh the CoNi-MOF precursor sample and add deionized water (sample: deionized water = 1 g: 100 ml). Weigh 5.2 wt% of chromium nitrate nonahydrate, perform ultrasonic treatment for 0.5 h, stir for 60 min, and after mixing evenly, transfer the solution to a stainless-steel autoclave lined with polytetrafluoroethylene, and heat it in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min, and then calcine it at 550 °C for 4 h and grind it to obtain Co2NiO4 / CrO x composite catalyst.

[0059] Example 3:

[0060] This example provides a Co2NiO4 / CrO xPreparation method of composite catalyst, the method comprising the following steps:

[0061] Step 1, preparing CoNi-MOF precursor by solvothermal method:

[0062] Add 1.5 g of cobalt nitrate and 1.625 g of nickel nitrate to a mixture of DMF:ethanol:water with a volume ratio of 15:1:1, and add 0.5328 g of 2,5-dihydroxyterephthalic acid thereto, stir magnetically for 1 h to form a homogeneous solution. Then, transfer the solution to a 200 mL stainless steel autoclave lined with polytetrafluoroethylene, and then heat in an oven at 135 °C for 4 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min to form CoNi-MOF precursor.

[0063] Step 2, in-situ growing CrO on the CoNi-MOF precursor by hydrothermal method x :

[0064] Weigh the CoNi-MOF precursor sample and add deionized water (sample:deionized water = 1 g:100 ml), weigh 5.2 wt% of chromium nitrate nonahydrate, perform ultrasonic treatment for 0.5 h, stir for 60 min, and after mixing evenly, transfer the solution to a stainless steel autoclave lined with polytetrafluoroethylene, and heat in an oven at 135 °C for 4 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min, and then calcine it at 550 °C for 4 h and grind it to obtain Co2NiO4 / CrO x composite catalyst.

[0065] Comparative example 1:

[0066] This comparative example gives a preparation method of Co2NiO4 single catalyst, the method comprising the following steps:

[0067] Add 1.5 g of cobalt nitrate and 1.625 g of nickel nitrate to a mixture of DMF:ethanol:water with a volume ratio of 15:1:1, and add 0.5328 g of 2,5-dihydroxyterephthalic acid thereto, stir magnetically for 1 h to form a homogeneous solution. Then, transfer the solution to a 200 mL stainless steel autoclave lined with polytetrafluoroethylene, and then heat in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min, and then calcine it at 550 °C for 4 h and grind it to obtain Co2NiO4 single catalyst.

[0068] Comparative example 2:

[0069] This comparative example gives a kind of CrOx Preparation method of a single catalyst, the method comprising the following steps:

[0070] Add 3.125 g of nickel nitrate to a mixture of DMF:ethanol:water with a volume ratio of 15:1:1, and add 0.5328 g of 2,5-dihydroxyterephthalic acid thereto, stir magnetically for 1 h to form a homogeneous solution. Then, transfer the solution to a 200 mL stainless steel autoclave with a polytetrafluoroethylene liner, and then heat it in an oven at 135 °C for 24 h. After cooling to room temperature, centrifuge the dark orange product, wash it repeatedly with methanol and deionized water, and finally dry it in a vacuum oven at 80 °C for 900 min, and then calcine it at 550 °C for 4 h, and grind it to obtain CrO x Single catalyst.

[0071] Testing and result analysis:

[0072] First, XRD and SEM morphology tests:

[0073] From Figures 1 to 5 It can be seen that the synthesized CoNi-MOF precursor is in a shuttle-like structure. The addition of chromium element does not change the main structure of the precursor, but grows in-situ on the shuttle-like structure.

[0074] From Figure 6 It can be seen that the diffraction peaks in the spectrum of the composite catalyst correspond to the corresponding XRD standard cards.

[0075] Second, specific surface area determination (BET):

[0076] From Table 1, it can be seen that the specific surface area of the catalyst in Example 1 is 27.25 m 2 / g, which is significantly increased compared with other comparative examples.

[0077] Table 1 Specific surface area determination results

[0078] catalyst <![CDATA[S BET (m 2 / g)]]> <![CDATA[V total (cm 3 / g)]]> D (nm) Example 1 27.25 0.148 21.84 Comparative Example 1 7.66 0.0617 32.22 Comparative Example 2 12.71 0.064 20.19

[0079] Example 4:

[0080] This example gives the application of the catalyst in the thermal catalytic oxidation decomposition of toluene.

[0081] In this example, the Co2NiO4 / CrO x composite catalyst is prepared by the preparation methods in Examples 1 to 3; the Co2NiO4 single catalyst is prepared by the preparation method in Comparative Example 1; the CrO x single catalyst is prepared by the preparation method in Comparative Example 2.

[0082] Specifically, 0.1 g of the catalysts corresponding to Examples 1 to 3 and Comparative Examples 1 and 2 were placed in a fixed-bed reactor. The reactant feed was toluene with a mass concentration of 1000 ppm, 20 vol% O2 and N2 balance gas. The total gas flow rate was controlled at 60 mL / min, the space velocity was 36000 mL / (g·h), and the reaction temperature was 50 - 370 °C. Toluene was thermally catalytically oxidized and decomposed into CO2 and H2O.

[0083] The catalytic performance evaluation results are shown in Table 2. The catalytic performance of the obtained catalysts was tested. 0.1 g of each catalyst was weighed and fixed in a quartz tube with quartz wool, and the tail gas was detected by a gas chromatograph. As can be seen from Table 2, the catalytic performance of the optimal catalyst Example 1 prepared by the present invention is excellent.

[0084] Table 2 Catalytic performance evaluation results

[0085]

[0086] From the comparison of the above Examples 1 to 3 and Comparative Examples 1 to 2, it can be seen that the present invention uses a first-step solvothermal method to prepare a CoNi-MOF precursor, and then CrO x is in-situ grown on the CoNi-MOF precursor. After calcination, a Co2NiO4 / CrO x composite catalyst is obtained. The prepared catalyst has a large specific surface area and high thermal stability. At the same time, the incorporation of CrO x increases the content and mobility of surface lattice oxygen (O x ) in Co2NiO4 / CrO 2- ), generating highly reducible Cr 6+ and Co 3+ , significantly improving its activity and selectivity.

Claims

1. A preparation method of Co2NiO4 / CrO x composite catalyst, characterized in that The method includes the following steps: Step 1: Prepare a CoNi-MOF precursor by the solvothermal method: Step 101: Add cobalt nitrate hexahydrate and nickel nitrate hexahydrate into dimethylformamide, add ethanol and deionized water thereto, use 2,5-dihydroxyterephthalic acid as a ligand and add it into the solution. The molar ratio of cobalt nitrate hexahydrate:nickel nitrate hexahydrate:2,5-dihydroxyterephthalic acid is 1:2:0.5 to 2:1:

1. Stir continuously at 300-500 rpm / min for 30-60 min until completely dissolved to obtain a mixed solution, denoted as A; Step 102: Add A into a polytetrafluoroethylene-lined hydrothermal autoclave, heat up to 120-150 °C, and react for 24-28 h to obtain a suspension, denoted as B; Step 103: After centrifuging and washing B for multiple times, dry it at 80-120 °C and grind it to obtain a spindle-shaped CoNi-MOF precursor powder, denoted as C; Step 2, in-situ growth of CrO on the CoNi-MOF precursor by hydrothermal method x :[[]]END]] Step 201: Add chromium nitrate nonahydrate into C, control the addition amount of chromium nitrate nonahydrate to be 5.2 wt% of sample C, and add deionized water. Perform ultrasonic treatment for 0.5-1 h and stir for 30-60 min to obtain a mixed solution, denoted as D; Step 202: Add D into a polytetrafluoroethylene-lined hydrothermal autoclave and use the same temperature and reaction time as in Step 102 to obtain a suspension, denoted as E; Step 203: Centrifuge and wash E, dry it under the same conditions as in Step 103, grind it, calcine it at 450 - 650 °C for 3 - 5 h, and grind it finely to obtain the finished Co2NiO4 / CrO x composite catalyst.

2. The preparation method of the Co2NiO4 / CrO composite catalyst according to claim 1, characterized in that x In Step 101, add cobalt nitrate hexahydrate and nickel nitrate hexahydrate into 100-160 mL of dimethylformamide (DMF).

3. The preparation method of the Co2NiO4 / CrO x composite catalyst, characterized in that In Step 101, the molar ratio of DMF:ethanol:deionized water is 10:1:1 to 15:1:

1.

4. The preparation method of the Co2NiO4 / CrO x composite catalyst, characterized in that In Step 201, the ratio of C:deionized water is 1 g:100 mL.

5. The Co2NiO4 / CrO prepared by the preparation method of the composite catalyst according to any one of claims 1 to 4 x composite catalyst x Application of the composite catalyst in the thermal catalytic oxidation and decomposition of toluene.

6. The application according to claim 5, characterized in that, Place 0.1 g of Co2NiO4 / CrO x composite catalyst in a fixed-bed reactor. The reactant feed is toluene with a mass concentration of 1000 ppm, 20 vol% O2 and N2 balance gas. Control the total gas flow rate to be 60 mL / min, the space velocity to be 36000 mL / (g•h), and the reaction temperature to be 50 - 370 °C. Thermally catalytically oxidize and decompose toluene to produce CO2 and H2O.

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