A spinel catalyst, its preparation method and use

Abstract

The application discloses a spinel catalyst and a preparation method and application thereof, and relates to the technical field of catalysts. The chemical formula of the spinel catalyst is M1Co2O4, and the doping metal M is any one or more of Fe, Ni, Cu, Zn, Mn and Cr. The high-entropy coordination and electronic coupling effect in the spinel catalyst lead to a high-spin state of active sites Co, accelerate the rupture of an ozone O-O bond, promote the formation of an intermediate M-*O, establish an interface catalytic reaction mediated by non-free radicals, make the mineralization of organic pollutants more thorough, have higher catalytic efficiency, and the longer life of surface atoms *O is helpful to continuous oxidation and has good persistence.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, more particularly to a spinel catalyst and a preparation method and application thereof. BACKGROUND

[0002] Waste gas with odor and toxicity includes various sulfur-containing volatile organic compounds (S-VOCs), which pose a significant threat to the ecological environment and human health. In response to increasingly stringent environmental regulations, ozone catalytic oxidation removal of VOC technology has become the focus of research. This technology provides a promising solution for deep purification of low-concentration and difficult-to-degrade waste gas due to its economic feasibility and efficiency. Existing ozone-activated catalysts require complex synthesis routes and complex process methods, and have low performance and low durability in catalyzing ozone oxidation of volatile organic pollutants, which greatly limits the development of ozone catalytic environmental remediation, especially ozone catalytic oxidation of gaseous S-VOCs.

[0003] The prior art discloses a catalyst for ozone oxidation and decomposition of organic pollutants in water and a method for catalytic ozone treatment of wastewater. 1-x N x Fe2O4, wherein 0 < x < 1, M and N are any one of metal elements Ni, Mn, Co, Zn, Mg, Cu, Cr, Pb, Sr, Ba and Ca, and M and N are different elements. It discloses a spinel ferrite as a catalyst for ozone oxidation and decomposition of organic pollutants in water. It discloses the technology of spinel ferrite as an ozone catalytic oxidation catalyst, but not for ozone catalytic oxidation of sulfur-containing volatile organic pollutants, and does not solve the problems of low performance and low durability of the catalyst for ozone catalytic oxidation of sulfur-containing volatile organic pollutants. SUMMARY

[0004] The present application aims to overcome the defects and deficiencies of the existing catalysts for ozone catalytic oxidation removal of volatile organic pollutants, especially sulfur-containing volatile organic pollutants, which have low performance and low durability, and to provide a spinel catalyst that can significantly improve the removal effect of ozone catalytic oxidation removal of volatile organic pollutants, especially sulfur-containing volatile organic pollutants S-VOCs, and has high catalytic performance and strong durability.

[0005] Still another object of the present application is to provide a preparation method of the spinel catalyst.

[0006] Still another object of the present application is to provide an application of the spinel catalyst in ozone catalytic oxidation.

[0007] The above objects of the present application are achieved by the following technical solutions:

[0008] A high-entropy spinel catalyst, characterized in that its chemical formula is M1Co2O4, wherein M is a doped metal, which is any one or more of Fe, Ni, Cu, Zn, Mn and Cr, but not Zn alone.

[0009] It should be noted that:

[0010] In the structure of spinel, the metal sites are distributed alternately with tetrahedral and octahedral sites, which are +2 and +3 valence respectively. The structure of spinel is defined as A1B2O4, where A represents tetrahedral +2 sites and B represents octahedral +3 sites. Different divalent metals are doped into the spinel to replace the original metal at the +2 sites.

[0011] The spinel catalyst of the present invention has a pure single-phase spinel structure. The spinel phase has a consistent particle morphology and uniform particle size, which makes the catalyst contain appropriate oxygen vacancies, which is more conducive to ozone catalytic oxidation reaction.

[0012] Furthermore, the spinel catalyst of the present invention is a specific multi-metal doped spinel with a specific multi-metal high-entropy coordination synergistic effect. The high-entropy coordination and electronic coupling effect lead to the high spin state of Co at the active site, which accelerates the breaking of the OO bond of ozone and promotes the formation of the key intermediate M-*O between the broken oxygen and the metal element of the catalyst, thereby establishing a non-radical-mediated interfacial catalytic reaction.

[0013] In heterogeneous catalytic ozonation, the ozone catalytic pathway includes radical-based oxidation (·OH / O2·). - ) and non-radical oxidation ( 1 The high-entropy spinel catalyst of this invention, with surface O as the main active substance, forms an ozone activation system. Compared with conventional free radical-mediated processes, the surface-adsorbed oxygen species *O and *O2 have higher average potentials, 2.43V and 1.35V respectively, resulting in more thorough mineralization of organic pollutants, higher selectivity, and fewer side reactions, significantly improving catalytic efficiency. Furthermore, compared with transient free radicals, the longer lifetime of the ozone-broken oxygen species *O contributes to sustained oxidation.

[0014] To achieve a better multi-metal high-entropy coordination synergistic effect, preferably, the number of doped metals M is greater than or equal to 4.

[0015] In a preferred embodiment, the spinel catalyst of the present application is doped with four or more different kinds of metal elements to form a high-entropy spinel catalyst, and the overall number of metal species is five or more. Through high-entropy configuration (doping of multiple metal elements, electronic interaction to achieve high-spin state of octahedral Co sites, enhanced interaction with ozone to form M-*O bond, realization of non-radical, i.e. non-radical activation path of surface *O, realization of accurate regulation of active sites, and high selectivity induction of non-radical generation path, which is more conducive to ozone catalytic oxidation.

[0016] In a further embodiment, the spinel catalyst of the present application can be, for example, (Fe)1Co2O4, (Ni)1Co2O4, (Cu)1Co2O4 or (FeNiCuZn)1Co2O4.

[0017] The present application also specifically protects a preparation method of a spinel catalyst, comprising the following steps:

[0018] S1. mixing Na2CO3 solution, cobalt salt solution and M metal salt solution drop by drop to obtain a mixed solution, adjusting the pH of the mixed solution to the precipitation pH, and reacting to obtain a precipitate,

[0019] S2. calcining the precipitate at 400-700°C for 2-4h to obtain a spinel catalyst.

[0020] It should be noted that:

[0021] In the preparation method of the spinel catalyst of the present application, by controlling the time and temperature of the calcination reaction of the precipitate, the preparation of a multi-metal doped spinel catalyst can be realized, and at the same time, the crystallinity of the spinel catalyst can be optimized and controlled. Suitable crystallinity can make the catalyst maintain the spinel crystal form and have suitable disorder degree after metal doping, and also make the catalyst have appropriate oxygen vacancies, which is beneficial to the catalytic reaction.

[0022] In a further embodiment, the pH in step S1 can be adjusted to 9.

[0023] In a further embodiment, preferably, the calcination temperature in S2 is 600°C, and the time is 3h.

[0024] The present application also specifically protects the use of a high-entropy spinel catalyst in ozone catalytic oxidation.

[0025] In the application of the present application, the high-entropy spinel catalyst can establish a non-radical-mediated interfacial catalytic reaction, and in ozone catalytic oxidation, organic pollutants are more completely mineralized, the selectivity is higher, the side reactions are fewer, and the problem of limited catalytic efficiency is effectively solved. The catalytic durability is stronger, and it can more effectively promote the complete degradation of ozone catalytic oxidation VOCs.

[0026] And the high-entropy spinel catalyst of the application can also be recycled, and after recycling catalysis, the catalyst can still maintain high catalytic activity, is easy to recover, and can be repeatedly used through regeneration, and is an environment-friendly material.

[0027] In a specific embodiment, the high-entropy spinel catalyst of the application is particularly suitable for ozone catalytic oxidation of sulfur-containing volatile organic pollutants S-VOCs.

[0028] The sulfur-containing volatile organic pollutants S-VOCs of the application particularly refer to CH3SH gas as a target gas S-VOCs.

[0029] In a specific embodiment, in order to achieve better ozone catalytic oxidation treatment effect, preferably, the concentration of CH3SH in the CH3SH gas is 40-60 ppm.

[0030] In a specific embodiment, the high-entropy spinel catalyst of the application can be applied to treat gas S-VOCs with CH3SH gas of different humidity as a target gas, especially high-humidity CH3SH gas. Preferably, the environmental humidity in the application is ≥60%, for example, it can be 75%.

[0031] In a specific embodiment, in order to achieve better ozone catalytic oxidation treatment effect, preferably, the concentration of ozone in the application is 30-60 ppm, for example, it can be 40 ppm.

[0032] The amount of the high-entropy spinel catalyst of the application is preferably 5-10 mg.

[0033] Compared with the prior art, the application has the following beneficial effects:

[0034] The spinel catalyst of the application is a multi-metal doped spinel, which has a multi-metal high-entropy coordination synergistic effect. The high-entropy coordination and electronic coupling effect lead to a high-spin state of the active site Co, accelerate the rupture of the O-O bond, and promote the formation of the key intermediate M-*O, establish a non-free radical-mediated interface catalytic reaction, make the mineralization of organic pollutants more complete, have higher selectivity and fewer side reactions, and can effectively solve the problem of limited catalytic efficiency. In addition, compared with transient free radicals, the longer lifetime of O helps to sustain oxidation and promotes complete degradation of VOCs.

[0035] The spinel catalyst of the application exhibits significant catalytic activity, can remove 100% of CH3SH under high-humidity conditions, and maintains more than 80% removal efficiency after 24 hours, and has good durability. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The degradation effect diagram of different catalysts.

[0037] Figure 2 Catalytic results for different gas atmospheres.

[0038] Figure 3 Results for persistent detection.

[0039] Figure 4 Results for scanning electron microscopy (SEM) detection.

[0040] Figure 5 Results for X-ray diffraction testing.

[0041] Figure 6 Results for in-situ infrared detection.

[0042] Figure 7 Results for in-situ Raman detection. DETAILED DESCRIPTION

[0043] The application will be further described in conjunction with the specific embodiments, but the embodiments do not limit the application in any form. Unless otherwise specified, the raw materials used in the embodiments of the application are commercially available raw materials.

[0044] Example 1

[0045] A spinel catalyst with the chemical formula (FeNiCuZn)1Co2O4, denoted as HE-Co3O4, is prepared as follows:

[0046] S1. Dissolve 5 mmol of Na2CO3 in 100 mL of deionized water, stir until uniform, and then pour into a reagent bottle for standby use;

[0047] Meanwhile, dissolve 5 mmol of mixed metal salt, which is a divalent nitrate salt of cobalt, iron, nickel, copper, and zinc, in 100 mL of deionized water, and stir until completely dissolved to obtain a mixed solution, wherein the mass ratio of the divalent nitrate salt of cobalt, iron, nickel, copper, and zinc in the mixed metal salt is 2:0.25:0.25:0.25:0.25,

[0048] Then, drop the above two solutions into 50 mL of deionized water, and carefully control the pH value to be kept at 9.5 throughout the process, and continuously stir for 1 hour. After that, collect the precipitate by suction filtration device, and rinse with deionized water to remove excess metal ions.

[0049] S2. Dry the washed precipitate for 12 hours, and then calcine it in a tube furnace at 600°C (5°C / min) under an air atmosphere for 3 hours. During the calcination process, due to the change in the coordination environment after the metal enters, a part of the Co changes to a higher valence state of trivalent. (FeNiCuZn)1Co2O4 is obtained.

[0050] Example 2

[0051] A spinel catalyst with the chemical formula (Fe)1Co2O4 was prepared according to the method of Example 1, except that the mixed metal salt was cobalt nitrate and iron nitrate in a molar ratio of 2:1.

[0052] Example 3

[0053] A spinel catalyst with the chemical formula (Ni)1Co2O4 was prepared according to the method of Example 1, except that the mixed metal salt was cobalt nitrate and nickel nitrate in a molar ratio of 2:1.

[0054] Example 4

[0055] A spinel catalyst with the chemical formula (Cu)1Co2O4 was prepared according to the method of Example 1, except that the mixed metal salt was cobalt nitrate and copper nitrate in a molar ratio of 2:1.

[0056] Example 5

[0057] A spinel catalyst with the chemical formula (FeNiCuZn)1Co2O4, denoted as HE-Co3O4, was prepared according to the method of Example 1, except that the calcination temperature was 600°C.

[0058] Example 6

[0059] A spinel catalyst with the chemical formula (FeNiCuZn)1Co2O4 was prepared according to the method of Example 1, except that the metal salt was cobalt nitrate and iron nitrate at 700°C.

[0060] Example 7

[0061] Application of a spinel catalyst in ozone catalytic oxidation, the specific application method is as follows:

[0062] In the process of catalytic ozonation of CH3SH, the reaction was carried out in a continuous flow fixed bed reactor at room temperature. 10 milligrams of catalyst sample was placed in the reactor, and the total gas flow was set to 100 milliliters per minute. The humidity of the inlet gas was adjusted to 50% by a humidity generator, and the ozone was generated by an ozone generator (YDG, YE-TG-02PII) with a concentration of 40 ppm, and the ozone flow was 10 milliliters per minute. CH3SH was introduced by mixing 1000 ppm of CH3SH (diluted with nitrogen) with clean air to a concentration of 50 ppm. After the inlet concentration (C0) of CH3SH was stable, the catalyst was added, and the outlet concentration (C) was monitored using a CH3SH sensor.

[0063] The outlet gas was collected in a gas bag and its composition was analyzed using a proton transfer reaction time-of-flight mass spectrometer. The tail gas was treated using waste catalyst and activated carbon to reduce atmospheric pollution.

[0064] The spinel catalysts of Examples 1-6 were applied to the above catalytic applications, respectively.

[0065] The specific catalytic effects are shown in Table 1 and Figure 1

[0066] Table 1

[0067] Example CH3SH removal rate 1 100％ 2 48％ 3 82％ 4 80％ 5 90％ 6 76％

[0068] Example 8

[0069] The application of a spinel catalyst in ozone catalytic oxidation is as follows:

[0070] The application was carried out according to Example 7, except that the amount of catalyst HE-Co3O4 was 5 mg.

[0071] The CH3SH removal rate was determined to be 72%.

[0072] Example 9

[0073] The application of a spinel catalyst in ozone catalytic oxidation is as follows:

[0074] The application was carried out according to Example 7, except that the amount of catalyst HE-Co3O4 was 7.5 mg.

[0075] The CH3SH removal rate was determined to be 81%.

[0076] Example 10

[0077] The application of a spinel catalyst in ozone catalytic oxidation is as follows:

[0078] The application was carried out according to Example 7, except that the humidity condition was 0.

[0079] The CH3SH removal rate was determined to be 100%.

[0080] Example 11

[0081] The application of a spinel catalyst in ozone catalytic oxidation is as follows:

[0082] The application was carried out according to Example 7, except that the humidity condition was 25%.

[0083] The CH3SH removal rate was determined to be 100%.

[0084] ​Example 12

[0085] The application of the spinel catalyst in ozone catalytic oxidation is as follows:

[0086] The application is carried out according to Example 7, except that the humidity condition is 75%.

[0087] The removal rate of CH3SH is 100%.

[0088] Example 13

[0089] The application of the spinel catalyst in ozone catalytic oxidation is as follows:

[0090] The application is carried out according to Example 7, except that the ozone gas is replaced by other gas atmosphere, including N2 atmosphere and O2 atmosphere.

[0091] The determination results are shown in Figure 2 From the figure, it can be seen that the spinel catalyst of the application can significantly catalyze and activate ozone to degrade CH3SH, rather than other gases in non-activated air.

[0092] Example 14 Durability and Stability Test

[0093] The application of the spinel catalyst in ozone catalytic oxidation is as follows:

[0094] The application is carried out according to Example 8.

[0095] The durability test results are shown in Figure 3 From the figure, it can be seen that the spinel catalyst of the application has good recycling effect, and its catalytic efficiency remains basically unchanged after 3 cycles, and maintains about 90% removal efficiency after 24 hours, with good durability.

[0096] Comparative Example 1

[0097] A spinel catalyst without doping the above-mentioned related metal elements, with a chemical formula of Co3O4, and a preparation method as follows:

[0098] S1. Dissolve 5 mmol of Na2CO3 in 100 ml of deionized water, stir until uniform, and then pour into a reagent bottle for standby;

[0099] At the same time, dissolve Co(NO3)2·6H2O in 100 ml of deionized water in the same amount, stir until completely dissolved,

[0100] The two solutions were then added dropwise into 50 ml of deionized water, and the pH was carefully controlled to remain at 9.5 throughout the process, and stirring was continued for 1 hour, after which the precipitate was collected by suction filtration and rinsed with deionized water to remove excess metal ions.

[0101] S2. The washed precipitate was dried for 12 hours, and then calcined in a tube furnace at 600°C (5°C / min) under air atmosphere for 3 hours to obtain Co304.

[0102] Reference is made to Example 7 for application.

[0103] The CH3SH removal rate was determined to be 20%.

[0104] Comparative Example 2

[0105] A spinel catalyst with the chemical formula (Ni)1Co2O4was prepared according to Example 1, except that the metal salts were cobalt nitrate and nickel nitrate.

[0106] Reference is made to Example 7 for application.

[0107] The CH3SH removal rate was determined to be 21%.

[0108] Results of detection

[0109] (1) Scanning electron microscope (SEM) detection

[0110] The spinel catalysts of Examples 1-5 were subjected to scanning electron microscope (SEM) detection, and the detection results are shown in FIG. 1. Figure 4

[0111] The scanning SEM images show that all of the spinel phases have consistent particle morphology and uniform particle size.

[0112] (2) X-ray diffraction (XRD) test

[0113] The spinel catalysts were subjected to XRD detection to determine the degree of crystallinity, and the detection results are shown in FIG. 2. Figure 5 Figure 5 The XRD patterns in FIG. 2 show diffraction peaks at 2θ values of 31.58°, 37.19°, 38.40°, 44.64°, 59.54°, and 65.21° on the (220), (311), (222), (400), (511), and (440) crystal planes, which can be identified as belonging to the spinel phase. ​​The cubic spinel phase of space group (JCPDS: PDF#42-1467). No diffraction peaks for Fe, Ni, Co, and Zn metal oxides were detected in 29-31, indicating that HE-Co3O4 possesses a pure single-phase spinel structure. Other synthesized binary cobalt-based spinel oxides, including Fe1Co2O4, Ni1Co2O4, Co1Co2O4, and Ze1Co2O4, also exhibit similar crystal structures.

[0114] (3) Product analysis: in situ infrared spectroscopy.

[0115] In the comparative examples of CH3SH ozonation catalyzed by Co3O4 and HE-Co3O4, in-situ DRIFTS analysis was performed, as follows: Figure 6 The study found that in the HE-Co3O4 catalytic reaction, CH3SH molecules are oxidized into a series of intermediate products, including SO, sulfates, sulfonates, and sulfites, ultimately being completely mineralized into inorganic substances. In contrast, the oxidation of CH3SH in the Co3O4 catalytic reaction is relatively weaker, with toxic intermediates such as CH3SSCH3 and CH3SO produced. 3- The gradual accumulation on the catalyst surface indicates that the breaking of CS bonds is the limiting step of CH3SH mineralization and the reason for the deactivation of the Co3O4 catalyst in Comparative Example 1.

[0116] (3) In-situ Raman quenching experiment and ESR test

[0117] To fully demonstrate that ozone activation occurs via a non-radical pathway of surface atoms *O, in-situ Raman spectroscopy was used to detect the formation of the key intermediate M-*O. Radical quenching experiments and ESR tests were conducted, and the non-radical contribution rates of different catalytic systems were compared. The detection results are as follows: Figure 7 As shown, from Figure 7 As can be seen from this, overall, ·OH, 1 O 2， O2 ·- The contribution of *O is very small; *O is the main active species in this system. This indicates that the ozone activation pathway of the catalyst in this invention is a non-radical activation pathway of surface *O.

[0118] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A spinel catalyst characterized in that, The chemical formula is M1Co2O4, wherein M is a doping metal, and M is any 4 of Fe, Ni, Cu, Zn, Mn, and Cr.

2. The spinel catalyst of claim 1, wherein the spinel catalyst has a spinel structure. The M is Fe, Ni, Cu, and Zn.

3. A process for the preparation of the spinel catalyst of claim 1 or 2, characterized in that, The method comprises the following steps: S1. mixing Na2CO3 solution, cobalt salt solution, and M metal salt solution drop by drop to obtain a mixed solution, adjusting the pH of the mixed solution to a precipitation pH, and reacting to obtain a precipitate, S2. calcining the precipitate at 400-700 ℃ for 2-4 h to obtain a spinel catalyst.

4. The preparation method according to claim 3, characterized in that, The calcination temperature in S2 is 600 ℃, and the time is 3 h.

5. Use of a spinel catalyst in catalytic ozonation, characterized in that, The chemical formula of the spinel catalyst is M1Co2O4, wherein M is a doping metal, and M is multiple of Fe, Ni, Cu, Zn, Mn, and Cr, and the number of the doping metal M is greater than or equal to 4.

6. The use according to claim 5, characterized in that, The application is catalytic oxidation of sulfur-containing volatile organic pollutants by ozone.

7. The use according to claim 6, characterized in that, The sulfur-containing volatile organic pollutants are CH3SH gas.

8. The use according to claim 7, characterized in that, The concentration of the CH3SH gas is 40-60 ppm.

9. The use according to claim 7, wherein the compound is ###00003### or a pharmaceutically acceptable salt thereof. The relative humidity in the application is greater than or equal to 60%.

10. The use according to claim 7, characterized in that, The concentration of ozone in the application is 30-50 ppm.

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